Re–Silane complexes as frustrated lewis pairs for catalytic hydrosilylation

Abstract

A pathway for the catalytic hydrosilylation of carbonyl substrates with M(C₆F₅)₃ (M = B, Al and Ga) was calculated by DFT (B3PW91-D3) and it was shown that in the case of the Al reagent, the carbonyl substrate binds irreversibly and inhibits catalysis by generating a stable carbonyl adduct. In contrast, the reduced electrophilicity of B(C₆F₅)₃ disfavors the binding of the carbonyl substrate and increases the concentration of an activated silane adduct which is the species responsible for catalytic turnover. A similar mechanism was found for both cationic and neutral Re(III) species. Further, it was shown by tuning the electrophilicity of the rhenium catalysts, conditions can be found that would enable the catalytic hydrosilylation of ketone and nitrile substrates that were unreactive in previously reported systems. Thus the mechanisms proposed in this work, lay the foundation for the design of new catalytic systems.