The unconventional reactivity of hydrosilanes and Lewis base combinations: beyond hydride donation

The combination of hydrosilanes with Lewis bases such as metal alkoxides is well established to form hypervalent hydridosilicates that can deliver hydrides to polarized π bonds such as those found in ketones and esters. However, a growing body of literature reveals that these systems are capable of far more diverse reactivity, arising from the in situ generation of a complex network of reactive intermediates, including silyl radicals, silicon-centered radical anions, hydrogen atom donors, and highly basic species. This review surveys the unconventional reactivity of hydrosilane-Lewis base combinations beyond conventional hydride transfer chemistry. Modern applications discussed include reductive hydrodefunctionalization of C-O, C-S, and C-C bonds, intramolecular cyclization and rearrangement reactions, C(sp²)-H and C(sp)-H silylation, hydrosilylation of alkenes, and the emerging use of these systems in intermolecular C(sp³)-C(sp³) bond formation. The breadth of synthetic outcomes described herein stems from the ability of hydrosilane-Lewis base systems to access fundamentally different reactive pathways depending on the substrate and reaction conditions. We anticipate that this framework will prove useful both for researchers seeking to apply existing methodology and for those interested in developing new transformations based on hydrosilane-Lewis base chemistry.