Catalytic Reduction of 1,6-Dihalohexanes by Nickel(I) Salen Electrogenerated at Glassy Carbon Cathodes in Dimethylformamide

Reaction between stoichiometric amounts of 1,6-dihalohexanes and electrogenerated nickel(I) salen in dimethylformamide containing tetramethylammonium tetrafluoroborate affords cyclohexane in up to 78% yield. Arising via a radical pathway, an ω-haloalkylnickel(II) species is a proposed intermediate for these reductions in which alkanes, 1-alkenes, and aldehydes are also produced. In cyclic voltammetric studies at scan rates of , formation of a passivating film on the surface of the carbon cathode has a dramatic effect on the catalytic reduction of 1,6-dihalohexanes, but this electrode fouling can be overcome by addition of acetic acid to the medium. For controlled-potential electrolyses involving the reduction of a 1,6-dihalohexane with catalytic amounts of electrogenerated nickel(I) salen in the presence of excess acetic acid, most of the substrate is converted into three different esters (hexyl acetate, 1,6-diacetoxyhexane, and dodecyl acetate) which arise via nucleophilic attack of acetate ion on the dihaloalkane.