A previous study has described that [[2,2′-[1,2-ethanediylbis(nitrilomethylidyne)]bis[phenolato]-N,N′,O,O′]nickel(I), also known as nickel(I) salen, can be electrogenerated from nickel(II) salen. Through the use of controlled–potential electrolysis, nickel(I) salen can catalytically reduce α,ω-dihaloalkanes. Early work focused on reduction of α,ω-dihaloalkanes substituted by mixed halogens, and revealed that this reduction could yield both straight-chain monomeric and dimeric products.¹ This research project involves the catalytic reduction of 5.0 and 10.0 mM solutions of 1,6-dibromohexane and 10.0 mM 1,6-diiodohexane by nickel(I) salen electrogenerated at a glassy carbon cathode in dimethylformamide containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF₄) as a supporting electrolyte. A point of major interest is to separate, identify, and quantitate the products that arise from this catalytic process. Cyclic voltammetry indicates that the reduction peaks for 1,6-dibromohexane are –1.64 V for direct reduction and –0.92 V in the presence of nickel(I) salen; all potentials are reported versus a cadmium mercury amalgam reference electrode with a potential of –0.76 V versus an aqueous saturated calomel electrode. Reduction potentials for 1,6-diiodohexane are –1.56 V and –0.97 V, respectively. Bulk electrolysis of nickel(II) salen in the presence of these substrates has been performed, and the various products were separated and identified with the aid of gas chromatography–mass spectrometry and electrospray ionization–mass spectrometry. The results revealed that there were small amounts of cyclohexane and dihalogenated dimers with a significant amount of starting material left after electrolysis. This low yield is assumed to be from the alkylation of the imino bond on the salen ligand on the basis of previous studies; dihaloalkylated salen species were identified with the aid of liquid chromatography–mass spectrometry.^1,2

Reference:

1. Mubarak, M. S.; Peters, D. G., Homogeneous Catalytic Reduction of α,ω-Dihaloalkanes with Electrogenerated Nickel(I) Salen. Electroanal. Chem. 1995, 388, 195–198.
2. Martin, E. T.; McGuire, C. M.; Peters, D. G., Catalytic Reduction of Organic Halides by Electrogenerated Nickel(I) Salen. Soc. Interface 2016, 25, 41–45.