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.

A noncovalent assembly of a pyridyl-functionalized hydrogenase active-site model complex and zinc tetraphenylporphyrin has been obtained and characterized. Upon light irradiation, fluorescence quenching by electron transfer was observed from the singlet excited state of the porphyrin to the diiron center, and the mechanism was verified by fluorescence lifetime and transient absorption spectroscopic measurements. In contrast to molecular dyads linked by covalent bonds, the assembled system was designed to avoid charge recombination via complex dissociation after photo-induced electron transfer. Visible light-driven hydrogen generation was observed from this self-assembled system. The assembling strategy employed in this study has the potential to be used for any other hydrogenase models in the future.