I
Anorganische Chemie
Homoleptic complexes of group 9 and 10 transition metals with
phosphine-functionalized N-heterocyclic carbene ligands
Von der Fakultät für Naturwissenschaften
Department Chemie
Der Universität Paderborn
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
Dr. rer. nat.
genehmigte Dissertation
von
Aziza A. Ahmida
aus Benghazi (Libyen)
Paderborn 2009
II
Date of submission: 23.11.2009
Date of examination: 18.12.2009
1. Referee: Prof. Dr. Gerald Henkel
2. Referee: PD. Dr. Hans Egold
The present work has been carried out during january 2005 and oktober 2009 at the
university of Paderborn, Faculty of Science, Department of Chemistry under
supervision of Prof. Dr G. Henkel.
III
Dedicated to
Dedicated toDedicated to
Dedicated to
Spirit of my parents
My brothers and sisters
IV
Abstract
This dissertation describes the synthesis of phosphane functionalized imidazolium salts and their
use in the preparation of chelating mixed phoshane carbene ligands. The novel ligands were used
for the synthesis of homoleptic complexes of Rh(I), Ir(I), Ni(II) and Pd(II). The reactivity of the
Rh(I) and Ir(I) complexes with respect to small molecules has been investigated and the catalytic
activity of the Pd(II) complexes for Suzuki coupling has been explored as well.
Starting from ethylvinylimidazolium iodide and HPPh
2
the imidazolium ligand precursors E5 and
E6 were synthesized in high yield. Their conversion to the aspired mixed phoshane carbene
ligand E7 has been accomplished in situ by deprotonation with K[N(SiMe
3
)
2
]. The degree of
conversion was almost quantitative as the reaction of the resulting solutions with CS
2
giving the
thiocarboxylate E8 proved.
In situ generated E7 reacts with 0.5 equivalents [Rh(µ-Cl)(COD)]
2
to give the novel homoleptic
Rh(I) complexes cis-E10, trans-E12, cis-E11, trans-E13 in high yields. All new complexes have
been structurally characterized by single crystal X-ray crystallography. NMR spectroscopic
stuidies of the dynamic behaviour of the complexes in solution have proved interconversion of
cis- and trans-isomer at elevated temperatures. A mechanism for this reaction has been proposed.
The oxidative addition of small molecules like O
2
, S
8
, CH
3
I, I
2
to cis-Rh(I) complexes E10 or
E11, respectively, afforded novel Rh(III) complexes E14, E15, E16, E17, E19. All new
complexes have been characterized by standard spectroscopic methods and single crystal X-ray
analysis. The complicated solution dynamics of the cis-peroxo-Rh(III) complex E14 was
explored in detail by
31
P NMR-spectroscopy. The synthesis of novel cis-Ir(I) complex E20 has
been achieved by reaction of E7 with [Ir(µ-Cl)(COD)]
2
.
It reacts with H
2
, O
2
, S
8
, CO, CH
3
I, I
2
giving the novel Ir(III) complexes, E21, E22, E23, E24, E25, E26. Their structures are described
in detail. The synthesis of novel homoleptic trans-Ni(II) and Pd(II) complexes, E27, E28 and
their structural spectroscopic properties is described as well. The interconversion between cis and
trans isomers of Pd(II) complex E28 at high temperature was again proved by
31
P NMR
spectroscopy. The catalytic activity of trans-Pd(II) complex E28 with respect to Suzuki coupling
was surveyed.
V
Acknowledgements
First of all thanks to Allah who enabled me to complete this work. I would like to express my
deepest gratitude to my supervisor Prof. Dr. Gerald Henkel for giving me the opportunity of
joining his group and giving me his valuable guidance and continuous encouragement through
out this work.
From the depths of my heart I would like to express my thanks to PD Dr. Hans Egold for fruitful
discussions throughout this work and continous encouragement. He constantally supported this
work with both general advice and detailed comments and proof-reading.
I am grateful to Dr. Ulrich Flörke for his efforts of recording X-ray data and refining the X-ray
structures described in this thesis.
Furthermore, I am gratful to Mr. Jörg Schröder for his useful advice on special working methods
for experiments under inert gas atmosphere.
My gratitude goes to Mrs Karin Stolte for the countless hours of recording 2D NMR spectra and
to Mrs Maria Busse and Mrs Christiane Gloger for carrying out the elemental analyses.
My special thanks goes to my ever helpful colleague Mehmet Özer who always gave me
assistance with any computer related issues.
Also I would like to express my appreciation to Dr Ishtiaq Ahmed for proof-reading.
Thanks to all members of the working group of Prof. Dr. Gerald Henkel. Especially to my
colleague Muhammad Ayaz for the nice working atmosphere in the lab.
Thank you for all friends who have been there for me during my stay in Germany – especially
Intisar Elsharaa and Zuhl Gürbüz.
I gratefully acknowledge the financial support of Libyian Ministry of Higher Education and
German Academic Exchange Service (DAAD).
Finally, a big thank to my family for their invaluable support during these five years.
VI
Contents
1 Introduction 1
1.1 N-Heterocylic carbenes (NHC) 1
1.2 Hybridisation and structures 3
1.2.1 Singlet vs triplet carbenes 3
1.2.2 Electronic properties of different types of singlet carbenes 3
1.2.3 Mesomeric effects. 4
1.2.4 Carbene containing two π-acceptors substituents 5
1.2.5 Carbenes with two π-donor substituents 5
1.2.6 Carbenes with π-donor and π-acceptor substituents 7
1.3 Synthesis of free carbenes 8
1.4 NHC-carbene complexes 12
1.4.1 Classification of Fischer and Schrock-carbene complexes. 12
1.4.2 Comparsion between NHC-ligands and phosphine ligands 13
1.5 Synthesis of imidazolium salts as educts for the preparation of free
NHC ligands and NHC complexes 14
1.6 Synthetic routes to N-heterocyclic carbene complexes 16
1.6.1 Substitution reaction with free NHCs 16
1.6.2 Reactions of imidazolium salts with small metal complexes comprising
basic ligands 18
1.6.3 Reaction of transition metal complexes with electron rich olefines. 18
1.6.4 Unusual methods 19
1.6.5 Transmetallition reactions 20
1.7 N-heterocyclic carbenes in catalysis 22
1.7.1 Hydrosilylation 23
1.7.2 Hydrogenation 23
1.8 Cross-coupling in homogeneous catalysis 24
1.8.1 Songashira coupling 25
1.8.2 Kumada coupling (Grignard cross coupling) 26
1.8.3 Stille coupling 26
1.8.4 Heck coupling 27
VII
1.8.5 Suzuki coupling 28
2 Aim of work 32
3 Results and discusion 34
3.1 Synthesis of ligand 34
3.1.1 Ligand precursors 34
3.1.2 Properties of the imidazolium salts 35
3.1.2.1 X-ray crystallographic analysis of 3-[2-(diphenylphosphino)ethyl]-1-
Ethylimidazolium-hexafluorophosphate (E6) 37
3.1.3 In situ synthesis of free carbene 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazol-2-ylidene(E7) 39
3.1.3.1 Identification of imidazol-2-ylidendithiocarboxylate (E8) 39
3.1.3.2 X-ray crystallographic analysis of 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazol-2-dithiocarboxylate E8 40
3.1.3.3 Electrochemistry of 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazolium-hexafluorophosphate (E6) 44
3.2 Rhodium complexes 45
3.2.1 Syntheses and characterization of cationic cis and
trans-rhodium(I) complexes with E7 45
3.2.2 Single crystals X-ray structure analyses of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]X
(X = Cl
(E10), PF
6
(E11)) 47
3.2.3
Single crystal X-ray structure analyses of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]X
(X = Cl (E12), PF
6
(E13)) 50
3.3 Equilibrium between cis and trans isomers at higher temperatures 54
3.4 Electrochemistry of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E11) 58
3.4.1 Electrochemistry of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl, (E12) 59
3.5 Synthesis of peroxo complexes 60
3.5.1 Synthesis and dynamic behaviour of cis and trans-[Rh(η
2
-
O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]X, (X = Cl
(E14), PF
6
(E15)) 60
3.5.2 X-ray crystallographic analyses of cis-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
(E14A, X = Cl or PF
6
) 64
VIII
3.5.3
Single crystal X-ray structure analysis of trans-[Rh(η
2
-O
2
)
(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
E15 66
3.6
Oxidative addition
of small molecules viz, (S
8,
CH
3
I, I
2
) to the cis-rhodium(I)
complex
E11 69
3.6.1 Synthesis and structure of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E16) 69
3.6.1.1 Single crystal X-ray structure analyses of cis-[Rh(η
2
-S
2
)
(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]. (E16) 71
3.6.2 Synthesis of cis-[Rh(CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E17, E18) 74
3.6.3 Synthesis of cis-[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
][I
3
], E19 74
3.6.3.1 Single crystal X-ray structure analysis of cis-
[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
][I
3
] (E19) 75
3.7 Iridium complexes 77
3.7.1 Synthesis of cis-[Ir(EtImCH
2
CH
2
PPh
2
)][PF
6
] (E20) 77
3.7.1.1 Single crystal X-ray structure analyses of cis-
[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E20) 78
3.8 Reaction of small molecules viz, (H
2
, O
2
, S
8,
CO, CH
3
I, I
2
) to cis-Iridium(I)
complex (E20) 82
3.8.1 Synthesis and characterization of
cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
](E21) 82
3.8.1.1 Single crystal X-ray structure analysis of
cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E21) 83
3.8.2 Synthesis and characterization of
cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E22) 85
3.8.2.1 Single crystal X-ray structure analysis of
cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E22) 87
3.8.3 Synthesis and characterization of
cis-[Ir(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E23). 89
3.8.3.1 Single crystal X-ray structure analysis of cis
[Ir(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E23) 90
3.8.4 Synthesis of five coordinate Iridium(I) complex
[Ir(CO)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E24) 92
IX
3.8.5 Synthesis of iridium(III)complex, trans-[Ir(CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
)]I
(E25) 92
3.8.5.1 Single crystal X-ray structure analysis of trans-
[Ir(CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
]I (E25) 94
3.8.6 Synthesis and characterization of cis-[Ir(I)
2
(EtImCH
2
CH
2
PPh
2
)
2
][I
3
]
(E26) 96
3.8.6.1 Single crystal X-ray structure analysis of cis-
[Ir(I)
2
(EtImCH
2
CH
2
PPh
2
)
2
][I
3
]
(E26) 97
3.8.7 Electro chemistry of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E20) 98
3.9 Nickel complex 99
3.9.1 Synthesis and spectroscopic characterization of
trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
][I]
2
(E27) 99
3.9.1.1 Single crystal X-ray structure analysis of trans
[Ni(EtImCH
2
CH
2
PPh
2
)
2
]
[I]
2
(E27) 100
3.10 Palladium complex 102
3.10.1 Synthesis and spectroscopic characterization of
trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28) 102
3.10.1.1 Single crystal X-ray structure analyses of
Trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28) 103
3.10.2 Equilibrium between cis- and trans-isomers of E28 at higher temperatures 105
3.10.3 Electrochemistry of trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28) 107
3.10.4 Suzuki-coupling with E28 108
4 Experimental Section 110
4.1 Material and Methods 110
4.1.1.General Consideration 110
4.1.2 Physical measurements 110
4.2 Synthesis of NHC-phoshane ligands 111
4.2.1 Synthesis of 3-ethyl-1-vinylimidazolium-3-iodide (E3) 111
X
4.3 Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazoliumiodide (E5) 112
4.4 Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium-hexa-
fluorophosphate (E6) 112
4.5 Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazol-2-dithio-carboxylate
(E8) 113
4.6 Synthesis of metal complexes 114
4.6.1 Synthesis of cis-complex [Rh(EtIMCH
2
CH
2
PPh
2
)
2
]Cl
(E10) 114
4.7 Synthesis of cis-complex [Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E11) 115
4.8 Synthesis of trans-complex [Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl, (E12) 116
4.9 Synthesis of trans-complex [Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E13) 116
4.10 Synthesis of cis-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][X]
(X = Cl or PF6) (E14) 117
4.11 Synthesis of trans-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E15) 118
4.12 Synthesis of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E16) 119
4.13. Synthesis of cis-[Rh(CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
], (E17) 120
4.14 Synthesis of cis-[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
][I
3
], (E19) 120
4.15 Synthesis of cis-[Ir(EtImCH
2
CH
2
PPh
2
)][PF
6
] (E20) 121
4.16 Synthesis of cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E21) 122
4.17 Synthesis of cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(E22) 123
4.18 Synthesis of cis-[Ir(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E23) 124
4.19 Synthesis of cis-[Ir(CO)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E24) 125
4.20 Synthesis of trans-[Ir(CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
)]I (E25) 125
4.21 Synthesis of cis-[Ir(I)
2
(EtImCH
2
CH
2
PPh
2
)
2
][I
3
] (E26) 126
4.22 Synthesis of trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
]
[I]
2
(E27) 127
4.23 Synthesis of trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28) 128
4.24 Synthesis of cis-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28) 129
4.25 Suzuki coupling reaction 130
5. Conclusions 131
6 Bibliography 135
7 Appendix 147
XI
List of Figures
1.1 The first isolated singlett carbenes 1
1.2 Transition metal complexes synthesised by Öfele and Wanzlik 1
1.3 Stable NHCs and their derivatives 2
1.4 Electronic configuration of carbenes 3
1.5 Molecular orbital diagram of a triplet carbene 4
1.6 Molecular orbital diagram for a singlet carbene 4
1.7 Molecular orbital diagram.of a (Z,Z)-carbene 5
1.8 Molecular orbital diagram.of (X,X)-carbene 6
1.9 Molecular orbital diagram of a (X,Y)-carbene 7
1.10 N-heterocyclic carbene complexes 11
1.11 Orbital diagrams of a Fischer-(I), Schrock-(II), and N-heterocyclic
carbene complexes (III) fragment 13
1.12 Schrock and Fischer carbene complexes 13
1.13 bis, tris, tetreakis carbene complexes 19
1.14 Principle of palladium catalyzed cross-coupling reactions (X = I, Br, Otf, Cl, F) 24
1.15 Simplified catalytic cycle for palladium mediated cross-coupling reactions 25
1.16 Some example of Pd(II) complexes which used in Heck raction 27
1.17 New mechanism for palladium catalysed cross-coupling reactions 31
3.1 Synthesis of 3-[2-(diphenylphosphino)ethyl]-ethylimidazoliumhexafluorophosphate 34
3.2 Structure of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium-
cation in crystals of E6 38
3.3 Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-imidazole-2-ylidene 39
3.4 Transformation of E7 to dithiocarboxylate E8 39
3.5
S
tructure of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazol-2-dithiocarboxylate E8 in
the crystal 41
3.6 Structure of 1,3-di-isopropyl-bis-4,5-methylimidazolium-dithio-carboxylate E9
in the crystal 42
3.7 Cyclovoltammogram of 3-[2-diphenylphosphino)ethyl]-1-imidazoliumhexa-
fluorophosphate E6 in THF 44
3.8 Synthesis of cis- and trans- Rh(I) complexes 45
XII
3.9 Structure of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E10 48
3.10 Structure of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E11 50
3.11 Structure of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E12 52
3.12 Structure of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E13 52
3.13
31
P-NMR spectrum of a mixture of cis and trans isomers E10 and E12 54
3.14 Temperature dependent
31
P NMR-spectrum of isomerization of cis-E10 to trans-E12 55
3.15 Temperature dependent
31
P-NMR spectra of thermal isomerization
of trans-E12 to cis-E10 56
3.16 The equilibrium between cis-E10 and trans-E12
isomers of [Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl 56
3.17 Postulated mechanisms for the interconversion of E10 and E12 57
3.18 Cyclovoltammogram of E11 in CH
3
CN 58
3.19 Cyclovoltammogram of E12 in CH
3
CN 59
3.20 Formation of cis- and trans-peroxo complexes E14, E15 60
3.21
31
P-NMR spectrum of peroxo adduct E14 at different temperature 62
3.22
31
P-NMR spectra of [Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]Cl at 343K 63
3.23a Structure of the ∆-isomer of cis-[Rh(η
2
O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in
crystals of E14A, (without hydrogen atoms) 64
3.23b Structure of the Λ-isomer of cis-[Rh(η
2
O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in an enantiomerically pure crystal of E14B, (without hydrogen atoms) 66
3.24 Structure of trans-[Rh(η
2
O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E15,
(without hydrogen atoms) 67
3.25 Synthesis of novel rhodium(III) complexes. 69
3.26
31
P-NMR spectra of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E16) 71
3.27 Structure of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E16,
(without hydrogen atoms) 72
3.28 Structure of cis-[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E19,
(without hydrogen atoms) 76
3.29 Synthesis of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E20) 77
XIII
3.30 Structure of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E20 79
3.31 Structure representation of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
]
+
and
cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E20 and E11 81
3.32 Reactions of small molecules with E20 82
3.33 Structure of cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E21,
(without hydrogen atoms) 84
3.34
31
P-NMR spectra of cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E22) at 70°C 86
3.35 Structure of cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E22,
(without hydrogen atoms) 88
3.36 Structure of cis-[Ir(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E23,
(without hydrogen atoms) 90
3.37 Structure of trans-[Ir(CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E25,
(without hydrogen atoms) 95
3.38 Chemical structure of the isomers in E26 96
3.39 Structure of the cis-[Ir(I)
2
(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E26,
(without hydrogen atoms) 97
3.40 Cyclovoltammogram of E20 in THF 98
3.41 Synthesis of trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
]
++
E27 99
3.42 Structure of trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
]
++
in crystals of E27,
(without hydrogen atoms) 101
3.43 Synthesis of cis- and trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28) 102
3.44 Structure of trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
]
2+
in crystals of E28,
(without hydrogen atoms) 104
3.45 Temperature dependent
31
P NMR-spectrum of isomerization of cis- to trans of E28 105
3.46 The equilibrium between cis-E28 and trans-E28 isomers of
[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] 106
3.47 Cyclovoltammogram of E28 in CH
3
CN 107
XIV
List of Tables
3.1
1
H-NMR-spectra of E5 and E6 in CD
3
CN 36
3.2
13
C-NMR-spectra of E5 and E6 in CD
3
CN 37
3.3 Selected Bond lengths [Å] and Bond Angles [º] for E6 38
3.4 Selected Bond lengths [Å] and Bond Angles [º] for E8 and E9 43
3.5 Selected bond lengths [Å] and bond angles [°] of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl
(E10) and cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E11) 49
3.6 Selected bond lengths [Å] and bond angles [º] for trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl
(E12) and trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E13) 53
3.7 Selected bond lengths [Å] and angles [º] of peroxo complex E14A 65
3.8 Selected bond lengths [Å] and angles [º] of peroxo complex E15 68
3.9 Selected bond lengths [Å] and angles [º] of [Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
(E16) 73
3.10 Selected bond lengths[Å] and angles [º] of E19 76
3.11 Selected bond lengths [Å] and angles [º] of cis-Ir(I)complex E20 80
3.12 Selected bond lengths [Å] and angles [º] for E11 and E20 81
3.13 Selected bond lengths[Å] and angles [º] of cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
]
+
(E21) 85
3.14 Selected bond lengths [Å] and angles [º] of cis-Ir(III)complex E22 89
3.15 Selected bond lengths [Å] and angles [º] for cis-iridium(III) complex E23 91
3.16 Selected bond lengths [Å] and angles [º] for the trans-iridium(III) complex E25 95
3.17 Selected bond lengths [Å] and angles [º] for trans-Nickel(II) complex E27 101
3.18 Selected bond lengths[Å] and angles [º] for trans-palladium(II) complex E28 104
3.19 Suzuki coupling of aryl halides and 3-ethoxyphenyl boronic acid for E28 108
XV
Abbreviations
Ac acetate
acac acetyl acetonate
OAc acetyl acetate
CD
3
CN acetonitrile-d
3
Ad adamantyl
Å angstrom(10
-10
m)
Bu butyl
Cat catalyst
C
6
D
6
benzene-d
6
δ chemical shift
COD 1,5-cyclooctadiene
CV cyclovoltametry
d doublet
dd double doublet
dba dibenzylidenaceton
DMSO dimethylsulfoxide
Et ethyl
Et
2
O diethyl ether
PPh
2
diphenylphosphane
ν frequency
hept heptet
Hz hertz
hr hour
Im imidazol-2-ylidene
iPr isopropyl
IR infrared
J scalar coupling constant (NMR)
m multiplet
XVI
Mes mesityl
NHC N-heterocyclic carbene
NHE normal hydrogen electrode
NMR nuclear magnetic resonance
ppm parts per milion
Ph Phenyl
q quartet
s singlet (NMR), strong (IR)
RT room temperature
t triplet
t
Bu tertiary-butyl
THF tetrahydrofuran
temp temperature
Me
3
Si trimethylsilyl
sept septet
1
1 Introduction
1.1 N-Heterocyclic carbenes (NHC)
Since the pioneering work of Curtius,
[1a]
Staudinger,
[1b]
and even earlier efforts
[1c]
carbenes have
played an important role as transient intermediates over the last five decades.
[2]
The application of
carbenes into organic chemistry and organometallic chemistry was introduced by Doering in the
1950s
[3]
and by Fischer 1964
[4]
respectively. Since then research on carbenes has rapidly
expanded, but almost no attempts were made to stabilize carbenes until the 1980s when Tomioka
started to study persistent triplet diaryl carbenes.
[5]
The first isolated singlet carbenes were
reported in 1988 by Bertrand
[6]
1 and in 1991 by Arduengo
[7]
2. The phosphino carbene 1 can be
distilled at 80-85 °C
0
/10
-2
Torr and the N-heterocyclic carbene (NHC) 2 is a crystalline solid
that melts above 240 °C (Figure 1.1).
12
N
N
Ad Ad
P
Me
3
Si N
i
Pr
2
N
i
Pr
2
Figure 1.1: The first isolated singlett carbenes.
Although the use of N-heterocyclic carbenes as ligands for transition metal complexes was
described almost 36 years ago by Öfele and Wanzlick who prepared compounds 3 and 4.
[8,9]
Figure 1.2: Transition metal complexes synthesised by Öfele and Wanzlik
In 1968 Wanzlick et al proposed that there is an unfavourable equilibrium between carbenes with
their corresponding dimers [eq.1]. His suggestion came from molecular weight measurements.
[10]
2
(eq. 1)
Lemal
[11,12]
proved Wanzlick’s hypothesis of a carbene dimer equilibrium between the
tetraaminoethylene 5 and the corresponding free carbene 6 (eq. 2) by NMR spectroscopy.
(eq. 2)
The particular stability of NHCs made them very popular and during the last years further
analogues were synthesized (Figure 1.3). In 1995 Arduengo proved
[13]
by preparation of NHC 7
that aromaticity is not needed to stabilize a free singlet carbene. In 1996 Alder even isolated an
example of the acyclic NHC 8.
[14]
This research area is continually expanding which can be seen from the isolation of novel four–
membered carbene
[15]
9 by Grubbs and the alkyl carbene
[16]
10 by Bertrand. These types of
NHCs are more electron rich, but also lack any aromatic character.
Figure 1.3: Stable NHCs and their derivatives
3
1.2 Hybridisation and structures
1.2.1 Singlet vs. triplet carbenes
Carbenes are neutral divalent carbon species linked to two adjacent groups by covalent bonds.
They possess two non-bonding electrons and six valence electrons. The non-bonding electrons
can be either spin paired (singlet state) or have parallel spins in different orbitals (triplet
state).Figure 1.4 shows the possible arrangements of these two electrons.
[17]
σσσσ
Ρ
π
Ρπ Ρπ Ρπ
Singlet Carbenes Triplet Carbene
Figure 1.4: Electronic configuration of carbenes.
[17]
1.2.2 Electronic properties of different types of singlet carbenes
Electronic effects generally control the spin multiplicity of a carbene although steric effects can
also play a role in the stabilization and spin multiplicity. The difference in energy between the σ
and p(π) orbitals can be used to predict the spin multiplicity of the carbene. The type of
substituents bonded to the carbene atom can influence the energy of orbitals by their electron
withdrawing or donating nature.The geometry of the carbenes substituted with inductive electron
donating residues leads to non linear structures (but closer to 180º than 120º) favoring triplet
states. This originates from the +I effect of the σ-electron donating substituents which induce a
small σ-p(π)
gap (HOMO/LUMO) between the non bonding σ orbital and anti bonding p(π)
orbital. In this case the energy gap is smaller than the spin pairing energy and therefore these
carbenes favors the triplet state (Figure 1.5).
[17]
4
Figure 1.5: Molecular orbital diagram of a triplet carbene.
[17]
σ-electron-withdrawing substituents favor the singlet state. Indeed σ-electron-withdrawing
substituents inductively stablize the σ nonbonding orbital by increasing its s character and leave
the p(π)orbital unchanged. The σ-p(π) gap is increased and the singlet state is favored. The free
electrons are paired in the non bonding σ-orbital (Figure 1.6).
[17]
Figure 1.6: Molecular orbital diagram for a singlet carbene.
[17]
1.2.3 Mesomeric effects
Substituents interacting with the carbene center can be classified into two types, namely X (for π-
electron-donating groups such as (-F, -Cl, -Br, -I, -NR
2
, -PR
2
, -OR, -SR, -SR
3
) and Z (for π-
electron with withdrawing groups such as (-COR, -CN, -CF
3
, -BR
2
, -PR
3+
). Therefore according
5
to the substituents singlet carbenes can be classified into highly bent (X,X) carbenes and linear or
quasi linear (Z,Z/X,Z) carbenes.
1.2.4 Carbenes containing two π
ππ
π-acceptor substituents
Most of the (Z,Z) carbenes are predicted to be linear singlet carbenes.
[18,19]
These carbenes are
best described by the superposition of two zwitterionic structures featuring a positive charge at
the carbene atom, an example of this type are diborylcarbenes 11.
[20]
For this type of compound, the symmetric combination of the substituents vacant orbitals
interacts with the p
y
-orbital of the carbon atom, which is perpendicular to the valance plane
(Figure 1.7). This interaction does not affect the p
x
-orbital. Therefore the (p
x
,p
y
)-degeneracy is
broken leading to a singlet state for this type of compounds.
[17]
Note that this pattern of
substituents results in a polarized two electron three-center π-system. Hence the C-Z bonds have
some multiple bond character.
Z----Z
P
y
P
x
π
Ρπ
σ
σ
E
P
z
Figure 1.7: Molecular orbital diagram of a (Z,Z)-carbene.
[17]
1.2.5 Carbenes with two π
ππ
π donor substituents
(X,X)-carbenes are predicted to be bent singlet carbenes.
[18,19]
The energy of the vacant p(π)
orbital on the carbene carbon atom is increased by interaction with the symmetric combination of
6
the substituents lone pairs. Thus the σ-p(π) gap is increased and the singlet state is favored
(Figure 1.8). Donation of the X-substituent lone pairs result in a polarized four electron three
center bonding system.The C-X bonds acquire some multiple bond character. This type of
carbenes can be described by the superposition of two zwitterionic structures with a negative
charge at the carbene center
Figure 1.8: Molecular orbital diagram of (X,X) carbene.
[17]
Representative examples for these carbenes are the transient dimethoxycarbene,
[21]
dihalocarbenes
[22]
and NHC–carbenes 13 in which the carbene electron deficiency is reduced by
the donation of the two nitrogen lone pairs while the carbene lone pair is stabilized by the
inductive effect of two electronegative nitrogen atoms.
13
N
N
R
R
R
R
As described above NHC-carbenes do not undergo electrophilic reactions like insertion or
cycloadditions. Furthermore, they can be handled in typical donor solvents including THF, liquid
ammonia or acetonitrile.
[23]
Wanzlick reported that delocalization of 6π electrons in unsaturated NHC five membered rings is
responsible for the stability of these carbenes.
[24]
Öfele and Hermann on the other hand, showed
that the addition of OsO
4
to the C-C double bond in the ring that little aromatic character exists
[25]
7
(eq. 3). This observation is supported by quantum mechanical calculations of the charge
distribution confirming these properties.
[26,27]
N
N
CH3
CH3
M(CO)5
M = Cr , Mo ,W
+OsO4
N
NOsO
OO
OM(CO)5
N
N
H
H
CH3
CH3
+2C5H5N
(eq. 3)
1.2.6 Carbenes with π
ππ
π-donor and π
ππ
π-acceptor substituents
(X,Z)-carbenes exist in the singlet state and are best described by the superposition of two
zwitterionic structures with a negative charge at the carbene center or as an allene type system. A
good example of this type of carbenes are phosphinosilylcarbenes.
[28]
.
CP SiR
3'
R
R
CP SiR
3'
R
RCP
R
R
SiR
3`
14b 14c
14a
This carbene combines electron donating and accepting interactions (Figure 1.9). The P-
substituent lone pair interacts with the empty p
y
-orbital of the carbon atom while the Si-
substituent vacant orbital interacts with the filled p
x
-orbital of carbon. These substituent effects
are both stabilizing and favor the singlet state. The vacant p
y
-orbital is destabilized while the
filled p
x
-orbital is stabilized.
E
y
x
P
y
P
X
Ρ
π
σσ
π
Figure 1.9: Molecular orbital diagram of a (X,Y)-carbene.
[17]
8
1.3 Synthesis of free carbenes
In the early 1960s, Wanzlick tried to prepare 1,3-diphenylimdazolidin-2-ylidene 16 from 15 by
thermal elimination of chloroform (eq. 4).
[29]
The formation of the electron-rich olefin is
generally seen in the saturated imdazolium based systems but not in the unsaturated imidazolium
systems. The formation of the olefin (dimer) may be indicative that the saturated carbenes are
less stable than the unsaturated carbenes. The increased stability of the unsaturated carbenes is
likely due to the stabilization of the p(π) orbitals by the aromatic π system.
[7]
N
N
N
N
H
CCl3
Ph
Ph
- HCCl3
Ph
Ph
15 16 17
N
NN
N
Ph
Ph
Ph
Ph
(eq. 4)
At that time, only the dimeric electron rich olefine 17 was isolated and cross coupling
experiments did not support an equilibrium between 17 and two carbene units of 16.
[30]
In 1970
Wanzlick and coworkers demonstrated that the imidazolium salt 18 could be deprotonated by
potassium tert-butoxide to afford the corresponding imidazole-2-ylidenes 19 which were not
isolated, (eq. 5)
[31]
but allowed to react with phenylisothiocyanate to give the betaine 20. The
analogous reaction of 21 with mercury chloride results in the formation of the mercury carbene
complex 23 (eq. 6).
[32]
N
N
N
N
Ph
Ph
Ph
Ph
HN
N
Ph
Ph
Ph
C
ClO
4
K
t
OBu
- HClO
4
Ph
Ph
Ph
Ph
S C N Ph
45%
Ph N-Ph
SH
18 19 20
(eq. 5)
9
(eq. 6)
However, in none of these examples the free carbene has been observed or isolated, respectively.
The first isolated crystalline carbene was obtained by Arduengo et al. in 1990 (eq. 7)
[7]
Compounds 25 was synthesized by deprotonation of 1,3-di-adamantylimidazolium chloride 24
with sodium or potassium hydride, respectively, in dimethylsulfoxide. The colorless crystals of
25 are airstable and melt at 240-241°C. The free NHC has been characterized by a variety of
spectroscopic methods.
(eq. 7)
Hermann and coworkers
[33]
showed that the deprotonation of imidazolium salts like 26 with NaH
occurs much faster in liquid ammonia. Carbenes with functional groups like e.g. alkoxy groups,
amino groups or phosphanido groups (27d-f) as well as chiral carbenes like 27g and bis-imidazol
-2-ylidenes like 27h have been prepared following this procedure (eq. 8).
(eq. 8)
10
In 1993 Kuhn and co-workers developed a new and versatile approach to alkyl substituted
NHCs.
[34]
In the first step they reacted the N,N-dialkylthioureas 29a-c with 3-hydroxyl-2-
butanone 28 to yield imidazole-2(3H)-thiones 30a-c in high yield. The latter were reduced with
potassium in boiling THF yielding the carbenes 31a-c (eq. 9).
(eq. 9)
In the same year Arduengo isolated and characterized the saturated carbene 33 by deprotonation
of the imidazolium salt 32 with potassium hydride in THF at room temperature (eq. 10).
[13]
(eq. 10)
In 1995 Enders et al. developed another synthetic method for the preparation of NHCs. 1,2,4-
triazol-5-ylidene 35 was obtained from the corresponding 5-methoxy-1,3,4-triphenyl-4,4-dihydro
11
-1,2,4-triazole 34 by thermal elimination of methanol at 80° C under reduced pressure (0.1 mbar)
(eq. 11).
[35]
Compound 35 became the first carbene to be commercially available.
(eq. 11)
Following the above described synthetic routes many different types of stable amino-carbenes
like imdazolidin-2-ylidenes 36,
[36]
tetrahydropyrimid-2-ylidene 37,
[37].
Imidazol-2-ylidenenes
38,
[7,33,38-41]
, 1,2,4-triazol-5-ylidenes 39
[36]
, 1,3-thiazol-2-ylidenes 40
,[42]
as well as acyclic
diamino-41,
[14,43]
aminooxy 42,
[44]
and aminothiocarbenes 43
[46]
have been isolated (Figure.1.10).
In all of these compounds, the carbene center bears two π-donor substituents, of which at least
one is an amino group. The superior π-donor ability and therefore the superior stabilizing effect
of amino groups has been evidenced experimentally.
Figure 1.10: N-heterocyclic carbene complexes.
[17]
12
1.4 NHC-Carbene complexes
1.4.1 Classification of Fischer and Schrock-Carbene Complexes
Carbene complexes have been divided into two types according to the nature of the formal metal-
carbon double bond.
[45]
The molecular orbital diagrams in (Figure 1.11)
[46]
depict the bonding of
Fischer (I)-and Schrock (II)-carbenes. In Fischer type carbene complexes a singlet carbene ligand
binds to the metal. Therefore Fischer carbenes like 45
[4]
(Figure 1.12) are linked to
the metal with
a σ-bond and have an empty p-orbital which is capable to accept electron density from the metal.
Hence the carbene atom is an electrophile. At least one organic substituent of the carbene atom is
able to act as a good π-donor. Consequently the empty p-orbital of the carbene atom is stabilized
by significant π-contribution from both the substituents and the metal. However, good π-back-
donation from the metal to the empty p-orbital of the carbene is critical. In order to be a good π-
donor the transition metal in Fischer carbene complexes like 45 (Figure 1.12) must belong to the
late transition metals and it should be preferably in a low oxidation state.
In Schrock type carbene complexes
[47]
a triplet carbene ligand binds to the metal. Schrock
carbene ligands have nucleophlic character and tend to bind well with early transition metals in
high oxidation states. Better π-donation from the filled p-orbital of the carbene to the d
π
-orbital of
the metal is achieved if the d-orbitals are empty thereby reducing electron repulsion in the
overlapping orbitals. Good organic substituents for Schrock carbenes no π-donor functions, such
as alkyl groups. Due to the presence of two π-donor substituents at the carbene center the N-
heterocyclic carbene complexes are similar to Fischer-type compounds, however imidazoline-2-
ylidenes bind to transition metals through σ-donation, π-backbonding being negligible. N-
heterocyclic carbene complexes (III) are also depicted in Figure 1.11. The stability of an NHC is
largly due to the π-donation from the p-orbitals of the adjacent nitrogen atoms to the empty p-
orbital of the carbene. Due to that the electron density around the carbene atom increases and the
σ-donating ability of the carbene ligands tends to increase the electron density at the metal center
as shown in (Figure 1.11).
[48]
13
Figure 1.11: Orbital diagrams of a Fischer-(I), Schrock-(II), and N-heterocyclic carbene complexes (III) fragment
[46]
Figure 1.12: Schrock (44) and Fischer (45) carbene complexes
1.4.2 Comparsion between NHC-ligands and phosphine ligands
NHCs act as nucleophilic two electron donor ligands that can substitute classical 2e
-
donor ligands
such as amide, ethers and phosphines in coordination chemistry.
[25,33,49-56]
Experimental studies in
1993 have demonstrated that NHC show bonding properties similar to those of trialkyl
phosphines and alkyl phosphinites.
[57]
Nolan et al. concluded from structural and
thermodynamical studies that generally NHC ligands are far better donor ligands than phosphines
and phosphinites.
[58]
Several advantages are gained in using NHC rather than phosphine
analogues. These include high M-L bond strengths compared to phosphine ligands.
[58,59-63]
This
property appears to foster higher ligand stability even under oxidizing reaction conditions (eq.
12).
(eq. 12)
14
Measurements of the carbonyl stretching frequencies of Ni(CO)
3
L have revealed that NHC
carbonyl complexes have lower C-O stretching frequencies than their phosphine
counterparts.
[59,63-65]
These data which have been confirmed by other studies suggest that NHCs
are stronger σ-donors than even the most basic tertiary phosphines.
[36]
Due to this strong σ-donor
character NHCs also stabilize metals in high oxidation states and their high M-L bond
dissociation energy renders them less susceptible to oxidative decomposition
.
1.5 Synthesis of imidazolium salts as educts for the preparation of free NHC
ligands and NHC complexes
There are three different routes to synthesize unsaturated imidazolium salts. The first route (eq
13) involves a reaction between potassium imidazol 46 and a primary halide to give the
substituted imidazol 47, followed by a second addition of a primary halide to yield the
imidazolium salts 48.
[66-68]
(eq. 13)
The second route (eq.14) involves a reaction between the trimethylsilyl-substituted imidazole 49
and two equivalents of a primary alkylchloride. The trimethylsilyl group is replaced, forming the
volatile trimethylsilylchloride and the alkyl substituted imidazolium salt 50.
[69]
(eq. 14)
In order to introduce a bulky substituent group at the nitrogen atoms of the ring, a reaction
between two molecules of primary amines, glyoxal and formaldehyde in the presence of
hydrochloric acid is carried out. The straightforward reaction and is depicted in (eq 15).
[6,54,70]
15
(eq.15)
A combination of the previous two methods allows the synthesis of bulky imidazolium salts by
firstly preparing a substituted imidazole through the formaldehyde/glyoxal route in the presence
of ammonium salt and a subsequently alkylation using a primary alkylhalide giving
unsymmetrically N-substituted derivatives (eq.16).
[71]
(eq 16)
By use of this route a potentially bidentate imidazoilum salt were synthesized through the
reaction of two equivalents of the alkylimidazol 51 with methylene iodide to yield the bis
imidazolium iodides 52 (eq. 17).
(eq. 17)
N-arylimidazoles are synthesized by reaction of aryl halide 53 and imidazole 54 in the presence
of the catalyst (CuOTf)
2.
PhH and the base Cs
2
CO
3
to yield an arylsubstituted imidazole 55
followed by alkylation (eq. 18).
[73]
(eq. 18)
A reaction between a secondary diamine 56 and triethylorthoformate 57 in the presence of
16
1 equivalent of ammoniumtetrafluoroborate at 120°C leads ring closure to give imidazolium salts
like 58 (eq.19).
[73,74]
(eq. 19)
1.6 Synthetic routes to N-heterocyclic carbene complexes
In the literature many methods have been described to prepare NHC-metal complexes. They vary
with the metal center of interest. NHCs can be introduced as imidazolium salts, as free carbenes
or via transmetallation routes. The most important synthetic approaches are given below.
1.6.1 Substitution reactions with free NHCs
Generation of a free NHC succeeds by deprotonation of an imidazolium salt precursor 59 with a
strong base such as hydride,
[8,75]
alkoxide,
[53]
Na / liquid NH
3[33b]
(eq. 20).
(eq.20)
The resulting imidazol-2-ylidenes 60 can be reacted with many metal metal complexes replacing
another two-electron donor ligand (e.g. CO, CH
3
CN, phosphane, thioether etc) giving a
substitution product (eq. 21).
[50,76,77]
17
(eq.21)
Substitution of two phosphane ligands by two NHC ligands in Grubbs’catalyst.The resulting
product is catalytically inactive as the NHC ligands does not dissociate at all (eq. 22).
[78]
(eq.22)
Deprotonation of 2,6-bis(arylimidazolium)pyridine 64 with KN(SiMe
3
)
2
gave the pincer carbene
ligand 65 which was reacted with RuCl
2
(PPh
3
)
3
to give the ruthenium pincer complex 66 which
shows catalytic activity with respect to transfer hydrogenation of carbonyl compounds (eq. 23)
[79]
(eq. 23)
18
1.6.2 Reaction of imidazolium salts with metal complexes comprising basic ligands
The NHC ligand can be generated by deprotonation of an imidazolium salt with a basic ligand
coordinated to a transition metal. In many of these cases the free base (e.g. alkoxide, acetate,
acetylacetonate etc) would not be able to deprotonate the imidazolium salt. Hence, the metal to
which it is coordinated to catalyses the deprotonation and traps the the liberated NHC by
coordination.
In a typical reaction Herrmann et al. synthesized a rhodium NHC-complex by reacting
[Rh(COD)(µ-OEt)]
2
with an imidazolium salt giving the novel complex 67 (eq. 24).
[80]
(eq. 24)
Light and coworkers prepared an iron (II) pincer-NHC-complex 69 by direct metallation of [Fe
(N(SiMe
3
)
2
]
2
, which is an active catalyst for polymerization, C-C bond formation or oxidation
reaction (eq.25).
[81]
[Fe(N(SiMe
3
)
2
]
2
Ar = 2,6-Pr
i2
C
6
H
3
Br
2
68 69
NNN
H
Ar
NN
H
Ar N
N
N
N
Fe
Ar Ar
Br
Br
N
(eq. 25)
1.6.3 Reaction of transition metal complexes with electron rich olefines
This method was introduced by Lappert. The reaction of electron-rich olefines like tetraalkyl
aminoethylenes with organometallic complexes (eq. 26) gives NHC complexes by insertion of
the transition metal into the carbon-carbon double bond. In this way mono-, bis-, tris-, and even
tetrakis carbene complexes of various metal have been prepared
.[82,83]
These examples are shown
in Figure 1.13
19
(eq. 26)
Figure 1.13: bis, tris, tetreakis carbene complexes.
1.6.4 Unusual methods
In a completely new approach a NHC complex was prepared by the deoxygenation of M (CO)
6
(M = Cr, Mo, w) with aminophosphine 75 to form the corresponding isocyanide complex 76,
which subsequently underwent intramolecular cyclization to give 77. The N-H moiety of carbene
complex 77 is converted into the alkylated species 78 by treatment of 77with an excess of sodium
hydride followed by an alkylating agent to give the NHC-complex aimed for.
[84]
This procedure
is quite similar to that reported by Angelici and co-workers.
[85]
20
1.6.5 Transmetallation reactions
Another synthetic method for the preparation of NHC-complexes is transmetalation of transition
metal carbene complexes. A typical example of transmetalation from tungsten to palladium is
shown below
[86]
(eq. 28).
N
N
Et
Et
NEt
EtN
EtN
NEt
W(CO)
5
+ (PhCN)
2
PdCl
2
Pd
Cl
Cl
2
(eq. 28)
Recently, a novel method for preparing NHC metal complexes via silver complexes has been
developed by Lin and Wang.
[87]
Silver NHC-complexes are readily prepared upon mixing the
corresponding imidazolium salts with Ag
2
O in methylene chloride at room temperature as shown
in (eq. 29)
(eq. 29)
Hermann and co-workers
[88]
synthesized rhodium and iridium complexes of new chiral N-
heterocyclic carbene ligands by transmetalation of corresponding silver(I) complexes (eq. 30).
21
(eq. 30)
Also homoleptic metal carbene complexes 87 were synthesized by co-condensation of metal
vapors (group 10) with imidazol-2-ylidene 86 (eq. 31) This synthetic route is straightforward but
limited by the experimental conditions.
[89]
(eq.31)
Oxidative addition of an imidazolium cation by activation of the C2-X (X = Me, I, H) bond has
been achieved with low valent precursors such as Pt(PPh
3
)
4
giving NHC-complexes.
[90,91].
Furthermore Fürstner has shown that oxidative addition of Vilsmaier salts 88 is a facile and
convenient method for the preparation of NHC complexes of Pd 89 (eq. 32).
[92]
(eq. 32)
22
Imidazolium salts react in some cases with strong nucleophiles like KOBu
t
by formation of a
neutral adduct in which the nucleophile is bonded to the C2 position. These adducts can eliminate
alcohol to unmask the carbene, which is then coordinated to the metal center
[73]
as illustrated in
(eq. 33).
(eq. 33)
1.7 N-heterocyclic carbenes in catalysis
Recentaly, N-heterocyclic carbenes have become a very important class of ligands in
organometallic chemistry and catalysis.
[93]
Their strong σ-donating ability, strong metal-carbon
bond and poor π-accepting ability leads to the formation of many stable metal complexes which
are good catalysts in numerous organic transformations.
[94]
The catalytic activity of various
rhodium carbene complexes has been investigated by Nile in 1977.
[95]
In 1981 Lappert introduced
imidazoline-2-ylidene instead of phosphane ligands complexes in catalytically active complexes
of rhodium and ruthenium. The first the use of an NHC-ligated complex 93 in the Mizoroki-Heck
reaction was reported by Hermann in 1995 (eq. 34).
[96]
(eq. 34)
Catalysts containing N-heterocyclic carbenes have been employed in a wide variety of
reactions
[97c-j]
including polymerization (e. g. copolymerization of ethylene and CO),
[97b]
hydrogenation,
[23,96a,97]
hydrosilylation,
[97k-q]
hydroboration,
[97r]
hydroformylation,
[97r-u]
allylic-
23
substitution,
[97u]
methylation, ruthenium catalyzed olefine metathesis, 2,4-transfer hydrogenation
reactions and cross coupling reactions to form C-C or C-N bonds.
[77b,82,83 98]
1.7.1 Hydrosilylation
Hermann and co-workers synthesized the chiral rhodium carbene complex 94 which was applied
as a catalyst in the asymmetric hydrosilylation of acetophenone according to (eq. 35).
[99]
Compared to standard hydrosilylation catalysts (e.g. H
2
PtCl
6
/ Ethanol, Karstedt’s catalyst) the
complex is active without an induction period and even at low temperatures.
(eq. 35)
1.7.2 Hydrogenation
The rhodium(I) complex 95 containing a pyrazoyl-N-heterocyclic carbene ligand is an efficient
catalyst for hydrogenation of styrene (eq. 36).
[100]
(eq. 36)
24
1.8 Cross-coupling in homogeneous catalysis
Cross-coupling reactions represent an extremely versatile tool in organic synthesis.
[101]
Indeed C-
C, C-N bond formations are the key steps in a wide range of preparative organic reactions. From
the synthesis of natural products
[102]
to supramolecular chemistry and material science, various
frequently used cross-copuling reactions are mediated by palladium catalysts (Figure 1.14).
[103]
X
R' R'
R
R
(4)
(5)
R'MgBr R'ZnBr
(6) (3)
ArSnBu
3
ArB(OH)
2
Ar
RR
Ar
R
R'
(1) (2) HC C
R'
R'
CCR'
R
(1) Heck
(2) Sonogashira
(3) Suzuki
(4) Negishi
(5) Kumada
(6) Stille
R
Figure 1.14: Principle of palladium catalyzed cross-coupling reactions (X = I, Br, Otf, Cl, F).
[103]
For several years aryl bromides and iodides were preferably used as substrates in such reactions.
The far more readily available and industrially important aryl chlorides are transformed very
sluggishly by standard palladium catalysts. The problem with aryl chlorides is the strength of the
C-Cl bond, which impedes the oxidative addition to 14 e
-
Pd (0)-phosphine complexes.
The mechanism of palladium cross-coupling reactions is shown in Figure 1.15. A zero valent
palladium species, stabilized by electrondonating and/or bulky ligands, undergoes oxidative
addition with an aryl halide to afford a Pd(II)(Ar)(X) complex. Ar-M then effects
transmetallation with this species removing the halide as MX to afford a Pd(Ar)(Ar’)
intermediate, which undergoes a reductive elimination to couple the two aryl moieties and
regenerate the palladium (0)species.
25
LnPd(0) Ar X
LnPd
Ar
X
Ar
Ar'
Ar Ar'
Ar' M
XM
LnPd
Ar'-M = organoboron acid
organostannane
organomagnesium
organosilicon
amine
Figure 1.15: Simplified catalytic cycle for palladium mediated cross-coupling reactions.
1.8.1 Sonogashira coupling.
This coupling reaction proceeds with terminal alkynes and aryl halides or vinyl halides. As an
example the palladium(0) species 96 which is also active in Heck and Suzuki C-C coupling, is
employed in a Sonogashira type coupling to make the bromo-enyen 97, a common building
block for natural products (eq. 37).
[104]
N
NN
N
R
R
R
R
Pd
Br
O
O
C
Br
O
O
C SiR3
'
+ HC C SiR3
'
96
CuI
Pr2NEt/DMF
-HI
/
97
(eq. 37)
Copper free conditions were reported for the Sonogashira coupling of aryl bromides with
alkenylsilanes Pd (OAc)
2
.
[105]
26
1.8.2 Kumada coupling (Grignard cross-coupling)
The coupling of aryl Grignard reagents with aryl halides, triflates or ethers which is catalysed by
nickel
[106]
or palladium,
[107]
is one of the earliest methods of the catalytic synthesis of
unsymmetrical biaryls. The coupling of aryl chlorides as sketched in (eq. 38) is afforded by a
NHC-catalyst of nickel. The latter is generated in situ from Ni(acac)
2
and imidazolium salts.
Catalysts like 98 or 99 effect the C-C coupling even at room temperature (3 mol% Ni).
N
NN
N
i
Pr
i
Pr
Pri
i
Pr
Ni
N
N
H
3
C
CH
3
Ni
N
N
H
3
C
CH
3
N
NCH
3
H
3
C99
98
CH
3
Cl BrMg OCH
3
+
CH
3
OCH
3
THF, 25°C,-MgBrCl
(eq. 38)
1.8.3 Stille coupling
For the palladium catalyzed cross-coupling of organostannanes and aryl halides or sulfonates (eq.
39) traditionally triaryl or trialkyl-phosphine ligands have been used.
(eq. 39)
Mixed NHC complexes of palladium like 100 are the most active catalysts in Stille reactions.
They are even able to couple 4-bromoacetophenone and phenyltributylstannane in toluene
without any promoting additives.
[108]
Nolan and co workers have shown that the Pd (OAc)
2
/imidazolium chloride system mediates the
catalytic cross coupling of aryl halides with organostannanes
[109]
The imidazolium salt 101 in
combination with Pd(OAc)
2
and TBAF(tetrabutyammonium fluoride) was found to be most
effective for the cross coupling of aryl bromides and electron deficient aryl chlorides with aryl
and vinyl stannanes.
27
100
N
N
H
Cl
101
N
N
PdI I
PPh
3
1.8.4 Heck coupling
Hermann and co-workers
[110]
reported NHC coordinated metal complexes for the first time in
Heck coupling for aryl chlorides and aryl bromides with n-butyl acrylate (eq. 40). The catalysts
used for these transformations contain the monodentate and bidentate NHC ligands 102, 103 as
shown in Figure 1.16. The work also demonstrated that the active catalyst can be generated in
situ using Pd(dba)
2
and the imidazolium salt 1,3-dimethylhydroimidazole-2-ylidene. Turnover
numbers as high as 250,000 have been observed for these Heck reactions with the NHC
containing catalysts.
[110]
Palladium catalysts used in Heck reactions have also been applied in
other cross coupling reactions.
.
(eq. 40)
N
NPd
I
I
PR
3
Br
102 103 104 105 106
S
N
N
S
Pd I
I
N
N
N
N
NN
Pd I
I
N
N
N
N
Pd I
IPPh
2
Figure 1.16: some example of Pd(II) complexes which used in Heck reaction.
28
1.8.5 Suzuki coupling
The coupling of organoboron derivatives with aryl, vinyl or alkyl halides or sulfonates (eq. 41)
has emerged as one of the most important carbon-carbon bond forming methods in the synthesis
of pharmaceutical agents, organic materials and natural products.
[111]
The air and moisture
stability of aryl boronic acids make this reagent particularly attractive when compared to Stille
(aryl stannanes) and Kumada (aryl Grignard) reagents. Traditionally monodentate phosphine
ligands have been used for the palladium catalyzed.Suzuki coupling of aryl chlorides is
accomploished with sterically crowded, electron rich phosphines.
[102,112]
Recently NHCs have
been used as ligands for a varity of transition metal–catalysed cross-coupling reactions including
the Suzuki reaction.
[83]
(eq. 41)
Caddick, Cloke and co-workers have shown that the use of a palladium/imidazolium salt system
like pd(dba)
2
/N,N-di-(2,6-diisopropylphenyl) imidazolium chloride(
i
pr•HCl) 107 in the presence
of KOMe at 40°C and tetra-n-butylammonium bromide as a co-catalyst acts as highly efficient
catalyst in Suzuki reactions.
[113]
The synthesis and catalytical application of air and moisture
stable (NHC)Pd(η
3
-C
3
H
5
)Cl 108 was reported by Nolan and co-workers. This catalyst has proven
to be highly active for Suzuki cross coupling of activated and unactivated aryl chlorides and
bromides, but a high reaction temperature was required to achieve acceptable yield.
[114]
Lebel et
al. found that N,N-di-(2,4,6-trimethylphenyl)-imidazolyidene (Imes, 109) also works as an
effective supporting ligand in Suzuki cross coupling reactions, but again high reaction
temperatures were required.
[115]
29
N
N
107
N
NN
N
Pd
110
N
NN
N
108
109
Pd
Cl
The use of the bis-NHC Pd(0) catalyst 109 by Hermann et al. was shown to be very efficient for
the room temperature cross coupling of both electron-rich and electron-poor aryl chlorides with
phenyl boronic acid. The extremely efficient reactions are generally completed in 20 minutes to a
few hours with high yields. The combination of Pd(OAc)
2
or Pd(dba)
2
with imidazolium salts as
ligand precursors allows for in situ generation of the active catalyst for Suzuki cross couplings of
aryl chlorides with aryl boronic acids.
[98d]
The Palladium/imidazolium salt system like Pd(0)/Ipr·HCl 96 or Pd(II) Imes⋅HCl 111 were found
to be efficient in mediating the Suzuki cross coupling of aryl chlorides and aryl triflates
[116]
with
various arylboronic acids. In this case electron rich and electron poor aryl chlorides as well as
sterically hindered substrates are converted in high yield under moderate reaction conditions.
N
NN
N
R
R
R
R
Pd
96
N
N
H
Cl
111
Glorius and co-workers
[117]
reported a Suzuki reaction for hindered and unhindered activated and
deactivated aryl chlorides with aryl boronic acids at room temperature. They used compound 112
30
which is a carbene ligand derived from a bisoxazolin system and Pd(OAc)
2
. The mixture acts a
highly efficient catalyst. The activity of this system was attributed to the steric flexibility of the
carbene ligand. For the first time di- and tri-ortho-substituted biaryl compounds were formed
under the reaction conditions and high turnover numbers were obtained Nolan and co-workers
have combined the use of highly electron donating and sterically demanding NHC ligands with a
palladacycle framework in compound 113. This catalyst displays the ability to cross couple
sterically hindered unactivated aryl chlorides with sterically demanding boronic acids at room
temperature in very short periods of time to lead to di- and tri ortho-substituted biaryls in high
yields.
[118]
The classical mechanism of Pd catalyzed cross coupling reactions (Figure 1.15) involves three
discrete steps: oxidative addition, transmetallation and finally reductive elimination. Recently a
reinvestigation of these type of reactions has shown that the mechanism is more complicated.
Initially a precatalyst like PdCl
2
(PPh
3
)
2
is reduced (either by nucleophiles or by independent
reduction) to the catalytically active Pd(0) species to afford the tricoordinated anionic complex
[Pd(PPh
3
)
2
Cl]
-
Then oxidative addition of ArX (Ar = aryl) to this intermediate gives a
pentacoordinated σ-aryl palladium(II) complex [PhPdXCl(PPh
3
)
2
]
-
. Subsequently the chloride
ligand is substituted by solvent giving the neutral complex [PhPdX(Solv)(PPh
3
)
2
]. Nucleophilic
attack of ArM (M = counter cation associated with the nucleophile used) on the pentacoordinated
neutral complex to yields an anionic penta coordintated complex ArPdX (Nu)(PPh
3
)
2-
, in which
Ar and Nu ligands are adjacent and so in a favourable position for fast reductive elimination
under formation of the catalytically active complex Pd
0
(PPh
3
)
2
X
-
, which intiates the next catalytic
cycle (Figure 1.16 (main cycle) ).
31
As catalytically reactions proceed halide anions and cations are progressively released due to
ArX and Mnu conversion The released ions are free and shall be considered as in (eq. 42), as
follow
(eq. 42)
Due to this possibility, the nature of the metal cation m plays a crucial role in the overall
mechanism by controlling possible comptitation between the main cycle in Figure 1.17 and
classical mechanism. When halide ions are free like in (eq. 42) or free halide ions added.Pd
0
L
2
X
-
and ArPdX(X)L
2-
are formed, the main cycle is expected to dominate .how ever the, the situation
is not so simple because the classical mechanism and main mechanism interconnected at the level
of intermediate ArPdX(solv)L
2
The nature of free-ion of nucleophile is also crucial in the
selection of mechanisms.when the nucleophile is a free anions, the metal cation has no influence
at all except therefore the classical mechanism and new mechanism are finely tuned by the ion-
pairing equlibria involving halide anions and metal cations are released while the reaction
proceeds.
[120]
Activation
PdCl
2
(PPh
3
)
2
Reduction
Pd Cl
L
L
0
PdAr
L
L
X
Cl
Pd
L
L
X
0
PdAr
L
L
X
X
PdAr
X
S
Pd
L
L
Ar
Nu
X
Ar X
Ar Nu
Nu
SL
L
Ar X
-X +X
main cycle
+Cl
-Cl
Figure 1.17: New mechanism for palladium catalysed cross-coupling reactions.
[120]
2. Aim of Work
32
2. Aim of work
After the isolation of the first stable carbene by Arduengo
[7]
, N-heterocyclic carbenes have
become an important class of ligands in organometallic chemistry and homogeneous catalysis
These ligands are often compared to tertiary phosphanes in their bonding to transition metals. In
general nucleophilic N-heterocyclic carbenes as mimics for phosphanes have attracted a
considerable amount of attention. These ligands are strong σ-donors with negligible π-acceptor
ability. Phosphanes and N-heterocyclic carbenes and can be combined in bidentate ligands giving
chelating ligands with extremely strong bonding properties. These ligands don’t dissociate from
the metal center, consequently only stoichiometric amounts of these ligands are needed in order
to stabilize metal centers even in very low oxidation states. However, research into the
organometallic chemistry of mixed bidentate phosphane-NHC donor ligands has been
surprisingly limited and the application of metal complexes with mixed phosphane-NHC donor
ligands in homogeneous catalysis has not been widely explored. There are examples of palladium
catalysed Heck,
[120]
Suzuki
[121]
cross coupling, rections using Pd, Ir
[122]
, Rh
[122]
and Ru complexes
with mixed phosphine-NHC ligands.
According to the introduction NHC-complexes have a great variety and uses. The aim of this
work is focused on the following questions:
1. Synthesis of homoleptic metal complexes of Rh(I), Ir(I), and Pd(II) with mixed phosphane
N-heterocyclic carbene ligands starting from the imidazolium salts [EtImCH
2
CH
2
PPh
2
][X]
(X = I, PF
6
) and the metal precursors [M
2
(µ-Cl)
2
(COD)
2
] (M = Rh, Ir), and [Pd(COD)Cl
2
].
2. Investigation of the reactivity of the Rh(I) and Ir(I)-complexes towards small molecules like
O
2
, H
2
, S
8
, CH
3
I, I
2
, CO. Spectroscopic characterization of the resulting complexes.
3. Survey on the catalytic acivitiy of the Pd(II) complex with respect to Suzuki-coupling.
Comparison of the catalytic acitivy with standard catalysts.
4. Synthesis of a first example of a homoleptic Nickel complex with mixed phosphane N-
heterocyclic carbene ligands.
2. Aim of Work
33
The main focus of this work lies on the synthesis and characterization of M(η
2
-L)
2
-complexes (M
=Rh, Ir, Pd; L = mixed phosphane N-heterocyclic carbene ligand) as described in the list above.
All complexes obtained within this work should be characterized by X-ray crystallographic
methods and
1
H,
13
C and
31
P-NMR spectroscopy. In addition some of the complexes will be
characterized by IR-spectroscopy and cyclovoltammetry.
3. Results and Discussion
34
3. Results and Discussion
3.1 Synthesis of ligand
3.1.1 Ligand precursors 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium-hexa
fluorophosphate (E6)
In 1996 Herrmann and co-workers
[33b]
first synthesized the ligand precursor E6 which has the
potential to coordinate to a metal center as a mixed bidentate phosphine-NHC ligand. In our
group the ligand precursors E6 was synthesized following on another way in a three steps
reaction sequence (Figure 3.1), the first step being alkylation of 1-vinyl imidazole E1 with an
excess of ethyl iodide E2 under reflux in methylene chloride to give 1-ethyl-3-vinylimidazolium
iodide E3 in good yield after recrystallization from methanol. The second step involves reaction
of E3 with potassium diphenylphosphide which was generated in situ from KOBu
t
and
diphenylphosphine E4 in THF under nitrogen atmosphere at ambient temperature. The reaction
proceeds via a nucleophilic attack of one of the lone pairs of the phosphorus atom at the vinyl
group forming a carbanion which is subsequently protonated by t-butanol affording the ligand
precursor E5 in good yield. Counter ion exchange with hexafluorophosphate is achieved in
degassed water. After working up the imidazolium salt E6 was isolated. Alternatively we have
also obtained E5 by refluxing the reaction mixture for 24h followed by addition of diethyl ether
to precipitate E5.
Figure 3.1: Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium-hexafluorophosphate.
3. Results and Discussion
35
3.1.2 Properties of the imidazolium salts
The resulting imidazolium salts E5 and E6 are white to yellow powders. They are extremely
hygroscopic and react with air to form the phosphine oxides.
E5 shows a low solubility in THF while E6 is very good
soluble in that solvent.
The data of the
1
H-NMR spectrum recorded in CD
3
CN of
the imidazolium salts E5 and E6 are shown in Table 3.1. As
both data sets are similar only the data of E6 are discussed
in detail. E6 exhibits resonances due to the aromatic protons
of the imidazolium ring H
7
, H
5
and H
6
at 8.51 (s), 7.39 (t)
and 7.31 (m) ppm, respectively. The observed chemical
shifts are in good agreement with similar imidazolium salts.
[123]
The strong deshielding of H
7
is
the direct consequence of the positive charge of the imidazolium ring. The protons of the
ethylene bridge show resonances at 2.72 (t) for H
1
and 4.32 (td) for H
2
, respectively. The lines of
the resonance of H
1
are slightly broadened most likely due to coupling with phosphorous.
However, this coupling is too weak to determine the exact coupling constant
2
J
PH
. The chemical
shifts of the ethylene and ethyl protons are in the expected range showing no further specific
features.
The
13
C resonances of the imidazolium carbon atoms C
7
, C
5
and C
6
appear at 134.9, 122.6, 122.1,
respectively. The deshielding of C
7
is typical for imidazolium salts and confirms the cationic
nature of ring
[93a].
The resonances of the carbon atoms of the ethylene bridge are found at 27.9
ppm for C
1
and 47.3 ppm for C
2
. The low field chemical shift of C
2
is a result of the high
electronegativity of the neighboring nitrogen atom. Both resonances are doublet due to coupling
with phosphorous. Interestingly the
1
J
PC
coupling constant (15 Hz) is smaller than the
2
J
PC
coupling constant (25 Hz). This observation is in accordance with the observed HP-coupling
constants discussed above. The
31
P{1H} NMR spectrum of E6 exhibits a resonance due to the
tertiary phosphours atom at -21.6 ppm as expected for alkyl diaryl phosphines
[124]
and signal for
PF
6-
at -144 ppm which is splited into a heptet with
1
J
PF
= 710 Hz.
N
N
X
P
1
2
3
4
6 5
H
789
10
11
E5, X= I
E6, X= PF6
3. Results and Discussion
36
Table 3.1:
1
H-NMR-spectra of E5 and E6 in CD
3
CN
E5 E6
δ H [ppm]
n
J
HH
[Hz] δ H [ppm]
n
J
HH
[Hz]
H1 2.78 (t)
3
J
HH
= 8.0 2.72 (t)
3
J
HH
= 7.7
H2 4.35 (td)
3
J
PH
= 9.2,
3
J
HH
= 7.8 4.32 (td)
3
J
PH
= 9.5,
3
J
HH
= 7.7
H3 1.45 (t)
3
J
HH
= 7.3 1.44 (t)
3
J
HH
= 7.1
H4 4.16 (q)
3
J
HH
= 7.3 4.11 (q)
3
J
HH
= 7.67
H5 7.46 (m)
3
J
HH
= 1.8 7.39 (t)
3
J
HH
= 1.7
H6 7.30 (t)
3
J
HH
= 1.8 7.31 (t)
3
J
HH
= 1.9
H7 8.92 (s) 8.51 (s)
H9 7.51 (m) 7.47 (m)
H10 7.49 (m) 7.41 (m)
H11 7.49 (m) 7.40 (m)
3. Results and Discussion
37
Table 3.2:
13
C-NMR-spectra of E5 and E6 in CD
3
CN.
E5 E6
δ C [ppm]
n
J
PC
[Hz] δ C [ppm]
n
J
PC
[Hz]
C1 28.0 (d)
1
J
PC
= 16 27.9 (d)
1
J
PC
= 15
C2 47.4 (d)
2
J
PC
= 27 47.3 (d)
2
J
PC
= 25
C3 14.5 (s) 14.5 (s)
C4 44.9 (s) 44.9 (s)
C5 121.9 (s) 122.6 (s)
C6 122.4 (s) 122.1 (s)
C7 135.8 (s) 134.9 (s)
C8 136.93 (d)
1
J
PC
= 12 136.8 (d)
1
J
PC
= 12
C9 132.7 (d)
2
J
PC
= 20 132.6 (d)
2
J
PC
= 20
C10 128.8 (d)
3
J
PC
= 7.0 128.8 (d)
3
J
PC
= 7.5
C11 129.24 (s) 129.3 (s)
3.1.2.1 X-ray crystallographic analysis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium
-hexafluorophoshate (E6)
Colorless crystals of E6 were grown by layering of hexane onto a THF solution of E6. E6
crystallized monoclinic in the space group P2(1)/n with four molecules per unit cell. Selected
bond lengths and angles are listed in Table 3.3. The molecular structure containing the atom
numbering schemes is shown in Figure 3.2. Crystallographic data are presented in the Table 7.1.
E6 contains an imidazole ring which is substituted at both nitrogen atoms. N(1) is bonding to an
ethyl group and N(2) is linked to an ethylene group which is bonded to the diphenyl phosphide
moiety. The bond lengths within the imidazole ring N(1)-C(1)[1.320(4) Å] and N(2)-
C(1)[1.322(4) Å] are identical. The bond lengths of N(1)-C(2) and N(2)-C(3) of 1.378(4) Å and
1.376(4) Å, respectively, are similar to the values reported in the literature.
[125]
The bond angles in the imidazole ring N(1)-C(1)-N(2) [109.1(3)°], C(3)-C(2)-N(1) [107.3(3)°],
C(2)-C(3)-N(2) [106.9(3)°], C(1)-N(1)-C(2) [108.2(3)°] and C(1)-N(2)-C(3) [108.5(3)°] are
similar to those reported in the literature.
[40a,126,127]
3. Results and Discussion
38
Figure 3.2: Structure of the 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium cation in crystals of E6.
Table 3.3: Selected Bond lengths [Å] and Bond Angles [º] for E6
Bond lengths
N(1)-C(1) 1.320(4) N(2)-C(4) 1.474(4)
N(2)-C(1) 1.322(4) C(2)-C(3) 1.343(5)
N(1)-C(2) 1.378(4) P(1)-C(11) 1.831(4)
N(2)-C(3) 1.376(4) P(1)-C(21) 1.836(3)
N(1)-C(6) 1.471(4) P(1)-C(7) 1.841(4)
Bond angles
N(1)-C(1)-N(2) 109.1(3) C(3)-C(2)-N(1) 107.3(3)
C(1)-N(1)-C(2) 108.2(3) C(2)-C(3)-N(2) 106.9(3)
C(1)-N(2)-C(3) 108.5(3) N(1)-C(6)-C(7) 111.9(3)
C(11)-P(1)-C(21) 99.41(5)
C(21)-P(1)-C(7) 99.90(16)
3. Results and Discussion
39
3.1.3 In situ synthesis of free carbene
3-[2-(diphenylphosphino)ethyl]-1-ethylimidazol-2-ylidene (E7)
The free NHC-phosphane mixed ligand 3-[2-(diphenylphoshino)ethyl]-1-imidazole-2-ylidene E7
was synthesized by deprotonation of the corresponding imidazolium salts E5 or E6, respectively,
in THF using the strong non nucleophilic base KN(SiMe
3
)
2
.
N
NX
PPh
Ph
KN(SiMe
3
)
2
N
NPPh
Ph
E7
E5, X = I
E6, X = PF
6
-KX
Figure 3.3: Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazole-2-ylidene.
The free NHC-phosphane hybrid ligand is extremely sensitive to oxygen, water and other
electrophiles and shows indication of decomposition on attemps to remove the solvent
completely. Therefore no attempt has been made to isolate it from solution. Instead we proved its
in situ formation through the reaction with CS
2
which gives the dithiocarboxylate compound E8
in high yield.
3.1.3.1 Identification of imidazol-2-ylidendithiocarboxylat (E8)
On addition of one equivalent of CS
2
to a solution of E7 in THF the color changes to deep red
indicating the formation of the zwitterionic dithiocarboxylate E8 which precipitates from the
solvent in high yield. The reaction is a simple nucleophilic attack of the carbene at the
electrophilic carbon of CS
2
. Recrystallization from CHCl
3
/ Et
2
O gives single crystals which are
suitable for X-ray diffraction analysis.
Figure 3.4: Transformation of E7 to dithiocarboxylate E8.
3. Results and Discussion
40
The absence of a resonance above 8 ppm in the proton NMR-
spectrum of E8 in CDCl
3
proves the deprotonation of the
starting material and indicates coordination to CS
2
.
The
aromatic protons are observed at 6.85-7.4 ppm and the protons
of the ethylene bridge show a resonances at 2.67 (t) for H
1
and
4.1 (q) for H
2
, respectively. The lines of the resonance of H
1
are
slightly broadened most likely due to coupling with phosphorous atom. The signal of methyl
group is observed at 1.44 (t). The
13
C resonance of the imidazolium carbon atom C
7
(quaternary
carbon) is shifted by 15 ppm to low field (149.5 ppm) compared to the corresponding carbon
atom of the imidazolium salt due to binding to CS
2
. The carbon atom of the CS
2
group exhibits a
low field signal at 224.7 ppm. The strong deshielding of this carbon must be attributed to its
bonding to a positively charged aromatic ring and to the electronegative sulfur atoms. The
remaining aromatic carbons of the imidazolium ring are observed at 117.3 ppm and 118.5 ppm
for C
5
and C
6
, respectively. Compared to the corresponding carbon atoms in the imidazolium salt
E6 they are shifted to high field by approximately 4 ppm. The carbon atoms of phenyl rings
exhibit signals in the same range as in the imidazolium salts.
3.1.3.2 X-ray crystallographic analysis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazol-
2-dithiocarboxylate (E8)
Red crystals of E8 suitable for X-ray crystallography were obtained by diffusion of diethyl ether
into a CHCl
3
solution of E8. E8 crystallized monoclinic in the space group C2/c with eight
molecules per unit cell. Selected bond lengths and angles are listed in Table 3.4. Molecular
structure containing the atom numberings is shown in Figure 3.5. Crystallographic data are
presented in the Table 7.2. In E8 the molecule contains of imidazole ring which substituted in the
three positions the N(1) binding with ethyl group and N(2) with ethylene group which bonded
with diphenyl phosphide and C1 bonded with CS
2
group.
The X-ray structure of E8 (Figure 3.5) confirms the addition of the free carbene to CS
2
. The C2
atom lies in the plane of the five remembered ring while S1 and S2 lie out of plane and the
dihedral angle formed by the two planes containing the CS
2
position and the imidazol ring is
72.6°. The bond angles in the imidazol ring, viz, C(6)-C(5)-(N1) and C(5)-C(6)-N(2) are
3. Results and Discussion
41
107.14(15) and 107.32(13) and C(1)-N(1)-C(5) and C(1)-N(2)-C(6) are 109.17(15) and
109.10(14), respectively. The N(1)-C(1)-N(2) angle is 107.26(14). All of these bond angles are
similar to values reported in the literature.
[40a,126,127]]
The bond lengths within the imidazol ring C(1)-N(1)[1.346 (2) Å] and C(1)-N(2) [1.343(2) Å]
are identical. The bond lengths of N(1)-C(5) and N(2)-C(6) of 1.384(2) Å and 1.385(2) Å,
respectively, are very similar to those found both in the pentamethylimidazolium cation
[128]
and
in 2-telluro-1,3-diisopropyl-4,5-dimethylimidazoline
[129]
confirming that the π-electrons are
completely delocalized over the five-membered aromatic ring. The bond length C(6)-C(5)
amounts to 1.344 (3 )Å which is indicates a double bond.
Figure 3.5: Structure of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazol-2-dithiocarboxylate E8 in the crystal.
The bond angle of S(1)-C(2)-S(2) is 129.40(10)° and the bond lengths of S(1)-C(1) and S(2)-C(2)
are 1.6717(17) and 1.6740(16), respectively, indicating delocalization of π-electrons over the S
2
C
moiety. This leads to a shortening of the C(1)-C(2) single bond by 0.05 Å to 1.491(2) Å But this
is considerably longer than that observed in the 1,1-dithiolateanion 2C
4
H
8
N
2
O.1/3K
2
S
2
3. Results and Discussion
42
(1.375(13) Å) where in the CS
2
group is oriented coplanar to the five membered substituted
imidazol ring.
[130]
It is helpful to compare the structure of the imidazol-dithiolate E8 with the higher symmetrical
imidazol CS
2
adduct, bis-1,3-isopropyl-bis-4,5-methylimidazoldithiocarboxylate E9. This was
crystallised by diffusion of diethyl ether into an acetonitrile solution. The crystals belong to the
monoclinic space group C2/c containing four molecules per unit cell.
Figure 3.6: Structure of 1,3-di-isopropyl-bis-4,5-methylimidazolium-dithio-carboxylate E9 in the crystal.
In E9 the molecules contains aromatic imidazol rings which are substituted in five positions the
aromatic carbons of imidazol ring C(5) and C(6) bonding with methyl group while N(1) and N(2)
substituted with isopropyl group and C1 of imidazol ring substituted with CS
2
group.
The imidazol ring in E9 is planar as in E8 but there is significant difference with respect to the
dihedral angles of the planes containing the CS
2
groups and the imidazol rings. In the compound
E9, the plane of the CS
2
group is perpendicular (dihedral angle, 89.14°) to the plane of the five
membered imidazol ring while in E8 the dihedral angle is 72.6°. The deviation from
3. Results and Discussion
43
perpendicular orientation in E8 seems to be due to a crystallographic packing effect. The bond
lengths and angles for both E8 and E9 are given in Table 3.4.
Table 3.4:.Selected Bond lengths [Å] and Bond Angles [º] for E8 and E9
Bond Lengths
E8 E9 E8 E9
C(1)-N(1) 1.346(2) 1.3365(16) C(5)-C(6) 1.344 (3) 1.349 (3)
C(1)-N(2) 1.343(2) 1.3365(16) C(1)-C(2) 1.491(2) 1.485(3)
N(1)-C(5) 1.384(2) 1.3970(17) S(1)-C(2) 1.6717(17)
1.6621(9)
N(2)-C(6) 1.385(2) 1.3970(17) S(2)-C(2) 1.6740(16)
1.6621(9)
P(1)-C(8) 1.8564(17) P(1)-C(10) 1.8383(16)
P(1)-C(9) 1.8380(16)
Bond Angles
E8 E9 E8 E9
N(1)-C(5)-C(6) 107.14(15) 107.10(8) C(1)-N(2)-C(6) 109.10(14)
108.59(12)
N(2)-C(6)-C(5) 107.32(15) 107.10(8) N(1)-C(1)-N(2) 107.26(14)
108.61(17)
C(1)-N(2)-C(5) 109.10(14) 108.59(12) S(1)-C(2)-S(2) 129.40(10)
129.47(12)
C(8)-P(1)-C(9) 96.88(7) C(8)-P(1)-C(10) 103.52(7)
3. Results and Discussion
44
3.1.3.3 Electrochemistry of 3-[2-(diphenylphosphino)ethyl]-1-ethyl-imidazolium-hexa-
fluorophosphate (E6)
-2 -1 0 1 2
-0,00005
0,00000
0,00005
0,00010
585 mV/NHE
669 mV
-921 mV -486 m V
-1005 mV/NHE
-570 mV/NHE
I(
µ
µ
µ
µ
A)
E(V vs Ag/ AgCl)
Figure 3.7: Cyclovoltammogram of E6 in THF.
The cyclovoltammogram of imidazolium salt E6 (0.1mol/L [NBu
4
][PF
6
] was obtained at a scan
rate of 200 mV/s in THF. The imidazolium salt shows irreversible oxidation wave at 586
mV/NHE and two reduction waves at -570 mV/NHE and -1005 mV/NHE.
3. Results and Discussion
45
3.2 Rhodium complexes
3.2.1 Syntheses and characterization of cationic cis-and trans-rhodium(I) complexes with E7
The syntheses of the cationic cis and trans Rh(I) complexes [Rh(EtImCH
2
CH
2
PPh
2
)
2
][X] (E10
(X = Cl), E11 (X = PF
6
) ) [Rh(EtImCH
2
CHPPh
2
)
2
]X (E12 (X = Cl), E13(X = PF
6
)) with the
bidentate phosphine-NHC ligand E5, E6 were carried out as outlined in Figure(3.8). The carbene
ligands were obtained by the reaction of imidazolium salt E5, E6 with the base KN(SiMe
3
)
2
in
THF solution at room temperature under an inert gas atmosphere. Subsequentaly addition of the
metal precursor [Rh(µ-Cl)(COD)]
2
afforded the novel cis and trans square planar Rh(I)
complexes.
N
NP
Ph
Ph
X
THF NN
P
THF
N NEt
N
EtN
Rh P
NNEt
EtN
N
Rh
P
P
Ph
Ph
Ph
X
trans cis
Ph
Ph
Ph
P
Ph
Ph Ph
Ph
X
E7
KN(SiMe3)2
E5, X = I
E6, X = PF6
E12, X = Cl
E13, X = PF6
E10, X = Cl
E11, X = PF6
[Rh( -Cl)(COD)]2
+
Figure 3.8: Synthesis of cis- and trans-Rh(I) complexes.
E12 was obtained only in case of imidazolium iodide salts as soluble product in THF solution
while the cis-isomer E10 which is also generated in this reaction as an orange yellow precipitate.
On starting with E6 the same reaction leads selectively to the cis complex E11 in high yield. In
the solid state the latter is a compound of yellow green color which in contrast to E10 is easily
soluble in THF. E13 was synthesized from E12 via counter ion exchange by adding NaPF
6
in
methyene chloride solution.
3. Results and Discussion
46
The new mononuclear bidentate phosphine-NHC Rh(I) complexes were characterized by
1
H,
13
C,
31
P-NMR spectroscopy and single crystal X-ray structure analyses.
Compared to the imidazolium salt E6 the
1
H-NMR spectra of all complexes E10, E11, E12, E13
show important differences with respect to the chemical shift and the multiplicities of the
resonances of the ethylene protons. As expected protons attached to C
2
cannot be observed due to
deprotonation and subsequent cordination to rhodium. The bidentate coordination of the ligands
can be infered from the presence of four diasterotopic proton resonances for the ethylene bridge
in the range of 2.50-2.56 and 3.73-3.80 ppm. The chemical shift of the resonance of the carbene
carbon C
2
were observed at low field in the
13
C {
1
H}-NMR spectra. The cis complex shows a ddd
at 183.0 ppm (
1
J
RhC
= 47 Hz,
2
J
PC, trans
= 103 Hz,
2
J
PC, cis
= 30 Hz) while for the trans complex a
doublet of triplett is found at 185.1 ppm (
1
J
RhC
= 39 Hz,
2
J
PC
= 17 Hz). These chemical shifts and
coupling constants compare well with values reported in the literature for the C
2
resonance of
other rhodium NHC complexes.
[49,59,131-135]
The appearance of the
1
J
(Rh-C2)
coupling constant
confirms the bonding of the carbene atom to the metal center in solutiuon. The number of
aromatic resonances proves that the phenyl rings of the PPh
2
residue are not equivalent in all
complexes.
The
31
P NMR resonances of the phosphorous atoms in the metal complexes E10, E11, E12 and
E13 were observed at 32.2 ppm for both cis complexes (d,
1
J
RhP
= 128 Hz) and at 25.9 ppm for
both trans complexes (d,
1
J
RhP
= 152 Hz). The resonances of the phosphorous atoms are shifted to
lower field compared to the values observed for the free ligands E5 (-21.4 ppm) and E6 (-22.1
ppm), respectively. This observation confirmes the coordination of phosphorous to the metal
center.
3. Results and Discussion
47
3.2.2 Single crystal X-ray structure analyses of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][X] (X=Cl
(E10), PF
6
(E11))
Single crystals of E10 and E11 suitable for X-ray diffraction analysis were obtained by slow
diffusion of diethyl ether into a concentrated acetonitrile solution of E10 and from concentrated
THF solution of E11, respectively.
Selected bond lengths and angles of both compounds are listed in Table 3.5. Molecular structure
containing the atomic numbering schemes are shown in Figure 3.9, Table 3.5 for E10 and Figure
3.10, Table 3.5 for E11, respectively., Crystallographic data are listed in the Table 7.3. The cis
complexes E10 and E11 crystallized in the triclinic space group P-1.The latter incorporated one
molecule of THF in the crystal lattice.The crystals contain two molecules per asymmetric unit.
As both complexes show only minor differences with respect to their structure only the structure
of complex E10 will be dicussed in detail.
In the complex E10 the Rh center is coordinated by two bidentate NHC-phosphane-ligands in a
square planar arrangement. The metal center forms with each ligand a six membered ring
exhibiting a distorted boat conformation. Both rings can be mapped onto each other by a 180°
rotation about the axis dividing the angles P(11)-Rh(1)-P(12) and C(101)-Rh(1)-C(120). Hence
the molecule is chiral as it belongs to the point group C
2
. The sums of angles at the Rh atoms
equals 360.1(2)° and 359.8(2)°, respectively, in accordance with the square planar geometry of
the complex. However, the angles C(120)-Rh(1)-P(12) of 81.19(15)° and P(11)-Rh(1)-P(12) of
98.74(6)° deviate strongly form the expected 90° angle in square planar complexes. This
observation can be traced back to the fact that the phenyl rings in these cis-isomers are quite close
to each other leading to sterical strain. The latter is reduced by a slight distortion from the ideal
square planar arrangement of the ligand atom. The repulsion of the two PPh
2
residues is also
strongly indicated by the angle C(101)-Rh(1)-P(12) which deviates by 8.34(12)° from the
expected 180° angle. Consequently this deviation can also be found in the angle C(120)-Rh(1)-
P(12). In E10, the Rh(1) atom is located only 0.036 Å above the coordination plane defined by C
(101), C(122), P(11) and P(12). The bite angles C(101)-Rh(1)-P(11) of 89.45(15°) and and
C(101)-Rh(1)-C(120) of 91.5(2), respectively, are close to the ideal angle of 90° expected for
square planar complexes. The dihedral angles of P(11)-Rh(1)-P(12) to C(101)-Rh(1)-C(120) and
C (101)-Rh(1)-P(11) to C(120)-Rh(1)-P(12) amount to 9.29° and 10.31°, respectively. Again this
slight distorsion must be attributed the sterical interaction of the PPh
2
residues. The bond lengths
3. Results and Discussion
48
of Rh(1)-C(101), Rh(1)-C(120), Rh(1)-P(11) and Rh(1)-P(12) are 2.033(6) Å, 2.034(5) Å,
2.2686(15) Å and 2.2781(16) Å, respectively, are similar to the those of other Rh-NHC complex
with monodentate ligands reported in the literature.
[131,133,136]
Figure 3.9: Structure of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E10
3. Results and Discussion
49
Table 3.5: Selected bond lengths [Å] and bond angles [°] of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl (E10)
and cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E11)
E10 E11
Bond Lengths
Rh(1)-C(101) 2.033(6) Rh(1)-C(135) 2.044(4)
Rh(1)-C(120) 2.034(5) Rh(1)-C(165) 2.057(4)
Rh(1)-P(11) 2.2686(15) Rh(1)-P(11) 2.2565(11)
Rh(1)-P(12) 2.2781(16) Rh(1)-P(12) 2.2739(11)
Bond Angles
C(101)-Rh(1)-P(11) 89.45(15) C(135)-Rh(1)-P(11) 88.75(12)
C(120)-Rh(1)-P(12) 81.19(15) C(165)-Rh(1)-P(12) 80.54(11)
P(11)-Rh(1)-P(12) 98.74(6) P(11)-Rh(1)-P(12) 99.27(4)
C(101)-Rh(1)-C(120) 91.5(2) C(135)-Rh(1)-C(165) 91.24(16)
C(120)-Rh(1)-P(11) 170.66(15) C(165)-Rh(1)-P(11) 174.23(12)
C(101)-Rh(1)-P(12) 170.46(15) C(135)-Rh(1)-P(12) 171.66(12)
For E11 the unit cell contains two independent molecules. In both of these molecules the
rhodium atoms show a slightly distorted square planar coordination sphere. The rhodium atoms
are 0.072 Å and 0.003 Å, respectively, located above the coordination plane. Apart from that
there are no significant differences with respect to bond angles and bond distances compared to
the structure of E10. Obviously the counterion does not interfere with structural arrangement of
the complexes.
3. Results and Discussion
50
Figure 3.10: Structure of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E11.
3.2.3 Single crystal X-ray structure analyses of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][X]
(X = Cl (E12), PF
6
(E13))
Single crystals of E12 and E13 suitable for X-ray diffraction analysis were obtained by slow
evaporation of a concentrated solution of E12 in THF and by layering of concentrated
dichloromethane of E13 solution with diethyl ether, respectively. Selected bond lengths and
angles of both compounds are listed in Table 3.6. Crystallographic data are presented in Table
7.4. Molecular structure containing atom numbering schemes are shown in Figure 3.11 for E12
and 3.12 for E13, respectively. E12 crystallized in the monoclinic space group Cc while E13
crystallized in the monoclinic in space group C2/c.
3. Results and Discussion
51
Crystals of the trans complex E12 contain 4 molecules in the unit cell. And crystals of E13
contains four molecules per unit cell in which two molecules of complex and two molecules of
diethyl ether incorporated in the unit cell In both complexes the arrangement around rhodium is
distorted square planar. The rhodium centers are coordinated by two bidentate ligands E7. The
ligating phosphorous atoms occupy trans coordination sites. The same holds for the ligating
carbon atoms. The sums of angles at the Rh atoms equals 359.35(6)° for E12 and 358.56(6)° for
E13. In E12 the rhodium atom is located only 0.133 Å from the coordination plane. In E13 the
rhodium atom is located 0.208 Å above the coordination plane defined by C(1), C(1A), P(1) and
P(1A). In E12 and E13 the six membered rings defined by Rh(1), P(1), C(7), C(6), N(2), C(1)
and Rh(1), C(1), N(2), C(6), C(7), C(16), P(1), respectively, have pseudo-boat conformation.
Both complexes show C
2
symmetry. The C
2
axis is perpendicular to the coordination plane
passing through the rhodium atom. The ligand bite angles in case of E12 C(1)-Rh(1)-P(1) and
C(1)-Rh(1)-P(1)#1 amount to 79.58(6)° and 100.09(6)°, respectively. They deviate by
approximately 10° from the ideal 90° angle expected for this type of complex. Due to that the
phenyl ring in the trans complex are quite close to each other leading to steric strain which cases
distortion around the Rh (1) center The C(1)#-Rh(1)-C(1) of 176.47 close to linearity 180° and
the P(1)#-Rh(1)-P(1) of 169.67(3) deviates from ideal angle 180° the rhodium carbene distance
of Rh(1)-C(1)# of 2.029(2) and Rh(1)-P(1)# of 2.2619(6)and 2.2620(6) respectively in E13. The
bite angle C(1)-Rh(1)-P(1) of 84.81(6) close to ideal angle 90°, the C(1)#-Rh(1)-P(1)# of
94.47(6) and C(1)#-Rh(1)-C(1) of 175.07(12) close to the linearity while P(1)#-Rh(1)-P(1) of
163.24(3) deviates from 180º. The Rhodium carbene and phosphour bond lengths of 2.031(2) Å
and 2.2551(5) Å, respectively. Are similar to those of other Rh-NHC complexes.
[124,137,138]
The
Rh-P bond length is longer than Rh-C bond by 0.2241(5) Å due to trans effect of phosphine
ligand.
3. Results and Discussion
52
Figure 3.11: Structure of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E12.
Figure 3.12: Structure of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E13.
3. Results and Discussion
53
Table 3.6: Selected bond lengths [Å] and bond angles [º] for
trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl (E12) and trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E13)
E12 E13
Bond Lengths
Rh(1)-C(1)A 2.029(2) Rh(1)-C(1)A 2.031(2)
Rh(1)-C(1) 2.029(2) Rh(1)-C(1) 2.031(2)
Rh(1)-P(1)A 2.2619(6) Rh(1)-P(1)A 2.2551(5)
Rh(1)-P(1) 2.2620(6) Rh(1)-P(1) 2.2551(5)
Bond Angles
C(1)-Rh(1)-P(1) 79.58(6) C(1)-Rh(1)-P(1) 84.81(6)
C(1)A-Rh(1)-P(1)A 79.59(6). C(1)A-Rh(1)-P(1)A 84.81(6)
C(1)-Rh(1)-P(1)A 100.09(6) C(1)-Rh(1)-P(1)A 94.47(6)
C(1)A-Rh(1)-P(1) 100.09(6) C(1)A-Rh(1)-P(1) 94.47(6)
P(1)A-Rh(1)-P(1) 169.67(3) P(1)A-Rh(1)-P(1) 163.24(3)
C(1)A-Rh(1)-C(1) 176.47(12) C(1)A-Rh(1)-C(1) 175.47(12)
.
3. Results and Discussion
54
3.3 Equilibrium between cis and trans isomers at higher temperatures
The interconversion of cis-complex and trans complex is studied by measuring
31
P-NMR of both
complexes at different temperatures and for different times. Generally
31
P-NMR spectra of the cis
isomers E10 shows a signal at 32 ppm which splitting to a doublet (
1
J
RhP
= 126 Hz), while the
trans complex E12 exhibits a doublet at 26 ppm (
1
J
RhP
= 153 Hz) as shown in Figure.3.13.
-120-100-80-60-40-20140 120 100 80 60 40 20 0 ppm
25
26
27
28
29
30
31
32
33
ppm
Figure 3.13:
31
P-NMR spectrum of a mixture of cis and trans isomers E10 and E12.
The relative stability of both isomers was checked by temperature dependent
31
P-NMR
spectroscopy. Initially the sample of the cis isomer dissolved in d
6
-DMSO shows a signal at 32
ppm and small signal of the trans isomers at 26 ppm as a side product with a ratio of cis to trans
of 10:1 Figure 3.14. The ratio has been determined by integration of the peaks as the phosphorous
atoms in both complexes most likely have similar relaxation times due to the similar structure of
the complexes. On heating for 2 h at 45°C the ratio of the isomers did not change. Increasing the
temperature to 80°C and heating for 21 h leads to a new ratio of 2:1. Heating at 100°C for 70 h
gives a spectrum with sharp peaks of both isomers in a ratio of cis to trans 1:2. Prolonged heating
3. Results and Discussion
55
at 120°C gave no change in ratio of both isomers indicating that an equilibrium due to
interconservion of both isomers (Figure 3.16).
25
26
27
28
29
30
31
32
33
34
35
ppm
0 min
2 h at 45°C
2h at 80°C
20 h at 90°C
70 h at 100°C
100 h at 120°C
2h at 45°C
Figure 3.14: Temperature dependent
31
P NMR-spectrum of isomerization of cis-E10 to trans-E12.
In order to prove the proposed interconversion the
trans
isomer was dissolved in CD
3
CN and
again temperature dependent
31
P-NMR spectra were recorded. The starting material contains both
isomers in a ratio of 10:1 (
trans
:
cis
) at room temperature. On heating the
trans
isomer at 50°C
for 2h there is no change in the ratio of both isomers. By increasing the temperature to 70°C and
heating again for 8 h there the ratio changes to 5:2 (
trans
:
cis
). Finally on heating at 78°C for 18
h the ratio of
trans
to
cis
becomes 2:1. Heating for another 24 h does not change the observed
ratio for both isomers confirming the above postulated equilibrium in solution as shown in Figure
(3.15)
3. Results and Discussion
56
25
26
27
28
29
30
31
32
33
34
ppm
o min
2 h at 55°C
5 h at 60°C
11 h at 75°C
18 h at 78°C
25 h at 78°C
23 h at 78°C
*
*
*:cis-E10
*:trans-E12
Figure 3.15: Temperature dependent
31
P-NMR spectra of thermal isomerization of trans-E12 to cis-E10.
Figure 3.16: The equilibrium between cis-E10 and trans-E12 isomers of [Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl.
The mechanism of interconversion of trans-E12 and cis-E10 can occur through two different
mechanisms as depicted in Figure 3.17. In mechanism A the reaction is initiated by a dissociation
of the phosphane moieties and subsequent pseudo rotation around rhodium atoms. Recoordination
of the phosphorous atom forms the cis complex. In mechanism B reaction occurs through a
tetrahedral transition state subsequent rearrangemen of the molecules. If the reaction proceeds via
pathway A the intermediate complex I should give a
31
P-NMR resonances at about -20 ppm
3. Results and Discussion
57
(compare to MePPh
2
, δ = -27. 1 ppm).
[124]
However, we did not observe any signal in the negative
range of the ppm scale. This strongly points toward mechanism B, but we cannot completely rule
out that the transformation via intermediate I (mechanism A) is so rapid that NMR-spectroscopy
is not able to detect it.
NNEt
N
EtN
Rh P
N NEt
EtN
N
Rh
P
P
Ph
Ph Cl
cis-E10
Ph
P
Ph
Ph
Ph
Ph
Cl
N NEt
N
EtN
Rh P
P
Ph
Ph
Ph
Ph
Cl
N
EtN
Rh PPh
Ph
Cl
P
Ph
Ph
NNEt
Ph
A1A2
B1B2
(I)
(II)
trans-E12
Figure 3.17: Postulated mechanisms for the interconversion of E10 and E12.
3. Results and Discussion
58
3.4 Electrochemistry of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E11)
-1,5 -1,0 -0,5 0,0 0,5 1,0 1,5
-0,000004
-0,000002
0,000000
0,000002
0,000004
0,000006
0,000008
328 mV
I(
µ
µ
µ
µ
A)
E(V vs Ag/AgCl)
524 mV / NHE
586mV
266mv/NHE
-604mV
-666mV / NHE
Figure 3.18: Cyclovoltammogram of E11 in CH
3
CN.
The cyclovoltammogramm of cis-rhodium(I) complex E11 (0.1 mol/L [NBu
4
][PF
6
]) was
obtained at a scan rate of 50 mV/s in acetonitrile. The cis-Rh(I) complex shows irreversible
oxidation waves at 266 mV/NHE and 542 mV/NHE and a reduction wave at -666 mV/NHE.
3. Results and Discussion
59
3.4.1 Electrochemistry of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl (E12)
0 2
0,00000
0,00005
0,00010
I(
µ
µ
µ
µ
A)
E(V vs Ag/ AgCl)
-546mV
476 mV/ NHE
572 mV
-642mV / NHE
Figure 3.19: Cyclovoltammogram of E12 in CH
3
CN.
The cyclovoltammogram of E11 (0.2 mol/L [NBu
4
][PF
6
]; 50 mV/s; Au/Pt/Ag-AgCl) shows quasi
irreversible electron transfers (Figure 3.19) The oxidation wave at 476 mV/NHE and reduction
wave at -642 mV/NHE.
3. Results and Discussion
60
3.5 Synthesis of peroxo complexes
3.5.1 Synthesis and dynamic behaviour of cis- and trans-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]X
(X = Cl (E14), PF
6
( E15))
The novel peroxo complexes E14 and E15 were synthesized by exposure of methylene chloride
solutions of E10 or E11, respectively, to air (Figure 3.20). The reactions are finished after a few
minutes. The color changes in both cases from yellow orange to pale brown.
N NEt
N
EtN
Rh P
N NEt
EtN
N
Rh
P
P
Ph
Ph Cl
cis-E10
Ph
P
Ph
Ph
Ph
Cl
Ph
Ph
+O
2
N NEt
N
Et
N
Rh
P
P
Ph
Ph Cl
Ph
Ph
O O +NNEt
N
EtN
Rh P
P
Ph
Ph
Ph
Cl
Ph
O O
trans-E15A
+ O
2
N NEt
EtN
N
Rh
P
P
Ph
Ph Cl
Ph
Ph
cis-E10
O
2
N
N
Et Rh
PPh
Ph
OO
P
Et
N
NPh
Ph
Cl
trans-E15B
cis-E14A
∆Τ
RT
trans-E12
− Ο
2
, ∆Τ
Figure 3.20: Formation of cis- and trans-peroxo complexes E14, E15.
The
31
P-NMR spectrum of E14 at room temperature shows a broad dublett at 27.5 ppm (d,
1
J
Rh-P
= 125 Hz) and an extremely broad peak at 8.5 ppm. In addition the signal of E15 at 26.5 ppm (d,
1
J
RhP
= 125 Hz) is observed. On heating to 343 K the peak at 27.5 ppm becomes a sharp dd (
1
J
RhP
= 125 Hz,
2
J
PP
= 20 Hz) and the peak at 8.5 ppm is transformed into a dublett (
1
J
RhP
= 125 Hz)
with much lower half band width than before. The observed transformation of the resonances
must be attributed to a fluxional process. E14 consists of two isomers (E14A and E14B) which
are in a dynamic equilibrium with each other. At 343 K the interconversion is so rapid that only 2
resonances for the two phosphorous atoms can be observed. On lowering the temperature to 303
K the interconversion slows down and the peaks broaden due to coalescence of the resonances of
E14A and E14B. This is confirmed by further temperature dependent
31
P-NMR spectra which
3. Results and Discussion
61
have been mesaured down to 233 K (Figure 3.21). In the low temperature range 4 sharp
resonances at 30.9 (dd,
1
J
RhP
= 125 Hz,
2
J
PP
= 20 Hz), 26.2 (dd,
1
J
RhP
= 125 Hz,
2
J
PP
= 20 Hz), 12.4
(dd,
1
J
RhP
= 85 Hz,
2
J
PP
= 20 Hz), -3.1 (dd,
1
J
RhP
= 85 Hz,
2
J
PP
= 20Hz) are detected which must be
assigned to E14A and E14B. From the intensities of the signals it becomes immediately clear that
the resonances at 30.9 ppm and 12.4 ppm belong to one of the isomers (E14A) and the resonances
at 26.2 ppm and -3.1 ppm belong to the other isomer (E14B). The most notable feature of their
31
P-NMR data are the coupling constants. The recorded
2
J
PP
value of 20 Hz is typical for a cis
arrangement of the two phosphorous atoms in each isomer. The
1
J
RhP
values of 125 Hz and 85 Hz
allow the assignment of the phosphorous atoms with respect to the Rh–O
2
plane. The phosphorous
atoms exhibiting a coupling constant of 125 Hz lie in the Rh–O
2
plane while those with 85 Hz are
perpendicular orientated with respect to that plane. The assignment is based on the observed
coupling constants in E15 and other Rh-O
2
complexes containing phosphorous ligator atoms.
[139]
In E15 both phosphorous lie in the Rh-O
2
plane and show a
1
J
RhP
coupling constant of 125 Hz.
Are similar to [Rh(O
2
)(P-N)(PPh
3
)Cl],
[139]
[Rh(O
2
)(4-C
5
F
4
N)(CNtBu)(PEt
3
)
2
]
[140]]
85Hz From the
coupling constants it is clear, that E14A and E14B have the same arrangement of the ligands
around the rhodium center. Hence the structural difference between both isomers must be
attributed to the conformation of the 6-membered rings which are part of both molecules. This
evaluation of the recorded data is confirmed by the single crystal X-ray analyses of E14A and
E16 which shows the same ligand arrangement as E14A, but another conformation of the 6-
membered rings. The latter conformation of the rings must be attributed to E14B too. A deeper
discussion of these structural aspects can be found in section 3.6.1.1.
3. Results and Discussion
62
-25
-20
-15
-10
-5
30
25
20
15
10
5
0
ppm
Figure 3.21:
31
P-NMR spectrum of peroxo adduct E14 at different temperature.
In order to find out if the addition of O
2
to cis-E10 is reversible a sample was heated during NMR
measurements (Figure 3.22). The first spectrum recorded at 303 K shows the signals of E14 and
small amounts of trans-complex E15B. On heating to 343 K some remarkable changes are
observed. Firstly, the signals of E14 a sharpened due to the rapid interconversion of E14A and
E14B (vide supra). Secondly, the intensity of the resonances of E15A has strongly increased and
the resonances of cis-E10 can be observed with low intensity. The latter observation is a clear
indication that the addition of O
2
to cis-E10 is reversible. At higher temperatures E14 releases O
2
and starts to isomerize to give E12 (vide supra) which subsequently reacts with O
2
to irreversibly
form E15A. Prologned heating gives an additional minor resonance at 4 ppm which must be
attributed to the isomerization product E15B, which shows a
1
J
RhP
-coupling constant of 88 Hz
typical for phosphorous perpendicular to the Rh-O
2
plane. The above discussed reaction pathways
can be proved in a single experiment. Therefore a sample of E14 is heated in the presence of
excess O
2
. The accompanying NMR spectra show the gradual conversion of E14 to E15A and
finally the formation of E15B. Form the spectrum recorded after 21 hours of heating it can be
concluded that E15A is thermodynamically more stable than E15B.
3. Results and Discussion
63
-10
-5
40
35
30
25
20
15
10
5
0
ppm
25.0
25.5
26.0
26.5
27.0
27.5
28.0
ppm
Figure 3.22:
31
P-NMR spectra of [Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]Cl at 343K.
Notable feature of The
1
H-NMR spectra of E15 inCD
3
CN is the absence of a signal at 8.5 ppm
which indicates the coordination of the carbene ligand to the Rh-atom. The protons H
5
and H
6
of
the imidazolium ring have been detected at 6.97 ppm (d,
3
J
HH
= 2 Hz) and 7.09 ppm (d,
3
J
HH
=
2Hz), respectively. Compared to the protons of the imidazolium salts the latter resonances are
shifted to high field. As a consequence of the coordination to Rh the protons of the ethylene
bridge become diasterotopic and they are shifted to high field δ = 1.84 (m, NCH
2
), 3.91 (dt, 1H
,
2
J
HH
= 15 Hz,
3
J
HH
= 7 Hz, PCH
2
) and 3.03 (dq, 1H,
2
J
HH
= 14 Hz,
3
J
HH
= 7 Hz, PCH
2
)]
The
13
C-NMR spectrum shows a high field shifted signal for the carbene atoms at 160.4 ppm (dt,
1
J
RhP
= 125 Hz,
2
J
PC
= 17 Hz) due to the formation of a rhodium (III) center. The carbon atoms of
the imidazolium ring C
5
and C
6
are observed at δ 125.2(s) ppm and 121.7(s), respectively.
1
H and
13
C-NMR data for E14 are given in the experimental section. The IR spectrum (KBr) of both E14
and E15 shows an absorption band at 845 cm
-1
attributable to oxygen-oxygen stretching band
which are typical for side-on coordinated peroxide.
[141]
3. Results and Discussion
64
3.5.2 X-ray crystallographic analyses of cis-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
(E14A)
Single crystals of cis-peroxo complex E14A suitable for X-ray diffraction were obtained by
layering a concentrated methylene chloride solution of E14 with diethyl ether. The peroxo
complex E14A with counterion Cl
-
crystallizes in space group P-1 with two molecules per unit
cell incorporating two chloride anions and four methylene chloride solvent molecules.
Crystallographic data are presented in the Table 7.5 and selected bond lengths and angles are
listed in Table 3.7. Molecular structure containing the atom numbering scheme is shown in
Figure 3.23a. The central rhodium atom is coordinated in a trigonal bipyramidal fashion by the
carbene carbon donor atoms and phosphorous donor atoms of the two bidentate NHC ligands.
The coordination is completed by the peroxo ligand. In E14A the carbene carbon atom C(35) and
phosphorous atom P(2) occupy axial positions of the trigonal bipyramid while the carbene atom
C(65), P(1) and the oxygen atoms of the peroxo ligand lie in the equatorial plane. The sum of the
bond angles formed around the Rh atom in the equatorial plane is 360°.
Figure 3.23a: Structure of the ∆-isomer of cis-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E14A,
with counterion Cl
-
, (without hydrogen atoms).
3. Results and Discussion
65
Table 3.7: Selected bond lengths [Å] and angles [º] of peroxo complex E14A
Bond Lengths
O(1)-O(2) 1.442(4) Rh(1)-C(35) 2.090(4)
Rh(1)-O(2) 2.030(3) Rh(1)-P(1) 2.3113(10)
Rh(1)-O(1) 2.062(3) Rh(1)-P(2) 2.3156(10)
Rh(1)-C(65) 2.048(3)
Bond Angles
O(1)-Rh(1)-O(2) 41.25(11) C(65)-Rh(1)-O(2) 102.87(13)
C(65)-Rh(1)-O(1) 143.41(13) C(35)-Rh(1)-P(2) 176.23(10)
O(1)-Rh(1)-P(1) 112.47(8) C(65)-Rh(1)-P(1) 103.91(10)
O(2)-Rh(1)-P(1) 153.02(8)
The dioxygen molecule is coordinated to rhodium in a side on fashion. The O(1)-O(2) bond
distance is 1.442(4) Å which is considerably longer than that of free dioxygen (1.21 Å) and
comparable to that of H
2
O
2
(1.49 Å). The bonding distance is typical for coordinated peroxides.
[142]
. The elongation of the O-O bond distance of the dioxygen unit is also observed in the
rhodium dioxygen complexes such as RhCl(O
2
)(PPh
3
)
3
, (1.413(9) Å) and [RhCl(O
2
)(PPh
3
)
2
]
2
(1.44(1) Å). The difference in the Rh(1)-O(1) and Rh(1)-O(2) bond lengths is 0.032(3) Å while
the O(1)-Rh(1)-O(2) angle is amounts to 41.25(11). The Rh-C bond lengths of 2.048 (3) and
2.090 (4) Å are close to those reported for comparable complexes.
[142-144]
The Rh-P bond lengths
are 2.3156(10) Å and 2.3113(10) Å which are typical values for phosphorous coordinated to
Rh(+III). The peroxide ligand is not symmetrically coordinated with respect to the axis
C(35)/P(2). It is shifted towards the carbene atom C(65) and lifted from the equatorial plane by
0.179 Å. Consequently the bond angle P(1)-Rh(1)-O(2) is larger than O(1)-Rh(1)-C(65) by about
9.6°. The bond angle formed by the axial ligands, C(35)-Rh(1)-P(2) is 176.23(10)
º
and thus close
to linearity.
In addition single crystals of cis–peroxo complex E14A as counter ion PF
6-
were obtained by
layering a concentrated acetonitrile solution of E14 with diethyl ether. In this case E14A
crystallized in the space group P2
1
2
1
2
1
with four molecules per unit cell incorporating one
acetonitrile molecule in the unit cell. Molecular structure containing the atomic numbering
3. Results and Discussion
66
scheme is shown in Figure 3.23b and Crystallographic data are presented in the Table 7.5. It must
be noted that in this case a crystal containing only one enantiomer of E14A is obtained. Hence
during crystallisation a spontaneous separation of the enantiomers takes place.
Figure 3.23b: Structure of the Λ-isomer of cis-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in enantiomerically pure
crystal of E14A with counterion PF
6-
, (without hydrogen atoms).
3.5.3 Single crystal X-ray structure analysis of trans-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(E15)
Red brown crystals of E15 were grown by layering a concentrated methylene chloride solution
with diethyl ether. E15 crystallizes in orthorhombic space group, Pna2(1) with four molecules
per unit cell in which two of the bidentate ligands are coordinated to the Rhodium(III) center.
Two molecules of methylene chloride are also found in the unit cell. Crystallographic data are
presented in theTable 7.6 and selected bond lengths and angles are listed in Table 3.8. Molecular
structure containing the atom numbering schemes is shown in Figure 3.24.
3. Results and Discussion
67
Figure 3.24: structure of trans-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E15, (without hydrogen atoms).
The geometry around the rhodium center is trigonal bipyramidal. The phosphorous atoms and the
peroxo ligand lie in the equatorial plane of the trigonal bipyramid. The sum of bond angles
formed by these donors around the rhodium atom is 360°. In the trans- peroxo complex E15, the
peroxo ligand is symmetrically coordinated with respect to the axis C(35)/C(65) and lies in the
equatorial plane. Hence, the angles P(1)-Rh(1)-O(1) and P(2)-Rh(1)-O(2) viz., 151.4(3 )° and
154.5(3) ° respectively, are almost identical. The two phosphourous donor atoms are also lying in
the equatorial plane of the trigonal bipyramidal structure. The most significant difference
between the structures of E14 and E15 is that the position of the peroxo ligand. In E14 the the
plane Rh(1)-O(1)-O(2) shows a significant torsion angle with respect to the equatorial plane of
the complex and the O
2
unit is shifted towards one of the other equatorial ligands. However, in
E15 the peroxo ligand is symmetrically embeded in the equatorial plane of the molecule.
Consequently in E14, the peroxo ligand exhibits almost identical bond distances Rh(1)-O(1) and
3. Results and Discussion
68
Rh(1)-O(2), 2.038(9) Å and 2.043(9) Å, respectively The bond lengths of Rh-C in E14 are
similar to those found in E15 while the bond distances of Rh-P in E14 are larger than the bond
distances in E15 by 0.037 Å.
Table 3.8: Selected bond lengths [Å] and angles [º] of peroxo complex E15
Bond lengths
O(1)-O(2) 1.444(12) Rh(1)-C(35) 2.104(12)
Rh(1)-O(2) 2.043(9) Rh(1)-P(1) 2.280(3)
Rh(1)-O(1) 2.038(9) Rh(1)-P(2) 2.272(3)
Rh(1)-C(65) 2.103(12)
Bond angles
O(1)-Rh(1)-O(2) 41.4(4) O(1)-Rh(1)-P(1) 151.4(3)
C(65)-Rh(1)-C(35) 176.0(5) O(2)-Rh(1)-P(2) 154.5(3)
O(1)-Rh(1)-P(2) 113.1(3) P(2)-Rh(1)-P(1) 95.42(12)
O(2)-Rh(1)-P(1) 110.1. (3)
3. Results and Discussion
69
3.6 Oxidative addition of small molecules viz, (S
8,
CH
3
I, I
2
) to the cis-
rhodium(I) complex E11
cis-Rhodium(I) complex E11 undergoes oxidative addition recations with small molecules like
elemental sulfur, methyl iodide and iodine under varying reaction conditions to give the novel
rhodium(III) complexes E16, E17 and E18 as shown in Figure 3.25. The synthesis of complexes
and their structures are discussed below.
N NEt
Rh
P
P
Ph
Ph
Ph
PF
6
S
8
E11
CH
3
I-50°C, I
2
Rh
PCl
I
N
N
Et
EtN
N
Ph
Ph I
3
E19
Rh
PCH
3
I
Ph
Ph
NNEt
P
Ph
PF
6
or
E17
Rh
PI
CH
3
Ph
Ph
NNEt
P
Ph
PF
6
E18
Rh
P
P
Et
N
N
N
EtN
S S Ph
Ph
Ph
Ph
PF
6
E16
H
2
CO
or
//
N
Et
N
Ph
N
N
Et
Ph
PPh
Ph
Ph
[Cl]
N
N
Et
Figure 3.25: Synthesis of novel rhodium(III) complexes.
3.6.1 Synthesis and structure of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E16)
The synthesis of the cis-rhodium(III) complex [Rh(η
2
-S
2
)(EtIm
CH
2
CH
2
PPh
2
)
2
][PF
6
] (E16) was accomplished by oxidative
addition of E11 with elementary sulfur at room temperature in
methylene chloride. In the course of the reaction the color of the
solution changed from yellowish brown to green. The solvent was
removed after one hour to give the product. Green crystals of the
Rh
P
P
N
N
N
N
S S Ph
Ph
PF6
Ph
b
c
d
e
a
e'
d'
a'
b' c'
h
i j
k
f'
g'
f
g
3. Results and Discussion
70
novel cis-Rh(III) complex, E16 were obtained in high yield (80 %) by layering a methylene
chloride solution with diethyl ether.
The X-ray crystal structures were corroborated by NMR and IR-spectroscopy. X-ray
crystallography, proves the formation of the novel cis-Rh(III) complex E16 in which the rhodium
is coordinated to two bidentate NHC-phosphine ligands and the disulfide molecule.
The
1
H-NMR spectrum of E16 shows signals of diasterotopic protons around 2.59-3.35 ppm (m,
2H e,) and around 3.06-3.30 ppm (m, e’, 2H) as well as around 4.50-5.01 ppm (m, d’, 2H) and
around 4.73-5.24 ppm (m, 2H ,d) which are shifted down field compared to the diasterotopic
protons in the starting material E11. The protons of the imidazol ring were observed at 7.04 ppm
(m, 1H, c), 7.15 ppm (m, 1H, b), 7.32 ppm (m, 1H, c’) and 7.71 ppm (s’, 1H, b), respectively.
Accordingly the
13
C-NMR spectrum shows four resonances which can be assigned to the carbon
atoms of the imidazolium rings at δ = 119.7 (d,
3
J
PC
= 5.0 Hz, c) and δ = 121.4 (s, c’) and δ =
123.5 (d,
3
J = 6 Hz, b) and δ = 124.9 (s, b`), respectively. Two high field signals have been
observed for carbene carbon atoms bound to the rhodium(III) center at 162.0 ppm (ddd,
1
J
RhC
= 161,
2
J
PC, cis
= 12.7,
1
J
PC, trans
= 40 Hz, a) and 169.5 ppm (ddd,
1
J
RhC
= 48 Hz,
2
J
PC, cis
= 6 Hz,
2
J
PC, trans
= 19 Hz, a’). Compared to cis E11 in which the carbene atoms show a resonance at
183.0 ppm the resonances of E16 are shifted to high field.
In the
31
P{
1
H}-NMR spectrum of E16 two signals are observed at δ = 3.7 (dd,
1
J
RhP
= 128 Hz,
2
J
PP
= 23 Hz) and δ = 18.5 (dd,
1
J
RhP
= 76.4 Hz,
2
J
PP
= 23 Hz) ppm. Compared to the starting
matrial E11 the phosphorous atoms of E16 are more shielded. This observation compares well
with the above described shielding of the carbene atoms. As discussed for the analogous Rh-O
2
-
complex E14 the rhodium-phosporous coupling constants give a clear indication of the position
of the phosphorous atoms within the complex (page 61). Hence, the signal at 3.7 ppm belongs to
the phosphorous atom in the Rh-S
2
plane, whereas the other phosphorous resonance belongs to
the remaining P-atom which is perpendicular to the Rh-S
2
plane. The IR spectra of E16 exhibit a
band at 557 cm
-1
which can be assigned to the S-S-stretching vibration of η
2
-S
2
ligand.
[145]
3. Results and Discussion
71
-140-120-100-80-60-40-2020
0
ppm
4
5
6
78
9
1011121314151617181920 ppm
3.450
3.561
3.829
3.939
18.007
18.116
18.625
18.734
Figure 3.26:
31
P-NMR spectra of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E16).
3.6.1.1 Single crystal X-ray structure analyses of cis-[Rh(η
ηη
η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(E16)
Green crystals of E16 suitable for X-ray crystallographic analysis were obtained by overlaying a
concentrated methylene chloride solution of E16 with diethyl ether. E16 crystallizes in the
monoclinic space group, P2(1)/c with four molecules per unit cell in which two of the bidentate
ligands are coordinated in a cis arrangement with respect to the rhodium(III) center. Two
molecules of methylene chloride are also found in the unit cell. Crystallographic data are
presented in the Table 7.7 and selected bond lengths and angles are listed in Table 3.9. Molecular
structure containing the atom numbering scheme is shown in Figure 3.27.
3. Results and Discussion
72
Figure 3.27: Structure of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E16, (without hydrogen atoms).
The arrangement of the ligating atoms around the rhodium(III) atom is distorted trigonal-
bipyramidal with two bidentate NHC-phosphane ligands and one disulfide ligand, which
occupies one position in the equatorila plane, coordinated to Rh. The equatorial plane of the
complex is formed by the carbene carbon atom C(35), phosphorous atom P(2) and the disulfide
ligand. The axial positions are occupied the carbene carbon atom C(65) and the phosphorous
atom P(1). The S
2
-ligand is not symmetrically coordinated with respect to the axis C(65)-Rh(1)-
P(1). The S(2) atom is slightly shifted from by 0.135 Å toward the P(2) atom. The sum of bond
angles formed at rhodium atom in the equatorial plane by the equatorially lying donor atoms is
3. Results and Discussion
73
360º indicating planarity. The six membered rings in E16 containing the rhodium center both
exhibit a boat form conformation.
In E16 the rhodium carbene bond lengths Rh(1)-C(65) and Rh(1)-C(35) are 2.058(4) Å and
2.061(5) Å, respectively, are similar to the bond lengths of rhodium carbene bond in the
analogous Rh-O
2
complex E14. The S(1)-S(2) bond lengths of 2.0412(17) are similar to the
Complex cis E16 shows an analogous structure compared to to cis-peroxo complex E14 but there
are some significant differences. Firstly the bond distance of Rh(1)-P(1) and Rh(1)-P(2) differ
from the value found in E14 by 0.0824 and 0.0166 Å, respectively. As expected for the bigger
sulfur atoms the bite angle S(1)-Rh(1)-S(2) is larger than the bite angle of O(1)-Rh(1)-O(2) by
9.18° and the equatorial bond angle of S(2)-Rh(1)-C(35) is smaller than the bond angle in E14,
O(1)-Rh(1)-P(1) by 5.06°. The bond angle P(2)-Rh(1)-S(1) are similar to the bond angle in P(1)-
Rh(1)-O(2) and The bond angle of S(2)-Rh(1)-P(2) is smaller than the bond angle P(1)-Rh(1)-
O(1) by 9.86°. The angle C(65)-Rh(1)-P(1) in E16 is smaller the respective angle C(35)-Rh(1)-
P(2) by 6.83°. The former angle deviates from linearity by 10.6° most likely due to more steric
strain in E16 than in E14 due to different conformations of the 6-membered rings containg the
rhodium center. values found in literature.
[146]
for S-S single bonds.
Table 3.9: Selected bond lengths [Å] and angles [º] of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E16)
Bond lengths
S(1)-S(2) 2.0412(17) Rh(1)-C(35) 2.061(5)
Rh(1)-S(2) 2.3985(13) Rh(1)-P(1) 2.3937(12)
Rh(1)-S(1) 2.3931(13) Rh(1)-P(2) 2.3322(13)
Rh(1)-C(65) 2.058(4)
Bond angles
S(1)-Rh(1)-S(2) 50.43(4) P(2)–Rh(1)–S(1) 153.03(4)
C(65)–Rh(1)–C(35) 91.33(17) C(65)–Rh(1)–P(1) 169.40(14)
P(2)–Rh(1)–S(2) 102.61(4) C(35)–Rh(1)–S(2) 157.59(14)
S(1)–Rh(1)–C(35) 107.41(14)
3. Results and Discussion
74
3.6.2 Synthesis of cis-[Rh(CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E17, E18)
Cis-Rh(III) complexes E17, E18 were synthesised as depicted in Figure(3.25) by oxidative
addition of one equivalent of methyl iodide to one equivalent of cis rhodium(I) complex E11 in
THF solution at room temperature. The reaction mixture was monitored by
31
P NMR spectra
which shows two signals at 13.39 ppm (dd,
2
J
PP
= 25 Hz,
1
J
RhP
= 88 Hz), -6.2 ppm (dd,
2
J
PP
= 24
Hz,
1
J
RhP
= 88 Hz). After removing the solvent under vacuum high yield 86 % of yellow product
which characterised by
1
H,
13
C and
31
P NMR spectroscopy, attempts to get crystals failed.
3.6.3 Synthesis of cis-[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
][I
3
], (E19)
The synthesis of rhodium(III) complex E19 was carried out by conducting an oxidative addition
reaction in THF between cis-rhodium(I) complex [Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] E11 and two
equivalents of iodine at -50°C (Figure(3.25)). The color of the reaction mixture changed from
yellow orange to dark brown yellow. The reaction was monitored by
31
P-NMR spectroscopy
which confirms the formation of five isomers in the solution. All signals are simple doublets with
similar chemical shifts and coupling constants between 85 and 90 Hz which are typicall for
1
J
RhP
coupling, confirming that the phosphourous atoms are orthognal to coordination plane of the
halides. In all isomers the phosphourous atoms are chemically equivalent and exhibit resonances
at 4.04 ppm (d,
1
J
RhP
= 90 Hz), 1.69 ppm (d,
1
J
RhP
= 90 Hz), -1.11ppm (d,
1
J
RhP
= 85 Hz), -2.78
ppm (d,
1
J
RhP
= 87 Hz) and -3.38 ppm (d,
1
J
RhP
= 85 Hz) with an integral ratio of 0.3:1:1:0.1:0.4.
The formation of five isomers may be attributed to a radical reaction mechanism. After
completion of the reaction the solvent was removed under vacuum to give a yellow brown crude
product in 65% yield which gives yellow brown crystals suitable for X-ray crystallography upon
recrystallization. The result of the single crystal X-ray analysis shows an unexpected iodine-
chloride adduct most likely resulting from the exchange of iodine with chloride from small
impurities of [Rh(COD)Cl]
2
in the starting material. In addition the counterion I
3-
is formed due
to reaction of iodide with excess I
2
. The NMR data strongly point towards 5 isostructural isomers
with different halide substitution. Besides E19 containing Cl
-
and I
-
coordinated to the rhodium
center, isomers containing I
3-
and I
-
or Cl
-
and I
3-
etc. may have formed.
The
1
H-NMR spectra of the mixture of isomers show the appearance of two signals of
diasterotopic protons at 2.69-3.65 ppm (m, CH
2
-CH
2
-P) and 2.81-3.49 (m, CH
2
-CH
2
-P) which are
shifted to down field compared to E10, confirm the formation of a rhodium(III) center. The
3. Results and Discussion
75
resonances of the NCH
2
-protons at 5.06 ppm and 6.22 ppm are shifted downfield compared to the
starting complex. The protons of imidazol ring were observed at low field at 7.24 ppm and 7.8
ppm, 7.15 ppm and 7.21 ppm. In the
13
C-NMR spectrum the resonances of the carbene atoms
coordinated to rhodium could not be detected most likely due to extremely long relaxation times
of these atoms.
3.6.3.1 Single crystal X-ray structure analysis of cis-[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
][I
3
]
(E19)
Yellow brown single crystals of E19 suitable for X-ray crystallography are grown by layering a
concentrated acetonitrile solution of E19 with diisopropyl ether. It crystallizes in the monoclinic
space group, P2(1)/c with four molecules per unit cell in which two of the bidentate ligands are
coordinated to the rhodium(III) atom with the carbene atoms in cis position. The crystal also
incorporated one acetonitrile molecule per unit cell. Full crystallographic data are presented in
the Table 7.8 and the selected bond lengths and angles are listed in Table 3.10. Molecular
structure containing the atom numbering scheme is shown in Figure 3.28. The structural
arrangement around rhodium atoms is octahedral and the sum of angles around rhodium(III)
center is 360°. The rhodium atom is located only 0.051 Å from the coordination plane spanned by
the halides and the carbene atoms. Generally, the ligand bite angles C(31)-Rh(1)-P(2) and C(1)-
Rh(1)-P(1) are close to the ideal angle of 90° expected in an octahedral enviroment. However, the
large iodine atom leads to noticable distortions of the geometry of this complex. For example the
angle P(1)-Rh(1)-P(2) which is expected to be 180° amounts only to 167.05(11)° as the
phosphorous atoms are bend away from the free electron pairs of the iodine ligand. Due to the
same reason the angle C(31)-Rh(1)-P(1) is widened from ideally 90° to 99.3(3)°. The bonding
distances of Rh(1)-C(1) and Rh(1)-C(31) are of equal length and similar to those found in the
literature.
[131,133,136]
3. Results and Discussion
76
Figure 3.28: Structure of cis-[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E19, (without hydrogen atoms).
Table 3.10: Selected bond lengths [Å] and angles [º] of E19
Bond lengths
I(1)-Rh(1) 2.7531(12) Rh(1)-P(2) 2.353(3)
Rh(1)-Cl(1) 2.442(3) Rh(1)-C(1) 2.038(11)
Rh(1)-P(1) 2.378(3) Rh(1)-C(31) 2.054(10)
Bond angles
C(31)-Rh(1)-P(2) 91.6 (3) P(1)-Rh(1)-Cl(1) 85.26(10)
C(1)-Rh(1)-P(1) 91.9(3) C(1)-Rh(1)-I(1) 175.2(3)
P(2)-Rh(1)-Cl(1) 83.85(10) P(2)-Rh(1)-P(1) 167.05(11)
C(31)-Rh(1)-P(1) 99.3(3) Cl(1)-Rh(1)-C(1) 91.5(3)
3. Results and Discussion
77
3.7. Iridium complexes
3.7.1 Synthesis of cis-[Ir(EtImCH
2
CH
2
PPh
2
)][PF
6
] (E20)
The novel cis-iridium(I) complex E20 was synthesized according to Figure 3.29. The first step of
the sequence involves the deprotonation of two equivalents of imidazolium salt E6 in THF
solution with one equivalent of potassium dimethylsilylamide at room temperature under inert
gas atmosphere to afford 1-ethyl-3-ethyldiphenylimidazole-2-ylidene E7. The formation of the
latter was indicated via its reaction with carbondisulfide. Then one equivalent of the metal
precursor [(Ir(µ-Cl)(COD)]
2
was added to the carbene solution. The colorless solution turned
immediately to orange red. Subsequently the reaction mixture was stirred for 1 hour. The
formation of novel cis cationic iridium(I) complex E20 was confrimed by measuring a
31
P-NMR
spectrum which exhibits a signal of the phosphorous atoms at 16.8 ppm which is similar to other
phosphorous resonances in iridium(I) complexes reported in the literature.
[135]
Figure 3.29: Synthesis of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E20).
3. Results and Discussion
78
The novel Iridium(I) complex is soluble in THF solution. After
removing of the solvent under vacuum an orange red crude product
was crystallized by layering a concentrated methylene chloride
solution with diethyl ether to give orange red crystals of E20 in high
yield. The structure of E20 was characterized by NMR spectroscopic
methods and single crystal X-ray analysis.
The
1
H-NMR spectrum of E20 shows the absence of the signal at 8.49
ppm proving the deprotonation of the imidazolium salt E6 and
indicating the coordination of the bidentate NHC-phosphane ligand to
iridium(I). The signals of the diastereotopic protons of the CH
2
-units were observed around 2.12-
2.59 ppm (m, 4H, e) and 4.36-4.91(m, 4H, d). Compared to the imidazolium salts E6 these
resonances are downfield shifted. In contrast the signals of the protons of the imidazol ring are
shifted to higher field with δ = 6.94 (d, 2H,
3
J
HH
= 1.3 Hz, b) and δ = 7.07 (d, 2H,
3
J
HH
= 2.1 Hz,
c), respectively. This shift is easy to understand as the deprotonation of the imidazolium rings
leads to a strong decrease of their aromaticity. The signals of aromatic protons of phenyl ring
were observed at 6.82-7.80 ppm.
The resonances in the
13
C-NMR spectrum of E20 shows the signal of carbenic carbon atom (a) at
at 174.4 ppm which appears as a double doublett (
2
J
PC (cis)
= 20 Hz,
2
J
PC (trans )
= 97 Hz) confirming
the stereochemistry of the whole complex. The double doublett arises from phosphorous carbon
coupling. It can only be explained by phosphorous atoms located in cis- and trans-position with
respect to the carbene atoms. The values of the coupling constants are similar to other iridium-
NHC metal complexes reported in the literature.
[131,135,136,147,148]
The
31
P-NMR spectrum of the iridium complex shows a signal at 16.9 ppm (s) which similar to
other value reported in the literature.
[135]
This observation confirms the coordination of iridium
atom to the bidentate ligands. The signal of [PF
6
] appears at high field at -144.0 ppm (hep,
1
J
PF
=
711 Hz).
3.7.1.1 Single crystal X-ray structure analyses of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E20)
Orange red single crystals of E20 suitable for single crystal X-ray crystallography are obtained
by layering diethyl ether onto concentrated methylene chloride solution. E20 crystallizes in the
3. Results and Discussion
79
monoclinic space group, P2(1)/n with four molecules per unit cell in which two of the bidentate
ligands are coordinated in a cis fashion to the iridium(I) center. The structural arrangement
around iridium atoms is square planar and the iridium atom lies in the plane of the ligating atoms
(deviation 0.003 Å) and the sum of angles around the iridium center is 360° as expected for
square planar complexes. Crystallographic data are presented in the Table 7.9 and selected bond
lengths and angles are listed in Table 3.11. Molecular structure containing the atom numbering is
shown in Figure 3.30.
Figure 3.30: Structure of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E20.
In E20 the phosphorous atoms lie on one side of the square and carbene atoms are on the other
side. In E20 both six membered rings form boat conformations. Similar pseudo-boat
conformations have also been observed in the reported X-ray structures of other Ir-NHC
complexes.
[149,150]
Generally, in E20 the bite angle P(1)-Ir(1)-C(35) deviates from the ideal 90°
angle by 5.6° and for P(2)-Ir(1)-C(65) by 3.5°. The deviation is most likely due to steric effects
3. Results and Discussion
80
imposed by the interaction of phenyl rings. Due to that the arrangement around the iridium atom
is gives as ligthly distorted square. The angle P(2)-Ir(1)-C(35) of 176.2(3)° is close to the
linearity while the angle P(1)-Ir(1)-C(65) which amounts to 174.1(4)° is a little bit more
distorted. The bond distances of Ir(1)-C(65) and Ir(1)-C(35) are 2.054(12) and 2.059(12), they are
similar to other iridium-NHC metal complexes which are found in the literature.
[59,97f,97h,151]
The
bond distance of Ir(1)-P(2) and Ir(1)-P(1) are 2.267(3) and 2.265(3), respectively, are within the
range reported in the literature for similar complexes.
[152-154]
Table 3.11: Selected bond lengths [Å] and angles [º] of cis-Ir(I) complex E20
Bond lengths
Ir(1)-C(65) 2.054(12) Ir(1)-P(1) 2.265(3)
Ir(1)-C(35) 2.059(12) Ir(1)-P(2) 2.267(3)
Bond angles
C(65)-Ir(1)-C(35) 89.8(5) C(35)-Ir(1)-P(2) 176.2(3)
C(65)-Ir(1)-P(2) 86.5(4) C(65)-Ir(1)-P(1) 174.1(4)
C(35)-Ir(1)-P(1) 84.4(3) P(1)-Ir(1)-P(2) 99.37(12)
The comparison between cis-Ir(I) complex E20 and the Rh(I) complex E11 shows the close
similarity of both complexes. There are only minor differences with respect to the observed
angles within both molecules. Most of the bonding distances are equal according to the standard
deviations determined (Table 3.12).
3. Results and Discussion
81
cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
]
+
cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
Figure 3.31: Structure representation of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
]
+
and cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E20 and E11.
Table 3.12: Selected bond lengths [Å] and angles [º] for E20 and E11
Bond length
E11 E20
Rh(1)-C(135) 2.044(4) Ir(1)-C(65) 2.054(12)
Rh(1)-C(165) 2.057(4) Ir(1)-C(35) 2.059(12)
Rh(1)-P(11) 2.2565(11) Ir(1)-P(2) 2.267(3)
Rh(1)-P(12) 2.2739(11) Ir(1)-P(1) 2.265(3)
Bond angles
E11 E20
C(135)-Rh(1)-C(165) 91.24(16) C(65)-Ir(1)-C(35) 89.8(5)
C(135)-Rh(1)-P(11) 88.75(12) C(65)-Ir(1)-P(2) 86.5(4)
C(165)-Rh(1)-P(12) 80.54(11) C(35)-Ir(1)-P(1) 84.4(3)
C(135)-Rh(1)-P(12) 171.66(12) C(65)-Ir(1)-P(1) 174.1(4)
C(165)-Rh(1)-P(11) 174.23(12) C(35)-Ir(1)-P(2) 176.2(3).
3. Results and Discussion
82
3.8 Reaction of small molecules viz, (H
2
, O
2
, S
8,
CO, CH
3
I, I
2
) with cis-
Iridium(I) complex E20.
The Cis-Iridium(I) complex E20 undergoes reactions with small molecules like hydrogen,
oxygen, elemental sulfur, methyl iodide and iodine in different solvents to afford the novel Ir(III)
complexes E21, E22, E23, E24, E25 and E26 as outlined in Figure 3.32. The synthesis of all
complexes and their structures are discussed in details below.
Ir P
EtN N
P
Ph
Ph
Ph
Ph
cis-E20
Ir
P
P
Et
N
N
N
EtN
S S Ph
Ph
PF6
Ph
Ph
S8
H2
Ir
P
N
N
HH
Ph
Ph
Ph
Et PF6PF6
Ir
P
NEt
N
Et
N
N
O
P
Ph
Ph
Ph
Ph
O
PF6
O2
CO
Ir
P
N
N
Et
EtN
N
P
CO
Ph
Ph
Ph
Ph
PF6
Ir
P
P
EtN N
N
N
Et I
Ph
Ph
Ph
Ph
I
I2CH3I
Ir
P
P
N
EtN
Ph
Ph
Ph
Ph
H3C
I
E21
E23 E22
E24
E25
E26
I3
N
NEt
P
Et
N
N
Ph
I
Et
N
N
Figure 3.32: Reactions of small molecules with E20.
3.8.1. Synthesis and characterization of cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
]
+
(E21)
Exposure of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
]
+
E20 to H
2
(1bar) in methylene chloride solution
afforded the novel hydride complex cis-[Ir(H
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
E21. The reaction was
3. Results and Discussion
83
completely finished within one hour. After the removal of the solvent under vacuum the yellow
product was isolated in high yield (70 %) and recrystallised by layering diethyl ether onto a
concentrated methylene chloride solution. The
1
H,
13
C and
31
P NMR spectra are in agreement
with solid state structure of E21 (Figure 3.33).
The most significant features in the
1
H-NMR spectrum of E21 are the hydride signals at δ = -9.79
(td,
2
J
PH cis
= 32 Hz,
2
J
HH
= 4 Hz) and -7.71 (ddd,
2
J
PH trans
= 129 Hz,
2
J
HH
= 4 Hz,
2
J
PH cis
= 18 Hz)
corresponding to a terminal hydride ligands bonded to the iridium center. The small
2
J
HH
coupling constant proves the cis arrangement of the hydride ligands. Their coupling patterns
indicates that one of them (δ = -9.79) is in trans position to one phosphorous atoms while the
other (δ = 7.71) is in cis position to both phosphorous atoms.
[155-157]
Coordination of the carbene ligands is confirmed by their
13
C-NMR resonances which are shifted
to high field δ = 160.2 (m) compared to the signals of E20 in which they appeared at 170 ppm.
The
31
P-NMR spectrum exhibits two signal due to the presence of inequivalent phosphorous
atoms at -0.86 (d,
2
J
PP
= 15 Hz) and -2.17 (d,
2
J
PP
= 15 Hz). The IR spectrum shows a sharp Ir-H
stretching mode at 2013 and 2050 cm
-1
which are in good agreement with other iridium hydride
complexes reported in the literature.
[158]
3.8.1.1 Single crystal X-ray structure analysis of cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(E21)
Single crystals of E21 were obtained by over layering diethyl ether onto a concentrated
methylene chloride solution. E21 crystallized in the monoclinic space group P2(1)/c with four
molecules in the unit cell. Figure 3.33 shows the Molecular structure of E21, the relevant bond
lengths and angles are presented in Table 3.13, Crystallographic data are presented in the Table
7.10. In E21 the iridium atom is coordinated with two hydride ligands in cis orientation and two
bidentate NHC-phosphane ligands. Both the phosphorous atoms and the carbene carbon atoms
adopt a cis coordination. Hence, the complex is in an all cis-configuration reflecting the
stereochemistry of the starting complex E20. The iridium atom exhibits a distorted octahedral
geometry. The carbene carbon atoms and the iridium center build an angle of 93.22(17)°. The
bond angle H(1)-Ir(1)-H(2) is 96.1(29)°deviates slightly from ideal angle due to strong
interaction of hydride ligand with one of the hydrogen atoms of the phenyl ring. The angles
C(35)-Ir(1)-P(2) and P(1)-Ir(1)-P(2) deviate by 11° from ideal 90° angle due to the interaction of
3. Results and Discussion
84
the phenyl rings. The angle C(65)-Ir(1)-P(1) deviates by 16° from linearity due to the steric
strain imposed by the phenyl rings. The angle C(65)-Ir(1)-H(2) is also diminished to 83.92° due
to interaction between the phenyl rings and the hydride ligand. The iridium carbene carbon bond
distances of 2.043(4) and 2.099(4) Å for Ir(1)-C(65) and Ir(1)-C(35), respectively, lie in the range
of previously reported Ir-C bond lengths.
[100]
The Ir-P distance amount to 2.2876(13) and
2.3174(12) Å. They are similar to other Ir-P bonds observed in Ir(III) phosphine complexes.
[159]
The iridium hydrogen bond distances are 1.68(3) and 1.70(3) Å.
Figure 3.33: Structure of cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E21, (without hydrogen atoms).
3. Results and Discussion
85
Table 3.13: Selected bond lengths [Å] and angles [º] of cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
]
+
(E21)
Bond Lengths
Ir(1)-C(65) 2.043(4) Ir(1)-P(2) 2.3174(12)
Ir(1)-C(35) 2.099(4) Ir(1)-H(1) 1.68(3)
Ir(1)-P(1) 2.2876(13) Ir(1)-H(2) 1.70(3)
Bond Angles
C(65)-Ir(1)-C(35) 93.22(17) C(35)-Ir(1)-P(2) 101.53(13)
C(35)-Ir(1)-P(1) 92.00(13) P(1)-Ir(1)-P(2) 101.95(4)
C(65)-Ir(1)-P(1) 163.80(13) C(35)-Ir(1)-H(2) 176.11
P(2)-Ir(1)-H(1) 173.01 C(65)-Ir(1)-H(2) 83.92
3.8.2 Synthesis and characterization of cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E22)
Exposure of complex E20 to air at room temperature in THF gives the complex cis-[Ir(η
2
-
O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] within 5 minutes. The formation of the peroxo complex is
immediately indicated by the change of the color of the solution from orange red to pale yellow.
31
P-NMR spectra prove complete conversion of the starting material. The formation of the
iridium peroxo complex is irreversible which has been proved by measuring the
31
P-NMR spectra
at different temperatures (230K-345K) in CD
3
CN solution. Over the whole temperature range
only the signals of E22 were observed, hence dissociation of oxygen can be excluded.
Peroxo complex E22 are characterised by
1
H,
13
C,
31
P-NMR spectra, IR-spectroscopy and single
crystal X-ray analysis. The significant features in
1
H-NMR spectrum is a significant downfield
shift of the protons of the imidazol rings compared to E20. Their resonances are observed at 7.14
(d, 1H,
3
J
HH
= 2 Hz) and 7.59 (d, 1H,
3
J
HH
= 2 Hz). In the
13
C-NMR spectrum the resonances of
3. Results and Discussion
86
the carbene atoms were strongly shifted to lower frequencies due to the formation of an
iridium(III) center. The signals are observed at 143.6 ppm (m) and 147.2 (m). The
31
P-NMR
spectrum shows two signals in close proximity at about -12.5 ppm (d,
2
J
PP
= 15 Hz) (compare
figure 4). The coupling constanr proves cis-orientation of the phosphorous atoms and indicates
that the stereochemistry of the starting complex E20 in preserved in this type of oxidative
addition. The IR spectrum shows a sharp peak which can be assigned to ν(O-O) band at 854 cm
-1
.
Its position is comparable e.g. with the
band of [(η
2
-O
2
)IrCl(CO)(PPh
3
)
2
]
[160]
which is located at
858 cm
-1
.
-10.5 -11.0 -11.5 -12.0 -12.5 -13.0 ppm
Peroxo complex at 70 °C
Figure 3.34:
31
P-NMR spectra of cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E22) at 70°C.
3. Results and Discussion
87
3.8.2.1 Single crystal X-ray structure analysis of cis-[Ir(η
ηη
η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(E22).
Yellow crystals of the novel cis-peroxo complex E22 suitable for X-ray diffraction were obtained
by layering a concentrated THF solution of E22 with di-isopropyl ether. The cis-peroxo complex
E22 crystallizes in the orthorhombic space group P2
1
2
1
2
1
with four molecules per unit cell
incorporating four THF molecules in the unit cell. Crystallographic data are presented in the
Table 7.11. Selected bond lengths and angles are listed in Table 3.14. Molecular structure
containing the atom numbering scheme is displayed in Figure 3.35. The geometry around the
iridium center is trigonal bipyramidal. The coordination polyhedron is formed by the peroxo
ligand, carbene carbon atom C(35) and the phosphorous atom P(2) lying in equatorial plane and
the axial donors C(65) of the carbene moiety and P(1) of the phosphane moiety. The arrangement
of all ligands gives a chiral complex as can be seen from Figure 3.32. As no chiral reagents were
used to prepare this complex a racemic product is expected. However, the space group of the
investigated crystal proves that it consists of one enantiomer only. Hence, in the course of the
crystallization a sponateous separation of the racemat took place giving crystals which are made
of only one of the two enantiomers. Unfortunaltely these two types of crystals could not be
separated by manual picking as no apparent differencies in their shape and color were observable
on inspection under the microscope. The sum of bond angles formed by the equatorially placed
donors, C(35), P(2) and the peroxo ligand around iridium is 359.8°. In E22, the peroxo ligand is
not symmetrically bonded with respect to the axis C(25)-Ir(1)-P(2). It is shifted towards the
phosphine donor atom P(1). The angles formed by the peroxo ligand are 149.08(11)° for P(2)-
Ir(1)-O(1) and 154.18(18) for C(35)-Ir(1)-O(2). Furthermore, the peroxo ligand is shifted from
equatorial plane by 0.023 Å and 0.011 Å for O(2) and O(1), respectively. The bond angle formed
by the axial ligands C(65)-Ir(1)-P(1) deviates from linearity by -11° due to the steric hindrance
imposed by the phenyl rings of the phosphane residues. The angles formed by the peroxo ligand
with the central iridium atoms e.g. O(2)-Ir(1)-O(1) with 42.24(14)° and the distance between
O(1)-O(2) with 1.482 (5) Å are typical for peroxo complexes of iridium
[161]
Consequently the
iridium center is in the formaloxidation state +3.
3. Results and Discussion
88
Figure 3.35: Structure of cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E22, (without hydrogen atoms).
The Ir-O bond lengths are almost equivalent with 2.045(3) and 2.069(4) Å. They are in the
typical range observed for known Ir(η
2
-O
2
) complexes.
[162]
The Ir(1)-P(2) and Ir(1)-P(1) distances
are 2.2857(15) Å and 2.3863 (16) Å and are similar to those observed in other reported
iridium(III) complexes.
[162]
3. Results and Discussion
89
Table 3.14: Selected bond lengths [Å] and angles [º] of cis-Ir(III) complex E22.
Bond lengths
O(1)-O(2) 1.482(5) Ir(1)-C(35) 2.034(5)
Ir(1)-O(2) 2.045(3) Ir(1)-P(1) 2.3863(16)
Ir(1)-O(1) 2.069(4) Ir(1)-P(2) 2.2857(15)
Ir(1)-C(65) 2.055(5)
Bond angles
O(2)-Ir(1)-O(1) 42.24(14) C(35)-Ir(1)-O(1) 112.08(19)
C(65)-Ir(1)-P(1) 168.98.(15) O(2)-Ir(1)-P(2) 106.48(11)
C(35)-Ir(1)-O(2) 154.19(18) P(2)-Ir(1)-P(1) 98.54(5)
O(1)-Ir(1)-P(2) 149.08 (11) C(35)-Ir(1)-P(2) 98.77(16)
3.8.3 Synthesis and characterization of cis-[Ir(η
ηη
η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E23).
The novel iridium(III) disulfide complex cis-[Ir(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
E23 was
synthesised by the reaction of one equivalent of the cis-iridium(I) complex E20 with 0.25
equivalents of elemental sulfur S
8
in THF (Figure 3.32). The color of the reaction mixture
changed from orange red to yellow orange and a suspension was formed. It was stirred over night
and was monitored by
31
P-NMR spectra which confirmed the formation of cis E23. The solvent
was evaporated under vacuum and the resulting yellow orange residue was redissolved in a
mixture of acetonitrile /THF. Overlaying with diethyl ether yielded yellow single crystals of E23
suitable for single crystal X-ray structure analysis.
The structure of the cis-iridium (III) complex E23 was corroborated by one and two dimensional
NMR-spectroscopy and IR spectroscopy. The significant features of the
1
H-NMR spectrum of
E23 are the downfield resonances of the aromatic protons of the imidazol ring (δ (ppm), 7.27 (d,
2H,
3
J
HH
= 2 Hz, b); 7.15 (s, 1H, b’); 7.03 (s, 1H, c’) and 7.65 (d, 1H,
3
J
HH
= 2 Hz, c). Compared
to the starting material E20 the resonances are shifted to higher frequencies on coordination of
sulfur. The
13
C spectrum shows the resonance of the carbene carbon atoms at 145 ppm (dd,
2
J
PC
=
132 Hz,
2
J
PC
= 9 Hz, a) and 149.7 ppm (d,
2
J
PC
= 12 Hz, a’). The large coupling constant of the
first signal shows that the corresponding carbon atom is located opposite to a phosphorous atom
while the small coupling constants of the second resonance proves that two phosphorous atoms
3. Results and Discussion
90
are in cis-position to the corresponding carbon atom. Compared to E20 the resonances are shifted
to high field due to the formation of an iridium(III) complex. The
31
P NMR spectrum of E23
shows two phosphorous signals at -12.7 ppm (d,
2
J
PP
= 18 Hz) and -30.7 ppm (d,
2
J
PP
=15 Hz))
consistent with the cis orientation of
31
P nuclei. The IR (KBr disc) spectrum of E23 shows a band
at 557 cm
-1
tentatively assigned as
ν(S-S) which is also observed in other reported iridium (III)
complexes with side on coordination of the S
2
-ligand.
[163]
3.8.3.1 Single crystal X-ray structure analysis of cis-[Ir(η
ηη
η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
E23
Yellow crystals of iridium(III)-disulfide complex E23 suitable for X-ray crystallography were
obtained by layering diethyl ether onto a mixture of an acetonitrile/THF solution of E23. E23
crystallizes in the monoclinic space group P2(1)/c with four molecules in the unit cell. The
crystallographic data are presented in the Table 7.12 and the selected bond lengths and angles are
given in Table 3.15. Moleculer structure of E23 is depicted in Figure (3.36)
Figure 3.36: Structure of cis-[Ir(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E23, (without hydrogen atoms).
3. Results and Discussion
91
The geometry around iridium(III) center is trigonal bipyramidal. The carbene and the
phosphorous donors are coordinated in cis position to iridium(III) and the disulfide ligand is
coordinated in a side on fashion. The sum of angles around iridium(III) in the equatorial plane
amounts to 359.7°. The disulfide ligand is slightly shifted from the equatorial plane by 0.037 and
0.030 Å for S(1) and S(2), respectively. The bond angle C(31)-Ir(1)-P(1) formed by the axial
ligands is 169.02(11)° and the bending of the axial ligands is due to the steric hindrance imposed
by the phenyl rings of the phosphane residues. The angles formed by the sulfide ligand S(1)-
Ir(1)-S(2) is 50.45(3)° and the S(1)-S(2) bond length amounts to 2.0581(14) Å is equal to the
bond length in S
8
(2.06Å). The bond distances between the iridium atom and carbenic carbon
atoms Ir(1)-C(1) and Ir(1)-C(31) are 2.052(4) Å and 2.063(4) Å, respectively. The bond lengths
Ir(1)-S(1) and Ir(1)-S(2) are equal with 2.4140(10) and 2.4156(11). The structure of the iridium
(III) sulfide complex E23 is analogous to the iridium(III) peroxo complex with marginal
differences in the bond parameters of both of the complexes. The Ir(1)-P(2) distance in E23 is
shorter than that in E22 by 0.07 Å and the equatorial angles C(35)-Ir(1)-O(1) in E22 is bigger
than that in E23 (C(1)-Ir(1)-S(1)) by 5°.
Table 3.15: Selected bond lengths [Å] and angles [º] for the cis-iridium(III) complex E23.
Bond lengths
S(1)-S(2) 2.0581(14) Ir(1)-C(31) 2.063(4)
Ir(1)-S(2) 2.4156(11) Ir(1)-P(2) 2.3071(10)
Ir(1)-S(1) 2.4140(10) Ir(1)-P(1) 2.3787(10)
Ir(1)-C(1) 2.052(4)
Bond angles
S(1)-Ir(1)-S(2) 50.45(3) C(1)-Ir(1)-S(2) 107.17(11)
C(31)-Ir(1)-P(1) 169.02.(11) P(2)-Ir(1)-S(1) 103.81(3)
C(1)-Ir(1)-S(1) 157.37(11) P(2)-Ir(1)-S(2) 154.26(4)
C(1)-Ir(1)-P(2) 98.53(11) P(2)-Ir(1)-P(1) 100.21(3)
3. Results and Discussion
92
3.8.4 Synthesis of five coordinate Iridium(I) [Ir(CO)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(E24)
The novel five coordinate iridium(I) carbonyl complex E24 was synthesized by bubbling carbon
monoxide gas through a solution of the cis iridium(I) complex E20 in THF at room temperature
for 30 minutes (Figure 3.32). The reaction was confirmed by a change of color from red orange to
light yellow. The reaction also was monitored by measuring
31
P-NMR spectra and IR spectra.
After removal of the solvent a yellow product was obtained in high yield (95%). The latter was
characterized by NMR- and IR spectroscopy. Attempts to get crystals of E24 failed
The most significant feature of the
13
C-NMR spectrum are two peaks of quaternary carbon atoms
at 191.2 (t,
2
J
PC
= 4.0 Hz) and 143.8 (t,
2
J
PC
= 13.0 Hz) ppm which can be assigned to CO and to
the carbene carbon atoms, respectively. The
13
C shift of the metal-bound carbene carbon is
significantly shifted to higher field in comparison to other iridium(I)-bound carbene carbon atoms
(170–185 ppm) reported in the literature.
[97g,131,136,164,165]
Octahedral iridium(III) complexes of
NHC normally have metal-bound carbene
13
C chemical shifts in the range of 127-145
ppm.
[149,151,166-168]
The unexspected high field shift of the carbene carbon atoms in E24 is most
likely because of the unusual trigonal-bipyramidal geometry of the iridium(I) complex. The
31
P-
NMR signal observed at δ = -12.0 (s) ppm confirms the chemical equivalence of the phosphorous
atoms, which are shifted to high field compared to phosphorous resonance of the starting material
observed at 16.9 ppm for E20.
The IR spectrum in THF solution of E24 shows a single CO absorption band at 1900 cm
-1
which
similar to other iridium carbonyl complexes.
[169]
3.8.5 Synthesis of the iridium(III)complex, trans-[Ir((CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
)]I (E25)
The cationic iridium(III) complex trans-E25 was synthesized by reaction of one equivalent of
E20 with excess of methyl iodide in THF solution at room temperature. The color of the reaction
mixture immediately changed from orange yellow to yellow brown. The progress of the reaction
was monitored by measuring
31
P-NMR spectra which show two signals at high field at δ = -25.1
ppm (d,
2
J
PC
= 20 Hz) and δ = -41.2 ppm (d,
2
J
PC
= 20 Hz) (structure E25A). The reaction was
stirred overnight followed by measuring another
31
P-NMR spectrum which showed the same
3. Results and Discussion
93
signals as before. Both spectra confirm the formation of two isomers E25A and E25B with cis
and trans orientation of the coordinated methyl group und the iodine atom, respectively. The
intregration of the phosphorous atoms in the
31
P-NMR spectrum gives a ratio of trans/cis of
approximately 1:4.
Subsequently the solvent was evaporated giving a crude yellow brown product. From the crude
product E25B was separated by fractional crystallization from aconcentrated THF solution. The
colorless single crystal of E25B was obtained which was suitable for x-ray crystallography. The
structure of the molecule is in a good agreement with
1
H-,
13
C- and
31
P-NMR spectroscopic data.
The
1
H-NMR-spectrum of E25B shows the signal of methyl protons at δ = 0.15 ppm (s). The
strong shielding of the protons must be attributed to their close proximity to the electron rich
metal center. The resonances of the protons of imidazol rings were observed in the range of δ =
7.36-7.92 ppm which is a slight downfield shift compared to imidazol protons of E20. The most
important feature of the
13
C-NMR spectrum is the resonance of the methyl group at δ = 0.4 ppm
which unexpectedly appears only as a singlett. Obviously the
2
J
CP
coupling constant is in this
case to small to be resolved by the NMR-spectrometer. Two signals were observed for the
unequivalent carbene carbon atoms at δ = 146.6 (dd,
2
J
PC, cis
= 13 Hz,
2
J
PC, trans
= 115 Hz) and
147.6 (dd,
2
J
PC
= 13 Hz,
2
J
PC, trans
= 115 Hz). These values are in the range of similar iridium(III)
complexes reported in the literature.
[59,149,168]
The
31
P NMR-spectrum shows two signals at -25.6
(d,
2
J
PC
= 20 Hz) and -42.4 ppm (d,
2
J
PP
= 20 Hz) for phosphourous donors of the bi-dentate
NHC-ligands as a dominant product. The coupling constant proves their mutual cis-coordination.
3. Results and Discussion
94
3.8.5.1 Single crystal X-ray structure analysis of trans-[Ir((CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
)]I
(E25)
Single crystals of E25 suitable for X-ray crystallography were grown by layering hexane onto
concentrated THF solution of complex. E25 crystallized in monoclinic space group P2(1)/c with
four molecules in the unit cell and iodide counter ions and THF molecules in the unit cell.
Crystallographic data are presented in the Table 7.13 and the selected bond lengths and angles are
given in Table 3.16. Molecular structure of E25 is depicted in Figure 3.37. The geometry around
iridium(III) ion is distorted octahedral with the sum of angles around iridium(III) being 360.52°
and the iridium atom is displaced from the plane by 0.022 Å. The bidentate NHC phosphane
ligands are coordinated in cis arrangement around iridium(III) center in which C(1), C(31), P(1)
and P(2) lie in the plane of molecule whereas the CH
3
and iodide lignads are trans to each other
and lie in the axial position. The significant features in this molecules the bite angle C(31)-Ir(1)-
P(2) deviates by 9° from ideal angle and the equatorial angle C(31)-Ir(1)-P (1) and C(1)-Ir(1)-
P(2) deviates by 7° and 11° from linearity and the axial angle C(60)-Ir(1)-I(1) slightly deviates
from linearity by 5°and the angle P(2)-Ir(1)-P(1) deviates from ideal angle by +10° may due to
the close contact of phenyl ring The bond length of Ir(1)-C(31) and Ir(1)-C(1) are 2.077(7) and
2.096(7) Å respectively the bond distance of Ir(1)-P(1) is longer than Ir(1)-P(2) by 0.0292 Å and
the bond length of Ir(1)-I(1) and Ir(1)-C(60) are 2.8005(7) and 2.128(7) respectively. Similar to
the value found in [{Ir(CO)I
2
(µ-I)Me}
2
]
2-
.
[170]
3. Results and Discussion
95
Figure 3.37: Structure of trans-[Ir((CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
)]
+
in crystals of E25, (without hydrogen atoms).
Table 3.16: Selected bond lengths [Å] and angles [º] for the trans-iridium(III) complex E25.
Bond lengths
I(1)-Ir(1) 2.8005(7) Ir(1)-C(60) 2.128(7)
Ir(1)-C(31) 2.077(7) Ir(1)-P(2) 2.3501(18)
Ir(1)-C(1) 2.096(7) Ir(1)-P(1) 2.3793(18)
Bond angles
C(31)-Ir(1)-C(1) 88.6(3) C(31)-Ir(1)-P(1) 172.9(2)
C(31)-Ir(1)-P(2) 81.2(2) C(60)-Ir(1)-I(1) 174.87(19)
C(1)-Ir(1)-P(1) 91.2(2) P(2)-Ir(1)-P(1) 99.58(6)
C(1)-Ir(1)-P(2) 168.7(2) C(60)-Ir(1)-P(1)/P(2) 86.7(2)/92.0(2)
3. Results and Discussion
96
3.8.6 Synthesis and characterization of cis-[Ir(I)
2
(EtImCH
2
CH
2
PPh
2
)
2
][I
3
]
(E26)
The synthesis of novel iridium(III) complex E26 was carried by conducting an oxidative addition
reaction in THF between cis-iridium(I) complex E20 and iodine at -50Cº, the color of the
reaction mixture changed from red orange to yellow, reaction was monitored by
31
P-NMR spectra
which confirm The formation of two isomers (A and B) in a ratio 1:3. In isomers A the
inequivalent phosphorous atom in cis position which shows the signal at -25.2 (d,
2
J
PP
= 20 Hz)
phosphorus cis to iodine), (-54.7 (d,
2
J
PP
= 20 Hz), (phosphorus trans to iodine) and in isomer B
shows the signal at -43.80 (s) in which the phosphorous atoms in trans position. The solvent
removed under vacuum to give high yield 65 % of yellow crude product which gives yellow
crystals suitable for X-ray crystallography which confirmed the formation of isomer B crude
product was characterised by NMR-spectroscopic method.
Figure 3.38: Chemical structure of the isomers in E26.
The significant features in the
1
H-NMR spectrum of E26 shows four signals of aromatic protons
of imidazol ring at downfield δ = 7.49 (d, 2H,
3
J
HH
= 2.2 Hz, b); 7.38 (s, 1H, b’); 7.03 (s, 1H, c’)
and 7.65 (d, 1H,
3
J
HH
= 2.2 Hz, c)) compared to the cis complex E20 which showe the resonances
of aromatic protons of imidazol ring at high field. In the
13
C-NMR spectrum the peak of the
iridium-carbene bound resonance could not be detected and four signals were observed for
carbon atoms of imidazol ring.
31
P spectra of crude product shows the presence of two signals consistent of presence of in
equivalent two phosphorous atoms in cis position at -25.2 (d,
2
J
PP
= 20 Hz) and -54.7 (d,
2
J
PP
= 20
Hz). In addtion another signal at -43.8 (s) which consistent in the presence of two equivalent
phosphorous atoms which are in agreement with X-ray crystallography which confirm the
formation of isomer B.
3. Results and Discussion
97
3.8.6.1 Single crystal X-ray structure analysis of cis-[Ir(I)
2
(EtImCH
2
CH
2
PPh
2
)
2
][I
3
] (E26)
Single crystals of E26 were grown by over layering diisopropyl ether into acetonitrile solution
E26 crystallized in monoclinic space group P2(1)/c with four molecules in the unit cell and their
counter ion and a cetonitrile. Due to the poor quality of the crystals, good set of data could not be
collected Structure representation of E26 is depicted in Figure 3.39. The geometry around
iridium(III) ion is distorted octahedral.
Figure 3.39: Structure of the cis-[Ir(I)
2
(EtImCH
2
CH
2
PPh
2
)
2
]
+
in crystals of E26, (without hydrogen atoms).
3. Results and Discussion
98
3.8.7 Electrochemistry of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E20)
-2 -1 0 1 2
-0,00020
-0,00015
-0,00010
-0,00005
0,00000
0,00005
0,00010
-1786 mV/NHE
-1691 mV
588 mV/NHE
683 mV
E(V vs Ag/AgCl)
I(
µ
µ
µ
µ
A)
Figure 3.40: Cyclovoltammogram of E20 in THF
The cyclovoltammogramm of cis-Ir(I) complex E20 (0.1mol/L [NBu
4
][PF
6
] was obtained at scan
rate 100 mV/s in THF. The Iridium(I) complex shows irreversible redox process at 588 mV/NHE
and reduction waves at -1786 mV/NHE.
3. Results and Discussion
99
3.9 Nickel complex
3.9.1 Synthesis and spectroscopic characterization of trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
][I]
2
(E27)
The synthesis of trans nickel(II) complex E27 is illustrated in Figure 3.41. E27 was synthesised
by reaction of one equivalent [Ni
7
S(S
t
Bu)
8
][BzEt
3
N]
with 2 equivalent of carbenes E7 at room
temperature in THF solution the reaction color changed immediately to brown black reaction was
completely finished in 30 min. reaction was monitored by measure
31
P-NMR spectra which
shows the signal of phosphorous atom as singlets δ = 21.0 ppm which confirm the presence of
two equivalent phosphorous atoms, which shifted to down field contrast to the signal of
imidazolium salts which appears at -21 ppm, after work up brown black residue was crystallised
by slow evaporated from concentrated acetonitrille solution of E27 to gives single yellow crystals
suitable of X-ray crystallography E27 was characterised by
1
H,
13
C and
31
P-NMR spectroscopy.
attempts to get this complex from NiCl
2
was failed.
Figure 3.41: Synthesis of trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
][I]
2
(E27).
The significant feature in the
1
H-NMR spectra of E27 the apsence of the signat at 8.5 ppm which
assign to the coordinatig of the bidentate ligand with nickel (II), the resonance of the sigmal
ofdisterotopic protonsof ethylene linkage was observed at δ = 4.0-6.1 ppm, in
13
C-NMR spectra
3. Results and Discussion
100
the carbenic carbon atom of E27 was observed as a triplet at δ = 174 ppm, which is in the normal
range of other nickel(II) complexes reported in the literature.
[171-173]
3.9.1.1 Single crystal X-ray structure analysis of trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
][I]
2
(E27)
Yellow single crystals from E27 were grown from slow evaporated of concentrated solution of
E27. trans-Nickel(II) complex was crystallized in monoclinic space group P2(1)/n with four
molecules in the unit cell and their counter ion and two molecules of acetonitrile. Figure 3.42
depicated the Molecular structure of E27 and selected bond lengths and angles are given in Table
3.17. Crystallographic data are presented in the Table 7.14. The Nickel(II) center is coordinated
by two bidentate NHC-phosphane ligands in a distorted square-planar environments with a sum
of four bond angles at Ni(1) of 358.68°. The two carbene-phosphane moieties are coordinated
trans to the two ethylene linkages situated on one side of coordination plane. Generally the C-Ni-
C angle is closer to linearity than the P-Ni-P angle, C(1)-Ni(1)-C(8) bond angle in E27 is
175.02(10), whereas the P(1)-Ni(1)-P(2) deviates by 16° from the ideal 180°. The bit angle C(8)-
Ni(1)-P(2) and C(1)-Ni(1)-P(1) deviates by 7° and 6° from the ideal 90°. The Ni-C and Ni-P
bond distance are within the normal range for Ni-NHC complexes reported in the literature.
[172-
176]
3. Results and Discussion
101
Figure 3.42: Structure of trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
]
++
in crystals of E27, (without hydrogen atoms).
Table 3.17: Selected bond lengths [Å] and angles [º] for trans-Nickel(II) complex E27.
Bond lengths
Ni(1)-C(1) 1.904(2) Ni(1)-P(2) 2.1909(7)
Ni(1)-C(8) 1.906(2) Ni(1)-P(1) 2.1925(7)
Bond angles
C(1)-Ni(1)-C(8) 175.02(10) C(8)-Ni(1)-P(1) 93.94(7)
P(2)-Ni(1)-P(1) 164.02(3) C(1)-Ni(1)-P(1) 84.07(7)
C(1)-Ni(1)-P(2) 97.75(7) C(8)-Ni(1)-P(2) 82.92(7)
3. Results and Discussion
102
3.10 Palladium complex
3.10.1 Synthesis and spectroscopic characterization of
Cis-and trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28)
trans- and cis-Pd(II) complex was synthesised by treatment two equivalent of imidazolium salts
with one equivalent of KN(SiMe
3
)
2
in THF solution at room temperature, after deprotonation of
imidazolium salts one equivalent of [Pd(COD)CL
2
] was added to carbene solution E7, as
depicted in Figure (3.43).
Figure 3.43: Synthesis of cis- and trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28).
The color of the reaction mixture changed to orange red which stirred for 1 hour to give high
yield (70 %) of orange red isomers product which gives single yellow crystals suitable for X-ray
crystallography of trans isomers. The product was characterized by
1
H,
13
C and
31
P-NMR
spectroscopy, and it is potential as a catalyst in Suzuki coupling reaction has been investigated.
The significant features in the
1
H-NMR spectrum of trans E28 include the absence of a resonance
at 8.5 ppm which is diagnostic for the loss of the carbonium protons confirm the coordination of
palladium(II) to carbene. Also the bidentate coordination of ligand around the palladium ion can
be detected from the presence of of four diasterotopic proton signal for the ethylene linkage in the
range of δ = 2.37-5.01 ppm. Addtionally two signals was observed for aromatic protons of
imidazol ring which shifted slightly up field δ = 7.15 and 7.34 ppm contrast to imidazolium salts.
In the
13
C-NMR spectrum, the resonance of the carbene-Pd carbon appears as triplt δ = 165.4
ppm (
2
J
PC
= 12 Hz).
31
P-NMR spectrum of crude product shows two signal δ = 17.7 (s) for cis
isomer and 17.9 (s) for trans isomer with a ratio 2:1 which confirm the formation of two isomers,
X-ray crystallography show the formation of trans-isomer.
.
3. Results and Discussion
103
3.10.1.1 Single crystal X-ray structure analysis of trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
]
2+
(E28)
X-ray-quality crystals of trans-E28 were grown by layering diethyl ethere onto acetonitrile
solution. trans-palladium(II) complex was crystallized in triclinic space group P-1 with two
molecules in the unit cell and their counter ion and one molecules of acetonitrile incorporated in
the unit cell. Figure 3.44 depicted the Molecular structure of E28 and selected bond lengths and
angles are given in Table 3.18. Crystallographic data are presented in the Table 7.15. The
geometry around the palladium(II) center is distorted square planar with a sum of four bond
angles at Pd(1) of 358.41°. The palladium centers are coordinated by two bidentate ligands E7.
The ligating phosphorous atoms occupy trans coordination sites. The same holds for the ligating
carbene atoms. The palladium(II) ion lie away from the coordination plane by 0.168 Å. The
formation of the six membered chelate ring of NHC-phosphane ligand distortes the coordination
geometry of the palladium only slightly with C(1)-Pd(1)-P(1) and C(31)-Pd(1)-P(2) bite angles
being reduced to 84.1(4) and 83.5(4) respectively, thid deviation from 90° ideal angle resulted
from the strain associated with the six membered ring. Generally The C-Pd-C angle is closer to
linearity than the P-Pd-P angle, C(1)-Pd(1)-C(31) bond angle in E28 is 173.8(5), whereas the
P(1)-Pd(1)-P(2) deviates by 16° from the ideal 180°. The Pd-C bond length at 2.030(13) Å and
2.032(12) Å fall within the normal range, the same trend was also observed in Pd-NHC
complexes.
[114,177]
The Pd-P bond distance are comparable to those in analogous complexes
containing Pd-NHC phosphane ligands.
[120,178]
3. Results and Discussion
104
Figure 3.44: Structure of trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
]
2+
in crystals of E28, (without hydrogen atoms).
Table 3.18: Selected bond lengths [Å] and angles [º] for trans-palladium(II) complex E28.
Bond lengths
Pd(1)-C(1) 2.030(13) Pd(1)-P(1) 2.308(3)
Pd(1)-C(31) 2.032(12) Pd(1)-P(2) 2.310(3)
Bond angles
C(1)-Pd(1)-C(31) 173.8(5) C(1)-Pd(1)-P(1) 84.1(4)
P(1)-Pd(1)-P(2) 164.46(13) C(31)-Pd(1)-P(1) 94.2(4))
C(31)-Pd(1)-P(2) 83.5(4) C(1)-Pd(1)-P(2) 96.5(4)
3. Results and Discussion
105
3.10.2 Equilibrium between cis- and trans-isomers of E28 at higher temperatures.
Generally, palladium(+II) and rhodium(+I) are isoelectronic and therfore they have similar
properties of their complexes are to be expected. Due to that we anticipated the interconversion
of cis-E28 and trans-E28 in close analogy to the isoelectronic cis-trans rhodium(I) complexes.
The interconversion of cis isomer to trans isomer is studied by measuring
31
P-NMR spectra of
E28 at different temperatures. The crude product of E28 shows the signal of the cis-isomer at
17.7 ppm (s) and small signal at 18.0 (s) ppm for trans complex with a ratio of 10:1 (cis:trans).
The relative stability of isomers was checked by temperature dependent
31
P-NMR spectroscopy
as shown in Figure 3.45.
16.5
17.0
17.5
18.0
18.5
19.0
ppm
at 0 min
1h at 60°C
2h at 60°C
2h at 70°C
3h at 80°C
5h at 80°C
24h at 80°C
48h at 80°C
Figure 3.45: Temperature dependent
31
P NMR-spectra of isomerization of cis- to trans- of E28
Initially a sample of the cis isomer dissolved in d
3
-CD
3
CN shows a signal at 17.7 ppm and small
signal of the trans-E28 at 18 ppm as side product with a ratio of cis to trans of 10:1. The ratio has
been determined by integration of the peaks as the phosphorous atoms in both complexes have
similar relaxation times, due to the similar structures of the complexes. On heating at 60°C for
one hour the ratio of isomers changed to 4:2 cis to trans. By increasing the temperature to 70°C
and heating for another two hours the ratio changed to 1:2 cis to trans. Prolonged heating for 24
hours gave no change in a ratio of cis to trans and appearance of a signal of a new side product at
3. Results and Discussion
106
19 ppm. Further heating at 80°C gave no change in the ratio of both isomers indicating that an
equilibrium due to interconservion of both isomers (Figure 3.46) has been reached.
Figure 3.46: The equilibrium between cis-E28 and trans-E28 isomers of [Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
.
3. Results and Discussion
107
3.10.3 Electrochemistry of trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
]
2+
(E28)
-2 0 2
0,0000
0,0001
I(mA)
E(V vs Ag /AgCl)
190mV / NHE
284 mV 914mV
820mV / NHE
-137mV
-231mV / NHE
Figure 3.47: Cyclovoltammogram of E28 in CH
3
CN.
The cyclovoltamogram of E28 (0.1 mo/L [NBu
4
][PF
6
] was obtained at a scan rate of 200 mV/s in
acetonitrile solution. The compound shows several irreversible oxidation waves at 190 mV/NHE,
820 mV/NHE and 1246 mV/NHE) and reduction peak at -231 mV /NHE.
3. Results and Discussion
108
3.10.4 Suzuki-coupling with E28
It is known that palladium complexes with mixed phosphane NHC ligands have been used in the
Heck coupling of aryl bromides and acrylates
[120,122]
, as well as in the copolymerization of
ethylene and CO.
[97b]
We examined if the palladium complex, trans-E28 is a suitable catalyst for
the closely related Suzuki coupling. The catalytic efficency of trans-E28 in this type of coupling
reaction between aryl halides and phenyl boronic acids is summarized in Table 3.19.
(eq. 44)
Table 3.19: Suzuki coupling of aryl halides and 3-ethoxyphenyl boronic acid for trans-E28.
Entry X R Time(h) Temperature(°C)
Yield %
1 Br 4-Me 8 80 21
2 Br 4-Me 16 80 42
3 Br 4-Me 24 80 57
4 Br 4-Me 63 80 50
5 Br 4-Me 48 65 8
6* Br 4-Me 48 80 98
7 Br 4-OMe 24 80 14
8 Br 4-COMe 24 80 34
9 Cl 4-Me 24 80 5
Reaction conditions: 1mmol of aryl halide, 1.5 mmol of phenylboronic acid, 2.0 mmol of Cs
2
CO
3
, 1 mol% of Pd
catalyst, 3 mL of 1,4-dioxane; isolated yield. * 24h at 80°C, cool down to room temperature, addition of another
mol% of Pd catalyst, heating for another 24h
3. Results and Discussion
109
The efficency of cationic trans NHC-Pd complex E28 (1 mol%) as catalyst was examined with
the base Cs
2
CO
3
in dioxane in the reaction of 3-ethoxy phenyl boronic acid with substituted aryl
halide contains electron donating and withdrawing groups under argon atmosphere. It is clear that
reaction times of approximately 24 h are needed for the production of unsymmetrical biaryl
products at 80°C in good yield. In general, E28 shows good activities for aryl bromide, the
activity with respect to aryl chlorides is very poor. Low conversion of substrates to product was
obtained at 65°C, increasing the temperature to 80°C resulted in a significant improvement in the
overall conversion of the substrates to the products. Excellent yield of coupling product (Table
3.18, entry 6, 98% yield) was achieved when the reaction was carried out for 24 h at 80°C and
subsequent additon of another mol % of catalyst and heating again for 24 h. The conversion of
substrates to products was firstly determined by integration of
1
H-NMR spectra, secondly by
separation of the pure product by plate chromatography In conclusion the catalytic activity of
E28 reaches its optimum in dioxane at 80°C and 24 h of reaction time.
4. Experimental Section
110
4. Experimental Section
4.1 Material and Methods
4.1.1 General Consideration
All manipulation were performed under pure dinitrogen atmosphere (99, 99.6%) dried with P
4
O
10
granulate using Schlenk techniques or in a nitrogen-filled glovebox and with absolute solvents.
Solvents were dried and distilled under an atmosphere of nitrogen or argon using standard
procedures
[179]
and also kept under nitrogen. Tetrahydrofuran (THF), diethyl ether and n-hexane,
were distilled from sodium-benzophenoneketyl. Acetonitrile and dichloromethane were distilled
from calcium hydride.
Chemicals were purchased from different companys and used as received: 1-vinyl-imidazol
(Acros), KPF
6
(Merck), diphenylphosphine (Aldrich), 1,5-cyclooctadiene (Riedel-deHaen),
Ethyliodide (Fluka), K
t
OBu (Merck), KN(SiMe
3
)
2
(Aldrich), CS
2
(Aldrich), rhodium chloride
hydrate (Degussa), iridium chloride hydrate (Alfa Aesar, Degussa), palladium chloride
(Degussa), cesium carbonate (Sigma-Aldrich), 4-bromotoluene (Sigma-Aldrich), 3-
ethoxyphenylboronic acid (Sigma-Aldrich), chlorotoluene (Sigma-Aldrich), 4-bromoanisol
(Sigma-Aldrich), 2-bromo-1,3-dimethylbenzene (Sigma-Aldrich), Iodine (Fluka), elemental
sulphur (Sigma-Aldrich), methyl iodide (Sigma-Aldrich), 4-bromoacetophenone (Sigma-
Aldrich). The bulk compressed gases carbon monoxide, and hydrogen were obtained from Air
Liquide Deutschland GmbH. The following compounds [Ir(µ-Cl)(COD)]
2[180]
, [Rh((µ-
Cl)(COD)]
2[181]
, [Pd(COD)Cl
2
]
[182]
and [Ni
7
S(S
t
Bu)
8
][BzEt
3
N]
[183]
were prepared as reported in
the literature.
4.1.2 Physical measurements
The
1
H,
13
C and
31
P NMR spectra were recorded on Bruker Avance 500 (
1
H: 500.13 MHz,
13
C:
125.76 MHz,
31
P: 202.46 MHz).The chemical shift are quoted in ppm.
1
H NMR and
13
C chemical
shifts were referenced to the residual proton signals of the deuterated solvent.
31
P NMR was
referenced externally using H
3
PO
4
(85% in H
2
O). Coupling constants (J) are given in Hz. The
assignment of the proton and carbon resonances was assured by measurement of DEPT, COSY,
HMQC and HMBC spectra.
IR spectroscopy: The infrared spectra were recorded on the FTIR spectrometer Nicolet P510.
4. Experimental Section
111
Crystal Structure Analyses Crystal data for all measured compounds are presented in the
appendix. X-ray diffraction data were collected with a Bruker-AXS SMART APEX CCD
diffractometer using MoK
α
radiation (λ = 0.71073 Å).
Elemental analyses: The elemental analyses were performed with a Perkin-Elmer-2400
analysator and a vario Micro Cube of the company elementar.
Cyclic voltammetry: Cyclic voltammetric measurements were performed with the electro
chemical device Metrohm 757 VA equipped with a potential 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 glassy C/Ag/AgCl or Au/Pt/saturated
Ag/AgCl serving as working, counter and refrence electrodes, respectively. CV curves were
obtained at scan rates of 100 mV/s working at 25 °C in MeCN/0.1mol l
-1
[Bu
4
N][PF
6
]. As most
of the complexes are exteremely air sensitive all experimental were performed in a glove box.
The dissolved complexes were transferred into the CV cell with a steel capillary under argon
pressure.
4.2 Synthesis of NHC-Phoshane ligands.
4.2.1 Synthesis of 3-ethyl-1-vinylimidazolium-3-iodide (E3)
1-vinylimidazol (20 g, 212.5 mmol) was dissolved in 50 mL CH
2
Cl
2
and
ethyliodide (49.8 g, 319.3 mmol) dissolved in 20 mL CH
2
Cl
2
was added.
The reaction mixture was stirred under reflux for 18 h. Subsequently the
solvent was removed under vacuum to give a crude white residue which crystallized from
methanol to yield a white crystaline precipitate E3 (45.18 g, 0.173 mmol, 81.7 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.47 (t, 3H,
3
J
HH
= 7.9 Hz, g), 4.31 (q, 2H, f ,
3
J
HH
= 7.5 Hz),
5.7 (dd, 1H,
2
J
HH
= 2.9 Hz, e’), 5.98 (dd, 1H,
2
J
HH
= 2.8 Hz, e), 7.35 (q , 2H , d,
3
J
HH
= 9.0 Hz) ,
7.78 (s, 1H, c), 8.01 (s, 1H, b), 9.73 (s, 1H, a).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.7 (s, CH
3
, g), 45.5 (s, CH
2
, f), 109.4 (s, CH
2
, e), 119.7 (s,
CH, b), 122.9 (s, CH, c), 128.9 (s, CH, d), 135.5 (s, CH, a).
E.A.: Anal. Found: C, 33.56; H, 4.32; N, 11.15, C
7
H
11
N
2
I requires C, 33.60; H, 4.40; N, 11.20 %
4. Experimental Section
112
4.3 Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazoliumiodide
(E5)
A solution of diphenylphosphane (1.99 g, 10.8 mmol), KO
t
Bu (0.11 g,
0.98 mmol) in 20 mL of THF was stirred at room temperature under
inert gas atmosphere for 5 min. The color of the reaction mixture
changed to orange yellow. 3-ethyl-1-vinylimidazoliumiodide (2.72 g,
10.8 mmol) (E3) was added. The reaction mixture was stirred at room
temperature for four days giving a colorless precipitate which was
washed with diethyl ether and dried under vacuum to give a high yield
of product E5 (3.62 g, 8.30 mmol, 79 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.5 (t, 3H,
3
J
HH
= 7.3 Hz, g), 2.78 (t, 2H, e,
3
J
HH
= 8 Hz),
4.16 (q, 2H,
3
J
HH
= 7.4 Hz, f), 4.35 (td, 2H,
3
J
PH
= 9.2 Hz,
3
J
HH
= 7.8 Hz, d), 7.46 (m, 1H, c,
3
J
HH
= 1.8 Hz), 7.30 (t, 1H, b,
3
J
HH
= 1.8 Hz), 8.92 (s, 1H, a), 7.49-7.55 (m, 10H, k, i , j).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.6 (s, CH
3
, g), 28.1 (d, CH
2
,
1
J
PC
= 15 Hz, e), 44.9( s , CH
2
,
f), 47.5 (d, CH
2
,
2
J
PC
= 25 Hz, d), 121.9 (s, CH, b or c), 122.5 (s, CH, b or c), 128.7 (d, CH, j,
3
J
PC
= 7 Hz), 129.2 (s, CH, i), 132.7 (d, CH, k ,
3
J
PC
= 20 Hz), 135.8 (s, CH, a), 136.9 (d, C
q
, h,
1
J
PC
=
12 Hz).
31
P-NMR (202 MHz, CD
3
CN): δ = -21.4 (s).
E.A: Anal. Found: C, 52.25; H, 4.68; N, 6.36, C
19
H
22
N
2
PI requires C, 52.31; H, 5.04; N, 6.42 %
4.4 Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium-hexa-
fluorophosphate (E6)
A solution of NaPF
6
(1.26 g, 7.5 mmol) was added to a suspension of
imidazolium iodide salt E5 (3.29 g, 7.5 mmol) in degassed water (10
mL) The reaction mixture was stirred overnight, the solid material
was filtered off and washed with degassed water and diethyl ether.
Finally it was dried under vacuum for 24 h to yield the colorless
4. Experimental Section
113
product E6 (2.6 g, 5.73 mmol, 75.8 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.44 (t, 3H,
3
J
HH
= 7.3 Hz, g), 2.72 (t, 2H,
3
J
HH
= 7.7 Hz,
2
J
PH
= 9.5 Hz, e), 4.11 (q, 2H, f,
3
J
HH
= 7.6 Hz), 4.32 (td, 2H,
3
J
PH
= 9.5 Hz,
3
J
HH
= 7.7 Hz, d), 7.39 (t,
1H,
3
J
HH
= 1.7 Hz, c), 7.31 (t, 1H,
3
J
HH
= 1.9 Hz, b) 7.40-7.47 (m, 10H, k, i , j), 8.51 (s, 1H, a).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.65 (s, CH
3
, g), 27.9 (d, CH
2
,
1
J
PC
= 15 Hz, e), 44.9 (s,
CH
2
, f), 47.3 (d, CH
2
,
2
J
PC
= 25 Hz, d), 122.6 (s, CH, c), 122.1 (s, CH, b), 128.7 (d, CH,
3
J
PC
= 7 Hz, j), 129.2 (s, CH, k), 132.7 (d, CH,
2
J
PC
= 20 Hz, i), 135.8 (s, CH, a), 136.9 (d, C
q
,
1
J
PC
=
12 Hz, h).
31
P-NMR (202 MHz, CD
3
CN): δ = -21.4 (s), -144.0 (hept,
1
J
PF
= 710 Hz).
4.5 Synthesis of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazol-2-dithio-
carboxylate (E8)
To a solution of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium
iodide E5 (200 mg, 0.46 mmol) in THF 20 mL was added
KN(SiMe
3
)
2
(100 mg, 0.46 mmol + 10 % excess). The reaction
mixture was stirred at room temperature for 90 min. After filtration
CS
2
(35 mg, 0.03 ml, 0.460 mmol) was added and the color changed
immeditely to red. The reaction mixture was stirred for 18 h. Then the
solvent was removed under vacuum to give a red crude product which was washed with diethyl
ether. Red crystalls were obtainede by layering diethyl ether onto a concentrated chloroform
solution of E8 (104 mg, 270 mmol, 58.8 %).
1
H-NMR (500 MHz, CDCl
3
): δ = 1.44 (t, 3H,
3
J
HH
= 7.3 Hz, g), 2.67 (t, 2H,
3
J
HH
= 7.8 Hz, e),
4.13 (q, 2H,
3
J
HH
= 7.3 Hz, f), 4.22 (q, 2H,
3
J
HH
= 7.8 Hz, d), 6.86-7.40 (m, 12H, b, c, Ph).
13
C- NMR (125 MHz, CDCL
3
): δ = 15.14 (s, CH
3
, g), 29.0 (d, CH
2
,
3
J
PC
= 16 Hz, e), 43.4 (s,
CH
2
, f), 46.1 (d, CH
2
,
3
J
PC
= 25 Hz, d), 117.3 (s, CH, b or c), 118.5 (s, CH, b or c), 128.8 (d, CH,
3
J
PC
= 7 Hz, j), 129.3 (s, CH, k), 132.7 (d, CH,
3
J
PC
= 19 Hz, i), 136.3 (d, C
q
,
3
J
PC
= 11 Hz, h),
149.4 (s, C
Carbene
, a), 224.6 (s, CS
2
, l).
31
P-NMR (200 MHz, CDCl
3
): δ = -21.1 (s).
N
NPPh
C
S S
c
b
g
fd
e
a
8
lh
i
jk
4. Experimental Section
114
4.6 Synthesis of metal complexes
4.6.1 Synthesis of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl
(E10)
KN(SiMe
3
)
2
(100 mg, 0.46 mmol) was added to a solution of
[EtImCH
2
CH
2
PPh
2
]I (200 mg, 0.46 mmol) in THF (20 mL). The
suspension was stirred at room temperature for 60 min. After
filtration and removel of KI, [Rh
2
(µ-Cl)
2
(COD)
2
] (57 mg,
0.230 mmol) was added to the filtrate. The color of the resulting
suspension changed from pale yellow to orange. The mixture was
allowed to stirr for another 15 min to give E10,
[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl which was isolated by filtration and
subsequently dried in vacuo. It was obtained as a pale yellow solid
product, which forms yellow single crystals by diffusion of diethyl ether into an acetonitrile
solution of E10 (100 mg, 0.132 mmol, 58.8 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.38 (t, 6H,
3
J
HH
= 7.1 Hz, g), 2.50-2.56 (m, 4H, e), 3.73-3.80
(m, 4H, f), 3.96-4.04 (m, 4H, d), 4.42-4.54 (m, 2H, b or c), 4.89-4.98 (m, 2H, b or c), 6.85-7.75
(m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.9 (s, CH
3
, g), 25.3 (s, CH
2
, e), 45.1 (s, CH
2
, f), 49.3 (s,
CH
2
, d), 119.4 (s, CH, b or c), 121.0 (s, CH, b or c), 127.5-127.6 (m, CH, j or k), 127.7-127.9 (m,
CH, j or k), 129.9-130.3 (m, CH, i), 135.5-135.7 (m, C
q
, h), 183.0 (ddd, C
Carbene
, a,
1
J
RhC
= 47 Hz,
2
J
PC, trans
= 103 Hz,
2
J
PC, cis
= 30 Hz).
31
P-NMR (202 MHz, CD
3
CN): δ = 32.0 (d,
1
J
RhP
= 128 Hz).
E.A: Anal. Found: C, 60.38; H, 5.28; N, 7.36, C
38
H
42
N
4
P
2
RhCl requires C, 60.44; H, 5.6; N,
7.42%.
N N
EtN
N
Rh
P
P
Ph
Ph
Ph
a
b c
d
e
fg
k
jih
E10
Cl
4. Experimental Section
115
4.7 Synthesis of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E11)
To a solution of 3-[2-diphenylphosphino)ethyl]-1-ethyl-imidazoliumhexafluorophosphate (195
mg, 0.46 mmol) in 10 mL THF was added KN(SiMe
3
)
2
(100
mg, 0.46 mmol) and the mixture was stirred at room
temperature under inert atmosphere for 30 min. [Rh
2
(µ-
Cl)
2
(COD)
2
]
(57 mg, 0.115 mmol) was then added to the
reaction mixture. The color changed from pale yellow to yellow
orange. After the removal of the solvent the residue was
crystallised from a concentrated THF solution to give yellow
crystals of E11 (0.18 g, 0.208 mmol, 92 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.38 (t, 6H,
3
J
HH
= 7.3 Hz, g), 2.50-2.56 (m, 4H, e), 3.73-3.79
(m, 4H, f), 3.96-4.03 (m, 4H, d), 4.43-4.54 (m, 2H, b or c), 4.89-4.97 (m, 2H, b or c), 6.84-7.78
(m, 20H, C
6
H
5
).
13
C-NMR (125 MHz, CD
3
CN): δ = 15.5 (s, CH
3
, g), 25 (s, CH
2
, e), 45.5 (s, CH
2
, f), 49.0 (s,
CH
2
, d), 118.7 (s, CH, b or c), 120.8 (s, CH, b or c), 127.9-128.1 (m, CH, j or k), 128.4-128.5 (m,
CH, j or k), 130.1 (t, CH,
3
J
PC
= 6, i), 134.2 (t, C
q
,
3
J
PC
= 8 Hz, h), 185.2 (ddd, C
Carbene
,
1
J
RhC
= 6
Hz,
2
J
PC
= 17 Hz, a).
31
P-NMR (202 MHz, CD
3
CN): δ = 32.0 (d,
1
J
RhP
= 128 Hz), -144.0 (hept,
1
J
PF
= 710 Hz).
E.A.: Anal. Found: C, 53.23; H, 5.23; N, 6.05, C
42
H
50
F
6
N
4
OP
3
Rh requires C, 53.85; H, 5.38; N,
5.98 %
N N
Rh
P
Ph
Ph
a
b c
d
e
fg
k
ji
h
E11
PF6
P
Ph
EtN
N
4. Experimental Section
116
4.8 Synthesis of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl (E12)
KN(SiMe
3
)
2
(111 mg, 0.460 mmol) was added to a solution of
[EtImCH
2
CH
2
PPh
2
]I (200 mg, 0.460 mmol) in 15 mL of THF.
The suspension was stirred at room temperature for 30 min.
After filtration a solution of [Rh
2
(µ-Cl)
2
(COD)
2
] (57 mg, 0.115
mmol) in 5 mL THF was added dropwise to the filtrate. The
color changed to orange and some precipitate formed giving E9
while the trans isomer E12 remained dissolved in the mother
liquor. The reactiom mixture was allowed to stirr for another 30 min. E10 was separated by
filtration and the filtrate was taken to dryness yielding a brown crude product which was
recrystallized from a concentrated THF solution to give E12 (42 mg, 0.058 mmol, 12.6 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.16 (t, 6H,
3
J
HH
= 8 Hz, g), 2.21-2.54 (m, 4H, e), 3.63-4.09
(m, 4H, f), 4.22-4.44 (m, 4H, d), 6.57 (d, 2H,
3
J
HH
= 1.9 Hz, c), 6.82 (d, 2H, b,
3
J
HH
= 2 Hz), 7.08-
7.66(m , 20H, Ph).
13
C-NMR (125 MHz, CD
CN): δ = 15.5 (s, CH
3
, g), 45.5 (s, CH
2
, f), 30.8 (d, CH
2
,
1
J
PC
= 15 Hz,
e), 48.7 (s, CH
2
, d), 118.7 (s, CH, c), 120.8 (s, CH, b), 128.0-128.6 (m, CH, j or k), 130.1-130.2
(m, CH, j or k), 134.2 (t, CH, i), 138.7 (t, C
q
,
1
J
PC
= 19 Hz,
2
J
PC
= 40 Hz, h), 185.1 (dt, C
Carbene
,
1
J
RhC
= 40 Hz,
2
J
PC,trans
= 103 Hz,
2
J
PC
,
cis
= 30 Hz, a).
31
P-NMR (202 MHz, CD
3
CN): δ = 26.0 (d,
1
J
RhP
= 152 Hz).
4.9 Synthesis of trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E13)
trans-E13 was prepared starting from E12. 250 mg (0.331
mmol) of E12 were disolved in CH
2
Cl
2
, and KPF
6
(60 mg,
0.331 mmol) was added. The reaction mixture was stirred for 2
hours. After filtration and removal of the solvent E13 was
obtained in good yield (42 mg, 0.058 mmol, 12.6 %). It was
recrystallised by layering diethyl ether onto a methylene
chloride solution.
NN
N
EtN
Rh P
P
Ph
Ph
Ph
a
bc
fg
d
e
k
jih
E12
Cl
4. Experimental Section
117
1
H-NMR (500 MHz, CD
3
CN): δ = 1.16 (t, 6H,
3
J
HH
= 8 Hz, g), 2.21-2.54 (m , 4H, e), 3.63-4.09
(m, 4H, f), 4.22-4.44 (m, 4H, d), 6.57 (d, 2H,
3
J
HH
= 2 Hz, c), 6.82 (d, 2H, b,
3
J
HH
= 2 Hz), 7.08-
7.66 (m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 15.5 (s, CH
3
, g), 45.5 (s, CH
2
, f), 30.8 (d, CH
2
,
1
J
PC
= 15 Hz,
e), 48.7 (s, CH
2
, d), 118.7 (s, CH, c), 120.8 (s, CH, b), 128.0-128.6 (m, CH, j or k), 130.1-130.2
(m, CH, j or k), 134.2 (t, CH, i), 138.7 (t, C
q
,
1
J
PC
= 19 Hz,
2
J
PC
= 40 Hz, h), 185.1 (dt, C
Carbene
,
1
J
RhC
= 40 Hz,
2
J
PC
= 17 Hz, a).
31
P-NMR (202 MHz, CD
3
CN): δ = 25.9 (d ,
1
J
RhP
= 152 Hz), -144.0 (hept,
1
J
RhF
= 710 Hz).
E.A: Anal. Found: C, 54.42; H, 6.09; N, 5.45, C
46
H
62
F
6
N
4
O
2
P
3
Rh requires C, 54.50; H, 6.12; N,
5.53 %
4.10 Synthesis of cis-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][X]
(X = Cl or PF
6
), (E14)
A solution of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][X] E10 or E11 (50 mg,
0.066 mmol) in CH
2
Cl
2
(10 mL) at room temperature was exposed to
air for 5 min. The color changed from orange to pale yellow. After
evaporation of the solvent [Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][X] E14
was obtained as pale yellow solid which gave yellow brown crystals
contaning both enantiomers, by layering a concentrated methylene
chloride solution with diethyl ether. Alternativelly layering a
concentrated acetonitrile solution with diethyl ether gave a mixture of enantiomerically pure
crystals (48 mg, 0.064 mmol, 97.0 %), ∆/Λ = 1/1.
31
P-NMR (202 MHz, CDCl
3
, 233 K): δ = -3.4 (dd,
1
J
RhP
= 85 Hz,
2
J
PP
= 20 Hz), 12.4 (dd,
1
J
RhP
=
85 Hz,
2
J
PP
= 20 Hz), 26.2 (dd,
1
J
RhP
= 125 Hz,
2
J
PP
= 20 Hz), 30.9 (dd,
1
J
RhP
= 125 Hz,
2
J
PP
= 20
Hz).
31
P-NMR (202 MHz, CDCl
3
, 343 K): δ = 8.5 (d,
1
J
RhP
= 125 Hz), 27.5 (dd,
1
J
RhP
= 126 Hz,
2
J
PP
=
20 Hz).
N NEt
N
Et
N
Rh
P
P
Ph
Ph Cl
Ph
Ph
O O
cis-O2,E14
4. Experimental Section
118
IR (KBr disc): ν[cm
-1
] 3410, 3053, 2365, 1739, 1651, 1435, 1248, 1167, 1119, 1100, 845(ν
OO
) ,
808, 746, 697, 534, 504.
4.11 Synthesis of trans-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E15)
A yellow orange solution of E11 (190 mg, 0.219 mmol) in 10
mL of acetonitile was stirred exposed to O
2
for 10 min at
room temperature. The solvent was removed under vacuum
to give a pale brown crude product which gave brown
crystals by layering a concentrated methylene chloride
solution of E15 with diethyl ether (170 mg, 0.199 mmol,
86.3 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.0 (t, 3H,
3
J
HH
= 7 Hz,
g), 1.84 (m, 2H, e), 3.91 (dt, 1H,
2
J
HH
= 15 Hz,
3
J
HH
= 4 Hz,
d), 3.03 (dq, 1H,
2
J
HH
= 14 Hz,
3
J
HH
= 7 Hz, f), 4.7 (dq, 1H,
2
J
HH
= 14 Hz,
3
J
HH
= 7 Hz, f), 6.97 (d,
1H,
3
J
HH
= 2 Hz, b), 7.09 (d, 1H,
3
J
HH
= 2 Hz , c), 7.48-7.59 (m, 16H, i , j), 7.63 (t, 2H,
3
J
HH
= 8
Hz ,K), 7.71 (t, 2H,
3
J
HH
= 9.8 Hz, k).
13
C-NMR (125 MHz, CD
3
CN): δ = 15.7 (s, CH
3
, g), 22.7 (d,
1
J
PC
= 26 Hz, e), 44.9 (s, CH
2
, d),
45.3 (s, CH
2
, f), 121.7 (s, CH, c), 125.2 (s, CH, b), 129.1, 131.5, 134.4 (d, CH,
2
J
PC
= 13 Hz, i, j,
k), 134.46 (d, C
q
,
1
J
PC
= 13 Hz, h), 160.4 (dt, C
Carbene
,
1
J
RhC
= 34 Hz,
2
J
PC
= 17 Hz, a)
IR (KBr disc): ν[cm
-1
] 3410, 3053, 2365, 1739, 1651, 1435, 1248, 1167, 1119, 1100, 850(ν
OO
),
808, 746, 697, 534, 504.
E.A: Anal. Found: C, 47.53; H, 4.50; N, 5.62, C
39
H
44
Cl
2
F
6
N
4
O
2
P
3
Rh requires C, 47.72; H, 4.52;
N, 5.71 %
N N
N
EtN
Rh P
P
Ph
Ph
Ph
O O
trans-E15
e
d
bc
a
fg
PF6
h
i
j
k
4. Experimental Section
119
4.12 Synthesis of cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E16)
To a solution of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (180 mg, 0.208
mmol) in 10 mL of dichloromethane 13 mg sulfur (0.416mmol)
was added at room temperature. The color changed from orange
yellow to green. Then the reaction mixture was stirred overnight.
Finally the solvent was evaporated under vacuum and green
crystals were obtained by layering diethylether onto a methylene
chloride solution of E16 (180 mg, 0.203 mmol, 92%).
1
H-NMR (500 MHz, CD
3
CN): δ = 0.6 (t, 3 H,
3
J
HH
= 15 Hz, g’),
1.2 (t, 3H,
3
J
HH
= 13 Hz, g), 2.22-2.60 (m, 2H, f
’
), 2.84-3.67 (m, 2H, f), 2.59-3.35 (m, 2H, e),
3.06-3.30 (m, 2H, e
’
), 4.50-5.01 (m, 2H, d
’
), 4.73-5.24 (m, 2H, d), 6.5-7.46 (m, 20H, Ph), 7.04
(m, 1H, c), 7.15 (m, 1 H, b), 7.32 (m, 1H, c
’
), 7.71 (s, 1H, b
’
).
13
C-NMR (125 MHz, CD
3
CN): δ = 12.7 (s, CH
3
, g), 14.7 (s, CH
3
, g
’
), 28.4 (d, CH
2
,
2
J
PC
= 38
Hz, e
’
), 30.2 (d, CH
2
,
1
J
PC
= 31 Hz, e), 44.4 (s, CH
2
, f), 46.5 (s, CH
2
, f
’
), 49.6 (s, CH
2
, d), 49.9 (s,
CH
2
, d
’
), 119.7 (d, CH,
4
J
PC
= 5 Hz, c), 121.4 (s, CH, c
’
), 123.5 (d , CH,
4
J
PC
= 6 Hz, b), 124.9 (s ,
CH, b
’
), 125.5-126.8 (d, CH,
3
J
PC
= 5 Hz, k), 128.4-130.4 (m, CH, j or k), 131.7-133.2 (q, CH,
3
J
PC
= 10 Hz, i), 140.2 (dd, C
q
,
1
J
PC
= 3 Hz,
2
J
RhC
= 30 Hz, h), 142.95 (dd, C
q
,
1
J
PC
= 3 Hz,
2
J
RhC
= 42 Hz, h’), 162.0 (ddd, C
Carbene
,
1
J
RhC
= 161 Hz,
2
J
PC
,
cis
= 13 Hz,
2
J
PC
,
trans
= 40 Hz, a), 169.5
(ddd, C
Carbene
,
1
J
RhC
= 48 Hz,
2
J
PC, cis
= 6 Hz,
2
J
PC
,
trans
= 19 Hz, a’).
31
P-NMR (202 MHz, CD
3
CN): δ = 4.2 (dd,
1
J
RhP
= 128 Hz,
2
J
PP
= 22 Hz), 19.5 (dd,
1
J
RhP
= 77
Hz,
2
J
PP
= 22 Hz), -144.0 (hept,
1
J
PF
= 710 Hz).
IR (KBr disc): ν[cm
-1
], 3456, 3187, 2950, 2836, 1651, 1434, 1331, 1263, 1020, 873, 744, 690,
557(ν
SS
)
, 519.
E.A.: Anal. Found: C, 43.67; H, 4.16; N, 5.21, S, 5.79, C
40
H
46
Cl
4
F
6
N
4
P
3
Rh S
2
requires C,
43.69; H, 4.18; N, 5.09, S, 5.82 %
Rh
P
P
N
N
N
N
S S Ph
Ph
PF6
Ph
b
c
d
e
a
e'
d'
a'
b' c'
h
ij
k
f'
g'
f
g
4. Experimental Section
120
4.13 Synthesis of cis-[Rh(CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E17)
To a solution of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (180 mg, 0.208 mmol) in 10 mL of THF
methyl iodide in excess (29.51 mg, 0.208 mmol, 1.5 mL) was
added dropwise over 10 min. The reaction mixture was stirred at
room temperature for 2 hours during this period of time the color
changed to pale yellow. The solvent was removed under vacuum to
give crude yellow product E17 (130 mg, 0.134 mmol, 61.6%).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.21 (t, 3H, g), 1.04 (t, 3H, g),
2.51-2.39 (m, 2H, d), 3.78 (s, 2H, CH
3
), 4.13-4.56 (m, 2H, e),
6.19 (s, 1H, b or c), 7.37 (s, 1H, b or c), 7.59 (s, 1H, b or c), 7.92-
7.12 (m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.9 (s, CH
3
, g), 15.5 (s, CH
3
, g), 25.3 (s, CH
2
, e), 27.8 (d,
CH
2
, e), 46.7 (s, CH
2
, f ), 48.7 (s, CH
2,
d
), 49.2 (s, CH
2
, d), 125.1 (s, CH, b or c), 119.9 (s, b or
c), 122.8 (s, CH, b or c), 127.0-135.2 (m, CH, Ph).
31
P-NMR (202 MHz, CD
3
CN): δ = 13.4 (dd,
2
J
PP
= 25 Hz,
1
J
RhP
= 88 Hz), 6.2 (dd,
2
J
PP
= 24 Hz,
1
J
RhP
= 88 Hz).
4.14 Synthesis of cis-[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
][I
3
] (E19)
A solution of cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (170 mg, 0.197 mmol) in 10 mL of THF was
cooled to -50°C. Then iodine (100 mg, 0.394 mmol) in 5 mL of
THFwas added through a needle steel capillary under argon
atmosphere. The reaction mixture was stirred for 1 hour at -50°C
and then allowed to warm to room temperature and eventually
stirred over night. Removal of the solvent afforded a yellow
brown crude product which was recrystallised by layering di-
isopropyl ether into a concentrated acetonitrile solution of E19
(140 mg, 0.122 mmol, 61 %).
Rh
P
CH3
I
N
N
Ph
Ph
NNEt
P
Ph
PF6
E17
bc
f
g
he
d
ij
k
Rh
P
P
Cl
I
N
N
Et
N
N
Ph
Ph
Ph
I3
E19
b
c
ed
k
j i
h
a
f
g
4. Experimental Section
121
1
H-NMR (500 MHz, CD
3
CN): δ = 0.18 (t, 3H,
3
J
HH
= 7 Hz, g), 1.10 (t, 3H,
3
J
HH
= 7 Hz, g’),
2.22-2.60 (m, 2H, f
’
), 2.84-3.67 (m, 2H, f), 2.69-3.65 (m, 2H, d), 2.81-3.49 (m, 2H, d), 5.06-3.19
(m, 2H, e), 6.22-3.19 (m, 2H, e), 7.04 (m, 1H, c), 7.15 (m, 1H, b), 7.32 (m, 1H,c
’
), 7.71 (s, 1H,
b
’
).
13
C-NMR (125 MHz, CD
3
CN): δ = 12.3 (s, CH
3
, g), 15.5 (s, CH
3
, g), 25.4 (d, CH
2
,
1
J
PC
= 26 Hz,
d), 27.1 (d, CH
2
,
1
J
PC
= 26 Hz, d’), 44.4 (s, CH
2
, f), 46.6 (s, CH
2
, f
’
), 49.0 (s, CH
2
, e), 50.0 (s,
CH
2
, e’), 120.8 (d, CH, b or c), 121.0 (s, CH, b or c), 126.6 (s, CH, b or c), 126.8 (d, CH, b or c),
127.1 (s, CH, i, j or k), 129.5 (s, CH, i, j or k), 135.4 (s, CH, i, j, k), 136.5 (dd, C
q
,
2
J
PC
= 5 Hz,
1
J
RhC
= 50 Hz, h), 136.8 (dd, C
q
,
2
J
PC
= 5 Hz,
1
J
RhC
= 50 Hz, h).
31
P-NMR (202 MHz, CD
3
CN): δ = 4.0 (d,
1
J
RhP
= 90 Hz), 1.7 (d,
1
J
RhP
= 90Hz), -1.1 (d,
1
J
Rh-P
=
85 Hz), -2.8 (d,
1
J
RhP
= 87 Hz), -3.4 (d,
1
J
RhP
= 85 Hz).
4.15 Synthesis of cis-[Ir(EtImCH
2
CH
2
PPh
2
)][PF
6
] (E20)
To a solution of 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazolium-hexafluorophosphate (195 mg, 0.46 mmol) in 10
mL of THF was added KN(SiMe
3
)
2
(100 mg, 0.46 mmol) and the
mixture was stirred at room temperature under inert atmosphere for
30 min. [Ir(COD)Cl]
2
(77 mg, 0.115 mmol) was then added. The
color changed to orange red. After the removel of the solvent under
reduced pressure an orange residue was obtained which yielded red
orange crystals by layering diethyl ether into methylene chloride solution E20 (0.13 g, 61.9%).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.05 (t , 6H,
3
J
HH
= 7 Hz, g), 2.12-2.59 (m, 4H, e), 3.76-3.9
(m, 4H, f), 4.36-4.90 (m, 4H, d), 6.94 (d, 2H, b,
3
J
HH
= 2 Hz), 7.06 (d, 2H, c,
3
J
HH
= 2 Hz), 6.82-
7.80 (m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.5 (t, CH
3
, g), 31.0-31.3 (m, CH
2
, e), 44.8 (s, CH
2
, f), 49.8
(s, CH
2
, d), 119.3 (s, CH, b), 120.1 (s, CH, c), 127.5-128.5 (m, CH, j or k), 130.1-130.7 (m, CH, j
or k), 132.8-135.7 (m, CH, i), 138 .5 (d, C
q
,
1
J
PC
= 50 Hz, h), 138.8 (d , C
q
,
1
J
PC
= 48 Hz, h),
174.4 (dd, C
Carbene
, a,
2
J
PC, cis
= 20 Hz;
2
J
PC, trans
= 98 Hz).
cis-E20
a
b
c
d
e
ij
k
f
gNN
Ir P
N
Et
NP
P
h
Ph
Ph
4. Experimental Section
122
31
P-NMR (202 MHz, CD
3
CN): δ = 16.5 (s), -144.4 (hept,
1
J
PF
= 711 Hz).
4.16 Synthesis of cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E21)
Into a solution cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E20), (130 mg,
0.136 mmol) in 10 mL of CH
2
Cl
2
H
2
gas was bubbled for 30 min.
The color changed immediately from orange red to pale yellow.
The solution was removed under vacuum to give a yellow crude
product, which gave yellow crystals by layering diethylether onto
methylene chloride solution of E21 (100 mg, 0.117 mmol, 83 %).
1
H-NMR (500 MHz, CD
2
Cl
2
): δ = -13.16 (td, 1H (2),
1
J
H1H2
= 4 Hz), - 11.5 (ddd, 1H (1),
2
J
P1H1
=
129 Hz,
2
J
P2H1
= 18 Hz,
2
J
P2H2
= 16 Hz,
1
J
H1H2
= 4 Hz), 0.47 (t, 3H,
3
J
HH
= 7.59, g’), 1.28 (t, 3H,
3
J
HH
= 7.34 Hz, g), 2.49-2.69 (m, 2H, f’), 2.68-2.95 (m, 2H, e’), 3.22-3.58 (m, 2H, f), 4.14-4.40
(m, 2H, d’), 4.40-4.47 (m, 2H, e), 6.86 (d, 1H,
3
J
HH
= 2 Hz, b), 7.05 (s, 1H, b’), 7.16 (s, 1H, c),
7.29 (d ,1H, c’), 6.60-7.49 (m, 20 H, Ph).
13
C-NMR (125 MHz, CD
2
CL
2
): δ = 13.1 (s, CH
3
, g’), 15.0 (s, CH
3
, g), 26.0 (s, CH
2
, d), 29.0 (s,
CH
2
, d’), 46.0 (d, CH
2
, f), 49.5 (s, CH
2
, d’), 49.9 (s, CH
2
, e), 117.8 (s, CH, b’), 118.5 (d, CH, b),
122.2 (d, CH, c’), 122.9 (s, CH, c), 133.8, 127.7, 130.4, 130.9 (m, CH, i, j, k), 152.9 (s, C
q
,
1
J
PC
=
8 Hz, h), 153.6 (s, C
q
,
1
J
PC
= 8 Hz, h’), 160.2 (m, C
Carbene
, a or a’).
31
P-NMR (202 MHz, CD
2
Cl
2
): δ = -0.86 (d,
2
J
PP
= 15 Hz), -2.17 (d,
2
J
PP
= 15 Hz), -144.0 (
1
J
PF
=
710 Hz).
IR (KBr disc): ν[cm
-1
], 2050(ν
HH
), 2013(ν
HH
), 1460, 1453, 1419, 1405, 1434, 1097, 877, 755,
741, 700, 557, 534, 517, 488.
E.A.: Anal. Found: C, 49.97; H, 5.72; N, 5.21, C
46
H
64
F
6
IrN
4
O
2
P
3
requires C, 49.90; H, 5.79; N,
5.07 %
Ir
P
P
N
N
N
NHH
Ph
Ph
Ph
PF6
E21
b
c
f
g
d
e
g' f' c' b'
d`
e'
1
2
1
2
aa' h
ij
k
4. Experimental Section
123
4.17 Synthesis of cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(E22)
A solution of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (130 mg, 0.136 mmol) in 10 mL of CH
2
Cl
2
exposed to air for 10 min. The color of the reaction mixture changed
immeditaly from orange red to pale yellow. The solvent was
evaporated to afford a yellow residue which was dried under
vacuum. Crystals were grown from a concentrated THF solution or
by layering diethyl ether onto a methylene chloride solution E22
(110 mg, 0.11 mmol, 84.6%).
1
H-NMR (500 MHz, CD
3
CN): δ = 0.55 (t, 3H,
3
J
HH
= 7 Hz, g),
1.32 (t, 3H,
3
J
HH
= 8Hz , g’), 2.36-2.73 (m, 2H, d), 2.98 (m, 2H, d’), 3.95 (m, 2H, f), 4.19 (m, 2H,
f’), 4.73 (m, 2H, e’), 3.89-4.54 (m, 2H, e), 6.98 (s, 1H, c’), 7.11 (s, 1H, b’), 7.14 (d, 1H,
3
J
HH
= 2
Hz, b), 7.59 (d, 1H,
3
J
HH
= 2 Hz, c), 6.95-7.36 (m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 13.2 (s, CH
3
, g), 15.7 (s, CH
3
, g’), 25.5 (s, CH
2
, d), 27.5 (s,
CH
2
, d’), 43.1 (s, CH
2
, f’), 45.7 (s, CH
2
, f), 47.4 (s, CH
2
, e’), 49.1 (s, CH
2
, e), 120.2 (s, CH, c),
122.8 (d,
3
J
HH
= 4 Hz, c’), 124.3 (s, CH, b), 127.6 (d, CH, b’), 130.6, 133.0, 132.7 (m, CH, Ph),
139.9 (d, C
q
,
1
J
PC
= 50 Hz, h), 143.7 (m, C
Carbene
, a), 147.2 (m, C
Carbene
, a’).
31
P-NMR (125 MHz, CD
3
CN, 323K): δ = -11.6 (d,
2
J
PP
= 15 Hz), -11.5 (d,
2
J
PP
= 13 Hz),
-144.0 (hept,
1
J
PF
= 713 Hz).
IR (KBr disc): ν[cm
-1
], 3500, 3054, 2475, 1435, 1419, 1409, 1260, 1098, 1059, 1028, 858((ν
OO
),
748, 696, 558, 531, 506.
Ir
P
N
N
N
N
O
P
Ph
Ph O
PF6
E22
Ph
b
c
fg
e
d
h
ij
k
d'
e'
c' b'
f' g'
4. Experimental Section
124
4.18 Synthesis of cis-[Ir(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E23)
To a solution of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
], (E20) (130 mg, 0.136 mmol) in 10 mL of
CH
2
Cl
2
. Sulfur (8.0 mg, 0.273 mmol) was added at once. The
color of the reaction mixture changed from orange red to yellow
orange. The reaction mixture was stirred over night.
Subsequently the solvent was removed under reduced pressure to
yield a yellow orange residue which gives yellow crystals (yield
= 110 mg, 0.112 mmol, 82%) by layering diethyl ether into a
solution of E23 in THF/acetonitrile (1/1).
1
H-NMR (500 MHz, CD
3
CN): δ = 0.56 (t, 3H,
3
J
HH
= 7 Hz, g);
1.25 (t, 3H,
3
J
HH
= 7 Hz, g’), 2.54-2.64 (m, 2H, f), 2.83-3.68 (m,
2H, f’), 2.61-3.45 (m, 2H, e’), 3.10-3.43 (m, 2H, d), 4.37-4.91 (m, 2H, e), 4.66-5.21(m, 2H, d’),
7.03 (s, 1H, c’), 7.15 (s, 1H, b’), 7.27 (d, 1H,
3
J
HH
= 2 Hz, b), 7.65 (d, 1H,
3
J
HH
= 2 Hz, c), 6.80-
7.43 (m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 12.6 (s, CH
3
, g), 14.8 (s, CH
3
, g’), 27.3 (t, CH
2
,
2
J
PC
= 49 Hz,
d), 29.7 (d, CH
2
,
2
J
PC
= 38 Hz, e’), 44.6 (CH
2
, d), 46.1 (s, CH
2
, f), 49.9 (s, CH
2
, d’), 51.1 (s, CH
2
,
e), 119.3 (d, CH,
3
J
HH
= 4 Hz, c’), 120.5 (s, CH, b), 123.1 (s, CH, b’), 124.5 (s, CH, c), 128.1,
133.2, 130.4 (m, CH, i, j, k), 138.5 (d, C
q
,
1
J
PC
= 39 Hz, h), 142.5 (d, C
q
,
1
J
PC
= 53 Hz, h’), 145.0
(dd, C
Carbene
,
2
J
PC
= 9 Hz, a’), 149.7 (d, C
Carbene
,
2
J
PC
= 12 Hz, a’).
31
P-NMR (202 MHz, CD
3
CN): δ = -12.7 (d,
2
J
PP
= 18 Hz), -30.7 (d,
2
J
PP
= 15 Hz).
IR (KBr disc): ν[cm
-1
], 3445, 2963, 2360, 1435, 1261, 1097, 1022, 802, 697, 669, 557
(
ν
SS
).
Ir
P
P
N
N
N
N
S S
Ph
Ph
PF6
Ph
h
ij
k
b
c
f
g
g'
f'
e
d
e'
d'
b'
c'
E23
4. Experimental Section
125
4.19 Synthesis of cis-[Ir(CO)(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (E24)
CO gas was bubbled for 30 min. through a red orange THF
solution (10 mL) of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
], E20
(130 mg, 0.136 mmol). The color changed to pale yellow.
Then the solvent was removed under reduced pressure to give
a yellow precipitate of E24 in high yield (130 mg, 0.132
mmol, 97 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 1.14 (t, 3H,
3
J
HH
= 7 Hz,
g), 1.64-2.11 (m, 2H, e), 3.06-3.56 (m, 2H, d), 3.90-4.4 (m,
2H, f), 6.8 (s, 1H, c), 7.06 (s, 1H, b), 6.50-7.64 (m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.9 (s, CH
3
, g), 27.4 (t, CH
2
,
2
J
PC
= 13 Hz, e), 45.6 (s, CH
2
,
f), 48.0 (s, CH
2
, d), 119.8 (s, CH, b), 124.4 (s, CH, c), 129.2, 129.6, 133.2, 130.3, 128.6 (m, CH,
Ph), 143.8 (t, C
Carbene
,
2
J
PC
= 13 Hz, a), 191.2 (t, CO,
2
J
PC
= 45 Hz).
31
P-NMR (202 MHz, CD
3
CN): δ = -12.0 (s), -144.4 (hept,
1
J
PF
= 710 Hz).
IR (CaF
2
): ν[cm
-1
], 2018, 1900 (ν
CO
).
4.20 Synthesis of trans-[Ir((CH
3
)(I)(EtImCH
2
CH
2
PPh
2
)
2
)]I (E25)
Methyl iodide was added dropwise over 10 min at room temperature (1mL, 0.136 mmol) to a
solution of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] (130 mg, 0.136
mmol) in 10 mL of THF. The reaction mixture was stirred at
room temperature for 1 h. The color changed from red orange to
pale yellow. A pale yellow precipitate was observed which was
collected by filtration. Subsequently the solvent was removed
under vacuum to give the pale yellow product E25, which gave
white crystals from concentrated THF solution (100 mg, 0.092
mmol, 68.4%).
Ir CO
NEt
NPF6
P
NN
P
Ph
Ph
Ph F
g
b
c
d
e
h
j
i
k
a
E24
Ir
P
P
N
N
N
NPF6
Ph
Ph
H3C
I
E 25A
h
i j
k
a
b
c
e
d
F
g
b' c'
e'
d'
F'
g'
Ph
4. Experimental Section
126
1
H-NMR (500 MHz, CD
3
CN): δ = 0.15 (s, 3H, CH
3
Ir), 0.9 (t, 3H,
3
J
HH
= 7 Hz, g), 1.35 (t, 3H,
3
J
HH
= 7 Hz, g’), 2.54-2.72 (m, 2H, e), 2.82-3.12 (m, 2H, e’), 2.9-3.13 (m, 2H, d), 3.25-3.44 (m,
2H, d’), 7.29 (m, 1H, b), 7.42 (m, 1H, c), 7.56 (m, 1H, b’), 7.56 (m, 1H, c’), 6.07 (t, 2H,
3
J
HH
= 8
Hz, Ph), 7.14 (t, 2H, Ph), 7.23 (t, 4H, Ph), 7.42 (m, 4H, Ph), 7.30 (m, 4H, Ph), 7.42 (m, 4H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 0.4 (s, CH
3
, CH
3
-Ir), 15.4 (s, CH
3,
g), 15.9 (s, CH
3,
g’), 29.4
(d, CH
2
,
2
J
PC
= 29 Hz, e), 30.2 (d, CH
2
,
2
J
PC
= 30 Hz, e’), 43.6 (s, CH
2
, f’), 44.6 (s, CH
2
, f’’), 47.1
(s, CH
2
, d), 47.8 (s, CH
2
, d’), 120.8 (d, CH,
2
J
CH
= 4 Hz, b), 122.1 (d, CH,
2
J
CH
= 4 Hz, c), 124.4
(d, CH,
2
J
CH
= 4 Hz, b’), 126.0 (d, CH,
2
J
CH
= 4 Hz, c’), 126.4 (d, CH,
2
J
PC
= 10 Hz, i), 127.4 (d,
CH,
2
J
PC
= 10 Hz, i or j), 128.5 (m, CH, i, k), 130.8 (s, CH, i, k, j), 132.3 (d, CH,
3
J
PC
= 7 Hz, j),
133.4 (d, CH,
3
J
PC
= 8 Hz, j), 134.1 (d, CH,
2
J
PC
= 10 Hz, i), 135.6 (d, CH,
3
J
PC
= 8 Hz, j), 144.1
(d, C
q
,
1
J
PC
= 14 Hz, h), 145.1 (d, C
q
,
1
J
PC
= 14 Hz, h), 146.6 (d, C
Carbene
,
2
J
PC
= 12 Hz, a), 147.6
(d, C
Carbene
,
2
J
PC
= 12 Hz, a’).
31
P-NMR (202 MHz, CD
3
CN): δ = -22.1 (d,
2
J
PP
= 20 Hz), - 41.4 (d,
2
J
PP
= 20 Hz), -144.0 (hept,
1
J
PF
= 710 Hz).
4.21 Synthesis of cis-[Ir(I)
2
(EtImCH
2
CH
2
PPh
2
)
2
][I
3
] (E26)
I
2
(69 mg, 0.272 mmol) in THF (3 mL) was added dropewise
through steel capilary needle over 10 min under argon
atmosphere to a solution of cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(130 mg, 0.136 mmol) in THF (10 mL) which was cooled to
-50°C. After the reaction mixture was stirred at this temperature
for 1 h, it was warmed to room temperature and stirred for
another 1 h. The color of the reaction mixture changed from red
orange to pale yellow. Now the solvent was removed under
vacuum to give yellow E26, which gave single crystals from
layering diisopropyl ether into concentrated acetonitrile solution of E26 (200 mg, 0.100 mmol,
74.07 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 0.71 (t, 3H,
3
J
HH
= 9 Hz, g), 1.23 (t, 3H,
3
J
HH
= 7 Hz, g’),
2.69-2.95 (m, 2H, d), 2.82-3.16 (m, 2H, d’), 2.96-3.93 (m, 2H, f), 3.95-4.79 (m, 2H, f’), 4.52-5.75
Ir
N
N
P
P
Ph
Ph
I3
E26
d'
e'
c' b'
f' g'
N
N
Ph
I I
bc
fg e
d
h
i j
k
a
a'
4. Experimental Section
127
(m, 2H, e), 4.52-5.74 (m, 2H, e’), 7.49 (s, 1H, c), 7.38 (d, 1H, b), 7.35 (s, 1H, b’), 7.43 (t, 1H, c’),
7.02-7.36 (m, 20 H, i, j, k).
13
C-NMR (125 MHz, CD
3
CN): δ = 15.3 (s, CH
3
, g), 15.6 (s, CH
3
, g’), 31.7 (d, CH
2
,
2
J
PC
= 45
Hz, d), 31.9 (d, CH
2
,
2
J
PC
= 45 Hz, d’), 46.4 (s, CH, f), 47.4 (s, CH, f’), 48.5 (s, CH, e), 49.6 (s,
CH, e’), 122.2 (s, CH, c), 122.6 (s, CH, b), 125.07 (s, CH, c’), 126.6 (s, CH, b’), 126.9 (s, CH,
Ph), 127.7 (t, CH,
3
J
PC
= 7 Hz, i, k, j), 128.8 (d, CH,
2
J
PC
= 10 Hz, i), 130.05 (s, CH, i, k, j), 131.0
(t, CH,
2
J
PC
= 7 Hz, i), 131.5 ( t, CH,
2
J
PC
= 7 Hz, i), 132.8 (d, CH,
3
J
PC
= 3 Hz, j), 133.5 (d, CH,
3
J
PC
= 4 Hz, j), 134.1 (CH,
3
J
PC
= 5 Hz, j), 136.4 (d, C
q
,
1
J
PC
= 15 Hz, h).
31
P-NMR (202 MHz, CD
3
CN): δ = 25.2 (d,
2
J
PP
= 20 Hz), -54.7 (d,
2
J
PP
= 20 Hz); -43.8 (s)
(trans-Isomer, side product).
4.22 Synthesis of trans-[Ni(EtImCH
2
CH
2
PPh
2
)
2
][I]
2
(E27)
KN(SiMe
3
)
2
(100 mg, 460 µmol) was added to a solution of
[EtImCH
2
CH
2
PPh
2
]I, E5 (200 mg, 460 µmol) in THF (20 mL).
The suspension was stirred at room temperature for 60 min. After
removal of KI by filtration [Ni
7
S(S
t
Bu)
8
][BzEt
3
N] (166 mg, 153
µmol) was added to the filtrate. The color of the resulting
suspension changed from pale yellow to black. After the reaction
mixture was stirred at room temperature for another 1 h, it was
concentrated giving a pale yellow precipitate which was collected
by filtration and crystallised by slow evaporation of a concentrated acetonitrile solution to give
E27 yellow crystals.
1
H-NMR (500 MHz, CDCl
3
): δ = 1.02 (t, 3H,
3
J
HH
= 7 Hz, g), 2.38-2.89 (m, 2H, e), 3.44-4.64
(m, 2H, e), 4.98 (m, 2H, f), 5.32 (m, 2H, d), 7.01 (s, 2H, b), 7.23 (s, 2H, c), 6.95-7.66 (m, 20H, i,
j, k).
13
C-NMR (125 MHz, CDCl
3
): δ = 15.3 (s, CH
3
, g), 25.0 (s, CH
2
, e), 47.0 (s, CH
2
, f), 50.0 (s,
CH
2
, d), 121.0 (s, CH, b), 124.0 (s, CH, c), 128.1, 129.2, 130.8, 132.6, 135.2 (CH, i, j, k), 164.2
(t, C
Carbene
,
2
J
PC
= 35 Hz, a).
4. Experimental Section
128
31
P-NMR (202 MHz, CDCl
3
): δ = 21.0 (s).
4.23 Synthesis of trans-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28)
To a solution of 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium-hexafluorophosphate E6
(195 mg, 0.46 mmol) in THF (10 mL) was added KN(SiMe
3
)
2
(118
mg, 0.46 mmol + 30%)
and the mixture was stirred at room
temperature under inert atmosphere for 30 min. Then [Pd(COD)Cl
2
]
(66 mg, 0.230 mmol) was added to the reaction mixture and the color
changed from pale yellow to yellow orange. The reaction mixture was
stirred another 2 h. A crude yellow product E28 was obtained after the
removel of the solvent under vacuum. Yellow crystals were obtained
by layering diethyl ether onto a concentrated acetonitrile solution of E28 (190 mg, 0.187 mmol,
75.0 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 0.91 (t, 3H,
3
J
HH
= 8 Hz, g), 2.81-2.89 (m, 2H, e), 2.91-3.05
(m, 2H, e), 3.32-3.75 (m, 2H, f), 3.86 (m, 2H, f), 4.79-4.99 (m, 2H, d), 6.72 (s, 2H, b), 7.20 (s,
2H, c), 6.79-7.53 (m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.1 (s, CH
3
, g), 28.5 (d, CH
2
,
2
J
PC
= 17 Hz, e), 45.8 (s, CH
2
,
f), 48.7 (s, CH
2
, d), 121.0 (s, CH, b), 124.1 (s, CH, c), 129.9 (t, CH,
3
J
PC
= 6 Hz, j or k), 129.6 (t,
CH,
3
J
PC
= 6 Hz, j or k), 130.7 (s, CH, i), 131.4 (s, CH, i), 132.9 (s, CH, i), 134.2 (t, CH,
2
J
PC
= 8
Hz, j), 134.3 (t, CH,
2
J
PC
= 8 Hz, j), 161.2 (d, C
q
,
1
J
PC
= 22 Hz, h), 162.3 (d, C
q
,
1
J
PC
= 22 Hz, h),
164.8 (t, C
Carbene
,
2
J
PC
= 12 Hz, a).
31
P-NMR (125 MHz, CD
3
CN): δ = 17.9 (s), -144.0 (hept,
1
J
PF
= 710 Hz).
4.24 Synthesis of cis-[Pd(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
2
(E28)
4. Experimental Section
129
To a solution of 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazolium-hexafluoro-phosphate E6 (195 mg, 0.46
mmol) in THF (10 mL) was added KN(SiMe
3
)
2
(118 mg,
0.46 mmol [30% excess])
. The mixture was stirred at room
temperature under inert atmosphere for 30 min. Now
[Pd(COD)Cl
2
]
(66 mg, 0.230 mmol) in 5mL of THF was
added dropwise to the reaction mixture and the color
changed from pale yellow to orange red. The reaction
mixture was stirred for another 2 h. The yellow product was
obtained after the removel of solvent under vacuum to give
cis-E28 (190 mg, 0.187 mmol, 75.0 %).
1
H-NMR (500 MHz, CD
3
CN): δ = 0.91 (t, 3H,
3
J
HH
= 7 Hz, g), 1.01 (t, 3H,
3
J
HH
= 7 Hz, g’),
2.89-2.73 (m, 2H, d), 2.78-2.93 (m, 2H, d’), 3.31-3.75 (m, 2H, f), 3.24 (m, 2H, f’), 3.71-4.08 (m,
2H, e), 5.03-4.74 (m, 2H, e’), 6.72 (s, 1H, b), 6.37 (s, 1H, b’), 7.16 (s, 1H, c), 7.34 (s, 1H, c’),
6.79-7.53 (m, 20H, Ph).
13
C-NMR (125 MHz, CD
3
CN): δ = 14.1 (s, CH
3
, g), 14.5 (s, CH
3
, g’), 27.6 (s, CH
2
, f`), 28.5
(s,CH
2
, f’), 30.1 (d, CH
2
,
2
J
PC
= 5 Hz, d), 30.4 (d, CH
2
,
2
J
PC
= 6 Hz), 45.9 (s, CH
2
, e), 48.9 (s,
CH
2
, e’), 121.1 (s, CH, b), 122.2 (s, CH, c), 124.2 (s, CH, c’), 129.9 (t, CH,
3
J
PC
= 6 Hz, j or i),
129.6 (t, CH,
3
J
PC
= 6 Hz, j or k), 130.7 (t, CH, j or i), 131.4 (s, CH, j or k), 132.9 (s, CH, j or k),
134.2 (t, CH,
2
J
PC
= 8 Hz, j), 134.3 (t, CH,
2
J
PC
= 8 Hz, j), 161.2 (d, C
q
,
1
J
PC
= 21 Hz, h), 161.3
(d, C,
1
J
PC
= 20 Hz, h), 164.8 (dd, C
Carbene
,
2
J
PC
= 23 Hz,
2
J
PC
= 134 Hz, a).
31
P-NMR (125 MHz, CD
3
CN): δ = 17.7 (s), -144.0 (hept,
1
J
PF
= 710 Hz).
4. Experimental Section
130
4.25 Suzuki coupling reaction.
A mixture of aryl halide (1 mmol), phenylboronic acid (1.5 mmol), cesium carbonate (2 mmol),
Pd(II)-NHC E28 (1 mol %, 0.009 g) and dioxane (3 mL) was stirred at 80°C for an appropriate
period of time (8-48 h) under nitrogen. The solution was allowed to cool to ambient temperature.
The reaction mixture was diluted with H
2
O (10 mL) and Et
2
O (10 mL) followed by twofold
extraction with Et
2
O. The combined organic layers were dried over Mg
2
SO
4
, filtered and
evaporated under reduced pressure to a give crude product. The pure product was isolated by
plate chromatography to give a biphenyl product as a colorless solid, which was characterized by
1
H-NMR spectroscopy.
.
5. Conclusion
131
5. Conclusion
The mixed bidentate phosphane imidazole donor ligands E5 3-[2-(diphenylphosphino)ethyl]-1-
ethylimidazoliumiodide and E6 3-[2-(diphenylphosphino)ethyl]-1-ethylimidazolium-hexafluoro-
phosphate were successfully synthesized and fully characterized (Figure 3.1). The counter ion
was exchanged due to the difficulties encountered by us in the crystallization process. The
formation of the carbene was investigated by addition of CS
2
. Single crystals from this product
E8 were investigated by single crystal X-ray analysis (Figure 3.5) and by NMR-spectroscopic
methods.
The novel cis-Rh(I) complexes [Rh(EtImCH
2
CH
2
PPh
2
)
2
][X], (X = Cl, PF
6
) E10 and E11,
respectively, were synthesized and characterized (Figure 3.8). These complexes were obtained in
high yield. E10 was obtained as yellow crystals from THF solution while E11 is highly soluble in
THF. Crystals of these complexes are suitable for single crystal X-ray analyses. They adopt a
square planar geometry around the rhodium(I) atom (Figure 3.9, 3.10). In addition the novel
trans-Rh(I) complex [Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl E12 was obtained by dropwise addition of the
metal precursor [Rh(µ-Cl)(COD)]
2
to an in situ generated carbene solution. E13
[Rh(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
] was obtained by a simple salt metathesis reaction. Both
complexes were characterized by standard spectroscopic methods. Single crystal X-ray analyses
of both complexes exhibit a square-planar environment around the Rh(I) atom (Figure 3.11, 3.12)
as expected for Rh(I) complexes.
cis-E10 can be converted to trans-E12 by heating. The interconversion at elevated temperatures
was discussed and fully elucitated by measuring
31
P-NMR spectra (Figures 3.14, 3.15). After
prolonged heating, the ratio of cis to trans amounts to 1:2. Further heating gave no further change
in ratio of both isomers indicating that the equilibrium is reached. A proposed mechanism of
interconversion of E10 cis-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl to E12 trans-[Rh(EtImCH
2
CH
2
PPh
2
)
2
]Cl
is showen (Figure 3.17).
Furthermore, the novel peroxo complexes E14 and E15, cis-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)]
+
and
trans-[Rh(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)]
+
, respectively, were synthesized (Figure 3.19).
31
P-NMR
spectra of these peroxo complexes at different temperatures show the formation of two
conformers of E14 (Figure 3.21). Also,
31
P-NMR spectra prove that the peroxo complex E14 is
capable of reversibl oxygen activation. These complexes were obtained in high yield and
5. Conclusion
132
characterized by NMR-spectroscopic methods. Single crystal X-ray analyses of E14 and E15
exihibt a trigonal-bipyramidal arrangement of the ligands around the Rh(III) atoms (Figure 3.23,
3.24). In the IR spectra of the complexes, absorption bands at 845 cm
-1
can be attributed to the
oxygen-oxygen stretching vibration typical for side-on coordinated peroxide ions.
The novel compound cis-[Rh(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)]
+
(E16) was synthesized as illustrated in
Figure (3.25). It was obtained in high yield and characterised by NMR spectroscopic methods.
Green single crystals of E16 shows a distorted trigonal bipyramidal arrangement around the
Rh(III) metal atom (Figure 3.27). The IR spectrum of E16 exihibits a band at 557 cm
-1
can be
assigned to the S-S stretching vibration of the η
2
-S
2
-ligand.
The novel rhodium(III) complexes E17 and E18 are isomers of formula [Rh(CH
3
)(I)(EtIm-
CH
2
CH
2
PPh
2
)
2
]I. These complexes were obtained by the reaction of E11 with MeI in high yield
(86%). Unfortunately, all attempts to get crystals of these complexes failed.
The novel complex E19, cis-[Rh(Cl)(I)(EtImCH
2
CH
2
PPh
2
)
2
][I
3
] was synthesized by reaction of
E11 with iodine. E19 was characterised by standard spectroscopic methodes. Interestingly, a
single crystal X-ray analysis revealed the formation of this unexpected iodide-chloride adduct
which most likely results from the exchange of iodide with chloride contained as small impurity
in the starting material. The counter ion I
3-
is formed by the reaction of iodide with excess I
2
.
Yellow brown single crystals of E19 reveal the formation of an octahedral Rh(III) complex
(Figure 3.28).
With respect to E10 the isoelectronic cis-iridium(I) complex, cis-[Ir(EtImCH
2
CH
2
PPh
2
)
2
][PF
6
]
(E20) was synthesized (Figure 3.29) and characterised by NMR spectroscopy. The
31
P-NMR
spectrum shows the signal of the phosphorous atoms at 16.8 ppm. A single crystal X-ray analysis
of red single crystals of E20 shows a square planar structure as expected for iridium(I) complexes
(Figure 3.30).
The synthesis of a series of the novel iridium(III) complexes E21, E22, E23, E25, E26,
cis-[Ir(H)
2
(EtImCH
2
CH
2
PPh
2
)
2
]
+
, cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)]
+
, cis-[Ir(η
2
-S
2
)(EtIm-
CH
2
CH
2
PPh
2
)]
+
, trans-[Ir(CH
3
)(I)(ImCH
2
CH
2
PPh
2
)
2
]
+
, cis-[Ir(I)
2
(ImCH
2
CH
2
PPh
2
)
2
]
+
also
described (Figure 3.32). E21 was obtained in high yield by reaction of E20 with H
2
and
characterised by NMR spectroscopy. The IR spectrum of E21 shows sharp Ir-H stretching mode
at 2013 and 2050 cm
-1
which are in a good agreement with data of other iridium hydride
5. Conclusion
133
complexes. Also single crystal X-ray analysis of E21 exhibits a distorted octahedral structure
around the Ir(III) atom (Figure 3.33).
E22 cis-[Ir(η
2
-O
2
)(EtImCH
2
CH
2
PPh
2
)]
+
was synthesized by reaction of E20 with oxygen and
fully characterized by standard spectroscopic methods. The reaction of iridium(I) with O
2
is
irreversible as confirmed by
31
P-NMR spectra (Figure 3.33). The IR spectrum shows a sharp
band which must be assigned to ν(O-O) at 854 cm
-1
. An X-ray single crystal analysis of E22
shows a trigonal-bipyramidal arrangement of the ligands around the iridium(III) atom (Figure
3.35).
E23 cis-[Ir(η
2
-S
2
)(EtImCH
2
CH
2
PPh
2
)]
+
was synthesized by reaction of E20 with sulfur and
characterized by standard spectroscopic methods. A single crystal X-ray analysis of E23 revealed
a distorted octahedral ligand field. In the IR spectrum, the ν(S-S) band is located at 557 cm
-1
.
According to a single crystal X-ray analysis the ligands in E23 adopt a trigonal-bipyramidal
environment around the Ir(III) atom (Figure 3.36).
The five-coordinate Ir(I) carbonyl complex E24 was synthesized by addition of CO to E20 and
identified by NMR-spectroscopic methods. The IR spectrum of E24 shows an absorption band of
CO at 2080 and 1900 cm
-1
. Unfortunately, all attempts to crystallize this complex failed.
We observed remarkable differences in the reactivity of E20, Ir(I) toward CO and H
2
compared
to the isoelectronic Rh(I) complex E10. The later shows no reactivity towards CO and H
2
at
room temperature, while E20 reacts with CO and H
2
even at room temperature.
In addition, the novel Ir(III) complexes E25 and E26, trans-[Ir(CH
3
)(I)(ImCH
2
CH
2
PPh
2
)
2
]
+
, cis-
[Ir(I)
2
(ImCH
2
CH
2
PPh
2
)
2
]
+
, were obtained by reaction of E20 with MeI and I
2
, respectively, in
high yields and characterized by NMR spectroscopy. Both complexes contain in solution two
isomers (A, B), which could not be seperated. Colorless single crystals of isomer B of both
complexes contain according to X-ray diffraction measurements in both cases a distorted
octahedral enviroment around the Ir(III) atoms (Figure 3.37, 3.39).
The new trans-Ni(II) and trans-Pd(II) complexes E27, E28 [Ni(EtImCH
2
CH
2
PPh
2
)
2
]
2+
[Pd(EtImCH
2
CH
2
PPh
2
)
2
]
2+
, respectively, were synthesized according to Figure 3.41 and 3.43 and
fully characterized by spectroscopic methods. Both complexes adopt a distorted square-planar
environment around the metal(II) atoms. The interconversion of cis to trans isomers in E28 at
high temperature was followed up by
31
P-NMR spectroscopy (Figure 3.45). The interconvertion
of cis to trans at 70°C lead to an equilibrium between both isomers with a ratio of 1:2.
5. Conclusion
134
The trans-Pd(II) complex E28 proved to be an effective catalyst for Suzuki coupling reactions.
Table 3.19 shows its activity for the coupling of substituted aryl halides containing electron
donating and withdrawing groups with phenyl boronic acids. Reaction times of about 24 h at
80°C are required for the production of unsymmetrical biaryl products in good yield.
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7. Appendix
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7. Appendix
Table 7.1: Crystal data and structure refinement for E6
E6
Identification code a1951
Empirical formula C
19
H
22
F
6
N
2
P
2
Formula weight 454.33
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/n
Unit cell dimensions a = 8.4391(8) Å
b = 13.6878(13) Å
c = 18.1986(17) Å
α = 90°
β = 97.623(2)°
γ = 90°
Volume 2083.6(3) Å
3
Z 4
Density (calculated) 1.448 Mg/m
3
Absorption coefficient 0.269 mm
-1
F(000) 936
Crystal size 0.37 x 0.31 x 0.19 mm
3
Theta range for data collection 1.87 to 27.88°
Index ranges -11 ≤ h ≤ 11, -18 ≤ k ≤ 18, -23 ≤ l≤ 23
Reflections collected 16418
Independent reflections 4923 [R(int) = 0.0874]
Completeness to theta = 27.88 99.5 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.9507 and 0.9071
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 4923 / 0 / 262
Goodness-of-fit on F2 0.998
Final R indices [I>2σ (I)] R1 = 0.0643, wR2 = 0.1544
R indices (all data) R1 = 0.1278, wR2 = 0.1942
Largest diff. peak and hole 0.521 and -0.373 e.Å
-3
7. Appendix
148
Table 7.2: Crystal data and structure refinement for E8 and E9
E8 E9
Identification code S1616 e1214
Empirical formula C
20
H
21
N
2
P S
2
C
12
H
20
N
2
S
2
Formula weight 384.48 256.42
Temperature 120(2) K 120(2) K
Wavelength 0.71073 Å 0.71073 Å
Crystal system Monoclinic Monoclinic
Space group C2/c C2/c
Unit cell dimensions a = 20.125(3) Å a = 13.9880(15) Å
b = 13.832(2) Å b = 9.0697(10) Å
c = 13.920(2) Å c = 11.5600(12) Å
α = 90° α = 90°
β = 90.884(3)° β = 110.895(2)°
γ = 90° γ = 90°
Volume 3874.7(10) Å
3
1370.1(3) Å
3
Z 8 4
Density (calculated) 1.318 Mg/m
3
1.243 Mg/m
3
Absorption coefficient 0.363 mm
-1
0.366 mm
-1
F(000) 1616 552
Crystal size 0.43 x 0.40 x 0.38 mm
3
0.48 x 0.40 x 0.40 mm
3
Theta range for data collection 1.79 to 27.88° 2.73 to 27.88°
Index ranges -26 ≤ h ≤ 24, -16 ≤ k ≤ 18, -15≤ l ≤ 18 -18 ≤ h ≤ 18, -11 ≤ k ≤ 11, -15 ≤ l ≤ 15
Reflections collected 11269 6678
Independent reflections 4450 [R(int) = 0.0295 1631 [R(int) = 0.0538
Completeness to theta = 27.88 96.3 % 100.0 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.8745 and 0.8597 0.979 and 0.829
Refinement method Full-matrix least-squares on F
2
Full-matrix least-squares on F
2
Data / restraints / parameters 4450 / 0 / 226 1631 / 0 / 77
Goodness-of-fit on F2 1.037 1.076
Final R indices [I>2σ (I)] R1 = 0.0387, wR2 = 0.1058 R1 = 0.0396, wR2 = 0.0947
R indices (all data) R1 = 0.0450, wR2 = 0.1100 R1 = 0.0504, wR2 = 0.0982
Largest diff. peak and hole 0.447 and -0.209 e.Å
-3
0.281 and -0.289 e.Å
-3
7. Appendix
149
Table 7.3: Crystal data and structure refinement for E10 and E11
E10 E11
Identification code s1615 a1772
Empirical formula C
38
H
42
Cl N
4
P
2
Rh C
42
H
50
F
6
N
4
O P
3
Rh
Formula weight 755.06 936.68
Temperature 120(2) K 120(2) K
Wavelength 0.71073 Å 0.71073 Å
Crystal system Triclinic Triclinic
Space group P-1 P-1
Unit cell dimensions a = 13.279(2) Å a = 11.032(2) Å
b = 16.172(2) Å b = 19.481(4) Å
c = 18.636(3) Å c = 20.305(4) Å
α = 103.457(4)° α = 81.115(4)°
β = 100.846(4)° β = 76.855(4)°
γ = 99.490(4)° γ = 87.308(4)°
Volume 3730.5(9) Å
3
4198.4(14) Å
3
Z 4 4
Density (calculated) 1.344 Mg/m
3
1.482 Mg/m
3
Absorption coefficient 0.647 mm
-1
0.586 mm
-1
F(000) 1560 1928
Crystal size 0.48 x 0.11 x 0.05 mm
3
0.39 x 0.33 x 0.05 mm
3
Theta range for data collection 1.33 to 27.88° 1.37 to 27.88°
Index ranges -17 ≤ h ≤ 17, -18 ≤ k ≤ 21, -24 ≤ l ≤ 24 -14 ≤ h ≤ 14, -25 ≤ k ≤ 25, -26 ≤ l≤ 25
Reflections collected 32822 36802
Independent reflections 17669 [R(int) = 0.1163] 19836 [R(int) = 0.0567
Completeness to theta = 27.88° 99.2 % 99.0 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.9684 and 0.7466 0.9713 and 0.8036
Refinement method Full-matrix least-squares on F
2
Full-matrix least-squares on F
2
Data / restraints / parameters 17669 / 0 / 833 19836 / 10 / 1048
Goodness-of-fit on F
2
0.836 0.971
Final R indices [I>2σ (I)] R1 = 0.0642, wR2 = 0.1158 R1 = 0.0557, wR2 = 0.1153
R indices (all data) R1 = 0.1376, wR2 = 0.1340 R1 = 0.1045, wR2 = 0.1342
Largest diff. peak and hole 0.930 and -0.925 e.Å
-3
0.925 and -0.579 e.Å
-3
7. Appendix
150
Table 7.4: Crystal data and structure refinement for E12 and E13
E12 E13
Identification code s1614 a1779
Empirical formula C
38
H
42
Cl N
4
P
2
Rh C
46
H
62
F
6
N
4
O
2
P
3
Rh
Formula weight 755.06 1012.82
Temperature 120(2) K 120(2) K
Wavelength 0.71073 Å 0.71073 Å
Crystal system Monoclinic Monoclinic
Space group Cc C2/c
Unit cell dimensions a = 11.8053(17) Å a = 20.601(3) Å
b = 16.513(2) Å b = 11.6546(18) Å
c = 18.900(3) Å c = 21.108(3) Å
α = 90° α = 90°
β = 98.510(3)° β = 108.900(3)°
γ = 90° γ = 90°.
Volume 3643.8(9) Å
3
4794.7(12) Å
3
Z 4 4
Density (calculated) 1.376 Mg/m
3
1.403 Mg/m
3
Absorption coefficient 0.662 mm
-1
0.521 mm
-1
F(000) 1560 2104
Crystal size 0.37 x 0.25 x 0.14 mm
3
0.46 x 0.24 x 0.05 mm
3
Theta range for data collection 2.14 to 27.88° 2.04 to 27.87
Index ranges -15 ≤ h ≤ 15, -21 ≤ k ≤ 21, -24 ≤ l ≤ 24 -27 ≤ h ≤ 27, -15 ≤ k ≤ 15, -27 ≤ l ≤ 27
Reflections collected 15598 20594
Independent reflections 4351 [R(int) = 0.0715] 5734 [R(int) = 0.0485
Completeness to theta = 27.88° 100.0 % 99.9 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.9130 and 0.7918 0.9744 and 0.7957
Refinement method Full-matrix least-squares on F
2
Full-matrix least-squares on F
2
Data / restraints / parameters 4351 / 0 / 209 5734 / 0 / 281
Goodness-of-fit on F2 1.021 1.042
Final R indices [I>2σ (I)] R1 = 0.0373, wR2 = 0.0726 R1 = 0.0358, wR2 = 0.0817
R indices (all data) R1 = 0.0472, wR2 = 0.0755 R1 = 0.0461, wR2 = 0.0863
Largest diff. peak and hole 0.692 and -0.788 e.Å
-3
0.946 and -0.281 e.Å
-3
7. Appendix
151
Table 7.5: Crystal data and structure refinement for E14A
E14A, counter ion [Cl] E14A, counter ion [PF
6
]
Identification code a1751 a1968
Empirical formula C
46
H
61
Cl
5
N
4
O
3
.50 P
2
Rh C
40
H
45
F
6
N
5
O
2
P
3
Rh
Formula weight 1068.09 937.63
Temperature 120(2) K 120(2) K
Wavelength 0.71073 Å 0.71073 Å
Crystal system Triclinic Orthorhombic
Space group P-1 P2
1
2
1
2
1
Unit cell dimensions a = 11.1357(17) Å a = 10.8163(4) Å
b = 12.1567(18) Å b = 10.8672(4) Å
c = 18.395(3) Å c = 34.6160(12) Å
α = 88.808(3)° α = 90°
β = 81.782(3)° β = 90°
γ = 69.035(3)° γ = 90°
Volume 2300.2(6) Å3 4068.9(3) Å3
Z 2 4
Density (calculated) 1.542 Mg/m
3
1.531 Mg/m
3
Absorption coefficient 0.779 mm-1 0.608 mm-1
F(000) 1106 1920
Crystal size 0.37 x 0.21 x 0.18 mm
3
0.44 x 0.27 x 0.19 mm
3
Theta range for data collection 1.79 to 27.88° 1.96 to 27.87°
Index ranges -14 ≤ h ≤ 14, -15 ≤ k ≤ 15, -24≤ l ≤ 24 -13 ≤ h ≤ 14, -14 ≤ k ≤ 14, -45 ≤ l ≤ 45
Reflections collected 20292 38882
Independent reflections 10876 [R(int) = 0.0254 9698[R(int) = 0.0679]
Completeness to theta = 27.88 99.1 % 99.9 %
Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents
Max. and min. transmission 0.8725 and 0.7615 0.8933 and 0.7759
Refinement method Full-matrix least-squares on F
2
Full-matrix least-squares on F
2
Data / restraints / parameters 10876 / 0 / 487 9698/ 0 / 515
Goodness-of-fit on F2 1.059 1.011
Final R indices [I>2σ (I)] R1 = 0.0562, wR2 = 0.1607 R1 = 0.0436, wR2 = 0.0985
R indices (all data) R1 = 0.0686, wR2 = 0.1700 R1 = 0.0505, wR2 = 0.1023
Largest diff. peak and hole 0.971 and -0.765 e.Å-
3
1.195 and -0.596 e.Å
-3
7. Appendix
152
Table 7.6: Crystal data and structure refinement for E15
E15
Identification code a1732
Empirical formula C
39
H
44
Cl
2
F
6
N
4
O
2
P
3
Rh
Formula weight 981.50
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group Pna2(1)
Unit cell dimensions a = 23.394(4) Å
b = 14.722(2) Å
c = 12.2306(19) Å
α = 90°
β = 90°
γ = 90°
Volume 4212.4(11) Å
3
Z 4
Density (calculated) 1.548 Mg/m
3
Absorption coefficient 0.713 mm-1
F(000) 2000
Crystal size 0.48 x 0.17 x 0.15 mm
3
Theta range for data collection 1.63 to 27.88°
Index ranges -30 ≤ h ≤ 30, -18 ≤ k ≤ 19, -16 ≤ l ≤ 15
Reflections collected 35987
Independent reflections 9726 [R(int) = 0.0684]
Completeness to theta = 27.88 100.0 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.9006 and 0.7260
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 9726 / 121 / 514
Goodness-of-fit on F
2
1.051
Final R indices [I>2σ (I)] R1 = 0.0480, wR2 = 0.0872
R indices (all data) R1 = 0.0670, wR2 = 0.0932
Largest diff. peak and hole 0.692 and -0.699 e.Å
-3
7. Appendix
153
Table 7.7: Crystal data and structure refinement for E16
E16
Identification code a1744
Empirical formula C
40
H
46
Cl
4
F
6
N
4
P
3
Rh S
2
Formula weight 1098.55
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions a = 18.487(3) Å
b = 14.982(3) Å
c = 18.296(3) Å
α = 90°
β = 117.209(4)°
γ = 90°
Volume 4506.9(13) Å
3
Z 4
Density (calculated) 1.619 Mg/m
3
Absorption coefficient 0.876 mm
-1
F(000) 2232
Crystal size 0.33 x 0.22 x 0.19 mm
3
Theta range for data collection 1.24 to 27.88°
Index ranges -24 ≤ h ≤ 23, -19 ≤ k ≤ 19, -19 ≤ l ≤ 24
Reflections collected 39010
Independent reflections 10736 [R(int) = 0.0799]
Completeness to theta = 27.88 100.0 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.8512 and 0.7608
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 10736 / 45 / 538
Goodness-of-fit on F
2
0.976
Final R indices [I>2σ (I)] R1 = 0.0588, wR2 = 0.1461
R indices (all data) R1 = 0.0951, wR2 = 0.1595
Largest diff. peak and hole 0.994 and -0.983 e.Å
-3
7. Appendix
154
Table 7.8: Crystal data and structure refinement for E19
Identification code a1832
Empirical formula C
40
H
45
Cl I
4
N
5
P
2
Rh
Formula weight 1303.71
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions a = 12.085(3) Å
b = 30.141(8) Å
c = 13.032(4) Å
α = 90°
β = 108.894(7)°
γ = 90°
Volume 4
Z 1.928 Mg/m
3
Density (calculated) 3.295 mm-1
Absorption coefficient 3.295 mm-1
F(000) 2496
Crystal size 0.18 x 0.10 x 0.04 mm
3
Theta range for data collection 1.78 to 27.88
Index ranges -15 ≤ h ≤ 15, -39 ≤ k ≤ 36, -16 ≤ l ≤ 17
Reflections collected 39508
Independent reflections 10699 [R(int) = 0.2268]
Completeness to theta = 27.88 99.9 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.8795 and 0.5885
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 699 / 0 / 479
Goodness-of-fit on F
2
0.854
Final R indices [I>2σ (I)] R1 = 0.0589, wR2 = 0.0738
R indices (all data) R1 = 0.2000, wR2 = 0.1035
Largest diff. peak and hole 0.981 and -0.930 e.Å
-3
7. Appendix
155
Table 7.9: Crystal data and structure refinement for E20
Identification code a1702
Empirical formula (C
38
H
42
Ir N
4
P
2
)(P F
6
)
Formula weight 953.87
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/n
Unit cell dimensions a = 15.659(2) Å
b = 16.405(2) Å
c = 16.608(2) Å
α = 90°
β = 114.886(3)°
γ = 90°
Volume 3870.0(9) Å
3
Z 4
Density (calculated) 1.637 Mg/m
3
Absorption coefficient 3.636 mm-1
F(000) 1896
Crystal size 0.40 x 0.32 x 0.30 mm
3
Theta range for data collection 1.50 to 27.88°
Index ranges -20 ≤ h ≤ 20, -21 ≤ k ≤ 19, -21≤ l ≤ 21
Reflections collected 33920
Independent reflections 9221 [R(int) = 0.0829]
Completeness to theta = 27.88 99.8 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.4084 and 0.3241
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 9221 / 120 / 469
Goodness-of-fit on F
2
0.844
Final R indices [I>2σ (I)] R1 = 0.0372, wR2 = 0.0556
R indices (all data) R1 = 0.0731, wR2 = 0.0612
Largest diff. peak and hole 0.967 and -0.944 e.Å
-3
7. Appendix
156
Table 7.10: Crystal data and structure refinement for E21
Identification code a1709
Empirical formula C
38
H
44
Cl Ir N
4
P
2
Formula weight 846.36
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions a = 11.235(3) Å
b = 19.771(5) Å
c = 19.027(4) Å
α = 90°
β = 102.568(4)°
γ = 90°
Volume 4125.2(16) Å
3
Z 4
Density (calculated) 1.363 Mg/m
3
Absorption coefficient 3.407 mm-1
F(000) 1696
Crystal size 0.38 x 0.35 x 0.23 mm
3
Theta range for data collection 1.50 to 27.88°
Index ranges -13 ≤ h ≤ 14, -26 ≤ k ≤ 25, -25 ≤ l ≤ 25
Reflections collected 35712
Independent reflections 9831 [R(int) = 0.0602]]
Completeness to theta = 27.88 100.0 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.5079 and 0.3575
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 9831 / 3 / 424
Goodness-of-fit on F
2
0.980
Final R indices [I>2σ (I)] R1 = 0.0397, wR2 = 0.0941
R indices (all data) R1 = 0.0543, wR2 = 0.0989
Largest diff. peak and hole 1.035 and -0.937 e.Å
-3
7. Appendix
157
Table 7.11: Crystal data and structure refinement for E22
Identification code a1871
Empirical formula C
42
H
50
F
6
Ir N
4
O
3
P
3
Formula weight 1057.97
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group P2
1
2
1
2
1
Unit cell dimensions a = 13.817(4) Å
b = 16.678(5) Å
c = 18.534(5) Å
α = 90°
β = 90°
γ = 90°
Volume 4271(2) Å
3
Z 4
Density (calculated) 1.645 Mg/m
3
Absorption coefficient 3.309 mm-1
F(000) 2120
Crystal size 0.47 x 0.12 x 0.11 mm
3
Theta range for data collection 1.64 to 27.88°
Index ranges -18 ≤ h ≤ 18, -21 ≤ k ≤ 21, -24 ≤ l ≤ 24
Reflections collected 37415
Independent reflections 10187 [R(int) = 0.0996]
Completeness to theta = 27.88 99.9 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.7123 and 0.3054
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 10187 / 45 / 528
Goodness-of-fit on F
2
0.977
Final R indices [I>2σ (I)] R1 = 0.0394, wR2 = 0.0738
R indices (all data) R1 = 0.0523, wR2 = 0.0774
Largest diff. peak and hole 1.637 and -0.636 e.Å
-3
7. Appendix
158
Table 7.12: Crystal data and structure refinement for E23
Identification code a1866
Empirical formula C
44
H
53
F
6
Ir N
5
O P
3
S
2
Formula weight 1131.14
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions a = 18.382(2) Å
b = 15.050(2) Å
c = 18.237(2) Å
α = 90°
β = 116.563(3)°
γ = 90°
Volume 4512.7(10) Å
3
Z 4
Density (calculated) 1.665 Mg/m
3
Absorption coefficient 3.224 mm-1
F(000) 2272
Crystal size 0.43 x 0.38 x 0.29 mm
3
Theta range for data collection 1.83 to 27.88°
Index ranges -24 ≤ h ≤ 24, -19 ≤ k ≤ 17, -22 ≤ l ≤ 23
Reflections collected 39199
Independent reflections 10754 [R(int) = 0.0433]
Completeness to theta = 27.88 100.0 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.4549 and 0.3378
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 10754 / 45 / 483
Goodness-of-fit on F
2
1.001
Final R indices [I>2σ (I)] R1 = 0.0342, wR2 = 0.0855
R indices (all data) R1 = 0.0468, wR2 = 0.0898
Largest diff. peak and hole 1.805 and -0.691 e.Å
-3
7. Appendix
159
Table 7.13: Crystal data and structure refinement for E25
Identification code a1825
Empirical formula C
43
H
53
I
2
Ir N
4
O P
2
Formula weight 1149.83
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions a = 14.259(2) Å
b = 13.699(2) Å
c = 22.408(4) Å
α = 90°
β = 96.028(4)°
γ = 90°
Volume 4353.1(13) Å
3
Z 4
Density (calculated) 1.754 Mg/m
3
Absorption coefficient 4.596 mm-1
F(000) 2240
Crystal size 0.25 x 0.20 x 0.17 mm
3
Theta range for data collection 1.44 to 27.88°
Index ranges -18 ≤ h ≤ 18, -17 ≤ k ≤ 18, -29 ≤ l ≤ 27
Reflections collected 38039
Independent reflections 10368 [R(int) = 0.1097]
Completeness to theta = 27.88 99.9 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.5088 and 0.3929
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 10368 / 0 / 475
Goodness-of-fit on F
2
0.919
Final R indices [I>2σ (I)] R1 = 0.0485, wR2 = 0.1015
R indices (all data) R1 = 0.0802, wR2 = 0.1106
Largest diff. peak and hole 1.165 and -0.947 e.Å
-3
7. Appendix
160
Table 7.14: Crystal data and structure refinement for E27
Identification code a1666
Empirical formula C
42
H
48
I
2
N
6
Ni P
2
Formula weight 1011.31
Temperature 153(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/n
Unit cell dimensions a = 11.4419(14) Å
b = 18.767(2) Å
c = 20.573(3) Å
α = 90°
β = 95.940(3)°
γ = 90°
Volume 4394.0(9) Å
3
Z 4
Density (calculated) 1.529 Mg/m
3
Absorption coefficient 1.955 mm
-1
F(000) 2024
Crystal size 0.38 x 0.25 x 0.20 mm
3
Theta range for data collection 1.47 to 27.88°
Index ranges -14 ≤ h ≤ 15, -24 ≤ k ≤ 24, -27 ≤ l ≤ 26
Reflections collected 38434
Independent reflections 10465 [R(int) = 0.0361]
Completeness to theta = 27.88 100.0 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.6958 and 0.5237
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 10465 / 0 / 482
Goodness-of-fit on F
2
1.045
Final R indices [I>2σ (I)] R1 = 0.0328, wR2 = 0.0716
R indices (all data) R1 = 0.0436, wR2 = 0.0753
Largest diff. peak and hole 0.769 and -0.288 e.Å
-3
7. Appendix
161
Table 7.15: Crystal data and structure refinement for E28
Identification code a1807
Empirical formula C
44
H
51
F
12
N
7
P
4
Pd
Formula weight 1136.20
Temperature 120(2) K
Wavelength 0.71073 Å
Crystal system Triclinic
Space group P-1
Unit cell dimensions a = 11.114(2) Å
b = 11.343(2) Å
c = 20.243(4) Å
α = 77.490(4)°
β = 83.580(5)°
γ = 85.301(4)°
Volume 2471.4(8) Å
3
Z 2
Density (calculated) 1.527 Mg/m
3
Absorption coefficient 0.590 mm
-1
F(000) 1156
Crystal size 0.42 x 0.20 x 0.20 mm
3
Theta range for data collection 1.04 to 27.10°
Index ranges -14 ≤ h ≤ 14, -14 ≤ k ≤ 14, -24 ≤ l ≤ 25
Reflections collected 20506
Independent reflections 10803 [R(int) = 0.0318]
Completeness to theta = 27.88 99.0 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.8911 and 0.7896
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 10803 / 30 / 560
Goodness-of-fit on F
2
1.179
Final R indices [I>2σ (I)] R1 = 0.0494, wR2 = 0.1339
R indices (all data) R1 = 0.0600, wR2 = 0.1402
Largest diff. peak and hole 0.947 and -0.960 e.Å
-3
162
Conference contributions:
3/09 GDCh-Jahrestagung 2009 Essen (poster: “Rhodium complexes with NHC-phosphine
hybride ligands and their reactivity towards oxygen”).
