Observation of a CuII 2(m-1,2-peroxo)/CuIII 2(m-oxo)2 Equilibrium and its Implications for Copper–Dioxygen Reactivit
Abstract
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.
A copper system has been uncovered in which an end-on peroxo [Cu2(O2)] core is in equilibrium with a bis-μ-oxo [Cu2(O)2] core. Calibration of computational methods to experimental thermodynamic results suggest that the electrophilic reactivity patterns recently attributed to an end-on-peroxo CuII2 species are, in fact, likely a result of an accessible bis-μ-oxo CuIII2 core, a structural type long associated with electrophilic reactivity.
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