Mesoporous SBA-15 with short mesochannels immobilized natural quinine for asymmetric Michael addition of chalcones

Article abstract of DOI:10.1007/s10562-011-0648-5

A heterogeneous catalyst of natural quinine supported on the mesoporous SBA-15 of short mesochannels was originally synthesized through a simple co-condensation approach for asymmetric organocatalysed Michael addition of malononitrile to chalcones. The ca

Full text of DOI:10.1007/s10562-011-0648-5

Catal Lett (2011) 141:1378–1383
DOI 10.1007/s10562-011-0648-5
Mesoporous SBA-15 with Short Mesochannels Immobilized
Natural Quinine for Asymmetric Michael Addition of Chalcones
•
Qiu Chen Cui Xin Lan-Lan Lou
•
•
•
Kai Yu Fei Ding Shuangxi Liu
•
Received: 12 April 2011 / Accepted: 11 June 2011 / Published online: 21 June 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A heterogeneous catalyst of natural quinine
supported on the mesoporous SBA-15 of short mesochan-
nels was originally synthesized through a simple co-con-
densation approach for asymmetric organocatalysed
Michael addition of malononitrile to chalcones. The cata-
lytic activity was greatly enhanced, compared with the
conventional analogue. Furthermore, the enantioselectivity
could also be significantly improved for all substrates.
cinchona alkaloids, quinine, has emerged as an efficient
catalyst for the conjugate addition of a,b-enones [11, 12].
However,thehighcostandthedifficultiesinseparationand
recycling of the catalyst restrict its use in industry. These
problems resulting from homogeneous process can be over-
come by the immobilization of chiral catalysts on organic
polymers and inorganic supports [13–16]. Among these sup-
ports mentioned above, the siliceous mesoporous material
SBA-15 with well-ordered pore arrays, large pore volume and
pore size has been of great interest. Variety of chiral cinchona
alkaloid catalysts were successfully immobilized on SBA-15
[17–19]. However, the rather long mesochannel of SBA-15 in
micrometer scale was often unfavorable for the mass transfer
and molecular diffusion [20].
Keywords Asymmetric catalysis Á Michael reaction Á
Immobilization Á Quinine Á Short-mesochannel SBA-15
1 Introduction
The mesoporous SBA-15 with short mesochannels has
fascinated researchers owing to facilitated mass transfer
and less possibility of pore blockage in the adsorption or
catalysis processes, especially when bulky molecules are
involved as adsorbates and reactants. Up to now, several
works were successful in providing the evidence for the
effect [21–23]. However, it is essential to point out that the
majority of the reports about applications of the mesopor-
ous SBA-15 with short mesochannels dealt with adsorption
or base catalysis, while the efforts toward the development
of asymmetric catalysis were scarce. The commercial
availability of quinine and advantage of the mesoporous
SBA-15 with short mesochannels as supports encouraged
us to investigate the heterogeneous catalysts’ utility in
asymmetric Michael addition. Excitingly, the incorporation
of chiral quinine onto the mesoporous SBA-15 materials
with short mesochannels was still rare.
The asymmetric Michael addition of carbanion nucleo-
philes to a,b-unsaturated systems is one of the most
important carbon–carbon bond forming reactions [1–5]. It
is worthwhile to note that malononitrile is an attractive
nucleophile to obtain 1,3-dicarbonyl derivatives or amines
[6, 7]. Among various catalysts, the cinchona alkaloid
derivatives such as 9-amino-9-deoxyepi-quinidine/cincho-
nine and thiourea-substituted cinchona alkaloid, have been
widely employed in the asymmetric Michael addition of
malononitrile to a,b-unsaturated systems [8–10]. However,
the preparation of those cinchona alkaloid derivatives is
often a very complex process. Recently, the natural
Q. Chen Á C. Xin Á L.-L. Lou Á K. Yu Á F. Ding Á S. Liu (&)
Institute of New Catalytic Materials Science and Key Laboratory
of Advanced Energy Materials Chemistry (Ministry of
Education), College of Chemistry, Nankai University,
Tianjin 300071, People’s Republic of China
Herein, we firstly reported a heterogeneous catalyst of
natural quinine immobilized on the mesoporous SBA-15
with short mesochannels by the co-condensation approach
for Michael addition of malononitrile to a,b-unsaturated
e-mail: sxliu@nankai.edu.cn
123

Mesoporous SBA-15 with Short Mesochannels
1379
carbonyl compounds. In comparison to the conventional
SBA-15, not only the higher chemical activity but also
enhanced enantioselectivity was obtained.
for pore size distributions. The scanning electron micros-
copy (SEM) photographs were taken using a Shimadu
SS-550 Scanning Electron Microscope operating at 15 kV.
The transmission electron microscopy (TEM) experiments
were performed on a Philips Tecnai G2F20 Transmission
Electron Microscope operating with a voltage of 120 kV.
Enantiomeric excess (ee) values were determined by HPLC
with a chiral AS-H column, using an Agilent-1200 chro-
matograph equipped with a VWD detector.
2 Experimental
2.1 Preparation of Catalyst
The route to synthesize the catalyst is shown in Scheme 1. The
mesoporous SBA-15 with short mesochannels and conven-
tional SBA-15 functionalized with mercapto groups were
prepared by a co-condensation process described in references
[22, 24] and denoted as SH-ST-SBA-15 and SH-SBA-15,
respectively. The template was removed by ethanol extraction
at 351 K. The thiol-functionalized mesoporous materials (1 g),
quinine (0.4 g), and AIBN (0.1 g) as radical initiator were
added into 25 mL of chloroform in a round-bottomed bottle.
Then the mixture was refluxed for 24 h [18]. The sample was
filtered, washed with chloroform, Soxhlet extracted and dried
under vacuum for 24 h. The quinine-functionalized mesopor-
ous SBA-15 with short mesochannels and conventional SBA-
15 were denoted as QN-ST-SBA-15 (1.47 wt% of N) and
QN-SBA-15 (1.51 wt% of N), respectively.
2.3 Typical Procedure for the Asymmetric Michael
Addition
A general process was as follows: the catalyst QN-ST-SBA-
15 or QN-SBA-15 (0.02 mmol) and chalcones substrate
(0.2 mmol) were added to 2 mL of dry toluene and stirred at
room temperature for 4 h. Then malononitrile (0.4 mmol)
was added and the reaction was conducted at room temper-
ature for 5 days. The catalyst was filtered and the reaction
products were analyzed by HPLC. The homogeneous reac-
tion was carried out with quinine (0.02 mmol), malononitrile
(0.4 mmol) and substrates (0.2 mmol) in 2 mL of dry tolu-
ene, at room temperature for 5 days.
The catalyst was reused for asymmetric addition of
malononitrile to chalcone. When a reaction was over, the
catalyst was filtered, washed thoroughly with toluene
(20 mL), acetone (20 mL) and dried before the next run.
2.2 Characterization
Powder XRD patterns of the samples were conducted with
R/max-2500 diffractometer with Cu Ka source and a step
size of 0.02°. FT-IR spectra were performed on a Bruker
Vector 22 spectrometer using self-supporting wafers. Ele-
mental analysis was obtained by using a Perkin-Elmer
240C analyzer. N2 adsorption–desorption analysis was
carried out at 77 K on a Micromeritics TriStar 3000
apparatus. The experimental data were further processed by
the BET equation for surface areas and by the BJH model
3 Results and Discussion
3.1 Characterization of the Catalyst
The FT-IR spectrum of QN-ST-SBA-15 (Fig. 1a) showed
an absorption band at 1594 cm-1 assigned to the –C=N–
stretching of the quinoline ring. The bands observed
Scheme 1 Depiction of the
immobilization of quinine onto
mesoporous supports
AIBN
Si
Si
OMe
S
HS
quinine
N
OH
H
N
123

1380
Q. Chen et al.
500
400
300
200
100
0
a
0.16
0.12
0.08
0.04
0.00
b
a
b
5
10
15
20
Pore Diameter (nm)
b
a
c
0.0
0.2
0.4
0.6
0.8
1.0
3000
2000
1000
Relative Pressure(P/P0)
ν/cm-1
Fig. 3 N2 adsorption–desorption isotherms and pore size distribu-
tions of (a) QN-ST-SBA-15 and (b) QN-SBA-15
Fig. 1 FT-IR spectra of (a) QN-ST-SBA-15, (b) used QN-ST-SBA-
15 after Soxhlet extraction with acetone, and (c) QN-ST-SBA-15 after
three runs
Table 1 Pore structural parameters of various materials
Sample
Mesopore
volume (cm3/g)
Surface
area (m2/g)
Pore
diameter (nm)
SH-ST-SBA-15
SH-SBA-15
1.0
880
519
315
317
6.3
6.1
5.9
5.0
0.60
0.46
0.39
QN-ST-SBA-15
QN-SBA-15
of quinine moiety onto SH-ST-SBA-15 might disturb the
ordered mesostructure by a certain degree [27]. The N2
adsorption–desorption isotherms and pore size distributions
of QN-SBA-15 and QN-ST-SBA-15 are shown in Fig. 3.
Both of the catalysts exhibited typical IV type isotherms
with a steep increase in adsorption at P/P0 = 0.45–0.75.
All the materials possess a narrow pore size distribution,
characteristic of well-ordered mesoporous materials. The
corresponding structural parameters calculated by N2
adsorption–desorption isotherms are listed in Table 1. It
was found that incorporation of quinine resulted in a
remarkably decrease in BET surface area, pore volume and
pore size, which suggested that quinine was successfully
immobilized on SBA-15. The pore size of QN-ST-SBA-15
is slightly larger than the typical one, which may be
attributed to the so-called salting out effect in the presence
of Zr(IV) ion [22]. Figure 4 shows the EM photographs of
QN-ST-SBA-15. The catalyst possesses a platelet mor-
phology and short mesochannels which are quite different
from typical SBA-15 with fiberlike morphology and long
mesochannels in micrometer scale. The well-ordered pore
arrays could be easily observed and the pore size of QN-
ST-SBA-15 may be directly measured to be about 6 nm, in
good accordance with the N2 sorption results.
a
b
1
2
3
4
5
2theta/degree
Fig. 2 Powder XRD patterns of (a) SH-ST-SBA-15 and (b) QN-ST-
SBA-15
between 2936 and 2870 cm-1 were assigned to –C–H
stretching vibrations, bands at 1632 and 1515 cm-1 which
are presented in the spectrum of quinine can also be
observed. All of these peaks indicated the successful
incorporation of quinine onto SBA-15. The elemental
analysis of QN-ST-SBA-15 showed that the loading of
quinine was about 0.52 mmol/g. Figure 2 shows the pow-
der XRD patterns of SH-ST-SBA-15 and QN-ST-SBA-15.
All of the diffractograms showed the well-resolved
reflections at (100) (intense and sharp), (110) and (200)
(weak and broad), suggesting the less ordered pore array
after introduction of 3-mercaptopropyltrimethoxysilane by
the co-condensation approach [22, 25, 26]. Moreover, the
decrease of peak intensity suggested that the incorporation
123

Mesoporous SBA-15 with Short Mesochannels
1381
Fig. 4 EM micrographs of QN-
ST-SBA-15: a SEM image, b, c,
d TEM images
Table 2 Asymmetric Michael addition of malononitrile to chalconesa
CN
NC
R1
O
O
catalyst, 5d
toluene, rt
CN
NC
+
*
R1
R2
R2
Entry
Catalyst
R1
R2
Yield (%)b
ee (%)c
1d
2
3e
4f
5
QN-ST-SBA-15
QN-ST-SBA-15
QN-ST-SBA-15
QN-ST-SBA-15
QN-SBA-15
Quinine
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
52
72
76
74
38
78
44
27
68
57
32
92
52
48
62
39
49
44
88
49
35
71
50
46
86
44
6
7
QN-ST-SBA-15
QN-SBA-15
Quinine
4-CH3OC6H4
8
4-CH3OC6H4
4-CH3OC6H4
4-FC6H4
4-FC6H4
4-FC6H4
Ph
9
10
11
12
13g
a
QN-ST-SBA-15
QN-SBA-15
Quinine
QN-ST-SBA-15
Reactions were performed with catalyst (0.02 mmol), chalcones substrate (0.2 mmol) and malononitrile (0.4 mmol) in solvent (2 mL) at room
temperature for 5 days
b
Isolated yield
c
Ee% were determined by HPLC with a chiral AS-H column. The absolute configuration was S
d
Reaction was performed for 3 days
e
Reaction was performed using 20 mol% catalyst
f
Reaction was performed at 323 K
g
The catalyst was filtered after 3 days, and the reaction was performed for another 2 days
123

1382
Q. Chen et al.
activity was improved (Table 3, entry 4). To make clear
what is responsible for the drop in the activity, the catalyst
after three runs was characterized by FT-IR (Fig. 1c). The
characteristic peaks remain mostly the same but a drop in
the intensity after the reaction, which shows that there were
no character changes of the quinine moiety in the whole
process. A new and strong absorption peak at 2196 cm-1
could be observed which was assigned to the characteristic
–C:N stretching vibrations of malononitrile. The used
catalyst after Soxhlet extraction was also characterized by
FT-IR (Fig. 1b). Compared with the catalyst before Soxhlet
extraction, the intensity of the absorption peak at
2196 cm-1 decreased while the intensities of the other
absorption peaks were enhanced. It indicates that the active
sites being covered by the adsorbed reactants might be the
main reason for the decrease of activity and enantioselec-
tivity. The results provided by elemental analysis have also
verified our assumptions. The N content of the catalyst in
the four runs was 1.47, 1.84, 1.91 and 1.76%, respectively
(Table 3).
Table 3 Recycle studies of the heterogeneous catalyst in the asym-
metric Michael addition of malononitrile to chalconea
Run
Yield (%)
ee (%)
N content (%)
1
2
3
4b
a
72
58
46
48
62
20
11
27
1.47
1.84
1.91
1.76
Reactions were performed in toluene at room temperature for
5 days
b
The catalyst was Soxhlet extracted with acetone and dried under
vacuum for 12 h
3.2 Catalytic Studies
The synthesized heterogeneous catalyst was evaluated in
the conjugate addition of malononitrile to chalcones. The
reaction results are summarized in Table 2. The QN-ST-
SBA-15 shows 52% yield and 48% ee for chalcone in
3 days with a loading of 10 mol% (Table 2, entry 1). When
the reaction time was prolonged to 5 days, 72% yield and
62% ee were obtained (Table 2, entry 2). As the amount of
catalyst was increased to 20 mol%, the catalytic activity
increased from 72 to 76% for yield (Table 2, entry 3) but
the enantioselectivity was significantly decreased. The
similar phenomenon was observed when the reaction was
carried out at 323 K (Table 2, entry 4). On the basis of
these results, a range of chalcones were examined as sub-
strates. In general, the QN-ST-SBA-15 was found to afford
both higher yield and ee value than QN-SBA-15 for all of
the substrates (Table 2, entry 2 vs. 5, entry 7 vs. 8, entry 10
vs. 11). This may be possibly attributed to the faster mass
transfer and specific morphology of the mesoporous SBA-
15 with short mesochannels. Furthermore, it is noteworthy
that substituted chalcone was less effective than chalcone
under similar conditions (Table 2, entry 2 vs. 7 and 10,
entry 5 vs. 8 and 11). The electron-withdrawing sub-
stituent, gave the product in higher yields and ee values
compared with the electron donating substituent (Table 2,
entry 7 vs. 10, entry 8 vs. 11). To make sure the catalysis is
indeed heterogeneous, the catalyst was filtered after 3 days
and the filtrate was allowed to react for another 2 days
[28]. Finally, it was found that no further reaction was
observed (Table 2, entry 1 vs. 13).
4 Conclusion
In summary, for the first time, chiral quinine was success-
fully immobilized on the mesoporous SBA-15 with short
mesochannels, and the prepared heterogeneous catalyst
exhibited both higher catalytic activity and enantioselec-
tivity than those of conventional counterpart for asymmetric
Michael addition of malononitrile to chalcones.
Acknowledgments The authors are grateful to the National Natural
Science Foundation of China (20773069), the Specialized Research
Fund for the Doctoral Program of Higher Education (200800551017
and 20100031120029), the Fundamental Research Funds for the
Central Universities, and MOE (IRT-0927) for financial support.
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123

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