Comparative Electrocatalysis of Hydrogen Production and Oxidation: Technetium vs 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 H2, the mechanisms of electrocatalytic H2 oxidation (HOR) and evolution (HER) catalyzed by the 4d technetium‐tri(thiolate) analogs, [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 H2 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.