Electroreduction of Benzaldehyde with a Metal–Ligand Bifunctional Hydroxycyclopentadienyl Molybdenum(II) Hydride

An electrocatalytic system for the hydrogenation of benzaldehyde to benzyl alcohol and dibenzyl ether is described. The molybdenum hydride (C5Ph4OH)­Mo­(CO)3(H) (3) is shown to be the actively hydrogenating species. This hydride is demonstrated to be remarkably acid-stable, leading to a ca. 67% Faradaic efficiency for aldehyde reduction over hydrogen evolution despite strongly acidic and reducing conditions. Hydride 3 is prepared via 1-proton-2-electron reduction of cation [(C5Ph4OH)­Mo­(CO)3(CH3CN)]­[OTf] ([2]­[OTf]), which is generated by protonation of the Mo(0) precursor [(C5Ph4O)­Mo­(CO)3(L)]­(1).