Catalytic reduction of iodoethane and 2-iodopropane at carbon electrodes coated with anodically polymerized films of nickel(II) salen

Article abstract of DOI:10.1021/ac00091a020

In acetonitrile containing tetramethylammonium tetrafluoroborate, nickel(II) salen undergoes anodic polymerization onto a carbon electrode. Nickel(II) in the polymer film exhibits reversible one-electron reduction to form nickel(I), which can catalytically reduce iodoethane or 2-iodopropane to form an ethyl or 2-propyl radical, respectively, and to regenerate nickel-(II). Kinetics studies with the aid of hydrodynamic voltammetry indicate that the catalytic reduction of iodoethane belongs to the ER regime of Saveant and co-workers, whereas catalytic reduction of 2-iodopropane is of the S classification. Controlled-potential electrolyses of iodoethane and 2-iodopropane at nickel-(II) salen-coated reticulated vitreous carbon cathodes give product distributions in accord with the relative importance of radical coupling and disproportionation. Direct reduction of iodoethane at a bare cathode generates products via a carbanion mechanism. Products obtained from direct reduction of 2-iodopropane depend on the potential employed; at a potential corresponding to the first voltammetric wave, product distributions are nearly identical with those obtained from the catalytic reduction, whereas at a potential after the second voltammetric wave, the products are derived from the 2-propyl carbanion.