Dinuclear Nickel Complexes as Catalysts for Electrochemical Reduction of Carbon Dioxide

Abstract

Dinuclear Ni(0) complexes [Ni 2 (μ-dppa) 2 (μ-CNR)(CNR) 2 ] (R = Me ( 1 ), n-Bu ( 2 ), and 2,6-Me 2 C 6 H 3 ( 3 ); dppa = bis(diphenylphosphine)amine) were synthesized in good yields by reacting Ni(COD) 2 with dppa and the corresponding isocyanide. The X-ray structure of complex 1 is reported. The electrochemistry and spectroelectrochemistry of each complex are also reported. Complex 2 exhibits an irreversible 1 e - reduction at −0.99 V vs ferrocene in its cyclic voltammogram. When the cyclic voltametry was performed in the presence of CO 2, a substantial current enhancement was observed for the reduction wave. Spectroelectrochemical as well as isotope labeling studies show that 2 is singly reduced to a radical anion species that is reactive toward CO 2, yielding the disproportionation products CO and CO 3 2 - . In the presence of H + donors (residual water), reduction of CO 2 to formate is a competing process.