Electrocarboxylation of chloroacetonitrile by a Cobalt(I) complex of terpyridine

Abstract

The electrocarboxylation of chloroacetonitrile (NC–CH 2–Cl RCl) mediated by [Co IIL 2] 2+ (L = terpyridine) was investigated by cyclic voltammetry. Electrochemical studies under argon atmosphere showed that the monoelectronic reduction of [Co IIL 2] 2+ yielded a Cobalt(I) complex which after the loss of a terpyridine ligand reacted with chloroacetonitrile. The oxidative addition of chloroacetonitrile on [Co IL] + gave an alkylCobalt(III) complex [R–Co IIIL] 2+ which was reduced into an alkylCobalt(II) complex, highly unstable and decomposed into an alkyl anion and a Cobalt(II) complex. Under carbon dioxide atmosphere, Cobalt(I) complex was shown to be unreactive towards CO 2 but CO 2 insertion was observed in the alkylCobalt(III) complex [R–Co IIIL] 2+ giving probably a CO 2 adduct [R–Co IIIL(CO 2)] 2+. This adduct presented a strong adsorption at the carbon electrode and was reduced at potential less cathodic than the one of alkylCobalt(III) complex. After reduction, the carboxylate RCO 2 − (NC–CH 2–CO 2 −) was released and a catalytic bielectronic carboxylation of chloroacetonitrile took place. Controlled potential electrolyses confirmed the catalytic process and gave for cyanoacetic acid faradic yields up to 60% under low overpotential conditions.