Asymmetric mannich reaction of malonates with aldimines using YbIII-pybox complexes supported on self-assembled organic-inorganic hybrid silica with an imidazolium framework

Article abstract of DOI:10.1002/ejoc.201402713

Yb(OTf)₃/iPr-pybox (3b) immobilized on a self-assembled organic-inorganic hybrid silica with ionic liquid phase (SAILP) (Catalyst A) behaves as an efficient and recyclable catalyst in the enantioselective Mannich reaction of malonate esters wit

Full text of DOI:10.1002/ejoc.201402713

FULL PAPER
DOI: 10.1002/ejoc.201402713
Asymmetric Mannich Reaction of Malonates with Aldimines Using
III
Yb -Pybox Complexes Supported on Self-Assembled Organic–Inorganic
Hybrid Silica with an Imidazolium Framework
[a]
[a]
[b]
Babak Karimi,* Ehsan Jafari, and Dieter Enders
Keywords: Asymmetric catalysis / SAILP / Heterogeneous catalysis / Ytterbium / Mannich reaction
Yb(OTf)
ganic–inorganic hybrid silica with ionic liquid phase (SAILP)
Catalyst A) behaves as an efficient and recyclable catalyst
in the enantioselective Mannich reaction of malonate esters
with N-Boc aldimines to afford the corresponding products
in good yields and enantioselectivities. In particular, it has
been shown that the use of catalyst A resulted in much supe-
3
/iPr-pybox (3b) immobilized on a self-assembled or- rior enantioselectivities in comparison with either 1:2
Yb(OTf) /3b on a periodic mesoporous organosilica with 10
percent imidazolium framework (catalyst C) or a catalyst
comprising 1:1 Yb(OTf) /3b on SAILP under the same reac-
3
(
3
tion conditions. Catalyst A could be recycled and reused at
least four times with only a slight decrease in either catalytic
activity or enantioselectivity.
employing YbIII chiral complexes has been identified for
this transformation. Therefore, it seems that there is still
Introduction
[
7]
Catalytic asymmetric Mannich reactions constitute much room to develop new variations of these catalysts in
[
8]
highly useful and efficient methods for the preparation of asymmetric Mannich reaction.
chiral β-amino carbonyl compounds through C–C bond
In this context, we recently disclosed a highly efficient
formation. This is an important organic transformation be- and enantioselective Strecker hydrocyanation of a wide
cause the prepared β-amino carbonyl compounds are sig- range of N-benzhydryl aldimines by utilizing a chiral
nificant chiral building blocks in the skeleton of important Yb(OTf) /3a complex, whereby the corresponding α-amino-
3
pharmaceutical and agrochemical molecules and they are nitriles were obtained in excellent yields and with enantio-
[1,2]
[9]
vital intermediates of organic chemistry.
In particular, meric excess (ee) values of up to 98% (Scheme 1). This
the use of malonate derivatives as nucleophiles in the Man- powerful catalyst in the form of Yb(OTf) /3b complex has
3
nich reaction of imines has attracted much attention be- subsequently been employed as an efficient and highly
cause the products of this reaction can be easily decarboxyl- enantioselective catalyst in the Mannich reaction of malon-
[
3]
ated to give the corresponding β-amino acid derivatives.
In this respect, despite the fact that much attention has been
dedicated to the development of new and efficient organo-
catalytic Mannich protocols by employing malonate-type
[
4]
nucleophiles, catalysis based on chiral metal complexes re-
[
5]
mains very limited. In addition, to our knowledge, there
has been no precedent example of asymmetric Mannich re-
actions using malonate derivatives in the presence of sup-
ported and recyclable metal catalysts. Adding to this ap-
peal, in contrast to the relatively well-developed enantiose-
lective Mannich reaction with a variety of chiral metal com-
plexes based on Al, Ti, Zr, or Cu etc.,[ only one report of
6]
[
a] Department of Chemistry, Institute for Advanced Studies in
Basic Sciences (IASBS),
Zanjan 45137-6731, Iran
E-mail: karimi@iasbs.ac.ir
http://www.iasbs.ac.ir/~karimi/karimi.htm
b] Department of Chemistry, Institute for Organische Chemie,
RWTH Aachen University,
[
Scheme 1. Enantioselective addition of dibenzyl malonate (2a) to
N-Boc imine or TMSCN to N-benzhydryl imines in the presence
of homogeneous chiral Yb(OTf) /3b complex.
3
Landoltweg 1, 52074 Aachen, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201402713.
Eur. J. Org. Chem. 2014, 7253–7258
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7253

B. Karimi, E. Jafari, D. Enders
FULL PAPER
ate esters with N-Boc imines at room temperature, and this
Thermal gravimetric (TG) analysis (Figure 1) of SAILP
has led to the formation of the corresponding Mannich ad- indicated no significant weight loss from room temperature
ducts with excellent yields and enantioselectivities in most to 300 °C, showing that the materials have thermal stability
[
7]
cases (Scheme 1). Meanwhile, to address the recyclability up to approximately 300 °C, but around 70% decrease in
issue, we have found that immobilization of this chiral weight was observed in the range of 300 to 700 °C for the
Yb(OTf) /3a catalyst system on a novel self-assembled or- SAILP, which could be related to the organic moieties of
3
ganic-inorganic silica with ionic liquid phase (SAILP) can the materials. The structure of the prepared materials was
result in a recoverable and heterogeneous catalyst system, further verified by using FTIR spectroscopy. As can be seen
which consistently showed even higher selectivities in the in Figure 2, characteristic SAILP peaks for Si–OH at
enantioselective Strecker reaction as compared with its 3400 cm–1 and Si–O–Si at 1100 cm confirmed the success-
homogeneous analogues,[ at higher reaction temperature ful incorporation of the inorganic silica segment in the ma-
–1
9]
(
–60 to –40 °C vs. –78 °C) in six successive reaction runs.[10] terials. In addition, the observed peaks for the aromatic and
–1
–1
aliphatic C–H (2933 cm ), C=C (1571 cm ), and C=N
–1
(
1635 cm ) absorbtion bands for the materials proved the
presence of imidazolium moieties in their structure.
Results and Discussion
The consistentlybetter catalytic performanceof Yb(OTf)3/
3
a@SAILP in the asymmetric Strecker reaction of
[
10]
imines, and the fact that there is no example of Mannich
reaction using supported chiral catalysts, made us ask if this
chiral supported catalyst system might be favorably em-
ployed in the enantioselective Mannich reaction of malon-
ates with imines. To do this, SAILP was prepared according
to the our previously reported procedure using 1,3-bis(3-
trimethoxysilylpropyl) imidazolium iodide (BTMSPI) as
the ionic liquid precursor through its hydrolysis and co-con-
densation under mildly acidic conditions (Scheme 2).
Figure 1. Thermal gravimetric analysis for SAILP.
Figure 2. FTIR spectrum of the pristine SAILP.
Scheme 2. Synthesis of self-assembled ionic liquid phase (SAILP),
Yb(OTf) /3b@SAILP (A, B), and Yb(OTf) /3b@PMO-IL (C).
3 3
The 13C CP-MAS NMR spectrum of pristine SAILP,
shown in Figure 3, clearly reveals three intense peaks at δ
The resulting yellow powder of SAILP was first charac- = 10.5, 24.7, and 52.8 ppm corresponding to carbon C-1
terized by simultaneous thermal analysis (STA), solid state attached to Si, middle carbon C-2 of the bridge propyl
1
3
29
C and Si NMR, FTIR and N sorption analysis to es- group, and carbon C-3 bound to the imidazolium nitrogen,
2
[
10]
tablish the textural and structural features of the materials. respectively.
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Asymmetric Mannich Reaction of Malonates with Aldimines
Figure 3. Solid-state 13C CP-MAS NMR spectrum of the pristine
SAILP.
Figure 4. Solid-state 29Si CP-MAS NMR spectrum of pristine
SAILP.
The appearance of another two intense peaks with
approximately 2:1 ratio at δ = 123.5 and 136.7 ppm corre-
spond to –CH=CH- and –N–CH–N– moieties of the imid-
azolium ring, respectively, and the absence of any ad-
ditional carbon signal clearly proves that all BTMSPI
groups were well consolidated in the framework of the ma-
terial.
characterized by N -sorption analysis (Figure S8) and by
2
transmission electron microscopy (TEM) (Figure 5). As can
be clearly seen, 2D hexagonal channels with pore diameter
of approximately 7–8 nm remained almost unchanged after
immobilizing the Yb(OTf) /3b complex. This value is in
3
good agreement with the average pore diameter estimated
from the Barrett–Joyner–Halenda (BJH) method from the
In addition, the 29Si CP-MAS NMR spectrum of SAILP
adsorption branch of the N -sorption isotherm (Fig-
2
showed an intense peak at δ = –68.4 ppm corresponding to
ure S10).
3
T sites [C-Si(OSi) ] and another signal at δ = –58.5 ppm
3
2
with lower intensity for T Si sites [C-Si(OH)(OSi) ] (Fig-
ure 4). The Si resonance related to partially condensed T
and complete condensed T sites, are significantly more in-
tense than observed for incomplete condensed T [C-Si-
2
2
3
1
(
OH) ] sites, evidencing the presence of organic moieties in-
3
side the framework of the material and confirming a high
degree of condensation of the silanol groups. Moreover, the
absence of signals concerning Q silicon sites [Q , Si(OSi)n
n
(OH)4–n] below δ = –100 ppm clearly demonstrate that no
significant hydrolytic Si–C bond cleavage had occurred and
that the bridge-bonded organic group survived intact in the
hybrid silica network under the synthetic conditions. More-
3
Figure 5. TEM image of 1:2 Yb(OTf) /3b complex supported on
a periodic mesoporous organosilica with 10 percent imidazolium
over, N -sorption analysis of SAILP materials showed typi-
2
framework (PMO-IL) (Catalyst C); scale bar: 20 nm.
cally an isotherm very similar to type II, which is in most
cases characteristic of nonporous or macroporous materials
according to the IUPAC classification.[
The total metal loading of the material was then mea-
sured by atomic absorption spectroscopy through a stan-
11]
Finally, the resulting SAILP was used as a support for dard addition protocol. Moreover, Yb(OTf) /3b@SAILP
3
the immobilization of chiral Yb(OTf) /3b complex. To do catalyst was further characterized by using TGA, FTIR,
3
this, the supported catalysts were generated by simply ex- and TEM analysis.
posing Yb(OTf) (10 mol-%) to either 2 or 1 equivalent of
Having characterized all Yb(OTf) /3b@SAILP samples,
3
3
isopropyl-pybox ligand in anhydrous CH Cl followed by we next proceeded to study and compare their catalytic per-
2
2
treatment with SAILP (200 mg) and evaporation of the sol- formance in the enantioselective Mannich reaction of ma-
vents to give catalyst A or B, respectively (Scheme 2). For lonate esters with N-Boc imines. Since in our previous study
the purpose of comparison, we also prepared another chiral it was realized that the highest ee values of Mannich ad-
supported catalyst (catalyst C) by immobilizing a 1:2 ducts could only be obtained by employing N-Boc protect-
Yb(OTf) /3b on a periodic mesoporous organosilica with ing imines and benzylmalonate under homogeneous condi-
3
[
7]
1
0 percent imidazolium framework (PMO-IL) by following tions, we began our investigation with catalyst A by em-
our previously reported procedure.
[12]
Catalyst C was also ploying essentially the same reaction constituents. Initially,
Eur. J. Org. Chem. 2014, 7253–7258
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7255

B. Karimi, E. Jafari, D. Enders
FULL PAPER
we found that reacting benzaldehyde N-Boc imine (2a, heteroaryl compound in reaction with dibenzylmalonate
mmol), benzylmalonate (3, 1.1 mmol), MeOH (1 equiv.), (Table 2, entry 12), indicating that no poisoning of the sup-
1
and catalyst A (10 mol-%) at room temperature for 24 h af- ported Yb catalyst occurred with heteroatom-containing
forded β-amino ester 4a in high yield (93%) and moderate substrates. Interestingly, the present supported Yb catalyst
enantioselectivity (46%) (Table 1, entry 1). Given that the also promoted the asymmetric Mannich reaction of ali-
level of enantioselectivity in this reaction was much inferior phatic aldimins, albeit with relatively low ee and yield with
[
7]
to that obtained by using homogeneous Yb(OTf) /pybox
respect to the aromatic substrates (Table 2, entry 13).
3
under the same catalyst loading, we hypothesized that the
reaction temperature may be crucial to enhance the
Table 2. Scope of the enantioselective heterogeneous Mannich reac-
tion of dibenzylmalonate and N-Boc imine derivatives using ionic
enantioselectivity. Indeed, when the reaction temperature liquid supported pybox catalyst A.[
a]
was decreased to 0 and –18 °C, the enantioselectivity in-
creased dramatically to 51 and 74%, respectively, under
otherwise the same reaction conditions (Table 1, entries 2
Yield [%][b]
ee [%][c][d]
Entry
R
1
2
3
4
5
6
7
8
9
Ph
82
86
88
89
87
88
81
83
82
82
81
87
71
74
74
70
74
70
75
73
72
75
73
77
78
55
2-BrC
3-BrC
4-BrC
2-ClC
4-ClC
2-MeC
3-MeC
4-MeC H
6
6
6
H
H
H
4
4
4
3). However, further decreasing the reaction temperature to
–40 °C resulted in a considerably lower enantioselectivity of
64% (Table 1, entry 4). It was also found that reducing the
6
H
H
4
6
4
amount of catalyst to 5 mol-% while maintaining the tem-
perature at –18 °C had a detrimental effect on both the
yield and the enantioselectivity of the reaction (Table 1, en-
6
H
4
4
4
6
H
6
try 5). The ratio of Yb/ligand was also found to be critical 10
4-isopropyl
1-naphthyl
2-furyl
1
1
1
1
2
3
to attain good enantioselectivity because the reaction in the
presence of catalyst B (10 mol-%) resulted in inferior selec-
tivity (Table 1, entries 6–9). It was also found that the use
of PMO-IL instead of SAILP did not show any positive
effect in improving the selectivity (Table 1, entry 10).
cyclohexyl
[
(
2
a] Reaction conditions: Catalyst A (10 mol-%), 1 (1 equiv.), 2a
1.1 equiv.). The reaction was performed in dichloromethane for
4 h. [b] Isolated yield. [c] Enantiomeric excesses were determined
by HPLC analysis on a CHIRALPAK AS column. [d] Absolute
configuration was determined to be R according to the reported
data.[
Table 1. Optimization of the reaction conditions.[a]
13]
Entry
Cat.
Temp. [°C]
Yield [%][b]
ee [%][c][d]
The key issue for all of the supported catalysts is their
easy and efficient separation from the reaction mixture and
having constant reactivity over repeated runs. In the next
stage of this research we tested the reusability of catalyst A
in the mentioned reaction. To do this, the catalyst was easily
separated from the reaction mixture after each run by cen-
trifugation and reused in the next cycle. The results indi-
cated that the catalyst did not show a considerable loss in
ee for the asymmetric Mannich reaction after reuse in thee
1
2
3
4
5
6
7
8
9
1
A
A
A
A
A
B
B
B
B
C
r.t.
0
93
88
82
71
65
77
95
90
79
91
46
51
74
64
58
34
22
63
55
34
–18
–40
–18
r.t.
r.t.
–18
–40
r.t.
[
e]
[
[
[
f]
f]
f]
0
[
(
a] Reaction conditions: Catalyst A–C (10 mol-%), 1a (1 equiv.), 2a consecutive runs (Table 3). These results reveal that the
1.1 equiv.) unless otherwise stated. The reaction was performed in present supported system not only has superior activity in
dichloromethane for 24 h. [b] Isolated yield. [c] Enantiomeric ex-
cesses were determined by HPLC analysis on a CHIRALPAK AS
column. [d] Absolute configuration was determined to be R accord-
asymmetric Mannich reaction of a wide range of aldimins
but also provides a highly recoverable heterogeneous Yb
catalyst for this reaction.
[
13]
ing to reported data. [e] 5 mol-% catalyst A was used. [f] 10 mol-
%
NEt was used.
3
Table 3. Asymmetric Mannich reaction with recyclable solid cata-
lyst.[
a]
Having optimized the reaction parameters (Table 1, en-
try 3), we then tested the scope and limitations of the asym-
Yield [%] (ee [%])[b][c]
Run 1
Run 2
Run 3
Run 4
metric Mannich reaction of various N-Boc-imine deriva-
tives and dibenzylmalonate in the presence of 10 mol-% cat- 82 (73)
alyst A for 24 h at –18 °C (Table 2). As indicated in Table 2,
a wide range of aromatic aldimins bearing either electron- (1.1 equiv.). The reaction was performed in dichloromethane for
81 (72)
81 (72)
75 (68)
[a] Reaction conditions: Catalyst A (10 mol-%), 1 (1 equiv.), 2a
2
4 h. After completion, the catalyst was separated by centrifugation
withdrawing or electron-donating groups at the ortho, meta
and para positions provided the corresponding β-amino
carbonyl compounds in good yields and enantioselectivities
and reused in another run. [b] Isolated yield. [c] Enantiomeric ex-
cesses were determined by HPLC analysis on a CHIRALPAK AS
column.
(Table 2, entries 1–11). Remarkably, the position and elec-
tronic nature of the substituent on the aromatic ring had a
very restricted effect on the ee values and yields. It is worth
mentioning that the supported catalyst A gave high yield
Conclusions
A series of heterogeneous chiral YbIII supported systems
and good enantioselectivity for 2-furyl N-Boc imine as a have been prepared by physical immobilization of various
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Asymmetric Mannich Reaction of Malonates with Aldimines
ratios of Yb(OTf) /iPr-pybox (3b) complexes on either a Framework: PMO-IL was synthesized according to our previous
3
methods.[
12a]
2
Typicaly, a molar ratio 0.013 P123: 26.515 H O: 5.300
self-assembled organic–inorganic hybrid silica with ionic li-
quid phase (SAILP) (Catalyst A and B) or a periodic meso-
porous organosilica with approximately 10% ionic liquid
framework (PI-10) (Catalyst C) and characterized in detail
by standard solid-state analytical techniques. Among the
developed catalysts, it was found that catalyst A, which is
KCl: 4.200 HCl: 1.000 Si was used. Pluronic P123 (1.67 g) was dis-
solved in a mixture of H O (10.5 g) and HCl (2 m, 46.14 g), then
2
KCl (8.8 g) was added and the system was stirred until a homogen-
eous solution was obtained. A pre-mixture of ionic liquid (0.95 g)
and tetramethoxyorthosilicate (2.74 g) in anhydrous methanol was
added to the solution and the mixture was stirred at 40 °C for 24 h.
The resulting mixture was then aged without stirring at 100 °C for
denoted as Yb(OTf) /3b@SAILP is an efficient and recycla-
3
ble chiral catalyst for the enantioselective Mannich reaction 72 h. The obtained PMO with surfactant was filtered, washed with
of malonates to N-Boc aldimines. The process is simple and deionized water, and dried at room temperature. The surfactant
applicable for a diverse range of N-Boc aldimines in good was extracted from the PMO-IL by a Soxhlet apparatus by using
ethanol (100 mL) and concd. aqueous HCl (3 mL). In a typical
yields and enantioselectivities. This is the first hetero-
extraction, as synthesized PMO (1 g) was washed four times with
the above-mentioned acidic ethanol solution over 12 h.
geneous catalyst for the asymmetric Mannich reaction in
which the catalyst could be readily recovered and reused
four times, thus making this procedure more environmen- General Procedure for the Preparation of YbIII Triflate/Complex
tally acceptable and economically attractive.
Followed by Immobilization of Yb(OTf)
SAILP (Catalyst A): A well-dried glass tube was charged with
Yb(OTf) (30 mg, 0.048 mmol) and the corresponding pybox li-
gand (29 mg, 0.096 mmol) under an argon atmosphere. After ad-
dition of CH Cl (1.0 mL) to the mixture, it was stirred vigorously
3
-pybox Complex onto
3
Experimental Section
2
2
General Procedure for the Preparation of 1,3-Bis(3-trimethoxysilyl-
propyl)imidazolium Iodide (BTMSPI): 1,3-bis(3-trimethoxysilyl-
at room temperature for 1 h until the mixture became homogen-
eous. To the resulting clear complex solution were added SAILP
propyl)imidazolium iodide (BTMSPI) was synthesized as described
(
200 mg) and additional anhydrous CH
and the resulting mixture was stirred for 12 h at room temp. The
excess of CH Cl was slowly removed under reduced pressure and
the resulting free-flowing yellow powder was then dried at 60 °C
overnight to furnish the supported catalyst Yb(OTf) /3b@SAILP.
2 2
Cl (2 mL) under argon
in our previous synthetic reports.[
12a]
First, a suspension of sodium
imidazolide in anhydrous THF was prepared from reaction be-
tween freshly dried imidazole (2 g) and NaH 95% (0.77 g) in a
flame-dried two-necked flask containing anhydrous THF (60 mL)
under an argon atmosphere. Then 3-iodopropyl-trimethoxysilane
2
2
3
The amount of Yb was further determined by atomic absorption
spectroscopy through standard addition protocol after acid wash-
ing of a weighed sample of the catalyst. Catalysts B and C were
prepared and characterized in the same way (see the Supporting
Information for more details).
(5.8 mL) was added to the stirred suspension and the mixture was
heated to reflux for 12 h. After cooling to room temperature, the
solvent was removed under reduced pressure until the oil contain-
ing NaCl was obtained. Then 3-(iodopropyl)trimethoxysilane
(5.8 mL) and anhydrous toluene (60 mL) was added and the mix-
ture was heated to reflux for 24 h. After cooling the reaction mix-
ture to room temperature, the toluene phase was separated by using
a clean and dry syringe. The resultant mixture was first washed
A Typical Catalytic Procedure for Asymmetric Mannich Reaction
Using Yb(OTf)
Yb(OTf) /pybox@SAILP A (equivalent to 10 mol-% Yb) in
Cl (1 mL) under an argon atmosphere, N-Boc imine 1
3
/3b@SAILP (Catalyst A): To a dispersion of
3
with absolute toluene (5ϫ 30 mL) to remove all unreacted starting CH
2
2
materials and then CH Cl (50 mL) was added to precipitate NaCl
from reaction mixture. Dichloromethane solution was transferred
into another well-dried flask. Pale-yellow IL (BTMSPI) was then
2
2
(1 mmol) was added and the resulting mixture was cooled to
–18 °C. After 30 min, dibenzyl malonate 2a (neat, 0.312 g,
1.1 mmol) and methanol (1 mmol) were added to the flask in one
portion. The reaction was maintained at the desired temperature
obtained after removal of solvent and dried under vacuum at room
1
temperature. H NMR (250 MHz, CDCl
3
, 25 °C, TMS): δ = 10.00 until complete consumption of imine was observed by thin-layer
(
s, 1 H, NCHN), 7.46 (d, J = 1.7 Hz, 2 H, CHCH), 4.32 (t, J = chromatography. After completion of the reaction, n-hexane
.1 Hz, 4 H, NCH ), 3.60 (s, 18 H, 6 OCH
), 2.00 (m, 4 H, (20 mL) was added to the reaction mixture at the same temperature
CH CH CH ), 0.62 (t, J = 8.1 Hz, 4 H, SiCH
63 MHz, CDCl
CHCH), 51.8 (NCH
SiCH ) ppm.
7
2
3
1
3
) ppm. C NMR and then the products were separated from the heterogeneous cata-
2
2
2
2
(
(
(
3
, 25 °C, TMS): δ = 136.1 (NCHN), 122.2
lyst by filtration or centrifugation. The excess of n-hexane was re-
), 5.8 moved in vacuo and the products were purified by flash chromatog-
raphy on silica gel using hexane/ethyl acetate.
2 2 2 2
), 50.8 (OMe), 24.1 (CH CH CH
2
General Procedure for the Preparation of Self-Assembled Silica with
Ionic Liquid Framework (SAILP) under Acidic Conditions: SAILP cle): Further experimental details, FT-IR, and H and C NMR
Supporting Information (see footnote on the first page of this arti-
1
13
was synthesized by using our previous synthetic report with slight
spectra of both starting Boc-imines and the products, HPLC chro-
[
10]
modification.
Typically, 1,3-bis(3-trimethoxysilylpropyl) imid-
matograms of the products, N adsorption-desorption analysis and
2
azolium iodide ionic liquid (10 mmol) was added to deionized
water (5 g) and 2.0 m HCl solution (22.5 g) with stirring at 40 °C
for 24 h under an argon atmosphere. The resulting mixture was
then transferred into a Teflon-lined autoclave and heated at 100 °C
for 72 h under static conditions. The obtained mixture was first
thoroughly washed with deionized water/ethanol solvent and then
a yellow powder was obtained after drying of the final material at
room temperature.
TEM images, and TGA analysis of the materials.
Acknowledgments
The authors acknowledge IASBS Research Councils and Iran
National Science Foundation (INSF) for support of this work.
General Procedure for Preparation of Periodic Mesoporous Organo-
silica with Approximately 10% Imidazolium Functions (PI-10) in the
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Eur. J. Org. Chem. 2014, 7253–7258
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B. Karimi, E. Jafari, D. Enders
FULL PAPER
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