Electrochemical Reduction of Primary Alkyl Halides with the Aid of a Structurally Modified Nickel Salen Catalyst

Abstract

Electrochemical reduction of primary alkyl halides has been extensively investigated through the use of [[2,2′-[1,2-ethanediylbis(nitrilomethylidyne)]bis[phenolato]]-(N,N′,O,O′)]nickel(II) (nickel salen) as a procatalyst. In these studies, there was a proclivity for the grafting of alkyl chains onto the imino (C=N) bonds of the nickel species, which lowers the yields of the desired reduction products significantly.1,2 In the present study, we have used a structurally modified nickel(II) salen-like species possessing methyl protecting groups to improve the performance of the catalyst.3 The efficacy of this modified nickel species as a procatalyst for electrochemical reductions of 1-bromo- and 1-iododecane has been studied with the aid of cyclic voltammetry and controlled-potential (bulk) electrolysis in N,N-dimethylformamide (DMF) containing tetra-n-butylammonium tetrafluoroborate (TBABF4) as a supporting electrolyte. Results indicate that a majority of the reduced substrate appears as a dimeric species (n-eicosane); in addition, smaller amounts of n-decane and 1-decene are found. A mechanism is proposed for the process that involves radical intermediates. Several products corresponding to the incorporation of DMF fragments into the reduced substrate were detected. Use of this procatalyst has also been investigated to overcome solvent incorporation under similar conditions in an acetonitrile medium. References Goken, D.M.; Ischay, M. A.; Peters, D. G.; Tomaszewski, J. W.; Karty, J. A.; Reilly, J. P.; Mubarak, M. S. J. Electrochem. Soc. 2006, 153, E71–E77. Raess, P. W.; Mubarak, M. S.; Ischay, M. A.; Foley, M. P.; Jennermann, T. B.; Raghavachari, K.; Peters, D. G. J. Electroanal. Chem. 2007, 603, 124–134. Ourari, A.; Ouennoughi, A.; Aggoun, D.; Mubarak, M. S.; Pasciak, E. M.; Peters, D. G. Polyhedron 2014, 67, 59–64. Figure 1