Hydrogenation of sulfoxides to sulfides mediated by incomplete cubane-type Mo3S4 clusters: synthetic applications and mechanistic insights†‡

Abstract

Homogeneous catalysts for the deoxygenation of sulfoxides to sulfides have not been widely explored. Herein, we report a green and efficient protocol for the catalytic hydrogenation of sulfoxides using an air-stable diamino Mo₃S₄ cluster complex under mild conditions (6 bar of H₂ pressure and 50 °C in acetonitrile). Our strategy exhibits excellent group tolerance so it can be widely applied in the late-stage functionalization of pharmacological drugs and other valuable products containing sulfide moieties. Kinetic studies in combination with control experiments and DFT calculations support the operation of a sulfur-based cluster catalysis mechanism similar to the one previously reported for the hydrogenation of azobenzene and semihydrogenation of alkynes. What differentiates this mechanism from the analogous previous ones is that after hydrogen activation at two of the bridging sulfides to form an hydrosulfide intermediate, hydrogen is transferred sequentially first as a proton and then as a hydride.