Nickel complex with internal bases as efficient molecular catalyst for photochemical H2 production

A Ni complex with internal bases that contain bipyridine-derived ligands, [Ni(L)2 (H2 O)2 ](BF4 )2 ([1](BF4 )2 , L=2-(2-pyridyl)-1,8-naphthyridine), and a reference complex that bears analogous bipyridine-derived ligands but without an internal base, [Ni(L')3 ](BF4 )2 ([2](BF4 )2 , L'=2-(2-pyridyl)quinoline), were synthesized and characterized. The electrochemical properties of these complexes were studied in CH3 CN, H2 O, and a mixture of EtOH/H2 O. The fluorescence spectroscopic studies suggest that both dynamic and the sphere-of-action static quenching exist in the fluorescein Fl(2-) /[1](2+) and Fl(2-) /[2](2+) systems. These noble-metal-free molecular systems were studied for photocatalytic H2 generation. Under optimal conditions, the turnover number of H2 evolution reaches 3230 based on [1](2+) , whereas [2](2+) displays only approximately one third of the turnover of [1](2+) . A plausible mechanism for the catalytic H2 generation by [1](2+) is presented based on DFT calculations.