Group 4 alkyl silyl complexes free of anionic [pi]-ligands : their syntheses, reactivities and applications in molecular approaches to metal silicide materials

This dissertation describes the synthesis and reactivity of Group 4 alkyl and alkyl silyl complexes. An overview and summary of my Ph.D. research appear in Chapter 1. The synthesis and reactivity of Group 4 alky! silyl complexes (Me₃ECH₂)₃MSi(SiMe₃)₃ (E = C, Si; M = Ti, Zr) are described in Chapter 2. The complexes were synthesized through the metathetic reactions of (Me₃ECH₂)₃MCI with LiSi(SiMe₃)₃(THF)₃ and were characterized by NMR spectroscopy. Three of the complexes were also characterized by X-ray crystallography, and their crystal structures are presented. The reactivity of (Me₃CCH₂)₃ZrSi(SiMe₃)₃ toward various silanes and toward insertion by 2,6-dimethylphenyl isocyanide was also investigated. The compound was found to be inert to reaction with alkyI silanes; and to react with phenylsilane, diphenylsilane or SiH₄ to give metathesis products and dark solids. The complex was found to react with one equivalent of the isocyanide to give the silyl insertion product (Me₃CCH₂)₃ZrC(=NXyl)-[Si(SiMe₃)₃]. Reaction with three equivalents or excess isocyanide gave the triple insertion product (Me₃CCH₂)[(Me₃CCH₂)(XylN=)C]₂ZrC(=NXyl)Si(SiMe₃)₃], which was inert to further reaction with isocyanide. The triple-insertion product was characterized by X-ray crystallography. New or improved syntheses of the trialkyl chloride and tetraalkyl precursors are presented in Chapter 3. Four improved syntheses and the crystal structure of (Me₃CCH₂)₃ZrCI, a previously-known compound, are presented. The compound was found to crystallize in polymeric chains of -CI-Zr(CH₂CMe₃)₃-CI-Zr(CH₂CMe₃)₃-, and with perfectly linear and symmetric bridging chloride ligands. Similar synthetic methods were used to make the previously unreported compounds (Me₃ECH₂)₃MCI (E = C, Si, M = Ti; E = Si, M = Zr). Improved syntheses of (Me₃ECH₂)₄M (E = C, Si, M = Ti, Zr), previously- known complexes, are also reported. The reactions of the complexes (Me₃CCH₂)₄M (M = Ti, Zr), (Me₃CCH₂)₃Ta=CHCMe₃, and (Me₃CCH₂)₃W=CCMe₃ with SiH₄ were investigated as possible routes to the synthesis of metal silicide materials. The reactions, described in Chapter 4, were found to produce neopentane gas and dark gray, brown, or black solids which were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), and other methods and were found to contain silicon, metals, carbon and oxygen. The reaction intermediates were apparently too oxophilic to allow the formation of silicide materials under the conditions used. The reaction of Si(SiMe₃)₄ with TiCl₄ was also investigated, as reported in Chapter 5. The reaction was found to produce TiCl₂ and CISiMe₃, along with CISi(SiMe₃)₃ and Cl₂Si(SiMe₃)₂, depending upon the amount of TiCl₄ available. The dichlorosilane Cl₂Si(SiMe₃)₂ appeared to be inert to further reaction with excess TiCl₄ at room temperature.