Heterogeneous aqueous CO2 reduction by rhenium(i) tricarbonyl diimine complexes with a non-chelating pendant pyridyl group.

Electrocatalytic CO2 reduction in water using a series of chlorotricarbonylrhenium(I) diimine complexes deposited on pyrolytic graphite electrodes is described. Two known CO2 reduction catalysts (with diimine = 4,4′-di-tert-butyl-2,2′-bipyridine or 2-(2′-quinolyl)benzimidazole), that are highly active in organic solvent, proved to be only weakly active in water. In contrast, Cl(CO)3Re(L) complexes with tridentate nitrogen-containing ligands (L = 4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine or 2,6-bis(2-benzimidazolyl)pyridine) were better CO2 reduction catalysts. In those Cl(CO)3Re(L) complexes, only two N-atoms of the ligand are coordinated to the rhenium, leaving the third arm of the ligands to support activated, CO2-bound intermediates. The 2,6-bis(2-pyridyl)pyridine (terpy) complex was the most active, with substantial activity at alkaline pH.