PENTACOORDINATE HYDRIDOSILICATES - SYNTHESIS AND SOME ASPECTS OF THEIR REACTIVITY

Pentacoordinate hydridosilicates [HSi(OR)4]- (where R = Me, Et, n-Bu, i-Pr, Ph) as their K+ salts are obtained from reactions of trialkoxy- (or phenoxy-) silanes with the respective alkoxide (or phenoxide). Compared to HSi(OEt)3, [HSi(OEt)4]K exhibits a wide range of reactivities: (1) it undergoes facile displacement reactions at silicon with Grignard reagents and PhLi; (2) it acts as a base and leads to proton abstraction in the case of PhC = CH and Ph3CH; (3) it is able to reduce carbonyl compounds to the related alcohols; (4) it reacts with primary organic halides through an ionic mechanism (a SET process can be invoked in the case of benzylic halides (RX), which afford the dimer RR in addition to the alkane RH); (5) the ability to donate one electron is confirmed in reactions with oxidizing agents (Cu+, Ag+, Cp(CO)2Fe+) and by direct ESR observation of stable radical intermediates.