Palladium iminophosphorane complexes: the pre-cursors to the missing link in triphenylphosphane chalcogenide metallacycles
Abstract
Herein we report on the synthesis, characterization and the ensuing chemistry of iminophosphorane palladacycles. Treatment of Ph3P[double bond, length as m-dash]N-(2-OHC6H4), 1, with sodium tetrachloropalladate gives 2 with the ligand as terdentate [C,N,O] allowing for only one μ-Cl ligand bonding the metal centers, resulting in a dinuclear complex. Treatment of 2 with PPh3 gives the mononuclear complex 3, whereas the reaction of 2 with diphosphanes Ph2P(CH2)nPPh2 in 1 : 2 ratio gives mixtures of 4 and 5 (n = 2) and 6 and 7 (n = 3). From them, the mononuclear complexes 4 and 6, and the dinuclear compounds, 5 and 7, were obtained with the parent ligand as bidentate [C,N]. The former two are of zwitterionic nature void of any counterion, with the phosphane ligand in the chelating mode. In a remarkable case of chemical serendipity, a solution of 2 left to stand produced crystals of complex 8: this is the missing link in the series of triphenylphosphane chalcogenide metallacycles. The experiment is repeatable; however, direct metallation of triphenylphosphane oxide was not possible.
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This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the author guidelines. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the ethical guidelines, outlined in our author and reviewer resource centre, still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. Accepted Manuscript rsc.li/dalton Dalton Transactions An international journal of inorganic chemistry www.rsc.org/dalton ISSN 1477-9226 PAPER Joseph T. Hupp, Omar K. Farha et al. Effi cient extraction of sulfate from water using a Zr-metal–organic framework Volume 45 Number 1 7 January 2016 Pages 1–398 Dalton Transactions An international journal of inorganic chemistry
DaltonTransactions ARTICLE Thisjournalis©TheRoyalSocietyofChemistry20xxJ.Name.,2013,00,1‒3|1 Pleasedonotadjustmargins Pleasedonotadjustmargins a. DepartamentodeQuímicaInorgánica,UniversidadedeSantiagodeCompostela, AvenidadasCienciass/n,15782SantiagodeCompostela,Spain. b. DepartmentofChemistry,TheUniversityofSheffield,SheffieldS37HF,UK †Footnotesrelangtothetleand/orauthorsshouldappearhere. ElectronicSupplementaryInformation(ESI)available:[X‒raytables.CCDC1855709 ( 2 ), 1855708 ( 3 ), 1855711 ( 4 ), 1855710 ( 7 ) and 1855707 ( 8 ).]. See DOI:10.1039/x0xx00000x Received00thJanuary20xx, Accepted00thJanuary20xx DOI:10.1039/x0xx00000x www.rsc.org/ PalladiumIminophosphoraneComplexes:thePre‒cursorstothe MissingLinkinTriphenylphosphaneChalcogenideMetallacycles Adolfo Fernández‒Figueiras, a Fátima Lucio‒Martínez, a PaulaMunín‒Cruz, a PaulaPolo‒Ces, a FranciscoReigosa, a HarryAdams, b M.TeresaPereira* ,a andJoséM.Vila* ,a Herein we report on the synthesis, characterization and the ensuing chemistry of iminophosphorane palladacycles. Treatment of Ph 3 P=N‒(2‒OHC 6 H 4 ), 1, with sodium tetrachloropalladate gives 2 with the ligand as terdentate [C,N,O] allowingforonlyone ‒Clligandbondingthemetalcenters,resultinginadinuclearcomplex.Treatmentof2withPPh 3 givesthemononuclearcomplex3,whereasreactionof2withdiphosphanesPh 2 P(CH 2 ) n PPh 2 in1:2ratiogivesmixturesof4, 5(n=2)and6,7(n=3).Fromthemthemononuclearcomplexes4,6,andthedinuclearcompounds,5,7,wereobtained withtheparentligandasbidentate[C,N].Theformertwoareofzwitterionicnaturevoidofanycouterion,withthe phosphane ligand in the chelating mode. In a remarkable case of chemical serendipity a solution of 2 left to stand producedcrystalsofcomplex8:thisisthemissinglinkintheseriesoftriphenylphosphanechalcogenidemetallacycles.The experimentisrepeatable,however,directmetallationoftriphenylphosphaneoxidewasnotpossible. INTRODUCTION Palladacyclesareanamplystudiedbranchoforganometallics due,toalargeextent,totheirquiteabundantapplications:as pre‒catalysts in cross‒coupling reactions, such as Suzuki‒Miyaura, 1‒3 Mizoroki‒Heck, 4,5 Negishi 6 orSonogashira; 7 asratherpowerfulanticanceragents, 8,9 attimescomparable to cis‒platin; 10 likewise, some exhibit very interesting luminescent properties 11 or, alternatively, they behave as metallomesogens. 12 Aparticularcaseofpalladacyclesarethosethatstemfromthe iminophosphoranes R 3 P=NR. These are organic substrates whichthemselvesexhibitawiderangeofrelevantapplications inclusive of their use as superbases, 13 as synthetic intermediates,inparticularfortheAza‒Wittigreaction, 14 oras building blocks for P–N back‒bone polymers. 15 Thehighly polarizedP=Ndoublebond,bearingapartialnegativecharge onthenitrogenatom,showsastrongσ‒donorbehaviorwith minor ‒acceptor properties enabling them as ligands which readily undergo the cyclopalladation reaction. 16‒20 The biologicalapplicationsandanticancerpropertiesofPd(II),Pt(II) and Au(III) cyclometallated iminophosphoranes, and of the analogouscoordinationspecies,havebeenstudiedduetothe non‒toxiccharacteroftheligands. 21‒23 Afurtheradvantageis thatthephosphorusatominthePR 3 fragmentcanbeusedas a“spectroscopicmarker”tostudytheinvitrostabilityandthe oxidation state by 31 P‒{ 1 H} NMR spectroscopy. 24 Moreover, theirluminescentpropertiesmakethempotentiallyusefulas molecular probes in theragnosis, 25 andalsotheyserveas pre‒catalystsinnumerouscatalyticprocesses. 26‐32 Following our research on palladacycles more recently we have come upon new findings when employing terdentate [C,N,S] and tetradentate [C,N:C,N] ligands, namely the auto‒catalysis in the Suzuki‒Miyaura reaction, 3 the coordinationofthebulkypotassiumcationbythesmallcrown etherrings, 33 andthechelate‒to‒bridgingshiftindiphosphane palladacycles, 34 all of which have contributed to expand the frontiers of this ever growing field. Then, we became interestedinstudyingrelatedsystemswithterdentate[C,N,O] ligandsalbeitexchangingtheC=NfortheP=Ndoublebond,in viewoftheinterestingpropertiesoftheR 3 P=NRligands.The immersioninthechemistryofiminophosphoraneswastoseek new trends in their reactivity and/or structural features, in order to further extend the scope of this chemistry. The ensuingresultsarepresentedherein. To address this study we have used phosphanes as ancillary ligands, which readily react with the synthesized terdentate [C,N,O] iminophosphorane palladacycle in a bridging and chelating fashion. Herein we give an account of the novel species encountered, namely two zwitterionic mononuclear complexeswithchelatingdiphosphane.Furthermore,wealso describearemarkablecaseofchemicalserendipitythat provided suitable crystals which gave rise to the molecular structure of the first cyclopalladated triphenylphosphane oxide, putting an end to the incomplete series of the triphenylphosphane chalcogenide metallacycles. Attempts to Page 1 of 7 Dalton Transactions Dalton Transactions Accepted Manuscript
ARTICLEJournalName 2|J.Name.,2012,00,1‒3 Thisjournalis©TheRoyalSocietyofChemistry20xx Pleasedonotadjustmargins Pleasedonotadjustmargins makethelattercompoundbydirectpalladationofthe phosphane oxide were to no avail, however the preparation couldberepeatedbywayofthisnewlyfoundexperiment. RESULTSANDDISCUSSION For the convenience of the reader the compounds and reactions are shown in Schemes 1 and 2. The compounds described in this paper were characterised by elemental analysis (C, H, N), IR and 1 H and 31 P‒{ 1 H} spectroscopy (see experimental section) and, in part, X‒ray single crystal diffraction. Ligand 1 wasreadilysynthesizedbytheStaudingerreaction 35 from triphenylphosphane and 2‒hydroxyphenyl azide. As opposedtotheligandsdescribedbyUrriolabeitiaetal., 18 the sp 2 carbon atoms available for metallation are on the phosphorusphenylrings,givingtheendotypespecies.Thus, treatmentof 1 withNa 2 PdCl 4 andNaAcOinrefluxingmethanol gavethedinuclearpalladacycle 2 asanair‒stableyellowsolid, whichwasfullycharacterized,incontrasttothetetranuclear species described by us when using the related terdentate [C,N,O]withC=Ndoublebonds. 36 IntheIRspectrumofthe complex the (P=N) stretching band (see experimental section)appearedatlowerfrequencythanthecorresponding one in the free ligand in accordance with nitrogen coordination to metal center. In the 1 H NMR spectrum four additional multiplets appear upon metallation of one of the phosphorus phenyl rings. The signal for the phosphorus nucleusinthe 31 P‒{ 1 H}NMRspectrumwasdownfieldshifted ca.38ppmafterpalladium‒nitrogencoordination.Complex 2 consists of two cyclopalladated fragments bonded through a single bridging chloride ligand. This situation is relatively unusualinpalladacyclechemistrywheremoreoftenthannot the ‒Cl ligand is accompanied by a bidentate ligand or by anotherbridgingchloride.Yethoweverinfrequent,afew exampleshavebeenreportedintheliterature.Theseare limited to either palladacycles or to other cyclometallated compoundsofcationic 37,38 oranionic 39 nature,whichneedthe corresponding counterion for electrical neutrality. Because palladation proceeds with deprotonation of the OH groups, andintheabsenceofanycounterion,wetentativelysuggest the extra negative charge is compensated by a H shared betweenthetwooxygenatomsthroughhydrogenbonding,to produceacharge‒neutralpalladiumcompound.Furtherdata regardingthisissuearediscussedbelowinthedescriptionof themolecularstructurefor 2 . Suitable crystals of 2 were grown by slowly evaporating an acetone solution of the compound. Crystal data are given in theSupportingInformation.TheORTEPillustrationofcomplex 2 isshowninFigure1.Thecrystalsconsistofdiscrete molecules separated by normal van der Waals distances, bearingtwoslightlydistortedsquare‒planarpalladacycle Scheme1. Reactionsequenceleadingtothesynthesisofthe iminophosphoranepalladacycles. Figure 1. Thermalellipsoidsplotfor 2 shownat50% probability level. Hydrogen atoms have been omitted for clarity,exceptH‒O(2).Selectedbonddistances(Å)andangles (deg)for 2 :Pd(1)‒C(25)1.960(3),Pd(1)‒N(1)2.010(3),Pd(1)‒O(1) 2.116(2),Pd(1)‒Cl(1)2.3373(9),Pd(2)‒C(26)1.963(3),Pd(2)‒N(2) 1.993(3), Pd(2)‒O(2) 2.123(2), Pd(2)‒Cl(1) 2.3421(9), P(1)‒N(1) 1.619(3), P(2)‒N(2) 1.611(3), C(25)‒Pd(1)‒N(1) 88.71(14), C(25)‒Pd(1)‒(O1) 169.85(12), N(1)‒Pd(1)‒O(1) 81.26(11), C(25)‒Pd(1)‒Cl(1) 95.12(11), N(1)‒Pd(1)‒Cl(1) 176.17(9), O(1)‒Pd(1)‒Cl(1) 94.91(7), C(26)‒Pd(2)‒N(2) 88.14(14), C(26)‒Pd(2)‒O(2) 168.60(13), N(2)‒Pd(2)‒O(2) 81.36(11), C(26)‒Pd(2)‒Cl(1) 95.81(12), N(2)‒Pd(2)‒Cl(1) 174.31(9), O(2)‒Pd(2)‒Cl(1)94.98(7),Pd(1)‒Cl(1)‒Pd(2)93.61(3). Page 2 of 7Dalton Transactions Dalton Transactions Accepted Manuscript
JournalName ARTICLE Thisjournalis©TheRoyalSocietyofChemistry20xxJ.Name.,2013,00,1‒3|3 Pleasedonotadjustmargins Pleasedonotadjustmargins Figure2. Tautomericequilibriumfor 2 . ___________________________________________________ subunits joined by a single chloride bridging ligand with a Pd‒Cl‒Pd bond angle of 93.61˚. Each palladium atom is bonded to the ligand through a P=N nitrogen atom, an aryl carbonatomandaphenoxy oxygenatom.Thebondlengths andanglesatpalladiumarefairlythesameforbothmetallated units. We propose a tautomeric structure where the two oxygenatomsexchangeahydrogenatom,necessaryto maintain neutrality, as is depicted in Figure 2. Due to the disorderofthecenterofthemolecule,alowthetadifference Fourierwasusedtoshowwherethepointofelectrondensity was.ThisshowedtheelectrondensitytobeclosertotheO(2) atom.Intramolecularhydrogenbondingisinagreementwith theshortO(1)‒O(2)distanceof2.406Å;thehydrogenatom has been calculated onto the O(2) atom with a distance of 0.952ÅandaH‒O(1)distanceof1.499Å;theO(1)∙∙∙H‒O(2) angleis157.35°.ThisfeaturecouldaccountforthePd‒Obond lengths in compound 2 , Pd(1)‒O(1) 2.116(2) and Pd(2)‒O(2) 2.123(2), as opposed to their analogues in compounds 3 , Pd(1)‒O(1) 2.0625(18), 7 , Pd(1)‒O(1) 2.066(2), and 8 , Pd(1)‒O(1)2.053(3).Recently,inarathersimilarcaseT.W.Lee et al. have described an iridium(III) compound where the O‒H∙∙∙Ohydrogenbondcontributestothestabilityofthe complex. 40 Therefore,theuniquefeatureofadinuclearsingle‐ bridgedchloridepalladacyclestructureismadepossiblebythe bridging O‒H‒O unit, whose asymmetry precludes the consideration of two totally equivalent palladacycle centers. Furthermore,DFTcalculationswereperformedforcompound 2 ,whichshowedthepresenceofastrongintramolecular hydrogenbondbetweentheO(2)‐HhydrogenandtheO(1) atom(seeSI). Treatment of 2 with triphenylphosphane gave the neutral mononuclearcompound 3 asayellowair‒stablesolid,which wasfullycharacterized,itsreactivitypatternresemblesthatof therelateddinuclear 41 ortetranuclear 42 palladacycles. TheIRspectrumshowedtheshiftofthe (P=N)stretchfrom 1313 cm ‒1 to 1280 cm ‒1 . Two doublets in the 31 P‒{ 1 H} NMR spectrum were assigned to the two distinct 31 P nuclei at δ32.38(PPh 3 )andδ37.91(P=N)with 3 J(PP)3.9Hz. Crystals of compound 3 were obtained by slow evaporation from an acetone solution. Crystal data are given in the Supporting Information. The ORTEP view of 3 isshownin Figure 3. The compound crystalizes with an acetone solvent molecule (omitted for clarity reasons). The structure is quite similartoanyoneofthepalladatedsubunitswhichcomprise thestructureofcompound 2 ,albeitwithatriphenylphosphane ligand bonded to palladium atom in place of the bridging chloride.Allbondlengthsandanglesarewithintheexpected values,withallowanceforlengtheningofthePd(1)‒N(1)bond, 2.053(2)Å,ascomparedtocomplex 2 ,1.993(3)and2.010(3) Å,duetothestrongertransinfluenceofthephosphaneligand vs.thebridgingchloride. Figure 3. Thermalellipsoidsplotfor 3 shownat50% probability level. Hydrogen atoms and an acetone solvent molecule have been omitted for clarity. Selected bond distances (Å) and angles (deg) for 3 : Pd(1)‒C(25) 2.013(3), Pd(1)‒N(1) 2.052(2), Pd(1)‒O(1) 2.0625(18), Pd(1)‒P(2) 2.2334(7), P(1)‒N(1) 1.617(2), C(25)‒Pd(1)‒N(1) 88.02(10), C(25)‒Pd(1)‒O(1) 169.23(9), N(1)‒Pd(1)‒O(1) 81.42(8), C(25)‒Pd(1)‒P(2) 92.02(8), N(1)‒Pd(1)‒P(2) 178.22(7), O(1)‒Pd(1)‒P(2)98.46(6). ___________________________________________________ Thereactionof 2 withthediphosphanesPh 2 P(CH 2 ) n PPh 2 (n=2, 3) in 1:2 molar ratio in acetone at room temperature gave mixturesofcompounds, 4 , 5 (n=2)and 6 , 7 (n=3).Inboth casestheycouldbesatisfactorilyseparatedbycentrifugating the corresponding reaction mixture to give solutions containing the mononuclear complexes 4 , 6 , with chelating diphosphane,andsolidscomprisingthedinuclearcompounds, 5 , 7 , with the bridging diphosphane (Scheme 1). Theformer two,ofzwitterionicnature,areinnovativeinthechemistryof iminophosphoranepalladacycles. The final products were air‒stable solids which were fully characterized. The IR spectra showed the downfield shift of the (P=N)stretchinallcasesappearingca.1280cm ‒1 .The 1 H NMR spectra of 5 and 7 showedonlyonesetofsignalsin accordance with the symmetrical nature of the complexes. Likewise,inthe 31 P‒{ 1 H}NMRspectratwosingletresonances wereassignedtothetwosetsofequivalentphosphorusnuclei, P=N and PPh 2 . Alternatively, the 31 P‒{ 1 H}NMRspectrafor complexes 4 and 6 showeddoubletsanddoubletsofdoublets signals,asappropriate,forthethreeinequivalent 31 P nuclei (see experimental); with (PPh 2 trans‒C) at higher field than (PPh 2 trans‒N)inagreementwiththegreatertransinfluence ofthephenylcarbonatom.Figures4and5showtheORTEP viewofthemoleculesof 4 and 7 ,respectively(seeSI). The molecular structure of 4 consists of discrete molecules withthepalladiumatombondedtotwochelatingligands:an iminophosphorane‐[C,N]andabis(diphenylphosphino)ethane‐ [P,P] in a slightly distorted square‒planar conformation. The bond distances are within the expectedvalues with differing Page 3 of 7 Dalton Transactions Dalton Transactions Accepted Manuscript
ARTICLEJournalName 4|J.Name.,2012,00,1‒3 Thisjournalis©TheRoyalSocietyofChemistry20xx Pleasedonotadjustmargins Pleasedonotadjustmargins Pd‒Plengthsduetothehighertransinfluenceofthe metallated phenyl carbon atom as opposed to the nitrogen atom.Thepalladium‒oxygendistanceof4.612Åprecludesany Figure 4. Thermal ellipsoids plot for 4 shown at 40% probability level. Hydrogen atoms have been omitted for clarity.Selectedbonddistances(Å)andangles(deg)for 4 : Pd(1)‒N(1) 2.102(2), Pd(1)‒P(2) 2.2348(8), P(1)‒N(1) 1.602(2), Pd(1)‒P(3)2.3548(8), C(25)‒Pd(1)‒N(1) 83.74(11), C(25)‒Pd(1)‒P(3) 176.62(8), N(1)‒Pd(1)‒P(3) 98.54(7), C(25)‒Pd(1)‒P(2) 92.89(8), N(1)‒Pd(1)‒P(2) 173.02(7), P(2)‒Pd(1)‒P(3)84.58(3). Figure5. Thermalellipsoidsplotfor 7 shownataredrawnat 50% probability level. Hydrogen atoms and a chloroform solventmoleculehavebeenomittedforclarity.Selectedbond distances (Å) and angles (deg) for 7 : Pd(1)‒C(25) 2.006(3), Pd(1)‒N(1)2.032(3),Pd(1)‒O(1)2.066(2),P(1)‒N(1)1.602(3), Pd(1)‒P(2) 2.2384(8), C(25)‒Pd(1)‒N(1) 87.55(11), C(25)‒Pd(1)‒O(1) 168.60(11), N(1)‒Pd(1)‒O(1) 81.63(9), C(25)‒Pd(1)‒P(2) 98.88(9), N(1)‒Pd(1)‒P(2) 173.38(7), O(1)‒Pd(1)‒P(2)91.85(7). ___________________________________________________ interaction between them. Likewise, no interaction between theP(1)andO(2),whichare3.020Åapart,wasobserved.As for complex 7 it may be envisaged as formed by two approximately square‒planar palladium centers bonded throughabis(diphenylphosphino)propaneligand. For compound 7 the X‒ray diffraction analysis shows a dinuclear molecular structure whereby the two palladated unitsarelinkedbyabridgingbidentatePh 2 P(CH 2 ) 3 PPh 2 ligand, Scheme2. Decompositionreactionof 2 togive 8 . ___________________________________________________ withthemetalcoordinationplanes[Pd,C,N,O,P]atanangleof 66.15˚. The structure is crystallographically centrosymmetric withtheinversioncentersituatedattheC(39)carbonbetween the two phosphorus atoms. The bond lengths and angles at palladiumaresimilartothosedepictedforthestructuresof 3 and 4 (videsupra);alongwiththestructuresfor 2 and 3 the palladiumcenterisbondedtofourdifferentatomsinaslightly distorted square‒planar environment; also, the Pd‒O bond lengthisshorterthanitscounterpartincomplex 2 (videsupra). RecentlyBhargavaetal. 43 havereportedthecyclometallation oftriphenylphosphanesulfideandselenidePh 3 P=X(X=S,Se) bytreatmentofthetinderivatives2‒Me 3 SnC 6 H 4 P(X)Ph 2 (X=S, Se) with [PdCl 2 (COD)], that proceeds with formation of the poorly soluble chloro‒bridged dimers [Pd 2 (μ‒Cl) 2 {κ 2 ‒2‒C 6 H 4 P(X)Ph 2 } 2 ] that contain the syn‒ and anti‒isomers; albeit no crystal structures were reported. However, the analogous chloro‒bridged palladium complex withPh 3 P=Oyetremainedunknown.Nextwegiveanaccount of this finding that completes the missing link in the chalcogenide series of complexes [Pd 2 (μ‒Cl) 2 {κ 2 ‒2‒C 6 H 4 P(X)Ph 2 } 2 ](X=O,S,Se).Whena chloroform solution of compound 2 waslefttostandin contact with air at room temperature prior to its use as startingmaterialformakingthecompoundsdescribedabove we observed the formation of yellow crystals, which were filtered off, conveniently dried and set aside. The correspondingX‒raycrystallographicanalysisprovedthemto becompound 8 (videinfra),whichweshouldliketocoinasa Page 4 of 7Dalton Transactions Dalton Transactions Accepted Manuscript
JournalName ARTICLE Thisjournalis©TheRoyalSocietyofChemistry20xxJ.Name.,2013,00,1‒3|5 Pleasedonotadjustmargins Pleasedonotadjustmargins Figure 6. Thermalellipsoidsplotfor 8 shownat40% probability level. Hydrogen atoms and a second molecule of the compound have been omitted for clarity. Selected bond distances (Å) and angles (deg) for 8 : Pd(1)‒C(1) 1.960(4), Pd(1)‒Cl(1) 2.3008(14), Pd(1)‒O(1) 2.053(3), Pd(1)‒Cl(1#) 2.4383(14), C(1)‒Pd(1)‒O(1) 86.79(16), C(1)‒Pd(1)‒Cl(1) 94.58(14), O(1)‒Pd(1)‒Cl(1) 178.61(9), C(1)‒Pd(1)‒Cl(1#) 176.40(14), O(1)‒Pd(1)‒Cl(1#) 92.26(9), Cl(1)‒Pd(1)‒Cl(1#) 86.40(5). ___________________________________________________ rather pleasant case of chemical serendipity. 44 Regrettably attempts to make compound 8 directly from triphenylphosphane oxide by standard ortho‒palladation procedureshavebeenunsuccessfulsofar.Then,oursynthetic strategy consisted in several attempts at again leaving a solution of 2 tostandatroomtemperatureexposedtoair, whereupon a precipitate was formed, void of any crystals in thiscase,whichwasfilteredoffanddriedtogiveayellow powder.Thisprocedurecouldberepeatedandforthe corresponding powdery solid the spectroscopic evidence seemedtoindicatethatcompound 8 hadbeenformed.Thus, the 31 P‒{ 1 H}NMRspectrumshowedasingletresonanceat 35.7ppmforthetwoequivalent 31 Pnuclei.TheIR spectrum showedabandca.1162cm ‒1 assignedtothe (P=O)stretch, andbandsat310and284cm ‒1 correspondingtothe (Pd‒Cl) stretches. Although it is not clear how 8 wasformedwe suggest that hydrolysis of the P=N double bond 45 produces o‒aminophenolandtheP=Obond,whichbindstothemetal through the oxygen atom, with the extra chloride ligand stemmingasaresidualimpurityfromtheinitialmetalreagent (Scheme 2). Furthermore, the hydrolysis of compound 2 in solutionwasalsoattempted.Thus,anNMRtubecontaininga solution of 2 in wet chloroform was monitored by 31 P‒{ 1 H} NMR.After72h.themajorproductshowedaresonanceatca. 35 ppm assigned to the presence of compound 8 .Itseems likely that triphenylphosphine oxide does not allow metallation of the aryl ring, whereas starting form 2 the palladium‒carbon bond is already formed. In any case, fine tuningtheprocessisadamantinordertogiveaclearpicture ofthepreparationandthisstudyispresentlyunderway. Crystaldatafor 8 aregivenintheSupportingInformationand the ORTEP illustration is shown in Figure 6 (together with selected bond lengths and angles). Each palladium atom, adopting a slightly distorted square‒planar disposition, is bonded by a chelating C 6 H 4 P(O)groupandtwobridging chloride ligands. The structure is of a centrosymmetric dinuclear palladacycle with two asymmetrically bridging chlorideatoms.Thephenylcarbonatomandtheoxygenatom are transtothedi‒μ‒chloride unit so that these two palladatedligandsareinan overallantiparallelarrangement. Theasymmetryresultsfromthedifferingtransinfluenceofthe C‒phenyl and oxygen atoms. The Pd 2 Cl 2 unit produces an intramolecularpalladium‒palladiumdistanceof3.456Åwhich islongerthanincomplex 2 ,3.411Å,inspitethatin 8 thetwo palladium atoms are held together by two bridging ligands, andexcludesthepossibilityofametal‒metalbond. EXPERIMENTALSECTION X‒ray structure determination. Crystallographic data of the structuresdescribed inthisworkwerecollectedonaBruker KappaAPEXIIdiffractometer(MoKαradiation,λ=0.71073Å) equipped with a graphite monochromator by the method of the ωandφscansat293K,integratedandcorrectedfor absorption and solved and refined using routine techniques. All non‒hydrogen atoms were refined anisotropically; hydrogen atoms were included in calculated positions and refinedinridingmode. General Procedures. Solvents were used without previous purification. Chemicals were reagent grade. The phosphanes PPh 3 ,PPh 2 (CH 2 ) 2 PPh 2 (dppe)andPPh 2 (CH 2 ) 3 PPh 2 (dppp)were purchased from Sigma‒Aldrich. Elemental analyses were carried out on a THERMO FINNIGAN, model FLASH 1112. IR spectrawererecordedwithaJASCOFT/IR‒4600spectrometer equippedwithanATR,modelATR‒PROONE.TheNMRspectra were recorded on Varian INOVA 400 or Bruker DPX‒250 spectrometers. Synthesis of 1 . 2‒hydroxyphenyl azide (300 mg, 2.22 mmol) wasaddedtoasolutionoftriphenylphosphane(582mg,2.22 mmol)indiethylether(20cm 3 ), the resulting mixture was stirred at room temperature for 18 hours. Compound 1 precipitatedfromthereactionmixtureasabrownpowderand wasisolatedbycentrifugationanddriedundervacuum.Yield 534mg,65%.C 24 H 20 NOP(369.40):calcd:C78.0,H5.5,N3.8; found:C77.9,H5.7,N3.8.IR: (P=N):1318cm ‒1 . 1 HNMR(400 MHz,CDCl 3 ,δ)6.45(m,2H,H‒Ar)6.65(m,1H,H‒Ar)6.89(m, 1H,H‒Ar)7.47(m,6H,m‒PPh 3 )7.55(m,3H,p‒PPh 3 )7.72(m, 6H, o‒PPh 3 ). 13 C‐{ 1 H} NMR (400 MHz, acetone‒d 6 ,δ) 150.6 ( C‒O)144.4(C‒N)139.7 ( C‒PC 6 H 5 )132.0,131.9(C o C 6 H 5 P)128.7, 128.5, 128.3 (C m , C p C 6 H 5 P) 119.3, 118.5 (C m C 6 H 4 N)118.2(C p C 6 H 4 N)115.5(C o C 6 H 4 N). 31 P‒{ 1 H} NMR(400MHz,CDCl 3 ,δ)4.83 (s,P).Synthesisof 2 .ApressuretubecontainingNa 2 PdCl 4 (150 mg,0.51mmol), 1 (182mg,0.51mmol)andmethanol(10cm 3 ) wassealedundernitrogen.Theresultingmixturewasheated at80˚Candafter4hoursNaAcO(42mg,0.51mmol)was addedtothereactionmixtureandstirredat80˚Cfor1hour. Compound 2 precipitatedfromthesolutionandwasisolated bycentrifugation,andthenwasdissolvedindichloromethane and filtered through silica to remove the black palladium formed. The solvent was removed under vacuum to give a yellow oil, which was recrystallized from Page 5 of 7 Dalton Transactions Dalton Transactions Accepted Manuscript
ARTICLEJournalName 6|J.Name.,2012,00,1‒3 Thisjournalis©TheRoyalSocietyofChemistry20xx Pleasedonotadjustmargins Pleasedonotadjustmargins dichloromethane/hexanetogivethedesiredproductasa yellowsolid.Yield167mg,67%.C 48 H 37 ClN 2 O 2 P 2 Pd 2 (984.06): calcd: C 58.6, H 3.8, N 2.9; found: C 58.5, H 3.9, N 2.9. IR (OH): 3375 cm ‒1 (P=N): 1313 cm ‒1 . 1 H NMR (400 MHz, acetone‒d 6 ,δ)6.31(m,1H,H‒Ar)6.53(m,2H,H‒Ar)6.75(m, 1H,H‒Ar)7.01(m,2H,H‒Ar)7.17(m,1H,H‒Ar)7.52(m,1H, H‒Ar) 7.65 (m, 4H, m‒PPh 2 )7.75(m,2H,p‒PPh 2 ) 7.97 (dd, 4 J(HP)2.6, 3 J(HH)7.6Hz,4H,o‒PPh 2 ). 13 C‐{ 1 H}NMR(400MHz, acetone‒d 6 ,δ) 156.9 ( C‒O) 149.8 (C‒Pd) 144.4 (C‒N) 138.7 ( C‒PC6H4)133.2(CoC6H5P)129.1,127.3,126.5(Cm,CpC6H5P)120.0, 119.9(CmC6H4N)118.6(CpC6H4N)117.8(CoC6H4N).31P‒{1H} NMR (400MHz,acetone‒d 6 ,δ)42.61(s,P). Synthesisof 3 .Triphenylphosphane(22mg,0.08mmol), 2 (41 mg,0.04mmol)andacetone(15cm 3 )wereaddedtoaflask andtheresultingmixturewasstirredfor18hours;thesolvent wasevaporatedtogiveayellowoil,whichwasrecrystallized fromdichloromethane/hexanetogivethedesiredproductasa yellowsolid.Yield55.4mg,89%.C 42 H 33 NOP 2 Pd (736.09): calcd: C 68.5, H 4.5, N 1.9; found: C 68.3, H 4.6, N 1.8. IR: (P=N):1280cm ‒1 . 1 HNMR(400MHz,acetone‒d 6 ,δ)5.93(m, 1H,H‒Ar)6.15(m,1H,H‒Ar)6.35(m,2H,H‒Ar)6.60(m,2H, H‒Ar)6.82(m,1H,H‒Ar)6.95(dd, 3 J(HP)12.2, 3 J(HH)7.2Hz, 1H,H‒Ar)7.44(m,6H,m‒PPh 3 )7.51(m,3H,p‒PPh 3 )7.66(m, 4H,m‒PPh 2 )7.74(m,2H,p‒PPh 2 )7.79(m,6H,o‒PPh 3 )7.97 (m,4H,o‒PPh 2 ). 13 C‐{ 1 H}NMR(400MHz,acetone‒d 6 ,δ)156.6 ( C‒O)147.3(C‒Pd)135.3 ( C‒PC6H4)133.2,133.0,132.7,131.1(Co PhP) 129.0, 128.8, 128.0, 127.8 (Cm, CpC 6H5P) 120.8 (CmC 6H4N) 117.9 (CpC 6H4N) 117.6 (CoC 6H4N). 31P‒{1H} NMR(400MHz, acetone‒d 6 ,δ)32.38(d, 3 J(PP)3.9Hz,PPh 3 )37.91(d, 3 J(PP)3.9 Hz,P=N). Synthesis of 4 and 5 . Bis(diphenylphosphino)ethane (34 mg, 0.08 mmol), 2 (41 mg, 0.04 mmol) were added in acetone (15cm 3 ) and the resulting mixture was stirred for 18 hours. Compound 5 precipitated from the mixture as a yellow powder, was isolated by centrifugation and washed with acetone(10cm 3 ).Evaporationofthesolventgaveayellowoil, whichwasrecrystallizedfromdichloromethane/hexanetogive 4 asayellowsolid. ( 4 )Yield:33mg,47%.C 50 H 42 NOP 3 Pd(872.22);calcd:C68.9,H 4.9,N1.6;found:C68.7,H5.0,N1.5.IR: (P=N):1279cm ‒1 . 1 HNMR(400MHz,CD 2 Cl 2 ,δ)6.07(m,1H,H‒Ar)6.29(d, 3 J(HH) 7.9 Hz, H‒Ar) 6.40 (m, 2H, H‒Ar) 6.85 (td, 3 J(HH) 7.5 Hz, 4 J(HP)1.8Hz,H‒Ar)6.93(m,2H)7.11(m,1H,H‒Ar)7.25(m, 4H,m‒Ar)7.38‒7.65(m,18H,H‒Ar)7.72(dd, 3 J(HP)11.9Hz, 3 J(HH)7.4Hz,4H,o‒Ar)7.86(dd, 3 J(HP)12.1Hz, 3 J(HH)7.5Hz, 2H, o‒Ar) 8.13 (m, 2H, o‒Ar). 13 C‐{ 1 H} NMR (400 MHz, acetone‒d 6 ,δ) 151.8 ( C‒O)145.2(C‒N)139.2 ( C‒PC6H4) 134.2, 133.5,131.8(CoPhP)129.0,128.5,128.3(Cm,CpC6H5P)119.7(Cm C6H4N) 118.8 (CpC 6H4N) 115.7 (CoC 6H4N) 31.6 (CH2) 28.9 (CH2). 31P‒{1H} NMR(400MHz,CD 2 Cl 2 ,δ)43.45(dd, 2 J(PP)27.7Hz, 3 J(PP) 15.5 Hz, PPh 2 trans‒C) 48.44 (d, 3 J(PP) 15.5 Hz, P=N) 59.56(d, 2 J(PP)27.7Hz,PPh 2 trans‒N). ( 5 ) Yield: 23 mg, 41 %. C 74 H 60 N 2 O 2 P 4 Pd 2 (1346.02): calcd: C 66.0,H4.5,N2.1;found:C65.8,H4.6,N2.2.IR: (P=N):1277 cm ‒1 . 1 HNMR(400MHz,CDCl 3 ,δ)6.41(m,4H,H‒Ar)6.53(m, 2H,H‒Ar)6.63(m,2H,H‒Ar)6.73(m,2H,H‒Ar)6.91(m,4H, H‒Ar)7.35‒7.61(m,24H,H‒PPh 2 )7.73‒7.89(m,18H,H‒Ar). 13 C‐{ 1 H}NMR(400MHz,acetone‒d 6 ,δ) 155.7 (C‒O) 147.2 (C‒Pd) 144.9 (C‒N) 138.9 (C‒PC 6 H 4 ) 134.0, 133.7 (C o PhP) 128.8,128.4,127.9(C m ,C p C 6 H 5 P)118.1(C m C 6 H 4 N)117.8(C p C 6 H 4 N)115.4(C o C 6 H 4 N)29.1(CH 2 ). 31 P‒{ 1 H}NMR(400MHz, CDCl 3 ,δ)34.22(s,PPh 2 )36.00(s,P=N). Compounds 6 and 7 were obtained following a similar procedure as for compounds 4 and 5 using Bis(diphenylphosphino)propaneinstead. ( 6 ):Yellowsolid.Yield:33.2mg,45%.C 51 H 44 NOP 3 Pd(886.24); calcd:C69.1,H4.6,N1.6;found:C68.9,H4.8,N1.4.IR: (P=N):1279cm ‒1 . 1 HNMR(400MHz,acetone‒d 6 ,δ)6.37(m, 1H,H‒Ar)6.61(m,1H,H‒Ar)6.79(m,2H,H‒Ar)7.04(m,2H, H‒Ar)7.27‒7.25(m,26H,H‒Ar)7.66(m,2H,H‒Ar) 7.89 (m, 4H,o‒Ar). 13 C‐{ 1 H}NMR(400MHz,acetone‒d 6 ,δ)153.8(C‒O) 147.3(C‒Pd)145.3(C‒N)139.9(C‒PC 6 H 4 )133.3,133.0,132.9 (C o PhP)129.7, 128.3,128.0(C m ,C p C 6 H 5 P) 121.4(C m C 6 H 4 N) 119.7(C p C 6 H 4 N)116.8(C o C 6 H 4 N)31.9(CH 2 )27.6(CH 2 )21.3 (CH 2 ). 31 P‒{ 1 H}NMR(400MHz,acetone‒d 6 ,δ)‒2.06(dd, 2 J(PP) 55.3Hz, 3 J(PP)19.0Hz,PPh 2 trans‒C)22.01(d, 2 J(PP)55.3Hz, PPh 2 trans‒N)43.97(d, 3 J(PP)19.0Hz,P=N). ( 7 ):Yellowsolid.Yield:18.0mg,32%.C 75 H 62 N 2 O 2 P 4 Pd 2 (1360.04);calcd:C66.2,H4.6,N2.1;found:C66.2,H4.7,N 2.1.IR: (P=N):1279cm ‒1 . 1 HNMR(400MHz,CD 2 Cl 2 ,δ)1.98 (m,2H,CH 2 )2.79(m,4H,CH 2 )6.08(m,2H,H‒Ar)6.31(m,2H, H‒Ar)6.37(d, 3 J(HH)7.8Hz,2H,H‒Ar)6.49(m,2H,H‒Ar)6.60 (m,4H,H‒Ar)6.81(m,4H,H‒Ar)7.16(m,8H,m‒Ar)7.30(m, 4H,p‒Ar)7.48 (td, 3 J(HH)7.7Hz, 4 J(HP)2.6Hz,8H,m‒PPh 2 ) 7.58(m,6H,p‒PPh 2 )7.76(m,8H,o‒Ar)7.88(dd, 3 J(HP)11.6 Hz, 3 J(HH)7.7Hz,8H,o‒PPh 2 ). 13 C‐{ 1 H}NMR(400MHz, acetone‒d 6 ,δ) 156.7 ( C‒O) 147.5 (C‒Pd) 145.2 (C‒N) 139.4 ( C‒PC6H4)123.0(CmC6H4N)120.6(CpC6H4N)117.5(CoC6H4N)28.5 (2CH2)20.6 (CH2).31P‒{1H} NMR(400MHz,CD 2 Cl 2 ,δ)30.25(s, PPh 2 )31.62(s,P=N). Conclusions Wehaveshownthatfortheiminophosphoraneligandderived from2‒aminophenol,palladacycleswiththeparentligandas terdentate[C,N,O]maybeprepared.Thepincer‒typebonding modeoftheiminophosphoranepromotesadinuclearspecies withonlyonebridgingchlorideligand,freeofanycounterion; a hydrogen atom between the two oxygen atoms ensures electricalneutrality.Theensuingcomplexmaybereactedto giveeithertypicalmononuclearanddinuclearpalladacycles,or alternativelybytheuseoftheappropriatediphosphane,new zwitterionicmetallacycleswithachelatingphosphorusligand. Themoststrikingfeaturedepictedhereinistheserendipitous unearthing of a dinuclear chloride‒bridged triphenylphosphaneoxidepalladacycle:themissinglinkinthe series of triphenylphosphane chalcogenide metallacycles, which completes the series. Although direct cyclopalladation ofthephosphaneoxidehasnotyetbeenpossible,attemptsto Page 6 of 7Dalton Transactions Dalton Transactions Accepted Manuscript
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