Highly Efficient Synthesis of p-Benzoquinones Catalyzed by Robust Two-Dimensional POM-Based Coordination Polymers

Abstract

Selective oxidation of alkyl-substituted phenols offers efficient access to p-benzoquinones (BQs) that serve as key components for synthesizing biologically active compounds, but rational manufacture of efficient recyclable catalysts for such a reaction remains a severe challenge. Herein, two crystalline 2D polyoxometalate-based coordination polymers (POMCPs), formulated as H3[CuI 3(L)3]2[PM12O40]·xH2O (M = Mo, x = 4 for 1; M = W, x = 6 for 2; and HL = 4-(1H-tetazol-5-yl)­pyridine), are prepared by a mineralizer-assisted one-step synthesis strategy and explored as heterogeneous catalysts for p-BQs synthesis. Both compounds have been characterized through elemental analysis, EDS analysis, infrared spectroscopy, UV–vis diffuse reflectance spectrum, EPR, XPS, BET, single-crystal, and powder X-ray diffraction. Single-crystal X-ray diffraction analysis indicates that both 1 and 2 exhibit an interesting 2D sheet structure composed of 2-connected Keggin type anions [PM12O40]3– and hexa-nuclear {CuI 6(HL)6} cluster-based metal–organic chains via Cu···O interactions. When used as catalysts, POMCPs 1 and 2 have excellent catalytic activities in the selective oxidation of substituted phenols to p-BQs with H2O2. Notedly, in the model reaction from 2,3,6-trimethylphenol (TMP) to the vitamin E key intermediate trimethyl-p-benzoquinone (TMBQ), the catalytic activities expressed by turnover frequency (TOF) of 1 and 2 can reach an unprecedented 2400 and 2000 h–1, respectively, at close to 100% TMBQ yield. The truly heterogeneous nature, stability, and structural integrity of both catalysts were ascertained by FTIR, PXRD techniques, and the following cycles. Mechanism studies reveal that both catalysts can involve a dual reaction pathway through a heterolytic oxygen atom transfer mechanism and homolytic radical mechanism. Moreover, the 2D POMCPs with highly accessible bilateral active sites and efficient mass transfer efficiency possess superior catalytic performance to their analogous 3D species.

A POM-based porous supramolecular framework for efficient sulfide–sulfoxide transformations with a low molar O/S ratio

“…[10][11][12][13] Polyoxometalates (POMs), as a subset of crystalline metal oxide catalysts with compatibility with various oxygen sources, good redox properties, tunable acidities and alkalinities, and good solubility stability, have broadly been proven to be effective and green in catalyzing the selective oxidation of organic substances. [14][15][16][17][18] Among them, many POM-based catalytic systems for oxidizing sulfides have been successfully established over the past dozen years. [19][20][21] Examples that have easily come to conception are the selective oxidation of a variety of thioethers and degradation of sulfur mustard gas simulants (2- [22][23][24][25] In recent years, increasingly more research has been gradually focused on the construction of POM-based heterogeneous catalysts.…”

“…Polyoxometalates (POMs), as a subset of crystalline metal oxide catalysts with compatibility with various oxygen sources, good redox properties, tunable acidities and alkalinities, and good solubility stability, have broadly been proven to be effective and green in catalyzing the selective oxidation of organic substances. 14–18 Among them, many POM-based catalytic systems for oxidizing sulfides have been successfully established over the past dozen years. 19–21 Examples that have easily come to conception are the selective oxidation of a variety of thioethers and degradation of sulfur mustard gas simulants (2-chloroethyl ethyl sulfide, CEES) catalyzed by inorganic POMs such as TBA 4 [α-Mo 8 O 26 ], TBA 12 H 13 PNb 12 O 40 (V V O) 2 (V 4 IV O 12 ) 2 , TBA 4 H 2 [BW 11 Mn(H 2 O)O 39 ], and TBA 8 [(γ-SiW 10 Ti 2 O 38 (OH) 2 ) 2 ] under homogeneous conditions.…”

Four Anderson-type [TeMo6O24]6−-based metal–organic complexes with a new bis(pyrimidine)-bis(amide): multifunctional electrochemical and adsorption performances

“…N-containing ligands due to their multiple coordination modes are often designed and selected for the construction of new POMOCs. 37,38 However, there are few reports on bis(pyrimidine)-bis(amide) ligands. Therefore, we firstly designed and synthesized a new rigid bis(pyrimidine)-bis(amide) ligand [ N , N ′-bis (4-pyrimidinecarboxamido)-1,4-benzene (L)] (Scheme 1) and introduced it into the Anderson-type POM-metal systems.…”

Two polymolybdate-directed Zn(ii) complexes tuned by a new bis-pyridine-bis-amide ligand with a diphenylketone spacer for efficient ampere sensing and dye adsorption

“…In particular, N-donor ligands, such as pyridine, pyrazole, triazole, and their derivatives, have received increasing attention in recent years due to their active role in the construction of multifunctional and stable POM-based frameworks. [18][19][20] Currently, various bis-amide derivatives with multiple N/O sites have been introduced to construct POMOCs. [21][22][23] For example, a flexible bis-pyrazine-bis-amide ligand, N,N′-bisIJ2pyrazinecarboxamide)-1,4-butane, was designed by Li's group, and furthermore a novel 3D metal-organic framework was constructed.…”