Photochemical reduction of carbon dioxide using nickel tetraazamacrocycles

2+Irradiation at 440 nm of a photosensitizer, Ru(bpy) 3 (bpy = 2,2'-bipyridine), in an ascorbate buffered solution at room temperature under one atmosphere of carbon dioxide in the presence of either of the 2+ nickel(II) complexes, [Ni(14-aneN 4 )] 2+ or [Ni(l2-aneN 4 )] (14-aneN 4 = 1,4,8,11-tetraazacyclotetradecane, 12-aneN 4 = 1,4,7,10-tetraazacyclododecane), results in the reduction of carbon dioxide.We have measured the quantum efficiency of co 2 reduction, and we report that both of the Ni(II) macrocycles reduce carbon dioxide to carbon monoxide with similar 2+ quantum yields; [Ni(12-aneN 4 )] produces formate in addition to carbon 14 monoxide.By using C-labeled carbon we were able to identify carbon dioxide as the only source of carbon in both carbon monoxide and formate.