Silica-supported terpyridine palladium(II) complex as an efficient and reusable catalyst for Heck and Suzuki cross-coupling reactions

Article abstract of DOI:10.1002/aoc.3084

Silica-supported terpyridine palladium(II) was prepared and used as an effective and recyclable catalyst in Mizoroki-Heck and Suzuki-Miyaura coupling reactions. The catalyst was very effective for the Mizoroki-Heck reaction of aryl halides with olefins and conversion was in most cases excellent. The catalyst showed good thermal stability (up to 230 °C) and could be recovered and reused for four reaction cycles. The Suzuki coupling of aryl iodides with aryl boronic acids in the presence of the catalyst was also investigated and the reaction proceeded with a short reaction time and excellent conversion.

Full text of DOI:10.1002/aoc.3084

Full Paper
Received: 25 June 2013
Revised: 2 October 2013
Accepted: 4 October 2013
Published online in Wiley Online Library: 26 November 2013
(wileyonlinelibrary.com) DOI 10.1002/aoc.3084
Silica-supported terpyridine palladium(II)
complex as an efficient and reusable catalyst
for Heck and Suzuki cross-coupling reactions
Mostafa M. Amini, Afsaneh Feiz, Minoo Dabiri and Ayoob Bazgir*
Silica-supported terpyridine palladium(II) was prepared and used as an effective and recyclable catalyst in Mizoroki–Heck and
Suzuki–Miyaura coupling reactions. The catalyst was very effective for the Mizoroki–Heck reaction of aryl halides with olefins and
conversion was in most cases excellent. The catalyst showed good thermal stability (up to 230 °C) and could be recovered and reused
for four reaction cycles. The Suzuki coupling of aryl iodides with aryl boronic acids in the presence of the catalyst was also investi-
gated and the reaction proceeded with a short reaction time and excellent conversion. Copyright © 2013 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web-site.
Keywords: Mizoroki–Heck reaction; Suzuki–Miyaura reaction; heterogeneous catalyst
[
14]
been used to catalyze alkyl cross-coupling reactions.
The
Introduction
Suzuki–Miyaura cross-coupling reaction has been reported in the
presence of polymer-supported terpyridine palladium complex,
[15]
Coupling reactions, including Mizoroki–Heck and Suzuki–Miyaura
reactions, provide single operational methods to form a new
carbon–carbon (Csp —Csp ) bond in modern synthetic chemis-
and the SBA-15-supported iron terpyridine complex has been used
2
2
to catalyze oxidative C—C cross-coupling reactions of tertiary
[
16]
try, and they have emerged as powerful tools in both academic
amines with carbon nucleophiles.
Very recently, we have
[
1–3]
and industrial laboratories.
The Heck reaction enables the di-
reported the synthesis of terpyridine-functionalized MCM-41
nanoporous silica for the removal of chromate in the environ-
rect cross-coupling of simple alkenes with aryl or vinyl halides.
The cross-coupling reactions of aryl halides with arylboronic
acids, often referred to as Suzuki coupling reactions, are versatile
methods for synthesizing unsymmetrical biaryls, which have a
crucial role in natural products and pharmaceutical com-
[
22]
ment.
Herein we wish to describe the synthesis of silica-
supported terpyridine palladium(II) complex (silica-terpy–Pd(II))
and demonstrate its catalytic activity in Mizoroki–Heck and
Suzuki–Miyaura reactions. Silica as an inorganic support has
several advantageous, such as excellent stability, good accessi-
bility and the fact that organic groups can be robustly anchored
[4–6]
pounds.
These coupling reactions have recently been consid-
ered because of their appropriate application in total synthesis
without protecting groups and their potential to simplify
[
12]
to the surface.
[
1–3]
functionalization of the aryl group.
These coupling reactions were mostly carried out by homo-
geneous palladium complexes, which cause difficulties in the
purification of the final product, recycling of the catalyst and
deactivation via aggregation into palladium nanoparticles. These
problems are of environmental and economic concern in large-
Experimental
Preparation of 3-Aminopropyl Triethoxysilane-
Functionalized Silica (APS)
[
2,7,8]
scale synthesis in industry.
. From industrial, economic and
environmental points of view, the development of a less expen-
sive, efficient and environmentally benign catalyst is still in high
demand. In this context, the continued development of reusable
heterogeneous catalysts can potentially reduce both cost and
Silica (with an average pore diameter of 60 ) was activated by
refluxing in hydrochloric acid (6 M) for 24 h and then washing
thoroughly with deionized water to neutral pH and drying before
carrying out surface modification. The activated silica (5.0 g) and
3-aminopropyltriethoxysilane (1.65 mmol) in dry toluene was
stirred under reflux conditions for 24 h. The solid material was
filtered off and washed with hot toluene for 12 h in a continu-
ous extraction apparatus (Soxhlet) and then dried in an oven
at 110 °C overnight to give APS.
[9–13]
waste.
polymers and carbonaceous material, inorganic compounds
such as silica, zeolites and metal oxides) and hybrid organic–
A number of organic compounds, such as organic
(
inorganic materials (mainly grafted silica) have been used as
supports for palladium nanoparticles. Alternatively, the grafting
of such supports with homogeneous catalysts often provides
good catalytic activity as well as possible recovery of the catalyst
[
8–13]
system by simple conduction.
*
Correspondence to: Ayoob Bazgir, Department of Chemistry, Shahid Beheshti
University, Tehran, Iran. Email: a_bazgir@sbu.ac.ir
Recently, the terpyridines, as tridentate ligands with efficient
and stable chelating ability to transition metals, have received
[
14–21]
increasing attention.
Terpyridine nickel complexes have
Department of Chemistry, Shahid Beheshti University, Tehran, Iran
Appl. Organometal. Chem. 2014, 28, 86–90
Copyright © 2013 John Wiley & Sons, Ltd.

Coupling reactions, including Mizoroki–Heck and Suzuki–Miyaura
Preparation of Terpyridine-Functionalized Silica (SiO
2
–Terpy) 5
The resulting APS (5.0 g) was reacted with terephthalaldehyde
(10 mmol) in methanol under reflux conditions for 24 h. The solid
material was filtered off and washed with MeOH, CHCl and DMF
3
to afford imino-functionalized silica 2. The imino-functionalized
silica 2 was added to a mixture of 2-acetylpyridine (10 mmol)
and NaOH (0.5 g, pH 11) in ethanol and refluxed for 24 h. Then
4
NH OAc (100 mmol) was added to the reaction mixture and
refluxed for a further 24 h. The solid was filtered off and washed
with toluene, MeOH, DMF, DMSO and water. The resulting mate-
rial was dried in an oven at 110 °C for 8 h.
Preparation of Palladium(II) Complex Supported on
Terpyridine-Functionalized Silica 6
The catalyst was prepared by stirring a mixture of SiO
2
–Terpy 5
(
2.0 g) and palladium acetate (0.96 mmol) in dry acetone (25 ml)
Figure 1. IR spectrum of (a) silica–terpy and (b) silica–terpy–Pd.
at room temperature. After stirring for 24 h, the resulting brown
solid was filtered and washed with acetone and dichloromethane.
Finally, the material was dried at 90 °C for 6 h.
General Experimental Procedure for the Heck Reaction
2 3
The catalyst (1.0 mol%) and K CO (1.2 mmol) was stirred
CHO
OH
OH
OH
EtO
EtO Si
EtO
Toluene
O
O Si
O
in N-methyl-2-pyrrolidone (NMP) (2.0 ml) for 10 min. Then
aryl halide (1.0 mmol) and olefin (1.0 mmol) were added
and magnetically stirred for an appropriate time (Table 2)
at 100 °C. After completion of the reaction, the reaction
mixture was cooled to room temperature and the catalyst
was separated by filtration. Conversions and yields of the
reactions were determined by gas chromatography (GC).
NH2
NH2
+
+
Reflux, 24h
APS
CHO
1
O
O
MeOH
Reflux, 24h
N
O Si
O
N
3
General Experimental Procedure for the Suzuki
Reaction
NaOH, EtOH
CHO
2
The catalyst (1.0 mol%) and K
2 3
CO (1.2 mmol) were stirred
in H O (2 ml) for 10 min. Then aryl halide (1.0 mmol) and
2
boronic acid (1.0 mmol) were added and magnetically
stirred for 0.5–1.5 h at 90 °C. After cooling the reaction
mixture to room temperature, the catalyst was separated
by filtration. Ethyl acetate (2 × 5 ml) was added to the fil-
trate. The organic layer was separated and dried with
O
O
O Si
O
N
EtOH (Reflux)
NH OAc
N
MgSO . Conversions and yields of the reactions were de-
N
4
termined by GC.
O
4
Results and Discussion
O
Synthesis of Silica–Terpy–Pd(II) Complex
O Si
O
N
N
Pd(OAc)2
Acetone, r.t.
Preparation of the catalyst is outlined in Scheme 1. The
activated silica was functionalized with 3-aminopropyl-
triethoxysilane, followed by condensation with terphtha-
N
N
[
23]
laldehyde 1 using known procedures
to give the
5
corresponding aldehyde-functionalized silica 2. The imino-
functionalized silica 2 was subsequently reacted with 2-
acetylpyridine 3 in alkaline conditions to afford bis-pyridyl-
functionalized silica 4. Amorphous silica-supported
O
O Si
O
N
N
N
terpyridine (SiO
of 4 and NH OAc in EtOH under reflux conditions similar
to the mesoporous silica counterpart.
SiO –Terpy 5 was then reacted with an acetone solution of
Pd(OAc) at room temperature to afford the silica-supported
terpyridine palladium(II) complex (silica–terpy–Pd(II)) 6.
2
–terpy) 5 was prepared via the reaction
Pd
OAc
N
4
OAc
[21]
The obtained
6
2
2
Scheme 1. Synthesis of catalyst.
Appl. Organometal. Chem. 2014, 28, 86–90
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. M. Amini et al.
a
Table 1. Optimization of Mizoroki–Heck reaction
The IR spectrum of 2 showed two adsorption peaks at 1706
À1
and 1646 cm
(SI), ascribed to aldehyde and imine groups,
Solvent, Cat.
Ph
respectively. This clearly confirms the functionalization of silica
CO2Me
K2CO3, 100 o
C
À1
by terphthalaldehyde. Bands at 1060 cm in the IR spectrum
Ph-I +
of 5 were assigned to the symmetric stretching vibration of
CO2Me
[
24]
Si—O
(Fig. 1). The peaks of the organic groups were
relatively weak because of their low content in functionalized
À1
b
Entry
Solvent
Catalyst (mol%) Time (h) Conversion (%)
silica. Bands observed at 1644 cm for 5 could be attributed
[
11]
to the C=N (pyridine ring) stretching frequency. . The C=N
1
2
3
4
5
6
7
8
9
H
2
O
1
1
1
2
2
1
1
1
1
1
46
88
63
33
58
76
85
74
bands of complex 6 were shifted to a lower frequency in the
IR spectrum (1619 cm ) compared to that of 5. The lowering
in frequency of the C=N peak is indicative of the formation
of a metal–ligand bond.
NMP
DMF
1
À1
1
Toluene
NMP
NMP
NMP
NMP
NMP
1
0.5
0.8
1.2
1
From the TGA of 5 (SI), loading of the terpyridine ligand that
À1
bound to the silica surface was calculated to be 0.48 mmol g
,
in accordance with CHN analysis. The loading of palladium in 6
c
À1
was determined to be 0.12 mmol g
by atomic adsorption
d
1
89
spectroscopy. In order to obtain an insight into the oxidation
state and coordination environment of palladium in silica–
terpy–Pd(II), X-ray photoelectron spectroscopy (XPS) was
performed (SI). The Pd 3d5/2 and Pd 3d3/2 binding energies
were determined to be 337.0 and 342.2 eV, respectively. These
values correspond to the Pd(II) binding energy of silica–terpy–
Pd(II) complex.
a
Reaction conditions: Ph–I (1 mmol), methyl acrylate (1 mmol),
CO (1.2 mmol), catalyst (based on content of Pd).
conversion determined by GC.
K
2
3
b
c
%
Reaction temperature = 80 °C.
d
Reaction temperature = 120 °C.
Table 2. Heck coupling of aryl halides with olefins
R1
R1
X
R2 Cat. (1 mol%), K2CO3
o
NMP, 100
C
+
R2
a
a
Entry
X
R
1
R
2
Time (h)
Conversion (%)
Yield (%)
1
2
3
4
5
6
7
8
9
I
H
H
H
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CN
CO
CO
CO
CO
CO
Ph
2
2
2
2
2
2
2
2
2
2
Me
1
2:5
1.2
2
88
87
80
89
96
97
95
98
61
82
87
77
72
80
96
95
52
74
54
83
81
75
84
90
88
91
91
53
78
63
71
65
75
92
88
48
69
49
I
Et
I
Bu
Me
Et
I
Me
COMe
I
4
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
I
NO
NO
2
Me
Et
3
2
8
CHO
H
Et
3
Bu
Bu
20
9
10
11
12
13
14
15
16
17
18
19
CHO
NO
Me
NO
NO
2
20
9
2
2
2
2
2
Me
Me
Bu
2
2
24
35
32
20
5
CO
2
H
Me
Me
2,4-NO
H
2
I
CO
NO
2
Me
Ph
6
Br
2
Ph
8
a
%
Determined by GC.
wileyonlinelibrary.com/journal/aoc
Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 86–90

Coupling reactions, including Mizoroki–Heck and Suzuki–Miyaura
Catalytic Activity of Silica–Terpy–Pd(II)
another flask containing K
heating of the catalyst-free solution for 2 h, no considerable progress
~10% by GC analysis) was observed.
Finally, the catalyst was tested in the Suzuki coupling reaction.
The Suzuki coupling of aryl iodides with aryl boronic acids in the
2 3
CO in NMP at 100 °C. Upon further
The catalytic activity of silica–terpy–Pd(II) 6 for Mizoroki–Heck
reaction was investigated. The coupling reaction of iodobenzene
with methyl acrylate was used as a model reaction to determine
(
2 3
the optimum reaction conditions in the presence of K CO as
2 3
presence of the silica–terpy–Pd(II) catalyst (1mol%) using K CO
a base (Table 1). NMP was the solvent of choice, and using it
in the reaction resulted in a high yield after 1 h. To study the
effect of the amount of catalyst, the reactions were carried out
at different amounts of 6 ranging from 0.5 to 1.2mol%. It was
found that by increasing the amount of catalyst from 0.5, 0.8
and 1.0 to 1.2mol%, the yield increased from 58%, 76%, and
as a base in water under stirring at 90 °C was also investigated
and the reaction proceeded with a short reaction time (0.5–1.5 h),
with excellent conversion and yield (Table 3). Under the same reac-
tion conditions the coupling of chlorobenzene and bromobenzene
failed to provide the target products.
Recyclability of the catalyst was also examined in the model
reaction of iodobenzene and phenylboronic acid. As shown in
Fig. 3, recovery was achieved in four successive reaction runs.
To check whether palladium was being leached out from the
solid support to the solution, a typical hot filtration test was
performed in the model reaction. After continuing the reaction
for 0.5 h, the catalyst was removed by filtration and the deter-
mined conversion was 40%. The resulting filtrate was subjected
to heating for a further 2 h. From the GC results it was revealed
that after separation of the catalyst no conversion took place in
the filtrate. Since no further conversion was observed, this indi-
cates that soluble species may not be involved in the reactions.
8
1
8% to 85%, respectively. Furthermore, results showed that
mol% catalyst in NMP was sufficient to push this reaction
forward. Further increases in the amount of catalyst did not
improve the yield. As can be observed from Table 1, the most
suitable reaction temperature was 100 °C.
To verify the effectiveness and generality of the catalyst and pro-
cedure, the reaction of various aryl halides and olefins were exam-
ined under optimized reaction conditions (Table 2). It is known that
the catalyst is very effective for reactions with aryl iodides and aryl
bromides as arylating agents. For all of the olefins that were exam-
ined, good conversion and yield were achieved. Aryl chlorides
have not typically been used in the Heck reaction because
oxidative addition occurs more easily with bromides and iodides.
However, the use of aryl chlorides is highly desirable, as they are
more cost effective and readily available over alternative reagents.
Therefore, we studied the Heck reaction with aryl chlorides under
the same reaction conditions. The catalytic system was able to
affect the Heck coupling reaction of aryl chlorides, and good
conversions and yields could be obtained after 20–35 h (entries
Table 3. Suzuki coupling of aryl iodides with aryl boronic acids
R1
HO
+
OH
R1
B
Cat. (1 mol%), K2CO3
H2O, 90 °C
13–16). Reactions involving aryl iodides or bromide gave moderate
conversions and yields with styrene (entries 17–19).
The recyclability of the silica–terpy–Pd(II) catalyst was also
examined by the coupling reaction of iodobenzene and methyl
acrylate as a test model. After completion of the reaction, the cat-
I
R2
R2
3
alyst was filtered and then washed with DMF, CHCl and water.
The recovered catalyst was dried at 100 °C for 5 h and then
reloaded with fresh reagents for further runs. Recovery was achieved
in four successive reaction runs (Fig. 2). To determine whether the
catalyst was actually functioning in a heterogeneous manner or
whether it was merely a reservoir or more active soluble palladium
species, we performed a hot filtration test after the reaction of
iodobenzene with methyl acrylate initiates and before the sub-
strates were consumed. The hot filtrates were then transformed to
a
a
Entry
R
1
R
2
Time (h) Conversion (%)
Yield (%)
1
2
3
4
H
H
H
1.5
1
90
92
94
89
88
89
91
86
Me
Me
Me
COMe
Me
0.5
1
[25]
a
%
determined by GC.
reaction times= 1.5 hour
reaction times= 1 hour.
Figure 3. Reusability of catalyst in the Suzuki reaction. Reaction
Figure 2. Reusability of catalyst in the Heck reaction. Reaction time = 1 h.
time = 1.5 h.
Appl. Organometal. Chem. 2014, 28, 86–90
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. M. Amini et al.
[
[
[
10] Y. Kitamura, S. Sako, A. Tsutsui, Y. Monguchi, T. Maegaw, Y. Kitade,
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Conclusion
Silica-supported terpyridinepalladium(II) complex as an active
catalyst has been developed for Mizoroki–Heck and Suzuki–
Miyaura coupling reactions. This catalyst was recovered and
reused four times with decreasing activities.
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We gratefully acknowledge financial support from the Research
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Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 86–90