From Ligand- to Metal-centered Reactivity: Metal Substitution Effect in Thiosemicarbazone-based Complexes for H 2 Production.

The quest to develop and optimize catalysts for H 2 production requires a thorough understanding in the possible catalytic mechanisms involved. Transition metals are very often the centers of reactivity in the catalysis, although this can change in the presence of a redox-active ligand. Investigating the differences in catalysis when considering ligand- and metal-centered reactivity is important to find the most optimal mechanisms for hydrogen evolution reaction. Here, we investigated this change of reactivity in two versions of a thiosemicarbazone-based complex, using Co and Ni metal centers. While the Ni version has a ligand-centered reactivity, Co switches it toward a metal-centered one. Comparison between the mechanisms show differences in rate-limiting steps, and shows the importance of identifying those steps in order to optimize the system for hydrogen production.