Dissociative electron transfer to organic chlorides: Electrocatalysis at metal cathodes

The reductive cleavage of a series of organic chlorides, including chloroaromatics, benzyl chlorides, activated chloroalkanes and polychloromethanes, was investigated at Ag, Cu, Pd and glassy carbon (GC) electrodes in CH3CN + 0.1 M (C2H5) 4NClO 4. The silver cathode was either a 2-mm diameter disc, fabricated from Ag wire, or nanoclusters of average diameter d = 304 nm, prepared by electrodeposition on GC. Ag, Cu and Pd electrodes have shown remarkable electrocatalytic properties for the reduction of several compounds. The peak potentials recorded at these electrodes, for example, at v = 0.1 V/s are positively shifted by 0.3–0.8 V with respect to the reduction potentials measured at a non catalytic electrode such as GC. Electrocatalysis is strictly related to the concerted nature of the dissociative electron transfer to the carbon–chlorine bond. No catalysis is observed when the dissociative electron transfer to RCl occurs according to a stepwise mechanism involving the intermediate formation of a radical anion. The catalytic surfaces affect the reaction scheme, offering a more favourable route possibly through the formation of strongly adsorbed activated complexes.