Hydroorganosilanes as Reducing Agents

Like the alkali metal, boron and aluminium hydride compounds, hydroorganosilanes are so polarised that the electron cloud is concentrated on the hydrogen atom, which aids the formation of the hydride anion. Combinations of hydroorganosilanes with organic and inorganic acids or with certain catalysts (the transition metal complexes, the peroxides, etc.), are especially suitable for the reduction of organic compounds. The relative ease of hydride anion formation follows this series [537, 538]  

Therefore the most frequently used is triethylsilane. Some other available hydroorganosilanes are butyl, dibutyl, tributyl, phenyl, diphenyl, triphenyl, methyl, phenylnaphthyl(l) and the hydrosiloxano polymers HSL94 [539] and PMHS [540] 

The great stability of hydroorganosilanes in acidic media makes possible reductions with H /H pairs the proton is derived from the acid. For example, a carbonyl 

The hydrogenation of nitriles proceeds only to the aldehyde stage, and is therefore a method for the preparation of aldehydes [541] (Eq. 4.8)  

The systems (HsC2)3SiH/H2S04 (33-50%) and (H5C2)3SiH/HCl (37-38%) have been used for the reduction of carbonyl compounds to alcohols (in acetonitrile at 25-30°C). Some of these reactions are summarised in Table 4.1. 

---