A new dinuclear rhodium(III) 'sandwich' polyoxometalate, [(WZnRh2/(III))(ZnW9O34)2]10-. Synthesis, characterization and catalytic activity

Ronny Neumann, Alexander M. Khenkin

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59 Citations (Scopus)

Abstract

The rhodium containing polyoxometalate, [(WZnRh2/(III))(ZnW9O34)2]10 was prepared by reaction of [(WZn3)(ZnW9O34)2]12- with RhCl3. The X-ray diffraction showed this compound to be isostructural to other compounds of this series. This was confirmed by the IR spectra. The elementary analysis and cyclic voltammetry measurements indicated that the polyoxometalate was of high purity. Epoxidation of alkenes with 30% aqueous H2O2 in 1,2-dichloroethane/water biphasis systems using [(WZnRh2/(III))(ZnW9O34)2]10 as catalyst showed high overall activity as compared to other noble metal substituted polyoxometalates of this series. The reactions were highly selective to epoxidation of cyclohexene and similar to previously reported [(WZnRh2/(II))(ZnW9O34)2]12-, except that hydrogen peroxide yields were measurably higher in the rhodium case. The [(WZnRh2(III))(ZnW9O34)2]10 catalyst appears to be stable under turnovers conditions. Using IR spectroscopy as a probe to compare active polyoxometalates (Rh and Mn) versus an inactive one (Zn), showed that in the former case peroxo-tungstate intermediates could be identified whereas for the inactive compound no such intermediate was observed. A possible mechanism taking into account reactivity, steric constraints and IR spectra assuming structural integrity under catalytic turnover conditions was put forth.

Original languageEnglish
Pages (from-to)169-180
Number of pages12
JournalJournal of Molecular Catalysis A: Chemical
Volume114
Issue number1-3
DOIs
Publication statusPublished - Dec 23 1996

Fingerprint

Rhodium
epoxidation
Epoxidation
rhodium
catalytic activity
Catalyst activity
catalysts
Catalysts
tungstates
Alkenes
Structural integrity
synthesis
Precious metals
noble metals
hydrogen peroxide
Hydrogen peroxide
integrity
Hydrogen Peroxide
alkenes
Olefins

Keywords

  • Epoxidation
  • Hydrogen peroxide activation
  • Rhodium polyoxometalate

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

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title = "A new dinuclear rhodium(III) 'sandwich' polyoxometalate, [(WZnRh2/(III))(ZnW9O34)2]10-. Synthesis, characterization and catalytic activity",
abstract = "The rhodium containing polyoxometalate, [(WZnRh2/(III))(ZnW9O34)2]10 was prepared by reaction of [(WZn3)(ZnW9O34)2]12- with RhCl3. The X-ray diffraction showed this compound to be isostructural to other compounds of this series. This was confirmed by the IR spectra. The elementary analysis and cyclic voltammetry measurements indicated that the polyoxometalate was of high purity. Epoxidation of alkenes with 30{\%} aqueous H2O2 in 1,2-dichloroethane/water biphasis systems using [(WZnRh2/(III))(ZnW9O34)2]10 as catalyst showed high overall activity as compared to other noble metal substituted polyoxometalates of this series. The reactions were highly selective to epoxidation of cyclohexene and similar to previously reported [(WZnRh2/(II))(ZnW9O34)2]12-, except that hydrogen peroxide yields were measurably higher in the rhodium case. The [(WZnRh2(III))(ZnW9O34)2]10 catalyst appears to be stable under turnovers conditions. Using IR spectroscopy as a probe to compare active polyoxometalates (Rh and Mn) versus an inactive one (Zn), showed that in the former case peroxo-tungstate intermediates could be identified whereas for the inactive compound no such intermediate was observed. A possible mechanism taking into account reactivity, steric constraints and IR spectra assuming structural integrity under catalytic turnover conditions was put forth.",
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T1 - A new dinuclear rhodium(III) 'sandwich' polyoxometalate, [(WZnRh2/(III))(ZnW9O34)2]10-. Synthesis, characterization and catalytic activity

AU - Neumann, Ronny

AU - Khenkin, Alexander M.

PY - 1996/12/23

Y1 - 1996/12/23

N2 - The rhodium containing polyoxometalate, [(WZnRh2/(III))(ZnW9O34)2]10 was prepared by reaction of [(WZn3)(ZnW9O34)2]12- with RhCl3. The X-ray diffraction showed this compound to be isostructural to other compounds of this series. This was confirmed by the IR spectra. The elementary analysis and cyclic voltammetry measurements indicated that the polyoxometalate was of high purity. Epoxidation of alkenes with 30% aqueous H2O2 in 1,2-dichloroethane/water biphasis systems using [(WZnRh2/(III))(ZnW9O34)2]10 as catalyst showed high overall activity as compared to other noble metal substituted polyoxometalates of this series. The reactions were highly selective to epoxidation of cyclohexene and similar to previously reported [(WZnRh2/(II))(ZnW9O34)2]12-, except that hydrogen peroxide yields were measurably higher in the rhodium case. The [(WZnRh2(III))(ZnW9O34)2]10 catalyst appears to be stable under turnovers conditions. Using IR spectroscopy as a probe to compare active polyoxometalates (Rh and Mn) versus an inactive one (Zn), showed that in the former case peroxo-tungstate intermediates could be identified whereas for the inactive compound no such intermediate was observed. A possible mechanism taking into account reactivity, steric constraints and IR spectra assuming structural integrity under catalytic turnover conditions was put forth.

AB - The rhodium containing polyoxometalate, [(WZnRh2/(III))(ZnW9O34)2]10 was prepared by reaction of [(WZn3)(ZnW9O34)2]12- with RhCl3. The X-ray diffraction showed this compound to be isostructural to other compounds of this series. This was confirmed by the IR spectra. The elementary analysis and cyclic voltammetry measurements indicated that the polyoxometalate was of high purity. Epoxidation of alkenes with 30% aqueous H2O2 in 1,2-dichloroethane/water biphasis systems using [(WZnRh2/(III))(ZnW9O34)2]10 as catalyst showed high overall activity as compared to other noble metal substituted polyoxometalates of this series. The reactions were highly selective to epoxidation of cyclohexene and similar to previously reported [(WZnRh2/(II))(ZnW9O34)2]12-, except that hydrogen peroxide yields were measurably higher in the rhodium case. The [(WZnRh2(III))(ZnW9O34)2]10 catalyst appears to be stable under turnovers conditions. Using IR spectroscopy as a probe to compare active polyoxometalates (Rh and Mn) versus an inactive one (Zn), showed that in the former case peroxo-tungstate intermediates could be identified whereas for the inactive compound no such intermediate was observed. A possible mechanism taking into account reactivity, steric constraints and IR spectra assuming structural integrity under catalytic turnover conditions was put forth.

KW - Epoxidation

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