Reversible Silylium Transfer between P‐H and Si‐H Donors

Abstract

The Mo=PR2 π* orbital in a Mo phosphenium complex acts as acceptor in a new PIII‐based Lewis superacid. This Lewis acid (LA) participates in electrophilic Si‐H abstraction from E3SiH to give a Mo‐bound secondary phosphine ligand, Mo‐PR2H. The resulting Et3Si+ ion remains associated with the Mo complex, stabilized by η1‐P‐H donation, yet undergoes rapid exchange with an η1‐Si‐H adduct of free silane in solution. The equilibrium between these two adducts presents an opportunity to assess the role of this new LA in catalytic reactions of silanes: is the LA acting as a catalyst or as an initiator? Preliminary results suggest that a cycle including the Mo‐bound phosphine‐silylium adduct dominates in the catalytic hydrosilylation of acetophenone, relative to a putative cycle involving the silane‐silylium adduct or “free” silylium.