Investigation of the catalytic behavior of a Cu coordination polymer capped polyoxometalate as an oxidation catalyst

The first decavanadate-based microporous hybrid, namely, [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O(1, cyclam = 1,4,8,11-tetraazacyclotetradecane) has been prepared by reaction of (VO3) -anions and {Cu(cyclam)} 2+ complexes in NaCl (aq) at pH 4.6-4.7, and characterized by elemental analyses, thermogravimetry, and X-ray diffraction techniques (powder, single-crystal). Compound 1 exhibits a POMOF-like supramolecular open-framework built up of covalent decavanadate/metalorganic layers with square-like voids, the stacking of which is aided by interlamellar cementing complexes and generates water-filled channels with approximate cross-sections of. 10.4 × 8.8 Å 2 . The framework is robust enough to remain virtually unaltered upon thermal evacuation of all water molecules of hydration, as demonstrated through single-crystal X-ray diffraction studies on the anhydrous phase 1a. This permanent microporosity renders interesting functionality to 1, such as selective adsorption of CO2 over N2 and remarkable activity as heterogeneous catalyst toward the H2O2-based oxidation of the highly-stable, tricyclic alkane adamantane.Porous crystalline materials such as metal organic frameworks (MOFs) have attracted great attention due to their wide range of relevant applications. 1 These materials are constructed by coordination of metal ions or metalcontaining units (nodes) to organic bridging ligands (linkers) to form open crystalline frameworks with permanent porosity. This feature qualifies them as suitable candidates for gas storage and separation, ion exchange, host-guest chemistry, magnetism, biomedicine and catalysis. 2 However, the synthesis of MOFs usually requires harsh conditions (e.g. high temperature or pressure, prolonged reaction times, harmful solvents, etc.), and removal of guest molecules from their cavities often leads to the collapse of the porous structure when flexible linkers are used. In this context, the incorporation of rigid and voluminous species such as metal clusters could increase the overall robustness

Section: Resultsmentioning

confidence: 99%

A Robust Open Framework Formed by Decavanadate Clusters and Copper(II) Complexes of Macrocyclic Polyamines: Permanent Microporosity and Catalytic Oxidation of Cycloalkanes

Martín-Caballero

Wéry

Reinoso³

et al. 2016

“…Polyoxometalates (POMs), as a kind of nanosized discrete anionic metal–oxide clusters, has shown great potential in the field of organic catalysis on account of their characteristics of tunable redox and Lewis acidity, etc . − Recently, some cases about POM-based catalysts toward the selective oxidation of alkylbenzenes have been reported; − however, the presence of noble metals in these catalysts is not conducive to mass preparation, , as the inherent problems of poor stability and easy aggregation in solution also hinder their further development.…”

Section: Introductionmentioning

confidence: 99%

“…Interestingly, polyanions in this set of compounds are symmetrically distributed on both sides of the [Cu 6 (trz) 6 ] macrocycle, thus forming a unique sandwich-type building unit for the construction of desired 3D skeletons. Both of HENU-2 and HENU-3 can be used as heterogeneous catalysts to effectively catalyze the selective oxidation of diphenylmethane and realize high conversion (>92%) with 100% selectivity toward benzophenone, which is superior than that of most POM-based catalysts for this catalytic reaction. ,− Moreover, HENU-2 performed good recyclability and stability as well.…”

Section: Introductionmentioning

confidence: 99%

Copper-Containing Polyoxometalate-Based Metal–Organic Frameworks as Highly Efficient Heterogeneous Catalysts toward Selective Oxidation of Alkylbenzenes

Wang

et al. 2019

With a one-pot assembly method, two copper-containing Keggin-type polyoxometalate-based metal–organic frameworks (POMOFs), i.e., [CuI 6(trz)6{PW12O40}2] (HENU-2, HENU = Henan University; trz = 1,2,4- triazole) and [CuI 3(trz)3{PMo12O40}] (HENU-3), were successfully prepared and structurally characterized. These two compounds, which are generated by the extension of a crown-like {Cu6(trz)6} macrocycle-based sandwich-type structural unit, possess identical noninterpenetration 3D frameworks except for the polyanions difference. Additionally, both of themare assessed as highly effective heterogeneous catalysts in facilitating the oxidation of alkylbenzenes to ketone products in the presence of tert-butyl hydroperoxide. Under optimized conditions, HENU-2 can achieve a 95.2% conversion of diphenylmethane in 20 h with a 100% selectivity toward benzophenone, and it was reused for three runs with constant high activity, which outperforms most POM-based catalysts for this catalytic reaction.

“…Polyoxometalates (POMs), as a class of nanosized discrete anionic metal-oxide clusters, have drawn enormous attention and are applied widely in many fields (e.g., magnetism, medicine, electrochemistry, and especially in catalysis) because of their unique physicochemical properties. − In recent years, many researchers have demonstrated POM-based catalysts did have praiseworthy catalytic performance for selective oxidation of DPM to BP. − However, POMs suffer from some intrinsic drawbacks, including low specific surface area, high water solubility, and difficult separation (reuse), which shackle the further industrial applications of POMs. ,,− Therefore, a promising solution is to select a proper carrier and load the POMs . Simultaneously, metal–organic frameworks (MOFs), which have tunable nanospaces providing satisfactory accommodation for multitudinous guest species, have been regarded as a new class of porous materials. − Thanks to their inherent tunability, MOFs have cumulative application in gas storage, magnetism, fluorescence, and catalysis.…”

Section: Introductionmentioning

confidence: 99%

A Copper-Containing Polyoxometalate-Based Metal–Organic Framework as an Efficient Catalyst for Selective Catalytic Oxidation of Alkylbenzenes

Wang

et al. 2021

A copper-containing polyoxometalate-based metal–organic framework (POMOF), CuI 12Cl2(trz)8[HPW12O40] (HENU-7, HENU = Henan University; trz = 1,2,4-triazole), has been successfully synthesized and well-characterized. In addition, the excellent catalytic ability of HENU-7 has been proved by the selective oxidation of diphenylmethane. Under the optimal conditions, the diphenylmethane conversion obtained over HENU-7 is 96%, while the selectivity to benzophenone is 99%, which outperforms most noble-metal-free POM-based catalysts. Moreover, HENU-7 is stable to reuse for five runs without an obvious loss in activity and also can catalyze the oxidation of different benzylic C–H with satisfactory conversions and selectivities, which implied the significant catalytic activity and recyclability.