Photochemical hydrogen production catalyzed by polypyridyl ruthenium–cobaloxime heterobinuclear complexes with different bridges

Abstract

Two heterobinuclear complexes [(bpy) 2Ru(bpy-4-CH 3,4′-CONH(4-py)Co(dmgBF 2) 2(OH 2)](PF 6) 2 ( 1, dmgBF 2 = (difluoroboryl)dimethylglyoximato) and [(bpy) 2Ru(bpy-4-CH 3,4′-CONHCH 2(4-py)Co(dmgBF 2) 2(OH 2)](PF 6) 2 ( 2) were prepared, in which the polypyridyl ruthenium photosensitizer and the cobaloxime catalyst are connected either by a conjugated bridge ( 1) or by an unconjugated one ( 2). Complexes 1 and 2 were used as photocatalysts for hydrogen generation. Under optimal conditions, the turnover numbers (ton) for hydrogen evolution were 38 for 1 and 48 for 2 in the presence of 300 equiv of both Et 3N and [Et 3NH][BF 4] in the acetone solution during an 8-h irradiation of visible light ( λ > ca. 400 nm). The complex 2 with an unconjugated bridge proved to be more efficient for photochemical hydrogen generation than the complex 1 with a conjugated bridge under the same reaction condition.