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Selective oxidation reactions of sulfides have been attracting chemists from different fields due to the wide applications of the products. In this work, two hybrid compounds of Evans–Showell type polyoxometalate, [Co(bpy)3]2[Co2Mo10O38H4]·6H2O (1) and [Cu3(bpy)3(H2O)6][Co2Mo10O38H4]·5H2O (2) (bpy = 2,2′-bipyridine), were designed to catalyze the oxidation of various sulfides. Their corresponding structures were determined by Fourier-Transform Infrared-Spectroscopy (FT-IR), X-ray diffraction (single-crystal and powder), and elemental mapping analysis, exhibiting three-dimensional supramolecular structures formed through extensive hydrogen bonding interactions. Compound 1, in the model reaction of selective oxidation of methyl phenyl sulfide (MPS) to methyl phenyl sulfoxide (MPSO), achieved complete conversion within 35 min and exhibited a dramatically higher turnover frequency (TOF) compared to those of the other various precursors. Compound 2 also exhibited excellent catalytic properties within 60 min, despite the significant difference in the three-dimensional stacking pattern from that of 1. Besides, more generally, both compounds showed satisfactory catalytic performance for different sulfide substrates. Finally, their excellent structural stability and recyclability under working conditions were confirmed using different tests. [ABSTRACT FROM AUTHOR]

Selective oxidation of substituted phenols is an ideal method for preparing functionalized p-benzoquinones (p-BQs), which serve as versatile raw materials for the synthesis of a variety of biologically active compounds. Herein, two new polyoxometalate-based supramolecular porous frameworks, K3(H2O)4[Cu(tza)2(H2O)]2[Cu(Htza)2(H2O)2][BW12O40]·6H2O (1) and H3K3(H2O)3[Cu(Htza)2(H2O)]3[SiW12O44]·14H2O (2) (Htza = tetrazol-1-ylacetic acid), were synthesized and structurally characterized by elemental analysis, infrared spectroscopy, thermal analysis, UV-vis diffuse reflectance spectroscopy, and single-crystal X-ray and powder diffraction. The single-crystal X-ray diffraction analysis indicates that both compounds possess unique petal-like twelve-nucleated Cu-organic units composed of triangular and hexagonal metal–organic loops. In 1, the Cu-organic units are isolated and [BW12O40]5− polyoxoanions are sandwiched between staggered adjacent triangular channels in the structure. However in 2, the Cu-organic units extend into a two-dimensional layered structure, and the [SiW12O44]12− polyoxoanions occupy the larger hexagonal channels in the stacked structure. Both compounds as heterogeneous catalysts can catalyze the selective oxidation of substituted phenols to high value-added p-BQs under mild conditions (60 °C) with TBHP as the oxidant, particularly in the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone (TMBQ, key intermediate in vitamin E production). Within 8–10 min, the yield of TMBQ is close to 100%, and oxidant utilization efficiency is up to 94.2% for 1 and 90.9% for 2. The turnover frequencies of 1 and 2 are as high as 5000 and 4000 h−1, respectively. No obvious decrease in the yield of TMBQ was observed after five cycles, which indicates the excellent sustainability of both compounds. Our study of the catalytic mechanism suggests that there is a two-site synergetic effect: (i) the copper ion acts as the catalytic site of the homolytic radical pathway; and (ii) the polyoxoanion acts as the active center of the heterolytic oxygen atom transfer pathway. [ABSTRACT FROM AUTHOR]