Alkyl group incorporation into nickel salen during controlled-potential electrolyses in the presence of alkyl halides

During the catalytic reductions of 1-iodooctane, 1-bromooctane, and 1-iodobutane by nickel(I) salen, electrogenerated from nickel(II) 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 remains) and the transition-metal complex loses its activity. For a system originally consisting of nickel(II) salen and either 1-iodooctane or 1-bromooctane, analyses of post-electrolysis solutions by means of high-performance liquid chromatography reveal that the original nickel(II) salen is largely transformed into three new species. Electrospray-ionization mass spectrometry indicates that one species is a monooctylated nickel(II) salen and another species is a dioctylated nickel(II) salen. Nuclear magnetic resonance spectrometry [i.e., correlated spectroscopy (COSY), nuclear Overhauser effect spectroscopy (NOESY), and total correlated spectroscopy (TOCSY) techniques] has been utilized to establish the sites of octylation. For the 1-iodobutane- nickel(II) salen system, at least three butylated nickel(II) salen species have been detected, among which are monobutylated and dibutylated complexes.