Facile one-pot approach to the synthesis of chiral periodic mesoporous organosilicas SBA-15-type materials

Article abstract of DOI:10.1016/j.jcat.2010.07.003

The synthesis of a chiral PMO SBA-15-type material from 100% purely organic monomers, 1,2-bis(triethoxysilyl)ethane and bis-silylated chiral ligands, by an easy one-pot methodology has been studied. Furthermore, these chiral periodic mesoporous solid materials with an incorporation as high as 50 mol% of dimethyl tartrate-derived chiral auxiliary precursor (Sharpless ligand) have been synthesized, without any reduction in the textural properties with reference to the ordering of the material. FTIR and NMR solid-state techniques confirm the presence of the chiral organic precursor in the SBA-15-type material framework. The thioanisole asymmetric oxidation reaction has been used to validate the heterogeneously synthesized catalyst activity, achieving moderate enantiomeric excess (ee) and satisfactory yield to sulfoxide up to 30% and 71%, respectively, corroborating the inclusion of the chiral tartrate moiety into the inorganic silica framework.

Full text of DOI:10.1016/j.jcat.2010.07.003

Journal of Catalysis 274 (2010) 221–227
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Facile one-pot approach to the synthesis of chiral periodic mesoporous organosilicas
SBA-15-type materials
*
Rafael A. Garcia , Rafael van Grieken, Jose Iglesias, Victoria Morales, Nelson Villajos
Department of Chemical and Environmental Technology, ESCET, Universidad Rey Juan Carlos, C/Tulipán s/n, 28933 Móstoles, Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of a chiral PMO SBA-15-type material from 100% purely organic monomers, 1,2-bis(trieth-
oxysilyl)ethane and bis-silylated chiral ligands, by an easy one-pot methodology has been studied. Fur-
thermore, these chiral periodic mesoporous solid materials with an incorporation as high as 50 mol% of
dimethyl tartrate-derived chiral auxiliary precursor (Sharpless ligand) have been synthesized, without
any reduction in the textural properties with reference to the ordering of the material. FTIR and NMR
solid-state techniques confirm the presence of the chiral organic precursor in the SBA-15-type material
framework. The thioanisole asymmetric oxidation reaction has been used to validate the heterogeneously
synthesized catalyst activity, achieving moderate enantiomeric excess (ee) and satisfactory yield to sulf-
oxide up to 30% and 71%, respectively, corroborating the inclusion of the chiral tartrate moiety into the
inorganic silica framework.
Received 2 April 2010
Revised 2 July 2010
Accepted 2 July 2010
Available online 5 August 2010
Keywords:
Chiral PMOs
SBA-15
Tartrate derivatives
Asymmetric synthesis
Enantioselectivity
Ó 2010 Elsevier Inc. All rights reserved.
1. Introduction
distorting the mesostructure. From this development, different
groups have reported synthesis of chiral PMOs with several chiral
Chiral periodic mesoporous organosilicates have been recently
developed as a variety of periodic mesoporous organosiliceous
materials (PMOs). Insertion of chirality inside the PMOs constitutes
a breakthrough for potential applications particularly as catalysts
for asymmetric synthesis. Hence, the development of novel heter-
ogeneous chiral ligands that could effectively induce asymmetry
might be crucial not only in organic synthesis, but it could allow
the preparation of new valuable materials for applications in areas
such as adsorption, chromatography, optical devices, and sensors
[1–9]. The chiral PMO synthesis is accomplished through anchor-
ing of chiral building blocks into the three-dimensional mesopor-
ous framework of the silica matrix, in which the bis-silylated
chiral organosilica precursors are homogenously distributed along
the pore walls, playing the role of organic bridges in the silica net-
work. These materials are characterized by a periodically organized
pore system with a defined pore diameter.
Pioneering work with an organic chiral auxiliary incorporated
into the framework of a MCM-41 inorganic material date from
2003, in which Garcia and co-workers develop a chiral PMO
MCM-41-based material from a mixture of chiral bis-silylated
binaphthyl or cyclohexadienyl precursor and tetraethoxysilane
(TEOS) as the sources of silica, under basic conditions [10]. Accord-
ingly, the chiral solid material was not purely PMOs, incorporating
a maximum content of chiral precursor around 15 wt% without
precursor moieties, such as bis-silylated vanadyl salen complexes,
chiral diurea ligands, BINOL and BINAP auxiliaries and chiral tar-
trate derivatives [11–18] extending the range of the applications.
A common feature in all these works is that TEOS is needed as silica
co-precursor to achieve the mesoscopic structure, which leads to
rather small chiral functionality loadings. In addition, ionic surfac-
tants are used as template, and therefore, MCM-41-like framework
materials are obtained. Subsequently, some investigations dealing
with the preparation of pure chiral mesoporous materials with
only organic monomers, that is, without TEOS as silica co-precur-
sor, have been published [19–22]. However, these works about
the preparation of PMOs from 100% chiral bis-silylated functional-
ities demonstrate the lack of mesoscopic ordering in the final
materials. Also, Fröba and co-workers have recently reported the
synthesis of chiral periodic mesoporous organosilica in the pres-
ence of non-ionic oligomeric surfactant as the supramolecular
structure-directing agent under acidic conditions [23]. Brij 76
was used as the template, leading to chiral benzylic ether-bridged
hybrid material with a high surface area. Finally, using the same
surfactant, MacQuarrie et al. have recently reported an elegant
method to prepare chiral PMO materials, employing a mixture of
enantiomerically pure biphenyl bis-siloxane with non-chiral
biphenyl bis-siloxane, although no application is reported [24].
Nonetheless, in most of the cases, the synthesis of the chiral
periodic mesoporous organosilicas takes place through a procedure
with multiple stages. As best, at least two steps are needed to
achieve the chiral PMOs [19]. Previously, the organic synthesis of
* Corresponding author. Fax: +34 914887086.
E-mail address: rafael.garcia@urjc.es (R.A. Garcia).
0021-9517/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2010.07.003

222
R.A. Garcia et al. / Journal of Catalysis 274 (2010) 221–227
Scheme 1. One-pot synthesis of chiral PMO SBA-15-like material.
the, usually non-commercial, chiral bis-organosilane is performed
following different reaction steps and further purification, with
the subsequent assemblage of the chiral precursor around the tem-
plating micelles. This tedious drawback is circumvented by the
procedure that we outline herein, in which a new, easy and
unprecedented one-pot approach to the synthesis of chiral SBA-
15-like material is accomplished, based on a tartrate-derived chiral
precursor and a non-chiral bis-organosilane, 1,2-bis(triethoxysi-
lyl)ethane. Interestingly, this chiral organic–inorganic material
could be prepared from purely organic monomers, without the
need of using silica sources, like TEOS, that lead to conventional
inorganic silica, in the presence of Pluronic 123 as templating
agent under acidic conditions (Scheme 1). Besides, the chiral pre-
cursor loadings incorporated without distorting the mesoscopic
structure are meaningfully higher than the previously reported
works [11,16,25–27]. The so-obtained chiral PMOs exhibit a good
activity and moderate enantioselectivity in the asymmetric sulfox-
idation of thioanisole, confirming the inclusion of the chiral tar-
trate moiety into the inorganic silica framework.
idene L-tartrate (DMT, ALDRICH) and ethanol (Scharlab) were used
as received without further purification. Dichloromethane was dis-
tilled from P2O5 prior its use as solvent for the catalytic tests.
2.2. Synthesis of SBA-15 chiral periodic mesoporous organosilica
In a typical synthesis, 2 g of Pluronic P123 and 19.7 g of KCl
were dissolved in 65 mL of 0.5 N hydrochloric acid in a round-bot-
tom flask at room temperature. After complete dissolution, the
mixture was warmed up to 40 °C, and 2.9 g of BTSE was added in
a single step. After 1 h, (N-methylaminopropyl)trimethoxysilane
and protected dimethyltartrate were added in order to obtain the
bis-silylated tartramide through an in-situ transamidation reac-
tion. Different materials were prepared in the molar range of BTSE
to tartramide from 100:0 to 30:80. The solution was then vigor-
ously stirred for 20 h at 40 °C and hydrothermally aged at 100 °C
for another 24 h. The product was then recovered by filtration be-
fore being air-dried. The surfactant removal consisted of an extrac-
tion step with ethanol. Typically, 1 g of as-made material was
treated with 100 mL of ethanol under reflux overnight. The solids
were then recovered by filtration while still warm and thoroughly
washed with fresh ethanol before air-dried.
2. Experimental
2.1. Chemicals
2.3. Characterization
Pluronic P123 (PEO20-PPO70-PEO20; Aldrich), 1,2-bis(trieth-
oxysilyl)ethane (BTSE, 99%, Aldrich), potassium chloride (KCl,
99%, Aldrich), hydrochloric acid (HCl, 35%, Scharlab), (N-methyla-
minopropyl)trimethoxysilane (GELEST), dimethyl-2,3-O-isopropyl-
The so-prepared materials were characterized by means of dif-
ferent analytical techniques. Nitrogen adsorption–desorption iso-
therms were collected at 77 K using a Micromeritics TriStar 3000

R.A. Garcia et al. / Journal of Catalysis 274 (2010) 221–227
223
unit. Previously, the samples were outgassed at 200 °C for 4 h un-
der nitrogen flow. The surface area measurements were performed
according to the BET method from nitrogen adsorption points in
the range P/P0 = 0.05–0.2. Pore size distribution was determined
applying the Barrett–Joyner–Halenda model (BJH) to the adsorp-
tion branch of the isotherm, assuming cylindrical pore geometry.
For each sample, the average pore size was estimated as the diam-
eter corresponding to the maximum of the pore size distribution
curve. Total pore volume was taken at a relative pressure P/P0 of
0.985
the chiral tartrate derivative employed as chiral precursor,
protected L-(+)-dimethyl tartrate (DMT), is mixed with the
(N-methyl-3-aminopropyl)trimethoxysilane under the weak acidic
conditions needed for synthesizing
a SBA-15-like framework
material, a transamidation reaction takes place, leading to the
bis-silylated chiral precursor. Besides, the presence of 1,2-bis(tri-
ethoxysilyl)ethane (BTSE) and the copolymer Pluronic P123
triblock copolymer provides the mesoscopic ordering to the final
material. Therefore, during the in-situ transamidation reaction,
the hydrolysis of the chiral and non-chiral bis-organosilane silica
precursors and the condensation of these latter species around mi-
celles formed by the structure-directing agent are readily accom-
plished leading to a chiral PMO material.
X-ray powder diffraction patterns were collected on a Philips
X’pert diffractometer equipped with an accessory for low-angle
measurements. XRD analyses were recorded using the Cu K
a line
in the 2h range from 0.5° to 10° with a step size of 0.02° and a
counting time of 10 s.
After the optimization of the aging time and the hydrolysis and
condensation stage, the progressive incorporation of higher
amounts of protected DMT was carried out. Thus, Table 1 summa-
rizes the physico-chemical properties of the obtained chiral PMOs.
Fig. 1 shows the N2 adsorption–desorption isotherms for the
synthesized materials. BET surface, pore size distribution (inset
in Fig. 1) and total pore volume are obtained by processing the
adsorption branch of the collected isotherm data. Chiral PMO-10,
20, 30 and 50 materials show type IV nitrogen adsorption–desorp-
tion curves, according to the IUPAC classification, which are typical
of mesoporous solids. The steep adsorption step detected around P/
P0 = 0.65–0.70, corresponding to the capillary condensation of
nitrogen in uniform pores, evidences the formation of well-struc-
tured solid materials with narrow pore sizes distributions, as it is
derived from the BJH analysis shown in the onset. On the other
hand, the ordering degree seems to be influenced by the content
of the organic functionality. Although the width of the pore size
distributions seems not to be greatly modified, the area below
the pore size distribution, which is the total pore volume, or at
least the mesopore volume, decreases when increasing the organic
ligand loading. Besides, the mean pore size is slightly shifted to
lower values because of the same reasons already exposed. Finally,
chiral PMO-70 exhibits a negligible yield to solid, indicating that
higher loadings of bis-organosilane inhibit the formation of these
materials. Thereby, a significant amount of BTSE must coexist in
the media besides the chiral precursors to provide enough meso-
scopic ordering to the final chiral PMO SBA-15-type materials.
Nevertheless, chiral periodic mesoporous solid materials with a ra-
tio BTSE/DMT as high as 50:50 have been synthesized, which,
according to the earlier reports, is the highest organic chiral load-
ing incorporated into the three-dimensional structure of a PMO
material, to the best of our knowledge. Although for this 50:50
precursor mixture, the incorporation of chiral functionality suffers
a slight decline compared to sample S20, as shown in Table 1
(HCNS column), it is still high enough and the material sufficiently
ordered, as to endorse the previous comment.
Fig. 2 displays the XRD patterns of the template-free synthe-
sized chiral PMOs at increasing chiral organic precursor loadings.
The presence of the characteristic diffraction at 2h = 0.8–0.9°, cor-
responding to the d100 basal plane of SBA-15-type materials, con-
firms the formation of a mesoporous structure for those solids.
These materials preserve the periodic structure even after template
P123 removal by washing with ethanol, related probably to the
beneficial action of hydrothermal treatment during the framework
consolidation.
As displayed in Table 1, a reduction in the BET surface area and
pore size diameter occurs as the chiral organic precursor loading is
increased. Additionally, and excepting the PMO-10 sample that
shows a slight decrease, the general trend points out to wall thick-
ness reinforcement as the pore size diameter declines, which is in
accordance with results previously described for other PMO mate-
rials [14]. The observed tendency may provide an idea of the
importance of the organic moiety in the final materials ordering.
FTIR analyses were collected, using the KBr buffer technique, on
a Mattson Infinity series apparatus in the wavelength range from
4000 to 400 cmÀ1 with a step size of 2 cmÀ1 and collecting 64 scans
for each analysis. The samples were also placed in a catalytic cham-
ber HVC-DPR (Harrick Scientific Company) where they were
heated at different temperatures under vacuum (<10–4 mbar) with
a 1.5 °C/min heating rate.
Solid-state 13C and 29Si MAS NMR experiments were performed
on a Varian Infinity 400 MHz spectrometer fitted with a 9.4 T mag-
net. These nuclei resonate at 100.53 and 79.41 MHz, respectively.
An H/X 7.5 mm MAS probe and ZrO2 rotors spinning at 6 kHz were
used. On CP experiments, the cross-polarization time was deter-
mined to guarantee the total proton polarization verifying the
Hartmann–Hann condition. For 13C acquisition,
of scans, repetition delay and contact time were 4.25
scans, 3 s and 1 ms, respectively. The 29Si CP experiments were
performed for 3000 scans, /2 pulse of 3.5 s and 15 s of repetition
p/2 pulse, number
l
s, 2000
p
l
time, while the contact period was 10 ms since cross-polarization
depends upon heteronuclear dipolar interaction, the greater dis-
tance the larger cross-polarization time. 13C and 29Si chemical
shifts were externally referenced to adamantane and tetramethyl-
silane, respectively.
2.4. Catalytic tests
Reaction tests for the asymmetric oxidation of sulfides were
carried out under a nitrogen atmosphere using standard Schlenk
techniques (Scheme 2). The PMO used as solid chiral ligand was
previously outgassed and dried in a Kugelrohr apparatus at
130 °C under vacuum (1 torr) overnight before being employed in
the catalytic tests. Inert conditions were ensured by passing a
continuous nitrogen stream through the reactor, which was main-
tained during the overall operation. Freshly distilled dichlorometh-
ane (50 mL) was then transferred into the reactor via syringe, and
the mixture was magnetically stirred. Titanium isopropoxide
(0.056 mmol) and 2-propanol (0.224 mmol) were added drop by
drop to the resultant suspension. The mixture was then aged for
2 h in order to promote the contact between the titanium species
and the chiral ligand sites present in the PMO material. After the
aging step, both cumyl hydroperoxide (CHP, 0.56 mmol) and
thioanisole (0.56 mmol) were added separately by dropping onto
the catalytic suspension. Sample aliquots were collected in order
to assess the evolution of the reaction. The mixture was allowed
to react for 24 h.
3. Results and discussion
The mesostructured organosilicas with chiral ligands incorpo-
rated into the framework were obtained following a new and easy
methodology, the procedure being represented in Scheme 1. Once

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R.A. Garcia et al. / Journal of Catalysis 274 (2010) 221–227
Table 1
Physico-chemical properties of chiral PMO.
Material
Organic %a
N2 adsorption analysis
X-ray diffraction (Å)
HCNS
b
c
d
e
f
ABET (m2 gÀ1
)
Dp (Å)
Vp (cm3 gÀ1
)
d100
a0
Wtg
% Nh
mmole tartramide/g materiali
S0
0
572
637
460
306
76
64.50
64.90
58.20
55.00
58.80
–
0.75
0.84
0.63
0.41
0.39
–
103.85
98.33
107.48
99.68
110.67
–
119.92
113.54
124.11
115.10
127.79
–
55.42
48.64
65.91
60.10
68.99
–
–
–
S10
S20
S50
S60
S70
10
20
50
60
70
1.76
4.53
4.04
1.65
–
0.63
1.62
1.44
0.59
–
–
a
b
c
d
e
f
Proportion of chiral tartramide precursor incorporated into the gel during the synthesis step in molar basis.
Specific surface area calculated by the BET method.
Pore size diameter calculated by the BJH method.
Total pore volume registered at P/P0 = 0.985.
Interplanar spacing.
Cell unit parameter calculated assuming hexagonal ordering.
Wall thickness calculated as Wt = a0 À Dp.
g
h
i
Calculated by elemental analysis.
Incorporation of the chiral functionality into the final material based on elemental analysis.
Fig. 1. N2 Adsorption–desorption isotherms and pore size distribution (inset) for
the synthesized chiral PMO materials.
Mesoscopic order is confirmed by TEM images (shown in Fig. 3) as
definitive evidence of the structure ordering achieved on these chi-
ral modified mesostructured materials. These samples show the
typical honeycomb structure from SBA-15-type mesostructured
materials.
Fig. 2. XRD patterns obtained for chiral PMO materials with SBA-15-like structure.
A key point in the chiral PMO one-pot synthesis lies in the
transamidation reaction between DMT and the organic tethering,
providing the mixture of the latter with BTSE the capability of
the assembly around micelles, in such a way the chiral silica for-
mation may take place. To check the formation of this amide pre-
cursor, FTIR analyses of the chiral PMO samples were acquired at
different treatment temperatures using a proper chamber as dis-
played in Fig. 4. At room temperature, an absorption band appears
at around 1640 cmÀ1, which could be assigned to an amide group
formation but also to physisorbed water. Subsequently, the tem-
perature was increased to 300 °C, and it was observed that the
intensity of the absorption band showed almost no decrease as
the outgassing temperature was increased, shifting to slightly low-
er wavenumbers, which undoubtedly supports the amide group
assigned to hydrogen-bonded SiOH groups perturbed by physically
adsorbed water, is seen. With the increase in the outgassing tem-
perature, the intensity of this band decreased and shifted to lower
wavenumbers because of dehydration and dehydroxylation at
higher temperatures in vacuum. Besides, the spectrum of the
PMO-0 reference material synthesized from pure BTSE, without
any chiral organic loading, showed complete absence of the signal
at 1640 cmÀ1 at high temperatures in vacuum, which confirms the
complete absence of adsorbed water in these conditions. Therefore,
FTIR analyses yielded insight into the inclusion of the chiral organic
species into the silica.
Accordingly, the incorporation of the organic species into the
framework of mesostructured material was definitely corrobo-
rated by the 13C NMR solid-state experiments. Fig. 5 shows the
peak assignments corresponding to the different functionalities
formation. Additionally, a broad adsorption at around 3300 cmÀ1
,

R.A. Garcia et al. / Journal of Catalysis 274 (2010) 221–227
225
factant elimination, revealing the chemistry of the surface modifi-
cation. The spectrum displays a main region centered at around
À70 ppm. This pattern corresponds to species containing the chiral
organic precursor, that is (AOA)3SiARASi(AOA)3, named Tn
groups, where R denotes the chiral and non-chiral organic group,
as previously confirmed by the 13C NMR solid-state experiments.
A large amount of cross-linked T3 surface species, compared to T2
and T1 species, is formed, indicating that the level of condensation
reached for these chiral materials is reasonably high. No presence
of Qn species is displayed in the spectrum, which confirms that no
carbonAsilicon bond cleavage occurred during the synthesis.
To evaluate the catalytic properties of the obtained chiral PMOs,
the asymmetric oxidation of thioanisole was employed as a test
reaction, using the chiral PMO as ‘‘solid” asymmetric ligand for
the induction of enantioselectivity into the final product (Scheme
2). Asymmetric sulfoxides are very useful auxiliaries in asymmetric
synthesis as chiral building blocks in multistep synthesis or as bio-
logically active compounds [28,29]. The best homogeneous condi-
tions were fixed for the reaction, so a molar combination of
Ti(OiAPr)4/chiral tartramide/i-PrOH 1:4:4 was chosen (Kagan cata-
lyst) as initial conditions for the heterogeneous oxidation reac-
tions. Cumyl hydroperoxide was used as oxidizing agent because
of the better performance of this oxidant in asymmetric sulfoxida-
tion, with the initial Ti(OiAPr)4/CHP molar ratio of 1:20. Under
these conditions, and for comparison purposes, the reaction
employing the homogeneous catalytic system formed by titanium
isopropoxide, L-(+)-diisopropyl tartrate and isopropanol was
accomplished. This catalytic system led to a very high substrate
conversion after reacting for 24 h (92%), inducing an enantiomeric
excess over the final product of 94% ee. With regard to the hetero-
geneous system presented in this work, the selected sample to car-
ry out the test reaction was the PMO-50 material, due to the high
tartramide incorporation in its structure (see Table 1), and to the
adequate textural properties showed by this sample. A blank reac-
tion was performed, as reference, in the presence of chiral PMO-50
but in the absence of any titanium source. In this way, neither
appreciable substrate conversion nor induced enantioselectivity
was accomplished, even for a long reaction time of 24 h. The influ-
ence of different variables on the activity and enantioselectivity of
the chiral PMO has been studied: two of the more crucial ones are
CHP/Ti and DMT/Ti molar ratio as is shown in Fig. 6. The CHP/Ti
molar ratio was the first optimized variable in order to reduce
the sulfone formation during the reaction, keeping constant the
other molar ratio in the homogeneous conditions values for all
the experiments performed. This is a crucial operating variable,
since slight variations cause large differences in the sulfone con-
centration obtained as secondary reaction product (Scheme 1).
These studies have established the optimal CHP/Ti molar ratio
around 10/1, higher values lead to a dramatic decrease in the sulf-
oxide formation due to the higher amount of sulfone obtained.
Once the CHP/Ti molar ratio was fixed, the influence of the tar-
trate/titanium molar ratio on the activity and enantioselectivity
of the reaction was checked. This variable influences on the distri-
bution of the population of different catalytic species in the reac-
tion media. It appears that there is an optimal value for the 16:1
ratio. Below this value, enantioselectivity decreases rapidly, be-
cause of a deficiency in chiral ligand, whereas beyond this molar
concentration, both catalytic activity and enantioselectivity dimin-
ish, probably because of a saturation of the coordination positions
to the metallic center, making the access to reactants difficult.
With regard to the catalytic behavior of the chiral PMO-50
material prepared, increasing sulfoxide yields are achieved for
longer reaction times, while the enantiomeric excess induced into
the final sulfoxides is kept constant during the overall reaction pro-
cess around 30% ee (60% and 71% sulfoxide yield at 3 and 24 h,
respectively), being similar to the values achieved with other
Fig. 3. TEM images recorded for sample PMO-50.
Fig. 4. FTIR spectra collected for sample PMO-50 at different temperatures.
incorporated into the silica-supported tartramide chiral species.
The lower shielding chemical shift at about 180 ppm corresponds
to quaternary carbons at the carbonyl groups, C@O, from the syn-
thesized amide, though however the presence of two peaks de-
notes different tartramide environments. The signal centered at
around 70 ppm corresponds to two chiral carbon atoms bonded
to hydroxyl groups, CHAOH. This fact and the complete absence
of the 130 and 104 ppm signals corresponding to the O-isopropyl-
idene protecting group indicate that the deprotection of the chiral
precursor ligand has been totally achieved. The signals centered at
32 and 51 ppm can be assigned to NCH3 and NCH2, respectively,
which denotes the presence of the nitrogen atom in the material.
Also, the two sharp peaks centered at 10 and 15 ppm were as-
signed to SiACH2 and SiACH2ACH2, respectively. The spectrum
shows two peaks centered at 20 and 59 ppm that could be related
to the presence of the residual ethoxy groups coming from non-
hydrolyzed ethoxide functionalities. Nevertheless, all these data
confirm the presence of the immobilized tartramide organic pre-
cursor in the inorganic material framework.
Finally, 29Si solid-state NMR was used to corroborate the pres-
ence of the chiral organic precursor and BTSE. The inset in Fig. 5
shows the 29Si NMR spectrum of the chiral PMO-50 after P123 sur-

226
R.A. Garcia et al. / Journal of Catalysis 274 (2010) 221–227
Fig. 5. 13C CP-MAS solid-state NMR spectrum of the chiral PMO-50 sample. In the inset, the 29Si CP-MAS solid-state NMR spectrum corresponding to the same sample is
sketched. Asterisks correspond to the residual ethoxy functionalities.
Scheme 2. Catalytic test: asymmetric oxidation of methyl phenyl sulfide (thioanisole).
Fig. 6. Representation of the effect of CHP/Ti (a) and DMT/Ti (b) molar ratio influence on the yield and the enantiomeric excess in the thioanisole asymmetric oxidation.
heterogeneous chiral precursors either on the same or on different
asymmetric synthesis [11,14]. On the other hand, the chiral PMO
has been successfully reused as solid chiral ligand in the sulfoxida-
tion reaction. In this case, lower sulfoxide yields are achieved,
whereas the induced enantioselectivity over the sulfoxide is main-
tained at a similar level to that obtained for the fresh catalyst. These
results confirm the heterogeneous behavior of the organic chiral
tartramide moieties as chiral periodic mesoporous organosilica.

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227
4. Conclusions
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As conclusions, we have demonstrated the successful synthesis
of a chiral PMO SBA-15-type material synthesis, from 100% purely
organic monomers in the absence of TEOS, by an easy one-pot
methodology, in which the chiral and non-chiral organosilica pre-
cursors are assembled, both together, around the non-ionic surfac-
tant. Chiral periodic mesoporous solid materials with a precursor
mixture ratio BTSE/DMT as high as 50:50, without any measurable
decline in the textural properties such as the materials’ ordering,
have been synthesized. Additionally, large incorporation of chiral
functionalities up to 1.62 mmole tartramide/g has been reached.
Likewise, FTIR and NMR solid-state techniques confirm the pres-
ence of the chiral organic precursor in the SBA-15-type material
framework. The thioanisole asymmetric oxidation reaction has
been used to validate the heterogeneously synthesized catalyst
activity, achieving enantiomeric excess (ee) and yield to sulfoxide
up to 30% and 71%, respectively. Finally, this approach afford a
new synthesis route for researchers trying to gain understanding
on the investigation into heterogeneous asymmetric synthesis,
glimpsing the potential applications of this method from the point
of view of incorporating not only tartramide moieties but other
homogeneous chiral auxiliaries into the three-dimensional meso-
structure of organic–inorganic silica support (chiral PMOs materi-
als) in only one step, which would mean
a higher overall
throughput than the more tedious procedures previously reported,
in which the organic chiral precursor has to previously prepared,
separated and purified and subsequently added in a second step
to the inorganic support synthesis media. Thus, not only Sharpless
chiral auxiliary, but BINOL and derivatives, Mn-Salen, etc. are sus-
ceptible to be heterogeneized following this methodology, being
part of the PMO silica wall structure.
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Acknowledgment
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The financial support of the Spanish government (CTQ2008-
05909/PPQ) is gratefully acknowledged.