Highly efficient, recyclable palladium catalyst immobilized on organic-inorganic hybrid material: Application in the heck reaction

Article abstract of DOI:10.1055/s-2007-966065

Palladium immobilized on organic-inorganic (silica gel) hybrid materials behaves as a very efficient heterogeneous catalyst in Heck reactions. Iodoarenes, bromoarenes, as well as activated chloroarenes react smoothly with olefins to afford the corresponding cross-coupling products in good to excellent yields under phosphine- and amine-free reaction conditions in the presence of palladium immobilized on 3-[(2-aminoethyl)amino]propyl-functionalized silica gel (Silica-AAPTS-Pd) or palladium immobilized on 3-aminopropyl-functionalized silica gel (Silica-APTS-Pd) as catalyst. The silica-supported palladium catalyst could be recovered and recycled by simple filtration of the reaction solution, and used for more than ten consecutive trials without significant loss of catalytic activity. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-966065

PAPER
1635
Highly Efficient, Recyclable Palladium Catalyst Immobilized on Organic–
Inorganic Hybrid Material: Application in the Heck Reaction
P
alladium Catalyst
o
Immobilize
n
d on Organic
g
–Inorganic
H
j
ybrid M
i
aterial Li,a Lei Wang,*a,b Pinhua Lia
a
Department of Chemistry, Huaibei Coal Teachers College, Huaibei, Anhui 235000, P. R. of China
Fax +86(561)3090518; E-mail: leiwang@hbcnc.edu.cn
b
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai
200032, P. R. of China
Received 21 February 2007; revised 2 April 2007
in recent years, because industries seek more environmen-
tally friendly chemical manufacturing processes.6 Howev-
er, applications of silica-immobilized catalysts in Heck
and Suzuki–Miyaura reactions have been less investigat-
Abstract: Palladium immobilized on organic–inorganic (silica gel)
hybrid materials behaves as a very efficient heterogeneous catalyst
in Heck reactions. Iodoarenes, bromoarenes, as well as activated
chloroarenes react smoothly with olefins to afford the correspond-
ing cross-coupling products in good to excellent yields under phos- ed, and usually employ a polystyrene-based support medi-
um rather than a silica-based support.7
phine- and amine-free reaction conditions in the presence of
palladium immobilized on 3-[(2-aminoethyl)amino]propyl-func-
tionalized silica gel (Silica-AAPTS-Pd) or palladium immobilized
The palladium-catalyzed coupling of olefins with aryl or
vinyl halides, known as the Heck reaction, is one of the
most important, reliable, and general reactions for car-
bon–carbon bond formation in organic synthesis.8 This
powerful reaction can lead to the construction of an sp2–
sp2 C–C bond at an unfunctionalized olefinic carbon in a
single transformation employing a wide variety of aryl
and vinyl halide substrates, and may be used for the syn-
thesis of multifunctional derivatives,9 including bioactive
compounds, natural products,10 pharmaceuticals, and
high-performance materials.11 Palladium compounds,
usually complexes with phosphine ligands, are very often
used as catalyst precursors in the Heck reactions. Phos-
phines play the role of stabilizers of in situ formed soluble
palladium(0) complexes, which are generally considered
to be the catalytically active forms.12 On the other hand,
phosphine-free catalysts have recently generated great in-
terest as a less complicated, environmentally friendly, and
cheaper alternative to phosphine-containing systems.13
However, the major disadvantage of phosphine-free cata-
lysts is their low stability and poor catalytic activity due to
the formation of usually catalytically inactive ‘palladium
black’ and absence of rate acceleration by such means as
back donation. In recent years, numerous efforts have
been made to develop more efficient catalyst systems. A
major challenge in this area has been the development of
new Heck reaction catalysts with higher reactivity toward
deactivated aryl bromides and, ultimately, toward the
more readily available aryl chlorides. Significant advan-
ces have been made in the past several years in meeting
these goals. These include the use of sterically bulky and
electron-rich phosphines,14 phosphorus-,15 nitrogen-,16
and sulfur-based17 palladacyles, and, very recently, nu-
cleophilic N-heterocyclic carbene (NHC) ligands.18 How-
ever, all of these catalyst systems suffer from drawbacks
of one kind or another, such as the high ligand sensitivity
toward air and moisture, the tedious multistep synthesis,
hence the high cost of the ligands, and the use of various
additives.
on 3-aminopropyl-functionalized silica gel (Silica-APTS-Pd) as
catalyst. The silica-supported palladium catalyst could be recovered
and recycled by simple filtration of the reaction solution, and used
for more than ten consecutive trials without significant loss of cata-
lytic activity.
Key words: Heck reaction, organic–inorganic hybrid material, pal-
ladium immobilization, heterogeneous catalysis
Transition-metal catalysts have been widely used in or-
ganic synthesis, with transition-metal-catalyzed carbon–
carbon and carbon–heteroatom bond-forming reactions
being of the most important fundamental transformations
in synthetic chemistry.1 Most of the reactions, however,
are performed in homogeneous media. The major prob-
lems associated with the recovery of homogeneous cata-
lysts and their separation from the reaction products, and
the difficulties associated with the recycling of the catalyt-
ic species have in part been addressed by immobilization
on heterogeneous solid supports such as polymers or sili-
cas. In addition, immobilizing catalysts onto the support
can reduce the high costs of transition-metal catalysts and
their toxic effects. This class of supported reagents can fa-
cilitate both the isolation and recycling of the catalyst by
filtration, thus providing environmentally clean process-
es. The grafting of ligands on the surface of organic or in-
organic polymers makes heterogeneous transition-metal
catalytic species possible and provides green alternatives
to homogeneous catalysts.2
Recent examples include the use of organic-polymer-sup-
ported palladium complexes as catalysts for the Suzuki–
Miyaura reaction,3 the Sonogashira reaction,4 and the
Heck reaction.5 The development of organic reagents
grafted onto silica gels has attracted increasing attention
SYNTHESIS 2007, No. 11, pp 1635–1642
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x.
x
x
.
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0
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Advanced online publication: 11.05.2007
DOI: 10.1055/s-2007-966065; Art ID: F03607SS
© Georg Thieme Verlag Stuttgart · New York

1636
H. Li et al.
PAPER
It is worth noting that homogeneous palladium catalysts
usually precipitate from solution, and recycling or recov-
ery of the expensive catalyst is difficult. To overcome this
drawback, palladium on carbon and palladium on differ-
ent metal oxides and hydroxides have been used.19 Al-
though palladium nanoparticles of different origins have
been utilized in the Heck arylation of unsubstituted acry-
lates and styrene with variable degrees of success, catalyst
recycling has been often unsuccessful.20
Table 1 Comparison of IR Spectroscopy Data of Functionalized
Silica and Functionalized-Silica-Immobilized Palladium Catalystsa
Sample
n
Si–O (cm–1)
n
C–H (cm–1)
Silica-AAPTS
Silica-AAPTS-Pd
Silica-APTS
Silica-APTS-Pd
1088
1035
1074
1026
2941
2934
2926
2912
In a preliminary communication, the preparation of highly
active 3-[(2-aminoethyl)amino]propyl-functionalized sil-
ica-gel-immobilized palladium (Silica-AAPTS-Pd) and
its subsequent use as an efficient and recyclable catalyst
for the Sonogashira reaction and Ullmann diaryl etherifi-
cation was reported.21 Here, the extension of the use of
Silica-AAPTS-Pd and Silica-APTS-Pd as catalysts in the
Heck reaction is reported.
a FT-IR spectroscopy of KBr samples.
Dn1 [nSi–O
– nSi–O (Silica-AAPTS-Pd)] and Dn2
(Silica-AAPTS)
[nSi–O (Silica-APTS) – nSi–O (Silica-APTS-Pd)] of 53 cm–1 and 48 cm–1,
respectively; this indicates the coordination of the biden-
tate 3-[(2-aminoethyl)amino]propyl and monodentate 3-
aminopropyl ligands with palladium.
The synthesis of the palladium catalysts immobilized on
organic–inorganic hybrid materials is illustrated in
Scheme 1. They were readily prepared in two-step proce-
dures. The silica gel (100–200 mesh) was treated with {3-
[(2-aminoethyl)amino]propyl}triethoxysilane (AAPTS)
or (3-aminopropyl)triethoxysilane (APTS) in dry toluene
at 120 °C for 24 hours to afford the [3-(2-aminoethyl)ami-
no]propyl-functionalized silica gel (Silica-AAPTS) or 3-
aminopropyl-functionalized silica gel (Silica-APTS)
(Scheme 1). The organic–inorganic hybrid materials sub-
sequently reacted with palladium acetate in ethanol at
room temperature for four hours to generate the corre-
sponding silica-supported palladium catalysts, Silica-
The silica gel (100–200 mesh) as support was commer-
cially available from Aldrich, and the surface area was
found to be 554 m2/g by the BET method used in dinitro-
gen sorption. Table 2 summarizes the results of analysis
studies for the modified silicas. The CHN analysis data
confirm that organic functionalization took place with the
intended ligands (analysis of the pure silica prior to mod-
ification showed only negligible amounts of carbon and
nitrogen). Upon functionalization of the silicas, giving
Silica-AAPTS and Silica-APTS, the total surface area of
the samples was observed to drop from the initial value of
554 to 406, and 554 to 439 m2/g, respectively. On the oth-
er hand, the pore volume of the samples was also found to
decrease from the initial value 0.75 to 0.51 and 0.75 to
0.53 cm3/g for Silica-AAPTS and Silica-APTS, respec-
tively. The corresponding changes were also seen for the
silica-supported palladium catalysts Silica-AAPTS-Pd
and Silica-APTS-Pd. The elemental analysis data in
Table 2 show that for Silica-AAPTS and Silica-APTS the
AAPTS-Pd
(Scheme 1).
and
Silica-APTS-Pd,
respectively
The infrared absorption bands of Silica-AAPTS and
Silica-APTS were compared with those of the related pal-
ladium complexes Silica-AAPTS-Pd and Silica-APTS-Pd
(Table 1). The positions of the nSi–O bands were shifted by
OH
OH
O
O
O
(EtO)3Si(CH2)3NH(CH2)2NH2
(AAPTS)
Si
Si
N
H
O
Si
Si
NH
NH
NH2
NH2
NH2
Pd(II)
OH
OH
O
O
Pd(OAc)2
EtOH
O
O
toluene
H
N
OH
OH
O
O
NH2
O
O
Silica-AAPTS
Silica-AAPTS-Pd
O
O
O
O
O
OH
OH
Si
Si
NH2
NH2
H2N
O
Si
Si
NH2
NH2
Si
Si
(EtO)3Si(CH2)3NH2
(APTS)
(II)
Pd
Pd(OAc)2
EtOH
O
O
O
O
O
O
OH
OH
toluene
O
O
O
O
H2N
O
O
OH
OH
Silica-APTS
Silica-APTS-Pd
Scheme 1
Synthesis 2007, No. 11, 1635–1642 © Thieme Stuttgart · New York

PAPER
Palladium Catalyst Immobilized on Organic–Inorganic Hybrid Material
1637
Table 2 Surface Area, Pore Volume, and Elemental Analysis Data of Immobilization Samples
Sample
Surface area,a S (m2/g)
Pore volume,a V (cm3/g)
Microanalysis (wt%)
Cb
Nb
Pdc
–
Silica
554
406
258
439
277
0.75
0.51
0.38
0.53
0.41
–
–
Silica-AAPTS
Silica-AAPTS-Pd
Silica-APTS
Silica-APTS-Pd
6.56
6.21
3.85
3.72
2.57
2.43
1.31
1.24
–
4.41
–
2.30
a BET method used in N2 sorption.
b CHN microanalysis.
c ICP analysis.
loading was readily quantified by CHN microanalysis and
was found to be 0.918 mmol/g for 3-[(2-aminoethyl)ami-
no]propyl and 0.935 mmol/g for 3-aminopropyl, on the
basis of the nitrogen percentage. The amount of palladium
metal present in Silica-AAPTS-Pd and Silica-APTS-Pd
was found to be 4.41 and 2.30 wt%, respectively, on the
basis of ICP analysis.
Table 3 Effect of Base on the Heck Reaction between Styrene and
Iodobenzene Catalyzed by Silica-AAPTS-Pda
Ph
Silica-AAPTS-Pd
PhCH CH2
PhI
+
base, DMA
Ph
Entry
Base
Yieldb (%)
1
2
3
4
5
6
7
K2CO3
Na2CO3
NaOAc
Cs2CO3
K3PO4
96
89
86
57
42
84
90
The Heck reaction of iodobenzene with styrene served as
model reaction in our initial screening of the catalytic ac-
tivity of Silica-AAPTS-Pd and Silica-APTS-Pd. The reac-
tion in N,N-dimethylformamide at 100 °C with either
Silica-AAPTS-Pd or Silica-APTS-Pd (1 mol% Pd) as cat-
alyst and with triethylamine as base gave the desired prod-
uct in 56% and 47% yield, respectively, after six hours,
and 68% and 60% yield, respectively, after 12 hours.
These results suggest that Silica-AAPTS-Pd is more ef-
fective than Silica-APTS-Pd in the Heck reaction.
Et3N
piperidine
a Reagents and conditions: styrene (1.00 mmol), PhI (1.00 mmol),
Silica-AAPTS-Pd (24 mg, 0.01 mmol Pd), base (2.00 mmol), DMA
(4 mL), 130 °C, 12 h.
The conversion of the reaction of iodobenzene with sty-
rene and the yield of the product increased significantly
when N,N-dimethylacetamide (DMA) was used as the sol-
vent, and potassium carbonate as the base, instead of tri-
ethylamine and N,N-dimethylformamide. Encouraged by
this result, we continued our screening to improve the
yield of the product by the optimization of the reaction
conditions.
b Isolated yields.
During further optimization of the reaction conditions,
when 1 mol% Silica-AAPTS-Pd was used, the reactions
were generally completed only after several hours, but the
time, as expected, is inversely proportional to the temper-
ature. A reaction temperature of 130 °C was found to be
optimal. Thus, the optimized reaction conditions for this
Heck reaction consist of the following: Silica-AAPTS-Pd
(2 mol%) as catalyst, potassium carbonate (2 equiv) as
base, N,N-dimethylacetamide as solvent, and a tempera-
ture of 130 °C for 12 hours (Scheme 2).
Several different bases were examined in the Heck reac-
tion catalyzed by Silica-AAPTS-Pd in N,N-dimethylacet-
amide (Table 3). Potassium carbonate was found to be an
excellent base, whereas other bases such as piperidine, so-
dium carbonate, sodium acetate, triethylamine, cesium
carbonate, and potassium phosphate were substantially
less effective (Table 3).
The solvent also plays an important role in the Heck reac-
tion (Table 4). Polar, aprotic solvents with high boiling
points, such as N,N-dimethylacetamide, N-methyl-2-pyr-
rolidinone, and N,N-dimethylformamide, are highly suit-
ed for this reaction, whereas less polar solvents, such as
xylene, result in formation of the product in only very
poor yields. The use of dimethyl sulfoxide, acetonitrile,
ethanol, and methanol as solvents lead to slower reactions
(Table 4).
To examine the versatility of this method, the Heck olefi-
nation of styrene with iodoarenes and bromoarenes con-
taining electron-rich, electron-poor, and electron-neutral
substituents was investigated (Scheme 2, Table 5, entries
1–5, 12–16). The conversions, regioselectivities (>99%
trans-products), and yields were satisfactory under the
standard reaction conditions. The haloarene olefination
was also tolerant of ortho substitution of the aryl iodide,
Synthesis 2007, No. 11, 1635–1642 © Thieme Stuttgart · New York

1638
H. Li et al.
PAPER
Table 4 Effect of Solvent and Temperature on the Heck Reactiona
without further purification. The Silica-AAPTS-Pd cata-
lyst could be recovered and reused for ten consecutive tri-
als without loss of activity (Figure 1). Additionally,
palladium leaching in Silica-AAPTS-Pd was determined.
The palladium content of the clear filtrates obtained upon
filtration after the reaction was <0.2 ppm by ICP analyses.
However, the desired product was isolated in only 72%
yield when Silica-AAPTS-Pd was used without thorough
washing and drying prior to the reaction of iodobenzene
with styrene under standard reaction conditions.
Ph
Silica-AAPTS-Pd
PhCH
CH2
PhI
+
solvent, K2CO3
Ph
Entry
Solvent
MeOH
EtOH
Temp (°C)
65
Yieldb (%)
1
2
3
4
5
6
7
8
34
42
62
88
96
76
90
16
78
MeCN
DMF
80
130
130
130
130
130
DMA
DMSO
NMP
xylene
a Reagents and conditions: styrene (1.00 mmol), PhI (1.00 mmol), Sil-
ica-AAPTS-Pd (24 mg, 0.01 mmol Pd), K2CO3 (2.00 mmol), solvent
(4 mL), heat, 12 h.
b Isolated yield.
Figure 1 Yields obtained in the model reaction of iodobenzene with
styrene with the recycled Silica-AAPTS-Pd catalyst under standard
reaction conditions. Each value represents the average of three runs.
and led to a good yield (Table 5, entry 6). The scope of
this catalytic system with other vinyl substrates, such as
ethyl acrylate (Table 5, entries 6–10, 17, 20) and acryloni-
trile (entry 11), was also examined, and excellent results
were obtained under identical conditions. For activated
chloroarenes (Table 5, entries 18, 19), cross-coupling
products were isolated in moderate yields under the
present reaction conditions. Fortunately, good to excellent
yields of the products were obtained when the reactions
were performed for prolonged periods (24 h) and at higher
palladium loading of the silica-supported catalyst (2% Pd)
(Table 5, entries 18, 19). The desired products were also
obtained in moderate yields from deactivated chloroare-
nes after longer reaction times (24 h) and at higher palla-
dium loading (2% Pd) (Table 5, entry 20). The results in
Table 5 also confirm that Silica-AAPTS-Pd is superior to
Silica-APTS-Pd for the Heck reaction under the present
reaction conditions (Table 5, entries 1, 2, 12, 13).
In conclusion, we have demonstrated the use in the Heck
reaction of a highly efficient and recyclable palladium cat-
alyst immobilized on organic–inorganic hybrid material.
Iodoarenes, bromoarenes, as well as activated chloro-
arenes reacted with olefins to afford the corresponding
cross-coupling products in good to excellent yields under
phosphine- and amine-free reaction conditions in the pres-
ence of only Silica-AAPTS-Pd, as well as Silica-APTS-Pd,
as catalyst. The silica-supported palladium catalyst could
be recovered and recycled by simple filtration of the reac-
tion solution and used for more than ten consecutive trials
without significant loss of catalytic activity.
Melting points were recorded on a WRS-2B melting point apparatus
1
and are uncorrected. All H NMR spectra were recorded at 300
MHz or 400 MHz on Bruker FT-NMR spectrometers, and chemical
shifts are given relative to TMS as internal standard. IR spectra were
obtained on a Nicolet NEXUS 470 spectrophotometer. CHN analy-
sis was performed on a Vario El III elementar instrument. Pd con-
tent was determined by a Jarrell-Ash 1100 ICP analysis. Specific
surface areas and pore volumes of the samples were determined in
a Micromeritics ASAP-2000 automated nitrogen physisorption ap-
paratus and calculated according to the BET method. Products were
purified by flash column chromatography (silica gel, 230–400
To investigate the possibility of catalyst recycling after
completion of the Heck reaction of iodobenzene with sty-
rene, the organic reaction solution (containing 0.2 g Sili-
ca-AAPTS-Pd) was vacuum-filtered through a sintered-
glass funnel, which was washed successively with dichlo-
romethane (1 mL), diethyl ether (1 mL), ethanol (1 mL),
and hexane (1 mL). After the recovered catalyst had dried
in an oven at 60 °C for four hours, it was reused directly
R2
Silica-AAPTS-Pd (1 mol% Pd)
X
K2CO3, DMA
R2
+
R1
R1
X = I, Br, Cl
Silica-APTS-Pd (1 mol% Pd)
E product
R2 = Ar, CO2R3, CN
Scheme 2
Synthesis 2007, No. 11, 1635–1642 © Thieme Stuttgart · New York

PAPER
Palladium Catalyst Immobilized on Organic–Inorganic Hybrid Material
1639
Table 5 Silica-Supported-Palladium-Catalyzed Heck Reactiona
R2
X
[Pd] cat. (1 mol%)
R2
+
K2CO3, DMA
R1
R1
1–14
Entry
1
X
I
R1
H
R2
Ph
Product
Catalystb
Yieldc (%)
1
A
B
96
88
2
I
p-OMe
Ph
2
A
B
99
90
3
4
I
p-Ac
p-CF3
m-CF3
o-CF3
H
Ph
Ph
Ph
3
4
A
A
A
A
A
A
A
A
A
97
99
91
87
99
99
92
94
93
I
5
I
5
6
I
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CN
6
7
I
7
8
I
p-OMe
m-NO2
p-NO2
p-Me
H
8
9
I
9
10
11
12
I
10
11
1
I
Br
Ph
A
B
96
83
13
Br
p-OMe
Ph
2
A
B
83
70
14
15
16
17
18
Br
Br
Br
Br
Cl
p-Me
p-Ac
p-CN
p-NO2
p-Ac
Ph
12
3
A
A
A
A
A
88
90
94
95
Ph
Ph
13
10
3
CO2Et
Ph
58
82d
19
20
Cl
Cl
p-CN
p-Me
Ph
13
14
A
A
63
90d
CO2Et
35
72d
a Reagents and conditions: olefin (1.00 mmol), organic halide (1.00 mmol), Silica-AAPTS-Pd (24 mg, 0.01 mmol Pd), K2CO3 (2.00 mmol),
DMA (4 mL), 130 °C, 12 h.
b Catalyst A = Silica-AAPTS-Pd, B = Silica-APTS-Pd.
c Isolated yields.
d Modified conditions: Silica-AAPTS-Pd (48 mg, 0.02 mmol Pd), 24 h.
mesh). The chemicals were purchased from commercial suppliers
(Aldrich, USA and Shanghai Chemical Company, China) and were
used without prior purification.
tered and the white powder was washed with distilled H2O until a
neutral pH was attained. The solid was again washed successively
with acetone (20 mL), MeOH (20 mL), and CH2Cl2 (20 mL), and
dried under vacuum at 150 °C for 48 h.
Silica-AAPTS-Pd
In a 50-mL round-bottom flask were introduced successively anhyd
toluene (20 mL), activated silica (3.00 g), and {3-[(2-aminoeth-
yl)amino)]propyl}triethoxysilane (AAPTS) (10 mL). The mixture
was refluxed for 24 h, and then filtered; the solid was washed suc-
To activate the silica gel (Aldrich, 100–200 mesh; 10.00 g), it was
placed in a round-bottom flask equipped with a reflux condenser.
Concd H2SO4 (80 mL) and HNO3 (15 mL) were added and the mix-
ture was heated in an oil bath at 140 °C for 24 h. The soln was fil-
Synthesis 2007, No. 11, 1635–1642 © Thieme Stuttgart · New York

1640
H. Li et al.
PAPER
cessively with acetone (5 mL) and CH2Cl2 (5 mL), and dried under
reduced pressure at 60 °C. This gave Silica-APPTS (3.38 g).
IR (KBr): 2897, 1708, 1600, 1517, 1368, 1357, 1265, 1178, 1074,
966, 867, 821, 756, 725, 692 cm–1.
In a small Schlenk tube, Silica-AAPTS {1.00 g, 0.918 mequiv 3-
[(2-aminoethyl)amino)]propyl/g} was mixed with Pd(OAc)2 (0.112
g, 0.5 mmol) in anhyd EtOH (5 mL). The mixture was stirred under
N2 for 4 h at r.t. It was then filtered, and the solid was successively
washed with acetone (3 mL) and MeOH (3 mL), and the solid was
dried under reduced pressure at r.t. for 16 h; this gave Silica-
AAPTS-Pd as a yellow powder (1.05 g).
1H NMR (400 MHz, DMSO-d6): d = 7.97 (d, J = 8.4 Hz, 2 H), 7.75
(d, J = 8.4 Hz, 2 H), 7.66 (d, J = 7.6 Hz, 2 H), 7.43–7.32 (m, 5 H),
2.51 (s, 3 H).
(E)-4-(Trifluoromethyl)stilbene (4)
Mp 132–134 °C (Lit.24 132–134 °C).
IR (KBr): 3025, 2846, 1626, 1554, 1418, 1326, 1167, 1111, 1070,
973, 827 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.58 (m, 4 H), 7.52 (d, J = 7.2 Hz,
2 H), 7.39 (m, 2 H), 7.29 (m, 1 H), 7.18 (d, J = 16.2 Hz, 1 H), 7.09
(d, J = 16.5 Hz, 1 H).
Silica-APTS-Pd
In a 50-mL round-bottom flask were introduced successively anhyd
toluene (20 mL), activated silica gel (3.00 g; prepared as described
in the above procedure), and (3-aminopropyl)triethoxysilane
(APTS) (10 mL). The soln was refluxed for 24 h, and then filtered,
and the solid was washed successively with acetone (5 mL) and
CH2Cl2 (5 mL), and dried under reduced pressure at 60 °C; this gave
Silica-APTS (3.26 g).
(E)-3-(Trifluoromethyl)stilbene (5)
Mp 67–68 °C (Lit.25 66–67 °C).
IR (KBr): 3039, 2854, 1619, 1558, 1497, 1452, 1342, 1169, 1116,
962, 805, 696 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.94 (m, 2 H), 7.68 (m, 4 H),
7.38 (m, 5 H).
In a small Schlenk tube, Silica-APTS (1.00 g, 0.935 mequiv 3-ami-
nopropyl/g) was mixed with Pd(OAc)2 (0.112 g, 0.5 mmol) in an-
hyd EtOH (5 mL). The mixture was stirred under N2 for 4 h at r.t.
The soln was filtered and the solid was washed successively with
acetone (3 mL) and MeOH (3 mL), and the solid was dried under
reduced pressure at r.t. for 16 h; this gave Silica-APTS-Pd as a yel-
low powder (1.03 g).
Ethyl (E)-3-[2-(Trifluoromethyl)phenyl]acrylate (6)
Oil.28
IR (film): 3084, 2986, 1720, 1632, 1489, 1389, 1317, 1165, 1125,
1037, 980, 766, 652 cm–1.
1H NMR (300 MHz, CDCl3): d = 8.09 (d, J = 15.9 Hz, 1 H), 7.76–
7.45 (m, 4 H), 6.41 (d, J = 15.9 Hz, 1 H), 4.29 (q, J = 7.2 Hz, 2 H),
1.35 (t, J = 6.0 Hz, 3 H).
Compounds 1–14 by Heck Coupling of Organic Halides with
Olefins; General Procedure
Under a N2 atmosphere, an oven-dried round-bottom flask was
charged with Silica-AAPTS-Pd (24 mg, 0.01 mmol Pd), K2CO3
(276 mg, 2.0 mmol), the appropriate olefin (1.0 mmol), the appro-
priate organic halide (1.0 mmol), and DMA (4 mL). The reaction
mixture was stirred at 130 °C for 12 h. After completion of the re-
action, the mixture was cooled to r.t., and vacuum-filtered through
a sintered glass funnel, which was washed with CH2Cl2 (2 × 3 mL).
The combined organic fractions were dried (Na2SO4), filtered, and
concentrated, and the residue was purified by flash chromatography
(silica gel); this gave the desired cross-coupling product.
Ethyl (E)-Cinnamate (7)
Oil.26
IR (film): 3074, 2954, 1709, 1621, 1497, 1312, 772, 687 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.67 (d, J = 16.4 Hz, 1 H),
7.62–7.50 (m, 2 H), 7.41–7.36 (m, 3 H), 6.60 (d, J = 16.0 Hz, 1 H),
4.18 (q, J = 7.2 Hz, 2 H), 1.25 (t, J = 7.0 Hz, 3 H).
Ethyl (E)-3-(4-Methoxyphenyl)acrylate (8)
Recycling of Silica-AAPTS-Pd; Typical Procedure
Mp 48–50 °C (Lit.22 47–48.8 °C).
After the reaction had been carried out, the mixture (containing ca.
1 g Silica-AAPTS-Pd) was vacuum-filtered through a sintered glass
funnel, which was washed successively with CH2Cl2 (5 mL), Et2O
(5 mL), EtOH (5 mL), and hexane (5 mL). After the collected sup-
ported catalyst had been dried in an oven at 60 °C for 4 h, it could
be reused directly without further purification.
IR (KBr): 2981, 1718, 1635, 1517, 1368, 1178, 984, 814 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.62 (m, 3 H), 6.92 (d, J = 8.8
Hz, 2 H), 6.45–6.41 (d, J = 16.0 Hz, 1 H), 4.17 (q, J = 7.2 Hz, 2 H),
3.77 (s, 3 H), 1.32 (t, J = 7.2 Hz, 3 H).
Ethyl (E)-3-(3-Nitrophenyl)acrylate (9)
(E)-Stilbene (1)
Mp 74–75 °C (Lit.27 74.3–74.6 °C).
Mp 120–122 °C (Lit.22 120 °C).
IR (KBr): 3075, 2982, 1717, 1644, 1525, 1480, 1354, 1328, 1187,
999, 872, 746, 664 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 8.54 (t, J = 1.6 Hz, 1 H), 8.22
(dd, J = 8.4, 1.6 Hz, 1 H), 8.19 (d, J = 8.0 Hz, 1 H), 7.77 (d, J = 16.4
Hz, 1 H), 7.70 (t, J = 8.0 Hz, 1 H), 6.83 (d, J = 16.0 Hz, 1 H), 4.20
(q, J = 7.2 Hz, 2 H), 1.27 (t, J = 7.0 Hz, 3 H).
IR (KBr): 3020, 1631, 1495, 1451, 1364, 962, 764, 692 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.61–7.60 (m, 4 H), 7.40–7.27
(m, 4 H), 7.24–7.13 (m, 4 H).
(E)-4-Methoxystilbene (2)
Mp 136–138 °C (Lit.23 135–137 °C).
IR (KBr): 2836, 1605, 1512, 1447, 1365, 1297, 1179, 1030, 967,
828, 689 cm–1.
Ethyl (E)-3-(4-Nitrophenyl)acrylate (10)
Mp 138–140 °C (Lit.27 139–139.8 °C).
1H NMR (400 MHz, DMSO-d6): d = 7.60 (d, J = 6.4 Hz, 2 H), 7.50
(d, J = 8.4 Hz, 2 H), 7.36 (t, J = 7.8 Hz, 2 H), 7.24 (t, J = 6.4 Hz, 1
H), 7.16 (d, J = 16.4 Hz, 1 H), 7.10 (d, J = 16.4 Hz, 1 H), 6.95 (d,
J = 8.8 Hz, 2 H), 3.80 (s, 3 H).
IR (KBr): 3075, 2982, 1717, 1644, 1525, 1446, 1354, 1188, 1034,
873, 767, 664 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 8.25 (d, J = 8.8 Hz, 2 H), 8.20
(d, J = 8.8 Hz, 2 H), 7.69 (d, J = 16.0 Hz, 1 H), 6.57 (d, J = 16.0 Hz,
1 H), 4.22 (q, J = 7.0 Hz, 2 H), 1.26 (t, J = 7.0 Hz, 3 H).
(E)-4-Acetylstilbene (3)
Mp 149–151 °C (Lit.22 148–150 °C).
(E)-3-(4-Tolyl)acrylonitrile (11)
Mp 72–73 °C (Lit.29 71–73 °C).
Synthesis 2007, No. 11, 1635–1642 © Thieme Stuttgart · New York

PAPER
Palladium Catalyst Immobilized on Organic–Inorganic Hybrid Material
1641
IR (KBr): 3062, 2956, 2216, 1653, 1624, 1618, 1181, 1110, 978,
801 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.58 (d, J = 16.4 Hz, 1 H),
7.53–7.23 (m, 4 H), 6.37 (d, J = 16.4 Hz, 1 H), 2.33 (s, 3 H).
2161. (d) Dahan, A.; Portnoy, M. Org. Lett. 2003, 5, 1197.
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Puglisi, A.; Cozzi, F. Chem. Rev. 2003, 103, 3401.
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and Hall: Glasgow, 1995. (b) Clark, J. H.; Macquarrie, D. J.
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(E)-4-Methylstilbene (12)
Mp 121–122 °C (Lit.22 120 °C).
IR (KBr): 3018, 2831, 1632, 1574, 1448, 1365, 969, 809, 749, 690
cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.59 (d, J = 7.6 Hz, 2 H), 7.50
(d, J = 8.0 Hz, 2 H), 7.41–7.24 (m, 3 H), 7.21–7.16 (m, 4 H), 2.31
(s, 3 H).
(7) For review, see: (a) Phan, N. T. S.; Van Der Sluys, M.;
Jones, C. W. Adv. Synth. Catal. 2006, 348, 597.
(b) Chandrasekhar, V.; Athimoolam, A. Org. Lett. 2002, 4,
2113. (c) Li, L.; Shi, J.; Yan, J. Chem. Commun. 2004,
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Sateesh, M.; Lewis, R. J. Am. Chem. Soc. 2005, 127, 10045.
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(E)-4-Cyanostilbene (13)
Mp 117–119 °C (Lit.22 117.4–117.7 °C).
IR (KBr): 2834, 2362, 1602, 1504, 1364, 973 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.83 (d, J = 8.4 Hz, 2 H), 7.80
(d, J = 8.4 Hz, 2 H), 7.66 (d, J = 7.6 Hz, 2 H), 7.56 (t, J = 7.4 Hz, 2
H), 7.44 (t, J = 8.4 Hz, 1 H), 7.31 (d, J = 16.5 Hz, 1 H), 7.19 (d,
J = 16.5 Hz, 1 H).
Ethyl (E)-3-(4-Tolyl)acrylate (14)
Oil.26
(8) (a) Heck, R. F. Acc. Chem. Res. 1979, 12, 146. (b) Heck, R.
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IR (film): 2981, 1713, 1632, 1514, 1412, 1365, 1311, 1175, 984,
814 cm–1.
1H NMR (400 MHz, DMSO-d6): d = 7.62 (d, J = 16.0 Hz, 1 H), 7.58
(d, J = 8.0 Hz, 1 H), 7.22 (d, J = 8.0 Hz, 2 H), 6.55 (d, J = 16.0 Hz,
1 H), 4.18 (q, J = 7.1 Hz, 2 H), 2.32 (s, 3 H), 1.25 (t, J = 7.0 Hz, 3
H).
Acknowledgment
We gratefully acknowledge financial support by the National Natu-
ral Science Foundation of China (20572031, 20372024), the Excel-
lent Scientist Foundation of Anhui Province, China (No.
04046080), the Scientific Research Foundation for the Returned
Overseas Chinese Scholars, State Education Ministry, China (No.
2002247), the Excellent Young Teachers Program of MOE, China
(No. 2024), and the Key Project of Science and Technology of State
Education Ministry, China (No. 0204069).
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