Noble metal (RuIII, PdII, PtII) substituted "sandwich" type polyoxometalates: Preparation, characterization, and catalytic activity in oxidations of alkanes and alkenes by peroxides

Ronny Neumann, Alexander M. Khenkin

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Abstract

The polyoxometalates substituted with noble metals, Pd(II), Pt(II) and Ru(III), K12{[WZnPdII 2(H2O) 2](ZnW9O34)2}· 38H2O, K12{[WZnPtII 2(H2O) 2](ZnW9O34)2}·36H 2O, and Na11{[WZnRuII 2(OH)(H2O)](ZnW 9O34)2}·42H2O, were prepared by exchange of labile zinc atoms with noble metal atoms from the isostructural starting material, Na12-{[WZn3(H2O)2](ZnW 9O34)2]}·46H2O. The X-ray crystal structure of the ruthenium compound shows a structure compatible with a sandwich-type structure type with a WRuZnRu (Ru and W, Zn at opposing sides) ring between two B-XW9O34 units. Magnetic susceptibility studies as a function of temperature provide convincing evidence of two ruthenium (III) centers with no magnetic interaction between them. The EPR spectrum is supportive of this formulation showing an anisotropic spectrum of a ruthenium (III) atom (S = 1/2) in an octahedral field. The IR and UV-vis spectra of the ruthenium compound as well as of the diamagnetic palladium and platinum compounds are consistent with an isostructural series of compounds. The water soluble polyoxometalates may be extracted into an organic phase e.g. 1,2-dichloroethane by the addition of methyltricaprylammonium chloride to form their quaternary ammonium salts. The catalytic activity of these compounds was tested for the oxidation of alkenes and alkanes using aqueous 30% hydrogen peroxide and 70% tert-butyl hydroperoxide as oxidants. The alkene oxidation proceeded in high reactivity and moderate selectivity to the epoxide product using 30% H2O2. Kinetic profiles as well as UV-vis and IR spectra before, during and after the reaction indicate that the catalysts are stable throughout the reaction. Formation of epoxides rather than ketonization in the reaction of terminal alkenes as well as low reactivity with iodosobenzene indicates that the reaction is tungsten centered and not noble metal centered. Oxidation of alkenes with tert-butyl hydroperoxide gave mostly allylic oxidation and/ or addition of tert-butyl alcohol to the double bond. Oxidation of cyclic alkanes such as cyclohexane and adamantane was successful with tert-butyl hydroperoxide with catalytic activity 10 times higher than previously found for transition metal substituted Keggin compounds. Ratios of hydroxylation of adamantane at tertiary vs secondary positions indicates different active species in the palladium-, platinum-, and ruthenium substituted-polyoxometalates.

Original languageEnglish
Pages (from-to)5753-5760
Number of pages8
JournalInorganic Chemistry
Volume34
Issue number23
Publication statusPublished - 1995

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Alkanes
Peroxides
Alkenes
peroxides
Precious metals
noble metals
alkanes
alkenes
catalytic activity
Catalyst activity
tert-Butylhydroperoxide
Ruthenium
Ruthenium Compounds
Oxidation
ruthenium compounds
preparation
oxidation
Adamantane
ruthenium
epoxy compounds

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

@article{d56de93308b9450d80b738c921abc42e,
title = "Noble metal (RuIII, PdII, PtII) substituted {"}sandwich{"} type polyoxometalates: Preparation, characterization, and catalytic activity in oxidations of alkanes and alkenes by peroxides",
abstract = "The polyoxometalates substituted with noble metals, Pd(II), Pt(II) and Ru(III), K12{[WZnPdII 2(H2O) 2](ZnW9O34)2}· 38H2O, K12{[WZnPtII 2(H2O) 2](ZnW9O34)2}·36H 2O, and Na11{[WZnRuII 2(OH)(H2O)](ZnW 9O34)2}·42H2O, were prepared by exchange of labile zinc atoms with noble metal atoms from the isostructural starting material, Na12-{[WZn3(H2O)2](ZnW 9O34)2]}·46H2O. The X-ray crystal structure of the ruthenium compound shows a structure compatible with a sandwich-type structure type with a WRuZnRu (Ru and W, Zn at opposing sides) ring between two B-XW9O34 units. Magnetic susceptibility studies as a function of temperature provide convincing evidence of two ruthenium (III) centers with no magnetic interaction between them. The EPR spectrum is supportive of this formulation showing an anisotropic spectrum of a ruthenium (III) atom (S = 1/2) in an octahedral field. The IR and UV-vis spectra of the ruthenium compound as well as of the diamagnetic palladium and platinum compounds are consistent with an isostructural series of compounds. The water soluble polyoxometalates may be extracted into an organic phase e.g. 1,2-dichloroethane by the addition of methyltricaprylammonium chloride to form their quaternary ammonium salts. The catalytic activity of these compounds was tested for the oxidation of alkenes and alkanes using aqueous 30{\%} hydrogen peroxide and 70{\%} tert-butyl hydroperoxide as oxidants. The alkene oxidation proceeded in high reactivity and moderate selectivity to the epoxide product using 30{\%} H2O2. Kinetic profiles as well as UV-vis and IR spectra before, during and after the reaction indicate that the catalysts are stable throughout the reaction. Formation of epoxides rather than ketonization in the reaction of terminal alkenes as well as low reactivity with iodosobenzene indicates that the reaction is tungsten centered and not noble metal centered. Oxidation of alkenes with tert-butyl hydroperoxide gave mostly allylic oxidation and/ or addition of tert-butyl alcohol to the double bond. Oxidation of cyclic alkanes such as cyclohexane and adamantane was successful with tert-butyl hydroperoxide with catalytic activity 10 times higher than previously found for transition metal substituted Keggin compounds. Ratios of hydroxylation of adamantane at tertiary vs secondary positions indicates different active species in the palladium-, platinum-, and ruthenium substituted-polyoxometalates.",
author = "Ronny Neumann and Khenkin, {Alexander M.}",
year = "1995",
language = "English",
volume = "34",
pages = "5753--5760",
journal = "Inorganic Chemistry",
issn = "0020-1669",
publisher = "American Chemical Society",
number = "23",

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TY - JOUR

T1 - Noble metal (RuIII, PdII, PtII) substituted "sandwich" type polyoxometalates

T2 - Preparation, characterization, and catalytic activity in oxidations of alkanes and alkenes by peroxides

AU - Neumann, Ronny

AU - Khenkin, Alexander M.

PY - 1995

Y1 - 1995

N2 - The polyoxometalates substituted with noble metals, Pd(II), Pt(II) and Ru(III), K12{[WZnPdII 2(H2O) 2](ZnW9O34)2}· 38H2O, K12{[WZnPtII 2(H2O) 2](ZnW9O34)2}·36H 2O, and Na11{[WZnRuII 2(OH)(H2O)](ZnW 9O34)2}·42H2O, were prepared by exchange of labile zinc atoms with noble metal atoms from the isostructural starting material, Na12-{[WZn3(H2O)2](ZnW 9O34)2]}·46H2O. The X-ray crystal structure of the ruthenium compound shows a structure compatible with a sandwich-type structure type with a WRuZnRu (Ru and W, Zn at opposing sides) ring between two B-XW9O34 units. Magnetic susceptibility studies as a function of temperature provide convincing evidence of two ruthenium (III) centers with no magnetic interaction between them. The EPR spectrum is supportive of this formulation showing an anisotropic spectrum of a ruthenium (III) atom (S = 1/2) in an octahedral field. The IR and UV-vis spectra of the ruthenium compound as well as of the diamagnetic palladium and platinum compounds are consistent with an isostructural series of compounds. The water soluble polyoxometalates may be extracted into an organic phase e.g. 1,2-dichloroethane by the addition of methyltricaprylammonium chloride to form their quaternary ammonium salts. The catalytic activity of these compounds was tested for the oxidation of alkenes and alkanes using aqueous 30% hydrogen peroxide and 70% tert-butyl hydroperoxide as oxidants. The alkene oxidation proceeded in high reactivity and moderate selectivity to the epoxide product using 30% H2O2. Kinetic profiles as well as UV-vis and IR spectra before, during and after the reaction indicate that the catalysts are stable throughout the reaction. Formation of epoxides rather than ketonization in the reaction of terminal alkenes as well as low reactivity with iodosobenzene indicates that the reaction is tungsten centered and not noble metal centered. Oxidation of alkenes with tert-butyl hydroperoxide gave mostly allylic oxidation and/ or addition of tert-butyl alcohol to the double bond. Oxidation of cyclic alkanes such as cyclohexane and adamantane was successful with tert-butyl hydroperoxide with catalytic activity 10 times higher than previously found for transition metal substituted Keggin compounds. Ratios of hydroxylation of adamantane at tertiary vs secondary positions indicates different active species in the palladium-, platinum-, and ruthenium substituted-polyoxometalates.

AB - The polyoxometalates substituted with noble metals, Pd(II), Pt(II) and Ru(III), K12{[WZnPdII 2(H2O) 2](ZnW9O34)2}· 38H2O, K12{[WZnPtII 2(H2O) 2](ZnW9O34)2}·36H 2O, and Na11{[WZnRuII 2(OH)(H2O)](ZnW 9O34)2}·42H2O, were prepared by exchange of labile zinc atoms with noble metal atoms from the isostructural starting material, Na12-{[WZn3(H2O)2](ZnW 9O34)2]}·46H2O. The X-ray crystal structure of the ruthenium compound shows a structure compatible with a sandwich-type structure type with a WRuZnRu (Ru and W, Zn at opposing sides) ring between two B-XW9O34 units. Magnetic susceptibility studies as a function of temperature provide convincing evidence of two ruthenium (III) centers with no magnetic interaction between them. The EPR spectrum is supportive of this formulation showing an anisotropic spectrum of a ruthenium (III) atom (S = 1/2) in an octahedral field. The IR and UV-vis spectra of the ruthenium compound as well as of the diamagnetic palladium and platinum compounds are consistent with an isostructural series of compounds. The water soluble polyoxometalates may be extracted into an organic phase e.g. 1,2-dichloroethane by the addition of methyltricaprylammonium chloride to form their quaternary ammonium salts. The catalytic activity of these compounds was tested for the oxidation of alkenes and alkanes using aqueous 30% hydrogen peroxide and 70% tert-butyl hydroperoxide as oxidants. The alkene oxidation proceeded in high reactivity and moderate selectivity to the epoxide product using 30% H2O2. Kinetic profiles as well as UV-vis and IR spectra before, during and after the reaction indicate that the catalysts are stable throughout the reaction. Formation of epoxides rather than ketonization in the reaction of terminal alkenes as well as low reactivity with iodosobenzene indicates that the reaction is tungsten centered and not noble metal centered. Oxidation of alkenes with tert-butyl hydroperoxide gave mostly allylic oxidation and/ or addition of tert-butyl alcohol to the double bond. Oxidation of cyclic alkanes such as cyclohexane and adamantane was successful with tert-butyl hydroperoxide with catalytic activity 10 times higher than previously found for transition metal substituted Keggin compounds. Ratios of hydroxylation of adamantane at tertiary vs secondary positions indicates different active species in the palladium-, platinum-, and ruthenium substituted-polyoxometalates.

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