Photochemical hydrogen production from 3d transition-metal complexes bearing o-phenylenediamine ligands

•A series of 3d transition-metal complexes bearing o-phenylenediamine ligands were prepared and structurally determined.•All o-phenylenediamine complexes exhibited photo-induced H2-evolving activity.•Replacement of o-phenylenediamine ligands with 8-aminoquinoline ligands dramatically decreased H2-evolving activity.•An obvious metal-ion dependency was observed for the catalytic systems including hydroquinone as a proton/electron donor.

A series of 3d transition-metal complexes bearing o-phenylenediamine (opda) ligands [M(opda)3]2+ (M = Mn2+, Co2+, Ni2+, and Zn2+) were systematically synthesized as perchlorate salts and their structures were determined. All the opda complexes exhibited hydrogen-evolving activities under photoirradiation conditions as in the case of previously reported [Fe(opda)3]2+, whereas replacement of the opda ligands with other aromatic amine ligands caused a dramatic decrease of hydrogen-evolving activities. These results support a ligand-based reaction mechanism for photochemical hydrogen evolution from [M(opda)3]2+, which involves 1ππ* excitation of the opda ligand followed by homolytic NH bond cleavage. In contrast to the non-catalytic reactions, an obvious metal-ion dependency was observed for the catalytic systems including hydroquinone as a proton/electron donor. The results of this work demonstrate a strategy for the design of a molecular photochemical hydrogen-production system under ambient temperature and pressure.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide