Hydrogen Evolving Mono‐Nuclear Manganese Complexes with Carefully Positioned Pyridine Base Ligands

Abstract

Enormous efforts have been made by the scientific community for the development of biomimetic/bioinspired complexes as alternative energy systems to overcome the energy crisis arising from the depletion of non‐renewable energy sources. In this regard, new bioinspired mononuclear Mn(I) carbonyl model complexes fac‐[(Mn(CO)3(κ2‐SN2C7H5)(κ1‐PPh2Py))] 1 and fac‐[(Mn(CO)3(κ2‐S2NC7H4)(κ1‐PPh2Py))] 2 with 2‐mercaptobenzimidazole (N,N) and 2‐mercaptobenzothiazole (S,N) ligands and a N‐based phosphine ligand (PPh2Py) have been synthesized, spectroscopically characterized and evaluated as electro‐catalysts for hydrogen generation. Contrary to similar mono‐nuclear (N,N/S,N)‐Mn‐PPh3 complexes reported earlier by our group, based on DFT calculations, it has been shown that the pyridine ring of the PPh2Py ligand placed in an axial position in the coordination sphere of the Mn(I) complexes provides a first site for protonation. Both the molecular complexes were tested as electrocatalysts for hydrogen generation in CH3CN. Complexes 1 and 2 effectively catalyzed electrochemical proton reduction with acetic acid as the proton source and displayed a turnover frequency (TOF / s‐1; O.P., η /V) of 610; 1.02 and 615; 1.12, respectively, for the electro‐catalytic process.