FORMATION OF A METAL HYDRIDE BOND AND THE INSERTION OF CO2 - KEY STEPS IN THE ELECTROCATALYTIC REDUCTION OF CARBON-DIOXIDE TO FORMATE ANION

The complex cis-[Ru(bpy)2(CO)H]+ was shown to be a catalyst for the electrochemical reduction of CO2 in CH3CN with added water. One product of the reduction is the formate anion. It is formed in a catalytic cycle which involves (1) one-electron, bpy-based reduction of cis-[Ru(bpy)2(CO)H]+ (2) insertion of CO2 into the Ru-H bond to give the once-reduced formato complex cis-[Ru(bpy)2(CO)(OC(O)H)]0, and (3) a subsequent, one-electron reduction of this complex, which leads to the loss of formate anion and the re-formation of cis-[Ru(bpy)2(CO)H]+ by the reduction of H2O. The formation of the hydrido complex following the two-electron reduction of either the formato complex or the acetonitrilo complex cis-[Ru(bpy)2(CO)(NCCH3)]2+ was demonstrated independently. A second major pathway for the reduction of CO2 was identified, which gave CO as a product. The mechanism of this reaction, which was identified earlier for cis-[Os(bpy)2(CO)H]+, appears to involve associative attack of CO2 on the twice-reduced formato or acetonitrilo complexes.