Selective monooxygenation of methane under mild conditions is an important target in the near-term with potential for important industrial, environmental, and societal impact. To date, some of the most promising synthetic materials competant for this reaction are copper exchanged zeolites with proposed asymmetric dicopper(II/I)-μ-oxyl active sites. Due to the challenge of characterizing and understanding the fundamental chemistry occurring in the defect sites of these materials, synthesis of a true small-molecule analogue of these active sites is an important goal. Mechanical stress applied by hydrostatic pressure in diamond anvil cells is an emerging method to translate macroscopic force into molecular level chemical changes. Under high-pressure conditions, we show a dicopper(II)-μ-hydroxo species undergoes a proton-involved redox reaction to generate a meta-stable asymmetric dicopper(II/I)-μ-oxyl species competant for oxidation of exogenous substrates. The asymmetry of the species is important; symmetric dicopper(II)-μ-O species are known, but none have been shown competant for the oxidation of recalcitrant C-H bonds. It has been proposed that the asymmetric stabilization of a copper(I) enhances the oxidative power of the core oxygen. The potent oxidant generated under hydrostatic pressure is moderately stable under ambient conditions and the mixed-valency has been characterized by XPS. In-situ Raman spectroscopy of the isotopic labeled bridging hydroxo reveals a 1H/2H kinetic isotope effect wherein compression of the molecule leads to deprotonation and activation of the bridging oxygen. Through the calibration of Ab-Initio and DFT computational methods with high-level synchotron experiments, we reveal the fundamental origins of the mechanochemical generation of this oxidant and plot the reaction landscape as a function of applied pressure and destabilization of the ground state. This study exemplifies the potential for mechanochemial methods to synthesize highly activate motifs inacessible to traditional methods; and for the first time provides a true small-molecule analogue for the active sites of copper exchanged zeolites.

High-pressure reactivity and kinetic isotope effect of a dicopper(II)-μ-hydroxo complex: mechanochemical generation of a potent oxidant

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