Doctoral Dissertations
Date of Award
8-1997
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Chemistry
Major Professor
Ziling Ben Xue
Committee Members
Clifton Woods, Ron Magid, Marcia Katz
Abstract
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.
Recommended Citation
McAlexander, Lenore Hoyt, "Group 4 alkyl silyl complexes free of anionic [pi]-ligands : their syntheses, reactivities and applications in molecular approaches to metal silicide materials. " PhD diss., University of Tennessee, 1997.
https://trace.tennessee.edu/utk_graddiss/9550