Electrocatalytic CO2 reduction with calix[8]arene/base metal platforms

[Display omitted] •Calixarene derivative with phenanthroline moiety acts as bidentate nitrogen ligands for base metals.•Molecular analogues neocuproine and 2,9-bis((4-(tert-butyl)phenoxy)methyl)-1,10-phenanthroline used for comparison.•The chelating phenanthroline protects the metal ions within large calix[8]arene cavity towards redistribution.•Co, Ni, and Cu complexes are catalyst precursors for electrochemical reduction of carbon dioxide.•Zn complexes are not electrochemically active. Base metal complexes were obtained with phenanthroline-functionalized calix[8]arenes as scaffolds in good yields. All complexes were characterized by spectroscopic and mass spectrometry techniques, and their electrochemical properties determined by cyclic voltammetry (CV). Electrocatalytic tests for CO2 and proton reduction reactions (CO2RR and HER, respectively) were carried out with all systems, with trifluoroethanol as proton source. The complex with general formulae [M(1,5-(2,9-dimethyl-1,10-phenanthro)-p-tert-butylcalix[8]arene)Cl2] (M = Co, Ni, Cu) presented a significant current increase around E = −2.2 to −2.5 V (relative to the ferricenium/ferrocene couple) under CO2 atmosphere, indicative of an electrocatalytic process; this was not the case for the Zn derivative. This behavior was compared to that of the analogous 2,9-dimethyl-1,10-phenanthroline derivatives, with the phenol-containing calix[8]arene complexes that feature –OH groups as intramolecular proton relays acting as more stable and efficient electrocatalysts for CO2RR.