Comparative Electrocatalysis of Hydrogen Production and Oxidation: Technetium versus Rhenium Tris(thiolate) Complexes

The development of an efficient catalyst that can selectively activate and generate hydrogen molecules is in urgent demand. Inspired by the 5d rhenium-tris(thiolate) complex that is capable of catalytically producing and oxidizing H-2, the mechanisms of electrocatalytic H-2 oxidation (HOR) and evolution (HER) catalyzed by the 4d technetium-tri(thiolate) analogs, and [TcL3] (L = diphenylphosphinobenzenethiolate, a noninnocent ligand), were investigated by DFT calculations, aiming at elucidating the role of the metal in metal-ligand cooperativity. DFT calculations anticipate high reactivity in both HOR and HER for [TcL3] beyond that of its Re counterparts. Substituting the Re metal for Tc in metal-tris(thiolate) complexes results in a greater thiyl-radical character in the Tc complex compared to that in Re. Even when both complexes evolve H-2 with similar [ECEC] mechanisms, the proton relays behave with a distinct disparity, featuring the S ligand in the Tc species as compared to the metal-hydride in Re. The HOR mechanism also bifurcates as [TcL3](2+) is predicted to mainly occur via the ligand-based pathway, in contrast to the predominant metal and ligand-based reactivity for Re. This study established the role of the metal in HER and HOR while emphasizing the utility of such metal-DPPBT cooperativity in the catalytic process.