Nickel Complexes Based on Molybdopterin-like Dithiolenes: Catalysts for CO2 Electroreduction

Molecular metal (M)-dithiolene complexes are mimics of the active sites of metalloenzymes such as formate dehydrogenases and CO-dehydrogenases. Recently, the first M-dithiolene (M = Ni) complex behaving as a catalyst for carbon dioxide electroduction has been reported. Here, using dithiolene ligands structurally similar to molybdopterin, new stable Ni-dithiolene complexes have been prepared and characterized. They all catalyze the electroreduction of CO2, generating formic acid as the major product (with a faradaic yield of 70% for the most active and selective one), together with minor amounts of CO and H-2. As in the case of the well-studied Ni(cyclam) complex, catalysis occurs exclusively using a Hg electrode. This suggests that Hg contributes to the activation of the catalyst transiently adsorbed at the surface of the electrode. Unexpectedly, significant differences in activity and selectivity are observed between stereoisomers, which also likely results from the interactions between the catalysts and the Hg electrode.