PHOTOCHEMICAL REDUCTION OF CARBON-DIOXIDE USING NICKEL TETRAAZAMACROCYCLES

Irradiation at 440 nm of a photosensitizer, Ru(bpy)32+ (bpy = 2,2′-bipyridine), in an ascorbate-buffered solution at room temperature under 1 atm of carbon dioxide in the presence of either of the nickel(II) complexes [Ni(14-aneN4)]2+ or [Ni(12-aneN4)]2+ (14-aneN4 = 1,4,8,11-tetraazacyclotetradecane, 12-aneN4 = 1,4,7,10-tetraazacyclododecane), results in the reduction of carbon dioxide. We have measured the quantum efficiency of CO2 reduction, and we report that both of the Ni(II) macrocycles reduce carbon dioxide to carbon monoxide with similar quantum yields; [Ni(12-aneN4)]2+ produces formate in addition to carbon monoxide. By using 14C-labeled carbon, we were able to identify carbon dioxide as the only source of carbon in both carbon monoxide and formate. © 1990 American Chemical Society.