Carbon dioxide reduction catalyzed by dinuclear ruthenium polypyridyl complexes

Dinuclear ruthenium complexes [(Ru(bid))₂(μ-bpp)(μ-OAc)] and [(Ru(trpy))₂(μ-bpp)(μ-X)]²⁺ [X=Cl^-, OAc^-, and OCHO^-; bpp=3,5-bis(2-pyridyl)pyrazolato; bid^-=(1Z,3Z)-1,3-bis(pyridin-2-ylmethylene)isoindolin-2-ide; trpy=2,2':6',2"-terpyridine] were tested as catalysts for the hydrogenative reduction of carbon dioxide in the solvent 2,2,2-trifluoroethanol in the presence of excess amine (triethylamine). Significant amounts of formic acid were produced by these catalysts, and a kinetic analysis based on initial rate constants was performed. These catalytic systems were investigated by using DFT calculations to elucidate the hydrogenative reduction mechanism. The results are compared with those obtained with previously reported mononuclear catalyst counterparts. Carbon footprints: New dinuclear ruthenium complexes that act as efficient catalysts for the hydrogenative reduction of carbon dioxide to formic acid have been prepared and fully characterized. The kinetics associated with the catalytic cycle were studied experimentally and a full catalytic cycle was determined on the basis of DFT calculations, which complement the experimental results.