Mechanistic Insights into the Electrochemical Reduction of CO2 Catalyzed by Iron Cyclopentadienone Complexes

In a previous paper we have demonstrated that the easily-synthesized class of iron(0) cyclopentadienone complexes constitutes a promising catalyst platform for the electrochemical conversion of CO2 to CO and H2O. One of the unusual features of these catalysts is that catalysis proceeds efficiently in aprotic electrolytes in the absence of acidic additives. Herein we present a detailed study of the underlying catalytic mechanisms. Using a combination of FTIR spectroelectrochemistry, DFT calculations, and nonelectrochemical control experiments, we have identified a number of catalytic intermediates including the active species and the product of catalyst deactivation. On the basis of these insights, we have carried out digital simulations in order to decipher the voltammetric profiles of the iron(0) cyclopentadienones. Further control experiments revealed that the anodic oxidation of the electrolyte constitutes the terminal proton source for the formation of CO and H2O. Taken together, our results suggest a competition between two coexisting catalytic pathways, one of which proceeds via a hitherto unknown Fe–Fe dimer as an active species.