Electrochemical Reduction of CO₂ Catalysed by Transition Metal Complexes

Abstract

Cobalt and nickel complexes of N,N’—1,2—phenylenebis(salicylideneiminato) (salophen = L) have been investigated by cyclic voltammetry and controlled potential electrolysis as potential catalysts for the electrochemical activation of CO ₂. In the case of [Ni(II)L], no catalysis was observed. The first electron uptake is ligand—based, yielding the radical anion [Ni(II)L].— which rapidly dimerizes. On the contrary, the electron transfer to [Co(II)L] is metal—centered giving the [Co(I)L]^- complex which in AN containing LiClO₄ as background electrolyte appears to catalyze the CO₂ reduction to CO and C0₃ ^2-, in a potential region where direct CO₂ reduction does not occur. Mechanistic investigations point to the interaction of CO₂ with [Co(I)(L)Li] to give a precursor complex containing a head—to—tail CO₂ dimer. Further reduction of the latter yields a Co—carbonyl complex which releases quite slowly the final CO₂ reduction product CO.