Reduction of carbon dioxide to oxalate by a binuclear copper complex

Reduction of carbon dioxide to products such as oxalate (C2O4(2-)) is an active area of research, as the process converts an environmental pollutant into more useful organic compounds. However, carbon dioxide reduction remains a major challenge. Here we demonstrate a three-step reaction sequence in which a copper complex converts carbon dioxide to oxalate under mild conditions. The copper(II) complex is reduced to copper(I) in solution, either electrochemically or using sodium ascorbate. The reduced complex selectively reacts with carbon dioxide from air and fixes it into oxalate, with the oxalate ion bridging between two copper atoms. The bound oxalate ion is released as oxalic acid on treatment with mineral acids, regenerating the original copper(II) complex. This completes the process for conversion of carbon dioxide into oxalate using a binuclear copper complex and a mild reducing agent.