17O MAS NMR study of 12-molybdophosphoric acid

Kozhevnikov, I. V.; Sinnema, A.; Bekkum, H. van; Fournier, Michel

doi:10.1007/bf00811483

Cited by 21 publications

(74 citation statements)

References 24 publications

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“…Note, however, that the protons cannot be found directly from X-ray data; their positions are localized on the basis of a sensible hydrogen-bonding scheme and the known geometry of the water molecule. Direct evidence of the predominant protonation of the terminal oxygens in solid PW and SiW has been obtained by 17 O NMR by comparison of solution and solid-state spectra for these HPAs. − The resonance for the terminal oxygen in solid PW exhibits a large 60 ppm upfield shift compared to the aqueous solution spectrum, whereas the bridging oxygen resonances have practically the same positions in both spectra (Figure ). − Since in aqueous solution PW is completely deprotonated (see below), this unambiguously identifies the terminal oxygens as the predominant protonation sites in solid HPA. The structure of proton sites in the dehydrated PW is shown in Figure .…”

Section: Acid Catalysis By Heteropoly Acidsmentioning

confidence: 92%

“…HPA- n in solution is an extremely complex system, and the higher the n value, the more complex the system. The HPA- n solutions contain a great number of polyanions, their positional isomers as well as monomeric metallospecies. , Figure shows the 31 P NMR spectrum for HPA-4 aqueous solution, which was used as the catalyst for oxidation of TMP to TMBQ …”

Section: Mechanismmentioning

confidence: 99%

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Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

1998

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ContentsI. Introduction 171 II. Acid Catalysis by Heteropoly Acids 172 A. HPA Catalysts 172 1. Structure 172 2. Acid Properties 173 3. Supported HPAs 175 4. Salts of HPAs 177 B. Homogeneous Reactions 177 1. Hydration of Olefins 178 2. Esterification and Related Reactions 179 3. Condensation 179 4. Miscellaneous Reactions 180 C. Biphasic Reactions 180 1. Polymerization of Tetrahydrofuran 180 2. Esterification 181 3. Other Reactions 181 D. Heterogeneously Catalyzed Liquid-Phase Reactions 181 1. Paraffin Alkylation 182 2. Friedel−Crafts and Related Reactions 182 3. Esterification, Hydrolysis, and Related Reactions 183 4. Miscellaneous Reactions 184 III. Multicomponent Polyoxometalates in Liquid-Phase Oxidation 184 A. Oxidation with Dioxygen 184 1. General Principles 184 2. Homogeneous Oxidation 185 3. Biphasic Oxidation 187 4. Heterogeneously Catalyzed Oxidation 188 5. Mechanism 189 B. Oxidation with Hydrogen Peroxide 191 1. Venturello−Ishii System 191 2. Other Polyoxometalate Systems 193 IV. Conclusion 194 V. Acknowledgments 195 VI. References 195 Ivan V. Kozhevnikov was born in Novosibirsk, Russia. He received his M.Sc. in chemistry from Novosibirsk University in 1969 and Ph.D. from Boreskov Institute of Catalysis (BIC) in 1972, where he studied with Professor E. S. Rudakov. After three years of postdoctoral studies at the Institute of Physicoorganic Chemistry in Donetsk, he returned to BIC and joined Professor K. I. Matveev group. In 1984 he received his D.Sc. degree and was promoted to Head of laboratory at BIC and appointed Professor at Novosibirsk University. He has held visiting positions at Lund University, Sweden (1990),

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Section: Acid Catalysis By Heteropoly Acidsmentioning

confidence: 92%

Section: Mechanismmentioning

confidence: 99%

Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

1998

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“…Several homogeneous and heterogeneous methods including CuCl 2 [29] or heteropy acids [30,31] have also been proposed for oxidation of TMP to TMQ. The present catalytic system exhibits a different selectivity in the oxidation of phenols providing biphenol products with high yield.…”

Section: Grafting Of 1 Onto Amorphous Silicamentioning

confidence: 99%

Synthesis and catalytic properties of a novel phthalocyanine covalently grafted onto silica

Mangematin

Sorokin

2001

J. Porphyrins Phthalocyanines

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ABSTRACT:The iron complex of 2(3),9(10), 16(17),23(24)-tetra [1,5-di(3-triethoxysilyl-propyl)biuryl]phthalocyanine (1) was prepared by reacting iron tetraaminophthalocyanine with 3-(triethoxysilyl)propyl isocyanate. This complex was directly grafted onto silica to give a supported catalyst without preliminary modification of silica support. This supported catalyst was successfully applied in clean catalytic oxidations by using molecular oxygen in combination with isobutyraldehyde. Cyclooctene, cyclohexene and styrene were oxidized to corresponding epoxides with 90, 78 and 74% yields, respectively. 2,3,6-Trimethylphenol was selectively oxidized to 2,2',3,3',5,5'-hexamethyl-4,4'-biphenol.

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“…The surprising result of the 17 O solution experiments is the number of resolvable peaks in the spectral region of terminal and bridging oxygen atoms for 1 and 2 (see Table 1). Based on similar work on the related molybdates and tungstates, we expected to see only two peaks for the bridging oxygen atoms; [25][26][27][28] one for the m 2 -O bridging two edge-sharing NbO 6 octahedra and one for the m 2 -O bridging two corner-sharing NbO 6 octahedra. Yet we observe four signals.…”

mentioning

confidence: 99%

[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces

et al. 2004

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Heteropolyanions are negatively charged clusters of cornersharing and edge-sharing early transition-metal MO 6 octahedra and heteroatom XO 4 tetrahedra, in which the tetrahedra are usually located in the interior of the cluster.[1] The geometry, composition, and charge of these clusters are varied through synthesis parameters, and cluster properties are highly tunable as a function of these characteristics. Heteropolyanions have been employed in a range of applications that include virus-binding inorganic drugs, [2] homogeneous and heterogeneous catalysts, [3,4] electro-optic and electrochromic materials, [5,6] metal and protein binding, [7] and as building blocks for nanostructuring of materials.[8] The aKeggin geometry, which was first structurally characterized in 1933 by J. F. Keggin [9] for the phosphotungstic acid (H 3 PW 12 O 40 ) is one of the most widely recognized and thoroughly studied heteropolyanion geometries.[10] Following Keggin's initial discovery, solid-state and solution chemistries of the heteropolytungstates and heteropolymolybdates (i.e., H 4 SiMo 12 O 40 ) with the Keggin geometry have been well developed. These Keggin ions have been synthesized with a variety of atoms in the XO 4 tetrahedral site, numerous addenda atom substitutions in the MO 6 octahedral sites, as acids, and as salt compounds with a range of counter cations. [11,12] Given the apparent ubiquity of the Keggin geometry, it is not surprising that the first-observed heteropolyniobate (reported Nyman et al. in 2002 [13] ) was a Keggin ion. However, we first identified [13] O 2 are chemically quite different from the related heteropolymolybdate and heteropolytungstate Keggin ions in their synthetic approach, their pH stability, and their charge. The Nb Keggin ions are synthesized and stable in basic solutions (pH 7-12.5) and decompose in acidic solutions, whereas the Mo and W Keggin ions are synthesized and stable in acidic solutions (pH % 1-3) and decompose in more basic solutions. The Nb Keggin ions are synthesized hydrothermally at 190 8C from amorphous, hydrous niobium oxide and alkoxides of germanium or silicon, whereas the Mo and W Keggin ions are generally precipitated at room temperature from tungstic or molybdic acid or alkali precursors. Use of sodium silicate or sodium germanate as precursors rather than the alkoxides results in mixtures that contain the heteropolyniobate only as a minor phase, with poorly crystalline sodium niobates [14] as the major phase. The general differences between synthesis of heteropolyniobates and synthesis of heteropolymolybdates and heteropolytungstates have been discussed in detail previously. [13] The hydrothermal formation of Na 16

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17O MAS NMR study of 12-molybdophosphoric acid

Cited by 21 publications

References 24 publications

Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

Synthesis and catalytic properties of a novel phthalocyanine covalently grafted onto silica

[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces

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17O MAS NMR study of 12-molybdophosphoric acid

Cited by 21 publications

References 24 publications

Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions

Synthesis and catalytic properties of a novel phthalocyanine covalently grafted onto silica

[SiNb12O40]16− and [GeNb12O40]16−: Highly Charged Keggin Ions with Sticky Surfaces

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[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces