Molecular oxygen and oxidation catalysis by phosphovanadomolybdates

Abstract

The history of aerobic catalytic oxidation mediated by a subclass of polyoxometalates, the phosphovanadomolybdates of the Keggin structure, [PV(x)Mo(12-x)O40](3+x)-, is described. In the earlier research it was shown that phosphovanadomolybdates catalyze oxydehydrogenation reactions through an electron-transfer oxidation of a substrate by the polyoxometalate that is then reoxidized by oxygen. These aerobic oxidations are selective and synthetically useful in various transformations, notably diene aromatization, phenol dimerization and alcohol oxidation. Oxygen transfer from the polyoxometalate to arenes and alkylarenes was also discussed as a homogeneous analog of a Mars-van Krevelen oxidation. "Second generation" catalysts include binary complexes of the polyoxometalate and a organometallic compound useful, for example, for methane oxidation and nanoparticles stabilized by polyoxometalates effective for aerobic alkene epoxidation.

Room-temperature isomerization of 1-butene to 2-butene over palladium-loaded silica nanospheres catalyst

“…First, butenylcarbenium ion intermediate is formed by abstraction of hydride, and then the anomeric carbon atom is attacked by the hydride to finish the catalytic cycle. During step (2), O species could promote the splitting of the C-H bond, and further facilitate the 1-butene double-bond-shift isomerization reaction [45,46]. We conclude that is the reason for the adding of O 2 could enhance the yield of 2-butene.…”

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]. Some organotin-functionalized Dawson-type polyoxotungstates [P2W17O61(SnR)] 7− have demonstrated strong nucleophilicity, while they have not yet acted as catalysts [92][93][94].…”

The kinetics and mechanism of oxidation of reduced phosphovanadomolybdates by molecular oxygen: theory and experiment in concert

“…[7][8][9] The experimental kinetic studies show that the reactions are first-order in both the polyoxometalate and O 2 , where the rate constants are somewhat higher for the two-electron reduced species. Solvents have a considerable effect, protic solvents being preferred over aprotic solvents-presumably the protons are aiding in the formation of coordinatively unsaturated sites (CUSs …”

“…Over the years, reactions involving C-H, C-C and C-M bond activation as well as oxidation of sulphides have been studied. [7][8][9] Importantly, the reduced catalyst, whose structure has been studied by EPR experiments 10,11 and DFT calculations, 12 can be re-oxidized by molecular oxygen. This spatiotemporal separation between the substrate oxidation and the catalyst regeneration is responsible for high selectivity of such reactions.…”