Pentacoordinate dihydridosilicates: Synthesis, structure, and aspects of their reactivity

Article abstract of DOI:10.1021/om00056a030

The reactions of H^- with trialkoxysilanes provide a unique and facile entry to anionic pentacoordinate dihydridosilicates [H₂Si(OR)₃]^-, isolated as stable crystalline products in the case of bulky R groups (R = i-Pr, s-Bu, c-C₆H₁₁). Their dynamic behavior (R = i-Pr and s-Bu) has been investigated by ²⁹Si and variable-temperature ¹H NMR. Intramolecular exchange of H atoms between axial and equatorial sites is indicated and was found to be significantly dependant on the nature of the solvent. Compared to HSi(OR)₃, K[H₂Si(OR)₃] are versatile reagents: (1) the silicon atom is an electrophilic center and this leads to nucleophilic displacements of the alkoxy groups with Grignard reagents and organolithiums; (2) they are able to reduce very easily carbonyl derivatives to alcohols without any catalyst; (3) they react with primary halides through an ionic mechanism leading to the alkane; (4) the reaction with benzylic halides is more complex and affords the dimer as the major product, the formation of which can be explained by a SET process; (5) the ability to donate one electron is confirmed in the reaction with Cp(CO)₂FeI and by direct ESR observation of stable radical intermediates.