Copper/α-ketocarboxylate chemistry with supporting peralkylated diamines: Reactivity of copper(I) complexes and dicopper-oxygen intermediates

To further understand copper-promoted oxidation reactions, the Cu(I) complexes LCuX (L = N,N-di-tert-butyl-N,Ndimethylethylenediamine; X = benzoylformate (BF) or p-nitro-benzoylformate) were synthesized, fully characterized by X-ray crystallography and spectroscopy in solution, and their reactivity with O₂ at -80 °C examined. Oxidative decarboxylation of the α-ketocarboxylate ligand was observed, but only to a significant extent when cyclohexene, cyclooctene, or acetonitrile was present. Spectroscopic and conductivity data are consistent with mechanistic postulates involving displacement of the α-ketocarboxylate by the additives to a small extent, followed by oxygenation of the LCu(I) moiety to yield copper-oxygen species that subsequently induce decarboxylation. To test these hypotheses, spectroscopic and kinetic studies of the reactions of Bu₄NBF with preformed μ-n²:n²-peroxodlcopper(II) and/or bls(μ-oxo) dicopper(III) complexes supported by L or N,N,N,N-tetramethylpropylenediamine were performed. In an illustration of a new mode of reactivity for such dicopper-oxygen cores, decarboxylation of the added α-ketocarboxylate was observed and the intermediacy of a carboxylate-brldged μ-n²:n ²-peroxodicopper(II) complex was implicated.