Base Catalysis by Mono- and Polyoxometalates

Abstract

Abstract:In sharp contrast with acid-, photo-, and oxidation-catalysis by polyoxometalates, base catalysis by polyoxometalates has scarcely been investigated. The use of polyoxometalates as base catalysts have very recently received much attention and has been extensively investigated. Numerous mono-and polyoxometalate base catalyst systems effective for the chemical fixation of CO 2 , cyanosilylation of carbonyl compounds, and C-C bond forming reactions have been developed. Mono-and polyoxometalate base catalysts are classified into four main groups with respect to their structures: (a) monomeric metalates; (b) isopolyoxometalates; (c) heteropolyoxometalates; and (d) transition-metal-substituted polyoxometalates. This review article focuses on the relationship among the molecular structures, the basic properties, and the unique base catalysis of polyoxometalates on the basis of groups (a)-(d). In addition, reaction mechanisms including the specific activation of substrates and/or reagents such as the abstraction of protons, nucleophilic action toward substrates, and bifunctional action in combination with metal catalysts are comprehensively summarized.

Valorisation of plastic waste via metal-catalysed depolymerisation

“…The highest BHET yield (74.7%) was achieved using zinc chloride (0.5% w/w), an EG/PET ratio of 14:1 and reflux conditions ( Table 2, entry 8). The use of [206,207], was also investigated [208]. The catalytic activity was found to decrease in the order Zn > Mn > Co > Cu > Ni, consistent with previous reports [209].…”

Electrochemical Properties of Polyoxometalate (H3PMo12O40)-Functionalized Graphitic Carbon Nitride (g-C3N4)

“…Over the last decade, polyoxometalates (H 3 PMo 12 O 40 ) have enthused many research activities over a broad spectrum of science, such as catalysis, materials, and medicine, because of their chemical properties such as redox potential, acidity, and solubility in various media [1,2]. The PMo 12 belongs to a large family of heteropolyanions with the so-called Keggin structure, where a tetrahedral XO 4 core (X = P in this case) serves as a template for the aggregation of 12 MoO 6 octahedral sharing corners and edges.…”

Polyoxometalate-Based Catalysts for CO2 Conversion

“…Various useful chemicals, including cyclic carbonate [19], dimethyl carbonate [70,71,72,73,74], urea [74], quinazoline-2,4-(1H,3H)-diones [74,75], 2-benzimidazolone [74], 2-oxazolidinones [18], α-methylene cyclic carbonate [74], and methacrylic acid [76,77] were able to be synthesized with POM-based catalyst (Scheme 2). Considering that several reviews have already given comprehensive summaries of representative progress on non-reductive CO 2 fixation by POM catalysts [69,78,79], herein we briefly introduced the recent advances about non-reductive CO 2 conversion to organic chemicals, which were not collected in the very recent review published in 2018 [79].…”