Peroxotungstate immobilized on ionic liquid-modified silica as a heterogeneous epoxidation catalyst with hydrogen peroxide

Article abstract of DOI:10.1021/ja043688e

Peroxotungstate immobilized on ionic liquid-modified SiO₂ is capable of heterogeneously epoxidizing a wide range of olefins with the maintenance of the catalytic activity of homogeneous analogue. The epoxidation was immediately stopped by the removal of the catalyst, and no tungsten species could be found in the filtrate after the removal of the catalyst. These results can rule out any contribution to the observed catalysis from the tungsten species that leached into the reaction solution, and the observed catalysis is truly heterogeneous in nature. Furthermore, the catalyst was reusable without the loss of the catalytic performance. Copyright

Full text of DOI:10.1021/ja043688e

Published on Web 12/23/2004
Peroxotungstate Immobilized on Ionic Liquid-Modified Silica as a
Heterogeneous Epoxidation Catalyst with Hydrogen Peroxide
Kazuya Yamaguchi, Chie Yoshida, Sayaka Uchida, and Noritaka Mizuno*
Department of Applied Chemistry, School of Engineering, The UniVersity of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
Received October 17, 2004; E-mail: tmizuno@mail.ecc.u-tokyo.ac.jp
H2O2-based catalytic epoxidation has received much attention
1-SiO2 showed the bands characteristic of the parent ionic liquid
1, for example, ν(CdN) (1654 cm-1) and ν(C-H) (2860, 2931,
and 2960 cm-1). The solid-state 13C CP MAS NMR spectrum of
1-SiO2 showed similar signals to those of 1, except for the near
disappearance of the resonances corresponding to the two carbon
atoms of the ethoxy group of 1 at 18.3 and 58.5 ppm (Figure S2).
These suggest that a condensation reaction between the surface
silanol groups of SiO2 and ethoxy group of 1 to form the covalent
Si-O-Si linkage occurred during the grafting process with the
maintenance of the main structure of 1. The 29Si MAS NMR
spectrum of SiO2 showed two signals at -111 and -101 ppm
corresponding to Q4 and Q3 species of the silica framework,
respectively (Qm ) Si(OSi)m(OH)4-m, Figure S3). For 1-SiO2,
additional signals appeared at -67 and -58 ppm assignable to T3
from an economic and environmental point of view.1 Soluble
transition metal-based catalysts such as tungsten, manganese,
molybdenum, and rhenium have been developed for the oxidation
with an aqueous H2O2.1 Among them, tungsten-based catalysts
including polyoxometalates show the high efficiency of H2O2
utilization and the high selectivity to the epoxides.2-6 The significant
development in tungsten-based catalysts is the Ishii-Venturello
system,3,4 followed by the Noyori’s halide-free method for the
oxidation of various substrates including olefins, alcohols, and
sulfides with sodium tungstate and alkylammonium hydrogen
sulfate.5 We also reported efficient routes for epoxidation of olefins
and allylic alcohols with H2O2 catalyzed by the divacant lacunary
silicotungstate [(n-C4H9)4N]4[γ-SiW10O34(H2O)2]6a and the dinuclear
peroxotungstate [{W(dO)(O2)2(H2O)}2(µ-O)]2- (W2),6b,c respec-
tively.
and T2 organosilica species, respectively (Tn ) RSi(OSi)n(OEt)3-n
,
Figure S4). The Q3/(Q3 + Q4) ratio was decreased from 0.24 to
0.11 by the grafting. The decrease of 0.13 corresponds to the
reaction of 54% of silanol groups. Elemental analysis of 1-SiO2
revealed that 365 µmol of ionic liquid fragments per gram of
1-SiO2 (0.85 ionic liquid fragments/nm2) existed and that 2.7
ethoxy groups of 1 reacted with 49% of silanol groups to form
covalent Si-O-Si linkage. The reacted amount of silanol groups
estimated with the elemental analysis data was in good agreement
with that by 29Si MAS NMR. The BET surface area of 1-SiO2
Although many efficient procedures based on the tungsten
catalysts for the oxidation with H2O2 have been developed, most
of them are homogeneous systems and share common drawbacks,
that is, catalyst/product separation and catalyst reuse are difficult.
The immobilization (heterogenization) of catalytically active species
onto solid supports can solve the catalyst recovery and recycle.7-11
For the development, insoluble bulk materials,8 impregnation of
homogeneous catalysts onto inert solid supports such as metal
hydroxides9 and polymers,10 and attachment of active species
through covalent or ionic bonds with supports11 have been utilized.
With regard to the immobilized tungsten-based catalysts for
epoxidation with H2O2, various supports such as anion-exchange
resins,11a,b surface-modified metal oxides,11b-g and layered double
hydroxide9a,b have been used. However, these systems have the
disadvantages: (i) some extent of tungsten leaching, (ii) low
accessibility of organic substrates and H2O2 because of the
hydrophilicity and/or the low surface area of the catalysts, (iii)
decomposition of H2O2 by the basic sites of the supports, and/or
(iv) the decrease in activities by the immobilization.12,13
Here, we synthesized peroxotungstate (W2) immobilized on
dihydroimidazolium-based ionic liquid-modifed SiO2 as an efficient
heterogeneous epoxidation catalyst with H2O2 to overcome disad-
vantages i-iv, especially iv. To our knowledge, this type of ionic
liquid-modifed supports haVe neVer been used to immobilize
polyoxometalates and peroxometalates.14
1-Octyl-3-(3-triethoxysililpropyl)-4,5-dihydroimidazolium chlo-
ride was synthesized by the reaction of 3-(2-imidazolin-1-yl)-
propyltriethoxysilane with 1-chlorooctane. The resulting compound
was further treated with sodium hexafluorophosphate in acetonitrile,
giving the corresponding ionic liquid 1 (Figure S1). Then, SiO2
(BET surface area 259 m2‚g-1, 4.7 silanol groups/nm2) was
vigorously stirred with a chloroform solution of the ionic liquid 1
for 24 h under reflux conditions to anchor covalently the ionic liquid
fragments to the SiO2 surface (1-SiO2). The IR spectrum of
was 184 m2‚g-1
.
Next, 1-SiO2 (1 g) was vigorously stirred with 10 mL of an
aqueous solution of potassium salt of W2 (0.1 M) at room
temperature (ca. 298 K) for 12 h. It was proved by elemental
analyses and 31P MAS NMR spectroscopy that K+ was not
-
incorporated into 1-SiO2 and that PF6 was leached during the
treatment, showing that the anion exchange between PF6- and W2
occurs during the treatment. The loading amount of W2 anion was
105 µmol‚g-1. The Raman bands of the W2/1-SiO2 agreed well
with those of the parent potassium salt of W2, showing the
maintenance of the W2 structure during the anion exchange process.
Further, the IR, 13C, and 29Si MAS NMR spectra of W2/1-SiO2
reveal that the structure of ionic liquid fragments is also preserved
during the immobilization process. The BET surface area of W2/
1-SiO2 was 203 m2‚g-1
.
The present W2/1-SiO2 could be applied to the epoxidation of
various olefins using H2O2 as shown in Table 1.15 For the
epoxidation of cis- and trans-olefins, the configuration around the
CdC double bonds was completely retained in the corresponding
epoxides, suggesting that the free-radical intermediates are not
involved in the present epoxidation. The regioselective epoxidation
of geraniol took place at the electron-deficient 2,3-allylic double
bond to afford 2,3-epoxy alcohol in high yield. The epoxidation of
secondary â,â-disubstituted allylic alcohol of 4-methyl-3-penten-
2-ol proceeded diastereoselectively to form the threo-epoxy alcohol
(threo/erythro ) 90/10). In addition, the epoxidation of (Z)-3-
9
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J. AM. CHEM. SOC. 2005, 127, 530-531
10.1021/ja043688e CCC: $30.25 © 2005 American Chemical Society

C O M M U N I C A T I O N S
Table 1. Epoxidation of Olefins with H2O2 Catalyzed by
W2/1-SiO2
activity and selectivity were comparable to those of the homoge-
neous analogue, showing that the homogeneous catalysis could be
heterogenized.
a
entry
olefin
time (h)
yield of epoxide (%)
1
2
3
4
5
6
7
8
9
10
cis-2-octene
trans-2-octene
cis-â-methylstyrene
cyclohexene
2-norbornene
cycloheptene
cyclooctene
geraniol
3
7
2
3
2.5
2
1
4
4
>99b
73c
Acknowledgment. This work was supported by the Core
Research for Evolutional Science and Technology (CREST)
program of the Japan Science and Technology Corporation (JST)
and a Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Science, Sports and Technology of Japan.
>99b
80
80d
>99
>99
95e
Supporting Information Available: Experimental section, effect
of alkyl chain length on the N1 position of dihydroimidazolium cation
on the epoxidation of cyclooctene, and Figures S1-S5. This material
is available free of charge via the Internet at http://pubs.acs.org.
4-methyl-3-penten-2-ol
(Z)-3-methyl-3-penten-2-ol
90f
4
90g
a Reaction conditions: Olefin (1 mmol), catalyst (W2: 1 mol % with
respect to olefin), H2O2 (30% aq solution, 0.2 mmol), CH3CN (0.5 mL),
1
333 K. Yields and selectivities were determined by GC or H NMR with
References
an internal standard technique. Selectivities to the corresponding epoxides
were >95% in all cases. Yield (%) ) epoxide (mmol) per initial H2O2
(mmol) × 100. b Only cis. c Only trans. d Only exo. e Only 2,3-epoxide.
f threo/erythro ) 90/10. g threo/erythro ) 40/60.
(1) (a) Lane, B. S.; Burgess, K. Chem. ReV. 2003, 103, 2457. (b)
Grigoropoulou, G.; Clark, J. H.; Elings, J. A. Green Chem. 2003, 5, 1
and references therein.
(2) (a) Neumann, R. Prog. Inorg. Chem. 1998, 47, 317. (b) Okuhara, T.;
Mizuno, N.; Misono, M. AdV. Catal. 1996, 41, 113. (c) Hill, C. L.; Prosser-
McCartha, C. M. Coord. Chem. ReV. 1995, 143, 407. (d) Kozhevnikov,
I. V. Catalysis by Polyoxometalates; John Wiley & Sons: Chichester,
U.K., 2002.
(3) Venturello, C.; D’Aloisio, R. J. Org. Chem. 1988, 53, 1553.
(4) Ishii, Y.; Yamawaki, K.; Ura, T.; Yamada, H.; Ogawa, M. J. Org. Chem.
1988, 53, 3587.
(5) Noyori, R.; Aoki, M.; Sato, K. Chem. Commun. 2003, 1977.
(6) (a) Kamata, K.; Yonehara, K.; Sumida, Y.; Yamaguchi, K.; Hikichi, S.;
Mizuno, N. Science 2003, 300, 964. (b) Kamata, K.; Yamaguchi, K.;
Mizuno, N. Chem.-Eur. J. 2004, 10, 4728. (c) Kamata, K.; Yamaguchi,
K.; Hikichi, S.; Mizuno, N. AdV. Synth. Catal. 2003, 345, 1193.
(7) Dusi, M.; Mallat, T.; Baiker, A. Catal. ReV. 2000, 42, 213.
(8) (a) Vasylev, M. V.; Neumann, R. J. Am. Chem. Soc. 2004, 126, 884. (b)
Musawir, M.; Davey, P. N.; Kelly, G.; Kozhevnikov, I. V. Chem. Commun.
2003, 1414. (c) Yamaguchi, K.; Mizuno, N. New J. Chem. 2002, 26, 972.
(d) Okuhara, T. Chem. ReV. 2002, 102, 3641 and references therein.
(9) (a) Sels, B. F.; De Vos, D. E.; Buntinx, M.; Pierard, F.; Mesmaeker, A.
K.-D.; Jacobs, P. A. Nature 1999, 400, 855. (b) Sels, B. F.; De Vos D.
E.; Jacobs, P. A. J. Am. Chem. Soc. 2001, 123, 8350. (c) Matsushita, T.;
Ebitani, K.; Kaneda, K. Chem. Commun. 1999, 265. (d) Yamaguchi, K.;
Mori, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc. 2000,
122, 7144. (e) Mori, K.; Yamaguchi, K.; Mizugaki, T.; Ebitani, K.;
Kaneda, K. J. Am. Chem. Soc. 2002, 124, 11573. (f) Yamaguchi, K.;
Mizuno, N. Angew. Chem., Int. Ed. 2002, 41, 4538. (g) Nozaki, C.;
Lugmair, C. G.; Bell. A. T.; Tilley, T. D. J. Am. Chem. Soc. 2002, 124,
13194. (h) Fujdala, K. L.; Drake, I. J.; Bell. A. T.; Tilley, T. D. J. Am.
Chem. Soc. 2004, 126, 10864.
Figure 1. Comparison of the reaction rates obtained by the use of W2/
1-SiO2 catalyst (heterogeneous) with those of [n-C12H25N (CH3)3]2[{W-
(dO)(O2)2(H2O)}2(µ-O)] (DTMA-W2, homogeneous) for the epoxidation
of olefins under the same reaction conditions. The reactions were carried
out under the conditions in Table 1. (1) 1-Octene, (2) trans-2-octene, (3)
2-norbornene, (4) 1-methyl-1-cyclohexene, (5) cyclohexene, (6) cis-2-octene,
and (7) cyclooctene.
(10) (a) Uozumi, Y.; Nakao, R. Angew. Chem., Int. Ed. 2003, 42, 194. (b)
Leadbeater, N. E.; Marco, M. Chem. ReV. 2002, 102, 3215. (c) McNamara,
C. A.; Dixon, M. J.; Bradley, M. Chem. ReV. 2002, 102, 3275. (d)
Bergbreiter, D. E. Chem. ReV. 2002, 102, 3345 and references therein.
(11) (a) Villa, A. L.; Sels, B. F.; De Vos, D. E.; Jacobs, P. A. J. Org. Chem.
1999, 64, 7267. (b) Hoegaerts, D.; Sels, B. F.; De Vos, D. E.; Verpoort,
F.; Jacobs, P. A. Catal. Today 2000, 60, 209. (c) Neumann, R.; Cohen,
M. Angew. Chem., Int. Ed. Engl. 1997, 36, 1738. (d) Sakamoto, T.; Pac,
C. Tetrahedron Lett. 2000, 41, 10009. (e) Neumann, R.; Miller, H. J.
Chem. Soc., Chem. Commun. 1995, 2277. (f) Gelbard, G.; Gauducheau,
T.; Vidal, E.; Parvulescu, V. I.; Crosman, A.; Pop, V. M. J. Mol. Catal.
A: Chem. 2002, 182/183, 257. (g) Ichihara, J.; Yamaguchi, S.; Nomoto,
T.; Nakayama, H.; Iteya, K.; Naitoh, N.; Sasaki, Y. Tetrahedron Lett.
2002, 43, 8231.
methyl-3-penten-2-ol, in which 1,3- and 1,2-allylic strains compete
with each other, was more erthro-selective (threo/erythro ) 40/
60). A similar regio- and diastereoselectivity for allylic alcohols
was also observed for the homogeneous W2-catalyzed epoxidation.6b,c
The epoxidation was completely stopped by the catalyst removal
(Figure S5). It was confirmed by ICP-AES analysis that no tungsten
species could be detected in the filtrate (below detection limit of
16 ppb). Further, W2/1-SiO2 could be easily recovered by the
filtration and reused at least three times for the epoxidation of
cyclooctene without the loss of the catalytic activity and selectivity
(99% yield, >99% selectivity under the conditions in Table 1 after
the third recycle). The above results can rule out any contribution
to the observed catalysis from the tungsten species that leached
into the reaction solution, and the observed catalysis is truly
heterogeneous in nature.
The catalytic activity of W2/1-SiO2 was compared with that of
the corresponding homogeneous analogue of [n-C12H25N(CH3)3]2-
[{W(dO)(O2)2(H2O)}2(µ-O)] (DTMA-W2) under the same condi-
tions. As shown in Figure 1, the reaction rates by the use of W2/
1-SiO2 were comparable to those of DTMA-W2. This fact
indicates that the homogeneous catalysis can be heterogenized with
retention of the W2 catalyst performance by the support on ionic
liquid-modified SiO2.
(12) A tungstate-exchanged layered double hydroxide, WO42-(MgAl)LDH, was
more than 100 times more active for oxidative bromination and bromide-
assisted epoxidation than the homogeneous analogue of NaWO4. See refs
9a and b.
(13) The sandwich-type polyoxometalate, [(Fe(OH2)2)3(A-R-PW9O34)2]9-, elec-
trostatically immobilized on cationic silica/alumina nanoparticles was more
active than the same quantity of the parent polyoxometalate for the aerobic
oxygenation of sulfides and autoxidation of aldehyde. See: (a) Okun, N.
M.; Anderson, T. M.; Hill, C. L. J. Am. Chem. Soc. 2003, 125, 3194. (b)
Okun, N. M.; Anderson, T. M.; Hill, C. L. J. Mol. Catal. 2003, 197, 283.
(14) Similar ionic liquid fragments have been confined onto solid supports
and then treated with catalytically active species such as Lewis acids and
Rh complexes to generate surface-immobilized catalysts. See: (a) Valk-
enberg, M. H.; deCastro, C.; Ho¨lderich, W. F. Appl. Catal., A 2001, 215,
185. (b) Mehnert, C. P.; Cook, R. A.; Dispenziere, N. C.; Afeworki, M.
J. Am. Chem. Soc. 2002, 124, 12932. (c) Mehnert, C. P.; Mozeleski, E.
J.; Cook, R. A. Chem. Commun. 2002, 3010.
(15) We synthesized W2 supported on triethylammonium cation-grafted SiO2.
The yield of cyclooctene oxide under the conditions in Table 1 was 14%
and much lower than that with W2/1-SiO2.
In conclusion, W2/1-SiO2 was capable of heterogeneously
epoxidizing a broad range of olefins with high selectivity. The
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