Capped Polyoxometalate-Based Metal-Organic Complex with Mixed-Valence Cu/Cu for Synergistic Catalytic Synthesis of -Benzoquinone.

The design and synthesis of efficient and environmentally friendly heterogeneous catalysts for the oxidation of phenols to benzoquinones are of great significance. Considering the highly catalytic activity of mixed-valence metals and polyoxometalates (POMs), a three-dimensional polyoxometalate-based metal-organic complex with mixed-valence Cu/Cu, [CuCu(pyca)(OH)(PMoOCu)(HO)]·3.5HO (, Hpyca = 2-pyrazinecarboxylic acid) has been successfully synthesized under solvothermal conditions. Surprisingly, complex not only combines the desired mixed-valent Cu/Cu and POM sites but also contains a rare double Cu-capped POM structure. Due to the ternary synergistic effect of Cu, Cu, and POM, complex exhibits excellent catalytic activity in the oxidation reaction of 2,3,6-trimethylphenol to the corresponding -benzoquinone. The conversion and selectivity can reach 98 and 99% within 5 min, respectively, and the turnover frequency (TOF) value is as high as 8167 h, which is superior to most catalysts.