Silicon-hydrogen bond reactivity

VII. Mechanism of Solvolysis of Reactive Silanes A. The Silicon-Hydrogen Bond... 

Carbonium ions can abstract hydride from potential hydride donors. The silicon-hydrogen bond is very reactive toward carbonium ions, resulting in reduction of the carbonium ion to the hydrocarbon. This reaction is preparatively useful for reduction of alcohols that can be converted to carbonium ions in trifluoroacetic acid. 

A proposed mechanism [9] for the hydrosilylation of olefins catalyzed by platinum(II) complexes (chloroplatinic acid is thought to be reduced to a plati-num(II) species in the early stages of the catalytic reaction) is similar to that for the rhodium(I) complex-catalyzed hydrogenation of olefins, which was advanced mostly by Wilkinson and his co-workers [10]. Besides the Speier s catalyst, it has been shown that tertiary phosphine complexes of nickel [11], palladium [12], platinum [13], and rhodium [14] are also effective as catalysts, and homogeneous catalysis by these Group VIII transition metal complexes is our present concern. In addition, as we will see later, hydrosilanes with chlorine, alkyl or aryl substituents on silicon show their characteristic reactivities in the metal complex-catalyzed hydrosilylation. Therefore, it seems appropriate to summarize here briefly recent advances in elucidation of the catalysis by metal complexes, including activation of silicon-hydrogen bonds. 

The negative pr and positive pi values obtained from the analysis suggest that the reactivity of the Si=C bond in 1-methylsilene (2a), the base compound in the analysis, is enhanced by substitution of the silicon hydrogen with resonance electron donors or... 

An uncharged nucleophile may also play the role of a Bronsted base if interaction with a protic substrate can increase its nucleophilicity [Eqs. (41) and (42)]. This pathway, formulated by Allen and Modena (137), seems to be important in many solvolytic reactions (7). There is evidence that more than one solvent molecule participates in the solvolysis of chlorosilanes (7,137,244). One functions as the nucleophile attacking silicon, while the others, forming hydrogen bonding complexes, enhance the nucleophilic reactivity. 

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