A new family of transition metal silyl complexes, their syntheses, characterization and reactivities

In this review, our studies of a new family of silyl complexes (RCH2)(3)MSiR3' (M = Ti, Zr), (RCH2)(2)Ta(=CHR)SiR3' and (RCH2)(2)W(=CR)SiR3', which are free of cyclopentadienyl (C-p) or other supporting anionic pi-ligands, and the reactions of alkylidene and amide complexes with silanes are summarized. We have conducted these studies with a two-fold interest: (1) mechanistic pathways in the formation of metal silicides (MSin) from molecular precursors; (2) fundamental chemistry of these reactions with silanes and the new silyl complexes-their syntheses, structures and reactivities, We have also explored the differences between carbon and silicon as well as alkyl and silyl ligands in the mechanistic pathways of the formation of silyl and alkyl alkylidene complexes. The formation of a silyl alkylidene complex (RCH2)(2)Ta (= CHR) SiR3 (R = SiMe3) from (RCH2)(2)TaCl2 and Li(THF)(3)SiR3 was found to go through "(RCH2)(2)Ta(=CHR)Cl" as an intermediate. In contrast, Ta(CH2R)(5)(R=CMe3, SiMe3) were found to be the intermediates in the formation of archetypical alkyl alkylidene complexes (RCH2)(3)Ta = CHR from (RCH2)(3)TaCl2. In addition, the reactions of amide (M-NR2) complexes and silanes were found to reversibly yield amide hydride complexes and aminosilanes. The significance of these results to the elucidation of mechanistic pathways in the formation of metal silicides and M-Si-N ternary meterials will be discussed.