Chirally functionalized mesoporous organosilicas with built-in BINAP ligand for asymmetric catalysis

Article abstract of DOI:10.1039/b913808k

The chirally functionalized periodic mesoporous organosilica (PMO) with C₂-symmetric chiral building blocks, BINAP (2,2′- bis(diphenylphosphino)-1,1′-binaphthyl), in the pore wall was successfully synthesized for the first time using a successive co-condensation and post-synthesis modification method. Chiral BINAPO (2,2′- bis(diphenylphosphinooxide)-1,1′-binaphthyl) bridging mesoporous organosilica with highly ordered 2-D hexagonal structure was first synthesized by co-condensation of (R)-5,5′-bis(3-triethoxysilylpropyl-1-ureyl)-2, 2′-bis(diphenylphosphinooxide)-1,1′-binaphthy with tetramethoxylsilane in the presence of block copolymer P123 as template under weakly acidic conditions. The BINAPO in the pore wall of PMO was reduced with trichlorosilane to generate BINAP using a post-synthesis modification method. The chiral PMO with built-in BINAP (coordination with [RuCl₂- (benzene)]₂) is an efficient solid catalyst for the asymmetric hydrogenation of β-keto esters with ee as high as 99%, which is among the highest ever reported for the chirally functionalized PMOs in asymmetric catalysis.

Full text of DOI:10.1039/b913808k

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Chirally functionalized mesoporous organosilicas with built-in BINAP
ligand for asymmetric catalysis†
a
a
Peiyuan Wang,ab Xiao Liu,ab Jie Yang,a Yan Yang,ab Lei Zhang, Qihua Yang and Can Lia
*
Received 10th July 2009, Accepted 25th August 2009
First published as an Advance Article on the web 21st September 2009
DOI: 10.1039/b913808k
The chirally functionalized periodic mesoporous organosilica (PMO) with C2-symmetric chiral
building blocks, BINAP (2,20-bis(diphenylphosphino)-1,10-binaphthyl), in the pore wall was
successfully synthesized for the first time using a successive co-condensation and post-synthesis
modification method. Chiral BINAPO (2,20-bis(diphenylphosphinooxide)-1,10-binaphthyl) bridging
mesoporous organosilica with highly ordered 2-D hexagonal structure was first synthesized by co-
condensation of (R)-5,50-bis(3-triethoxysilylpropyl-1-ureyl)-2,20-bis(diphenylphosphinooxide)-1,10-
binaphthy with tetramethoxylsilane in the presence of block copolymer P123 as template under weakly
acidic conditions. The BINAPO in the pore wall of PMO was reduced with trichlorosilane to generate
BINAP using a post-synthesis modification method. The chiral PMO with built-in BINAP
(coordination with [RuCl2-(benzene)]2) is an efficient solid catalyst for the asymmetric hydrogenation
of b-keto esters with ee as high as 99%, which is among the highest ever reported for the chirally
functionalized PMOs in asymmetric catalysis.
PMOs has attracted much research attention because the devel-
1. Introduction
opment of high-performance chiral solid catalysts is of extreme
importance and ongoing academic and industrial interest.18–21
Previous studies show that several chirally functionalized PMOs
have been synthesized using 100% chiral organosilane
compounds or mixtures of tetraethoxylsilane (TEOS) and chiral
organosilane as precursor under hydrothermal conditions.22–26
However, only limited numbers of chiral PMOs have been tested
in the asymmetric catalysis and the reported enantioselectivity
was usually lower than 40%.22,23,26 The low chiral inducibility of
chirally functionalized PMOs may be partly due to the fact that
there still is a lack of methods to incorporate some efficient but
air/moisture sensitive chiral ligands in the pore wall of PMOs and
partly due to the difficulties in construction of highly ordered
porous structure using the silane precursor containing large and
flexible organic groups. The synthesis of highly efficient chirally
functionalized PMOs for asymmetric catalysis still remains
a challenge.
Mesoporous materials with well-ordered pore structure, large
surface area, uniform pore size distribution and tunable pore
diameter have potential applications in the fields of catalysis,
biotechnology, adsorption and separation.1–6 The periodic mes-
oporous organosilicas (PMOs) with bridging organic groups
distributed uniformly in the framework represent a recent
breakthrough in material science.7–12 The organic groups in the
framework of PMOs not only modify the surface properties of
the materials, but also endow the PMOs with novel bulk prop-
erties, such as improved hydrothermal and mechanical stabilities,
extending the ‘‘pore surface chemistry’’ of the hybrid materials to
the ‘‘pore wall chemistry’’.13–16 The unique properties of the
PMOs make them attractive in a range of applications, especially
in catalysis. It has been demonstrated that the PMOs generally
show higher catalytic activity than the pure mesoporous silica
counterparts due to their enhanced surface hydrophobicity. They
can efficiently catalyze many reactions, such as acid/base reac-
tions, hydrogenation, selective oxidation, C–C coupling reaction
and even asymmetric reactions.17
Among the various chiral blocks, the C2-symmetric bisphos-
(2,20-bis(diphenylphosphino)-1,10-
phine
ligand
BINAP
binaphthyl) reported by Noyori and Takaya in 1980 represents
one of the most efficient chiral ligands. BINAP and its derivatives
have been widely used in chiral synthesis and extensively inves-
tigated especially in asymmetric hydrogenation.27,28 The immo-
bilization of BINAP has been a long-term research area in
heterogeneous asymmetric catalysis. Though BINAP has been
immobilized onto different kinds of supports, such as polymers,
clays, silica, zirconium phosphonate, Fe3O4, etc.,29–35 the incor-
poration of BINAP in the pore wall of PMOs has never been
reported probably due to the instability of BINAP towards
oxygen during the hydrothermal process.
Chirally functionalized PMOs with a combination of a rigid
nanoporous structure and homogeneously distributed chiral
ligands in the pore wall may be potential chiral solids for
asymmetric catalysis. The synthesis of chirally functionalized
aState Key Laboratory of Catalysis, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, 116023,
China. E-mail: yangqh@dicp.ac.cn; Fax: +86 (0)411 84694447; Tel:
+86 (0)411 84379552
bGraduate School of the Chinese Academy of Sciences, Beijing, 100049,
China
Here we present the successful fusion of air sensitive BINAP in
the pore wall of PMO by a successive co-condensation and post-
synthesis modification method, as illustrated in Scheme 1. After
† Electronic supplementary information (ESI) available: FT-IR spectra
of BINAP, [RuCl2(benzene)]2 and Ru-BINAP. See DOI:
10.1039/b913808k
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Scheme 1 Synthesis of chiral PMO with (R)-BINAP bridging in the pore wall.
coordination with [RuCl2(benzene)]2, the chiral mesoporous
materials can efficiently catalyze the asymmetric hydrogenation
of b-keto esters with an ee as high as 99%.
silylated by reaction with hexamethyldisilazane in hexane (1.0 g
of PMO-BINAPO was refluxed in 25 mL of hexane and 1 mL of
hexamethyldisilazane for 12 h). Under inert atmosphere, the
silylated material was suspended in 20 mL of dry toluene con-
taining 1.0 mL of HSiCl3. The mixture was heated to reflux for
40 h. HSiCl3 (0.5 mL) was added to the mixture at 2, 7 and 18 h
respectively. Using the Schlenk technique, the solid product was
filtered and washed with CH2Cl2. After drying under vacuum at
room temperature, the obtained material was denoted as
PMO-BINAP.
2. Experimental
2.1. Materials
Poly(alkylene oxide) block copolymer (P123, EO20PO70EO20)
and [RuCl2(benzene)]2 were purchased from Sigma-Aldrich
Company, (USA). Trichlorosilane (HSiCl3) was purchased from
Alfa-Aesar, (USA). 2,20-Bis(diphenylphosphino)-1,10-binaphthyl
((R)-BINAP) was obtained from Shijiazhuang Shengjia Chem-
ical Co, Ltd., (China). Tetramethoxysilane (TMOS) was
obtained from Nanjing Shuguang Chemical Group (China).
Other reagents were purchased from Shanghai Chemical
Reagent Inc. of the Chinese Medicine Group. All solvents were
of analytical quality and dried by standard methods.
Coordination of PMO-BINAP with Ru complexes: PMO-
BINAP (0.5 g) was placed in freshly distilled, degassed ethanol–
benzene (10 mL (9 : 1)). To this mixture [RuCl2(benzene)]2 (0.2 g,
0.8 mmol) was added and the resulting mixture was stirred at 60 ꢀC
for 24 h followed by hot filtration and several washing with meth-
anol and CH2Cl2. Elemental analysis of Ru is 0.412 mmol gꢁ1.
2.3. Asymmetric hydrogenation
Desired amounts of catalysts (Ru/PMO-BINAP), anhydrous
methanol (1 mL) and substrates (110 mL, 1.0 mmol) were added
in a test tube under argon. The test tube was transferred into
a stainless steel autoclave and sealed. After purging with H2 five
times, the final H2 pressure was adjusted to 4 MPa. After
agitation at 50 ꢀC for 24 h, H2 pressure was released. The catalyst
was separated with centrifugation and the organic solution was
passed through a mini silica-gel column. The conversion of
b-keto esters and enantiomeric excess of products were analyzed
on an Agilent 6890 gas chromatograph equipped with a flame
ionization detector and a Supelco g-DEX 225 capillary column
(30 m ꢂ 0.25 mm ꢂ 0.25 mm). For recycling the catalyst, all the
liquids were collected carefully in vacuum after reaction. The
residual catalyst was used directly for the next catalytic reaction.
2.2. Synthesis
The organosilane precursor, (R)-5,50-bis(3-triethoxysilylpropyl-
1-ureyl)-2,20-bis(diphenylphosphinooxide)-1,10-binaphthy
(compound 1) was synthesized from (R)-BINAP in multistep
reactions according to a reported procedure.36
BINAPO-containing chiral PMO, denoted as PMO-BINAPO,
was synthesized by the co-condensation of compound 1 and
TMOS with block copolymer P123 as a templating agent. 1.0 g of
P123, 2.0 g of NaCl, and 0.30 mL of NH4F solution (0.25 M) were
mixed with 3.0 mL of HCl solution (0.1 M) and 27 mL of water.
The solution was stirred at 40 ꢀC for 3 h. Then, a mixture of TMOS
(1.216 g), chiral silane 1 (1.179 g) and ethanol (4.00 g) was added to
the above solution under vigorous stirring. The resultant mixture
was further stirred at 40 ꢀC for 20 h and then aged at 80 ꢀC for 24 h.
ThemolarratioofSi : P123 : NaCl : NH4F : H2O : HCl : ethanol
is 1 : 0.017 : 3.42 : 0.0075 : 166 : 0.03 : 8.7. As-synthesized mate-
rial was extracted with ethanol under refluxing conditions for 24 h
to remove the surfactant. After filtration, the powder was dried at
80 ꢀC overnight.
2.4. Characterizations
X-Ray powder diffraction (XRD) patterns were recorded on
a Rigaku RINT D/Max-2500 powder diffraction system using
Cu Ka radiation. The nitrogen sorption experiments were per-
formed at ꢁ196 ꢀC on an ASAP 2020 system. The samples were
outgassed at 120 ꢀC for 5 h before the measurements. The
BINAP-containing chiral PMO, denoted as PMO-BINAP,
was synthesized from PMO-BINAPO. PMO-BINAPO was first
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Brunauer–Emmett–Teller (BET) surface area was evaluated
from data in the relative pressure range of 0.05 to 0.25. The total
pore volumes were estimated from the amount adsorbed at
a relative pressure of 0.99. Pore diameters were determined from
the adsorption branch using the Barrett–Joyner–Halenda (BJH)
method. Transmission electron microscopy (TEM) was per-
formed using a FEI Tecnai G2 Spirit at an acceleration voltage of
120 kV. 13C (100.5 MHz) cross-polarization magic-angle spin-
ning (CP-MAS), 31P (161.8 MHz), and 29Si (79.4 MHz) MAS
solid-state NMR experiments were recorded on a Varian infinity-
plus 400 spectrometer equipped with a magic-angle spin probe in
a 4-mm ZrO2 rotor. 13C and 29Si signals were referenced to
tetramethylsilane, and 31P NMR signal was referenced to H3PO4
(85 wt %). The experimental parameters were 8-kHz spin rate, 3-s
pulse delay, 4-min contact time, 1500–3000 scans for 13C
CP-MAS NMR experiments; 4-kHz spin rate, 180-s pulse delay,
10-min contact time, 116 scans for 29Si MAS NMR experiments;
10-kHz spin rate, 3-s pulse delay, 200 scans for 31P MAS NMR
experiments.
Fig. 2 TEM images of PMO-BINAPO (a, b) and PMO-BINAP (c).
7.7 nm, BET surface area of 331 m2 gꢁ1 and a total pore volume
of 0.61 cm3gꢁ1 (Table 1). The above results show that PMO-
BINAPO has highly ordered 2-D hexagonal mesostructure with
large mesopore.
The FT-IR spectrum was employed for characterization of the
chemical composition of PMO-BINAPO (Fig. 3). In the FT-IR
spectrum of PMO-BINAPO, the ureylene stretching vibration is
clearly observed at 1660 (overlapped with H2O) and 1537 cmꢁ1
and the sharp peak at 1437 cmꢁ1 is ascribed to P–C (aryl)
vibration of BINAPO ligand.36 The peak at 3057 cmꢁ1 is ascribed
to C–H (aryl) vibration of the BINAPO ligand. The vibrations of
propyl group can be found at 2900 cmꢁ1. The vibration of P]O
is overlapped with those of Si–O–Si in the range of 1000 to
1260 cmꢁ1. The absence of the C–H vibration peaks of P123
surfactant at 1375 cmꢁ1 suggests almost complete removal of the
surfactant during the ethanol extraction process.37
To further clarify the composition of PMO-BINAPO, 29Si
MAS NMR and 13C CP/MAS NMR were performed (Fig. 4).
29Si MAS NMR spectrum of PMO-BINAPO shows both the T
and Q silicon sites. The main signal at ꢁ112.3 ppm and the
shoulder peak at ꢁ103.5 ppm correspond to Q4 [Si(OSi)4] and Q3
[Si(OH)(OSi)3] Si species, respectively. The broad peak centered
at ꢁ66.7 ppm could be ascribed to the mixture of T3 [SiC(OSi)3]
and T2 [SiC(OH)(OSi)2] organosilicon species. The absence of T0
[SiC(OH)3] site confirms that the chiral moiety is actually inte-
grated with both ends in the pore walls, instead of dangling in the
pore as a pendant group. The peak area ratio of ST/(ST +
SQ) z 20.4%, which agrees well with the silicon molar concen-
tration of compound 1 in the initial mixture (20%), indicates that
the weakly acidic synthesis conditions are efficient for stoichio-
metric incorporation of the organic groups in the mesoporous
network. In the 13C CP/MAS NMR spectrum of PMO-BINAPO,
signal at 154.5 ppm is from the carbonyl carbon (C]O). Signals
in the range of 150–110 ppm can be ascribed to the aryl carbons
of BINAPO. Signals at 42.8, 18.5 and 9.1 ppm are due to C3, C2,
and C1 carbon species of Si–C1H2C2H2C3H2. The signals at 16.4
and 59.3 ppm may originate from the ethoxy groups formed
during the surfactant-extraction process. No carbon species
associated with the surfactant are observed, showing the effi-
ciency of the ethanol extraction method. The amount of the
chiral ligand PMO-BINAPO was 0.45 mmol gꢁ1 based on P
elemental analysis. The results of structural and compositional
characterization show that highly ordered chiral PMO with
BINAPO ligands distributed in the framework can be obtained
under hydrothermal conditions.
3. Results and discussion
3.1. Synthesis and characterization of PMO-BINAPO
Due to the instability of BINAP towards oxygen during the
hydrothermal process, compound 1, (R)-5,50-bis(3-triethoxy-
silylpropyl-1-ureyl)-2,20-bis(diphenylphosphino-oxide)-1,10-
binaphthyl, was used as precursor for the synthesis. The XRD
pattern of PMO-BINAPO is shown in Fig. 1A. Three well-
resolved diffraction peaks were observed with d spacings of 9.8,
5.7 and 4.9 nm, which could be indexed to (100), (110) and (200)
diffraction peaks of a highly ordered P6mm mesophase, respec-
tively. The highly ordered pore structure of PMO-BINAPO was
further confirmed by the TEM image (Fig. 2). A honeycomb
structure as well as parallel fringe pore wall could be clearly
observed in the TEM images of PMO-BINAPO with incidence
direction parallel and perpendicular to the pore axis, respec-
tively. The nitrogen sorption isotherm of PMO-BINAPO is of
type IV with an H1 hysteresis loop in the relative pressure P/P0 of
0.60 to 0.80, which is characteristic of mesoporous materials with
large mesopores (Fig. 1B). PMO-BINAPO has pore diameter of
Fig. 1 XRD patterns (A) and nitrogen adsorption isotherms (B) of
PMO-BINAPO (a), PMO-BINAPO (after silation) (b), PMO-BINAP
(c) and Ru/PMO-BINAP (d).
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Table 1 Structural and textural properties of chiral PMOs
Sample
d spacing/nm
BET surface area/m2gꢁ1
Pore volume/cm3gꢁ1
Pore diameter/nma
PMO-BINAPO
9.8
9.4
9.4
8.5
331
280
201
211
0.61
0.53
0.25
0.42
7.7
6.6
4.6
7.1
PMO-BINAPO(after silylation)
PMO-BINAP
Ru/PMO-BINAP
a
Calculated using the BJH model on the adsorption branch of the isotherm.
during the post-synthesis modification process. The additional
signal at 11.5 ppm is due to the silicon species connected with
methyl group from the silylation process. The peak area ratio of
ST/(ST + SQ) is ꢃ18.9%, which is similar to that of PMO-
BINAPO (ꢃ20.4%). This indicates that no Si–C bond cleavage
occurred during the post-synthesis modification process.
In the 13C CP/MAS NMR spectrum of PMO-BINAP (Fig. 4),
the chemical shifts of carbonyl carbon (C]O) and aryl carbons
of BINAPO and C2, and C1 carbon species of Si–C1H2C2H2C3H2
are almost the same as that of PMO-BINAPO. The chemical
shift of C3 carbon species of Si–C1H2C2H2C3H2 appears at
47.5 ppm and is different from that of PMO-BINAPO
(42.8 ppm), which further confirms the successful reduction of
BINAPO to BINAP. The signal at 60.3 ppm is from the ethoxy
groups. In addition, the new signal at 2.0 ppm can be ascribed to
methyl group from the silylation process. 31P MAS NMR is
a powerful technique to characterize the chemical state of
phosphorus (Fig. 4). PMO-BINAPO shows a broad peak
centered at about 29.7 ppm assigned to phosphorus of phosphine
oxide in the 31P MAS NMR spectrum. For PMO-BINAP, the
signal at ꢁ16.5 ppm which can be assigned to the reduced,
unprotected phosphine shows the successful reduction of
BINAPO to BINAP. The weak peak at 29.7 ppm is from some
phosphine oxide buried in the pore wall which cannot be accessed
by the reducing agent (HSiCl3). The NMR results show the
successful reduction of BINAPO to BINAP in the pore wall by
post-synthesis modification method.
Fig.
3 FT-IR spectra of compound 1 (a), PMO-BINAPO (b),
PMO-BINAP (c) and Ru/PMO-BINAP (d).
3.2. Synthesis and characterization of PMO-BINAP and Ru/
PMO-BINAP
For application of the chiral PMO-BINAPO in asymmetric
catalysis, it is desirable to reduce BINAPO into BINAP. The
composition of PMO-BINAP after reduction was analyzed by 29Si
MAS NMR and 13C/CP MAS NMR (Fig. 4). Similar to PMO-
BINAPO, both T and Q silicon sites were observed in the 29Si
MAS NMR spectrum of PMO-BINAP. Compared with PMO-
BINAPO, the decrease in intensity of Q3 site [Si(OH)(OSi)3] and
upfield shift of T site indicate further framework condensation
The FT-IR spectrum (Fig. 3) of PMO-BINAP shows the
ureylene stretching vibration (1660 and 1537 cmꢁ1), P–C (aryl)
vibration (1437 cmꢁ1), C–H (aryl) vibration (3057 cmꢁ1) and the
Fig. 4 Solid state 29Si MAS (left), 13C CP MAS (middle) and 31P MAS (right) NMR spectra of PMO-BINAPO (a) and PMO-BINAP (b); *: side bands.
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vibrations of propyl group (2900 cmꢁ1). In addition, the signal
related with Si–H vibration is observed at around 2245 cmꢁ1 38
Ru-BINAP (Fig. S1†), the vibration at 1382 cmꢁ1 is probably
from [RuCl2(benzene)]2 and the vibration at around 1516 cmꢁ1
indicates the successful coordination of [RuCl2(benzene)]2 with
BINAP (Fig. 3d). Above characterizations confirm that BINAP
ligand in chiral PMO (PMO-BINAP) can coordinate with
[RuCl2(benzene)]2 for the formation of heterogeneous asym-
metric catalyst.
,
which shows the existence of trichlorosilane on the surface and in
the pore channel of PMO-BINAP.
Ru/PMO-BINAP was synthesized by coordination of PMO-
BINAP with [RuCl2(benzene)]2 because the combination of Ru
complex and BINAP could generate efficient catalyst for asym-
metric hydrogenation. The Ru/P molar ratio in Ru/PMO-
BINAP was ꢃ1/1.2. For the homogeneous Ru/BINAP catalyst,
the Ru/P molar ratio should be 1/2. The higher Ru/P molar ratio
in Ru/PMO-BINAP is probably due to the fact the Ru complex
can also react with surface hydroxyl group in the mesoporous
channel in addition to coordination with BINAP.
3.3. Catalytic performance of Ru/PMO-BINAP
The catalytic performance of Ru/PMO-BINAP was tested in the
asymmetric hydrogenation of b-keto esters. As shown in Table 2,
the metal complex, [RuCl2(benzene)]2, shows a conversion of
13.9% in the hydrogenation of methyl acetoacetate and gives the
racemic product. Ru/PMO-BINAP shows a complete conversion
with 93.5% ee. Under similar conditions, the ee value obtained on
homogeneous Ru/BINAP is 99%. The lower enantioselectivity of
Ru/PMO-BINAP is probably due to the existence of uncoordi-
nated [RuCl2(benzene)]2 on chiral PMO (the molar ratio of
Ru : Pz 1 : 1.2). The conversion and ee do not change obviously
with the S : C ratio varying from 100 to 1000. Even when the
S : C ratio decreased to 2000, methyl acetoacetate could still be
transformed into methyl-3-hydroxybutyrate with 91.0% conver-
sion and 89.5% ee. Moreover, a number of different b-keto esters
can be converted into the corresponding chiral alcohol on Ru/
PMO-BINAP with S : C ¼ 1000 (Table 3). The structures of the
b-keto esters significantly affect the catalytic performance of Ru/
PMO-BINAP. b-Keto esters bearing larger substituents in the R2
position result in higher enantioselectivity than those bearing
smaller one. For benzyl acetoacetate, the ee could reach as high
as 99.0%. We also found that for methyl propionylacetate with
proper steric hindrance of R1, the ee could reach as high as
99.1%. The above results suggest that Ru/PMO-BINAP is an
efficient catalyst for asymmetric hydrogenation. The recycling
ability of Ru/PMO-BINAP was primarily investigated in the
hydrogenation of methyl acetoacetate. For the first cycle,
complete conversion of the substrate with 90.4% ee was observed
(Table 2). The slight decreasing of ee is probably due to the air-
sensitivity of the catalytically active Ru-hydride species.33,36 The
further recycling ability of the catalyst is under investigation.
The structural order of PMO-BINAP and Ru/PMO-BINAP
was characterized by XRD and N2 sorption isotherm and
compared with that of PMO-BINAPO (after silylation) (Fig. 1).
Compared with PMO-BINAPO, only one sharp diffraction peak
was observed in the XRD pattern of PMO-BINAPO (after
silylation). The disappearance of (110) and (200) may be due to
the reduced contrast between the pore and wall after silyation.
PMO-BINAP displays a broad diffraction peak in its XRD
pattern. It is interesting to mention that Ru/PMO-BINAP shows
a sharp diffraction peak similar to PMO-BINAPO after silya-
tion. Therefore, the broad diffraction peak of PMO-BINAP is
not from the deterioration of the structural order. It is probably
due to the decreased contraction between the pore and wall (the
existence of Si–H species was observed in the FT-IR specrum of
PMO-BINAP). The TEM image of PMO-BINAP clearly shows
hexagonal pore arrangement, further confirming that this sample
still has ordered 2-D hexagonal mesostructure. The d spacings of
the sample decrease in the order of PMO-BINAPO > PMO-
BINAP > Ru/PMO-BINAP (Table 1), probably due to the
framework contraction in each modification step (each modifi-
cation step involves high temperature treatment).
After silylanized with hexamethyldisilazane, PMO-BINAPO
(after silylation) also shows type IV nitrogen sorption isotherm
pattern with H1 hysteresis loop. After deoxidized with tri-
chlorosilane, however, PMO-BINAP shows type IV nitrogen
sorption isotherm pattern with H3 hysteresis loop. It is worthy to
mention that Ru/PMO-BINAP shows a type IV nitrogen sorp-
tion isotherm pattern with an H1 hysteresis loop similar to PMO-
BINAPO. Moreover, the pore volume and pore diameter of Ru/
PMO-BINAP is greatly increased compared with that of PMO-
BINAP. On passing from PMO-BINAP to Ru/PMO-BINAP,
important changes of textural properties were observed. There
are three reasons for the corresponding change. (1) Before
reduction, PMO-BINAPO was silylanized with hexamethyldisi-
lazane. In this process, a decreased surface area and pore
diameter was observed. (2) During the reduction process of
BINAPO into BINAP, some trichlorosilane was adsorbed onto
the surface of the material (this was identified by FT-IR spec-
troscopy, Fig. 3c), which caused the further reduction of pore
diameter and pore volume. (3) In the process of coordination of
PMO-BINAP with [RuCl2(benzene)]2, the adsorbed tri-
chlorosilane was removed in the boiling ethanol solution. The
vibrations related with Si–H cannot be observed at around
2245 cmꢁ1 in the FT-IR spectrum of Ru/PMO-BINAP (Fig. 3d).
Therefore, the surface area and pore diameter of Ru/PMO-
BINAP was increased. Compared with the FT-IR spectrum of
Table 2 Asymmetric hydrogenation of methyl acetoacetate catalyzed by
Ru/PMO-BINAP with various ratios of substrate to catalyst.a
Catalyst
S : C
Conversion (%)
E.e. (%)
[RuCl2(benzene)]2
Ru/BINAP
1000
1000
100
200
500
13.9
99.0
99.0
99.0
99.0
99.0 (99.0)b
91.0
0
99.9
94.2
93.7
93.4
93.5 (90.4)b
89.5
Ru/PMO-BINAP
Ru/PMO-BINAP
Ru/PMO-BINAP
Ru/PMO-BINAP
Ru/PMO-BINAP
1000
2000
a
Conversions and ee values were determined by GC on a Supelco g-DEX
225 capillary column. All the reactions were carried out under a hydrogen
b
pressure of 4 MPa in 1.0 mL methanol at 50 ꢀC for 24 h. The data in
parentheses are the result of the first recycling.
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4 Y. Wan and D. Y. Zhao, Chem. Rev., 2007, 107, 2821.
5 M. E. Davis, Nature, 2002, 417, 813.
Table 3 Asymmetric hydrogenation of b-keto esters catalyzed by
Ru/PMO-BINAP.a
6 F. Hoffmann, M. Cornelius, J. Morell and M. Froba, Angew. Chem.,
Int. Ed., 2006, 45, 3216.
7 T. Asefa, M. J. MacLachan, N. Coombs and G. A. Ozin, Nature,
1999, 402, 867.
8 S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna and O. Terasaki,
J. Am. Chem. Soc., 1999, 121, 9611.
R
Conversion (%)
E.e. (%)
9 B. J. Melde, B. T. Holland, C. F. Blanford and A. Stein, Chem.
Mater., 1999, 11, 3302.
10 W. J. Hunks and G. A. Ozin, J. Mater. Chem., 2005, 15, 3716.
11 M. P. Kapoor and S. Inagaki, Bull. Chem. Soc. Jpn., 2006, 79, 1463.
12 F. Hoffmann, M. Cornelius, J. Morell and M. Froba, J. Nanosci.
Nanotechnol., 2006, 6, 265.
13 M. C. Burleigh, M. A. Markowitz, S. Jayasundera, M. S. Spector,
C. W. Thomas and B. P. Gaber, J. Phys. Chem. B, 2003, 107, 12628.
14 S. Shylesh, R. K. Jha and A. P. Singh, Microporous Mesoporous
Mater., 2006, 94, 364.
R1 ¼ Me, R2 ¼ Et
99.0
99.0
99.0
99.0
99.0
99.0
99.0
99.0
92.2
92.5
95.1
99.0
93.2
99.1
93.2
92.8
R1 ¼ Me, R2 ¼ iPr
R1 ¼ Me, R2 ¼ tBu
R1 ¼ Me, R2 ¼ CH2–Ph
R1 ¼ Me, R2 ¼ CH2–CHCH2
R1 ¼ Et, R2 ¼ Me
R1 ¼ iPr, R2 ¼ Me
R1 ¼ 40-OMe–Ph, R2 ¼ Et
a
Conversions and ee values were determined by GC on a Supelco g-DEX
225 capillary column. Unless otherwise specified, all the reactions were
carried out under a hydrogen pressure of 4 MPa in 1.0 mL methanol at
50 ꢀC for 24 h with S : C ¼ 1000.
15 E. B. Cho, K. W. Kwon and K. Char, Chem. Mater., 2001, 13, 3837.
16 W. P. Guo, X. Li and X. S. Zhao, Microporous Mesoporous Mater.,
2006, 93, 285.
17 Q. H. Yang, J. Liu, L. Zhang and C. Li, J. Mater. Chem., 2009, 19,
1945.
18 F. Cozzi, Adv. Synth. Catal., 2006, 348, 1367.
19 Z. Wang, G. Chen and K. L. Ding, Chem. Rev., 2009, 109, 322.
20 K. Ding and Y. Uozumi, Handbook of Asymmetric Heterogeneous
Catalysis. WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim,
2008, pp. 1–24.
4. Conclusions
In summary, we have successfully incorporated air sensitive
C2-symmetric chiral building blocks, BINAP, in the pore wall of
PMO by post-synthesis reduction of highly ordered PMO with
BINAPO bridging chiral ligand which was synthesized by
co-condensation method under hydrothermal conditions. The
NMR results show the successful reduction of BINAPO to
BINAP in the pore wall by post-synthesis modification method.
No obvious deterioration of structural order was observed
during the post-synthesis modification process. The chiral PMO
has demonstrated excellent enantioselectivity (the highest ee up
to 99%) in asymmetric hydrogenation of b-keto esters. The
generality of this synthesis strategy should allow the synthesis of
versatile high-performance chiral solids for a wide range of
organic transformations.
€
€
21 G. Ertl, H. Knozinger, F. Schuth and J. Weitkamp, Handbook of
Heterogeneous Catalysis. 2 edn, Wiley-VCH Verlag GmbH & Co.
KGaA, Weinheim, 2008, vol. 8, pp. 1–56.
22 C. Baleizao, B. Gigante, D. Das, M. Alvaro, H. Garcia and
A. Corma, Chem. Commun., 2003, 1860.
23 C. Baleizao, B. Gigante, D. Das, M. Alvaro, H. Garcia and
A. Corma, J. Catal., 2004, 223, 106.
24 M. Alvaro, M. Benitez, D. Das, B. Ferrer and H. Garcia, Chem.
Mater., 2004, 16, 2222.
25 M. Benitez, G. Bringmann, M. Dreyer, H. Garcia, H. Ihmels,
M. Waidelich and K. Wissel, J. Org. Chem., 2005, 70, 2315.
26 D. M. Jiang, Q. H. Yang, H. Wang, G. R. Zhu, J. Yang and C. Li,
J. Catal., 2006, 239, 65.
27 R. Noyori and H. Takaya, Acc. Chem. Res., 1990, 23, 345.
28 R. Noyori, Angew. Chem., Int. Ed., 2002, 41, 2008.
29 D. J. Bayston, J. L. Fraser, M. R. Ashton, A. D. Baxter,
M. E. C. Polywka and E. Moses, J. Org. Chem., 1998, 63, 3137.
30 C. Chapuis, M. Barthe and J. Y. D. Laumer, Helv. Chim. Acta, 2001,
84, 230.
Acknowledgements
31 S. Shimazu, K. Ro, T. Sento, N. Ichikuni and T. Uematsu, J. Mol.
Catal. A: Chem., 1996, 107, 297.
32 T. Sento, S. Shimazu, N. Ichikuni and T. Uematsu, J. Mol. Catal. A:
Chem., 1999, 137, 263.
33 A. G. Hu, H. L. Ngo and W. B. Lin, J. Am. Chem. Soc., 2003, 125,
11490.
34 A. G. Hu, H. L. Ngo and W. B. Lin, Angew. Chem., Int. Ed., 2003, 42,
6000.
This work was supported by the National Basic Research
Program of China (2009CB623503), NSFC (20621063,
20673113) and Programme for Strategic Scientific Alliances
between China and the Netherlands (2008DFB50130). We thank
Prof. Yonggui Zhou for the useful discussions.
35 A. G. Hu, G. T. Yee and W. B. Lin, J. Am. Chem. Soc., 2005, 127,
12486.
References
1 A. Corma, Chem. Rev., 1997, 97, 2373.
36 A. R. McDonald, C. Muller, D. Vogt, G. P. M. van Klinka and
G. van Koten, Green Chem., 2008, 10, 424.
37 O. Muth, C. Schellbach and M. Froba, Chem. Commun., 2001, 2032.
38 A. Mehdi and P. H. Mutin, J. Mater. Chem., 2006, 16, 1606.
2 A. Stein, B. J. Melde and R. C. Schroden, Adv. Mater., 2000, 12, 1403.
3 M. Vallet-Regi, F. Balas and D. Arcos, Angew. Chem., Int. Ed., 2007,
46, 7548.
8014 | J. Mater. Chem., 2009, 19, 8009–8014
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