CATALYTIC REDUCTION OF IODOETHANE AND 2-IODOPROPANE AT CARBON ELECTRODES COATED WITH ANODICALLY POLYMERIZED FILMS OF NICKEL(II) SALEN

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 ethylor 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.