Phosphonation of aryl halides by copper(I) complexes of trialkyl phosphites

Abstract

The copper complexes [Cu₃(O₂CMe)₅{P(OR)₃}₂](1; R = Me or Et), [Cu(O₂CMe){P(OR)₃}(bpy)](2; R = Me or Et)(bpy is 2,2′-bipyridine), and [Cu(O₂CMe){P(OEt)₃}₂] react with certain 2-halogenoazobenzene compounds, ArX, at room temperature to form the corresponding dialkyl arylphosphonates, ArP(O)(OR)₂, and the products, ArH and Ar₂, of reductive substitution and biaryl coupling. The ester, MeCO₂R, and a copper(I) halide complex (e.g. [CuX{P(OR)₃}]) are also formed. Kinetic studies of the reactions of some of these copper complexes with 2′-acetamido-6-bromo-4′-diethylamino-2,4-dinitroazobenzene in alcohol solution show that the phosphonation reactions are equal concentration second-order processes in each case. The effects of a radical scavenger and of light on the reaction suggest the involvement of radicals in the formation of ArH and Ar₂, but not in the formation of ArP(O)(OR)₂. The effects of different substituents in ArX, of changes in solvent, and of various additives on these reactions are investigated. A mechanism involving concerted nucleophilic substitution within the coordination sphere of copper(I) is proposed.