New Insights into Mechanism of Molybdenum(VI)–Dioxo Complex Catalyzed Hydrosilylation of Carbonyls: An Alternative Model for Activating Si–H Bond

Recently, a series of oxo/nitrido-ReV/MoVI/RuVI/MnV complexes were demonstrated to be efficient catalysts in activating silanes and catalyzing hydrosilylations of unsaturated organic substrates. In the present study, the high-valent molybdenum(VI)–dioxo complex MoO2Cl2 catalyzed hydrosilylations of carbonyls was reinvestigated using density functional theory method. Previous experimental and theoretical investigations suggested a [2 + 2] addition pathway for MoO2Cl2 catalyzed hydrosilylations of ketones. In the present study, we propose an ionic outer-sphere mechanistic pathway to be the most favorable pathway. The key step in the ionic outer-sphere pathway is oxygen atom of C═O bonds nucleophilically attacking the silicon atom in an η1-silane molybdenum adduct. The Si–H bond is then cleaved heterolytically. This process features a novel SN2@Si transition state, which then generates a loosely bound ion pair: anionic molybdenum hydride paired with silylcarbenium ion ([MoO2Cl2H]− [SiR3(OCR′R″)]+) in solvent...