Formation of reactive microporous networks from alkoxyvinylsilylated siloxane cages

Article abstract of DOI:10.1246/bcsj.20090283

A bifunctional siloxane cage, where double four-membered ring (D4R) silicate was capped with alkoxyvinylsilyl groups, was synthesized as a novel building block for the formation of inorganicorganic microporous solids in order to show its usefulness for synthesizing silica-based nanomaterials with unique structures and properties. The nanobuilding blocks were connected to each other either by hydrolysis and condensation of alkoxysilyl groups to form SiOSi linkages or by hydrosilylation of vinyl groups with hydrogen-terminated D4R (H₈Si₈O₁₂), which was used as a linking agent, to form Si-CH₂CH₂-Si linkages. Xerogel obtained by hydrosilylation showed a significant increase in the surface area upon removal of alkoxy groups by post treatment. The molecular design of bifunctionally- silylated D4R units provides a new approach to the formation of microporous networks with uniform distribution of reactive groups that allow post-modification.

Full text of DOI:10.1246/bcsj.20090283

424
Bull. Chem. Soc. Jpn. Vol. 83, No. 4, 424–430 (2010)
© 2010 The Chemical Society of Japan
Formation of Reactive Microporous Networks from
Alkoxyvinylsilylated Siloxane Cages
Yoshiaki Hagiwara,1 Atsushi Shimojima,2 and Kazuyuki Kuroda*1,3
1Department of Applied Chemistry, Waseda University, Ohkubo-3, Shinjuku-ku, Tokyo 169-8555
2Department of Chemical System Engineering, The University of Tokyo, Hongo-7, Bunkyo-ku, Tokyo 113-8656
3Kagami Memorial Research Institute for Materials Science and Technology, Waseda University,
Nishiwaseda-2, Shinjuku-ku, Tokyo 169-0051
Received October 28, 2009; E-mail: kuroda@waseda.jp
A bifunctional siloxane cage, where double four-membered ring (D4R) silicate was capped with alkoxyvinylsilyl
groups, was synthesized as a novel building block for the formation of inorganic-organic microporous solids in order to
show its usefulness for synthesizing silica-based nanomaterials with unique structures and properties. The nanobuilding
blocks were connected to each other either by hydrolysis and condensation of alkoxysilyl groups to form Si-O-Si
linkages or by hydrosilylation of vinyl groups with hydrogen-terminated D4R (H8Si8O12), which was used as a linking
agent, to form Si-CH2CH2-Si linkages. Xerogel obtained by hydrosilylation showed a significant increase in the surface
area upon removal of alkoxy groups by post treatment. The molecular design of bifunctionally-silylated D4R units
provides a new approach to the formation of microporous networks with uniform distribution of reactive groups that allow
post-modification.
8¹
Nanoporous silica-based materials are widely used as
is also known that D4R silicate anions (Si8O20 ) are formed
almost quantitatively from various silicate sources in aqueous
solutions of tetramethylammonium hydroxide,17-20 and can be
functionalized at all corners by silylation with a variety of
organochlorosilanes.21-28 The construction of porous solids by
interconnecting these D4R-derivatives with Si-O-Si or Si-R-
Si linkages have been extensively studied so far.29-43 We have
recently reported the synthesis of silica-based nanomaterials
from alkoxysilylated D4R units (Si8O12(OSiMe3¹n(OEt)n)8,
n = 1-3).44 These derivatives form siloxane networks by sol-
gel processes, and the resulting xerogels exhibited different
structures and surface areas, depending on the number of
alkoxy groups (n). Therefore, it is quite interesting to design
silicate-based D4R units in a more sophisticated way to prepare
silica-based nanomaterials incorporating functional groups
instead of methyl groups within the structures.
catalysts, adsorbents, and membranes.1-4 Among various
synthetic routes to such materials, a building block approach
based on the interconnection of well-defined siloxane species
has received significant interest.5 The use of designed oligo-
meric precursors leads to a better control of the final structures
and properties than that of conventional monomeric precursors,
such as tetraalkoxysilanes and organotrialkoxysilanes.
The siloxane cage with a double four-membered ring (D4R)
structure is particularly useful as a building block because of its
rigid and symmetric framework.6-9 The D4R structure with
specific Si-O-Si angles and very small internal space, being
able to accommodate atomic hydrogen and fluoride ions,10-12
provides unique properties different from those derived from
amorphous networks. Si atoms on the corners can partly be
replaced with other elements like Al and Ti, which will also
lead to the design of well-defined heterogeneous catalysts. D4R
derivatives with the general formula of RSi8O12, where R = H
or organic groups, can be obtained by hydrolysis and poly-
condensation of the corresponding trifunctional silanes.13-16 It
In this paper, we report the synthesis of two types of
microporous solids by using bifunctional, alkoxyvinylsilylated
D4R siloxane cage as a novel nanobuilding block (Scheme 1).
The first one is prepared by hydrolysis and polycondensation of
Scheme 1. Formation of microporous networks from alkoxyvinylsilylated D4R silicate 1.
Published on the web March 18, 2010; doi:10.1246/bcsj.20090283

Y. Hagiwara et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
425
1/100/150. After stirring for 30 min, precipitates of pyridine
hydrochloride were removed by filtration to give a clear solution.
The precursor 1 ((Vi(i-PrO)2Si)8Si8O20) was isolated as a clear
viscous liquid by the removal of the unreacted silylating agent,
followed by gel permeation chromatography (GPC) using THF as
the eluent.
Synthesis of Sol-Gel-Derived Hybrid Xerogel 1G. Hydroly-
sis and polycondensation of the precursor 1 was conducted in a
mixture of THF, H2O, and 6 M HCl. The molar ratio of 1/THF/
H2O/HCl was 1:16:16:0.64. The mixture was initially in an
emulsion state, but it became a clear solution during stirring at
room temperature and finally formed a transparent gel after 1 h.
The xerogel 1G obtained by drying under vacuum was pulverized
before characterization.
alkoxy groups to form porous siloxane networks, while vinyl
groups remain intact. The other is prepared by hydrosilylation
of vinyl groups with various linkers, containing ¸SiH groups,
to form ethylene-bridged siloxane networks while alkoxy
groups largely remain. Because there are lots of substances
possessing ¸SiH groups, novel hybrid materials can be
designed by appropriate selection of starting materials. In this
study we have chosen hydrogen-terminated D4R (H8Si8O12)
because it also acts as a building block. In both of the systems,
functional groups, i.e., vinyl groups or alkoxy groups, can be
uniformly placed in the porous networks, which provides a
unique opportunity for post modification.
Experimental
Synthesis of Ethylene-Bridged Hybrid Gel 2G by Hydro-
silylation with H8Si8O12. Hydrosilylation of the precursor 1 with
H8Si8O12 was conducted in a mixture of platinum tetramethyl-
divinyldisiloxane complex and toluene (20 mL per gram of 1). The
molar ratio of 1/H8Si8O12/Pt was 1:1:0.04. The mixture was
stirred at room temperature for 3 h and then at 80 °C for 2 days in a
closed vessel until gelation occurred. The hybrid gel 2G obtained
by washing with hexane and drying under vacuum was pulverized
before characterization.
Materials. Cage-like octameric tetramethylammonium (TMA)
silicate (TMA8Si8O20¢xH2O) with
a double four-membered
siloxane ring was prepared by hydrolysis and polycondensa-
tion of tetraethoxysilane (Tokyo Kasei Kogyo) in an aqueous
solution containing tetramethylammonium hydroxide pentahydrate
((CH3)4N(OH)¢5H2O, Sigma-Aldrich, 97%). Hydrated crystals
obtained by concentrating the resulting solution were vacuum
dried to reduce the water content (where x was decreased from 65
up to 29).44 Trichlorovinylsilane (Tokyo Kasei Kogyo, >98%) and
2-propanol (dehydrated, Wako Pure Chemical Industries, 99.5%)
were used for the synthesis of silylating agent of chlorodiiso-
propoxyvinylsilane (Vi(i-PrO)2SiCl). H8Si8O12 was synthesized
from trichlorosilane (Tokyo Kasei Kogyo, >98%) according to
a literature procedure.45 Poly(oxyethylene)-poly(oxypropylene)-
poly(oxyethylene)-type triblock copolymer (EO20PO70EO20, P123)
was purchased from Sigma-Aldrich and used for the synthesis of
mesostructured films. Platinum tetramethyldivinyldisiloxane com-
plex in xylene (2 wt %) was obtained from Sigma-Aldrich and used
as a catalyst for hydrosilylation. Other chemicals, including hexane
(Kanto Chemical., 96%), pyridine, tetrahydrofuran (THF), toluene
(dehydrated, Wako Pure Chemical Industries, 99.5%), KOH, 1
and 6 M HCl aq. (Wako Pure Chemical Industries) were used as
received.
Synthesis of Chlorodiisopropoxyvinylsilane as Silylating
Agent. The silylating agent was synthesized by the dropwise
addition of 2-propanol (23.6 mL) into a mixture of trichloro-
vinylsilane (ViSiCl3, 25 g) and THF (50 mL) under nitrogen
atmosphere. The molar ratio of 2-propanol to trichlorovinylsilane
was 2. HCl gas generated by this reaction was passed out of the
vessel and trapped by KOH aq. After the addition, the solvent,
unreacted trichlorovinylsilane, and dichloroisopropoxyvinylsilane
(Vi(i-PrO)SiCl2) were removed by stirring the mixture at 40 °C
for 30 min under reduced pressure. The resulting clear liquid
mainly consisting of chlorodiisopropoxyvinylsilane (Vi(i-PrO)2-
SiCl) (ca. 80%) and triisopropoxyvinylsilane (Vi(i-PrO)3Si) (ca.
20%) was used as the silylating agent without further purifica-
tion. 29Si NMR (99.3 MHz, CDCl3): ¤ ¹46.6 (Vi(i-PrO)2SiCl),
¹62.3 (Vi(i-PrO)3Si). 13C NMR (125.65 MHz, CDCl3): ¤ 136.2
(SiCH=CH2), 131.7 (SiCH=CH2), 65.4 (SiOCH(CH3)2), 25.4
(SiOCH(CH3)2).
Characterization.
were obtained on
Liquid-state 29Si and 13C NMR spectra
JEOL Lambda-500 spectrometer with
a
resonance frequencies of 99.25 and 125.65 MHz, respectively.
Solid-state 29Si and magic-angle spinning (MAS) NMR measure-
ments were performed on a JEOL JNM-CMX-400 spectrometer at
a resonance frequency of 79.42 MHz, with a pulse width of 45°,
and a recycle delay of 100 s. Solid-state 13C MAS NMR spectra
were obtained on the same spectrometer at a resonance frequency
of 100.54 MHz with a contact time of 5 ms and a recycle delay of
20 s. Deconvolution of the spectrum was performed by using a
Gaussian function on Spinsight software ver. 4.3.2. Chemical
shifts for 13C and 29Si NMR were referenced to tetramethylsilane at
0 ppm. Mass spectrometric results were acquired using a GC-Mate
II by fast atom bombardment ionization. Powder X-ray diffraction
(XRD) patterns were recorded on a Mac Science M03XHF22
diffractometer with Mn-filtered Fe K¡ radiation or on a Rigaku
RINT-Ultima III powder diffractometer with monochromated
Cu K¡ radiation. FT-IR spectra of the products in KBr pellets
were obtained under vacuum using a JASCO FT/IR-6100
spectrometer with a nominal resolution of 0.5 cm¹1. Nitrogen
adsorption-desorption measurements were performed with an
Autosorb-1 instrument (Quantachrome Instruments, Inc.) at 77 K.
Samples were preheated at 120 °C for 3 h under 1 © 10¹2 Torr.
BET surface areas were calculated from the data in the relative
pressure range between 0.05 and 0.30. Water vapor adsorption
isotherms at 25 °C were collected on a Belsorp 18 (Bel Japan,
Inc.). Samples were outgassed at 120 °C for 8 h prior to the
measurements.
Results and Discussion
8¹
Alkoxyvinylsilylation of D4R Silicate (Si8O20 ). Figure 1a
shows the 29Si NMR spectrum of the precursor 1 (in CDCl3)
obtained by silylation of D4R silicate with chlorodiisoprop-
oxyvinylsilane (Vi(i-PrO)2SiCl). The spectrum shows two
signals at ¹69.1 and ¹110.7 ppm with the integral intensity
ratio of 1:1. These signals can be assigned to the T1 and Q4
units of the silylated D4R silicate,46 being shifted upfield
from the T0 signal of the silylating agent (Vi(i-PrO)2SiCl,
Synthesis of Alkoxyvinylsilylated D4R Silicate 1. Alkoxy-
vinylsilylated D4R silicate 1 was synthesized by silylation
8¹
of D4R silicate (Si8O20 ) with chlorodiisopropoxyvinylsilane
(Vi(i-PrO)2SiCl). TMA8Si8O20¢29H2O crystal (2 g) dispersed in
THF (20 mL) was added into a mixture of the silylating agent,
pyridine (14.5 mL), and THF (100 mL) with vigorous stirring
at 0 °C. The molar ratio of D4R/Vi(i-PrO)2SiCl/pyridine was

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Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Porous Networks with Silylated Siloxane Cages
¹
(or Si-O ) corners than isopropoxy groups.48 The precursor
1 was soluble in THF but not in ethanol, in contrast to
diethoxy(methyl)silylated D4R44 which is soluble both in
ethanol and THF. This difference should be due to the decrease
in the polarity of vinyl and isopropoxy groups if compared with
methyl and ethoxy groups.
Vinyl groups of precursor 1 were not polymerized by
thermal treatment with stirring in the presence of azobisiso-
butyronitrile, suggesting that the reactivity of the vinyl groups
is suppressed by the presence of neighboring bulky isopropoxy
groups. Because isopropoxy groups of 1 can be hydrolyzed, as
shown later, the interactions between hydrolyzed silanol groups
and poly(ethylene oxide) chains of triblock copolymer P123
((EO)70(PO)20(EO)70) lead to the formation of a mesostructured
film 1F similar to that reported previously (Supporting
Information, Figure S1).44
Characterization of Sol-Gel-Derived Hybrid Xerogel 1G.
The solid-state 29Si MAS NMR spectrum (Figure 1b) of the
xerogel 1G, prepared by hydrolysis and polycondensation of 1,
shows five signals corresponding to Tm (ViSi(OH)3¹m(OSi)m,
m = 1, 2, and 3) and the Qn (Si(OSi)n(OH)4¹n, n = 3 and 4)
units. From the (T2 + T3)/(T1 + T2 + T3) ratio, it is estimated
that 94% of the terminal silyl groups of 1 are connected to each
other via siloxane bonds. Also the (T2 + 2T3)/2(T1 + T2 + T3)
ratio, which evaluates the degree of polymerization, suggests
that 67% of isopropoxy groups formed siloxane bonds. These
results indicate that eleven isopropoxy groups out of sixteen
per precursor were polymerized at least. These values are
comparable to those for the xerogel derived from (Me(EtO)2-
Si)8Si8O20,44 suggesting that both products have similar net-
work structures. The presence of the Q3 signal is indicative of
the partial cleavage of the Si-O-Si bonds in 1. However, the
Q3/(Q3 + Q4) ratio (ca. 10%) is much smaller than that for the
conventional silica xerogels prepared under similar condi-
tions. The solid-state 13C CP/MAS NMR spectrum (Figure 2b)
shows the signals due to vinyl groups (ca. 130 ppm) together
with small signals of the residual isopropoxy groups. The
relative signal intensity ratio of isopropoxy to vinyl groups is
much smaller than that for the precursor 1 (Figure 2a).
Figure 3 compares the FT-IR spectra of 1 and 1G. The
spectrum of 1 (Figure 3a) shows the presence of vinyl groups,
as confirmed by the bands assigned to the C=C stretching
vibration (1601 cm¹1) and the C-H stretching vibrations of
-CH= (3022 cm¹1) and =CH2 (3062 cm¹1). These bands are
still observed for 1G (Figure 3b), while the C-H stretching
vibrations of -CH3 (at 2975 and 2898 cm¹1) are significantly
decreased by hydrolysis of isopropoxy groups. Both spectra
also show the bands due to Si-O-Si network at 1000-
Figure 1. (a) Liquid-state 29Si NMR spectrum of 1 in
CDCl3 and (b) solid-state 29Si MAS NMR spectrum of 1G.
Figure 2. (a) Liquid-state 13C NMR spectrum of 1 in CDCl3
and (b) solid-state 13C CP/MAS NMR spectrum of 1G
(ꢀ: SSB, : THF hydroperoxide).
¹46.6 ppm) and the Q3 signal of the D4R silicate ((Me4N)8-
Si8O20¢29H2O, ¹96.3 ppm), respectively. The 13C NMR spec-
trum of 1 (Figure 2a) shows the signals of the vinyl group
(136.1 ppm (SiCH=CH2) and 130.5 ppm (SiCH=CH2)) and the
isopropoxy group (65.4 ppm (SiOCH(CH3)2) and 25.4 ppm
(SiOCH(CH3)2)).47 These results and the MS data (m/z found:
1930.1 [M ¹ H]+; calcd for C64H135O36Si16: 1929.5) indicate
that all the corner Q3 sites of D4R silicate were reacted with Si-
Cl groups of the silylating agents with the retention of the vinyl
and isopropoxy groups in the silylated product. Si-Cl groups in
the silylating agent are more active for the reaction with Si-OH
1100 cm and at around 550 cm¹1. Importantly, the band at
¹1
573 cm¹1, which is associated with the skeletal vibration of the
double four-membered siloxane ring, is clearly observed for
1G, suggesting that the D4R units are retained even after the
reaction.38,43,49,50 The retention of the D4R units was also
confirmed by the XRD pattern of 1G (Supporting Information,
Figure S2) to observe a broad peak at around 2ª = 7°, being
very similar to that of xerogel derived from diethoxy(methyl)-
silylated-D4R unit,44 suggesting that a certain structural order
is present. Also, the shoulder peak at 3643 cm¹1 is indicative of
the presence of silanol groups in the networks.1

Y. Hagiwara et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
427
Figure 5. 29Si MAS NMR spectra of ethylene-bridged hy-
brid xerogel 2G (a) before and (b) after the acid treatment
(ꢀ: Si due to tetramethyldivinyldisiloxane of the Pt
catalyst).
Figure 3. FT-IR spectra of (a) 1 and (b) 1G.
the framework mainly due to the flexible Si-O-Si linkages. In
contrast, the isotherm of xerogel derived from (Me(EtO)2Si)8-
¹1 44
Si8O20 (BET surface area is 600 m2 g
)
does not show such
a hysteresis though both gels formed similar networks as
described above. These results suggest that the accessible pores
of 1G become narrower probably due to the difference in size
between methyl and vinyl groups inside pores.
Calcination of 1G at 550 °C greatly reduces the porosity
(surface areas lower than 10 m2 g¹1) because of the serious
structural deformation. The decrease in the IR absorption band
due to D4R units (Supporting Information, Figure S3a) partly
supports the deformation. The acid-treatment of 1G with a
mixture of HCl and EtOH also showed a similar decrease
though the IR peak due to D4R units is observed for the
acid-treated sample (Supporting Information, Figure S3b). The
reason for this result is not well understood, but further
condensation between remaining silanol groups in the networks
could reduce the size of pore entrances of the sample.
Figure 4. Nitrogen adsorption-desorption isotherms of 1G.
The open and filled symbols denote adsorption and
desorption, respectively.
Characterization of Ethylene-Bridged Hybrid Xerogel
2G. Figure 5a shows the 29Si MAS NMR spectrum of 2G.
The signals at ¹53.8 and ¹64.5 ppm can be assigned to the
ethylene-bridged T1 and T3 sites (¸SiO)(i-PrO)2Si-CH2CH2-
The nitrogen adsorption isotherm of 1G (Figure 4) is
basically classified into type I, characteristic of microporous
silica, and the BET surface area is calculated to be 160 m2 g
1
3
¹1
CH2
2
.
Si(OSi)3), denoted as CH T and
T , respectively) formed by
The isotherm shows a hysteresis not closed in the low relative
pressure range. A similar isotherm has been reported by
Morrison et al. for xerogel consisting of D4R units intercon-
nected to each other via Si-CH2CH2-SiMe2-CH2CH2-Si link-
ages.37 Such behavior may be attributed to the micropores with
narrow windows with almost the same width of pore entrance
as that of adsorbate molecules.51 In such cases, adsorption
isotherms may not reflect stable equilibrium in adsorption
measurements, and the flexibility of the networks may also
affect the behavior. The decrease in the nitrogen uptake was
observed when the same sample was measured again after the
first measurement, which suggests irreversible deformation of
hydrosilylation of the vinyl groups of 1 with SiH groups of
H8Si8O12.36 The signals at ¹67.6 and ¹82.4 ppm are assigned
to unreacted diisopropoxyvinylsilyl groups (denoted as ViT1
site) of 1 and hydridosilyl groups (denoted as HT3 site) of
1
H8Si8O12, respectively.36 The integral intensity ratios of CH T =
2
1
1
3
3
3
H
CH2
CH2
CH2
ð
T þ ViT Þ and
T =ð T þ T Þ respectively, both
indicating the degree of forming Si-CH2CH2-Si linkages, are
about 69% and 77%. Notably, in contrast to 1G, the absence of
Q3 site in 2G suggests that D4R units are mostly retained
without the cleavage of Si-O-Si linkages. The residual Pt
catalyst in 2G is also confirmed by the presence of tetra-
methyldivinyldisiloxane, the signal of which appeared at

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Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Porous Networks with Silylated Siloxane Cages
Figure 7. Nitrogen adsorption-desorption isotherms of
ethylene-bridged hybrid xerogel 2G (a) before and (b)
after the acid treatment. The open and filled symbols
denote adsorption and desorption, respectively.
Figure 6. 13C CP/MAS NMR spectra of ethylene-bridged
hybrid xerogel 2G (a) before and (b) after the acid
treatment.
9.1 ppm. The 13C CP/MAS NMR spectrum of 2G (Figure 6a)
shows a new signal at around 5 ppm assigned to ethylene
groups, indicating the formation of Si-CH2CH2-Si linkages.
The signals due to isopropoxy groups (at 65.8 and 26.0 ppm)
and unreacted vinyl groups (at 135.4 and 131.6 ppm) are
also observed, respectively, which is consistent with the
29Si MAS NMR data.
To examine the reactivity of alkoxy groups in the network of
2G, the sample was acid-treated. By stirring it in a 1:1 mixture
of EtOH and 1 M HCl, most of the isopropoxy groups are
hydrolyzed and eliminated. After the acid treatment, the
relative intensity ratios of the 13C CP/MAS NMR signals of
isopropoxy groups to those of ethylene bridges and residual
vinyl groups in 2G are significantly decreased (Figure 6b).
However, the partial cleavage of the Si-O-Si networks upon
the acid treatment was revealed by 29Si MAS NMR (Figure 5b).
The Q3/(Q3 + Q4) ratio indicates that the degree of the
cleavage is at least about 20%. All of the signals became
broader after the acid treatment, which is possibly due to the
variation in their environments caused by the cleavage and/or
by the distortion of the siloxane networks by hydrolysis of the
alkoxy groups.
Figure 8. Water adsorption-desorption isotherms of ethyl-
ene-bridged hybrid xerogel 2G (a) before and (b) after
the acid treatment. The open and filled symbols denote
adsorption and desorption, respectively.
The pore accessibility of 2G before and after the acid
treatment was investigated by nitrogen and water adsorption
measurements. On the basis of the nitrogen adsorption/
desorption isotherm of 2G (Figure 7a), the BET surface area
is calculated to be 80 m2 g¹1. When 2G was calcined at 550 °C,
the BET surface area increased to 300 m2 g¹1 (data not shown).
More strikingly, after the acid treatment the BET surface area
(at 2975 and 2900 cm¹1, respectively. Supporting Information,
Figure S4). The reason for the lower surface area of calcined
2G than that of acid-treated 2G is possibly due to the thermal
rearrangement of the siloxane networks accompanied with
a partial collapse of D4R framework, as confirmed by the
¹1
decrease in the band at around 550 cm (Supporting Informa-
tion, Figures S4a and S4c), and the following decomposition of
Si-CH2CH2-Si bonding. Furthermore, the water adsorption/
desorption isotherms (Figure 8) reveal that the water uptake of
2G is greatly increased after the acid treatment. This result is
attributable to the increase in the pore accessibility of H2O
molecules and to the increase in hydrophilicity of the pore
surface. As confirmed by the increase in the IR band at
¹1
noticeably increased up to 600 m2 g (Figure 7b). This fact
indicates that the inaccessible space in 2G can now be accessed
with N2 molecules because of the elimination of isopropoxy
groups to leave the spaces. Both calcination and acid-treatment
basically eliminate isopropoxy groups from 2G, as confirmed
by the disappearance and decrease in the IR bands due to -CH3

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429
3652 cm¹1 (Supporting Information, Figures S4a and S4b), the
ratio of Si-OH groups increased on the pore surface and the
effect of a small amount of residual vinyl groups (Figure 6b)
should be lowered.
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A novel bifunctional siloxane cage, where double four-
membered ring (D4R) silicate is capped with alkoxyvinylsilyl
groups, was synthesized as a novel building block for the
formation of microporous solids. Two different types of
microporous networks were obtained either by hydrolysis and
polycondensation of alkoxy groups or by hydrosilylation of
vinyl groups with H8Si8O12, and the resulting materials have
uniform distribution of vinyl groups and alkoxy groups,
respectively. The vinyl groups contained in the sol-gel-derived
xerogel will be useful for post-modification such as bromina-
tion, epoxidation, hydroformylation, and metathesis. The
xerogel obtained by hydrosilylation showed a significant
increase in the surface area upon removal of alkoxy groups
by post treatment. Thus the use of such bifunctional nano-
building blocks should be very important for the design of
novel microporous silica-based materials.
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We thank Mr. Yoshiyuki Kuroda, Mr. Yoji Doi, Ms. Azusa
Takai, Mr. Takanori Sakakibara, and Mr. Kota Fukumoto
(Waseda University) for helpful discussion and measurements.
This work was supported in part by the Elements Science and
Technology Project, and a Waseda University Grant for Special
Research Projects (No. 2009B-172). The work was performed
under the Global COE program “Practical Chemical Wisdom.”
The A3 Foresight Program “Synthesis and Structural
Resolution of Novel Mesoporous Materials” supported by the
Japan Society for the Promotion of Science (JSPS) is greatly
appreciated.
Supporting Information
Synthesis procedure of 1F, XRD patterns of 1F (Figure S1),
XRD pattern of 1G (Figure S2), IR spectra of acid-treated and
calcined 1G (Figure S3), and IR spectra of 2G (Figure S4). This
material is available free of charge on the web at http://www.csj.jp/
journals/bcsj/.
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