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M. Hajjami, M. Cheraghi
reaction is typically carried out with phosphine-based or
phosphine-free homogeneous Pd catalysts in organic sol-
vents [8]. However, homogeneous catalysts have several
drawbacks such as purification of the products, removal of
palladium from organic products and recycling of the cat-
alyst [9, 10]. Meanwhile, heterogeneous catalysts are the
first option due to their inherent advantages of stability,
simple separation, and better handling compared to
homogeneous catalysts [11, 12]. However, immobilization
of homogeneous catalysts decreases the catalytic activity or
selectivity [13]. This drawback can be overcome by
nanomaterials, because nanocatalysts can be used as a
bridge gap between homogeneous and heterogeneous cat-
alysts [14]. Among different nanoparticles, MCM-41, is
commonly used as a heterogeneous support for the
immobilization of homogeneous catalysts [15, 16].
Because of some advantages such as large specific surface
area ([1000 m2g-1), high mechanical, chemical and ther-
mal stability (up to 900 °C), homogeneous hexagonal pore
80 °C for 24 h. The solid product was obtained by filtra-
tion, washed with ethanol and dried at 60 °C.
2.2 General Procedure for C–C Coupling Reaction
Using Sodium Tetraphenyl Borate
A mixture of aryl halide (1 mmol), sodium tetraphenyl
borate (0.5 mmol), Na2CO3 (1.5 mmol), and Pd-TEDETA-
MCM-41 (0.002 g, 0.57 mol %) was stirred in PEG at
80 °C and the progress of the reaction was monitored by
TLC. After completion of the reaction, the mixture was
cooled down to room temperature and catalyst was sepa-
rated by simple filtration and washed with diethyl ether and
the reaction mixture was extracted with H2O and diethyl
ether. The organic layer was dried over Na2SO4 (1.5 g).
Then the solvent was evaporated and pure biphenyl
derivatives were obtained in good to excellent yields. For
more purification of biphenyls the preparative TLC plate
was used in n-hexane/acetone (7:3). After desired biphenyl
separated enough, ethyl acetate was used for recovering the
product from silica gel and finally the pure biphenyls was
obtained.
˚
arrays (between 20–100 A), ease of functionalization, rel-
atively hydrophobic nature and facile separation [17, 18].
Previously Pd-grafted functionalized various supported
materials have been reported as catalyst in C–C coupling
reactions. For example, biogenous iron oxide was used as a
support for immobilized palladium and used in the Suzuki–
Miyaura coupling reactions [19]. Also Poly(vinylidene
dichloride)-diethylene triamine supported palladium com-
plex was applied for the Heck reactions [20]. Herein a new
Pd-based MCM-41 mesoporous catalyst has been reported
for the Suzuki reactions.
2.3 General Procedure for Coupling of Aryl Halides
with Phenylboronic Acid
A mixture of aryl halide (1 mmol), phenylboronic acid
(1 mmol), Na2CO3 (1.5 mmol), and Pd-TEDETA-MCM-
41 (0.002 g, 0.57 mol %) were added to a reaction vessel.
The resulting mixture was stirred in H2O or PEG at 50 °C
and the progress of the reaction was monitored by TLC.
After completion of the reaction, catalyst was separated by
simple filtration and washed with ethylacetate and the
reaction mixture was extracted with H2O and diethylether
and organic layer dried over anhydrous Na2SO4 (1.5 g).
Then the solvent was evaporated and pure biphenyl
derivatives were obtained in good to excellent yields. For
more purification of biphenyls the preparative TLC plate
was used in n-hexane/acetone (7:3). After desired biphenyl
separated enough, ethyl acetate was used for recovering the
product from silica gel and finally the pure biphenyls was
obtained.
2 Experimental
2.1 Preparation of Catalyst
The mesoporous MCM-41 was synthesized according to
our reported procedure [21]. Then, 1 g of 3-choloro-
propyltriethoxysilane (CPTES) was added to a suspension
of MCM-41 (1 g) in n-hexane (30 mL) and allowed to
reflux for 24 h under N2 atmosphere. Then, the reaction
mixture was cooled down to room temperature, filtered and
the resulting solid washed with n-hexane. The solid was
dried under vacuum to get white solid (Cl-MCM-41). Then,
for the Preparation of N,N,N’’,N’’-tetraethyldiethylenetri-
amine on MCM-41 (TEDETA-MCM-41), the above men-
tioned solid (1 g) was refluxed with 2 mmol of N,N,N’’,N’’-
tetraethyldiethylenetriamine in toluene for 48 h under N2
atmosphere. The resulting solid (TEDETA-MCM-41) was
filtered, washed with ethanol and water and dried in vac-
uum. Finally, for Preparation of Pd-TEDETA-MCM-41,
the TEDETA-MCM-41 (1 g) was mixed with 0.5 g of
Pd(OAc)2 in 15 mL of ethanol. The mixture was stirred at
3 Results and Discussion
3.1 Catalyst Preparation
In continuation of our studies [14, 16, 21–23], herein, we
report the Pd-TEDETA-MCM-41 as a recoverable and
reusable catalyst for the C–C coupling reactions in PEG as
green solvent. The catalyst was prepared by the concise
route outlined in Scheme 1. Initially, the MCM-41
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