Homogeneous oxidative coupling catalysts: stoichiometry, characterization and kinetics of [(diamine)(μ-halo)copper(I)]2oxidation by dioxygen in aprotic solvent

Copper(I) halides dissolve in deoxygenated methylene chloride and nitrobenzene solutions of equimolar N,N,N′-triethylethylenediamine (TriEED) to give air-sensitive colorless or pale yellow copper(I) dimers [(TriEED)(μ-X)Cu]2, X = Cl, Br or I. Dioxygen uptake, analytical, cryoscopic and spectral data show that copper(I) dimers are oxidized to μ-oxo complexes, [(TriEED)2(μ-X)2(μ-O)Cu2], which react with carbon dioxide to form μ-carbonato analogues, [(TriEED)2X2(μ-CO3)Cu2]. Both oxo and carbonato complexes are homogeneous oxidative coupling catalysts for oxidation of 2,6-dimethylphenol to mixture of diphenoquinone (DPQ) and polyphenyleneoxide (PPO). Kinetic data for oxidation of [(TriEED)(μ-X)Cu]2 by dioxygen in nitrobenzene obey the third-order rate law d[[(TriEED)2(μ-X)2(μ-O)Cu2]]/dt = k D[[(TriEED)(μ-X)Cu]2]2[O2]. Comparison of the kinetic data with data for oxidation of [(TEED)(μ-Br)Cu]2, TEED = N,N,N′,N′-tetraethylethylenediamine (the fully alkylated diamine), by dioxygen indicate that N–H in (TriEED) speeds the reaction by a factor of 220 due to an intermolecular attractive force between N–H of (TriEED) and the incoming dioxygen, helping to assemble the activated complex.