Liquid-Phase Selective Oxidation by Multimetallic Active Sites of Polyoxometalate-Based Molecular Catalysts

Abstract

The catalytic oxidation is an area of the key technologies for converting petroleum-based feedstocks to useful chemicals such as diols, epoxides, alcohols, and carbonyl compounds. Many efficient homogeneous and heterogeneous oxidation systems based on polyoxometalates (POMs) with green oxidants such as H 2 O 2 and O 2 have been developed. This chapter summarizes the remarkable oxidation catalyses by POMs with multimetallic active sites. The multifunctionality of multimetallic active sites in POMs such as cooperative activation of oxidants, simultaneous activation of oxidants and substrates, stabilization of reaction intermediates, and multielectron transfer leads to their remarkable activities and selectivities in comparison with the conventional monometallic complexes. Finally, the future opportunities for the development of shape-and stereoselective oxidation by POM-based catalysts are described.

Base Catalysis by Mono- and Polyoxometalates

“…into the vacant sites has been used to synthesize several metal-substituted POMs with controlled multinuclear active sites in both aqueous and organic media [7,11,23]. These molecular catalysts exhibit significant activity and selectivity for a wide range of reactions [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] [92][93][94].…”

Keggin-type lacunary and transition metal substituted polyoxometalates as heterogeneous catalysts: A recent progress

“…Lacunary silicotungstates (SiW 11 ) have been the obvious choice for the study, especially acid catalysed reactions, because of the high stability of the fragmented lacunary species (73)(74)(75). Numbers of reports are available for synthesis and characterization of supported mono-lacunary silicotungstates (SiW 11 ); Lefebvre et al reported review covering synthesis of inorganic hybrid materials with encapsulated polyoxometalates in 2010 (76).…”

Simple and Green Adipic Acid Synthesis from Cyclohexanone and/or Cyclohexanol Oxidation with Efficient (NH4)xHyMzPMo12O40 (M: Fe, Co, Ni) Catalysts

“…The POMs based on molybdenum, particularly, can act as effective catalysts for the H2O2-and O2-based green oxidations [15][16][17]. Furthermore, they are oxidatively stable and can undergo stepwise multi electron redox process without any structural modification.…”

“…Furthermore, they are oxidatively stable and can undergo stepwise multi electron redox process without any structural modification. With transition-metalsubstituted POMs, it was reported that their remarkable catalytic activities were due to the multifunctional character of multimetallic active sites as simultaneous activation of oxidants and substrates, reaction intermediates stabilization, oxygen-transfer and multielectron transfer [15][16][17]. In previous studies, we have underlined the efficiency of transitionmetal-substituted POMs [18][19][20][21] as catalysts in the clean oxidation of cyclohexanone and mixture of cyclohexanone/cyclohexanol to adipic acid in the presence of hydrogen peroxide without solvent, phase-transfer agents and adding acid.…”