Nickel Complex with Internal Bases as Efficient Molecular Catalyst for Photochemical H 2 Production

A Ni complex with internal bases that contain bipyridine‐derived ligands, [Ni(L) 2 (H 2 O) 2 ](BF 4 ) 2 ([ 1 ](BF 4 ) 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 ](BF 4 ) 2 ([ 2 ](BF 4 ) 2 , L′=2‐(2‐pyridyl)quinoline), were synthesized and characterized. The electrochemical properties of these complexes were studied in CH 3 CN, H 2 O, and a mixture of EtOH/H 2 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 H 2 generation. Under optimal conditions, the turnover number of H 2 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 H 2 generation by [ 1 ] 2+ is presented based on DFT calculations.