Catalytic reduction of alpha,omega-dihaloalkanes with nickel(I) salen as a homogeneous-phase and polymer-bound mediator

Catalytic reductions of 1,3-dibromopropane, 1,4-diiodobutane, and 1,4-dibromobutane with homogeneous-phase and polymer-bound nickel(I) salen in acetonitrile containing tetramethylammonium tetrafluoroborate have been investigated with the aid of cyclic voltammetry and controlled-potential electrolysis. Reduction of 1,3-dibromopropane with electrogenerated solution-phase nickel(I) salen leads primarily to the formation of cyclopropane, whereas propylene is the predominant product when the reduction is catalyzed with nickel(I) salen confined in a polymer film on the surface of a carbon electrode. Successful catalytic reduction of 1,4-dihalobutanes requires the presence of an acid, with acetic acid having been used in this investigation; products derived from these reactions are cyclobutane, n-butane, 1-butene, n-octane, n-dodecane, n-hexadecane, and n-eicosane, and the yield of cyclobutane can exceed 70% if the concentration of acetic acid is properly chosen. Formation of an omega-haloalkylnickel(II) intermediate is proposed as a key step for all of these catalytic reductions.