Co-electrocatalytic CO 2 reduction mediated by a dibenzophosphole oxide and a chromium complex.

We report a co-electrocatalytic system for the selective reduction of CO 2 to CO, comprised of a previously reported molecular Cr complex and 5-phenylbenzo[ b ]phosphindole-5-oxide (PhBPO) as a redox mediator. Under protic conditions, the co-electrocatalytic system attains a turnover frequency (TOF) of 15 s -1 and quantitative selectivity for CO. It is proposed that PhBPO interacts with the Cr-based catalyst, coordinating in an axial position trans to an intermediate hydroxycarbonyl species, M-CO 2 H, mediating electron transfer to the catalyst and lowering the barrier for C-OH bond cleavage.