Synthesis and Properties of Hybrid Mesoporous Materials
FULL PAPER
of the resulting mesoporous materials. Excellent crystallinity
and narrow pore distribution, exclusively in the mesoporous
obtained with a JEOL 1200X electron microscope operating at 120 keV.
The samples were prepared directly by dispersing the powders over
carbon copper grids. Elemental analysis was determined on a Carlo Erba
region, were only achieved for T POSS/BTEB silicon molar
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106 elemental analyzer, whilst the Al content was determined by atomic
ratios of 5–25%. The resultant organic–inorganic materials
were very stable and could be heated at 6508C without any
structural modification. It was possible to functionalize
these mesoporous materials by using post-synthesis treat-
ments, even if strong-acid treatments were required. Thus,
amino groups were covalently incorporated onto the aryl
linkers within the crystalline framework. The resultant
hybrid organic–inorganic materials with the amino groups
were active and selective catalysts for performing base-cata-
lyzed CꢀC bond-forming reactions, such as Knoevenagel
absorption spectroscopy (Spectra AA 10 Plus, Varian). Thermogravimet-
ric analysis (TGA) and differential thermal analysis (DTA) were con-
ducted in a stream of air on a Metler Toledo TGA/SDTA 851E analyzer.
IR spectra were obtained in a Nicolet 710 spectrometer (resolution:
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1
ꢀ2
4
cm ) by using a conventional grease-less cell. Wafers of 10 mgcm
were outgassed at 1008C overnight.
Nitrogen-adsorption isotherms were measured at 77 and 87.3 K on a Mi-
cromeritics ASAP 2010 volumetric adsorption analyzer. Before the meas-
urements, the samples were degassed for 12 h at 1008C. The BET specific
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surface area was calculated from the nitrogen-adsorption data in the
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relative pressure range 0.04–0.2. The total pore volume was obtained
from the amount of N that was adsorbed at a relative pressure of about
.99. External surface area and micropore volume were estimated by
2
condensations and Henry-type reactions.
0
using the t-plot method in the range t=3.5–5. The pore diameter and
pore-size distribution were calculated by using the Barret–Joyner–Halen-
[
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da (BJH) method on the adsorption branch of the nitrogen isotherms.
Experimental Section
Solid-state MAS NMR spectra were recorded at RT under magic angle
spinning (MAS) on a Bruker AV-400 spectrometer. The single-pulse
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Si NMR spectra were acquired at 79.5 MHz with a 7 mm Bruker BL-7
probe by using pulses of 3.5 ms, which corresponded to a flip angle of 3/4
Synthesis of the hybrid mesoporous materials (HYB-POSS-BTEB): Or-
dered porous hybrid materials were synthesized from polyhedral oligo-
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p radians and a recycle delay of 240 s. The H to C cross-polarization
meric silsesquioxanes, also called T
with an appropriate amount of disilane, (R’O)
bridging silsesquioxane. Organic linkers were conformed by silyl-aryl
units from 1,4-bis(triethoxysilyl)benzene (BTEB), which reacted with
cubic POSS siloxane groups. The final reaction mixture had the molar
8
POSS, as the main building blocks,
SiꢀRꢀSi
(OR’) , as the
1
(
CP) spectra were acquired by using a 908 pulse for H nuclei of 5 ms,
3
A
H
U
G
R
N
U
3
1
3
a contact time of 5 ms, and a recycle time of 3 ms. The C NMR spectra
were recorded with a 7 mm Bruker BL-7 probe and at a sample spinning
rate of 5 kHz. The C NMR and Si NMR spectra were referenced to
adamantine and tetramethylsilane, respectively.
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2 2
composition: SiO /C18TMABr/HCl/H O, 1:0.33:0:133.
Catalytic tests: Knoevenagel reactions were carried out in a closed conic
vessel under a nitrogen atmosphere and magnetic stirring.
The first step of the synthesis involved the preparation of a gel by mixing
HCl (37%, 14.7 g), distilled water (30.5 g), and octadecyltrimethylammo-
nium bromide (2.15 g, C18TMABr, Aldrich). Next, a solution of the ap-
Benzylidene malononitrile. A mixture of benzaldehyde (4.8 mmol) and
malononitrile (3.3 mmol) was magnetically stirred at 303 K under a nitro-
gen atmosphere and the catalyst (40 mg, 2.1 mol% N) was added. MeCN
(1 mL) was used as the solvent.
propriated amount of
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T POSS (octakis(tetramethylammonium)silses-
quioxane, ABCR) and BTEB (Aldrich) in EtOH was added and the re-
sultant mixture was vigorously stirred for 2 h at RT. After that, the mix-
ture was left to stand in a polypropylene flask for 2 days at 373 K. The
mesoporous material was recovered by filtration, washed with hot dis-
tilled water until the pH value of the washings reached pH 7, and dried
in air at 333 K for 18 h. The surfactant was removed from the synthesized
Ethyl cyanocinnamate. A mixture of benzaldehyde (3 mmol) and ethyl
cyanoacetate (2.1 mmol) was magnetically stirred at 333 K under a nitro-
gen atmosphere and the catalyst (40 mg, 3.4 mol% N) was added. EtOH
(
1 mL) was used as the solvent.
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material by calcination under a nitrogen atmosphere (2.5 mLs ) in
Ethyl-2-benzylideneacetoacetate. A mixture of benzaldehyde (3 mmol)
and ethyl acetoacetate (2.1 mmol) was magnetically stirred at 353 K
under a nitrogen atmosphere and the catalyst (40 mg, 3.4 mol% N) was
added. EtOH (1 mL) was used as the solvent.
a quartz reactor; the material was heated from RT to 4008C over 3 h at
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a rate of 2.18Cmin , and maintained at 4008C for 1 h. Afterwards,
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a flow rate of 2.5 mLs of air was applied for 4 h.
The samples were termed HYB-xP-yB, where x and y were the number
The synthesis of cyanocoumarin was carried out in a closed conic vessel
under a nitrogen atmosphere and magnetic stirring.
of moles of silicon in the starting gel that originated from T
BTEB silsesquioxanes, respectively.
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POSS and
A
mixture of salicylaldehyde (1.3 mmol) and ethyl cyanoacetate
Post-synthesis incorporation of amino (NH
hybrid materials (HYB-POSS-BTEB-NH ): To incorporate amino groups
onto the bridged benzene groups, which formed the linkers between the
building blocks, HYB-POSS-BTEB (0.5 g) was suspended in H SO
15.2 g, 98%, Aldrich) and HNO (3.47 g, 65%, Panreac) for 3 d at RT.
2
) groups into the mesoporous
(
1.2 mmol) at 353 K was magnetically stirred under a nitrogen atmos-
2
phere and the catalyst (40 mg, 6.2 mol% N) was added.
The Henry reaction was carried out in a closed conic vessel under a nitro-
gen atmosphere and magnetic stirring.
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4
(
3
The acid mixture was pre-prepared and slowly added over the solid.
Then, cold distilled water (300 mL) was added and the resultant solution
was stirred for 4 h at RT. The pale-yellow solid was recovered by filtra-
tion, washed with distilled water, and dried in air at 333 K for 8 h. The
dried solid was suspended in a pre-prepared solution of HCl (15 mL,
Nitrostyrene. A mixture of benzaldehyde (1.9 mmol) and nitromethane
(14 mmol) was magnetically stirred at 373 K under a nitrogen atmosphere
and the catalyst (40 mg, 3.7 mol% N) was added.
In all of these reactions, samples were taken periodically during the reac-
tion and analyzed by GC (HP-5 column, 30 mꢄ0.25 mmꢄ0.25 mm) with
an FID detector. The temperature program was: 808C for 2 min, heating
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2
7%, Aldrich) and SnCl (1.59 g, 98%, Aldrich) and stirring was main-
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tained for an additional 3 d at RT. Next, distilled water (300 mL) was
added into the solution and stirring was continued for a further 4 h. The
yellow sample was recovered by filtration and washed with distilled
water and EtOH. Finally, the amino-substituted solid was dried in air at
to 3008C at a rate of 308Cmin , then at that temperature for 5 min.
3
33 K for 8 h.
Characterization techniques: XRD analysis was carried out on a Philips
X’PERT diffractometer that was equipped with a proportional detector
and a secondary graphite monochromator. The data were collected step-
wise over the range 2q=2–208, at steps of 0.028, an accumulation time of
Acknowledgements
The authors thank the Spanish MICINN (Consolider Ingenio 2010-MUL-
TICAT (CSD2009–00050) and MAT2011–29020-C02–01) for their finan-
2
0 s/step, and Cu Ka radiation (l=1.54178 ꢃ). TEM micrographs were
Chem. Eur. J. 2012, 00, 0 – 0
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers!
Diaz, Urbano
