New chemistry for heteropolyanions in anhydrous nonpolar solvents. Coordinative unsaturation of surface atoms. Polyanion oxygen carriers

Katsoulis, Dimitris E.; Pope, Michael T.

doi:10.1021/ja00321a064

Cited by 170 publications

(81 citation statements)

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“…, [14] the bubbling of dry, highpurity CO 2 (99.99 %) into a solution of O 39 ] in toluene showed a slight but visible color change from light brown to darker brown. The UV/Vis spectra showed an increase in the optical density at 450 nm and a decrease in optical density at 600 nm, although the spectra with and without the addition of CO 2 are very similar ( Figure 1).…”

Section: Resultsmentioning

confidence: 99%

Photochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium‐Substituted Polyoxometalate

Khenkin

Efremenko

Weiner

et al. 2010

Chemistry A European J

149

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A polyoxometalate of the Keggin structure substituted with Ru(III), (6)Q(5)[Ru(III)(H(2)O)SiW(11)O(39)] in which (6)Q=(C(6)H(13))(4)N(+), catalyzed the photoreduction of CO(2) to CO with tertiary amines, preferentially Et(3)N, as reducing agents. A study of the coordination of CO(2) to (6)Q(5)[Ru(III)(H(2)O)SiW(11)O(39)] showed that 1) upon addition of CO(2) the UV/Vis spectrum changed, 2) a rhombic signal was obtained in the EPR spectrum (g(x)=2.146, g(y)=2.100, and g(z)=1.935), and 3) the (13)C NMR spectrum had a broadened peak of bound CO(2) at 105.78 ppm (Delta(1/2)=122 Hz). It was concluded that CO(2) coordinates to the Ru(III) active site in both the presence and absence of Et(3)N to yield (6)Q(5)[Ru(III)(CO(2))SiW(11)O(39)]. Electrochemical measurements showed the reduction of Ru(III) to Ru(II) in (6)Q(5)[Ru(III)(CO(2))SiW(11)O(39)] at -0.31 V versus SCE, but no such reduction was observed for (6)Q(5)[Ru(III)(H(2)O)SiW(11)O(39)]. DFT-calculated geometries optimized at the M06/PC1//PBE/AUG-PC1//PBE/PC1-DF level of theory showed that CO(2) is preferably coordinated in a side-on manner to Ru(III) in the polyoxometalate through formation of a Ru-O bond, further stabilized by the interaction of the electrophilic carbon atom of CO(2) to an oxygen atom of the polyoxometalate. The end-on CO(2) bonding to Ru(III) is energetically less favorable but CO(2) is considerably bent, thus favoring nucleophilic attack at the carbon atom and thereby stabilizing the carbon sp(2) hybridization state. Formation of a O(2)C-NMe(3) zwitterion, in turn, causes bending of CO(2) and enhances the carbon sp(2) hybridization. The synergetic effect of these two interactions stabilizes both Ru-O and C-N interactions and probably determines the promotional effect of an amine on the activation of CO(2) by [Ru(III)(H(2)O)SiW(11)O(39)](5-). Electronic structure analysis showed that the polyoxometalate takes part in the activation of both CO(2) and Et(3)N. A mechanistic pathway for photoreduction of CO(2) is suggested based on the experimental and computed results.

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Section: Resultsmentioning

confidence: 99%

Photochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium‐Substituted Polyoxometalate

Khenkin

Efremenko

Weiner

et al. 2010

Chemistry A European J

149

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“…Polyoxometalates and heteropolyoxometalates (POMs) are widely known as functional materials in catalytic oxidation 25 reactions, [1][2][3][4][5][6][7][8][9][10][11][12][13][14] metallorganic-POM hybrid catalysts. 9 In particular, the facile incorporation of transition-metals into lacunary-type POMs has attracted significant interest for preparation of oxidation catalysts with high activity.…”

Section: Introductionmentioning

confidence: 99%

Remarkable enhancement of catalytic activity of a 2 : 1 complex between a non-planar Mo(v)–porphyrin and a ruthenium-substituted Keggin-type heteropolyoxometalate in catalytic oxidation of benzyl alcohols

et al. 2012

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oxidation proceeded via formation of a catalyst-substrate complex, and electron-withdrawing substituents at the para position of benzyl alcohol accelerated the reaction. The rate constants of the oxidation reactions correlate to the bond dissociation energies of the C-H bonds of the substrate. A linear correlation was observed for logarithm of the rate constants of oxidation reactions of benzyl alcohols with that of hydrogen abstraction by cumyl peroxyl radical, indicating the reaction proceeds via hydrogen 20 abstraction. The observed kinetic isotope effect (KIE) indicates that the hydrogen abstraction occurs from the benzyl group rather than the hydroxy group.

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“…In addition to reporting the kinetics of oxidant consumption and O2 yields with Co 2+ (aq) and CoOx catalysts, we used a new POM extraction method, [27a] based on earlier work, [30] which quantitatively removes Co4POM from the aqueous layer and transports it to an organic solvent (typically toluene) layer. The extraction leaves all other components in the system (essentially all the Co 2+ and insoluble cobalt hydroxides / oxides) in the aqueous layer.…”

Section: Pom-based Wocsmentioning

confidence: 99%

Polyoxometalate Multi‐Electron‐Transfer Catalytic Systems for Water Splitting

Sumliner

Fielden

et al. 2014

Eur J Inorg Chem

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The viable production of solar fuels requires a visible-light absorbing unit, a H2O (or CO2) reduction catalyst (WRC) and a water oxidation catalyst (WOC) that work in tandem to split water or reduce CO2 with H2O rapidly, selectively and for long periods of time. Most catalysts and photosensitizers developed to date for these triadic systems are oxidatively, thermally and/or hydrolytically unstable. Polyoxometalates (POMs) constitute a huge class of complexes with extensively tunable properties that are oxidatively, thermally and (over wide and adjustable pH ranges) hydrolytically stable. POMs are some of the fastest and most stable WOCs to date. This Microreview updates the very active POM WOC field, reports the first POM WRCs and initial selfassembling metal oxide semiconductor-photosensitizer-POM catalyst triad photoanodes. The complexities of investigating these POM systems, including but not limited to the study of POM-hydrated metal ion-metal oxide speciation processes, are outlined. The achievements and challenges in POM WOC, WRC and triad research are outlined. IntroductionMeasurements and models make it ever more certain that the planet will face a serious energy shortage as the availability of economically accessible fossil fuels fails to keep pace with global energy needs. [1] Data and analysis also indicate that the environmental change caused by fossil fuel combustion will become increasingly problematic. Although green and alternative energy sources are rapidly becoming more available and less expensive, the net consumption of environmentally worrisome fossil fuel is not dropping significantly. Increases in both global population and average global standard of living paint a less-thanrosy picture for our energy future. [1b, 1g, 2] Solar remains the most likely source of sustainable energy for the medium and longer-term future. The other renewable sources of energy, with the arguable exception of biofuels provided the energy production efficiency (photosynthesis and other efficiencies) can be significantly increased, will not likely be sufficient to power the planet. In addition, high density energy will be needed in enormous quantities moving forward; electricity and other sources of energy will not provide sufficient energy density for our major transportation needs (ships, aircraft). Unlike the production of solar electricity, which is a now a rapidly maturing technical area and a major and growing market sector, production of solar fuel is in its infancy.The principal reactions for the generation of solar fuel are H2O splitting to produce H2 and O2 (eq. 1) and H2O splitting coupled to CO2 reduction (eq. 2). Technology is needed so both these processes can be driven by terrestrial sunlight and proceed with high rates and selectivity to the desired products. A factor in the slow rates observed for H2O oxidation by many systems is that it is a four-electron, four-proton process, hence the need for a catalyst that can facilitate the multiple proton-coupled electron transfer (PCET) processes with lo...

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New chemistry for heteropolyanions in anhydrous nonpolar solvents. Coordinative unsaturation of surface atoms. Polyanion oxygen carriers

Cited by 170 publications

References 0 publications

Photochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium‐Substituted Polyoxometalate

Photochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium‐Substituted Polyoxometalate

Remarkable enhancement of catalytic activity of a 2 : 1 complex between a non-planar Mo(v)–porphyrin and a ruthenium-substituted Keggin-type heteropolyoxometalate in catalytic oxidation of benzyl alcohols

Polyoxometalate Multi‐Electron‐Transfer Catalytic Systems for Water Splitting

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