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

The electrocarboxylation of chloroacetonitrile (NC-CH2-Cl=RCl) mediated by [(CoL2)-L-II](2+) (L=terpyridine) was investigated by cyclic voltammetry. Electrochemical studies under argon atmosphere showed that the monoelectronic reduction of [(CoL2)-L-II](2+) yielded a Cobalt(I) complex which after the loss of a terpyridine ligand reacted with chloroacetonitrile. The oxidative addition of chloroacetonitrile on [(CoL)-L-I](+) gave an alkylCobalt(III) complex (R-(CoL)-L-III](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 CO2 but CO2 insertion was observed in the alkylCobalt(III) complex [R-(CoL)-L-III](2+) giving probably a CO2 adduct [R-(CoL)-L-III(CO2)](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 RCO2- (NC-CH2-CO2-) 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. (C) 2011 Elsevier Ltd. All rights reserved.