Electrocatalytic reduction of carbon dioxide mediated by transition metal complexes with terdentate ligands derived from diacetylpyridine

The electrochemical characterization and electrocatalytic activity, towards the reduction of carbon dioxide, of transition metal complexes with terdentate ligands derived from diacetylpyridine are presented. We have prepared Fe, Co and Ni complexes of (i) 2,6-bis-[1-(phenylimino)ethyl]pyridine (DAPA), (ii) BrDAPA, (iii) vinyl-DAPA (v-DAPA), (iv) 2,6-bis[1-(benzylimino)ethyl]pyridine (DAPB), (v) 2,6-bis[1-(2-methylpyridylimino)ethyl]pyridine (DAPMP), and (vi) 2,6-bis[1-(2-ethylpyridylimino)ethyl]pyridine (DAPEP). In general, we find that all of these materials exhibit electrocatalytic behavior towards the reduction of CO2 in non-aqueous solvent. The electrocatalytic activity was dependent on both the metal center and the ligand. The trends can be rationalized in terms of electronic effects arising from the ligand and on whether the redox process is ligand or metal localized.