Association of Keggin-type anions with cationic meso-substituted porphyrins: synthesis, characterization and oxidative catalytic studies
New compounds based on the association of polyoxometalates and cationic porphyrins or metalloporphyrins were prepared with the aim of obtaining new bi-functional catalysts. A combined study on the syntheses, characterization and catalytic activity of these compounds was performed. The new compounds...
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Published in | Journal of molecular catalysis. A, Chemical Vol. 231; no. 1; pp. 35 - 45 |
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Main Authors | , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Amsterdam
Elsevier B.V
20.04.2005
Elsevier |
Subjects | |
Online Access | Get full text |
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Summary: | New compounds based on the association of polyoxometalates and cationic porphyrins or metalloporphyrins were prepared with the aim of obtaining new bi-functional catalysts. A combined study on the syntheses, characterization and catalytic activity of these compounds was performed. The new compounds have the general formula (porphyrin)
x
H
y
[XM
12O
40]·
z solv,
x
=
0.75 or 1, X
=
P or Si and M
=
W or Mo. The porphyrins used were 5,10,15,20-tetrakis(4-pyridyl)porphyrin, 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin, 5,10,15-tris(2,6-dichorophenyl)-20-(4-pyridyl)porphyrin, and 5,10,15-tris(2,6-dichlorophenyl)-20-(1-methyl-4-pyridinio)porphyrin, either as free bases or complexed with Mn
III (one case with Zn
II). A few compounds with metal substituted Keggin anions ([PW
11Y(H
2O)O
39]
n−
, Y
=
Mn, Fe, Ni, Zn) were also prepared. All compounds were characterized by spectroscopic and analytical techniques. The oxidation of
cis-cyclooctene, geraniol and (+)-3-carene by hydrogen peroxide catalysed by the polyoxometalate/Mn
IIIporphyrin associations and co-catalysed by ammonium acetate was examined. Some of the associations significantly increased the percentage of conversion of the substrates relatively to the respective metalloporphyrin alone. However, the regio-, chemo- and stereoselectivity of the oxidation reactions catalysed by metalloporphyrins were globally preserved: c
is-cyclooctene was selectively epoxidised to epoxycyclooctane; geraniol gave 6,7-epoxygeraniol as the major product and (+)-3-carene was preferably oxidised to the α-3,4-epoxycarane. In the conditions studied, the polyoxoanions seem to contribute mainly to stabilise the metalloporphyrin against deactivation during catalytic cycles.
The preparation, characterization and catalytic application of new organic/inorganic hybrids with polyoxometalates and cationic porphyrins or metalloporphyrins are described. At 60
°C, some of the new compounds catalysed the epoxidation with H
2O
2 of
cis-cyclooctene, geraniol and (+)-3-carene with higher conversions than the corresponding metalloporphyrins alone. The polyoxometalates contributed, in general, to the stabilization of the metalloporphyrins in catalytic conditions.
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ISSN: | 1381-1169 1873-314X |
DOI: | 10.1016/j.molcata.2004.12.021 |