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Issue 10, 2015
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Synthesis and oxidation catalysis of a Ti-substituted phosphotungstate, and identification of the active oxygen species

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Abstract

In this paper, we report the synthesis of a Ti-substituted phosphotungstate, TBA6[(γ-PW10O36)2Ti4(μ-O)2(μ-OH)4] (I, TBA = tetra-n-butylammonium), and its application to H2O2-based oxidation. Firstly, an organic solvent-soluble dilacunary phosphotungstate precursor, TBA3[γ-PW10O34(H2O)2] (PW10), has been synthesized. By the reaction of PW10 and TiO(acac)2 (acac = acetylacetonate) in an organic medium (acetonitrile), I can be obtained. Compound I possesses a tetranuclear Ti core which can effectively activate H2O2 and shows high catalytic performance for several oxidation reactions, such as epoxidation of alkenes, oxygenation of sulfides, oxidative bromination of unsaturated compounds, and hydroxylation of anisole, giving the corresponding oxidation products with high efficiencies and selectivities. The catalytic performance of I is much superior to those of previously reported Ti-substituted polyoxometalates. In addition, I is highly durable during catalysis and can be reused several times while keeping its high catalytic performance. Furthermore, we have successfully isolated the truly catalytically active species for the present I-catalyzed oxidation, TBA6[(γ-PW10O36)2Ti4(μ-η22-O2)4] (II), and its anion structure has been determined by X-ray crystallographic analysis. All of the four Ti2-μ-η22-peroxo species in II are active for stoichiometric oxidation (without H2O2), and II is included in the catalytic cycle for I-catalyzed oxidation.

Graphical abstract: Synthesis and oxidation catalysis of a Ti-substituted phosphotungstate, and identification of the active oxygen species

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Supplementary files

Article information


Submitted
08 Jul 2015
Accepted
03 Aug 2015
First published
07 Aug 2015

Catal. Sci. Technol., 2015,5, 4778-4789
Article type
Paper
Author version available

Synthesis and oxidation catalysis of a Ti-substituted phosphotungstate, and identification of the active oxygen species

E. Takahashi, K. Kamata, Y. Kikukawa, S. Sato, K. Suzuki, K. Yamaguchi and N. Mizuno, Catal. Sci. Technol., 2015, 5, 4778
DOI: 10.1039/C5CY01031D

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