A 1:1 Copper−Dioxygen Adduct is an End-on Bound Superoxo Copper(II) Complex which Undergoes Oxygenation Reactions with Phenols

Employing a strongly electron-donating tripodal tetradentate ligand along with a reaction strategy designed to suppress binuclear peroxo complex formation, an end-on bound superoxo−copper(II) complex CuII(NMe2−TMPA)(O2-)+ (1) has been generated in solution UV−vis (THF, −85 °C): λmax = 418 nm (ε, 4300 M-1 cm-1), 615 nm (ε, 1100), 767 nm (ε, 840). Resonance Raman spectroscopy employing isotopically substituted dioxygen (including mixed isotope 16/18O2) proves the end-on superoxo CuII(O2-) structural formulation, ν(O−O) = 1121 cm-1; ν(Cu−O) = 472 cm-1. The first demonstration of CuII(O2-) oxidative reactivity with exogenous substrates, likely involving H-atom abstraction chemistry, comes with the finding that 1 effects the oxygenation and hydroperoxylation of substituted phenols.