Selective Synthesis and Electrochemical Behavior oftrans(Cl)- andcis(Cl)-[Ru(bpy)(CO)₂Cl₂] Complexes (bpy = 2,2‘-Bipyridine). Comparative Studies of Their Electrocatalytic Activity toward the Reduction of Carbon Dioxide

A synthetic procedure for the selective preparation (ca. 75% isolated yield) of trans(Cl)- and cis(Cl)-[Ru(bpy)(CO)2Cl2] complexes 1 and 2, using an oligomeric [Ru(CO)2Cl2]n precursor, is described. The synthetic methodology also gives access to the cis(CO)-[Ru(bpy)(CO)2(C(O)OMe)Cl] complex 3. In contrast to 1, which gives strongly adherent polymeric [Ru(bpy)(CO)2]n molecular films, electrochemical reduction of 2 and 3 forms dimers 5 and 6 by a one-electron reduction process accompanied by loss of a chloro ligand. Complexes 2, 3, 5, and 6 function as efficient homogeneous electrocatalysts for the selective reduction of CO2 to CO (95−97% faradaic yield) in aqueous acetonitrile.