Cobalt(II) tris(2-pyridylmethyl)amine complexes [Co(TPA)X](+) bearing coordinating anion (X = Cl-, Br-, I- and NCS-): synthesis and application for carbon dioxide reduction

Four cobalt(II) complexes supported by the tripodal ligand tris(2-pyridylmethyl)amine (TPA) and ancillary coordinated anion (X), [Co(TPA)X]+ (X = Cl−, Br−, I− and NCS−) (1–4), have been prepared. Magnetic susceptibility measurement and electronic spectroscopy indicate that they are five-coordinated high spin cobalt(II) complexes. The structures of 2–4 have been determined by X-ray crystallography. Reduction of CO2 to CO has been observed upon irradiation of complexes 1–4 in the presence of fac-Ir(ppy)3 (ppy = C-deprotonated 2-phenylpyridine anion) and under CO2 atmosphere using blue LEDs. All of these Co complexes were found to be efficient and stable CO2 reduction catalyst with TON(CO) > 1000 and CO selectivity > 90% under 65 h of irradiation. Among them, [Co(TPA)Br]+ showed the best performance in CO2 reduction with TON(CO) > 1400 after 65 h. The coordinated anion X played an important role in the photo-catalysis. Density functional theory (DFT) calculation has also been performed to examine the mechanism and role of coordinated anion X in visible-light induced CO2 reduction.Department of Applied Biology and Chemical Technolog