Design of heterogeneous catalysts via multiple active site positioning in organic-inorganic hybrid materials

Article abstract of DOI:10.1021/ja034594s

Catalytic materials bearing multiple sulfonic acid functional groups and positioned at varying distances from one another on the surface of mesoporous solids are prepared to explore the effects that the spatial arrangement of active sites have on catalytic activity and selectivity. A series of organosiloxane precursors containing either disulfide or sulfonate ester functionalities (synthons of the eventual sulfonic acid groups) are synthesized. From these molecular precursors, a variety of organic - inorganic hybrid, mesostructured SBA-15 silica materials are prepared using a postsynthetic grafting procedure that leads to disulfide and sulfonate ester modified silicas: [Si]CH₂CH₂CH₂SS-pyridyl, 2·SBA, [Si]CH₂CH₂CH₂SSCH₂ CH₂CH₂[Si], 3·SBA, [Si]CH₂CH₂(C₆H₄) (SO₂)OCH₂CH₃, 4·SBA, and [Si]CH₂CH₂(C₆H₄) (SO₂)OC₆H₄O(SO₂) (C₆H₄)CH₂CH₂[Si], 6·SBA ([Si] = (≡SiO)x(RO)_3-xSi, where x = 1, 2). By subsequent chemical derivatization of the grafted species, thiol and sulfonic acid modified silicas are obtained. The materials are characterized by a variety of spectroscopic (¹³C and ²⁹Si CP MAS NMR, X-ray diffraction) and quantitative (TGA/DTA, elemental analysis, acid capacity titration) techniques. In all cases, the organic fragment of the precursor molecule is grafted onto the solid without measurable decomposition, and the precursors are, in general, attached to the surface of the mesoporous oxide by multiple siloxane bridges. The disulfide species 2·SBA and 3·SBA are reduced to the corresponding thiols 7·SBA and 8·SBA, respectively, and 4·SBA and 6· SBA are transformed to the aryl sulfonic acids 11·SBA and 12·SBA, respectively. 7·SBA and 8·SBA differ only in terms of the level of control of the spatial arrangement of the thiol groups. Both 7·SBA and 8·SBA are further modified by oxidation with hydrogen peroxide to produce the alkyl sulfonic acid modified materials 9·SBA and 10·SBA, respectively. The performances of the sulfonic acid containing SBA-15 silica materials (with the exception of 12·SBA) are tested as catalysts for the condensation reaction of phenol and acetone to bisphenol A. The alkyl sulfonic acid modified material 10·SBA derived from the cleavage and oxidation of the dipropyl disulfide modified material 3·SBA is more active than not only its monosite analogue 9· SBA, but also the presumably stronger acid aryl sulfonic acid material 11·SBA. It appears that a cooperative effect between two proximal functional groups may be operating in this reaction.

Full text of DOI:10.1021/ja034594s

Published on Web 07/11/2003
Design of Heterogeneous Catalysts via Multiple Active Site
Positioning in Organic-Inorganic Hybrid Materials
,
†
V e´ ronique Dufaud* and Mark E. Davis*
Contribution from the DiVision of Chemistry and Chemical Engineering,
California Institute of Technology, Pasadena, California 91125
Received February 10, 2003; E-mail: mdavis@cheme.caltech.edu
Abstract: Catalytic materials bearing multiple sulfonic acid functional groups and positioned at varying
distances from one another on the surface of mesoporous solids are prepared to explore the effects that
the spatial arrangement of active sites have on catalytic activity and selectivity. A series of organosiloxane
precursors containing either disulfide or sulfonate ester functionalities (synthons of the eventual sulfonic
acid groups) are synthesized. From these molecular precursors, a variety of organic-inorganic hybrid,
mesostructured SBA-15 silica materials are prepared using a postsynthetic grafting procedure that leads
to disulfide and sulfonate ester modified silicas: [Si]CH
CH CH [Si], 3‚SBA, [Si]CH CH (C )(SO )OCH CH , 4‚SBA, and [Si]CH
)CH CH [Si], 6‚SBA ([Si] ) (tSiO) (RO)3-xSi, where x ) 1, 2). By subsequent chemical derivatization
of the grafted species, thiol and sulfonic acid modified silicas are obtained. The materials are characterized
2
CH
2
CH
2
SS-pyridyl, 2‚SBA, [Si]CH
2
CH
2
CH
2
SSCH
2
-
2
2
2
2
H
6 4
2
2
3
2
CH (C )(SO
2
6
H
4
2
)OC
6
H
4
O(SO )-
2
(C H
6 4
2
2
x
13
29
by a variety of spectroscopic ( C and Si CP MAS NMR, X-ray diffraction) and quantitative (TGA/DTA,
elemental analysis, acid capacity titration) techniques. In all cases, the organic fragment of the precursor
molecule is grafted onto the solid without measurable decomposition, and the precursors are, in general,
attached to the surface of the mesoporous oxide by multiple siloxane bridges. The disulfide species 2‚SBA
and 3‚SBA are reduced to the corresponding thiols 7‚SBA and 8‚SBA, respectively, and 4‚SBA and 6‚
SBA are transformed to the aryl sulfonic acids 11‚SBA and 12‚SBA, respectively. 7‚SBA and 8‚SBA differ
only in terms of the level of control of the spatial arrangement of the thiol groups. Both 7‚SBA and 8‚SBA
are further modified by oxidation with hydrogen peroxide to produce the alkyl sulfonic acid modified materials
9‚SBA and 10‚SBA, respectively. The performances of the sulfonic acid containing SBA-15 silica materials
(with the exception of 12‚SBA) are tested as catalysts for the condensation reaction of phenol and acetone
to bisphenol A. The alkyl sulfonic acid modified material 10‚SBA derived from the cleavage and oxidation
of the dipropyl disulfide modified material 3‚SBA is more active than not only its monosite analogue 9‚
SBA, but also the presumably stronger acid aryl sulfonic acid material 11‚SBA. It appears that a cooperative
effect between two proximal functional groups may be operating in this reaction.
Introduction
Dual, organic functionalization of periodic, mesoporous silicas
2
-6
has been reported. Typically, two types of organosilanes are
used simultaneously to provide surface functionalized silicas.
While one of the organic groups provides for the catalytic site,
the other (may be alkyl, aryl, benzyl, or vinyl) normally is not
another active site and is present to mediate the surface
properties, for example, hydrophobicity. These methodologies
do not provide for functional group positioning and control over
uniformity.
An ongoing objective in the preparation of solid catalysts is
the creation of structural uniformity. By analogy to soluble
catalysts, structural homogeneity may lead to high selectivity.
Clearly, results from zeolite-based catalysts suggest that there
can be a strong correlation between mesoscopic/macroscopic
uniformity and high selectivity.
A particularly attractive class of solids for investigating
structure-property relationships are organic-inorganic hybrid
1
Avnir and Blum have recently reported the use of multiple
organic functionalities in accomplishing reaction networks
materials. One type of these hybrid solids utilizes inorganic
materials to provide surface area and porosity and has organic
functional groups attached to the surface. The organic groups
can be randomly distributed or organized in some fashion, and
are the active sites for catalytic reactions. Of current interest
are (i) the creation of multiple organic groups in precise
arrangements to study the effects of cooperativity, and (ii) the
use of multiple organic group types to catalyze multistep reaction
pathways.
7,8
within a single vessel. Mutually destructive organic function-
(
1) Wight, A. P.; Davis, M. E. Chem. ReV. 2002, 102, 3589-3613 and
references therein.
(2) Macquarrie, D. J.; Jackson, D. B.; Tailland, S.; Wilson, K.; Clark, J. H.
Stud. Surf. Sci. Catal. 2000, 129, 275-282.
(
(
(
3) Asefa, T.; Kruk, M.; MacLachan, M. J.; Coombs, N.; Grondey, H.; Jaroniec,
M.; Ozin, G. A. J. Am. Chem. Soc. 2001, 123, 8520-8530.
4) Margolese, D.; Melero, J. A.; Christiansen, S. C.; Chmelka, B. F.; Stucky,
G. D. Chem. Mater. 2000, 12, 2448-2459.
5) Hall, S. R.; Fowler, C. E.; Lebeau, B.; Mann, S. Chem. Commun. 1999,
201-202.
†
Present address: Laboratoire de Chimie, Ecole Normale Sup e´ rieure
de Lyon, 46 all e´ e d’Italie, 69364 Lyon cedex 07, France.
(6) Bhaumik, A.; Tatsumi, T. J. Catal. 2000, 189, 31-39.
10.1021/ja034594s CCC: $25.00 © 2003 American Chemical Society
J. AM. CHEM. SOC. 2003, 125, 9403-9413
9
9403

A R T I C L E S
Dufaud and Davis
Scheme 1
Scheme 2
alities, for example, acids and bases, were entrapped separately
in sol-gel-derived silicas and used together within a single
reaction vessel to catalyze a sequence of reaction steps that in
the absence of the “sol-gel protected” active centers would
not proceed because of the annihilation of the active sites. Each
solid contains a single type of organic group, and no method
of control of functional group positioning was used.
disulfides and other sulfur species.15,18,19 To avoid these
problems, we either protect the thiol functionality with a
reversible blocking reagent such as a pyridyl group (precursor
2) or use a sulfonate ester precursor (precursor 4) to generate
the sulfonic acid function.
To produce ordered, dimeric sites for comparison to the
isolated sites that are generated from precursors 2 and 4,
precursors 3 and 6 were synthesized (Scheme 1). Starting from
the symmetrical dipropyl disulfide (precursor 3), two alkyl
sulfonic acid groups in close proximity to one another may be
produced by conversion to alkyl sulfonic acid centers, and from
the molecular precursor bis(arylsulfonate ester) (precursor 6),
two aryl sulfonic acid sites can be generated by removal of the
phenyl spacer.
Katz and Davis combined molecular imprinting with sol-
gel synthesis techniques to prepare microporous, amorphous
silicas with tailored microcavities containing multiple amino-
9
propyl functional groups covalently attached to the silica. The
controlled positioning of two and three organic groups was
accomplished, and the methodology has been extended to
mesoporous materials.10
Here, we report on the synthesis and characterization of
organic-functionalized, mesoporous silicas. The goal of our work
is to develop methodologies to prepare uniform arrangements
of organic functional groups on solid surfaces to access their
ability to act in a cooperative fashion when accomplishing
chemical reactions. Specifically, thiol and sulfonate ester
Disulfide Microstructures (Unsymmetrical, 2; Symmetri-
cal, 3). The unsymmetrical propylpyridyl disulfide 2 was
obtained by reacting 3-mercaptopropyltrimethoxysilane, (CH3O)3
-
Si-(CH
2
)3SH, 1, with 2,2′-dithiodipyridine (Aldrithiol) via a
thiol-disulfide interchange reaction (Scheme 2).20,21 If the thiol
1 is present in excess (2.5 equiv per disulfide bond), the product
functional groups were organized onto the ordered mesoporous
is the symmetrical dipropyl disulfide 3 (Scheme 2). After
solid SBA-151
1-14
through the use of designed organosilane
coupling to surface silanol groups. The sulfur-containing
moieties were converted to sulfonic acids, and the solids were
tested as catalysts for the condensation reaction between acetone
and phenol to produce bisphenol A. Particular attention was
given to the characterization of the materials at each step of
the preparation.
(7) Gelman, F.; Blum, J.; Avnir, D. J. Am. Chem. Soc. 2000, 122, 11999-
12000.
(
8) Gelman, F.; Blum, J.; Avnir, D. Angew. Chem., Int. Ed. 2001, 40, 3647-
3649.
(
9) Katz, A.; Davis, M. E. Nature 2000, 403, 286-289.
(
(
(
10) Ini, S.; Defreese, J. L.; Parra-Vasquez. N.; Katz, A. Mater. Res. Soc. Symp.
Proc. 2002, 723, M2.3.1-M2.3.7.
11) Zhao, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredrickson, G. H.; Chmelka, B.
F.; Stucky, G. D. Science 1998, 279, 548-552.
12) Zhao, D.; Huo, Q.; Feng, J.; Chmelka, B. F.; Stucky, G. D. J. Am. Chem.
Soc. 1998, 120, 6024-6036.
Results and Discussion
(
(
(
13) Zhao, D.; Sun, J.; Li, Q.; Stucky, G. D. Chem. Mater. 2000, 12, 275-279.
14) Kruk, M.; Jaroniec, M. Chem. Mater. 2000, 12, 1961-1968.
15) Van Rhijn, W. M.; De Vos, D.; Sels, B. F.; Bossaert, W. D.; Jacobs, P. A.
J. Chem. Soc., Chem. Commun. 1998, 317-318.
I. Synthesis of Molecular Precursors. A route to the
preparation of mesoporous silica supported sulfonic acids
involves the creation of a thiol containing silica, typically a
(
(
16) Bradley, R. D.; Ford, W. T. J. Org. Chem. 1989, 54, 5437-5443.
17) Bossaert, W. D.; De Vos, D. E.; Van Rhijn, W. M.; Bullen, J.; Grobet, P.
J.; Jacobs, P. A. J. Catal. 1999, 182, 156-164.
mercaptopropyl functionalized silica, that is then oxidized, in a
second step, with hydrogen peroxide.1
5-18
(18) Diaz, I.; Marquez-Alvarez, C.; Mohino, F.; Perez-Pariente, J.; Sastre, E. J.
Catal. 2000, 193, 283-294.
A drawback of this
approach when starting from a thiolsilane is the concurrent
formation of disulfide groups that can produce a material that
has various types of functional groups, notably partially oxidized
(19) Lim, M. H.; Blanford, C. F.; Stein, A. Chem. Mater. 1998, 10, 467-470.
(
20) Guo, W.; Pleasants, J.; Rabenstein, D. L. J. Org. Chem. 1990, 55, 373-
376.
(21) Houk, J.; Whitesides, G. M. J. Am. Chem. Soc. 1987, 109, 6825-6836.
9404 J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003

Design of Heterogeneous Catalysts
A R T I C L E S
Figure 3. C{ H} NMR spectrum of 4 in CD2Cl2; CP-MAS 13C NMR
spectrum of 4‚SBA. S denotes resonances from the solvent, and * marks
spinning sidebands.
13
1
Figure 1. C{ H} NMR spectrum of 2 in CD2Cl2; CP-MAS 13C NMR
1
3
1
spectrum of 2‚SBA. S denotes resonances from the solvent.
Scheme 3
ppm to the methoxy groups. In addition, downfield signals from
all of the carbons of the pyridyl moiety are observed.
Monosulfonate Ester Microstructure, 4. The preparation
of arylsulfonic acid esters was achieved by the reaction of an
alcohol with the appropriate sulfonyl chloride in the presence
2
2
of an organic base. The sulfonyl chloride used here was the
commercially available 2-(4-chlorosulfonylphenyl)ethyltrichlo-
rosilane), (Cl)3Si-(CH2)2-C6H4-SO2Cl. The reaction to the
2
3
desired sulfonic acid ester was not clean. Thus, the reaction
of this chloride with ethanol in pyridine (Scheme 3) leads to
precursor 4 in a relatively low yield (30%). Precursor 4 was
1
13
13
characterized by H and C NMR. In particular, the C NMR
spectrum (Figure 3) exhibits two resonances at 14.8 and 67.3
ppm characteristic of the methyl and the methylene carbons of
the ethylsulfonate group, respectively, and the signals of the
ethoxysilane groups at 18.4 and 58.5 ppm. The alkyl carbon
linked to the aromatic ring resonates at 29.4 ppm, while the
carbon that attached to the silicon atom gives a chemical shift
of 12.4 ppm. All of the resonances of the carbons of the aromatic
ring are also observed in the 160-120 ppm region.
Disulfonate Ester Microstructure, 6. A two-step synthetic
scheme was used to prepare 6 (Scheme 4). The first step
involved the preparation of the aryl ester of para-vinylben-
zenesulfonic acid by condensation of para-vinylbenzenesulfonic
chloride with hydroquinone in the presence of pyridine to
produce 5, CH2dCH-C6H4-(SO2)O-C6H4-O(SO2)-C6H4-
1
3
C{ H} NMR spectrum of 3 in C6D6; CP-MAS 13C NMR
1
Figure 2.
spectrum of 3‚SBA. S denotes resonances from the solvent.
reaction (less than 3 h for 2; 4 days to 1 week for 3), both
disulfide compounds are obtained in nearly quantitative yield
by extraction with petroleum ether to remove the pyridine-2-
thione.
Precursors 2 and 3 were characterized by H and 13C NMR
spectroscopy and GC/MS in the case of 3. The 13C NMR spectra
of both compounds (Figures 1 and 2 for 2 and 3, respectively)
exhibit in the 0-50 ppm region four signals: the resonances at
around 40 and 22 ppm are attributed to the carbons of a propyl
moiety situated, respectively, in R and â positions of the
disulfide bond, the resonance at around 10 ppm to the carbon
directly attached to the silicon atom, and the resonance at 48
1
(
22) Tipson, S. R. J. Org. Chem. 1944, 9, 235-241.
(
23) The starting 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane is sold as a
solution in methylene chloride with 30% free sulfonic acid and small
amounts of silylsulfonic acid condensation products. The sulfonic acid may
react with EtOH to form diethyl ether and water, the latter inducing
hydrolysis and condensation of the chlorosilane groups.
J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003 9405

A R T I C L E S
Dufaud and Davis
grafting17,41 and the co-condensation methods.15,17,18,40,42 Most
studies used the commercially available mercaptopropyltri-
methoxysilane and, in a subsequent oxidation step, transformed
the thiol to a sulfonic acid. Stucky and co-workers, however,
report the addition of hydrogen peroxide with the mercapto-
propyltrimethoxysilane or the 2-(4-chlorosulfonylphenyl)ethyl-
trichlorosilane) in the reaction mixture to oxidize in situ the
Scheme 4
4
,40
thiol functionalities.
We have explored these different methods, but in this report
we concentrate on the postsynthetic modification of the meso-
porous silica and subsequent chemical modification of these
surface functional groups. We will report results from the co-
condensation synthesis strategy at a later time.
II. A. Grafting Reaction. SBA-15 type silicas were used as
supports and were prepared by the acid catalyzed, nonionic
1
1-14
assembly pathway described elsewhere.
The structure
directing agent (Pluronic 123) was removed by calcination in
air at 500 °C, and the organic-free mesoporous silica was
rigorously dried under a flow of helium at 200 °C prior to the
grafting reaction. The molecular precursors, 1-6, were then
reacted with the SBA-15 silica in toluene under reflux condi-
tions. The unreacted precursors were removed by Soxhlet
extraction with methylene chloride overnight, and the collected
organic-inorganic hybrid materials are denoted 1‚SBA-6‚SBA.
Quantitative determinations of the organic content of the
hybrid mesoporous silicas were performed by thermogravimetric
analysis (TGA) in air and by elemental analysis. The results
are summarized in Table 1. The TGA data for several hybrid
materials are given in the Supporting Information. Generally,
three weight loss regions were observed. A first weight loss
occurred at temperatures up to about 100 °C and was endo-
thermic. This weight loss can be assigned to the desorption of
water. A second weight loss followed at temperatures ranging
from 150 to 650 °C, and this loss presumably arises from the
decomposition of the organic and the desorption of its fragments
(depending on the nature of the organic fragments, several
desorption peaks could be observed in this region). The third
significant weight loss peak occurred at temperatures above 650
°C and is due to the release of water formed from the
condensation of silanols in the silica structure. For the purpose
of reporting organic content in Table 1, the weight loss between
150 and 650 °C is taken as an estimate of the total amount of
the organic. The functional group loadings for 1‚SBA-6‚SBA
are found to be 0.1-1.0 mmol/g of dry SiO2 as determined by
TGA and 0.2-0.9 mmol/g of dry SiO2 as determined by sulfur
analysis. The TGA data can overestimate the organic content
because some weight loss below 650 °C can be due to silanol
CHdCH2, in 60% yield.24 The vinyl groups of 5 were then
hydrosilylated with triethoxysilane in the presence of chloro-
platinic acid as the catalyst and 1,2-dichloroethane as the
25
26
solvent. Different hydrosilylation conditions were attempted,
but the best results were obtained when carrying out the reaction
at 80 °C for several days and led to only 10% yield of the fully
silylated product. The desired compound was a mixture of
Markovnikov and anti-Markovnikov addition products, and this
mixture is collectively referred to as 6 (Scheme 4 shows only
the bis-anti-Markovnikov product). The complete silylation of
1
both double bonds was evidenced by H NMR spectroscopy,
in particular, by the total disappearance of the signals at 5.4,
5
(
.85, and 6.7 ppm typical of the carbons of the vinylic chain
see Supporting Information). The 13C NMR spectrum of 6 is
given in Figure 4.
II. Synthesis of Organic-Inorganic Hybrid Materials.
Two major routes have been widely investigated to chemically
modify the surface of periodic mesoporous silicas via covalently
bound organic functionalities. The postsynthesis procedure
involves the reaction of an organosilane directly with surface
silanols of a surfactant-free mesoporous oxide and further
modification or derivatization of the grafted species to create
2
7-30
new functionalities.
The second approach, the so-called one-
pot synthesis, combines the sol-gel3 and supramolecular
1
templating techniques to generate, in a single step, ordered
organically modified mesoporous silica-based nanocom-
posites.4
,15,19,32-40
A number of groups report the synthesis of
(
32) Burkett, S. L.; Sim, S. D.; Mann, S. J. Chem. Soc., Chem. Commun. 1996,
thiol and sulfonic acid modified ordered silicas by both the
1367-1368.
(33) Fowler, C. E.; Burkett, S. L.; Mann, S. J. Chem. Soc., Chem. Commun.
1997, 1769-1770.
(
24) Prib, O. A.; Gritsai, N. I. Ukr. Khim. Zh. 1968, 34, 368-370.
25) Ojima, I. In The Chemistry of Organic Silicon Compounds; Patai, S.,
Rappoport, Z., Eds.; John Wiley and Sons Ltd.: New York, 1989; pp 1479-
(
(34) Lim, M. H.; Blanford, C. F.; Stein, A. J. Am. Chem. Soc. 1997, 119, 4090-
4091.
1
526.
(35) Lim, M. H.; Stein, A. Chem. Mater. 1999, 11, 3285-3295.
(36) Macquarrie, D. J. J. Chem. Soc., Chem. Commun. 1996, 1961-1962.
(37) Macquarrie, D. J.; Jackson, D. B. J. Chem. Soc., Chem. Commun. 1997,
1781-1782.
(
26) Several attempts were undertaken to increase the yield of the reaction by
changing, for example, the nature of the catalyst. For the particular case of
the Speier’s catalyst (chloroplatinic acid solubilized in 2-propanol), no
silylated products were obtained even at higher temperatures.
(38) Macquarrie, D. J.; Jackson, D. B.; Tailland, S.; Utting, K. A. J. Mater.
Chem. 2001, 11, 1843-1849.
(
(
(
(
27) Brunel, D. Microporous Mesoporous Mater. 1999, 27, 329-344.
28) Clark, J. H.; Macquarrie, D. J. Chem. Commun. 1998, 853-860.
29) Moller, K.; Bein, T. Chem. Mater. 1998, 10, 2950-2963.
(39) Richer, R.; Mercier, L. Chem. Mater. 2001, 13, 2999-3008.
(40) Melero, J. A.; Stucky, G. D.; Van Grieken, R.; Morales, G. J. Mater. Chem.
2002, 12, 1664-1670.
30) Fryxell, G. E.; Liu, J.; Hauser, T. A.; Nie, Z.; Ferris, K. F.; Mattigod, S.;
Gong, M.; Hallen, R. T. Chem. Mater. 1999, 11, 2148-2154.
(41) Van Rhijn, W. M.; De Vos, D. E.; Bossaert, W. D.; Bullen, J.; Wouters,
B.; Grobet, P.; Jacobs, P. A. Stud. Surf. Sci. Catal. 1998, 117, 183-190.
(42) Diaz, I.; Marquez-Alvarez, C.; Mohino, F.; Perez-Pariente, J.; Sastre, E. J.
Catal. 2000, 193, 295-302.
(
31) The sol-gel approach corresponds to the inclusion of the organosiloxane
precursor in an appropriate concentration along with the siloxane precursor,
generally tetraethyl orthosilicate (TEOS), during the formation of the oxide.
9406 J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003

Design of Heterogeneous Catalysts
A R T I C L E S
Figure 4. C{ H} NMR spectrum of 6 in CD2Cl2; CP-MAS 13C NMR spectrum of 6‚SBA.
Table 1. Organic and Acid Group Content of SBA-15 Type Silica Materials Containing Disulfide, Thiol, and Sulfonic Acid Fragments
quantitative analysis of loading (mmol/g SiO
)a
1
3
1
2
derived from
sulfur analysis
measured by
TGA/DTAb
measured by acid
capacity titration
sample
precursor
functional group
S wt %
1‚SBA
2‚SBA
3‚SBA
4‚SBA
6‚SBA
7‚SBA
8‚SBA
9‚SBA
10‚SBA
11‚SBA
12‚SBA
1
2
3
4
6
2
3
2
3
4
6
[Si]-propyl-SH
1.4
4.1
3.3
1.2
0.5
2.0
2.7
1.4
1.7
0.47
0.79
0.62
0.48
0.19
0.71
0.93
0.54
0.65
0.29
<0.2
0.6
n.d.c
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.33
0.38
0.26
0.035
[Si]-propyl-SS-pyridyl
0.87
0.85
0.56
0.13
1.3
0.80
0.66
0.80
0.47
0.40
[Si]-propyl-SS-propyl-[Si]
[Si]-CH2CH2aryl-SO3Et
[Si]-CH2CH2aryl-SO3-aryl-SO3-arylCH2CH2-[Si]
[Si]-propyl-SH
[Si]-propyl-SH HS-propyl-[Si]
[Si]-propyl-SO3H
[Si]-propyl-SO3H HO3S-propyl-[Si]
[Si]-CH2CH2aryl-SO3H
0.76
<0.5
[Si]-CH2CH2aryl-SO3H HO3S-arylCH2CH2-[Si]
a
SiO2 content in the solid derived from the value of dry mineral analyzed by TGA/DTA at 950 °C; mmol of organic functionality reported (e.g., in going
b
c
from 3‚SBA to 8‚SBA, the value should double if there are no losses). Weight loss of the organic moiety measured between 150 and 650 °C. n.d. denotes
not determined.
condensation that gives off water. Overall, the TGA data are in
reasonable agreement with the elemental analysis results in most
but not all cases.
Physicochemical (X-ray powder diffraction) and textural
property (nitrogen sorption isotherms) data for the different
hybrid materials are summarized in Table 2. X-ray diffraction
patterns of the supported organic species exhibit three clear
peaks in the 2θ-range of 0.6-3°, characteristic of hexagonally
ordered mesophases with d(100) spacing varying from 89 to
solution phase spectra of the corresponding molecular precur-
sors. Examination of Figures 1-4 leads to the conclusion that
the organic functional groups remained intact during the grafting
of the precursor and subsequent workup. Note that in the
disulfide precursors 2 and 3, the signal corresponding to the
carbon atom adjacent to the thiol group (c) of precursor 1 (see
Figure 5) has been shifted downfield to around 40 ppm, whereas
the signal of the â-carbon has been shifted upfield to around
2
2 ppm. Corresponding peaks are resolvable in the CP-MAS
9
8 Å. The structure of the organic-inorganic hybrid materials
NMR of the modified oxides. In Figure 3, it is not possible to
resolve in the solid-state NMR spectrum the 10 signals that one
might expect, but the peak at 67.3 ppm would indicate the
presence of the sulfonate ester group (g). In Figure 4, the signals
corresponding to the two types of phenyl moieties are well
resolved; the central spacer is at 123 ppm, and the tether is at
128 ppm. For comparison to the materials prepared from
precursors 2-6, 1 was grafted onto SBA-15, and the 13C NMR
spectrum from the material obtained is given in Figure 5.
is thus preserved throughout the grafting process. Nitrogen
adsorption-desorption results from the organically modified
SBA-15 silica materials show a type IV isotherm typical of
mesoporous solids. A decrease in specific surface area between
SBA-15 and the modified materials is observed and is attribut-
able to the presence of the organic fragments.
The integrity of the organic fragment after grafting was
1
3
confirmed by C CP-MAS NMR spectroscopy. Figures 1-4
show the NMR spectra of the modified solids along with the
J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003 9407

A R T I C L E S
Dufaud and Davis
Table 2. Physical and Textural Properties of SBA-15 Type Silica Materials Containing Disulfide, Thiol, and Sulfonic Acid Fragments
XRD textural properties
a
b
c
S
BET (m g-1)
2
sample
precursor
functional group
d
100 (Å)
wall thickness (Å)
D
p
(Å)
SBA-15
105
93
89
89
98
41.2
51.4
48.8
43.8
53.2
60.9
56.8
n.d.
80
56
54
59
60
58
54
60
55
61
806
545
580
647
765
669
656
619
520
697
2‚SBA
3‚SBA
4‚SBA
6‚SBA
7‚SBA
8‚SBA
9‚SBA
10‚SBA
11‚SBA
2
3
4
6
2
3
2
3
4
[Si]-propyl-SS-pyridyl
[Si]-propyl-SS-propyl-[Si]
[Si]-CH2CH2aryl-SO3Et
[Si]-CH2CH2aryl-SO3-aryl-SO3-arylCH2CH2-[Si]
[Si]-propyl-SH
[Si]-propyl-SH HS-propyl-[Si]
[Si]-propyl-SO3H
[Si]-propyl-SO3H HO3S-propyl-[Si]
[Si]-CH2CH2aryl-SO3H
103
96
n.d.d
n.d.
100
n.d.
54.5
a
d(100) spacing. b Calculated by (a0 - pore size) with a0 ) 2d100/
3. c Pore size from desorption branch using the BJH method of analysis. d n.d.
x
denotes not determined.
Figure 5. C{ H} NMR spectrum of 1 in CD2Cl2; CP-MAS 13C NMR
1
3
1
spectrum of 1‚SBA. S denotes resonances from the solvent.
The 29Si CP-MAS NMR spectra of the modified oxides, 1‚
SBA-4‚SBA, are presented together with the nonmodified silica
support SBA-15 in Figure 6. The peaks observed in the spectral
region associated with tertiary silicon atoms, from -40 to -75
ppm, indicate unambiguously the presence of organosiloxane
moieties.43 Furthermore, multiple peaks are obtained from each
of the modified oxides, suggesting different degrees of linkage
of the organosiloxane group with the silica surface. All four
Figure 6. CP-MAS 29Si NMR spectra of calcined SBA-15, 1‚SBA, 2‚
SBA, 3‚SBA, and 4‚SBA.
1
2
modified oxides exhibit principally T and T sites, that is, an
anchoring of the organic species via one or two Si-O-Si bonds.
It is important that only the oxide modified by the dipropyl
disulfide, 3‚SBA, exhibits a signal at -41 ppm corresponding
out at 55 °C in the presence of a slight excess of tris(2-
carboxyethyl)-phosphine TCEP‚HCl (2 equiv per disulfide
46
13
unit) and were monitored by CP-MAS C NMR spectroscopy.
0
to a T site. This precursor is unique in that it contains two
In the case of the reduction of the pyridyl-propyl disulfide
linkage of 2‚SBA to produce the surface thiol 7‚SBA, the 13
C
polymerizable alkoxysilane moieties and perhaps, in the context
of a postsynthetic grafting procedure, it is impossible to find
sufficient available surface silanols for further condensation.
NMR spectrum (Figure 7) showed the total disappearance of
the resonances at 40 and 23 ppm characteristic of the carbons
of the propyl chain situated, respectively, in R and â positions
from the disulfide bond as well as those in the 160-115 ppm
region corresponding to the carbons of the pyridyl group.
Simultaneously, a new resonance at 27.5 ppm appeared that
can be assigned to the adjacent and central methylene carbons
2
3
4
Peaks assignable to Q , Q , and Q silicon sites are discernible
in all five spectra.
II. B. Chemical Modification of the Grafted Species. Thiol
Site Generation by Cleavage of Disulfide Linkages. Orga-
nophosphines have been used as reducing agents to cleave S-S
4
4-46
13
bonds.
The reductions of 2‚SBA and 3‚SBA were carried
of a propylthiol moiety (by analogy to the C NMR of 1‚SBA
that was synthesized directly). Taken together, these observa-
tions indicate quantitative cleavage of all of the disulfide bonds
present in the material to yield clean disulfide-free mercapto-
propyl functionalities. Also, the clean conversion of the dimeric
(
43) The conventional notation for the silicon atom type is used. A capital letter
Q or T indicates the type of silicon atom, Q or quaternary having four
Si-O bonds as in a siloxane, and T or tertiary having three Si-O bonds,
as in an organosiloxane. The capital letter is followed by the number of
Si-O-Si bonds attached to the center. Thus, the central silicon atom of
1
2
3
RSi(OSi)(OR′)
44) Kirley, T. L. Anal. Biochem. 1989, 180, 231-236.
45) Ruegg, U. T.; Rudinger, J. Methods Enzymol. 1977, 47, 111-126.
2 2 3
is T , of RSi(OSi) (OR′) is T , and of RSi(OSi) is T .
(
(
(46) Burns, J. A.; Butler, J. C.; Moran, J.; Whitesides, G. M. J. Org. Chem.
1991, 56, 2648-2650.
9
408 J. AM. CHEM. SOC. VOL. 125, NO. 31, 2003
9

Design of Heterogeneous Catalysts
A R T I C L E S
Figure 7. CP-MAS 13C NMR spectra of (left) 2‚SBA, 7‚SBA, and 9‚SBA; (right) 3‚SBA, 8‚SBA, and 10‚SBA, corresponding to the subsequent disulfide
cleavage and oxidation reaction.
disulfide, 3‚SBA, to an analogous mercaptopropyl containing
material, 8‚SBA, is observed. Note that 8‚SBA differs from 7‚
SBA in that the mercaptopropyl moieties are placed in pairs on
the surface of the mesoporous silica. Another effect of the
transformation of 2‚SBA and 3‚SBA is the significant decrease
of the intensity of the signal at 48 ppm corresponding to
methoxy groups. The 29Si CP-MAS NMR spectra of the
materials after this transformation (see Supporting Information)
27.5 ppm, characteristic of the carbon directly linked to the thiol
functional group, and the appearance of new peaks at 18 and
54 ppm, typical of n-alkyl sulfonic acids. Weak signals at 22,
39, and 64 ppm can also be seen in the spectra from 9‚SBA
and 10‚SBA. These resonances have been observed previously
4
7
for this type of oxidation and have been attributed to disulfide
15,19
and partially oxidized disulfide species.
The formation of
nonacidic sulfur containing side products could explain the
difference between sulfur loading and the acid capacity titration
for these materials reported in Table 1 (0.54 mmol/g SiO2 vs
0.33 mmol/g SiO2 for 9‚SBA, 0.65 mmol/g SiO2 vs 0.38 mmol/g
SiO2 for 10‚SBA). Also, it is noted that some organic is lost
from the treatments with H2O2 (7‚SBA vs 9‚SBA; 8‚SBA vs
10‚SBA).
1
show significant decreases of T signals and increases in the
2
3
T and T signals. Thus, the reduction conditions appear to
facilitate further reaction between unreacted SiOCH3 of the
organosiloxane and the silica surface.
The surface area measurements show for both materials that
the reduction of the disulfide linkage is accompanied by an
increase in the specific surface area (Table 2). The powder X-ray
diffraction patterns of these solids still indicate the hexagonal
ordering (Table 2 and Supporting Information).
The oxidation of thiol to sulfonic acid is accompanied by a
decrease in the specific surface area from the value obtained
after reduction, and this effect has also been reported by other
4,15,19
Sulfonic Acid Active Site Generation. Two methods were
used to produce the desired catalytically active sulfonic acid
surface functional groups. A procedure commonly employed
is the mild oxidation of thiol surface functional groups by
authors.
The X-ray powder diffraction patterns exhibit three
clear peaks, indicating that the hexagonal ordering of the
material is maintained.
Sulfonate Ester Transformation. The sulfonate ester moi-
eties in 4‚SBA and 6‚SBA were hydrolyzed in an aqueous
1
5-18
H2O2 ,
and this method was applied to 7‚SBA and 8‚SBA.
A second method used here involved the hydrolysis of sulfonate
ester surface functional groups and was exploited with 4‚SBA
and 6‚SBA.
48
solution of sulfuric acid at 60 °C overnight. The solids were
filtered, washed, and dried at 80 °C.
For 4‚SBA, 13C CP-MAS NMR (see Supporting Information)
Oxidation of the Surface Thiol Functional Groups. The
oxidation of the mercaptopropyl groups was performed using
the procedure described by Margolese et al.4 In a typical
reaction, 300 mg of the thiol containing material was suspended
in aqueous H2O2, and the suspension was stirred at room
temperature overnight under an atmosphere of argon. The solid
was filtered, acidified with sulfuric acid, washed, and finally
confirmed the complete transformation of ethyl sulfonate to
sulfonic acid as was evidenced by the total disappearance of
the peak at 67.3 ppm attributed to the methylene carbons of
that group. Also, the resonance at 58 ppm attributed to the
ethoxysilane fragment disappears. These data compare favorably
with those reported by Melero et al. for arenesulfonic modified
dried at 80 °C overnight (9‚SBA and 10‚SBA).
(47) The chemical shifts are consistent with those calculated for molecular
alkylsulfonic acid, for example, 1-propane sulfonic acid.
The 13C CP-MAS NMR spectra of 9‚SBA and 10‚SBA
(
48) Bentley, T. W.; Jurczyk, S.; Roberts, K.; Williams, D. J. J. Chem. Soc.,
(Figure 7) show the complete disappearance of the signal at
Perkin Trans. 2 1987, 293-300.
J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003 9409

A R T I C L E S
Dufaud and Davis
Scheme 5
Table 3. Synthesis of Bisphenol A with Sulfonic Acid Functionalized SBA-15 Silicas and para-Toluene Sulfonic Acida
per site yield of bisphenol Ab
p, p′/o, p′ molar ratio
catalyst
functional group
GCc
36
9.6e
13
8.8
18
NMRd
GCc
NMRd
para-toluene sulfonic acid
-propane sulfonic acid
CH3aryl-SO3H
CH3CH2CH2-SO3H
29
2
1.8
3
10
12
2.6
n.d.
3.0
6.4
8.3
e
1
1
9
1
n.d.f
11
1‚SBA
[Si]-CH2CH2aryl-SO3H
[Si]-propyl-SO3H
‚SBA
8.4
18
0‚SBA
[Si]-propyl-SO3H HO3S-propyl-[Si]
a
Reagents and conditions: phenol/acetone molar ratio ) 7/1; acetone/-SO3H site ) 300; 85 °C, 24 h. b mol of bisphenol A/mol of active site. Analysis
c
d
e
performed using biphenyl as external standard in acetonitrile. Analysis performed using mesitylene as external integration standard in CD3OD. Analysis
performed using liquid chromatography. f n.d. denotes not determined.
SBA-15 materials obtained by co-condensation of 2-(4-chloro-
sulfonylphenyl)ethyltrichlorosilane) and TEOS in the absence
and presence of H2O2.40 The acid capacity via titration methods
indicates the presence of acidic functional groups (presumably
arylsulfonic acid groups) with a loading very similar to the sulfur
loading as measured by elemental analysis (0.29 mmol/g SiO2
vs 0.26 mm/g SiO2, respectively, Table 1).
For 6‚SBA, the 13C CP-MAS NMR spectrum was of poor
quality (likely due to low organic loading), but the total
disappearance of the signal at 123 ppm characteristic of the
phenyl spacer of 6 was observed. The acid capacity measure-
ment showed very little sulfonic acid. Because of these low
values, we did not use this material for the catalytic reaction
studies.
counterparts. Results from 9‚SBA and 11‚SBA provide a
comparison between alkyl and aryl sulfonic acid modified
mesoporous silica materials. Finally, the effects of dimeric sites
in 10‚SBA are compared to the individual sites of 9‚SBA to
probe the importance of positioning of the catalytic groups.
The batch, condensation reaction was carried out in the
absence of solvent in a sealed glass vessel at 85 °C for 24 h.
Phenol was in excess (7 mol per mol of acetone), and the
acetone/acid active site molar ratio was fixed at 300. At the
end of the reaction period, a sample was analyzed by gas
chromatography with the addition of a known amount of an
1
external standard. An independent sample was analyzed by H
NMR with an external proton integration standard. The results
of the two methods were consistent and are reported in Table
3.
III. Catalysis. Sulfonic acid functionalized mesoporous
materials have been synthesized and successfully tested in a
At these reaction conditions, the two structural isomers of
bisphenol A were formed with all of the catalysts studied (see
Scheme 5). The “per site yield” listed in Table 3 represents the
total molar quantity of the two isomers divided by the total molar
equivalents of acid as determined (in the case of solid acids)
by titration.
large number of acid-catalyzed reactions such as condensation
or esterification reactions.1
7,19,40,49,50
To evaluate the catalytic
performances of the aryl and alkyl sulfonic acid containing SBA-
5 silicas and to address the question of whether the spatial
1
arrangement of the active sites is of importance, the condensa-
tion of phenol and acetone to produce bisphenol A (Scheme 5)
was investigated. Bisphenol A is an important raw material for
resin and polymer production. It is conventionally manufactured
by condensation of phenol and acetone catalyzed by ion-
exchange resins.51 However, because the thermal stability of
resins can be limited, the search for alternative, thermally stable,
solid acids continues. The use of heteropolyacid compounds
supported on MCM-41 type silicas or clays as well as zeolites
such as H-ZSM-5 and H-Y, and the use of silica supported
sulfonic acids have been reported.5
para-Toluene sulfonic acid is the most active catalyst studied.
The regioselectivity of the condensation vis- a` -vis the phenol
group is as expected, that is, predominantly para-activation with
respect to the hydroxyl group with some ortho-activated side
product. The solid aryl sulfonic acid catalyst, 11‚SBA, is about
one-third less active than the homogeneous system at roughly
the same selectivity.
9
‚SBA exhibited a lower activity than 11‚SBA, as might be
expected given the lower acid strength of the alkyl sulfonic acid
1-55
4
0
as compared to the aryl sulfonic acid. However, the change
in the regioselectivity of the reaction is unexpected. The ratio
of p,p′-bisphenol A to o,p′-bisphenol A is much higher for the
propylsulfonic acid modified SBA-15, 9‚SBA, than the aryl
sulfonic acid modified SBA-15, 11‚SBA (10 vs 3). Additionally,
the regioselectivity of 9‚SBA is high as compared to the
analogous homogeneous catalyst (1-propane sulfonic acid) at
an equivalent reaction rate. Because the regioselectivity of the
heterogeneous catalyst is so different from that of the homo-
geneous catalyst, leaching from the solid must not occur to any
significant extent. However, to test further for any indications
of leaching, 9‚SBA was filtered from a solution that was reacted
The catalytic activity and selectivity of 9‚SBA, 10‚SBA, and
1‚SBA and the homogeneous catalysts 1-propane sulfonic acid
and para-toluene sulfonic acid were tested at the same reaction
conditions (see below). The 9‚SBA and 11‚SBA solids are used
to compare heterogeneous analogues to their homogeneous
1
(
(
49) Corma, A. Chem. ReV. 1997, 97, 2373-2419.
50) Rhijn, W. M.; De Vos, D. E.; Sels, B. F.; Bossaert, W. D.; Jacobs, P. A.
Chem. Commun. 1998, 317-318.
(
(
(
(
(
51) Yadov, G. D.; Kirthivasan, N. Appl. Catal., A 1997, 154, 29-53.
52) Singh, A. P. Catal. Lett. 1992, 16, 431-435.
53) Nowinska, K.; Kaleta, W. Appl. Catal., A 2000, 203, 91-100.
54) Das, D.; Lee, J.-F.; Cheng, S. Chem. Commun. 2001, 2178-2179.
55) Wieland, S.; Panster, P. Stud. Surf. Sci. Catal. 1997, 108, 67-74.
9410 J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003

Design of Heterogeneous Catalysts
A R T I C L E S
for 24 h. The filtrate was then reacted for an additional 24 h at
(3.36 g, 15.3 mmol) in CH
Cl
2 2
(20 mL). The initially colorless solution
turned yellow immediately after the addition of 1 due to the production
of pyridine-2-thione. After the complete addition of 1, the solution was
stirred an additional hour, and the solvent was removed in vacuo. The
unsymmetrical disulfide was then extracted with dry petroleum ether,
filtered, and dried under vacuum. Precursor 2 was obtained in 95%
yield as a moisture-sensitive yellow liquid.
8
5 °C (absence of solid), and no further conversion was
observed.
The catalyst produced by placing two organic functionalities
in close proximity on the silica surface, 10‚SBA, exhibited not
only the highest activity of the heterogeneous systems but also
the highest regioselectivity of all of the systems considered here.
The principal difference in the performance related to spatial
arrangement of the functional groups, that is, between 9‚SBA
and 10‚SBA, is of activity rather than regioselectivity, as the
per site yield is practically doubled by having pairs of alkyl
sulfonic acid groups (18 vs 8.8 by GC). Additionally, 10‚SBA
is even more active than 1-propane sulfonic acid (18 vs 9.6).
While there must be some cooperative effect occurring, the exact
nature of this effect cannot be conclusively obtained from the
data presented here.
For 2: 1H NMR, CD
2 2 2
.77 ppm (quintet, 2H, SiCH CH CH
2
Cl
2
, δ 0.71 ppm (m, 2H, SiCH
2
CH
SS, JHH ) 7.13 Hz), 2.8 ppm
SS, JHH ) 7.5 Hz), 3.48 ppm (s, 3H, OCH ),
2 2
CH SS),
3
1
(
3
t, 2H, SiCH
7.06, 7.67, 7.73, and 8.42 ppm (m, 5H of the pyridyl group); C{ H}
NMR, CD Cl , δ 8.8 ppm (SiCH CH CHSS), 22.9 ppm (SiCH CH
CH SS), 42.1 ppm (SiCH CH CH SS), 50.8 ppm (s, OCH ), 119.7,
20.9, 137.4, 149.9, and 161.1 ppm (pyridyl carbons).
Synthesis of [(CH O) Si-(CH -S-] , 3. An excess of 3-mer-
2
CH
2
CH
2
3
1
3
1
2
2
2
2
2
2
-
2
2
2
2
3
1
3
3
2
)
3
2
captopropyltrimethoxysilane (4.45 g, 22.6 mmol) was added rapidly
via a syringe to a solution of 2,2′-dithiodipyridine (2 g, 9.07 mmol) in
CH Cl (20 mL), and the yellow solution was stirred at room
2 2
temperature during 4 days. Precursor 3 was then purified by extraction
with petroleum ether as described above. The reaction yielded 3
quantitatively as a yellow liquid.
A number of groups have disclosed the utility of using mixed
thiol/sulfonic acid catalytic systems to enhance activity and
selectivity.5
5-58
However, Cheng and co-workers reported
recently that catalysts containing incompletely oxidized sulfur
species exhibited lower catalytic activity.54 From the data given
in Table 1, the acid capacity of the propylsulfonic acid modified
materials is always less than the sulfur elemental analyses, and
this could indicate the presence of nonsulfonic acid sites on
the surface. It may be that these sites are playing a role in the
catalysis and that the enhancement observed between 9‚SBA
and 10‚SBA could be due to the systematic proximity of the
sulfonic acid sites and the nonsulfonic acid sites. However, the
current level of characterization of these materials does not allow
us to confidently test this hypothesis. Alternatively, the enhance-
ment of activity may be due to cooperation between two
proximal sulfonic acid groups on the surface, and the nonacidic
sites may not participate at all.
Among our future studies, we are most interested in testing
these various hypotheses. The synthesis of large quantities of
clean diacid materials such as 12‚SBA and of materials derived
from molecular precursors having both thiol and acid functional
synthons should provide quantitative formation of sulfonic acid
dimer sites (like that obtained with 11‚SBA for monomeric sites
For 3: 1H NMR, CD
1.85 ppm (quintet, 2H, SiCH CH CH SS,
2
Cl
2
, δ 0.66 ppm (m, 2H, SiCH
JHH ) 7.2 Hz), 2.52 ppm
SS, JHH ) 7.2 Hz), 3.46 ppm (s, 3H, -OCH );
Cl , δ 8.7 ppm (SiCH CH CH SS), 22.9 ppm
SS), 42.8 ppm (SiCH CH CH SS), 50.2 ppm (-OCH ).
O) Si-(CH -S-), 163
O) Si- fragment).
OEt (with Et ) -CH
. 2-(4-Chlorosulfonylphenyl)ethyltrichlorosilane) (8 mL of a 50%
2 2 2
CH CH SS),
3
2
2
2
3
(t, 2H, SiCH
2
CH
C{ H} NMR, CD
SiCH CH CH
2
CH
2
3
13
1
2
2
2
2
2
(
2
2
2
2
2
2
3
+
+
GC-MS: 390 (M ), 196 (M - (CH
3
3
2 3
)
3
((CH O)
3
Si-(CH
2 3
) - fragment), 121 ((CH
3
3
Synthesis of (EtO)
3
Si(CH -SO
2
)
2
C
6
H
4
2
2 3
CH ),
4
methylene chloride solution, 16.2 mmol) was added dropwise through
a septum to a solution of dry ethanol (9.44 mL, 162 mmol) and pyridine
(30 mL) at 0 °C. After the addition, the solution was kept at 0 °C an
additional 2 h, and the mixture was allowed slowly to warm at room
temperature. The reaction mixture was stirred at 25 °C overnight, and,
after the removal of pyridine under vacuum, 4 was extracted with
petroleum ether (30% yield).
For 4: 1H NMR, CD
Cl
), 1.22 ppm
OCH CH
), 3.82 ppm (quadruplet,
, JHH ) 6.5 Hz), 4.08 ppm (quadruplet, 2H, SO OCH
, JHH ) 7.2 Hz), 7.42 ppm (d, 2H, phenyl protons situated in â of
2
2
2 2
, δ 1 ppm (m, 2H, SiCH CH
3
(
J
2
t, 3H, SiOCH
2
CH
3
, JHH ) 7.2 Hz), 1.3 ppm (t, 3H, SO
2
2
3
,
3
2 2
HH ) 7.2 Hz), 2.82 ppm (m, 2H, SiCH CH
3
H, SiOCH
2
CH
3
2
2
-
3
CH
the ethyl chain, JHH ) 8.3 Hz), 7.80 ppm (doublet, 2H, phenyl protons
3
3
-
Table 1) and sites containing a single sulfonic acid and a
3
13
1
situated in â of the sulfonate ester group, JHH ) 8.2 Hz); C{ H}
NMR, CD Cl , δ 12.4 ppm (SiCH CH ), 14.8 ppm (SO OCH CH ),
8.4 ppm (SiOCH CH ), 29.4 ppm (SiCH CH ), 58.5 ppm (SiOCH
), 67.3 ppm (SO OCH CH ), 128 and 128.9 ppm (carbons of the
single thiol to give clearer evidence for any cooperative effects.
2
2
2
2
2
2
3
1
2
3
2
2
2
-
Experimental Section
CH
3
2
2
3
All manipulations were conducted under a strict inert atmosphere
aromatic ring), 133 ppm (quaternary carbon of the aromatic ring
attached to the ethyl chain), 152 ppm (ipso carbon attached to the ethyl
sulfonate group).
or vacuum conditions using Schlenk techniques. The solvents (CH
Cl , petroleum ether, and toluene) were dried by passing them through
a drying column and stored over activated 4 Å molecular sieves.
,2′-Dithiodipyridine (Aldrithiol), tetraethoxysilane (TEOS), and
2
-
2
Synthesis of (EtO) Si(CH ) -C H -(SO )O-C H -O(SO )-
3
2
2
6
4
2
6
4
2
2
C
6
H
4
2 2 3
-(CH ) Si(OEt) , 6. The synthesis of 6 was achieved in two
poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) block
copolymer (Pluronic 123, mw: 5000) were purchased from Aldrich
Chemical and used without further purification. 3-Mercaptopropyltri-
methoxysilane and 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane), 50%
in methylene chloride, were obtained from Gelest. Tris(2-carboxyethyl)-
phosphine (TCEP‚HCl) was purchased from Pierce.
steps: esterification of the para-styrene sulfonyl chloride with hydro-
quinone in the presence of pyridine leading to the formation of a
diolefinic compound containing two sulfonate ester moieties, CH
2
d
CH-C -(SO )O-C -O(SO )-C -CHdCH , 5, and hydrosi-
H
6 4
2
H
6 4
2
H
6 4
2
lylation of the two double bonds in 5 with triethoxysilane in the presence
of chloroplatinic acid as the catalyst to yield 6.
Synthesis Procedure. A. Preparation of Molecular Precursors.
(a) Preparation of CH dCH-C H -(SO )O-C H -O(SO )-
2
6
4
2
6
4
2
Synthesis of (CH
g, 5.1 mmol) in dry CH
temperature over a period of 2 h to a solution of 2,2′-dithiodipyridine
3
O)
3
Si-(CH
2
)
3
-SS-C
5
H
5
N, 2. A solution of 1 (1
C H -CHdCH , 5. Hydroquinone (0.7 g, 6.35 mmol) was dissolved
6
4
2
2
2
Cl (5 mL) was added dropwise at room
in dry pyridine (20 mL), and the solution was cooled to 0 °C 1 h prior
to the addition of the para-styrene sulfonyl chloride (2083 g, 14 mmol),
introduced via a syringe under an argon atmosphere. The mixture kept
at 0 °C an additional 2 h was allowed to warm to room temperature
and left overnight. The reaction was quenched with an acidified aqueous
solution (75 g of crushed ice and 25 mL of concentrated hydrochloric
(
(
(
56) Jerabek, K.; Odnoha, J.; Setinek, K. Appl. Catal. 1988, 37, 129-138.
57) Gupta, S. R.; Dwivedi, M. C. Chem. Age India 1971, 22, 339-348.
58) Jerabek, K.; Li, G. H.; Setinek, K. Collect. Czech. Chem. Commun. 1989,
5
4, 321-325.
J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003 9411

A R T I C L E S
Dufaud and Davis
1
2
acid), and the solution was diluted with methylene chloride. The organic
layer was first neutralized by successive washings with sodium
bicarbonate solution and then washed with a brine solution. The
combined organic extracts were then dried over magnesium sulfate.
After filtration, the solvent was evaporated under reduced pressure.
Finally, 5 was recrystallized from the resultant white powder with a
(-OCH
3
3
); CP-MAS 29Si NMR, δ -49 ppm (T ), -57 ppm (T ), -101.7
4
ppm (Q ), -110.5 ppm (Q ). Elemental analysis, wt % C, 2.4; S, 1.4.
For 2‚SBA, [Si]-propyl-SS-pyridyl functional group: CP-MAS
C NMR, δ 8.75 ppm (SiCH CH CH SS-), 22 ppm (SiCH CH CH -
SS-), 41.5 ppm (SiCH CH CH SS-), 120.6, 138.1, 148.6, and 160.3
ppm (s, carbons of the pyridyl moiety); CP-MAS Si NMR, δ -49
ppm (T ), -57 ppm (T ), -101.7 ppm (Q ), -110.5 ppm (Q ).
Elemental analysis, wt % C, 7.3; S, 4.1; N, 0.57.
For 3‚SBA, [Si]-propyl-SS-propyl-[Si] functional group: CP-
SS-), 21.8 ppm (SiCH
SS-), 49.8 ppm (-OCH
Si NMR, δ -41 ppm (T ), -49 ppm (T ), -57 ppm (T ), -95 ppm
(Q ), -104 ppm (Q ), -113 ppm (Q ). Elemental analysis, wt % C,
6.0; S, 3.3.
13
2
2
2
2
2
2
2
2
2
29
1
2
3
4
mixture of HCCl
For 5: 1H NMR, CD
1 Hz), 5.85 ppm (d, 1H, arylCHdCH
3
and petroleum ether and was obtained in 60% yield.
Cl , δ 5.42 ppm (d, 1H, arylCHdCH
, cisJ )
J ) 18 Hz), 6.7 ppm
, JHH ) 10.9 and 17.6 Hz), 6.84
ppm (s, 4H, protons of the central phenyl moiety), 7.45 ppm (d, 2H,
2
2
2
trans
1
2
,
3
13
(
complex multiplet, 1H, arylCHdCH
2
MAS C NMR, δ 7.5 ppm (SiCH
2
CH
2
CH
2
2 2
CH -
CH
2
SS-), 41 ppm (SiCH
2
CH
2
CH
2
3
2
); CP-MAS
3
3
29
0
1
aryl protons, JHH ) 8.4 Hz), 7.62 ppm (d, 2H, aryl protons, JHH ) 8
1
3
1
2
3
4
Hz); C{ H} NMR, CD
2
Cl
2
, δ 118.6 ppm (Aryl-CHdCH
2
), 123.8
ppm (-CH of the central phenyl ring), 127 and 129 ppm (-CH of the
aromatic ring), 133.5 ppm (quaternary carbons of the central phenyl
For 4‚SBA, [Si]-CH CH aryl-SO Et functional group: CP-MAS
2
2
3
13
ring), 135.1 ppm (-CHdCH
2
), 143.8 ppm (quaternary carbon of the
C NMR, δ 13.3 ppm (large singlet attributed to SiCH CH , SO -
2
2
2
aromatic ring attached to the vinyl chain), 148.1 ppm (quaternary carbon
of the aromatic ring attached to the sulfonate ester group).
2 3 2 3 2 2 2
OCH CH , SiOCH CH ), 28.3 ppm (SiCH CH ), 58 ppm (SiOCH -
CH ), 67.2 ppm (SO OCH CH ), 128 ppm (-CH of the aromatic ring),
3
2
2
3
(
H
b) Preparation of (EtO) Si(CH
2
)
2
-C
and Related Isomers Referred to as 6. The
addition of triethoxysilane, HSi(OEt) , in the presence of chloroplatinic
6
H
4
-(SO
2
)O-C
6
H
4
-O(SO
2
)-
133 ppm (quaternary carbon of the aromatic ring attached to the ethyl
3
C
6
4
2 2 3
-(CH ) Si(OEt)
chain), 151 ppm (quaternary carbon of the aromatic ring attached to
2
9
1
3
the ethylsulfonate ester group); CP-MAS Si NMR, δ -48 ppm (T ),
2
2
3
4
acid, to the di-olefinic compound 5 produced 6 as a mixture of anti-
Markovnikov and Markovnikov addition products. Typically, 1 g of 5
-57 ppm (T ), -93 ppm (Q ), -102 ppm (Q ), -110 ppm (Q ).
Elemental analysis, wt % C, 5.2; S, 1.2.
(
22.62 mmol) was first dissolved in the minimum amount of 1,2-
For 6‚SBA, [Si]-CH CH aryl-SO -aryl-SO -arylCH CH -[Si]
2
2
3
3
2
2
functional group and related isomers: CP-MAS 13C NMR, δ 16 ppm
dichloroethane (1 mL), and 5 mg of H PtCl ‚6H O (0.0122 mmol) was
2
6
2
then added to the solution. Triethoxysilane (0.82 g, 5 mmol) was added
dropwise to this mixture at 80 °C over 15 min. After 4 days of reaction
at the same temperature, the fully silylated products were purified by
extraction with petroleum ether.
(large singlet, attributed to -CH- and -CH - carbons directly
2
attached to a silicon atom and to -CH carbons of not condensed
3
ethoxysilane fragments), 24.1 ppm (-CH(Si)-CH ), 28.4 ppm (Si-
3
CH -CH ), 59 ppm (broad signal) (SiOCH CH ), 123.9 ppm (-CH
2
2
2
3
For 6: 1H NMR, CD
ppm (m, Si-OCH CH and CH(Si)-CH
, JHH ) 7.6 Hz), 2.71 ppm (m, 2H, SiCH
ppm (m, Si-OCH CH ), 6.82 ppm (s, 4H, aryl protons of the central
phenyl moiety), 7.3 and 7.6 ppm (two doublets, 4H, aryl protons, JHH
, δ 0.86 ppm (m, 2H, SiCH
), 2.66 ppm (quadruplet, 1H,
CH ), 3.73
CH
), 1.12
of the central phenyl ring), 129.7 ppm (-CH of the aromatic ring),
151 ppm (broad peak, quaternary carbons of the aromatic ring).
Elemental analysis, wt % C, 2.7; S, 0.5.
2
Cl
2
2
2
2
3
3
3
-
CH(Si)-CH
3
2
2
2
3
Chemical Modification of the Grafted Species. Thiol Sites
Generation by Cleavage of Disulfide Linkages. The reduction of
disulfide bonds in 2‚SBA and 3‚SBA was achieved using a water-
soluble trivalent phosphine, the tris(2-carboxyethyl)-phosphine (TCEP‚
HCl). Typically, 0.5-1 g of disulfide containing mesoporous silica
materials was suspended in water, and a solution of TCEP (2 equiv of
TCEP per disulfide unit) in water and methanol (1:2) was added via a
syringe at room temperature. The mixture was stirred at 25 °C for 1 h,
warmed at 55 °C, and kept at that temperature for 1-3 days. After
filtration, the solid was sequentially washed with water and methanol
to remove the unreacted phosphine and the organic reaction products.
For 7‚SBA, [Si]-propyl-SH functional group: CP-MAS 13C NMR,
3
1
3
1
)
1
1
8.8 and 7.6 Hz, respectively); C{ H} NMR, CD
6 ppm (-CH and -CH , carbons directly attached to a silicon atom),
8.2 ppm (Si-OCH CH ), 25.4 and 25.6 ppm (CH(Si)-CH ), 29.2
CH ), 58.7 and 59.3 ppm (Si-OCH CH ), 123.7 ppm
-CH of the central phenyl ring), 128.6 and 128.8 ppm (-CH of the
2 2
Cl , δ 15.1 and
2
2
3
3
ppm (SiCH
(
2
2
2
3
aromatic ring), 129.8 ppm (quaternary carbon of the aromatic ring
attached to the substituted ethyl branch), 132.1 ppm (quaternary carbon
of the central phenyl ring), 148.1 ppm (quaternary carbon of the
aromatic ring linked to the sulfonate ester moiety).
B. Preparation of Organic-Inorganic Hybrid Materials. SBA-
5 mesoporous silica was prepared according to the procedure described
1
δ 10 ppm (SiCH
2
CH
2
2
CH
2
SH), 27.5 ppm (SiCH
2
2
CH
2
CH
2
SH), 50.7 ppm
9
3
by Stucky and co-workers using poly(ethyleneoxide)-poly(propyl-
eneoxide)-poly(ethyleneoxide) triblock copolymer (Pluronic 123) as
(-OCH
3
2
). CP-MAS Si NMR, δ -57 ppm (T ), -66 ppm (T ), -93
3
4
ppm (Q ), -100.1 ppm (Q ), -110.5 ppm (Q ). Elemental analysis,
wt % C, 2.7; S, 2.0.
4
the structure directing agent (SDA) and acid catalysis. The SDA was
removed quantitatively from the as-synthesized material by calcination
at 500 °C overnight under air as was evidenced by TGA analysis and
infrared spectroscopy.
Following calcination, the oxide was dried rigorously under a flow
of helium at 200 °C during 15 h and transferred under argon in a
Schlenk tube. The calcined SBA-15 silica material was characterized
using classical methods such as XRD, nitrogen adsorption, and TGA
analysis.
Grafting Reaction. The organosilane (∼500 mg) was added to a
suspension of SBA-15 (1 g) in dry toluene and stirred at 25 °C for 2
h and then heated at 90-100 °C. After several hours (2-4 h), volatiles
including toluene and methanol (or ethanol) were distilled. The addition
of fresh toluene, heating, and distillation sequences were repeated twice.
The unreacted organic compound was then removed by a soxlhet
For 8‚SBA, [Si]-propyl-SH HS-propyl-[Si] functional groups:
CP-MAS 13C NMR, δ 10 ppm (SiCH CH CH SH), 27.5 ppm (Si-
2
2
2
2
9
CH -CH -CH -SH), 51 ppm (-OCH ). CP-MAS Si NMR, δ -47
2
2
2
3
1
2
3
2
ppm (T ), -57 ppm (T ), -66 ppm (T ), -91.6 ppm (Q ), -101 ppm
3
4
(Q ), -119.7 ppm (Q ). Elemental analysis, wt % C, 3.4; S, 2.7.
Sulfonic Acid Active Site Generation. (a) Oxidation of the
Corresponding Thiol. The oxidation of mercaptopropyl groups of 7‚
SBA and 8‚SBA was performed using the procedure described by
4
Stucky and co-workers. First, 0.3 g of the thiol containing material
was suspended in 10 g of aqueous 30 wt % H
was stirred at 25 °C overnight under an argon atmosphere. The
subsequent acidification was carried out in 1 M H SO solution at the
2 2
O , and the suspension
2
4
same temperature for 2 h. Finally, the solid was washed with water
and ethanol and dried at 70 °C.
For 9‚SBA, [Si]-propyl-SO H functional group: CP-MAS 13C
2 2
extraction in CH Cl overnight, and the resulting solid was finally dried
in an oven at 70 °C overnight.
For 1‚SBA, [Si]-propyl-SH functional group: CP-MAS 13C NMR,
3
NMR, δ 10 ppm (SiCH CH CH SO H), 17.9 ppm (SiCH CH CH -
2
2
2
3
2
2
2
3 2 2 2 3
SO H), 54 ppm (SiCH CH CH SO H). In addition to these resonances,
δ 8.7 ppm (SiCH
2
CH
2
CH
2
SH), 27 ppm (SiCH
2
CH
2
CH
2
SH), 48.9 ppm
peaks with weak intensity were also observed at 23, 37.5, and 64 ppm
9412 J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003

Design of Heterogeneous Catalysts
A R T I C L E S
1H or 13C NMR resonances in the deuterated solvents: C
attributed to disulfide and partially oxidized species. CP-MAS 29Si
D
6
, δ 7.15
6
2
3
2
1
13
1
NMR, δ -57.5 ppm (T ), -66.8 ppm (T ), -92 ppm (Q ), -101 ppm
ppm for H, 128 ppm for C; CD
for C.
2
Cl
2
, δ 5.32 ppm for H, 53.8 ppm
3
4
13
(
Q ), -110.5 ppm (Q ). Elemental analysis, wt % C, 1.9; S, 1.4.
For 10‚SBA, [Si]-propyl-SO H HO S-propyl-[Si] functional
group: CP-MAS C NMR, δ 10 ppm (SiCH CH CH SO H), 17.9 ppm
SiCH CH CH SO H), 54 ppm (SiCH CH CH SO H). In addition to
these resonances, peaks with weak intensity were also observed at 23,
7.5, and 64 ppm attributed to disulfide and partially oxidized species.
3
3
The acid capacities of the sulfonic acid mesoporous materials were
determined by ion-exchange with an aqueous solution of sodium
chloride (NaCl, 2 M; suspension allowed to equilibrate during 24 h)
followed by titration with a solution of 0.01 N NaOH (aq).
Catalytic Experiments. The condensation of phenol and acetone
to produce bisphenol A was carried out in a sealed glass vessel at 85
°C during 24 h. The solid catalysts were dried at 90 °C under vacuum
overnight prior to the catalytic experiments. A typical experiment
consisted of 5-7 g of phenol and 0.5-1 g of acetone with 0.07-0.1
g of sulfonic acid containing SBA-15 silica materials.
13
2
2
2
3
(
2
2
2
3
2
2
2
3
3
2
9
2
3
2
CP-MAS Si NMR, δ -58 ppm (T ), -66 ppm (T ), -92 ppm (Q ),
3
-
101 ppm (Q ), -110.5 ppm. Elemental analysis, wt % C, 2.5; S, 1.7
b) Sulfonate Ester Transformation. The hydrolysis of the sulfonate
ester moiety in 4‚SBA and 6‚SBA was carried out with a H SO
(
2
4
aqueous solution (1 wt %) at 60 °C during 15 h. The solid was then
filtered, washed carefully with a large amount of water, and dried at
At the end of the reaction, the products were analyzed by both gas
chromatography and liquid NMR spectroscopy. In the case of GC
analysis, biphenyl in acetonitrile was used as an external standard. The
suspension was first centrifuged, and the resulting solution was analyzed
on a Hewlett-Packard 5890 Series II gas chromatograph equipped with
a flame ionization detector and a HP-5 capillary column (30 m × 0.25
8
0 °C in an oven.
For 11‚SBA, [Si]-CH
C NMR, δ 12 ppm (large singlet attributed to SiCH
2
CH
2
aryl-SO
3
H functional group: CP-MAS
CH ), 28 ppm
), 127 and 128 ppm (-CH of the aromatic ring), 140
1
3
2
2
(
s, SiCH CH
2
2
ppm (quaternary carbon of the aromatic ring attached to the ethyl chain),
1
48 ppm (quaternary carbon of the aromatic ring attached to the sulfonic
mm × 0.25 µm). For the NMR analysis, mesitylene in CD
3
OD was
2
9
2
3
acid group). CP-MAS Si NMR, δ -57 ppm (T ), -67.4 ppm (T ),
-
used as an external integration standard. The quantification of the
products in this case was based on the methyl peaks of the products
and mesitylene.
2
3
4
91 ppm (Q ), -100.7 ppm (Q ), -111 ppm (Q ). Elemental analysis,
wt % C, 2.5; S, 0.8.
For 12‚SBA, [Si]-CH
functional group: CP-MAS C NMR, δ 12.8 ppm (large singlet
2
CH
2
aryl-SO
3
H HO
3
2 2
S-arylCH CH -[Si]
1
3
Acknowledgment. V.D. acknowledges the Centre National
de la Recherche Scientifique for a sabbatical leave in the
laboratory of Professor Davis at Caltech and the NATO Division
Affairs for a fellowship. We thank Dr. Chris Dillon and Helen
Chuang for assistance with the catalytic experiments and Drs.
Gerald P. Niccolai and Andrea P. Wight for fruitful discussions.
attributed to SiCH CH ), 28 ppm (SiCH CH ), 128 ppm (-CH of the
2
2
2
2
aromatic ring), 140 ppm (quaternary carbon of the aromatic ring
attached to the ethyl chain), 148 ppm (quaternary carbon of the aromatic
ring attached to the sulfonic acid group). Elemental analysis, wt % C,
2
.2; S, <0.5.
Characterization. X-ray powder diffraction (XRD) data were
acquired on a BRUCKER D5005 diffractometer using Cu K
λ ) 1 054 184 Å). A Netzsch thermoanalyzer STA 449C was used
for simultaneous thermal analysis combining thermogravimetric (TGA)
and differential thermoanalysis (DTA) at a heating rate of 10 °C/min
in air. Nitrogen adsorption and desorption isotherms were measured at
Supporting Information Available: 1H NMR spectra of the
molecular precursors 5 and 6: hydrosilylation of 5. 13C CP-
MAS NMR spectra of 4‚SBA and 11‚SBA: transformation of
R
radiation
(
29
the sulfonate ester to the sulfonic acid. Si CP-MAS NMR
spectra of 4‚SBA and 11‚SBA: transformation of the sulfonate
7
7 K. All of the organic-inorganic hybrids were evacuated at 180 °C
29
ester to the sulfonic acid. Si CP-MAS NMR spectra of 2‚
for 24 h before the measurements. Specific surface areas were calculated
following the BET procedure. Pore size distribution was obtained by
using the BJH pore analysis applied to the desorption branch of the
nitrogen adsorption/desorption isotherm. Elemental analyses for C, S,
and N were performed by Quantitative Technologies Inc., NJ.
SBA and 7‚SBA: cleavage of the disulfide linkage of the
2
9
disulfide functionalized 2‚SBA. Si CP-MAS NMR spectra of
‚SBA and 8‚SBA: cleavage of the disulfide linkage of the
3
disulfide functionalized 3‚SBA. Powder X-ray diffraction pat-
terns of (a) transformation of ethylsulfonate 4‚SBA into sulfonic
acid 11‚SBA; (b) cleavage of disulfide bond in 2‚SBA to
produce surface thiol species 7‚SBA; (c) cleavage of disulfide
bond in 3‚SBA to produce surface thiol species 8‚SBA. TGA
measurements of 1‚SBA, 2‚SBA, 3‚SBA, and 4‚SBA (PDF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
13
29
Solid-state CP MAS C and Si NMR measurements were recorded
on a Bruker Avance DSX-200 spectrometer operating at 200.2, 50.3,
1
13
29
and 39.8 MHz for H, C, and Si, respectively, and using a Bruker
mm CP MAS probe. A typical spinning rate for CP MAS experiments
is 4 kHz. A 2 ms cross polarization contact time was used to acquire
7
29
13
Si and C CP MAS spectra with a repetition delay of 1.5 and 32 000
scans. 13C and 29Si MAS spectra were referenced to tetramethylsilane.
Liquid NMR spectra were recorded on a Varian Mercury-300
spectrometer. All chemical shifts were measured relative to residual
JA034594S
J. AM. CHEM. SOC.
9
VOL. 125, NO. 31, 2003 9413