Electrochemistry of nickel(II) and copper(II) N,N′ -ethylenebis(acetylacetoniminato) complexes and their electrocatalytic activity for reduction of carbon dioxide and carboxylic acid protons

The effect of the metal center of [ML] complexes [M = Ni(II), Cu(II); L = N,N′-ethylenebis(acetylacetoniminato)] on their electrochemistry and electrocatalytic activity for the reduction of CO2 and protons has been studied using cyclic voltammetry and bulk electrolysis. The two complexes exhibit different electrochemistries, which are not significantly dependent on the nature of the solvent. The electrocatalytic activity of [NiL] is significantly higher than that of [CuL] for CO2 reduction, due to the higher stability of the electrochemically generated [Ni(I)L] complex, relative to the Cu(I) analog. The diffusion coefficient of [NiL] calculated from the steady-state diffusion limiting current is 3.0 × 10−6 cm2 s−1. The catalytic efficiency of [NiL] in non-aqueous solvents in terms of i p(CO2)/i p(N2) per nickel center is smaller than that of [Ni(cyclam)]2+, but greater than those of sterically hindered mononuclear [Ni(1,3,6,8,10, 13,15-heptaazatricyclo(11.3.1.1) octadecane)]2+ or multinuclear [Ni3 (X)]6+ where X = 8,8′,8″-{2,2′,2″(-nitrilotriethyl)-tris(1,3,6,8,10,13,15-heptaazatricyclo(11.3.1.1) octadecane}. Both [NiL] and [CuL] are also electrocatalysts for the reduction of carboxylic acid protons, with the catalytic pathway being different for acetic and trifluoroacetic acids in MeCN.