Doctoral Dissertations
Date of Award
5-1996
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Chemistry
Major Professor
Ziling B. Xue
Committee Members
James L. Adcock, Charles S. Feigerle, Peter K. Liaw, Clifton Woods
Abstract
This dissertation describes the research results about chemistry of early- transition-metal silyl complexes, mechanisms of the formation of tantalum alkyl- alkylidene and silyl-alkylidene complexes and related organometallic chemistry. An overview and summary of my Ph.D. research project are provided in Chapter 1. Chapter 2 describes the synthesis and characterization of a new family of early- transition-metal silyl complexes free from anionic π-ligands. These silyl complexes are (Me3CCH22)3TiSi(SiMe3)3 (1), (Me3ECH2)2Ta(=CHEMe3)Si (SiMe3)3 (E = C, 2; Si, 3) and (Me3CCH2)22W(=CCMe3)Si(SiMe3)3 (4). Complexes 2 and 4 represent, to our knowledge, the first stable alkylidene and alkylidyne silyl complexes of early- transition-metal elements. Chapter 3 illustrates the kinetic and mechanistic studies of the formation of Schrock-type alkylidene complexes (Me3ECH2)3Ta-CHEMe3 (E = C, 8; Si, 9) and a bridged-alkylidyne complex (Me3SiCH2)2Ta(µ-CSiMe3)2Ta(CH2SiMe3)2 (6). (Me3ECH2)5Ta (E = C, 11; Si, 12) are the precursors to the alkylidene complexes 8 and 9. With the elimination of EMe4, the quantitative conversion of 12 to 9 follows first-order kinetics. The further conversion of 9 to 6 follows second-order kinetics. Chapter 4 presents the mechanistic investigation of the formation of silyl-alkylidene complex 3 from the reaction of (Me3SiCH2)3 TaCl2 with LiSi(SiMe3)3(THF)3. An intermediate (Me3SiCH2)3Ta(Cl)Si(SiMe3)3 (5) is formed in the first step. The decomposition of 5 with the elimination of HSi(SiMe3)3 gives "(Me3SiCH2)2Ta(=CHSiMe3)(Cl)" (10) which then reacts with LiSi(SiMe3)3(THF)3, to form the final product 3. In the absence of LiSi(SiMe3)3(THF)3, complex 10 will dimerize to produce an unusual bis(alkylidene) complex (Me3SiCH2)4(Cl)2Ta2(=CHSiMe3)2 (7). The mechanisms presented in these two chapters demonstrate two different reaction pathways leading to two types of alkylidene complexes: alkyl alkylidene and silyl alkylidene complexes. The final chapter describes the further study of the bis(alkylidene) complex 7. Two nonsymmetric bridged-alkylidyne complexes (PMe3)2(CI)M(µ-CSiMe3)2M(CI) (CH2SiMe3)2 (M = Ta, 13; Nb, 14) are synthesized. The characterization and reactivities of complexes 7, 13 and 14 are reported.
Recommended Citation
Li, Liting, "Early-transition-metal silyl complexes free of anionic ligands : comparative studies of alkyl and silyl ligands. " PhD diss., University of Tennessee, 1996.
https://trace.tennessee.edu/utk_graddiss/9780