Direct synthesis of oxalic acid via oxidative CO coupling mediated by a dinuclear hydroxycarbonylcobalt(III) complex

Oxidative coupling of CO is a straightforward but currently underdeveloped economically benign synthetic route to target alpha-diketones. Here, the authors synthesize a rare coplanar dinuclear hydroxycarbonylcobalt(III) complex and demonstrate that the Co - carboxylate bonds can be easily cleaved leading to the formation of oxalic acid. Oxidative coupling of CO is a straightforward and economic benign synthetic route for value-added alpha-diketone moiety containing C-2 or higher carbon compounds in both laboratory and industry, but is still undeveloped to date. In this work, a rare coplanar dinuclear hydroxycarbonylcobalt(III) complex, bearing a Schiff-base macrocyclic equatorial ligand and a mu-kappa(1)(O):kappa(1)(O')-acetate bridging axial ligand, is synthesized and characterized. The Co(III)-COOH bonds in this complex can be feasibly photocleaved, leading to the formation of oxalic acid. Moreover, the light-promoted catalytic direct production of oxalic acid from CO and H2O using O-2 as the oxidant with good selectivity (> 95%) and atom economy at ambient temperature and gas pressure based on this dicobalt(III) complex have been achieved, with a turnover number of 38.5. The C-13-labelling and O-18-labelling experiments confirm that CO and H2O act as the sources of the -COOH groups in the dinuclear hydroxycarbonylcobalt(III) complex and the oxalic acid product.

Automated summary

This article reports the synthesis of a rare coplanar dinuclear hydroxycarbonylcobalt(III) complex and demonstrates that the Co - carboxylate bonds can be easily cleaved, leading to the formation of oxalic acid. The authors also achieved the direct production of oxalic acid from CO and H2O using this complex as a catalyst, with high selectivity and atom economy.