During the catalytic reductions of 1-iodooctane, 1-bromooctane, and 1-iodobutane by nickel͑I͒ salen, electrogenerated from nickel͑II͒ salen at a carbon cathode in dimethylformamide containing 0.10 M tetraethylammonium tetrafluoroborate, less than 100% of the alkyl halide is converted into hydrocarbon products ͑although virtually none of the original alkyl halide remains͒ and the transition-metal complex loses its activity. For a system originally consisting of nickel͑II͒ salen and either 1-iodooctane or 1-bromooctane, analyses of post-electrolysis solutions by means of high-performance liquid chromatography reveal that the original nickel͑II͒ salen is largely transformed into three new species. Electrospray-ionization mass spectrometry indicates that one species is a monooctylated nickel͑II͒ salen and another species is a dioctylated nickel͑II͒ salen. Nuclear magnetic resonance spectrometry ͓i.e., correlated spectroscopy ͑COSY͒, nuclear Overhauser effect spectroscopy ͑NOESY͒, and total correlated spectroscopy ͑TOCSY͒ techniques͔ has been utilized to establish the sites of octylation. For the 1-iodobutane-nickel͑II͒ salen system, at least three butylated nickel͑II͒ salen species have been detected, among which are monobutylated and dibutylated complexes.

Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate and characterize the reductive intramolecular cyclization of ethyl 2-bromo-3-(3',4'-dimethoxyphenyl)-3-(propargyloxy)propanoate (1) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)nickel(I), [Ni(tmc)](+), electrogenerated at glassy carbon cathodes in dimethylformamide containing tetraalkylammonium salts. Cyclic voltammograms for reduction of [Ni(tmc)](2+) in the presence of 1 reveal that [Ni(tmc)](+) catalytically reduces 1 at potentials more positive than those required for direct reduction of 1. During controlled-potential electrolyses of solutions containing [Ni(tmc)](2+) and 1, catalytic reduction of the latter proceeds via one-electron cleavage of the carbon-bromine bond to form a radical intermediate that undergoes cyclization to afford 2-(3',4'-dimethoxyphenyl)-3-(ethoxycarbonyl)-4-methylenetetrahydrofuran (2). In the presence of a base (either electrogenerated or deliberately added as potassium tert-butoxide), 2 rearranges to give 2-(3',4'-dimethoxyphenyl)-3-(ethoxycarbonyl)-4-methyl-2,5-dihydrofuran (3). A mechanistic scheme is proposed to explain the results obtained by means of cyclic voltammetry and controlled-potential electrolysis.

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+ catalytically reduces these two compounds at potentials significantly more positive than those required for direct reduction of the bromo

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