A palladium complex immobilized onto mesoporous silica: a highly efficient and reusable catalytic system for carbon–carbon bond formation and anilines synthesis

Article abstract of DOI:10.1007/s11243-017-0151-y

A palladium complex supported on functionalized mesoporous silica MCM-41 proved to be a highly efficient, recoverable catalyst for C–C coupling reactions and amination of aryl halides to afford anilines. The nanocatalyst was characterized by FT-IR spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption–desorption isotherms and inductively coupled plasma analysis. The catalyst could be reused for several consecutive runs without significant loss of activity. The excellent yields of products, simple reaction procedures and short reaction times are the main advantages of this methodology.

Full text of DOI:10.1007/s11243-017-0151-y

Transit Met Chem
DOI 10.1007/s11243-017-0151-y
A palladium complex immobilized onto mesoporous silica:
a highly efficient and reusable catalytic system for carbon–carbon
bond formation and anilines synthesis
Mohsen Nikoorazm1
Nourolah Noori1 Bahman Tahmasbi1 Sara Faryadi1
•
•
•
Received: 11 December 2016 / Accepted: 16 May 2017
Ó Springer International Publishing Switzerland 2017
Abstract A palladium complex supported on functional-
ized mesoporous silica MCM-41 proved to be a highly
efficient, recoverable catalyst for C–C coupling reactions
and amination of aryl halides to afford anilines. The
nanocatalyst was characterized by FT-IR spectroscopy,
X-ray diffraction, transmission electron microscopy, scan-
ning electron microscopy, thermogravimetric analysis, N2
adsorption–desorption isotherms and inductively coupled
plasma analysis. The catalyst could be reused for several
consecutive runs without significant loss of activity. The
excellent yields of products, simple reaction procedures
and short reaction times are the main advantages of this
methodology.
palladium complexes onto solid supports can facilitate
separation and hence reusability of such catalysts [6].
Various solid supports for heterogeneous catalysts have
been investigated, including zeolites, carbon nanotubes,
mesoporous silica, alumina, metal–organic frameworks
(MOFs), organic polymers and polystyrene or resins [7–12].
Among the above supports, mesoporous silica (MCM-41)
has received great attention because of its large surface areas,
˚
controllable pore sizes of 20–100 A, abundant surface silanol
groups and high hydrothermal stability, which permits ready
material diffusion, easy functionalization with organic groups
and grafting of catalytically active species [13, 14].
Anilines are an important class of organic chemicals,
being widely applied as intermediates in many different
applications, including the production of agrochemicals,
rubber processing agents, isocyanates, pigments, pharma-
ceuticals, and dyes [15–17]. Hence, the development of
highly efficient methods for the synthesis of anilines via
direct amination of aryl halides under mild reaction con-
ditions has attracted attention in both synthetic and green
chemistry [8].
Introduction
To date, the most important catalytic systems employed for
the formation of carbon–carbon bonds via Suzuki, Stille and
Heck reactions consist of homogeneous palladium catalysts
[1–3]. However, these catalysts still suffer from the draw-
backs of difficult separation and catalyst recycling from the
reaction mixture, as well as environmental pollution, which
is unacceptable for the production of fine chemicals and
pharmaceuticals [4, 5]. To overcome these problems,
heterogeneous catalysts prepared by immobilization of
In this paper, we report the synthesis of a palladium
complex supported on MCM-41, together with its charac-
terization and screening as a catalyst for some important
coupling reactions such as Suzuki, Stille and Heck. The
catalyst was also found to be a highly efficient heteroge-
neous catalyst for the synthesis of anilines.
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-017-0151-y) contains supplementary
material, which is available to authorized users.
Experimental
& Mohsen Nikoorazm
e_nikoorazm@yahoo.com
Materials and methods
1
Cetyltrimethylammonium bromide (CTAB, 98%), tetra-
ethyl orthosilicate (TEOS, 98%), NaOH, isatoic anhydride
Department of Chemistry, Faculty of Science, Ilam
University, P.O. Box 69315516, Ilam, Iran
123

Transit Met Chem
and solvents were purchased from Merck, Aldrich or Fluka
and used without further purification. The catalyst was
characterized by XRD patterns; powder X-ray diffraction
(XRD) data were obtained on a Philips diffractometer with
Cu Ka radiation at 40 kV and 30 mA. The particle size and
morphology were investigated with a JEOL JEM-2010
scanning electron microscope (SEM), on an accelerating
voltage of 20 kV. FT-IR spectra were recorded with KBr
pellets utilizing a VERTEX 70 model Bruker FT-IR
spectrometer. N2 adsorption–desorption isotherms and BJH
pore size were recorded with a (BELSORP-MINI) instru-
ment. TEM analysis was recorded using a Philips CM10
microscope with an operating voltage of 20 kV. Thermo-
gravimetric analysis (TGA) curves were recorded between
30 and 900 °C in air with a heating rate of 10 °C min-1
using a Shimadzu DTG-60 automatic thermal analyzer. Pd
content was measured by inductively coupled plasma
optical emission spectrometry (ICP-OES).
(Pd-ABA-MCM-41) was dried at room temperature
(Scheme 1).
General procedure for synthesis of biphenyl
derivatives
A mixture of NaPh4B (0.5 mmol), phenylboronic acid
(1 mmol) or triphenyltin chloride (Ph3SnCl) (0.5 mmol)
plus aryl halide (1 mmol), base (K2CO3, 3 mmol) and Pd-
ABA-MCM-41 (8 mg, 1.3 mol%) as catalyst in PEG
(poly(ethylene glycol)) solvent was stirred at 80 °C for the
required time. The progress of the reaction was monitored
by TLC. After completion of the reaction, the mixture was
cooled to room temperature, then the catalyst was sepa-
rated by filtration, and solvent was evaporated. The prod-
ucts were extracted with diethyl ether and water. The
solvent was evaporated to give the product.
General procedure for Heck coupling reaction
Preparation of SH-MCM-41
A mixture of aryl halide (1.0 mmol), n-butyl acrylate
(1.2 mmol), base (K2CO3, 3 mmol), catalyst (15 mg,
2.27 mol%) and DMF (2 mL) was stirred at 120 °C. After
completion of the reaction, the reaction mixture was cooled
to room temperature. The catalyst was separated by filtra-
tion, and the products were extracted with dichloromethane
and water. The solvent was evaporated to give the
products.
For the synthesis of pure siliceous MCM-41, NaOH solution
(3.5 mL of 2 M) was added to deionized water (480 mL) at
80 °C. CTAB (1 g) was then added as the template. The
resulting mixture was stirred at 80 °C until the solution
became uniform. TEOS (5 mL) was then slowly added, and
the resulting solution was refluxed for 2 h. The product was
filtered off, washed with deionized water and dried in an
oven at 50 °C for 24 h, followed by calcination at 550 °C
for 5 h with a heating rate of 2 °C/min. This procedure gave
mesoporous MCM-41. Subsequently, a mixture of MCM-41
(1 g) and (3-mercaptopropyl)-triethoxysilane (3-MPTES)
(1 g) in n-hexane (25 mL) was refluxed for 24 h. The pro-
duct SH-MCM-41 was filtered off, washed with n-hexane
and dried under vacuum.
General procedure for amination of aryl halides
A mixture of aryl halide (1 mmol), ammonium hydroxide
(25%) (1 mL) and Pd-ABA-MCM-41(10 mg, 1.6 mol%)
as catalyst was stirred at room temperature for the required
time (Table 10). The progress of the reaction was followed
by TLC. After completion of the reaction, the product was
extracted with ethyl acetate (3 9 10 mL). The combined
extracts were dried with Na2SO4 followed by the evapo-
ration of the solvent, yielding the corresponding product.
Preparation of ABA-MCM-41
A mixture of SH-MCM-41 (1 g) and isatoic anhydride
(2.5 mmol, 0.408 g) in ethanol (30 mL) was stirred under
reflux for 8 h. After completion of the reaction, the mixture
was cooled to room temperature and the resulting solid was
filtered off, washed with ethanol and finally dried to obtain
ABA-MCM-41 (Scheme 1).
Results and discussion
Synthesis and characterization of the catalyst
Preparation of Pd-ABA-MCM-41
First, (3-mercaptopropyl)-triethoxysilane supported on
MCM-41 (SH-MCM-41) was synthesized, and then
2-aminobenzamide immobilized on MCM-41 (ABA-
MCM-41) was prepared by the reaction of SH-MCM-41
with isatoic anhydride. Finally, the 2-aminobenzamide
complex of Pd immobilized on MCM-41 (Pd-ABA-MCM-
41) was obtained via reaction of palladium(II) acetate and
ABA-MCM-41 (Scheme 1). The catalyst has been
Pd-ABA-MCM-41 was prepared by mixing Pd(OAc)2
(0.25 mmol) and ABA-MCM-41 (0.5 g) in ethanol
(20 ml). The mixture was stirred at 80 °C for 20 h. Then,
sodium borohydride (0.6 g) was added, and the mixture
was kept under reflux for 4 h. The resulting black solid was
filtered off and washed with ethanol. Finally, the product
123

Transit Met Chem
Scheme 1 Synthesis of Pd-
ABA-MCM-41 catalyst
NaOH
80 oC
O
O
MPTES
CTAB + TEOS
MCM-41-SH
ABA-MCM-41
MCM-41
EtOH
i
H
S
S
MCM-41
n-Hexane, 80 oC
24h
O
SH-MCM-41
O
O
O
O
O
O
i
S
S
+
O
MCM-41
80 oC 8 h
,
N
H
H2N
ABA-MCM-41
O
O
Pd(OAc)2, EtOH, NaBH4
Reflux, 24h
Si
S
O
1
-4
M
C
M
Pd
O
N
H
Pd-ABA-MCM-41
characterized by transmission electron microscopy (TEM),
scanning electron microscopy (SEM), energy-dispersive
X-ray spectroscopy (EDS), X-ray diffraction (XRD), ther-
mogravimetric analysis (TGA), N2 adsorption–desorption
(BET), FT-IR and inductively coupled plasma atomic
emission spectroscopy (ICP-OES).
Figure 1 shows the low-angle powder X-ray diffraction
patterns of MCM-41 and Pd-ABA-MCM-41. The pattern
of the MCM-41 shows three reflection peaks corresponding
to d100, d110 and d200 which are typical confirming the
presence of the ordered hexagonal mesoporous structure of
MCM-41. Upon post-synthetic grafting, Pd-ABA-MCM-41
present well-defined (100) reflections in the XRD pattern;
however, there are no well-resolved peaks (110, 200);
furthermore, the intensity of the peak at d100 was decreased
with an increasing loading of palladium, indicating that the
hexagonal mesostructures are less ordered due to intro-
duction of the palladium complex into the mesoporous
channels of MCM-41.
Fig. 1 XRD patterns of Si-MCM-41 (blue line) and Pd-ABA-MCM-
41 (red line). (Color figure online)
Figure 2 shows the N2 adsorption–desorptions of
MCM-41 and Pd-ABA-MCM-41. Based on the IUPAC
classification, the samples exhibit the shape of type IV
curves, typical of mesoporous materials. The fact that the
p/p0 value of the catalyst is shifted to a lower value
compared to MCM-41 suggests that the accessible pore
size of Pd-ABA-MCM-41 decreases upon introduction of
the palladium complex. The textural properties of the
samples are summarized in Table 1; it can be seen that the
BET surface area, pore volume and diameter comparing
MCM-41/Pd-ABA-MCM-41 have lower surface areas,
which can be readily explained by filling of pores with the
immobilized palladium complex. As a consequence,
incorporation of Pd results in a slight increase in wall
thickness.
Fig. 2 N2 isotherms of a MCM-41 and b Pd-ABA-MCM-41
123

Transit Met Chem
Wall diam. (nm)
Table 1 Textural properties of
MCM-41 and Pd-ABA-MCM-
41
Sample
SBET (m2/g)
Pore diam. (nm)
Pore vol. (cm3/g)
MCM-41
1372
729
2.45
2.02
1.51
0.44
0.808
1.91
Pd-ABA-MCM-41
Fig. 3 SEM image of a MCM-41 and b Pd-ABA-MCM-41
Fig. 5 TGA curves of a MCM-41 and b Pd-ABA-MCM-41
As shown in this figure, the EDS spectrum of the catalyst
showed the presence of C, N, S, O, Si and Pd species. The
ICP-OES results showed that the amount of Pd incorporated
Fig. 4 TEM image of Pd-ABA-MCM-41 catalyst
Figure 3 shows the morphologies of MCM-41 and Pd-
ABA-MCM-41 as observed by SEM, which confirms the
presence of uniform spherical particles for both samples. The
morphology of Pd-ABA-MCM-41 (Fig. 3b) is similar to that
of MCM-41 (Fig. 3a), suggesting that there is no significant
change in the MCM-41 upon incorporation of palladium.
Figure S1 in supplementary data shows a typical EDS
spectrum taken from the Pd-ABA-MCM-41. The EDS
spectra confirm the presence of Pd in the modified MCM-41.
into the mesoporous silica was 1.6 9 10-3 mol g-1
.
To investigate the dispersion of palladium particles on
the MCM-41 support, a sample of Pd-ABA-MCM-41 was
examined using TEM (Fig. 4). The images clearly show
that the palladium particles are dispersed on the surface of
the support. The places with darker contrast could be
assigned to the presence of Pd. The small dark spots in the
image could be attributed to local concentrations of Pd,
probably located in the channels. The larger dark spots
123

Transit Met Chem
5 wt% was observed for MCM-41 (Fig. 5a), which is
attributed to adsorbed water. The TGA curve of Pd-ABA-
MCM-41 (Fig. 5b) shows three weight losses (under 100,
170–350 and 480–600), respectively. The first weight loss
(6 wt%) is assigned to adsorbed water, and second
(12 wt%) may be due to adsorbed water and solvent
molecules as well as organic material. The third weight
loss (4 wt%) is attributed to decomposition of the organi-
cally modified framework.
Figure 6 shows the FT-IR spectra of MCM-41, SH-
MCM-41, ABA-MCM-41, Pd-ABA-MCM-41 and recov-
ered Pd-ABA-MCM-41 in the range 400–4000 cm-1. The
spectrum of MCM-41 shows two peaks at 795 and
1079 cm-1 corresponding to the symmetric and asym-
metric Si–O–Si vibrations, plus a peak at 460 cm-1
attributed to Si–O–Si bending and band in the
3000–3600 cm-1 region, assigned to the silanol OH
Table 3 Comparison of Pd-ABA-MCM-41 with the corresponding
homogeneous catalyst in the coupling of iodobenzene with PhB(OH)2
under the optimized conditions
Entry Substrate
Catalyst
Time (min) Yield (%)a
Fig. 6 FT-IR spectra of a MCM-41, b SH-MCM-41, c ABA-MCM-
41, d Pd-ABA-MCM-41 and e recovered catalyst
b
1
2
3
a
Iodobenzene
–
300
60
–
Iodobenzene Pd-ABA
Iodobenzene Pd-ABA-MCM-41
95
96
65
over the channels most likely correspond to Pd nanoparti-
cle agglomerates on the external surface.
Isolated yield
b
TG analyses of MCM-41 and Pd-ABA-MCM-41 are
shown in Fig. 5. A one-step weight loss of approximately
No reaction
Table 2 Optimization of
Entry
Catalyst (mol%)
Solvent
Base
Temperature (°C)
Time (min)
Yield (%)a
different parameters for the
reaction of iodobenzene with
NaBPh4 catalyzed by Pd-ABA-
MCM-41
b
1
0
PEG
PEG
PEG
PEG
PEG
DMSO
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
80
40
rt
1440
40
–
2
0.48
0.8
1.3
1.6
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
30
85
96
99
87
80
75
60
3
40
4
40
5
40
6
40
7
40
8
1,4-Dioxan
H2O
K2CO3
K2CO3
–
40
9
40
b
10
11
12
13
14
15
16
17
18
a
PEG
1440
40
–
PEG
Na2CO3
(Et)3N
KOH
88
PEG
40
90
PEG
40
38
PEG
NaHCO3
NaHSO4
K2CO3
K2CO3
K2CO3
40
Trace
Trace
90
PEG
40
PEG
40
PEG
40
35
PEG
85
Trace
Isolated yield, reaction conditions: iodobenzene (1.0 mmol), 0.5 mmol of NaBPh4 and solvent (2 mL)
b
No reaction
123

Transit Met Chem
groups. The functionalized SH-MCM-41 showed a band at
3443 cm-1 which is characteristic of the hydrogen-bonding
silanol groups and adsorbed water, whilst a band at about
2900 cm-1 is associated with CH2 stretching vibrations.
From Fig. 6c (ABA-MCM-41), the band at 1640 cm-1
provides clear evidence of the C=O group, whilst a signal
at 1479 cm-1 (C=C bond) and also bands centered at 1480
and 1300 cm-1 can be assigned to (N–H) and (C–N)
stretching vibrations, respectively; these results suggest
that the isatoic anhydride ligand was chemically absorbed
onto the surface of MCM-41. Curve (d) shows the result of
complexion of Pd with ABA-MCM-41. Curve (e), for a
sample of recovered catalyst, indicates that the structure of
the catalyst remains intact during the catalytic reaction.
Table 4 Suzuki–Miyaura coupling reactions of aryl halides with NaBPh4 catalyzed by Pd-ABA-MCM-41
Cat(1.3 mol%)
X
NaBPh4
+
R
R
PEG,K2CO3
60 oC
1a–1o
Aryl halide
2a–2o
Entry
1
Product
2a
Time (h)
Yield (%)a
Mp (°C)
TON
73.84
TOF (h-1
)
0.66
1
96
94
97
94
95
97
96
94b
67–68 [19]
111.87
I
I
I
2
3
4
5
6
7
8
2b
2c
2d
2e
2f
80–82 [20]
42–44 [22]
111–113 [19]
53–54 [22]
85–86 [19]
69 [19]
72.30
74.61
72.30
73.07
74.61
73.84
72.30
72.30
226.09
45.18
36.15
149.22
49.22
10.32
OCH3
CH3
0.33
1.6
2
r
B
I
N
O2
NH2
CN
0.5
1.5
7
Br
2g
2h
Br
Br
Oil [19]
9
2i
3
93
92
94
96
96
97
96
52–54 [22]
93–94 [21]
56–58 [19]
162–164 [19]
42–44 [22]
71–73 [22]
228–230 [22]
71.53
70.76
72.30
73.84
73.84
74.61
73.84
23.84
16.64
241
Br
Br
Br
Br
Br
Br
Br
NH2
10
11
12
13
14
15
2j
4.25
0.3
0.5
0.3
1
CH2OH
CHO
OH
2k
2l
147.68
246.13
74.61
49.22
2m
2n
2o
CH3
Cl
1.5
COOH
Reaction conditions: 1 mmol of aryl halide, 0.5 mmol of sodium tetraphenylborate, 1.5 mmol of K2CO3 and 1.3 mol% of catalyst in 2 mL of
PEG solvent at 60 °C
a
Isolated yield
b
Was used amount of catalyst (1.95 mol%)
123

Transit Met Chem
Catalysis of Suzuki and Stille reactions
concentrations on the reaction was examined (Table 2,
entries 2–5). An important observation is that the reaction
did not proceed in the absence of the catalyst, even after a
long time (Table 2, entry 1). As shown in Table 2, per-
forming the reaction in the presence of Pd-ABA-MCM-41
(1.3 mol%) leads to a yield of 96% (Table 2, entry 4).
Upon increasing the amount of the nanocatalyst, no
Initially, the Suzuki and Stille coupling reactions were
selected to evaluate the catalytic performance of the Pd-
ABA-MCM-41. Iodobenzene with sodium tetraphenylb-
orate was chosen as blank substrate for the model reac-
tion. First, the influence of various palladium
Table 5 Suzuki–Miyaura coupling reactions of aryl halides with phenylboronic acid catalyzed by Pd-ABA-MCM-41
Cat(1.3mol%)
X
+
B(OH)2
R
R
PEG,K2CO3
60 oC
2a–2o
1a–1o
Entry
Aryl halide
Product
Time (h)
1.10
Yield (%)a
96
Mp (°C)
TON
73.84
TOF (h-1
)
1
2a
2b
2c
2d
2e
2f
67–68 [19]
80–82 [20]
42–44 [22]
111–113 [19]
53–54 [22]
85–86 [19]
69 [19]
67.12
I
2
3
4
5
6
7
8
1.5
0.66
1.25
2
97
95
74.61
73.07
72.30
73.84
74.61
73.07
74.61
49.74
110.71
57.84
36.92
74.61
48.71
9.94
OCH3
CH3
NO2
NH2
CN
I
I
94
Br
I
96
1
97
Br
2g
2h
1.5
7.5
95
Br
Br
97b
Oil [19]
9
2i
4
93
95
94
96
95
98
95
52–54 [22]
93–94 [21]
56–58 [19]
162–164 [19]
42–44 [22]
71–73 [22]
228–230 [22]
71.53
73.07
72.30
73.84
73.07
75.38
73.07
17.88
16.23
72.30
98.45
48.71
68.52
36.53
Br
Br
Br
Br
Br
Br
Br
NH2
10
11
12
13
14
15
2j
4.5
1
CH2OH
2k
2l
CHO
OH
0.75
1.5
1.1
2
2m
2n
2o
CH3
Cl
COOH
Reaction conditions: 1 mmol of aryl halide, 1 mmol of phenylboronic acid, 1.5 mmol of K2CO3 and 1.3 mol% of catalyst in 2 mL of PEG
solvent at 60 °C
a
Isolated yield
b
Was used amount of catalyst (1.95 mol%)
123

Transit Met Chem
significant improvement in yield was observed (Table 1,
entry 5).
reaction (Table 2, entry 4). Moreover, PEG has the addi-
tional advantage that it is miscible with water, facilitating
product extraction and purification.
In the next step, the effect of different solvents on the
coupling reaction was investigated (Table 2, entries 4,
6–9). The reaction rate was greatly affected by the choice
of solvent; it was found that PEG is the best solvent for this
Next, we examined the effect of different bases on the
coupling reaction in PEG solvent. As shown in Table 2,
K2CO3 proved to be an effective base for the reaction, with
Table 6 Stille coupling reactions of aryl halides with triphenyltin chloride catalyzed by Pd-ABA-MCM-41
Entry
1
Aryl halide
Product
2a
Time (h)
1
Yield (%)a
96
Mp (°C)
TON
73.84
TOF (h-1
)
67–68 [19]
73.84
I
2
3
4
5
6
7
8
2b
2c
2d
2e
2f
1.25
0.33
1
94
95
80–82 [20]
42–44 [22]
111–113 [19]
53–54 [22]
85–86 [19]
69 [19]
72.30
73.07
75.38
74.61
73.84
73.07
73.07
57.84
221.42
75.38
37.30
67.12
52.19
9.13
I
OCH3
CH3
NO2
NH2
CN
I
98
Br
I
2
97
1.1
1.4
8
96
Br
2g
2h
95
Br
Br
95b
Oil [19]
9
2i
3.25
4
94
96
95
98
97
95
96
52–54 [22]
93–94 [21]
56–58 [19]
162–164 [19]
42–44 [22]
71–73 [22]
228–230 [22]
72.30
73.84
73.07
75.38
74.61
73.07
73.84
22.24
18.46
Br
Br
Br
Br
Br
Br
Br
NH2
10
11
12
13
14
15
2j
CH2OH
2k
2l
0.4
0.66
0.5
1
182.67
114.21
149.22
73.07
CHO
OH
2m
2n
2o
CH3
Cl
1.5
49.22
COOH
Reaction conditions: 1 mmol of aryl halide, 0.5 mmol of triphenyltin chloride, 1.5 mmol of K2CO3 and 1.3 mol% of catalyst in 2 mL of PEG
solvent at 60 °C
a
Isolated yield
b
Was used amount of catalyst (1.95 mol%)
123

Transit Met Chem
Catalysis of Mizoroki–Heck coupling reactions
high yields of product. A control experiment, conducted in
the absence of base, did not give any significant amount of
the product (Table 2, entry 10).
The Mizoroki–Heck coupling of iodobenzene with n-butyl
acrylate in the presence of Pd-ABA-MCM-41 was chosen
as a model reaction to optimize the amount of nanocatalyst,
solvent, base and temperature. The results of these exper-
iments are presented in Table 7. Initially, K2CO3 was used
as base and DMF as solvent in the presence of
0.8–2.27 mol% of Pd-ABA-MCM-41 at 100 °C (Table 7,
entries 2–5). The best results were achieved using
2.27 mol% of the catalyst (Table 7, entry 5).
The effect of temperature on the coupling reaction
was tested in the range of room temperature to 80 °C,
and it was found that the temperature has a great effect
on the product yield. Table 2 shows that the reaction is
very slow below 60 °C (Table 2, entries 17 and 18),
whereas the conversion increased with temperatures
higher than 40 °C. The optimum temperature is 60 °C
(Table 1, entry 4).
The optimization was further explored with various
solvents in place of DMF (Table 7, entries 6–8). Changing
the solvent did not provide any improvements in the
reaction yield and indicated that aprotic solvents (DMF and
DMSO) are more effective than protic solvents (PEG and
water).
In order to compare the efficiency of Pd-ABA-MCM-
41 with that of the corresponding homogeneous catalyst,
the free catalyst (designated Pd-ABA) has been synthe-
sized and its catalytic activity compared with that of Pd-
ABA-MCM-41 in the coupling of iodobenzene with
PhB(OH)2. The results are shown in Table 3; the catalytic
activity of heterogeneous catalyst is comparable to that of
Pd-ABA; hence, the heterogeneous catalyst showed the
advantages of both homogeneous (high catalytic activity)
and heterogeneous (stability, easy and rapid recovery and
recycling) catalysts. The reaction did not proceed in the
absence of catalyst, even after a long reaction time
(Table 3, entry 1).
Next, we focused on the effect of alternative bases on
the coupling reaction (Table 7, entries 9–11). The results
showed that K2O3 was still the most effective choice,
giving excellent product yields and short reaction time
(Table 7, entry 5). Finally, the effects of various temper-
atures were investigated, ranging from 60 to 100 °C
(Table 7, entries 5, 12 and 13). These experiments revealed
that the reaction proceeds efficiently at 100 °C (Table 7,
entry 5).
To explore the general application of the catalyst, the
optimized conditions were employed in Suzuki and Stille
reactions of sodium tetraphenylborate, phenylboronic acid
or triphenyltin chloride with various aryl halides (Tables 4,
5, 6). The reactions proceeded well with a wide range of
aryl iodides and bromides, with and without electron-
withdrawing or electron-donating groups. In most cases,
the reaction is completed in 0.5–11 h with good to excel-
lent yields.
Using the optimized reaction conditions, we tested the
catalytic activity of Pd-ABA-MCM-41 for a range of
substrates, with the results as shown in Table 8. Various
aryl halides containing either electron-withdrawing or
electron-donating groups were examined. Generally, elec-
tron-withdrawing groups gave good yields of the corre-
sponding products (Table 8, entries 8, 9, 11 and 12),
Table 7 Optimization of
Entry
Catalyst (mol%)
Solvent
Base
Temperature (°C)
Yield (%)a
reaction conditions for the
Mizoroki–Heck coupling of
iodobenzene with butyl acrylate
for 50 min
b
1
–
DMF
DMF
DMF
DMF
DMF
PEG
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Et3N
100
100
100
100
100
100
100
100
100
100
100
80
–
2
0.8
40
3
1.3
72
4
1.6
84
5
2.27
2.27
2.27
2.27
2.27
2.27
2.27
2.27
2.27
97
6
55
7
DMSO
H2O
90
8
Trace
60
9
DMF
DMF
DMF
DMF
DMF
10
11
12
13
a
75
KOH
30
K2CO3
K2CO3
40
60
25
Isolated yield
b
No reaction after 24 h
123

Transit Met Chem
Table 8 Heck reaction of various aryl halides and n-butyl acrylate catalyzed by Pd-ABA-MCM-41 catalyst
Bu
CO2
X
Cat(2.27 mol%)
Bu
CO2
+
K CO , DMF,100º
C
2
3
R
R
Entry
Aryl halide
Product
4a
Time (h)
1
Yield (%)
98
Mp (°C)
TON
43.17
TOF (h-1
)
1
2
3
4
Oil [25]
Oil [23]
Oil [25]
Oil [26]
43.17
I
4b
4c
4d
2
97
94
95
42.73
41.40
41.85
21.36
23.65
9.3
H
3C
I
1.75
4.5
H
3CO
I
CH3
I
5
4e
4.75
97
Oil [27]
42.73
8.99
I
OCH3
6
7
4f
1.5
0.5
95
96
Oil [23]
Oil [23]
41.85
42.29
27.9
Br
Br
4g
84.58
N
8
4h
4i
4j
2.25
1
98
98
97
Oil [23]
43.17
43.17
42.73
19.18
43.17
20.34
Br
Br
Cl
9
39–42 [23]
Oil [26]
NC
10
2.10
Cl
11
12
4k
4l
1
5
96
93
58–63 [24]
39–42 [23]
42.29
40.96
42.29
8.19
N
O2
Br
NC
Cl
Reaction conditions: aryl halid (1 mmol), n-butyl acrylate (1.2 mmol), K2CO3 (3 mmol), Pd-ABA-MCM-41 (2.27 mol%) and DMF (2 mL),
100 °C
compared to electron-donating groups (Table 8, entries 2
and 3). Also, aryl halides with ortho-substituents proved to
be poor substrates, which can be attributed to steric hin-
drance (Table 8, entries 4 and 5).
optimization of catalyst concentration, solvent and base
(Table 9).
Initially, the effect of catalyst loading was studied,
employing quantities of the catalyst ranging from 0.8 to
1.9 mol% (Table 9, entries 2–5). As evident from Table 9,
the best result was obtained with 1.6 mol% of the catalyst
(Table 9, entry 4). The reaction did not proceed at all in the
absence of the catalyst (Table 9, entry 1).
Catalysis of aryl halide amination
Finally, the activity of the catalyst was examined in the
amination of aryl halides. For the synthesis of aniline
derivatives, the reaction between iodobenzene and aqueous
ammonia was chosen as a model reaction for the
Next, the effects of base were investigated. The use of
K2CO3, Et3N, Na2CO3, KOH and no added base was
examined (Table 9, entries 4, 6–9). Et3N proved to be the
123

Transit Met Chem
Table 9 Optimization of
conditions for the amination of
aryl halides
Entry
Solvent
Base
Catalyst (mol%)
Time (h)
Yield (%)a
1
–
–
–
24
17
10
7
–
2
–
–
0.8
1.3
1.6
1.9
1.6
1.6
1.6
1.6
1.6
1.6
1.6
1.6
1.6
60
65
74
78
98
80
85
72
57
68
75
65
50
3
–
–
4
–
–
5
–
–
6
6
–
Et3N
Na2CO3
K2CO3
KOH
Et3N
Et3N
Et3N
Et3N
Et3N
2.5
5
7
–
8
–
7
9
–
18
10
24
14
24
48
10
11
12
13
14
PEG
DMF
Ethanol
DMSO
1,4-Dioxan
Reaction conditions: iodobenzene (1 mmol), aqueous ammonia (1 mL) at room temperature
a
Isolated yield
Table 10 Coupling of ammonia with various aryl halides in the presence of Pd-ABA-MCM-41
X
NH2
Cat(1.6 mol%)
Et3N, r.t
+
NH3
Entry
1
Aryl halide
Product
Time (h)
2.5
Yield (%)a
Mp (°C)
TON
61.25
TOF (h-1
)
98
97
Oil [18]
24.5
I
NH2
NH2
2
3.25
Oil [18]
60.62
18.65
Br
3
4
5
6
5
3.5
4
95
96
94
97
68–70 [28]
43–44 [18]
57–58 [28]
47–49 [18]
59.37
60
11.87
17.14
14.68
6.06
Br
I
Cl
NH2
NH2
NH2
Cl
H
H
3C
H
3C
58.75
60.62
I
3CO
H
3CO
Br
10
NH2
7
8
2.5
98
97
146–148 [28]
56–58 [27]
61.25
60.62
24.5
Br
N
O2
N
NH2
O2
4.25
14.26
Br
NH2
N
N
9
8
2
95
96
186–190 [27]
87–88 [28]
59.37
60
7.42
30
HO
NC
Br
Br
HO
NC
NH2
NH2
10
Reaction conditions: aryl halide (1 mmol), aqueous ammonia (1 mL), Et3N (3 mmol) and catalyst (1.6 mol%) at room temperature
a
Isolated yield
123

Transit Met Chem
Table 11 Recyclability of Pd-
ABA-MCM-41 in the Suzuki–
Miyaura, Mizoroki–Heck
reactions and synthesis of
aniline
Entry Reaction type
Substrate
Run 1a Run 2a Run 3a Run 4a Run 5a Run 6a
1
2
3
a
Suzuki reaction
Heck reaction
Iodobenzene 96
Iodobenzene 97
95
95
96
94
95
93
92
94
93
90
93
92
90
91
90
Synthesis of aniline Iodobenzene 98
Isolated yield (%)
most effective base (Table 9, entry 6), giving higher yields
and shorter reaction times than other bases (Table 9, entry
3). A low yield was obtained without any added base
(Table 9, entry 4).
test for the coupling of iodobenzene with phenylboronic
acid. In this experiment, the yield of product obtained after
half of the standard reaction time was 55%. The reaction
was then repeated, and after half of the standard reaction
time, the catalyst was filtered out and the filtrate was
allowed to react further. However, after this hot filtration,
no further reaction was observed. The yield of reaction in
this stage was 58%, confirming that leaching of palladium
had not occurred. This result indicates that the catalytic
reaction is truly heterogeneous in nature.
Subsequently, a series of solvents as well as the absence
of added solvent were investigated in the presence of
1.6 mol% of the catalyst and 1 mL of aqueous ammonia
(Table 9, entries 6, 10–14). The best result was obtained in
the absence of added solvent (Table 9, entry 6).
Hence, according to the above results, we chose Et3N as the
base and 1.6 mol% of palladium catalyst at room temperature
as the best conditions for the amination of aryl halides.
With these mentioned reaction conditions in hand, we
explored the scope of the reaction with a range of substituted
aryl halides with both electron-donating and electron-with-
drawing groups. The corresponding products were obtained
in excellent yields (Table 10). This experimental procedure
is very convenient and simple and has the ability to tolerate
several other functional groups such as CH3, OH, NO2, CN
and OCH3 under the optimized conditions. The bulky
1-bromonaphthalene and sterically hindered ortho-halides
were efficiently coupled with ammonia, giving good yields
of the desired products (Table 10, entries 6 and 8).
Conclusions
In summary, we have successfully applied a heterogeneous
palladium catalyst for the Suzuki–Miyaura and Mizoroki–
Heck reactions and also the synthesis of anilines. The catalyst
is effective for a wide range of aryl halides including chlo-
rides, bromides and iodides and also shows high activity,
affording a diverse range of products in excellent yields.
Furthermore, the simple procedure reported here offers sev-
eral significant advantages, such as good reaction times, high
yields, easy handling, operational simplicity and easy workup.
Other notable features are low loading of Pd and recyclability.
Reusability of the catalyst
Acknowledgements Authors thank the research facilities of Ilam
University, Ilam, Iran, for financial support of this research project.
Reusability is an important feature that determines the
applicability of heterogeneous catalysts. To investigate the
recycling efficiency of the present catalyst, iodobenzene
was chosen for the Suzuki–Miyaura and Mizoroki–Heck
cross-coupling reactions and also synthesis of aniline under
the optimized conditions for each reaction. After comple-
tion of each reaction, the product was extracted from the
reaction mixture using diethyl ether, dichloromethane and
ethyl acetate for the Suzuki–Miyaura, Mizoroki–Heck and
aniline reactions, respectively. The catalyst was separated
by centrifugation, washed with ethanol and reused in sub-
sequent runs. These experiments showed that the catalyst
can be recovered and reused for at least six times with only
slight decreases in its activity (Table 11).
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