B. Karimi et al.
[
19]
Conclusion
previous reported procedure.
(
(
In a typical synthesis, Pluronic P123
1.67 g) and KCl (8.8 g) were added to a solution of distilled water
10.5 g) and HCl (2m, 46.14 g) with stirring at 408C. After a clear homo-
We have demonstrated for the first time that an ionic liquid
based periodic mesoporous organosilica is an effective and
powerful support for the immobilization and stabilization of
Pd nanoparticles on the Suzuki-coupling reaction in water.
Our study showed that this innovative system could be suc-
cessfully applied as an effective and reusable catalyst for the
Suzuki coupling of a variety of activated and deactivated
haloarenes with arylboronic acids. Interestingly, it was found
that while hot filtration tests and selective catalyst poisons
showed the presence of soluble Pd species during the reac-
tion process, atomic spectroscopy and catalyst recovery stud-
ies illustrated that no significant decrease has been seen in
the activity and metal content of recovered Pd@PMO-IL.
Furthermore, the TEM image of the recovered catalyst
showed the presence of well-distributed Pd nanoparticles in
the mesochennels of the PMO-IL material. Based on these
results, we conclude that although the PMO-IL nanostruc-
ture acts as reservoir for the soluble Pd species, it can also
operate as a nanoscaffold to recapture the Pd nanoparticles
into the mesochannels, thus preventing extensive agglomera-
tion of Pd nanoparticles. This remarkable ability of the
PMO-IL mesostructure may be attributed to ionic liquid
units that effectively manage the reaction through prevent-
ing Pd agglomeration and releasing and recapturing Pd
nanoparticles during reaction process. Since the supported
ionic liquid catalysis systems have many advantages over
traditional catalysts, we therefore speculate that this innova-
tive system would open a new gate for the design and syn-
thesis of new types of supported metal catalysts based on
PMO-IL with high and yet tunable loading of ionic liquid
moieties.
geneous solution had been produced, a pre-prepared mixture of ionic
liquid (0.86 g) and tetramethoxysilane (2.74 g), in absolute methanol was
rapidly added and stirred at the same temperature for 24 h. The resulting
mixture was then transmitted into a Teflon-lined autoclave and statically
heated at 1008C for 72 h. The obtained solid material was filtered,
washed completely with deionized water, and dried at room temperature.
The extraction of surfactant was accomplished four times by a Soxhlet
apparatus by using ethanol (100 mL) and concentrated HCl (3 mL, for
each time) for 1 g of sample over 12 h. The final PMO material was de-
noted as PMO-IL.
Preparation of Pd@PMO-IL catalyst: Pd@PMO-IL was also prepared
[
17]
based on a literature procedure with a slight modification. Palladium
acetate (27 mg, 0.12 mmol) was added to a well-dispersed solution of
ionic liquid based periodic mesoporous ionic liquid (PMO-IL) (1 g,
À1
1.0 mmol IL g ) in DMSO (4.5 mL) under an argon flow. The system
was stirred at 608C for 5 h and then at 1008C for 1 h. After cooling the
reaction solution to room temperature, the resulting mixture was washed
with CH Cl (3ꢁ10 mL) to remove unreacted Pd ACHTNUTGRENNUNG( OAc) . The final mate-
2 2 2
rial was obtained after drying by evacuation at 508C for 12 h. Elemental
analysis showed that the loading of Pd was 0.1 mmol Pd/g solid.
General procedure for the Suzuki coupling reaction by using Pd@PMO-
IL as the catalyst: The Suzuki reaction was performed by using arylbor-
onic acid (1.1 mmol), aryl halide (1.0 mmol), K CO (3 mmol), and cata-
2 3
lyst (0.002–0.01 equiv to aryl halide) in distilled water at 60–908C. The
reaction progress was monitored by GC analysis after completion of the
reaction; the mixture was allowed to cool to room temperature and was
then filtered and washed with H
phase was separated and dried over MgSO
2
O and diethyl acetate. The organic
and the solvent was then re-
4
moved under reduced pressure. Pure products were obtained after recrys-
tallization or by isolation of the residue by column chromatography on
silica.
Acknowledgements
The authors thank the Institute for Advanced Studies in Basic Science
(
IASBS) and the Iran National Science Foundation (INSF) for support-
ing this work.
Experimental Section
General procedure for the synthesis of 1,3-bis(trimethoxysilylpropyl)imi-
[
2] a) F. Bellina, A. Carpita, R. Rossi, Synthesis 2004, 2419–2440; b) D.
[
18]
dazolium chloride: The alkyl imidazolium based ionic liquid was syn-
thesized by a modification of a literature procedure. In a typical experi-
ment, sodium imidazolide (3.002 g, 30 mmol) and 3-chloropropyl-trime-
thoxysilane (6.082 g, 30 mmol) were added to a well-dried flask contain-
ing super dry THF (100 mL) and stirred at 658C for 24 h under an argon
atmosphere. After cooling the reaction mixture to room temperature, the
solvent was removed under reduced pressure and the oil obtained was
transferred to another flask containing 3-chloropropyl-trimethoxysilane
[
[
(
30 mmol) in absolute toluene (100 mL) and refluxed for 48 h in the ab-
sence of light. After cooling the solution to room temperature, the reac-
tion mixture was first washed thoroughly with toluene (5ꢁ50 mL) and
then super dry CH Cl was added to precipitate NaCl. The supernatant
2 2
dichloromethane solution was transferred into another well-dried flask.
A yellow viscous ionic liquid (1) was obtained after removal of the sol-
[
vent and drying under vacuum. The spectral data for IL 1 is as follows.
1
H NMR (250 MHz, CDCl
d, 2H, J=1.7 Hz; CHCH), 4.32 (t, 4H, J=7.1 Hz; NCH
OCH ), 2.00 (m, 4H; CH CH CH ), 0.62 ppm (t, 4H, J=8.1 Hz;
SiCH ); C NMR (63 MHz, CDCl , 258C, TMS): d=136.08 (NCHN),
22.20 (CHCH), 51.76 (NCH ), 50.77 (OMe), 24.12 (CH CH CH ),
.81 ppm (SiCH ).
3
, 258C, TMS): d=10.00 (s, 1H; NCHN), 7.46
(
6
2
), 3.60 (s, 18H;
[
3
2
2
2
1
3
2
3
1
5
2
2
2
2
2
General procedure for the synthesis of ionic liquid based periodic meso-
porous organosilica (PMO-IL): PMO-IL was prepared according to a
8052
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 8047 – 8053