Hydrosilane cleavage reactions accelerated by tartaric acid and dimethyl sulphoxide

Tartaric acid reacts spontaneously with triethoxysilane (HTES) liberating hydrogen gas, but alkyl or arylhydrosilanes are essentially inert under these conditions. Other alpha-hydroxyacids reacted similarly with HTES. The reaction of tartaric acid in tetrahydrofuran is a second order process, consistent with a reaction pathway involving first transesterification of HTES by tartaric acid and subsequent Si-H cleavage. In dimethyl sulphoxide (DMSO) the reaction is much faster, and has a more complex rate profile. The initial stages of the reaction follow second order kinetics. It is proposed that the reaction proceeds via extracoordinate intermediates involving DMSO. This has the consequence of facilitating transesterification to produce many different Si-H-containing intermediates, such as 3-7, and increasing the nucleophilicity of the silicon hydride. The reaction products are amorphous solids. Examination by Si-29 NMR spectroscopy of the organically modified sol-gel oligomer obtained from these condensations, shows the presence of sharp peaks compatible with extracoordinate species which, in time, change to broad signals consistent with Q(4) (SiO2) species.