Catalytic and stoichiometric reaction chemistry of metal silicon complexes
Abstract
Transition metal silicon complexes are central in a variety of important catalytic transformations of organosilicon compounds. Many of these processes involve unsaturated silicon complexes as key intermediates. This thesis explores two aspects of transition metal silicon chemistry: the stoichiometric reactions of a stable disilene complex of tungsten Cp${\rm \sb2W(\eta\sp2-Me\sb2Si=SiMe\sb2})$, and the development and elucidation of new catalytic routes to polysilanes. The tungsten disilene complex has been found to react with a variety of polar reagents to yield products resulting from one-atom insertion into the Si-Si bond. Thus, reactions with chalcogenide sources yields the four-membered ring compounds cyclo-Cp${\rm \sb2W(SiMe\sb2ESiMe\sb2)(E=O, S, Se, Te}).$ One-atom net insertion into the Si-Si bond also occurs in the reaction of tungsten disilene complex with diazoalkanes yielding hydrazone-type insertion products. Further studies show the trimethylsilyldiazomethane insertion product undergoes photochemical rearrangement and extrusion of HCN to yield the corresponding amine insertion product. In contrast, the reaction of ethylene, a nonpolar reagent, leads to insertion into the W-Si bond and formation of cyclo-Cp${\rm \sb2W(SiMe\sb2SiMe\sb2CH\sb2CH\sb2}).$ Although the disilene complex is unreactive towards hydrogen gas, the hydrogenation of the Si-Si bond is catalyzed by a variety of platinum complexes. Evidence is presented for the formation of bimetallic adducts with the catalytically active complexes. The molecular structure of the adduct with Wilkinson's catalyst has been determined by crystallographic methods. The catalytic studies explored in this thesis include the ruthenium-catalyzed transfer dehydrocoupling of a number of secondary silanes in the presence of an olefin as a hydrogen acceptor. In the dehydrocoupling of Me${\rm \sb2SiH\sb2},$ moderate weight polysilanes (n = 15 $-$ 20) are produced, whereas dehydrocoupling of bulkier secondary silanes yields only small oligomers. Alkyl group redistribution between silicons is competitive with dehydrocoupling, leading to a polysilane which is highly branched. Further studies reveal that the dehydrocoupling of primary silanes is catalyzed by (Me${\rm \sb3P)\sb3RU(H)\sb3(SiMe}\sb3).$ Without the presence of a hydrogen acceptor. The differences between primary and secondary silicons can be traced to the steric congestion associated with the key catalytic intermediate, (${\rm Me\sb3P)\sb3RU(H)\sb2(SiR\sb3)\sb2}.$
Subject Area
Chemistry|Organic chemistry
Recommended Citation
Hong, Paula, "Catalytic and stoichiometric reaction chemistry of metal silicon complexes" (1995). Dissertations available from ProQuest. AAI9532198.
https://repository.upenn.edu/dissertations/AAI9532198