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4-Vinyl-and 6-vinylterpyridine (4-v-tpy; 6-v-tpy) complexes of chromium, nickel, cobalt, iron, mthenium and osmium have been prepared. These materials can be electropolymerized onto glassy carbon electrodes and the resulting films have been characterized, by cyclic voltammetry and rotated disk electrode voltammetry in aqueous media and under nitrogen and carbon dioxide atmospheres. The electropolymerized films exhibit electrocatalytic activity toward the reduction of CO2 with formaldehyde as virtually the only product. The magnitude of the catalytic effect and the efficiency are a function of the metal center and the location of the vinyl group(s) within the ligand. The catalytic activity of complexes having metal-based redox processes at negative potentials was superior to that of complexes where the relevant redox processes were ligand based. Complexes of first row transition metals were more active than those of the second or third row owing to the lower stability of the complexes. The presence of coordinating anions suppressed the electrocatalytic activity with HPCL-2 causing a complete inhibition. Electropolymerized films of [Cr(4-v-tpy)2]2+ exhibited a current efficiency of 87%. Turnovers in excess of 15 000 were achieved with electropolymerized films of [Fe(4-v-tpy)2]2+. The kinetics of the reaction were relatively slow, especially when compared to the analogous process in non-aqueous solvents such as DMF. This has been ascribed to differences in the overall reaction and products.

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