Heck arylation of conjugated alkenes with aryl bromides or chlorides catalyzed by immobilization of palladium in MCM-41

Article abstract of DOI:10.1007/s10562-013-1013-7

A new 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-2N-PdCl₂] was conveniently synthesized from commercially available and cheap 3-(2-aminoethylamino) propyltrimethoxysilane via immobilization on MCM-41, followed by reacting with palladium chloride. It was found that this heterogeneous palladium complex is a highly efficient catalyst for Heck arylation of conjugated alkenes with aryl bromides or chlorides using tetrabutylammonium bromide as additive and can be reused for at least six consecutive trials without any decreases in activity.

Full text of DOI:10.1007/s10562-013-1013-7

Catal Lett (2013) 143:681–686
DOI 10.1007/s10562-013-1013-7
Heck Arylation of Conjugated Alkenes with Aryl Bromides
or Chlorides Catalyzed by Immobilization of Palladium
in MCM-41
•
Fang Yao Jiaqin Liu Mingzhong Cai
•
Received: 28 January 2013 / Accepted: 21 April 2013 / Published online: 4 May 2013
Ó Springer Science+Business Media New York 2013
Abstract A new 3-(2-aminoethylamino)propyl-function-
alized MCM-41-immobilized palladium(II) complex [MCM-
41-2N-PdCl2] was conveniently synthesized from com-
mercially available and cheap 3-(2-aminoethylamino)
propyltrimethoxysilane via immobilization on MCM-41,
followed by reacting with palladium chloride. It was found
that this heterogeneous palladium complex is a highly
efficient catalyst for Heck arylation of conjugated alkenes
with aryl bromides or chlorides using tetrabutylammonium
bromide as additive and can be reused for at least six con-
secutive trials without any decreases in activity.
palladium complexes remain a challenge because they are
expensive, cannot be recycled, and difficult to separate
from the product mixture, which is a particularly significant
drawback for their application in the pharmaceutical
industry. The immobilization of catalytically active spe-
cies, i.e. organometallic complexes, onto a solid support to
produce a molecular heterogeneous catalyst is one potential
solution to the latter two problems [5].
The high costs of the transition metal catalysts coupled
with toxic effects associated with many transition metals has
led to an increased interest in immobilizing catalysts onto a
support. Heterogeneous catalysis also helps to minimize
wastes derived from reaction workup, contributing to the
development of green chemical processes [6, 7]. Although a
number of heterogeneous palladium catalysts were reported
to be effective for Heck reaction [8–11], very few catalysts
were shown to have good catalytic activity for Heck aryla-
tion of alkenes with unactivated bromoarenes [12–14] and
chloroarenes [15]. Among these reported heterogeneous
palladium catalysts, most of them are the supported phos-
phine palladium complexes which suffer from severe dis-
advantages that have so far precluded their practical
applications. It is known that catalysts containing phosphine
ligands are unstable at high temperatures [16–18]. Further-
more, the procedure for preparing the polymer-supported
phosphine palladium complexes is rather complicated since
the non-crosslinked poly(chloromethylstyrene) is not com-
mercially available and the chloromethylation requires the
use of carcino-genic chloromethyl methyl ether. Therefore,
the development of phosphine-free heterogeneous palladium
catalysts having a high activity and stability is a topic of
enormous importance.
Keywords Supported palladium catalyst Á Bidentate
nitrogen palladium complex Á Functionalized MCM-41 Á
Heck arylation Á Heterogeneous catalysis
1 Introduction
The palladium-catalyzed reaction of aryl and alkenyl
halides with alkenes (the Heck reaction) represents one of
the most versatile tools in modern synthetic chemistry and
has great potential for industrial applications [1–4]. The
Heck reaction is generally catalyzed by soluble palladium
complexes such as Pd(OAc)2 and PdCl2 with phosphine
ligands. However, industrial applications of homogeneous
F. Yao Á J. Liu Á M. Cai (&)
Department of Chemistry, Jiangxi Normal University,
Nanchang 330022, People’s Republic of China
e-mail: caimzhong@163.com
F. Yao
Recent developments on the mesoporous material MCM-
41 provided a new possible candidate for a solid support
for immobilization of homogeneous catalysts [19–21].
Department of Chemistry and Pharmaceutical Engineering, West
Branch of Zhejiang University of Technology, Quzhou 324000,
People’s Republic of China
123

682
F. Yao et al.
MCM-41 has a regular pore diameter of ca.5 nm and a spe- material MCM-41-2N. The nitrogen content was found to
cific surface area[700 m2/g [22]. Its large pore size allows be 1.84 mmol/g by elemental analysis.
passage of large molecules such as organic reactants and
metal complexes through the pores to reach to the surface of 2.2 Preparation of MCM-41-2N-PdCl2
the channel [23–25]. In addition, the regular pore size of
MCM-41 can provide shape selectivity not provided by silica In a small Schlenk tube, 3.3 g of the above-functionalized
gel. To date, some palladium complexes on functionalized MCM-41 (MCM-41-2N) was mixed with 0.226 g
MCM-41support have beenpreparedand successfully usedin (1.27 mmol) of PdCl2 in 50 mL of dry acetone. The mix-
Heck reactions [26–29], however, they exhibited poor cata- ture was refluxed for 72 h under an argon atmosphere. The
lytic activity for unactivated bromoarenes as the substrates solid product was filtered by suction, washed with acetone,
and no activity for chloroarenes. In continuing our efforts to distilled water and acetone successively and dried at 70 °C/
develop greener synthetic pathways for organic transforma- 26.7 Pa under Ar for 5 h to give 3.47 g of a yellow pal-
tions, our new approach, described in this paper, was to design ladium complex [MCM-41-2N-PdCl2]. The nitrogen and
and synthesize a novel 3-(2-aminoethylamino)propyl-func- palladium content was found to be 1.63 and 0.33 mmol/g,
tionalized MCM-41-immobilized palladium(II) complex, respectively.
which was used as an effective, phosphine-free and recyclable
palladium catalyst for the Heck arylation of conjugated 2.3 General Procedure for the Arylation of Styrene
alkenes with aryl bromides or chlorides.
with Aryl Bromides or Chlorides
A mixture of aryl halide (2.0 mmol), styrene (3.0 mmol),
Bu3N (3.0 mmol), TBAB (1.2 g), and the MCM-41-2N-
PdCl2 complex (18 mg, 0.006 mmol of Pd) was stirred
2 Experimental
All chemicals were reagent grade and used as purchased. under Ar in an oil bath at 110–135 °C for 6–36 h. The
The mesoporous material MCM-41 was prepared accord- mixture was cooled, extracted with Et2O (3 9 20 mL). The
ing to a literature procedure [30]. All reactions were per- ammonium salt and the palladium catalyst were reused in
formed under an inert atmosphere of dry argon using the next run. The combined ether solution was washed with
distilled dried solvents. All arylation products were char- 5N HCl (2 9 10 mL), brine (3 9 10 mL), and dried over
acterized by comparison of their spectra and physical data MgSO4 and concentrated under a reduced pressure. The
with authentic samples. IR spectra were determined on a crude product was recrystallized from EtOH.
Perkin-Elmer 683 instrument. 1H NMR (400 MHz) spectra
were recorded on a Bruker Avance 400 MHz spectrometer 2.4 General Procedure for the Arylation of Butyl
with TMS as an internal standard in CDCl3 as solvent. 13
C
Acrylate with Aryl Bromides or Chlorides
NMR (100 MHz) spectra were recorded on a Bruker
Avance 400 MHz spectrometer in CDCl3 as solvent. Pal- A mixture of aryl halide (2.0 mmol), butyl acrylate
ladium content was determined with inductively coupled (3.0 mmol), Bu3N (3.0 mmol), TBAB (1.2 g), and the
plasma atom emission Atomscan16 (ICP-AES, TJA Cor- MCM-41-2N-PdCl2 complex (18 mg, 0.006 mmol of Pd)
poration). X-ray photoelectron spectra were recorded on was stirred under Ar in an oil bath at 120–140 °C for 5–48 h.
XSAM 800 (Kratos). X-ray powder diffraction patterns The mixture was cooled, extracted with Et2O (3 9 20 mL).
were obtained on Damx-rA (Rigaka).
The ammonium salt and the palladium catalyst were reused
in the next run. The combined ether solution was washed
with 5N HCl (2 9 10 mL), brine (3 9 10 mL), and dried
over MgSO4 and concentrated under a reduced pressure. The
2.1 Preparation of MCM-41-2N
A solution of 1.54 g of 3-(2-aminoethylamino)propyltri- residue was purified by column chromatography on silica gel
methoxysilane in 18 mL of dry chloroform was added to a (hexane/EtOAc = 19/1).
suspension of 2.2 g of the MCM-41 in 180 mL of dry
toluene. The mixture was stirred for 24 h at 100 °C. Then 2.5 General Procedure for the Arylation of Acrylamide
the solid was filtered and washed by CHCl3 (2 9 20 mL),
and dried in vacuum at 160 °C for 5 h. The dried white
solid was then soaked in a solution of 3.1 g of Me3SiCl in
with Aryl Bromides or Chlorides
A
mixture of aryl halide (2.0 mmol), acrylamide
100 mL of dry toluene at room temperature under stirring (3.0 mmol), Bu3N (3.0 mmol), TBAB (1.2 g), and the
for 24 h. Then the solid was filtered, washed with acetone MCM-41-2N-PdCl2 complex (18 mg, 0.006 mmol of Pd)
(3 9 20 mL) and diethyl ether (3 9 20 mL), and dried in was stirred under Ar in an oil bath at 120–140 °C for
vacuum at 120 °C for 5 h to obtain 3.49 g of hybrid 10–48 h. The mixture was cooled, extracted with hot EtOH
123

Heck Arylation of Conjugated Alkenes
683
(3 9 20 mL). The ammonium salt and the palladium cat-
alyst were reused in the next run. The combined extract was
poured into water (50 mL), the precipitated product was
isolated by suction and washed with water (3 9 10 mL).
The crude product was recrystallized from EtOH.
the reaction were tested. The results are summarized in
Table 2. The arylation reactions of styrene with bromo-
benzene in solvents such as p-xylene, DMF and NMP
afforded (E)-stilbene in low yields (entries 1–3). However,
in the presence of tetrabutylammonium bromide (TBAB),
the arylation reactions proceeded effectively to give
(E)-stilbene in moderate to good yields (entries 4–6).
Jeffery and Calo [31, 32] also reported that the catalytic
activity of homogeneous palladium catalysts could be
enhanced in the presence of TBAB in the Heck reactions.
We were pleased to find that the reaction proceeded very
smoothly in the absence of organic solvent using TBAB
(1.2 g) as the additive to afford (E)-stilbene in excellent
yield (entry 7). For the temperatures tested [100, 110, and
130 °C], 110 °C gave the best result. We then turned our
attention to investigate the effect of bases on the arylation
reaction. For the bases evaluated [Bu3N, DBU, NaOAc,
Na2CO3, and Cs2CO3], Bu3N was found to be the most
effective. Other bases such as DBU, NaOAc, Na2CO3 and
Cs2CO3 were substantially less effective. The amount of
supported palladium catalyst was also screened, and
0.3 mol% loading of palladium was found to be optimal
(entry 14), a lower yield was observed and a longer reac-
tion time was required when the amount of the catalyst was
decreased (entries 15 and 16). Thus, the optimized reaction
conditions for this arylation reaction are the MCM-41-2N-
PdCl2 (0.3 mol%) with TBAB as additive and Bu3N as
base at 110 °C under Ar for 8 h (entry 14).
3 Results and Discussion
A
new
3-(2-aminoethylamino)propyl-functionalized
MCM-41-immobilized palladium complex [MCM-41-2N-
PdCl2] was very conveniently synthesized from commer-
cially available and inexpensive 3-(2-aminoethylamino)
propyltrimethoxysilane via immobilization on MCM-41,
followed by reacting with palladium chloride (Scheme 1).
The X-ray powder diffraction (XRD) analysis of the MCM-
41-2N-PdCl2 indicated that, in addition to an intense dif-
fraction peak (100), two higher order peaks (110) and (200)
with lower intensities were also detected, and therefore
the chemical bonding procedure did not diminish the
structural ordering of the MCM-41. Elemental analyses and
X-ray photoelectron spectroscopy (XPS) were used to
characterize the 3-(2-aminoethylamino)propyl-functional-
ized MCM-41-immobilized palladium(II) complex. The N
: Pd mole ratio of the MCM-41-2N-PdCl2 was determined
to be 4.94. The XPS data for MCM-41-2N-PdCl2, MCM-
41-2N, PdCl2 and metal Pd are listed in Table 1. It can be
seen that the binding energies of Si2p and O1s of MCM-41-
2N-PdCl2 are similar to those of MCM-41-2N and the
binding energy of Cl2p of MCM-41-2N-PdCl2 is similar to
that of PdCl2. However the difference of N1s binding
energies between MCM-41-2N-PdCl2 and MCM-41-2N is
0.9 eV. The binding energy of Pd3d5/2 in MCM-41-2N-
PdCl2 is 0.7 eV less than that in PdCl2, but 2.2 eV larger
than that in metal Pd. These results show that a coordina-
tion bond between N and Pd is formed.
Table 1 XPS data for MCM-41-2N-PdCl2, MCM-41-2N, PdCl2 and
metal Pd
Sample
Pd3d5/2
337.4
N1s
Si2p
O1s
Cl2p
MCM-41-2N-PdCl2
MCM-41-2N
PdCl2
400.5
399.6
103.4
103.2
533.1
533.1
199.1
338.1
335.2
199.2
The arylation reaction of styrene with bromobenzene
was chosen as a model reaction, and the influences of
various reaction parameters such as solvent, base, additive,
reaction temperature, and palladium catalyst quantity on
Metal Pd
The binding energies are referenced to C1s (284.6 eV) and the energy
differences were determined with an accuracy of 0.2 eV
Scheme 1 Preparation of the
MCM-41-2N-PdCl2 complex
123

684
F. Yao et al.
Yield (%)a
Table 2 Reaction condition screening for the arylation reaction of styrene with bromobenzene
Entry
Solvent
Base
Additive (g)
Pd catalyst (mol%)
Temp. (°C)
Time (h)
1
p-Xylene
DMF
NMP
p-Xylene
DMF
NMP
None
None
None
None
None
None
None
None
None
None
Bu3N
Bu3N
Bu3N
Bu3N
Bu3N
Bu3N
Bu3N
Bu3N
Bu3N
DBU
None
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.3
0.2
0.1
130
130
130
130
130
130
130
110
100
110
110
110
110
110
110
110
24
24
24
24
24
24
2
25
36
39
64
73
82
92
96
68
79
60
51
57
96
90
79
2
None
3
None
4
TBAB (0.6)
TBAB (0.6)
TBAB (0.6)
TBAB (1.2)
TBAB (1.2)
TBAB (1.2)
TBAB (1.2)
TBAB (1.2)
TBAB (1.2)
TBAB (1.2)
TBAB (1.2)
TBAB (1.2)
TBAB (1.2)
5
6
7
8
3
9
24
24
24
24
24
8
10
11
12
13
14
15
16
NaOAc
Na2CO3
Cs2CO3
Bu3N
Bu3N
Bu3N
16
30
All reactions were performed using 2.0 mmol of PhBr, 3.0 mmol of styrene, 3.0 mmol of base in 1.0 mL of solvent under Ar
a
Isolated yield
To examine the scope for this heterogeneous Heck ary-
lation reaction, we have investigated the reaction of con-
jugated alkenes with a variety of aryl bromides or chlorides
under the optimized reaction conditions (Scheme 2) and the
results are outlined in Table 3. As shown in Table 3, the
Heck arylation reactions of styrene with a variety of aryl
bromides proceeded smoothly using TBAB as additive and
Bu3N as base at 110 °C to afford the corresponding
(E)-stilbenes in excellent yields (entries 1–7). The trans-
selectivity was always near quantitative and no cis-product
was observed. The reactivity of aryl bromides with elec-
tron-withdrawing groups was higher than that of aryl bro-
mides with electron-donating groups, but the reaction of
4-bromoanisole having strong electron-donating group
could also give (E)-4-methoxystilbene in 92 % yield (entry
7). The results above prompted us to investigate the aryla-
tion reactions of aryl chlorides with styrene. It is well
known that aryl chlorides are not reactive in Heck arylation
reactions of olefins unless a special and expensive ligand is
present. However, with our catalytic system, the reactions
of aryl chlorides having either electron-withdrawing or
electron-donating groups also proceeded effectively at
130–135 °C to afford the corresponding (E)-stilbenes in
good yields on longer reaction times (entries 8–11).
butyl (E)-cinnamates in good to excellent yields (entries
12–15). Both electron-withdrawing and electron-donating
substituents on aryl bromides were well tolerated. The
reactivity of aryl chlorides was obviously lower than that of
aryl bromides. The reactions of aryl chlorides having
electron-withdrawing groups at 140 °C could afford mod-
erate yields of desired coupled products (entries 16 and 17),
but the reaction of aryl chloride with electron-donating
group was very slow and only trace of desired product was
formed (entry 18). For the arylation of acrylamide, the
results similar to those with butyl acrylate were observed.
The reactions of acrylamide with a variety of aryl bromides
could also proceed smoothly at 120 °C to afford the cor-
responding (E)-cinnamamides in good to excellent yields
(entries 19–23). The reactions of only aryl chlorides with
strong electron-withdrawing substituents such as 4-nitro or
4-trifluoromethyl groups could take place at 140 °C to give
the desired coupled products in moderate yields on longer
reaction times (entries 24 and 25). The high catalytic
activity of our system may be attributed to the combination
of MCM-41-supported bidentate nitrogen palladium com-
plex with TBAB as an efficient additive. It is generally
believed that high surface area of heterogeneous catalyst
results in high catalytic activity. Considering the fact that
MCM-41 support has an extremely high surface area and
the catalytic palladium species is anchored on the inner
surface of the mesopore of MCM-41 support, we expect
that MCM-41-supported bidentate nitrogen palladium cat-
alyst will exhibit high activity and good reusability. It was
observed by Herrmann et al. [33], Reetz et al. [34] and
This catalytic system was also applied to the arylation
reactions of other conjugated alkenes such as butyl acrylate
and acrylamide with a variety of aryl bromides or chlo-
rides, the results are also summarized in Table 3. The Heck
arylation of butyl acrylate with various aryl bromides
proceeded smoothly at 120 °C to give the corresponding
123

Heck Arylation of Conjugated Alkenes
685
Scheme 2 Heterogeneous
arylation of conjugated alkenes
with aryl bromides or chlorides
Table 3 Arylation of conjugated alkenes with aryl bromides or
chlorides catalyzed by MCM-41-2N-PdCl2
Table 4 Arylation reaction of bromobenzene with styrene catalyzed
by recycled catalyst
Entry
R
H
X
Y
Temp. Time Product Yield
(%)a
Cycle
Yield (%)a
Cycle
Yield (%)a
(°C)
(h)
1
3
5
96
94
95
2
4
6
96
95
94
1
Br Ph
110
110
110
110
110
110
110
130
135
135
135
120
120
120
120
140
140
140
8
3a
3b
3c
3d
3e
3f
96
98
98
97
98
95
92
78
81
84
73
87
91
84
95
51
59
Trace
85
90
92
83
81
64
61
2
4-CHO Br Ph
6
3
3-NO2
4-Cl
Br Ph
Br Ph
Br Ph
Br Ph
6
Reaction conditions: 2.0 mmol of bromobenzene, 3.0 mmol of sty-
rene, 3.0 mmol of Bu3N, and 0.3 mol% MCM-41-2N-PdCl2, 1.2 g of
TBAB as additive at 110 °C for 8 h under Ar
4
6
5
4-CN
4-Me
6
a
6
16
24
30
24
20
36
8
Isolated yield
7
4-MeO Br Ph
Cl Ph
4-CHO Cl Ph
3g
3a
3b
3h
3f
8
H
We also investigated the possibility to reuse of the cat-
alyst by using the arylation reaction of bromobenzene with
styrene. After carrying out the reaction, the mixture was
cooled, extracted with diethyl ether for three times. The
ammonium salt and the palladium catalyst were reused
directly in the next run without further purification and
almost consistent activity was observed for six consecutive
cycles (Table 4, entries 1–6). In addition, palladium
leaching in the supported catalyst was also determined. The
palladium content of the catalyst was determined by ICP
analysis to be 0.33 mmol/g after six consecutive runs, no
palladium had been lost from the MCM-41 support. In
general, the continuous recycle of resin-supported palla-
dium catalysts is difficult owing to leaching of the palla-
dium species from the polymer supports, which often
reduces their activity within a five-recycle run. The high
stability and excellent reusability of this heterogeneous
palladium catalyst should result from the chelating action of
bidentate 2-aminoethylamino ligand on palladium and the
mesoporous structure of the MCM-41 support. The result is
important from a practical point of view. The high catalytic
activity, excellent reusability and the easy accessibility of
the MCM-41-2N-PdCl2 complex make it a highly attractive
heterogeneous palladium catalyst for the parallel solution
phase synthesis of diverse libraries of compounds.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
4-NO2
4-Me
H
Cl Ph
Cl Ph
Br CO2Bu
Br CO2Bu
3i
4-Cl
6
3j
4-MeO Br CO2Bu
4-NO2 Br CO2Bu
4-CHO Cl CO2Bu
24
5
3k
3l
48
40
48
12
10
10
24
30
48
48
3m
3l
4-NO2
4-Me
H
Cl CO2Bu
Cl CO2Bu
3n
3o
3p
3q
3r
3s
3t
Br CONH2 120
Br CONH2 120
Br CONH2 120
Br CONH2 120
3-NO2
4-Cl
4-Me
4-MeO Br CONH2 120
4-NO2
4-F3C
Cl CONH2 140
Cl CONH2 140
3u
All reactions were performed using 2.0 mmol of aryl halide,
3.0 mmol of alkene, 3.0 mmol of Bu3N, 0.006 mmol of MCM-41-
2N-PdCl2, 1.2 g of TBAB as additive under Ar
a
Isolated yield
Buchwald et al. [35] that in the Heck reaction, the addition
of tetraalkylammonium salts to conventional solvents led
to higher catalytic activities. The ammonium salts effects
are multiple. A possible explanation for TBAB acting as
such a good additive is that the bulkiness of tetrahedral
n-Bu4N?, by forcing the bromide ion away from the cation,
renders the bromide ion more nucleophilic and available
for catalyst activity and stability than the planar ammonium
cation can.
4 Conclusions
In summary, we have developed a novel, practical and
environmentally friendly catalyst system for the Heck
arylation of conjugated alkenes with aryl bromides or chlo-
rides by using 3-(2-aminoethylamino)propyl-functionalized
123

686
F. Yao et al.
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MCM-41-supported palladium complex [MCM-41-2N-
PdCl2] as catalyst and tetrabutylammonium bromide
(TBAB) as additive with Bu3N as base. The Heck arylation
reactions generated the corresponding trans-coupled prod-
ucts stereoselectively in good to excellent yields. This novel
heterogeneous palladium catalyst can be conveniently pre-
pared from commercially available and inexpensive
reagents and exhibits high catalytic activity and can be
reused at least six times without any decreases in activity.
The Heck arylation reactions of styrene, butyl acrylate and
acrylamide with aryl bromides or chlorides catalyzed by the
MCM-41-2N-PdCl2 complex provide a better and practical
procedure for the stereoselective synthesis of a variety of
(E)-stilbenes, butyl (E)-cinnamates and (E)-cinnamamides,
respectively.
Acknowledgments We gratefully acknowledge the financial sup-
port of this work by the National Natural Science Foundation of
China (Project No. 20862008) and the Natural Science Foundation of
Jiangxi Province in China (Project No. 2010GZH0062).
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