Nature of asynchronous hydrogen transfer in ketone hydrogenation catalyzed by Ru complex

Three different reaction pathways-concerted hydride transfer, concerted proton transfer, and stepwise hydrogen transfer-in the carbonyl hydrogenation step of the catalytic cycle for ketone hydrogenation catalyzed by Ru complexes are investigated in this work. Our results from this study suggest that hydride and proton asynchronous transfers in the ketone hydrogenation process are stepwise in general. It is the nature of the substrate, electron withdrawing effect, and characteristics of catalytic ligands that make one of two transition states disappear in the concerted mechanism.