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

Abstract

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 [Cu II (NMe 2 −TMPA)(O 2 - )] + ( 1 ) has been generated in solution [UV−vis (THF, −85 °C): λ max = 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 16/18 O 2 ) proves the end-on superoxo Cu II (O 2 - ) structural formulation, ν(O−O) = 1121 cm -1; ν(Cu−O) = 472 cm -1 . The first demonstration of Cu II (O 2 - ) 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.