Synthesis of small molecule Cu2O2 adducts has provided insight into the related biological systems and their reactivity patterns including the interconversion of the CuII2(μ-η2:η2-peroxo) and CuIII2(μ-oxo)2 isomers. In this study, absorption spectroscopy, kinetics, and resonance Raman data show that the oxygenated product of [(BQPA)CuI]+ initially yields an “end-on peroxo” species, that subsequently converts to the thermodynamically more stable “bis-μ-oxo” isomer (Keq = 3.2 at −90 °C). Calibration of density functional theory calculations to these experimental data suggest that the electrophilic reactivity previously ascribed to end-on peroxo species is in fact a result of an accessible bis-μ-oxo isomer, an electrophilic Cu2O2 isomer in contrast to the nucleophilic reactivity of binuclear CuII end-on peroxo species. This study is the first report of the interconversion of an end-on peroxo to bis-μ-oxo species in transition metal-dioxygen chemistry.

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Synthesis of small-molecule Cu 2 O 2 adducts has provided insight into the related biological systems and their reactivity patterns including the interconversion of the Cu II 2 (mh 2 :h 2 -peroxo) and Cu III 2 (m-oxo) 2 isomers. In this study, absorption spectroscopy, kinetics, and resonance Raman data show that the oxygenated product of [(BQPA)Cu I ] + initially yields an "end-on peroxo" species, that subsequently converts to the thermodynamically more stable "bis-m-oxo" isomer (K eq = 3.2 at À90 8C). Calibration of density functional theory calculations to these experimental data suggest that the electrophilic reactivity previously ascribed to end-on peroxo species is in fact a result of an accessible bis-m-oxo isomer, an electrophilic Cu 2 O 2 isomer in contrast to the nucleophilic reactivity of binuclear Cu II end-on peroxo species. This study is the first report of the interconversion of an end-on peroxo to bis-m-oxo species in transition metal-dioxygen chemistry.[**] These studies were supported by the NIH (DK031450 to E.I.S.;GM60353 to K.D.K.; postdoctoral fellowship GM085914 to M.K.E.).