An alternate route for the synthesis of hybrid mesoporous organosilica with crystal-like pore walls from allylorganosilane precursors

Article abstract of DOI:10.1021/ja043062o

The bridged allylorganosilanes 1,4-bis(diallylethoxysilyl)benzene and 1,4-bis(triallylsilyl)benzene are presented as new precursors for the surfactant-assisted synthesis of ordered mesoporous organosilica with pore walls having crystal-like molecular-scal

Full text of DOI:10.1021/ja043062o

Published on Web 05/14/2005
An Alternate Route for the Synthesis of Hybrid Mesoporous
Organosilica with Crystal-Like Pore Walls from
Allylorganosilane Precursors
Mahendra P. Kapoor,†,‡ Shinji Inagaki,*,† Shushiro Ikeda,§ Kiyomi Kakiuchi,§
Masahiko Suda,| and Toyoshi Shimada*,|
Contribution from the Toyota Central R&D Laboratories, Inc., Nagakute,
Aichi 480-1192, Japan, Graduate School of Materials Science, Nara Institute of Science and
Technology (NAIST), 8916-5, Takayama, Ikoma, Nara 630-0192, Japan, and Department of
Chemical Engineering, Nara National College of Technology, 22 Yata-cho, Yamatokoriyama,
Nara 639-1080, Japan
Received November 17, 2004; E-mail: inagaki@mosk.tytlabs.co.jp; shimada@chem.nara-k.ac.jp
Abstract: The bridged allylorganosilanes 1,4-bis(diallylethoxysilyl)benzene and 1,4-bis(triallylsilyl)benzene
are presented as new precursors for the surfactant-assisted synthesis of ordered mesoporous organosilica
with pore walls having crystal-like molecular-scale periodicity. This approach provides a new route to the
formation of periodic mesostructures with crystal-like pore walls. The synthesis method presented is
applicable to the preparation of mesoporous organosilica with bulky organic groups, the precursors of which
are typically impossible to obtain in high purity.
Introduction
crystal-like domains exhibiting a structural periodicity with a
spacing of 7.6 and 11.6 Å for the benzene- and biphenylene-
Hybrid mesoporous organosilica is a periodic solid that can
be designed to carry organic, inorganic or even biological
functionalities.1 The unique structural properties of this materials
make it potentially applicable in a wide range of advanced
applications, including separation technology, filtration, sensing,
environmental cleanup, catalysis, and optoelectronics.2 Crystal-
lization of the pore walls of originally amorphous mesoporous
material is an important improvement required to achieve greater
functionality. The present authors have attempted crystallization
through the surfactant-mediated synthesis of benzene- and
biphenylene-bridged silica under precise control of the nano-
architecture.3,4 The materials synthesized by this route display
a hexagonal arrangement of mesopores and pore walls with
bridged silica, respectively. This periodicity has been attributed
to π-π stacking of the bridging functional groups.
A wide range of synthetic routes to mesoporous organosilica
with different mesophases and morphologies have been reported,
including the use of cationic, neutral and nonionic surfactants
and even surfactant mixtures under basic, acidic and neutral
conditions.1-5 The most commonly used organosilicon precur-
sors contain a trialkoxy leaving group [(OR′)3], such as the
trialkoxy derivatives of bridged organosilicon molecules
(R′O)3Si-R-Si(OR′)3. However, the range of suitable alkoxy-
silane precursors is limited because alkoxysilane precursors
containing relatively large organic groups are difficult to obtain
in high purity due to the limitations of distillation and
chromatographic separation for such nonvolatile compounds.
It is therefore vital to discover a alternative precursors for the
synthesis of novel mesoporous organosilicas. Alkoxy, halide,
acyloxy, and amino groups on silicon atoms have also been
used for Si-O-Si bond formation.6 However, these functional
groups are highly reactive toward hydrolysis, rendering the
silicon compounds difficult to handle under hydrolytic condi-
tions and during purification by silica gel chromatography. Our
group has also developed a new method for functionalizing the
surface of FSM-16 silica using allylorganosilanes at toluene
reflux temperatures.7
* Corresponding authors.
† Toyota Central R&D Laboratories, Inc.
§ Nara Institute of Science and Technology.
| Nara National College of Technology.
‡ Present address: Taiyo Kagaku, 1-3 Takaramachi, Yokkaichi, Mie 510-
0844, Japan; E-mail: mkapoor@taiyokagaku.co.jp.
(1) (a) Inagaki, S.; Guan, S.; Fukushima, Y.; Ohsuna, T.; Terasaki, O. J. Am.
Chem. Soc. 1999, 121, 9611. (b) Melde, B. J.; Holland, B. T.; Blanford, C.
F.; Stein, A. Chem. Mater. 1999, 11, 3302. (c) Asefa, T.; MacLachlan, M.
J.; Coombs, N.; Ozin, G. A. Nature 1999, 402, 867 (d) Yoshina-Ishii, C.;
Asefa, T.; Coombs, N.; MacLachlan M. J.; Ozin, G. A. Chem. Commun.
1999, 2539.
(2) (a) Fan, H.; Lu, Y.; Stump, A.; Reed, S. T.; Bear, T.; Schunk, R.; Perez-
Luna, V.; Lopez, G. P.; Brinker, C. J. Nature 2000, 405, 56. (b) Sayari,
A.; Hamoudi, S. Chem. Mater. 2001, 13, 3151. (c) Lu, Y.; Fan, H.; Doke,
N.; Loy, D. A.; Assinik, R. A.; LaVan D. A.; Brinker, C. J. J. Am. Chem.
Soc. 2000, 122, 5258. (d) McInal, M. D.; Scott, J.; Mercier, L.; Kooyman,
P. J. Chem. Commun. 2001, 2282. (e) Rogers, J. A.; Bao, Z.; Makhija, A.;
Braum, P. AdV. Mater. 1999, 11, 741.
(3) (a) Inagaki, S.; Guan, S.; Ohsuna, T.; Terasaki, O. Nature 2002, 416, 304.
(b) Kapoor, M. P.; Yang, Q.; Inagaki, S. Chem. Mater. 2004, 16, 1209. (c)
Kapoor, M. P.; Inagaki, S. Chem. Lett. 2004, 33, 88.
(5) (a) Yang, Q.; Kapoor, M. P.; Inagaki, S. J. Am. Chem. Soc. 2002, 124,
9694. (b) Goto, Y.; Inagaki, S. Chem. Commun. 2002, 2410. (c) Hamoudi,
S.; Kaliaguine, S. Chem. Commun. 2002, 2118. (d) Sayari A.; Yang, Y.
Chem. Commun. 2001, 2582. (e) M. P. Kapoor, Setoyama, N.; Yang, Q.;
Ohashi, M.; Inagaki, S. Langmuir 2005, 21, 443. (f) Kapoor, M. P.; Inagaki,
S. Chem. Mater. 2002, 14, 3509. (g) Okamoto, K.; Kapoor, M. P.; Inagaki,
S. Chem. Commun. 2005, 1423.
(4) (a) Kapoor, M. P.; Yang, Q.; Inagaki, S. J. Am. Chem. Soc. 2002, 124,
15176. (b) Kapoor, M. P.; Yang, Q.; Goto, Y.; Inagaki, S. Chem. Lett.
2003, 32, 914.
(6) Vansant, E. F.; Vrancken, C. Stud. Surf. Sci. Catal. 1995, 93.
9
8174
J. AM. CHEM. SOC. 2005, 127, 8174-8178
10.1021/ja043062o CCC: $30.25 © 2005 American Chemical Society

Synthesis of Hybrid Mesoporous Organosilica
A R T I C L E S
Scheme 1. Synthesis of Benzene-Silica Mesoporous Hybrids from
Allylorganosilane Precursors
Table 1. Parameters for Mesoporous Benzene-silica Hybrid
Synthesis Using 1,4-bis(diallylethoxysilyl)benzene
preparation
surfactant (g)
precursor (g)
NaOH (6N) (g)
H2O (g)
synthesis temp.
1
2
3
4
0.57
0.56
0.46
0.56
0.72
1.22
1.67
0.42
0.40
0.50
0.41
0.75
1.0
0.24
0.40
0.20
0.38
0.50
0.7
23
20
22
20
33
22
50
35 ( 3
50
70
92 ( 3
92 ( 3
92 ( 3
92 ( 3
5
6a
7b
2.0
4.0
a Equimolar ratio of precursor and TEOS. b 1,4-bis(triethoxysilyl)ben-
zene3.
The present paper deals with the preparation and of a new
family of bridged allylorganosilane precursors that upon sur-
factant-assisted assembly afford ordered mesoporous organo-
silica having pore walls with molecular-scale periodicity
(Scheme 1). The approach provides important insights into the
development of molecular-scale periodicity, spurring new debate
on the formation of periodic mesostructures with crystal-like
pore walls.
lithium chips (8.4 g, 1.20 mol) in THF (100 mL) along with a pressure-
equalizing dropping funnel and magnetic stirrer. The reaction flask was
cooled to -10 °C in a NaCl-ice water bath. Under vigorous stirring, a
solution of allyl phenyl ether (13.7 mL, 0.10 mol) in THF (50 mL)
was then added dropwise to the mixture over 2 h through the dropping
funnel. After further stirring for 1 h, the supernatant was transferred to
a solution of 1,4-bis(triethoxysilyl)benzene (3.2 g, 8.0 mmol) in THF
(100 mL) via a cannula and stirred for 1 h at 0 °C. The resultant mixture
was then poured into water and extracted with ether. The organic
extracts were dried over MgSO4 and filtered. Evaporation of solvents
and purification of the residual oil by column chromatography on silica
gel (hexane/AcOEt ) 40:1 as eluent) gave a colorless oil (2.29 g, 76%).
1H NMR (500 MHz, CDCl3) δ 1.78-1.79 (m, 12H), 4.80-4.86 (m,
12H), 5.69-5.74 (m, 6H), 7.41 (s, 4H). 13C NMR (125 MHz, CDCl3)
δ 19.4, 114.3, 133.3, 133.7, 136.4. 29Si NMR (CDCl3) δ -7.60.
Elemental Anal. Calcd for C24H34Si2: C, 76.12; H, 9.05. Found: C,
76.05; H, 9.09.
Experimental Section
General. Two stable allylorganosilane precursors, 1,4-bis(diallyl-
ethoxysilyl)benzene and 1,4-bis(triallylsilyl)benzene, were synthesized
and purified by silica gel column chromatography under ambient
conditions. All reactions were carried out in a nitrogen atmosphere with
dry, freshly distilled solvents under anhydrous conditions unless
otherwise noted. Tetrahydrofuran (THF) and diethyl ether were distilled
from sodium benzophenone. All reagents were of highest commercial
quality and used without further purification unless otherwise noted.
1H nuclear magnetic resonance (NMR) spectra were recorded on a
JEOL JNM ECP-500 (500 MHz) spectrometer. The chemical shifts
are reported with respect to either tetramethylsilane (0.00 ppm) or
CHCl3 (7.26 ppm) as an internal standard, using the following for
multiplicities: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet;
b, broad. 13C NMR spectra were recorded on a JEOL JNM-500 (125
MHz) spectrometer with CDCl3 (77.0 ppm) as an internal standard.29Si
NMR spectra were acquired on a JEOL JNM-500 (99 MHz) spectrom-
eter. Infrared spectra (IR) were recorded on a JASCO Fourier transform
IR (FT-IR) spectrometer, and elemental analyses were performed on a
Perkin-Elmer 2400 analyzer.
Synthesis of 1,4-Bis(diallylethoxysilyl)benzene. To a 500 mL, three-
necked round-bottom flask fitted with an N2 inlet adapter was added
1,4-bis(triethoxysilyl)benzene (13.4 g, 33.3 mmol) at 0 °C along with
a magnet stirrer and rubber septum. A solution of allylmagnesium
bromide (1.0 M in ether, 200 mL, 0.20 mol) was slowly added dropwise.
After complete addition of the Grignard reagent, the mixture was
allowed to warm to room temperature and stirred for a further 9 h.
The mixture was poured into aqueous 5% HCl solution (150 mL) and
extracted with ether. The organic extracts were neutralized with
saturated aqueous NaHCO3 solution, washed with brine, dried over
MgSO4, and filtered. Evaporation of solvents and purification of the
residual oil by column chromatography on silica gel (hexane/AcOEt
1
) 40:1 as eluent) gave a colorless oil (11.8 g, 92%). H NMR (500
1,4-Bis(triethoxysilyl)benzene was prepared according to the litera-
ture procedure.8 To a solution of magnesium turnings (15 g, 0.61 mol)
and tetraethoxysilane (450 mL, 2.0 mol) in THF (300 mL) under
nitrogen was added a small crystal of iodine, and the mixture was
brought to reflux. A solution of 1,4-dibromobenzene (48 g, 0.20 mol)
in 100 mL of THF was then added dropwise over 5 h. Within 30 min
of initiating the addition, the reaction became mildly exothermic. The
reaction mixture was refluxed for 1 h after completion of dibromide
addition. The resultant gray mixture was then allowed to cool to room
temperature. Hexane (500 mL) was added to precipitate any remaining
magnesium salt, and the mixture was quickly filtered under nitrogen
to afford a clear light-yellow solution. The solvent was removed by
rotary evaporation, and the residue was distilled under vacuum (0.2
mmHg, 140 °C) to give a clear oil (41.1 g, 50%). 1H NMR (500 MHz,
CDCl3) δ 1.16 (t, J ) 7.0 Hz, 18H), 3.79 (q, J ) 7.0 Hz, 12H), 7.60
(s, 4H). 13C NMR (125 MHz, CDCl3) δ 18.1, 58.6, 133.0, 134.0. 29Si
NMR (99 MHz, CDCl3) δ -57.5. Elemental Anal. Calcd for C18H34O6-
Si2: C, 53.70; H, 8.51. Found: C, 53.67; H, 8.56.
MHz, CDCl3) δ 1.12 (t, J ) 7.0 Hz, 6H), 1.83-1.89 (m, 8H), 3.69 (q,
J ) 7.0 Hz, 4H), 4.81-4.89 (m, 8H), 5.70-5.79 (m, 4H), 7.50 (s,
4H). 13C NMR (125 MHz, CDCl3) δ 18.3, 21.1, 59.2, 114.7, 132.8,
133.1, 136.8. 29Si NMR (99 MHz, CDCl3) δ -1.78. Elemental Anal.
Calcd for C22H34O2Si2: C, 68.34; H, 8.86. Found: C, 68.61; H, 8.99.
Synthesis of Mesoporous Benzene-Silica Solid. Refer to the
synthesis parameters presented in Table 1. For the best synthesis
(preparation 5), 1,4-bis(diallylethoxysilyl)benzene (0.75 g) was sus-
pended in an aqueous solution of octadecyltrimethylammonium chloride
(C18TMACl) surfactant (0.72 g in 33 g ion-exchanged water) containing
6N sodium hydroxide (0.5 g) and stirred to promote hydrolysis at
ambient temperature for 20 h followed by aging at 95 °C for a further
20 h. The resultant white precipitate was then recovered by filtration
and washed repeatedly with distilled water. The benzene-silica meso-
porous solid was finally collected after removal of the surfactant by
solvent extraction.3 The yield of the final product was approximately
34%.
One-pot co-condensation of 1,4-bis(diallylethoxysilyl)benzene and
tertaethyl orthosilicate (TEOS) was also attempted using an equimolar
ratio of both silica precursors under similar reaction conditions
(preparation 6; Table 1). The synthesis parameters for mesoporous
materials derived from 1,4-bis(triethoxysilyl)benzene3 are also presented
in Table 1 for comparison (preparation 7).
Synthesis of 1,4-Bis(triallylsilyl)benzene. To a 500 mL, three-
necked round-bottom flask equipped with a reflux condenser was added
(7) (a) Shimada, T.; Aoki, K.; Shinoda, Y.; Nakamura, T.; Tokunaga, N.;
Inagaki, S.; Hayashi, T. J. Am. Chem. Soc. 2003, 125, 4688. (b) Aoki, K.;
Shimada, T.; Hayashi, T. Tetrahedron Asymmetry 2004, 15, 1771.
(8) Shea, K. J.; Loy, D. A.; Webster, O. J. Am. Chem. Soc. 1992, 114, 6700.
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A R T I C L E S
Kapoor et al.
Figure 2. Nitrogen adsorption (b) and desorption (O) isotherms and pore-
size distribution (inset) for hybrid mesoporous benzene-silica prepared from
1,4-bis(diallylethoxysilyl)benzene.
Figure 1. PXRD diffraction patterns of hybrid mesoporous benzene-silica
prepared from 1,4-bis(diallylethoxysilyl)benzene: (a) as-synthesized, (b)
solvent extracted (preparation 5, Table 1).
In other typical syntheses, 0.22 g of 1,4-bis(triallylsilyl)benzene
precursor was mixed in an alkaline aqueous solution (6N NaOH, 0.17
g; H2O, 15 g) of C18TMACl surfactant (0.24 g) and hydrolyzed at
ambient temperature for 48 h followed by aging at 92 ( 3 °C for a
further 24 h. The material was recovered by filtration, drying and
surfactant removal by solvent extraction as described in ref 3.
Characterization. Powder X-ray diffraction (PXRD) patterns were
measured on a Rigaku RINT-2200 diffractometer with CuKR radiation
(40 kV, 30 mA) from 1° to 40° (2θ) in 0.01° steps at a scan speed of
1°(2θ) min-1. Porosimetry measurements (N2 isotherms) were obtained
on a Quantachrome Autosorb-1 sorptometer at -196 °C. Prior to
measurement, all samples were outgassed at 80 °C and 10-4 Torr.
Brunauer-Emmett-Teller (BET) surface areas were calculated from
the linear section of the BET plot (P/P0 ) 0.05-0.3). Pore-size
distributions were determined using the Barrett-Joyner-Halenda (BJH)
method from the adsorption branch of the isotherms. 13C cross-
polarization (CP) and 29Si magic-angle spinning (MAS) NMR spectra
were recorded on a Bruker-300 spectrometer at 75.47 and 59.62 MHz
using 4 mm zirconia rotors and a sample spinning frequency of 3 kHz,
respectively. The chemical shifts for all spectra were referenced to
tetramethylsilane at 0 ppm.
Figure 3. (a) 29Si and (b) 13C NMR spectra of hybrid mesoporous benzene-
silica prepared from 1,4-bis(diallylethoxysilyl)benzene.
The nitrogen adsorption isotherm indicates a type-IV isotherm
based on the International Union of Pure and Applied Chemistry
(IUPAC) classification, confirming the existence of uniform
mesopores (Figure 2). However, a small hysteresis related to
capillary condensation in the interparticle mesopores was
observed at relative pressure above P/P0 ) 0.8. The BJH pore
diameter, BET surface area, and mesopore volume were 23.5
Å, 744 m2 g-1, and 0.53 cm3 g-1, respectively.
The 29Si and 13C MAS NMR results also confirmed that the
pore walls of the mesoporous benzene-silica are composed of
a covalently bonded network of O1.5Si-C6H4-SiO1.5 units. The
two sharp resonance at -72.2 and -80.7 ppm in the 29Si NMR
spectrum are assigned to Tn silica species T2[SiC(OH)(OSi)2]
and T3[SiC(OSi)3], respectively, indicating the complete removal
of the allyl leaving group (i.e., complete deallylation during
hydrolysis). No signals due to SiO4 species (Si sites attached
to four oxygen atoms Qn, n ) 1-4) were detected between -98
and -110 ppm, indicating essentially no evidence for Si-C
bond cleavage during the sol-gel process or synthesis (Figure
3a). The 13C NMR spectrum displays a resonance at 133.6 ppm
due to carbons on the benzene ring, and another resonance (*)
due to the spinning sidebands. The absence of signals due to
allyl carbons,7 which would appear at around 135, 113 and 23
ppm in the 13C NMR spectra, also confirms the complete
elimination of allyl groups during synthesis (Figure 3b). The
signals below 50 ppm are probably due to partial ethanolysis
of surface silanols (Si-OH) during template removal by HCl/
ethanol extraction and possible traces of the surfactant.3-7
Structural Evolution. Figure 4 shows the PXRD patterns
obtained during development of the mesoporous materials
prepared from 1,4-bis(diallylethoxysilyl)benzene. The peak
intensities and sharpness of the patterns, which indicate the
degree of structural ordering, depend heavily on the synthesis
parameters. No precipitate appeared when condensation was
Results and Discussion
Mesoporous Hybrids from 1,4-Bis(diallylethoxysilyl)ben-
zene Precursor. The PXRD patterns (Figure 1a) of the
as-synthesized benzene-silica hybrid mesoporous material de-
rived from 1,4-bis(diallylethoxysilyl)benzene display a d100
reflection peak at 41.6 Å and sharp peaks at d ) 7.6, 3.8 and
2.5 Å at intermediate scattering angles (2θ ) 10-40°),
indicating that the pore walls are formed of crystal-like domains
with a spacing of 7.6 Å in the channel direction. The surfactant-
free material (Figure 1b) also exhibited a well-defined pattern
with diffraction peaks in the low-angle region (d100 spacing of
45.7 Å). The PXRD peak (d100) was strengthened significantly
upon solvent extraction due to the enhancement of contrast of
density between framework and pore channels. The as-
synthesized material displayed a slightly smaller lattice constant
of a ) 48.1 Å. The molecular-scale periodicity was fully
retained upon surfactant removal, indicating substantial frame-
work ordering with crystalline pore walls. The final material
was identical to the materials synthesized from the alkoxy
derivative of the benzene-bridged precursor [1,4-bis(triethox-
ysilyl)benzene],3 which exhibited weaker peaks related to
molecular-scale periodicity.
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Synthesis of Hybrid Mesoporous Organosilica
A R T I C L E S
Figure 4. PXRD patterns showing the evolution of hybrid mesoporous
benzene-silica prepared from 1,4-bis(diallylethoxysilyl)benzene: (a) prepa-
ration 2 (50 °C), (b) preparation 3 (70 °C), (c) preparation 4 (92 ( 3 °C),
and (d) preparation 5 (92 ( 3 °C).
Figure 5. PXRD patterns of hybrid mesoporous benzene-silica prepared
from a mixture of 1,4-bis(diallylethoxysilyl)benzene and TEOS: (a) as-
synthesized, (b) solvent extracted (preparation 6, Table 1)
performed at below 40 °C (preparation 1). The mesostructured
materials could be formed after 4 days’ aging of the initial gel
at 50 °C, although the resultant material displayed poor
molecular-scale periodicity and the apparent collapse of struc-
tural order following surfactant removal by solvent extraction
(preparation 2; Figure 4a). The material synthesized at 70 °C
was also poorly ordered, with relatively lower molecular-scale
periodicity (preparation 3; Figure 4b). An additional hump
centered around a d spacing of 9.3 Å was observed for the
materials prepared at both 50 and 70 °C, indicating incomplete
condensation. The 29Si NMR spectra of these materials revealed
the presence of Tn silicon sites and some Un species, suggesting
that some allyl groups remained. The stable, structurally ordered
mesoporous benzene-silica materials were obtained when the
gel was aged at 92 ( 3 °C. The structural ordering and
molecular-scale periodicity could be clearly in this preparation
(preparation 4; Figure 4c). The modified initial gel composition
also yields a highly ordered mesoporous material, as described
above (preparation 5, Figure 4d). These results indicate that the
basicity of the reaction mixture is an important factor determin-
ing the structural order and crystallinity of the products.
Ordered Hybrids from Mixed Precursors. Materials were
also prepared via the co-condensation of equimolar ratios of
1,4-bis(diallylethoxysilyl)benzene and TEOS under basic condi-
tions (preparation 6; Table 1). The ordered mesoporous material
obtained exhibited molecular-scale periodicity in the pore walls
(Figure 5). The d100 reflection peak (d100 spacing of 45.2 Å)
for the surfactant-free materials was weaker than that for the
benzene-silica hybrid material prepared from 1,4-bis(dial-
lylethoxysilyl)benzene. This material also displayed relatively
broad peaks at d spacings of 7.8, 3.8, and 2.5 Å at intermediate
scattering angles, indicating relatively poor crystallinity com-
pared to the parent material. A significantly strengthening of
the d100 peak was also observed for this material upon solvent
extraction.
Figure 6. (a) 29Si and (b) 13C NMR spectra of hybrid mesoporous benzene-
silica prepared from a mixture of 1,4-bis(diallylethoxysilyl)benzene and
TEOS.
Figure 7. Nitrogen adsorption (b) and desorption (O) isotherms and pore-
size distribution (inset) of hybrid mesoporous benzene-silica prepared from
a mixture of 1,4-bis(diallylethoxysilyl)benzene and TEOS.
size distribution curve indicated that the pore size was highly
uniform (Figure 7). The BJH pore diameter, BET surface area
and mesopore volume were 26.1 Å, 1014 m2 g-1, and 0.73 cm3
g-1, respectively
Mesoporous Hybrids from 1,4-Bis(triallylsilyl)benzene
Precursor. In another approach, a stable 1,4-bis(triallylsilyl)-
benzene precursor without a alkoxy group was synthesized and
the formation of mesostructures under basic conditions was
The 29Si and 13C MAS NMR results confirmed the presence
of both Tn (-71.6 and -81.9 ppm) and Qn (-92.3, -100.9,
-108.4 and -111.8 ppm) silicon species in the materials and
the presence of a covalently bonded network of O1.5Si-C6H4-
SiO1.5 units (Figure 6). The nitrogen adsorption isotherms had
type-IV character with a small hysteresis loop, and the pore-
9
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A R T I C L E S
Kapoor et al.
mixture. The reaction pathway for the deallylation of allyl-
organosilane precursors under acidic conditions has been
reported for the protodesilylation of allylic silanes.7,9 However,
under basic conditions, it is likely that deallylation starts with
nucleophilic attack by hydroxide ions toward the silicon atom
of the precursors. Detailed study of this mechanism is currently
in progress.
Conclusion
Hybrid mesoporous benzene-silica with crystal-like pore walls
was synthesized for the first time using new allylorganosilane
precursors. The formation of hybrid organosilica with meso-
scopic pore ordering and molecular-scale periodicity of the pore
walls can be achieved using both the alkoxy derivative of the
precursors and the allylorganosilane precursors themselves. This
achievement represents a small step toward the discovery of
alternative organosilane precursors and syntheses for the
preparation of mesoporous organosilica with bulky organic
groups, the existing precursors of which are difficult to obtain
in high purity. Our group is currently involved in extensive
research in this area, and the findings will be presented soon.
Figure 8. PXRD patterns of hybrid mesoporous benzene-silica prepared
from 1,4-bis(triallylsilyl)benzene: (a) as-synthesized, (b) solvent extracted.
attempted. The PXRD pattern of the surfactant-free material
clearly shows the successful formation of a mesostructure with
a d100 spacing of 35.5 Å (Figure 8). The other two broad
reflections at d ) 9.5 and 4.4 Å are due to the molecular-scale
periodicity of the pore walls. However, the peaks are not as
sharp as observed for the benzene-silica mesoporous materials
prepared from 1,4-bis(triethoxysilyl)benzene3 and 1,4-bis(di-
allylethoxysilyl)benzene. This material exhibits structural order-
ing, with a BET surface area of 968 m2 g-1 and a BJH pore
diameter of 23.2 Å.
The 1,4-bis(diallylethoxysilyl)benzene precursor is preferable
to 1,4-bis(triethoxysilyl)benzene in terms of cost and the ease
of handling and purification during synthesis. However, the final
yield of the allylorganosilanes precursor is slightly lower (ca.
34.1%) than that for the trialkoxyorganosilane precursor3
(36.7%). The triethoxy derivative of the benzene precursor
releases ethanol during the hydrolysis reaction, whereas propane
is the main leaving species in the hydrolysis of 1,4-bis-
(diallylethoxysilyl)benzene or 1,4-bis(triallylsilyl)benzene.7 Pro-
pane is unreactive toward silica and readily leaves the reaction
Acknowledgment. S. Ikeda is grateful for a postdoctoral
fellowship with the Venture Business Laboratory of the Nara
Institute of Science and Technology. This work was supported
in part by a Grant-in-Aid for Scientific Research from the
Ministry of Education, Culture, Sports, Science and Technology
of Japan (No. 16310094) and by the Core Research for
Evolutional Science and Technology (CREST) program of the
Japan Science and Technology (JST) Agency.
JA043062O
(9) (a) Chan, T. H.; Fleming, I. Synthesis 1979, 761. (b) Sommer, L. H.; Tyler,
L. J.; Whitmore, F. C. J. Am. Chem. Soc. 1948, 70, 2872. (c) Morita, T.
Okamoto Y.; Sakurai, H. Tetrahedron Lett. 1980, 21, 835. (d) Schenk, U.;
Hunger M.; Weitkamp, J. Magn. Reson. Chem. 1999, 37, 75.
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8178 J. AM. CHEM. SOC. VOL. 127, NO. 22, 2005