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Synthesis and oxidation catalysis of a Ti-substituted phosphotungstate, and identification of the active oxygen species
In this paper, we report the synthesis of a Ti-substituted phosphotungstate, TBA 6 [(γ-PW 10 O 36 ) 2 Ti 4 (μ-O) 2 (μ-OH) 4 ] ( I , TBA = tetra- n -butylammonium), and its application to H 2 O 2 -based oxidation. Firstly, an organic solvent-soluble dilacunary phosphotungstate precursor, TBA 3 [γ-PW...
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| Published in: | Catalysis science & technology 2015-01, Vol.5 (10), p.4778-4789 |
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| Main Authors: | , , , , , , |
| Format: | Article |
| Language: | English |
| Subjects: | |
| Citations: | Items that this one cites Items that cite this one |
| Online Access: | Get full text |
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| Summary: | In this paper, we report the synthesis of a Ti-substituted phosphotungstate, TBA
6
[(γ-PW
10
O
36
)
2
Ti
4
(μ-O)
2
(μ-OH)
4
] (
I
, TBA = tetra-
n
-butylammonium), and its application to H
2
O
2
-based oxidation. Firstly, an organic solvent-soluble dilacunary phosphotungstate precursor, TBA
3
[γ-PW
10
O
34
(H
2
O)
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 H
2
O
2
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, TBA
6
[(γ-PW
10
O
36
)
2
Ti
4
(μ-η
2
:η
2
-O
2
)
4
] (
II
), and its anion structure has been determined by X-ray crystallographic analysis. All of the four Ti
2
-μ-η
2
:η
2
-peroxo species in
II
are active for stoichiometric oxidation (without H
2
O
2
), and
II
is included in the catalytic cycle for
I
-catalyzed oxidation. |
|---|---|
| ISSN: | 2044-4753 2044-4761 |
| DOI: | 10.1039/C5CY01031D |