Anion-Receptor Mediated Oxidation of Carbon Monoxide to Carbonate by Peroxide Dianion

The reactivity of peroxide dianion O₂^2– has been scarcely explored in organic media due to the lack of soluble sources of this reduced oxygen species. We now report the finding that the encapsulated peroxide cryptate, [O₂⊂<i>m</i>BDCA-5t-H₆]^2– (<b>1</b>), reacts with carbon monoxide in organic solvents at 40 °C to cleanly form an encapsulated carbonate. Characterization of the resulting hexacarboxamide carbonate cryptate by single crystal X-ray diffraction reveals that carbonate dianion forms nine complementary hydrogen bonds with the hexacarboxamide cryptand, [CO₃⊂<i>m</i>BDCA-5t-H₆]^2– (<b>2</b>), a conclusion that is supported by spectroscopic data. Labeling studies and ¹⁷O solid-state NMR data confirm that two-thirds of the oxygen atoms in the encapsulated carbonate derive from peroxide dianion, while the carbon is derived from CO. Further evidence for the formation of a carbonate cryptate was obtained by three methods of independent synthesis: treatment of (i) free cryptand with K₂CO₃; (ii) monodeprotonated cryptand with PPN­[HCO₃]; and (iii) free cryptand with TBA­[OH] and atmospheric CO₂. This work demonstrates CO oxidation mediated by a hydrogen-bonding anion receptor, constituting an alternative to transition-metal catalysis