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,N′-dimethylethylenediamine; 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-η2:η2-peroxodicopper(II) and/or bis(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-bridged μ-η2:η2-peroxodicopper(II) complex was implicated.