Influence of nitro substituents on the redox, electronic, and proton reduction catalytic behavior of phenolate-based [N2O3]-type cobalt(iii) complexes

Abstract

We report on the synthesis, redox, electronic, and catalytic behavior of two new cobalt(III) complexes, namely [Co^III(L¹)MeOH] (1) and [Co^III(L²)MeOH] (2). These species contain nitro-rich, phenolate-based pentadentate ligands and present dramatically distinct properties associated with the position in which the –NO₂ substituents are installed. Species 1 displays nitro-substituted phenolates, and exhibits irreversible redox response and negligible catalytic activity, whereas 2 has fuctionalized phenylene moieties, shows much improved redox reversibility and catalytic proton reduction activity at low overpotentials. A concerted experimental and theoretical approach sheds some light on these drastic differences.