Silver as a powerful electrocatalyst for organic halide reduction: the critical role of molecular structure

The remarkable electrocatalytic properties of silver for organic halide reductions, related to its strong specific interactions with halide ions, and therefore modulated by the surface state and by the nature of the supporting electrolyte, have been shown by us recently. The key role played by the molecular structure is now described together with its effect on the reaction pathway, in terms of not only the intrinsic (RX)-X-... reactivity modification but also of elements connected to the heterogeneous nature of the process, including the accessibility of the leaving group and the possible presence of adsorption auxiliary groups stabilizing the postulated (RXMe)-X-...-Me-... intermediate. The present discussion is supported by: (a) cyclovoltammetric investigations on a wide set of aliphatic and aromatic halides performed on silver, mercury and glassy carbon; and (b) a systematic program of preparative electroreductions carried out on variously configurated haloadamantanes in different operating conditions. The haloadamantane case, yielding a mixture of adamantane and dimers in a ratio heavily affected by the operating conditions, is very appropriate for an elucidation of the factors favouring monoelectronic dimerisation versus bielectronic halogen replacement by hydrogen. (C) 2001 Elsevier Science Ltd. All rights reserved.