Direct synthesis and application of bridged diamino-functionalized periodic mesoporous organosilicas with high nitrogen contents

Article abstract of DOI:10.1016/j.jssc.2017.07.040

Bridged diamino-functionalized periodic mesoporous organosilicas [BD-PMO(Et), Et = ethyl] materials were synthesized directly by co-condensation of 2-bis (triethoxysilyl)ethane (BTEE) and 1,4-bis[3-(tirmethoxysilyl)-propyl]ethylenediamino (BTMSEN) under acidic conditions with pluronic triblock copolymer P123 as a template. The nitrogen content in BD-PMO(Et) could be adjusted up to 40% without disturbing the ordered mesoporous structure. These materials were proved to be effective heterogeneous catalysts for the liquid-phase reactions such as Knoevenagel and Henry condensations as well as in the intermolecular cross-double-Michael addition reaction between α-methyl-β-nitrostyrene and α, β-unsaturated ketone. They exhibited comparable catalytic activities with homogeneous catalyst piperazine and can be reused for several times without any negative environmental impact.

Full text of DOI:10.1016/j.jssc.2017.07.040

Journal of Solid State Chemistry 255 (2017) 70–75
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Direct synthesis and application of bridged diamino-functionalized periodic
mesoporous organosilicas with high nitrogen contents
⁎
Feng-Xia Zhu, Pu-Su Zhao , Xiao-Jun Sun, Li-Tao An, Yong Deng, Jia-Min Wu
Jiangsu Key Laboratory for Chemistry of Low-Dimensional Materials, Huaiyin Normal University, Huaian, Jiangsu 223300, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Bridged diamino-functionalized periodic mesoporous organosilicas [BD-PMO(Et), Et = ethyl] materials were
synthesized directly by co-condensation of 2-bis (triethoxysilyl)ethane (BTEE) and 1,4-bis[3-(tirmethoxysilyl)-
propyl]ethylenediamino (BTMSEN) under acidic conditions with pluronic triblock copolymer P123 as a
template. The nitrogen content in BD-PMO(Et) could be adjusted up to 40% without disturbing the ordered
mesoporous structure. These materials were proved to be effective heterogeneous catalysts for the liquid-phase
reactions such as Knoevenagel and Henry condensations as well as in the intermolecular cross-double-Michael
addition reaction between α-methyl-β-nitrostyrene and α, β-unsaturated ketone. They exhibited comparable
catalytic activities with homogeneous catalyst piperazine and can be reused for several times without any
negative environmental impact.
Diamino-bridged PMO
Solid base-catalyst
Water-medium and solvent-free organic
reactions
Green chemistry
1. Introduction
traditional inorganic silica, these PMO with their skeletal organic groups
can present enhanced surface hydrophobicity and thus benefit to organic
Since the discovery of the MCM family of mesoporous molecular
molecules diffusion and adsorption in aqueous medium [19]. Although a
few groups attempt to introduce amine functionality in the PMO
framework under basic conditions, these methods have limited success.
For example, Hossain and Mercier reported the synthesis of an
ethylenediamino-PMO by a base promoted co-condensation method.
Unfortunately, they obtained poorly ordered mesostructural material
with limited amine content (up to 5%) [20]. Herein, we describe the
synthesis of a bridged diamino-functionalized PMO (BD-PMO(Et)) with
an ordered mesoporous structure and variable nitrogen loadings were
prepared under acid conditions. The nitrogen content can be adjusted up
to 40% without disruption of the ordered mesoporous structure. This
heterogeneous amine catalyst, BD-PMO(Et), displayed matchable cata-
lytic efficiency with homogeneous catalyst in water-medium
Knovevenagel, solvent-free Henry, and Michael addition reactions. In
addition, this catalyst could be used repetitively (up to 6 times) without
significantly deactivation, which ultimately reduces cost and waste.
sieves by Mobil scientists, a variety of porous materials such as
meosoporous metal oxides [1], meosoporous silicas [2], meosoporous
carbon [3] and metal oganic framwork [4–6] have been synthesized
using different templating approaches and reactions. Recent develop-
ments in this field have expanded this class of materials to periodic
mesoporous organosilicas (PMO). To date, most surface functionalized
PMO consisting of functional groups, such as amines, thiols, and
cyanogen groups, have been used for the adsorption of heavy metal
ions [7,8], catalysis [9,10] and immobilization of catalyst [11,12]. Of the
various groups functionalized PMO [13–17], the amine group has been
most used. The versatile applications provided by the amine have
included base-catalyzed reactions (e.g., aldol, Knovenagel, Henry cou-
plings) and reagents/ligands (e.g., functional group immobilization,
adsorption of heavy metal ions and the synthesis of nanoparticles).
Most of the amine functionalized PMO have been prepared by post
grafting methods. These methods attached pendant organic groups,
which could decrease access to the amine functional group due to the
channel blockage [18]. Encircling this problem, the co-condensation
method has been developed to prepare PMO with highly accessible
functional groups. This method has additional advantages for preparing
PMO with uniformly dispersed functional groups throughout the frame-
work. Most importantly, the functional groups at the surface of the walls
do not aggregate and therefore do not block the channel. In contrast to
2. Experimental section
2.1. Synthesis of the bridged diamino-functionalized PMO (BD-
PMO(Et))
A typical synthesis procedure of bridged diamino-functionalized
PMO is described as follows:
⁎
Corresponding author.
E-mail address: zhaopusu@163.com (P.-S. Zhao).
http://dx.doi.org/10.1016/j.jssc.2017.07.040
Received 9 May 2017; Received in revised form 21 July 2017; Accepted 31 July 2017
Available online 03 August 2017
0022-4596/ © 2017 Published by Elsevier Inc.

F.-X. Zhu et al.
Journal of Solid State Chemistry 255 (2017) 70–75
A mixture of P123 (1.0 g) and KCl (3.0 g) was dissolved in aqueous
.50 mol/L HCl (31 mL) under vigorous stirring to get a clear solution,
which was stirred at 40 °C for 4 h. Then, 5(1-x) mmol of 1, 2-
bis(triethoxysilyl)ethane (BTEE) was added and stirred for 2 h at
0 °C. Finally, 5x mmol of 1,4-bis[3-(trimethoxysilyl)-propyl]ethylene-
diamine (BTMSEN) was added and the reaction mixture was stirred for
4 h at 40 °C, where x is the molar ratio of BTMSEN in the initial silane
P P
(D ) and pore volume (V ) were calculated based on the BET method and
0
the BJH method, respectively. The surface electronic states were analyzed
by X-ray photoelectron spectroscopy (XPS, Perkin-Elmer PHI 5000 C). All
the binding energy (BE) values were calibrated by using the standard BE
value of contaminant carbon (C1S = 284.6 eV) as a reference.
4
2
2.3. Activity test
mixture, defined by (BTMSEN/(BTMSEN + BTEE)). The molar ratio of
the different components of the mixture is 1 Si: 0.017 P123: 4.5 KCl:
The Knovevenagel condensation reaction between aldehyde and
ethyl cyanoacetate (Reaction 1), Henry reaction between aldehyde
and nitromethane (Reaction 2), and the intermolecular cross-double-
Michael addition reaction between α-methyl-β-nitrostyrene and α, β-
unsaturated ketone (Reaction 3) were used as probes to evaluate the
basic catalytic performances of BD-PMO(Et). The Reaction 1 was
carried out at 40 °C in a 10 mL round-bottomed flask containing a
catalyst with 0.016 mmol nitrogen, 1.0 mmol ethyl cyanoacetate,
1.2 mmol aldehyde, 4.0 mL distilled water and n-decane as an internal
standard. After stirring for 4 h, the products were extracted by ethyl
1
2
.6 HCl: 171 H O, where Si referred to the total silicon source. The
resulting mixture was kept static at 100 °C for another 24 h. The white
solid product was recovered by filtration and dried at 80 °C in vacuum.
The block co-polymer P123 was removed by refluxing the sample in an
acidic ethanol solution for 24 h. For 1.0 g of sample, 500 mL of ethanol
and 40 mL of concentrated HCl (37 wt%) were used.
Deprotonation of the bridged-diamino groups was performed by
stirring the extracted samples in saturated Na
2 3
CO aqueous solution
(
0.10 g of sample/10 mL of Na CO solution) for 24 h at 25 °C. Thus
2
3
treated samples were thoroughly washed with deionized water until the
pH value of the filtrate is neutral. The deprotonated samples were
denoted as BD-PMO(Et)-x.
For comparison, the BD-PMO(Et) was also prepared by traditional
grafting method and denoted as BD-PMO(Et)-G, where G refers to
grafting method. Briefly, A mixture of P123 (1.0 g) and KCl (3.0 g) was
dissolved in aqueous 0.50 mol/L HCl (31 mL) under vigorous stirring
to get a clear solution, which was stirred at 40 °C for 4 h. Then, BTEE
acetate, followed by analysis on a GC-17A gas chromatograph
(SHIMADZU) equipped with a JWDB-5, 95% dimethyl-1-(5%)-diphe-
nylpolysiloxane column and a flame ionization detector (FID). The
column temperature was programmed from 80 °C to 250 °C at a speed
2
of 10 °C/min. N was used as carrier gas. The conversions and yields
determined on the GC were calibrated by using commercially available
samples. Besides the target product, no side products were detected in
Reaction 1. The Reaction 2 was carried out at 90 °C by stirring a
mixture containing a catalyst with 0.024 mmol nitrogen, 1.0 mmol
aldehyde, 4.0 mL nitromethane and n-decane as an internal standard.
After reaction for 5 h, product analysis was performed on the GC under
the above identical conditions. The Reaction 3 was carried out at
40 °C in a 10 mL flask containing 0.50 mmol α-methyl-β-nitrostyrene,
1.0 mmol α,β-unsaturated ketone, 0.50 mmol DMAP and 2.0 mL
dimethyl sulphoxide (DMSO), and a catalyst with 0.0080 mmol nitro-
gen. After vigorous stirring for 16 h, the catalyst was removed by
(
5.0 mmol) was added at 40 °C. After being stirred for 24 h at 40 °C,
The resulting mixture was kept static at 100 °C for another 24 h. The
white solid product was recovered by filtration and dried at 80 °C in
vacuum. P123 was removed by refluxing the sample in an acidic
ethanol solution for 24 h. The as-received PMO(Et) was added into
1
0 mL of dry toluene solution containing 0.50 mmol of BTMSEN, After
stirring for 24 h at room temperature, the solid was centrifuged and
dried at 40 °C under a vacuum condition, followed by Soxhlet-extrac-
tion with dichloromethane for another 24 h to remove physisorbed
nitrogen species on the support. The nitrogen loading was determined
as 0.039 mmol/g by elemental analysis.
centrifugation and washed with CH
2 2
Cl for several times. The organic
layer was diluted with CH Cl . Then the organic phase was washed
2
2
with water and brine. The combined organic layer was dried over
anhydrous magnesium sulfate. The solvent was removed under re-
duced pressure and the remains were diluted with 10 mL tetrahydro-
furan (THF). The liquid products were quantitatively analyzed on a
high pressure liquid chromatograph (HPLC, Waters) equipped with an
AD-H column i-propanol/hexane = 5/95, flow rate = 1.0 mL/min, λ =
254 nm, from which the conversion, selectivity and yield to target
product were determined by using normalization. The conversion was
calculated based on α-methyl-β-nitrostyrene since α, β-unsaturated
ketone was greatly excessive. The reproducibility was checked by
repeating each result at least three times and found to be within
acceptable limits ( ± 5%).
In order to determine the catalysts durability, the catalysts were
centrifuged after each reaction and the clear supernatant liquid was
decanted slowly. The catalyst was washed thoroughly with distilled
water and ethanol, followed by drying at 80 °C for 8 h under vacuum
condition. The recovered catalyst was reused with fresh reactants under
nearly identical reaction conditions.
For comparison, the ordered mesoporous silica catalyst containing
-
1
CH
5 framework, denoted as BD-SBA-15, was synthesized by using co-
condensation of tetraethylorthosilicate (TEOS) and BTMSEN. First,
.0 mL of TEOS was introduced into 38 mL of aqueous solution
2 2 2 2 2 2
-CH -N-CH -CH N-CH -CH fragments incorporated into SBA-
2
containing 30 mL of 2.0 mol/L HCl and 1.0 g of P123. After prehy-
drolysis of TEOS at 40 °C for 80 min, a desirable amount of BESPDS
was added dropwise into the solution, followed by rapid stirring for
2
0 h. After being aged at 100 °C for 24 h, the white precipitate was
filtrated and then dried at vacuum overnight. Finally, the surfactants
and other organic substances were extracted, and washed away
according to the above methods. Deprotonation of the bridged-diamino
groups was the same as the above method used.
2
.2. Characterization
The nitrogen contents in the BD-PMO(Et)-x samples were analyzed on
a CHN analyzer (Elementar Vario ELIII, Germany). All the samples were
combusted completely at 1000 °C in pure oxygen. Fine structure of the
samples was analyzed by Fourier transform infrared (FT-IR) spectra
collected on a Nicolet Magna 550 spectrometer by using the KBr method.
Chemical environment was probed by solid-state NMR spectra recorded on
a Bruker AV-400 spectrometer. Thermogravimetric analysis and differential
thermal analysis (TG/DTA) were conducted on a DT-60 to examine the
thermal stability. The mesoporous structure was examined by low-angle X-
ray powder diffraction (XRD, Rigaku D/Max-RB, CuKα radiation) and
3. Results and discussion
3.1. Structural characteristics
The FT-IR spectra of the solvent-extracted BD-PMO-20(Et) (Fig. 1)
revealed that the surfactant was mostly removed by extracting the solid
in acidic ethanol since no significant signal characteristic of the P123
molecule was found. The FT-IR spectra also revealed that some organic
moieties remained, as indicated by the presence of absorbances at
transmission electron microscopy (TEM, JEOL JEM2010, 200 kV). N
2
−
1
−1
adsorption-desorption isotherms were measured at −196 °C using a
Quantachrome Nova 4000e analyzer. Specific surface area (SBET), pore size
1422, 1267, 1167, 783 and 694 cm . Sharp peaks at 1000–1100 cm
confirmed the formation of siloxane bonds [21–24]. Furthermore, the
7
1

F.-X. Zhu et al.
Journal of Solid State Chemistry 255 (2017) 70–75
x = 10%
x = 20%
x = 30%
x = 40%
1
2
3
4
2
Theta (degree)
Fig. 1. The IR spectrum of the BD-PMO(Et)-20.
Fig. 2. The Low-angle XRD spectrum of BD-PMO(Et)-x samples.
FT-IR spectra strongly supports the presence of absorption bands at
−
1
BTMSEN molar percentage equal to 40%. This suggested that the
channel arrays lose regularity. The ordered structure of BD-PMO(Et)-
1
643 and 3400 cm , which were attributed to N-H bonds [25,26],
−
1
while the relatively broad peaks at 783 and 1167 cm indicated the
presence of an N–H wagging vibration and the antisymmetrical stretch
of a C-N-C moiety, respectively. A peak belonging to a secondary amine
was also clearly visible at 694 cm in each spectrum [22–26]. These
FT-IR spectra confirmed that the organic moieties were linked
covalently to the silica framework in the final hybrid materials BD-
PMO-20(Et).
20 could be further confirmed by TEM images (Fig. 3).
Fig. S3 revealed that all the surfactant-free mesoporous samples
−1
BD-PMO(Et)-x exhibit typical type-IV isotherms with a sharp capillary
condensation step in the relative pressure range of 0.45 ~ 0.55,
indicative of uniform mesopores. With the increase of the BTMSEN
contents, the nitrogen condensation shifted to low relative pressure (P/
0
P ), indicating the decrease of mesopore size. This could be attributed
Solid-state NMR measurements were conducted on the BD-
1
3
29
to the geometrical constrictions of the triblock copolymer template to
accommodate a high content of diamino bridging groups in the pore
walls [32]. The surface area and pore volume also decreased with the
increased diamino contents, due to the mesostructural degeneration.
Textural data for all the samples prepared using different BTMSEN
concentrations were provided in Table S1.
PMO(Et)-20 sample. Fig. S1 shows the C CP MAS NMR and Si
1
3
CP MAS NMR spectra of BD-PMO(Et)-20. In the C NMR spectrum,
the strong signal at 5.0 ppm can be ascribed to the bridging ethyl group
[
27–29]. The signals at 10, 22, 43, 39, and 51 ppm were attributed to
1
2
3
4
5
1
2
3
the C, C, C,
NH CH CH NH CH CH CH Si≡, respectively [27,30]. The signals
C
and
C
carbons in ≡Si CH
2 2 2
CH CH -
4
5
3
2
1
2 2 2 2 2
X-ray photoelectron spectroscopy (XPS) results (Fig. 4) showed the
presence of peaks at binding energies of ca. −101, −284, −399, and
−532 eV corresponding to Si2p, C1s, N1s, and O1s ionization processes,
respectively [33,34]. Particularly, the high-resolution N 1s spectrum in
Fig. 4 indicated the presence of nitrogen atoms in the solvent-extracted
materials, which also supported the BTMSEN functionalization in
mesoporous organosilica materials.
at 58.7 ppm could be ascribed to the ethoxy groups (only one of the two
ethyl carbons) generated during the ethanol extraction process [28].
2
9
Si CP MAS NMR spectrum showed two dominant broad peaks at −59
2
3
and −67 ppm, corresponding to
≡CSi(OSi) ) silicon sites, respectively [27–29]. Small shoulder around
2
50 ppm could be ascribed to T (≡CSi(OH) (OSi)) silicon site. Due to
T
2
(≡CSi(OH)(OSi) ) and T
(
−
3
1
the similar chemical shift, it was difficult to distinguish the Si atoms
connected to the ethyl from that connected to the diamine. The absence
of signals corresponding to Q sites in the range of −90 to −110 ppm
confirmed the retaining of the Si-C bonds during the synthesis process.
The NMR results, together with the IR results, confirmed the integra-
tion of the both organic functionalities in the BD-PMO(Et)-20 sample.
Thermogravimetric analyses of the surfactant-free BD-PMO(Et)-20
material showed three major weight losses at 25–800 °C in air atmo-
sphere (Fig. S2). A weight loss of less than 8% below 150 °C was
observed, probably due to desorption of physisorbed water [31]. Also,
the lack of the characteristic peak for template P123 removal at ~
3.2. Catalytic activity
3.2.1. The Knovevenagel reaction
Table 1 showed the results of the Knovevenagel condensation of
benzaldehyde with ethyl cyanoacetate over different catalysts. All the
reactions were found to proceed to the olefin products and no
intermediate alcohols or other side products were detected. The BD-
PMO(Et)-G exhibited much lower activity and selectivity than the BD-
PMO(Et)-20 with the similar nitrogen loadings. This could be mainly
attributed to the narrower pore channel and the lower ordering degree
of mesoporous structure, leading to the enhanced diffusion limit [35].
For the BD-PMO(Et) series catalysts, the activity first increased and
then decreased with the increase of N loading. The BD-PMO(Et)-10
catalyst with low N loading (0.019 mmol/g) exhibited poor activity due
to the relatively long distance between the neighboring N active sites.
Taking into account that either Reaction 1 needed two kinds of
molecules adsorbed on the neighboring N active sites (see Scheme 1),
the big space between the neighboring N active sites would diminish
their synergetic effect. Meanwhile, the BD-PMO(Et)-30 with very high
N loading (0.056 mmol/g) also showed poor activity possibly due to the
steric hindrance which retarded the diffusion and even the adsorption
of organic molecules on the N active sites. The BD-PMO(Et)-20 with
the N loading of 0.041 mmol/g was determined as an optimum
catalyst, which exhibited equivalent catalytic efficiencies with the
1
70 °C in the DTG curves demonstrates that most of the template was
removed by the ethanol/HCl extraction [25]. Moreover, a gradual
weight loss in the range of 250–450 °C was proportional to the content
of the diamino groups incorporated in the framework. The result
implied that the diamino-bridged groups can be stable up to 250–
4
50 °C in air.
A series of samples with the different nitrogen content under acidic
conditions were prepared. Fig. 2 shows the variation of the XRD
patterns for samples BD-PMO(Et)-10, BD-PMO(Et)-20, BD-PMO(Et)-
3
0, and BD-PMO(Et)-40, prepared with different BTMSEN molar ratio
in the aqueous solution. All samples exhibited a prominent peak in the
diffraction pattern at 2θ ≈ 0.90°. With increasing nitrogen content, the
position of the sharp lowest angle peak remained almost constant.
Nevertheless, the reflections at higher angle became less well resolved
and their intensity decreased and disappeared completely for a
7
2

F.-X. Zhu et al.
Journal of Solid State Chemistry 255 (2017) 70–75
Fig. 3. The TEM images of the BD-PMO(Et)-20 sample along (100) and (110) planes, respectively.
O1s
399.3 eV
C1s
Si2p
N1s
0
100
200
300
400
500
600
392
396
400
404
408
Binding energy(eV)
Binding energy (eV)
Fig. 4. The XPS spectra of BD-PMO(Et)-20 sample.
Table 1
Table 2
Knovevenagel condensation reaction between benzaldehyde and ethyl cyanoacetate over
BD-PMO(Et).
Knovevenagel condensation reaction between carbonyl compounds and ethyl cyanoace-
tate over BD-PMO(Et)-20.
a
a
Entry
Catalyst
N Loading
mmol/g)
Conv. (%)
Yield （%）
Entry R1
R2
Run Temperature (°C) Time (h) Conv. (%) Yield
(
（%）
1
2
3
4
5
6
7
Piperazine
BD-PMO(Et)-G
BD-SBA-15
BD-PMO(Et)-10
BD-PMO(Et)-20
BD-PMO(Et)-30
BD-PMO(Et)-40
/
98
91
81
88
96
82
79
98
91
81
88
96
82
79
1
2
3
4
5
6
7
8
9
OCH3
H
NO2
H
H
H
H
H
H
H
H
H
CH3
H
H
H
H
H
1
1
1
1
2
3
4
5
6
40
40
40
100
40
40
40
40
40
6
4
2
10
4
4
4
4
4
97
96
99
27
95
96
93
92
88
97
96
99
27
95
96
93
92
88
0.045
0.039
0.019
0.041
0.056
0.077
a
Reaction conditions： catalyst containing 0.016 mmol N; 1.2 mmol benzaldehyde;
O; T= 40 °C; t= 4 h.
1
.0 mmol ethyl cyanoacetate; decane; 4.0 mL H
2
a
Reaction conditions: catalyst containing 0.016 mmol N; 1.2 mmol carbonyl com-
O.
pounds; 1.0 mmol ethyl cyanoacetate; decane; 4.0 mL H
2
Scheme 2. Henry reaction between aldehyde and nitromethane.
Scheme 1. Knovevenagel condensation reaction between carbonyl compounds and
ethyl cyanoacetate.
The catalytic reactions between various aldehyde and ethyl cyanoa-
cetate were carried out in water over catalyst BD-PMO(Et)-20. The
results were summarized in Table 2. All the reactions showed relatively
high conversions of BD-PMO(Et)-20 and absolutely high selectivities to
the target products. The substituting groups in the aromatic rings had
great influence on the catalytic activity. Consistent with aldehyde
addition reaction, the presence of the electron-withdrawing group
corresponding piperazine homogeneous catalyst. Table 2 compares the
performance of the catalysts containing similar N loadings around 20%
with different hydrophobicity. The BD-PMO(Et)-20 catalyst gave
relatively higher conversions than BD-SBA-15, which could mainly be
attributed to the organic groups within the PMO skeleton which
enhance surface hydrophobicity, and promote the diffusion and
adsorption of organic molecules on the catalysts, especially in aqueous
medium. (Schemes 2 and 3)
2
(-NO ) at the para-position of benzaldehyde increased the reaction
rate, while the electron-donating groups (-OCH
slowed the reaction.
3
) on benzaldehyde
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F.-X. Zhu et al.
Journal of Solid State Chemistry 255 (2017) 70–75
Scheme 3. The intermolecular cross-double-Michael addition reaction between α-methyl-β-nitrostyrene and α, β-unsaturated ketone.
Table 3
significantly deactivation. From the low-angle XRD and TEM (Fig. 5) of
the used BD-PMO(Et)-20, it can be seen that the catalyst BD-PMO(Et)-
a
H reaction between aldehyde and nitromethane over BD-PMO(Et)-20.
2
0 still remained certain ordered structure after being used in water
Entry
R
Run
Conv. (%)
Yield （%）
mediated the Knovevenagel for 6 times.
1
2
3
4
5
6
7
OCH
H
Cl
3
1
1
1
2
3
4
5
89
97
99
99
95
92
87
89
97
99
99
95
92
87
4. Conclusions
NO
H
2
The bridged diamino-functionalized highly ordered periodic meso-
porous organosilica materials (BD-PMO) were synthesized successfully
via co-polymerization of ethane and diamino bridging group silanes.
These materials possessed highly ordered mesostructures, uniform
pore sizes, high specific surface areas and the relatively stronger base
property because of high diamino loading for base-catalyzed reactions.
Such catalyst not only exhibited higher activity in water-medium
Knovevenagel, solvent-free Henry and the intermolecular cross-dou-
ble-Michael addition reactions, but also displayed matchable catalytic
efficiency with homogeneous catalyst. Importantly, because of diamino
group incorprated into the framwork of BD-PMO, the catalyst could be
used repetitively for several times without significantly deactivation in
these organic reactions, which could reduce the cost and diminish the
environmental pollution. The BD-PMO could also be used as complex-
ing agent for metal, which offered more opportunities for designing
powerful immobilized catalysts and eliminating pollution from heavy
metallic ions for industrial applications.
H
H
a
Reaction conditions: catalyst containing 0.024 mmol N; 1.0 mmol aldehyde; 3.0 mL
nitromethane; T= 90 °C; decane; t= 5 h.
Acknowledgement
This work was supported by the National Natural Science
Foundation of China (20825724), Chinese Education Committee
(
20070270001), Shanghai Government (S30406, 07dz22303) and
Natural Science Foundation of Jiangsu Provincial Department of
Education (No. 15KJA150003).
Fig. 5. The small-angle XRD pattern of the BD-PMO(Et)-20 sample after being reused
for 6 times in Knovevenagel condensation reaction. The inset is the TEM image.
3
.2.2. The Henry reaction
Appendix A. Supporting information
Henry reactions between aldehyde and nitromethane were also
carried out with the BD-PMO catalysts. The catalytic results were
shown in Table 3. From GC and GC/Mass analyses, it was found that all
of the catalyzed reactions gave an α,β-unstaurated olefinic products,
and no β-nitro alcohol product was detected. This is consistent with the
reactions occurring through an imine intermediate. It had been
proposed that this mechanism required the presence of a significant
number of spatially isolated amino groups which act as the basic sites
Supplementary data associated with this article can be found in the
online version at doi:10.1016/j.jssc.2017.07.040.
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3
.2.3. The intermolecular cross-double-Michael addition reaction
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