Hydrogen evolution was observed from the noble-metal-free catalyst systems, comprising Rose Bengal, BF x -bridged cobaloximes, and triethylamine, in an aqueous solution under irradiation of visible light. Two types of BF x -bridged cobaloximesnamely, the annulated cobaloximes [Co(dmgBF2)2(H2O)2] (1, dmgBF2 = (difluoroboryl)dimethylglyoximate anion) and [Co(dpgBF2)2(H2O)2] (2, dpgBF2 = (difluoroboryl)diphenylglyoximate anion), and the clathrochelated cobaloximes [Co(dmg(BF)2/3)3](BF4) (3) and [Co(dpg(BF)2/3)3](BF4) (4)were used as catalysts. Among the four cobalt complexes, complex 1 displayed the highest hydrogen-evolving efficiency, with turnovers up to 327. Complexes 2 and 4 that bear the diphenylglyoximate ligands exhibited much lower efficiencies as compared with their analogues 1 and 3 that have the dimethylglyoximate ligands. The hydrogen-evolving efficiency of the annulated cobalt(II) complex 1 that contains two labile axial ligands is more than three times as high as that of the encapsulated cobalt(III) complex 3 that has a single macrobicyclic ligand. The different pathways for formation of the cobalt(I) species from these two types of cobaloximes are discussed on the basis of the results obtained from fluorescence and laser flash photolysis spectroscopic studies.

Among three noble-metal-free molecular devices (1-3) containing a porphyrin photosensitizer and a cobaloxime catalyst, the one with a zinc porphyrin unit displayed apparently higher efficiency for photoinduced H(2) production than complex 2 with a magnesium porphyrin and 3 with a free-base porphyrin, possibly due to the formation of a TEAZnPor-Co triad in solution.

A molecular catalyst system containing only earth‐abundant elements is combined with g‐C3N4 as photosensitizer. The in situ generated complexes serve as catalysts for visible‐light‐driven H2 production in aqueous solution, and do not require organic solvent or a Brønsted acid. H2 evolution from the Ni‐based catalyst system can be maintained for over 60 h, demonstrating that the combination is a promising approach to improve the lifetimes of molecular catalysts towards photochemical H2 production.