Non-metal Lewis Acid-Catalyzed Reduction of Phosphine Oxides with Silanes: Mechanistic Study and Reaction Optimization.

Abstract

Non-metal Lewis acid (NM LA)-catalyzed silane-mediated reductions represent an important strategy for the conversion of phosphine oxides to phosphines. Although a variety of catalytic systems have been developed, their underlying reaction mechanisms remain insufficiently understood. Herein, we have elucidated two unified mechanistic manifolds for these transformations based on combined computational and experimental studies: a push-pull mechanism and a silane-activation mechanism. Guided by these mechanistic insights, we further improve the conventional Brønsted acid-catalyzed silane-mediated P═O reduction by integrating NM LAs and Brønsted acids into a cooperative catalytic system. This system operates through two sequential steps: (1) NM LA-catalyzed dehydrogenative activation between Brønsted acids and phenylsilane, generating a highly reactive silane species in situ; and (2) reduction of phosphine oxides mediated by the resulting activated silane. The developed protocol exhibits broad substrate scope and high efficiency in the reduction of diverse phosphine oxides. Moreover, it is readily scalable, providing a practical approach for synthetic and industrial applications.