Acids, Bases, or Free Radicals

The use of Lewis acids as catalysts for the hydrosilation of unsaturated compounds, hydrocarbons in particular, has seen a surge of interest and activity over the last dozen years. This is a refreshing and bold development since Lewis acids are also excellent catalysts for polymerization of olefins and acetylenes. 

Fluoride-on-alumina promoted hydrosilation of benzaldehyde with Et3SiH, affording benzyloxytriethylsilane quantitatively was described recently. The formation of benzylbenzoate as a byproduct via self-condensation of benzaldehyde, is totally suppressed in DMF as a solvent, whereas in hexane or THF, it is the major product formed. Other basic species such as KNH2/AI2O3, MgO or CaO showed much lower activity compared to KF/AI2O3. 

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