Six-Electron CO₂ Reduction Involving Participation by Benzimidazole-Derived Bidentate Ligands in Ruthenium Complexes

The selective reduction of CO2 to liquid fuels by molecular catalysts remains a significant challenge. In this paper, four Ru complexes containing bidentate polypyridyl ligands were synthesized. Each complex also contains a secondary or tertiary amine as part of a benzimidazole moiety. All of the complexes are active in the hydroboration of CO2 to formate, while two of the complexes reduce CO2 to the methoxy oxidation state upon the addition of pinacol borane. 1H and 13C{1H} NMR studies of these chemical reductions suggest the importance of amines in this process, while electrochemical measurements also indicate reactivity with CO2.