JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Polystyrene-anchored Pd(II) Pyridine Complex
Table 5. The Heck and Sonogashira reactions catalyzed by the
recycled catalysta
corresponding products in excellent yields. The electron-
neutral, or electron-poor aryl chlorides were reacted with
phenylacetylene to generate the corresponding cross-cou-
pling products in low yields under the standard reaction
conditions (entries 20-22).
Heck
yield (%)b
Sonogashira
yield (%)b
Entry
Cycle
1
2
3
4
5
1
2
3
4
5
98
98
97
95
93
98
98
96
95
93
One of the purposes for designing this heterogeneous
catalyst is to enable recycling of the catalyst for use in sub-
sequent reactions. The reusability of the catalyst was tested
upon the reaction of iodobenzene with methyl acrylate
(Heck reaction) and iodobenzene with phenylacetylene
(Sonogashira reaction) as the representative reactants and
in the presence of 1 mol% of PS-mapy-Pd(II) in order to
study the recyclability of this heterogeneous catalyst. Simi-
larly, the reactions for the repeated runs were conducted af-
ter separation of the organic compounds from the reaction
mixture by extraction, and the recovered solid catalyst was
recycled for another run. The recycling process was re-
peated for five cycles without any significant loss of effi-
ciency (Table 5). To determine the degree of leaching of the
metal from the heterogeneous catalyst, the catalyst was re-
moved by filtration after the reaction was completed, and
the palladium content of the filtrate was determined by ICP.
It was shown that less than 0.2% of the total amount of the
original palladium species was lost into the solution during
the course of the reaction. This leaching level was negligi-
ble, confirmed by the excellent recoverability and reusabil-
ity of the heterogeneous catalyst.
a Reaction conditions: iodobenzene (1.0 mmol), methyl acrylate
(Heck reaction) (1.5 mmol), iodobenzene (1.0 mmol), phenyl
acetylene (Sonogashira reaction) (1.0 mmol), PS-mapy-Pd(II)
complex (0.01 mmol), base (2.0 mmol), 70 °C (for Heck
reactions), room temperature (for Sonogashira reactions).
b GC yield.
dried in vacuo for 12 h. The 2-methylaminopyridine function-
alized polymer 2 (2.0 g) was treated with ethanol (30 mL) for 30
min. An ethanolic solution of PdCl2(PhCN)2 (1.0 g) was added,
and the resulting mixture was heated to 80 °C for 20 h. The result-
ing bright yellow colored polymer, impregnated with the metal
complex, was filtered and washed with ethanol to obtain PS-
mapy-Pd(II) 3 (Scheme I).
General procedure for the Heck reaction: A mixture of
an aryl halide (1.0 mmol), an alkene (1.5 mmol), PS-mapy-Pd(II)
(0.01 mmol), and KOH (2.0 mmol) in water (5 mL) was stirred at
70 ºC for 5 h. After completion of the reaction, the mixture was
filtered to recover the catalyst. The polymer was washed with wa-
ter and acetonitrile, vacuum-dried, and stored for a new run. After
GC analysis, the solvent was removed under vacuum, and the
crude product was subjected to silica gel column chromatography
using CHCl3–CH3OH (95:5) as eluent to afford the pure product.
General procedure for the Sonogashira coupling reac-
tion: An aryl halide (1.0 mmol) and a terminal alkyne (1.0 mmol)
were added to a mixture of PS-mapy-Pd(II) (0.01 mmol), Et3N
(2.0 mmol), and water (3 mL) in a glass flask under vigorous stir-
ring. The mixture was stirred at room temperature for 3 h under
aerobic conditions. After completion of the reaction, the mixture
was filtered to recover the catalyst. The polymer was washed with
water and acetonitrile, vacuum-dried, and stored for a new run.
After GC analysis, the solvent was removed under vacuum, and
the crude product was subjected to silica gel column chromatog-
raphy using CHCl3–CH3OH (95:35) as eluent to afford the pure
product.
CONCLUSION
The first example of the Heck and Sonogashira reac-
tions catalyzed by the cheap and air stable 2-methylamino-
pyridine-functionalized polystyrene resin-supported Pd(II)
complex as catalyst was described. The ease of preparation
of the complex, indefinite shelf life, and stability toward air
make it an ideal complex for the above transformations.
Moreover, the catalyst could be reused for five consecutive
cycles without a significant loss in its catalytic activity.
These advantages make the process highly valuable from
the synthetic and environmental points of view.
EXPERIMENTAL
Preparation of polymer-anchored PS-mapy-Pd(II) 3: To
a 250-mL round bottom flask equipped with a magnetic stirrer bar
and containing DMF (15 mL) were added chloromethylated poly-
styrene (2 g, 1.25 mmol/g of Cl) and 2-methylaminopyridine (7.0
mmol). The reaction mixture was stirred for 20 h at 100 °C, and
was subsequently filtered and washed thoroughly with DMF, and
ACKNOWLEDGEMENT
We gratefully acknowledge the financial support of
the Research Council of Shahrood University of Technol-
J. Chin. Chem. Soc. 2014, 61, 279-284
© 2014 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
283
Bakherad, Mohammad
