1SchrockRRHoveydaAHAngewChemIntEd2RobbinsJBazanGCMurdzekJSOReganMBSchrockRR29023SchrockRRInReactionsofCoordinatedLigandsBratermanPREdPlenumNewYork198 ID: 202588
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DimersthatContainUnbridgedW(IV)/W(IV)DoubleBondsLourdesPiaH.Lopez,RichardR.Schrock,andPeterMuÈllerDepartmentofChemistry,MassachusettsInstituteofTechnology,Cambridge,Massachusetts02139edNoember9,2005CompoundsthatcontainanunbridgedWWbondcanbepreparedthroughbimoleculardecompositionofvariousimidoalkylidenecomplexes.OnetypeofWWspeciesis[W(NR)(CH2,6-dimethylphenyl(Ar)or2,6-diisopropylphenyl(Ar);Rpentafluorophenylorhexafluoroisopropyl),whichisfoundinbothheterochiralandhomochiralforms.Theothertypeis[W(NR)(OR-butylorhexafluoro--butyl).AllspeciescontainanunbridgedW(IV)/W(IV)doublebondwithaWWbonddistanceof2.42.5…,a90anglebetweentheimidoligandsandtheWWbond,andanrelationshipoftheimidoligands.ThereisnoindicationthatWWbondsarebrokenspontaneously;forexample,heterochiralandhomochiral[W(NR)(CHspeciesdonotHighoxidationstateimidoalkylidenecomplexesoftungstenandmolybdenum,especiallythoseofthetypeM(NR)(CHR,comprisealargeclassofwell-definedolefinmetathesisAlthoughthereislittledoubtconcerningmanydetailsofolefinmetathesisreactions,relativelylittleisknownabouthowcatalyticintermediatesdecomposeandthereverseofthosereactions,i.e.,ifandhowalkylidenesmightberegenerated.Evidencesuggeststhattherearetwomaindeactivationpath-ways.OneisrearrangementofintermediatemetalacyclobutaneAsecondisbimolecularcouplingofalkylidenestogiveolefins.Thepossibilitythatathird,formationofacyclopropane,isoperativeincertaincircumstancescannotbeexcluded.Bimoleculardecompositionofalkylidenesisslowestforneopentylideneorneophylidenecomplexesandmostrapidformethylenecomplexes.M(NR)(OR(olefin)complexeshavebeenobserved,andinonecaseanethylenecomplexhasbeenisolatedandcrystallographicallycharacterized.Alkylideneswerebelievedtodecomposetogivebimetallicspeciesthatcontainbridgingimidoligands.Theonlycrystal-lographicallycharacterizedspeciesintheliteratureis[Mo(;Mo2.654(1)…),whichisformedinareactionbetweenMo(NAr)(CH-t-Bu)-andethylene(eq1).1).(í-NAr)(O-t-Bu)2]2hasapproximatelyatetrahedralarrangementofligandsabouteachmetal.However,theMocoreisflat;theOOdihedralangleis,andtheOOangleis.Nevertheless,protonNMRspectrashownoevidenceofinequivalent-butoxideligandsatroomtemperature.Sincenopropylenewasobservedasaproductofthisreaction,reaction,(í-NAr)(O-t-Bu)2]2wasproposedtoformviabimolec-ulardecompositionofintermediateMo(NAr)(CHspecies(eq1).Evidentlyneitheranethylenecomplexnoramolybdacyclopentanecomplexisstablewithrespecttoforma-tionof[Mo(,andanybackreactionbe-tween[Mo(andethyleneisslow.Acom-poundwiththeempiricalformulaW(NAr)[OCMe(CF(accordingtoNMRandelementalanalyses)wasproposedtobeabimetalliccomplexbridgedbyimidoligands,i.e.,i.e.,(3)2]2}2.5Thiscompound,whichwasisolatedfromthereactionbetweenW(NAr)(CH-t-Bu)[OCMe(CFand3-hexene,isformedupondecompositionofobservable,butunstable,orangeW(NAr)(CHEt)[OCMe(CF,viabimolecu-larcouplingofpropylidenes.Otherpropylidenecomplexes,O-t-Bu,OCMe),werealsofoundtobeunstablewithrespecttoformationofdimersviabimoleculardecomposition.AnattemptedX-raystudyofbrowncrystallineªW(NAr)[OCMe(CFºwasofsufficientqualitytoconcludethatitwasadimericspecies.However,severedisorderpreventedasolutionofthisstructureandevenaconclusionastowhetherbridgingimidoligandswerepresentornot.TheCNMRspectrumofªW(NAr)[OCMe(CFrevealedtwoCFcarbonresonances,whichwouldbeconsistentwithastructureinwhichnoplaneofsymmetryrunsthroughtheWRheniumcomplexesofthetypeRe(C-t-Bu)(CH-t-Bu)(OR)whichareisoelectronicwithW(NAr)(CH-t-Bu)(OR)havebeenshowntobeviableolefinmetathesiscatalystswhenORissufficientlyelectronwithdrawing(e.g.,OCMe(CFComplexesinwhichORisO-t-BuorORreactwithCHOEttoyieldobservablebutunstableintermediatespeciesthatdecomposetoyieldthethe()()2]2complexes(eq2).X-raystudiesshowedthat (1)Schrock,R.R.;Hoveyda,A.H.Angew.Chem.,Int.Ed.(2)Robbins,J.;Bazan,G.C.;Murdzek,J.S.;O'Regan,M.B.;Schrock,R.R.,2902.(3)Schrock,R.R.InReactionsofCoordinatedLigands;Braterman,P.R.,Ed.;Plenum:NewYork,1986.(4)Tsang,W.C.P.;Jamieson,J.Y.;Aeilts,S.A.;Hultzsch,K.C.;Schrock,R.R.;Hoveyda,A.H.,1997. (5)Schrock,R.R.;DePue,R.T.;Feldman,J.;Yap,K.B.;Yang,D.C.;Davis,W.M.;Park,L.Y.;DiMare,M.;Schofield,M.;Anhaus,J.;Walborsky,E.;Evitt,E.;KruÈger,C.;Betz,P.(6)Toreki,R.;Schrock,R.R.J.Am.Chem.Soc.,3367.(7)Toreki,R.;Vaughan,G.A.;Schrock,R.R.;Davis,W.M.J.Am.Chem.Soc.,127. 10.1021/om050961sCCC:$33.502006AmericanChemicalSocietyPublicationonWeb03/14/2006 thesedecompositionproductsareMMdimersthatcontainunbridgedmetalmetaldoublebond(2.3836(8)…whenORand2.396(1)…whenORO-t-Bu)andastaggered,ethane-likegeometry.Thesecompoundsreportedlydonotreactreadilywithvariousphosphines,olefins,oracetylenes,althoughtheirreactivitywasnotexploredingreatdetail.Uponirradiationwith360nmlight,the[Re(C-t-Bu)(OR)complexesaretransformedinto[Re(whosestructuresappeartocontain-C-t-Bugroups,accordingtoNMRstudiesandanX-raystudyofaderivative.OurinterestinthepossibilityofsynthesizingM(NR)(CHRspeciesinsitu(MMoorW)ledustoexplorereactionsbetweenMo(NAr)(CH-t-Bu)(CHorW(NAr)-andalcohols.Wefoundthatonlyoneneopentylgroupwasprotonatedtoyieldspeciesofthetype-t-Bu)(OR);insomecasesM(NAr)(CH(OR)wasformedinsteadandthencouldbetransformedintoM(NAr)(CH-t-Bu)(CH-t-Bu)(OR)uponheating.AswebegantoexplorethechemistryofM(NAr)(CH-t-Bu)(CHBu)(OR)andrelatedcomplexes,wefoundthatM(NAr)(CH-)complexesdecomposebimolecularlytogivedimersthatdonotcontainbridgingimidoligands,i.e.,speciesanalogoustotheRespeciesshownineq2.Wethenrevisitedtungstenbisalkoxidecomplexesthatwehadassumedtocontainbridgingimidoligandsandfoundthattheytoodonotcontainbridgingligands.Theresultsoftheseinvestigationsarereportedinfullhere.SynthesesandStructuresof[W(NAr)(CHComplexes(ORorOCH(CF)isformeduponadditionofCOHtoW(NAr)-AlthoughW(NAr)(CHisstableinsolutionatroomtemperatureforhours,itdecomposesinafirst-ordermanneruponheatingto60inC)togiveneopentaneandW(NAr)(CH-t-Bu)(CH).Apreparativereactionismoreconvenientlycarriedoutat80C.W(NAr)(CH-t-Bu)(CH)canbeisolatedonlywhenthedecompositioniscarriedoutunderrelativelydiluteconditions.WeproposethatW(NAr)(CH-t-Bu)-isadimerinthesolidstateanalogoustoitsmolybdenumanalogue,[Mo(NAr)(CH-t-Bu)(CH,whichcontainsbridgingpentafluorophenoxidesthatbehaveasdonorstotheneopentylideneligand.relativelyconcentratedbenzeneortoluenesolutionsofW(NAr)-)areheatedat80Cforseveralhours,)isformedbutthende-composestogivedi--butylethyleneandasparinglysolubleredcompound.TheHNMRspectrumofthisspeciesshowsonlyimidoandneopentylligandresonances.AsingleseptetisobservedfortheCprotonsintheNAr(N-2,6-i-Prligand,andtworesonancesareobservedfortheisopropylmethylgroups,consistentwithrapidlyrotatingArringsthroughwhichamirrorplanedoesnotpass.Thetwodoubletsobservedfortheneopentylmethyleneprotons(3.09and2.47ppm,14.5Hz)areassignedtodiastereotopicneopentylmethyleneprotons.TheFspectrumshowsthreedistinctresonancesforthefivefluorineatomsoftheOCligand.AllNMRdataareconsistentwithadimericspeciesinwhichnomirrorplanepassesthroughanyligand.AnX-raydiffractionstudy(Tables1and2;Figures1aand1b)revealedthatthecompoundis[W(NAr)(CHinwhichtheWWbondisnotbridged.Thestruc-tureadoptsastaggeredethane-likegeometryinwhichthetwoimidoligandsarewithrespecttooneanotherandthetwoendsofthemoleculearerelatedbyaninversioncenter.Thereforeitisachiraldimer.Themostimportantfeatureofthestructureof[W(NAr)(CHisthepresenceoftheunbridgedW(IV)/W(IV)doublebond,eventhoughimidoandalkoxideligandsarepresentthatcould,andoftendo,bridgemetalmetalbonds.Table2listsselectedbondlengthsandanglesofof()(2-t-Bu)(OC6F5)]2.TheWWbonddistanceof2.4443(2)…iswellwithintherangeofWWbondlengthsfoundinothercompoundsreportedhereandothersfoundintheliterature(seeDiscussionsection).TheWNbondlengthandWCangle(1.745(2)…and165.37(19))arenotunusual,whiletheC(20)angle(119.25(19))istypicalofaneopentylgroupthatisrelativelyundistortedbystericpressure.TherelativelylargeWC(13)angle(146.57(18)),ontheotherhand,mustbeascribedtoasignificantdegreeofbonding,possiblyincombinationwithsomestericpressurethatopensuptheWC(13)angle.Finally,astrikingfeatureofthemoleculeisthevirtual90angle(90.38(7))betweentheimidoligandsandtheWWbondvector.(Theorientationofneopentylidyneligandsinisoelectronicandisostructural[Re(C-t-Bu)(OR)O-t-BuorOCMe-)complexesiswhatonemightexpectonthebasisofstericrepulsionsbetweenalkylidyneligands,althoughananaly-sisofthebondingandenergeticsofmodelcompoundssug-gestedthatthisarrangementisalsopreferredelectronically.SinceanelectronicbarriertorotationabouttheReRebondin[Re(C-t-Bu)(OR)specieswaspredicted,weexpecttheretobeabarriertorotationabouttheWWbondinin()(2-t-Bu)(OC6F5)]2.WhenW(NAr)(CH-t-Bu)(CH)istreatedwith2-penteneatroomtemperature,twoproductsareformed,oneofthembeingbeing()(2-t-Bu)(OC6F5)]2.Thisreac-tionisbelievedtoinvolveformationofW(NAr)(CHR)(CH)(RMeorEt)species,whichdecomposemorerapidlyinabimolecularfashionthandoesW(NAr)(CH-t-).Thesamemixtureisobtainedwhen)isaddedtoasolutionof2-penteneatroomtemperature.Inthemoresolubleproducttheresonancesarebroad,consistentwitharateofrotationoftheArringsinthatspeciesontheorderoftheNMRtimescale.TheCrings,however,arefreelyrotatingontheNMRtimescale,astheyareinin()(2-t-Bu)-(OC6F5)]2.Thesecond,moresolubleproductwasfoundtobeasymmetricanalogueofof()(2-t-Bu)(OC6F5)]2,i.e.,homochiral[W(NAr)(CH(Tables1and2;Figures2aand2b).Despitetheinherentdifferencesinthe (8)Toreki,R.;Schrock,R.R.;Davis,W.M.J.Organomet.Chem.,69.(9)Sinha,A.;Schrock,R.R.,1643.(10)Lopez,L.P.H.;Schrock,R.R.J.Am.Chem.Soc.,9526.(11)Sinha,A.;Lopez,L.P.H.;Schrock,R.R.;Hock,A.;Mueller,P.,inpress. (12)Barckholtz,T.A.;Bursten,B.E.;Niccolai,G.P.;Casey,C.P.Organomet.Chem.,153. DimersthatContainUnbridgedWWBondsOrganometallics,Vol.25,No.8,2006 molecularsymmetry()andspectroscopicbehaviorofof()(2-t-Bu)(OC6F5)]2versushetero-[W(NAr)-(CH2-t-Bu)(OC6F5)]2(videsupra),thebondlengthsandanglesinthecoordinationsphereofof()(2-t-Bu)-(OC6F5)]2arevirtuallyindistinguishablefromthoseinin()(2-t-Bu)(OC6F5)]2(Table2).However,theCWdihedralanglesinthetwostructuresaresignificantlydifferent.InIn()(2-t-Bu)(OC6F5)]2theCWdihedralangleis,whileinin()(2-t-Bu)(OC6F5)]2itis41.Asaconsequence,theCringinchiraldimerisdirectedfromtheimidoligand,whileinthechiraldimeritispointedtheimidogroup.Thisstructuraldifferencemightleadtoslightdifferencesinstericcongestioninthetwoisomersand,therefore,totheobservedslowerrateofrotationofthei-Prringsinin()(2-t-Bu)(OC6F5)]2.Sofarwehaveseennointerconversionofof()(CH2-t-Bu)(OC6F5)]2andhomo-[W(NAr)(CH2-t-Bu)(OC6F5)]2uponheatingsolutionsofoneortheother.ApparentlytheWWbondsdonotcleavespontaneouslyintopseudo-trigonal)fragmentsanalogoustostructurallycharacterizedW(N-t-Bu)[OSi(t-Bu)MostlikelythelargesiloxligandsinW(N-t-Bu)[OSi(t-Bu)preventformationofof()3]2}2,whilethedoublebondsinin()(2-t-Bu)(OC6F5)]2andhomo-[W(NAr)(CH2-t-Bu)-(OC6F5)]2aresimplytoostrongtocleavehomolyticallyunderrelativelymildconditions.AlthoughW(NAr)(CH-t-Bu)(CHW(NAr)(CH-t-Bu)(CH(3)2]isrela-tivelystablethermally,upontreatingaconcentratedsolutionofW(NAr)(CH-t-Bu)(CHW(NAr)(CH-t-Bu)(CH(3)2]inpentanewith2-pentene,theinitiallyyellowreactionmixtureturnedredwithinminutesandredcrystalsweredepositedoveraperiodofdaysC.TwoproductswereobservedwhosesolubilitiesandNMRpropertiesareanalogoustothoseforfor()(CH2-t-Bu)(OC6F5)]2andhomo-[W(NAr)(CH2-t-Bu)(OC6F5)]2.Thereforeweproposethatthesespeciesareare(3)2]}2andhomo-{W(NAr)(CH2-t-Bu)-[OCH(CF3)2]}2;themoresolubleisomershowsslowerrotationoftheNArringsontheNMRtimescale,asfoundforchiral[W(NAr)(CHAnX-raystructuralstudyofthemoresolubleproductcon-firmsthatitisis(3)2]}2(Tables1and2,Figure3).Thiscompoundsharesthesamegeneralfeaturesasas()(2-t-Bu)(OC6F5)]2showninFigure2,e.g.,astaggeredethane-likegeometry,groups,closeto90Wangles(91.55(14)and92.67-),andaW(IV)/W(IV)doublebond(2.4537(3)…).TheWdihedralanglein (13)Eppley,D.F.;Wolczanski,P.T.;VanDuyne,G.D.Angew.Chem.,Int.Ed.Engl.,584. Table1.CrystalDataandStructureRefinementforfor()(2-t-Bu)(OC6F5)]2,Homo-[W(NAr)(CH2-t-Bu)(OC6F5)]2,andHomo-{W(NAr)(CH2-t-Bu)[OCH(CF3)2]}2empiricalformulaCfw1226.631318.761194.58temp(K)193(2)194(2)K194(2)crystsystmonoclinicmonoclinicorthorhombicspacegroupnPbcaunitcelldimens,…10.5289(6)13.1211(15)18.3215(7),…9.9479(6)11.1659(13)19.8284(7),…22.5331(14)18.596(2)26.2556(10,deg909090,deg94.8380(10)100.116(3)90,deg909090volume(…)2351.7(2)2682.2(5)9538.3(6)density(calcd;Mg/m)1.7321.6331.664abscoeff(mm)4.9654.3604.900(000)120013004672crystsize(mm)0.450.300.200.070.95range(deg)1.81to27.881.82to26.021.70to28.29indexrangesno.ofreflnscollected146371699765656no.ofindepreflns[(int)]5558[0.0236]5181[0.0302]11836[completenessto99.2%98%99.9%abscorrsemiempiricalsemiempiricalsemiempiricalmax.andmin.transmn0.3174and0.21350.7500and0.47590.1203and0.0898no.ofdata/restraints/params5558/81/3125181/343/41811836/17/535goodness-of-fiton1.0281.0261.064indices[)]R10.0200R10.0225R10.0470wR20.0504wR2indices(alldata)R10.0246R10.0291R10.0484wR20.0531wR2largestdiffpeakandhole(e…)0.756and0.7740.902and0.4932.920andInallcasesthewavelengthwas0.71073…andtherefinementmethodwasfull-matrixleast-squareson Table2.SelectedBondDistances(…)andAngles(deg)inHeterochiralandHomochiral[W(NAr)(CHandHomochiral W2.4443(2)2.4492(3)2.4537(3)N1.745(2)1.747(3)1.757(5)1.747(5)O1.9339(18)1.924(2)1.908(4)1.915(5)C2.135(3)2.134(3)2.123(6)2.123(7)W90.38(7)91.06(8)91.55(14)92.67(16)O132.40(9)136.23(11)131.0(2)129.5(2)C106.28(11)102.46(12)105.9(2)106.5(2)C110.23(10)109.23(12)109.3(2)110.3(3)W113.15(6)109.94(7)112.89(14)111.68(17)W97.99(7)102.72(9)101.86(17)101.98(18)W165.37(19)171.4(2)166.4(4)168.0(4)W146.57(18)156.4(2)146.7(4)148.4(5)W119.25(19)115.9(2)117.8(4)119.3(5)Organometallics,Vol.25,No.8,2006Lopezetal. (3)2]}2is-9°,whileitis4141()(2-t-Bu)(OC6F5)]2.Synthesisof[W(NArBisalkoxidecomplexesofthetypeW(NArhavebeenpreparedfromW(NAr(dme),whichwaspreparedthroughbase-catalyzedprotontransferinW(NHArhasnotbeenreported.Itcanbepreparedfrom(dme),whichwassynthesizedinamanneranalogoustothatforW(NAr)(CH-t-Bu)(OTf)i.e.,bytreatingW(NArwith2equivoftriflicacid.HNMRspectrumofyellow-orangeW(NArshowsasingletat6.87ppm(16Hz)fortheneopentylideneproton.ThisiscomparabletoHof6.74ppmobservedforW(NAr)(CH-t-Bu)(CH6.61ppmreportedforW(NPh)(CH-t-Bu)(CHwasobtainedasaredoiluponadditionofLiCH-t-ButoCl.AttemptstosynthesizeW(NArviaalkylationofW(NAr(THF)with3equivoft-BuCHMgClatCconsistentlygaveamixtureofW(NArClandW(NAraccordingtoNMRspectra,andpossiblyother(unidentified)products,fromwhichW(NArcouldnotbeisolatedinpureform.AdditionofpentafluorophenoltoW(NAryieldsW(NAr),aproductanalogoustothatobtaineduponadditionofpentafluorophenoltoW(NAr)-Heatingatoluene-solution(0.10M)ofW(NAr)to60CyieldswhatweproposetobeW(NAr9.36ppm),althoughalleffortstoisolatethisspeciesprovedunsuccessfulasaconsequenceofitsfaciledecompositiontoyieldt-BuCHCH-t-Buand[W(NAr)(CH(eq3).Thebasic (14)Pedersen,S.F.;Schrock,R.R.J.Am.Chem.Soc.,7483. Figure1.(a)Thermalellipsoiddrawingofthemolecularstructureofheterochiral[W(NAr)(CH.(b)Chem3Dviewfromtheendofheterochiral[W(NAr)(CH Figure2.(a)Thermalellipsoiddrawingofthemolecularstructureofhomochiral[W(NAr)(CH.(b)Chem3Dviewfromtheendofhomochiral[W(NAr)(CH DimersthatContainUnbridgedWWBondsOrganometallics,Vol.25,No.8,2006 problemappearstobethatW(NAr)islessstericallycrowdedthanW(NAr)(CH)andsodecomposestoyieldaneopentylidenecomplexmoreslowlythanW(NAr)(CH),whileW(NAr),againforstericreasons,ispronetodecomposebimolecularlythanisW(NAr)(CH-t-Bu)(CH).ThereforeonlyarelativelysmallquantityofW(NAr)(amaximumof10%)hasbeenobserved.Asexpected,[W(NArinequivalentneopentylmethyleneprotons,characteristicofdimericspeciesofthisgeneraltype,andthereforealmostcertainlyalsocontainsanunsupportedW(IV)/W(IV)doublebond.Webelieve[W(NArtobeahet-erochiraldimeronthebasisofitsformationviacouplingofneopentylidenecomplexesandtheequivalenceofall2,6-NgroupsontheHNMRtimescale.However,itispossiblethatthehinderedrotationofArringsinthehomochiraldimersdiscussedaboveisaconsequenceofbulkyisopropylgroupsbeingpresentandnotanintrinsicpropertyofhomochiraldimersregardlessofthenatureoftheimidogroup.Thereforewecannotsaywithcertaintythat[W(NArisinfactheterochiral.SynthesesandStructuresofof(3)2]2}2,[W(NAr¢)(OCMe2CF3)2]2(Ar¢)2,6-Me2C6F3),and[W(NAr)-Upondiscoveryofthe[W(NR)(CHcomplexesdescribedabove,weconsideredthepossi-bilitythatonlymonoalkoxidespeciesofthisgeneraltypehadunbridgedMMbonds.However,someinconsistensiesintheliteratureconcerningtheproductsofdecompositionofW(NAr)-complexes,asdescribedintheIntroduction,suggestedthatthismaynotbethecase.UnstableW(NArW(NAr(3)2]2decomposestoyieldyield(3)2]2º,whichwasproposedtobebe(3)2]2}2.5CrystalsofthiscompoundsuitableforX-raydiffractionstudieswereobtainedinthesamemannerasdescribedintheliterature.TheX-raystudywasmarredbyacomplexdisorder(seeExperimentalSection).However,thedisorderwassolvedsatisfactorilyandthisspecieswasfoundtobebe(3)2]2}2,inwhichtheWWbondisunsupportedbybridgingligands(2.4751(4)…;Tables3and4andFigure4.Structuralfeaturesofthisdimerareanalogustothoseforthemonoalkoxidedimersdescribedabove.above.()(2CF3)]2and[W(NArpreparedinamanneranalogoustothatemployedtoprepareprepare(3)2]2}2,asshownineq4.X-raydiffractionstudiesshowedthatbothareunbridgeddimersthatarevirtuallyidenticaltoto(3)2]2}2(Tables3and4,Fig-ures5and6).InprotonNMRspectraofbothcompounds,thetwomethylgroupsoftheOCligandsareinequiva-lent,consistentwiththe-symmetricstructure.[W(NAr)-isthespeciesreportedherethatisobtainedinthelowestyieldandnotreproducibly.ClearlyformationoftheWWbondisverysensitivetothesizeofthecovalentlyboundligandsandconditionsinamannerthatisnotyetTherearerelativelyfewexamplesofMMbondsinthelit-erature,andmostofthosethatareknowncontainbridginglig-ands.Forexample,Caseyreported(),whichcontainsaReRedoublebond(2.723(1)…)inwhichtwoofthecarbonylligandsareªsemibridgingº.BridgedW(IV)/W(IV)doublebondsarefoundin[K(18-crown-[K(18-crown-2(í-H)(í-O)(OC-t-Bu)6](2.445(1)…),…),2(-O2C-t-Bu)4(í-MeCCMe)2](2.4888(2)…),…),2(-O2C-t-Bu)4(í-PhCCMe)2](2.4925(2)…),andWofcomplexesthatcontainametalmetaldoublebondandnopotentiallybridgingligandsincludemacrocyclecomplexessuchas[M(octaethylporphyrin)]Ru,Os)and[Ru-Thecompound(i-PrO)bridgingligands)couldbesaidtobeaddimerinwhicha (15)Casey,C.P.;Sakaba,H.;Hazin,P.N.;Powell,D.R.J.Am.Chem.,8165.(16)Casey,C.P.,1552.(17)Budzichowski,T.A.;Chisholm,M.H.;Folting,K.;Huffman,J.C.;Streib,W.E.J.Am.Chem.Soc.,7428.(18)Byrnes,M.J.;Chisholm,M.H.;Gallucci,J.;Wilson,P.J.,2240.(19)Chisholm,M.H.;Streib,W.E.;Tiedtke,D.B.;Wu,D.D.Eur.J.,1470.(20)Collman,J.P.;Barnes,C.E.;Swepston,P.N.;Ibers,J.A.J.Am.Chem.Soc.,3500.(21)Warren,L.F.;Goedken,V.L.J.Chem.Soc.,Chem.Commun.(22)Chisholm,M.H.;Folting,K.;Kramer,K.S.;Streib,W.E.,1549. Figure3.Thermalellipsoiddrawingofthemolecularstructureofhomochiral[W(NAr)(CH Figure4.Thermalellipsoiddrawingofthemolecularstructureofof(3)2]2}2(onemoleculeoftwo). Organometallics,Vol.25,No.8,2006Lopezetal. Wbondispresent(2.52429(9)…),althoughalternativeexplanationsarepossible.WebelievethatunbridgedMcomplexesofthetype[Re(C-t-Bu)(OR)andtheWspeciesreportedhere,aretheonlysymmetricMMcomplexesthatarestableatroomtemperatureandinwhichpotentiallybridgingligandsarepresent.TheyalsoappeartocontaintheshortestWWbondsknown.ThefactthattheyalsohaveCHRrelativesthatareolefinmetathesiscatalystsisalsoanoteworthyfeatureofsuchspecies.ThereforeonecouldviewtherelationshipbetweentheunbridgedMMbondsdescribedhereandMCbondsintheirrelativesasanalogoustotherelationshipbetweenMMbondsandMCbondsalkynemetathesiscatalysts;forexample,alkynescanreactwithMbondstoyieldalkylidynesTherecentfindingthatMMspeciescaninitiateolefinmetathesisreac-raisesthepossibilitythatMMspeciescanreactwithCbondstoyieldMCspecies,thereverseofthereactioninwhichtheyareformed.However,thereareseveralalternativepossibilities,sowhetherthisistrueornotisunknown.TheWWbondedspeciesreportedherearecharacterizedbya90Nangleanda180Ndihedralangle.The90Nanglesuggeststhatthethreearoundthemetalcenterareformedfromthethreemutuallyperpendicular,essentiallypured,anddorbitals,whilethefourbondsareformedfromthethreeporbitalsandsomecombinationofsanddorbitals.Inmodelsof[Re(C-t-Bu)- (23)Toreki,R.;Schrock,R.R.;Vale,M.G.J.Am.Chem.Soc.,3610.(24)Murdzek,J.S.;Schrock,R.R.InCarbyneComplexes;VCH:NewYork,1988. (25)Schrock,R.R.;Listemann,M.L.;Sturgeoff,L.G.J.Am.Chem.,4291.(26)Listemann,M.L.;Schrock,R.R.,74.(27)Chisholm,M.H.;Hoffman,D.M.;Northius,J.M.;Huffman,J.C.,839.(28)Schrock,R.R.;Lopez,L.P.H.;Hafer,J.;Singh,R.;Sinha,A.;Mueller,P.,5211. Table3.CrystalDataandStructureRefinementfor[W(NAr,[W(NAr,and[W(NAr)(OR (¢)(ORF6)2]2[W(NAr¢)(ORF3)2]2[W(NAr)(ORF3)2]2empiricalformulaCfw1330.281114.381226.58temp(K)100(2)193(2)193(2)Kcrystsystmonoclinicmonoclinicmonoclinicspacegroupunitcelldimens,…17.1623(5)10.4324(7)19.7134(8),…13.2753(4)13.2926(9)11.1767(4),…36.7743(11)14.0726(10)21.4229(8),deg909090,deg96.4960(10)97.1920(10)90.0250(10),deg909090volume(…)8324.7(4)1936.1(2)4720.1(3)824density(calcd;Mg/m)2.1231.9111.726abscoeff(mm)5.6696.0314.956(000)505610722400crystsize(mm)0.150.050.110.050.30range(deg)1.26to29.572.12to28.271.90to28.28indexrangesno.ofreflnscollected3315771342832828no.ofindepreflns[(int)]23350[0.0594]4790[0.0185]11707[completenessto100.0%99.9%100.0%abscorrsemiempiricalsemiempiricalsemiempiricalmax.andmin.transmn0.7647and0.48350.7525and0.55670.5235and0.3179no.ofdata/restraints/params23352/3692/14034790/0/24111707/562/671goodness-of-fiton1.2751.0291.087indices[)]R10.0622R10.0218R10.1385wR20.0563wR2indices(alldata)R10.0727R10.0249R10.1438wR20.0588wR2largestdiffpeakandhole(e…)3.175and1.5031.813and0.9461.625andInallcasesthewavelengthwas0.71073…andtherefinementmethodwasfull-matrixleast-squareson Table4.SelectedBondLengths(…)andAngles(deg)in[W(NAr,[W(NAr,and[W(NAr)(OR (¢)(ORF6)2]2[W(NAr¢)(ORF3)2]2[W(NAr)(ORF3)2]2WdW2.4751(4)2.4909(2)2.4925(3)N1.755(7),1.737(6)1.751(2)1.749(5),1.754(5)O1.902(6),1.892(5)1.9239(18)1.914(4),1.919(4)O1.915(5),1.909(5)1.860(2)1.878(4),1.876(4)W92.4(2),93.8(2)92.59(7)94.92(16),93.75(15)O114.5(3),111.8(3)114.90(9)114.86(18),119.2(2)O117.2(3),120.2(3)119.55(9)116.9(2),117.0(2)O112.0(3),112.6(3)110.19(9)109.80(19),108.8(2)W104.88(18),102.48(18)104.29(6)104.72(14),104.10(14)W113.7(2),113.10(18)113.53(6)112.41(14),113.86(15)W170.3(7),169.5(6)172.42(9)169.6(4),166.7(4)W135.4(5),132.9(5)132.61(17)137.5(4),134.1(4)W151.4(6),163.3(5)153.09(18)152.0(4),159.9(4)DimersthatContainUnbridgedWWBondsOrganometallics,Vol.25,No.8,2006 O-t-BuorOCMe(CF)complexesthatthearrangementofthemultiplyboundalkylidyneligandswasenergeticallypreferred.Astaggeredstructureissensibleonthebasisofstericargumentsalone.WecanimaginethatMMbondsmightbeformedthroughcouplingofalkylidenesasshownineq5.One(bondeffectivelyreactsinamanneranalogoustoa(polarized)Cbondwiththeother()bondtoforma1,3-dimetallacyclobutaneintermediate.Whatamountstoacom-poundofthistyperecentlyhasbeenobservedthroughNMRThecompoundis[W(NAr)(-diolate.AkeyfeatureofitsNMRspectrumisasingletresonanceat185.9ppmflankedwithsetsoftungstensatellites(78.9,36.7Hz),characteristicofthemethylenecarbonbeingcoupledtotwodifferentWnuclei.Theproton-coupledspectrumrevealsthatthemethylenecarboniscoupledtotwoinequivalentprotons(148,131Hz)locatedat8.20and7.37ppmintheprotonNMRspectrum.Thefactthatthisspeciescanbeobservedandthatnocarboncarbonbondhasyetformedsuggeststhatitmayhavetorearrangefirsttoa1,2-dimetalacyclicspeciesfromwhicholefincanbelostreadily.Infact,a1,2-dimetallacyclicspeciesthatcontainsonebridgingalkoxidehasbeenobservedtoformreversiblywhenethyleneisaddedto(CFMoreover,(CFwillmetathesizecertainolefinsslowly.Thereforethereissomepossibilitythatmonomericalkylidenesareformedfromthe1,2-dimetalacyclobutane.Thatisnotyetknown.InanycaseitseemsclearthatMMbondsformfromalkylidenesinsmallstepsastheolefinisformedandejected.WhetheraMMbondactuallyformsislikelytodependonanumberoffactors,amongthemtheoverallstericbulkofthecovalentlyboundligandsinvolved(imido,alkoxide,alkyl)andwhatligands(e.g.,olefins)bindtothemetalinamonomerordimerandtherebypreventformationoftheMMspecies.ReductionofW(N-t-Bu)(Silox))hasproducedpseudo-trigonalplanarW(N-t-Bu)(Silox)ofhypothetical(Silox),presum-ablybecausedimerizationispreventedbythebulkoftheSiloxgroups.Recently,reductionofW(NArbeenshowntoyield(CFwhilesodiumamalgamreductionofMo(N-t-Bu)[OSi-hasbeenreportedtoyieldyield(t-Bu)3]2}2(í-Hg).30Thespectroscopyofof(t-Bu)3]2}2(í-Hg),alongwithcalculations,allowedthestrengthofthecomponentoftheMoMobondin[Mo(NAr)(CHtobeestimatedas27kcal/mol.Ifthecomponentisworth27kcal/mol,wemightguessthattheentiredoublebond(includingtheportion)willbeworth75kcal/molandthatWWbondsprobablywouldbestrongerthanMobonds.ThefindingsinthispaperareconsistentwithWbondsbeingrelativelystrongandthefailuretoseescramblingbetweenheterochiralandhomochiraldimers.FuturestudieswillbeconcernedwithreactionsthatinvolveWbondsalongthelinesthathaveappearedinapreliminaryExperimentalDetailsGeneralProcedures.Allair-sensitiveworkwascarriedoutinaVacuumAtmospheresdryboxunderadinitrogenatmosphereorbystandardSchlenktechniques.Allsolvents,exceptmethylenechlorideanddimethoxyethane,werespargedwithnitrogenandpassedthroughacolumnofactivatedalumina.MethylenechloridewasdistilledfromCaH,whiledimethoxyethanewasdistilledfrombenzophenoneketylbeforebeingdegassed(freezethaw)threetimes.Alldeuteratedsolvents,aswellasthealco-holsandphenolsused,weredegassedbeforebeingbroughtintothebox.Allsolventswerestoredover4…molecularsieves.Alllithiumalkoxideswerepreparedthroughadditionoftothealcohol.W(NAr)ClW(NAr)Cl(3)2],10and{W(NAr¢)[OCMe(CF3)2]2}25werepreparedasdescribedintheliterature. (29)Tsang,W.C.P.;Hultzsch,K.C.;Alexander,J.B.;Bonitatebus,P.J.J.;Schrock,R.R.;Hoveyda,A.H.J.Am.Chem.Soc.,2652. (30)Rosenfeld,D.C.;Wolczanski,P.T.;Barakat,K.A.;Buda,C.;Cundari,T.R.J.Am.Chem.Soc.,8262.(31)Schrock,R.R.;Murdzek,J.S.;Bazan,G.C.;Robbins,J.;DiMare,M.;O'Regan,M.J.Am.Chem.Soc.,3875. Figure5.Thermalellipsoiddrawingofthemolecularstructureof Figure6.Thermalellipsoiddrawingofthemolecularstructureof Organometallics,Vol.25,No.8,2006Lopezetal. HandCNMRchemicalshiftsarelistedinpartspermillionreferencedtoeithertheresidualprotonsorCatomsofthedeuteratedsolvents.FNMRshiftsarereportedrelativetousedasanexternalreference.HNMRspectrawereobtainedonaninstrumentoperatingat300MHz(unlessotherwisenoted),CNMRspectrawereobtainedonaninstrumentoperatingat125MHz,whileFNMRspectrawereobtainedona282MHzinstrument.Allspectrawererecordednear22-andand(3)2]}2.ToarapidlystirredsolutionofW(N-2,6-i-PrW(N-2,6-i-Pr(3)2](470mg,0.704mmol)inaminimumamountofpentaneatroomtemperaturewasaddeddropwise1.52mL(14.1mmol)of-2-pentene.Themixturewaslefttostirovernight.Thevolatileswereremovedinvacuotogivearedoil.MinimumamountofpentanewasaddedandthesolutionkeptatC.Darkredcrystals,formedoveraperiodoftwoweeks,werecollectedonafritandwashedwith31mLofcoldpentanetogive60mgoftheproductasamixtureof-andchiralisomersinapproximatelya7:1ratio(11%yield).yield).(3)2]}2:1HNMR(C,500MHz)7.10(t,2),7.03(d,4),4.89(m,2),4.44(m,2),3.07(m,2),2.37(d,2,15Hz),2.04(d,2,15Hz),1.61(d,6),1.32(d,6),1.25(d,6),1.02(s,18),1.01(d,6).6).(3)2]}2:1HNMR(C,500MHz)7.09(t,2),7.01(d,4),5.22(m,2),3.85(m,4),2.59(d,2,14Hz),2.42(d,2,15Hz),1.30(d,12),1.23(d,12),0.99(s,18).Anal.CalcdforCW:C,40.22;H,4.89;N,2.35.Found:C,40.36;H,5.01;N,2.32.2.32.()(2CMe3)(OC6F5)]2.AsampleofW(NAr)-)(1.010g)wasdissolvedinaminimumamountoftoluene,andthesolutionwasheatedat80Cfor48h.Aredsolidcrystallizedoutofsolution,wascollectedonafrit,andwaswashedliberallywithpentane;yield585mg(70%):HNMR,500MHz)7.17(d,4),7.08(t,2),3.86(m,4),3.09(d,2,14.5Hz),2.47(d,2,14.5Hz),1.30(d,12),1.01(s,18),0.99(d,12);FNMR(C159.29(d,4),164.80(t,167.80(t,2).Anal.CalcdforCW:C,45.04;H,4.60;N,2.28.Found:C,44.88,H,4.54,N,2.33.2.33.()(2-t-Bu)(OC6F5)]2.AsolutionofW(NAr)-)(700mg,1.024mmol)in10mLofpentanewasaddeddropwisetoarapidlystirredsolutionof2.21mL(20.85mmol)of-2-pentenein10mLofpentane.Solidsformedwithin20min.Thedarkredreactionmixturewasstirredovernight.Theinsolubleproductwascollectedonafrit,washedwithliberalamountsofpentane(25C),anddriedtogive40mgofred-orangered-orange()(2-t-Bu)(OC6F5)]2,whichwasidenticaltothecompoundpreparedviatheprecedingmethod.Thefiltratewascollectedandconcentratedtodryness.Theresiduewascollectedonafrit,washedwithpentane,anddriedtogive250mgofredred()(2-t-Bu)(OC6F5)]2;yield40%:NMR(C,500MHz)6.86(br,6),4.49(br,2),3.06(br,2),2.60(d,2,15Hz),2.19(d,2,15Hz),1.72(br,6),1.36(br,6),1.25(br,6),1.12(s,18),0.88(br,6);FNMR(C158.6(d,4),164.3(t,4),167.1(t,2).Neopentylmagnesiumchloride(3.41mL,1.35M)wasaddeddropwisetoarapidlystirredsolutionofW(N-2,6-Me(dme)(1.75g,2.298mmol)in20mLofetheratC.After8h,allvolatileswereremovedinvacuo.Theproductwastakenupin20mLofpentane,thesolutionwasfilteredthroughabedofCelite,andthefiltratewasconcentratedtodrynesstogiveayellow-orangesolid(1.13g)in90%yield:HNMR(C7.00(2,3),6.87(t,1),6.78(s,1,15.5Hz),2.48(s,6),2.37(d,2,14Hz),1.18(s,9),1.16(s,18),0.78(d,2,14Hz).Anal.CalcdforWNCC,53.6;H,8.02;N,2.72.Found:C,53.48,H,8.11,N,2.71.(500mg,0.970mmol)wasdissolvedinpentaneandwastreatedwith1equivofHOC(179mg).Theresultingyellowsolutionwasstirredfor1h,afterwhichthevolatileswereremovedinvacuo.Theresiduewascollectedonafritandwashedwithcoldpentanetogiveayellowpowder;yield420mg(62%):HNMR6.91(d,2),6.78(t,1),4.15(m,2),2.61(s,6),2.21(s,6,9.6Hz),1.10(s,27);FNMR(C156.9(d,2),165.2(t,2),170.9(t,1).Anal.CalcdforWNOF:C,49.8;H,6.05;N,2.00.Found:C,49.75,H,6.11,N,1.95.ObservationofW(NArW(NAr(3)2].Hexafluor-oisopropylalcohol(6.7L,1.1equiv)wasaddedviasyringetoasolutionofW(NAr(30mg,0.058mmol)in0.80mLofCinanNMR(JY)tube.AprotonNMRspectrumshowedthatW(NArW(NAr(3)2]hadformedquan-HNMR(C6.90(d,2),6.78(t,1),5.19(m,1),2.57(s,6),2.01(s,6),1.07(s,27);FNMR(C(C(3)2].Toasolutionof300mg(0.493mmol)ofW(NAr)(CH(Cl)in5mLofbenzenewasaddedasasolid1equivofLiOCH(CF.Thereactionmixturewasheatedat60Covernightasitwasbeingstirred,afterwhichitwasfilteredthroughabedofCelite,andthefiltratewasconcentratedtodrynesstogivethedesiredproductasaredoilinvirtuallyquantitativeyield(320mg):HNMR(C8.96(s,15Hz),7.05(m,3),4.50(m,1),3.70(m,2),2.58(d,1,15Hz),2.13(d,1,15Hz),1.28(d,6),1.26(d,6),1.14(s,9),1.12(s,9);FNMR(C74.0(q,3)and(q,3).3).(¢)(CH2-t-Bu)(OC6F5)]2.AsolutionofW(NAr)preparedasdescribedabovefrom1.03g(1.472mmol)ofW(NArinaminimumamountofbenzenewasheatedat60Cfor48h.TheresultingredsolutionwascooledtoC.Theredsolidthatcrystallizedoutofthesolutionwascollectedonafritandwashedwithpentane.Thefiltratewasthenconcentratedtodryness,andtheresiduecollectedonafritandwashedwithpentanetogivearedpowder.Combinedyield:427mg(52%);HNMR(toluene-,500MHz)6.98(d,4),6.94(t,2),3.08(d,2,14.5Hz),2.46(s,12),2.36(d,2,14.5Hz),0.91(s,18);FNMR(C158.8(d,4),164.2(t,4),167.80(t,2).Anal.CalcdforCW:C,40.96;H,3.62;N,2.51.Found:C,40.84;H,3.68;N,2.57.(dme)(1.00g,1.31mmol)wasdissolvedin30mLofTHF.ThesolutionwascooledtoC,and352mg(2.627mmol)ofwasadded.Themixturewasallowedtowarmtoroomtemperatureasitwasbeingstirred.After12h,thereactionmixturewasconcentratedtodrynessinvacuo.Theresiduewasthenextractedintopentane,andthemixturewasfiltered.Removalofvolatilesinvacuoafforded670mgofayellowpowder,whichwaspurebyNMR(81%yield):HNMR(C8.48ppm(s,1),6.93(d,2),6.86(t,1),2.28(s,6),1.31(s,6),1.25(s,6),1.13(s,9);FNMR(C82.1ppm(s).AccordingtotheNMRdataandproperties,thiscompoundisidenticaltothatpublished.published.(¢)(OCMe2CF3)2]2.AsolutionofW(N-2,6-Me(4.70g,7.49mmol)in20mLofpentanewastreatedwith10equivof2-pentene(8.1mL,75mmol)atroomtemperature.Theyellow-orangesolutionimmediatelyturnedred.Themixturewasstirredovernight,duringwhichtimeyellowish-brownmicrocrystalswereformed.Thesolidswerecollectedonafrit,washedwithliberalamountsofpentane,anddriedinvacuotogive3.48gofproduct(83%yield):HNMR(toluene-(m,6),2.54(s,12),1.26(s,12),1.19(s,12);FNMR(toluene-82.72(s).Anal.CalcdforC:C,34.49;H,3.80;N,2.51.Found:C,34.28;H,3.74;N,2.49.SinglecrystalssuitableforX-raydiffractionstudiesweregrownintoluenesolutionatat()(2CF3)2]2.cis-2-Pentene(1.58mL,14.6mmol)wasaddedtoarapidlystirredsolutionofW(N-2,6-i-Pr(500mg,0.732mmol)in5mLofpentaneatDimersthatContainUnbridgedWWBondsOrganometallics,Vol.25,No.8,2006 roomtemperature.Theresultingredsolutionwasstirredfor16h.Removalofvolatilesinvacuogavearedoil,intowhichwasadded1mLofpentane.ThesolutionwaskeptatC.Red-browncrystalssuitableforX-raydiffractionstudieswereformedoveraperiodoftwoweeks.Severalcrystalsweremanuallyisolatedandsubjectedtocrystallographicstudies.Theremainingproductwascollectedonafrit,washedwith21mLofcoldpentane,anddriedtogive18mgoftheproduct(5%yield):HNMR(C7.16(m,6),4.02(m,4)1.34(s,12)1.31(brs,24),1.25(s,12);FNMR(C82.2(s).X-rayDiffractionStudies.Low-temperaturedatawerecollectedonaSiemensPlatformthree-circlediffractometercoupledtoaBruker-AXSSmartApexCCDdetectorwithgraphite-monochro-matedMoKradiation(0.71073…),performing-and-scans.Allstructuresweresolvedbydirectmethodsusingandrefinedagainstonalldatabyfull-matrixleastsquareswithSHELXL-97.Allnon-hydrogenatomswererefinedanisotropically.Allhydrogenatoms(excepthydrogenatomsoncarbonthatbindsdirectlytotungsten)wereincludedinthemodelatgeometricallycalculatedpositionsandrefinedusingaridingmodel.AllhydrogenatomsboundtocarbonatomsdirectlylinkedtotungstenhavebeentakenfromthedifferenceFouriersynthesisandrefinedsemi-freelywiththehelpofdistancerestraints.Theisotropicdisplacementparametersofallhydrogenatomswerefixedto1.2timesthevalueoftheatomstheyarelinkedto(1.5timesformethylgroups).DetailsofthedataqualityandasummaryoftheresidualvaluesoftherefinementsarelistedinTables1and3.Boththe-andand()(2-t-Bu)(OC6F5)]2crys-tallizeinmonoclinicspacegroupswithhalfamoleculeintheasymmetricunit,andinbothstructurestheonecrystallographicallyindependentt-Bugroupisdisordered.Thesedisorderswererefinedwiththehelpofsimilarityrestraintson12and13distancesanddisplacementparametersaswellasrigidbondrestraintsforanisotropicdisplacementparameters.Theratioswererefinedfreely,whileconstrainingthetotaloccupancyofbothcomponentstounity.Inadditiontothehalfmoleculeofof()(2-t-Bu)-(OC6F5)]2,thereishalfatoluenemoleculeintheasymmetricunit.Thissolventmoleculeisdisorderedoverfourpositions,involvingthecrystallographic2-fold.Itwasnecessarytoconstrainthesixcarbonatomsofthephenylringsinbothcrystallographicallyindependentcomponentstobeperfectlyhexagonal.Thestructuresof[W(NArand[W(NAr)(ORshowwhole-moleculedisorder.Inthestructureof[W(NAr,bothcrystallographicallyindependentmoleculesshowatleast3-fold(ifnot4-fold)whole-moleculedisorder.Themajorcomponentshaveoccupanciesof87.4%and86.3%,respectively;theoccupanciesoftheminorcomponentsrefinedto8.8%and3.9%foronemoleculeand9.8%and3.9%fortheother.Thewhole-moleculedisorderof[W(NAr)(ORisonly2-fold,andtheratioconvergedat95:5.Inbothstructures,onlysomeofthelighteratomsoftheminorcomponentscanbefoundandtherefinementofthosepositionswasnotstable.Therefore,onlythetungstenpositionsweremodeledasinvolvedinthewhole-moleculedisorderandtheoccupanciesofthelighteratomswereleftat100%.Thisleadstosomewhatinflatedlookingthermalellipsoidsforthoselighteratoms.Furthermore,inthestructuresofboth[W(NAr[W(NAr()(F3)2]2severalCFandCCHgroupsaredisor-deredwithinthemaincomponentofthewhole-moleculedisorder.Thesedisorderswererefinedwiththehelpofsimilarityrestraintson12and13distancesanddisplacementparametersaswellasrigidbondrestraintsforanisotropicdisplacementparameters.Theratioswererefinedfreely,whileconstrainingthetotaloccupancyofbothcomponentstounity.WethanktheNationalScienceFounda-tion(CHE-9988766andCHE-0138495)forsupportingthisSupportingInformationAvailable:Crystaldataandstructurerefinement,atomiccoordinatesandequivalentisotropicdisplace-mentparameters,bondlengthsandangles,anisotropicdisplacementparameters,andhydrogencoordinatesforfor()(2-t-Bu)(OC6F5)]2(03265A),homo-[W(NAr)(CH2-t-Bu)(OC6F5)]2(04148),homo-{W(NAr)(CH2-t-Bu)[OCH(CF3)2]}2(04097),{W(NAr¢)[OC-Me(CF3)2]}2(04231),[W(NAr(04102),andand()(2CF3)2]2(04107).ThisinformationisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.Dataforthefourstructuresarealsoavailabletothepublicathttp://www.recipro-calnet.org/.Thenumberinparenthesesaboveidentifieseachstructureatthissite. (32)Sheldrick,G.M.ActaCrystallogr.Sect.A,467.(33)Sheldrick,G.M.SHELXL97;UniversitaÈtGoÈttingen:GoÈttingen,Germany,1997.Organometallics,Vol.25,No.8,2006Lopezetal.