New Heterogeneous Polyoxometalate Based Mesoporous Catalysts for Hydrogen Peroxide Mediated Oxidation Reactions

Article abstract of DOI:10.1021/ja036702g

Inorganic-organic hybrid mesoporous materials were prepared by cocrystallization of a "sandwich" type polyoxometalate, [ZnWZn ₂(H₂O)₂(ZnW₉O₃₄) ₂]^12-, and branched tripodal organic polyammonium salts, tris[2-(trimethylammonium)ethyl]-1,3,5-benzenetricarboxylate or 1,3,5-tris[4-(N,N,N-trimethylammonium-ethylcarboxyl)phenyl]benzene trications. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed formation of three-dimensional perforated coral-shaped amorphous materials with the organic cations surrounding polyoxometalate anions. N ₂ sorption analysis showed that the hybrid materials have a BET surface area of ～30-50 m² g^-1 and an average pore diameter of 36 A leading to the classification of these materials as mesoporous materials with moderate surface areas. These hybrid materials behaved as very effective and selective heterogeneous catalysts for the epoxidation of allylic alcohols and oxidation of secondary alcohols to ketones with hydrogen peroxide as oxidant. The activity and selectivity of the heterogeneous catalysts based on the hybrid materials was similar to those of homogeneous catalysts based on the same [ZnWZn₂(H₂O) ₂(ZnW₉O₃₄)₂]^12- polyoxometalate.

Full text of DOI:10.1021/ja036702g

Published on Web 12/30/2003
New Heterogeneous Polyoxometalate Based Mesoporous
Catalysts for Hydrogen Peroxide Mediated Oxidation
Reactions
Maxym V. Vasylyev and Ronny Neumann*
Contribution from the Department of Organic Chemistry,
Weizmann Institute of Science, Israel, 76100
Received June 16, 2003; E-mail: Ronny.Neumann@weizmann.ac.il.
Abstract: Inorganic-organic hybrid mesoporous materials were prepared by cocrystallization of a “sandwich”
type polyoxometalate, [ZnWZn2(H2O)2(ZnW9O34)2]12-, and branched tripodal organic polyammonium salts,
tris[2-(trimethylammonium)ethyl]-1,3,5-benzenetricarboxylate or 1,3,5-tris[4-(N,N,N-trimethylammonium-
ethylcarboxyl)phenyl]benzene trications. Scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) showed formation of three-dimensional perforated coral-shaped amorphous materials
with the organic cations surrounding polyoxometalate anions. N2 sorption analysis showed that the hybrid
materials have a BET surface area of ∼30-50 m2 g-1 and an average pore diameter of 36 Å leading to the
classification of these materials as mesoporous materials with moderate surface areas. These hybrid
materials behaved as very effective and selective heterogeneous catalysts for the epoxidation of allylic
alcohols and oxidation of secondary alcohols to ketones with hydrogen peroxide as oxidant. The activity
and selectivity of the heterogeneous catalysts based on the hybrid materials was similar to those of
homogeneous catalysts based on the same [ZnWZn2(H2O)2(ZnW9O34)2]12- polyoxometalate.
O34)2]}q-, (TM ) transition metal) Figure 1. These and other
Introduction
transition-metal-substituting polyoxometalates have been used
for oxidative transformations with iodosobenzene,3 N-oxides,4
periodate,5 ozone,6 nitrous oxide,7 sulfoxides,8 and molecular
oxygen9 as oxygen donors.
Oxidation reactions with hydrogen peroxide such as the
epoxidation of alkenes10 and also oxidation of alcohols11 as
“green” methods for organic synthesis have over the past decade
gained significant impetus and have been very recently reviewed.
Soluble metal oxides, especially tungsten-, molybdenum-, and
rhenium-based catalysts play an important role among the many
metal-based catalysts that have been investigated and reported.
The diversity of research fields connected to the chemistry
of polyoxometalates is significant and includes their application
in many areas, including structural chemistry, analytical chem-
istry, surface chemistry, medicine, electrochemistry, and pho-
tochemistry.1 However, perhaps one of the most extensively
studied applications of polyoxometalates has been in the area
of catalysis, where their use as both Brønsted acid catalysts and
oxidation catalysts has been going on since the late 1970s.2 A
basic premise behind the use of polyoxometalates in oxidation
chemistry is the fact that polyoxometalates are oxidatively stable.
This, a priori, leads to the conclusion that for practical purposes
polyoxometalates would have distinct advantages over widely
investigated organometallic compounds that are vulnerable to
decomposition due to oxidation of the ligand bound to the metal
center. Since polyoxometalate synthesis is normally carried out
in water by mixing the stoichiometrically required amounts of
monomeric metal salts and adjusting the pH to a specific acidic
value, many structure types are accessible by variation of the
reaction stoichiometry, replacement of one or more addenda
atoms with other transition or main group metals, and pH
control. Thus, many structural variants of such transition-metal-
substituting polyoxometalates are known but among the more
significant for catalysis is the transition-metal-substituting
“sandwich” type polyoxometalates, {[(WZnTM2(H2O)2][(ZnW9-
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124, 8788-8789. (b) Ben-Daniel, R.; Neumann, R. Angew. Chem., Int.
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Mesoporous Catalysts for Oxidation Reactions
A R T I C L E S
temperatures, which are usually ambient, the catalyst and
product phases may be separated by phase separation; the
catalyst phase is reused and the product is worked up in the
usual manner. Numerous biphasic media have been discussed
in the literature that include using catalysts in aqueous, fluorous,
ionic liquid, super critical fluid, and other liquid phases. Since
heteropoly acids can form complexes with or be dissolved in
diethyl ether, an interesting twist especially useful for oxidation
with the acidic H5PV2Mo10O40 was use the inexpensive poly-
(ethylene glycol) as solvent for aerobic oxidation of alcohols,
dienes, and sulfides and Wacker type oxidations.20 Beyond the
simple use of poly(ethylene glycol) as solvent, the attachment
of both hydrophilic poly(ethylene glycol) and hydrophobic poly-
(propylene glycol) to silica by the sol-gel synthesis leads to
solid particles that upon dispersion in organic solvents lead to
liquidlike phases termed solvent-anchored supported liquid-
phase catalysis.21 The balance of hydrophilicity-hydrophobicity
of the surface is important for tweaking the catalytic activity.
Finally, it has been shown that a Na12[(WZnZn2(H2O)2]-
[(ZnW9O34)2] assembled in situ in water is a very effective
catalyst for oxidation of alcohols with hydrogen peroxide in
aqueous biphasic media.22
Polyoxometalate based hybrid compounds23 have been con-
structed either by formation of covalent bonds between organic
and inorganic moieties or by creation of electrostatic interac-
tions24 between the inorganic and organic components. Poly-
oxometalates are also important as building units of supramo-
lecular complexes since they can exhibit diverse self-assembly
properties for such supramolecular materials, thus controlling
the formation of n-dimensional organic-inorganic hybrid
networks in self-organization processes. Previously such an
approach was used to prepare well-defined polyoxometalate-
containing films.25 To realize the potential self-assembly proper-
Figure 1. Ball and stick model of the [(WZnTM2(H2O)2][(ZnW9O34)2]}q-
polyoxometalate.
In this context, it was also found that the transition-metal-
substituting polyoxometalates were stable and effective catalysts
for oxidation with hydrogen peroxide.12 For example, the
manganese analogue of this polyoxometalate was originally
successfully used for the epoxidation of more nucleophilic
alkenes13 and then for oxidation of additional functional units.14
Just recently, the [(WZnZn2(H2O)2][(ZnW9O34)2]}12- compound
has been investigated as an exceptionally active catalyst for the
chemo- and diastereoselective oxidation of allylic alcohols with
hydrogen peroxide.15
Along with the development of concepts, synthetic techniques,
and mechanistic understanding of the use of polyoxometalates
as efficient oxidation catalysts, future practical application of
polyoxometalate oxidation catalysis will also require methods
for catalyst “engineering” to aid in catalyst recovery and recycle.
In general one can discern between two broad approaches. The
first basic approach is to immobilize a catalyst with proven
catalytic properties onto a solid support leading to a catalytic
system that may be filtered and reused. Such approaches include
concepts such as simple use of catalysts as insoluble bulk
material,16 which in some cases dissolves under reaction
conditions,17 impregnation of a catalyst onto a solid and usually
inert matrix,18 and attachment through covalent or ionic bonds
of a catalyst to a support.19 The second basic approach is to
use biphasic liquid-liquid systems, such that at separation
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Fujibayashi, S.; Nakayama, K.; Hamamoto, M.; Sakaguchi, S.; Nishiyama,
Y.; Ishii, Y. J. Mol. Catal. A 1996, 110, 105-117. (c) Nakayama, K.;
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Khenkin, A. M.; Neumann, R.; Sorokin, A. B.; Tuel, A. Catal. Lett. 1999,
63, 189-192. (e) Gall, R. D.; Hill, C. L.; Walker, J. E. Chem. Mater. 1996,
8, 2523-2527.
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2278. (b) Okun, N. M.; Anderson, T. M.; Hill, C. L. J. Am. Chem. Soc.
2003, 125, 3194-3195. (c) Okun, N. M.; Anderson, T. M.; Hill, C. L. J.
Mol. Catal. A 2003, 197, 283-290.
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1740. (b) Cohen, M.; Neumann, R. J. Mol. Catal. A 1999, 146, 293-300.
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125, 5280-5281.
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R.; Delmont, R.; Proust, A.; Gouzerh, P. Chem. Eur. J. 2000, 6, 1184-
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C. J.; Cabuil, V. Chem. Mater. 2001, 13, 3061-3083. (d) Hu, C.; Wang,
Y.; Li, Y.; Wang, E. Chem. J. on Internet 2001, 3 at http://www.chemis-
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(b) Le Maguere`s, P.; Hubig, S. M.; Lindeman, S. V.; Veya, P.; Kochi, J.
K. J. Am. Chem. Soc. 2000, 122, 10 073-10 082. (c) Clemente-Leo´n, M.;
Coronado, E.; Gime´nez-Saiz, C.; Go´mez-Garc´ıa, C. J.; Mart´ınez-Ferrero,
E.; Almeida, M.; Lopes, E. B. J. Mater. Chem. 2001, 11, 2176-2180. (d)
Otero, T. F.; Cheng, S. A.; Alonso, D.; Huerta, F. J. Phys. Chem. B 2000,
104, 10528-10533. (e) Otero, T. F.; Cheng, S. A.; Huerta, F. J. Phys.
Chem. B 2000, 104, 10522-10527. (f) Freund, M. S.; Karp, C.; Lewis, N.
S. Inorg. Chim. Acta 1995, 240, 447-451. (g) Cheng, S. A.; Ferna´ndez-
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Gime´nez-Saiz, C. J. Phys. Chem. B 2002, 106, 7585-7591. (h) Ferna´ndez-
Otero, T.; Cheng, S. A.; Coronado, E.; Mart´ınez-Ferrero, E.; Go´mez-Garc´ıa,
C. J. Chem. Phys. Chem. 2002, 3, 808-811. (i) Polarz, S.; Smarsly, B.;
Go¨ltner, C.; Antonietti, M. AdV. Mater. 2000, 12, 1503-1507. (j) Yun, S.
K.; Maier, J. Chem. Mater. 1999, 11, 1644-1649. (k) Coronado, E.; Galan-
Mascaros, J. R.; Gimenez-Saiz, C.; Gomez-Garcia, C. J.; Triki, S. J. Am.
Chem. Soc. 1998, 120, 4671-4681.
(12) (a) Khenkin, A. M.; Hill, C. L. MendeleeV Commun. 1993, 140-141. (b)
Zhang, X.; Chen, Q.; Duncan, D. C.; Lachicotte, R. J.; Hill, C. L. Inorg.
Chem. 1997, 36, 4381-4386. (c) Zhang, X.; Chen, Q.; Duncan, D. C.;
Campana, C. F.; Hill, C. L. Inorg. Chem. 1997, 36, 4208-4215. (d) Zhang,
X.; Anderson, T. M.; Chen, Q.; Hill, C. L. Inorg. Chem. 2001, 40, 418-
419. (e) Nozaki, C.; Kiyoto, I.; Minai, Y.; Misono, M.; Mizuno, N. Inorg.
Chem. 1999, 38, 5724-5729. (f) Mizuno, N.; Nozaki, C.; Kiyoto, I.;
Misono, M. J. Catal. 1999, 182, 285-288. (g) Mizuno, N.; Kiyoto, I.;
Nozaki, C.; Misono, M. J. Catal. 1999, 181, 171-174. (h) Mizuno, N.;
Nozaki, C.; Kiyoto, I.; Misono, M. J. Am. Chem. Soc. 1998, 120, 9267-
9272.
(13) Neumann, R.; Gara, M. J. Am. Chem. Soc. 1994, 116, 5509-5510. (b)
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Neumann, R.; Khenkin, A. M.; Juwiler, D.; Miller, H.; Gara, M. J. Mol.
Catal. 1997, 117, 169-183.
(15) (a) Adam, W.; Alsters, P. L.; Neumann, R.; Saha-Mo¨ller, C. R.; Sloboda-
Rozner, D.; Zhang, R. Synlett 2002, 2011-2014. (b) Adam, W.; Alsters,
P. L.; Neumann, R.; Saha-Mo¨ller, C. R.; Sloboda-Rozner, D.; Zhang, R. J.
Org. Chem. 2003, 68, 1721-1728.
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Mol. Catal. A 2001, 168, 299-301.
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A R T I C L E S
Vasylyev and Neumann
Scheme 1. Synthetic Pathway for the Preparation of the Benzene-1,3,5-tricarboxylic Acid Tris(2-trimethylammonium ethyl) Ester Cation, 1
Scheme 2. Synthetic Pathway for the Synthesis of Benzene-1,3,5-[tri(phenyl-4-carboxylic acid)] Tris(2-trimethylammonium ethyl) Ester, 2
ties it is important to correctly design an organic component
for the hybrid material synthesis.
The tripodal cation, 1, was simply prepared by acylation of
N,N-dimethylaminoethanol with 1,3,5-benzenetricarbonyl trichlo-
ride to yield the benzene-1,3,5-tricarboxylic acid tris(2-di-
methylaminoethyl) ester, which was quaternized with dimethyl
sulfate to yield the methyl sulfate salt of 1.
The synthesis of tripodal cation 2 began by self-condensation
of 4-bromacetophenone to yield 1,3,5-tris(4-bromophenyl)-
benzene according to a literature procedure. Lithiation followed
by carboxylation with carbon dioxide yielded 1,3,5-tris(4-
carboxyphenyl)benzene. After preparation of the acyl chloride
derivative, esterification with N,N-dimethylaminoethanol yielded
the benzene-1,3,5-[tris(phenyl-4-carboxylic acid)] tris-(2-di-
methylamioethyl) ester, which was quaternized by methylation
with an excess of dimethyl sulfate to yield the methyl sulfate
salt of 2.
In this paper, therefore, we report on the synthesis of two
tripodal polyammmonium cations and their utilization as build-
ing blocks together with a “sandwich”-type polyoxometalate,
[(WZnZn2(H2O)2][(ZnW9O34)2]}12-, to yield a mesoporous ma-
terial of moderate surface area. The hybrid material is an active
and recyclable catalyst for the oxidation of allylic alcohols and
alcohols with hydrogen peroxide. The [(WZnZn2(H2O)2][(ZnW9-
O34)2]}12- polyoxometalate was chosen because of (a) its known
catalytic activity in liquid-phase hydrogen peroxide mediated
oxidations, (b) its stability toward oxidative and hydrolytic
decomposition, and (c) its ellipsoid egg shape, Figure 1,
perceived to impair a closed-packed structure, thus favoring the
formation of a porous material.
Cocrystallization of 1 equiv of Q7Na5[(WZnZn2(H2O)2]-
[(ZnW9O34)2] (Q ) tetrabutylammonium) dissolved in DMSO
with 4 equiv of the methyl sulfate salts of 1 and 2, also dissolved
in DMSO, yielded white, amorphous solids almost immediately
upon mixing the solutions, 1-POM and 2-POM, respectively.
The materials were insoluble in a wide array of solvents: DMF,
DMSO, NMP, THF, acetonitrile, acetone, chlorinated hydro-
carbons, hydrocarbons, alcohols, and water.
Results and Discussion
Synthesis and Characterization of the Organic-POM
Hybrid Mesoporous Materials. The tripodal polyammonium
cations, benzene-1,3,5-tricarboxylic acid tris(2-trimethylammo-
nium ethyl) ester (1) and benzene-1,3,5-tris(phenyl-4-carboxylic
acid) tris(2-trimethylammonium ethyl) ester (2) were synthesized
according to synthetic Schemes 1 and 2, respectively.
The IR spectra of both materials, 1-POM and 2-POM, show-
ed via the expected absorption maxima that both the polyoxo-
metalate anion moiety {[(WZnZn2(H2O)2][(ZnW9O34)2]}12-
(934, 874 and 765 cm-1) and the cations 1 (νC-H(Ar) 3027,
(25) (a) Clemente-Leo´n, M.; Mingotaud, C.; Agricole, B.; Go´mez-Garc´ıa, C.
J.; Coronado, E.; Delhaes, P. Angew. Chem., Int. Ed. Engl. 1997, 36, 1114-
1116. (b) Clemente-Leo´n, M.; Agricole, B.; Mingotaud, C.; Go´mez-Garc´ıa,
C. J.; Coronado, E.; Delhaes, P. Langmuir 1997, 13, 2340-2347. (c)
Clemente-Leo´n, M.; Coronado, E.; Delhaes, P.; Go´mez-Garc´ıa, C. J.;
Mingotaud, C. AdV. Mater. 2001, 13, 574-577. (d) Ichinose, I.; Tagawa,
H.; Mizuki, S.; Lvov, Y.; Kunitake, T. Langmuir 1998, 14, 187-192. (e)
Moriguchi, I.; Fendler, J. H. Chem. Mater. 1998, 10, 2205-2211. (f)
Caruso, F.; Kurth, D. G.; Volkmer, D.; Koop, M. J.; Mu¨ller, A. Langmuir,
1998, 14, 3462-3465. (g) Kurth, D. G.; Volkmer, D.; Kuttorf, M.; Mu¨ller,
A. Chem. Mater. 2000, 12, 2829-2835.
ν
ν
C-H(Alk) 2964, νCdO 1731, νCdC 1637 cm-1) or 2 (νC-H(Ar) 3033,
C-H(Alk) 2961, νCdO 1713, νCdC 1636, 1606 cm-1) were retained
in the hybrid materials. Unfortunately, all attempts to slow rapid
precipitation by dilution to obtain crystalline materials for X-ray
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Mesoporous Catalysts for Oxidation Reactions
A R T I C L E S
Figure 2. Typical SEM images of hybrid materials 1-POM (left) and 2-POM (right).
Figure 3. TEM images of materials 1-POM (left) and 2-POM (right).
diffraction analysis were unsuccessful, but investigation by
means of electron microscopy was possible and used to
determine the morphology of complexes 1-POM and 2-POM.
The scanning electron micrographs, Figure 2, of 1-POM and
2-POM revealed the formation of three-dimensional perforated
coral-shaped amorphous materials. The channels and cavities
observed in Figure 2 have various inner diameters and are
arranged in irregular way.
Unfortunately, the dielectric properties of the materials did
not permit more highly magnified images to be obtained. Figure
3 shows a typical transmission electron microscope (TEM)
image in which the specimen appears to be granular with small
highly contrasting dots situated within a more poorly contrasting
substance. The diameter average found for the black dots is ca.
1.8 nm, which is approximately the cross-section diameter of
the {[(WZnZn2(H2O)2][(ZnW9O34)2]}12- polyanion (dimensions
of ∼1.0 to ∼1.5 nm for the X-ray crystal structure of
{[WZnZn2(H2O)2][(ZnW9O34)2]}12-).26 We believe that the
poorly contrasting substances are the organic polycations
surrounding polyoxometalate anions.
Figure 4. Adsorption isotherm and BET plot (insert) for 1-POM. (b - N2
adsorption; O - N2 desorption).
of type H3, Figure 4.27 The isotherms and adsorption-desorption
curves are typical for mesoporous materials. BET surface areas
of 51 and 27 m2 g-1 were calculated for 1-POM and 2-POM,
respectively. Pore size distribution curves calculated by Barret-
Joyner-Halenda (BJH) method indicated an average pore size
of 36 ( 6 Å for both hybrid materials. The N2 sorption
N2 sorption analyses were carried on both the 1-POM and
2-POM materials. The isotherms of 1-POM and 2-POM are
best described as type IV isotherms, noting especially the steep
slope at high relative partial pressures, with a hysteresis loop
(26) Tourne, C. M.; Tourne, G. F.; Zonnevijlle, F. J. Chem. Soc., Dalton Trans.
1991, 143-155.
(27) The isotherms were measured three times on each sample and showed no
significant changes, indicating the materials are stable.
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A R T I C L E S
Vasylyev and Neumann
in 1,2-dichloroethane.15 Chemoselectivity toward oxidation was
somewhat lower that in the biphasic liquid/liquid system pos-
sibly because the formation of the proposed template intermedi-
ate15 that leads to epoxidation versus alcohol oxidation is
hindered in a heterogeneous catalyst. The results indicate that
for these heterogeneous catalysts, similar to the homogeneous
catalytic system,15 metal alkoxide bonding of the allylic alcohol
to peroxo-metal catalytic center of the polyoxometalate provides
assistance in oxygen transfer in a stereoselective way depending
on the allylic strain. Thus, for Z-3-penten-2-ol and 4-methyl-
3-penten-2-ol with 1,3 allylic strain there is a high threo:erythro
diasteroselectivity, whereas as for E-3-penten-2-ol with no allylic
strain there is low diasteroselectivity. Diastereoselectivity is not
effected by the porous nature of 1-POM and 2-POM; no shape
selective features of the materials are observed.
Table 1. Epoxidation of Primary Allylic Alcohols with H2O2
Catalyzed by 1-POM and 2-POM
Finally, the hydrogen peroxide mediated oxidation catalyzed
by 1-POM and 2-POM of aliphatic secondary alcohols has been
tested as well (catalyst/alcohol substrate/hydrogen peroxide, 30%
aqueous molar ratios of 1:250:500 in acetonitrile at 60 °C). The
results, presented in Table 3, show high conversion, especially
with 2-POM based on the more extended tripodal cation and
full selectivity to the ketone product. Notably, also there appear
to be no shape constraints on catalytic activity, since it was
observed that the linear 2-pentanol and cyclic cyclooctanol
reacted at the same rates; the kinetic profiles were essentially
identical.
The stability of the mesoporous materials under catalytic
conditions was tested by catalyst recycle-recovery experiments
using cyclooctanol as a model substrate. Both 1-POM and
2-POM showed nearly quantitative conversion and selectivity
to cyclooctanone over five reaction cycles (1 mmol cyclooctanol,
2 mmol H2O2 (30% aqueous), 0.004 mmol catalyst, 0.5 mL
acetonitrile, 60 °C, 5 h). The catalyst was recovered after each
cycle by filtration. After the fifth catalytic cycle the IR spectra
measured showed no significant structural changes for 1-POM
or 2-POM. Also, repeat measurements of the adsorption
isotherms showed the same isotherm with calculated surface
experiments thus lead to the classification of 1-POM and
2-POM as mesoporous solids with moderate surface areas.28
Catalytic Oxidation with Hydrogen Peroxide. A principle
application of the mesoporous hybrid materials, 1-POM and
2-POM, was as new heterogeneous catalysts for oxidation
reaction with hydrogen peroxide. Therefore, we performed
several experiments to test the catalytic activity of 1-POM and
2-POM. Epoxidation of allylic alcohols was conducted at
catalyst/allylic alcohol substrate/hydrogen peroxide (30% aque-
ous) molar ratios of 1:500:1000 in acetonitrile. The results in
Table 1 for the oxidation of primary allylic alcohols show that
both 1-POM and 2-POM effectively catalyze the epoxidation
of the primary allylic alcohols in excellent conversion and
chemoselectivity.
To probe the diastereo- and chemoselectivity of epoxidation
reactions catalyzed by 1-POM and 2-POM, the epoxidation of
chiral allylic alcohols was further studied, Table 2. The results
reveal that these chiral allylic alcohols were oxidized with these
heterogeneous catalysts with reactivities and diastereochemose-
lectivities comparable to reactions carried out with the
{[WZnZn2(H2O)2][(ZnW9O34)2]}12- polyoxometalate dissolved
Table 2. Epoxidation of Chiral Allylic Alcohols with H2O2 Catalyzed by 1-POM and 2-POM
9
888 J. AM. CHEM. SOC. VOL. 126, NO. 3, 2004

Mesoporous Catalysts for Oxidation Reactions
A R T I C L E S
Table 3. Oxidation of Secondary Alcohols with 30% H2O2
Catalyzed by 1-POM and 2-POM
4.50 (brt, J ) 5 Hz, 6 H), 8.54 (s, 3 H) ppm. IR (film casted from
solution) ν 3038, 2962, 2874, 1723, 1614, 1578, 1475, 1359, 1233,
1173, 1085, 1010, 993, 956 cm-1
.
1,3,5-Tris(4-carboxyphenyl)benzene.29 1,3,5-tri(4-bromophenyl)-
benzene30 (2 g, 3.7 mmol) was dissolved in 25 mL of anhydrous THF
under Ar. The stirred solution was cooled to -60 °C and a 1.6 M
solution of n-BuLi in hexanes (7 mL, 11.2 mmol) was added dropwise.
A light-green precipitation of the aryllithium derivative was formed.
Predried gaseous carbon dioxide was passed into the mixture at -60
°C to give a colorless precipitate of the lithium salt. The mixture was
allowed to warm and was quenched with 50% aqueous acetic acid.
The solid product was filtered and recrystallized from acetic acid to
give 0.93 g (57%) of white microcrystals. 1H NMR (DMSO-d6) δ 8.05
(s, 12 H), 8.08 (s, 3 H) ppm. IR (film casted from solution) ν 3071,
substrate
catalyst
conversion, mol %
2-pentanol
POM-1
POM-2
POM-1
POM-2
POM-1
POM-2
POM-1
POM-2
POM-1
POM-2
POM-1
POM-2
POM-1
POM-2
92
94
86
94
62
89
40
90
92
92
94
99
99
100
2-hexanol
2-heptanol
2-octanol
2985, 1697, 1608, 1423, 1318, 1294, 1245 cm-1
.
cyclopentanol
cyclohexanol
cyclooctanol
Benzene-1,3,5-[tris(phenyl-4-carboxylic acid)] Tris(2-dimethyla-
mioethyl) Ester. Into a flask flushed with Ar, 0.5 g (1.1 mmol) of
1,3,5-tri(4-carboxyphenyl)benzene was placed and 20 mL of anhydrous
THF was added. Oxalyl chloride (20 mL, 21 mmol) was slowly added
dropwise with a syringe pump. The mixture was refluxed for 10 h and
then the excess oxalyl chloride was distilled off. To the resulting solid
20 mL of anhydrous THF was added. The solution was cooled with an
ice bath and pyridine (0.05 mL, 0.6 mmol) was added followed by
dropwise addition of 0.34 mL (3.63 mmol) of N,N-dimethylamino-
ethanol. The solution was allowed to warm and stirred for 24 h and
then quenched with an aqueous sodium hydrogen carbonate solution
and extracted with chloroform (3 × 50 mL). The organic phase was
dried over anhydrous sodium sulfate, filtered, and evaporated to give
areas and pore sizes of similar values ((3%). Furthermore,
filtered solutions of acetonitrile and hydrogen peroxide heated
for 5 h at 60 °C in the presence1-POM or 2-POM showed no
catalytic activity or evidence of zinc or tungsten metals.
Conclusions
1
0.3 g (42%) of light oily solid. H NMR (DMSO-d6) δ 2.2 (s, 18 H),
Mesoporous catalytic materials has been formed by preparing
insoluble inorganic-organic hybrid compounds based on a
tripodal organic triammonium cation and a catalytically active
polyoxometalate species, [WZnZn2(H2O)2][(ZnW9O34)2]}12-
The mesoporosity of the material, average pore diameter 36 Å,
allows oxidation of a number of organic substrates irrespective
of the molecular shape. Based on similar molecular designs, a
future goal will be certainly to obtain crystalline materials with
well-defined pores so that shape-selective catalytic oxidation
based on polyoxometalates may be envisioned.
2.6 (t, J ) 6 Hz) 4.4 (t, J ) 6 Hz), 8.07 (s, 12 H), 8.09 (s, 3 H) ppm.
13C NMR (DMSO-d6) δ 165.48, 144,19, 140.63, 129,75, 129.04, 127,
61, 125.75, 62.71, 57.27, 45.41 ppm. IR (film casted from solution) ν
2948, 2862, 2821, 2771, 1716, 1608, 1597, 1456, 1392, 1369, 1338,
.
1274, 1183, 1115, 1018, 850, 767, 701 cm-1
.
Benzene-1,3,5-[tris(phenyl-4-carboxylic acid)] Tris(2-trimethyl-
ammonium ethyl) Ester (2). To a solution of benzene-1,3,5-[tris-
(phenyl-4-carboxylic acid)] tris(2-dimethylamioethyl)ester (0.4 g, 0.61
mmol) in anhydrous THF (20 mL) 0.17 mL (1.84 mmol) of dimethyl
sulfate was added. In ∼2 min the quaternary ammonium salt 2 started
to precipitate. The mixture was stirred for additional 6 h and filtered;
the solid was washed with anhydrous ether and dried under high vacuum
to give 0.45 g (72%) of a white hygroscopic solid. 1H NMR (DMSO-
d6) δ 3.21 (s, 27 H), 3.36 (s, 9 H), 3.84 (br t, J ) 6 Hz, 6 H), 4.75 (brt,
J ) 6 Hz, 6 H), 8.12 (s, 15 H) ppm. 13C NMR (DMSO-d6) δ 164.97,
144.49, 140.60, 129.96. 128.50, 127.71, 125.91, 63.96, 58.79, 52.94,
52.79 ppm. IR (film casted from solution) ν 3130, 3040, 3003, 2950,
1713, 1607, 1481, 1376, 1272, 1246, 1114, 1059, 1008, 953, 894, 847,
Experimental Section
Benzene-1,3,5-tricarboxylic Acid Tris(2-dimethylaminoethyl) Es-
ter. A solution of 1.0 g (3.8 mmol) of 1,3,5-benzenetricarbonyl
trichloride in 6 mL of CH2Cl2 was added to a solution of 1 g (1.13
mL, 11.3 mmol) of N,N-dimethylethanolamine and 0.5 g of sodium
hydroxide in 6 mL of water over 15 min with rapid stirring, which
was then continued for 3 h. The organic layer was separated, diluted
with 20 mL of CH2Cl2, washed with water, dried over anhydrous sodium
sulfate, and concentrated under vacuum. The product is light oil (0.95
g, 59%) and was additionally dried under high vacuum for 3 h. The
product was sufficiently pure enough to use without further purification.1H
NMR (C6D6) δ 2.14 (18 H, s), 2.42 (6 H, t, J ) 5 Hz), 4.34 (6 H, t, J
) 5 Hz), 9.17 (3 H, s) ppm. 13C NMR (CDCl3) δ 45.45, 57.39, 63.17,
130.93, 134.45, 164.65 ppm. IR (film casted from solution) ν 3087,
2971, 2947, 2863, 2822, 2771, 1731, 1607, 1457, 1396, 1367, 1325,
1239, 1154, 1109, 1062, 1041, 1016, 931, 852, 821, 781, 740, 721
764, 747 cm-1
.
(n-Bu4N)7Na5[(WZnZn2(H2O)2][(ZnW9O34)2]. Na12{[WZnZn2(H2O)2]-
[(ZnW9O34)2]}26 (1.52 g, 0.25 mmol) was dissolved in 10 mL of water
and to this solution 0.84 g (3 mmol) of n-tetrabutylammonium chloride
dissolved in 5 mL of water was added. The mixture was stirred
vigorously and acidified by one drop of HCl (conc). Acidification
initiated precipitation of quaternary ammonium salt of POM. White
precipitate was filtered off, washed 3 times with water, and dried under
high vacuum for 48 h. Elemental analysis C112H252N7Na5O68W19Zn5
exptl (calcd): C 19.88 (20.02); H 3.63 (3.78); N 1.44 (1.46); Na 1.10
(1.71); Zn 4.95 (4.87); W 50.32 (51.98); O (16.19). IR (KBr) ν 2961,
cm-1
.
Benzene-1,3,5-tricarboxylic Acid Tris(2-trimethylammonium eth-
yl) Ester Cation, 1. To a solution of 0.5 g (1.2 mmol) of benzene-
1,3,5-tricarboxylic acid tris(2-dimethylaminoethyl) ester in 5 mL of
CHCl3 was 0.37 mL (0.49 g, 3.9 mmol) of dimethyl sulfate. The mixture
was refluxed for 1.5 h, cooled, and filtered. The hygroscopic solid
formed was dried under high vacuum and stored in desiccator. 1H NMR
(DMSO-d6) δ 3.19 (s, 27 H), 3.36 (s, 9 H), 3.84 (br t, J ) 5 Hz, 6 H),
2935, 2874, 1483, 952, 886, 774 cm-1
.
POM-1 and POM-2. (n-Bu4N)7Na5[WZnZn2(H2O)2][(ZnW9O34)2]
(0.0485 mmol) was dissolved in 5 mL of DMSO and to this solution
was added to solution of 1 or 2 (0.194 mmol in 5 mL of DMSO).
(29) Weber, E.; Hecker, M.; Koepp, E.; Orlia, W.; Czugler, M.; Csoregh, I. J.
Chem. Soc., Perkin Trans. 2 1988, 1251-1257.
(30) Palomero, J.; Mata, J. A.; Gonzalez, F.; Peris, E. New J. Chem. 2002, 26,
291-297.
(28) Kruk, M.; Jaroniec, M. Chem. Mater. 2001, 13, 3169-3183.
9
J. AM. CHEM. SOC. VOL. 126, NO. 3, 2004 889

A R T I C L E S
Vasylyev and Neumann
Within ∼1 min the mixture became milky and a white solid started to
precipitate. The mixture was left for 24 h to complete the precipitation
and then the solid was separated from the liquid by centrifugation.
POM-1 and POM-2 were thoroughly washed with 10 mL of DMSO,
ethanol (2 × 10 mL), and diethyl ether (2 × 10 mL) and dried under
high vacuum for 10 h. POM-1: Elemental analysis C96H168N12O92W19-
Zn5 exptl (calcd): C 16.35 (17.00); H 2.79 (2.50); N 2.29 (2.48); W
49.76 (51.50); Zn 4.91 (4.82); O (21.70). IR (KBr) ν 3026, 2964, 1731,
values in Table 1. Hydrogen peroxide conversion was essentially
quantitative.
General Procedure for the Catalytic Epoxidation of Chiral Allylic
Alcohols by POM-1 and POM-2. In a typical reaction, the specific
substrate 1 (1 mmol) and dimethyl isophthalate (0.4 mmol), as internal
standard, were dissolved in 0.15 mL of acetonitrile. POM-1 or POM-2
(0.001 mmol) were added and the reaction was initiated by addition of
30% H2O2 (0.2 mL, 2.0 mmol) to the solution at ∼21 °C with magnetic
stirring (∼1000 rpm) under an ambient atmosphere. After 2 h, 1 mL
of CH2Cl2 was added to the reaction mixture. The resulted mixture
was stirred for 15 min and the organic phase of the mixture was
separated and dried over Na2SO4, and the solvent was removed (20
°C, 50 mbar). The conversions, yields, and product ratios were
1637, 1482, 1375, 1331, 1247, 1120, 1010, 938, 877, 765, 737 cm-1
.
POM-2: Elemental analysis C168H216N12O92W19Zn5 exptl (calcd): C
25.31 (26.22); H 2.62 (2.83); N 2.23 (2.18); W 43.31 (45.39); Zn 4.04
(4.25); O (19.13). IR (KBr) ν 3033, 2961, 2874, 1713, 1636, 1607,
1478, 1380, 1275, 1187, 1115, 1017, 937, 875, 766, 699 cm-1
.
1
determined by H NMR analysis directly on the crude mixture. There
TEM Studies. A JEOL 100CX transmission electron microscope,
with accelerating voltage of 100 kV, was used to obtain the morphology
of the material. Specimens of materials were prepared by dispersing
the particles in ethyl alcohol by ultrasonic treatment and dropping them
onto a holey carbon film supported on a copper grid. The samples were
unstable under electron beam radiation, fading during observation in
20-40 s.
SEM Studies. A Fei (Philips) XL 30 ESEM-FEG with accelerating
voltage of 10 kV was used. Specimens of materials were prepared by
dispersing the particles in ethyl alcohol by ultrasonic treatment and
dropping them onto a silicon slides.
is a ca. (5% error for the values in Table 2. Hydrogen peroxide
conversion was essentially quantitative.
General Procedure for Catalytic Oxidation of Secondary Alco-
hols by POM-1 and POM-2. In a typical reaction, the specific substrate
1 (0.5 mmol) was dissolved in 0.15 mL of acetonitrile and POM-1 or
POM-2 (0.002 mmol) was added. The reaction was initiated by addition
of 30% H2O2 (0.1 mL, 1.0 mmol) to the solution at ∼60 °C with
magnetic stirring (∼1000 rpm) under an ambient atmosphere. After 5
h vials were cooled by ice bath and then opened and 1 mL of EtOAc
was added to the reaction mixture. The resulted mixture was stirred
for 15 min and the organic phase of the mixture was separated and
dried over Na2SO4. Conversions of the substrate were measured by
GLC using a 5% phenymethylsilicone (30 m, 0.32 mm ID, 0.25 µm
coating) column. There is a ca. (2% error for the values in Table 3.
Hydrogen peroxide conversion was essentially quantitative.
General Procedure for Catalytic Oxidation of Primary Allylic
Alcohols by POM-1 and POM-2. In a typical reaction, the specific
substrate (1 mmol) was dissolved in 0.15 mL of acetonitrile and POM-1
or POM-2 (0.001 mmol) was added. The reaction was initiated by
addition of 30% H2O2 (0.2 mL, 2.0 mmol) to the solution at ∼21 °C
with magnetic stirring (∼1000 rpm) under an ambient atmosphere. After
4 h, 1 mL of EtOAc was added to the reaction mixture. The resulted
mixture was stirred for 15 min and the organic phase of the mixture
was separated and dried over Na2SO4. Conversions of the substrate
were measured by GLC using a 5% phenymethylsilicone column (30
m, 0.32 mm i.d., 0.25 µm coating). Products were identified by GC-
MS analysis using the same column. There is a ca. (2% error for the
Acknowledgment. We thank the Minerva Foundation, the
European Commission (SUSTOX, G1RD-CT-2000-00347) and
the Helen and Martin Kimmel Center for Molecular Design for
supporting this research. R.N. is the Rebecca and Israel Sieff
Professor of Organic Chemistry.
JA036702G
9
890 J. AM. CHEM. SOC. VOL. 126, NO. 3, 2004