Anorganische Chemie
Oxygen activation and transfer
mediated by copper(I) complexes
with polyfunctional bisguanidine ligands
Von der Fakult¨at f¨ur Naturwissenschaften
Department Chemie
der Universit¨at Paderborn
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
- Dr. rer. nat.-
genehmigte Dissertation
von
Sonja Herres-Pawlis
aus Schwelm
Paderborn 2005
Datum der Einreichung: 9.9.2005
Datum der m¨undlichen Pr¨ufung: 20.10.2005
Erster Gutachter: Prof. Dr. Gerald Henkel
Zweiter Gutachter: Prof. Dr. Stephan Schulz
Die experimentellen Untersuchungen zu dieser Arbeit wurden im Zeitraum von November
2002 bis August 2005 unter Anleitung von Prof. Dr. G. Henkel im Department Chemie der
Universit¨at Paderborn durchgef¨uhrt.
To B
To my family
To my dear Alex
Tudo est´a bem quando termina bem.
Brasilian proverb
Abstract
In this thesis in the field of Bioinorganic Chemistry, biological relevant copper complexes
were synthesised which are capable to activate and transfer molecular oxygen.
As ligand systems, substituted guanidines were used because the N donor functions of these
ligands resemble the basic δimin donor functions of the histidine residues which contribute
to copper coordination in almost all copper enzymes.
In order to approach the functionality of tyrosinase and catechol oxidase, a synthetic
protocol was developed which allows the unrestricted modification of the spacer as well as
of the guanidine unit. By using this modular principle, a library of bisguanidine ligands
was built up. This ligand library contains members with total flexibility of the guanidine-
connecting spacers as well as of the substitution pattern of the guanidine moieties. Via
modification of the spacer, it is possible to change the denticity, the ”bite” angle and the
coordination geometry, whereas via modification of the guanidine moities, the σdonating
and πaccepting properties of the Nimine atom can directly be influenced. The reaction of
the obtained bisguanidines with copper(I) salts yielded copper(I) bisguanidine complexes
which were investigated towards their ability to activate molecular oxygen. As result, the
observed ability to bind oxygen under formation of Cu2O2adduct complexes was correlated
with the degree of conjugation within the guanidine units.
The ligand matrix was screened regarding the oxidation capability of its Cu(II)/Cu(III)O2
complexes. The possibility of controlling the oxidation selectivity of these Cu(II)/Cu(III)O2
species by peripheric modifications is a particularly attractive feature of this ligand design.
The studies presented in the following may contribute to a better understanding of
oxygen transport and activation in biological systems. Furthermore, this information can
support the directed oxygenation of organic substrates.
Abstract
Im Rahmen dieser Doktorarbeit auf dem Gebiet der Bioanorganischen Chemie wurden biol-
ogisch relevante Kupferkomplexe synthetisiert, die in der Lage sind, Sauerstoff zu aktivieren
und eine Oxidationsaktivit¨at zu entfalten.
Als Ligandensysteme werden substituierte Guanidine verwendet. Die N-Donorfunktionen
dieser Liganden ¨ahneln den basischen δ-Imin-Donorfunktionen der Histidinreste, die in bi-
ologischen Systemen an der Koordination des Kupfers in den meisten kupferhaltigen En-
zymen beteiligt sind. Um der Funktionalit¨at der Tyrosinase und der Catechol-Oxidase
m¨oglichst nahe zu kommen, wurde ein Syntheseprotokoll entwickelt, das es erm¨oglicht,
sowohl die Spacer als auch die Guanidineinheit frei zu w¨ahlen. Mit Hilfe dieses modu-
laren Prinzips wurde eine Bibliothek aus Bisguanidinliganden aufgebaut. Diese Liganden-
bibliothek enth¨alt Vertreter mit vollst¨andiger Flexibilit¨at sowohl der die Guanidineinheit
verbindenden Spacer als auch der Substitutionsmuster dieser Guanidineinheiten. Durch
geeignete Wahl der Spacer ist es m¨oglich, die Z¨ahnigkeit, den ”Ligandenbiß” und die Ko-
ordinationsgeometrie zu variieren, w¨ahrend durch die Modifikation der Guanidineinheiten
direkt die σ-Donor- und π-Akzeptoreigenschaften am Nimin-Atom beeinflußt werden k¨onnen.
Die erhaltenen Bisguanidine wurden mit Kupfer(I)salzen zu Kupfer(I)bisguanidinkomplexen
umgesetzt, welche auf ihre F¨ahigkeit zur Aktivierung von molekularem Sauerstoff hin unter-
sucht wurden. Als Ergebnis konnte die F¨ahigkeit dieser Komplexe, Sauerstoff unter Bildung
von Cu2O2-Adduktkomplexen zu binden, mit dem Ausmaß der Konjugation innerhalb der
Guanidineinheiten korreliert werden.
Die Ligandenmatrix wurde hinsichtlich der Oxidationseigenschaften ihrer Cu(II)/Cu(III)O2-
Komplexe untersucht. Die Kontrolle ¨uber die Oxidationsselektivit¨at der Cu(II)/Cu(III)O2-
Komplexe durch periphere Modifikationen ist eine besonders attraktive Eigenschaft dieses
Ligandendesigns.
Die im folgenden geschilderten Untersuchungen sollen zu einem tieferen Verst¨andnis von
Sauerstofftransport und -aktivierung in biologischen Systemen f¨uhren und diese Information
f¨ur die gezielte Oxygenierung organischer Substrate nutzbar machen.
Acknowledgement
First of all, I would like to thank all the persons who have supported me and this thesis.
I thank my mentor Prof. Dr. G. Henkel very cordially for the challenging subject, the great
freedom in research and our long and fruitful discussions.
My gratitude goes also to Prof. Dr. S. Schulz for the friendly adoption of the correferate of
this work.
Furthermore, I would like to thank Dr. U. Fl¨orke for carrying out the crystal structure
analyses and the expert advice in questions concerning X-ray crystallography.
For the numerous and sometimes very difficult NMR measurements, my gratitude goes to
K. Stolte and PD Dr. H. Egold who always gave advice, not only in NMR matters. For the
very numerous mass spectrometric and gaschromatographic measurements, I thank Dr. H.
Weber, K. Stolte and M. Zukowski. In addition, my gratitude for the elemental analyses
goes to M. Busse and H. Mulka. Furthermore, my gratitude goes to Dr. T. Seshadri for
teaching me ”organic synthesis”. I would like to thank also Prof. Dr. H. Marsmann for the
19F NMR experiments and helpful advice.
Special thanks go to Prof. Dr. F. Tuczek, F. Studt and O. Sander for the Raman
measurements at the University of Kiel.
I would like to thank all members of the AK Henkel for the lively time in the lab
and the good atmosphere in our bureau, but especially Dr. O. Seewald and A. Neuba for
many helpful discussions and the correction of this manuscript.
I gratefully acknowledge the financial support of the Fonds der Chemischen Industrie
in form of a Fonds fellowship and of the University of Paderborn in form of a Promotions-
abschlußstipendium.
Last, but not least, I would like to thank very cordially my parents Dr. G. Herres
and H. Platberg-Herres as well as my grandmother H. Platberg for all the love and
encouragement.
Finally, my thanks go to my dearest husband Dr. A. Pawlis who did not have an easy time
with me, but gave me all his love, encouragement, printing ink and ”Schnittchen”.
Contents
1 Introduction 1
1.1 Bioinorganic chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 The bioinorganic chemistry of copper . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Copper proteins in biological systems . . . . . . . . . . . . . . . . . . . . . . 3
1.3.1 Overview of the biological processes under participation of copper en-
zymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.2 Copper enzyme-mediated oxygen activation and transfer . . . . . . . 4
1.3.3 Oxygen transport by hemocyanin . . . . . . . . . . . . . . . . . . . . 6
1.3.4 Activation of molecular oxygen by type 3-centers . . . . . . . . . . . 8
1.4 Technical application of copper compounds in catalytic oxidative transforma-
tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.5 Biomimetic model systems for type 3-copper centres . . . . . . . . . . . . . . 13
1.5.1 Reactions of Cu(I) complexes with molecular oxygen under formation
of Cu/O2adduct complexes . . . . . . . . . . . . . . . . . . . . . . . 13
1.5.2 Ligand systems and their influence on the formation of Cu/O2adduct
complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5.3 Reactions of d10 precursor complexes with triplet oxygen . . . . . . . 16
1.5.4 Complexes with µ-η2:η2-peroxo and bis(µ-oxo) dicopper cores . . . . 19
1.6 Guanidines - model systems for the enzymatic environment . . . . . . . . . . 20
1.6.1 Peralkylated Bisguanidine Ligands . . . . . . . . . . . . . . . . . . . 21
1.6.2 Synthesis methods for guanidines . . . . . . . . . . . . . . . . . . . . 23
2 Objective and outline 26
2.1 Objective of the present work . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2 Outline of the present work . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
iii
Contents iv
3 Bisguanidine ligands 28
3.1 Synthesis of the ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.1.2 Realisation of a modular approach . . . . . . . . . . . . . . . . . . . 28
3.2 Crystal structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.2.1 Crystal structure of N,N,N´,N´-tetraethylchloroformamidinium chloride 34
3.2.2 Crystal structures of selected bisguanidine ligands . . . . . . . . . . . 35
3.3 NMR spectroscopy of selected bisguanidine ligands . . . . . . . . . . . . . . 39
3.4 Electrochemistry of selected bisguanidine ligands . . . . . . . . . . . . . . . . 44
3.5 Synthesis of a fluorinated bisguanidine ligand . . . . . . . . . . . . . . . . . 45
3.6 Conclusion: Bisguanidine ligands . . . . . . . . . . . . . . . . . . . . . . . . 47
4 Copper(I) bisguanidine complexes 48
4.1 General topologies of copper(I) bisguanidine complexes . . . . . . . . . . . . 48
4.2 Synthesis of mononuclear copper(I)bisguanidine complexes . . . . . . . . . . 49
4.2.1 Crystal structures of mononuclear copper bisguanidine complexes . . 49
4.2.2 Electrochemistry of mononuclear copper bisguanidine complexes . . . 52
4.3 Synthesis of dinuclear copper(I)bisguanidine complexes with linear copper co-
ordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.3.1 Crystal structures of dinuclear copper(I) bisguanidine complexes . . . 54
4.3.2 Electrochemistry of dinuclear copper(I) bisguanidine complexes . . . 59
4.4 Synthesis of polynuclear copper(I)bisguanidine chains . . . . . . . . . . . . . 60
4.4.1 Synthesis of polynuclear Cu(DMEG2p) chains . . . . . . . . . . . . . 60
4.4.2 Synthesis of further polynuclear copper(I)bisguanidine chains . . . . . 63
4.5 Synthesis of a dinuclear copper(I)benzimidazolyle-guanidine complex with lin-
ear copper coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.5.1 Crystal structure of [Cu2(TMGbenzPA)2][PF6]2(C14) . . . . . . . . 68
4.5.2 Electrochemistry of [Cu2(TMGbenzPA)2][PF6]2(C14) . . . . . . . . 70
4.6 Conclusion of the Syntheses of Copper(I)Bisguanidine complexes . . . . . . . 71
5 Oxygen activation with Cu(I) bisguanidine complexes 72
5.1 Cu2O2Bisguanidine species . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.2 UV/Vis-Spectroscopy of Cu2O2Bisguanidine species . . . . . . . . . . . . . 73
5.2.1 UV/Vis-Spectroscopy of Cu2O2species with aliphatic bisguanidine lig-
ands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Contents v
5.2.2 UV/Vis-Spectroscopy of Cu2O2species with aromatic bisguanidine lig-
ands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.2.3 UV/Vis-Spectroscopy of Cu2O2species with sterically demanding bis-
guanidine ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.2.4 UV/Vis-Spectroscopy of Cu2O2species with the fluorinated bisguani-
dine ligand BFPPG2p . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.3 Interpretation of the results . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.3.1 Correlation of P/O-core development with structural properties . . . 80
5.3.2 σdonor and πacceptor capabilities of the ligands . . . . . . . . . . . 82
5.4 Kinetics of the activation of dioxygen . . . . . . . . . . . . . . . . . . . . . . 85
5.4.1 Kinetics of copper/dioxygen chemistry . . . . . . . . . . . . . . . . . 85
5.4.2 Kinetic results of the reaction of dinuclear copper complexes with O287
5.4.3 Kinetic results of the reaction of the mononuclear copper complex
[Cu(btmgp)I] with O2. . . . . . . . . . . . . . . . . . . . . . . . . . 90
5.5 Conclusion of the O2Activation with Copper(I) Bisguanidine Complexes . . 93
6 Products of hydroxylation reactions 94
6.1 Hydroxylation of copper btmgp complexes . . . . . . . . . . . . . . . . . . . 94
6.1.1 Crystal structures of btmgp containing hydroxylation products . . . . 94
6.1.2 Discussion of the reaction mechanism . . . . . . . . . . . . . . . . . . 99
6.1.3 Electrochemistry of [Cu2(btmmO)2][PF6]2·2MeCN C15 . . . . . . . . 100
6.2 Hydroxylation of copper TMG2MePA complexes . . . . . . . . . . . . . . . . 101
6.2.1 Crystal structures of TMG2MePA containing hydroxylation products 101
6.2.2 Electrochemistry of [Cu2(TMMoG2MePA)2][PF6]2C16 . . . . . . . . 106
6.3 Hydroxylation of copper DMEG2p complexes . . . . . . . . . . . . . . . . . . 106
6.4 Hydroxylation of copper DPipG2p complexes . . . . . . . . . . . . . . . . . . 109
6.5 Hydroxylation of copper TMG2ch complexes . . . . . . . . . . . . . . . . . . 111
6.6 Hydroxylation of a copper MorphDMG2p complex and subsequent reaction . 113
6.7 Conclusion of the Hydroxylation Properties of Copper bisguanidine complexes 116
7 Catalytic activity of copper bisguanidine systems 117
7.1 General remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
7.2 Reactions with 2,4-ditertbutylphenol and 2,6-ditertbutylphenol . . . . . . . . . 118
7.3 Reactions with 3,5-ditertbutylcatechol . . . . . . . . . . . . . . . . . . . . . . 122
7.4 Screening of the library of bisguanidine ligands regarding the oxidation activity126
Contents vi
7.5 Conclusion of the catalytic results . . . . . . . . . . . . . . . . . . . . . . . . 129
8 Experimental Section 130
8.1 Material and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8.1.1 General Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8.1.2 Physical measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8.2 Synthesis of educt compounds . . . . . . . . . . . . . . . . . . . . . . . . . . 131
8.3 Synthesis of product compounds . . . . . . . . . . . . . . . . . . . . . . . . . 132
8.3.1 Synthesis of substituted ureas . . . . . . . . . . . . . . . . . . . . . . 132
8.3.2 Synthesis of Vilsmeier salts . . . . . . . . . . . . . . . . . . . . . . . . 132
8.3.3 Synthesis of guanidine ligands . . . . . . . . . . . . . . . . . . . . . . 136
8.3.4 Synthesis of copper(I)bisguanidine complexes . . . . . . . . . . . . . . 148
8.3.5 Synthesis of copper(II)complexes . . . . . . . . . . . . . . . . . . . . 153
8.3.6 Catalytic reactions with 2,4-ditertbutylphenol, 2,6-ditertbutylphenol
and 3,5-ditertbutylcatechol . . . . . . . . . . . . . . . . . . . . . . . . 156
9 Conclusion and Perspective 157
Bibliography 161
10 Appendix 168
List of Figures
1.1 ”Classic” copper centers in biologic systems [2] . . . . . . . . . . . . . . . . . 3
1.2 ”Non-classic” copper centers in biologic systems [8] . . . . . . . . . . . . . . 4
1.3 Selected Cu enzymes und proteins that activate O2[8] . . . . . . . . . . . . 5
1.4 Phenolase activity (1), catecholase activity (2) . . . . . . . . . . . . . . . . . 5
1.5 Dinuclear µ−η2:η2peroxo copper active site of oxyhemocyanin from Octopus
dofleini [27] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.6 Overall structure of catechol oxidase from sweet potatoes [17] . . . . . . . . 8
1.7 Coordination sphere of the dinuclear copper centre in the met state [17] . . . 9
1.8 Mechanism of cresolase and catecholase activity of tyrosinase and/or catechol
oxidase [17] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.9 PTU inhibitor complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.10 Copper-catalysed processes in industry . . . . . . . . . . . . . . . . . . . . . 12
1.11 CunOmcores in characterised complexes (for crystallographically charac-
terised species, significant metrical parameters (˚
A) are given) [45] . . . . . . 14
1.12 Reaction of [Cu2(XYL-O−)]+with O2. . . . . . . . . . . . . . . . . . . . . . 14
1.13 Reaction of [(TMPA)CuI(RCN)]+with O2. . . . . . . . . . . . . . . . . . . 15
1.14 Overview of ligand families . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.15 Reaction of mononuclear Cu(I) precursor complexes with molecular oxygen . 18
1.16 Equilibrium between µ-η2:η2-peroxo and bis(µ-oxo) dicopper cores . . . . . . 19
1.17 Delocalisation of the positive charge in a guanidinium cation . . . . . . . . . 20
1.18 Reaction of guanidine derivatives with a halogenealkane . . . . . . . . . . . . 23
1.19 Synthesis of guanidines after Bredereck . . . . . . . . . . . . . . . . . . . . . 23
1.20 Guanidines via reaction of isocyaniddichlorides with amines . . . . . . . . . . 24
1.21 Formation of the reactive iminium salt species in the Vilsmeier synthesis . . 24
1.22 Mechanism of the reaction of a peralkylated urea with phosgen . . . . . . . . 25
vii
List of Figures viii
1.23 Mechanism of the condensation of chloroformamidinium chlorides with amines
under use of an auxiliary base . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1 Generation of the chloroformamidinium chlorides . . . . . . . . . . . . . . . 29
3.2 Reaction between the chloroformamidinium chloride and the bisamine . . . . 30
3.3 Guanidine portions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.4 Spacer units (G assigns the position of the attached guanidine moiety) . . . 32
3.5 Schematic representation of the variable moduls within bisguanidine ligands 32
3.6 Molecular structure of V2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.7 Molecular structure of L5-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.8 Molecular structure of L7-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.9 Molecular structure of L1-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.10 Molecular structure of L11-1 (left) and of [H2L1-2]I2·Et2O(right) . . . . . 38
3.11 Rotation around the C=N double bond . . . . . . . . . . . . . . . . . . . . . . 40
3.12 Coalescence behaviour of TMG2PA (L1-4) between 293 and 233 K . . . . . . 41
3.13 Eyring plot (308 - 343 K) for the syn-anti exchange in btmgp (L1-1) . . . . 41
3.14 Eyring plot (293 - 318 K) for the syn-anti exchange in TMG2doo (L1-2) . . 42
3.15 Eyring plot (213 - 233 K) for the syn-anti exchange in TMG2PA (L1-4) . . . 42
3.16 Cyclovoltammogram of L1-4 in CH2Cl2. . . . . . . . . . . . . . . . . . . . 44
3.17 Cyclovoltammogram of L1-5 in CH2Cl2. . . . . . . . . . . . . . . . . . . . 45
3.18 Synthesis of the fluorinated bisguanidine ligand BFPPG2p . . . . . . . . . . 45
4.1 Topologies of copper(I) bisguanidine complexes . . . . . . . . . . . . . . . . 48
4.2 Complexation of CuI with bisguanidine ligands . . . . . . . . . . . . . . . . 49
4.3 Complexation of CuI with TMG2PA under oxidation of the copper . . . . . . 49
4.4 Molecular structure of C1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.5 Molecular structure of C2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.6 Cyclovoltammogram of C1 in CH2Cl2. . . . . . . . . . . . . . . . . . . . . 52
4.7 Cyclovoltammograms of C2 in MeCN (20 mV/s - 200 mV/s) . . . . . . . . . 53
4.8 Complexation of [Cu(MeCN)4][PF6] with propylene-briged bisguanidine ligands 53
4.9 Complexation of CuI with cyclohexyl-bridged bisguanidine ligands . . . . . . 54
4.10 Structure of [Cu2(btmgp)2]2+ in crystals of C3 . . . . . . . . . . . . . . . . . 54
4.11 Molecular structures of [Cu2(DMEG2p)2]2+ in crystals of C5 (left) and of
[Cu2(DMPG2p)2]2+ in crystals of C8 (right) . . . . . . . . . . . . . . . . . . 55
List of Figures ix
4.12 Molecular structures of [Cu2(TMG2ch)2]2+ in C4 (left) and of
[Cu2(DMEG2ch)2]2+ in C6 and C7 (right) . . . . . . . . . . . . . . . . . . . 56
4.13 Molecular structure of C9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.14 Correlation between the Cu...Cu separations and the H...H distances . . . . 57
4.15 Schematic representation of the almost orthogonal pzorbitals in DMEG groups 58
4.16 Cyclovoltammograms of C8 in MeCN . . . . . . . . . . . . . . . . . . . . . . 59
4.17 Section of the molecular structure of C10 . . . . . . . . . . . . . . . . . . . 61
4.18 A view normal to the 001-plane in crystals of C10 . . . . . . . . . . . . . . 62
4.19 Section of the molecular structure of C11 . . . . . . . . . . . . . . . . . . . 62
4.20 A view normal to the 001-plane in crystals of C11 . . . . . . . . . . . . . . 63
4.21 Section of the molecular structure of C12 . . . . . . . . . . . . . . . . . . . 64
4.22 Section of the molecular structure of C13 . . . . . . . . . . . . . . . . . . . 65
4.23 View on the crystal packing in C12 . . . . . . . . . . . . . . . . . . . . . . 66
4.24 View on the crystal packing in C13 . . . . . . . . . . . . . . . . . . . . . . 67
4.25 Reaction of TMG2PA with [Cu(MeCN)4][PF6] . . . . . . . . . . . . . . . . . 69
4.26 Molecular structure of C14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.27 Cyclovoltammogram of C14 in CH2Cl2. . . . . . . . . . . . . . . . . . . . . 70
5.1 Equilibrium between µ-η2:η2-peroxo and bis(µ-oxo) dicopper bisguanidine
complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.2 Time-dependent UV/Vis absorption spectra (every 2 min) observed upon in-
troduction of O2gas into CH2Cl2solution of C9 (0.25 mM, -80◦C) during 30
min; inset: spectrum after 2 h (0.33 mM) . . . . . . . . . . . . . . . . . . . . 73
5.3 UV/Vis absorption spectrum observed upon introduction of O2gas into a
solution of C5 in MeCN/CH2Cl2(1:10) (0.5 mM, -80◦C) after 30 min, inset:
spectrum after 1 h (0.25 mM) . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.4 a)Time-dependent UV/Vis absorption spectra (every 2 min) observed upon
introduction of O2gas into CH2Cl2solution of C8 (0.2 mM, -80◦C) during 30
min; inset: spectrum after 2 h (0.5 mM); b)Time-dependent UV/Vis absorp-
tion spectra (every 30 s) observed upon introduction of O2gas into MeCN
solution of C8 (0.25 mM, -40◦C) during 8 min; inset: spectrum after 1 h (0.5
mM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
List of Figures x
5.5 Time-dependent UV/Vis absorption spectra (every 1 min) observed upon in-
troduction of O2gas into CH2Cl2solution of C4 (1 mM, -80◦C) during 10
min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.6 Time-dependent UV/Vis absorption spectra (every 50 s) observed upon in-
troduction of O2gas into CH2Cl2solution of C6 (0.2 mM, -80◦C) during 400
s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.7 Time-dependent UV/Vis absorption spectra (every 2 min) observed upon in-
troduction of O2gas into CH2Cl2solution of [Cu(DPPG2p)]I (0.35 mM, -80◦C)
during 24 min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.8 Time-dependent UV/Vis absorption spectra (every 2 min) observed upon in-
troduction of O2gas into CH2Cl2solution of [Cu(TMG2MePA)][PF6] (0.1
mM, -80◦C) during 22 min . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.9 Time-dependent UV/Vis absorption spectra (every 1 min during 30 min, then
every 5 min during further 150 min) observed upon introduction of O2gas
into CH2Cl2solution of [Cu2(DMPG2mX)2]I2(0.1 mM, -80◦C) . . . . . . . 77
5.10 Time-dependent UV/Vis absorption spectra (every 30 min) observed upon
introduction of O2gas into CH2Cl2solution of [Cu(B(TMPip)G2p)]I (0.3 mM,
25◦C) during 600 min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.11 Resonance Raman spectrum of [Cu(B(TMPip)G2p)]I (≈80 mM, 25◦C,
CH2Cl2), excitation wavelength: 350 nm . . . . . . . . . . . . . . . . . . . . 78
5.12 Time-dependent UV/Vis absorption spectra (every 2 min) observed upon in-
troduction of O2gas into CH2Cl2solution of [Cu((DMPip)DMG2p)]I (0.15
mM, 25◦C) during 60 min . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.13 Time-dependent UV/Vis absorption spectra (every 20 min) observed upon
introduction of O2gas into CH2Cl2solution of [Cu(BFPPG2p)]I (0.35 mM,
25◦C) during 400 min; inset: magnification of the first hour with spectra every
2 min during 60 min) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.14 Competition of p-πconjugation and steric repulsion within the guanidine centre;
arrows indicate twist from ideal conjugation (pale) . . . . . . . . . . . . . . . . 82
5.15 Partial molecular orbital diagram showing the frontier orbitals of the P-core,
adapted from [35] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.16 Bonding situation comprising a bisguanidine ligand attached to the Cu2O22+
core portion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.17 General mechanism of dioxygen-uptake by Cu(I) complexes . . . . . . . . . . 85
List of Figures xi
5.18 First-order plot based on the absorption change at 350 nm (P-core) for the
reaction of C8 at -80 ◦C with O2. . . . . . . . . . . . . . . . . . . . . . . . 87
5.19 Eyring plot for C3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5.20 Eyring plot for C8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.21 Eyring plot for C9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.22 Proposed mechanism of the reaction of dinuclear copper complexes with O2. 90
5.23 Schematic kinetics of dioxygen-uptake by Cu(I) complexes . . . . . . . . . . 91
5.24 Hypothetical mechanism for the reaction of [Cu(btmgp)I] with O2as model
for the numerical fit (left: chemical description, right: kinetical description) . 91
5.25 Fitting of the absorbance of the reaction of [Cu(btmgp)I] with O2by MAT-
LAB 6.5 (blue: calc. concentration of the precursor a, green: calc. con-
centration of the intermediate Cu-O2adduct b, red: calc. and measured
concentration of the O-core species c) . . . . . . . . . . . . . . . . . . . . . . 92
6.1 Activation of oxygen with [Cu(btmgp)I] and [Cu2(btmgp)2][PF6]2. . . . . . 95
6.2 Molecular structure of [Cu2(btmmO)2I]+in crystals of
[Cu2(btmmO)2I]I·1
2EtOH (left), magnification of the µ-iodo bridged Cu2O2
unit [112] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
6.3 Molecular structure of [Cu2(btmmO)2]2+ in crystals of C15 . . . . . . . . . 97
6.4 Molecular structure of [Cu2(btmgp)2(µ-OH)2]2+ [113] . . . . . . . . . . . . . 99
6.5 Cyclovoltammogram of C15 in CH2Cl2. . . . . . . . . . . . . . . . . . . . . 101
6.6 Activation of oxygen with [Cu(TMG2MePA)][X] (X = PF−
6, ClO−
4, BF−
4and
I−) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.7 Molecular structure of [Cu2(TMMoG2MePA)2]2+ in crystals of C16 and C17 104
6.8 Molecular structure of [Cu2(TMMoG2MePA)2]2+ in crystals of C18 . . . . . 105
6.9 Molecular structure of [Cu2(TMG2MePA)2(µ-OH)2]2+ in crystals of C19 and
C20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
6.10 Cyclovoltammogram of C16 in CH2Cl2. . . . . . . . . . . . . . . . . . . . . 106
6.11 Activation of oxygen with [Cu2(DMEG2p)]2[PF6]2(C5) . . . . . . . . . . . . 107
6.12 Molecular structure of [Cu2(MMoEG2p)2]2+ in crystals of C21 . . . . . . . . 108
6.13 Activation of oxygen with [Cu2(DPipG2p)2][PF6]2(C9) . . . . . . . . . . . . 109
6.14 Molecular structure of [Cu2(DPipG2p)2(µ-OH)2]2+
2in crystals of C22 . . . . 110
6.15 Activation of dioxygen with [Cu2(TMG2ch)2][X]2(X = I−, PF−
6and ClO−
4) . 111
6.16 Molecular structure of [Cu2(TMMoG2ch)2]2+ in crystals of C23,C24 and C25112
List of Figures xii
6.17 Perspective showing the double-chair conformation of [Cu2(TMMoG2ch)2]2+
in crystals of C23,C24 and C25 . . . . . . . . . . . . . . . . . . . . . . . . 113
6.18 Activation of oxygen with [Cu2(MorphDMG2p)2][PF6]2. . . . . . . . . . . . 114
6.19 Molecular structure of [Cu2(MorphDMG2p)2(µ-F)2]2+
2in crystals of C26 . . 115
7.1 Oxygenation and oxidation reactions . . . . . . . . . . . . . . . . . . . . . . 118
7.2 Reaction product of 2,4-ditertbutylphenol with the retention time of 20:16 min 119
7.3 Reaction product of 2,6-ditertbutylphenol with the retention time 22:53 min 120
7.4 Possible coupling products of 2,4-ditertbutylphenol and 2,6-ditertbutylphenol . 120
7.5 Mechanistic pathways proposed for the oxidative coupling of dialkylphenols
[160] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
7.6 Simplified orbital representation of the two-elctron phenol oxidation within a
(µ-phenoxo)(µ-hydroxo)dicopper species (adapted from [160]) . . . . . . . . 121
7.7 UV/vis absorption spectrum observed upon addition of 50 mg 3,5-
ditertbutylcatechol into a solution of [(DMPG2mX)2Cu2O2]2+ in CH2Cl2(0.5
mM, -80◦C) (first section: every 5 min, second section: every 10 min) . . . . 123
7.8 Plot of the absorption at 400 nm (3,5-DTBQ) vs. the time for the reaction of
[(DMPG2mX)2Cu2O2]2+ in CH2Cl2(0.5 mM, -80◦C) with 3,5-DTBC (6.6 mM)124
7.9 Plot of the absorption at 400 nm (3,5-DTBQ) vs. the time for the reaction
of [(DMPG2mX)2Cu2O2]2+ in CH2Cl2(0.5 mM, -80◦C) with 3,5-DTBC (13.2
mM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
7.10 Reaction product of 3,5-ditertbutylcatechol with the retention time of 13:02 min125
7.11 Hypothetical mechanism of the reaction of 3,5-DTBC via 3,5-DTBQ to 6,8-
di-tert-butyl-2,3-dihydro-2,2-dimethylbenzo[b][1,4]dioxine . . . . . . . . . . . 126
7.12 Overview of the reaction yields (conversion x selectivity) selected complexes 129
9.1 Schematic summary of the synthesised bisguanidine ligands . . . . . . . . . . 158
9.2 Schematic summary of the synthesised bisguanidine copper complexes . . . . 160
List of Tables
1.1 Characteristic spectral features of some CunOmadduct complexes . . . . . . 15
1.2 pKS-values of the conjugated acids of guanidines in water and MeCN [88, 89] 21
3.1 Overview of the chloroformamidinium chlorides (reactions starting from the
urea are marked with an asterisk) . . . . . . . . . . . . . . . . . . . . . . . . 30
3.2 Overview of the synthesised ligands with aromatic spacers . . . . . . . . . . 32
3.3 Overview of the synthesised ligands with aliphatic spacers . . . . . . . . . . 33
3.4 Selected distances and angles of the molecules in crystals of L5-1 and L7-1
(average values) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.5 Selected distances and angles of the molecules in crystals of L1-4,L11-1 and
of the ligand cation in crystals of [H2L1-2]I2·Et2O(average values) . . . . . 39
3.6 Quotient ρfor L5-1,L7-1,L1-4,L11-1 and of the ligand cation in crystals
of [H2L1-2]I2·Et2O(average values) . . . . . . . . . . . . . . . . . . . . . . 39
3.7 Comparison of NMR spectroscopic shifts of the NMe2groups at 298 K (*:Ref.
[109]) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.8 Comparison of coalescence parameters of the syn-anti isomerisation; a) tem-
perature range limited by solvent (Tmin 183 K);b) Ref. [109]; c) Ref. [129];
d) Ref. [130] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.1 Selected distances and angles of C1 . . . . . . . . . . . . . . . . . . . . . . . 50
4.2 Selected distances and angles of C2 . . . . . . . . . . . . . . . . . . . . . . . 52
4.3 Selected distances and angles of the copper(I) complexes C3 -C9 . . . . . . 55
4.4 Dihedral angles [◦] between the CN3-guanidine plane and the Cimin-Namin-
(Calkyl)2-planes (mean values and ranges of individuals) . . . . . . . . . . . . 58
4.5 Cyclovoltammetric data for C3,C5,C8 and C9 (MeCN, v = 100 mV/s, 25◦C) 60
4.6 Selected distances and angles of the copper(I) chains C10 and C11 . . . . . 61
xiii
List of Tables xiv
4.7 Selected distances and angles of the copper(I) chains in crystals of C12 and
C13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.8 Dihedral angles [◦] between the CN3-guanidine plane and the Cimin-Namin-
(Calkyl)2-planes (mean values and ranges of individuals) . . . . . . . . . . . . 67
4.9 Selected distances and angles of C14 . . . . . . . . . . . . . . . . . . . . . . 70
5.1 Correlation of the dihedral angles [◦] between the CN3-guanidine plane and
the Cimin-Namin-(Calkyl)2-planes with the capability of stabilising a P or O-core 81
5.2 Kinetic data for the formation of copper-dioxygen species (first order kinet-
ics)[28b] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5.3 Kinetic data for the reaction of [Cu(btmgp)I] with O2, k at 193 K . . . . . . 93
6.1 Selected distances and angles of [Cu2(btmmO)2I]+[112] . . . . . . . . . . . . 97
6.2 Selected distances and angles of [Cu2(btmmO)2]2+
2in crystals of C15 (The
primed atoms are derived from the unprimed ones by inversion.) . . . . . . . 98
6.3 Selected distances and angles of [Cu2(btmgp)2(µ-OH)2]2+ (The primed atoms
are derived from the unprimed ones by inversion.) [112, 113] . . . . . . . . . 99
6.4 Selected distances and angles of the bis(µ-alkoxo) and bis(µ-hydroxo) dicop-
per(II) complex cations containing the tripodal ligand TMG2MePA . . . . . 103
6.5 Selected distances and angles of the bis(µ-alkoxo) dicopper(II) complex cation
in crystals of C21 in comparison with btmgp and TMG2MePA containing
complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
6.6 Selected distances and angles of the bis(µ-hydroxo) dicopper(II) complex
cation [Cu2(DPipG2p)2(µ-OH)2]2+ in crystals of C22 in comparison with bt-
mgp and TMG2MePA containing complexes . . . . . . . . . . . . . . . . . . 110
6.7 Selected distances and angles of the bis(µ-alkoxo) dicopper(II) complex cation
[Cu2(TMMoG2ch)2]2+ in crystals of C23,C24 and C25 in comparison with
[Cu2(btmmO)2]2+ in C15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
6.8 Selected distances and angles of the complex cation [Cu2(MorphDMG2p)2(µ-
F)2]2+ in crystals of C26 in comparison with [Cu2(DPipG2p)2(µ-OH)2]2+ C22
(X = F−or OH−, resp.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
7.1 Screening of representative copper bisguanidine complexes towards their cat-
alytic abilities in % conversion (% selectivity) (*: related to GC/MS data,
absolute maximum yield 66 %) . . . . . . . . . . . . . . . . . . . . . . . . . 127
List of Abbreviations
Bu butyl
Bn benzyl
btmmo bis(trimethylmethoxyguanidino)propane
tBu tert-Butyl
Cys cysteine
δchemical shift (NMR), deformational vibration (IR)
d dublett (NMR)
dd double dublett (NMR)
extinction coefficient
en ethylenediamine
EI electron impact ionisation (MS)
Et ethyl
Hex hexyl
His histidin
J coupling constant (NMR)
k reaction constant
kDa kilodalton
LMCT Ligand to Metal Charge Transfer
m multiplett (NMR), medium (IR)
M molar
Me methyl
MeCN acetonitrile
Met methionine
MMoEG2p bis(methylmethoxyethyleneguanidino)propane
˜νvalence vibration (IR)
NHE normal hydrogen electrode
Ph phenyl
Pr propyl
R alkyl rest
s singulett (NMR), strong (IR)
t triplett (NMR)
THF tetrahydrofuran
TMMoG2ch bis(trimethylmethoxyguanidino)cyclohexane
TMMoG2MePA bis(trimethylmethoxyguanidino)-N-methyl-diphenyleneamine
vs very strong (IR)
vw very weak (IR)
w weak (IR)
List of Compounds
L1-2 TMG2doo C1 [Cu(TMG2PA*)I]
L1-3 TMG2ch C2 [Cu(DMorphG2p)I]
L1-4 TMG2PA C3 [Cu2(btmgp)2][PF6]2
L1-5 TMG2MePA C4 [Cu2(TMG2ch)2][I]2
L1-6 TMG2mX C5 [Cu2(DMEG2p)2][PF6]2
L1-7 TMG2py C6 [Cu2(DMEG2ch)2][Cu2I4]
L2-1 TEG2pC7 [Cu2(DMEG2ch)2][Cu4I6]
L2-6 TEG2mX C8 [Cu2(DMPG2p)2][PF6]2
L2-7 TEG2py C9 [Cu2(DPipG2p)2][PF6]2
L3-1 TiPG2pC10 [Cu(DMEG2p)]n[PF6]n
L4-1 DMEG2pC11 [Cu(DMEG2p)]n[I]n
L4-2 DMEG2doo C12 [Cu(TMG2mX)]n[I]n
L4-3 DMEG2ch C13 [Cu(DPPG2p)]n[CuI2]n
L4-6 DMEG2mX C14 [Cu2(TMGbenzPA)2][PF6]2
L4-7 DMEG2py C15 [Cu2(btmmO)2][PF6]2
L5-1 DMPG2pC16 [Cu2(TMMoG2MePA)2][PF6]2
L5-2 DMPG2doo C17 [Cu2(TMMoG2MePA)2][ClO4]2
L5-5 DMPG2MePA C18 [Cu2(TMMoG2MePA)2][BF4]2
L5-6 DMPG2mX C19 [Cu2(TMG2MePA)2(µ-OH)2][Cu2I4]
L5-7 DMPG2py C20 [Cu2(TMG2MePA)2(µ-OH)2][I3]2
L6-1 DPPG2pC21 [Cu2(MMoEG2p)2][PF6]2
L7-1 DPipG2pC22 [Cu(DPipG2p)2(µ-OH)2][PF6]2
L8-1 B(DMPip)G2pC23 [Cu2(TMMoG2ch)2][I]2
L9-1 B(TMPip)G2pC24 [Cu2(TMMoG2ch)2][PF6]2
L10-1 DImG2pC25 [Cu2(TMMoG2ch)2][ClO4]2
L11-1 DMorphG2pC26 [Cu2(MorphDMG2p)2(µ-F)2][PF6]2
L11-2 DMorphG2doo
L12-1 DSMorphG2p
L13-1 MorphDMG2p
L14-1 (DMPip)DMG2p
BFPPG2p
1 Introduction
1.1 Bioinorganic chemistry
Bioinorganic Chemistry is an interdisciplinary research field between Inorganic Chemistry
and Biochemistry. On the one hand, knowledge about inorganic reaction mechanisms
can be applied on biochemical processes. On the other hand, the elegant and efficient
solutions which have been developed by nature supply with indications for new applications
of inorganic chemistry.[1] Thus, the most important tasks of bioinorganic chemistry lie
in structural elucidation of metallo-biomolecules and the investigation of the complex
functions of metal active sites in biologic systems.[2, 3] Living organisms have to maintain
a steady state far from the thermodynamic equilibration in a permanently changing
environment by continuous supply with nutrients and energy. Equilibrium means death for
an organism. The biologic role of inorganic substances is the control of the nutrient flux
and the production of dynamic three-dimensional structures.[1]
The structural characterisation of metallo-biomolecules and also the investigation of corre-
sponding model systems contribute to the clarification and the comprehension of biologi-
cal processes. As these biomolecules have molecular masses sometimes of more than 106
g/mol, their crystallisation is difficult and the application of X-ray diffraction is limited.
Hence the concept of model compounds, which has been developed by Wieghardt,[4] Holm
and Ibers,[5] came to great importance. It can be distinguished between replicative and
speculative models.[3] Replicative models reproduce as exact as possible the coordinational
surrounding of the metal of a structural characterised metalloprotein. The absence of the
protein matrix in these small-molecular compounds facilitates the characterisation consider-
ably. Without exact structural information, the structural proposals are made as speculative
models. At the same time, newly gained insights regarding the model or the enzyme must
be transferable to each other. A particularly significant example for the importance of these
models is the reinterpretation of the coordination of molecular oxygen (end-on →side-on)
1
CHAPTER 1. INTRODUCTION 2
in the transport protein hemocyanin. The structural suggestion could be confirmed by an
X-ray structure analysis of oxy-hemocyanin after the synthesis of the corresponding model
complex.[2]
1.2 The bioinorganic chemistry of copper
Copper is a so-called coinage metal with a natural abundance in the earth shell of 0.007 %
and belongs to the 11th group of the periodic system. However, it differs in its special prop-
erties clearly from its group homologues silver and gold. Copper is for many organisms an
essential trace element although even small doses of copper(II)salts are extremely poisonous
for algae, fungi and bacteria. The total quantity of this element in the body of a human
adult amounts up to 150 mg. In higher organisms like humans, genetically caused diseases
of the copper metabolism lead to illnesses like the Wilson disease (pathologic accumulation
of copper in liver and brain), the Menke kinky hair syndrome (disruption of the intracellu-
lar copper transport, severe disfunction of the mental and physical development of babies
accompagnied by frizzly hair) and the amytrophic lateralsclerosis (ALS, neurodegenerative
illness caused by genetic defect of the [CuZn] dismutase).[2]
Furthermore, regarding its complex chemical properties, copper differs from its heavier ho-
mologues as well as from its neighbours of the 3d row (Ni, Zn) which generally have even
numbered electron configurations in their complex compounds by its relatively high stabil-
ity of the d9configuration (Cu(II)). Copper(I) ions are very flexibel with regard to their
coordination number due to their d10 configuration and the resulting lack of ligand field
stabilisation. In addition, very short Cu...Cu distances in polynuclear complexes indicate
possible attractive d10-d10 interactions.[6, 7] One origin of the high reactivity of Cu(I) com-
pounds towards triplet oxygen is the orbital mixing (3d/4s or 3d/4p). In aqueous solutions,
the smaller Cu(II) ions are more stable then the Cu(I) ions as they possess a higher hydra-
tion enthalpy. Hence, Cu(I) ions disproportinate easily in aqueous solutions. The Cu(II)-d9
system is a classical example for the Jahn-Teller effect. In this system, the square-planar
environment is favorised, in some cases complemented by weaker coordination of an axial
ligand.
CHAPTER 1. INTRODUCTION 3
1.3 Copper proteins in biological systems
1.3.1 Overview of the biological processes under participation of
copper enzymes
Regarding their function, copper proteins can be divided into two main groups: pure electron
transferring proteins and systems which interact with molecular oxygen or its metabolites.
Besides these groups, some huge proteins have several functions like the ceruloplasmin in
the regulation of the iron metabolism. Copper proteins divide up after their structural,
functional and analytical characteristics into the ”classic” types (Figure 1.1) and the recent
”non-classic” types (Figure 1.2).[8]
Coordinational geometry Function, abundance, spectroscopic
characteristics
Type 1 CuN N
S
NH
HN
CH3
S-
(Cys-)
(Met)
(His) (His) electron transfer; blue copper proteins, e.g.
plastocyanin, azurin; strongly distorted
polyhedron; intensive LMCT (Cys-CuII); weak
63,65Cu hyper fine coupling and g-anisotropy
Type 2 Cu
N
H2O
NN NH
HN
HN
(His)(His)
(His) catalysis, redox activity; amine oxidases,
galactose oxidase, (CuZn)-superoxide
dismutase, cytochrome-c-oxidase; largely
planar; no intensive absorptions, only
forbidden ligand field transitions, normal CuII
epr parameter
Type 3
Cu
N
NN NH
HN
HN
(His)
(His)
(His)
Cu
N
X
NN
HN
NH
NH
(His)
(His)
(His)
O2 transport and activation;
hemocyanin, tyrosinase;
bridged dimer, Cu-Cu distance 360 pm;
after O2 uptake intensive absorptions at
350 and 600 nm, LMCT transitions O22- to
CuII; store and transport form; epr inactive
due to antiferromagnetic coupled d9 centres
Figure 1.1: ”Classic” copper centers in biologic systems [2]
CHAPTER 1. INTRODUCTION 4
Coordinational geometry Function, abundance, spectroscopic
characteristics
Type
(2+3)-
Trimer Cu
Cu
Cu
N(His)
N(His)
(His)N
(His)N
HO
(His)N
(His)N
OH
N(His)
O2 activation for oxidase function;
ascorbat oxidase, laccase;
intensive LMCT (Cys-CuII); normal CuII epr
parameter
CuA
(His)
(His)
(Cys-)
(Cys-)
(Glu)
(Met)
Cu S
Cu
S
O
N
N
S
NH
HN electron transfer;
N2O reductase, cytochrome-c-oxidase;
absorption in the near IR (MMCT), very weak
Cu hyper fine splitting due to two equivalent
Cu; small g-factor
MT-Cu diverse centres
regulation, store and transport form; CUP2;
metallothioneins, Cu transport ATPase, no
oxidised form
Figure 1.2: ”Non-classic” copper centers in biologic systems [8]
1.3.2 Copper enzyme-mediated oxygen activation and transfer
Copper containing enzymes that activate O2act as dioxygenases, monooxygenases and oxi-
dases (Figure 1.3).[8, 10, 11, 12] The nuclearity of the active site does not correlate directly
with the type of reactivity, e.g. mononuclear Cu enzymes perform all three types of reac-
tions. Copper-containing oxidases constitute one of the major classes of biocatalysts that
participate in dioxygen processing.[10] They possess mononuclear, dinuclear or trinuclear
copper-active sites, many of which involve histidine imidazoles as supporting ligands.[13]
Typical examples of the mononuclear active site are found in dopamine β-monooxygenase,
peptidylglycine α-amidating monooxygenase and quercetin 2,3-dioxygenase which catalyse
the oxygenation of various organic substrates by molecular oxygen.[11, 14] A series of copper-
containing amine oxydases, lysyl oxydase and galactose oxidase also contain a mononuclear
copper active site.
The most important dinuclear copper-active sites are found in hemocyanin, tyrosi-
nase and catechol oxidase.[10, 15, 16, 17, 18, 19, 20] Tyrosinases are widely distrib-
uted throughout bacteria, fungi, plants and animals, catalysing the ortho-hydroxylation
of phenols to catechols (phenolase activity, equation 1 in Figure 1.4) and the ox-
idation of catechols to o-quinones (catecholase activity, equation 2 in Figure 1.4).
CHAPTER 1. INTRODUCTION 5
Cu/O2
O2H2O
Cytochrome c
Oxidase
Cu, Fe
O2-
O2 + O22-
Superoxide
Dismutase
Cu, Zn
RCH2NH2 + O2
RCHO
+ H2O2 + NH3
Amine
Oxidase
Lysyl
Oxidase
Cu, organic
RCHO + H2O2
RCH2OH + O2
Cu, organic
Galactose
Oxidase
Dopamine
β-Hydroxylase OH
HO
NH2
OH
HO
NH2
OH 1 Cu
Peptidylglycine
α−Hydroxylating
Monooxygenase
-OOC
HN O
OH
-OOC
HN O
Tyrosinase
OHHO
OH
+ O2
Tyrosinase
Catechol
Oxidase
1 Cu
2 Cu
OO
Hemocyanin
(O2 transport)
O2
O2
2 Cu
Ascorbate Oxidase
Laccase
FET3
Ceruloplasmin
O2
H2O
3 Cu
Particulate Methane
Monooxygenase
CH4 + O2
CH3OH
n Cu?
Figure 1.3: Selected Cu enzymes und proteins that activate O2[8]
R
OH
+ O2 + 2 H+
R
OH
OH
+ H2O
R
OH
OH
+2 e- + 2 H+
R
O
O
(1)
(2)
Figure 1.4: Phenolase activity (1), cate-
cholase activity (2)
These two processes are also referred as
”cresolase activity” or ”monophenolase ac-
tivity” and ”diphenolase activity”, respec-
tively. Such reactions represent the initial
steps of vertebrate pigmentation (melanin
biosynthesis) and the browning of fruits and
vegetables.[10, 15] Catechol oxidases are ubiq-
uitous plant enzymes which also catalyse the
oxidation of a broad range of catechols to the
corresponding o-quinones (catecholase activ-
ity), but lack the phenolase activity. The most plausible function proposed for plant cat-
echol oxidases is a role in the disease resistance of higher plants. The enzyme is cytosolic
or membrane-bound, whereas possible substrates are kept separated in the vacuole. After
disruption of the cell by wounding or infection, the membrane is lysed, and these two com-
CHAPTER 1. INTRODUCTION 6
ponents can come in contact. This causes the formation of quinones which spontaneously
polymerise to melanins. Some parasites have been found to use inhibitors of the catechol
oxidases, indicating that the catechol oxidase/diphenol system is an obstacle against the
colonisation of the host.[21] As further functions of catechol oxidases, a role located in the
thylakoid membrane during the photosynthesis has been discussed. Regarding the func-
tion of tyrosinase in mammals and insects, there is no controversy. In mammals, tyrosinase
initiates the formation of pigmentation. The absence or inactivation of the enzyme leads
to forms of albinism (tyrosinase-negative albinism and occultaneous albinism). In insects,
tyrosinases are involved in sclerotisation, i.e., the hardening of the chitinous cuticle and
defense.[21] Although the crystal structure of tyrosinase has yet to be solved, chemical and
spectroscopic investigations have unambigously demonstrated that the structure of the din-
uclear copper-active site in tyrosinase is very similar to those of catechol oxidase and the
dioxygen carrier protein, hemocyanin, whose structures have been determined by X-ray crys-
tallographic analysis.[9, 22, 23, 24, 25, 26, 27] In addition to these copper enzymes, there
are some other copper-containing monooxygenases such as particulate methane monooxyge-
nase (pMMO) and ammonia monooxygenase (AMO), in which the active site is believed to
constitute a multi-copper reaction center.[10]
1.3.3 Oxygen transport by hemocyanin
Hemocyanin (Hc) is a protein with a type-3-copper site, initially studied in the early 70´s,[28]
and the crystal structure of its active form was first reported in 1993 by Magnus and
coworkers.[24, 25] Hcs are copper-containing respiratory proteins, freely dissolved in the
hemolymph of many arthropod and mollusc species.[29] This function is related to the
capacity of Hc to bind molecular oxygen reversibly at the active site that is a dinuclear
copper centre. The protein is thus found in two different forms, i.e. deoxy-Hc, contain-
ing a [Cu(I)Cu(I)] pair with a Cu-Cu distance of 4.6 ˚
A, and oxy-Hc. In the latter form,
dioxygen was found to bridge between both copper(II)ions separated by a distance of 3.6 ˚
A,
reflecting an electron transfer process from Cu(I) to dioxygen, where the peroxide dianion is
coordinated as a bidentate ligand in a µ−η2:η2fashion (Figure 1.5).
Hcs can be divided into two classes depending on their biological source: the arthropodan
(e.g., lobsters and spiders) and the molluscan (e.g., octopus and snails) hemocyanins. These
have different subunit organisations and only a weak evolutionary relationship.[26] Molluscan
Hcs are hollow cylindrical molecules with molecular masses of 3.4 MDa to 9 MDa or greater.
CHAPTER 1. INTRODUCTION 7
Figure 1.5: Dinuclear µ−η2:η2peroxo copper active site of oxyhemocyanin from Octopus
dofleini [27]
Each subunit has a molecular mass on the order of 400 kDa. These associate as decamers, di-
decamers, or sometimes larger assemblies. The decamer is the smallest cooperative unit, and
this is the structure found in cephalopods and chitons, whereas most gastropods have tail-
to-tail dimers of such decamers. Each subunit contains 7 or 8 beads 50 to 60 ˚
A in diameter,
and each of these is a ”functional unit” containing one binuclear copper site and about 400
amino acid residues. Functional units are more protease resistant than the intervening or
”linker” regions, allowing their isolation.[27] Octopus dofleini hemocyanin is formed by ten
nearly identical polypeptides (the subunits) arranged in an antiparallel fashion around a
molecular 5-fold axis of symmetry. Magnesium or other cations are necessary for a stable
decamer, without which it dissociates into subunits. The Hc oxygen binding-site consists
of six histidine residues which coordinate two copper atoms and it is not exposed to the
solvent exterior. Each copper atom is coordinated by the N2of three histidine side-chains.
When viewed down the copper-copper axis, the ligands emanate nearly trigonally from each
copper atom and the two sets are partially staggered with respect to each other. The peroxide
bonding can be regarded as bifurcated Cu to O2−
2bonding, each Cu atom is thus coordinated
as a tetrahedron flattened with respect to the Cu-Cu axis.
CHAPTER 1. INTRODUCTION 8
1.3.4 Activation of molecular oxygen by type 3-centers
Figure 1.6: Overall structure of catechol oxidase from
sweet potatoes [17]
Catechol oxidases are found in
plant tissues and in some insects
and crustaceans,[30] whereas
tyrosinases can be isolated from
a broader variety of plants, fungi,
bacteria, mammalians, crus-
taceans and insects.[10, 30] The
structure of the catechol oxidase
from the sweet potatoe Ipomoea
batatas could be elucidated by
means of X-ray crystallography in
its met state as well in the deoxy
state by Krebs et al. (Figure
1.6). [17] Indeed, the active site
of the catechol oxidase exhibits
great similarities to the active site in hemocyanin. The catechol oxidase from Ipomoea
batatas (ibCO) has an ellipsoidal shape with axes of about 55, 45 and 45 ˚
A. The secondary
structure is dominated by α-helical regions. Both copper atoms forming the metal centre are
coordinated by three histidine N atoms. An unusual covalent thioether bond joins Cys92 to
the coordinating His109 (Figure 1.7). An analogous thioether bridge has been reported to
occur in tyrosinase from Neurospora crassa, in hemocyanin from Helix pomatia[31, 32] and
from Octopus dofleini.[27] The involvement of the Cys-His bridge in the catalytic pathway
is possible, but a structural function is also under discussion.
The active site is situated in a hydrophobic pocket. In the met state with both copper
atoms in the oxidation state +II, the two cupric ions are at a distance of 2.9 ˚
A. They are
bridged by a hydroxide ion at a distance of 1.8 ˚
A. The coordination sphere of each copper
atom can be described as a trigonal pyramid with His109 and His240 in the apical position,
respectively. In the deoxy or reduced state, both copper atoms are reduced to the oxidation
state +I with a Cu-Cu distance of 4.4 ˚
A. The coordination numbers are 4 for CuA (three
His ligands and a coordinating water molecule) and 3 for CuB (three His ligands). The
coordination sphere is distorted trigonal pyramidal for CuA and square-planar for CuB
with one vacant coordination site. [17]
CHAPTER 1. INTRODUCTION 9
Figure 1.7: Coordination sphere of the dinuclear copper centre in the met state [17]
The inhibitor complex with phenylthiourea has with 4.2 ˚
A a large Cu-Cu distance compared
with the met state.[17] The sulfur atom of the inhibitor substitutes the bridge of the met
state. The coordination sphere are identical with those of the met state, but a conformational
change of the amino acid residues takes place under rotation of the aromatic ring of Phe261.
The small changes of the spatial structure lead to the conclusion that the pocket of the
active site is rigid; the observed differences can be merely attributed to movements of the
copper atoms in this pocket. By means of the inhibitor complex, it has been proven that the
Phe261 is located above the active centre acting as gate which can rotate when the inhibitor
is bound. Thus, access of the substrate to the catalytic site seems to be controlled by this
”gate residue”. With this gate, the enzyme is supposed to differentiate between phenolic
and catecholic substrates. The metal centres in hemocyanin, tyrosinase and catechol oxidase
have very similar coordination spheres, but the substrate differentiation is determined by
the enzymatic pocket. Comparison of the ibCo structure with arthropodan hemocyanin
structures reveals that the hemocyanins have an aditional N-terminal domain. The size
and the position of this domain suggests that it acts a shield hindering the free access
of phenolic substrates to the dicopper centre. The phenyl alanine residue Phe49 of the
”shield region” reaches into the pocket of the oxygen-binding site. In the case of Limulus
polyphemus hemocyanin, Phe49 was shown to superimpose exactly on the position of the
CHAPTER 1. INTRODUCTION 10
substrate in an ibCO-substrate complex, thus blocking substrate binding. This means that
in hemocyanins, the gate is so narrow that only O2can pass it without the possibility of
further reaction.[20] This hypothesis is supported by the observation that spider hemocyanin
shows weak catecholase activity after proteolysis.
For the mechanism of the tyrosinase or catecholoxidase mediated phenol or catechol oxida-
tions with molecular dioxygen, several proposals have been made. The mechanism primarily
developed by Solomon et al.[10] and extented with recent results [15, 31] is presented in
Figure 1.8.[17] This mechanism suggests the oxy state to be the starting point of cresolase
activity (inner circle). This state is present in the resting form of tyrosinase in a proportion
of about 15 % (85 % met state). A monophenol substrate binds to the oxy state and is
monooxygenated to o-diphenol. This diphenol subsequently binds to the copper centre of
met tyrosinase in a bidentate binding mode proposed on the basis of a model compound
(see section 1.5.2).[33] Oxidation of the diphenol substrate leads to the reduced state of the
dinuclear copper centre. Reoxidation of the reduced state to the oxy state occurs by attack
of dioxygen and closes the catalytic cycle.
The mechanism of catecholase activity (outer circle) starts from the oxy and met states.
Cu Cu
O
O
His
His
His
His
His
His
Cu Cu
O
O
His
His
His
His
His
His
3H+
OH
O
2 H+
Cu Cu
O
O
His
His
His
His
His
His
H+
O
2 H+
OH
OH
Cu Cu
O
H
His
His
His
His
His
His
met-state
O
OH
OH
O
O
H2O +
Cu Cu
O
H
His
His
His
His
His
His
OO
2 H+
OH
OH
H+
OH
Cu Cu
O
H
His
His
His
His
His
His
O
inhibitor complex
oxy-state deoxy-state
Cu Cu
His
His
His
His
His
His
O2
H+
O
O
H2O +
Phenolase
cycle
Catecholase
cycle
Figure 1.8: Mechanism of cresolase and catecholase activity of tyrosinase and/or catechol
oxidase [17]
A diphenol substrate binds to the met state, followed by the oxidation of the substrate to
the first quinone and the formation of the reduced state of the enzyme. Binding of dioxy-
CHAPTER 1. INTRODUCTION 11
gen leads to the oxy state which is subsequently attacked by the second diphenol molecule.
Oxidation to the second quinone forms the met state again and closes the catalytic cycle.
CuII CuII
S
H2NNHis
His
His
His
His
His
Figure 1.9: PTU inhibitor
complex
Alternative reaction mechanisms include a radical mechanism
proposed by Kitajima and Moro-oka [34] and a mechanism
involving a Cu(III) intermediate based on measurements of
model compounds.[35] Krebs et al. postulate on the basis of
the crystal structure of the phenylthiourea (PTU) inhibitor
complex only a monodentate attack of the catechol at one
of the copper atoms.[17] Very recently, Stack et al. have re-
ported that the electrophilic reaction observed for tyrosinase
does not exclude the intermediacy of bis(µ-oxo)dicopper(III)-
core components.[36] It is discussed that, during the coordi-
nation of the phenolate to the µ-η2:η2-peroxodicopper(II) core, the peroxo bond is cleaved
reductively under formation of the Cu(III) species. The distinct difference between catechol
oxidase and tyrosinase has yet not been explained. A lag phase in the monophenolase activity
of tyrosinase has been found and studied and is proposed to be a result of temporary inhi-
bition of the met state of tyrosinase by excess of the monophenol substrate (Figure 1.8).[15]
Monophenolase activity increases when the diphenol product displaces the monophenol from
met tyrosinase and allows the continuation of the catalytic cycle.
1.4 Technical application of copper compounds in catalytic
oxidative transformations
Industrially,[37] copper has long been used as a catalyst in the Glaser process, which couples
terminal acetylenes to give diacetylenes using cuprous chloride and molecular oxygen (process
1 in Figure 1.10). This is a historically important (but now obsolete) catalytic process for
producing the precursor to chloroprene which is then used to produce neoprene rubber. An-
other important industrial process which utilises copper/dioxygen chemistry is the oxidative
coupling of 2,6-xylenol to form a para-phenylene oxide polymer by coupling an oxygen of
one phenol molecule to the para carbon of another to form an aromatic polyether by the
trade name PPO (process 2 in Figure 1.10).[38] This polyether is a high melting plastic that
is extremely resistant to heat and to water, and it is useful as an engineering thermoplastic.
Another less common process also uses copper(I)chloride to catalyse the analogous oxidation
CHAPTER 1. INTRODUCTION 12
of 2,6-diphenylphenol to form an even more rigid and higher melting material than PPO.
A further important copper-catalysed process is the oxidative decarbonylation of benzoic
acid to phenol which was patented by Dow Chemical in 1955 (process 3 in Figure 1.10).[39]
Behind the Cumol process it is the second most important process (200,000 t/a) in industrial
phenol production.
Cl
Chloropren (1)
(2)
(3)
OH O
*
n
O
C
O
OH OH
OH O
O
(4)
[Cu]
[Cu]
[Cu]
[Cu]
Figure 1.10: Copper-catalysed processes in industry
Also of technical interest is the oxidation of aromatic substrates such as phenols to
quinones,[40] e.g. 2,3,6-trimethylphenol to trimethyl-p-benzoquinone, an important vita-
min E precursor, that had been claimed by a patent of the Mitsubishi Gas Corp. in the mid
1980´s.[41] Aerobic oxidation of catechols to o-quinones and the hydroxylation of arenes are
just two more copper induced catalytic processes that are currently studied.[35] The oxidative
carbonylation of alcohols attracted particular attention in the past because a row of products
(e.g. polyurethanes, polycarbonates) are based on the organic carbonates that are formed in
that catalysis.[42] An important industrial process that indirectly utilises copper/dioxygen
chemistry is the Wacker process which produces acetaldehyde from ethylene.[43] In this
process, both palladium chloride and cupric chloride are used. Although the copper cat-
alyst is not directly involved in the oxidation of the ethylene substrate, it is crucial for
catalysing the re-oxidation of Pd(0) to Pd(II) to sustain the catalytic cycle. Synthetically,
copper/dioxygen reactivity has been utilised in a similar fashion, in the osmium-catalysed
hydroxylation of olefins. Cupric chloride/O2is used to catalyse the re-oxidation of osmium
from a formal oxidation state of +6 to +8. Other synthetic uses of Cu/O2catalysts include
the oxidation of various substrates such as aniline, aromatic diamines, alcohols and thiols.[44]
CHAPTER 1. INTRODUCTION 13
1.5 Biomimetic model systems for type 3-copper centres
1.5.1 Reactions of Cu(I) complexes with molecular oxygen under
formation of Cu/O2adduct complexes
Reproducing complex biological reactivity within a simple synthetic molecule is a challenging
endeavour with two goals. First, the sequence of examining biological reactivity, creating
similar chemical architectures, and determining functional reaction conditions for model
systems is a process that allows the biological code of reactivity to be deciphered. This
process is greatly aided by X-ray structural data as the atomic arrangement at the active
site fully encodes the observed reactivity. Second, the greater availability of such structural
information now allows a shift in the role of synthetic modeling from structural and spec-
troscopic endeavours to development of functional and catalytic models. Functional models
can provide an opportunity to examine a biological reactivity at a small-molecule level in
detail through systematic and comparative studies. Although one goal of modeling is re-
production of reactivity, the extension of this reactivity towards catalytic applications in
industry is an even more important objective as tailored ligand design can lead to effective
and environmental friendly oxidation catalysts. There are many recent reviews describing
different aspects of Cu/O2adduct formation, characterisation and subsequent reactivity to-
ward substrates.[16, 45, 46, 47, 48, 49, 50, 51, 52, 53]
The expanded research efforts during the past two decades to stabilise and characterise
Cu/O2species formed by the oxygenation of Cu(I) complexes can be attributed partly to
a greater accessibility of appropriate spectroscopic tools and to a better appreciation of the
appropriate reaction conditions. Low temperature, aprotic solvents and weakly coordinat-
ing anions are now standard conditions. This approach contrasts with earlier studies that
relied on using ambient temperatures and coordinating anions; under these conditions, most
Cu(I) complexes react with O2in a 4:1 stoichiometry without any measurable accumula-
tion of intermediates. The ensuing products are Cu(II) complexes ligated by oxide-level
ligands - oxide, hydroxide, or water - created by O2reduction.[45] Lower reaction temper-
atures enhance the lifetime of the initially formed Cu/O2species by reducing the entropic
costs of formation and by attenuating subsequent reactions. This strategy has yielded well-
characterised thermally sensitive species with Cu:O2reaction stoichiometries of 1:1, 2:1 and
3:1. An overview of this diverse array of Cu/O2species is given in Figure 1.11. Table 1.1
summarises the characteristic spectroscopic features of some CunOmadduct complexes.
CHAPTER 1. INTRODUCTION 14
CuIIL
LCuII O
O
CuIIIL
LCu O
O
µ-η2:η2- peroxo
Cu...Cuavg 3.51
O-Oavg 1.42
Cu-Oavg 1.92
CuIIL
LCu O
O
η1-superoxo
CuIIL
O
LCuII OOH
LCuII O
ES
bis(µ3-oxo)
Cu...Cuavg 2.65/2.71
O...Oavg 2.32
CuII-Oavg 1.98
CuIII-Oavg 1.85
η1-hydroperoxo
O-O 1.46
Cu-O 1.89
O
LCuII O
SS
η2-superoxo
O-O 1.22
Cu-O 1.84
Cu(II)
O
LCuIII O
MP
η2-peroxo
O-O 1.44
Cu-O 1.85
Cu(III)
Cu:O2 =1:1
trans-µ-1,2-peroxo
Cu...Cu 4.36
O-O 1.43
Cu-O 1.85
O
LCuII OCuIIL
TP
SP
bis(µ-oxo)
Cu...Cuavg 2.80
O...Oavg 2.32
Cu-Oavg 1.82
O
2:1
O
LCuII
O
CuIIL
η1-superoxo
CuIIIL
O
OH
LCuIII
µ-1,1-hydroperoxo
3:1 4:1
OO
CuIIL
LCuII
CuIIL
LCuII
cis-µ4-η2:η2- peroxo
Cu...Cu 2.99/3.03
O-O 1.45
Cu-O 1.95
O
OCuIIL
LCuII
CuIIL
LCuII
trans-µ4-η2:η2- peroxo
Cu...Cu 2.90/3.90
O-O 1.50
Cu-Oavg 1.99
III
III
Figure 1.11: CunOmcores in characterised complexes (for crystallographically characterised
species, significant metrical parameters (˚
A) are given) [45]
1.5.2 Ligand systems and their influence on the formation of Cu/O2
adduct complexes
N N
py
py py
+ O2
O
CuICuI
py
N N
py
py
py
O
CuII CuII
py
OO
Figure 1.12: Reaction of [Cu2(XYL-O−)]+
with O2
In 1984, Karlin et al. [67] reported the first
case of reversible dioxygen binding to copper,
where the reaction product was also proven
to possess an intact O-O bond. This in-
volves a dicopper complex with a bridging
phenoxide ligand. The dicopper(I) complex
[Cu2(XYL-O−)]+reversibly reacts with one
mole of O2at -80◦C to form the adduct
[Cu2(XYL-O−)(O2)]+(Figure 1.12). This species is a peroxo-dicopper(II) complex as de-
termined from resonance Raman (ν(O-O) 803 cm−1) and X-ray absorption spectroscopic
studies. Structural insights from EXAFS spectroscopy (Cu...Cu 3.31 ˚
A) and a mixed iso-
tope (16O - 18O) resonance Raman experiment suggest that the peroxo ligand is terminally
bound, consistent with the presence of two peroxo-to-copper(II) charge transfer bands, as-
signed as π∗
σ(505 nm) and π∗
v(610 nm) transitions. In 1988, Karlin and coworkers [57, 58]
characterised the first copper-dioxygen adduct X-ray crystallographically. The reversible
oxygenation of the precursor complex [(TMPA)CuI(RCN)]+yielded the trans-µ-1,2-peroxo
dicopper species [(TMPA)Cu2(O2)]2+ (Figure 1.13).
CHAPTER 1. INTRODUCTION 15
Table 1.1: Characteristic spectral features of some CunOmadduct complexes
Coordination mode UV/Vis: λmax/nm[/M−1cm−1] Raman: ν(O-O)/cm−1references
η1-superoxo 400-430(4000-8000) O16-O18: 800-900 Karlin et al.[51]
580-600(1000-1700) ∆[O18]: 50-60
η2-superoxo 450-510(200-300) O16-O18: 1050-1200 Solomon et al.[54]
660-700(40-90) ∆[O18]: 50-60 (smaller
ν(Cu-O) at 550 cm−1)
η2-peroxo 400-420(2300-2400) O16-O18: 960-970 Tolman et al.[55, 56]
600(broad, 220) ∆[O18]: 50
trans-µ1,2-peroxo 435(3000-2400) O16-O18: 830-845 Karlin et al.[57, 58]
520-550(9000-15000) ∆[O18]: 40-50(smaller Suzuki et al.[59]
590-625(7000)(sh) ν(Cu-O) at 550 cm−1)
µ-η2:η2-peroxo 330-365(20000) O16-O18: 710-765 Kitajima et al.[34, 60]
530-600(850), further band at ∆[O18]: 40 Kodera et al.[62]
420-490 for butterfly core[68]
bis(µ-oxo) 290-330(10000-12000) O16-O18: 580-600 Tolman et al.[63]
390-430(13000-15000) ∆[O18]: 20-25
µ-1,1-hydroperoxo 350-395(3000-4200) O16-O18: 850-890 Itoh et al.[64]
450(1600)(sh) ∆[O18]: 50
630(400) (very weak)
bis(µ3-oxo) 290(12500) O16-O18: - Stack et al.[65]
355(15000) ∆[O18]:-
480(1400), 620(800)
µ4-peroxo 390(9500) O16-O18: 880-890 Krebs et al.[66]
590(600) ∆[O18]: 40
O
OCuII N
py
py
2
py
CuII
N
py
py
py
+ O2
NCMe
CuII
N
py
py
py
2+ 2 MeCN
Figure 1.13: Reaction of [(TMPA)CuI(RCN)]+with O2
In 1994, Kitajima and coworkers [34, 61] used a sterically hindered tridentate ligand
in characterising CuII[HB(3,5-iPr2pz)3]2(O2) (HB(3,5-iPr2pz)3= hydrotris(3,5-diisopropyl-
pyrazolyl)borate anion, see also Figure 1.14), which has a side-on ligated µ-η2:η2-
peroxodicopper(II) structure with physical properties closely matching those of Limulus
polyphemus oxy-hemocyanin. This important contribution to synthetic modelling of metal-
loproteins in fact preceded confirmation of the protein Cu2O2side-on structure.
CHAPTER 1. INTRODUCTION 16
Since then, the research field of bioinorganic copper-dioxygen chemistry has flourished.[45,
48, 49] Central topic are the investigations on the influence of N donor ligands on the
formation and structure of the Cu/O2adduct complexes as well as the mechanisms of the
oxygen-uptake reactions. In Figure 1.14, the most prominent ligand families are depicted.
Since the copper centres in biological systems like hemocyanin and catechol oxidase are
coordinated by three terminal histidine functions, the use of multidentate N donor ligand
systems has been successful in the synthesis of model complexes. Especially the use of bi-
and tridentate N donor systems was fruitful for the stabilisation of the (4+1) square-planar
coordination of the Cu atoms in the diverse oxo states. Besides the denticity, the hardness
of the ligands can be tuned by the use of harder aminic or softer aromatic or iminic N donor
functions. By using different alkyl substitution patterns, the electronic properties of the N
donor function can be modified. The bite as well as the steric demands of the ligands are
also essential parameters. This may be illustrated by the example of the HB(3,5-iPr2pz)3
system: Kitajima et al. were able to show that, by substitution of the iPr groups against
tBu groups, no longer the µ-η2:η2-peroxodicopper(II) complex is formed upon oxygenation
but the mononuclear η2-peroxo complex.[68]
1.5.3 Reactions of d10 precursor complexes with triplet oxygen
The reaction of Cu(I) precursors with molecular oxygen is influenced by many factors and
not yet fully understood. During the reaction of Cu(I) to Cu(II), the coordination spheres
have to change drastically. The spheric symmetrical Cu(I) ion (d10) is found in coordina-
tion numbers of 2 to 5 with domination of linear, trigonal planar and distorted tetrahedral
arrangements. The Cu(II) ion (d9) favourises coordinational environments with four strongly
bound equatorial ligands and 1 or 2 weaker bound axial ligands (Jahn-Teller-effect). The
change of the coordinational environment results in an energetic barrier which dictates ki-
netics as well as thermodynamics of this system.[84] By the coordinating ligand, the redox
properties of the Cu(I)/Cu(II) systems are strongly influenced. Soft donor functions like
S, P or unsaturated N systems stabilise Cu(I) compounds whereas N and O donor systems
favourise Cu(II) compounds. Furthermore, the redox potentials can be influenced by the
size of the chelate rings and the polarity of the solvent.
In spite of the strong O-O bond (118 kcal/mol) is oxygen known to be a strong oxidant.
Although the oxidation products are thermodynamically favoured, the course of the reac-
tion is kinetically inhibited. So, the educts are relatively inert under normal conditions. In
CHAPTER 1. INTRODUCTION 17
HB N
N
NN
NR1
R2
R1
R2N
R1
R2
N
N
NR2
R3
R1
NR1R2
NR1R2
NR1R2
NR1R2
NR1R2
NR1R2
N NEt2N
R1NR2R3
Bidentate ligands
Tridentate ligands
R1,R2cd, Stack [69] R1,R2ed and R1,R2pd, Stack [46, 70]
PhPyNEt2, Tolman [73] R1Py1R2,R3, Itoh [74]
P
N
NH
But
But
SiMe3
SiMe3
PN2, Hofmann[71]
N
N
R2
R1
R2
R3
R3
R3
R3
R1,R2DkR3, Tolman [72]
Tetradentate ligands
TpR1,R2, Kitajima [34]
N N
N
N
H
N
N
H
bitripy, Kodera [62]
NN
py
py
py
n
py
N N
py
py
py
py
R
R1N
N
N
R2
R2
R1Py2R2, Karlin [80]
R1,R2,R3tacn, Tolman [48]
"Wieghardt´s ligand" Py2-Nn, Karlin [76] Py2-m-xylR, Karlin [77]
N
N
N
R
R
N
N
NR
R
R4dtn-m-xyl, Tolman [78] N N
N
N
N
N
NN N N
L66, Casella [81]
N
NN
Me2N
N
NMe2
pzdien, Meyer [79]
N
R
R
R
R´
N
NR1R2
NR1R2
1R2RN
R,R´-tpa, Karlin [58]
R´
R´
R13R23tren, Schindler [82] N
N
NN
O
CO2MeMeO2C
bisp, Comba [83]
N
HOHOH
tBu
tBu
tBu
But
H3bpa, Wieghardt [75]
Figure 1.14: Overview of ligand families
CHAPTER 1. INTRODUCTION 18
fact, the redox reactions with the transfer of 4 e−to O2under formation of water (E0= +
1.23 V) or of 2 e−to hydrogen peroxide (E0= + 0.69 V) are thermodynamically favoured,
whereas processes under stepwise electron transfer (formation of O−
2: E0= - 0.16 V) are un-
favourable. One reason for this behaviour is the triplet state of oxygen. The 3O2molecule is
a diradical with the orbital occupation of [KK](σz)2(Πx,Πy)4(Π∗
x)1(Π∗
y)1. Therefore, the 3O2
molecule can react in spin-permitted processes with a molecule that has unpaired electrons
or the reaction has to lead to a product with triplet ground state. Nevertheless, even at low
temperatures (-80◦C), a very fast reaction of 3O2with Cu(I) complexes can be observed.
This result is somehow surprising as Cu(I) possesses with its d10 configuration a closed 3d
electron shell and thus is diamagnetic. However, the greater spin-orbital coupling in metal
ions leads to a decrease of the kinetic barrier for a spin reverse and the spin restriction is no
langer in force. During the binding of the oxygen to the metal centre, it comes to a classical
σdonor and πacceptor binding mode. The O-O bond is weakened and, formally seen, elec-
trons are transferred to the oxygen which is reduced under oxidation of the metal. In the last
years, the reaction kinetics of the formation of Cu/O2adduct complexes were investigated
by means of stopped-flow methodes by Zuberb¨uhler and Schindler.[85, 50] The connections
are complex and strongly related to the corresponding systems. In Figure 1.15, the reac-
tion of a monomeric precusor complex Awith oxygen is shown. First, a fast, reversible
side-on-binding of an oxygen molecule under formation of the mononuclear complex Btakes
place. Then, this complex reacts with a second precusor molecule in an irreversible, rate-
determining step to the dinuclear complex C. Itoh et al. observed a second-order kinetic for
this step.[86] By temperature-depending measurements the activation enthalpy (∆H‡) and
CuI
N
N
N
+O2CuII
N
N
N
O
O
AB
CuI
N
N
N
rate determining CuII
N
N
N
O
O
C
CuII
N
N
N
2
Figure 1.15: Reaction of mononuclear Cu(I) precursor complexes with molecular oxygen
the activation entropy (∆S‡) can be determined. Generally, the values of ∆H‡are in the
range of 10-50 kJ/mol which is quite small. Contrastingly, the values for ∆S‡are strongly
negative in the range of -100 to -300 kJ/mol. Thus, the stability of the oxygen binding is
CHAPTER 1. INTRODUCTION 19
controlled by favourable enthalpies and unfavourable entropies such that Cu2O2compounds
should not be observed at room temperature.[85] However, in the meantime, Kodera at al.
synthesised a µ-η2:η2-peroxo dicopper system which is stable at 25◦C in CH2Cl2for one
day.[62] Gorun and coworkers also reported on the synthesis of a room temperature stable
µ-η2:η2-peroxodicopper complex, by replacing C-H bonds in the vicinity of the Cu2O2core
with C-F bonds.[87]
1.5.4 Complexes with µ-η2:η2-peroxo and bis(µ-oxo) dicopper cores
The reactions of the Cu(I) precursors with molecular oxygen can be observed very well by
means of UV/Vis and resonance Raman spectroscopy. The crystallisation is possible only
under special conditions. Fortunately, the distinction between the µ-η2:η2-peroxo and bis(µ-
oxo) dicopper cores (P- and O-cores, respectively) can be made with these spectroscopic
methods.[48] Figure 1.16 depicts some structural features of these two cores. In the UV/Vis
CuII
CuII
O
O
CuIII
CuIII
O
O
µ-η2:η2- peroxo
P-core
bis-µ-oxo
O-core
CuI
CuI
O
O
1.4Å
1.9 Å
3.6 Å
1.8 Å
2.8 Å
Figure 1.16: Equilibrium between µ-η2:η2-peroxo and bis(µ-oxo) dicopper cores
spectra, the P-core shows characteristic absorptions at 350 nm (≈20000 M−1cm−1, assigned
to the peroxo-Cu(II) charge transfer) and at 550 nm (≈1000 M−1cm−1), whereas the O-
core has a pair of characteristic absorptions at 300 nm and 400 nm with an extinction
coefficient of approximately 14000 M−1cm−1. These bands can be assigned to O2−-Cu(III)
charge transfers. The P-core is antiferromagnetically coupled, both cores are EPR-silent. In
the resonance Raman spectrum, the O-O bond of the P-core can be detected at 750 cm−1,
whereas the O-core exhibits a Cu2O2breathing mode at 600−1. A closer discussion of the
MO situation of these two cores can be found in section 5.1. Tolman et al. reported that the
equilibrium between these two species can be shifted by the solvents and the counterions. [63]
Coordinating solvents favour the formation of a bis(µ-oxo) species whereas non-coordinating
solvents stabilise the µ-η2:η2-peroxo species. Furthermore, a change in the substitution
pattern of a ligand system (e.g. diamines, tacn) can switch the P/O equilibrium totally to
one side. [45, 49] Generally, tridentate ligand systems favour merely the P-core and bidentate
CHAPTER 1. INTRODUCTION 20
systems the O-core, but there are numerous counter-examples for this trend. [48] In spite of
great efforts in this field, not all types of influence have been fully understood.
1.6 Guanidines - model systems for the enzymatic
environment
The synthesis and characterisation of novel ligand systems plays an important role for co-
ordination chemistry as the coordinating ligands determine the formed complexes regarding
their thermodynamic and kinetic stability, their solubility and their redox properties. The
purpose of this thesis is the synthesis of biomimetic oxygen activating copper complexes.
Therefore, the ligand design has to be orientated by efficient solutions of Nature. Suited lig-
and systems are ligands with N donor functions which are similar to the basic δimin function
of histidine, one of the most versatile and successful systems found in biologic coordination
chemistry. The essential amino acid histidine coordinates several metals in high oxidation
states, e.g. copper in all type 3-centres, iron in hemerythrin, manganese in manganese cata-
lase and manganese superoxid dismutase. In the CuZn superoxid dismutase, histidine acts
as well as bridging ligand between the two metals.[2] Furthermore, the desired bio-inspired
ligand system should be multidentate, chelating and neutral. The stabilisation of higher
oxidation states like Cu(III) succeeds better with a strongly basic molecule. The demanded
basicity and biomimetic coordination properties are combined by guanidine systems.
Peralkylated guanidines belong to the strongest organic neutral bases known. They are sev-
eral magnitudes superior in basicity than tertiary amines due to the excellent stabilisation
of the positive charge in their protonated form (Figure 1.17).[88]
N N
N+
RH
CH3
CH3
CH3
H3CN N+
NRH
CH3
CH3
CH3
H3CN+N
NRH
CH3
CH3
CH3
H3CN N
NRH
CH3
CH3
CH3
H3C
Figure 1.17: Delocalisation of the positive charge in a guanidinium cation
The type and number of substituents influence considerably the basicity of the guanidine
function as it is shown in Table 1.2.[88, 89] This possibility of variation is important for the
complexation properties and the stabilisation of higher metal oxidation states. Via intro-
duction of a methyl group (no. 2), the basicity decreases compared with the unsubstituted
parent compound guanidine (no. 1) as the symmetry in the equivalence of the resonance
CHAPTER 1. INTRODUCTION 21
structures of the conjugated guanidinium cation is disturbed. This effect can not be fully
compensated by a single methyl group by hyperconjugation, whereas in the case of multi-
ple methyl substitution (nos. 5 and 6), this effect is overcompensated. The torsion of the
substituent planes can also be decisive: the full substitution with sterically demanding alkyl
groups (no. 7) leads to a slight diminuishing of the basicity in comparison to pentamethyl-
guanidine (no. 6). By the twisting of the substituent planes, the efficiency of the conjugation
as well as the hyperconjugative effect is reduced. Such a distortion can be hindered by the
integration of the guanidine groups into a cycle (no. 8) resulting in a slightly higher basicity.
However, the introduction of acceptor and aryl substituents generally leads to a decrease
of the basicity (nos. 3 and 4) which can be traced back to the good donor qualities of the
substituents.
Table 1.2: pKS-values of the conjugated acids of guanidines in water and MeCN [88, 89]
No. R1R2R3R4R5pKS(H2O) pKS(MeCN)
1 H H H H H 13.6
2 Me H H H H 13.4
3 Ph H H H H 10.77
4 Ac H H H H 8.20
5 H Me Me Me Me 13.6 23.3
6 Me Me Me Me Me 15.6 25.0
7iPr iPr iPr iPr iPr 13.8
8 R R R R Me 25.43
R = -(CH2)3-
Guanidines are ubiqitous in Nature, e.g. in the essential amino acid arginin which is
present in almost all proteins. In organic synthesis, guanidines are used as phase trans-
fer catalysts,[90] as non-nucleophile bases and as solvents in form of ionic liquids.[91] In
technical systems, guanidines are found as components or intermediates in the production
of pharmazeutics and pesticids like chloronicotinylguanidine. Some guanidinium salts have
come to importance as impregnants or flameproofing agents as well as emulsifiers or antistatic
agents in textile industry.
1.6.1 Peralkylated Bisguanidine Ligands
In 1965, guanidines were investigated as neutral ligands for the first time by Longhi and
Drago who supposed good donor properties by the high basicity of tetramethylguanidine
CHAPTER 1. INTRODUCTION 22
(TMG).[92] In 1970, Snaith, Wade and Wyatt synthesised extremely hydrolysis sensible
adducts of TMG and aluminium alkyls.[93] Later, Pruszynski et al. designed the first chelat-
ing guanidine ligands.[94]
Today, guanidines are emerging as a potentially useful ligand class due to their versatile coor-
dination chemistry. Neutral guanidines [(R2N)2C=NR], guanidinates(1-) [(RN)2CNR2]−and
guanidinates(2-) [(RN)2C=NR]2−are capable of exhibiting a variety of coordination modes
and a range of donor properties leading to compatibility with a remarkably wide range of
metal ion requirements from all parts of the periodic table. [95, 96, 97, 98, 99] Furthermore,
numerous complexes are reported in which guanidinium cations are present, but these are
not located within the coordination sphere of the metal ion and consequently merely rep-
resent counterions.[100, 101] Whilst application of the negatively charged guanidinates has
become more widespread in coordination chemistry, the use of the neutral guanidines has
not received similar attention to date.[95] Bailey and coworkers investigated the behaviour of
monodentate guanidine ligands [102] whereas Coles et al. introduced bicyclic guanidine sys-
tems into coordination chemistry.[96, 97, 98] Mostly, these systems are not peralkylated, but
meanwhile, peralkylated phosphorus [103] or silicon [104] bridged systems have been devel-
oped. Pruszynski et al.,[94] Pohl et al.[105, 106] and Sundermeyer et al.[107, 108, 109, 110]
investigated peralkylated guanidine systems with organic bridges. Furthermore, Kuhn et
al.[111] developed imidazolin-based systems which belong to the bisguanidine class of lig-
ands. In guanidine complexes, coordination occurs almost exclusively via donation of the
lone-pair of the Nimine atom into appropriate acceptor orbitals of the metal.
In search of bifunctional nitrogen donor ligands able to stabilise unusually high metal oxi-
dation states, our interests were attracted by peralkylated guanidyl-type systems. Follow-
ing this approach, bis-tetramethylguanidinopropylene (btmgp) was synthesised as the first
member of a series of bifunctional peralkylated guanidine ligands designed for use in bio-
mimetic coordination chemistry.[105, 106, 112] A great advantage of guanidine ligands lies
in their stability towards fragmentation reactions. We could show that btmgp-containing
copper-dioxygen complexes react only with the peripheric substituents under conservation
of the guanidine scaffold [113] in contrast to other systems where dealkylation reactions are
observed.[49]
CHAPTER 1. INTRODUCTION 23
1.6.2 Synthesis methods for guanidines
Alkylation of tetrasubstituted guanidines
The simpliest method for the synthesis of chelating guanidine systems is the reaction of
guanidine derivatives with dihalogenoalkanes (Figure 1.18).[105] Unfortunately, this method
requires a great excess of the guanidine, long reaction times and only btmgp can be synthe-
sised in sufficient yields. The reason for these difficulties lies in the occuring side reactions
such as polyalkylation or elimination reactions.
C
NH
1R2RN NR1R2
2- 2 HX
X
X
C
N
1R2RN
NR1R2
C
N
NR1R2
NR1R2
Figure 1.18: Reaction of guanidine derivatives with a halogenealkane
The Bredereck method
In the so-called Bredereck method,[114] several pentaalkyl- and aryltetraalkylguanidines
can be accessed by combining peralkylated ureas with phosphoroxychloride. This method is
based on the activation of the urea by the phosphoroxychloride for the following reaction with
the amine (Figure 1.19). Although an equimolar reaction of urea, POCl3and amine seems
possible, the use of amines and POCl3in excess is advantageous. In addition, thioureas are
more reactive than ureas due to the higher nucleophilicity of the sulfur atom facilitating the
primary attack of POCl3. Disadvantageous in this method are the generally long reaction
times of 8 h.
C
O
1R2RN NR1R2
POCl3R3NH2
-HPO2Cl2
-HCl
PO2Cl2
C
Cl
1R2RN NR1R2C
NR3
1R2RN NR1R2
Figure 1.19: Synthesis of guanidines after Bredereck
Reaction of isocyaniddichlorides with amines
A further possibility for the preparation of pentasubstituted guanidines is the reaction of iso-
cyaniddichlorides with secondary amines (Figure 1.20).[115] This synthetic strategy is useful
CHAPTER 1. INTRODUCTION 24
for the synthesis of unsymmetrically substituted guanidines due to the principal possibility
of isolating the intermediately obtained chloroformamidines.
C
NR1
Cl Cl
R2R3NH
-HCl C
NR1
2R3RN Cl
R4R5NH
-HCl C
NR1
2R3RN NR4R5
Figure 1.20: Guanidines via reaction of isocyaniddichlorides with amines
Condensation of amines with Vilsmeier salts
The most efficient method to synthesise peralkylated guanidine systems is the strategy ana-
logue to the Vilsmeier synthesis.[116] In classic organic synthesis, activated aryls like phenols
and dialkylanilines are formylated via the Vilsmeier synthesis. By reaction of a equimolar
mixture of a N,N-disubstituted formamid and phosphoroxychloride with an activated aromat
and subsequent hydrolysis, the formylation product can be obtained in good yields (Figure
1.21). In the primary reaction of the formamid with the phosphoroxychlorid via a Vilsmeier
complex, a chloromethaniminium salt is formed as reactive intermediate which attacks the
aromatic core electrophilicly.
C
O
H
N R1
R2
P
O
Cl
Cl
Cl
C
O
H
N R1
R2
P
O
Cl Cl
C
O
H
N R1
R2
P
O
Cl Cl
Cl
Vilsmeier complex
CH
O
Cl
N R1
R2
P
O
Cl Cl
NC
H
R1
R2
Cl NC
R1
R2
H
Cl
PO2Cl2
Chlormethane iminium salt
Figure 1.21: Formation of the reactive iminium salt species in the Vilsmeier synthesis
For the synthesis of guanidines, one can take advantage of the strong activation of the
ureas in form of iminium salts. Therefore, peralkylated ureas are transformed into the
corresponding chloroformamidinium chlorides (sometimes called Vilsmeier salts) by use of
CHAPTER 1. INTRODUCTION 25
phosphoroxychloride or thionylchloride. Phosgene is a clean alternative to these both as the
accompanying by-product CO2leaves the reaction mixture.
C
Cl
1R2RN NR3R4
Cl-
C
O
1R2RN NR3R4
O
ClCl
C
O
1R2RN NR3R4
O-
Cl
Cl - CO2
chloroformamidinium chloride
Figure 1.22: Mechanism of the reaction of a peralkylated urea with phosgen
In the second step, the reaction of the Vilsmeier salt with an amine in the presence of an
auxiliary base like triethylamine is following to give the protonated form of the peralkylated
guanidine. This guanidinium chloride can be deprotonated with 50% aqueous KOH solution
to yield the free guanidine base. Guanidines can be obtained crystalline, but they are mostly
of oily or waxy consistence. This synthetic strategy was developed by Kantlehner et al.[117]
who added an auxiliary base in equimolar amounts to the reaction mixture. This auxiliary
base removes the formed HCl and facilitates considerably the progress of the reaction to the
intermediate guanidinium chloride (a similar consideration might explain the more efficient
course of the Bredereck method by using an excess of amine). By Kantlehner´s method,
pentasubstituted guanidines are obtained in good yields.
C
Cl
1R2RN NR3R4
H2N R´
1R2RN NR3R4
Cl NH´R
H
Cl-
Cl-
-HCl
auxiliary base
C
1R2RN NR3R4
NHR´
Cl-
+ KOH
C
1R2RN NR3R4
NR´
- H2O, KCl
Figure 1.23: Mechanism of the condensation of chloroformamidinium chlorides with amines
under use of an auxiliary base
2 Objective and outline
2.1 Objective of the present work
The modelling of the active sites of metalloproteins is one of the most challenging tasks in
bioinorganic chemistry. Copper proteins form part of the stimulating field of research as
copper enzymes are mainly involved in oxidation bio-reactions. Thus, the understanding of
the structure-function-relationship of their active sites will allow the design of effective and
environmental friendly oxidation catalysts.
A key research objective of this work is to understand how supporting ligand struc-
tural features influence the relative stabilities and interconversions of copper-oxygen adduct
species, and especially the effects which control the equilibrium between µ-η2:η2-peroxo
and bis(µ-oxo) dicopper cores that are relevant to proposed metalloprotein active site
intermediates. A systematic investigation provides with new insights into this field which is
still controversely discussed.
Hence, an important topic of this work is the design and the synthesis of biomimetic ligands
with the subsequent synthesis of the corresponding copper(I) complexes. In search of
bifunctional nitrogen donor ligands able to stabilise unusually high metal oxidation states,
peralkylated guanidyl-type systems appear to be suited for use in biomimetic coordination
chemistry. Great significance is attached to the structural characterisation of copper(I)
bisguanidine complexes in order to analyse correlations between structure and function.
The main focus lies on the activation of molecular oxygen mediated by the synthesised
copper(I) bisguanidine complexes. The mechanisms of dioxygen activation are still under
discussion and, even more, the mechanisms of the following reactions are far from clear.
The subsequent reactions of the generated Cu2O2species have to be studied because they
give information about the degree of the oxidation potentials. At this stage, efficient use
of this potential is restricted due to a lack of accessible ligands demonstrating that a
synthetic protocol has to be developed which supports the designing of oxidation catalysts.
26
CHAPTER 2. OBJECTIVE AND OUTLINE 27
By suitable modification of the guanidine substitution patterns in such complexes, their
hydroxylation potential shall be redirected from the ligand to external substrates. As the
ligands are bidentate, the reaction centre should easily be accessible for external substrates
and well suited for substrate pre-coordination. A further important focus which is based
on the development of efficient copper containing oxidation catalysts is their screening in
suited test reactions and the investigation of their reaction mechanisms.
2.2 Outline of the present work
The present thesis deals with the above-descibed topics in a systematic order in the chapters
3 to 7. These chapters are based on each other, but they can be read independently.
In Chapter 3, a modular approach and an efficient synthetic protocol for the synthesis of
bisguanidine ligands are presented. Furthermore, this chapter sheds light on characteristic
features of these biomimetic ligands like typical structural properties and their coalescence
behaviour in NMR spectroscopy. The synthesis of copper(I) complexes containing these
ligands and their structural and electrochemical properties are treated in Chapter 4. These
copper(I) bisguanidine complexes serve as precursors for the highly reactive Cu2O2species
which are discussed in Chapter 5. Additionally, Chapter 5 provides with a correlation of
the structure of these precursors and their reactivity in the activation of dioxygen. This
correlation is completed with an intensive discussion of the theoretical foundations and a
study of the kinetics of the Cu2O2adduct formation. In Chapter 6, the products of the
hydroxylation reactions of selected ligands by subsequent reactions of the Cu2O2adducts
are presented and their structural features are set in comparison. A possible hydroxylation
mechanism has to be discussed as well. Finally, in Chapter 7, the oxidation potential of the
reactive Cu2O2species is directed towards external substrates, namely 2,4-ditertbutylphenol,
2,6-ditertbutylphenol and 3,5-ditertbutylcatechol. These substrates have been chosen as test
substrates for the investigation of oxidation and oxygenation reactions mediated by the
copper(I) bisguanidine catalysts. Chapter 8 contains the experimental part of this thesis.
New insights obtained from the investigations of this work and the resulting possibilities for
future studies are summarised in Chapter 9.
3 Bisguanidine ligands
3.1 Synthesis of the ligands
3.1.1 Motivation
By suitable modification of the guanidine substitution patterns in bisguanidine complexes, it
is intended to redirect their hydroxylation potential from the ligand to external substrates.
As the ligands are bidentate, the reaction centre should easily be accessible for external
substrates and well suited for substrate pre-coordination. In addition, the oxygen is shielded
against too fast reaction with these substrates by the spatially demanding guanidine moieties
resulting in enhanced oxidation selectivities. At this stage, efficient use of this potential is
restricted due to a lack of accessible ligands demonstrating that a synthetic protocol has to
be developed which supports these objectives.
For this purpose, a modular approach for bisguanidine compounds had to be developed which
provides a library of biomimetic ligands (Figure 3.5). This library contains members with
complete flexibilities in the spacers connecting the guanidine functionalities as well as in the
substitution patterns of the guanidine moieties. Via modification of the spacer, it is possible
to vary the denticity, the bite angle and the coordination geometry, whereas via modification
of the guanidine moities, the σ-donating and π-accepting properties of the Nimine atom might
be influenced. In order to increase the steric demand of the guanidine moieties and thus the
oxygen-shielding effect in their complexes, a series of chloroformamidinium chlorides from
secondary amines containing the required bulky substituents had to be prepared. By this
method, the transformation of almost every aliphatic secondary amine into the corresponding
chloroformamidinium chloride should be possible.
3.1.2 Realisation of a modular approach
The synthesis of the ligands was accomplished following a general procedure that allows
the condensation of almost every aliphatic urea with almost every primary amine to form a
28
CHAPTER 3. BISGUANIDINE LIGANDS 29
guanidine compound. This condensation proceeds via the transformation of the urea compo-
nent into its corresponding chloroformamidinium chloride which is sometimes referred to as
Vilsmeier salt.[117] Conventional chloroformamidinium chlorides are obtained in good yields
by reaction of the specific peralkylated ureas with phosgene in toluene or acetonitrile.[117]
The biomimetic approach requires spatially demanding substituents at the guanidine moi-
eties because sterically hindered systems are expected to control the access of substrates to
the oxygen in the corresponding copper-dioxygen complexes. Therefore, a straightforward
synthetic protocol starting with bulky secondary amines has been developed (Schemes 3.1
and 3.2). This one-pot synthesis consists of the combination of two equivalents of the cor-
responding secondary amine with two equivalents of phosgene in acetonitrile. In the first
reaction step, the alkyl substituted urea is formed and triethylamine acts as auxiliary base
by capturing the released HCl (Scheme 3.1, Reaction (1)). In the second step, a further
equivalent of phosgene transforms this urea into the chloroformamidinium chloride. A possi-
bility for the synthesis of non-symmetric chloroformamidinium chlorides and the subsequent
formation of non-symmetric substituted bisguanidine ligands is the reaction of carbamoyl
chlorides with secondary amines in the presence of one equivalent of NEt3(Scheme 3.1, Re-
action (2)). In the second step, one equivalent of phosgene transforms this non-symmetric
urea into the chloroformamidinium chloride.
COCl2
-CO2
C
2R1RN NR3R4
Cl
Cl
C
O
2R1RN NR3R4
COCl2, 2 NEt3
- 2 NEt3HCl
R1
NH
R2R4
HN
R3
+
COCl2
-CO2
C
2R1RN NR3R4
Cl
Cl
C
O
2R1RN NR3R4
NEt3
- NEt3HCl
R4
HN
R3
+
C
O
2R1RN Cl
(1)
(2)
Figure 3.1: Generation of the chloroformamidinium chlorides
Reaction of the mixture containing the chloroformamidinium chloride in the presence of
triethylamine as an auxiliary base with a bisamine leads to the bis-hydrochloride of the
ligand. Separation from the by-product NEt3HCl is accomplished by adding 1 equiv. of
NaOH per guanidine functionality und removing the resulting NEt3and the solvent under
reduced pressure. The hydrochloride is not isolated but deprotonated by using a two-phase
system of MeCN/50 % aqueous KOH in order to obtain the pure free base which needs no
further purification (Scheme 3.2).
Table 3.1 gives an overview of the prepared chloroformamidinium chlorides. Using these chlo-
CHAPTER 3. BISGUANIDINE LIGANDS 30
+NH2
NH2
2
2. NaOH, -2 NEt3HCl
3. 50% KOH
N
C
3R4RN
NR1R2
N
CNR3R4
NR1R2
C
2R1RN NR3R4
1. 2 NEt3
Cl
Cl
Figure 3.2: Reaction between the chloroformamidinium chloride and the bisamine
roformamidinium chlorides, the guanidine moieties shown in Figure 3.3 could be synthesised.
Within this figure, Gx assigns the guanidine moiety associated to the chloroformamidinium
chloride Vx, RSassigns the connection with the spacer.
Table 3.1: Overview of the chloroformamidinium chlorides (reactions starting from the urea
are marked with an asterisk)
Substituents R1- R4Chloroformamidinium chloride
R1, R2, R3, R4: -Me Tetramethylchloroformamidinium Chloride* (V1)
R1, R2, R3, R4: -Et Tetraethylchloroformamidinium Chloride* (V2)
R1, R2, R3, R4: -iPr Tetraisopropylchloroformamidinium Chloride (V3)
R1, R4: -Me, R2-R3:-(CH2)2- Dimethylethylenechloroformamidinium Chloride* (V4)
R1, R4: -Me, R2-R3:-(CH2)3- Dimethylpropylenechloroformamidinium Chloride* (V5)
R1, R4: -nPr, R2-R3:-(CH2)3- Dipropylpropylenechloroformamidinium Chloride* (V6)
R1-R2, R3-R4: -(CH2)5- Dipiperidylchloroformamidinium Chloride* (V7)
R1-R2, R3-R4: -CH(Me)(CH2)3CH(Me)- Bis(dimethylpiperidyl)chloroformamidinium Chloride (V8)
R1-R2, R3-R4: -C(Me)2(CH2)3C(Me)2- Bis(tetramethylpiperidyl)chloroformamidinium Chloride (V9)
R1-R2, R3-R4: -CHNCHCH- Diimidazolylchloroformamidinium Chloride* (V10)
R1-R2, R3-R4:-(CH2)2O(CH2)2- Dimorpholinochloroformamidinium Chloride (V11)
R1-R2, R3-R4:-(CH2)2S(CH2)2- Dithiomorpholinochloroformamidinium Chloride (V12)
R1, R2: -Me, R3-R4:-(CH2)2O(CH2)2- Morpholinodimethylchloroformamidinium Chloride (V13)
R1, R2: -Me, R3-R4:-CHMe(CH2)3CHMe- Dimethylpiperidinodimethylchloroformamidinium Chloride (V14)
The spacers shown in Figure 3.4 are used as constituents of bisguanidine ligands for several
reasons: the propan-1,3-yl (p) spacer is a typical aliphatic spacer with a suitable ”bite” for 3d-
metal coordination, [11,14,16,20] the flexible (3,6-di-oxa)octan-1,8-yl (doo) spacer offers more
donor functions for metal coordination whereas the cyclohexan-1,3-yl (ch) system is more
rigid. The aromatic systems diphenyleneamine (PA), N-Methyl-diphenyleneamine (MePA)
and pyridin-2,6-yl (py) offer a further N donor function whilst the m-xylol-α,α’-yl (mX) unit
has a great ”bite” and more flexibility than the other spacers.
CHAPTER 3. BISGUANIDINE LIGANDS 31
N
N N
dimethylpropylene-
guanidino
DMPG (G5)
dipiperidino-
guanidino
DPipG (G7)
dimorpholino-
guanidino
DMorphG (G11)
dimethylethylene-
guanidino
DMEG (G4)
N N
N
N N
N
N
NN
N N
N
N N
N
N
N
O
N
O
N
N N N
N
dipropylpropylene-
guanidino
DPPG (G6)
tetramethyl-
guanidino
TMG (G1)
tetraethyl-
guanidino
TEG (G2)
dithiomorpholino-
guanidino
DSMorphG (G12)
N
N
S
N
S
diimidazolyl-
guanidino
DImG (G10)
N N
N
tetraisopropyl-
guanidino
TiPG (G3)
N
N N
bis(dimethyl)piperidino-
guanidino
B(DMPip)G (G8)
N
NN
bis(tetramethyl)piperidino-
guanidino
B(TMPip)G (G9)
RSRSRS
RS
RS
RS
RS
RS
RS
RS
RS
RS
morpholinodimethyl-
guanidino
MorphDMG (G13)
N
N N
O
RS
piperidinodimethyl-
guanidino
(DMPip)DMG (G14)
N
N N
RS
Figure 3.3: Guanidine portions
CHAPTER 3. BISGUANIDINE LIGANDS 32
G G G O O G
GG
G
G
N
G GH
N
G GMe
propan-1,3-yl (p)(3,6-di-oxa)octan-1,8-yl (doo)
m-xylol-α,α'-yl
(mX)
cyclohexan-1,3-yl (ch)
diphenyleneamine (PA)N-methyl-
diphenyleneamine (MePA)
NGG
pyridin-2,6-yl (py)
Figure 3.4: Spacer units (G assigns the position of the attached guanidine moiety)
The modular approach which is illustrated in Figure 3.5 allows a systematic tuning of the
properties of polyguanidine ligands. By combining the varieties of the spacer and the guani-
dine moiety, a library of bisguanidine ligands could be built up (Tables 3.3 and 3.2).
+I
N
N
Cu
N
R3
R2
N
R1
R4
N
R2
R3
N
R4
R1
L
L = I- or MeCN
Figure 3.5: Schematic representation of the variable moduls within bisguanidine ligands
Table 3.2: Overview of the synthesised ligands with aromatic spacers
Guanidine moities PA MePA mX py
TMG (G1) TMG2PA TMG2MePA TMG2mX TMG2py
(L1-4) (L1-5) (L1-6) (L1-7)
TEG (G2) TEG2mX TEG2py
(L2-6) (L2-7)
DMEG (G4) DMEG2mX DMEG2py
(L4-6) (L4-7)
DMPG (G5) DMPG2MePA DMPG2mX DMPG2py
(L5-5) (L5-6) (L5-7)
CHAPTER 3. BISGUANIDINE LIGANDS 33
Table 3.3: Overview of the synthesised ligands with aliphatic spacers
Guanidine moities p doo ch
TMG (G1) TMG2p TMG2doo TMG2ch
(L1-1) (L1-2) (L1-3)
TEG (G2) TEG2p
(L2-1)
TiPG (G3) TiPG2p
(L3-1)
DMEG (G4) DMEG2p DMEG2doo DMEG2ch
(L4-1) (L4-2) (L4-3)
DMPG (G5) DMPG2p DMPG2doo
(L5-1) (L5-2)
DPPG (G6) DPPG2p
(L6-1)
DPipG (G7) DPipG2p
(L7-1)
B(DMPip)G (G8) B(DMPip)G2p
(L8-1)
B(TMPip)G (G9) B(TMPip)G2p
(L9-1)
DImG (G10) DImG2p
(L10-1)
DMorphG (G11) DMorphG2p DMorphG2doo
(L11-1) (L11-2)
DSMorphG (G12) DSMorphG2p
(L12-1)
MorphDMG (G13) MorphDMG2p
(L13-1)
(DMPip)DMG (G14) (DMPip)DMG2p
(L14-1)
CHAPTER 3. BISGUANIDINE LIGANDS 34
3.2 Crystal structures
3.2.1 Crystal structure of N,N,N´,N´-tetraethylchloroformamidinium
chloride
Deprotonation of chloroformamidinium salts is the most popular way to generate
diaminocarbenes,[118, 119] but the chlorformamidinium chlorides themselves represent
adducts between the corresponding carbenes and molecules of chlorine. The synthesis of
V2 is accomplished by a standard method for Vilsmeier salts,[117] but to our knowledge no
structure has been reported. Kuhn et al.[120] and Arduengo et al. [121] reported the struc-
ture of the dichlor-adducts of carbenes containg the cyclic imidazolyl fragment. Acyclic car-
benes have been synthesised by Alder al. [122] and Bertrand et al. [123], but to this point of
knowledge chlorformamidium chlorides have been regarded as salt-like precursors of carbenes.
Figure 3.6: Molecular structure of V2
The crystal structure of V2 shows that a
linear C-Cl-Cl fragment and not an iso-
lated chloride ion is existing in the solid
state. The synthesis of V2 is accomplished
in good yields by combining tetraethylurea
with phosgene in toluene as it is shown
in Figure 3.1. Following the literature
procedure,[117] the Vilsmeier salt N,N,N´,N´-
tetraethylchloroformamidinium chloride can
be obtained from the toluene solution by fil-
tration as honey-like yellowish oil which crys-
tallises in the triclinic space group P1 upon
standing after several months . The struc-
ture (Figure 3.6) shows a planar arrangement of N1, N2, C1 and Cl1, deviations from the
best plane range from -0.003(1) to 0.008(1) ˚
A. Angles at C1 are N-C-N 125.9(1)◦, N-C-Cl
117.0◦(average) and the C-Cl distance measures 1.736(1) ˚
A as expected for a C(sp2)-Cl
bond. Cl1 has an almost linear coordination of C-Cl-Cl amounting to 175.7(1)◦and the
Cl-Cl distance is 3.1523(5) ˚
A long which is clearly shorter than a van der Waals contact.
This Cl coordination is similar to that from the related imidazol compound [120] with Cl-Cl
3.159(3) ˚
A and C-Cl-Cl 166.1(1)◦. Compared with other chloroformamidinium salts, the
C-Cl distance is slightly elongated. Several imidazolium systems reported in the literature
CHAPTER 3. BISGUANIDINE LIGANDS 35
[120, 121, 124, 125] exhibit a C-Cl distance of 1.68 ˚
A which is not dependent from the ac-
companying anion (Cl−,[120, 121] PO2Cl−
2, [124] SO2Cl−[125]). The single acyclic system
[(NMe2)2CCl]2[PtCl6] shows a C-Cl distance of 1.724 ˚
A.[126] Thus, the C-Cl distance is not
determined by the anion but by the type of formamidinium system. This relation is not fully
understood and requires more structural data of related acyclic systems.
Regarding from the synthetic side, V2 can be seen as Vilsmeier salt, whereas the structural
analysis shows that it is as well a dichloro-carbene adduct. The reactivity of V2 as chlorofor-
mamidinium salt is strongly electrophilic. Hence, we use it in the synthesis of bisguanidine
ligands as Vilsmeier salt. In the reaction with suited reagents like Hg(SiMe3)2, the carbene
can be generated.[123]
Therefore, compound V2 can be regarded both as a Vilsmeier salt and as a charge-transfer
adduct of a carbene with dichlorine. Chloroformamidinium chlorides seem to prefer the
adduct-structure to the ionic salt-like structure.
3.2.2 Crystal structures of selected bisguanidine ligands
Single crystals of L5-1 and L7-1 could be obtained by slow evaporation of the acetonitrile
solution under glove-box conditions. L5-1 crystallises triclinic in the space group P1 with
two molecules per unit cell, whereas L7-1 crystallises monoclinic in the space group P 21/n
with four molecules per unit cell. The results of the structure analyses are shown in the
Figures 3.7 and 3.8, while selected bond lengths and angles are collected in Table 3.4, and
parameters relating to the data collection and refinement are listed in the Tables A1 and A2.
Figure 3.7: Molecular structure of L5-1
In L5-1, the C-N single-bond
lengths range from 1.375 (3) to
1.407 (3) ˚
A, and the mean of
the C6=N3 and C10=N4 double
bonds is 1.284 ˚
A. The mean of
the N1-C6-N2 and N5-C10-N6 an-
gles is 114.8◦, and the mean of the
C6-N3-C7 and C9-N4-C10 angles
119.5◦. Thus, the guanidyl dou-
ble bonds in L5-1 are clearly lo-
calised. The same is valid for the related compound L7-1.
CHAPTER 3. BISGUANIDINE LIGANDS 36
Table 3.4: Selected distances and angles of the molecules in crystals of L5-1 and L7-1 (av-
erage values)
Distances (˚
A) L5-1 L7-1
N=C 1.276 1.284
Cimine-Namine 1.398 1.391
Angles (◦)
Namine-C-Namine 113.9 114.8
Figure 3.8: Molecular structure of L7-1
The molecule L7-1 lies roughly on a
non-crystallographic twofold axis run-
ning through C13, with a trans arrange-
ment of the guanidyl groups relative to
the C12-C13-C14 centre. The resulting
torsion angles are N1-C12-C13-C14 =
70.3 (1)◦and N4-C14-C13-C12 = 68.8
(1)◦. The C-N single bonds range from
1.392 (1) to 1.404 (1) ˚
A, while the C=N
double bonds, C1=N1 and C14=N4,
have similar values, with a mean of
1.276 ˚
A. The mean of the N2-C1-N3 and
N5-C15-N6 angles is 113.9◦, and that
one of the C1-N1-C12 and C15-N4-C14
angles is 119.9◦. Thus, the guanidyl
double bonds in L7-1 are clearly localised as well. Similar double-bond localisation is
observed in bis(tetramethylguanidino) naphthalene,[109] with equally unprotonated imine
N and NR2amino groups having a mean C=N bond length of 1.282 (3) ˚
A and a mean C-N
bond length of 1.384 (1) ˚
A. In bis(tetramethylguanidino)biphenyl,[94] with a protonated
imine N atom, strong delocalization is observed among the three C-N bonds, which are in
the range 1.31 (1) - 1.34 (1) ˚
A. 2-Cyanoguanidine, with C-N bonds in the range 1.3327 (3)
- 1.3441 (3) ˚
A,[127] and, to a lesser extent, tetrabenzylcyanoguanidine, with C=N = 1.315
˚
A and C=N = 1.370 ˚
A,[128] also show delocalisation, but this is due to the cyano groups
attached to the imine N atom. Substitution of the NH2groups in cyanoguanidine with
NBz2leads to the observed increase in localisation.
CHAPTER 3. BISGUANIDINE LIGANDS 37
In order to discuss structural features of the diverse kinds of ligands, three crystal structures
have been chosen for a nearer look: the structure of L1-4 denotes typical properties of aro-
matic bisguanidine ligands, whereas L11-1 represents a typical aliphatic bisguanidine ligand.
Compound [H2L1-2]I2·Et2O contains a typical bisprotonated bisguanidine system. Single
crystals of [H2L1-2]I2·Et2O were grown by slow diffusion of diethyl ether into acetonitrile
solutions. Single crystals of L1-4 are obtained by crystallisation at -25◦C whereas L11-
1crystallised by slow evaporation of the acetonitrile solution. L1-4 and [H2L1-2]I2·Et2O
crystallise monoclinic in the space group P21n with eight and two molecules per unit cell,
respectively. L11-1 crystallises monoclinic with the space group C2/c and four molecules
per unit cell. The results of the structure analyses are shown in Figures 3.9 - 3.10, while
selected bond lengths and angles are collected in Table 3.5, and parameters relating to the
data collection and refinement are listed in the Tables A2 and A3.
Figure 3.9: Molecular structure of L1-4
Crystals of L1-4 contain two crystallographically independent but otherwise identical mole-
cules. One of them (A) is shown in Figure 3.9. The structural features of this aromatic
guanidine ligand (N=C 1.281, Cimine-Namine 1.365, Nimine-Carom 1.402 ˚
A ) are comparable
with those reported for TMGN (N=C 1.282, Cimine-Namine 1.384, Nimine-Carom 1.399 ˚
A).[109]
Remarkable is the trigonal-planar environment of the N atom which connects both phenyl
rings. The corresponding N-C bonds are drastically shortened to 1.400 ˚
A which indicates
a delocalisation of the free amine electron pair into the phenyl π-system. The phenyl rings
are twisted against each other by an angle of 36.7◦. The dihedral angles between the CN3-
CHAPTER 3. BISGUANIDINE LIGANDS 38
guanidine plane and the Cimine-Namine-(Calkyl)2-planes within the guanidine moieties have
a mean value of 31.9◦(individual values from 22.2 to 38.6). Furthermore, the N-H group
forms a bifurcated hydrogen bridge to the imine N atoms (av. 2.235 ˚
A, corrected for N-H
1.080 ˚
A).
The molecular structure of L11-1 is depicted in Figure 3.10. The molecule lies on a crystallo-
Figure 3.10: Molecular structure of L11-1 (left) and of [H2L1-2]I2·Et2O(right)
graphic two-fold axis which runs through the center of the spacer. The geometric parameters
of this ligand are in good agreement with those of the aliphatic guanidine ligand DPipG2p
(L7-1): N=C 1.272, Cimine-Namine 1.402 ˚
A compared with DPipG2p: N=C 1.276, Cimine-
Namine 1.399 ˚
A. The guanidine moieties are planar as expected. The dihedral angles between
the CN3-guanidine plane and the Cimine-Namine-(Calkyl)2-planes are larger (on average 36.0◦;
individual values from 29.0 to 42.9◦) than those of L1-4 as the steric hindrance forces the
NR2units to twist around the Cimine-Namine axis. The N=C double bonds are clearly lo-
calised in contrast to the bisprotonated form of L1-2 where the double bond is delocalised
over the guanidine centre. Compound [H2L1-2]I2·Et2Ocomprises the bis-protonated form
of TMG2doo, two iodine anions and a diethylether molecule. The centroid of the cation lies
on a crystallographic inversion centre. The bond lengths are typical for a protonated guani-
dine: C=NH+1.349(3), Cimine-Namine av. 1.336 ˚
A compared with [H2btmgp] 2+: C=NH+
1.334, Cimine-Namine 1.341 ˚
A.[106] The bonds in the guanidine centre are of equal length.
Therefore, the conjugation is enhanced although the dihedral angles are diminished only to
a small extent (on average 30.8◦; individual values from 29.8 to 31.8◦). The iodide ions are
stabilised by N-H...I hydrogen bonds with H...I distances of 2.768 ˚
A.
CHAPTER 3. BISGUANIDINE LIGANDS 39
Table 3.5: Selected distances and angles of the molecules in crystals of L1-4,L11-1 and of
the ligand cation in crystals of [H2L1-2]I2·Et2O(average values)
Distances (˚
A) L1-4 L11-1 [H2L1-2]I2·Et2O
N=C 1.282 1.273 1.349
Cimine-Namine 1.365 1.402 1.336
Angles (◦)
Namine-C-Namine 113.6 112.0 120.1
As a structural parameter that allows estimation of charge delocalisation within the guani-
dine moiety by comparing the shortest C=N bond distance ato the average of the other two
C-NR2distances band c, the value ρ= 2a/(b+c) was established.[107] Table 3.6 summarises
the ρvalues for the above discussed ligands.
Table 3.6: Quotient ρfor L5-1,L7-1,L1-4,L11-1 and of the ligand cation in crystals of
[H2L1-2]I2·Et2O(average values)
ρ
L5-1 0.924
L7-1 0.912
L1-4 0.936
L11-1 0.909
[H2L1-2]I2·Et2O1.009
In the free guanidines L5-1,L7-1,L1-4 and L11-1,ρhas values of 0.90 to 0.94 assigning a
clear localisation of the guanidine double bond. The greater value for L1-4 can be explained
by the fact that the aromatic spacer contributes to the delocalisation in the system.[109] The
guanidinium cation [H2L1-2]I2·Et2Oshows a perfect charge delocalisation with ρ= 1.009.
3.3 NMR spectroscopy of selected bisguanidine ligands
The chemical shifts of the dimethylamino groups of the ligands containing the tetram-
ethylguanidine moiety are listed in Table 3.7 for comparison purposes. The 1H and 13C
NMR spectra of the guanidine ligands with aliphatic spacers exhibit two seperate sig-
nals for the methyl groups. On heating, these two signals approach each other and
CHAPTER 3. BISGUANIDINE LIGANDS 40
coincide on reaching the coalescence temperature. Compared with the aliphatic sit-
uation described above, the aromatic systems exhibit only one signal for the methyl
groups at room temperature. This signal splits into two resonances of equal intensity
if the temperature is lowered (Figure 3.12). This behaviour is caused by a syn-anti ex-
change typical for guanidines which has been discussed for selected TMG systems by
Kessler and Leibfritz.[129] In the case of pentasubstituted guanidines, a rotation around
the C-NR2single bonds as well as a syn-anti isomerisation can take place (Figure 3.3).
N
NMe2
Me2N
N
NMe2
NMe2
Figure 3.11: Rotation around the C=N
double bond
The rotation around a C-NR2single bond is too
rapid with respect to the NMR timescale to re-
sult in individual resonances even at low temper-
atures. This is not the case for the syn-anti ex-
change which can principally be caused by rotation
around the C=N bond or by inversion.[129] The
coalescence behaviour of selected guanidine ligands
was investigated by EXSY 1H NMR spectroscopy.
The kinetic data were determined from the result-
ing Eyring plots (Figs. 3.13 - 3.15 and Table 3.8).
Table 3.7: Comparison of NMR spectroscopic shifts of the NMe2groups at 298 K (*:Ref.
[109])
1H13C
btmgp (L1-1) 2.56 2.65 38.6 39.4a)
H2btmgpCl2(H2L1-1Cl2) 2.94 3.02 40.1 40.5a)
TMG2doo (L1-2) 2.51 2.60 38.6 39.5
H2TMG2dooI2(H2L1-2I2) 2.95 3.09 40.0 40.4
TMG2ch (L1-3) 2.42 2.49 39.1 39.6
TMG2PA (L1-4) 2.68 38.6
TMG2MePA (L1-5) 2.58 39.9
TMG2mX (L1-6) 2.65 38.7
TMG2py (L1-7) 2.73 39.9
TMGN 2.65* 39.4*
H2TMGN(PF6)22.95* 41.6*
Table 3.8 clearly shows that aromatic tetramethyl guanidines have lower activation barriers
for the syn-anti exchange than aliphatic ones. Our findings thus are in accordance with data
CHAPTER 3. BISGUANIDINE LIGANDS 41
Figure 3.12: Coalescence behaviour of TMG2PA (L1-4) between 293 and 233 K
Figure 3.13: Eyring plot (308 - 343 K) for the syn-anti exchange in btmgp (L1-1)
CHAPTER 3. BISGUANIDINE LIGANDS 42
Figure 3.14: Eyring plot (293 - 318 K) for the syn-anti exchange in TMG2doo (L1-2)
Figure 3.15: Eyring plot (213 - 233 K) for the syn-anti exchange in TMG2PA (L1-4)
CHAPTER 3. BISGUANIDINE LIGANDS 43
for related systems reported in the literature.[109, 129] In aromatic systems like TMG2PA
and TMGN, the C=N bond is weakened by conjugation with the adjacent aromatic system
resulting in lower energy barriers whereas in aliphatic systems like btmgp, TMG2doo or
[Bz2TMG]+which lack these effects, the free energies of activation have to be considerably
higher. The data for the free energy of btmgp and TMG2doo are in good agreement with the
values reported for simple alkyl substituted guanidines like pentamethylguanidine (TMG-
CH3) and tetramethyl-ethyl- or tetramethyl-propyl-guanidine (TMG-C2H5and TMG-C3H7,
resp.).
Table 3.8: Comparison of coalescence parameters of the syn-anti isomerisation; a) tempera-
ture range limited by solvent (Tmin 183 K);b) Ref. [109]; c) Ref. [129]; d) Ref.
[130]
Solvent Tc[K] ∆H‡[kJ/mol] ∆S‡[J/(mol·K)] ∆G‡
0[kJ/mol]
btmgp (L1-1) d6-DMSO 375 92.4±1.5 46.2±0.8 78.6±1.7
TMG2doo (L1-2) d6-DMSO 348 77.0±0.8 21.8±0.3 70.5±0.9
TMG2PA (L1-4) CD2Cl2267 41.5±2.3 -40.9±2.7 53.7±3.0
TMG2MePA (L1-5) CD2Cl2242 - a)
TMG2py (L1-7) CD2Cl2229 - a)
TMGN CD2Cl2253b)53.4b)48.3b)
TMGPh CDCl3/CS2238c)50.7c)
TMGBz+
2CDCl3276d)61.1d)
TMG-CH3CDCl3346c)78.2c)
TMG-C2H5CDCl3338c)76.2c)
TMG-C3H7CDCl3326c)73.2c)
In the case of btmgp and TMG2doo, an inversion mechanism appears to be unlikely due to
the restrictions introduced by the second guanidyl function attached to the same linker. This
means that a rotation takes place which is facilitated if we go from smaller to larger alkyl
chains. Having this in mind and taking the data for comparable monoguanidine molecules
into account which are nearly identical,[129] a unique rotational mechanism for all these
systems can be postulated. The inductive effect of homoaromatic neighbourhoods can be
enhanced by using a more electron rich system like pyridin as has been observed for TMG2py
(Tc = 229 K). The aromatic ligand TMG2MePA exhibits coalescence of the methyl singlets
at 242 K. A similiar value was found for TMGPh (TC = 238 K),[129] whereas the methyl
signal of the TMG2PA molecule splits into two components below 267 K. This tempera-
ture is remarkably high in comparison with those reported for other aromatic systems like
TMGN (253 K).[109] Additionally, TMG2PA has a negative activation entropy for the ro-
CHAPTER 3. BISGUANIDINE LIGANDS 44
tation around the C=N bond indicating that hydrogen bonds participate in the exchange
mechanism (Figure 4). It is assumed that the bifurcated hydrogen bond between the amino-
hydrogen and the two guanidine nitrogen atoms stabilises the conformation observed in the
crystal resulting in a raised activation barrier of rotation and thus in a higher coalescence
temperature.
3.4 Electrochemistry of selected bisguanidine ligands
Selected guanidine ligands have been investigated on their redox properties by means of
cyclovoltammetry. The cyclovoltammogram of L1-4 (0.1 mol/L [NBu4][PF6]; 50 mV/s;
Au/Pt/Ag-AgCl) exhibits a quasireversible electron transfer at 94 mV/NHE (Figure 3.16)
which can be indicative for the reduction of the aminic hydrogen atom to molecular hydrogen.
The cyclovoltammogram of L1-5 (0.1 mol/L [NBu4][PF6]; 50 mV/s; Au/Pt/Ag-AgCl) shows
two electron transfers (Figure 3.17). The first redox transition at 105 mV/NHE is irreversible.
The second redox wave at 496 mV/NHE can be classified as quasireversible. Both redox
transitions belong to redox processes which are delocalised in the aromatic system. Thus,
they can not assign exactly special redox processes.
Figure 3.16: Cyclovoltammogram of L1-4 in CH2Cl2
The cyclovoltammograms of the aliphatic ligands L4-1,L5-1,L7-1 and L11-1 do not show
any significant electron transfers in the range of -2 and +2 V in CH2Cl2and in MeCN as
solvent. btmgp has been reported to be oxidised at potentials between 1 and 1.4 V/SCE.[112]
Appearently, ligands with differently substituted guanidine moieties are more redox stable
than btmgp. Probably, they are oxidised at potentials of more than 2 V/NHE which is
outside the window given by the solvent.
CHAPTER 3. BISGUANIDINE LIGANDS 45
Figure 3.17: Cyclovoltammogram of L1-5 in CH2Cl2
3.5 Synthesis of a fluorinated bisguanidine ligand
In order to direct the oxidation potential of the copper complexes towards external substrates,
the ligand has to be shielded against self-oxidation. This approach has proven to be suc-
cessful as Gorun and coworkers have shown with their fluorinated hydro(trispyrazolyl)borate
system which supports a room-temperature stable µ-η2:η2-peroxo dicopper core.[87]
All attempts to fluorinate suited ligand precursors by electrofluorination resulted in ex-
tremely small yields, and the subsequent reaction to the desired ligand failed due to
HF evolution. Another pathway to a fluorinated ligand was the substitution of an urea
with perfluorinated side-chains and the subsequent transformation into the correspond-
ing chloroformamidinium chloride (Figure 3.18, (1)) which reacts in the following reac-
tion with 1,3-diaminopropane to the desired ligand (Figure 3.18, (2)). Going this path-
HN NH
O
1. NaH
2. C3F7IC3F7N NC3F7
O
COCl2
C3F7N
NC3F7
C3F7N NC3F7
Cl Cl-
2+
NH2NH2
N N
C3F7N
NC3F7
C3F7N NC3F7
Cl Cl-
BFPPG2p
(1)
(2)
Figure 3.18: Synthesis of the fluorinated bisguanidine ligand BFPPG2p
CHAPTER 3. BISGUANIDINE LIGANDS 46
way, trimethyleneurea was deprotonated twice by NaH in THF, and heptafluoropropylio-
dide was added. The reaction occurs immediately, but the by-product NaI can not be
removed efficiently. It turned out that NaI reacts with phosgene in the subsequent reaction
to iodophosgene which is unstable and decomposes into iodine and carbon monoxide. The
iodine could be proven with the iodine-starch-test of the dark violet solution. The genera-
tion of iodine disturbs the formation of the desired fluorinated chloroformamidiniumchloride.
Therefore, the NaI has to be totally separated from the solution. Literature reported syn-
thesis [131] of subsituted ureas were carried out in dioxane because of the small solubility of
NaI in dioxane, but even this small solubility turned out to be too great for the subsequent
reaction with phosgene. Different methods of deprotonation were tested, e.g. deprotona-
tion with lithium-n-butylate or lithium-t-butylate in hexane or dichloromethane at -80◦C,
but the reaction with trimethyleneurea yielded no results. Deprotonation with LiH (as at-
tempt to obtain LiI instead of NaI) did not work either. The most effective deprotonation
method is that one using NaH in THF (16 h at reflux). Hence, after the deprotonation step,
the solvent was evaporated and another solvent added which is not able to dissolve NaI,
e.g. dichloromethane. This method failed as the generated and only partly redissolved bis-
deprotonated trimethyleneurea did not react with the heptafluoropropyliodide. Refluxing of
this reaction mixture is difficult as well because of the low boiling point of heptafluoroiodine
(34.5◦C). A more effective method appeared to be the precipitation and subsequent filtration
of NaI from the starting solution. The volumes of precipitation solvents like diethylether
were very great, such that the concentration of the compounds got very low. Reconcentra-
tion of the filtrated solutions failed because of the volatility of the fluorinated urea.
Finally, the deprotonation was carried out in diethylether with NaH. Taking into account
that the reflux temperature of diethylether is smaller, the reaction mixture has to be refluxed
during 36 h, followed by the addition of heptafluoropropyliodide to the ice-cooled solution
and further 36 h of mild reflux. By filtration over chromatographic silica, the extremely
fine precipitate of NaI could be removed. The obtained diethylether solution containing the
bis(heptafluoropropyl)trimethyleneurea was purged with phosgene at 0◦C for 5 min. The
reaction mixture was warmed up to room temperature and stirred for 30 min. The colour
of the red solution changed to greenish-brown due to decomposition reactions of the gener-
ated fluorinated chloroformamidinium chloride. So, this chloroformamidinium solution was
instanteneously added to a MeCN solution of 1,3-diaminopropane. The resulting reaction
mixture was not heated as usually due to thermal decomposition but only stirred 48 h at
room temperature. The workup was carried out as described for the other ligands. Due
CHAPTER 3. BISGUANIDINE LIGANDS 47
to the thermal instability of several reaction intermediates, the yield was mostly very small
(10-15 %). An optimisation of this reaction sequence is under investigation.
3.6 Conclusion: Bisguanidine ligands
The assembly of bisguanidine molecules starting from secondary amines and phosgene for
use in biomimetic coordination chemistry, especially in the field of copper-controlled oxygen
activation, has provided a set of bifunctional N-donor ligands. Each member of this set is
expected to influence the redox capabilities of its corresponding Cu(I) complexes towards
molecular oxygen in a specific fashion depending on the spatial demands of the guanidine
functionalities as well as on the conformational freedom possible within the steric limits
allowed by the spacer fragments connecting these units. In contrast to established literature
procedures, the described method to arrive at bisguanidine molecules is not dependent from
predefined peralkylated urea precursors as we start from secondary amines as simple building
blocks and thus define the urea intermediates by simply choosing suitably substituted educts.
The synthetic protocol has been optimised to obtain overall yields in the range from 65 to
95 %. The modular approach allows the universal modification of the aliphatic guanidine
substitution as well as of the spacers with respect to rigidity, extension of the backbone and
additional donor functions.
In general, such a matrix of bisguanidine ligands can also be screened regarding their ability
to stabilise complexes of other transition metals in unusually high oxidation states.
4 Copper(I) bisguanidine complexes
4.1 General topologies of copper(I) bisguanidine complexes
The neutral bisguanidine ligands can be synthesised in gram scale and they are capable of
coordinating metal centres in a chelating and as well a bridging mode to form mononuclear
and dinuclear complexes or even polynuclear chains. In both coordination modes, the ligands
show great flexibility ranging from linear via trigonal-planar to square-planar coordination
of the metal centre. The topologies of copper(I) bisguanidine complexes are summarised
in Figure 4.1. The square-planar coordination is often found in bis(µ-alkoxo)- and bis(µ-
hydroxo) bridged dinuclear copper complexes. This type of complexes is discussed in section
6.1.
N N
Cu
I
N N
Cu Cu
N
N
Y2-
Y2- = 2 PF6-,
2 I-, Cu2I42-,
Cu4I62- N
Cu
N
Z-
Z- = PF6-
N
N
n
N
Cu
I
N
n
N N
N
Cu
NN
N
n
Cu
II
chelating,
trigonal planar bridging,
trigonal planar
bridging,
linear bridging,
linear
NCu
NN
N
n
bridging,
distorted trigonal planar
I
bridging,
distorted trigonal planar
Figure 4.1: Topologies of copper(I) bisguanidine complexes
48
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 49
4.2 Synthesis of mononuclear copper(I)bisguanidine
complexes
In general, mononuclear copper(I) bisguanidine complexes were synthesised in good yields
by combining CuI with 1.05 equiv. of the bisguanidine ligand in dry acetonitrile and stirring
for 30 min (Scheme 4.2).
N
C
R2N
R2N
N C
NR2
NR2
Cu
NC
R2N
R2N
N C
NR2
NR2
CuI
MeCN
+
I
Figure 4.2: Complexation of CuI with bisguanidine ligands
4.2.1 Crystal structures of mononuclear copper bisguanidine complexes
By using TMG2PA in the reaction with CuI (Figure 4.3), the copper is oxidised to Cu(II) and
the proton from the acidic Namine function is reduced to hydrogen. The hydrogen combines
to dihydrogen which purges off the solution. Probably, the relieve of the hydrogen atom is
facilitated by agostic interactions between the N-H bond and the Cu(I) ion. During this
reaction, a dark green solid is formed which can be recrystallised as green needles from
MeCN/diethylether. C1 crystallises orthorhombic in the space group Pbca. Crystals of
C1 contain eight isolated molecules per unit cell. The results of the structure analyses are
shown in Figure 4.4, while selected bond lengths and angles are collected in Table 4.1, and
parameters relating to the data collection and refinement are listed in Table A4.
N
NN
NMe2
Me2N
Me2N
NMe2
H
N
N N
NMe2
Me2N
Me2N
NMe2
Cu
I
+CuI - 0,5 H2
Figure 4.3: Complexation of CuI with TMG2PA under oxidation of the copper
The copper(II) ion is coordinated in a distorted butterfly (C2v) geometry. The distance of
the Cu to the N1N2N3 plane measures 0.484 ˚
A, the iodine atom lies 2.487 ˚
A below this
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 50
Table 4.1: Selected distances and angles of C1
Distances (˚
A) Angles (◦)
Cu-I 2.5941(8) Namide-Cu-Nimine 84.2
Cu-Namide 1.903(4) Namide-Cu-I 144.2(2)
Cu-Nimine 1.961 Nimine-Cu-Nimine 151.1(2)
Namide-Carom 1.394 Carom-Namide-Carom 124.2(5)
Nimine-Carom 1.418
Nimine-Cimine 1.348
Figure 4.4: Molecular structure of C1
plane. The three N donor functions of the ligand surround the copper centre not planar
as the Nimine-Cu-Nimine angle of 151.1(2)◦shows. The sum of the six angles at the copper
centre is 668.6◦, thus, the coordination can be described as a distorted tetrahedron (ideal
tetrahedron: 656◦, square-planar geometry: 720◦). The bite angle (Namide-Cu-Nimine) of the
ligand is 84.2◦indicating the degree of distortion of the tetrahedral geometry. The phenyl
rings are twisted about 36.8◦out of the plane, the corresponding torsion angle in the ligand
is 36.7◦. The Cu-I distance is relatively long with 2.5941(8) ˚
A, but shorter than the sum
of the van-der-Waals-radii with ≈2.77 ˚
A. The Namide atom is surrounded distorted trigonal
planar (angle sum: 352◦). The ligand is deprotonated at this position because the redox
potential is lowered by coordination under the redox potential for hydrogen evolution. The
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 51
negative charge is delocalised from one guanidine group via the aromatic rings to the other
guanidine group. This delocalisation is indicated by several points: the Namide-Carom bonds
are with 1.394 ˚
A relatively short (standard N-Carom bond: 1.42 ˚
A) and the Nimine-Cimine
bonds are with 1.348 ˚
A longer than those in other guanidine complexes which assigns a
weakened double bond character. The angle between the two CN3-guanidine planes is 72.5◦.
The structural parameter ρis calculated to be 1.002 assigning perfect delocalisation within
the guanidine moiety. This is due to the aromatic spacer and the deprotonation of the
aminic N atom. By using DMorphG2p in the reaction with CuI, the mononuclear complex
[Cu(DMorphG2p)I] (C2) can be synthesised. Colourless single crystals are obtained in good
yields by vapour diffusion of diethylether into the MeCN containing reaction mixture. C2
crystallises orthorhombic in the space group Pnma. Crystals of C2 contain four isolated
molecules C2 per unit cell. The results of the structure analyses are shown in Figure 4.5,
while selected bond lengths and angles are collected in Table 4.2, and parameters relating
to the data collection and refinement are listed in Table A4.
Figure 4.5: Molecular structure of C2
The copper centre is coordinated almost ideal trigonal-planar with a sum of the angles of
358◦. The Cu-Nimine and Cu-I distances are in the range observed for [Cu(btmgp)I].[105, 112]
Regarding the other structural details, the similarities are obvious. With regard to the
dihedral angles between the CN3-guanidine plane and the Cimin-Namin-(Calkyl)2-planes within
the guanidine moieties, there are as well only small differences: in [Cu(btmgp)I] the torsion
within the guanidine moiety amounts to 37.4◦[35.9 - 38.9◦] whereas in C2 the torsion is
33.3◦[26.4 - 40.2◦].[112] The structural parameter ρis calculated to be 0.942, a typical value
for Cu(I) guanidine systems.[108]
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 52
Table 4.2: Selected distances and angles of C2
Distances (˚
A) C2 [Cu(btmgp)I]
Cu-I 2.4815(4) 2.491
Cu-Nimine 1.997(2) 2.006
N=C(av) 1.298(2) 1.295
Angles (◦)
Nimine-Cu-Nimine 102.6(1) 103.3
Nimine-Cu-I 127.51(4) 128.3
Namine-C-Namine(av) 114.9(2) 155.1
4.2.2 Electrochemistry of mononuclear copper bisguanidine complexes
The cyclovoltammogram of complex C1 (0.1 mol/L [NBu4][PF6]; 100 mV/s; Au/Pt/Ag-
AgCl) exhibits two electron transfers (Figure 4.6). The redox transition at -115 mV/NHE is
reversible and can be assigned to the Cu(II)/Cu(I) redox pair. The reversible redox transition
at 756 mV/NHE can be attributed to the iodine ion (E◦(I2/2I−) = +535 mV/NHE).
Figure 4.6: Cyclovoltammogram of C1 in CH2Cl2
In Figure 4.7, the cyclovoltammograms of C2 (0.1 mol/L [NBu4][PF6]; Au/Pt/Ag-AgCl) are
depicted. The oxidation wave is clearly irreversible and shifts strongly with the scan velocity
to higher potentials. Normalised to the NHE, the average oxidation potential of C2 can be
calculated to be -0.05 V/NHE.
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 53
Figure 4.7: Cyclovoltammograms of C2 in MeCN (20 mV/s - 200 mV/s)
4.3 Synthesis of dinuclear copper(I)bisguanidine complexes
with linear copper coordination
The complexes containing propylene-briged bisguanidine ligands were synthesised in good
yields by combining [Cu(MeCN)4][PF6] with 1.05 equiv. of the bisguanidine ligand in dry
acetonitrile and stirring for 30 min (Scheme 4.8). The kinetic data (see Section 5.4) are
indicative for the dinuclear nature of these complexes in solution as well.
N
C
R2N
R2N
N C
NR2
NR2
Cu Cu
N C NR2
NR2
NC
R2N
R2N
2 PF6-
NC
R2N
R2N
N C
NR2
NR2
[Cu(MeCN)4][PF6]
MeCN
+
2-
Figure 4.8: Complexation of [Cu(MeCN)4][PF6] with propylene-briged bisguanidine ligands
The complexes containing cyclohexyl-briged bisguanidine ligands were synthesised analo-
gously by combining CuI with 1.05 equiv. of the bisguanidine ligand in dry acetonitrile and
stirring for 30 min (Scheme 4.9). As the ligands TMG2ch and DMEG2ch are given as racemic
mixture of the cis and trans compound, two types of complexes were expected. Nevertheless,
only the complexes of the cis isomers with a bis-equatorial arrangement of the substituents
at the cyclohexyl ring crystallised. For both ligands, the corresponding cis isomer is bet-
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 54
ter suited to coordinate the copper in this bridging mode which is shown in Figure 4.12.
Possibly, the trans isomers are under these conditions subject to further reactions (e.g. cy-
clisation) preventing them from coordinating the copper. When an excess of CuI is present
in the reaction mixture, the trans complex did not form anyway. The excess of CuI was
added to the counterion iodine instead, in order to form the polynuclear counterions Cu2I2−
4
and Cu4I2−
6. The resulting complex salts C3 -C9 are soluble in polar aprotic media such as
MeCN, CH2Cl2and THF, but insoluble in diethylether and hydrocarbons. All compounds
are extremely sensitive to air and moisture due to the high proton affinity of guanidines
which is caused by delocalisation of the positive charge in the guanidine moiety.
NC
R2N
R2NN C NR2
NR2
CuI
MeCN
+
NC
R2N
R2NN C NR2
NR2
N C NR2
NR2
NC
R2N
R2N
Cu Cu Y2-
Y2- = 2 I-, Cu2I42-, Cu4I62-
2+
Figure 4.9: Complexation of CuI with cyclohexyl-bridged bisguanidine ligands
4.3.1 Crystal structures of dinuclear copper(I) bisguanidine complexes
Figure 4.10: Structure of [Cu2(btmgp)2]2+ in
crystals of C3
Single crystals of the compounds C3 -
C9 suitable for X-ray crystallography were
grown by slow diffusion of diisopropyl ether
into acetonitrile solutions. All compounds
are obtained as colourless needles expect
C7 which forms bright yellow needles. The
complex salts C3,C4 and C9 crystallise
monoclinic (C3: P21/n, C4: P21/c, C9:
C2/c) whereas the complex salts C5 -C8
crystallise triclinic in the space group P1.
The unit cell in crystals of C3 and C4 con-
tains two molecules, in crystals of C5,C6,
C7 and C8 only one molecule and in crys-
tals of C9 four molecules. Additionally, in
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 55
crystals of C4 0.37 MeCN per sum formula and in C5 one molecule of MeCN per asymmetric
unit is present. The results of the structure analyses are shown in Figures 4.10 - 4.13, while
selected bond lengths and angles are collected in Table 4.3 (* shortest H...H contact between
parallel propylene spacer groups; the H-H vector passes through the centroid of the corre-
sponding complex cation), and parameters relating to the data collection and refinement are
listed in the Tables A5 - A8.
Table 4.3: Selected distances and angles of the copper(I) complexes C3 -C9
Distances (˚
A) C3 C4 C5 C6 C7 C8 C9
Cu...Cu 4.121(1) 5.034(1) 4.488(1) 5.054(1) 4.974(1) 4.358(1) 4.723(1)
Cu-Nimine 1.876(2) 1.859(6) 1.878(2) 1.878(2) 1.877(2) 1.872(1) 1.876(3)
1.878(2) 1.865(5) 1.873(2) 1.882(2) 1.888(2) 1.867(1) 1.856(3)
N=C 1.323(3) 1.295(8) 1.310(3) 1.313(2) 1.309(4) 1.323(2) 1.310(3)
1.315(3) 1.312(8) 1.318(3) 1.308(2) 1.317(3) 1.325(2) 1.297(4)
Angles (◦)
Nimine-Cu-Nimine 176.7(1) 174.7(3) 175.3(1) 174.9(1) 176.3(1) 177.2(1) 176.8(1)
Namine-C-Namine 116.0(2) 114.0(6) 110.0(2) 109.9(2) 108.8(2) 117.5(1) 114.7(4)
116.8(2) 115.1(6) 110.9(2) 109.4(2) 109.7(2) 117.6(1) 116.0(4)
H...H* 3.37 2.19 3.00 2.08 2.28 3.26 2.30
ρ0.971 0.959 0.967 0.956 0.966 0.976 0.959
Figure 4.11: Molecular structures of [Cu2(DMEG2p)2]2+ in crystals of C5 (left) and of
[Cu2(DMPG2p)2]2+ in crystals of C8 (right)
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 56
Figure 4.12: Molecular structures of [Cu2(TMG2ch)2]2+ in C4 (left) and of
[Cu2(DMEG2ch)2]2+ in C6 and C7 (right)
Figure 4.13: Molecular structure of C9
The dinuclear complex cations present in all seven compounds exhibit molecular ring struc-
tures (Figures 4.10 - 4.13) with significant differences in the folding of their propylene chains
and in their corresponding interligand H...H separations passing through the centroids of the
molecules. The copper centres show almost linear twofold coordination from two nitrogen
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 57
donor atoms of different ligands with N-Cu-N angles of 176.7(1), 174.7(3), 175.3(1), 174.9(1),
176.3(1), 177.2(1) and 176.8(1)◦for C3 to C9, respectively. The centroids of the molecules
lie on crystallographic inversion centres resulting in perfectly planar Cu2N4moieties. Cor-
responding Cu-N, N=C, N-C and propyl-bridge C-C distances vary only very slightly from
C3 to C9 (averaged values in the order C3 -C9): Cu-N 1.877, 1.862, 1.875, 1.880, 1.883,
1.869, 1.866 ˚
A, N=C 1.319, 1.305, 1.314, 1.311, 1.313, 1.324, 1.309 ˚
A, C-Namine 1.358, 1.348,
1.359, 1.371, 1.360, 1.357, 1.364 ˚
A and N-C(spacer) 1.474, 1.502, 1.474, 1.484, 1.483, 1.474,
1.471 ˚
A. The Cu-N-C and N-C-C ring angles vary slightly in a non-systematic manner, the
C-C-C angles are 111.6(2), 114.3(5), 112.7(2), 113.3(2), 114.3(2), 112.4(1) and 115.6(3)◦for
C3 to C9. These differences may be traced back to variations in the Cu...Cu separations
(4.121(1), 5.034(1), 4.488(1), 5.054(1), 4.974(1), 4.358(1), 4.723(1) ˚
A). The variation in the
Cu...Cu separations can be correlated with the non-bonding H...H separations as it is shown
in Figure 4.14. This correlation is nearly linear: when the spacer is stretched, the hydro-
gen atoms at the center of the spacer are approaching each other and the copper centres
are reaching for a longer distance. Only C9 does not lie on this correlation line because
the sterically demanding piperidine subsituents have other secondary interactions than the
TMG, DMEG or DMPG systems. The structural parameter ρfor these complexes lies in
the range of 0.96 to 0.98.
Figure 4.14: Correlation between the Cu...Cu separations and the H...H distances
In C3, the N=C(N)2planes of the guanidine moieties are nearly perpendicular to each
other with a dihedral angle of 86.3◦. For C4,C7, and C8, these angles are similar with
82.4, 83.6 and 80.0◦, respectively. For C5,C6 and C9, they are diminuished to 68.4,
70.6 and 71.5◦, respectively. There is no clear tendency, therefore these differencies can
only be traced back to crystal packing. Compared with the free ligands DMPG2p and
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 58
Table 4.4: Dihedral angles [◦] between the CN3-guanidine plane and the Cimin-Namin-
(Calkyl)2-planes (mean values and ranges of individuals)
Compound Angles Compound Angles
btmgp n/a [Cu2(btmgp)2][PF6]2(C3) 34.1 [32.3 - 35.9]
TMG2ch n/a [Cu2(TMG2ch)2]I2(C4) 35.9 [31.1 - 39.3]
DMEG2p n/a [Cu2(DMEG2p)2][PF6]2(C5) 17.4 [12.7 - 23.1]
DMEG2ch n/a [Cu2(DMEG2ch)2][Cu2I4] (C6) 15.9 [14.2 - 17.3]
[Cu2(DMEG2ch)2][Cu2I4] (C7) 13.1 [11.5 - 13.4]
DMPG2p 25.9 [19.7 - 31.8] [Cu2(DMPG2p)2][PF6]2(C8) 24.8 [16.7 - 33.5]
DPipG2p 40.7 [39.2 - 42.7] [Cu2(DPipG2p)2][PF6]2(C9) 37.6 [32.2 - 43.2]
DPipG2p, the C=N bonds in C8 and C9 are clearly elongated by about 0.04 ˚
A whereas the
remaining geometric ring parameters show no relevant influence from copper complexation.
The N=C(N)2planes in these ligands show dihedral angles of 23.1◦and 31.5◦. Compared
with the complexes C3,C4,C8 and C9 (116.4, 114.6, 117.6, 115.4◦), the Namine-C-Namine
angles in C5,C6 and C7 are diminished to 110.5, 109.7 and 109.3◦, as the short ethylene
linker in the DMEG guanidine moietiy introduces steric strain as it is illustrated in Figure
4.15. Table 4.4 summarises the dihedral angles between the CN3-guanidine plane and the
Cimin-Namin-(Calkyl)2-planes within the guanidine moieties in the crystalline free bases and
in the solid complex salts. It is assumed that the deviation of an individual angle from the
mean value reflects mainly packing forces of the crystals. In solution, however, these angles
are not subjected to anisotropic interactions with the solvent. For that reason, the following
discussion is based on the assumption that the mean angle found in the crystalline state
comes close to the situation in solution.
C N1
N2
N3
A
A
B
B
R
Figure 4.15: Schematic representation of the
almost orthogonal pzorbitals in
DMEG groups
The tetramethylguanidino groups present in
btmgp and TMG2ch show a torsional ef-
fect in the dihedral angles between the
CN3-guanidine plane and the Cimin-Namin-
(Calkyl)2-planes of around 35◦whereas in
dimethylethyleneguanidine containing sys-
tems like DMEG2p and DMEG2ch, the eth-
ylene linker imposes geometric strain on the
guanidine centres resulting in a very small av-
eraged dihedral angle of around 15◦(Figure
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 59
4.15). By choosing a propylene linker, the averaged dihedral angle increases to about 25◦
as the system gains more constitutional flexibility. Without any linker, the pzorbitals twist
like in TMG and dipiperidylguanidines to avoid the steric hindrance. Thus, the dihedral
angles in dipiperidylguanidines reach their maximum value of around 39◦.
4.3.2 Electrochemistry of dinuclear copper(I) bisguanidine complexes
The copper(I) complexes C3,C5,C8 and C9 were also investigated cyclovoltammetrically
to determine their redox activities. In Figure 4.16, the cyclovoltammogram of C8 (0.1
mol/L [NBu4][PF6]; 100 mV/s, C/Pt/Ag-AgCl) is depicted as exemplified. The oxidation
wave at -0.23 V/NHE is clearly irreversible. In the course of these measurements, irreversible
oxidation waves at ca. -0.2 V attributable to the oxidation of Cu(I) to Cu(II) are observed
for all the complexes (Table 4.5). This behaviour is not surprising as the initially linear
coordination of Cu(I) requires subsequent rearrangement processes on changing the oxidation
state of copper. Interestingly, no correlation between the oxidation potentials of the copper(I)
complexes C3,C5,C8 and C9 and their abilities to stabilise P- or O-core complexes could
be found (see section 5.1).
Figure 4.16: Cyclovoltammograms of C8 in MeCN
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 60
Table 4.5: Cyclovoltammetric data for C3,C5,C8 and C9 (MeCN, v = 100 mV/s, 25◦C)
Copper complex (+1/+2) Eox [V/NHE]
[Cu2(btmgp)2][PF6]2(C3) -0.18
[Cu2(DMEG2p)2][PF6]2(C5) -0.23
[Cu2(DMPG2p)2][PF6]2(C8) -0.21
[Cu2(DPipG2p)2][PF6]2(C9) -0.29
4.4 Synthesis of polynuclear copper(I)bisguanidine chains
4.4.1 Synthesis of polynuclear Cu(DMEG2p) chains
The ligand DMEG2p is not only capable of stabilising dinuclear copper complexes with lin-
ear coordination but also of polynuclear chains with linear as well as trigonal-planar copper
coordination modes. The decision between dinuclear complex and polynuclear chain is made
by the choice of the solvent: if the complex is formed by reaction of [Cu(MeCN)]4[PF6] and
DMEG2p in acetonitrile, the dinuclear compound C5 crystallises upon addition of ether. By
using THF instead, the copper bisguandine chain of C10 with linear copper coordination
(Figures 4.17 and 4.18) can be obtained. The reaction of CuI and DMEG2p in THF yields
the copper bisguanidine chain of C11 exhibiting a trigonal-planar copper coordination which
is illustrated in the Figures 4.19 and 4.20. Both copper bisguanidine chains crystallise upon
additin of apolar solvents like diethyl or diisopropyl ether monoclinic in the space group
P21/n. The unit cells contain four molecules, but in crystals of C10 two additional mole-
cules of acetonitrile per asymmetric unit are present originating from the educt compound
[Cu(MeCN)]4[PF6]. Selected bond lengths and angles are collected in Table 4.6, and para-
meters relating to the data collection and refinement are listed in the Tables A8 and A9,
respectively.
The chain structures exhibit several interesting features: in crystals of C10, the copper
centres are coordinated almost linearly (N-Cu-N 178.7◦) whereas in crystals of C11, one
copper centre is coordinated T-shaped with an N-Cu1-N angle of 163.5◦and N-Cu-I angles
of 98.0◦and the other one trigonal-planar with an N-Cu2-N angle of 115.5◦and N-Cu2-
I angles of 122.2◦. This coordinational difference is further denoted in the different Cu-
N bonds which measure around the T-shaped Cu1 centre about 1.918 ˚
A and around the
trigonal-planar Cu2 centre about 2.013 ˚
A. At the same time, the Cu1-I1 distance is as long
as 2.9291(5) ˚
A whereas the Cu2-I2 distance in the trigonal situation has been determined
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 61
Table 4.6: Selected distances and angles of the copper(I) chains C10 and C11
Distances (˚
A) C10 C11
Cu-Nimine Cu1-N1 1.877(2) Cu1- N4 1.915(3)
Cu1-N4 1.872(2) Cu1 -N3 1.920(3)
Cu2-N7 1.873(2) Cu2 -N10 2.002(3)
Cu2-N10 1.878(2) Cu1 -N7 2.024(3)
Cu-I Cu1- I1 2.9291(5)
Cu2- I2 2.5413(5)
N=C(av) 1.308 1.291
Angles (◦)
Nimine-Cu-Nimine N4-Cu1-N1 177.9(1) N4-Cu1-N3 163.5(1)
N7-Cu2-N10 179.5(1) N10-Cu2-N7 115.5(1)
Nimine-Cu-X N4-Cu1-I1 97.1(1)
N3-Cu1-I1 98.9(1)
N10-Cu2-I2 124.2(1)
N7-Cu2-I2 120.2(1)
Namine-C-Namine(av) 109.7 109.0
ρ0.951 0.933
Figure 4.17: Section of the molecular structure of C10
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 62
Figure 4.18: A view normal to the 001-plane in crystals of C10
Figure 4.19: Section of the molecular structure of C11
to 2.5413(5) ˚
A. Compared to C10 with strictly twofold coordination, the averaged Cu-N
distances in C11 are elongated by about 0.09 ˚
A to 1.965 ˚
A due to the higher coordination
number. The Namine-C-Namine angles in C10 and C11 have the characteristic value for
DMEG2p containing systems in which the ethylene linker tights the Namine atoms together.
In Figures 4.18 and 4.20, a view normal to the 001-plane is given in order to illustrate the
crystal packing. In both structures, the stacking of the almost planar DMEG moieties is
clearly recognisable. In the packing of C11, one can distinguish the two different Cu-I units
which are alligned by turns.
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 63
Figure 4.20: A view normal to the 001-plane in crystals of C11
4.4.2 Synthesis of further polynuclear copper(I)bisguanidine chains
By using TMG2mX as coordinating ligand, a copper bisguanidine chain molecule with an
intermediate between trigonal-planar and linear coordination of the copper centres can be
synthesised. The reaction of CuI and TMG2mX in MeCN yields the copper bisguanidine
chain of C12 exhibiting a very distorted trigonal-planar copper coordination which is illus-
trated in the Figures 4.21 and 4.23. Crystals of C12 could be obtained by vapour diffusion
of diethylether into the reaction mixture. C12 crystallises in the monclinic space group
P21/n with four molecules per unit cell. By using DPPG2p as coordinating ligand, a cop-
per bisguanidine chain molecule with T-shaped coordination of the copper centres and a
strong Cu...Cu interaction can be synthesised. The reaction of CuI and DPPG2p in MeCN
yields the copper bisguanidine chain [Cu(DPPG2p)]n[CuI2]n(C13) which is depicted in the
Figures 4.22 and 4.24. Crystals of C13 could be obtained by evaporation of a acetoni-
trile/dichloromethane solution in the glove-box. C13 crystallises in the orthorhombic space
group P212121with four molecules per unit cell. In the [CuX2] unit, the halide positions
are occupied by iodine (85 %) and by chlorine (15 %). As possible source for chlorine,
the dichloromethane and the synthesis process of the ligand have to be considered (chloro-
formamidinium chlorides). The presence of chlorine was confirmed by microanalysis, too.
Selected bond lengths and angles of C12 and C13 are collected in Table 4.7, and para-
meters relating to the data collection and refinement are listed in the Tables A9 and A10,
respectively.
In crystals of C12, the copper centres are coordinated in a distorted (2+1) trigonal-planar
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 64
Table 4.7: Selected distances and angles of the copper(I) chains in crystals of C12 and C13
Distances (˚
A) C12 C13
Cu-Nimine Cu1 -N1 1.911(2) Cu1 -N1 1.903(3)
Cu1-N4 1.905(2) Cu1 -N4 1.906(2)
Cu-I 3.1423(5) Cu2-I1 2.3935(7)
Cu2-I2 2.3898(6)
N=C(av) 1.314 1.313
Angles (◦)
Nimine-Cu-Nimine N4-Cu1-N1 169.8(1) N1-Cu1-N4 178.9(1)
Nimine-Cu-X N1-Cu1-I1 94.5(1) N1-Cu1-Cu2 91.2(1)
N4-Cu1-I1 95.6(1) N4-Cu1-Cu2 88.1(1)
Namine-C-Namine(av) 116.0 115.7
ρ0.960 0.959
Figure 4.21: Section of the molecular structure of C12
geometry (N-Cu-N 169.8(1)◦). The copper lies only 0.008(1) ˚
A above the N1N4I1A plane.
The Cu-I distance is relatively long with 3.1423(5) ˚
A, thus, it can be regarded as contact
due to the clear distortion of the N-Cu-N angle which measures in a linear coordinational
environment like in C10 up to 178◦(averaged). Compared to C10 with strictly twofold
coordination, the averaged Cu-N distances in C13 are slightly elongated by about 0.03 ˚
A
to 1.908 ˚
A due to the higher coordination number. This mode of coordination represents an
intermediate between linear coordination with non-coordinating anion and a trigonal-planar
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 65
Figure 4.22: Section of the molecular structure of C13
coordination where the iodine acts as third donor. The Namine-C-Namine angles are in the
range of other tetramethyl guanidines.
In crystals of C13, the Cu1 centre is coordinated T-shaped with an N-Cu1-N angle of
178.9(1) and averaged N-Cu1-Cu2 angles of 89.7◦. The Cu...Cu distance measures 2.6732(6)˚
A
and the Cu-I distances average to 2.392 ˚
A. The Cu2 centre is as well coordinated T-shaped
with an I1-Cu2-I2 angle of 169.63(2)◦and averaged I-Cu2-Cu1 angles of 95.2◦. The coordi-
nation axes of the CuN2and the CuI2unit are approximately perpendicular to each other
as the torsion angles indicate (N1-Cu1-Cu2-I1 91.1◦, N4-Cu1-Cu2-I2 90.3◦). It is instructive
to compare the structure of C13 with similar systems with Cu...Cu interactions: Siemeling
et al. characterised a similar perpendicular Npy,2Cu...CuCl2constellation with a Cu...Cu
separation of 2.810(2) ˚
A [132] whereas K¨ohn was able to crystallise the [Cl2Cu...CuCl2]2−
dianion stabilised in a complex salt exhibiting a Cu...Cu separation of 2.92 ˚
A.[133] Very re-
cently, K¨ohn found a cuprophilic interaction of only 2.54 ˚
A in a dinuclear structure stabilised
by triazacyclohexanes.[134] Shorter contacts have only been observed by Str¨ahle et al.[135]
Thus, complex C13 represents a rare example of this structural class with a remarkably
short Cu...Cu distance of 2.6732(6)˚
A. Upon closer consideration, it has to be mentioned
that this close Cu...Cu contact in C13 is not stabilised by a ligand bridging the copper
centres like in Str¨ahles system. Such close contacts may be interpreted in terms of weak
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 66
bonding interactions between the two d10 metal centres. Attractive interactions between
formally closed-shell metal centres are documented for several metals.[136] In the case of
gold, the term aurophilicity has been coined to describe this special kind of metal-metal
bonding interaction,[137] but the question of whether a similar metallophilicity [138] exist in
the case of the other two coinage metals, copper and silver, is still a matter of controversy.
An interesting case is the trinuclear copper complex [Cu(CH3C6H4-N5C6H4CH3)3], where the
metal centres have an average distance of only 2.35 ˚
A.[135] This existence of cuprophilic inter-
action has both been supported [139] and refuted [140] at various levels of theory. Generally,
weak metallophilic effects are easily blurred or even overruled by other secondary interac-
tions. Therefore, crystal packing forces may very well overrule weak cuprophilic interactions
explaining the greater distances in Siemelings system under account of all similarities.[141]
However, compared to C12 with distorted trigonal-planar coordination, the averaged Cu-N
distances in C13 are in good accordance which shows that the CuI2moiety acts as weak
donor.
In Figures 4.23 and 4.24, the best view is given in order to illustrate the crystal packing. In
both structures, the stacking of the guanidine moieties supports the crystallisation in spite
of the flexible propylene chains in C13. Furthermore, the N2Cu...CuI2unit in C13 seems
to stabilise the packing.
Figure 4.23: View on the crystal packing in C12
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 67
Figure 4.24: View on the crystal packing in C13
Table 4.8 summarises the dihedral angles between the CN3-guanidine plane and the Cimin-
Namin-(Calkyl)2-planes within the guanidine moieties in the complexes C10 -C13. The ligand
DMEG2p shows in these two complexes dihedral angles of around 16.7◦, the tetramethyl
system TMG2mX of 35.5◦and the dipropylpropylene system DPPG2p of 28.5◦.
Table 4.8: Dihedral angles [◦] between the CN3-guanidine plane and the Cimin-Namin-
(Calkyl)2-planes (mean values and ranges of individuals)
Compound Angles
[Cu(DMEG2p)PF6]x(C10) 15.7 [12.2 - 19.0]
[Cu(DMEG2p)I]x(C11) 17.8 [14.5 - 21.6]
[Cu(TMG2mX)I]x(C12) 35.5 [29.4 - 40.1]
[Cu(DPPG2p)..CuI2]x(C13) 28.5 [22.5 - 34.3]
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 68
4.5 Synthesis of a dinuclear
copper(I)benzimidazolyle-guanidine complex with
linear copper coordination
By using TMG2PA in the reaction with [Cu(MeCN)]4[PF6], the copper is not oxidised
to Cu(II), but a cyclisation of the bisguanidine ligand to a benzimidazole-monoguanidine
system occurs and the dinuclear complex compound Bis2-(2-(2-(dimethylamino)-1H-
benzo[d]imidazol-1-yl)phenyl)-1,1,3,3-tetramethylguanidine copper(I)hexafluorophosphate
([Cu2(TMGbenzPA)2][PF6]2, (C14) is formed. A proposed mechanism is illustrated in
reaction scheme 4.25. Firstly, the copper is coordinated by the TMG2PA ligand, then
the acidic proton is abstracted under nucleophilic attack of the amide on one of the basic
guanidine groups. It might be possible that these steps are occurring simultaneously
resulting in a abstraction of HNMe2. In this cyclisation reaction, the driving force is the
formation of a aromatic benzimidazole compound. The former guanidine N=C bond is
now part of the heterocyclic benzimidazole system. During all these steps, the copper is
stabilised by the coordinating solvent acetonitrile. Finally, the mononuclear complex cation
dimerises to yield complex C14 because the coordinational environment with two strong
ligand N donors is better than only one N donor from the ligand and one from MeCN.
Appearently, in this case, this reaction is preferred to an oxidation of the copper and proton
reduction to hydrogen (see section 4.2).
4.5.1 Crystal structure of [Cu2(TMGbenzPA)2][PF6]2(C14)
Colourless single crystals could be obtained by vapour diffusion of diethylether into MeCN
solution. C14 crystallises monoclinic in the space group P21/n. Crystals of C14 consist of
isolated molecules, the unit cell contains two molecules of C14. The results of the structure
analysis are shown in Figure 4.26, while selected bond lengths and angles are collected in
Table 4.9, and parameters relating to the data collection and refinement are listed in Table
A10.
The dinuclear complex cation C14 exhibits a molecular ring structure (Figure 4.26) similar
to those of the complexes C3 -C9. In C3 -C9, the ligand has a propylene spacer resulting
in a twelve-membered heterocycle whereas in C14, the cyclisated ligand has a benzimidazol-
phenylene spacer resulting in a fourteen-membered heterocycle. Hence, the Cu...Cu separa-
tion is with 4.704(1) ˚
A longer than in the comparable C3 (4.121(1) ˚
A) . The copper centre
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 69
N
H
NN
Me2N NMe2Me2NNMe2
[Cu(MeCN)4][PF6]
N
N
NMe2
N
NMe2
NMe2
CuI
N
N
Me2N
N
NMe2
Me2NCuI
2 PF6-
N
NN
Me2NNMe2Me2NNMe2
Cu
H
MeCN
N
NN
Me2NNMe2Me2NNMe2
Cu
MeCN
- H+
-NMe2-
N
N
NMe2
N
NMe2
NMe2
CuI
PF6-
PF6-
NCMe
Dimerisation
- 2 MeCN
Figure 4.25: Reaction of TMG2PA with [Cu(MeCN)4][PF6]
Figure 4.26: Molecular structure of C14
shows almost linear twofold coordination from two nitrogen donor atoms of different ligands
with N-Cu-N angles of 173.8(3)◦. The centroid of this molecule lies on the crystallographic
CHAPTER 4. COPPER(I) BISGUANIDINE COMPLEXES 70
Table 4.9: Selected distances and angles of C14
Distances (˚
A) C14 C3
Cu...Cu 4.704(1) 4.121(1)
Cu-Nimine 1.879(5) 1.876(2)
1.895(6) 1.878(2)
N=C(gua) 1.324(9) 1.319
N=C(benz) 1.307(8)
Angles (◦)
Nimine-Cu-Nimine 173.8(3) 176.7(1)
inversion centre resulting in a perfectly planar Cu2N4moiety. The Cu-Nimine distances are
in good agreement with those found in C3 -C9. The N=C bond of the benzimidazole part
of the TMGbenzPA ligand is not significantly shorter than the N=Cguanidine bond. However,
the calculation of the structural parameter ρshows that the ”real” guanidine moiety has a
ρvalue of 0.974 with good delocalisation, whereas the cyclisated guanidine moiety has a ρ
value of 0.947 with stronger localisation of the C=N double bond.
4.5.2 Electrochemistry of [Cu2(TMGbenzPA)2][PF6]2(C14)
The cyclovoltammogram of C14 (0.1 mol/L [NBu4][PF6]; 50 mV/s; Au/Pt/Ag-AgCl) shows
three irreversible electron transfers (Figure 4.27). The first oxidation wave at 442 mV/NHE
Figure 4.27: Cyclovoltammogram of C14 in CH2Cl2
might be indicative for the oxidation of Cu(I) to Cu(II) whereas the oxidation waves at 988
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 71
and 1363 mV/NHE belong to redox processes which are delocalised in the aromatic system.
Thus, they can not be assigned exactly to special redox processes.
4.6 Conclusion of the Syntheses of Copper(I)Bisguanidine
complexes
It could be shown that bisguanidine complexes are able to stabilise copper(I) complexes in
several coordination modes. The different topologies are summarised in the first section of
this chapter. The presented ligands support the formation of mono-, bi- and polynuclear
complexes, sometimes with solvent-depending equilibria between two coordination modes.
Especially the ligand DMEG2p has shown to be very flexible: in crystals of C15, the co-
ordination is bridging linear, whereas in the isomer C10, the ligand stabilises by linear
coordination a polynuclear chain. By introducing further donor atoms like iodine in C11,
the coordination changes to a trigonal-planar mode. Finally, in Chapter 6, the chelating
coordination with this ligand in the copper(II) complex C21 will be described.
5 Oxygen activation with Cu(I)
bisguanidine complexes
5.1 Cu2O2Bisguanidine species
As mentioned in Section 1.5.4, the supporting ligands can tune the equilibrium between
µ-η2:η2-peroxo and bis(µ-oxo) dicopper cores (Figure 5.1). There are multiple influences
which are imposed on this sensitive equilibrium, e.g. the denticity, the ligand bite, electronic
factors dictating the σdonor strength and steric factors imposing steric strain.[48] In the
following section, the influences of bisguanidine ligands on Cu2O2species will be discussed.
+II
+II
N
N
Cu O
O
Cu
N
N
N
R3
R2
N R1
R4
N
R2
R3
N
R4
R1
N
R3
R2
N
R1
R4
N
R2
R3
N
R4
R1
+III
+III
N
N
Cu
O
O
Cu
N
N
N
R3
R2
N R1
R4
N
R2
R3
N
R4
R1
N
R3
R2
N
R1
R4
N
R2
R3
N
R4
R1
2+ 2+
NN
Cu
NR3
R2
N
R1
R4
N
R2
R3NR4
R1
O2
L
L = solvent
molecule
+I
bis(µ-oxo) dicopper core
O-core
µ-η2:η2-peroxo dicopper core
P-core
Figure 5.1: Equilibrium between µ-η2:η2-peroxo and bis(µ-oxo) dicopper bisguanidine com-
plexes
72
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 73
5.2 UV/Vis-Spectroscopy of Cu2O2Bisguanidine species
5.2.1 UV/Vis-Spectroscopy of Cu2O2species with aliphatic
bisguanidine ligands
Upon reaction of [Cu(DMorphG2p)I] (C2), [Cu2(btmgp)2][PF6]2(C3) and
[Cu2(DPipG2p)2][PF6]2(C9) with O2, intensive LMCT absorption bands at 300 (≈
16000 mol/(Lcm)) and 390 nm (≈17000 mol/(Lcm)) are observed which are characteristic
for all O-core complexes known so far (Figure 5.2). These species are unstable even at
-80◦C in dichloromethane. The initial red solutions change their colours to bluish-green
upon warming up to room temperature within 1 - 2 h.[142]
Figure 5.2: Time-dependent UV/Vis absorption spectra (every 2 min) observed upon intro-
duction of O2gas into CH2Cl2solution of C9 (0.25 mM, -80◦C) during 30 min;
inset: spectrum after 2 h (0.33 mM)
Treatment of a 0.2 mM solution of [Cu2(DMEG2p)2][PF6]2(C5) in CH2Cl2with dioxygen
at -80◦C resulted in a green colour of the solution. At higher concentrations, the solution
turns dark brown. The UV/Vis spectrum observed 1 h after introduction of molecular
oxygen is shown in Figure 5.3. The spectrum is dominated by a strong absorption band
at 355 nm (= 17000 mol/(Lcm)) indicative of the predominant formation of the P-core
complex. The shoulder at 320 nm (= 9500 mol/(Lcm)) is assigned to the formation of
O-core contributors. [Cu2(DMPG2p)2][PF6]2(C8) reacts with O2in dichloromethane under
predominant formation of a P-core complex which can be identified by LMCT absorptions at
350 nm (= 21200 mol/(Lcm))and at 550 nm (= 900 mol/(Lcm)). The band at ca. 300 nm
(= 13500 mol/(Lcm)) originates from O-core components which are formed concomitantly
with the P-core (Figure 5.4a). The O-core absorption at 390 nm is not resolved.
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 74
Figure 5.3: UV/Vis absorption spectrum observed upon introduction of O2gas into a solution
of C5 in MeCN/CH2Cl2(1:10) (0.5 mM, -80◦C) after 30 min, inset: spectrum
after 1 h (0.25 mM)
Figure 5.4: a)Time-dependent UV/Vis absorption spectra (every 2 min) observed upon in-
troduction of O2gas into CH2Cl2solution of C8 (0.2 mM, -80◦C) during 30
min; inset: spectrum after 2 h (0.5 mM); b)Time-dependent UV/Vis absorption
spectra (every 30 s) observed upon introduction of O2gas into MeCN solution
of C8 (0.25 mM, -40◦C) during 8 min; inset: spectrum after 1 h (0.5 mM)
In contrast, reaction of C8 with O2in acetonitrile at -40◦C results in the immediate formation
of an O-core complex shown by the UV/Vis absorption bands at 290 (= 13000 mol/(Lcm))
and 390 nm (= 15800 mol/(Lcm)) (Figure 5.4b). By using MeCN as solvent, the equilibrium
between P- and O-core is shifted almost completely to the O-core side. These results show
that coordinating solvents are better suited to stabilise the O-core than non-coordinating
ones and thus confirm reports of other groups published in the literature.[45, 49, 48]
Compound [Cu2(TMG2ch)2][I]2(C4) reacts with O2in dichloromethane under formation of
an O-core complex which can be identified by LMCT absorptions at 295 nm (= 16500
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 75
mol/(Lcm))and at 370 nm (= 11300 mol/(Lcm)) (Figure 5.5). The band at 370 nm is
blue-shifted in comparison with other O-core complexes. Possibly, there are small amounts of
P-core components which might shift the band from 400 nm to 370 nm. Interestingly, the red
solution of this O-core species decays relatively fast within 20 min, hence the measurement
had to be carried out using higher concentrations of the precursor complex. Treatment of a
Figure 5.5: Time-dependent UV/Vis absorption spectra (every 1 min) observed upon intro-
duction of O2gas into CH2Cl2solution of C4 (1 mM, -80◦C) during 10 min
0.4 mM solution of [Cu2(DMEG2ch)2][Cu2I4] (C6) in CH2Cl2with dioxygen at -80◦C resulted
in a greenish-blue colour of the solution. At higher concentrations, the solution turns dark
brown. The UV/Vis spectra measured every 50 s are depicted in Figure 5.6. The spectrum
is dominated by a strong absorption band at 360 nm (= 18500 mol/(Lcm)) indicative of
the formation of the P-core complex.
Figure 5.6: Time-dependent UV/Vis absorption spectra (every 50 s) observed upon intro-
duction of O2gas into CH2Cl2solution of C6 (0.2 mM, -80◦C) during 400 s
The reaction of [Cu(DPPG2p)I] with dioxygen in dichloromethane at -80◦C yields a red
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 76
solution with an intensive absorption at 355 nm (= 19700 mol/(Lcm))(Figure 5.7). This
species is stable for about 3 hours at -80◦C. It has to be mentioned that there is no distinct
side band of O-core components which is developed using the similar ligand DMPG2p (Figure
5.4).
Figure 5.7: Time-dependent UV/Vis absorption spectra (every 2 min) observed upon intro-
duction of O2gas into CH2Cl2solution of [Cu(DPPG2p)]I (0.35 mM, -80◦C)
during 24 min
5.2.2 UV/Vis-Spectroscopy of Cu2O2species with aromatic
bisguanidine ligands
All TMG2MePA containing complexes, e.g. [Cu(TMG2MePA][X] (X = PF−
6, ClO−
4, BF−
4and
I−), exhibit upon reaction with O2a dominant absorption at 395 nm (≈21000 mol/(Lcm))
which is not influenced by the counteranion (Figure 5.8). This characteristic O-core absorp-
tion is accompanied by a broad absorption at 550 nm (≈2800 mol/(Lcm)) which might be
caused by aromatic side-products (not P-core). The solution is dark brown and turns upon
warming up black.
Upon reaction of [Cu2(DMPG2mX)2]I2with O2, an intensive LMCT absorption band at 350
(= 16500 mol/(Lcm)) assigning the development of a P-core species and a characteristic
isosbestic point at 425 nm are observed (Figure 5.9). These species are unstable even at -
80◦C in dichloromethane. The initial red solution changes its colour to brownish-green upon
warming up to room temperature within 1 - 2 h.
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 77
Figure 5.8: Time-dependent UV/Vis absorption spectra (every 2 min) observed upon in-
troduction of O2gas into CH2Cl2solution of [Cu(TMG2MePA)][PF6] (0.1 mM,
-80◦C) during 22 min
Figure 5.9: Time-dependent UV/Vis absorption spectra (every 1 min during 30 min, then
every 5 min during further 150 min) observed upon introduction of O2gas into
CH2Cl2solution of [Cu2(DMPG2mX)2]I2(0.1 mM, -80◦C)
5.2.3 UV/Vis-Spectroscopy of Cu2O2species with sterically demanding
bisguanidine ligands
The reaction of [Cu(B(TMPip)G2p)]I containing a highly sterically demanding ligand with
dioxygen proceeds very slowly at low temperatures. Thus, the reaction was observed at room
temperature (Figure 5.10). As the strong absorption bands at 295 nm (= 18100 mol/(Lcm))
and 370 nm (=9700 mol/(Lcm)) indicate, an O-core species is formed which is stable for
two weeks at room temperature. This behaviour can be explained by the extreme shielding
effect of the tetramethylpiperidino groups. The O-core can only hydroxylate N-CH3groups
(see section 6.1) but not this environment, so, the course of subsequent reactions is hindered.
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 78
Resonance Raman measurements have been carried out in order to prove the existence of
this room-temperature stable O-core. The resulting resonance Raman spectrum is depicted
in Figure 5.11. The peak at 583 cm−1belongs to the Cu2O2breathing mode; this vibration
is characteristic and diagnostic for an O-core.[48] At the same time, this resonance Raman
spectrum shows that there are no detectable P-core components present which could shift
the second absorption band to 370 nm. This blue-shifted band appears to be characteristic
for some bisguandine Cu2O2species.
Figure 5.10: Time-dependent UV/Vis absorption spectra (every 30 min) observed upon in-
troduction of O2gas into CH2Cl2solution of [Cu(B(TMPip)G2p)]I (0.3 mM,
25◦C) during 600 min
Figure 5.11: Resonance Raman spectrum of [Cu(B(TMPip)G2p)]I (≈80 mM, 25◦C,
CH2Cl2), excitation wavelength: 350 nm
The UV/Vis absorption spectrum of [Cu((DMPip)DMG2p)]I with dioxygen (Figure 5.12)
exhibits the two characteristic absorption bands of an O-core species (290 nm (= 19500
mol/(Lcm)) and 370 nm (= 10400 mol/(Lcm))). This result shows that the guanidine
moieties do not have to be such sterically demanding to stabilise a room-temperature stable
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 79
O-core species like it is the case in [Cu(B(TMPip)G2p)]I. The ligand (DMPip)DMG2p pos-
sesses only one dimethylpiperidino unit and one dimethylamino unit attached to the Cimine
atom, but the sterical shielding seems to be great enough to support this O-core complex.
The smaller guanidine moieties are reflected in an O-core formation which is more than five
times faster than it would preceed with [Cu(B(TMPip)G2p)]I, but nevertheless, this species
is stable for one week.
Figure 5.12: Time-dependent UV/Vis absorption spectra (every 2 min) observed upon intro-
duction of O2gas into CH2Cl2solution of [Cu((DMPip)DMG2p)]I (0.15 mM,
25◦C) during 60 min
5.2.4 UV/Vis-Spectroscopy of Cu2O2species with the fluorinated
bisguanidine ligand BFPPG2p
The shielding effect of relatively inert substituents at the guanidine centres can be combined
with a smaller twist within the guanidine centre by using the fluorinated ligand BFPPG2p.
The heptafluoropropyl chains are inert to hydroxylation and shield the Cu2O2core against
other decomposition reactions. The propylene backbone within the guanidine moiety tights
the Namine atoms together as can be seen in DMPG2p and DPPG2p. Both ligands support
P-cores at low temperatures. By attaching long fluorinated groups to the guanidine moiety,
the lifetime of the generated P-core species should be enhanced.
Figure 5.13 denotes the time-dependent absorption spectra observed during the reaction of
[Cu(BFPPG2p)]I in dichloromethane with dioxygen at room temperature. The P-core is as-
signed by the characteristic absorption band at 358 nm (= 21400 mol/(Lcm)), accompanied
by a weak band at 600 nm(= 540 mol/(Lcm)). The inset shows that the band is relatively
narrow and develops homogeneously. Figure 5.13 illustrates that the P-core species forms
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 80
very slowly in the time range of the O-core species of [Cu(B(TMPip)G2p)]I. The brown-red
solution of the generated P-core is stable for around four days. This stability is remarkable
compared with the stabilities of complexes which have been reported in the literature by
Kodera et al.[62] (τ1/2= 25.5 h) and Gorun et al.[87]
Figure 5.13: Time-dependent UV/Vis absorption spectra (every 20 min) observed upon in-
troduction of O2gas into CH2Cl2solution of [Cu(BFPPG2p)]I (0.35 mM, 25◦C)
during 400 min; inset: magnification of the first hour with spectra every 2 min
during 60 min)
5.3 Interpretation of the results
5.3.1 Correlation of P/O-core development with structural properties
The above described results for the activation of dioxygen have to be correlated with struc-
tural properties of the investigated systems. Therefore, in Table 5.1, the dihedral angles
between the CN3-guanidine plane and the Cimin-Namin-(Calkyl)2-planes are set in connection
with the capability of the Cu(I) compound of stabilising a P- or O-core complex.
Appearently, twisted systems like C2,C3,C4 and C9 with angles around 35◦favour the
stabilisation of an O-core complex, whereas ”flat” systems with angles around 16◦incorpo-
rated in C5 and C6 support P-core complexes. C8 and C13 have angles which are in the
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 81
Table 5.1: Correlation of the dihedral angles [◦] between the CN3-guanidine plane and the
Cimin-Namin-(Calkyl)2-planes with the capability of stabilising a P or O-core
Complex Angle P-core O-core
[Cu(DMorphG2p)I] (C2) 33.3 x
[Cu2(btmgp)2][PF6]2(C3) 34.1 x
[Cu2(TMG2ch)2]I2(C4) 35.9 x
[Cu2(DMEG2p)2][PF6]2(C5) 17.4 x
[Cu2(DMEG2ch)2][Cu2I4] (C6) 15.9 x
[Cu2(DMPG2p)2][PF6]2(C8) 24.8 x x
[Cu2(DPipG2p2)][PF6]2(C9) 37.6 x
[Cu(DPPG2p)]n[CuI2]n(C13) 28.5 x
middle of this range with 24.8 and 28.5◦, respectively. Hence, it can be understood why C8
shows solvent-depending behaviour. The sensitive P/O-core equilibrium can be shifted at
this point only by a change from a coordinating solvent to a non-coordinating one.
This correlation can be expanded by regarding the other systems for which no crystal data
could be obtained. [Cu(TMG2MePA)][X] (X = PF−
6, ClO−
4, BF−
4and I−) stabilises an O-core,
perhaps because it incorporates a tetramethylguanidino unit. The TMG unit is generally
twisted around 35◦as further examples like [Mn(btmgp)Br2] (34.2◦)[143] and [Cu(btmgp)I]
(35.7◦)[112] show. [Cu2(DMPG2mX)2]I2incorporating a DMPG unit which is twisted to a
smaller degree stabilises a P-core. The sterically demanding systems [Cu(B(TMPip)G2p)]I
and [Cu((DMPip)DMG2p)]I stabilise both an O-core. Since both systems contain sub-
stituents based on a twisted piperidino unit (vide supra, C9), this behaviour is in agreement
with the other observations. The higher sterical demand results in an enhancement of the
stability of the generated O-core. Even the fluorinated system [Cu(BFPPG2p)]I can be fit-
ted into this correlation as the ligand BFPPG2p descends from its unfluorinated predecessor
DPPG2p (vide supra, C13). DPPG2p supports a P-core at low temperatures, BFPPG2p
does the same at room temperature. This may be due to a shielding effect of the inert
fluorinated groups, but also to a sterical effect as these groups demand for more space than
their unfluorinated analoga.
In summary, it can be recorded that the twist of the guanidine moiety determines the for-
mation of P- or O-core and that the sterical demand tunes the stability of the generated
core.
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 82
5.3.2 σdonor and πacceptor capabilities of the ligands
In order to explain the reaction behaviour of the copper(I) complexes with molecular oxy-
gen, we have to look at the special coordination properties of the guanidine ligands de-
scribed above. The dihedral angles within the guanidine moieties are decisive for the dis-
cussion of these coordination properties (vide supra). Depending on the residues attached
to the guanidine systems, the resulting Cu2O2species are either bis(µ-oxo)dicopper(III) or
µ-η2:η2-peroxo dicopper(II) complexes or mixtures of both. The direction in which the
equilibrium is driven depends on the degree of planarisation of the guanidine moieties.
C N
R
N
N
R3
R4
R1
R2
Figure 5.14: Competition of p-πconju-
gation and steric repulsion
within the guanidine centre;
arrows indicate twist from
ideal conjugation (pale)
Within a guanidine residue, the observed struc-
ture is predominantly the result of an interplay
of two major driving forces, one of them deter-
mined by electronic, the other one by steric inter-
actions. Both types of interaction are competing
against each other: as the π-orbitals of the periph-
eral NaminC3portions search for reasonably good π
interactions with the central CN3unit, this prereq-
uisite demands for one common plane hosting all
the involved C and N atoms. On the other hand,
spatial demands of the substituents at the amin
nitrogen atoms require propeller-like twists of the
NC3portions around their N-Cimine bonds and thus prevent from a coplanar arrangement
with the central CN3group. Furthermore, pyramidalisation tendencies of the peripheral
NaminC3portions can be observed which are amplified if both N atoms are part of a hete-
rocyclic ring as realised in DMPG and in DMEG moieties. The degree of pyramidalisation
depends on the steric strain in the heterocycle but has no influence on the coordination
properties.
It turned out that the result of the interplay between electronic (p-πconjugation) and steric
forces (repulsion of the substituents, Figure 5.14) is decisive for the equilibrium between the
bis(µ-oxo)- and the µ-η2:η2-peroxo dicopper core. Small dihedral angles between adjacent
NaminC3and CN3units indicative for a good conjugation of the πorbitals in the guanidine
moiety favour the µ-η2:η2-peroxo dicopper core whereas moderately larger ones induce a
shift of the equilibrium towards the formation of the bis(µ-oxo)-dicopper state. The above
reported dihedral angles are not a result of packing forces, but an inherent property of the
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 83
particular guanidine moiety as a large number of crystalline examples show: the TMG unit
mostly exhibits dihedral angles of around 35◦whereas the DMEG unit is almost ”flat” with
about 16◦.[143] The DMPG unit has dihedral angles of 25◦, the DPPG unit of 28◦and the
DPipG and DMorphG units of 37◦. These values are averaged over crystal structures of the
ligands and of the complexes with different coordination modes (linear, trigonal) as well as
different counteranions which influence the packing.
A bonding description of the P-core was developed through a detailed correlation of spectral
features, structural parameters and theoretical calculations by Solomon et al.[10, 144] Fur-
thermore, it is reported that strictly σ-donating ligands should be better suited to stabilise
O-core complexes whereas ligands with π-acceptor properties should favour the formation of
their P-core counterparts.[45, 48] The key aspects of the theoretical description are repro-
duced in Figure 5.15. On the left hand side, the d9configuration of the two Cu(II) ions is
σ*
2 dx2-y2
OCu
Cu O
O22-
πσ*
HOMO
LUMO
πv*
2 dz2
2 dxy
2 dxz and dyz
πv-symmetry
2 Cu2+
b3u
b3u*
b3u
πσ*
πv*
b3u
b1g b2g
b2g
au + b1u + b2g + b3g
ag + b2u
ag + b2u
b1g + b3u
b1g
b1g*
D2h
b1g
Figure 5.15: Partial molecular orbital diagram showing the frontier orbitals of the P-core,
adapted from [35]
shown. The right hand side depicts the anti-bonding orbitals of the peroxide ion. Signifi-
cantly, back-donation of electron density from the Cu(II) dx2−y2orbitals into the peroxide σ∗
orbital in the HOMO rationalizes the weak O-O bond. Therefore, strong σ-donating ligands
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 84
transfer electron density via the Cu(II) dx2−y2orbitals into the peroxide σ∗orbital, so that
the O-O-bond is disrupted reductively.
In Figure 5.16, the bonding situation comprising a bisguanidine ligand attached to the
Cu2O22+ core portion is illustrated. In an attempt to elucidate the principal factors that
R3R4
R1R2
C
N N
R3
R4R1
R2
σ∗ dx2-y2πv*C
N
N
NR3
R4
R1
R2
C
N
N
N
R3
R4
R1
R2
dxz , dyz
rotation
around 90°
C
C
N
N
N
NN
LUMO
OCuII
CuII
O
Figure 5.16: Bonding situation comprising a bisguanidine ligand attached to the Cu2O22+
core portion
control the P-core/O-core equilibrium, the degree of conjugation within the guanidine moi-
ety is correlated with the reaction behaviour of the corresponding copper(I) complex towards
oxygen. This correlation applies to bisguanidine ligands with propylene or cyclohexane back-
bones, respectively. In the σ-plane (Figure 5.16, left), the interaction of the σ-lobes of the
coordinating imin nitrogen atoms with the Cu(II) dx2−y2orbital is denoted. Orthogonally to
the σ-plane, the empty π∗-orbitals (Figure 5.16, right) of the guanidine moieties representing
the LUMO possess the correct symmetry (b2g) to accept electron density from the filled dxz
and dyz orbitals of Cu(II). In the next step, electron density from the peroxide-π∗
v-orbital
can now be transferred into the partially depleted dxz and dyz orbitals of Cu(II). In this
stage, the degree of p-πconjugation within the guanidine system is of interest. Enhanced
p-πoverlap lowers the energy of the LUMO of the guanidine residue and makes it more
accessible for πback-donation. In consequence, small modifications of the ligand geometries
changing the guanidine conjugation are suited to influence the equilibrium between P- and
O-core complex states. In the DMPG and DMEG moieties, the alkylene linkers tight the
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 85
amin nitrogen atoms together and the averaged guanidine dihedral angles are very small
(vide supra). The guanidine conjugation is thus enhanced. Contrarily, in btmgp, DPipG2p
and DMorphG2p the NR2moieties are twisted around their Namine-Cimine bonds, and the
guanidine conjugation is hindered. For that reason, the LUMO is raised in energy, and back-
donation is diminished. Now, the σ∗-donating effect of the imin nitrogen atoms dominates
the coordination and the O-core is stabilised.
5.4 Kinetics of the activation of dioxygen
5.4.1 Kinetics of copper/dioxygen chemistry
Kinetic measurements are of great importance for the understanding of the formation of
Cu2O2species. They provide information about kinetic-thermodynamic parameters, reaction
mechanisms and reactive intermediates which might be observable on a faster time-scale (i.e.,
milliseconds, for stopped-flow experiments).
The kinetics of copper/dioxygen chemistry have been thoroughly investigated by Karlin and
Zuberb¨uhler.[85, 145] A suited method uses the time-dependent course of the absorbance of
an characteristic absorption band to follow the reaction. Basis for closer examination is the
well-known law of Lambert and Beer (A=·c·d) with the absorption A, the extinction
coefficient and the layer thickness d.
To facilitate the considerations, a first-order reaction is regarded as example. Indeed, Itoh et
al. reported for the reaction of several copper systems with O2first-order rate laws because
the primary uptake of O2under formation of a mononuclear copper/O2species can be rate-
determining (Figure 5.17, process A).[86] According to this figure, dioxygen initially binds
O2
process A
+
process B
[LCuO2CuL]
[LCuIIO2]
[LCuI]k1, K1
k-1
k2, K2
k-2
+[LCuI]
(a)(b)(c)
Figure 5.17: General mechanism of dioxygen-uptake by Cu(I) complexes
to a Cu(I) centre to form a 1:1 adduct (process A). This adduct usually, but not always,
reacts with a second Cu(I) complex to form one or more dinuclear Cu2O2species (process
B). Further reaction with [LCu(I)] can occur to give tri- or tetranuclear adducts. While this
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 86
general picture encompasses the oxygenation pathways observed to date, differences in details
are often significant, and reflect important influences of supporting ligand structure on the
O2activation mechanism. For the assumption of a first-order rate law, the consideration has
to start with a second order rate-law for the general case (eq. 5.1).
d[cCu]
dt =−k·[cCu]·[cO2] (5.1)
[cCu] = concentration of the copper(I) complex
[cO2] = concentration of the oxygen
As oxygen is given in excess, [cO2] is a constant which gives the following kinetic equation:
d[cCu]
dt =−k∗·[cCu] (5.2)
with k∗=k·[cO2].
This pseudo-first-order kinetic can be integrated as follows:
Zc
cCu
1
[cCu]·d[cCu] = −k∗·Zt
0
dt (5.3)
ln [cCu]
[cCu]0
=−k∗·t(5.4)
Regarding that [cCu]0= [cCu]t+ [cCu2O2]t= [cCu2O2]∞with [cCu2O2]tas concentration of the
Cu2O2species at the time t and [cCu2O2]∞as concentration of the Cu2O2species at t→ ∞,
equation 5.5 can be derived:
[cCu2O2]
[cCu2O2]0
=[cCu2O2]∞−[cCu2O2]t
[cCu2O2]∞
(5.5)
Applying Lambert-Beer´s law gives
A0=c·[cCu]0·d(5.6)
A∞=Cu2O2·[cCu2O2]∞·d(5.7)
At=c·[cCu]t·d+Cu2O2·[cCu2O2]t·d(5.8)
With A0as absorbance for t= 0, A∞as absorbance for t→ ∞ and Atas absorbance for
the moment t, the algebraic combination of the equations 5.5 - 5.8 leads to equation 5.9.
[cCu]
[cCu]0
=[cCu2O2]∞−[cCu2O2]t
[cCu2O2]∞
=A∞−At
A∞−A0
(5.9)
Combined with eq. 5.1, we obtain eq. 5.10:
ln A∞−At
A∞−A0
=−k∗·t(5.10)
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 87
Eq. 5.10 corresponds a linear function:
ln(A∞−At) = −k∗·t+ ln(A∞−A0) (5.11)
with the abscissa ln(A∞−A0). The plot of ln(A∞−At) versus the time tgives a linear plot
which is also referred to as first-order plot.[146]
5.4.2 Kinetic results of the reaction of dinuclear copper complexes
with O2
The increase of the absorbance of the corresponding absorption bands during the reaction
of C3,C8 and C9 with dioxygen in excess obeys first-order kinetics (Figure 5.18).
R2 = 0,9983
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0 500 1000 1500 2000 2500 3000 3500
t(s)
ln(Ainf-A)
Figure 5.18: First-order plot based on the absorption change at 350 nm (P-core) for the
reaction of C8 at -80 ◦C with O2
Moreover, the same first-order rate constants were obtained for reactions starting from dif-
ferent concentrations of C8 in CH2Cl2. This observation indicates that the reaction of the
copper(I) complexes with dioxygen is first-order with respect to the copper complex but of
the order 0 with respect to O2if it is used in excess. The activation parameters (∆H‡and
∆S‡) for the formation of the O-core complexes of C3 and C9 and the P-core complex of
C8 have been determined from the temperature dependence of k (-40 to -80 ◦C). The Eyring
plots for the reaction of C3,C8 and C9 with O2are depicted in the Figures 5.19 - 5.21.
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 88
The first-order rate constants (k) determined at -80 ◦C and the activation parameters for
the formation of the copper-dioxygen species are summarised in Table 5.2. The kinetic data
given below are in accordance with comparable systems reported in the literature which
exhibit small activation enthalpies and very negative activation entropies.[86, 147] A small
activation enthalpy is indicative for the high driving force for the reaction of a copper(I)
complex with dioxgen whereas a negative activation entropy is the result of a reaction where
two molecules are combined to form a new one.
Table 5.2: Kinetic data for the formation of copper-dioxygen species (first order kinetics)[28b]
Compound k1[s−1]∆H‡[kJ/mol] ∆S‡[J/(mol*K)]
[Cu2(btmgp)2][PF6]2(C3) 1.6(1)*10−19(1) -210(5)
[Cu2(DMPG2p)2][PF6]2(C8) 7.9(3)*10−412(1) -230(2)
[Cu2(DPipG2p)2][PF6]2(C9) 6.3(3)*10−542(1) -104(3)
y = -1088.8x - 1.4994
R2 = 0.994
-7.5
-7.3
-7.1
-6.9
-6.7
-6.5
-6.3
-6.1
0.0042 0.0044 0.0046 0.0048 0.005 0.0052 0.0054
1/T in 1/K
ln(k/T)
Figure 5.19: Eyring plot for C3
In comparison with C3 and C8, complex C9 shows a higher activation enthalpy and a
smaller negative activation entropy which can be traced back to the steric demands of the
piperidyl units.
The observed reaction with molecular oxygen has to be associated with a rearrangement
of the bisguanidine ligands because the target area of this reaction is affected by significant
H...H interactions between protons belonging to adjacent propylene spacers. This interaction
has been discussed in section 4.3. The corresponding ligand conformation represents the
maximum stretch of the propylene spacer which leads to a maximum intraligand N...N
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 89
y = -1462.6x - 4.8437
R2 = 0.9957
-12.6
-12.4
-12.2
-12
-11.8
-11.6
-11.4
-11.2
-11
-10.8
0.0042 0.0043 0.0044 0.0045 0.0046 0.0047 0.0048 0.0049 0.005 0.0051 0.0052
1/T in 1/K
ln(kT/)
Figure 5.20: Eyring plot for C8
y = -5073.6x + 11.243
R2 = 0.9977
-16
-15
-14
-13
-12
-11
-10
0.0042 0.0043 0.0044 0.0045 0.0046 0.0047 0.0048 0.0049 0.005 0.0051 0.0052
1/T in 1/K
ln(k/T)
Figure 5.21: Eyring plot for C9
separation of 5.034(1) ˚
A(C6). On going to shorter N...N separations as realized in the
complex cations of C3,C5,C7,C8 and C9, the propylene chain folds up allowing for
longer H...H contacts as can be seen from Table 4.3 and Figures 4.10 - 4.13. This would
principally facilitate potential oxygen insertion but is in contradiction with the requirements
of a resulting N2Cu2O2N2moiety demanding for intraligand N...N distances which are at
least 5.5 ˚
A in lengths. Thus, the situation under discussion does not allow any insertion of
oxygen into this region without rearrangement of the ligands.
Based on the kinetic data, the following mechanism for the reaction with molecular oxygen
can be proposed (Figure 5.22): the Cu(I) precursor complex areacts in a sequence of first-
order reactions with an excess of dioxygen to the P-core complex. The oxygen uptake within
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 90
step Ais rate-determining. In the cases of C3 and C9, the P-core complexes are less
stable than their O-core counterparts, so that the reaction proceeds immediately via step
B. In the case of C8, the P-core complex is more stable, and its formation was investigated
kinetically. Reaction step Aalso includes the rearrangement of the bisguanidine moities
from non-chelating ligands into chelating ones. The corresponding reaction path is currently
under investigation.
O2 (excess)
B
CuII
N
N
CuII
O
O
NN
CuIII
N
N
CuIII
O
O
NN
A
N
N
N
NR2
R2N
N
R2N
NR2
a
=
P-core
O-core
[Cu2L2]2+ +
Figure 5.22: Proposed mechanism of the reaction of dinuclear copper complexes with O2
5.4.3 Kinetic results of the reaction of the mononuclear copper
complex [Cu(btmgp)I] with O2
As described in the previous section, dinuclear copper(I) complexes are predefined for the
uptake of O2in a first-order reaction because two copper centres are already close to each
other. For a mononuclear copper(I) complex, the situation becomes more complicated as
the different reaction rates for the oxygenation of the mononuclear precursor (process A)
and the addition of a further precursor molecule (process B) have to be taken into account
(see Figure 5.17). Both processes can be rate-determining. Additionally, in several cases,
these processes were found to be reversible, a fact which complicates the rate equations
considerably.
The increase of the absorbance of the corresponding absorption bands during the reaction
of [Cu(btmgp)I] with O2in excess could not be fitted after a simple first- or second-order
rate law. Hence, the fitting had to take all reaction steps into consideration. The fact that
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 91
k1
k-1
ab
k2
k-2
a + b c
O2
+[LCuIIO2]
[LCuI]
(a)(b)
[LCuO2CuL]
[LCuIIO2]
(b)(c)
+
[LCuI]
(a)
Figure 5.23: Schematic kinetics of dioxygen-uptake by Cu(I) complexes
oxygen is given in excess facilitates the equations to a lesser extent. Finally, the fitting had
to be performed by numerical analysis of the equation system by MATLAB 6.5. In Figure
5.23, the reaction of a mononuclear Cu(I) complex with O2is schematically denoted. From
this scheme, the rate equations for the reversible case are derived as listed in the following
passage.
dca
dt =−k1·ca+k−1·cb−k2·ca·cb+k−2·cc(5.12)
dcb
dt =k1·ca−k−1·cb−k2·ca·cb+k−2·cc(5.13)
dcc
dt =k2·ca·cb−k−2·cc(5.14)
The numerical fitting by MATLAB 6.5 was not successful with this equation system. It
appeared to exist a concurrence reaction which consumes species bto give more cthan
expected. Consequently, the mechanism had to be corrected in order to take these find-
ings into account. The following hypothetical mechanism was proposed (Figure 5.24). The
concurrence reaction is supposed to be the reaction of two intermediate Cu-O2adducts b
forming the O-core species cas well, but under additional consumption of band release of
O2. This release of O2has no consequences for the kinetic equations since oxygen is given
in excess anyway. It turned out that the fitting with the following corrected rate equations
(5.15 - 5.17) was better.
k1
k-1
ab
k2
k-2
a + b c
O2
+[LCuIIO2]
[LCuI]
(a)(b)
[LCuO2CuL]
[LCuIIO2]
(b)(c)
+
[LCuI]
(a)
[LCuO2CuL]
[LCuIIO2]
(b)(c)
+
[LCuIIO2]
(b)
k3
b + b c
O2
+k-3
Figure 5.24: Hypothetical mechanism for the reaction of [Cu(btmgp)I] with O2as model for
the numerical fit (left: chemical description, right: kinetical description)
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 92
dca
dt =−k1·ca+k−1·cb−k2·ca·cb+k−2·cc(5.15)
dcb
dt =k1·ca−k−1·cb−k2·ca·cb+k−2·cc−k3·c2
b+k−3·cc(5.16)
dcc
dt =k2·ca·cb−k−2·cc+k3·c2
b−k−3·cc(5.17)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
0
1
2
3
4
5
6
7
Figure 5.25: Fitting of the absorbance of the reaction of [Cu(btmgp)I] with O2by MATLAB
6.5 (blue: calc. concentration of the precursor a, green: calc. concentration of
the intermediate Cu-O2adduct b, red: calc. and measured concentration of the
O-core species c)
As k−1,k−2and k−3were calculated to be zero, all three reactions are irreversible. A
summary of the calculated kinetical data is given in Table 5.3. The small values for the
activation enthalpies and the large negative activation entropies fall in line with values
reported by Karlin et al.[145] All these reactions are entropy-driven because one molecule is
generated from two precursors. The activation enthalpy for reaction 3is smaller than for 2
which results in a preference for reaction pathway 2at higher temperatures. Interestingly,
the differences between the two solvents are not really significant, although an influence of
the solvent was expected.[85]
In conclusion, it has to be recorded that dinuclear and mononuclear Cu(I) complexes behave
with respect to their kinetics totally different in the Cu-O2adduct formation which is in
accordance with the literature.[85, 86] The dinuclear precursors, possessing a predefined
reaction site for the oxygen-uptake, react in a first-order reaction whereas the mononuclear
precursors react via a more complex pathway.
CHAPTER 5. O2ACTIVATION WITH CU(I) BISGUANIDINE LIGANDS 93
Table 5.3: Kinetic data for the reaction of [Cu(btmgp)I] with O2, k at 193 K
Solvent CH2Cl2THF
k1[s−1] 50(1) 53(1)
∆H‡
1[kJ mol−1] 7(1) 2(1)
∆S‡
1[J mol−1K−1)] -170(7) -210(8)
k2[M−1s−1] 6.4(1)*1048.3(1)*103
∆H‡
2[kJ mol−1] 5(1) 11(1)
∆S‡
2[J mol−1K−1)] -240(8) -140(5)
k3[M−1s−1] 7.6(1)*1045.6(1)*104
∆H‡
3[kJ mol−1] 2(1) 1(1)
∆S‡
3[J mol−1K−1)] -130(6) -180(7)
5.5 Conclusion of the O2Activation with Copper(I)
Bisguanidine Complexes
Due to their ability to delocalise the positive charge over the guanidine moiety, these ligands
are able to stabilise high metal oxidation states which are established in a variety of copper
complexes containing the Cu2O22+ core portion. The analysis of the bonding situation com-
prising this site attached to a bisguanidine residue reveals that the coordination properties
of the imine nitrogen donor atoms depend on the substitution pattern within the guanidine
moieties. Thus, it is possible to influence directly the reactivity of the copper(I) bisguani-
dine complexes towards molecular oxygen by introducing properly designed substituents.
Sterically demanding alkyl groups raise the energy of the LUMO which has the appropri-
ate symmetry to accept electrons from the Cu2O22+ core portion and thus destabilise the
P-core state within these complexes. On the other hand, integrating both amine groups of a
guanidine residue into a five- or six-membered ring favours the P-core over the O-core state
by strengthening the π-conjugation within the ligand and thus lowering the energy of the
LUMO. Based on these interrelations between steric features of the ligands and the electron
distribution within the Cu2O22+ core portions of dinuclear Cu2O2complexes, new insights
into the mechanism of dioxygen activation are provided and strategies towards ligand mod-
ification can be developed which are directed towards tailored reaction systems capable to
hydroxylate substrates in pre-defined positions.
6 Products of hydroxylation reactions
6.1 Hydroxylation of copper btmgp complexes
6.1.1 Crystal structures of btmgp containing hydroxylation products
The reaction of both precursor complexes [Cu(btmgp)I] and [Cu2(btmgp)2][PF6]2(C3) with
dioxygen (Scheme 6.1) was investigated by low temperature UV/Vis monitoring (section
5.1).
The primarily formed species are bis-µ-oxodicopper(III) complexes containing the Cu2O2
core with fully reduced oxygen and copper in the oxidation state +3 in both cases. Crystals
obtained from these reactions in form of red needles were not suited for X-ray diffraction.
Upon reaction of [Cu(btmgp)I] and C3 with O2, intensive LMCT absorption bands at 300
and 400 nm are observed which are characteristic for the O-core complexes known so far.
These species are unstable even at -80 ◦C in dichloromethane. The initial red solutions
change their colours to bluish-green upon warming up to room temperature within 1 -
2 h. This behaviour was described by Schneider for the first time for bisguanidine cop-
per complexes.[112] From these solutions, two different complex types could be isolated in
equal amounts (vide infra): the reaction of precursor [Cu(btmgp)I] with oxygen yields the
novel bis(µ-alkoxo)(µ-iodo)-bridged dinuclear copper complex [Cu2(btmmO)2I]+containing
an iodide ion in a novel bridging situation as well as the hydroxo-bridged dinuclear copper
complex [Cu2(btmgp)2(µ-OH)2]2+. In a similar manner, precursor C3 reacts to the bis(µ-
alkoxo)-bridged dinuclear copper complex [Cu2(btmmO)2]2+ (C15) and the hydroxo-bridged
dinuclear copper complex [Cu2(btmgp)2(µ-OH)2]2+.[113]
The complex cation [Cu2(btmmO)2I]+which occurs in crystals of [Cu2(btmmO)2I]I·1
2EtOH
is formed in the reaction of [Cu(btmgp)I] with oxygen; its unexpected properties derive from
the coordination by two N donor functions, two bridging oxygen atoms from the hydroxylated
ligands and the presence of an iodide ion as a third bridge (Figure 6.2). Selected distances
and angles of [Cu2(btmmO)2I]+are listed in Table 6.1.[112]
94
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 95
O2
O2
N
NMe2
N
N
NMe2
N
Cu
Me2NN
N
N
Me2NN
Cu
O
O
CH2
Me
H2C
Me
I
N
NMe2
Me2N
N
NMe2
Me2N
Cu
Me2N NMe2
N
N
Me2N NMe2
Cu O
O
H
H
Cu
N
N
N
Cu
N
NMe2
NMe2
NMe2
NMe2
Me2N
Me2N
NMe2
NMe2
N N
NMe2
NMe2
NMe2
Me2NCu
I
Me2
Me2
N
NMe2
N
N
NMe2
N
Cu
Me2NN
N
N
Me2NN
Cu
O
O
CH2
Me
H2C
Me
Me2
Me2
+
2+
2+
2+
N
NMe2
Me2N
N
NMe2
Me2N
Cu
Me2N NMe2
N
N
Me2N NMe2
Cu O
O
H
H
2+
[Cu2(btmgp)2][PF6]2
[Cu2(btmgp)2(OH)2][PF6]2
[Cu2(btmmO)2][PF6]2
[Cu(btmgp)I]
[Cu2(btmmO)2I]I
[Cu2(btmgp)2(OH)2]I2
I-
2 I-
2 PF6-
2 PF6-
2 PF6-
Figure 6.1: Activation of oxygen with [Cu(btmgp)I] and [Cu2(btmgp)2][PF6]2
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 96
Figure 6.2: Molecular structure of [Cu2(btmmO)2I]+in crystals of [Cu2(btmmO)2I]I·1
2EtOH
(left), magnification of the µ-iodo bridged Cu2O2unit [112]
The other component has been shown by X-ray diffraction and vibrational spectroscopy
to represent the bis(µ-hydroxo)-dicopper(II) species [Cu2(btmgp)2(OH)2]2+ (see Fig. 6.4)
which occurs in crystals of [Cu2(btmgp)2(OH)2]I2(C15).
The bis(µ-hydroxo)-dicopper(II) species is also formed if C3 is used as the precursor complex
instead of [Cu(btmgp)I]. In this case, however, the complex salt [Cu2(btmgp)2(OH)2][PF6]2
has been isolated. Moreover, as a non-coordinating counteranion has been used, the bis(µ-
alkoxo)-dicopper(II) species [Cu2(btmmO)2]2+ obtained as the other reaction product and
identified in crystals of [Cu2(btmmO)2][PF6]2·2MeCN (C15) lacks the iodide bridge present
in [Cu2(btmmO)2I]+(Fig. 6.3).
The reaction of [Cu(btmgp)I] and [Cu2(btmgp)2][PF6]2(C3) with molecular oxygen
transforms one half of the coordinated bis(tetramethyl)guanidinopropane molecules into
bis(trimethylmethoxy)guanidino-propane ligands which have been identified as the alkoxo
components within the bis(µ-alkoxo)dicopper(II) complexes [Cu2(btmmO)2I]I·1
2EtOH and
[Cu2(btmmO)2][PF6]2·2MeCN (C15) (Figures 6.2 and 6.3). This oxidation reaction de-
serves attention due to the fact that no other tool capable to introduce one single -CH2OH
functionality into bis(tetramethyl)guanidinopropane is known so far.
Selected distances and angles of the crystal structure of C15 are listed in Table 6.2, and pa-
rameters relating to the data collection and refinement are listed in Table A11. Both complex
cations [Cu2(btmmO)2I]+and [Cu2(btmmO)2]2+ shown in Figs. 6.2 and 6.3, respectively,
contain the Cu2(btmmO)2entity; they differ, however, with respect to their bridging states.
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 97
Table 6.1: Selected distances and angles of [Cu2(btmmO)2I]+[112]
Distances (˚
A) Angles (◦)
Cu(1)...Cu(2) 2.8026(7) O(1)-Cu(1)-O(2) 77.67(9)
Cu(1)-O(1) 1.972(2) O(1)-Cu(2)-O(2) 76.99(9)
Cu(1)-O(2) 1.944(2) Cu(1)-O(1)-Cu(2) 91.10(9)
Cu(2)-O(1) 1.953(2) Cu(1)-O(2)-Cu(2) 90.78(9)
Cu(2)-O(2) 1.992(2) N(1)-Cu(1)-N(4) 91.3(1)
Cu(1)-N(1) 1.973(3) N(7)-Cu(2)-N(10) 93.2(1)
Cu(1)-N(4) 1.968(3)
Cu(2)-N(7) 1.961(3)
Cu(2)-N(10) 2.002(2)
Figure 6.3: Molecular structure of [Cu2(btmmO)2]2+ in crystals of C15
The complex cation [Cu2(btmmO)2I]+is an extension of the complex cation in C15 and
can be derived thereof by introducing an iodide ligand as a third bridge. This modification
results into a fold of the Cu2O2heterocyclic unit along the O...O vector allowing the Cu
atoms to approach the iodide ligand at distances of 3.237 ˚
A (Fig. 6.2, right). The resulting
Cu...Cu distance is as short as 2.803(1) ˚
A, and the dihedral angle within the butterfly-shaped
Cu2O2core portion is 131.8(1)◦.
In crystals of [Cu2(btmmO)2I]I·1
2EtOH, each copper atom is surrounded by its ligands in
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 98
Table 6.2: Selected distances and angles of [Cu2(btmmO)2]2+
2in crystals of C15 (The primed
atoms are derived from the unprimed ones by inversion.)
Distances (˚
A) Angles (◦)
Cu...Cu 3.035(1) O(1)-Cu(1)-O(1’) 75.65(8)
Cu(1)-O(1) 1.910(2) Cu(1)-O(1)-Cu(1’) 104.35(8)
Cu1-O(1’) 1.932(2) N(1)-Cu(1)-N(4) 93.34(9)
Cu(1)-N(1) 1.961(2)
Cu(1)-N(4) 1.961(2)
a square-pyramidal manner resulting in the blue colour of the compound. The apical po-
sition of the N2O2I pyramid is occupied by iodine. Crystals of C15 contain the complex
cation [Cu2(btmmO)2]2+ which lacks the iodide bridge. Each copper atom is surrounded by
a cisoid N2O2donor set in a square-planar manner. The resulting colour of the compound
is red. Due to completely planar CuN2O2fragments - the complex cations are situated on
inversion centers -, the Cu...Cu distance amounts to 3.035(1) ˚
A and thus is much longer
than in [Cu2(btmmO)2I]+. Due to the reduced number of ligand donor functions, the av-
eraged Cu-N and Cu-O bond distances within C15 (1.949(2) and 1.921(2) ˚
A, respectively)
are shorter than the corresponding bond distances within [Cu2(btmmO)2I]+(1.976(2) and
1.965(2) ˚
A, respectively). The introduction of the iodide bridge and the resulting fold of the
Cu2O2core portion in [Cu2(btmmO)2I]+is accompanied by a change in the conformation
of the six-membered chelate heterocycle formed by the propylene-bridged N donor func-
tions. Thus, on going from [Cu2(btmmO)2]2+ to [Cu2(btmmO)2I]+, the chair conformation
is switched to the boat-like structure. The other chelate rings which involve the oxygen
donor functions are twisted. It is interesting to note that the iodide bridge of the complex
cation [Cu2(btmmO)2I]+as well as the isolated iodide counterion has survived the O-core
state of the reaction intermediate [Cu2O2(btmgp)2]2+ which contains copper in the oxidation
state +3.
Both the dicationic bis(µ-hydroxo)-dicopper(II) species [Cu2(btmgp)2(µ-OH)2]2+ (Fig. 6.4)
in crystals of [Cu2(btmgp)2(OH)2][I]2and [Cu2(btmgp)2(OH)2][PF6]2are isostructural
demonstrating that the counterions have only limited influence on the overall structure.[112,
113] This influence, however, can be detected if the Cu...Cu distances (3.008(2) vs. 3.032(1)
˚
A) are compared, but is virtually undetectable regarding the average Cu-O and Cu-N dis-
tances and the corresponding valence angles which are almost identical. Due to crystallo-
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 99
graphic site symmetries (i) the Cu2O2cores in both dications are strictly planar. The chelate
heterocycles adopt in both complexes the chair conformation. Selected distances and angles
of the crystal structure of [Cu2(btmgp)2(µ-OH)2]2+ are listed in Table 6.3.
Figure 6.4: Molecular structure of [Cu2(btmgp)2(µ-OH)2]2+ [113]
Table 6.3: Selected distances and angles of [Cu2(btmgp)2(µ-OH)2]2+ (The primed atoms are
derived from the unprimed ones by inversion.) [112, 113]
Distances (˚
A) Angles (◦)
Cu...Cu’ 3.008(2) O-Cu-O’ 78.6(2)
Cu-O 1.953(5) Cu-O-Cu’ 101.4(2)
Cu-O’ 1.934(5) N(1)-Cu-N(2) 94.0(2)
Cu-N(1) 1.999(5)
Cu-N(2) 1.975(5)
6.1.2 Discussion of the reaction mechanism
The formation of equal amounts of [Cu2(btmmO)2I]I·1
2EtOH and [Cu2(btmgp)2(OH)2][I]2
and of [Cu2(btmgp)2(OH)2][PF6]2and [Cu2(btmmO)2][PF6]2·2MeCN, respectively, is in ac-
cordance with the idea that both the bis(µ-alkoxo)- and the bis(µ-hydroxo)dicopper(II)
species may originate from a common precursor complex, the hitherto non-identified
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 100
species [Cu2(btmmO)(OH)(btmgp)]2+. Possible mechanisms for the formation of the (hy-
pothetical) (µ-alkoxo)(µ-hydroxo)dicopper(II) complex have been discussed by Itoh et
al.,[86, 149, 52, 150] and a recent quantum mechanical calculation arrives at the same
suggestion.[151] However, the fact that no such complexes have ever been observed so far
raises the question whether this assumption reflects the chemical reality or not. Our results
clearly show that the Cu(III) species [Cu2(µ-O)2(btmgp)2]2+ formed as an intermediate is
not reduced by iodide ions and thus might be indicative for a mechanism different from
the ones cited above which are based either on the abstraction of an H atom followed by
a rearrangement step or on a concerted insertion of O into a C-H bond.[48] An alternative
reaction pathway which might also result in the formation of the (hypothetical) (µ-alkoxo)(µ-
hydroxo)dicopper(II) intermediate could be initiated by the nucleophilic attack of an oxygen
atom of the Cu2(µ-O)2core directed towards a methyl group followed by interception of
the released hydride ion as a third ligand bridge and subsequent rearrangement. Though
this hypothesis is speculative in nature, the formation of a hydride bridge seems chemically
possible in the light of the observation that iodide ions do not reduce Cu(III) in the O-core
stage. Moreover, if the interception of the hydride ion is slow compared to a competing elec-
trophilic attack of the Cu2(µ-O)2core activated in such a manner towards a methyl group of
the second ligand, then the formation of the (µ-alkoxo)(µ-hydroxo)dicopper(II) intermediate
is avoided and the bis(µ-alkoxo)dicopper(II) complex is directly formed under proton release.
The hydride ion which is now accessible to the system is suited to attack a protonated O-
core of another reaction intermediate in a nucleophilic manner resulting in the formation of
the bis(µ-hydroxo)dicopper(II) complex [Cu2(btmgp)2(µ-OH)2]2+. The proton required to
initiate this reaction step might originate from ubiquitous catalytic proton sources. Once
started, the reaction is driven by protons released during the formation of [Cu2(btmmO)2]2+
2.
6.1.3 Electrochemistry of [Cu2(btmmO)2][PF6]2·2MeCN C15
The cyclovoltammogram of 15 (0.1 mol/L [NBu4][PF6]; 50 mV/s; Au/Pt/Ag-AgCl) shows a
single reversible electron transfer at 1.27 V/NHE (Figure 6.5) which assigns the Cu(II)/Cu(I)
redox pair of complex C15. The form of the cyclovoltammogramm indicates that at approx-
imately 1.9 V/Ag-AgCl, the ligand begins to get oxidised.
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 101
Figure 6.5: Cyclovoltammogram of C15 in CH2Cl2
6.2 Hydroxylation of copper TMG2MePA complexes
6.2.1 Crystal structures of TMG2MePA containing hydroxylation
products
The reaction of several TMG2MePA containing precursor complexes [Cu(TMG2MePA)][X]
( X = PF−
6, ClO−
4, BF−
4and I−) with dioxygen (Scheme 6.6) was investigated by low tem-
perature UV/Vis monitoring (section 5.1).
Similar to the reaction of bmtgp supported complexes, the primarily formed species are
bis-µ-oxodicopper(III) complexes containing the Cu2O2core with fully reduced oxygen and
copper in the oxidation state +3 in both cases. Unfortunately, no crystals suitable for X-ray
diffraction could be obtained from these reactions. From these solutions, two different com-
plex types could be isolated in equal amounts: the bis(µ-alkoxo)-bridged dinuclear copper
complexes [Cu2(TMMoG2MePA)2]2+ and the hydroxo-bridged dinuclear copper complexes
[Cu2(TMG2MePA)2(µ-OH)2]2+.
Crystals of [Cu2(TMMoG2MePA)2][PF6]2(C16), [Cu2(TMMoG2MePA)2][ClO4]2(C17) and
[Cu2(TMMoG2MePA)2][BF4]2(C18) could be isolated by vapour diffusion of diisopropy-
lether into acetonitrilic solutions as green needles. The corresponding bis(µ-hydroxo) dicop-
per species could only be crystallised in form of [Cu2(TMG2MePA)2(µ-OH)2][Cu2I4] (C19)
(dark green needles) and [Cu2(TMG2MePA)2(µ-OH)2][I−
3]2(C20) (bright yellow needles)
after the reaction of [Cu(TMG2MePA)]I with dioxygen. A reaction mechanism for the con-
comitant formation of both species is assumed which ressembles the mechanism described
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 102
+III
+III
[(TMG2MePA)Cu]X
X = I-, PF6-, BF4-, ClO4-
NMe2
Me2N
Cu
O
O
Cu
N
N
N Me
Me2N
NMe2
Me2N
NMe2
N
N
N
Me
NMe2
Me2N2+
O2, MeCN, - 40°C
50% 50%
+II
+II
NMe2
Me2N
Cu
O
O
Cu
N
N
N Me
Me2N
NMe2
Me2N
NMe2
N
N
N
Me
NMe2
Me2N2+
+II+II
NMe2
N
Cu
O
O
Cu
N
N
N Me
Me2N
NMe2
Me2NN
N
N
N
Me
NMe2
Me2N2+
Me
Me
H
H
Figure 6.6: Activation of oxygen with [Cu(TMG2MePA)][X] (X = PF−
6, ClO−
4, BF−
4and I−)
above for btmgp supported complexes. The reaction starting from the bis-µ-oxodicopper(III)
complex will proceed either via a very unstable (µ-alkoxo)(µ-hydroxo)dicopper(II) complex
state or via a hydride transition state (vide supra) to the two coupled product species.
All five complex salts crystallise in the triclinic space group P1. Crystals of C16,C17,C18
and C19 contain one molecule per unit cell. Crystals of C20 contain two molecules per unit
cell, in crystals of C16 1.8 molecules of MeCN are also present. The results of the structure
analyses are shown in Figures 6.7 - 6.9, while selected bond lengths and angles are collected
in Table 6.4, and parameters relating to the data collection and refinement are listed in the
Tables A11 - A13. As the bis(µ-hydroxo) dicopper complexes C16 and C17 are isostruc-
tural, only the structure of C16 is denoted in the Figures. Similarily, the bis(µ-hydroxo)
dicopper complexes C19 and C20 are isostructural, therefore, only complex C19 has been
depicted in Figure 6.9.
Reaction of [Cu(TMG2MePA)][X] (X = PF−
6, ClO−
4, BF−
4and I−)
with molecular oxygen transforms one half of the coordinated N-
methyl-bis(tetramethyl)guanidinodiphenyleneamine molecules into N-methyl-
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 103
Table 6.4: Selected distances and angles of the bis(µ-alkoxo) and bis(µ-hydroxo) dicopper(II)
complex cations containing the tripodal ligand TMG2MePA
Distances (˚
A) C16 C17 C18 C19 C20
Cu...Cu 3.068(1) 3.058(1) 2.991(1) 3.051(1) 3.044(1)
Cu-Nimine 1.988 1.990 2.036 2.007 1.998
Cu-Namine 2.349 2.348 2.147 2.344 2.398
Cu-O 1.934 1.931 1.914 1.936 1.940
N=C(av) 1.333 1.325 1.331 1.318 1.319
Angles (◦)
Nimine-Cu-Nimine 97.5 97.5 109.5 99.4 97.4
Nimine-Cu-Namine 77.2 77.6 79.9 77.4 76.9
O-Cu-O 75.1 75.3 77.2 76.0 76.6
Namine-C-Namine(av) 118.1 118.2 118.6 116.3 116.7
ρ0.986 0.981 0.991 0.969 0.975
bis(trimethylmethoxy)guanidino-diphenyleneamine ligands which have been identified
as the alkoxo components within the bis(µ-alkoxo)dicopper(II) complexes C16,C17 and
C18 (Figs. 6.7 and 6.8). Both complex cations C16 and C18 shown in Figs. 6.7 and 6.8,
respectively, contain the Cu2(TMMoG2MePA)2entity but they differ from the coordination
mode of their copper centres. In crystals of C16 and C17, each copper atom is surrounded
by its ligands in a square-pyramidal manner. The apical position of the N2O2N pyramid is
occupied by the amine function of TMG2MePA. This coordination comes clear by regarding
the Cu-Nimine distances which measure 1.989 ˚
A in average and the Cu-Namine distances of
2.349 ˚
A defining the apical position. The N2O2donor set provides a good square-planar en-
vironment with Cu-O distances of 1.933 ˚
A. However, the Nimine-Cu-Nimine angles are slightly
widened up to 97.5◦and the O-Cu-O angles are diminuished to 75.2◦due to conformational
and geometrical restrictions of the ligand which offers the apical N donor function with the
amine group. In crystals of C18, the situation is totally different although the counterion
only has been changed from the non-coordinating sphere-symmetrical hexafluorophosphate
or perchlorate to the similar tetrafluoroborate. The Cu-Nimine distances are elongated to
2.036 ˚
A whereas the Cu-Namine distance is drastically shortened to 2.147 ˚
A. Thus, the
coordination of the copper centre can be described as distorted trigonal bipyramidal with
the N2 and O1 atoms as apices and the Nimine atoms and the O1A atom as equatorial
donors. The deviation of the copper atom of this plain (N1N3O1A) amounts up to 0.065(1)
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 104
˚
A. As a measure for the degree of trigonality, the structural index parameter τ= (β−α)/60◦
[152] was established by Addison and Reedijk.[153] For C16 and C17,τis almost zero
(0.06 for C16, 0.05 for C17) indicating a perfectly planar square-pyramidal coordination.
For C18,τis calculated to be 0.55 which denotes the high degree of trigonalisation clearly.
The angle between the apical positions is 170.3(1)◦which shows the deviation from an ideal
trigonal pyramid with 180◦. However, although the coordination has changed seriously, the
equivalency of the two Nimine donor functions has been kept. These findings illustrate that
the equilibrium between the two coordinational modes is very fragile and that the energy of
the transition state is so small that packing forces can switch the equilibrium to the other
side. The values of the structural parameter ρlie between 0.97 and 0.99 indicating a good
delocalisation of the positive charge within the guanidine moiety in the stabilisation of the
Cu(II) complexes C16 -C20.
Figure 6.7: Molecular structure of [Cu2(TMMoG2MePA)2]2+ in crystals of C16 and C17
In crystals of C19 and C20 (Figure 6.9), the geometric centre of the cation lies on a crystal-
lographic inversion centre and the resulting Cu2O2core is thus strictly planar. The Cu atom
is coordinated in a square-pyramidal manner by two guanidine N atoms, one amine N atom
and the two bridging O atoms like in C16 and C17. The structural index parameter τis
calculated to be 0.12 for C19 and 0.05 for C20 indicating an almost ideal square-pyramidal
coordination. The Cu-Nimine, Cu-Namine and Cu-O distances and the corresponding an-
gles are according with those of C16 and C17. The Namine-C-Namine angles are slightly
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 105
Figure 6.8: Molecular structure of [Cu2(TMMoG2MePA)2]2+ in crystals of C18
diminuished to 116.5◦because the NMe2is not forced to spread like in the hydroxylated
ligands in C16,C17 and C18.
Figure 6.9: Molecular structure of [Cu2(TMG2MePA)2(µ-OH)2]2+ in crystals of C19 and
C20
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 106
6.2.2 Electrochemistry of [Cu2(TMMoG2MePA)2][PF6]2C16
The cyclovoltammogram of 16 (0.1 mol/L [NBu4][PF6]; 50 mV/s; Au/Pt/Ag-AgCl) shows an
irreversible electron transfer at 1.065 V/NHE (Figure 6.10). This oxidation wave is caused
by the oxidation of the ligand (see section 3.4). The form of the cyclovoltammogramm
indicates that several redox processes occur which can not be attributed to single electron
transfers. This behaviour might be due to the aromatic spacer of the ligand.
Figure 6.10: Cyclovoltammogram of C16 in CH2Cl2
6.3 Hydroxylation of copper DMEG2p complexes
The reaction of the DMEG2p containing precursor complex [Cu2(DMEG2p)2][PF6]2(C5)
with dioxygen (Scheme 6.11) was investigated by low temperature UV/Vis monitoring (sec-
tion 5.1). Although at low temperatures a µ−η2:η2-peroxo complex is formed, the alkoxy-
lated product complex [Cu2(MMoEG2p)2][PF6]2(C21) can be isolated analogously to the
reaction of btmgp and TMG2MePA supported complexes via bis-µ-oxodicopper(III) com-
plexes. Thus, the P-core complex converts at higher temperatures to the O-core which
hydroxylates the DMEG2p ligand at one of its N-CH3functions to form the MMoEG2p
ligand. The accompanying bis(µ-hydroxo) dicopper(II) complex which forms equimolarily
could not be crystallised. From the reaction solution in MeCN, red crystals of the bis(µ-
alkoxo) dicopper(II) complex [Cu2(MMoEG2p)2][PF6]2(C21) could be obtained by vapour
diffusion of diisopropylether. The complex salt C21 crystallises in the monoclinic space
group P21/c. Crystals of C21 contain two crystallographically independent but otherwise
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 107
identical molecules and a total of eight molecules per unit cell. A view of the structure of
[Cu2(MMoEG2p)2]2+ in crystals of C21 is shown in Figure 6.12, while selected bond lengths
and angles are collected in Table 6.5, and parameters relating to the data collection and
refinement are listed in Table A14.
O2
Cu
N
N
N
Cu
N
MeN
N
Me
NMe
NMe
Me
N
N
Me
MeN
Me
N
N
NMe
MeN
N
NMe
N
Cu
MeN NMe
N
N
MeN N
Cu
O
O
CH2
H2C
2+
2+
N
NMeMeN
N
NMe
MeN
Cu
MeN NMe
N
N
MeN NMe
Cu O
O
H
H
2+
[Cu2(DMEG2p)2][PF6]2
[Cu2(DMEG2p)2(OH)2][PF6]2
[Cu2(MMoEG2p)2][PF6]2
2 PF6-
2 PF6-
2 PF6-
Figure 6.11: Activation of oxygen with [Cu2(DMEG2p)]2[PF6]2(C5)
Table 6.5: Selected distances and angles of the bis(µ-alkoxo) dicopper(II) complex cation in
crystals of C21 in comparison with btmgp and TMG2MePA containing complexes
Distances (˚
A) C21 C15 C16
Cu...Cu’ 3.032(1) 3.035(1) 3.068(1)
Cu-Nimine 1.939 1.961 1.988
Cu-Namine 2.349
Cu-O 1.921 1.921 1.934
N=C(av) 1.308 1.313 1.333
Angles (◦)
Nimine-Cu-Nimine 95.1 93.3 97.5
O-Cu-O 74.4 75.7 75.1
Cu-O-Cu’ 105.6 104.4 -
Namine-C-Namine(av) 109.9 116.3 118.1
The centroid of the cation lies on a crystallographic inversion centre and the resulting Cu2O2
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 108
Figure 6.12: Molecular structure of [Cu2(MMoEG2p)2]2+ in crystals of C21
core is thus strictly planar. The Cu atom is coordinated in a planar quadratic manner by
two guanidine N atoms and the two bridging O atoms. The deviation of the Cu atom from
the N2O2plane (averaged deviation: 0.022 ˚
A) is 0.002(1) ˚
A, and the chelate heterocycle
adopts a chair conformation. The Cu-N distances are slightly shortened in comparison with
the other bis(µ-alkoxo) dicopper(II) complex cations, whereas the geometric parameters as
Cu-O distances and O-Cu-O and Cu-O-Cu angles of the Cu2O2core are almost identical.
The bite angle Nimine-Cu-Nimine of 95.1◦is comparable with those of the already described
bis(µ-alkoxo) dicopper(II) complexes. The Namine-C-Namine angles are diminuished towards
the tetramethyl guanidine systems as the ethylene linker in the ligand DMEG2p tights the
Namine atoms together. The structural parameter ρis calculated to be 0.949, a value which
is rather small regarding the values of around 0.98 for TMG2MePA containing complexes.
This may be due to the aliphatic spacer in C21 which does not support the delocalisation
within the guanidine moiety.
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 109
6.4 Hydroxylation of copper DPipG2p complexes
The reaction of the DPipG2p containing precursor complex [Cu2(DPipG2p)2][PF6]2(C9)
with dioxygen (Scheme 6.6) was investigated by low temperature UV/Vis monitoring (section
5.1). Analogously to the reaction of btmgp and TMG2MePA supported complexes, the bis-
µ-oxodicopper(III) complex reacts presumably to two products, a bis(µ-alkoxo) and a bis(µ-
hydroxo) dicopper(II) complex. From the reaction solution in MeCN, only blue crystals
of the bis(µ-hydroxo) dicopper(II) complex [Cu2(DPipG2p)2(µ-OH)2][PF6]2(C22) could be
obtained by vapour diffusion of diisopropylether. The complex salt C22 crystallises in the
monoclinic space group P21/n. Crystals of C22 contain two molecules per unit cell. The
projection of [Cu2(DPipG2p)2(µ-OH)2]2+
2as the result of the structure analysis is shown in
Figure 6.14, while selected bond lengths and angles are collected in Table 6.6, and parameters
relating to the data collection and refinement are listed in Table A14.
N
N
N
Cu
N
2+
2 PF6-
Cu O2
N
N
Cu
N
N
Cu O
O
H
H
2+
2 PF6-
hydroxylated by-products
NN N
N
N
N
N
N
NN
N
N
N
N
N N
Figure 6.13: Activation of oxygen with [Cu2(DPipG2p)2][PF6]2(C9)
The centroid of the cation lies on a crystallographic inversion centre and the resulting Cu2O2
core is thus strictly planar. The Cu atom is coordinated in a planar quadratic manner by
two guanidine N atoms and the two bridging O atoms. The deviation of the Cu atom from
the N2O2plane is 0.036 (1) ˚
A, and the chelate heterocycle adopts a chair conformation. The
presence of the hydroxo H atom was confirmed from Fourier maps. The Cu...Cu and mean
Cu-O distances (3.0740 (6) and 1.935 (2) ˚
A) are clearly elongated compared with those of
di-µ-oxo-bridged Cu2O2moieties, which are in the ranges 2.743 (1) - 2.906 (1) and 1.796 (6) -
1.865 (3) ˚
A, respectively. Similar observations hold for related Fe complexes.[48] As pointed
out by Que and Tolman,[48] the significant differences between the short (in M2(µ-O)2)
and long (in M2(µ-OH)2) M-O distances are obviously a suitable measure for distinguishing
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 110
Figure 6.14: Molecular structure of [Cu2(DPipG2p)2(µ-OH)2]2+
2in crystals of C22
Table 6.6: Selected distances and angles of the bis(µ-hydroxo) dicopper(II) complex cation
[Cu2(DPipG2p)2(µ-OH)2]2+ in crystals of C22 in comparison with btmgp and
TMG2MePA containing complexes
Distances (˚
A) C22 [Cu2(btmgp)2(µ-OH)2]2+ C20
Cu...Cu’ 3.0740(6) 3.008(2) 3.051(3)
Cu-Nimine 1.975 1.987 2.007
Cu-Namine 2.344
Cu-O 1.935 1.944 1.936
N=C(av) 1.314 1.317 1.318
Angles (◦)
Nimine-Cu-Nimine 96.0 94.0 99.4
O-Cu-O 74.8 78.6 76.0
Cu-O-Cu’ 105.2 101.4 104.0
Namine-C-Namine(av) 116.8 116.4 116.3
between these two species. The bite angle Nimine-Cu-Nimine of 96.0◦is comparable with those
of the already described bis(µ-hydroxo) dicopper(II) complexes. The structural parameter
ρis calculated to be 0.964, a value which is only slightly smaller than those calculated for
TMG2MePA containing complexes.
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 111
6.5 Hydroxylation of copper TMG2ch complexes
The reaction of the TMG2ch containing precursor complexes [Cu2(TMG2ch)2][X]2(X = I−,
PF−
6and ClO−
4) with dioxygen (Scheme 6.7) was investigated by low temperature UV/Vis
monitoring (section 5.1). Analogously to the reaction of btmgp and TMG2MePA supported
complexes, the bis-µ-oxodicopper(III) complex reacts presumably to two products, a bis(µ-
alkoxo) and a bis(µ-hydroxo) dicopper(II) complex. The O-core hydroxylates the TMG2ch
ligand at one of its N-CH3functions in order to form the novel TMMoG2ch ligand providing
a N2O donor set. From the reaction solution in MeCN, only red crystals of the bis(µ-alkoxo)
dicopper(II) complexes [Cu2(TMMoG2ch)2][X]2(X = I−, PF−
6and ClO−
4) could be obtained
by vapour diffusion of diisopropylether. The corresponding bis(µ-hydroxo) dicopper(II) com-
pound does not crystallise but is formed as blue amorphous product. The complex salts C23,
C24 and C25 crystallise in the monoclinic space group P21/n. Crystals of C23,C24 and
C25 contain two molecules per unit cell. The results of the structure analysis is shown in
Figure 6.16, while selected bond lengths and angles are collected in Table 6.7, and parameters
relating to the data collection and refinement are listed in Table A15 and A16.
O2
Cu
N
N
N
Cu
N
NMe2
NMe2
NMe2
NMe2
Me2N
Me2N
NMe2
NMe2
N
NMe2
N
N
NMe2
N
Cu
Me2NN
N
N
Me2NN
Cu
O
O
CH2
Me
H2C
Me
Me2
Me2
2+
2+
N
NMe2
Me2N
N
NMe2
Me2N
Cu
Me2N NMe2
N
N
Me2N NMe2
Cu O
O
H
H
2+
[Cu2(TMG2ch)2][X]2
[Cu2(TMMo2ch)2(OH)2][X]2
[Cu2(TMMo2ch)2][X]2
X = I-, PF6-, ClO4-
2 X-
2 X-
2 X-
X = I-
PF6-
ClO4-
(C23)
(C24)
(C25)
X = I-
PF6-
ClO4-
Figure 6.15: Activation of dioxygen with [Cu2(TMG2ch)2][X]2(X = I−, PF−
6and ClO−
4)
The precursor complexes [Cu2(TMG2ch)2][X]2(X = I−, PF−
6and ClO−
4) contain the cis
isomer of the TMG2ch ligand in its bis-equatorial conformation coordinating in a bridging
mode. Interestingly, after the reaction with oxygen, the TMMoG2ch ligand coordinates the
Cu2O2core in a chelating mode under conformational change to the bis-axial conformation.
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 112
Figure 6.16: Molecular structure of [Cu2(TMMoG2ch)2]2+ in crystals of C23,C24 and C25
Table 6.7: Selected distances and angles of the bis(µ-alkoxo) dicopper(II) complex cation
[Cu2(TMMoG2ch)2]2+ in crystals of C23,C24 and C25 in comparison with
[Cu2(btmmO)2]2+ in C15
Distances (˚
A) C23 C24 C25 C15
Cu...Cu’ 3.0581(8) 3.0525(6) 3.045(1) 3.035(1)
Cu-Nimine 1.945 1.945 1.945 1.961(2)
Cu-O 1.929 1.923 1.919 1.921
N=C(av) 1.311 1.319 1.311 1.313
Angles (◦)
Nimine-Cu-Nimine 94.3 94.3 94.7 93.3
O-Cu-O 75.1 75.0 75.0 75.7
Cu-O-Cu’ 104.9 105.0 105.0 104.4
Namine-C-Namine(av) 116.6 116.6 117.7 116.3
ρ0.972 0.966 0.976 0.965
This result shows that the energetic barrier between the bridging and the chelating mode as
well as between the bis-equatorial and the bis-axial conformation is small. The centroid of
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 113
Figure 6.17: Perspective showing the double-chair conformation of [Cu2(TMMoG2ch)2]2+ in
crystals of C23,C24 and C25
the cations lies on a crystallographic inversion centre and the resulting Cu2O2core is thus
strictly planar. The Cu atom is coordinated in a planar quadratic manner by two guanidine
N atoms and the two bridging O atoms. The deviation of the Cu atom from the N2O2
plane is 0.017(1), 0.019(1) and 0.014(1) ˚
A (for C23,C24 and C25 with averaged plane
deviations of 0.022, 0.022 and 0.029 ˚
A), respectively, and the chelate heterocycle adopts
a chair conformation. The cyclohexyl ring exhibits the chair conformation as well. Due
to the inversion centre, the two cyclohexyl rings of each side of the complex cation are
oriented to opposite directions and thus do not disturb each other sterically. The Cu-N
distances are significantly shortened in comparison with the other bis(µ-alkoxo) dicopper(II)
complex cations, whereas the geometric parameters as Cu-O distances and O-Cu-O and Cu-
O-Cu angles of the Cu2O2core are almost identical. The bite angles Nimine-Cu-Nimine are
comparable with those of the already described bis(µ-alkoxo) dicopper(II) complexes. The
Namine-C-Namine angles are according to those of the other tetramethyl guanidine systems.
The structural parameters ρfor C23,C24 and C25 are calculated to be around 0.97, a
value which is slightly smaller than those calculated for TMG2MePA containing complexes.
This might be due to the aliphatic spacer.
6.6 Hydroxylation of a copper MorphDMG2p complex and
subsequent reaction
The reaction of the MorphDMG2p containing precursor complex
[Cu2(MorphDMG2p)2][PF6]2with dioxygen (Scheme 6.6) gives the bis(µ-fluoro) di-
copper(II) complex [Cu2(MorphDMG2p)2(µ-F)2][PF6]2(C26). Analogously to the reaction
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 114
of other bisguanidine supported complexes, the reaction leads via a bis-µ-oxodicopper(III)
complex presumably to two products, a bis(µ-alkoxo) and a bis(µ-hydroxo) dicopper(II)
complex. The bis(µ-hydroxo) dicopper(II) complex reacts in the following step with
the present hexafluorophosphate ions abstracting fluorine ions and crystallising from the
reaction solution in MeCN as blue crystals of the bis(µ-fluoro) dicopper(II) complex
[Cu2(MorphDMG2p)2(µ-F)2][PF6]2(C26) by vapour diffusion of diisopropylether. Cu(II)
complexes are known to be able to abstract fluorine from hexafluorophosphate as has
been discussed by Holm et al.[154] The complex salt C26 crystallises in the monoclinic
space group P21/n. Crystals of C26 contain two molecules per unit cell. The structure
as the result of the structure analysis is shown in Figure 6.19, while selected bond lengths
and angles are collected in Table 6.8, and parameters relating to the data collection and
refinement are listed in Table A16.
N
N
N
Cu
N
2+
2 PF6-
Cu O2
N
N
Cu
N
N
Cu O
O
H
H
2+
2 PF6-
hydroxylated by-products
N
O
N N
O
N
N
O
N
O
N
N
N
O
N
N
N
N
O
N
N
O
N
O
N
N
Cu
N
N
Cu F
F
2+
2 PF6-
N
O
N N
O
N
N
O
N
O
N
N
F-
Figure 6.18: Activation of oxygen with [Cu2(MorphDMG2p)2][PF6]2
Table 6.8: Selected distances and angles of the complex cation [Cu2(MorphDMG2p)2(µ-
F)2]2+ in crystals of C26 in comparison with [Cu2(DPipG2p)2(µ-OH)2]2+ C22
(X = F−or OH−, resp.)
Distances (˚
A) C26 C22
Cu...Cu’ 3.0376(8) 3.0740(6)
Cu-Nimine 1.960 1.975
Cu-X 1.948(2) 1.935
N=C(av) 1.308 1.314
Angles (◦)
Nimine-Cu-Nimine 96.5(1) 96.0
X-Cu-X 77.0(1) 74.8
Cu-X-Cu’ 103.0(1) 105.2
Namine-C-Namine(av) 115.5 116.8
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 115
Figure 6.19: Molecular structure of [Cu2(MorphDMG2p)2(µ-F)2]2+
2in crystals of C26
The geometric centre of the cation lies on a crystallographic inversion centre and the resulting
Cu2F2core is thus strictly planar. The Cu atom is coordinated in a square-planar manner
by two guanidine N atoms and the two bridging F atoms. The deviation of the Cu atom
from the N2F2plane is 0.059(1) ˚
A, and the chelate heterocycle adopts a chair conformation.
The Cu...Cu and Cu-F distances (3.0376(8) and 1.960 ˚
A) are slightly shortened compared
with those of di-µ-hydroxo-bridged Cu2O2moieties due to the higher electronegativity of
fluorine. The bite angle Nimine-Cu-Nimine of 96.5◦and all the other characteristics (see
Table 6.8) are comparable with those of the already described bis(µ-hydroxo) dicopper(II)
complexes. Interestingly, no significant difference between the two halfs of the guanidine
moieties (dimethylamino and morpholino) can be made; the corresponding N=C bonds and
the Namine-C-Namine are equal to another. The morpholine rings in chair conformation are
oriented to each other which appears to help the packing of the complex cation (Figure 6.19).
The structural parameter ρis calculated to be 0.962, a typical value for a Cu(II) guanidine
complex.[108]
CHAPTER 6. PRODUCTS OF HYDROXYLATION REACTIONS 116
6.7 Conclusion of the Hydroxylation Properties of Copper
bisguanidine complexes
The reaction products have been identified as alkoxo-bridged dinuclear copper complexes
demonstrating that the bidentate permethylated guanidine ligands have been hydroxylated
in an unprecedented manner.[86, 149, 52, 150] An insertion of an oxygen atom into a C-H-
bond of an N-methyl-group a-standing to an amino-group by a rearrangement of a bis(µ-
oxo)dicopper(III) species is the first time to the best of our knowledge, although it has been
previously reported that the carbon adjacent to an amino or phenyl group was hydroxylated
by bis(µ-oxo)dicopper(III) species [86, 149] and that the β-carbon was hydroxylated via
different intermediates,[148, 150] even when this position was unactivated.[155]
7 Catalytic activity of copper
bisguanidine systems
7.1 General remarks
An important topic of the present work is the determination of the tyrosinase and catecholase
activity of several of the oxygenated copper bisguanidine complexes described in Chapter 6.
Generally, phenolic substrates should be ortho-hydroxylated in a tyrosinase-like reaction
(Figure 7.1, reaction 1). For this reaction, 2,4-ditertbutylphenol was selected as a sub-
strate because the sterically demanding tertbutyl groups prevent undesired side reactions,
e.g. the ring opening reaction known from iron-containing catechol-dioxygenases in na-
ture and in model systems.[3] In addition, reactions with the differently substituted sub-
strate 2,6-ditertbutylphenol were carried out in order to test the para-hydroxylation activity
of the oxygenated copper bisguanidine complexes (Figure 7.1, reaction 2). Since in 2,6-
ditertbutylphenol the ortho-position is occupied, only a para-hydroxylation reaction can oc-
cur. This hydroxylation can be followed by an oxidation to the para-quinone. A reason for
the test of this reaction type is the interest in the para-hydroxylation of 2,3,5-trimethylphenol
to 2,3,5-trimethyl-p-hydroquinone and subsequent oxidation to 2,3,5-trimethyl-p-quinone, an
important educt compound in the synthesis of vitamin E. Its derivatives possess as antioxi-
dants strong antimutagene activity.[156]
In order to test the catecholase reactivity, 3,5-ditertbutylcatechol was used as a substrate
because due to its small redox potential of -1.19 V, this catechol can be easily oxidised
to 3,5-ditertbutylquinone (Figure 7.1, reaction 3). Again, the sterically demanding tertbutyl
groups prevent side reactions like a C-C bond breaking between the two C=O bonds.
For the investigation of these different reactivities, the above-mentioned copper bisguani-
dine complexes were oxygenated at low temperatures and at room temperature followed by
addition of the substrates. The results of theses experiments are presented in the following
sections.
117
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 118
ButOH
cat.,
O2(1)
(2)
tBu
OH
tBu
tBu
cat.,
O2OH
tBu
tBu
HO
cat.,
O2
ButOH
tBu
OH
ButOH
tBu
OH
ButO
tBu
O
(3)
2,4-ditertbutylphenol
(2,4-DTBP)
2,6-ditertbutylphenol
(2,6-DTBP)
3,5-ditertbutylcatechol
(3,5-DTBC)
O
tBu
tBu
O
cat.,
O2
Figure 7.1: Oxygenation and oxidation reactions
7.2 Reactions with 2,4-ditertbutylphenol and
2,6-ditertbutylphenol
All attempts to react 2,4-ditertbutylphenol and 2,6-ditertbutylphenol at low temperatures (-
40◦- -80◦C) failed. After detecting the formation of the oxygenated copper species by UV/vis
spectroscopy, the addition of 2,4-ditertbutylphenol and 2,6-ditertbutylphenol did not lead to
any reaction. Thus, these experiments were carried out at room temperature after the follow-
ing procedure: 0.033 mmol of the Cu(I)bisguanidine complex in 10 mL of dichloromethane
was oxygenated by stirring for 2 min in the presence of air. Afterwards, 100 mg (0.5 mmol)
of substrate was added to the stirred solution. This reaction mixture typically changed its
colour from blue-green to yellow, red or brown (depending from the selected complex). After
16 h of stirring at room temperature, the reaction was quenched by the addition of 10 mL of
5% perchloric acid.[157] After 5 min of stirring, the phases were separated and the aqueous
phase was extracted with dichloromethane. The organic phases were combined and dried
with Na2SO4. These solutions were analysed by means of gaschromatographic separation
and mass spectrometric analysis in order to determine the conversion and the selectivity of
the reactions.
In fact, by carrying out these experiments at room temperature it remains unclear if the
oxidising species is a specific state (like O- or P-core) or a product of the decay of these
species.
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 119
It turned out that the substrates 2,4-ditertbutylphenol and 2,6-ditertbutylphenol were not
hydroxylated but coupled. In all of the obtained GC/MS data for the reaction of 2,4-DTBP,
the 410 m/z peak with a retention time of 20:16 min is present (Figure 7.2), whereas for
the reaction of 2,6-DTBP, the 410 m/z peak with a retention time of 22:53 min is found
(Figure 7.3). Since both substrates possess a molecular mass of 206 g/mol, the peak at 410
m/z appears to be indicative for their dimer. The most probable reaction pathway is the
C-O coupling reaction in the ortho- or para-position, respectively. Figure 7.4 shows possi-
ble coupling products. The reaction in the ortho- or para-position to the hydroxyl group
is favourised over the reaction in the ortho- or para-position to the tertbutyl groups.[116]
Furthermore, the constitution of the reaction products was confirmed by 1H-NMR analysis.
SCAN GRAPH. Flagging=Low Resolution M/z. Highlighting=Base Peak.
Scan 1216#20:16. Entries=179. Base M/z=57. 100% Int.=0,21286.
Low Resolution M/z
50 100 150 200 250 300 350 400
Intensity (%age)
0
10
20
30
40
50
60
70
80
90
100
57
91
105 190
283
339 - 56
339
M+ - 56 - 15
395
M+ - 15
410
M+
354
M+ - 56
227
283 - 56
Figure 7.2: Reaction product of 2,4-ditertbutylphenol with the retention time of 20:16 min
Similar observations have been described by Ackermann [158] and Reedijk.[159] The mech-
anism of this reaction has been subject of much discussion during the last decades, and
several mechanistic proposals have been made accordingly.[160] These proposals include the
coupling of dialkylphenols by a radical pathway or by an ionic mechanism, both for C-O and
C-C coupling. For this discussion, only the C-O coupling is taken into account and depicted
in the Figures 7.5 and 7.6. There are three possible reaction pathways: a) an attack of
a phenol radical occurs at the para-position of another phenol, b) a phenoxonium species
attacks electrophilically another phenol in para-position and c) a phenol attacks nucleophili-
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 120
SCAN GRAPH. Flagging=Low Resolution M/z. Highlighting=Base Peak.
Scan 1373#22:53. Entries=204. Base M/z=207. 100% Int.=0,00546.
Low Resolution M/z
50 100 150 200 250 300 350 400
Intensity (%age)
0
10
20
30
40
50
60
70
80
90
57
73
115
133
179
207
241
253
281
327 355
410
M+
395
M+ - 15
Figure 7.3: Reaction product of 2,6-ditertbutylphenol with the retention time 22:53 min
OH
tBu
tBu
cat.,
O2OH
tBu
tBu
O
tBu
tBu
2,6-DTBP
ButOH
cat.,
O2
tBu
ButO
tBu
2,4-DTBP
tBu
HO
tBu
But
tBu
tBu
But
OH
OH
C-O coupling product C-C coupling product
C-O coupling product C-C coupling product
OH
tBu
tBu
HO
But
But
Figure 7.4: Possible coupling products of 2,4-ditertbutylphenol and 2,6-ditertbutylphenol
cally the para-position of a coordinated phenoxonium species which has been generated by
a two-electron-transfer within a (µ-phenoxo)(µ-hydroxo)dicopper species (Figure 7.6).
Several theoretical works came to the consideration that, regarding the calculated atomic
charges of the monomeric species, the electrophilic pathway (b) is not a viable option, since
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 121
O
R
R
a) radical
OH
R
R
HOH
R
R
O
R
R
O
R
R
b) electrophilic
OH
R
R
HOH
R
R
O
R
R
- H
- H
OH
R
R
c) nucleophilic
O
R
R
HOH
R
R
O
R
R
- H
δ-δ+
Figure 7.5: Mechanistic pathways proposed for the oxidative coupling of dialkylphenols [160]
CuII CuII
dx2-y2dz2
O-
O-
H
2 e- transfer CuICuI
O+
O-
H
CuICuI
O+
O-
H
Oxonium
species
nucleophilic attack of
another phenol
Figure 7.6: Simplified orbital representation of the two-elctron phenol oxidation within a
(µ-phenoxo)(µ-hydroxo)dicopper species (adapted from [160])
it would require the attack of a cation with a positively charged oxygen atom on the para
carbon of the phenol.[161] The radical pathway is regarded to be unlikely as well because
it is known that a radical initiator mainly yields the C-C coupling product. Furthermore,
the results of calculations favour a phenoxonium cation over a phenoxy radical as the key
intermediate species. This strongly supports a mechanism, which involves the formation
of a phenolate-bridged dinuclear copper(II) species as the catalytically intermediate. This
bridging phenolate may experience a two-electron oxidation, resultung in a phenoxinium
cation that is possibly still coordinated to the dinuclear copper(I) species, as its oxygen still
bears a partial negative charge. The cation can then be attacked by a phenol (as shown in
Figure 7.6) or by a phenolate to give the coupled phenylether. The calculated data clearly
show that the singlet cation is a likely subject for nucleophilic attack on its para carbon.[160]
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 122
The triplet cation on the other hand is definitely not a target, since the para carbon bears a
partial negative charge. It is not immediately obvious which one of the cationic species will be
formed after the two-electron oxidation of a phenolate anion. It can be argued, however, that
in the case of a dinuclear (µ-phenoxo)(µ-hydroxo)bridged copper(II) catalytic intermediate,
the copper ions are almost certain to be strongly antiferromagnetically coupled.[162] This
means that the unpaired electrons of the copper ions will have opposite spins. It stands
to reason that after the double one-electron oxidation of the phenolate, the transferred
electrons will form electron pairs with the unpaired electrons of the copper ions, as shown
schematically in Figure 7.6. To make this possible, these transferred electrons must have
opposite spins. Therefore, the overall spin state of the bridging phenolate (S = 0) will not
change upon being oxidised to the cation. So, it can be concluded that the phenoxonium
cation formed in this reaction will be in the singlet state.[160]
7.3 Reactions with 3,5-ditertbutylcatechol
The reaction of 3,5-ditertbutylcatechol with oxygenated copper bisguanidine species containg
aliphatic or aromatic ligands proceeded even at low temperatures very fast. The formation
of the oxidised product, 3,5-ditertbutyl-o-quinone, could be observed by means of UV/vis
spectroscopy. 3,5-ditertbutyl-o-quinone shows a diagnostic absorption band at 400 nm. The
development of this absorption band is a good probe to investigate the kinetics of the oxida-
tion reaction. As example for this type of reactions, the time-dependent UV/Vis absorption
spectra of the reaction of [(DMPG2mX)2Cu2O2]2+ at -80◦C in CH2Cl2with 3,5-DTBC is
presented in Figure 7.7. Very often, the oxidation reaction proceeds too fast even at -80◦C
to be followed by UV/vis spectroscopy. This was the case with all bisguanidine ligands
incorporating an aliphatic spacer. Generally, these ligands show higher oxidation activitites
(see Table 7.1. Appearently, copper dioxygen species supported by bisguanidine ligands with
aromatic spacers are milder oxidants. The observation of the absorption band at 400 nm
was only possible when there was not already another absorption band present like it is
in O-core species the case which exhibit at 300 and 400 nm very strong absorption bands.
Hence, the observation of the 3,5-ditertbutyl-o-quinone absorption band is only possible by
using aromatic bisguanidine ligands which stabilise a P-core upon reaction with dioxygen.
The absorption at 400 nm can be plotted directly versus the time for a kinetic analysis as
it is depicted in Figure 7.8. Oxygen was present in excess, the solution had a concentration
of 6.6 mM of substrate which is an excess, too. In the first 70 minutes, the reaction remains
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 123
Figure 7.7: UV/vis absorption spectrum observed upon addition of 50 mg 3,5-
ditertbutylcatechol into a solution of [(DMPG2mX)2Cu2O2]2+ in CH2Cl2(0.5 mM,
-80◦C) (first section: every 5 min, second section: every 10 min)
relatively slowly. The kinetic constant kobs can be fitted by a zeroth order plot directly from
the absorption vs. time plot to be 0.0009 M/min. In the second part of the plot, the reaction
proceeds faster with a zeroth order constant of 0.0031 M/min. Possibly, the protons released
in the oxidation reactions in the first 100 min facilitate further oxidation reactions resulting
in a three times higher reaction rate. The kinetic results can be explained by a nearer look
at the kinetic equations: mostly, the reaction is depending in first order from the catalyst, in
first order from the substrate and in first order from the oxygen.[53] If the catalyst complex
already contains two copper molecules, the prerequisite for the two-electron oxidation from
catechol to quinone are given. If a dinuclear catalyst complex has to be formed before the
catalytic reaction, the kinetics are more complicated.[53] Hence, in the present case, the
observed kinetic constant kobs is described by the following equations:
−dc
dt =vr=k∗ccatcsubscO2
kobs =k∗ccatcsubscO2
Oxygen is present in excess; during the reaction, the concentration of the catalyst complex
ccat remains constant, unless there are side reactions. The substrate concentration csubs is
also comparably high and remains constant as well. Under these conditions, the plot has to
be of zeroth order, otherwise, the reaction does not proceed catalytically.
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 124
y = 0,0031x + 0,1512
R2 = 0,9988
y = 0,0009x + 0,3749
R2 = 0,9802
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 100 200 300 400 500
t [min]
A
Figure 7.8: Plot of the absorption at 400 nm (3,5-DTBQ) vs. the time for the reaction of
[(DMPG2mX)2Cu2O2]2+ in CH2Cl2(0.5 mM, -80◦C) with 3,5-DTBC (6.6 mM)
Attempts to vary the concentration of the catalyst complex were not successful because the
concentration range for these low temperature UV/Vis measurements is very narrow. The
same reason restricted the variation of the substrate concentration. Figure 7.9 shows the
absorption vs. time plot at -80◦C for a substrate concentration of 13.2 mM. The reaction
proceeds faster as the reaction constant of 0.0041 M/min assigns. This observation is in
accordance with data reported in the literature [158] referring to Michaelis-Menten kinetics
often found in catalytic systems.
Finally, to determine the conversion and the selectivity of the catecholase reaction, the
experiments were carried out at room temperature after the following procedure, analogously
to that described above for the reaction of 2,4- and 2,6-DTBP. 0.033 mmol of the Cu(I)
bisguanidine complex in 10 mL of dichloromethane were oxygenated by stirring for 2 min in
the presence of air. Afterwards, 100 mg (0.45 mmol) of 3,5-DTBC were added to the stirred
solution. This reaction mixture usually changed its colour from blue-green to dark brown.
After 16 h of stirring at room temperature, the reaction was quenched by the addition of 10
mL of 5% perchloric acid. After 5 min of stirring, the phases were separated and the aqueous
phase was extracted with dichloromethane. The combined organic phases were dried with
Na2SO4. These solutions were analysed by means of gaschromatographic separation and
mass spectrometric analysis in order to determine the conversion and the selectivity of the
reactions.
Since the reaction product 3,5-DTBQ is highly reactive, the presence of 3,5-DTBQ could not
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 125
y = 0.0041x + 0.2578
R2 = 0.9932
0
0.5
1
1.5
2
2.5
0 100 200 300 400 500
t [min]
A
Figure 7.9: Plot of the absorption at 400 nm (3,5-DTBQ) vs. the time for the reaction of
[(DMPG2mX)2Cu2O2]2+ in CH2Cl2(0.5 mM, -80◦C) with 3,5-DTBC (13.2 mM)
be proved in the GC/MS analysis, but a succeeding product with m/z of 278 and a retention
time of 13:02 min instead. The formation of this subsequent product can be understood by
regarding the following mechanism (see Figure 7.11).
SCAN GRAPH. Flagging=Low Resolution M/z. Highlighting=Base Peak.
Scan 779#12:59. Entries=107. Base M/z=207. 100% Int.=0,44187.
Low Resolution M/z
50 100 150 200 250 300
Intensity (%age)
0
10
20
30
40
50
60
70
80
90
100
57
77
91
108
133
149
177
192
207
207 = 222 - 15
263
M+ - 15
278
M+
222
M+ - 56
Figure 7.10: Reaction product of 3,5-ditertbutylcatechol with the retention time of 13:02 min
3,5-DTBC is known to abstract isobutene in a retro-Friedel-Crafts reaction with Cu(II) as
Lewis acid.[163] The isobutene can react with the quinone in a Diels-Alder reaction to the
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 126
cat.,
O2
ButOH
tBu
OH
ButO
tBu
O
H OH
H
OH
+
m/z 56
2
Diels-Alder
reaction ButO
tBu
O
m/z 220 m/z 278
m/z 222
cat.,
O2totally oxidised
products, non
aromatic
aqueous
workup remain in the aqueous phase,
not submitted to GC/MS
analysis
6,8-di-tert-butyl-2,3-dihydro-2,2-
dimethylbenzo[b][1,4]dioxine
Figure 7.11: Hypothetical mechanism of the reaction of 3,5-DTBC via 3,5-DTBQ to 6,8-di-
tert-butyl-2,3-dihydro-2,2-dimethylbenzo[b][1,4]dioxine
aromatic compound 6,8-di-tert-butyl-2,3-dihydro-2,2-dimethylbenzo[b][1,4]dioxine.[164] The
driving force of this reaction is the fact that after the Diels-Alder reaction, the aromaticity
is restored. However, in the GC/MS data, very often no educt is found and 100 % of
the product are present. Thus, all the 3,5-DTBC should have reacted to quinone, but the
GC/MS analysis only refers to the organic phase. Comparative studies with unsubstituted
catechol show that under these conditions the catechol is oxidised to the point that the C-
C bond between the hydroxy functions is broken.[165] Finally, these non-aromatic, totally
oxidised residues end up in the aqueous phase and are not submitted to GC/MS analysis.
Hence, referring only to the organic phase, the GC/MS data reflect at maximum 66 % yield
corrected to the educt compound. The data reported in Table 7.1 are strictly related to the
results in the organic phase.
7.4 Screening of the library of bisguanidine ligands
regarding the oxidation activity
Based on the results described above, the catalytic oxidation activity of all copper bisguani-
dine complexes has to be investigated. Therefore, the library of bisguanidine ligands has
to be screened regarding the conversion and the selectivity in the oxidation reactions with
2,4-DTBP, 2,6-DTBP and 3,5-DTBC. Table 7.1 summarises the results of the screening of
a representative part of the bisguanidine ligand library.
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 127
Table 7.1: Screening of representative copper bisguanidine complexes towards their catalytic
abilities in % conversion (% selectivity) (*: related to GC/MS data, absolute
maximum yield 66 %)
No. Catalyst 2,4-DTBP 2,6-DTBP 3,5-DTBC*
1 [Cu(btmgp)I] 100%(60%) 100%(80%) 100%(95%)
2 [Cu2(btmgp)2][PF6]290%(95%) 80%(100%) 100%(100%)
3 [Cu2(TMG2ch)2]I2100%(80%) 100%(100%) 95%(90%)
4 [Cu2(TMG2ch)2][PF6]295%(95%) 90%(100%) 100%(90%)
5 [Cu(DMEG2p)I] 100%(100%) 100%(100%) 100%(95%)
6 [Cu2(DMEG2p)2][PF6]280%(95%) 100%(100%) 100%(95%)
7 [Cu(DMEG2ch)I] 100%(80%) 95%(100%) 95%(95%)
8 [Cu2(DMEG2ch)2][PF6]220%(100%) 10%(100%) 100%(100%)
9 [Cu2(DMPG2p)2][PF6]2100%(95%) 40%(95%) 100%(80%)
10 [Cu(DPPG2p)]n[CuI2]n90%(80%) 50%(100%) 80%(90%)
11 [Cu(TiPG2p)I] 40%(100%) 50%(20%) 100%(100%)
12 [Cu2(DPipG2p)2][PF6]2100%(50%) 100%(100%) 100%(20%)
13 [Cu(B(DMPip)G2p)I] 100%(95%) 70%(100%) 60%(95%)
14 [Cu(B(TMPip)G2p)I] 20%(95%) 15%(100%) 20%(95%)
15 [Cu(DMorphG2p)I] 50%(100%) 70%(90%) 100%(100%)
16 [Cu(TMG2MePA)I] 90%(90%) 95%(90%) 90%(20%)
17 [Cu(TMG2mX)I] 70%(80%) 20%(95%) 85%(95%)
18 [Cu(DMEG2mX)I] 80%(90%) 30%(95%) 95%(95%)
19 [Cu(DMPG2mX)I] 95%(70%) 100%(95%) 100%(90%)
20 [Cu(TMG2py)I] 0%(-) 0%(-) 60%(95%)
21 [Cu(TEG2py)I] 30%(100%) 0%(-) 20%(95%)
22 [Cu(MorphDMG2p)I] 40%(100%) 70%(95%) 10%(100%)
23 [Cu((DMPip)DMG2p)I] 40%(100%) 30%(60%) 100%(100%)
24 [Cu(BFPPG2p)I] 70%(95%) 80%(100%) 90%(95%)
Special attention has been paid to the role of the counterion (coordinating or non-
coordinating) and the type of the spacer (aromatic or aliphatic). Conversion and selectivity
are based on the gaschromatographic data. The mass spectrometric analysis assured that
the product could be identified (vide supra). All catalytic experiments were carried out after
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 128
the procedure already described in the sections 7.2 and 7.3.
Comparing the activity of copper iodine and copper hexafluorophosphate containing com-
plexes, complexes based on CuI reach better conversions (entries No. 1, 3, 5, and 7). Possi-
bly, the iodine acts as co-catalyst in the electron transfer. Incorporating the same guanidine
moiety, complexes with aliphatic bisguanidine ligands (Nos. 1 - 10) seem to be better cat-
alysts than those with aromatic bisguanidine ligands (Nos. 15 - 20). When the guanidine
groups get highly sterically demanding, the conversion is decreasing (Nos. 11, 13, 14, 15)
as the access to the active centre is made more difficult. Perhaps, by using a substrate
with smaller subsituents, the conversion can be enhanced. The optimisation of the catalyst-
substrate-relationship is object to further investigations. However, the selectivity in exactly
these systems is relatively high. The non-symmetric systems (Nos. 22 and 23) do not show
sufficient conversion bot relatively good selectivities. The perfluorinated system of No. 24
exhibits average conversions and very good selectivities. This can be explained by the ex-
traordinary stability of the oxygenated species (see section 5.2) which is too stable to be a
strong oxidant. The properties of a mild oxidant are accompanied by higher selectivities as
potential side reactions are supressed.
Figure 7.12 denotes the reaction yields of selected catalyst complexes. Catalyst no. 5 incor-
porating an aliphatic ligand is an effective catalyst for all three reactions as the reactions
yields are at their maximum values. Catalyst no. 9 contains a similar ligand with slightly
bigger guanidine moieties, but the yield of the coupling reaction of 2,6-DTBP decreases
drastically. This trend is confirmed by catalyst no. 11, a highly sterically hindered system
with tetra-iso-propylguanidine groups, which generally shows lower conversions (Table 7.1).
Catalyst no. 15 also shows lower yields for 2,4- and 2,6-DTBP, but with reversed relation:
now, the reaction with 2,6-DTBP is favourised over the reaction with 2,4-DTBP. Probably,
the dimorpholinoguanidino unit can fold up better than the other systems. Until this point
of discussion, the yields for the reaction with 3,5-DTBC were very good. In the case of no.
16, the aromatic TMG2MePA system supports such a strong oxidant that the reaction prod-
ucts are destroyed oxidatively resulting in only 20% yield for the product with 3,5-DTBC
and almost 90% yield for the phenolic substrates. Contrarily, the pyridine-based systems of
nos. 20 and 21 are such weak catalysts that they only oxidise 3,5-DTBC sufficiently. The
small difference of tetramethylguanidino (No. 20) to tetraethylguanidino (No. 21) units
results in 30% more yield for the 2,4-DTBP dimerisation for No. 21 but 40 % less yield for
the oxidation of 3,5-DTBC. Catalyst no. 22, a non-symmetric system, is the single catalyst
which exhibits clearly better yields for both of the phenolic substrates than for the catechol.
CHAPTER 7. CATALYTIC ACTIVITY OF COPPER BISGUANIDINE SYSTEMS 129
No. 5 No. 9 No. 11 No. 15 No. 16 No. 20 No. 21 No. 22
2,4-DTBP
2,6-DTBP
3,5-DTBC
0
10
20
30
40
50
60
70
80
90
100
2,4-DTBP
2,6-DTBP
3,5-DTBC
Figure 7.12: Overview of the reaction yields (conversion x selectivity) selected complexes
7.5 Conclusion of the catalytic results
In summary, bisguanidine copper complexes represent a new class of oxidation catalysts.
The ability of oxidation is depending from the accessibility of the reaction centre: ”small”
ligands result in better oxidation catalysts whereas sterically demanding systems show with
substrates like 2,4-DTBP and 2,6-DTBP reduced conversions by high selectivity. The re-
sults show that the reactivity of the catalysts can be controlled by the steric impact of the
guanidine substituents. Ligands with high steric demands are supposingly better suited for
the oxidation of substrates with smaller substituents like 2,6-dimethylphenol. The poly-
merisation of 2,6-dimethylphenol is an important research field [38] as the polymerisation
product PPO is a high melting, very resistant plastic. Examples like no. 20 and 21, where
the difference between methyl and ethyl groups changes the catalytic situation totally, reveal
that there are numerous effects imposed on the reaction centre which can not be predicted.
For each substrate can be designed a suited catalytic system by comparing the electronic
features of the ligand spacer, the steric demand of the substituents and the role of the coun-
terion. The present screening of the library of bisguanidine ligands provides with some clues
in tailored ligand design for copper-catalysed reactions.
8 Experimental Section
8.1 Material and Methods
8.1.1 General Remarks
All manipulations were performed under pure dinitrogen (99,996%) dried with P4O10 gran-
ulate using Schlenk techniques or a glovebox and with abs. solvents. Solvents were purified
according to literature procedures and also kept under nitrogen. Triethylamine and 1,3-
diaminopropane were used as purchased from Fluka.
8.1.2 Physical measurements
NMR spectroscopy: The 1H, 13C and 19F spectra were recorded with the spectrometers
Bruker AMX 300 (1H: 300.13 MHz, 13C: 75.47 MHz, 19F: 282.38 MHz) and WMX 500 (1H:
500.13 MHz, 13C: 125.77 MHz), respectively. The solvents and temperatures are noted for
every substance.
EXSY 1H NMR measurements: Temperature variable EXSY spectra of compounds
L1-1,L1-2 and L1-4 were recorded with the pulse program noesygpph from Bruker’s pulse
program library. The mixing time tm was optimised according to the literature [166] and
amounted to 200 ms. As the observed exchange process of the methyl groups is a simple
two-side case with equal populations and uncoupled spins the exchange rate constant is cal-
culated [166] from the integrals of diagonal- and cross-peaks: k = τ−m−1ln[(r+1)/(r-1)]
with r = (ID1+ID2)/(IC1+IC2) and ID1, ID2= Integrals of the diagonal peaks; IC1, IC2=
Integrals of the cross-peaks.
IR spectroscopy: The infrared spectra were recorded with the FT-IR spectrometer Nicolet
P510.
UV/Vis spectroscopy: The UV/Vis spectra were recorded with a Perkin-Elmer Lambda
45 spectrometer in combination with the Hellma UV/Vis-low temperature-interface (1cm
path length cell), excess O2.
Crystal Structure Analyses: Crystal data for all compounds are presented in the Ap-
pendix. X-ray diffraction data were collected with a Bruker-AXS SMART APEX CCD
diffractometer using MoKαradiation (λ= 0.71073 ˚
A). Data reduction and absorption cor-
rection were performed with SAINT and SADABS.[167] The structures were solved by direct
and conventional Fourier methods and all non-hydrogen atoms refined anisotropically with
full-matrix least-squares procedures based on F2(SHELXTL [167]). Hydrogen atoms were
derived from difference Fourier maps and placed at idealized positions, riding on their parent
C atoms, with isotropic displacement parameters Uiso(H) = 1.2Ueq(C) and 1.5Ueq(C methyl).
130
CHAPTER 8. EXPERIMENTAL SECTION 131
All methyl groups were allowed to rotate but not to tip.
Mass spectrometry: The EI mass spectra were recorded at a Finnigan MAT 40 mass
spectrometer with 70 eV and 200◦C source temperature; the CI mass spectra at the same
spectrometer with isobutane as reactand gas and 130◦C source temperature. The GC-MS
unit contains a F-S capillar DB5 30m (0.25mm, 0.2 µm, 1 µL split 1:150, He: 0.4 bar). The
temperature program was 80◦C, 1 min; 10◦/min; 300◦C.
Elemental analyses: The elemental analyses were performed with a Perkin-Elmer 2400
analysator. Microanalyses for hexafluorophosphate containing compounds were performed
at the Mikroanalytisches Labor, Ilse Beetz, Kronach, Germany.
Cyclic voltammetry: Cyclovoltammetric measurements were performed with the electro-
chemical device Metrohm E 505 equipped with a potentiostat Model VersaStat by EG&G
in combination with the PC-program Electrochemical Analysis Software 3.0 Model 250 by
EG&G. The electrochemical cell was operated under argon, with glassyC/glassyC/Ag/AgCl
or Au/Pt/saturated Ag/AgCl serving as working, counter and reference electrodes, respec-
tively. CV curves were obtained at scan rates of 100mV/s working at 25◦C in MeCN/0.1
mnBu4NPF6. As the complexes are extremely air sensitive, the copper(I) solutions were
transferred into the CV cell with a steel capillar under argon pressure.
8.2 Synthesis of educt compounds
Tetrakis(acetonitrile)copper(I)hexafluorophosphate [Cu(MeCN)4][PF6]Caution!
The following procedure should be carried out in a well-ventilated hood because of the tox-
icity of the HF fumes evolved from HPF6.To a mechanically stirred suspension of 4.0 g
(28 mmol) of copper(I)oxide in 80 mL of MeCN in a 125 mL Erlenmeyer flask is added
10 mL of 60-65% HPF6(about 113 mmol of HPF6) in 2 ml protions. The reaction is
very exothermic and may cause the solution to boil. However, the reaction temperature
is not critical and the warming is beneficial in that the product remains dissolved. After
addition of the final portion of HPF6, the solution is stirred for about 3 min and is then
filtered hot through a medium-porosity frit to remove small amounts of undissolved black
solid (some white [Cu(MeCN)4][PF6] may begin to crystallise before filtration; if so, it is
washed with a minimum amount of MeCN). The pale-blue solution is cooled in a freezer to
about -20◦C for several hours (addition of an equal volume of diethyl ether and cooling to
0◦C yields equivalent results), whereupon a blue-tinged white microcrystalline precipitate of
[Cu(MeCN)4][PF6] forms. The solid is collected by filtration, washed with diethyl ether, and
immediately redissolved in 100 mL of MeCN. A small amount of blue material, presumably
a Cu2+ species, remains undissolved and is removed by filtration. To the filtrate (which may
still retain a slight blue colour) is added 100 mL of diethyl ether, and the mixture is allowed
to stand for several hours at -20◦C. The precipitated complex may still retain a bluish cast,
in which case a second recrystallisation may be necessary if high purity is desired. This
second recrystallisation is carried out using 80 mL each of MeCN and diethyl ether. The
product is pure white and is dried in vacuo for about 30 min immediately after being washed
with diethyl ether. The yield is 12.5 g (60%) and is dependent on recrystallisation losses.
CHAPTER 8. EXPERIMENTAL SECTION 132
1,3-Bis(N,N,N´,N´-tetramethylguanidino)propane (btmgp):[105, 112]
1,3-Dibromopropane (14 mL, 0.14 mmol) was added to freshly distilled N,N,N´,N´-
tetramethylguanidine (100 mL, 0.80 mol) and heated to 100◦C for 12 h. During this time,
the reaction mixture solidified. The excess of tetramethylguanidine was distilled off and a
freshly prepared sodium ethoxide solution [6.6 g (0.28 mol) Na in 70 mL ethanol/70 mL
THF] was added to the pale brown residue. The mixture was stirred for 5 h. The resulting
NaBr was filtered off and the solvents, together with any remaining tetramethylguanidine,
were removed under reduced pressure at room temperature. The product was isolated by
vacuum distillation (b.p. 110◦C/0.05 mbar). Yield: 15.2 g (41 %)
1H-NMR (300 MHz, CDCl3, 25◦C): δ= 1.56 (qi, 2H, CH2,3J= 6.7 Hz), 2.44 (s, 12H,
CH3), 2.99 (t, 4H, CH2,3J= 6.7 Hz) ppm. 13C-NMR (75 MHz, CDCl3, 25◦C): δ= 35.2
(CH2), 38.5 (CH3), 39.3 (CH3), 47.3 (CH2), 159.6 (Cgua) ppm. IR (film between NaCl plates,
˜ν[cm−1]): 2994m, 2931s, 2913s, 2870vs, 2836s, 2799m, 1622vs (˜ν(C=N)), 1494m, 1451m,
1363vs, 1310w, 1234m, 1184w, 1135s, 1108w, 1092w, 1062m, 1025w, 1011m, 984w, 957w,
913m, 881w, 810w, 746m, 725w, 648w, 577m, 501w, 436vw.
8.3 Synthesis of product compounds
8.3.1 Synthesis of substituted ureas
N,N,N´,N´-Dipropylpropyleneurea. Based on a literature procedure,[131] N,N´-
trimethyleneurea (Fluka, 0.05 mol, 5 g) was treated in freshly destilled dioxane (200 mL)
with NaH (0.11 mol, 2.64 g). The reaction mixture was heated to reflux for 16 h and then
cooled to room temperature. After propyl iodide (0.2 mol, 34.0 g, 59.2 mL) was added, the
reaction mixture was heated to reflux for further 16 h and filtered to remove precipitated NaI.
After evaporation of the solvent, vacuum destillation of the residual oil yields the product
as yellow oil yield ca. 60 %. 1H-NMR (500 MHz, CDCl3, 25◦C): δ= 0.83 (t, 6H, CH3), 1.50
(m, 4H, CH2), 1.89 (m, 2H, CH2), 3.23 (m, 8H, CH2) ppm. 13C-NMR (125 MHz, CDCl3,
25◦C): δ= 11.2 (CH3), 21.0 (CH2), 22.5 (CH2), 45.7 (CH2), 49.7(CH2), 155.9 (C. quart) ppm.
N,N,N´,N´-Bis(heptafluoropropyl)propyleneurea. N,N´-trimethyleneurea (Fluka,
0.05 mol, 5 g) was treated in freshly destilled diethylether (200 mL) with NaH (0.11 mol,
2.64 g). The reaction mixture was heated to reflux for 36 h and then cooled with ice-water.
After heptafluoropropyl iodide (0.1 mol, 29.2 g, 24 mL) was added, the reaction mixture
was heated to reflux for further 36 h and filtered over chromatographic silica to remove
precipitated NaI. Isolation is impossible due to the high volatility (b.p. ≈25◦C)
19F (282.38 MHz, C6D6, 25◦C): δ= -83.3 (t, 6F, CF3), -133.5 (t, 2F, CF2), -139.3 (m, 2F,
CF2) ppm.
8.3.2 Synthesis of Vilsmeier salts
Caution! Phosgene is a severe toxic agent that can cause pulmonary embolism and in the
case of heavy exposition may be lethal. Use only in a well-ventilated fume hood.
CHAPTER 8. EXPERIMENTAL SECTION 133
N,N,N´,N´-Tetramethylchloroformamidinium Chloride (V1):
N N
Cl
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C, phosgene
was passed at 0◦C through a solution of tetramethylurea (Fluka,
48.4 g, 417 mmol, 50 mL) in dry toluene (300 mL) for 60 min.
The reaction mixture was stirred 2 h at room temperature and for
further 24 h at 30◦C. After the mixture cooled to room temperature,
the white solid was filtrated and washed with dry diethyl ether.
The residual white powder was dried in vacuo, yield: 95 %.
N,N,N´,N´-Tetraethylchloroformamidinium Chloride (V2):
N N
Cl
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C, phosgene
was passed at 0◦C through a solution of tetraethylurea (Fluka, 263
mmol, 50 mL) in dry toluene (300 mL) for 60 min. The reaction
mixture was stirred 2 h at room temperature and for further 24
h at 40◦C. After the mixture cooled to room temperature, the
toluene was decanted. The residual yellow oil was washed with dry
diethylether and dried in vacuo, yield: 95 %.
1H-NMR (500 MHz, CDCl3, 25◦C): d= 1.30 (t, 12H, CH3), 3.71 (q,
8H, CH3) ppm.
N,N,N´,N´-Tetraisopropylchloroformamidinium chloride (V3):
N N
Cl
Cl-
In a Schlenk flask fitted with a condensor cooled to -40◦C, phosgene
was passed through a solution of diisopropylamine (0.2 mol, 20.2
g, 14.5 mL) and NEt3(0.2 mol, 20.2 g, 27.9 mL) in dry MeCN
(200 mL) at 0◦C (attention: highly exothermic) for 15 min. The
formation of the urea took place immediately, the solution was not
stirrable due to its high viscosity. After 30 min, the reaction mixture
was allowed to come to room temperature and it was stirred again.
Then, the mixture was heated for 40 h to 40◦C. After the mixture
cooled to room temperature, the solvent was evaporated under reduced pressure in order
to obtain the product with NEt3HCl as by-product as colourless wax, yield ca. 80 % (22.6 g).
N,N,N´,N´-Dimethylethylenchloroformamidinium Chloride (V4):
NN
Cl
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C,
phosgene was passed at 0◦C through a solution of 1,3-dimethyl-
2-imidazolidinone (Fluka, 68.5 g, 600 mmol) in dry toluene (300
mL) for 50 min. The reaction mixture was stirred for 2 h at room
temperature and for another 12 h at 40◦C. After the mixture
cooled down to room temperature, the white precipitate formed
was collected by filtration, washed three times with dry diethyl
ether, and dried in vacuo, yield: 95 %.
CHAPTER 8. EXPERIMENTAL SECTION 134
N,N,N´,N´-Dimethylpropylenchloroformamidinium Chloride (V5):
N N
Cl
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C,
phosgene was passed at 0◦C through a solution of N,N,N´,N´-
Dimethylpropyleneurea (Fluka, 76.9 g, 600 mmol) in dry toluene
(300 mL) for 50 min. The reaction mixture was stirred for 2 h at
room temperature and for another 24 h at 40◦C. After the mixture
cooled down to room temperature, the white precipitate formed
was collected by filtration, washed three times with dry diethyl
ether, and dried in vacuo, yield: 95 %.
N,N,N´,N´-Dipropylpropylenchloroformamidinium Chloride (V6):
N N
Cl
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C,
phosgene was passed at 0◦C through a solution of N,N,N´,N´-
Dipropylpropyleneurea (90 mmol, 16.6 g) in dry toluene (150 mL)
for 20 min. The reaction mixture was stirred for 2 h at room
temperature and for another 80 h at 40◦C. After the mixture
was cooled to room temperature, the toluene was decanted. The
residual orange oil was washed with dry diethylether and dried in
vacuo, yield: 80 %. 1H-NMR (500 MHz, CDCl3, 25◦C): δ= 0.86 (t, 6H, CH3), 1.65 (m, 4H,
CH2), 2.19 (m, 2H, CH2), 3.62 (t, 4H, CH2), 3.87 (t, 4H, CH2) ppm. 13C-NMR (125 MHz,
CDCl3, 25◦C): δ= 10.8 (CH3), 19.6 (CH2), 20.7 (CH2), 49.5 (CH2), 57.7 (CH2), 151.1 (C.
quart) ppm.
N,N,N´,N´-Dipiperidylchloroformamidinium Chloride (V7):
Cl
N N
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C, phosgene
was passed at 0◦C through a solution of 1,1´-carbodipiperidine
(Aldrich, 12.5 g, 63.8 mmol) in dry MeCN (200 mL) for 30 min.
The reaction mixture was stirred 6 h at room temperature and
for another 36 h at 40◦C. After the mixture cooled down to room
temperature, the solvent was evaporated under reduced pressure in
order to obtain the product as colourless oil, yield ca. 70 %.
N,N,N´,N´-Bis(dimethylpiperidyl)chloroformamidinium chloride (V8):
Cl
N N
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C, phosgene
was passed through a solution of cis-2,6-dimethylpiperidine (0.1
mol, 11.3 g, 9.3 mL) and NEt3(0.1 mol, 10.1 g, 14.0 mL) in dry
MeCN (200 mL) at 0◦C for 15 min. After 30 min, the reaction
mixture was allowed to come to room temperature and heated for
36 h to 40◦C. After the mixture cooled to room temperature, the
solvent was evaporated under reduced pressure in order to obtain
the product as well as NEt3HCl as colourless powder, yield ca. 65 %.
CHAPTER 8. EXPERIMENTAL SECTION 135
N,N,N´,N´-Bis(tetramethylpiperidyl)chloroformamidinium chloride (V9):
Cl
NN
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C, phosgene
was passed through a solution of 2,2,6,6-tetramethylpiperidine (0.1
mol, 14.1 g, 11.7 mL) and NEt3(0.1 mol, 10.1 g, 14.0 mL) in dry
MeCN (200 mL) at 0◦C for 15 min. After 30 min, the reaction
mixture was allowed to come to room temperature and heated for
50 h to 40◦C. After the mixture cooled to room temperature, the
solvent was evaporated under reduced pressure in order to obtain
the product as well as NEt3HCl as yellow powder, yield ca. 57 %.
N,N,N´,N´-Diimidazolylchloroformamidinium chloride (V10):
Cl
N N N
N
Cl-
In a Schlenk flask fitted with a condensor cooled to -30◦C, phosgene
was passed at 0◦C through a solution of 1,1´-carbonyl-diimidazole
(Fluka, 154 mmol, 25 g) in dry MeCN (300 mL) for 15 min. The
reaction mixture was stirred for 2 h at room temperature and
for another 30 h at 40◦C. After the mixture was cooled to room
temperature, the excess of phosgene and the MeCN were evaporated
under reduced pressure. The yellow residue was dried in vacuo,
yield: 80 %.
N,N,N´,N´-Dimorpholinochloroformamidinium chloride (V11):
Cl
N
O
N
O
Cl-
In a Schlenk flask fitted with a condensor cooled to -40◦C, phosgene
was passed through a solution of morpholine (0.2 mol, 17.4 g, 17.5
mL) and NEt3(0.2 mol, 20.2 g, 27.9 mL) in dry MeCN (250 mL)
at 0◦C (attention: highly exothermic) for 15 min. The formation of
the urea took place immediately, the solution was not stirrable due
to its high viscosity. After 30 min, the reaction mixture was allowed
to come to room temperature and it was stirred again. Then, the
mixture was heated for 50 h to 40◦C. After the mixture cooled to room temperature, the
solvent was evaporated under reduced pressure in order to obtain the product with NEt3HCl
as by-product as yellow oil, yield ca. 70 %.
N,N,N´,N´-Dithiomorpholinochloroformamidinium chloride (V12):
Cl
N
S
N
S
Cl-
In a Schlenk flask fitted with a condensor cooled to -40◦C, phosgene
was passed through a solution of thiomorpholine (0.49 mol, 5 g)
and NEt3(0.97 mol, 9.7 g, 13.4 mL) in dry MeCN (150 mL) at
0◦C for 15 min. After 30 min, the reaction mixture was allowed to
come to room temperature and heated for 50 h to 40◦C. After the
mixture cooled to room temperature, the solvent was evaporated
under reduced pressure in order to obtain the product as well as
NEt3HCl as yellow powder, yield ca.45 %.
CHAPTER 8. EXPERIMENTAL SECTION 136
8.3.3 Synthesis of guanidine ligands
General synthesis of bisguanidine ligands with chloroformamidinium chlorides
V1, V2, V4, V5, V6, V7 and V10:
A solution of the chloroformamidinium chloride (40 mmol) in dry MeCN (60 mL) was
added dropwise under vigorous stirring to an ice-cooled solution of a bisamine (20 mmol)
and triethylamine (5.57 mL, 4.04 g, 40 mmol) in dry MeCN (30 mL). After 3 h at reflux, a
solution of NaOH (1.6 g, 40 mmol) in water was added. Under vacuum, solvents and NEt3
were evaporated. In order to deprotonate the bis-hydrochloride, 50 wt % KOH (aq, 25 mL)
was added and the free base was extracted into the MeCN phase (3x25 mL). The organic
phase was dried with Na2SO4over charcoal. After filtration over Celite, the solvent was
evaporated under reduced pressure.
General synthesis of bisguanidine ligands with chloroformamidinium chlo-
rides V3, V8, V9, V11, V12:
The reaction mixture containing the chloroformamidinium chloride (40 mmol) in dry MeCN
(60 mL) was added dropwise under vigorous stirring to an ice-cooled solution of a bisamine
(20 mmol) and triethylamine (5.57 mL, 4.04 g, 40 mmol) in dry MeCN (30 mL). After 3
h at reflux, a solution of NaOH (4.8 g, 120 mmol) in water was added. Under vacuum,
solvents and NEt3were evaporated. In order to deprotonate the bis-hydrochloride, 50 wt %
KOH (aq, 25 mL) was added and the free base was extracted into the MeCN phase (3x25
mL). The organic phase was dried with Na2SO4over charcoal. After filtration over Celite,
the solvent was evaporated under reduced pressure.
2-(2-(2-(tetramethylguanidino)ethoxy)ethoxy)-N-(tetramethylguanidino)ethane-
amine, TMG2doo (L1-2):
O O N
Me2NNMe2
N
Me2NNMe2
Colourless oil, yield: 96 %. 1H-NMR (500 MHz, CDCl3,
25◦C): δ= 2.51 (s, 12H, CH3), 2.60 (s, 12H, CH3),
3.19 (t, 4H, CH2,3J= 6.9 Hz), 3.44 (t, 4H, CH2,3J
= 6.9 Hz), 3.51 (s, 4H, CH2) ppm. 13C-NMR (125
MHz, CDCl3, 25◦C): δ= 38.6 (CH3), 39.5 (CH3), 49.4
(CH2), 70.2 (CH2), 73.3 (CH2), 160.8 (Cgua) ppm. IR (film between NaCl plates, ˜ν[cm−1]):
2995w, 2868vs, 2800w, 1619vs (˜ν(C=N)), 1496m(˜ν(C=N)), 1452m(˜ν(C=N)), 1367vs,
1299w, 1236m, 1137s(˜ν(C-O-C)), 1064m(˜ν(C-O-C)), 991w. EI-MS (m/z, (%)): 344.4 (1)
[M+], 300 (5) [M+- NMe2], 230 (2) [M+- (NMe2)2CN], 186 (7) [M+- (NMe2)2CN(CH2)2O],
173 (8) [M+- NMe2, NC(NMe2)2], 141 (71) [M+- (NMe2)2CN(CH2)2O], 129 (44) [M+-
(NMe2NCH3CN(CH2)2O(CH2)2], 114 (6) [M+- (NMe2)2CN(CH2)2O(CH2)2], 100 (17), 85
(100) [M+- (NMe2)2CN(CH2)2O(CH2)2N, CH3], 71 (17) [M+- (NMe2)2CN(CH2)2O(CH2)2,
NMe2]. elemental analysis, calcd. for C16H36N6O2: C 55.77, H 10.54, N 24.40 ; found : C
55.54, H 10.89, N 24.15.
CHAPTER 8. EXPERIMENTAL SECTION 137
[H2TMG2doo]I2·Et2O ([H2L1-2]I2·Et2O):
O O NH
Me2NNMe2
HN
Me2NNMe22 I-, Et2O
Compound L1-2 (688 mg, 2 mmol) was dissolved in
THF (10 mL) and added to a suspension of ammonium
iodide (576 mg, 4 mmol) in THF (10 mL). The reaction
mixture was refluxed for 2 h and the solvent removed
under reduced pressure. The resulting precipitate was
dissolved in acetonitrile (15 mL) and filtered. Diethylether was added to the colourless
filtrate by vapor diffusion to form [H2L1-2]I2as colourless needles. 1H-NMR (500 MHz,
CD3CN, 25 ◦C): δ= 2.95 (s, 12H, CH3), 3.09 (s, 12H, CH3), 3.37 (t, 4H, CH2,3J=
5.2 Hz), 3.61 (s, 4H, CH2), 3.78 (t, 4H, CH2,3J= 5.2 Hz), 8.8 (s, very broad, 2H)
ppm. 13C-NMR (125 MHz, CDCl3, 25◦C): δ= 40.0 (CH3), 40.4 (CH3), 45.3 (CH2),
69.4 (CH2), 70.4 (CH2), 162.2 (Cgua) ppm. IR (KBr, ˜ν[cm−1]): 3456m(˜ν(N-H)),
3178m(˜ν(N-H)), 2943w, 2858w, 1620vs (˜ν(C=N)), 1584vs (˜ν(C=N)), 1462m, 1450m,
1404s, 1315w, 1173w, 1135m, 1115m, 1092m, 889w. elemental analysis (after drying in
vacuo), calcd. for C16H38N6O2I2: C 31.99, H 6.38, N 14.00 ; found : C 32.19, H 6.23, N 13.93.
N1,N3-bis(1,1,3,3-tetramethyl-guanidine)-cyclohexane-1,3-diamine, TMG2ch
(L1-3):
N
Me2NNMe2
Me2NNMe2
N
Colourless oil, yield: 95 %. 1H-NMR (500 MHz, CDCl3,
25 ◦C): δ= 1.0-1.6 (m, 8H, CH2from ring), 2.42 (s,
12H, CH3), 2.49 (s, 12H, CH3), 3.44 (m, 2H, CH) ppm.
13C-NMR (125 MHz, CDCl3, 25 ◦C): δ= 20.0 (CH2),
32.6 (CH2), 33.7 (CH2), 39.1 (CH3), 39.6 (CH3), 50.7
(CH), 159.2 (Cgua) ppm. IR (film between NaCl plates,
˜ν[cm−1]): 2993m, 2925m, 2856m, 1618vs(˜ν(C=N)),
1496vs (˜ν(C=N)), 1450s, 1402m, 1363m, 1236m, 1126s, 1056w, 1012w. EI-MS: m/z (%):
310.3 (49) [M+], 267 (11) [M+-NMe2+H], 212 (5), 195 (50), 151 (75), 100 (52), 85 (55), 71
(100), 57 (22). elemental analysis calcd. for C16H34N6: C 61.88, H 11.04, N 27.08 ; found :
C 61.72, H 11.38, N 26.90.
2,2´-Bis[2N-(1,1´,3,3´-tetramethyl-guanidine)]-diphenyleneamine, TMG2PA
(L1-4):
Me2N
NMe2
NN
N
H
NMe2
NMe2
Off-white powder, after recrystallisation colourless
needles, yield: 81 %, m.p. 128◦C. 1H-NMR (500 MHz,
CDCl3, 25 ◦C): δ= 2.68 (s, 24H, CH3), 6.53 (dd, 2H,
3J= 7.72 Hz, 4J= 1.5 Hz), 6.71 (dt, 2H, 3J= 7.60 Hz,
4J= 1.5 Hz), 6.82 (dt, 2H, 3J= 7.70 Hz, 4J= 1.5 Hz),
6.95 (s, 1H, N-H), 7.37 (dd, 2H, 3J= 7.70 Hz, 4J = 1.6
Hz) ppm. 1H-NMR (300 MHz, CD3CN, 25◦C): δ= 2.64
(s, 24H, CH3), 6.44 (dd, 2H, 3J= 7.6 Hz, 4J= 1.3 Hz), 6.67 (dt, 2H, 3J= 7.60 Hz, 4J=
1.3 Hz), 6.77 (dt, 2H, 3J= 7.60 Hz, 4J= 1.3 Hz), 7.24 (s, 1H, N-H), 7.30 (dd, 2H, 3J=
7.60 Hz, 4J= 1.3 Hz) ppm. 13C-NMR (75 MHz, CD3CN, 25◦C): δ= 38.6 (CH3), 112.8,
CHAPTER 8. EXPERIMENTAL SECTION 138
116.9, 119.9, 120.0, 135.5, 140.4, 159.4 (Cgua) ppm. IR (KBr, ˜ν[cm−1]) : 3446vw, 3302w
(˜ν(N-H)), 3062w, 3033w, 2993w, 2941m, 2916m, 2873m, 2841m, 2808w, 2789w, 1597vs (˜ν
(C=N)), 1591vs (˜ν(C=N)), 1570vs (˜ν(C=N)), 1565vs (˜ν(C=N)), 1512vs, 1508vs , 1483s,
1437m, 1419s, 1379vs, 1338m, 1265m, 1230m, 1215m, 1140s, 1111m, 1062w, 1051w, 1034w,
1020s, 922w, 911w, 852w, 777m, 731s, 710w, 654w, 619w, 552w. UV/Vis (CH2Cl2,λmax
[nm] ([M−1cm−1]): 242 (13900), 323 (10100). EI-MS (CH2Cl2, m/z (%)): 350 (100) [M+-
45], 305 (10) [M+- 90], 58 (18). elemental analysis calcd. for C22H33N7: C 66.80, H, 8.41,
N 24.79, found: C 66.45, H 8.74, N 24.40.
N-methyl-2,2´-bis[2N-(1,1´,3,3´-tetramethyl-guanidine)]-diphenylene-amine,
TMG2MePA (L1-5):
Me2N
NMe2
NN
N
Me
NMe2
NMe2
Dark red-violet powder, yield: 76 %, m.p. 95◦C
1H-NMR (300 MHz, CDCl3, 25◦C): δ= 2.58 (s, 24H,
CH3), 3.38 (s, 3H, N-CH3), 6.45 (m, 2H), 6.75 - 6.85
(m, 6H). 13C-NMR (75 MHz, CD3CN, 25◦C): δ= 39.9
(CH3), 68.3 (CH3), 115.6, 117.8, 120.7, 122.8, 130.6,
131.6, 159.2 (Cgua). IR (KBr, ˜ν[cm−1]): 3180vw, 2941w,
2870w, 2793w, 1626vs (˜ν(C=N)), 1552vs (˜ν(C=N)),
1504m, 1473m, 1458m, 1438m, 1414m, 1402m, 1308m, 1254w, 1227w, 1165m, 1127vs,
1065m, 1036m, 906w, 877w, 849w, 762m, 747m, 619m, 503w. UV/Vis (CH2Cl2,λmax [nm]
([M−1cm−1]): 260 (12900), 322 (4300), 517 (450). EI-MS (CH2Cl2, m/z (%)): 409 (100)
[M+], 364 (70) [M+- 45], 319 (52) [M+- 90], 58 (75), 44 (33) [NMe+
2]. elemental analysis
calcd. for C23H35N7: C 67.45, H 8.61, N 21.94, found: C 67.84, H 8.88, N 21.85.
N,N´-bis(1,1,3,3-tetramethyl-guanidine)-m-xylylene-a,a´-diamine, TMG2mX
(L1-6):
N
Me2N
NMe2
Me2N
NMe2
N
Colourless oil, yield: 96 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 2.65 (s, 24H,
CH3), 4.40 (s, 4H, CH2), 7.13 (m, 3H, CH), 7.28 (s, 1H,
CH) ppm. 13C-NMR (125 MHz, CDCl3, 25◦C): δ= 38.7
(CH3), 52.9 (CH2), 124.4 (CH), 125.7 (CH), 127.4 (CH),
143.0 (quart. C), 160.1 (Cgua) ppm. IR (film between
NaCl plates, ˜ν[cm−1]): 2996w, 2925m, 2884m, 2796w,
1554vs (˜ν(C=N)), 1457m, 1423m, 1390s, 1346w, 1238w,
1155m, 1108w, 1062w, 1031w. EI-MS (m/z (%)) = 332.4(42) [M+], 279 (11), 234 (12)
[M+-C(NMe2)2+ 2H], 213 (28), 175 (18), 149 (42), 116 (31), 105 (68) [CH2-Ph-CH+
2+1],
91 (13) [C7H+
7], 85 (82), 72(80), 57 (59). elemental analysis calcd. for C18H32N6: C 65.01,
H 9.71, N 25.29, found: C 64.92, H 10.06, N 25.02.
CHAPTER 8. EXPERIMENTAL SECTION 139
N2,N6-bis(1,1,3,3-tetramethyl-guanidine)pyridine-2,6-diamine, TMG2py (L1-7):
NN
Me2NNMe2
Me2NNMe2
N
Colourless waxy solid, yield: 93 %.
1H-NMR (500 MHz, CDCl3): δ= 2.73 (s, 24H, CH3),
6.30 (d, 2H, 3J= 7.48 Hz), 7.37 (t, 1H, 3J= 7.48 Hz)
ppm. 13C-NMR (125 MHz, CDCl3): δ= 39.9 (CH3),
107.7 (CH), 138.4 (CH), 158.0 (quart. C), 161.4 (C3gua)
ppm. IR (KBr, ˜ν[cm−1]): 3062m, 2993m, 2937s, 2871s,
1604s, 1552vs (˜ν(C=N)), 1539vs (˜ν(C=N)), 1411vs,
1389vs, 1225s, 1213s, 1132vs, 1058m, 1022s, 1003m, 912m, 812s, 739m, 614w, 555w, 514w,
441w. EI-MS (m/z (%)) = 305.3(81) [M+], 290(9) [M+-CH3], 261 (11) [M+-NMe2], 245
(15), 202 (48), 189 (22), 161 (12), 132 (31), 116 (49) [H2N=CN2Me4+], 85 (50), 72(100).
elemental analysis calcd. for C15H27N7: C 58.97, H 8.91, N 32.11, found: C 58.72, H 9.16,
N 32.02.
N1,N3-bis(1,1,3,3-tetraethyl-guanidine)-propane-1,3-diamine, TEG2p (L2-1):
N
Et2N
NEt2
Et2N
NEt2
N
Colourless oil, yield: 97 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.00 (s, 24H,
CH3), 1.78 (m, 2H, CH2), 3.00 (q, 8H, CH2), 3.12 (q,
8H, CH2), 3.14 (t, 4H, CH2) ppm. 13C-NMR (125
MHz, CDCl3, 25◦C): δ= 12.9 (CH3), 13.6 (CH3), 35.9
(CH2), 41.3 (CH2CH3), 42.5 (CH2CH3), 48.7 (CH2),
158.0 (Cgua) ppm. IR (film between NaCl plates, ˜ν[cm−1]): 2966m, 2929m, 2870m,
1610vs (˜ν(C=N)), 1454w, 1400m, 1375m, 1336w, 1300w, 1261s, 1219w, 1134w. EI-MS
(m/z (%)): 382.4(73) [M+], 353(19) [M+-Et]310 (5) [M+-NEt2], 228 (12) [M+-C(NEt2)2],
205(62), 198(57), 142 (51), 113 (100) [CH2N=C(NEt2)+
2], 85 (42), 72(41) [NEt2]. elemen-
tal analysis calcd. for C21H46N6: C 65.90, H 12.12, N 21.97, found: C 65.61, H 12.37, N 22.02.
N1,N3-bis(1,1,3,3-tetraethyl-guanidine)-m-xylylene-a,a´-diamine, TEG2mX
(L2-6):
N
Et2N
NEt2
Et2N
NEt2
N
Colourless oil, yield: 95 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.07 (s, 24H,
CH3), 3.10 (q, 8H, CH2), 3.22 (q, 8H, CH2), 4.36 (s, 4H,
CH2), 7.22 (m, 3H, CH), 7.29 (s, 1H, CH) ppm. 13C-
NMR (125 MHz, CDCl3, 25◦C): δ= 13.4 (CH3), 41.4
(benzyl-CH2), 42.7 (CH2), 124.9 (CH), 126.5 (CH), 127.6
(CH), 143.3 (quart. C), 159.1 (Cgua) ppm. IR (film be-
tween NaCl plates, ˜ν[cm−1]): 2968m, 2929m, 2870m,
1604vs (˜ν(C=N)), 1450m, 1403m, 1375m, 1338w, 1302w, 1261s, 1203w, 1132w, 1068w. EI-
MS (m/z (%)): 444.4(70) [M+], 372 (22) [M+-NEt2], 275 (75) [M+-HN=C(NEt2)2], 172 (39)
[H2N=C(NEt2)+
2], 119(31), 105(75) [CH2-Ph-CH+
2+1], 91 (11) [C7H+
7], 72(100) [NEt2]. ele-
mental analysis calcd. for C26H48N6: C 70.21, H 10.89, N 18.91, found: C 70.06, H 11.20, N
18.74.
CHAPTER 8. EXPERIMENTAL SECTION 140
N2,N6-bis(1,1,3,3-tetraethyl-guanidine)-pyridine-2,6-diamine, TEG2py (L2-7):
NN
Et2NNEt2
Et2NNEt2
N
Colourless oil, yield: 95 %. 1H-NMR (500 MHz,
CDCl3, 25◦C): δ= 1.06 (m, 24 H, CH3), 3.07 (m, 16
H, CH2), 6.22 (d, 2 H, 3J= 7,8 Hz), 7.22 (t, 1 H, 3J
= 7,8 Hz ). 13C-NMR (125 MHz, CDCl3, 25◦C): δ=
12.82 (CH3), 42.66 (CH2), 104.99 (CH), 138.48 (CH),
157.90 (Cquat), 159.37 (Cgua). IR (film between NaCl
plates, ˜ν[cm−1]): 3064vw, 2970s, 2931m, 2871m, 1556vs
(˜ν(C=N)Gua), 1531vs (˜ν(C=N)Gua), 1483m, 1446vs,
1417vs (˜ν(C=N)py), 1377s, 1356 m, 1269vs, 1198m, 1136vs, 1057m. EI-MS (m/z (%)): 417
(8) [M+], 388 (2) [M+- Et], 345 (1) [M+- NEt2], 274 (3) [M+- 2 NEt2+ H], 263 (52) [M+
- C(NEt2)2+ 2 H], 191 (49) [M+- C(NEt2)2- NEt2+ 2 H], 172 (58) [H2N=C(NEt2)+
2],
163 (52) [M+- C(NEt2)2- NEt2- Et + 3 H], 100 (70) [H2N=C(NEt2)+
2- NEt2], 72 (100)
[NEt2], 29 (61) [Et]. elemental analysis calcd. for C23H43N7: C 66.13, H 10.38, N 23.49,
found: C 65.81, H 10.55, N 23.64.
N1,N3-bis(1,1,3,3-tetraisopropyl-guanidine)-propane-1,3-diamine, TiPG2p (L3-
1):
N
N
N
N
N
N
Off-white powder, yield: 81 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.23 (d, 24H,
CH3), 1.46 (d, 24H, CH3), 1.59 (m, 2H, CH2), 3.31 (t,
4H, CH2), 3.40 (m, 4H, CH), 3.82 (m, 4H, CH) ppm.
13C-NMR (125 MHz, CDCl3, 25◦C): δ= 19.2 (CH3),
21.4 (CH3), 31.6 (CH2), 36.7 (CH2), 45.2 (CH), 47.4
(CH), 157.7 (Cgua) ppm. IR (KBr, ˜ν[cm−1]): 2972s,
2845m, 2774m, 2721m, 1699s, 1622vs (˜ν(C=N)), 1525vs,
1473s, 1451m, 1405m, 1309m, 1153m, 765w. EI-MS (m/z (%)): 494.4(0.1) [M+], 459 (1)
[M+-Me], 429 (5), 401 (1), 355(8), 314(13), 281(5), 230(90) [(iPr2N)2C=NH+
2+2H], 215(19),
175(9), 149(11), 114(20) [(iPr2N)2CH+
2], 112(18) [(iPr2N)2C+], 86(100) [iPr-N-CH-CH+
3+H],
56(81) [iPrNH+], 41 (76). elemental analysis calcd. for C29H62N6: C 70.37, H 12.64, N
16.99, found: C 70.16, H 12.90, N 16.95.
N1,N3-bis-(1,3-dimethyl-imidazolidin-2-ylidene)-propane-1,3-diamine, DMEG2p
(L4-1):
NN
N
NN
N
Colourless oil which slowly crystalises, yield: 95 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ=1.57 (m, 2H,
CH2), 2.60 (s, 12H, CH3), 2.95 (b, 8H, CH2), 3.26 (t,
4H, CH2) ppm. 13C-NMR (125 MHz, CDCl3, 25◦C): δ=
32.1 (CH2), 36.3 (CH3), 45.0 (CH2), 49.3 (CH2), 157.3
(Cgua) ppm. IR (film between NaCl plates, ˜ν[cm−1]):
2931s, 2831s, 1660vs (˜ν(C=N)), 1651vs (˜ν(C=N)),
1485s, 1435m, 1422m, 1384m, 1336w, 1263m, 1241w,
CHAPTER 8. EXPERIMENTAL SECTION 141
1113w. EI-MS: m/z (%) 266.3 (39) [M+], 249 (4) [M+-Me], 205 (5), 152 (10), 140 (60)
[CH2CH2N=CN2C4H+
10], 126 (80) [CH2N=CN2C4H+
10], 114 (100) [H2N=CN2C4H+
10], 98 (32),
84 (25), 70 (24). elemental analysis, calcd. for C13H26N6: C 58.61, H 9.84, N 31.55 ; found:
C 58.93, H 9.58, N 31.49.
2-(2-(2-( 1,3-dimethylimidazolidin-2-ylideneamino)ethoxy)ethoxy)-N-( 1,3-
di-methylimidazolidin-2-ylideneamino)-ethanamine, DMEG2doo (L4-2):
NN NN
N O O N
Colourless oil, yield: 98 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 2.77 (s, 6H,
CH3), 2.79 (s, 6H, CH3), 3.15 (s, 8H, CH2), 3.59 (b, 8H,
CH2), 3.66 (s, 4H, CH2). 13C-NMR (125 MHz, CDCl3,
25◦C): δ= 31.5 (CH3), 36.3 (CH3), 47.4 (CH2), 49.4
(CH2), 70.5 (CH2), 73.7 (CH2), 157.9 (Cgua). IR (film
between NaCl plates, ˜ν[cm−1]): 2915w, 2858m, 1666vs (˜ν(C=N)), 1617vs (˜ν(C=N)), 1483m,
1441m, 1383m, 1302w, 1122s(˜ν(C-O-C)), 1023m. EI-MS (m/z, (%)): 340.2 (1) [M+], 325
(1) [M+-Me], 184 (4), 140 (9) [CH2CH2N=CN2Me2C2H+
4], 126 (100) [CH2N=CN2Me2C2H+
4],
112 (8), 85 (3). elemental analysis calcd. for C16H32N6O2: C 56.43, H 9.48, N 24.69, found:
C 56.21, H 9.76, N 24.81.
N1,N3-bis(1,3-dimethylimidazolidin-2-ylidene)cyclohexane-1,3-diamine,
DMEG2ch (L4-3):
NN
N
NN
N
Colourless powder, yield: 93 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.16-1.72 (m,
8H, CH2from ring), 2.71 (s, 12H, CH3), 3.05 (m, 8H,
CH2), 4.05 (m, 2H, CH) ppm. 13C-NMR (125 MHz,
CDCl3, 25◦C): δ= 20.0 (CH2), 25.6 (CH2), 35.7 (CH2),
45.1 (CH2), 49.0 (CH3), 53.2 (CH), 155.8 (Cgua) ppm.
IR (KBr, ˜ν[cm−1]): 2933s, 2852s, 1660vs(˜ν(C=N)),
1637vs (˜ν(C=N)), 1477m, 1442m, 1410m, 1379s, 1259s,
1226s, 1142w, 1119w, 1095w, 1065w, 1032s, 991m, 953s, 908m, 877m, 877m, 850m, 766w,
719m, 669w, 642m, 580m, 538w, 503w. EI-MS (m/z (%)): 306.2 (11) [M+], 263 (19), 193
(100) [M+- N=CN2(C2H4)Me2-H], 152 (35), 114 (32) [H2N=CN2(C2H4)Me+
2], 98 (29), 70
(23), 55 (15). elemental analysis calcd. for C16H30N6: C 62.69, H 9.87, N 27.43, found: C
62.41, H 10.03, N 27.56.
CHAPTER 8. EXPERIMENTAL SECTION 142
N1,N3-bis(1,3-dimethylimidazolidin-2-ylidene)-xylylene-a,a´-diamine,
DMEG2mX (L4-6):
NN
N
NN
N
Colourless oil, yield: 96 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 2.78 (s, 12H,
CH3), 3.18 (t, 8H, CH2), 4.67 (s, 4H, CH2), 7.24
(m, 3H, CH), 7.39 (s, 1H, CH) ppm. 13C-NMR (125
MHz, CDCl3, 25◦C): δ= 31.5 (CH3), 45.06 (CH2),
49.54 (CH2), 50.89 (CH2), 124.4 (CH), 125.4 (CH),
127.7 (CH), 143.2 (Cquat), 157.7 (Cgua) ppm. IR (film
between NaCl plates, ˜ν[cm−1]): 2935m, 2843m, 1655vs
(˜ν(C=N)),1483m, 1437m, 1384m, 1350w, 1269s, 1230w, 1199w, 1065w. EI-MS (m/z
(%)): 328.3(19) [M+], 313.2(8) [M+-Me], 232.2(78), 215(26), 126(56) [CH2N=CMe2C2H+
4],
114(100) [H2N=CMe2C2H+
4], 112(60) [N3C5H+
10], 106(81), 91.1(40) [C7H+
7]. elemental
analysis calcd. for C18H28N6: C 65.81, H 8.60, N 25.60, found: C 65.61, H 8.97, N 25.42.
N2,N6-bis(1,3-dimethylimidazolidin-2-ylidene)pyridine-2,6-diamine, DMEG2py
(L4-7):
NN
N
NN
N
N
Colourless waxy solid, yield: 92 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 2.65 (s, 12H,
CH3), 3.30 (s, 8H, CH2), 6.23 (d, 2H, 3J = 7.7 Hz),
7.23 (t, 1H, 3J = 7.7 Hz) ppm. 13C-NMR (125 MHz,
CDCl3, 25◦C): δ= 34.9 (CH3), 48.2 (CH2), 108.2
(CH), 138.6 (CH), 157.8 (Cquat), 160.9 (Cgua) ppm. IR
(KBr, ˜ν[cm−1]): 3161w, 3064w, 2919m, 2852m, 1616vs
(˜ν(C=N)), 1569s(˜ν(C=N)), 1541vs, 1429s, 1281s,
1236m, 1193w, 1144w, 1038m, 955m, 808m, 702w, 669w, 582w. EI-MS (m/z (%)) = 301.2
(89) [M+], 300 (100) [M+-H], 245 (9), 205 (39) [M+- CN2Me2C2H+
4+2H], 204 (58) [M+-
CN2Me2C2H+
4+H], 189 (9), 132 (7), 114 (11), 98 (8) [N=CN2Me2C2H+
4], 70 (29). elemental
analysis calcd. for C15H23N7: C 59.76, H 7.70, N 32.54, found: C 59.49, H 7.91, N 32.60.
N1,N3-bis(tetrahydro-1,3-dimethylpyrimidin-2(1H)-ylidene)-propane-1,3-
diamine, DMPG2p (L5-1):
N
N
N
N
N
N
Colourless oil which slowly crystallises, yield: 94 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.50 (m, 2H,
CH2), 1.68 (m, 4H, CH2), 2.70 (s, 12H, CH3), 2.95
(m, 8H, CH2), 3.02 (t, 4H, CH2); 13C-NMR (125 MHz,
CDCl3, 25◦C): δ= 20.9 (CH2), 32.3 (Ca), 39.3 (CH3),
45.8 (Cb), 48.4 (CH2), 157.5 (Cgua) IR (KBr, ˜ν[cm−1]):
2921s, 2858s, 1621vs (˜ν(C=N)), 1576s(˜ν(C=N)), 1541s,
1458m, 1419m, 1375m, 1321m, 1271w, 1236w, 1113w,
1047w, 1016w, 708w, 669w, 607w, 557w, 522w. CI-MS: m/z 294.25 (M+). elemental analysis
calcd. for C15H30N6: C 61.17, H 10.28, N 28.55, found: C 61.53, H 10.01, N 28.42.
CHAPTER 8. EXPERIMENTAL SECTION 143
2-(2-(2-(tetrahydro-1,3-dimethylpyrimidin-2(1H)-ylideneamino)ethoxy)ethoxy)-
N-(tetrahydro-1,3-dimethylpyrimidin-2(1H)-ylideneamino)-ethanamine,
DMPG2doo (L5-2):
O O
NN
N
NN
N
Colourless oil, yield: 93 %.
1H-NMR (300 MHz, CDCl3, 25◦C): δ= 1.58 (m, 4H,
CH2), 1.88 (m, 8H, CH2), 2.85 (s, 12H, CH3), 3.20 (t,
4H, CH2), 3.54 (b, 8H, CH2). 13C-NMR (125 MHz,
CDCl3, 25◦C): δ= 21.6 (CH2), 38.4 (CH3), 39.1 (CH3),
48.1 (CH2), 49.6 (CH2), 70.5 (CH2), 73.9 (CH2), 160.1
(Cgua). IR (film between NaCl plates, ˜ν[cm−1]): 2925w, 2865m, 1635vs (˜ν(C=N)), 1620vs
(˜ν(C=N)), 1558m, 1541s, 1458m, 1386m, 1309w, 1261m, 1101s(˜ν(C-O-C)), 1045m, 850w,
742w, 627s. EI-MS (m/z, (%)): 368.4 (1) [M+], 266 (21), 205 (8), 152 (9), 173 (8) [M+-
NMe2, NC(NMe2)2], 141 (65) [M+- (NMe2)2CN(CH2)2O], 128 (100) [H2N=CN2Me2C3H+
6],
98 (34), 70 (48). elemental analysis calcd. for C18H36N6O2: C 58.65, H 9.85, N 22.81, found:
C 58.42, H 10.16, N 22.73.
N-methyl-2,2´-bis[tetrahydro-1,3-dimethylpyrimidin-2(1H)-ylidene]-di-
phenyleneamine, DMPG2MePA (L5-5):
NN
N
Me
N
N
N
N
Dark red-violet oil, yield: 68 %.
1H-NMR (300 MHz, CDCl3, 25◦C): δ= 1.65 (m, 4H,
CH2) ppm, 1.9 (m, 8H, CH3), 2.9 (s, 15H, CH3), 6.7
(m, 4H, CH), 6.95 (m, 4H, CH). 13C-NMR (125 MHz,
CD3CN, 25◦C): δ= 21.1 (CH2), 38.0 (CH3), 48.6 (CH2),
69.1 (N-CH3), 115.2, 117.6, 122.1, 124.6, 136.5 (Cquat),
142.1(Cquat), 153.3 (Cgua) ppm. IR (KBr, ˜ν[cm−1]):
3065w, 3025w, 2940m, 2869m, 2345w, 1621vs
(˜ν(C=N)), 1563vs (˜ν(C=N)), 1546vs (˜ν(C=N)), 1452s, 1417s, 1317s, 1120m, 1052m, 746s.
EI-MS (CH2Cl2, m/z (%)): 433.6 (1) [M+], 419 (2) [M+- 14], 323 (5), 285 (3), 252 (100),
213 (98), 181 (33), 128 (30) [H2N=CN2Me2C3H+
6], 112 (29), 69 (48), 58 (69). elemental
analysis calcd. for C25H35N7: C 69.24, H 8.14, N 22.62, found: C 69.02, H 8.49, N 22.49.
N1,N3-bis(tetrahydro-1,3-dimethylpyrimidin-2(1H)-ylidene)- xylylene-a,a´-
diamine, DMPG2mX (L5-6):
NN
N
NN
N
Colourless oil, yield: 95 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.83 (q, 4H,
CH2), 2.86 (s, 12H, CH3), 3.07 (t, 8H, CH2), 4.36 (s,
4H, CH2), 7.21 (m, 3H, CH), 7.33 (s, 1H, CH) ppm.
13C-NMR (125 MHz, CDCl3, 25◦C): δ= 20.5 (CH2),
39.0 (CH3), 48.3 (CH2), 51.57 (CH2), 124.9 (CH), 126.5
(CH), 127.9 (CH), 142.6 (Cquat), 157.6 (Cgua) ppm. IR
(film between NaCl plates, ˜ν[cm−1]): 2635m, 2843m,
1655vs (˜ν(C=N)), 1483m, 1437m, 1402w, 1385m, 1350w, 1269s, 1231w, 1199w, 1065w.
CHAPTER 8. EXPERIMENTAL SECTION 144
EI-MS: m/z (%) = 356.3 20) [M+], 229(15), 178 (5), 149 (7), 128(100) [H2N=CN2Me2C3H+
6],
99 (22), 57 (23). elemental analysis calcd. for C20H32N6: C 67.36, H 9.05, N 23.58, found:
C 67.12, H 9.41, N 23.47.
N2,N6-bis(tetrahydro-1,3-dimethylpyrimidin-2(1H)-ylidene)pyridine-2,6-di-
amine, DMPG2py (L5-7):
N
N N
N
N N
N
Colourless waxy solid, yield: 94 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.90 (m, 4H,
CH2), 2.78 (s, 6H, CH3), 2.84 (s, 6H, CH3), 3.17 (m,
8H, CH2), 5.74 (d, 1H, 3J= 7.7 Hz), 5.89 (d, 1H, 3J
= 7.7 Hz), 7.10 (t, 1H, 3J= 7.7 Hz) ppm. 13C-NMR
(125 MHz, CDCl3, 25◦C): δ= 22.2 (CH2), 35.6 (CH3),
39.2 (CH3), 47.8 (CH2), 104.7 (CH), 138.5 (CH), 157.8
(Cquat), 161.9 (Cgua) ppm. IR (KBr, ˜ν[cm−1]): 3010w,
2902w, 2856w, 1624vs (˜ν(C=N)), 1529vs, 1448s, 1413s,
1317s, 1252m, 1221m, 1157w, 1109w, 1059m, 802w, 756w, 709w, 474w. EI-MS (m/z (%))
= 329.2 (62) [M+], 314 (4) [M+-Me], 245 (33), 219 (100) [M+- CN2Me2C3H+
6+2H], 218
(48) [M+- CN2Me2C3H+
6+H], 191 (9), 148 (28), 112 (25) [N2Me2C3H+
6], 109 (19), 70 (11).
elemental analysis calcd. for C17H27N7: C 61.96, H 8.27, N 29.77, found: C 61.65, H 8.42,
N 29.93.
N1,N3-bis(tetrahydro-1,3-dipropylpyrimidin-2(1H)-ylidene)propane-1,3-di-
amine, DPPG2p (L6-1):
N
N
N
Pr
Pr
N
N
NPr
Pr
Yellowish oil, yield: 89 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 0.83 (t, 12H,
CH3), 1.44 (q, 2H, CH2), 1.56 (m, 8H, CH2), 1.91 (m, 4H,
CH2), 3.19 (m, 20H, CH2) ppm. 13C-NMR (125 MHz,
CDCl3, 25◦C): δ= 11.6 (CH3), 21.3 (CH2), 22.7 (CH2),
46.1 (CH2), 49.9 (CH2), 53.7 (CH2), 158.0 (Cgua) ppm.
IR (film between NaCl plates, ˜ν[cm−1]): 2960s, 2931m,
2871m, 1633vs (˜ν(C=N)), 1604vs (˜ν(C=N)), 1500m,
1456m, 1363m, 1325w, 1296m, 1263w, 1207s, 1099m.
EI-MS (m/z (%)): 406.4 (9) [M+], 391 (1) [M+-Me], 363 (1) [M+-Pr], 240 (10), 211 (15), 184
(28) [H2N=CN2Pr2C3H+
6], 155 (100), 113 (38), 70 (32), 98 (29), 70 (23), 55 (15). elemen-
tal analysis calcd. for C23H46N6: C 67.92, H 11.41, N 20.67, found: C 67.61, H 11.67, N 20.72.
CHAPTER 8. EXPERIMENTAL SECTION 145
N1,N3-bis(piperidin-1-yl)methylene)propane-1,3-diamine, DPipG2p (L7-1):
N
N
N
N
N
N
Colourless crystals, yield: 84 %. 1H-NMR (500 MHz,
CDCl3,δ= 1.48-1.61 (m, 24H, Pip-CH2), 1.80 (q,
2H, CH2), 3.02 (t, 16H, Pip-CH2), 3.18 (t, 4H, CH2).
13C-NMR (125 MHz, CDCl3, 25◦C): δ= 24.8 (Pip),
25.9 (Pip), 34.5 (Ca), 46.7 (Cb), 49.1 (Pip), 160.0
(Cquart.). IR (KBr, ˜ν[cm−1]): 2978m, 2962m, 2927vs,
2877m, 2846m, 2835m, 2808m, 1626vs (˜ν(C=N)), 1608s
(˜ν(C=N)), 1442m, 1398s, 1367s, 1346m, 1327m, 1246s,
1209s, 1199m, 1168w, 1159w, 1134m, 1124m, 1089w, 1032m, 1012w, 981w, 956m, 926w,
910m, 879m, 850m, 725w, 636vw. EI-MS: m/z (%) 430 (42) [M+], 346 (10) [M+-Pip], 237
(13), 222 (81), 196 (12), 154 (41), 126 (43), 85 (51) [HPip+], 84 (100) [Pip+], 69 (22). elemen-
tal analysis calcd. for C25H46N6: C 69.71, H 10.77, N 19.52, found: C 69.47, H 10.95, N 19.52.
N1,N3-bis(bis(2,6-dimethylpiperidin-1-yl)methylene)propane-1,3-diamine,
B(DMPip)G2p (L8-1):
N
N
N
N
N
N
Yellowish oil, yield: 76 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.01 (d, 24H,
CH3), 1.53 (m, 16H, CH2), 1.61 (m, 2H, CH2), 1.68
(m, 8H, CH2), 2.58 (m, 8H, CH), 2.70 (t, 4H, CH2)
ppm. 13C-NMR (125 MHz, CDCl3, 25◦C): δ= 21.5
(CH2), 23.0 (CH3), 24.9 (CH2-Pip), 33.9 (CH2-Pip), 39.8
(CH2), 52.4 (CH), 157.0 (Cgua) ppm. IR (film between
NaCl plates, ˜ν[cm−1]): 2958s, 2931s, 2871m, 1693vs
(˜ν(C=N)), 1651vs (˜ν(C=N)), 1643vs (˜ν(C=N)), 1537s, 1479m, 1415m, 1373w, 1311m,
1275w, 1236w, 1159m. EI-MS (m/z (%)): 542 (0.01) [M+], 430 (1) [M+-Me2Pip], 292 (13)
[M+-N=C(Me2Pip)2], 279 (14) [M+-CH2N=C(Me2Pip)2+H], 237 (9) [(Me2Pip)2CH+], 183
(22), 149 (48), 112 (43) [Me2Pip+], 98 (100) [CH3CH(CH2)3CHCH3], 56 (39). elemen-
tal analysis calcd. for C33H62N6: C 72.99, H 11.52, N 15.49, found: C 72.64, H 11.75, N 15.61.
N1,N3-bis(bis(2,2,6,6-tetramethylpiperidin-1-yl)methylene)propane-1,3-di-
amine, B(TMPip)G2p (L9-1):
N
N
N
N
N
N
Yellow oil, yield: 72 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.05 (s, 48H,
CH3), 1.18 (m, 2H, CH2), 1.50 (m, 8H, CH2), 3.17 (t,
16H, CH2), 3.29 (t, 4H, CH2) ppm. 13C-NMR (125 MHz,
CDCl3, 25◦C): δ= 13.2 (CH3), 13.9 (CH3), 16.3 (CH2),
35.0 (CH2), 40.4 (CH2), 41.1 (CH2), 42.2 (CH2), 56.7
(Cquat), 156.4 (Cgua) ppm. IR (film between NaCl plates,
˜ν[cm−1]): 2970s, 2935m, 2733w, 1645vs (˜ν(C=N)),
1531vs, 1454m, 1379s, 1351m, 1271s, 1223m, 1182w. EI-MS (m/z (%)): 654 (0.01) [M+],
408 (2), 340 (4), 308 (8) [(Me4Pip)2C=NH+
2], 268 (6), 240 (13), 184(21), 157 (28), 140 (11)
CHAPTER 8. EXPERIMENTAL SECTION 146
[Me4Pip], 126 (35) [Me4Pip-N], 109 (58), 84 (22) [(Me2C(CH2)3], 69 (37) [MeC(CH2)3], 58
(100). elemental analysis calcd. for C41H78N6: C 75.16, H 12.01, N 12.83, found: C 74.91,
H 12.37, N 12.72.
N1,N3-bis(di(imidazol-1-yl)methylene)propane-1,3-diamine, DImG2p (L10-1):
N
N
N
N
NN
N
NN
N
Yellow powder, yield: 58 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.92 (m, 2H,
CH2), 3.3 (m, 4H, =N-CH2-), 7.12 (s, 8H, =N-CH=CH-
N-), 7.71 (s, 4H, -N-CH=N-) ppm. 13C-NMR (125
MHz, CDCl3, 25◦C): δ= 21.3 (CH2), 40.0 (CH2), 121.9
(CH=CH), 135.1 (CH), 155.2 (Cgua) ppm. IR (KBr, ˜ν
[cm−1]): 3122m, 3035m, 2935m, 2843m, 2698m, 2607m,
1791m, 1689s, 1652vs, 1533vs, 1482s, 1442vs, 1373m,
1324s, 1257s, 1222w, 1197w, 1141m, 1095s, 1064s, 1035m. EI-MS (m/z (%)): 362,3(0,1)
[M+], 212(10), 179(21), 151 (22), 123(35), 116(24), 68(100) [C3H4N+
2]. elemental analysis
calcd. for C17H18N10: C 56.33, H 5.01, N 38.66, found: C 56.43, H 5.16, N 38.41.
N1,N3-bis(dimorpholinomethylene)propane-1,3-diamine, DMorphG2p (L11-1):
N
N
O
N
O
N
N
O
NO
White powder, after recrystallisation colourless needles,
yield: 71 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.75 (q, 2
H, CH2), 3.02-3.38 (broad, 18 H, CH2), 3.64-6.76
(m, 14 H, CH2) ppm. 13C-NMR (125 MHz, CDCl3,
25◦C): δ= 25.58, 44.0, 47.2, 48.5, 157.3 (Cgua) ppm.
IR (KBr, ˜ν[cm−1]): 2967m, 2898m, 2844m, 1633vs
(˜ν(C=N)), 1600vs (˜ν(C=N)), 1436s, 1386m, 1357m,
1268vs, 1228m, 1114vs (˜ν(C-O)), 1027m, 883s, 601m. EI-MS (m/z (%)): 438.3(6) [M+],
408 (11) [M+-CH2O], 393 (12) [M+-CH3CH2O], 363 (21) [M+-2(CH2O)-(CH3CH2O)],
283 (13) [M+-C3H6NC(Morph)], 254 (6) [M+-C6H6NC(Morph)-(CH2O), 226 (14) [M+-
CH2NC(Morph)2], 196 (42) [M+-C3H6NC(Morph)2], 171 (17) [M+-CNC3H6NC(Morph)2],
127 (61) [M+-CNC3H6NC(Morph)2-C3H6], 86 (37) [Morph]. elemental analysis calcd. for
C21H38N6O4: C 57.50, H 8.74, N 19.17, found: C 57.31, H 8.97, N 18.87.
2-(2-(2-(dimorpholinomethyleneamino)ethoxy)ethoxy)-N-(dimorpholino-
methylene)ethanamine, DMorphG2doo (L11-2):
O O
N
N
O
N
O
N
N
O
N
O
White powder, after recrystallisation colourless needles,
yield: 65 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 3.1-3.3 (broad,
16 H, Morph-CH2), 3.41 (t, 4 H, CH2), 3.61 (t, 4 H,
CH2), 3.66 (s, 4H, CH2), 3.69 (m, 16 H, Morph-CH2)
ppm. 13C-NMR (125 MHz, CDCl3, 25◦C): δ= 47.2
(Morph-CH2), 48.3, 66.8 (Morph-CH2), 67.1, 70.5, 163.8 (Cgua) ppm. IR (KBr, ˜ν[cm−1]):
CHAPTER 8. EXPERIMENTAL SECTION 147
2972m, 2893s, 2856s, 1647m(˜ν(C=N)), 1621vs (˜ν(C=N)), 1458m, 1413s, 1390s, 1360m,
1300m, 1265vs, 1228m, 1115vs (˜ν(C-O)), 1070m, 1032s, 991w, 966w, 881s, 833w, 611w.
EI-MS (m/z (%)): 512.6(0.1) [M+], 426 (4) [M+-Morph], 314 (5) [M+-NC(Morph)2],
270 (19) [M+-NC(Morph)2-(CH2)2O)], 226 (18) [M+- NC(Morph)2-2(CH2)2O)], 200 (22)
[(Morph)2CNH−2+], 169 (52), 127 (100), 114 (69), 86 (37)[Morph], 70 (69) [Morph-O].
elemental analysis calcd. for C24H44N6O6: C 56.21, H 8.66, N 16.40, found: C 56.10, H
8.87, N 16.64.
N1,N3-bis(dithiomorpholinomethylene)propane-1,3-diamine, DSMorphG2p
(L12-1):
N
N
S
N
S
N
N
S
NS
Yellowish powder, yield: 66 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.25 (q, 2H,
CH2), 2.65 (m, 16, CH2), 3.2 (m, 16H, CH2), 3.4 (t, 4H,
CH2) ppm. 13C-NMR (125 MHz, CDCl3, 25◦C): δ=
13.5 (CH2), 27.0 (SMorph-CH2), 42.3 (SMorph-CH2),
46.6 (CH2), 158.0 (Cgua) ppm. IR (KBr, ˜ν[cm−1]):
2969m, 2911m, 1733m, 1621vs (˜ν(C=N)), 1533s, 1405s,
1374m, 1292m, 1251m, 1205m, 1170m. EI-MS (m/z
(%)): 502.1(23) [M+], 487(76), 469 (98) [M+-S], 443(45) [M+-SEt], 400(33) [M+-SMorph],
384 (34), 298 (9) [M+-2SMorph], 196 (23) [M+-3SMorph], 143 (100) [HN=C-SMorph+],
102(44) [SMorph+], 87 (38), 69 (30). elemental analysis calcd. for C21H38N6S4: C 50.18, H
7.63, N 16.73, found: C 50.02, H 7.41, N 16.45.
bis(N1, N1-(morpholino)-N3, N3-dimethyl-methylene)propane-1,3-diamine,
(Morph)DMG2p (L13-1):
N
N
N
O
N
N
O
N
Yellowish oil, yield: 78 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.77 (q, 2
H, CH2), 2.57 (s, 12H, CH3), 2.78-2.98 (broad,18 H,
CH2), 3.06-3.37 (m, 14 H, CH2) ppm. 13C-NMR (125
MHz, CDCl3, 25◦C): δ= 36.1 (CH2), 39.1 (CH3), 47.1
(Morph-CH2), 48.7, 49.6, 159.3 (Cgua) ppm. IR (film
between NaCl plates, ˜ν[cm−1]): 2975m, 2891m, 2852m,
1633s(˜ν(C=N)), 1623vs (˜ν(C=N)), 1457m, 1423s,
1397s, 1355m, 1304m, 1255s, 1225m, 1112vs (˜ν(C-O)),
1075m, 1037s, 969w, 866m, 754w, 619w. EI-MS (m/z
(%)): 354.3 (25) [M+], 309 (9)[M+-NMe2], 279 (12), 241 (33), 198 (12), 184 (69), 154 (23),
127 (48), 86 (100) [Morph+], 72 (84). elemental analysis calcd. for C17H34N6O2: C 57.58, H
9.67, N 23.72, found: C 57.78, H 10.02, N 23.39.
CHAPTER 8. EXPERIMENTAL SECTION 148
bis(N1, N1-(2,6-dimethylpiperidin-1-yl)-N3, N3-dimethyl-methylene)propane-
1,3-diamine, (DMPip)DMG2p (L14-1):
N
N
N
N
N
N
Yellowish oil, yield: 71 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.03-1.54
(m, 14H, CH2), 2.79 (s, 12H, CH3), 2.91 (d, 12H,
Pip-CH3), 3.18-3.49 (m, 8H, CH2) ppm. 13C-NMR (125
MHz, CDCl3, 25◦C): δ= 20.4 (CH2), 23.0 (CH2), 30.3
(Pip-CH3), 31.2 (Pip-CH3), 36.2 (CH2-Pip), 36.4 (CH3),
38.5 (CH2), 53.8 (CH), 159.1 (Cgua) ppm. IR (film
between NaCl plates, ˜ν[cm−1]): 2953s, 2935s, 2873m,
1683s(˜ν(C=N)), 1655vs (˜ν(C=N)), 1647vs (˜ν(C=N)),
1526m, 1475m, 1418m, 1372w, 1314m, 1272m, 1231w,
1153m. EI-MS (m/z (%)): 406.3 (0.01) [M+], 362 (0.5) [M+-NMe2], 294 (1) [M+-Me2Pip],
237 (33) [(Me2Pip)2CH+], 183 (45), 149 (51), 124 (100), 112 (43) [Me2Pip+], 98 (71)
[CH3CH(CH2)3CHCH3], 56 (68). elemental analysis calcd. for C23H46N6: C 67.92, H 11.41,
N 20.67, found: C 67.71, H 11.75, N 20.34.
N1,N3-bis(tetrahydro-1,3-bis(heptafluoropropyl)pyrimidin-2(1H)-
ylidene)propane-1,3-diamine, BFPPG2p:
C3F7N
NC3F7
N N
C3F7N
NC3F7
In a Schlenk flask fitted with a condensor cooled to
-40◦C, phosgene was passed through the etheric solution
of N,N,N´,N´-Bis(heptafluoropropyl)propyleneurea
(0.05 mmol) at 0◦C for 15 min. After 15 min, the
reaction mixture was allowed to come to room temper-
ature. The reaction with 1,3-diaminopropane had to be
carried out immediately due to the thermal instability
of the intermediately formed Vilsmeier salt. The general
procedure described above was changed regarding time and temperature of reaction: room
temperature and 36 h. The product was obtained as yellow oil, yield: 8 %.
1H-NMR (500 MHz, CDCl3, 25◦C): δ= 1.66 (m, 4H, CH2), 1.81 (m, 2H, CH2), 3.15 (m,
4H, CH2), 3.36 (m, 8H, CH2) ppm. 13C-NMR (125 MHz, CDCl3, 25◦C): δ= 21.5 (CH2),
22.6 (CH2), 30.5 (CH2), 40.8 (CH2), 157.1 (Cgua) ppm. IR (film between NaCl plates, ˜ν
[cm−1]): 2944s, 2864m, 1577vs (˜ν(C=N)), 1525m, 1328m, 1130m, 1064m, 956w, 833w.
8.3.4 Synthesis of copper(I)bisguanidine complexes
General synthesis of bisguanidine copper(I) complexes:
1 mmol of a copper(I) salt was added to a stirred solution of the ligand (1.05 mmol) in
MeCN (15 mL). After 30 min of stirring, diethylether (20 mL) was added to obtain the
colourless product.
CHAPTER 8. EXPERIMENTAL SECTION 149
[Cu(TMG2PA*)I](C1):
N
N N
NMe2
Me2N
Me2N
NMe2
Cu2+
I-
To a suspension of CuI (190 mg, 1 mmol) in 10 mL
of THF a solution of TMG2PA (435 mg, 1.1 mmol) in
10 mL of THF was added dropwise. After 30 min of
stirring, the red suspension turned dark green. After
evaporation of the solvent under reduced pressure, 15
mL of MeCN were added. Dark green crystals suitable
for X-ray diffraction were obtained by slow diffusion of
diethylether, yield: 77 % (450 mg).
m.p. 189◦C. IR (KBr, ˜ν[cm−1]): 3045w(˜ν(CHarom)), 2925m (˜ν(CHaliph)), 2881w, 2792w,
1612m(˜ν(C=N)), 1570s(˜ν(C=N)), 1557vs (˜ν(C=N)), 1518vs (˜ν(C=N)), 1475vs, 1466vs,
1439m, 1417s, 1396vs, 1352m, 1329m, 1284m, 1263m, 1230w, 1211m, 1180w, 1159m, 1142m,
1109w, 1061w, 1034m, 920w, 911w, 862w, 843w, 804w, 739m, 733m, 559w. UV/Vis (CH2Cl2,
λmax [nm] ([M−1cm−1]): 290 (14000), 345 (10500), 645 (1700). EI-MS (CH2Cl2, m/z (rel.
intensity)): 584 (5) [M+], 457 (5) [M+- I], 395 (6) [M+- CuI], 350 (100) [M+- CuI -NMe+
2],
306 (42) [M+- CuI -2 NMe+
2], 263 (38), 234 (51), 205 (44), 161 (82), 118 (22), 85 (57), 58
(37) [CH2NMe+
2], 44 (70) [NMe+
2]. elemental analysis calcd. for C22H32N7CuI: C 45.17, H
5.51, N 16.76, found: C 45.65, H 5.24, N 16.17.
[Cu(DMorphG2p)I](C2):
N
N
O
N
O
N
N
O
N
O
Cu
I
To a suspension of CuI (190 mg, 1 mmol) in 10 mL of
THF a solution of DMorphG2p (481 mg, 1.1 mmol) in
10 mL of THF was added dropwise. After 30 min of
stirring, diethylether (20 mL) was added to obtain the
colourless product, yield: 90 % (565 mg). Crystals suit-
able for X-ray diffraction were grown by slow diffusion
of diethylether into MeCN.
IR (KBr, ˜ν[cm−1]): 2964m(˜ν(CHaliph)), 2902m, 2852w, 1560vs (˜ν(C=N)), 1427s, 1382m,
1357m, 1330s, 1263m, 1236m, 1114s(˜ν(C-O)), 1066s, 1031w, 887w. elemental analysis
calcd. for C21H38N6O4CuI: C 40.12, H 6.10, N 13.38, found: C 40.35, H 6.44, N 12.97.
[Cu2(btmgp)2][PF6]2(C3):
Cu
N
N
N
Cu
N
NMe2
NMe2
NMe2
NMe2
Me2N
Me2N
NMe2
NMe2
2+
2 PF6-
[Cu(MeCN)4][PF6] (372 mg, 1 mmol) was added to a
stirred solution of btmgp (284mg, 1.05 mmol) in MeCN
(15 mL). After 30 min of stirring, diethylether (20 mL)
was added to obtain the colourless product, yield: 90
% (430 mg). Crystals suitable for X-ray diffraction were
grown by slow diffusion of diethylether into MeCN.
1H-NMR (300 MHz, CDCl3, 25 ◦C): δ= 2.28 (m, 2H,
Hb), 2.89 (s, 12H, CH3), 2.91 (s, 12H, CH3), 3.32 (m,
4H, Ha) ppm. IR (KBr, ˜ν[cm−1]): 3435w, 2953m(˜ν(CHaliph)), 2931m(˜ν(CHaliph)), 2881m,
2853w, 1564s(˜ν(C=N)), 1558s(˜ν(C=N)), 1539s(˜ν(C=N)), 1477m, 1464m, 1456m, 1427m,
CHAPTER 8. EXPERIMENTAL SECTION 150
1416m, 1408m, 1398s(˜ν(C=N)), 1362m(˜ν(C=N)), 1337vw, 1240w, 1169m(˜ν(C=N)),
1161w, 1123w, 1070m(˜ν(C=N)), 1024w, 1011w, 899w, 876m, 839vs (˜ν(P-F)), 779w, 557m.
UV/Vis (CH2Cl2,λmax [nm] ([M−1cm−1]): no bands, shoulder at 360 (233). elemental
analysis, calcd. for C26H60N12Cu2P2F12 : C 32.60, H 6.31, N 17.55 ; found : C 32.66, H
6.39, N 17.52.
[Cu2(TMG2ch)2][I]2(C4):
NC
Me2N
Me2NN C NMe2
NMe2
N C NMe2
NMe2
NC
Me2N
Me2N
Cu Cu
2+
2 I-
CuI (190 mg, 1 mmol) was added to a stirred solution of
TMG2ch (326 mg, 1.05 mmol) in MeCN (15 mL). After
30 min of stirring, diethylether (20 mL) was added to
obtain the colourless product, yield: 45 % (225 mg).
Crystals suitable for X-ray diffraction were grown by
slow diffusion of diethylether into MeCN.
IR (KBr, ˜ν[cm−1]): 2929m(˜ν(CHaliph)), 1616vs
(˜ν(C=N)), 1572vs (˜ν(C=N)), 1560vs (˜ν(C=N)), 1458m,
1403 m, 1232m, 1171w, 1142m, 1036m, 899w, 808w, 545w. elemental analysis calcd. for
C32H68N12Cu2I2: C 38.36, H 6.84, N 16.78, found: C 38.02, H 7.21, N 16.47.
[Cu2(DMEG2p)2][PF6]2(C5):.
N
N
N
Cu
N
2+
2 PF6-
N
N
N
NN
N
N
N
Cu
[Cu(MeCN)4][PF6] (372 mg, 1 mmol) was added to a
stirred solution of DMEG2p (279 mg, 1.05 mmol) in
MeCN (15 mL). After 30 min of stirring, diethylether (20
mL) was added to obtain the colourless product, yield:
82 % (389 mg). Crystals suitable for X-ray diffraction
were grown by slow diffusion of diisopropylether into
MeCN.
1H-NMR (500 MHz, CD3CN, 25 ◦C): δ= 1.82 (m, 2H,
CH2), 3.00 (s, 12H, CH3), 3.46 (b, 8H, CH2), 3.65 (t,
4H, CH2) ppm. 13C-NMR (125 MHz, CD3CN, 25 ◦C): δ= 35.0 (Ca), 35.6 (CH3), 45.2
(Cb), 49.2 (CH2), 162.4 (Cgua) ppm. IR (˜ν[cm−1]): 2929s, 2894s, 1631s(˜ν(C=N)), 1601vs
(˜ν(C=N)), 1512m(˜ν(C=N)), 1490m, 1459m, 1419m, 1400m, 1345w, 1300s, 1232w, 1208w,
1121w, 1076w, 1034w, 970vw, 839vs (˜ν(P-F)), 723w, 646w, 557vs, 484w. elemental analysis
(after drying in vacuo), calcd. for C26H52N12Cu2P2F12 : C 32.88, H 5.52, N 17.70 ; found :
C 33.19, H 5.28, N 17.93.
CHAPTER 8. EXPERIMENTAL SECTION 151
[Cu2(DMEG2ch)2][Cu2I4] (C6) and [Cu2(DMEG2ch)2][Cu4I6] (C7):
NN
N
N
Cu Cu
Y2-
Y2- = Cu2I42- (C6),
Cu4I62- (C7)
N
N
N
N
N
N
N
N
2+
CuI (190 mg, 1 mmol) was added to a stirred solution
of DMEG2ch (321 mg, 1.05 mmol) in MeCN (15 mL).
After 30 min of stirring, diethylether (20 mL) was added
slowly. The next day, colourless crystals of C6 and
yellow crystals of C7 were grown. In a repetition of
this experiment, only colourless crystals of C6 were
obtained, yield: 42 % (208 mg).
IR (KBr, ˜ν[cm−1]): 2931m(˜ν(CHaliph)), 1623vs
(˜ν(C=N)), 1583vs (˜ν(C=N)), 1560vs (˜ν(C=N)), 1508m,
1457 m, 1419m, 1374m, 1295m, 1122w, 1035m, 964w,
879w, 806w, 528w. elemental analysis calcd. for C32H60N12Cu4I4(C6): C 27.96, H 4.40, N
12.23, found: C 28.61, H 4.44, N 12.36.
[Cu2(DMPG2p)2][PF6]2(C8):
N
N
N
Cu
N
2+
2 PF6-
N
N
N
N
N
N
N
N
Cu
[Cu(MeCN)4][PF6] (372 mg, 1 mmol) was added to a
stirred solution of DMPG2p (308.7 mg, 1.05 mmol) in
MeCN (15 mL). After 30 min of stirring, diethylether (20
mL) was added to obtain the colourless product, yield:
86 % (433 mg). Crystals suitable for X-ray diffraction
were grown by slow diffusion of diisopropylether into
MeCN.
1H-NMR (500 MHz, CD3CN, 25 ◦C): δ= 1.62 (m, 2H,
CH2), 1.71 (m, 4H, CH2), 2.95 (s, 12H, CH3), 3.15 (m, 8H, CH2) ppm. 13C-NMR (125
MHz, CD3CN, 25 ◦C): δ= 22.3 (CH2), 34.8 (Ca), 40.1 (CH3), 46.3 (Cb), 49.7 (CH2), 160.6
(Cgua) ppm. IR (KBr, ˜ν[cm−1]): 2953s, 2919s, 2864s, 2831m, 1564vs (˜ν(C=N)), 1552vs
(˜ν(C=N)), 1537vs (˜ν(C=N)), 1473s, 1453s, 1419s, 1403vs (˜ν(C=N)), 1376s, 1354s, 1325s,
1313s, 1272w, 1236s, 1206w, 1162w, 1113w, 1084m, 1050m, 1014m, 837vs (˜ν(P-F)), 769s,
557s, 511m. elemental analysis, calcd. for C30H60N12Cu2P2F12: C 35.82, H 6.01, N 16.71 ;
found : C 35.64, H 6.07, N 16.58.
[Cu2(DPipG2p)2][PF6]2(C9):.
N
N
N
Cu
N
2+
2 PF6-
Cu
N
N
NN
N
N
N N
[Cu(MeCN)4][PF6] (372 mg, 1 mmol) was added to a
stirred solution of DPipG2p (452 mg, 1.05 mmol) in
MeCN (15 mL). After 30 min of stirring, diethylether (20
mL) was added to obtain the colourless product, yield:
82 % (524 mg). Crystals suitable for X-ray diffraction
were grown by slow diffusion of diisopropylether into
MeCN.
1H-NMR (500 MHz, CD3CN, 25 ◦C): δ= 1.48-1.58
(m, 24H, Pip-CH2), 1.71 (q, 2H, CH2), 3.05 (t, 16H,
Pip-CH2), 3.55 (t, 4H, CH2) ppm. 13C-NMR (125 MHz, CD3CN, 25 ◦C): δ= 24.0 (Pip),
CHAPTER 8. EXPERIMENTAL SECTION 152
25.2 (Pip), 25.6 (Pip) 33.8 (Ca), 47.6 (Cb), 49.3 (Pip), 160.2 (Cgua) ppm; IR (KBr, ˜ν
[cm−1]): 2934m(˜ν(CHaliph)), 2852m(˜ν(CHaliph)), 1626s(˜ν(C=N)), 1554s(˜ν(C=N)), 1548s
(˜ν(C=N)), 1491m(˜ν(C=N)), 1440m, 1372m, 1341w, 1261w, 1253m, 1236w, 1211w, 1203w,
1163m, 1114w, 1078m, 1023m, 1016w, 985w, 907w, 839vs (˜ν(P-F)), 787m, 705w, 581w,
555m. elemental analysis, calcd. for C50H92N12Cu2P2F12: C 46.98, H 7.25, N 13.15 ; found
: C 46.99, H 7.22, N 13.19.
[Cu(DMEG2p)]n[PF6]n(C10):
N
Cu
NN
N
n
PF6-
NN= DMEG2p
[Cu(MeCN)4][PF6] (372 mg, 1 mmol) was added to a
stirred solution of DMEG2p (279 mg, 1.05 mmol) in
THF (15 mL). After 30 min of stirring, diethylether (20
mL) was added to obtain the colourless product, yield:
86 % (433 mg). Crystals suitable for X-ray diffraction
were grown by slow diffusion of diethylether into THF.
IR (KBr, ˜ν[cm−1]): 2933w(˜ν(CHaliph)), 1634vs
(˜ν(C=N)), 1595vs (˜ν(C=N)), 1487w, 1372m, 1298m,
1139w, 1037w, 962w, 838vs (˜ν(P-F)), 803w, 692w, 637w. elemental analysis calcd. for
C26H52N12Cu2P2F12 : C 32.88, H 5.52, N 17.70 ; found : C 33.27, H 5.23, N 18.05.
[Cu(DMEG2p)]n[I]n(C11):
N
Cu
I
N
n
N N
= DMEG2p
N
N
CuI (190 mg, 1 mmol) was added to a stirred solution
of DMEG2p (279 mg, 1.05 mmol) in MeCN (15 mL).
After 30 min of stirring, diethylether (20 mL) was added
to obtain the colourless product, yield: 86 % (433 mg).
Crystals suitable for X-ray diffraction were grown by
slow diffusion of diethylether into MeCN.
IR (KBr, ˜ν[cm−1]): 2931w(˜ν(CHaliph)), 1635vs
(˜ν(C=N)), 1595vs (˜ν(C=N)), 1488w, 1371m, 1299m,
1139w, 1037m, 962w, 800w, 694w, 640w. elemental
analysis calcd. for C26H52N12Cu2I2: C 34.21, H 5.75, N 18.42 ; found : C 33.97, H 5.49, N
18.02.
[Cu(TMG2mX)]n[I]n(C12):
NN= TMG2mX
NCu
NN
N
n
I
CuI (190 mg, 1 mmol) was added to a stirred solution
of TMG2mX (349 mg, 1.05 mmol) in MeCN (15 mL).
After 30 min of stirring, diethylether (20 mL) was added
to obtain the colourless product, yield: 90 % (470 mg).
Crystals suitable for X-ray diffraction were grown by
slow diffusion of diethylether into MeCN.
IR (KBr, ˜ν[cm−1]): 3053w(˜ν(CHarom)), 2999m
(˜ν(CHaliph)), 2932s, 2891s, 2842s, 2792m, 1558vs (˜ν(C=N)), 1525vs (˜ν(C=N)), 1473vs
(˜ν(C=N)), 1425s, 1385vs, 1350vs, 1225s, 1145s, 1069s, 1036s, 993m, 910m, 881s, 796s, 735w,
CHAPTER 8. EXPERIMENTAL SECTION 153
703s, 630w, 595m, 541w, 506w. elemental analysis calcd. for C36H64N12Cu2I2: C 41.37, H
6.18, N 16.09 ; found : C 41.02, H 6.43, N 16.37.
[Cu(DPPG2p)]n[CuI2]n(C13):
N
Cu
NN
N
n
Cu
II
NN= DPPG2p
CuI (190 mg, 1 mmol) was added to a stirred solution
of DPPG2p (426 mg, 1.05 mmol) in MeCN (15 mL).
After 30 min of stirring, the solvent was removed under
reduced pressure. From the residual oil crystals suitable
for X-ray diffraction were grown after 3 months.
IR (KBr, ˜ν[cm−1]): 2962m(˜ν(CHaliph)), 2873w, 1604vs
(˜ν(C=N)), 1508s(˜ν(C=N)), 1457m, 1374m, 1324w,
1211m, 1101w, 943w, 892w, 752w, 640w.
[Cu2(TMGbenzPA)2][PF6]2(C14):
N
N
NMe2
N
NMe2
NMe2
CuI
N
N
Me2N
N
NMe2
Me2NCuI
2 PF6-
2+
To a solution of 375 mg (1 mmol) [Cu(MeCN)4][PF6]
in 10 ml of MeCN a solution of 366 mg (1,05 mmol)
TMG2PA in 10 mL of MeCN was added dropwise. The
reaction mixture was refluxed for 2 h. An colourless solu-
tion formed. Crystals suitable for X-ray diffraction were
grown by slow diffusion of diisopropylether into MeCN,
yield: 58 % (648 mg). IR (KBr, ˜ν[cm−1]): 3070vw
(˜ν(CHarom)), 2939w(˜ν(CHaliph)), 1622vs(C=N), 1579vs
(˜ν(C=N)), 1567vs (˜ν(C=N)), 1522vs, 1491s, 1471vs, 1454m, 1423vs, 1414vs, 1405vs, 1396vs,
1317m, 1294w, 1280w, 1255vw, 1147w, 837vs (˜ν(P-F)), 742m, 557s.
8.3.5 Synthesis of copper(II)complexes
[Cu2(btmmO)2][PF6]2·2CH3CN (C15):
N
NMe2
N
N
NMe2
N
Cu
Me2NN
N
N
Me2NN
Cu
O
O
CH2
Me
H2C
Me
Me2
Me2
2+
2 PF6-
A solution of 287 mg (0.3 mmol) of
[Cu2(btmgp)2][PF6]2(C3) in 50 mL of MeCN
was treated at -40◦C with pure oxygen. The
formerly colourless solution turns to red and
upon warming to dark blue. Single crystals were
obtained by vapour diffusion of pentane into this
solution in red needles. Yield: 46 % (151 mg).
1H-NMR (300 MHz, CDCl3,δ= 1.26 (s, 18H,
CH3), 1.62 (s, 18H, CH3), 2.93 (m, 12H), 3.04
(s, 6H, CH2), 3.42 (s, 4H, -CH2O-) ppm. IR
(KBr, ˜ν[cm−1]): 2931m(˜ν(CHaliph)), 2907m(˜ν(CHaliph)), 2811w, 1621s(˜ν(C=N)), 1574s
(˜ν(C=N)), 1556s(˜ν(C=N)), 1520m(˜ν(C=N)), 1473m, 1456m, 1446m, 1428m, 1417m,
1400s(˜ν(C=N)), 1371m, 1348w, 1336w, 1272w, 1238w, 1214w, 1203w, 1169m, 1145w,
1115w, 1088m, 1068m, 1043m(˜ν(C-O)), 999w, 931m, 904m, 837vs (˜ν(P-F)), 793m, 785w,
CHAPTER 8. EXPERIMENTAL SECTION 154
702w, 586w, 557s, 431w.
UV/vis (CH2Cl2,λmax [nm] ([M−1cm−1]): 252 (12700), 296 (3300), 393 (1200), 550 (470);
elemental analysis (after drying in vacuo), calcd. for C26H58O2N12Cu2P2F12: C 31.61, H
5.92, N 17.02 ; found: C 31.09, H 5.76, N 17.03.
[Cu2(TMMoG2MePA)2][PF6]2(C16):
+II+II
NMe2
N
Cu
O
O
Cu
N
N
N Me
Me2N
NMe2
Me2NN
N
N
N
Me
NMe2
Me2N2+
Me
Me
X = PF6- (C16),
ClO4- (C17),
BF4- (C18)
2 X-
A solution of 309 mg (0.5 mmol) of
[Cu(TMG2MePA)][PF6] in 50 mL of MeCN
was treated at room temperature with dioxygen.
After standing for one week, dark green crystals
suitable for X-ray diffraction were obtained, yield:
41 % (133 mg).
IR (KBr, ˜ν[cm−1]): 3066w(˜ν(CHarom)), 2937m
(˜ν(CHaliph)), 2889m, 1549vs (˜ν(C=N)), 1487vs,
1425vs, 1338m, 1269m, 1161m, 1030s(˜ν(C-O)),
840vs (˜ν(P-F)), 756m, 630w, 557vs, 475w.
[Cu2(TMMoG2MePA)2][ClO4]2(C17): A solution of 286 mg (0.5 mmol) of
[Cu(TMG2MePA)][ClO4] in 50 mL of MeCN was treated at room temperature with
dioxygen. After standing for three weeks, dark green crystals suitable for X-ray diffraction
were obtained, yield: 47 % (142 mg).
IR (KBr, ˜ν[cm−1]): 3063w(˜ν(CHarom)), 2964w(˜ν(CHaliph)), 2935w(˜ν(CHaliph)), 1635s
(˜ν(C=N)), 1616s(˜ν(C=N)), 1585s(˜ν(C=N)), 1558vs (˜ν(C=N)), 1521vs, 1488s, 1457s,
1398vs, 1338m, 1261s, 1094vs (˜ν(Cl-O)), 1035s(˜ν(C-O)), 916w, 802m, 752m, 702m, 669m,
622s, 594m, 526m, 458w.
[Cu2(TMMoG2MePA)2][BF4]2(C18): A solution of 280 mg (0.5 mmol) of
[Cu(TMG2MePA)][BF4] in 50 mL of MeCN was treated at room temperature with
dioxygen. By vapour diffusion of diisopropylether, dark green crystals suitable for X-ray
diffraction were obtained, yield: 39 % (115 mg).
IR (KBr, ˜ν[cm−1]): 3069w(˜ν(CHarom)), 2971w(˜ν(CHaliph)), 2936w(˜ν(CHaliph)), 1638s
(˜ν(C=N)), 1619s(˜ν(C=N)), 1581vs (˜ν(C=N)), 1555vs (˜ν(C=N)), 1523vs, 1487s, 1395s,
1338m, 1265s, 1036s(˜ν(C-O)), 919w, 805w, 754m, 706m, 673m, 623m, 597w, 528w.
[Cu2(TMG2MePA)2(µ-OH)2][Cu2I4] (C19) and [Cu2(TMG2MePA)2(µ-OH)2][I3]2
(C20):
+II
+II
NMe2
Me2N
Cu
O
O
Cu
N
N
N Me
Me2N
NMe2
Me2N
NMe2
N
N
N
Me
NMe2
Me2N2+
H
H
2 X-
X = Cu2I42- (C19),
I3- (C20)
A solution of 300 mg (0.5 mmol) of
[Cu(TMG2MePA)]I in 50 mL of MeCN was
treated at room temperature with dioxygen. By
vapour diffusion of diisopropylether, dark green
crystals of C19 suitable for X-ray diffraction were
obtained, yield: 34 % (107 mg). Additionally,
after further vapour diffusion of diisopropylether,
bright yellow crystals of C20 suitable for X-ray
CHAPTER 8. EXPERIMENTAL SECTION 155
diffraction were obtained, yield: 8 % (46 mg). IR (KBr, ˜ν[cm−1]): 3466w(˜ν(O-H)), 3062w
(˜ν(CHarom)), 2974w(˜ν(CHaliph)), 1622s(˜ν(C=N)), 1585vs (˜ν(C=N)), 1552s(˜ν(C=N)),
1525s, 1485s, 1396m, 1339w, 1262m, 914w, 807w, 757w, 707m, 675w, 625w, 522vw.
[Cu2(MMoEG2p)2][PF6]2(C21):
N
NMe
MeN
N
NMe
N
Cu
MeN NMe
N
N
MeN N
Cu
O
O
CH2
H2C
2+
2 PF6-
A solution of 475 mg (0.5 mmol) of
[Cu2(DMEG2p)2][PF6]2in 50 mL of MeCN
was treated at room temperature with dioxygen.
By vapour diffusion of diisopropylether, dark red
crystals of C21 suitable for X-ray diffraction were
obtained, yield: 42 % (206 mg).
IR (KBr, ˜ν[cm−1]): 2933s, 2892s, 1625s(˜ν(C=N)),
1606vs (˜ν(C=N)), 1504m, 1495s, 1461m, 1416s,
1402m, 1343m, 1303s, 1127m, 1078w, 1034w(˜ν(C-
O)), 838vs (˜ν(P-F)), 726w, 641w, 558vs, 482vw.
[Cu2(DPipG2p)2(µ-OH)2][PF6]2(C22):
N
N
Cu
N
N
Cu O
O
H
H
2+
2 PF6-
NN N
N
NNN
N
A solution of 262 mg (0.2 mmol) of
[Cu2(DPipG2p)2][PF6]2(C9) in 50 mL of MeCN
was treated at room temperature with dioxygen.
After standing for one week, dark blue crystals
suitable for X-ray diffraction were obtained, yield:
45 % (121 mg).
IR (KBr, ˜ν[cm−1]): 3446vw (˜ν(O-H)), 2937s
(˜ν(CHaliph)), 2852s, 1533vs (˜ν(C=N)), 1495s
(˜ν(C=N)), 1446vs, 1371s, 1335m, 1253m, 1226m,
1205m, 1164w, 1141m, 1110m, 1070w, 1020m,
948m, 917w, 839vs (˜ν(P-F)), 744m, 622w, 597w,
557m, 487w.
[Cu2(TMMoG2ch)2][I]2(C23):
N
NMe2
N
N
NMe2
N
Cu
Me2NN
N
N
Me2NN
Cu
O
O
CH2
Me
H2C
Me
Me2
Me2
2+
2 X-
(C23)
(C24)
(C25)
X = I-
PF6-
ClO4-
A solution of 500 mg (0.5 mmol) of
[Cu2(TMG2ch)2][I]2(C4) in 50 mL of MeCN
was treated at room temperature with dioxygen.
By vapour diffusion of diisopropylether, dark red
crystals of C23 suitable for X-ray diffraction were
obtained, yield: 41 % (212 mg).
IR (KBr, ˜ν[cm−1]): 2941m(˜ν(CHaliph)), 1616vs
(˜ν(C=N)), 1576vs (˜ν(C=N)), 1458m, 1396s,
1313w, 1224w, 1164w, 1060w, 1033m(˜ν(C-O)),
885w, 723w.
[Cu2(TMMoG2ch)2][PF6]2(C24): A solution
CHAPTER 8. EXPERIMENTAL SECTION 156
of 519 mg (0.5 mmol) of [Cu2(TMG2ch)2][PF6]2in 50 mL of MeCN was treated at room
temperature with dioxygen. By vapour diffusion of diisopropylether, red crystals of C24
suitable for X-ray diffraction were obtained, yield: 44 % (235 mg).
IR (KBr, ˜ν[cm−1]): 2941w(˜ν(CHaliph)), 1613s(˜ν(C=N)), 1544vs (˜ν(C=N)), 1475s, 1393s,
1236m, 1168m, 1033m(˜ν(C-O)), 903m, 845w, 837vs (˜ν(P-F)), 783w, 622m, 563w.
[Cu2(TMMoG2ch)2][ClO4]2(C25): A solution of 473 mg (0.5 mmol) of
[Cu2(TMG2ch)2][ClO4]2in 50 mL of MeCN was treated at room temperature with
dioxygen. By vapour diffusion of diisopropylether, dark red crystals of C25 suitable for
X-ray diffraction were obtained, yield: 39 % (191 mg).
IR (KBr, ˜ν[cm−1]): 2943w(˜ν(CHaliph)), 1618s(˜ν(C=N)), 1541vs (˜ν(C=N)), 1473m,
1396s, 1234w, 1166w, 1093vs (˜ν(Cl-O)), 1034m(˜ν(C-O)), 908w, 848w, 786w, 678w, 624m,
568w.
[Cu2(MorphDMG2p)2(µ-F)2][PF6]2(C26):
N
N
Cu
N
N
Cu F
F
2+
2 PF6-
N
O
N N
O
N
N
O
N
O
N
N
A solution of 563 mg (0.5 mmol) of
[Cu2(MorphDMG2p)2][PF6]2in 20 mL of MeCN
was treated at room temperature with dioxygen.
Dark blue crystals suitable for X-ray diffraction
were grown by slow diffusion of diisopropylether
into MeCN, yield: 48 % (278 mg). IR (KBr, ˜ν
[cm−1]): 2924m(˜ν(CHaliph)), 2856m(˜ν(CHaliph)),
1616s(˜ν(C=N)), 1558vs (˜ν(C=N)), 1468s, 1398s,
1267m, 1111s, 1066m, 887w, 840vs (˜ν(P-F)), 759w,
617w, 555w.
8.3.6 Catalytic reactions with 2,4-ditertbutylphenol,
2,6-ditertbutylphenol and 3,5-ditertbutylcatechol
In order to have exactly the same conditions for the catalytical screening, 0.1 mmol of Cu(I)
bisguanidine complex was freshly prepared in 30 mL of CH2Cl2(see section 8.3.4. for prepa-
ration). This stem solution was divided in three parts of 10 mL each which were oxygenated
by stirring for 2 min in the presence of air. Afterwards, to each part, 100 mg (0.48 mmol)
of 2,4-ditertbutylphenol or of 2,6-ditertbutylphenol or 100 mg (0.45 mmol) of 3,5-DTBC were
added to the stirred solution, respectively. After 16 h of stirring at room temperature, the
reaction was quenched by the addition of 10 mL of 5% perchloric acid. After 5 min of stir-
ring, the phases were separated and the aqueous phase was extracted with CH2Cl2. The
combined organic phases were dried with Na2SO4. These solutions were analysed by means
of gaschromatographic separation and mass spectrometric analysis in order to determine the
conversion and the selectivity of the reactions.
As comparative experiment, this procedure was carried out with pure CH2Cl2instead of
the Cu(I) complex solutions. The GC/MS analyses revealed that the educts remained un-
changed.
9 Conclusion and Perspective
The assembly of bisguanidine molecules starting from secondary amines and phosgene for
use in biomimetic coordination chemistry, especially in the field of copper-controlled oxygen
activation, has provided a set of bifunctional N-donor ligands. Each member of this set ad-
justs the redox capabilities of its corresponding Cu(I) complexes towards molecular oxygen
in a specific fashion depending on the spatial demands of the guanidine functionalities as
well as on the conformational freedom possible within the steric limits allowed by the spacer
fragments connecting these units. In contrast to established literature procedures, this
method to arrive at bisguanidine molecules is not dependent from predefined peralkylated
urea precursors as we start from secondary amines as simple building blocks and thus
define the urea intermediates by simply choosing suitably substituted educts. The synthetic
protocol has been optimised to obtain overall yields in the range from 65 to 95 %. The
modular approach allows the universal modification of the aliphatic guanidine substitution
as well as of the spacers with respect to rigidity, extension of the backbone and additional
donor functions. In general, such a matrix of bisguanidine ligands can also be screened
regarding their ability to stabilise complexes of other transition metals in unusually high
oxidation states.
By applying this modular approach, 30 new bisguanidine ligands have been synthesised
and characterised which are depicted on Figure 9.1. Furthermore, the crystal structures
of L1-4,L5-1,L7-1,L11-1 and [H2L1-2]I2·Et2O are discussed regarding their charac-
teristics as these ligands are the first unprotonated guanidine ligands to be crystallised.
Furthermore, the multi-step synthesis of the first fluorinated bisguanidine ligand BFPPG2p
was successfully accomplished. Starting with this library of bisguanidine ligands, several
copper(I) bisguanidine complexes could be crystallised which are summarised in Figure 9.2:
the mononuclear compounds C1 and C2 are examples for the chelating coordination mode
of these ligands. In fact, in the course of the synthesis of C1, the Cu(I) is oxidised to Cu(II)
under deprotonation of the ligand and reduction of the released proton. C1 exhibits a dis-
torted butterfly-like coordination geometry whereas C2 is coordinated trigonal-planar like
its predecessor [Cu(btmgp)I]. The dinuclear complexes C3 -C9 contain twelve-membered
heterocyclic structures with linear coordinated Cu(I) atoms. The folding of their propylene
chains and their corresponding interligand H...H separations can be correlated with the
Cu...Cu distances which vary between 4.121 and 5.054 ˚
A. C10 -C13 exhibit molecular chain
structures with great differences in the Cu coordination: in crystals of C10, the copper is
157
CHAPTER 9. CONCLUSION AND PERSPECTIVE 158
N
NN
O
N
N
O
NN
NN
N
NN
N
NMe2
NMe2
Me2N
NMe2
N
L1-3
L13-1 L14-1
N
NEt2
NEt2
Et2N
NEt2
N
NN
N
NN
NNN
N
NN
N
L2-1 L3-1 L4-1
NN
N
NN
N
L4-3
NN
N
NN
N
L5-1
NN
N
Pr
Pr
NN
NPr
Pr
L6-1
N
NN
N
NN
L7-1
N
NN
N
NNN
NN
N
NN
L8-1 L9-1
N
N
ON
O
N
N
O
NON
N
SN
S
N
N
S
NS
L12-1
L11-1
L10-1
N
NN
N
NN
NNN
N
Me2N
NMe2
NN
N
Me
NMe2
NMe2
Me2N
NMe2
NN
N
H
NMe2
NMe2
NN
NMe2
NMe2
Me2N
NMe2
NNN
N
NN
N
NN
N N
N
N N
N
NN
Et2NNEt2
Et2N NEt2
N
NN
N
NN
NNN
N
NN
N
N
Me2NNMe2
Me2NNMe2
NN
Et2NNEt2
Et2NNEt2
N
NN
N
Me
N
N
N
N
O O
N
N
ONO
N
N
O
NO
O O N
Me2N NMe2
N
Me2N NMe2
L1-2
NN NN
N O O N
L4-2
O O
NN
N
NN
N
L5-2 L11-2
L1-4 L1-5 L5-5
L1-6 L2-6 L4-6 L5-6
L1-7 L2-7 L4-7 L5-7
C3F7N
NC3F7
N N
C3F7N
NC3F7
BFPPG2p
Figure 9.1: Schematic summary of the synthesised bisguanidine ligands
coordinated linearly, whereas in C11 (by using the same ligand L4-1), the Cu1 atom is
coordinated distorted trigonal and the Cu2 atom trigonal-planar. In C12, a coordination
mode in between these two is realized. C13 exhibits a twisted double T-shaped structure
CHAPTER 9. CONCLUSION AND PERSPECTIVE 159
motif with a N2Cu..CuI2unit. The Cu...Cu interaction of 2.6732(6) ˚
A is quite short. The
dinuclear complex C14 was obtained after a cyclisation reaction of ligand L1-4 and the
subsequent coordination of Cu(I). In summary, it could be shown that the novel bidentate
guanidine ligands are capable of stabilising µ-η2:η2-peroxo dicopper(II) cores as well as
bis(µ-oxo) dicopper(III) cores. It turned out that the decision between these two cores is
made by the inherent torsion of the guanidine system. Twisted systems like C2,C3,C4
and C9 with angles around 35◦favour the stabilisation of an O-core complex, whereas ”flat”
systems with angles around 16◦incorporated in C5 and C6 support P-core complexes. C8
and C13 have angles which are in the middle of this range with 24.8 and 28.5◦, respectively.
Hence, it can be understood why C8 shows solvent-depending behaviour. The sensitive
P/O-core equilibrium can be shifted at this point only by a change from a coordinating
solvent to a non-coordinating one. In an attempt to elucidate the principal factors that
control the P-core/O-core equilibrium, the degree of conjugation within the guanidine
moiety has been successfully correlated with the reaction behaviour of the corresponding
copper(I) complex towards oxygen. Additionally, the ligands determine not only whether a
P-core or an O-core is formed, but they also tune the stability by shielding effects of highly
sterically demanding groups. By using these effects, two rare examples of room-temperature
stable O-cores and one room-temperature stable P-core could be observed.
The combination of the modular approach with this correlation allows the prediction of the
properties of a desired bisguanidine ligand.
Some of the observed bis(µ-oxo) dicopper(III) cores insert oxygen in a non-
activated C-H-bond of the ligands. The formation of the novel ligands
bis(trimethylmethoxyguanidino)propane (btmmO), bis(trimethylmethoxyguanidino)-N-
methyl-diphenyleneamine (TMMoG2MePA), bis(methylmethoxyethyleneguanidino)propane
(MMoEG2p) and bis(trimethylmethoxyguanidino)cyclohexane (TMMoG2ch) represent the
first hydroxylations of an N-methyl group. These ligands could be obtained complex-
stabilised in the bis(µ-alkoxo)-bridged dinuclear copper complexes C15 (btmmo), C16 -
C18 (TMMoG2MePA), C21 ((MMoEG2p) and C23 -C25 (TMMoG2ch). On the other
hand, the corresponding bis(µ-hydroxo)-bridged dinuclear copper complexes C19,C20 and
C22 were obtained as well. In C15,C21 -C25, the copper(II) atoms are coordinated
in a square-planar manner, in C16,C17,C19 and C20 square-pyramidal and in C18
trigonal-bipyramidal. C26 was crystallised after the reaction of a bis(µ-hydroxo)-bridged
dinuclear copper complex with the hexafluorophosphate anion to give the corresponding
bis(µ-fluoro)-bridged dinuclear copper complex with square-planar coordination.
Finally, the generated Cu2O2species were screened regarding their suitability as ox-
idation catalysts in the reactions with 2,4-ditertbutylphenol, 2,6-ditertbutylphenol and
3,5-ditertbutylcatechol. In fact, the investigated systems did not show tyrosinase activity
but very efficient catechol oxidase activity. 2,4-ditertbutylphenol and 2,6-ditertbutylphenol
have been oxidatively coupled to phenylethers. 3,5-ditertbutylcatechol has been successfully
CHAPTER 9. CONCLUSION AND PERSPECTIVE 160
N
NMe2
N
N
NMe2
N
Cu
Me2NN
N
N
Me2N
N
Cu
O
O
CH2
Me
H2C
Me
Me2
Me2
2+
2 X-
(C23),
(C24),
(C25)
X = I-
PF6-
ClO4-
N
NMe
MeN
N
NMe
N
Cu
MeN NMe
N
N
MeN
N
Cu
O
O
CH2
H2C
2+
2 PF6-
C21
NMe2
Me2N
Cu
O
O
Cu
N
N
N Me
Me2N
NMe2
Me2N
NMe2
N
N
N
Me
NMe2
Me2N2+
H
H
2 X-
X = Cu2I42- (C19),
I3- (C20)
N
N N NMe2
Me2N
Me2N
NMe2
Cu
I
C1
NN
O
N
O
N
N
O
NO
Cu
I
C2
Cu
N
N
N
Cu
N
NMe2
NMe2
NMe2
NMe2
Me2N
Me2N
NMe2
NMe2
2+
2 PF6-
C3
NC
Me2N
Me2NN C NMe2
NMe2
N C NMe2
NMe2
NC
Me2N
Me2N
Cu Cu
2+
2 I-
C4
N
N
N
Cu
N
2+
2 PF6-
N
N
N
NN
N
N
N
Cu
C5
NN
N
N
Cu Cu
Y2-
Y2- = Cu2I42- (C6),
Cu4I62- (C7)
N
N
N
N
N
N
N
N
2+
N
N
N
Cu
N
2+
2 PF6-
N
N
N
N
N
N
N
N
Cu
C8
N
N
N
Cu
N
2+
2 PF6-
Cu
NN
N
N
N
N
N N
C9
N
N
Cu
N
N
Cu F
F
2+
2 PF6-
N
O
N N
O
N
N
O
N
O
N
N
C26
N
N
Cu
N
N
Cu
O
O
H
H
2+
2 PF6-
NN N
N
NNN
N
C22
+II+II
NMe2
N
Cu
O
O
Cu
N
N
N Me
Me2N
NMe2
Me2NN
N
N
N
Me
NMe2
Me2N2+
Me
Me
X = PF6- (C16),
ClO4- (C17),
BF4- (C18)
2 X-
N
NMe2
N
N
NMe2
N
Cu
Me2NN
N
N
Me2NN
Cu
O
O
CH2
Me
H2C
Me
Me2
Me2
2+
2 PF6-
C15
NN
NMe2N
NMe2
NMe2
CuI
N
N
Me2N
N
NMe2
Me2NCuI
2 PF6-
2+
C14
N
Cu
NN
N
n
CuII
NN= DPPG2p
C13
NN= TMG2mX
N
Cu
NN
N
n
I
N
Cu
I
N
n
N N
= DMEG2p
N
N
N
Cu
NN
N
n
PF6-
NN= DMEG2p
C10 C11
C12
Figure 9.2: Schematic summary of the synthesised bisguanidine copper complexes
CHAPTER 9. CONCLUSION AND PERSPECTIVE 161
oxidised to 3,5-ditertbutyl-o-quinone at low temperatures, this product reacts at room
temperature to a substituted benzodioxine as subsequent product. The ability of oxidation
is depending from the accessibility of the reaction centre: ”small” ligands stabilise stronger
oxidation catalysts whereas sterically demanding systems show with substrates like 2,4-
DTBP and 2,6-DTBP reduced conversions by high selectivity.
A perspective for further investigations would be the screening of this library of bisguanidine
ligands and their copper(I) complexes for catalytic reactions like the coupling of benzyl-
halogenids and the selective mono-dealkylation of substituted anilines. The possibility of
controlling the oxidation selectivity by peripheric modifications is a particularly attractive
feature of this ligand design. In general, such a matrix of bisguanidine ligands can also
be screened regarding their ability to stabilise complexes of other transition metals in
unusually high oxidation states, concerning that these ligands have proven to be stable
against fragmentation reactions.
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10 Appendix
Table A1: Crystal data and structure refinement for V2 and L5-1
V2 L5-1
Identification code h1257 h1036
Empirical formula C9H20Cl2N2C15H30N6
Formula weight 227.17 294.45
Temperature 120(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Triclinic Triclinic
Space group P1 P1
Unit cell dimensions a = 7.9140(11) ˚
A a = 6.9057(7) ˚
A
b = 8.5959(12) ˚
A b = 7.6661(7) ˚
A
c = 9.5177(14) ˚
A c = 16.3568(16) ˚
A
α= 112.389(2)◦α= 89.307(3)◦
β= 94.883(3)◦β= 82.355(2)◦
γ= 98.166(2)◦γ= 73.152(2)◦
Volume 585.70(14) ˚
A3821.07(14)˚
A3
Z 2 2
Density (calculated) 1.288 Mg/m31.191 Mg/m3
Absorption coefficient 0.516 mm−10.075 mm−1
F(000) 244 324
Crystal size 0.45 x 0.30 x 0.28 mm30.20 x 0.15 x 0.10 mm3
Theta range for data collection 2.34 to 27.48◦1.26 to 28.31◦
Index ranges -10≤h≤10, -11≤k≤11, -12≤l≤12 -8≤h≤9, -9≤k≤10, -21≤l≤21
Reflections collected 5402 7147
Independent reflections 2637 [R(int) = 0.0187] 4053 [R(int) = 0.0465]
Completeness to theta = 27.48◦: 98.2 % = 28.31◦: 99.0 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.8690 and 0.8010 0.916 and 0.833
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 2637 / 0 / 122 4053 / 0 / 194
Goodness-of-fit on F21.076 0.836
Final R indices [I¿2sigma(I)] R1 = 0.0308, wR2 = 0.0795 R1 = 0.0540, wR2 = 0.0820
R indices (all data) R1 = 0.0360, wR2 = 0.0876 R1 = 0.1233, wR2 = 0.1130
Largest diff. peak and hole 0.350 and -0.186 e·˚
A30.232 and -0.165 e·˚
A3
168
CHAPTER 10. APPENDIX 169
Table A2: Crystal data and structure refinement for L7-1 and L1-4
L7-1 L1-4
Identification code h1085 h920
Empirical formula C25H46N6C22H33N7
Formula weight 430.68 395.55
Temperature 120(2) K 153(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Monoclinic
Space group P21/n P21/n
Unit cell dimensions a = 10.0619(7) ˚
A a = 18.577(4) ˚
A
b = 19.8127(13) ˚
A b = 13.218(3) ˚
A
c = 12.7511(8) ˚
A c = 20.144(4) ˚
A
α= 90◦α= 90◦
β= 99.594(2)◦β= 113.24(3)◦
γ= 90◦γ= 90◦
Volume 2506.4(3) ˚
A34545.0(16)˚
A3
Z 4 8
Density (calculated) 1.141 Mg/m31.156 Mg/m3
Absorption coefficient 0.069 mm−10.072 mm−1
F(000) 952 1712
Crystal size 0.40 x 0.35 x 0.20 mm30.30 x 0.15 x 0.12 mm3
Theta range for data collection 1.92 to 28.34◦1.26 to 28.31◦
Index ranges -13≤h≤13, -22≤k≤26, -12≤l≤17 -23≤h≤23, -17≤k≤17, -20≤l≤26
Reflections collected 19511 24735
Independent reflections 6205 [R(int) = 0.0437] 10255 [R(int) = 0.1887]
Completeness to theta = 28.34◦: 99.2 % = 28.31◦: 90.5 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.989 and 0.751 0.991 and 0.978
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 6205 / 0 / 280 10255 / 0 / 539
Goodness-of-fit on F20.863 0.587
Final R indices [I¿2sigma(I)] R1 = 0.0420, wR2 = 0.0838 R1 = 0.0550, wR2 = 0.0764
R indices (all data) R1 = 0.0682, wR2 = 0.0899 R1 = 0.2976, wR2 = 0.1195
Largest diff. peak and hole 0.217 and -0.154 e·˚
A30.171 and -0.196 e·˚
A3
CHAPTER 10. APPENDIX 170
Table A3: Crystal data and structure refinement for L11-1 and [H2L1-2]I2•Et2O
L11-1 [H2L1-2]I2•Et2O
Identification code s1157 h1063
Empirical formula C21H38N6O4C20H48I2N6O3
Formula weight 438.57 674.44
Temperature 120(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Monoclinic
Space group C2/c P21/n
Unit cell dimensions a = 16.4003(11) ˚
A a = 8.1966(4) ˚
A
b = 8.2314(4) ˚
A b = 14.0360(7) ˚
A
c = 16.6413(9) ˚
A c = 12.3715(6) ˚
A
α= 90◦α= 90◦
β= 92.310(2)◦β= 93.983(1)◦
γ= 90◦γ= 90◦
Volume 2244.7(2) ˚
A31419.87(12)˚
A3
Z 4 2
Density (calculated) 1.298 Mg/m31.578 Mg/m3
Absorption coefficient 0.091 mm−12.245 mm−1
F(000) 952 680
Crystal size 0.40 x 0.38 x 0.28 mm30.30 x 0.28 x 0.06 mm3
Theta range for data collection 2.45 to 28.24◦2.20 to 28.29◦
Index ranges -21≤h≤21, -10≤k≤10, -22≤l≤22 -10≤h≤10, -18≤k≤16, -16≤l≤16
Reflections collected 13601 12043
Independent reflections 2771 [R(int) = 0.0347] 3515 [R(int) = 0.0204]
Completeness to theta = 28.24◦: 100.0 % = 28.29◦: 99.7 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.908 and 0.797 0.984 and 0.677
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 2771 / 1 / 145 3515 / 0 / 153
Goodness-of-fit on F21.030 1.048
Final R indices [I¿2sigma(I)] R1 = 0.0385, wR2 = 0.1043 R1 = 0.0266, wR2 = 0.0718
R indices (all data) R1 = 0.0475, wR2 = 0.1076 R1 = 0.0304, wR2 = 0.0743
Largest diff. peak and hole 0.344 and -0.182 e·˚
A31.194 (near I1 position)
and -0.402 e·˚
A3
CHAPTER 10. APPENDIX 171
Table A4: Crystal data and structure refinement for C1 and C2
C1 C2
Identification code h878 s1144
Empirical formula C22H32CuIN7C21H38CuIN6O4
Formula weight 584.99 629.01
Temperature 133(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Orthorhombic Orthorhombic
Space group Pbca Pnma
Unit cell dimensions a = 18.1280(13) ˚
A a = 12.2998(6) ˚
A
b = 14.7193(10) ˚
A b = 26.4227(13) ˚
A
c = 18.2744(13) ˚
A c = 7.7061(4) ˚
A
α= 90◦α= 90◦
β= 90◦β= 90◦
γ= 90◦γ= 90◦
Volume 4876.2(6) ˚
A32504.4(2)˚
A3
Z 8 4
Density (calculated) 1.594 Mg/m31.668 Mg/m3
Absorption coefficient 2.185 mm−12.144 mm−1
F(000) 2360 1280
Crystal size 0.08 x 0.06 x 0.05 mm30.30 x 0.14 x 0.10 mm3
Theta range for data collection 2.10 to 28.28◦1.54 to 28.24◦
Index ranges -22≤h≤23, -19≤k≤18, -16≤l≤24 -16≤h≤16, -35≤k≤35, -10≤l≤10
Reflections collected 29665 29926
Independent reflections 5897 [R(int) = 0.0759] 3164 [R(int) = 0.0353]
Completeness to theta = 28.28◦: 97.3 % = 28.24◦: 100.0 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.845 and 0.899 0.992 and 0.829
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 5897 / 0 / 280 3164 / 0 / 154
Goodness-of-fit on F20.538 1.058
Final R indices [I¿2sigma(I)] R1 = 0.0421, wR2 = 0.0521 R1 = 0.0237, wR2 = 0.0569
R indices (all data) R1 = 0.1633, wR2 = 0.0722 R1 = 0.0282, wR2 = 0.0581
Largest diff. peak and hole 0.533 and -0.457 e·˚
A30.684 and -0.293 e·˚
A3
CHAPTER 10. APPENDIX 172
Table A5: Crystal data and structure refinement for C3 and C4
C3 C4
Identification code h910 h1251
Empirical formula C26H60Cu2F12N12P2C32.74H69.11Cu2I2N12.37
Formula weight 957.88 1017.05
Temperature 153(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Monoclinic
Space group P21/n P21/c
Unit cell dimensions a = 8.1774(13) ˚
A a = 11.9909(18) ˚
A
b = 15.574(3) ˚
A b = 14.999(2) ˚
A
c = 16.218(3) ˚
A c = 12.707(2) ˚
A
α= 90◦α= 90◦
β= 96.473(3)◦β= 104.348(4)◦
γ= 90◦γ= 90◦
Volume 2052.3(6) ˚
A32214.1(6) ˚
A3
Z 2 2
Density (calculated) 1.550 Mg/m31.526 Mg/m3
Absorption coefficient 1.205 mm−12.392 mm−1
F(000) 992 1032
Crystal size 0.25 x 0.20 x 0.18 mm30.20 x 0.15 x 0.10 mm3
Theta range for data collection 1.82 to 28.28◦1.75 to 28.34◦
Index ranges -10≤h≤9, -19≤k≤20, -21≤l≤20 -15≤h≤16, -17≤k≤20, -16≤l≤16
Reflections collected 12491 22633
Independent reflections 4731 [R(int) = 0.0471] 5509 [R(int) = 0.0665]
Completeness to theta = 28.28◦: 93.1 % = 28.34◦: 99.9 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.812 and 0.752 0.7959 and 0.6462
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 4731 / 0 / 252 5509 / 0 / 231
Goodness-of-fit on F21.033 0.984
Final R indices [I¿2sigma(I)] R1 = 0.0457, wR2 = 0.1077 R1 = 0.0527, wR2 = 0.0675
R indices (all data) R1 = 0.0589, wR2 = 0.1153 R1 = 0.1657, wR2 = 0.0880
Largest diff. peak and hole 0.912 and -0.423 e·˚
A30.784 and -0.934 e·˚
A3
CHAPTER 10. APPENDIX 173
Table A6: Crystal data and structure refinement for C5 and C6
C5 C6
Identification code h1142 h1160
Empirical formula C30H58Cu2F12N14P2C32H60Cu4I4N12
Formula weight 1031.92 1374.68
Temperature 293(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Triclinic Triclinic
Space group P1 P1
Unit cell dimensions a = 7.8306(4) ˚
A a = 9.0784(4) ˚
A
b = 11.6499(6) ˚
A b = 10.4432(5) ˚
A
c = 12.4737(7) ˚
A c = 12.7231(6) ˚
A
α= 78.019(1)◦α= 72.778(1)◦
β= 81.700(1)◦β= 74.856(1)◦
γ= 81.184(1)◦γ= 87.240(1)◦
Volume 1092.5(1) ˚
A31111.59(9) ˚
A3
Z 1 1
Density (calculated) 1.568 Mg/m32.054 Mg/m3
Absorption coefficient 1.140 mm−14.703 mm−1
F(000) 532 664
Crystal size 0.20 x 0.12 x 0.1 mm30.35 x 0.25 x 0.20 mm3
Theta range for data collection 1.68 to 28.24◦1.73 to 28.20◦
Index ranges -10≤h≤10, -14≤k≤15, -16≤l≤16 -12≤h≤12, -13≤k≤13, -16≤l≤16
Reflections collected 14028 14059
Independent reflections 5385 [R(int) = 0.0398] 5429 [R(int) = 0.0140]
Completeness to theta = 28.24◦: 99.6 % = 28.20◦: 99.6 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.968 and 0.813 0.990 and 0.726
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 5385 / 0 / 276 5429 / 0 / 239
Goodness-of-fit on F20.936 1.082
Final R indices [I¿2sigma(I)] R1 = 0.0439, wR2 = 0.0905 R1 = 0.0186, wR2 = 0.0496
R indices (all data) R1 = 0.0607, wR2 = 0.0952 R1 = 0.0201, wR2 = 0.0503
Largest diff. peak and hole 0.747 and -0.572 e·˚
A30.608 and -0.551 e·˚
A3
CHAPTER 10. APPENDIX 174
Table A7: Crystal data and structure refinement for C7 and C8
C7 C8
Identification code h1162 h1015
Empirical formula C16H30Cu3I3N6C30H60Cu2F12N12P2
Formula weight 877.78 1005.92
Temperature 120(2) K 150(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Triclinic Triclinic
Space group P1 P1
Unit cell dimensions a = 10.3549(5) ˚
A a = 9.5773(4) ˚
A
b = 11.0573(5) ˚
A b = 10.4201(5) ˚
A
c = 11.4562(5) ˚
A c = 10.7034(5) ˚
A
α= 77.379(1)◦α= 103.290(1)◦
β= 73.050(1)◦β= 96.936(1)◦
γ= 83.821(1)◦γ= 90.605(1)◦
Volume 1223.05(10) ˚
A31031.13(8) ˚
A3
Z 2 1
Density (calculated) 2.384 Mg/m31.620 Mg/m3
Absorption coefficient 6.386 mm−11.204 mm−1
F(000) 828 520
Crystal size 0.22 x 0.15 x 0.12 mm30.40 x 0.40 x 0.18 mm3
Theta range for data collection 1.89 to 28.20◦1.97 to 26.37◦
Index ranges -12≤h≤13, -14≤k≤14, -13≤l≤15 -11≤h≤11, -13≤k≤13, -13≤l≤13
Reflections collected 15537 11105
Independent reflections 6003 [R(int) = 0.0342] 4181 [R(int) = 0.0182]
Completeness to theta = 28.20◦: 99.5 % = 26.37◦: 99.5 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.906 and 0.711 0.986 and 0.899
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 6003 / 0 / 275 4181 / 0 / 266
Goodness-of-fit on F20.957 1.074
Final R indices [I¿2sigma(I)] R1 = 0.0251, wR2 = 0.0511 R1 = 0.0262, wR2 = 0.0685
R indices (all data) R1 = 0.0305, wR2 = 0.0524 R1 = 0.0274, wR2 = 0.0692
Largest diff. peak and hole 0.920 and -0.607 e·˚
A30.338 and -0.182 e·˚
A3
CHAPTER 10. APPENDIX 175
Table A8: Crystal data and structure refinement for C9 and C10
C9 C10
Identification code h1091 h1150
Empirical formula C50H92Cu2F12N12P2C30H58Cu2F12N14P2
Formula weight 1278.38 1031.92
Temperature 120(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Monoclinic
Space group C2/c P21/n
Unit cell dimensions a = 30.457(6) ˚
A a = 12.4821(5) ˚
A
b = 9.1394(18) ˚
A b = 25.0668(9) ˚
A
c = 21.278(4) ˚
A c = 15.0517(6) ˚
A
α= 90◦α= 90◦
β= 95.375(4)◦β= 109.987(1)◦
γ= 90◦γ= 90◦
Volume 5897(2) ˚
A34425.8(3) ˚
A3
Z 4 4
Density (calculated) 1.440 Mg/m31.549 Mg/m3
Absorption coefficient 0.859 mm−11.126 mm−1
F(000) 2688 2128
Crystal size 0.22 x 0.15 x 0.10 mm30.45 x 0.25 x 0.20 mm3
Theta range for data collection 1.34 to 28.52◦1.62 to 28.24◦
Index ranges -40≤h≤40, -11≤k≤12, -28≤l≤22 -16≤h≤16, -33≤k≤33, -20≤l≤20
Reflections collected 26613 55794
Independent reflections 7392 [R(int) = 0.0596] 10946 [R(int) = 0.0445]
Completeness to theta = 28.52◦: 98.5 % = 28.24◦: 100.0 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.937 and 0.119 0.948 and 0.807
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 7392 / 0 / 354 10946 / 30 / 551
Goodness-of-fit on F20.584 1.081
Final R indices [I¿2sigma(I)] R1 = 0.0456, wR2 = 0.0627 R1 = 0.0494, wR2 = 0.1469
R indices (all data) R1 = 0.1760, wR2 = 0.0792 R1 = 0.0651, wR2 = 0.1540
Largest diff. peak and hole 0.397 and -0.453 e·˚
A30.908 and -0.691 e·˚
A3
CHAPTER 10. APPENDIX 176
Table A9: Crystal data and structure refinement for C11 and C12
C11 C12
Identification code h1118 h1014
Empirical formula C26H52Cu2I2N12 C18H32CuIN6
Formula weight 913.68 522.94
Temperature 120(2) K 150(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Monoclinic
Space group P21/n P21/n
Unit cell dimensions a = 9.1809(4) ˚
A a = 16.4723(10) ˚
A
b = 29.8038(13) ˚
A b = 8.2834(5) ˚
A
c = 12.7247(6) ˚
A c = 17.4478(10) ˚
A
α= 90◦α= 90◦
β= 90.251(1)◦β= 111.441(1)◦
γ= 90◦γ= 90◦
Volume 3481.8(3) ˚
A32215.9(2) ˚
A3
Z 4 4
Density (calculated) 1.743 Mg/m31.567 Mg/m3
Absorption coefficient 3.031 mm−12.393 mm−1
F(000) 1824 1056
Crystal size 0.40 x 0.35 x 0.20 mm30.40 x 0.28 x 0.10 mm3
Theta range for data collection 1.37 to 28.20◦1.46 to 26.37◦
Index ranges -12≤h≤12, -39≤k≤37, -16≤l≤16 -20≤h≤20, -9≤k≤10, -17≤l≤21
Reflections collected 43526 14325
Independent reflections 8565 [R(int) = 0.0364] 4529 [R(int) = 0.0401]
Completeness to theta = 28.20◦: 99.9 % = 26.37◦: 99.9 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.947 and 0.766 0.906 and 0.230
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 8565 / 0 / 387 4529 / 0 / 243
Goodness-of-fit on F21.108 1.043
Final R indices [I¿2sigma(I)] R1 = 0.0336, wR2 = 0.0843 R1 = 0.0364, wR2 = 0.0734
R indices (all data) R1 = 0.0402, wR2 = 0.0865 R1 = 0.0456, wR2 = 0.0771
Largest diff. peak and hole 0.991 and -1.150 e·˚
A31.006 and -0.804 e·˚
A3
CHAPTER 10. APPENDIX 177
Table A10: Crystal data and structure refinement for C13 and C14
C13 C14
Identification code h1152 h965
Empirical formula C23H46Cl0.31Cu2I1.69N6C40H52Cu2F12N12P2
Formula weight 759.19 1117.96
Temperature 120(2) K 153(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Orthorhombic Monoclinic
Space group P212121P21/n
Unit cell dimensions a = 11.6357(6) ˚
A a = 8.111(2) ˚
A
b = 13.1877(7) ˚
A b = 22.126(6) ˚
A
c = 19.4201(10) ˚
A c = 12.998(3) ˚
A
α= 90◦α= 90◦
β= 90◦β= 92.739(4)◦
γ= 90◦γ= 90◦
Volume 2980.0(3) ˚
A32330.1(11) ˚
A3
Z 4 2
Density (calculated) 1.692 Mg/m31.593 Mg/m3
Absorption coefficient 3.227 mm−11.075 mm−1
F(000) 1515 1144
Crystal size 0.40 x 0.20 x 0.20 mm30.20 x 0.06 x 0.02 mm3
Theta range for data collection 1.87 to 28.24◦1.82 to 28.33◦
Index ranges -15≤h≤15, -17≤k≤17, -25≤l≤25 -10≤h≤10, -29≤k≤29, -17≤l≤17
Reflections collected 37639 26716
Independent reflections 7374 [R(int) = 0.0392] 5592 [R(int) = 0.3381]
Completeness to theta = 28.24◦: 100.0 % = 28.33◦: 96.4 %
Absorption correction Semi-empirical from equivalents Face-indexed
Max. and min. transmission 0.977 and 0.671 0.959 and 0.785
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 7374 / 3 / 329 5592 / 318 / 314
Goodness-of-fit on F21.072 0.542
Final R indices [I¿2sigma(I)] R1 = 0.0282, wR2 = 0.0671 R1 = 0.0466, wR2 = 0.0675
R indices (all data) R1 = 0.0322, wR2 = 0.0688 R1 = 0.3041, wR2 = 0.1227
Largest diff. peak and hole 0.980 and -0.274 e·˚
A30.287 and -0.300 e·˚
A3
CHAPTER 10. APPENDIX 178
Table A11: Crystal data and structure refinement for C15 and C16
C15 C16
Identification code h918 h975
Empirical formula C30H64Cu2F12N14O2P2C24.80H36.70CuF6N7.90OP
Formula weight 1069.97 670.03
Temperature 153(2) K 153(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Triclinic
Space group P21/c P1
Unit cell dimensions a = 9.2716(6) ˚
A a = 10.6797(6) ˚
A
b = 16.6780(11) ˚
A b = 11.0477(6) ˚
A
c = 15.4515(11) ˚
A c = 13.9297(8) ˚
A
α= 90◦α= 100.877(1)◦
β= 100.309(1)◦β= 109.994(1)◦
γ= 90◦γ= 99.403(1)◦
Volume 2350.7(3) ˚
A31469.73(14) ˚
A3
Z 2 2
Density (calculated) 1.512 Mg/m31.514 Mg/m3
Absorption coefficient 1.065 mm−10.870 mm−1
F(000) 1108 694
Crystal size 0.34 x 0.20 x 0.16 mm30.40 x 0.25 x 0.2 mm3
Theta range for data collection 1.81 to 28.29◦1.61 to 28.26◦
Index ranges -11≤h≤12, -22≤k≤15, -20≤l≤20 -14≤h≤14, -14≤k≤14, -18≤l≤18
Reflections collected 14728 17061
Independent reflections 5422 [R(int) = 0.0391] 6822 [R(int) = 0.0220]
Completeness to theta = 28.29◦: 92.7 % = 28.26◦: 93.7 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.116 and 0.082 0.503 and 0.428
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 5422 / 15 / 288 6822 / 0 / 389
Goodness-of-fit on F20.907 1.062
Final R indices [I¿2sigma(I)] R1 = 0.0435, wR2 = 0.0925 R1 = 0.0379, wR2 = 0.0993
R indices (all data) R1 = 0.0671, wR2 = 0.0992 R1 = 0.0428, wR2 = 0.1048
Largest diff. peak and hole 0.539 and -0.387 e·˚
A30.641 and -0.336 e·˚
A3
CHAPTER 10. APPENDIX 179
Table A12: Crystal data and structure refinement for C17 and C18
C17 C18
Identification code h1097 h1070
Empirical formula C49.16H72.74Cl2Cu2N15.58O10 C46H68B2Cu2F8N14O2
Formula weight 1239.99 1149.84
Temperature 120(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Triclinic Triclinic
Space group P1 P1
Unit cell dimensions a = 10.5848(10) ˚
A a = 10.1726(10) ˚
A
b = 10.8801(10) ˚
A b = 12.8486(13) ˚
A
c = 13.7502(13) ˚
A c = 13.5829(13) ˚
A
α= 100.689(2)◦α= 109.395(2)◦
β= 110.562(2)◦β= 99.991(2)◦
γ= 98.145(2)◦γ= 108.506(2)◦
Volume 1419.6(2) ˚
A31508.8(3) ˚
A3
Z 1 1
Density (calculated) 1.450 Mg/m31.265 Mg/m3
Absorption coefficient 0.913 mm−10.775 mm−1
F(000) 649 598
Crystal size 0.20 x 0.20 x 0.04 mm30.45 x 0.12 x 0.07 mm3
Theta range for data collection 1.64 to 28.33◦1.67 to 28.36◦
Index ranges -14≤h≤14, -14≤k≤12, -17≤l≤18 -13≤h≤13, -17≤k≤17, -14≤l≤18
Reflections collected 13715 13022
Independent reflections 6999 [R(int) = 0.0598] 7417 [R(int) = 0.0587]
Completeness to theta = 28.33◦: 98.8 % = 28.36◦: 98.3 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.992 and 0.544 0.943 and 0.423
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 6999 / 21 / 395 7417 / 563 / 342
Goodness-of-fit on F20.804 0.824
Final R indices [I¿2sigma(I)] R1 = 0.0507, wR2 = 0.0802 R1 = 0.0832, wR2 = 0.2001
R indices (all data) R1 = 0.1011, wR2 = 0.0896 R1 = 0.1670, wR2 = 0.2258
Largest diff. peak and hole 0.477 and -0.520 e·˚
A31.172 and -0.642 e·˚
A3
CHAPTER 10. APPENDIX 180
Table A13: Crystal data and structure refinement for C19 and C20
C19 C20
Identification code h1022 h1108
Empirical formula C46H72Cu4I4N14O2C46H72Cu2I6N14O2
Formula weight 1614.94 1741.66
Temperature 120(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Triclinic Triclinic
Space group P1 P1
Unit cell dimensions a = 10.365(3) ˚
A a = 12.8344(5) ˚
A
b = 12.062(4) ˚
A b = 13.2872(6) ˚
A
c = 13.206(4) ˚
A c = 20.8307(9) ˚
A
α= 112.398(5)◦α= 97.149(1)◦
β= 92.525(6)◦β= 103.345(1)◦
γ= 105.352(6)◦γ= 112.581(1)◦
Volume 1452.5(7) ˚
A33100.4(2) ˚
A3
Z 1 2
Density (calculated) 1.846 Mg/m31.866 Mg/m3
Absorption coefficient 3.618 mm−13.719 mm−1
F(000) 790 1676
Crystal size 0.18 x 0.10 x 0.04 mm30.35 x 0.18 x 0.02 mm3
Theta range for data collection 1.69 to 27.88◦1.03 to 28.33◦
Index ranges -13≤h≤13, -15≤k≤15, -17≤l≤17 -17≤h≤17, -17≤k≤17, -27≤l≤27
Reflections collected 18866 39396
Independent reflections 6911 [R(int) = 0.1248] 15344 [R(int) = 0.0701]
Completeness to theta = 27.88◦: 99.7 % = 28.33◦: 99.3 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.939 and 0.654 0.989 and 0.825
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 6911 / 0 / 325 15344 / 0 / 649
Goodness-of-fit on F20.933 0.886
Final R indices [I¿2sigma(I)] R1 = 0.0746, wR2 = 0.1416 R1 = 0.0486, wR2 = 0.0870
R indices (all data) R1 = 0.1548, wR2 = 0.1671 R1 = 0.0967, wR2 = 0.1075
Largest diff. peak and hole 1.012 and -0.952 e·˚
A31.722 (0.95 ˚
A from I22 position)
and -0.936 e·˚
A3
CHAPTER 10. APPENDIX 181
Table A14: Crystal data and structure refinement for C21 and C22
C21 C22
Identification code h1154 h1125
Empirical formula C26H50Cu2F12N12O2P2C50H94Cu2F12N12O2P2
Formula weight 979.80 1312.39
Temperature 120(2) K 120(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Monoclinic
Space group P21/c P21/n
Unit cell dimensions a = 15.4730(8) ˚
A a = 12.3581(9) ˚
A
b = 21.9757(11) ˚
A b = 16.7472(13) ˚
A
c = 13.1940(6) ˚
A c = 14.7430(11) ˚
A
α= 90◦α= 90◦
β= 113.507(1)◦β= 93.156(2)◦
γ= 90◦γ= 90◦
Volume 4114.0(4) ˚
A33046.6(4) ˚
A3
Z 4 2
Density (calculated) 1.582 Mg/m31.431 Mg/m3
Absorption coefficient 1.208 mm−10.836 mm−1
F(000) 2008 1380
Crystal size 0.40 x 0.08 x 0.07 mm30.40 x 0.35 x 0.25 mm3
Theta range for data collection 1.44 to 28.24◦1.84 to 27.88◦
Index ranges -20≤h≤20, -29≤k≤28, -17≤l≤17 -14≤h≤16, -22≤k≤22, -19≤l≤17
Reflections collected 51075 35133
Independent reflections 10156 [R(int) = 0.0625] 7264 [R(int) = 0.0501]
Completeness to theta = 28.24◦: 99.9 % = 27.88◦: 100.0 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.940 and 0.694 0.985 and 0.777
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 10156 / 107 / 533 7264 / 16 / 402
Goodness-of-fit on F20.966 1.035
Final R indices [I¿2sigma(I)] R1 = 0.0490, wR2 = 0.0829 R1 = 0.0549, wR2 = 0.1378
R indices (all data) R1 = 0.1323, wR2 = 0.0967 R1 = 0.0920, wR2 = 0.1618
Largest diff. peak and hole 0.542 and -0.448 e·˚
A30.984 and -0.864 e·˚
A3
CHAPTER 10. APPENDIX 182
Table A15: Crystal data and structure refinement for C23 and C24
C23 C24
Identification code h1177 h1204
Empirical formula C32H66Cu2F12N12O2P2C32H66Cu2I2N12O2
Formula weight 1067.99 1031.85
Temperature 123(2) K 123(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Monoclinic
Space group P21/n P21/n
Unit cell dimensions a = 9.1841(10) ˚
A a = 8.8505(7) ˚
A
b = 20.907(2) ˚
A b = 20.7116(15) ˚
A
c = 12.1186(13) ˚
A c = 11.6387(8) ˚
A
α= 90◦α= 90◦
β= 93.388(2)◦β= 90.962(2)◦
γ= 90◦γ= 90◦
Volume 2322.9(4) ˚
A32133.2(3) ˚
A3
Z 2 2
Density (calculated) 1.527 Mg/m31.606 Mg/m3
Absorption coefficient 1.077 mm−12.487 mm−1
F(000) 1108 1044
Crystal size 0.25 x 0.20 x 0.20 mm30.25 x 0.20 x 0.13 mm3
Theta range for data collection 1.94 to 28.22◦1.97 to 28.08◦
Index ranges -12≤h≤12, -27≤k≤27, -16≤l≤15 -11≤h≤11, -27≤k≤27, -15≤l≤13
Reflections collected 23325 20358
Independent reflections 5714 [R(int) = 0.0733] 5193 [R(int) = 0.0576]
Completeness to theta = 28.22◦: 99.8 % = 28.08◦: 99.9 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.976 and 0.772 0.977 and 0.859
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 5714 / 29 / 324 5193 / 0 / 233
Goodness-of-fit on F21.006 0.892
Final R indices [I¿2sigma(I)] R1 = 0.0449, wR2 = 0.1031 R1 = 0.0441, wR2 = 0.0821
R indices (all data) R1 = 0.0657, wR2 = 0.1124 R1 = 0.0651, wR2 = 0.0877
Largest diff. peak and hole 0.854 and -0.389 e·˚
A30.854 and -0.995 e·˚
A3
CHAPTER 10. APPENDIX 183
Table A16: Crystal data and structure refinement for C25 and C26
C25 C26
Identification code h1301 h1202
Empirical formula C32H66Cl2Cu2N12O10 C38H74Cu2F14N14O4P2
Formula weight 976.95 1246.13
Temperature 120(2) K 123(2) K
Wavelength 0.71073 ˚
A 0.71073 ˚
A
Crystal system Monoclinic Monoclinic
Space group P21/n P21/n
Unit cell dimensions a = 8.780(2) ˚
A a = 11.1872(11) ˚
A
b = 21.045(5) ˚
A b = 19.1481(19) ˚
A
c = 11.837(3) ˚
A c = 12.2954(12) ˚
A
α= 90◦α= 90◦
β= 93.070(4)◦β= 91.595(2)◦
γ= 90◦γ= 90◦
Volume 2184.1(9) ˚
A32632.8(4) ˚
A3
Z 2 2
Density (calculated) 1.485 Mg/m31.572 Mg/m3
Absorption coefficient 1.162 mm−10.971 mm−1
F(000) 1028 1292
Crystal size 0.42 x 0.22 x 0.18 mm30.40 x 0.32 x 0.23 mm3
Theta range for data collection 1.94 to 27.48◦1.97 to 28.46◦
Index ranges -11≤h≤11, -27≤k≤25, -15≤l≤15 -14≤h≤12, -25≤k≤25, -16≤l≤16
Reflections collected 18812 22595
Independent reflections 5011 [R(int) = 0.0682] 6619 [R(int) = 0.0598]
Completeness to theta = 27.48◦: 99.8 % = 28.46◦: 99.7 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.8182 and 0.6411 0.933 and 0.623
Refinement method Full-matrix least-squares on F2Full-matrix least-squares on F2
Data / restraints / parameters 5011 / 0 / 264 6619 / 6 / 339
Goodness-of-fit on F21.011 0.857
Final R indices [I¿2sigma(I)] R1 = 0.0581, wR2 = 0.1345 R1 = 0.0498, wR2 = 0.0931
R indices (all data) R1 = 0.1117, wR2 = 0.1483 R1 = 0.0962, wR2 = 0.1043
Largest diff. peak and hole 0.509 and -0.800 e·˚
A30.855 and -0.558 e·˚
A3
List of Publications:
S. Herres, P. Hesemann, J.J.E. Moreau; Polystyrene Resins Incorporating BINOL Units:
New Materials For Asymmetric Catalysis, Eur. J. Org. Chem. 2003, 99-105
S. Herres, U. Fl¨orke, G. Henkel; N,N´-Bis(dipiperidin-1-ylmethylene)-propane-1,3-diamine
and N,N´-bis-(1,3-dimethylperhydropyrimidin-2-ylidene)propane-1,3-diamine, Acta Crys-
tallogr. Sect. C,2004,60, o358-o360
S. Herres, U. Fl¨orke, G. Henkel; The first di-µ-hydroxo-bridged binuclear copper complex
containing a bisguanidine ligand, Acta Crystallogr. Sect. C 2004,60, m659-m660
S. Herres-Pawlis, U. Fl¨orke, G. Henkel; Catena-Poly[[µ-cyano-[1,3-bis(tetramethylguanidi-
no)propane]dicopper(I)]-µ-cyano], Acta Crystallogr. Sect. E 2005,61, m79-m81
S. Herres, A.J. Heuwing, U. Fl¨orke, J. Schneider, G. Henkel; Hydroxylation of a Methyl
Group: Synthesis of [Cu2(btmmO)2I]+and of [Cu2(btmmO)2]2+ Containing the Novel
Ligand (bis(trimethylmethoxy)guanidino-propane (btmmO) by Copper-Assisted Oxygen
Activation, Inorg. Chim. Acta 2005,358, 1089-1095
S. Herres-Pawlis, U. Fl¨orke, G. Henkel; Tuning of Copper(I)-Dioxygen Reactivity by
Bisguanidine Ligands, Eur. J. Inorg. Chem. 2005, 3815-3824
S. Herres-Pawlis, A. Neuba, O. Seewald, T. Seshadri, H. Egold, U. Fl¨orke, G. Henkel; A
library of peralkylated bisguanidine ligands for use in biomimetic coordination chemistry,
Eur. J. Org. Chem. 2005, pub. adv.
U. Fl¨orke, S. Herres-Pawlis, A.J. Heuwing, A. Neuba, O. Seewald, G. Henkel; The
di-protonated 1,3-bis(N,N,N´,N´-tetramethylguanidinium)propane cation: packing and
conformational changes, Acta Crystallogr. Sect. C 2005, submitted
CHAPTER 10. APPENDIX 185
Fellowships and awards:
05/03 - 04/05 Fonds Fellowship of the Fonds der Chemischen Industrie
03/04 Aventis [i]Lab Award
05/05 - 10/05 ”Promotionsabschlußstipendium” of the University of Paderborn
Conference contributions:
10/03 GDCh-Jahrestagung 2003 Munich (Poster: ”Neuartige Kupferkomplexe mit
aliphatischen und aromatischen Bisguanidin-Liganden”)
03/04 GDCh-JungChemikerForum-Fr¨uhjahrssymposium 2004 Heidelberg (Oral
presentation: ”Tuning of Copper(I)-Dioxygen Reactivity by bisguanidine ligands”)
07/04 36th International Conference on Coordination Chemistry 2004 Merida, Mexico
(Oral presentation ”Introduction of peralkylated bisguanidine ligands into
copper-dioxygen chemistry: a double variety in ligand modification” and
Poster ”A novel aromatic tridentate peralkylated bisguanidine ligand and
its features in copper-dioxygen chemistry”)
01/05 Workshop on Biomimetic Oxygen Activation, Schloß Rauischholzhausen
(Oral presentation: ”Oxygen Activation and Transfer Mediated By Copper(I)
Complexes with Bisguanidine Ligands” and Poster: ”A Modular Approach in
Bisguanidine Ligand Synthesis and its Features in Oxygen Activation and Transfer”)
04/05 6th Conference on Inorganic Chemistry 2005, Funchal, Madeira
(Oral presentation: ”A Library of Peralkylated Bisguanidine Ligands for
Use in Copper-Dioxygen Chemistry”)
07/05 Symposium on the Activation of Dioxygen and Homogeneous Organic Catalysis
(ADHOC) 2005 Cologne (Poster: ”A Library of Peralkylated Bisguanidine Ligands
for Copper Containing Oxidation Catalysts”)
09/05 GDCh-Jahrestagung 2005 D¨usseldorf (Oral presentation: ”Eine Bibliothek
aus Bisguanidin-Liganden zur Synthese von kupferhaltigen Oxidationskata-
lysatoren”, Poster: ”Sauerstoffaktivierung und -transfer durch Kupfer-Bis-
guanidin-Komplexe” and ”Mangankomplexe mit polyfunktionellen Bisguanidin-
liganden”)
