Cyanide substitution in aryl halides by copper(I) complexes derived from formamide and from formaldehyde oxime

Abstract

The copper complexes [Cu₃(CN)₄L₄][L = MeCN, pyridine (pyr)], [Cu(CN)(pyr)₂] and [Cu₂(O₂CMe)(CN)] derived from formamide, and [Cu₃(O₂CMe)₅(MeCONH₂)(CH₂NOH)₂] and [Cu(O₂CMe)(CH₂NOH)₂] derived from formaldehyde oxime (formaldoxime) react with 2′-acetamido-6-bromo-4′-diethylamino-2,4-dinitroazobenzene, ArBr, to form the corresponding aryl cyanide, ArCN, and the products ArH and Ar₂ of reductive substitution and biaryl coupling. Copper(I) bromide complexes are also formed. Kinetic studies of these reactions in acetonitrile solution show that the cyanation reactions are equal concentration, second-order processes in each case. The effect of a radical scavenger on the reaction suggests the involvement of radicals in the formation of Ar₂, but not in the formation of ArCN. A mechanism involving concerted nucleophilic substitution within the co-ordination sphere of copper(I) is proposed.