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

The
reactivity of peroxide dianion O22– 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⊂mBDCA-5t-H6]2– (1), 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⊂mBDCA-5t-H6]2– (2), 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.