Calix[8]arene-based Ni(II) complexes for electrocatalytic CO2 reduction.

• Calixarene derivative with phenanthroline moiety acts as nitrogen ligand for nickel complexes. • The chelating phenantrholine places nickel (II) ions within large calix[8]arene cavity. • Ni(II) complexes are catalyst precursors for electrochemical reduction of carbon dioxide. The electrochemical behavior and catalytic activity for the electroreduction of CO 2 of complexes of Ni(II) containing phenanthroline-based ligands, with or without a calixarene scaffold, were tested. The complexes were characterized by spectroscopic techniques, and their electrocatalytic properties determined by cyclic voltammetry. With water as proton source the complex [(1,5-(2,9-dimethyl-1,10-phenanthro)- p-tert -butylcalix[8]arene)NiCl 2 ] (1) presented a significant increase in current at E = −2.36 V (relative to Ag/AgCl reference electrode) when reduced under an atmosphere of CO 2 , indicating that an electrocatalytic process occurs. Thus, calix[8]arenes that feature a phenanthroyl moiety as bidentate N -ligands, and an intramolecular proton source in the phenolic –OH groups, afford Ni(II) electrocatalysts for the reduction of CO 2. [ABSTRACT FROM AUTHOR]