Polymer-Supported Carbene Complexes of Palladium

FULLPAPER

N-HeterocyclicCarbenes,Part25[=]

Polymer-SupportedCarbeneComplexesofPalladium:

Well-Defined,Air-Stable,RecyclableCatalystsfortheHeckReaction

JürgenSchwarz,[a]VolkerP.W.Böhm,[a]MichaelG.Gardiner,[b]ManjaGrosche,[a]WolfgangA.Herrmann,*[a]WolfgangHieringer,[a]andGabrieleRaudaschl-Sieber[a]

dicarbenechelatecomplexesofformula[cis-CH22PdX2](X Br,I;R (CH2)nOH;n 2,3)havebeenpreparedandstructurallycharacterized(forX I,n 2).Thecomplexeswereimmobilizedonafunctionalizedpolystyrenesupport(Wangresin)throughoneoftheoxygencentres.ThecomplexesefficientlycatalyzetheHeckreactionofactivatedandnon-activatedarylbromides,arerecyclableunderaerobicconditionsandexhibithardlyanyleaching,whichisinlinewithourtheoreticalinvestigationsonliganddissociationenergiesrelatedtoPd0andPdIIcentres.

Keywords:CÀCcoupling´carbenecomplexes´catalysts´immobiliza-tion´palladium

Introduction

TherecentadvancesregardingefficientcatalystsfortheHeckreactionhavetypifiedthosemadeinthewiderfieldofpalladium-catalyzedCÀCandC±heteroatomcouplingreac-tionsinthelastfiveyears,bytheuseofwell-definedcatalyststhatareappropriatetothetaskinsteadofcommerciallyavailablemetalsourcesorthosewhichdonotbenefitfromanyligandactivation.[1]Thishasresultedinsystemswhichconvertdeactivatedarylbromidesand,insomecases,activatedarylchlorideswithdecentturnovernumbers.Thereactionnowshowspromisefortheindustrialproductionofimportantchemicals,forexample,styreneandcinnamicesterderivativesthatarerequiredasprecursorsforpolymers,UVabsorbersandantioxidants,andasintermediatesinpharma-ceuticals.[2]Thefieldhasbeenreviewedrecently;[1,3]specif-ically,majorimprovementshaveincluded,i)airandthermallystablePdIIcatalysts,[4]ii)Pd0complexesofhighlybasic,

stericallyhinderedphosphines,[5]iii)watersolublecatalystsystems[6]andiv)theuseofmoltensaltsasreactionmedia.[7]However,apracticallyusefulheterogeneouscatalystisstilltobedeveloped.[2]

Herein,wereportourstudiesofaheterogeneous,anchoredmolecularcatalystfortheHeckreactionthatexhibitsexcellentactivitiestowardsactivatedandnon-activatedbromoarenesubstrates.Thecatalystsystemwaschosenowingtoi)thehighactivityofthemolecularcatalystinthehomogeneouslycatalyzedconversionofdeactivatedarylhalides,[8]ii)itsstabilityunderthereactionconditionscommonlyemployedfortheHeckreactionandiii)theoreticalinvestigationsthatanticipatednegliblepalladiumleachingfromthesupport.

ResultsandDiscussion

InearlierreportsonthehomogeneouscatalysisoftheHeckreaction,weP,C-pallada-cycliccomplexes,[{o26422],[4a,7,8c]andN(NHC)complexes,[cis-CH22PdX2],[8a,b]areefficientcatalysts.TheoreticalinvestigationsofthedissociationofNHCligandsfrompalladiumcentres:Tofurthervalidatethechoiceofdicarbenecomplexesasbeingsuitableforheterogeneouscatalyticapplications,wehavestudiedanumberofmodelreactionstoaccessthebindingstrengthofimidazolin-2-0947-6539/00/0610-1773$17.50+.50/0

[a]Prof.Dr.W.A.Herrmann,Dr.J.Schwarz,Dipl.-Chem.V.P.W.Böhm,

Dipl.-Chem.M.Grosche,Dr.W.Hieringer,Dr.G.Raudaschl-SieberAnorganisch-ChemischesInstitutTechnischeUniversitätMünchen

Lichtenbergstrasse4,85747Garching(Germany)E-mail:lit@arthur.anorg.chemie.tu-muenchen.de[b]Dr.M.G.Gardiner

SchoolofChemistry,TheUniversityofSydneySydney,N.S.W.,2006(Australia)

[=]ForPart24,seeW.Baratta,W.A.Herrmann,P.Rigo,J.Schwarz,J.

Organomet.Chem.2000,593±594,489±493.

Chem.Eur.J.2000,6,No.10

WILEY-VCHVerlagGmbH,D-69451Weinheim,2000

FULLPAPER

ylidene-basedcarbeneligands,[9]ascomparedwithphosphineligands,topalladium(0)andpalladium(ii)metalcentres.Apreviousstudyonthebondingoftheformerligandstocoinagemetalcomplexessuggestedveryhighbindingener-gies,whichmainlyoriginatefromalargelyelectrostaticligand-to-metals-donorinteractionwithonlylittlepback-bonding.[10]Incontrast,phosphinesingeneralareconsideredtohavenon-negligiblep-acceptorands-donorabilities,dependingonthesubstituents.[11]WehavecalculatedthePdÀPbindingenergiesforbothPH3andPMe3,thelatterbeingastrongers-donorthantheformer.ItwasshowninpreviousstudiesthatPMe3dissociationenergiescomparemuchbetterwiththoseforphosphineligandscommonlyusedincatalysis(i.e.,PPh3,PCy3)thanwithPH3dissociationenergies.[12,27]

Themodeltwo-coordinatePd0complex,[Pd(PH3)(NHC)],dissociatesbylossofPH3orthefreeNHC,withrelativedissociationenergiesof 30.1and 41.3kcalmolÀ1(Table1),

Table1.DissociationenergiesofreactionsdepictedinScheme1calcu-latedatBP86/DZVP.Reaction1234567

SubstituentsR1 R2 HR1 R2 HR1 R2 H

R1 Me;R2 HR1 R2 H

R1 Me;R2 HR2 HR2 MeR1 HR1 MeR2 H

DE[kcalmolÀ1] 30.141.327.638.461.054.478.374.844.962.450.2

W.A.Herrmannetal.

Scheme1.Dissociationreactions1±7subjecttotheoreticalcalculations.

respectively(Reactions1and2inScheme1).Incomparison,theanalogousreactionsatapalladium(ii)centrewerefoundtofurtherdisfavourthedissociationofthecarbeneligand.ThelossofPH3from[PdCl2(PR3)(NHC)]requires 27.6kcalmolÀ1( 38.4kcalmolÀ1forPMe3),relativetothelossofNHC,whichrequires 61.0kcalmolÀ1(Reactions3and4inScheme1).ThestrongertranseffectofPMe3ascomparedwithPH3slightlydecreasesthedissociationenergyofthecarbeneligandto54.4kcalmolÀ1.FurtherdissociationoftheremainingligandtoyieldPdCl2andthefreeligand(Reactions5and6inScheme1)requires 78.3kcalmolÀ1forNHCand44.9kcalmolÀ1forPH3(62.4kcalmolÀ1forPMe3).However,thelatterprocessesreflectliganddissociationfromahighlyelectron-deficientmetalcentre.Thus,dimeroroligomerformationcanassistthedissociationprocessinsolution,whichwedidnotconsiderinthisstudy.Thepalladacycleof[cis-CH22PdCl2]isenergeticallyslightlymoredisfavouredthanthedissociationofthecorrespondingmonodentatecarbeneligandandrequires 50.2kcalmolÀ1(Reaction7,Scheme1).

Thecalculationsshow,inaccordwithearlierstudiesonothertransitionmetals[12,27]andinagreementwithmore

qualitativeconsiderations,[11]thatPMe3isconsiderablymoretightlyboundtopalladium(ii)thanPH3.Still,thephosphinedissociationprocessismorelikelytotakeplacethanNHCdissociation.SubstitutionofNÀHbyNÀMeintheNHCintroducesonlyminorchangesinthedissociationenergiesaslongasstericeffectsarenegligibleandelectronicfactorsdominate.OnecananticipatefromtheseinitialresultsthatforNHCcomplexes,stericeffectscanbetunedindependentlyofelectroniceffectsbythechoiceoftheN-boundsubstituents.Thecalculationsclearlydemonstratethatimidazolin-2-ylidene-basedcarbeneligandsbindtobothPd0andPdIIcentressubstantiallystrongerthanphosphineligands,whichhavetraditionallybeensuccessfulinthistypeofcatalyticprocesses.[1±4]Inaccordwithpreviousstudies,[10]thetrendsindissociationenergiesidentifythecarbeneligandsasstrongsdonors,withverylittlep-acceptorcharacter.Thedissoci-ationenergiesincreaseintheorderPH3<PMe3<NHC(H)%NHC(Me),correlatingwiththeelectrondeficienciesatthepalladiumcentresinthevariouscomplexes.

Insummary,theresultshighlightthestrongbindingoftheimidazolin-2-ylidene-carbeneligandstobothPd0andPdIIdihalidesystemsrelativetophosphineligands;thisleadustobelievethatthissystemishighlysuitableforattachmenttosolidsupportsowingtoitsanticipatedlowlevelofleaching.Synthesisandcharacterizationofmolecularcarbenecom-plexes:The1,1'-di(alkyl)-3,3'-methylenediimidazoliumdiha-lidesalts1aand1bwerepreparedfromtheappropriatealkyl

0947-6539/00/0610-1774$17.50+.50/0

Chem.Eur.J.2000,6,No.10

WILEY-VCHVerlagGmbH,D-69451Weinheim,2000

CatalystsfortheHeckReaction

bromidesandN,N'-diimidazolylmethanebyadaptationsofstandardprocedures.[13]Thedicarbenepalladium(ii)dibro-midecomplexes2aand2bweresynthesizedbyouroptimizedprocedure(Scheme2).[14]

Crystalsofcomplex2bsuitableforX-raystructuredeterminationweregrownbyvapordiffusionofethanolintoaconcentrateddimethylsulfoxidesolution.Thecrystalstruc-turedeterminationofcomplex2bshowedthecompoundtobemonomeric,withthedicarbeneligandchelatingthepalladium(ii)centreinacisfashionwiththesix-memberedC3N2Pdringinaboatconformation.Themoleculepossessesnon-crystallographicCssymmetrythatpassesthroughthepalladiumandmethylenecarboncentres(Figure1).Thereisalsoanon-coordinatingmoleculeofdimethylsulfoxideinthe

1773±1780

molecule.ThisweakinteractionresultsinshortO´´´Odistances(2.733(7)and2.746(7) )andlargeOÀHÀOangles(175(10)8and164(6)8).Summariesofimportantbondlengthsandanglesforcomplex2bappearinTable2.

ThePdÀCbondlengthsofcomplex2b,1.991(5)and1.994(5) ,comparewiththosefoundinthecationic[13a]and[8b]dicarbenepalladiumcomplexes[cis2Pd(NCCH3)2]2 [2PF6]Àand[cis- ,andCH22PdI2]at1.966(2)and1.972(3)

1.988(7)and1.989(8) ,respectively.TheyalsoagreewellwiththecalculatedPdÀC ofthemodelchelatecompound,[cis-CH222],presentedinthetheoreticalpartofthisstudy(seeabove).Angulardistortionsfromtheidealsquare-planargeometryforthe

palladiumcentresincomplex2bareminimal,withtheex-ceptionofthoseintroducedbythesix-memberedchelateringforthebidentatedicarbeneli-gand.[13]

CÀCandCÀNbondlengthswithintheimidazolin-2-yli-dene-basedringsystemsincomplex2bareconsistentwithpreviousobservations.

[13,14,15]Otherbondlengthsandangleswithinthemoleculeof2bareunexceptionalanddonotre-quirecomment.1

Hand13CNMRspectraofcomplexes2aand2bareinagreementwiththeirassigned

Table2.Selectedbondlengths[ ]andangles[8]forcompound2b.I1ÀPdI2ÀPdPdÀC1PdÀC11O17ÀC16N2ÀC1N5ÀC9N5ÀC4N10ÀC14N12ÀC11N12ÀC15I1-Pd-I2I1-Pd-C1I1-Pd-C11I2-Pd-C1I2-Pd-C11C1-Pd-C11N12-C13-C14N12-C15-C16C1-N2-C3C3-N2-C6C1-N5-C4C9-N10-C14C9-N10-C11C13-N12-C15N2-C1-N5Pd-C1-N2N5-C4-C3

2.6755(5)C6ÀC72.6546(5)C13ÀC141.991(5)C15ÀC161.994(5)O8ÀC71.393(9)N2ÀC31.355(6)N2ÀC61.448(6)N5ÀC11.374(7)N10ÀC111.379(7)N10ÀC91.350(6)N12ÀC131.471(7)C3ÀC489.73(2)N2-C6-C792.65(14)O8-C7-C6169.75(15)N5-C9-N10174.52(14)N10-C11-N1293.24(13)Pd-C11-N1083.59(19)Pd-C11-N12107.2(5)N10-C14-C13111.5(5)O17-C16-C15109.8(4)C1-N2-C6123.7(5)C1-N5-C9111.2(4)C4-N5-C9125.6(4)C11-N10-C14122.8(4)C11-N12-C15122.9(5)C11-N12-C13104.9(4)Pd-C1-N5133.9(4)N2-C3-C4106.1(5)

1.508(9)1.333(8)1.506(9)1.394(9)1.373(7)1.454(8)1.347(6)1.353(6)1.449(6)1.390(7)1.338(8)

112.5(5)113.8(5)109.2(4)104.5(4)120.3(3)135.2(4)106.6(5)113.1(6)126.4(5)122.1(4)126.3(4)111.3(4)126.4(5)110.4(4)121.1(3)107.9(5)

Scheme2.Reactionschemefortheformationof2a,2b,3aand3b.

crystallattice.ThetwoÀOHgroupsoftheN-substituentsdonotinteractwiththedistortedsquare-planarcoordinatedpalladiumcentre;insteadHbondingisobservedwiththeoxygenatomofthenon-coordinating

dimethylsulfoxide

Figure1.Molecularstructureofcompound2b.

Chem.Eur.J.2000,6,No.10

WILEY-VCHVerlagGmbH,D-69451Weinheim,20000947-6539/00/0610-1775$17.50+.50/0

FULLPAPER

structures.Theappearanceofequivalentmethyleneprotonresonancesforcomplexes2aand2bindicatesthatinversionoftheboat-shapedsix-memberedchelateringsisrelativelyfastonthe1HNMRtimescale.Suchfluxionalringsystemshavebeennotedpreviouslyinrelatedcomplexes,ashaveexampleswhichwereconformationallyrigidatroomtemper-ature.[8b,13,14,16]TheIRspectraofcomplexes2aand2bshowstrongÀOHabsorptionbandsat3446.0cmÀ1(2a)and3422.2cmÀ1(2b).Otherphysicalandspectroscopyfeaturesareunexceptionalandwillnotbecommentedonfurther.Synthesis,structuralandspectroscopiccharacterizationofpolymer-supportedcatalysts:Thep-bromomethylphenyl-functionalizedpolystyrene(Wangresin)waschosen,owingtothereadyattachmentoftheaccessible1,1'-{n-HO(CH2)n}(n 2,3)disubstituted(dicarbene)palladium(ii)dihalidecomplexes2aand2btothesupportthroughanetherlinkagebyadaptationsofexistingproceduresfortheattachmentofamines[17]andcarboxylicacids(Scheme2).[18]

Solid-state13CNMRspectraofthepalladium-loadedpolymers3aconfirmthepresenceoftheimidazolin-2-ylidenecarbeneligandsystem;thecharacteristicresonancesforboththecarbenecarbonandthemethylenecarbonoftheNCH2Nbridgeofthetwoimidazolin-2-ylideneringsystems(d 160.04and69.45,respectively)appearingclosetothosefoundinthemolecularanalogue2a(d 164.45and67.48,respec-tively).

TheIRspectraofthepalladiumloadedpolymers3aand3bretainÀOHabsorptionbands(3443.6cmÀ1and3448.3cmÀ1,respectively),shiftedonlyslightlyfromthosefoundforcomplexes2aand2b(3446.0cmÀ1and3422.2cmÀ1,respec-tively),buthaveintensitiesoftheorderofa50%reductionrelativetothoseobservedforcomplexes2aand2b.Thisindicatesthepresenceofresidualalcoholfunctionalitiesofthepolymer-attachedpalladiumcomplex,whichpossiblyexistsasthemono-etherspeciesdepictedinScheme2.Thepalladiumloadingofthepolymers3aand3bwereconsis-tentlyfoundtobeintherangeof1.0±1.2%,whichissubstantiallylessthanthecalculatedpalladiumloadingforonemoleculeofcomplexes2aand2bbeingboundtothesiteofeachp-bromomethylphenylfunctionalgroupofthepoly-styrenesupport(6.95%,2a;6.67%,2b).Thisfact,coupledwiththeresidualalcoholicfunctionalgroupsfoundonthepolymers3aand3b,indicatesthatmanyofthep-bromo-methylphenylfunctionalgroupsareinaccessibleforgraftingthepalladiumcomplexesandthatthereisonlyasmallamountofp-bromomethylphenylfunctionalgroupsavailablewhichcanformethereallinkagestobothalcoholicfunctionalgroupsofthesamepalladiumcomplex.

CatalysisoftheHeckreaction:Thepalladium-catalyzedarylationofolefinshasfoundwideapplicationinorganicsynthesis.Inthisreactionhomogeneouscatalyticsystemshaveshowntobehighlyefficient.InordertomaketheHeckreactionmoreattractiveforindustry,severalheterogeneousvariantshavepreviouslybeenpresented.[19]AnefficientexampleusesPd0graftedMCM-41material,[20]whichissynthesizedbyvapordepositionofavolatilepalladiumcomplexontotheinsidewallsoftheporousframework,W.A.Herrmannetal.

followedbyreduction.Otherexamplesusenanostructuredpalladiumclustersstabilizedbypropylenecarbonate[21]orhydrophilicpalladiumcomplexesanchoredinsupportedaqueousphases(glass-beadtechnology).[22]

TheN-heterocyclicdicarbenecomplexes2aand2bandtheirimmobilizedcounterparts3aand3bareexcellentcatalystsforthearylationofolefinswitharylbromides.Thecatalyticactivityofthesematerialswasinvestigatedindetailwithactivated,non-anddeactivatedarylhalides,andwithstyreneorn-butylacrylateasthevinylicsubstrate(Tables3and4).

Fullconversionsareobtainedforthecouplingofp-bromoacetophenonewithstyreneorn-butylacrylateafter15hourswithaslittleas0.02±0.15mol%ofheterogeneouscatalysts3aand3b(entries1,2,6,14and15,Table4).Reactionbetweenbromobenzeneandn-butylacrylategivesturnovernumbersofupto4100(entries3,4,9±11,16and17,Table4),whichiscomparablewithmanyofthecommonlyusedhomogeneousHeckcatalysts.Evenlessreactive,deac-tivatedbromobenzenederivativesbearingelectron-donatingethergroupscanbeconvertedwithturnovernumbersintherangeof103±104(entries13,18,19and21,Table4).Whenstyreneisemployedasthevinylicsubstrate,conversionsaregenerallyloweredbyabout10±15%andsubstantialamounts(5±10%)oftheisomersIIandIIIareobtained(Scheme3).Heterogeneouscatalysts3aand3bexhibitnosignificantdifferenceintheircatalyticactivityandselectivity.Yieldsandproductdistributionsaresimilartothoseobtainedwiththeanalogoushomogeneouscatalysts2aand2b(Table3),andtheturnoverfrequencies(hÀ1)areloweredbyaboutoneorderofmagnitudeintheheterogeneouscase.InlinewithpreviousstudiesonhomogeneousHeck-typecatalysis,wefoundthatsaltadditivessuchas[Bu4N] BrÀor[Ph4P] ClÀ[8c,23]enhancetheactivityofcatalysts2aand2b,andthatactivatedchlorobenzenescanbeconverted(entries18±21,Table3).Bywayofcontrast,suchsaltadditiveshavenoinfluenceonthecatalyticactivityof3aand3b,anditisnotpossibletoconvertchlorobenzenesevenunderharshreactionconditions(entry5,Table4).

Theheterogeneouscatalysts3aand3barenotsensitivetoairandmoisture,andthereactionscanbecarriedoutinairbyusingtechnicalgradesolvents,withnochangeinselectivitiesorconversion.Thecatalystsremainhighlyactiveaftercompletereactions,anduponadditionofmoresubstratecatalysisisresumed.

Afterseparationandwashing,theheterogeneouscatalystscanbereusedunderthesameorsimilarreactionconditionsasfortheinitialrunwithoutanyneedforregeneration(Scheme4).Therecyclingofcatalyst3awasinvestigatedindetailforthereactionofp-bromoacetophenonewithstyrene(entry4,Table4).

Thecatalystwasused15timeswithoutdetectablelossofactivity.Thelimitsofthissystemcanbeseenwhenonly0.02%3aareusedforthecouplingofp-bromoacetophenonewithn-butylacrylate(entry6,Table4).Inthiscase,thecatalystcanonlyberecycledsixtimesbeforetheconversionslowlydropsdownto80%intheseventhrun[totalturnovernumber(TON) 35500].Ontheotherhand,noticeabledeactivationisdisplayedinthecaseoflessreactivebromo-0947-6539/00/0610-1776$17.50+.50/0

Chem.Eur.J.2000,6,No.10

WILEY-VCHVerlagGmbH,D-69451Weinheim,2000

CatalystsfortheHeckReaction

Table3.HomogeneousHeckcouplingcatalysis.[a]Entry12345678910111213141516171819202122

Arylhalide4-MeCOC6H4Br4-MeCOC6H4BrC6H5BrC6H5BrC6H5Br

4-MeOC6H4Br4-MeOC6H4Br4-MeOC6H4Br4-MeOC6H4Br4-MeCOC6H4Br4-MeCOC6H4BrC6H5BrC6H5Br

4-MeOC6H4Br4-MeOC6H4Br4-MeOC10H6Br4-MeOC10H6Br4-O2NC6H4Cl4-O2NC6H4Cl4-MeCOC6H4Cl4-MeCOC6H4ClC6H5Cl

Alkene

CH2 C(H)COO-nBuCH2 C(H)Ph

CH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)Ph

CH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)Ph

CH2 C(H)COO-nBuCH2 C(H)Ph

CH2 C(H)COO-nBuCH2 C(H)Ph

CH2 C(H)COO-nBuCH2 C(H)Ph

CH2 C(H)COO-nBuCH2 C(H)Ph

CH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBu

Catalyst

(mol%Pd)[d]

t[h]Conversion[b](T[8C])[%]

1773±1780

Yield[%][c]

[e]

(TON)

2a(0.15)3(150)1002a(0.15)5(150)1002a(0.15)16(160)962a(0.15)60(160)1002a(0.15)60(160)1002a(0.15)0.17(170)722a(0.15)0.67(170)802a(0.15)2.5(170)1002a(0.15)12(160)902b(0.15)4(160)1002b(0.15)6(160)1002b(0.15)60(160)932b(0.15)60(160)952b(0.15)3(160)922b(0.15)3(160)862b(0.02)60(160)962b(0.02)60(160)892b(1)[f]19(150)82

[f]

2b(1)72(150)99

[f]

2b(1)19(150)592b(1)[f]72(150)59

[f]

2b(1)30(160)0>99(667)

96(667)96(640)>99(667)

93(667)72(480)80(533)>99(667)

84(600)>99(667)

93(667)90(620)88(633)92(613)80(573)96(4800)84(4450)8(82)99(99)59(59)59(59)0(0)

[a]Reactionswereperformedinsealedpressuretubeswithouttheexclusionofoxygen/moistureandwithnon-driedsolvents.YieldsandproductidentificationweredeterminedbyGC-MS.Typicalreactionconditions:Amolarratioof1:1.25:1.5wasusedforthearylhalide(10mmol)/alkene/base[Na(OAc)(anhyd.)].DMAc(10mL)wasusedasthesolvent.[b]Conversionofthearylhalidewithdiethyleneglycol-n-butyletherasinternalstandard.[c]GCyieldinofthetransisomerbasedonthearylhalide.[d]Basedonarylhalide.[e]TON [molesofcouplingproduct(allisomers)]/(molesofPd).[f]20%[Bu4N] BrÀwasadded.

benzenederivatives;neverthelessatotalturnovernumberofabout21000isreachedforthecouplingofbromobenzenewithn-butylacrylate(entry11,Table4).

Theleachingofactivespeciesfromheterogeneouscatalystsintosolutionisacrucialquestioninordertoidentifywhethertheactivecentresareattachedtothesolidsupportorwhether

Table4.HeterogeneousHeckcouplingcatalysis.[a]Entry123456789101112131415161718192021

Arylhalide4-MeCOC6H4Br4-MeCOC6H4BrC6H5BrC6H5Br

4-MeCOC6H4Cl4-MeCOC6H4Br4-MeOC10H6Br4-MeOC10H6BrC6H5BrC6H5BrC6H5Br

4-MeOC6H4Br4-MeOC6H4Br4-MeCOC6H4Br4-MeCOC6H4BrC6H5BrC6H5Br

4-MeOC10H6Br4-MeOC10H6Br4-MeOC6H4Br4-MeOC6H4Br

Alkene

CH2 C(H)COO-nBuCH2 C(H)C6H5

CH2 C(H)COO-nBuCH2 C(H)C6H5CH2 C(H)C6H5

CH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)COO-nBuCH2 C(H)C6H5

CH2 C(H)COO-nBuCH2 C(H)C6H5

CH2 C(H)COO-nBuCH2 C(H)C6H5

CH2 C(H)COO-nBuCH2 C(H)C6H5

CH2 C(H)COO-nBu

theyaredissolvedpalladiumcomplexes.Theobservedsimilaritiesbetweentheheterogeneouslycatalyzedreactionsandtheresultsobtainedusingthehomogeneousanalogues2aand2bmightsuggestthatthecatalystforthesereactionsisadissolvedpalladiumspecies.Totestthis,weisolatedthecatalyst3aafter20%conversion(entry11,Table4)and

Catalyst

(mol%Pd)[d]t[h]Conversion[b](T[8C])[%]Yield[%][c]

[e]

(TON)

3a(0.15)15(150)1003a(0.15)15(150)1003a(0.15)48(160)823a(0.15)48(160)723a(0.15)50(170)03a(0.02)12(150)1003a(0.02)12(150)413a(0.02)36(150)973a(0.02)12(150)423a(0.02)24(150)713a(0.02)36(150)813a(0.02)12(150)453a(0.02)36(150)533b(0.02)60(150)1003b(0.02)60(150)1003b(0.02)60(150)753b(0.02)60(150)823b(0.02)60(150)823b(0.02)60(150)953b(0.02)60(150)383b(0.02)60(150)42>99(667)

95(667)82(547)61(480)0(0)>99(5000)

41(2050)97(4850)42(2100)71(3550)81(4050)45(2250)53(2650)94(5000)>99(5000)

67(3750)82(4100)80(4100)95(4750)38(1900)42(2100)

[a]Reactionswereperformedinsealedpressuretubeswithouttheexclusionofoxygen/moistureusingnon-driedsolvents.YieldsandproductidentificationweredeterminedbyGC-MS.Typicalreactionconditions:Amolarratioof1:1.25:1.5wasusedforthearylhalide(10mmol):alkene:base(Na(OAc)(anhyd.)).DMAc(10mL)wasusedasthesolvent.[b]Conversionofthearyl-halideusingdiethyleneglycol-n-butyletherasinternalstandard.[c]GCyieldofthetransisomerbasedonarylhalide.[d]Basedonarylhalide.[e]TON [molesofcouplingproduct(allisomers)]/(molesofPd).

Chem.Eur.J.2000,6,No.10

WILEY-VCHVerlagGmbH,D-69451Weinheim,2000

0947-6539/00/0610-1777$17.50+.50/0

FULLPAPER

W.A.Herrmannetal.

Wangresinthroughetherlinkages.Highactivity,easyaccessibilityandexceptionalstabilityoftheimmobilizedcarbenecomplexesprovideanexcellentexampleforanewgenerationofheterogeneousHeckcatalysts.Thesecatalystsarerecyclablewithveryhighefficiencyandexhibitleastleachingforheterogeneouspalladium(ii)complexes;thisisinlinewithourtheoreticalinvestigationsonliganddissociationenergies.Detailedinvestigationsfocusingondifferentimmo-bilizationtechniquesandcatalyticactivityoffurthercouplingreactionsareongoing.

Scheme3.TheHeckreaction(ªcat.[Pd]ºdenotescatalyticamountsof2a,2b,3aor3b

).

ExperimentalSection

Generalprocedures:Allsolventswereusedasreceivedastechnicalgradesolvents.N,N'-Diimidazolylmethanewaspreparedaccordingtoliteratureprocedures.[24]4-(Bromomethyl)phenoxymethylpolystyrene(WangResin)wasobtainedfromNovabiochemasa1.00mmolgÀ1substitutionloading.OtherchemicalswereobtainedfromAldrichandusedasreceived.1Hand13

CNMRspectrawererecordedonaJOELJNM-GX400spectrometerinCDCl3,[D6]DMSOandD2Oandreferencedtotheresidual1Hresonancesofthesolvents.Solid-state13CNMRspectrawererecordedonaBrukerMSL300spectrometerequippedwitha4mmCP-BBMASprobeheadandreferencedtoadamantaneasanexternalstandard.Thesampleswerepackedin4mmZrO2rotorswithKeLFcaps.ElementalanalyseswereperformedbythemicroanalyticallaboratoryattheTechnicalUniversityofMunich.Meltingpointsweredeterminedinglasscapillariesunderair.IRspectrawererecordedonaFT-IRPerkin±Elmer1680spectrometer.MassspectrawererecordedonaVarianMAT311aspectrometerwithFABionisation(xenon/p-nitrobenzylalcoholmatrix).GCMSwasperformedonaHewlett±Packard5890instrument.Yieldsofcatalysisexperimentsweredeterminedbyusingdiethyleneglycol-n-butyletherasaninternalstandard.Synthesisof1,1'-di(3-hydroxypropyl)-3,3'-methylenediimidazoliumdibro-mide(1a)and1,1'-di(hydroxyethyl)-3,3'-methylenediimidazoliumdiiodide(1b):AstirredsolutionofN,N'-diimidazolylmethane(0.50g,3.38mmol)and3-bromo-1-propanol(0.95g,6.80mmol)or2-iodo-1-ethanol(1.17g,6.80mmol),respectively,iniso-propanol(5mL)washeatedinasealedpressuretubeat1008Cfor12h.Theiso-propanolwasremovedinvacuotogiveawhitesolid,whichwaswashedwithTHF(15mL).Recrystallisationfromethanolgavetheproductsascolourlessrods.Yields:1.18g(2.77mmol,82%),1a;1.55g(3.16mmol,93%),1b.

Compound1a:M.p.>3008C;1HNMR(400MHz,[D6]DMSO,258C):d 9.77(s,2H;NCHN),8.22(d,3J 1.84Hz,2H;NCH),7.97(d,3J 1.84Hz,2H;NCH),6.83(s,2H;NCH2N),4.31(t,3J 4.09Hz,4H;CH2OH),3.41(t,3J 6.21Hz,4H;CH2OH),1.01(m,4H;CH2);13CNMR(100.53MHz,[D6]DMSO,258C):d 138.2(NCHN),123.7(NCH),122.4(NCH),62.5(NCH2N),56.5(CH2),47.4(CH2),25.9(CH2);elementalanalysiscalcd(%)forC13H22N4Br2O2(426.15):C36.64,H5.20,N13.15;foundC36.89,H5.16,N13.29.

Compound1b:M.p.>3008C;1HNMR(400MHz,[D6]DMSO,258C):d 9.42(s,2H;NCHN),7.98(s,2H;NCH),7.80(s,2H;NCH),6.68(s,2H;NCH2N),4.27(br,4H;CH2OH),3.61(br,4H;NCH2);13CNMR(100.53MHz,[D6]DMSO,258C):d 138.2(NCHN),124.2(NCH),122.4(NCH),59.4(NCH2),58.6(NCH2N),52.7(CH2OH);elementalanalysiscalcd(%)forC11H18N4O2I2(492.10):C26.85,H3.69,N11.39;foundC27.07,H3.74,N11.68.

Synthesisof[{1,1'-di(3-hydroxypropyl)-3,3'-methylenediimidazolin-2,2'-diylidene}palladium(ii)dibromide](2a)and[{1,1'-di(hydroxyethyl)-3,3'-methylenediimidazolin-2,2'-diylidene}palladium(ii)diiodide](2b):Astir-redsolutionof1,1'-di(hydroxy-n-propyl)-3,3'-methylenediimidazoliumdi-bromide1a(380mg,0.89mmol)or1,1'-di(hydroxyethyl)-3,3'-methylene-diimidazoliumdiiodide1b(434mg,0.89mmol),respectively,andPd(OAc)2(200mg,0.89mmol)inDMSO(5.0mL)washeatedat608Cfor12hoursandthenat1308Cforfurther2hours,duringwhichtimethereactionsolutionhadturnedpaleyellowfrombeinginitiallyorange.TheremainingDMSOwasthenremovedinvacuoat708Ctogiveayellowsolid,whichwaswashedwithTHF(3mL)togivetheproductsaspurepowders.TheproductswerethencrystallizedbylayeringsaturatedDMSO

0947-6539/00/0610-1778$17.50+.50/0

Chem.Eur.J.2000,6,No.10

Scheme4.Recyclingoftheheterogeneouscatalyst3a.^:R1 COMe,R2 C6H5;T 1508C;t 15h;0.15%3a.&:R1 COMe,R2 CO2-nBu;T 1608C;t 12h;0.02%3a.~:R1 H,R2 CO2-nBu;T 1608C;t 36h;0.02%3a.Afterthereactiontime,methanolwasaddedtothereactionmixturetodissolovethesaltsandreactionproducts.Thecatalystwascollectedbyfiltrationanddriedinvacuoforfurtheruse.Conditions:amolarrationof1.1:1.25:1.5wasusedforthearylhalide(10mmol)/alkene/base{Na(OAC)(anhydrous)}.DMAc(10mL)wasusedasthesolvent.

monitoredtheresultingfiltrateunderidenticalreactionconditionsforafurther40hours;noadditionalconversionwasdetecteduponremovalof3a.Whilethismethoddoesnotallowustoquantifytheleachingphenomenon,itclearlydemonstratestheabsenceofactivespeciesinsolution.

Elementalanalysisoftheusedcatalyst3ashowedthepalladiumcontenttobereducedby0.6wt%(foracatalystwith1.0wt%loading)afterthefirstrun.However,elementalanalysisofthesamecatalystafterfourrunsshowedessentiallythesamepalladiumcontent(0.39%vs.0.36%),indicatingsignificantlossofpalladiumonlyduringthefirstrun.Consistently,adecreaseofpalladiumleachingintotheproductwasobservedforrecycledcatalyst3a(38ppminthefirstrunvs.4ppminthethirdrun).

Whereasthereactionmechanismofrelatedhomogeneoussystemswasinvestigatedindetailbyourgroup,[8a]themechanismoftheheterogeneouslycatalyzedrectionsremainsunclear.However,theidenticalproductdistributionsinhomogeneousandheterogeneousreactionsindicatethataPd0/PdIIcycleisapplicableforboth.Althoughwenevernoticedinductionperiods,weassumethatlossofpalladiumoccursduringtheactivationstepofprecatalysts3aand3bintheinitialcatalyticrun(formationofcatalyticallyactivePd0species).

Insummary,palladium(ii)complexesofN-heterocycliccarbenescansuccessfullybeattachedtopolystyrene-based WILEY-VCHVerlagGmbH,D-69451Weinheim,2000

CatalystsfortheHeckReaction

solutionswithethanol.Yields:356mg(0.67mmol,75%),2a;489mg(0.82mmol,92%),2b.

Compound2a:M.p.>3008C;1HNMR(400MHz,[D6]DMSO,258C):d 7.60(s,2H;NCH),7.37(s,2H;NCH),6.29(s,2H;NCH2N),4.14(br,4H;CH2OH),3.38(br,4H;NCH2),1.71(br,4H;CH2);13CNMR(100.53MHz,[D6]DMSO,258C):d 158.8(Ccarbene),122.7(NCH),121.8(NCH),67.5

Ä 3446.0(OH),(NCH2N),58.2(CH2),48.6(CH2),25.6(CH2);IR(KBr):n

À1 1635.7cm(CC);FABMS:m/z(%):451(55)[MÀBr],369(100)[MÀ

2Br] ;elementalanalysiscalcd(%)forC13H20N4Br2O2Pd(530.56):C29.43,H3.80,N10.56;foundC29.83,H3.94,N10.67.

Compound2b:M.p.2938C;1HNMR(400MHz,[D6]DMSO,258C):d 7.60(s,2H;NCH),7.36(s,2H;NCH),6.30(s,2H;NCH2N),3.94(br,2H;CH2OH),3.44(br,4H;NCH2);13CNMR(100.53MHz,[D6]DMSO,258C):d 164.45(Ccarbene),123.27(NCH),121.89(NCH),63.75(NCH2N),60.90

Ä 3422.2(OH),1636.6cmÀ1(C C);FAB(CH2),54.53(CH2);IR(KBr):n

MS:m/z(%):469(49)[MÀI] ,342(100)[M À2I] ;elementalanalysiscalcd(%)forC11H16I2N4O2Pd´C2H6OS(674.63):C23.14,H3.29,N8.30;foundC23.21,H3.22,N8.38.

Immobilisationof2aand2bon4-(bromomethyl)phenoxymethylpoly-styrene

Preparationofcatalysts3aand3b:Asolutionof2a(100mg,0.19mmol)or2b(113mg,0.19mmol),4-(bromomethyl)phenoxymethylpolystyrene

di-iso-propylethylamine(73mg,(188mg,c(Br) 1.00mmolgÀ1),

0.57mmol)andCsI(15mg,0.06mmol)inDMF(4.0mL)wasstirredfor48hatroomtemperature.ThepaleyellowbeadswerecollectedandwashedwithN,N-dimethylacetamide(DMAc;3Â6mL)andMeOH(2Â10mL),anddriedinvacuo.

Compound3a:13CNMR(solidstate,300MHz,nr 10kHz,258C):d

Ä 3443.6(OH),160.0(br,Ccarbene),69.5(br,NCH2N);IR(KBr):n

À1 1635.6cm(CC);elementalanalysiscalcd(%)foraloadingof1.0%

palladium:N0.53;foundPd1.0,N0.59.

Compound3b:IR(KBr):nÄ 3448.3(OH),1636.5cmÀ1(C C);elementalanalysiscalcd(%)forforaloadingof1.1%palladium:N0.58;foundPd1.1,N0.62.

GeneralprocedureforHeckcatalysis:ThereactionsforHeckcouplingstudiesweretypicallyconductedasfollows:Thearylhalide(1.0equiv,10mmol),alkene(1.2equiv,12mmol),base(1.5equiv,15mmol),saltadditive(ifused),internalstandard(100mgdiethyleneglycol-n-butyl-ether)andcatalystwereaddedtoathick-walled17cmAcepressuretube;thesolvent(10mL)andamagneticstirrerwereadded.Thetubewassealedwithano-ringedTefloncapandheatedtotheappropriatetemperatureoftheexperiment.Thereactionprogresswasmonitoredbytheremovalofasmallaliquotofthereactionmixture,whichwasanalyzedbyGC-MS.Thepressuretubeswerethencooledtoroomtemperature;asmallaliquotofthereactionmixturewastakenforGC-MSanalysisofthereaction.Productswereidentifiedbycomparisonwithauthenticsamples.Incaseofheterogeneouscatalysts3aand3b,methanolwasaddedtothereactionmixturetodissolveallsaltsandreactionproducts.Thecatalystwascollectedbyfiltrationanddriedinvacuoforfurtheruse.

Computationaldetails:ThegeometriesofthemodelcomplexeswereoptimizedattheBP86[25]leveloftheoryincombinationwiththeDZVPbasisset[26]onallatoms.Thisbasisset,incombinationwiththeA1setofauxiliaryfittingfunctionsforthedensityandtheexchange-correlationpotential,wasdesignedtoreducethebasissetsuperpositionerror(BSSE).Otherwise,noeffortsweremadetocorrectforthebasissetsuperpositionproblem,whichtendstocancelwiththebasissetincompletenesserrorformedium-sizedbasissets.Theaccuracyofthismethodhasbeenshowninapreviousstudy.[27]Theresultingenergy-minimizedstructureswerecharac-terizedbycalculatingtheeigenvaluesoftheforce-constantmatrix.AllcalculationswerecarriedoutwiththeDGauss4.0program.[28]

X-raydiffractionstudiesforcompound2b:AllX-raydatawerecollectedonaNoniusKappaCCDdetectionsystemat173Kwithgraphite-monochromatedMoKaradiation.Atotalnumberof15948reflectionsweremeasuredand4187uniquereflections(Rint 0.0363)wereusedinthefull-matrixleast-squaresrefinement.Theintensitiesofthereflectionswerecorrectedforabsorptioneffects.[29]Thestructurewassolvedbydirectmethods[30]andrefinedbyfull-matrixleast-squarescalculationswithSHELXL-97.[31]Allheavyatomsofthecompoundwererefinedwithanisotropictemperaturefactors.Allhydrogenatomswerefoundfromtheelectron-densitymapsandwererefinded.Crystallographicdataand

Chem.Eur.J.2000,6,No.10

1773±1780

experimentaldetailsofcompound2baregiveninTable5.SelectedstructuralparametersaregiveninTable2.Crystallographicdata(excludingstructurefactors)DC-135476.CopiesofthedatacanbeobtainedfreeofchargeonapplicationtoCCDC,12UnionRoad,CambridgeCB21EZ,UK(fax:( 44)1223-336-033;e-mail:deposit@ccdc.cam.ac.uk).

Table5.Crystaldataanddetailsofthestructuredeterminationforcompound2b.

formulaC11H16I2N4O2Pd´C2H6OS

674.64Mw

crystalsystemtriclinic

Å(No.2)spacegroupP1

a[ ]8.8260(3)b[ ]9.0680(3)c[ ]13.5670(4)a[8]107.4390(17)b[8]94.6290(15)g[8]93.9990(16)

1027.49(6)V[ 3]

Z2

2.1811calcd[gcmÀ3]

4.0m[mmÀ1]

crystalsize[mm]0.20Â0.13Â0.10T[K]173l[ ]0.71073qmin/max2.3/26.4F(000)640totalreflections15948uniquereflections4187observedreflections[I>2s(I)]3789

0.0321R1(Fo)[a]

2[b]

0.0822wR2(Fo

[c]

1.05goodnessoffit

À1.46/1.31D1min/max[e À3]

2221/2

[b]wR2 {S[w(FoÀFc2 2]/S[w(Fo ]}.[a]R1 SjjFojÀjFcjj/SjFoj.

2221/2

[c]Goof {S[w(FoÀFc ]/(nÀp).

Acknowledgement

WearegratefultoDr.KarlÖfeleforsuggestionsandfruitfuldiscussionsaswellasM.BarthandS.SpindlerforPdtraceanalyses.ThisworkwassupportedbytheAlexandervonHumboldt-Stiftung(fellowshipforMGG),theFondsderChemischenIndustrie(Ph.D.fellowshipsforJSandVPWB),AventisandtheBayerischeForschungsverbundKatalyse(FORKAT).WealsothankDEGUSSA-HÜLSAGforagenerousgiftofpalladium(ii)acetate.

[1]Reviews:a)R.F.Heck,PallladiumReagentsinOrganicSynthesis,

AcademicPress,London,1985;b)A.deMeijere,F.E.Meier,Angew.Chem.1994,106,2473±2506;Angew.Chem.Int.Ed.Engl.1994,33,2379±2411;c)J.Tsuji,PalladiumReagentsandCatalysts,Wiley,Chichester,1995;d)W.A.Herrmannin,AppliedHomogeneousCatalystswithOrganometallicCompounds(Eds.:B.Cornils,W.A.Herrmann),Wiley-VCH,Weinheim,1996,pp.712±726.

[2]D.Garbe,inUllmann sEncyclopaediaofIndustrialChemistry,

Vol.A7(Eds.:W.Gerhartz,J.S.Yamamoto,I.T.Campbell,R.Pfefferkorn,J.F.Rounsville),VCH,Weinheim,1999,pp.99ff.

[3]Reviews:a)V.V.Grushin,H.Alper,Chem.Rev.1994,94,1047±1062;

b)T.H.Riermeier,A.Zapf,M.Beller,Top.Catal.1998,4,301±309.[4]a)W.A.Herrmann,C.Brossmer,C.-P.Reisinger,T.H.Riermeier,K.

Öfele,M.Beller,Chem.Eur.J.1997,3,1357±1364;b)M.Ohff,A.Ohff,D.Milstein,mun.1999,357±358;c)M.Ohff,A.Ohff,M.E.vanderBoom,D.Milstein,J.Am.Chem.Soc.1997,119,

0947-6539/00/0610-1779$17.50+.50/0

WILEY-VCHVerlagGmbH,D-69451Weinheim,2000

FULLPAPER

11687±11688;d)B.L.Shaw,S.D.Perera,E.A.Staley,mun.1998,1361±1362;e)A.L.Boyes,I.R.Butler,S.C.Quayle,TetrahedronLett.1998,39,7763±7766;f)M.T.Reetz,E.West-ermann,R.Lohmer,G.Lohmer,TetrahedronLett.1998,39,8449±8452.

a)A.F.Littke,G.C.Fu,.Chem.1999,64,10±11;b)K.H.Shaughnessy,P.Kim,J.F.Hartwig,J.Am.Chem.Soc.1999,121,2123±2132.

a)L.U.Gron,A.S.Tinsley,TetrahedronLett.1999,40,227±230;b)S.

Ãt,TetrahedronLemaire-Audoire,M.Savignac,C.Dupuis,J.-P.Gene

Ãt,M.Savignac,anomet.Lett.1996,37,2003±2006;c)J.-P.Gene

Chem.1999,576,305±317;d)A.E.S.Gelpke,J.J.N.Veerma,M.S.Goedheijt,P.C.J.Kramer,P.W.N.M.Leuween,H.Hiemstra,Tetrahedron1999,55,6657±6670.

V.P.W.Böhm,W.A.Herrmann,Chem.Eur.J.2000,6,1017±1025;W.A.Herrmann,V.P.W.Böhm,anomet.Chem.1999,572,141±145.

a)W.A.Herrmann,M.Elison,J.Fischer,C.Köcher,G.R.J.Artus,Angew.Chem.1995,107,2602±2605;Angew.Chem.Int.Ed.Engl.1995,34,2371±2374;b)W.A.Herrmann,C.-P.Reisinger,M.Spiegler,anomet.Chem.1998,572,93±96;c)W.A.Herrmann,V.P.W.Böhm,C.-P.Reisinger,anomet.Chem.1999,576,23±41;d)D.S.McGuiness,K.J.Cavell,B.W.Skelton,A.H.White,Organometallics1999,18,1596±1605;e)C.Zhang,J.Huang,M.T.Trudell,S.P.Nolan,.Chem.1999,64,3804±3805.

a)C.Heinemann,T.Müller,Y.Apeloig,H.Schwarz,J.Am.Chem.Soc.1996,118,2023±2038.b)C.Boehme,G.Frenking,J.Am.Chem.Soc.1996,118,2039±2046.

C.Boehme,G.Frenking,Organometallics1998,17,5801±5809.C.Tolman,Chem.Rev.1977,77,313±348.

O.D.Häberlen,N.Rösch,J.Phys.Chem.1993,97,4970±4973.

a)M.G.Gardiner,W.A.Herrmann,C.-P.Reisinger,J.Schwarz,M.Spiegler,anomet.Chem.1999,572,239±247;b)W.A.Herr-mann,J.Schwarz,M.G.Gardiner,M.Spiegler,anomet.Chem.1999,575,80±86.

J.Schwarz,W.A.Herrmann,M.G.Gardiner,Organometallics1999,20,4081±4087.

W.A.Herrmannetal.

[15]W.A.Herrmann,L.J.Goossen,G.R.J.Artus,C.Köcher,Organo-metallics1997,16,2472±2477.

[16]W.P.Fehlhammer,T.Bliss,U.Kernbach,I.Brücgam,anomet.

Chem.1995,490,149±153.

[17]a)K.Ngu,D.V.Patel,TetrahedronLett.1997,38,973±978;b)B.

Raju,T.P.Kogan,TetrahedronLett.1997,38,4965±4970.

[18]a)J.W.Corbett,TetrahedronLett.1989,30,6741±6747;b)J.W.

Corbett,Bioorg.Med.Chem.Lett.1997,7,1371±1376.

[19]a)R.S.Varma,K.P.Naicker,P.J.Liesen,TetrahedronLett.1999,40,

2075±2078;b)L.Djakovitch,K.Köhler,J.Mol.Catal.A1999,142,275±284;c)R.L.Augustine,S.T.O Leary,J.Mol.Catal.A1995,95,277±285;d)K.Kaneda,M.Higushi,T.Imanaka,J.Mol.Cat.1990,63,L33±L36.

[20]a)C.P.Mehnert,J.Y.Jing,mun.1997,2215±2216;b)C.P.

Mehnert,D.W.Weaver,J.Y.Jing,J.Am.Chem.Soc.1998,120,12289±12296.

[21]M.T.Reetz,G.Lohmer,mun.1996,1921±1922.

[22]M.S.Anson,M.P.Leese,L.Tonks,J.M.J.Williams,J.Chem.Soc.

DaltonTrans.1998,3529±3538.

[23]M.T.Reetz,G.Lohmer,R.Schwickardi,Angew.Chem.1998,110,

492±495;Angew.Chem.Int.Ed.1998,37,481±483.

[24]S.Julia,P.Sala,J.delMazo,M.Sancho,C.Ochoa,J.Elguero,J.-P.

Fayet,M.-C.Vertut,J.Heterocycl.Chem.1982,19,1141±1145.

[25]a)A.D.Becke,Phys.Rev.A1988,38,3098±3100;b)J.P.Perdew,

Phys.Rev.B1986,33,8822±8824,erratumPhys.Rev.B1986,34,7406.[26]N.Godbout,D.R.Salahub,J.Andzelm,E.Wimmer,Can.J.Chem.

1992,70,560±571.

[27]R.Schmid,W.A.Herrmann,G.Frenking,Organometallics1997,16,

701±708.

[28]a)J.Andzelm,E.J.Wimmer,J.Chem.Phys.1992,96,1280±1303;

DGauss,Release4.0,OxfordMolecular,1998.[29]R.H.Blessing,Cryst.Rev.1987,1,3±57.

[30]A.L.Spek,ActaCrystallogr.Sect.A1990,46,C34.

[31]G.M.Sheldrick,SHELXL-97.ProgramforCrystalStructureRefine-ment,UniversityofGöttingen(Germany),1997.

Received:September2,1999[F2016]

[5]

[6]

[7]

[8]

[9]

[10][11][12][13]

[14]

WILEY-VCHVerlagGmbH,D-69451Weinheim,20000947-6539/00/0610-1780$17.50+.50/0Chem.Eur.J.2000,6,No.10

本文来源：https://www.bwwdw.com/article/wyv4.html