Synergistic Metal–Ligand Redox Cooperativity for Electrocatalytic CO2 Reduction Promoted by a Ligand-Based Redox Couple in Mn and Re Tricarbonyl Complexes

Abstract

Electrocatalytic CO2 reduction is demonstrated for the Mn and Re tricarbonyl complexes, [M(Me2OQN)(CO)3(CH3CN)] (M = Mn or Re) containing the 5,7-dimethyl-8-oxyquinolate (Me2OQN–) ligand. In comparison to the related 2,2′-bipyridyl (bpy) reference complexes, [M(bpy)(CO)3(CH3CN)]+ (M = Mn or Re), the Me2OQN–-based precatalysts exhibit an onset of catalytic current with the input of one less equivalent of electrons. This behavior is attributed to the formal Me2OQN(•/−) redox couple which contributes toward each catalytic cycle in tandem with the formal Mn(I/0) and Re(I/0) redox couples. In addition to computational support for synergistic metal–ligand redox cooperativity, electrochemistry (cyclic voltammetry and controlled potential electrolysis), spectroelectrochemistry (FTIR and EPR), and pulse radiolysis coupled with time-resolved infrared spectroscopy (PR-TRIR) provide structural insight into the electronic properties of the one-electron- and two-electron-reduced species..