The nanocomposites of SO3H-hollow-nanosphere and chiral amine for asymmetric aldol reaction

Article abstract of DOI:10.1039/b909002a

The nanocomposites formed by SO₃H-hollow-nanospheres and chiral amines are highly efficient catalysts for the direct asymmetric aldol reaction of cyclohexanone and 4-nitrobenzaldehyde. The catalyst showed 91% yield with 96% ee under optimized reaction conditions. SO₃H-hollow-nanospheres were synthesized by oxidation of thiol-hollow-nanospheres, which were fabricated through a one-pot co-condensation of 1,2-bis(trimethoxysilyl)ethane and 3-mercaptopropyltrimethoxysilane around F127 micelles in the presence of NaOAc. Chiral amines could be combined with SO₃H-hollow-nanospheres through facile electrostatic interactions. The obtained nanocomposites showed a much higher reaction rate than the catalyst formed from the combination of chiral amine and SO₃H-mesoporous-organosilica (ribbon shaped particles with particle size of tens of micrometres) in the direct asymmetric aldol reaction. This is mainly attributed to the hollow spherical morphology and nano-scale particle size (16-20 nm) of the SO₃H-hollow-nanospheres. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b909002a

www.rsc.org/materials
Volume 19 | Number 45 | 7 December 2009 | Pages 8497–8692
Green Materials
ISSN 0959-9428
PAPER
QihuaYang et al.
FEATURE ARTICLE
Nanocomposites of SO H-hollow-
nanospheres and chiral amines as
catalysts for asymmetric aldol reactions silver to semiconductors
Steven M. Howdle et al.
3
Deposition in supercritical fluids: from

PAPER
www.rsc.org/materials | Journal of Materials Chemistry
The nanocomposites of SO H-hollow-nanosphere and chiral amine for
3
asymmetric aldol reaction†‡
Jinsuo Gao,x Jian Liu,x Shiyang Bai, Peiyuan Wang, Hua Zhong, Qihua Yang* and Can Li*
Received 6th May 2009, Accepted 16th June 2009
First published as an Advance Article on the web 16th July 2009
DOI: 10.1039/b909002a
The nanocomposites formed by SO H-hollow-nanospheres and chiral amines are highly efficient
3
catalysts for the direct asymmetric aldol reaction of cyclohexanone and 4-nitrobenzaldehyde. The
3
catalyst showed 91% yield with 96% ee under optimized reaction conditions. SO H-hollow-
nanospheres were synthesized by oxidation of thiol-hollow-nanospheres, which were fabricated
through a one-pot co-condensation of 1,2-bis(trimethoxysilyl)ethane and 3-
mercaptopropyltrimethoxysilane around F127 micelles in the presence of NaOAc. Chiral amines could
3
be combined with SO H-hollow-nanospheres through facile electrostatic interactions. The obtained
nanocomposites showed a much higher reaction rate than the catalyst formed from the combination of
chiral amine and SO H-mesoporous-organosilica (ribbon shaped particles with particle size of tens of
3
micrometres) in the direct asymmetric aldol reaction. This is mainly attributed to the hollow spherical
morphology and nano-scale particle size (16–20 nm) of the SO
3
H-hollow-nanospheres.
Introduction
triblock copolymer micelles with a core–shell-corona structure) or
2 2
special reagents (e.g. diethoxydimethylsilane [Me Si(OEt) ]) are
Recently nanoparticles have been shown to be excellent supports
for catalysis because of the short diffusion lengths as a result of
1
small nanoparticle sizes. Among them, hollow nanospheres with
needed for the synthesis of silica hollow nanospheres with
a uniform size distribution. In view of their application, e.g.
catalysis, hollow nanospheres with functionality are generally
3d,7
low densities and high thermal and mechanical stability may be
potential catalytic materials. Compared with bulk particles, only
a limited number of papers has reported the application of
hollow nanospheres in catalysis probably due to the difficulty of
necessary.
However, many of the hollow spheres described
above lack the functionalities, and often have a rather large
particle size ranging from at least 50 nm to micrometres. It is
necessary to develop a methodology for the synthesis of hollow
nanospheres that permits precise control of the particle size and
easy tuning of the functionalities.
2
the synthesis of hollow nanospheres.
Uniform hollow nanospheres can be prepared through tem-
plating approaches using colloidal crystalline or polymer micelles
In this paper, thiol-hollow-nanospheres (SH-HNS) with
particle sizes of 16–20 nm were facilely synthesized in NaOAc
aqueous solutions with F127 serving as a single micelle template
3–6
as the templates. In this case, the hollow nanospheres with
3–5
uniform particle sizes of typically 10 to 500 nm were fabricated.
Colloidal crystalline templates based on spherical nanoparticles
8
based on our previous work. By subsequent oxidation of
3
4
5
including polymers, inorganic oxides, and metals have been
applied for the synthesis of hollow nanospheres with particle sizes
larger than 100 nm. Polymer micelles are used for the synthesis of
2 2 3 3
SH-HNS by H O , SO H-hollow-nanospheres (SO H-HNS)
were obtained, which exhibited higher catalytic activity than
Nafionꢀ NR50 in the esterification of lauric acid with ethanol,
suggesting the successful incorporation of the sulfonic acid
groups in the hollow-nanospheres.
6
silica hollow spheres with diameters less than 100 nm. However,
the template micelles are unstable during the synthesis and the
formation of the second-order or higher-order aggregates cannot
be avoided. Special triblock copolymer micelles (such as ABC
Recently, metal-free chiral organic molecules such as amino
acids have been demonstrated for their potential applications in
9,10
the field of asymmetric catalysis.
Because of the easy purifi-
cation of the product and the possible recovery and reuse of the
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023,
P. R. China. E-mail: yangqh@dicp.ac.cn; canli@dicp.ac.cn; Web:
http://www.hmm.dicp.ac.cn; http://www.canli.dicp.ac.cn; Fax: +86-411-
catalyst, much research endeavor has been paid on the devel-
11
opment of organocatalyst-based chiral solids. The chiral
diamine in combination with protonic acid-containing materials,
such as heteropolyacids and ion-exchange polymers, was
demonstrated to be an efficient catalyst in asymmetric catalysis
8
4694447; Tel: +86-411-84379552; +86-411-84379070
This paper is part of a Journal of Materials Chemistry theme issue on
†
Green Materials. Guest editors: James Clark and Duncan Macquarrie.
Electronic supplementary information (ESI) available: Photograph of
11h,i
involving aldol and Michael addition reactions.
The previous
‡
separation of the catalyst, Nitrogen sorption measurement of
functionalized hybrid hollow nanosphere and nanocomposites, TEM
studies showed that the protonic acid-containing materials had
an important influence on the catalytic properties of the chiral
images and SEM image of SO
3
H-PMO10, and TEM images of
1
nanocomposites, FT-IR of SO H-HNS10, H NMR of the reaction
diamine. The efficient solid acid catalyst, SO
3
H-hollow-nano-
3
spheres which have enough anchoring sites (acid exchange
+
capacity of 0.48 mmol H g ), unique morphology and high
solution. See DOI: 10.1039/b909002a
x These authors contributed equally to this work.
ꢀ1
8
580 | J. Mater. Chem., 2009, 19, 8580–8588
This journal is ª The Royal Society of Chemistry 2009

mechanical and thermal stability may be desirable counterpart
materials for chiral diamines. Through acid–base interactions of
Formation of chiral solid catalysts through acid–base
interactions
chiral amines and SO H-hollow-nanospheres, the nano-
3
Desired amounts of SO
3
H-HNS10 or SO
3
H-PMO10 with a total
Cl (5 mL) solution
composite obtained was used as a solid chiral catalyst in the
direct asymmetric aldol reaction of cyclohexanone and 4-nitro-
acid content of 0.16 mmol were added to a CH
2
2
containing chiral diamine PCYDN (0.048 g, 0.24 mmol). The
mixture was stirred overnight at room temperature. The solid
material was separated by filtration and washed sequentially with
benzaldehyde. For comparison, SO
with 2-D hexagonal mesostructure and ribbon-like
morphology was also used as counterpart material for chiral
diamines. The catalytic results showed that SO H-hollow-
nanosphere was a better counterpart material than the SO H-
3
H-mesoporous-ethanesilica
a
2 2 2 2
CH Cl , ethanol, and CH Cl . The solid was dried under vacuum
3
at room temperature to give the chiral solid catalysts. The
3
corresponding catalysts synthesized using SO H-HNS10
3
mesoporous-ethanesilica, which was probably due to the unique
hollow spherical morphology with particle sizes in the nanoscale.
The hollow nanospheres functionalized with catalytically active
sites may have potential applications in the field of heteroge-
neous catalysis.
and SO H-PMO10 as counterpart materials were denoted
3
as PCYDN@SO
respectively.
3 3
H-HNS10 and PCYDN@SO H-PMO10,
Characterization
X-Ray diffraction (XRD) patterns were recorded on a Rigaku
RINT D/Max-2500 powder diffraction system using Cu Ka
radiation of 0.15406 nm wavelength. The nitrogen sorption
experiments were performed at 77 K on a Micromeritrics ASAP
Experimental
All materials were of analytical grade and used as received without
any further purification. Triblock copolymer EO106PO EO
70
106
(
(
(
F127), EO70PO20EO70 (P123) and 1,2-bis(trimethoxysilyl)ethane
BTME) were purchased from Sigma-Aldrich Company Ltd.
USA). 3-Mercaptopropyltrimethoxysilane (MPTMS) was from
2
020. The Brunauer–Emmett–Teller (BET) specific surface areas
were calculated using adsorption data at a relative pressure range
of P/P
0
¼ 0.05–0.25. Pore size distributions were derived from the
Gelest, Inc. (Germany). Other reagents were obtained from
Shanghai Chemical Reagent. Inc., of the Chinese Medicine
Group. N,N-Dipropyl cyclohexanediamine (PCYDN) was
adsorption branch using a Barrett–Joyner–Halenda (BJH)
method. The total pore volumes were estimated from the
amounts adsorbed at a relative P/P of 0.99. Transmission elec-
0
10a
synthesized according to the published method. SO
3
H-meso-
2
tron microscopy (TEM) was performed using a FEI Tecnai G
porous-ethanesilica (SO H-PMO10) was prepared according to
3
Spirit at an acceleration voltage of 120 kV. Before examination,
the samples were dispersed in anhydrous ethanol and deposited
on a holey carbon film on a Cu grid. Scanning electron micros-
copy (SEM) was undertaken on a FEI Quanta 200F scanning
electron microscope operating at an accelerating voltage of
12a
our previous report.
Synthesis
1
–30 kV. The X-ray photoelectron spectroscopy (XPS) was
Synthesis of thiol functionalized ethanesilica hollow nanospheres
performed using a Shimadzu KROTAS AMICUS spectrometer
equipped with a monochromated Mg Ka X-ray source. UV
Raman spectra were recorded on a homemade UV Raman
spectrometer. The 244 nm laser lines from Kimmon were chosen
as an excitation source. The power of the UV laser lines was
below 4.0 mW. The wave number of Raman spectra was cor-
(
SH-HNS). In a typical synthesis, 0.80 g of F127 and 1.38 g
(
16.80 mmol) of sodium acetate were dissolved in 28 mL of
ꢁ
deionized water (600 mM NaOAc) at 20 C under vigorous
stirring. When the copolymer was dissolved, the mixture of
BTME and MPTMS was added under stirring. The molar
composition of the mixture was Si/F127/NaOAc/H
2
O ¼ 1 :
ꢀ
1 1
ꢁ
rected, and the spectra error was ꢂ2 cm . H NMR spectra were
0
.0063 : 1.68 : 155.6. The resultant mixture was stirred at 20 C
ꢁ
recorded in CDCl on a 400 MHz NMR spectrometer with TMS
3
for 24 h and aged at 100 C under static conditions for 24 h. The
solid product was recovered by filtration and air-dried at room
temperature overnight. Finally, the surfactant was extracted by
refluxing 1.0 g of as-synthesized material in 200 mL of ethanol
containing 1.5 g of concentrated aqueous HCl solution for 24 h.
The surfactant-free samples were denoted as SH-HNSn, where n
13
as the internal standard. C (100.5 MHz) CP MAS NMR
experiments were recorded on a Varian infinity-plus 300 spec-
trometer with the following experimental parameters: 4.00 kHz
spin rate; 2.00 min contact time; 5.00 s pulse delay.
(
n ¼ 10, 20, 30, 40) is the mol% ratio of MPTMS/(BTME +
Catalytic reactions
MPTMS) in the initial mixture.
General procedure for the esterification reaction. The reaction
was carried out in a 50 mL two-necked round flask, which was
placed in a thermostactic bath with a reflux condenser and
Synthesis of SO
spheres (SO H-HNS). 1.0 g of SH-HNSn was dispersed in 40 g of
H O (30 wt%). The resultant mixture was stirred for 12 h at 298
3
H functionalized ethanesilica hollow nano-
3
ꢁ
a magnetic stirrer bar. The catalyst was pretreated at 120 C for
2
2
K. After filtration, the solid material was stirred in 200 mL of
.1 M H SO for 12 h at room temperature for acidification.
6 h under vacuum before the catalytic reaction. Lauric acid
(2 mmol) and ethanol (40 mmol) were added to the flask con-
taining 0.088 mmol of catalyst under an argon atmosphere. The
0
2
4
After being thoroughly washed with deionized water, the solid
ꢁ
ꢁ
product was dried at 60 C overnight. The sample was denoted as
mixture was stirred at 80 C. Reaction products were collected by
SO H-HNSn. The acid exchange capacities of SO
3
3
H-HNSn were
a syringe in regular intervals and analysed using a precalibrated
gas chromatograph (Agilent 6890) equipped with an FID
12a
determined by acid–base titration method.
This journal is ª The Royal Society of Chemistry 2009
J. Mater. Chem., 2009, 19, 8580–8588 | 8581

detector and OV-1 capillary column (30 m ꢃ 0.25 mm ꢃ
0
.25 mm). Tetradecane was used as internal standard.
Typical procedure for the direct asymmetric aldol reaction.
Desired amounts of solid catalyst (chiral amine amounts of
.0125 mmol) were added to a suspension of cyclohexanone
0.1 mL) and H O (0.1 mL). The mixture was stirred for 20 min
followed by the addition of 4-nitrobenzaldehyde (0.019 g,
.125 mmol). The resulting mixture was stirred at room
temperature for 12 h. After centrifugation at the rate of
000 r/min (Fig. S1 in ESI‡), the organic portion was concen-
0
(
2
0
8
trated and purified by column chromatography on silica gel to
afford the desired product. The enantiomeric excess was deter-
mined by HPLC on a chiralpak AD-H column at 254 nm
ꢁ
ꢀ1
(
(
hexane/isopropanol 80 : 20), 25 C, 0.5 mL min ; t ¼ 24
R
major), tR ¼ 31 (minor). After centrifugation, the catalyst was
separated and washed with ethyl ether (4 ꢃ 4 mL). The catalyst
could be directly used for the next run after drying under
vacuum.
Results and discussion
Structure and morphology of SH-HNSn and SO H-HNSn
3
The TEM images of SH-HNSn are shown in Fig. 1a–d. All
SH-HNSn samples were hollow nanospheres irrespective of the
initial molar fraction of MPTMS. The hollow nanospheres have
particle sizes in the range 16–20 nm with wall thicknesses of
about 3–4 nm. The aggregation of the nanospheres could also be
observed. The textural properties of SH-HNSn were analyzed by
a N2 sorption technique. All samples show typical type IV
isotherms, suggesting that these samples have mesopores
(
Fig. 2A). It is noteworthy that there are two capillary conden-
sation steps in the adsorption isotherm for SH-HNS10,
SH-HNS20 and SH-HNS30, suggesting that these samples have
two types of mesopore. The diameter of the primary mesopore is
in the range 6.5–5.9 nm, which could be ascribed to the inner void
of the hollow nanosphere (Fig. 2B and Table 1). The secondary
mesopore has pore diameter of 32 to 34 nm, corresponding to the
8
interparticle void formed by the packing of the nanospheres.
Unlike SH-HNSn (n ¼ 10, 20, 30), SH-HNS40 only shows one
capillary condensation step in the adsorption isotherm, which is
from the intervoid space among the nanospheres. As shown in
Table 1, the BET surface area of SH-HNSn decreases with the
increase in the molar fraction of MPTMS.
Fig. 1 TEM images of thiol- and sulfonic-functionalized organic–inor-
ganic hybrid hollow nanospheres: (a) SH-HNS10; (b) SH-HNS20; (c)
SH-HNS30; (d) SH-HNS40; (e) SO
SO H-HNS30; (h) SO H-HNS40.
3 3
H-HNS10; (f) SO H-HNS20; (g)
3
3
The –SH group could be easily oxidized into –SO
3
H as
H-hollow-nano-
H-HNS) were successfully prepared by oxidation of
SH-HNS using H as an oxidant. The TEM images of SO H-
HNSn are shown in Fig. 1e–h. The TEM image of SO H-HNS10
12b
demonstrated by the previous report.
spheres (SO
SO
3
3
degree of SO
3
H-HNSn (n ¼ 10, 20, 30) is greatly improved,
2
O
2
3
probably due to the repulsion of the negatively charged nano-
spheres. Only bulk particles were observed in the TEM image of
3
shows the existence of hollow nanospheres. In addition to the
existence of hollow nanospheres, spherical aggregates with
particle sizes in the range 80–160 nm could be also observed in
the TEM images of SO H-HNS20 and SO H-HNS30 (as noted
SO
3
H-HNS40. The existence of spherical particles in the TEM
images of SO H-HNS20 and SO H-HNS30, and complete loss of
3
3
hollow nanosphere morphology of SO H-HNS40 show that the
3
nanostructure of SH-HNSn synthesized with a molar fraction of
MPTMS larger than 10% is unstable under oxidation conditions.
This is probably due to the fact that the transformation of –SH
3
3
by the circle in Fig. 1f, g). The particle size and wall thickness of
hollow nanospheres for samples SO
3
H-HNSn (n ¼ 10, 20, 30) are
almost the same as the parent SH-HNSn (n ¼ 10, 20, 30).
to –SO
3
H in the shell makes the hollow spherical morphology
Compared with the samples before oxidation, the dispersion
unstable during the oxidation process.
8
582 | J. Mater. Chem., 2009, 19, 8580–8588
This journal is ª The Royal Society of Chemistry 2009

Fig. 2 (A) Nitrogen adsorption and desorption isotherms and (B) BJH
pore size distribution curve for the thiol-functionalized organic–inor-
ganic hybrid hollow nanospheres: (a) SH-HNS10; (b) SH-HNS20; (c)
SH-HNS30; (d) SH-HNS40.
Fig. 3 (A) Nitrogen adsorption and desorption isotherms and (B) BJH
pore size distribution curve for the sulfonic acid-functionalized organic–
3 3
inorganic hybrid hollow nanospheres: (a) SO H-HNS10; (b) SO H-
HNS20; (c) SO H-HNS30; (d) SO H-HNS40.
3
3
2 3
Almost no N could be adsorbed into SO H-HNS40, suggesting
The nitrogen sorption isotherms of SO
3
H-HNSn (n ¼ 10,
the particles observed in the TEM image of SO H-HNS40 are
3
2
0, 30) are of type IV (Fig. 3A). SO H-HNS10 exhibits a similar
3
nonporous. The results from TEM and N sorption show that
2
N sorption isotherm to SH-HNS10. The existence of two kinds
2
the stability of the nanostructure of SH-HNS decreases with the
increase in the molar fraction of MPTMS.
of mesopores could be clearly observed from the pore size
distribution curve of SO H-HNS10. Compared with SH-HNS10,
3
the pore diameter of the primary pore (6.5 nm from the inner
void of the hollow nanospheres) does not change (Fig. 3B). The
3
Composition of SH-HNSn and SO H-HNSn
3
secondary mesopore of SO H-HNS10 (23 nm) is slightly smaller
than that of parent material SH-HNS10 (32 nm). This is
The XPS technique was used for the characterization of
reasonable because the secondary mesopore is from the inter-
SH-HNS20 and SO H-HNS20 (Fig. 4). The XPS spectrum
3
particle void among the nanospheres. The N
2
sorption result
of SH-HNS20 displays only one peak with a binding energy of
166 eV for the S2p electron of –SH. A dominant peak with
a binding energy of 172 eV was observed in the XPS spectrum of
further confirms that the hollow nanostructure of SH-HNS10
synthesized with a low molar fraction of MPTMS is stable during
the oxidation process. SO H-HNS20 and SO H-HNS30 have
3
3
SO H-HNS20, which could be assigned to the binding energy for
3
ꢀ
two capillary condensation steps in the adsorption isotherms.
the S2p electron of –SO3 species. A very weak peak at 166 eV
The first hysteresis loop at a relative pressure P/P of 0.4–0.75 is
0
(corresponding to –SH) was observed for the S2p binding energy.
The above results confirm that most –SH could be transformed
of H1 type and the second hysteresis loop at a relative pressure
P/P
0
of 0.8–1.0 is of H3 type, suggesting the co-existence of two
to –SO H by the oxidation method. The UV-Raman spectrum of
3
types of mesostructure in these two samples. Combined with the
TEM results, the first mesopore, in the range 6.1–5.9 nm, is from
the cavities of the hollow nanospheres and the secondary meso-
pore, in the range 11–13 nm, is from the porous spherical
the SO H-HNS10 is displayed in Fig. 5. The symmetric and
3
asymmetric vibration modes of –SO H were clearly observed at
3
ꢀ1
1045 and 1165 cm respectively in the UV-Raman spectrum of
SO H-HNS10. The CH vibrations of bridging –CH CH – and
2
3
2
particle. For samples SO
3
H-HNSn (n ¼ 10, 20, 30), the BET
–CH CH CH SO H species in SO H-HNSn appeared at
3
2
2
ꢀ
2
3
1
surface area is obviously increased after oxidation (Table 1).
1411 cm . The titration results show the acid exchange
Table 1 Physical and textural properties of organic–inorganic hybrid hollow nanospheres, sulfonic functionalized PMOs, and nanocomposites of
SO H functionalized hollow nanospheres and chiral amines
3
BET surface
Pore
volume (cm g
Primary
pore (nm)
Secondary
pore (nm)
Acid exchange capacities
ꢀ1
2
area (m g
ꢀ1
3
ꢀ1
a
)
b
b
+
(mmol H g
Sample
)
)
SH-HNS10
SH-HNS20
SH-HNS30
SH-HNS40
570
435
335
231
670
507
397
0.36
694
639
549
1.68
1.23
1.38
1.74
1.45
0.81
0.51
0.02
0.85
1.37
0.71
6.5
6.5
5.9
—
6.5
6.1
5.2
—
32
27
34
64
23
13
11
—
—
19
—
—
—
—
—
0.48
1.13
1.54
1.97
0.39
—
SO
SO
SO
SO
SO
3
3
3
3
3
H-HNS10
H-HNS20
H-HNS30
H-HNS40
H-PMO10
c
6.8
6.5
6.8
PCYDN@ SO
PCYDN@ SO
3
H-HNS10
H-PMO10
3
—
a
b
The total pore volume determined at the relative pressure of 0.99. Calculated from the adsorption branch by using the BJH method. Ref. 12a.
c
This journal is ª The Royal Society of Chemistry 2009
J. Mater. Chem., 2009, 19, 8580–8588 | 8583

hollow nanospheres. The catalytic activity of SO H-HNSn
3
(
n ¼ 10, 20, 30) is higher than that of Nafionꢀ NR50, showing
that the sulfonic acid functionalized hollow nanospheres are
efficient solid acid catalysts. The activity of SO
H-HNSn (n ¼ 10,
0, 30) decreases with the increasing amount of sulfonic acid
groups in the hollow nanospheres. This is probably due to the
fact that some of the –SO H in the shell cannot be accessed by the
reactants during the catalytic process. The activity of SO H-
3
2
3
3
HNS40 is the lowest among all the materials. This could be
related to its nonporous textural properties.
Characterization of the nanocomposite formed by the acid–base
3
interaction of SO H-HNS and chiral diamine
Fig. 4 X-Ray photoelectron spectra (XPS) for thiol- and sulfonic-
functionalized organic–inorganic hybrid hollow nanospheres.
It has been reported that the chiral amine could combine with
protonic acids, such as TfOH, MsOH, p-TsOH, polyoxometalate
acids and polystyrene/sulfonic acids, to form efficient asymmetric
aldol reaction catalysts. SO
activity, was chosen as the counterpart material for the chiral
amine to form the chiral nanocomposite, PCYDN@SO H-
HNS10, for the asymmetric catalysis. The C CP MAS NMR
spectra of SO H-HNS10 and PCYDN@SO H-HNS10 are dis-
played in Fig. 7. For SO H-HNS10, the signals at 16, 19, and
5 ppm could be assigned to C , C , and C from propylsulfonic
3
H-HNS10, with the highest catalytic
3
13
3
3
3
1
2
3
5
1
2
3
13
groups (-Si-C H C H C H SO H), respectively. The signal at
3
2
2
2
1
3
5
4
.7 ppm is ascribed to the bridging –CH CH –. The peak at
2 2
9 ppm is from the methoxy of unhydrolyzed silane precursors,
14
due to the mild conditions of the synthesis. The peaks at 58 and
1 ppm could be assigned to the ethoxy group formed during the
surfactant extraction process. Compared with SO H-HNS10,
a new peak at 11 ppm appears in the C CP MAS NMR spec-
trum of PCYDN@SO H-HNS10, which can be ascribed to the
methyl carbon atoms of propyl in the PCYDN group. The
7
3
13
Fig. 5 UV-Raman spectrum of sulfonic-functionalized organic–inor-
3
ganic hybrid hollow nanospheres, SO H-HNS10.
3
11a
13
peak at 49 ppm cannot be observed in the C CP MAS NMR
3
capacities for SO H-HNSn are in the range 0.48–1.97 mmol
spectrum of PCYDN@SO H-HNS10, suggesting the further
3
+
H g (Table 1).
ꢀ1
condensation of the unhydrolyzed silane precursor during the
acid–base interaction process in the presence of an organic base,
PCYDN. The signals for the bridging –CH CH – and propyl
The catalytic performance of SO H-HNSn was evaluated in
3
the esterification of lauric acid with ethanol. Fig. 6 shows time
profiles for the esterification of lauric acid with ethanol catalyzed
2
2
13
sulfonic acid group remain unchanged in the C CP MAS NMR
spectrum of PCYDN@SO H-HNS10.
by SO H-HNSn. The product yield increases with the reaction
3
3
3
time, suggesting that the –SO H group is incorporated into the
FT-IR was also used to characterize the chemical composition
of the chiral amine (Fig. S2 in ESI‡). The peaks at 2935 and
ꢀ1
2
861 cm
3
in the FT-IR spectra of SO H-HNS10 and
Fig. 6 Esterification of lauric acid with ethanol catalyzed by SO
HNSn (n ¼ 10, 20, 30, 40): (a) SO H-HNS10; (b) SO H-HNS20; (c)
SO H-HNS30; (d) SO H-HNS40; (e) Nafion.
3
H-
1
3
3
3
Fig. 7
3
C CP MAS NMR spectra of SO H-HNS10 and PCYDN@-
3
3
SO
3
H-HNS10.
8
584 | J. Mater. Chem., 2009, 19, 8580–8588
This journal is ª The Royal Society of Chemistry 2009

PCYDN@SO H-HNS10 were assigned to the CH stretching of
3
Table 2 The solvent effect on the direct asymmetric aldol reaction
between cyclohexanone and 4-nitrobenzaldehyde
a
14
CH of propyl and Si–CH –CH –Si. The CH deformation of
2
2
2
vibration propyl and Si–CH –CH –Si were observed at 1450 and
2
2
ꢀ
1 14
297 cm . After the chiral amine was introduced, a new peak
1
ꢀ1
appeared at 1465 cm , which was ascribed to the characteristic
15,16
CH deformation vibration of diaminocyclohexene.
IR result together with the NMR result confirms the successful
interaction of SO H-hollow-nanospheres with a chiral diamine.
For comparison, SO H-PMO10 with acid exchange capacities
of 0.39 mmol H g was also used as a counterpart material for
The FT-
b
,
c d
ee
Syn/anti (%) anti
3
Yield
Solvent (%)
c
Catalysts
3
+
ꢀ1
e
H-HNS10 Neat
PCYDN@SO
3
95
Trace
10/90
n.d
90
n.d
91
93
92
92
93
96
92
94
94
95
n.d
—
—
the chiral diamine. SO H-PMO10 with a highly ordered 2-D
3
DMF
CH CN 35
hexagonal mesostructure has a BET surface area of ca.
3
17/83
11/89
7/93
12/88
11/89
8/92
12/88
9/91
15/85
13/87
n.d
2
94 m g , a total pore volume of 0.85 cm g and a pore
ꢀ1
3
ꢀ1
THF
CHCl
CH Cl
2 2
41
40
47
6
3
diameter of 6.8 nm (Fig. S3–S5 in ESI‡ and Table 1). The
material with a ribbon-like morphology has a particle size of tens
Toluene 77
of micrometres (Fig. S3 in ESI‡). The TEM and N
isotherm show that the morphology of PCYDN@SO
and PCYDN@SO H-PMO10 are almost the same as their
parent materials (Fig. S4, S6 in ESI‡). The surface area and pore
volume of the PCYDN@SO H-HNS10 and PCYDN@SO H-
2
sorption
H
2
O
75
91
24
e
PCYDN@SO
3
H-PMO10 Neat
CH Cl
3
H-HNS10
2
2
3
Toluene 49
H O
2
52
Trace
No reaction
No reaction
PCYDN
Neat
Neat
Neat
3
3
SO
SO
3
H-HNS10
H-PMO10
—
—
PMO10 were lower than the parent materials, suggesting the
incorporation of the chiral diamine. Elemental analysis was used
to determine the content of chiral amine in the materials. The
molar ratio of sulfonic acid and chiral diamine in
3
a
Reaction conditions: catalysts (10 mol% of chiral diamine),
cyclohexanone (0.1 mL), solvent (0.4 mL), 4-nitrobenzaldehyde
b
0.125 mmol), RT, 12 h. Isolated yield after separation by silica gel.
(
c
d
Determined by HPLC. The products had a 1 S,2R configuration.
0
PCYDN@SO H-PMO10 (1.44) was higher than in PCYDN@
3
e
SO
SO
3
H-HNS10 (1.32). This may be caused by high accessibility of
3
Chiral diamine content in PCYDN@SO H-HNS10 and PCYDN@
+
SO H-PMO10 is 0.27 and 0.36 mmol H g , and molar ratio of
3
+
H /chiral diamine is 1.44 and 1.32, respectively.
ꢀ1
3
H groups in the hollow nanospheres.
The catalytic performance of PCYDN@SO
asymmetric aldol reaction
3
H-HNS10 in the
enantioselectivity could be obtained in proline-catalyzed aldol
17e,j
Recently, chiral amine–protonic acids have been proved to be
effective catalysts in organic catalysis because of their divergent
nature, which results in the formation of either nucleophilic
reaction in the presence of a large excess of water.
Later
studies showed that a chiral catalyst in an emulsion formed from
water and cyclohexanone significantly enhanced the reactivity
11d
9f,11i
enamines or electrophilic iminium ions.
The combination of
and stereoselectivity of the direct asymmetric aldol reaction.
chiral amines with polyoxometalate acids and polystyrene/
sulfonic acids results in effective catalysts for the direct asym-
However, attempts to investigate the water effect of chiral
amine–protonic acid for asymmetric aldol reactions have not
been reported. Herein, we employed water as the reaction
11h,i
metric aldol reaction.
3
The SO H-HNS10 with the highest
catalytic activity in the esterification reaction was chosen as
carrier material for PCYDN, which was an effective catalyst for
direct asymmetric aldol reaction when combined with protonic
acids. The control experiments showed that either the support or
PCYDN could hardly catalyze the direct asymmetric aldol
reaction (Table 2). To our delight, in the direct asymmetric aldol
reaction of cyclohexanone and para-nitrobenzaldehyde, the
reaction proceeded smoothly in the presence of PCYDN@
3
medium for the asymmetric aldol reaction on PCYDN@SO H-
HNS10. Compared with neat conditions (cyclohexanone as
solvent), the enantioselectivity was increased to 96% accompa-
nied by a slight decreasing of activity. The catalytic performance
of the catalyst in different amounts of water is summarized in
Table 3. The results showed that the enantioselectivity (ꢄ96% ee)
was higher than in the neat conditions (90% ee) in the presence of
water and the amount of water had almost no influence on the
enantioselectivity. However, the yield was largely dependent on
the amount of water. With the water amounts increasing from
0 to 0.1 mL, the yield increased gradually. However, as the water
amounts exceed 0.1 mL, the yield decreased. Although many
research groups have observed the positive effect on the catalyst
efficiency after the addition of water, the reason is still not very
3
SO H-HNS10 without solvent. After reaction for 12 h, 95%
isolated yield with 90% ee was obtained (Table 2).
Due to the fact that the solvent may play an important role in
the asymmetric catalysis, different types of solvents were
screened for this reaction (Table 2). In DMF, no reaction was
2 2
detected. Other organic solvents, such as toluene, CH Cl ,
17
CHCl , generally lead to decreased yield compared with the
3
clear. In our case the relation of the water amounts with the
reaction yield may be explained in view of hydrophilicity/
reaction performed without the solvent though the enantiose-
lectivity was slightly improved. Recently, processes using water
as a reaction medium have attracted a great deal of attention
because water is safe, inexpensive, environmental friendly and in
hydrophobicity of the catalyst. PCYDN and SO H-HNS10 have
3
hydrophobicity and hydrophilicity, respectively. The combina-
tion of organic and inorganic counterparts may result in a cata-
lyst with amphiphilicity. Therefore, the presence of appropriate
amounts of water may facilitate the dispersion of the catalyst in
10e,17
some cases endows unique properties on the reaction.
Recently Barbas and Hayashi independently reported that high
This journal is ª The Royal Society of Chemistry 2009
J. Mater. Chem., 2009, 19, 8580–8588 | 8585

Table 3 Effect of water amounts on the catalytic properties of
PCYDN@SO H-HNS10 in the direct asymmetric aldol reaction
Table 5 The recycling results of PCYDN@SO
asymmetric aldol reaction
3
H-HNS10 in the direct
a
a
3
b
Yield (%)
c
,
c d
ee (%) anti
b
Yield (%)
c
c
,
d
entry
Syn/anti
H
2
O (mL)
Syn/anti
ee (%) anti
1
2
3
4
91
82
60
35
9/91
96
94
96
95
0
0
0
0
0
0
0
0
.4
.3
.2
.15
.1
75
73
76
84
91
81
74
97
8/92
9/91
13/87
14/86
9/91
12/88
8/92
10/90
96
96
95
95
96
96
96
90
16/84
8/92
11/89
a
Reaction conditions: catalyst (10 mol% of chiral diamine),
O (0.4 mL) aldehyde (0.5 mmol), RT.
Isolated yield after separation by silica gel. Determined by HPLC.
.07
.05
cyclohexanone (0.4 mL) H
2
b
c
e
d
0
The products had a 1 S,2R configuration.
a
Reaction conditions: catalyst (10 mol% of chiral diamine),
cyclohexanone (0.1 mL), 4-nitrobenzaldehyde (0.125 mmol), RT, 12 h.
b
c
Isolated yield after separation by silica gel. Determined by HPLC.
d
0
e
The products had a 1 S,2R configuration. 0.2 mL of cyclohexanone
catalyzed aldol reactions conform to the generally accepted
enamine mechanism based on a proline-catalyzed aldol reaction,
wherein the catalysts form enamines with the ketone donors to
give the aldol adducts. On the other hand, a pathway to dehy-
dration might involve an aldimine species, which undergoes
a Mannich-type reaction with the ketone enamine to give the
b-aminoketone, followed by subsequent elimination leading to
was used and reaction time is 10 h.
the reaction medium, which will have an influence on the cata-
lytic activity of the catalyst.
The scope and limitations of the direct asymmetric aldol
10
dehydration product.
reaction catalyzed by PCYDN@SO
3
H-HNS10 were also exam-
The recycling capacity of the nanocomposites was also inves-
tigated as shown in Table 5. The obvious loss of the activity was
1
observed though the ee remained almost the same. We used H
ined (Table 4). PCYDN@SO H-HNS10 could efficiently cata-
3
lyze the reaction involving an aromatic aldehyde with an
electron-withdrawing group and ee values were in the range
NMR to determine if there was leaching of the chiral amine.
After the reaction was completed, some aliquots of the reaction
9
1–96%. However, the catalyst showed no catalytic activity for
the aromatic aldehyde bearing an electron-donating group,
whereas other chiral diamine–protonic acids, such as diamine–
TFA, diamine–polyoxometalate acid, and diamine–polystyrene-
sulfonic acid, could catalyze the reaction. The reason is unclear at
present and it might be related with the acid strength of the
propylsulfonic acid. The mechanism of chiral amine–protonic
acid-catalyzed aldol reaction is the subject of an extensive
3
solution were dissolved in CDCl , and no characteristic chemical
10a
1
shifts of chiral amine (0.65 ppm) were observed in H NMR
spectrum (Fig. S7 in ESI‡). After the catalyst was used 4 times,
the nitrogen elemental analysis was almost the same as the fresh
catalyst, so there was no leaching of chiral amine in the reaction.
Some other unknown reasons caused the loss of activity of the
catalyst in the recycle reaction.
3
investigation. Here we assume that PCYDN@SO H-HNS10-
The influence of the morphology on the catalytic properties of the
chiral solid
Table 4 Direct asymmetric aldol reaction of aldehyde with cyclohexa-
none on PCYDN@SO H-HNS10
3
a
Pore structure and morphology of the porous materials may play
an important role in their catalytic properties. For comparison,
SO H-PMO10 with a highly ordered 2-D hexagonal meso-
3
structure and ribbon-like morphology (particle size of tens of
micrometres) was also used for the synthesis of chiral solids. In
the asymmetric aldol reaction between para-nitrobenzaldehyde
b
Yield (%)
c
c
ee (%) anti
R
Syn/anti
Time (h)
4
3
2
4
4
4
4
4
4
-NO
2
2
2
97
97
97
98
9/91
12/88
7/93
16/84
6/94
n.d.
96
93
91
94
95
15
19
24
20
36
and cyclohexanone, PCYDN@SO
rable yield and ee to PCYDN@SO
conditions (Table 3). PCYDN@SO H-PMO10 also exhibited
a similar solvent effect to PCYDN@SO H-HNS10, suggesting
3
H-PMO10 gave a compa-
-NO
-NO
-CN
3
H-HNS10 under neat
3
3
-CF
-Cl
3
98
trace
trace
trace
trace
that the two materials had similar catalytic active sites.
-Br
-MeO
-H
The time profiles of PCYDN@SO H-HNS10 and
3
PCYDN@SO H-PMO10 for asymmetric aldol reaction between
3
para-nitrobenzaldehyde and cyclohexanone are displayed in
Fig. 8. When the yield was below 80%, the product yield
increased linearly with the reaction time, showing that no deac-
tivation occurred during the catalytic process. In 8 h, the yield on
a
Reaction conditions: catalyst (10 mol% of chiral diamine),
O (0.1 mL), aldehyde (0.125 mmol), RT.
Isolated yield after separation by silica gel. Determined by HPLC.
cyclohexanone (0.1 mL), H
2
b
c
8
586 | J. Mater. Chem., 2009, 19, 8580–8588
This journal is ª The Royal Society of Chemistry 2009

Acknowledgements
This work was supported by National Natural Science Foun-
dation of China (20621063, 20673113) and National Basic
Research Program of China (2009CB623503).
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