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CHEMISTRY OFCHELATE-STABILIZEDTUNGSTEN(VI) DIALKYLCOMPLEXES SHU-YU STEVE WANG ADISSERTATIONPRESENTEDTOTHEGRADUATE SCHOOL OFTHEUNIVERSITY OFFLORIDA INPARTIALFULFILLMENT OFTHE REQUIREMENTS FORTHEDEGREE OF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1998 Tomy wife Becky and my son Kyle ACKNOWLEDGMENTS My sincere appreciation isextended tomyresearch advisor.Dr. Jim Boncella, for hisexcellent guidence and support Jimhelped mefromunderstanding fundamental concepts todeveloping self-confidence and self-reliance. His advice,patience, and encouragementmotivatedmeduring those frustrationperiods andremindedmetobe humble when things went well. I ameternally grateful forwhatIlearnedfromJim, professionally andpersonally. I amalso grateful toDr. KhalilAbboudforhishelp, enthusiasm andpatience. He taughtmeeverything Iknow aboutcrystallography, fromthe basic concepts tohow to get highqualitycrystals. He also helped me solveall the nine X-raycrystal structuresin this dissertation, including the one with Ri=1.65%. Iwouldlike tothankthe members ofmycommittee. ProfessorsLisaMcElwee- White, DavidRichardson, KenWagener andAnthony Brennan fortheirhelp, advice and encouragement. Discussions with ProfessorsPhil Brucat, Bill Weltner, and Bill Dolbier are alsoinstrumental forthekinetics andmechanism workin Chapter4. Sincere thanks andaffection is alsoextendedtopastandpresentmembers ofthe Boncellagroup. Dr. Dan VanderLende andDr. Will Vaughan taughtme how to workwith air- andmoisture-sensitivechemicals andhow muchfun itcan beworidngday andnight Dr. Faisal Shafiq andDr. Dave Knoeppel helped with myexperimentaltechnique,provided me with valuable insightintochemistry and showedme whataprofessional chemistshould be. Percy Doufou, Jerrold Miller, Jon Penney, Perla Izsak, Carlos Ortiz, LeighHuff, Ryan Mills, Ken Weakley, andTimFoleyhavecreatedanenjoyableresearchenvironment andhelpedmewith myEnglish and understandingofAmerican Cultures. My parents have been the biggestpush formy desire toleam andstrengthen myself. Theirlove, guidance and supporthelpedme to bring outthe bestofmyself. The importantvaluesthey instilledin me will always help me withmy life. Finally, andmostimportandy, I would like to thankmy wife andmy bestfriend, Becky. She has beenvery understanding and supportive throughoutthese years andnever complained aboutspendingnumerous nights alone because Ihadanother "ovemighta*." Herlove has mademy life wonderful andwcathwhile. And the best gift she gaveme, our son Kyle, has been the bestcure when my experimentsdidnotwork and the biggest inspiration helpingme throughthosedifficulttimes. iv TABLEOFCONTENTS ACKNOWLEDGMENTS ABSTRACT CHAPTERS INTRODUCTION AND BACKGROUND 1. 1 Synthesis of Transition Metal Alkyl Complexes 1 DecompositionofTransitionMetal Alkyl Complexes 4 P-H Elimination and Abstraction 4 Decomposition of Metallacycles 7 a-H Elimination 8 2 SYNTHESIS, STRUCTURE AND REACTIVITY OF DIALKYL . COMPLEXES 13 Synthesis ofW(VI) Dialkyl Complexes 13 Structure Study forW(VI) Dialkyl Complexes 15 Pentacoordinated Complexes 25 Berry Pseudorotation 26 Turnstile Process 26 Fluxionality ofCompounds withBulky Alkyl Groups 28 Equilibrium Between SP andTBP Isomers of7 31 Coordination ofTrimethylphosphine 35 Insertion Reaction ofIsocyanide and 6 49 METATHESIS REACTION AND THE CHEMISTRYOF 3 . TUNGSTA(VI)METALLACYCLOPENTANE 52 Synthesis of the Alkylidene Complex 52 OlefinMetathesis 53 Metathesis Reactions of 1-Pentene 56 Formation ofMetallacyclopentane Complex 58 Mechanismofthe FormationofMetallacyclopentane Complex 63 Conclusions 70 4 MECHANISTIC INVESTIGATIONS OFTHE DECOMPOSITION OF p-H . CONTAININGW(VI) DIALKYLCOMPLEXES 72 Introduction 72 Synthesis ofTungsten(IV) Olefin Complexes 73 Mechanistic Studies 77 V Phosphine Dependence 82 DeuteriumLabeling Experiment 84 Mechanistic Study of the Formation of ethylene complex, 39 89 Mechanistic Study ofthe Formation ofstyrene complex, 40 91 CalculationofEntropy ofActivation 99 a- vs p-Abstraction Reactions 102 Discussion and Conclusion 104 5 HYDROGENOLYSIS AND HYDROGENATION REACTIONS 106 . Introduction 106 Synthesis ofHydridotungsten(VI) Complexes 107 Reactivity ofW(VI) Dihydrides, 44 and 45 112 Catalytic Hydrogenation Reactions 114 Introduction 114 Catalytic Hydrogenation ofAlkenes by 44 or40 115 Synthesis and Reactivity ofW(NPh)[o-(Me3SiN)2C6H4](Tj6-PhEt), 43 118 EXPERIMENTAL PROCEDURES 6 122 . Materials andMethods 122 Syntheses 123 PPPrrreeepppaaarrraaatttiiiooonnnoofoffW(W[N(oPN-hP()hM[)eo[3-oS(-iM(NeMH3eS)i32NSC)i2N6C)H624HC,461]H(4C]H(3C)l2)2,,32 111222334 PPPrrreeepppaaarrraaatttiiiooonnnooofffWWW(((NNNPPPhhh)))[[[ooo--(-(M(MeMe3e3SS3iiSNNi))N22)CC26C6HH64H4]]4((]CC(HHC22HCC2HDC23HC)23H,)432-)d2,<4j,5 111222554 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](CH2CH2Ph)2 ,6 126 PPrreeppaarraattiioonn ooffWW((NNPPhh))[[<o?--((MMee33SSiiNN))22CC66HH44]]((CCHH22CCHD(2CPhH)32),26)2-^,47 112277 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](Ph)2 ,8 128 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](CH2Ph)2 ,9 129 PPPPrrrreeeeppppaaaarrrraaaatrrriiiioooonnnnooooffffWWWW((((NNNNPPPPhhhh)))[)[[<[oo?o----((((MMMMeeee333S3SSiSiiNiNN)N)))222CCC2C666HHH6H444]]]4(((]CCC(HHHC222HCCC2H((SiCC3()HHCC33lH))323,)P)12h33,))212,0,1121 111133231190 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](CH2CH2Ph)Cl ,14 132 Prepararion of W(NPh)[o-(Me3SiN)2C6H4](CH2C(CH3)3)Cl, 15 133 Preparation ofW(NPh)[o-(Me3SiN)2C6H4][Tj2-(tBu)NCCH2CH2Ph]2 ,26 133 Preparation ofW(NPh)[o-(Me3SiN)2C6H4][(tBu)NC(CH2CH2Ph)= C(CH2CH2Ph)N(tBu)] ,27 134 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](CHCMe3)(PMe3), 34 134 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](CH2CH2CH2CH2), 35 135 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](CHt-BuCH2CH2), 36 136 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](ri2-C2H4)(PMe3)2, 39 136 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](ri2-CH2=CHPh)(PMe3)2, 40 137 Preparation ofW(NPh)[o-(Me3SiN)2C6H4](Ti2-CH2=CHCH3) (PMe3>2, 41 137 VI 1 PPrreeppaarraattiioonn ooffWW((NNPPhh))[[oo--((MMee33SSiiNN))22CC66HH44]]((HH))22((DPPMPeE3)),2,4454 113389 Kinetics Study 140 Phosphine Dependence 142 Hydrogenation Reaction 142 Crystallographic Studies 143 X-ray datacollection and structure refinement forcompounds 3, 10 and 21 143 X-ray datacollection and structure refinement forcompounds 35 and 39 144 X-ray datacollection and structure refinement forcompound6 144 X-ray datacollection and structure refinement forcompound7 145 APPENDICES A TABLES OFCRYSTALLOGRAPHIC DATA 146 B TABLES OF KINETICS STUDIES 226 C INPUT FOR KINFIT SIMULATION PROGRAM 230 D SCHEMATIC SUMMARY OFTHE REACTIVITIES OF TUNGSTEN(VI) DLALKYL COMPLEXES 232 LIST OF REFERENCES 234 BIOGRAPHICAL SKETCH 244 VI • AbstractofDissertationPresentedtotheGraduate School oftheUniversityofFloridainPartialFulfillmentofthe Requirementsforthe DegreeofDoctorofPhilosophy CHEMISTRY OFCHELATE-STABILIZEDTUNGSTEN(VI) DIALKYLCOMPLEXES By Shu-Yu Steve Wang May, 1998 Chairman: James M. Boncella MajorDepartment: Chemistry A numberoftungsten(VI) imidodialkylcomplexescontaining thechelatingdiamido ligand, [o-(NSiMe3)2C6H4], have been synthesizedwith the formulae : W(NPh)[o- (NSiMe3)2C6H4]R2, R = Me(3), Et(4), /i-Pr(5), CH2CH2Ph(6), CH2CHMe2(7), Ph(8), CH2Ph(9), CH2CMe3(10), CH2CMe2Ph(ll), CH2SiMe3(12). Mono alkyl complexes, W(NPh)[o-(NSiMe3)2C6H4]RCl, R = Et, CH2CH2Ph, CH2CHMe2, 13 - 15, were also isolated by reacting the dichloride complex, W(NPh)[o-(NSiMe3)2C6H4]Q2, 2, with one equivalentofappropriateGrignardreagent NMR The stmcturesofthese compounds have been fully characterizedby spectroscopy and the X-ray crystal structures of3, 6, 10, and 15 have been determined. Allcomplexesdisplayfluxional behaviorbetween the the trigonal bipyramidal (TBP) and squarepyramidal (SP) geometriesin solution. Thesolid state structures reveal the preference forSP structureforsmall alkyls (e.g. 3) and thepreferenceofTBP structure for bulky alkyls (e.g. 10). Lewis base, PMe3 and r-BuNC, adducts can be observed and the coordination modes arediscussed. II* Vlll Mechanisms forthe transferreactions of4 and 6 with addedPMe3 are proposed. In thediethyl (4) case, thereaction involvespre-coordination ofPMes followed byrate-limiting P-H abstraction. Thereaction of6 withPMc3 follows twocompeting pathways. One isphosphine independent P-H abstraction, and theotheris PMe3 induced P-Helimination/reductiveelimination. Otherreactions involving thesedialkyl complexes, such as themetathesisreactions ofa-olefins, insertion ofr-BuNC, isomerization and hydrogenation ofunsaturated hydrocarbons are alsodiscussed in thisdissertation. ix chapter 1 INTRODUCnONAND BACKGROUND Much attention andeffort has been focusedontransitionmetal alkylcomplexes becauseoftheirinvolvementin manyorganic andorganometallic transformations as wellas in catalyticreactionswith hydrocarbons in homogeneous and heterogeneous systems.!*2 Examples include the useofearly transition metal (group 3-6) alkylsin olefin polymerization andmetathesisreactions,^ Fischer-Tropschreactions thatare catalyzed by iron andrathetuumalkyls,^cobaltandrhodium alkyls used in hydroformylation andacetic CO acid synthesis,^ palladiumandplatinum alkyls usedin thecopolymerization of and ethylene andhydrogenation ofalkenes.^ The studyoftheproperties andreactivitiesof these compounds isessentialtodevelop an understandingoftheirrolein these transformations andforthedesign ofnovel catalystsforfurtherapplications. T Synthesis of sition MetalAlkvl Complexes The studyofmetal-alkyl complexes originated withFrankland's discovery ofZnEt2 in 1849. Numerous attempts toprepare transition metalanalogs were largely unsuccessful. A fewthermally stablecompounds such as [PtIMe3]4 and [AuBrEt2l2wereisolatedand characterized, butmostofthe wcx'konlyresultedin the formation oforganic decomposition products andlow-valentmetal species.^ Itwaslaterrealizedthatthermally stablealkylscould bepreparedwhen "stabilizing" ligands, such as Cp (T|5-cyclopentadienyl), CO, orPR3 arepresent. Examples ofsuch 1