Ligand effects of ruthenium 2,2′-bipyridine and 1,10-phenanthroline complexes on the electrochemical reduction of CO2

Abstract
Electrochemical reduction of CO2catalysed by [RuL1(L2)(CO)2]2+[L1,L2=(bipy)2, (bipy)(dmbipy), (dmbipy)2, or (phen)2], [Ru(phen)2(CO)Cl]+(phen = 1,10-phenanthroline), and [RuL(CO)2Cl2][L = 2,2′-bipyridine (bipy) or 4,4′-dimethyl-2,2′-bipyridine (dmbipy)] were carried out by controlled-potential electrolysis at –1.30 V vs. saturated calomel electrode in acetonitrile–water (4 : 1, v/v), MeOH, or MeCN–MeOH (4 : 1, v/v). In acetonitrile–water (4 : 1, v/v) no difference in activities between the catalysts was observed, however in MeOH the amounts of carbon monoxide produced became larger than those of HCO2 upon introduction of the dmbipy ligand. This is attributed to the equilibrium constants among the reaction intermediates [RuL1(L2)(CO)2]2+, [RuL1(L2)(CO)-{C(O)OH}]+, and [RuL1(L2)(CO)(C02 )]+ which become smaller on substitution of bipy by dmbipy, because of the donor property of the CH3 group.

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