Capped Polyoxometalate-Based Metal–Organic Complex with Mixed-Valence Cu<sup>I</sup>/Cu<sup>II</sup> for Synergistic Catalytic Synthesis of <i>p</i>-Benzoquinone
Zhixuan An, Xiaohui Li, Zhong Zhang, Xiuli Wang
Abstract
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 I /Cu II, [Cu 2 I Cu 2 II (pyca) 4 (OH) 3 (PMo 12 O 40 Cu 2 II )(H 2 O) 4 ]·3.5H 2 O ( 1, Hpyca = 2-pyrazinecarboxylic acid) has been successfully synthesized under solvothermal conditions. Surprisingly, complex 1 not only combines the desired mixed-valent Cu I /Cu II and POM sites but also contains a rare double Cu-capped POM structure. Due to the ternary synergistic effect of Cu I, Cu II, and POM, complex 1 exhibits excellent catalytic activity in the oxidation reaction of 2,3,6-trimethylphenol to the corresponding p -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 –1, which is superior to most catalysts.