Palladium 2-mercapto-N-propylacetamide complex anchored onto MCM-41 as efficient and reusable nanocatalyst for Suzuki, Stille and Heck reactions and amination of aryl halides

Article abstract of DOI:10.1002/aoc.3512

A palladium 2-mercapto-N-propylacetamide complex supported on functionalized MCM-41 was prepared by a post-grafting method and considered as an efficient catalyst for C?C cross-coupling reactions between various aryl halides and sodium tetraphenylborate, phenylboronic acid, triphenyltin chloride or alkenes. Also, this catalyst shows good reactivity towards amination of aryl halides. This nanocatalyst was characterized using thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, inductively coupled plasma and transmission electron microscopy techniques. Further results indicated that the heterogeneous catalyst could be recovered easily and reused several times without any loss of its catalytic activity. Copyright

Full text of DOI:10.1002/aoc.3512

Full paper
Received: 4 March 2016
Revised: 15 April 2016
Accepted: 18 April 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3512
Palladium 2-mercapto-N-propylacetamide
complex anchored onto MCM-41 as efficient
and reusable nanocatalyst for Suzuki, Stille and
Heck reactions and amination of aryl halides
Mohsen Nikoorazm*, Arash Ghorbani-Choghamarani, Nourolah Noori
and Bahman Tahmasbi
A palladium 2-mercapto-N-propylacetamide complex supported on functionalized MCM-41 was prepared by a post-grafting
method and considered as an efficient catalyst for C–C cross-coupling reactions between various aryl halides and sodium
tetraphenylborate, phenylboronic acid, triphenyltin chloride or alkenes. Also, this catalyst shows good reactivity towards
amination of aryl halides. This nanocatalyst was characterized using thermogravimetric analysis, X-ray diffraction, scanning
electron microscopy, Fourier transform infrared spectroscopy, inductively coupled plasma and transmission electron microscopy
techniques. Further results indicated that the heterogeneous catalyst could be recovered easily and reused several times without
any loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: MCM-41; palladium; heterogeneous; C–C coupling reaction; amination
mesoporous MCM-41 as a good support is that it possesses ther-
Introduction
mal, mechanical and chemical stability. It also has an extremely
high surface area (1000 m2 gÀ1), and large channels from 1.5 to
Homogeneous palladium catalysis has gained enormous relevance
in various coupling reactions such as Heck, Stille, Sonogashira,
Suzuki and Buchwald–Hartwig reactions.[1,2] Many products can
be synthesized using this methodology for the first time or in a
much more efficient way than before. This type of homogeneous
catalysis provides high reaction rate and often affords high yields
and selectivity.[3]
10 nm, ordered in a hexagonal array, and large pore volume, which
allows for the easy diffusion of substrates to active sites.[28]
In the current paper, we report the synthesis of functionalized
mesoporous MCM-41 by the immobilization of a Pd complex onto
mesoporous MCM-41 silica, and successfully demonstrate its
application as a heterogeneous catalyst for C–C coupling reactions
and synthesis of anilines. Also, this catalytic system offers simplicity
of operation, heterogeneous nature, excellent yields, short reaction
times and simple work-up in cross-coupling reactions for the forma-
tion of carbon–carbon bonds and amination with aryl halides.
Anilines are important organic compounds, and commonly used
for various applications, such as in the agrochemical, pharmaceuti-
cal, cosmetic, resin, dye and toiletry industries.[4–6] Traditionally,
these compounds have been prepared by C–N bond formation,
although ammonia is an attractive and low-cost nitrogen source
for the industrial production of anilines.[7,8] The palladium-catalysed
amination of aryl halides is a powerful and valuable tool for the
construction of arylamines.[9–12] However, homogeneous catalysis
has a number of drawbacks, in particular the lack of separation
and reusability, which is a significant environmental and economic
concern in large-scale synthesis.[13] These problems have to be
overcome in the application of homogeneous Pd-catalysed cou-
pling reactions in industry, which is still a challenge. The immobili-
zation of homogeneous catalysts on various insoluble supports
(especially porous materials with high surface areas) can lead to
the simplification of catalyst recycling via filtration.[14–16] In general,
various supports have been employed to fabricate heterogeneous
Pd catalysts, such as carbon,[17] metal oxides,[18,19] ionic liquids,[20]
molecular sieves (SBA-15 and MCM-41)[21–26] and polymers.[27] In
this study, mesoporous MCM-41 has been considered as a very
good support for a Pd complex. The reason for the use of
Experimental
Materials and Instrumentation
Analytical-grade cetyltrimethylammonium bromide (CTAB),
tetraethylorthosilicate (TEOS; 98%), sodium hydroxide (NaOH), aryl
halides, sodium tetraphenylborate, phenylboronic acid, triphenyltin
chloride and other materials were purchased from Aldrich, Merck or
Fluka and used without further purification. The progress of all the
reactions was monitored by TLC. Powder X-ray diffraction (XRD)
*
Correspondence to: M. Nikoorazm, Department of Chemistry, Ilam University, PO
Box 69315516, Ilam, Iran. E-mail: e_nikoorazm@yahoo.com
Department of Chemistry, Faculty of Science, Ilam University, PO Box 69315516,
Ilam, Iran
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

Nikoorazm M., Ghorbani-Choghamarani A., Noori N. and Tahmasbi B.
patterns of samples were recorded using a Philips X’pert diffractom-
eter with monochromatized Cu Kα radiation under the conditions
of 40 kV and 30 mA. Fourier transform infrared (FT-IR) spectra were
recorded using KBr pellets with a VRTEX 70 FT-IR spectrometer
(Bruker). Thermogravimetric analysis (TGA) of samples was con-
ducted using a Shimadzu DTG-60 automatic thermal analyser in
the temperature range 30–900 °C at a heating rate of 10 °C minÀ1
in air. Scanning electron microscopy (SEM) images were obtained
with a VEGA TESCAN. The content of Pd was determined using in-
ductively coupled plasma optical emission spectrometry (ICP-OES;
PerkinElmer optima 8000). Transmission electron microscopy
(TEM) images were obtained with a Philips CM10 microscope, work-
ing at 200 kV accelerating voltage.
drops hydrochloric acid, was added dropwise and the reaction
was heated at 110 °C under reflux conditions for 48 h. Then, the fi-
nal product was filtered and washed several times with dry ethanol
and dried at room temperature.
Preparation of Heterogeneous Catalyst
The functionalized material (1 g) described above was mixed with
Pd(OAc)2 (0.5 g) in ethanol (20 ml) under reflux for 16 h. Subse-
quently, sodium borohydride (0.6 g) was added to this mixture
and kept under reflux for 4 h (Scheme 1). Finally, the resulting black
precipitate was filtered off and washed several times with ethanol
to remove any unanchored metal ion and dried at room tempera-
ture to afford Pd-MPA@MCM-41.
General Procedure for Synthesis of MCM-41
Nanosized MCM-41 was prepared using the sol–gel method with
CTAB as the template, TEOS as the silicon source and sodium
hydroxide as pH control agent. In a typical procedure, CTAB
(2.74 mmol, 1 g) was added to a solution of deionized water
(480 ml) and NaOH (2 M, 3.5 ml) at 80 °C. When the solution became
homogeneous (after complete dissolution), TEOS (5 ml) was added
dropwise to the solution under continuous stirring at 80 °C, and the
obtained gel was aged under reflux for 2 h. The mixture was
allowed to cool to room temperature and the resulting product
was filtered and washed with distilled water. It was then subjected
to Soxhlet extraction with ethanol for 24 h and dried in an oven at
60 °C. The obtained material was calcined at 550 °C in air for 5 h and
is designated as MCM-41.
Typical Procedure for Synthesis of Baryls
In a 5 ml round-bottom flask, a reaction mixture of aryl halide
(1.0 mmol), NaBPh4 (0.5 mmol) or Ph3SnCl (0.5 mmol) or PhB(OH)2
(1 mmol), K2CO3 (1.5 mmol), Pd-MPA@MCM-41 (10 mg, 1.7 mol%)
and poly(ethylene glycol) (PEG; 2 ml) were stirred magnetically at
100 °C for the appropriate time (Table 1). The reaction progress
was monitored by TLC. After completion of the reaction, the mix-
ture was cooled to room temperature. Then, the catalyst was easily
recovered by filtration and the filtrate was poured into water (10 ml)
and extracted with diethyl ether (3 × 10 ml). The combined organic
layers were dried over Na2SO4 (1.5 g), followed by the evaporation
of the solvent, yielding the pure product.
Preparation of MCM-41 Coated by (3-Aminopropyl)
triethoxysilane (APTES)
Table 1. Optimization of various parameters for the reaction of
iodobenzene with NaBPh4 or PhB(OH)2 or Ph3SnCl catalysed by
Pd-MPA@MCM41a
An amount of 1.0 g of the obtained MCM-41 was refluxed with
APTES (1 g) in n-hexane (100 ml) under nitrogen atmosphere for
24 h. After the completion of the reaction, APTES-functionalized
MCM-41 (APTES@MCM-41) was filtered as a white solid, washed
with n-hexane and dried under vacuum (Scheme 1).
Entry Catalyst Solvent
(mol%)
Base
Temperature Time
Yield
(%)b
(°C)
(min)
1
2
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
PEG
PEG
PEG
PEG
PEG
PEG
PEG
DMSO
DMF
1,4-
—
100
100
100
100
100
100
100
100
100
100
1440
85
85
85
85
85
85
85
85
85
0
95
K2CO3
Na2CO3
(Et)3N
Preparation of APTES@MCM-41 Coated by 2-Mercaptoacetic
acid
3
90
4
80
5
KOH
35
MCM-41@APTES (1 g) was first suspended in dry toluene (30 ml).
Subsequently, 4 mmol of 2-mercaptoacetic acid, containing a few
6
NaHCO3
NaHSO4
K2CO3
K2CO3
K2CO3
Trace
Trace
86
7
8
9
81
10
73
Dioxane
11
12
13
14
15
16
17
18
19
1.7
1.7
1.7
1.7
1.7
0
H2O
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
100
80
85
85
58
58
60
85
Trace
0
40
85
r.t.
85
0
100
100
100
100
1440
85
0
2
96
1.3
0.8
85
83
85
Trace
aReaction conditions: iodobenzene (1.0 mmol), base (1.5 mmol),
0.5 mmol of NaBPh4 or 1 mmol of PhB(OH)2 or 0.5 mmol of Ph3SnCl
and solvent (2 ml).
bIsolated yield.
Scheme 1. Synthesis of Pd-MPA@MCM-41 catalyst.
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Appl. Organometal. Chem. (2016)

Synthesis of Pd-MPA@MCM-41 for C–C and C–N bond formation
Typical Procedure for Heck Reaction Catalysed by Pd-MPA
@MCM-41
three-peak pattern with a very strong reflection at 2θ = 2.21° due
to the d100 plane and also two other weaker reflections at
2θ = 3.63° and 4.23°, due to higher order d110 and d200 planes, re-
spectively, indicating the formation of a well-ordered mesoporous
material with hexagonal symmetry. The XRD pattern of Pd-MPA@-
MCM-41 exhibits three reflections in the region of 2θ = 2–4.60°.
Also, this sample shows the same pattern indicating that the struc-
ture of the MCM-41 is well retained. The comparison study of XRD
patterns of MCM-41 and Pd-MPA@MCM-41 shows that after
grafting of Pd through complex formation into MCM-41, the d110
and d200 reflections with weaker intensities are observed. In order
to observe the peaks associated with the palladium nanoparticles,
the wide-angle XRD pattern of Pd-MPA@MCM-41 was recorded.
Figure 1 shows three peaks at 40.12°, 46.16° and 68.14° correspond-
ing to (111), (200) and (220) lattice planes of the palladium
nanoparticles.[29]
For the Heck coupling reaction, a reaction tube equipped with a
magnetic stirring bar was charged with aryl halide (1 mmol), butyl
acrylate (1.2 mmol), K2CO3 (3 mmol), Pd-MPA@MCM-41
(2.5 mol%) and 2 ml of dimethylformamide (DMF), and the ob-
tained mixture was heated at 120 °C for the appropriate time. The
progress of reaction was monitored by TLC. After the reaction was
completed, the reaction mixture was allowed to cool to room tem-
perature. The catalyst was then removed by filtration, washed with
acetonitrile (2 × 10 ml) and dried at 50 °C for reuse. The residual
mixture was extracted with CH2Cl2 and the obtained organic layer
was dried over Na2SO4.
General Procedure for Synthesis of Anilines
In a typical procedure, to a mixture of aryl halide (1 mmol) and am-
monium hydroxide (28%, 1 ml, 0.003 mol), 1.7 mol% of Pd-MPA@-
MCM-41 was added and the reaction mixture was stirred at room
temperature for an appropriate time. The progress of the reaction
was followed by TLC. After the reaction was completed, the product
was extracted with ethyl acetate (3 × 10 ml). The obtained extracts
were dried with Na2SO4 followed by evaporation of the solvent
which afforded the corresponding aniline with excellent yield.
FT-IR Spectroscopy
Figure 2 shows the FT-IR spectra of MCM-41, MCM-41-nPr-NH2,
MCM-41-MPA, Pd-MPA@MCM-41 and recovered Pd-MPA@MCM41
in the range 400–4000 cmÀ1. Figure 2(a) is the spectrum of MCM-
41, which shows a band at 463 cmÀ1 which is attributed to the
Si–O bending vibration. The band at 1100–1200 cmÀ1 is due to
Si–O–Si asymmetric stretching and the band at 3000–3600 cmÀ1
can be attributed to the silanol OH groups. MCM-41-nPr-NH2 spec-
trum (Fig. 2(b)) is confirmed by C–H stretching vibration at
2959 cmÀ1, and two bands belonging to N–H group appear at
1650 and 1468 cmÀ1. In Fig. 2(c) (MCM-41-MPA spectrum) it is clear
that the band at 1640 cmÀ1 evidences the presence of the C–O
bond, which is assigned to the stretching vibration of C–O in amide,
Results and Discussion
We prepared and characterized Pd-MPA@MCM-41 as a highly effi-
cient and reusable heterogeneous catalyst for Suzuki, Stille and
Heck reactions and amination of aryl halides.
X-ray Diffraction
Figure 1 shows low-angle XRD patterns of calcined MCM-41 and
Pd-MPA@MCM-41. The XRD pattern of MCM-41 shows a typical
Figure 1. Low-angle powder XRD patterns of calcined MCM-41 and Pd-
MPA@MCM-41 (top). Wide-angle powder XRD pattern of Pd-MPA@MCM-
41 (bottom).
Figure 2. FT-IR spectra: (a) MCM-41; (b) MCM-41-nPr-NH2; (c) MCM-41-
MPA; (d) Pd-MPA@MCM-41; (e) recovered Pd-MPA@MCM-41.
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
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Nikoorazm M., Ghorbani-Choghamarani A., Noori N. and Tahmasbi B.
and the band centred at 3440 cmÀ1 is assignable to (N–H)
stretching vibration band. Figure 2(d) shows the complexion of
Pd ions with MCM-41-MPA. The spectrum of recycled Pd-MPA@-
MCM-41 (Fig. 2(e)) indicates that the catalyst is stable during the
C–C coupling reaction.
SEM/EDS Analysis
As depicted in Fig. 3, the SEM images of MCM-41 and Pd-MPA@-
MCM-41 samples (Figs 3(a) and (b), respectively) reveal that these
materials have been formed with a spherical structure. The SEM
image of Pd-MPA@MCM-41 (Fig. 3(b)) confirms that the catalyst is
made up of uniform nanometre-sized particles, and also no signifi-
cant changes in the surface morphology occur upon the insertion
of the Pd complex onto MCM-41 The EDS analysis of Pd-MPA@-
MCM-41 (Fig. 3(c)) indicates that Pd particles are well dispersed
onto the MCM-41 surface, which agrees well with the XRD pattern.
Also, in order to estimate the exact amount of Pd loaded on the
mesoporous catalyst, ICP-OES analysis was performed, from which
the amount is found to be 1.69 × 10À3 mol gÀ1
.
TEM Analysis
Figure 4 shows TEM images of MCM-41 and Pd-MPA@MCM-41. As
shown in Fig. 4(a), the TEM image of MCM-41 indicates well-
ordered hexagonal arrays of mesoporous arrangement and long-
range mesoporous architecture (100 nm). Also, the catalyst sample
exhibits a similar type of array of regular hexagonal arrangement, as
Figure 4. TEM images of (a) parent MCM-41 and (b) synthesized Pd-
MPA@MCM-41 catalyst.
shown in Fig. 4(b). Therefore, it can be concluded that both of the
samples have a similar type of morphology.
Thermogravimetric Analysis
TGA curves of MCM-41 and PdMPA@MCM-41 are presented in
Fig. 5. The TGA curve of calcined MCM-41 shows a weight loss of
about 6% between room temperature and 100 °C attributed to
the loss of physically adsorbed water. The TGA curve of Pd-MPA@-
MCM-41 catalyst shows a three-step weight loss. The first step of
weight loss (about 3%) appearing at 25–100 °C seems to be due
to the removal of adsorbed water; the second weight loss appears
in the range 250–350 °C (10%) mainly related to the decomposition
Figure 3. SEM images of (a) MCM-41 and (b) Pd-MPA@MCM-41. (c) EDS
pattern of Pd-MPA@MCM-41.
Figure 5. TGA curves of (a) MCM-41 and (b) Pd-MPA@MCM-41.
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Synthesis of Pd-MPA@MCM-41 for C–C and C–N bond formation
of the organically modified moieties on MCM-41; and the third
weight loss (about 5%) appears at above 600 °C as a result of the
condensation of the silanol groups.
The effect of temperature on the activity of Pd-MPA@MCM-41 was
investigated in the range 25–100 °C and it is found that the reaction
temperature has a great effect on the outcome of the reaction.
Table 1 shows that the reaction is very slow or even that there is
no reaction below 60 °C (Table 1, entries 13–15), while the product
conversion increases on increasing temperature above 60 °C. The
reaction can proceed completely at 100 °C (Table 1, entry 2).
Catalytic Results
After confirming the exact characteristics of Pd-MPA@MCM-41,
the catalytic activity of this mesoporous compound was explored
in C–C cross-coupling reactions of various aryl halides with different
phenylating agents. Initially, in order to optimize the reaction con-
ditions, iodobenzene as an example of a non-activated aryl iodide
was selected as a model substrate for the coupling reaction with
sodium tetraphenylborate or phenylboronic acid or triphenyltin
chloride as coupling partner in the presence of a catalytic amount
of Pd-MPA@MCM-41 and various types of bases and solvents at
different temperatures (Table 1).
Because the desired cross-coupling product is not obtained in
any noticeable amounts in the absence of base, the effect of bases
on the outcome of the reaction is significant (Table 1, entry 1).
Table 1 shows that among the various studied bases, K2CO3 is more
effective for this coupling reaction. Therefore, we chose K2CO3 as
the base in all of the coupling reactions (Table 1, entry 2).
Subsequently, the effect of various solvents on the outcome of
the C–C coupling reaction was investigated (Table 1). The reaction
rate is greatly affected by the kind of applied solvent. Among the
commonly used solvents such as dimethylsulfoxide (DMSO), PEG,
DMF 1,4-dioxane and water, the best result is obtained for PEG in
terms of the conversion and product selectivity (Table 1, entry 2).
Moreover, PEG solvent has an important advantage, which makes
it a unique solvent: its water solubility makes product extraction
and purification very easy.
Also, we investigated the effects of the amount of catalyst in the
coupling reaction. As evident from Table 1, the yield of product in-
creases with increasing catalyst amount. The reaction is complete
within 85 min with excellent conversion and high yield using
1.7 mol% of catalyst (Table 1, entry 2). When the amount of catalyst
decreases to 0.8 mol%, a trace formation of biphenyl product is
obtained (Table 1, entry 19). However, when a higher amount of
catalyst (2 to 3 mol%) is used, the catalyst still functions fairly well,
but the conversion is slightly increased (Table 1, entry 18).
Under the obtained optimized conditions, we examined the gen-
eral applicability of Pd-MPA@MCM-41 with various aryl halides. As
evident from Tables 2–4, a wide range of aryl halides containing
electron-withdrawing or electron-donating groups are efficiently
coupled with phenylating agents to produce the corresponding
biaryl product in excellent isolated yield. The results including reac-
tion time, product yield, melting point, turnover number (TON) and
turnover frequency (TOF) are summarized in Tables 2–4.
As is obvious from Tables 2–4, in all cases excellent isolated yields
(>90%) are obtained, regardless of the nature of the substituent
present on the aryl halides (electron-withdrawing or electron-
donating groups), which confirms the reliability of these synthetic
methods. Upon comparing the results in Tables 2–4, the electronic
effect of substrates is obvious. Aryl halides containing electron-
withdrawing substituents give lower reaction times compared to
those containing electron-donating substituents. Also aryl chlorides
Table 2. Coupling of various aryl halides with NaBPh4 in presence catalysta
Entry
Aryl halide
Iodobenzene
Product
Time (h)
Yield (%)b
M.p. (°C)
TON
TOF (hÀ1
)
1
2
2a
2b
2c
1.4
1.1
0.33
1.5
2.5
1
95
95
97
93
94
97
94
92c
92
90
91
92
96
97
95
67–68[30]
80–82[30]
42–44[33]
111–113[30]
53–54[33]
85–86[30]
69[30]
55.88
55.88
57.05
54.70
55.29
57.05
55.29
36.8
39.9
50.80
172.90
36.47
22.11
57.05
33.30
3.34
4-Iodoanisole
3
4-Iodotoluene
4
4-Bromonitrobenzene
4-Iodoaniline
2d
2e
2f
5
6
4-Bromobenzonitrile
Bromobenzene
7
2 g
2 h
2i
1.66
11
8
1-Bromonaphthalene
4-Bromoaniline
Oil[30]
9
4.5
5.25
0.3
0.33
0.5
1
52–54[33]
93–94[32]
56–58[30]
162–164[30]
42–44[33]
71–73[33]
228–230[33]
54.11
52.94
53.52
54.11
56.47
57.05
55.88
12.02
10.08
162.2
163.96
112.94
57.05
27.94
10
11
12
13
14
15
4-Bromobenzyl alcohol
4-Bromobenzaldehyde
4-Bromophenol
2j
2 k
2 l
2 m
2n
2o
4-Bromotoluene
4-Bromochlorobenzene
4-Bromobenzoic acid
2
aReaction conditions: 1 mmol of aryl halide,0.5 mmol of sodium tetraphenylborate, 1.5 mmol of K2CO3 and (1.7 mol%) of catalyst in 2 ml of PEG solvent at
100 °C.
bIsolated yield.
cAmount of catalyst used was 2.5 mol%.
Appl. Organometal. Chem. (2016)
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Nikoorazm M., Ghorbani-Choghamarani A., Noori N. and Tahmasbi B.
Table 3. Coupling of various aryl halides with PhB(OH)2 in presence catalysta
Entry
Aryl halide
Iodobenzene
Product
Time (h)
Yield (%)b
M.p. (°C)
TON
TOF (hÀ1
)
1
2
2a
2b
2c
2
1.7
1
95
95
94
93
95
97
94
97c
91
94
93
94
95
96
95
67–68[30]
80–82[31]
42–44[33]
111–113[30]
53–54[33]
85–86[30]
69[30]
55.88
55.88
55.29
54.70
55.88
57.05
55.29
38.8
27.94
32.87
55.29
37.72
18.62
43.89
25.13
3.23
4-Iodoanisole
3
4-Iodotoluene
4
4-Bromonitrobenzene
4-Iodoaniline
2d
2e
2f
1.45
3
5
6
4-Bromobenzonitrile
Bromobenzene
1.3
2.2
12
5.1
6
7
2 g
2 h
2i
8
1-Bromonaphthalene
4-Bromoaniline
Oil[30]
9
52–54[33]
93–94[32]
56–58[30]
162–164[30]
42–44[33]
71–73[33]
228–230[33]
53.52
55.29
54.70
55.29
55.88
56.47
55.88
10.49
9.21
10
11
12
13
14
15
4-Bromobenzyl alcohol
4-Bromobenzaldehyde
4-Bromophenol
2j
2 k
2 l
2 m
2n
2o
0.75
0.75
1
72.94
73.72
55.88
37.64
22.35
4-Bromotoluene
4-Bromochlorobenzene
4-Bromobenzoic acid
1.5
2.5
aReaction conditions: 1 mmol of aryl halide,1 mmol of phenylboronic acid, 1.5 mmol of K2CO3 and (1.7 mol %) of catalyst in 2 ml of PEG solvent at 100 °C.
bIsolated yield.
cAmount of catalyst used was 2.5 mol%.
Table 4. Coupling of various aryl halides with Ph3SnCl in presence catalyst
Entry
Aryl halide
Iodobenzene
Product
Time (h)
Yield b
%
Mp ( °C )
TON
TOF (hÀ1
)
1
2
2a
2b
2c
1.8
1.5
0.4
1.5
2.7
1.1
1.9
12
96
94
95
92
96
95
94
94c
92
93
93
94
97
95
96
67–68[30]
80–82[31]
42–44[33]
111–113[30]
53–54[33]
85–86[30]
69[30]
56.47
55.29
55.88
54.11
56.47
55.88
55.29
37.6
31.37
36.86
139.70
36.07
20.91
50.80
29.10
3.13
4-Iodoanisole
3
4-Iodotoluene
4
4-Bromonitrobenzene
4-Iodoaniline
2d
2e
2f
5
6
4-Bromobenzonitrile
Bromobenzene
7
2 g
2 h
2i
8
1-Bromonaphthalene
4-Bromoaniline
Oil[30]
9
4.7
5.5
0.5
0.7
0.6
1.2
2.2
52–54[33]
93–94[32]
56–58[30]
162–164[30]
42–44[33]
71–73[33]
228–230[33]
54.11
54.70
54.70
55.29
57.05
55.88
56.47
11.51
9.94
10
11
12
13
14
15
4-Bromobenzyl alcohol
4-Bromobenzaldehyde
4-Bromophenol
2j
2 k
2 l
2 m
2n
2o
109.41
78.99
95.09
46.56
25.66
4-Bromotoluene
4-Bromochlorobenzene
4-Bromobenzoic acid
aReaction conditions: 1 mmol of aryl halide,0.5 mmol of triphenyltin chloride, 1.5 mmol of K2CO3 and (1.7 mol%) of catalyst in 2 ml of PEG solvent at 100 °C.
bIsolated yield.
cAmount of catalyst used was 2.5 mol%.
are coupled with phenylating reagents to afford the corresponding
product in excellent yields (Table 2–4, entries 14, 16–18). This clearly
shows the efficiency of the present catalytic system.
In order to explore more reactions of the described catalyst,
the Heck reaction was selected as another C–C cross-coupling
reaction. Initially, we optimized the reaction conditions and inves-
tigated the effect of the amount of catalyst, solvent, base and
temperature on the coupling reaction between iodobenzene
and butyl acrylate as a model reaction in DMF as solvent in the
presence of K2CO3 as base with a catalyst loading of 2.5 mol%
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

Synthesis of Pd-MPA@MCM-41 for C–C and C–N bond formation
Table 5. Optimization of reaction conditions for C C coupling reaction
of iodobenzene with butyl acrylate for 40 min
improvement in the conversion (98%) is obtained for reaction at
120 °C after 40 min (Table 5, entry 4). To study the generality of this
Heck cross-coupling reaction, under the optimized conditions
(Table 6) we examined the reaction of n-butyl acrylate with a wide
array of aromatic aryl halides.
Table 7 summarizes the catalytic activity of the described Pd-
MPA@MCM-41 heterogeneous catalyst that was examined through
reaction of aryl halides with aqueous ammonia for the synthesis of
aniline derivatives under various conditions.
At first, we selected iodobenzene as an example of a non-
activated aryl halide with aqueous ammonia as a model reaction
in the absence of base with a catalytic loading of 1.7 mol% of Pd
at room temperature. Influences of various parameters were exam-
ined to find the best possible combination. Parameters such as
amount of catalyst, solvent and base were screened using the same
model reaction (Table 7).
Entry Catalyst Solvent
(mol%)
Base
Temperature
(°C)
Yield
(%)a
b
1
2
—
1.49
1.66
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
DMF
DMF
DMF
DMF
PEG
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Et3N
120
120
120
120
120
120
120
120
120
100
80
—
50
85
98
50
75
60
75
30
40
25
3
4
5
6
DMSO
DMF
DMF
DMF
DMF
DMF
7
8
9
KOH
10
11
K2CO3
K2CO3
aIsolated yield.
bNo reaction after 24 h.
To investigate the influence amount of catalyst, systematic stud-
ies were done in the presence of different amounts of the catalyst
Table 7. Optimization of amination of aryl halidesa
of Pd at 120 °C. To study the influence of the catalyst, the model
reaction was carried out in the absence of the catalyst. No con-
version is seen even when the reaction lasts for 24 h (Table 5,
entry 1). However, when a similar reaction is conducted in the
presence of catalyst (Pd-MPA@MCM-41, 2.5 mol%), the reaction
is completed within 40 min with an excellent conversion and a
high yield (98%) (Table 5, entry 4).
In the next step, several solvent systems were assessed. Among
the studied solvents, the use of DMF givea acceptable conversion
(98%) and, as a result, this solvent was chosen as the preferred sol-
vent in terms of yield (Table 5, entry 4). After optimization of the cat-
alyst amount and solvent, various bases such as Et3N, KOH, K2CO3
and Na2CO3 were also screened for their effect on the model reac-
tion (Table 5, entries 4, 7–9). A superior yield and a shorter reaction
time are obtained when K2CO3 is employed as base (Table 5, entry 4).
As evident from Table 5, the coupling reaction yields are likely to
change in response to temperature changes in the presence of
2.5 mol% of catalyst (Table 5, entries 4, 10 and 11). An obvious
Entry
Solvent
Base
Catalyst (mol%) Time (h) Yield (%)b
1
2
—
—
—
—
—
1.7
1.36
0.85
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
1.7
3.5
5.75
8
97
85
75
50
65
77
70
45
90
80
88
70
3
—
4
PEG
—
24
5
DMF
EtOH
DMSO
1,4-Dioxane
—
—
24
24
24
80
15
12
7
6
—
7
—
8
—
9
(Et)3N
Na2CO3
K2CO3
KOH
10
11
12
—
—
22
aReaction conditions: iodobenzene (1 mmol), aqueous ammonia (1 ml)
at room temperature.
bIsolated yield.
Table 6. Coupling of aryl halides with butyl acrylate (Heck reaction) in the presence of catalytic amounts of Pd-MPA@MCM41a
Entry
Aryl halide
Iodobenzene
Product
Time (h)
Yield %
Mp ( °C)
TON
TOF (hÀ1
)
1
2
4a
4b
4c
1
98
96
94
94
97
95
96
97
98
96
97
92
Oil[36]
Oil[34]
39.2
38.4
37.6
37.6
38.8
38
39.2
4-Iodotoluene
1.15
1.5
5
33.39
25.06
7.52
3
4-Iodoanisole
Oil[36]
4
2-Iodoanisole
4d
4e
4f
Oil[37]
5
2-Iodoanisole
4.75
1.75
0.5
3
Oil[38]
8.16
6
Bromobenzene
Oil[34]
21.71
76.8
7
3-bromopyridine
4-Bromochlorobenzene
4-Bromobenzonitrile
Chlorobenzene
4 g
4 h
4i
Oil[34]
38.4
38.8
39.2
38.4
38.8
36.8
8
Oil[34]
12.93
31.36
15.36
29.84
3.06
9
1.25
2.5
1.3
12
39–42[34]
Oil[37]
10
11
12
4j
4-Bromonitrobenzene
4-Chlorobenzonitrile
4 k
4 l
58–63[35]
39–42[34]
aReaction conditions: aryl halide (1 mmol), n-butyl acrylate (1.2 mmol), K2CO3 (3 mmol), Pd-MPA@MCM-41 (2.5 mol%) and DMF (2 ml), 120 °C.
Appl. Organometal. Chem. (2016)
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Nikoorazm M., Ghorbani-Choghamarani A., Noori N. and Tahmasbi B.
Table 8. Amination of aryl halides in presence of Pd-MPA@MCM-41 using aqueous ammoniaa
Entry
Aryl halide
Iodobenzene
Product
Time (h)
Yield (%)b
M.p. (°C)
TON
TOF (hÀ1
)
1
2
2a
2b
2c
2d
2e
2f
3.5
3.75
7
96
93
95
94
95
93
98
96
94
97
Oil[7]
Oil[7]
68–70[39]
43–44[7]
57–58[39]
47–49[7]
146–148[39]
56–58[5]
56.47
54.70
55.88
55.29
55.88
54.70
57.69
56.47
55.29
57.05
16.13
14.58
7.98
Bromobenzene
3
4-Bromochlorobenzene
4-Iodotoluene
4
4
13.82
10.16
3.03
5
4-Iodoanisole
5.5
18
3
6
2-Bromonaphthalene
4-Bromonitrobenzene
2-Bromopyridine
4-Bromophenol
7
2 g
2 h
2i
19.23
8.06
8
7
9
12
2.5
186–190[40–42]
87–88[39]
4.60
10
4-Bromobenzonitrile
2j
22.82
aReaction conditions: aryl halide (1 mmol), aqueous ammonia (1 ml) and catalyst (10 mg, 1.7 mol%) at room temperature.
bIsolated yield.
from 0.85 to 1.7 mol% at room temperature under solvent-free con-
ditions (Table 7, entries 1–3). The findings reveal that with increas-
ing catalyst concentration a general increasing trend is seen in
isolated yields of products. Therefore, the best yield is obtained in
the presence of 1.7 mol% of Pd (Table 7, entry 3).
To find the best reaction conditions, the effects of various sol-
vents, such as DMF, PEG, EtOH, DMSO and 1,4-dioxane, were inves-
tigated (Table 7, entries 4–8). Under solvent conditions the reaction
is not complete after 24 h. Finally, we carried out the amination of
aryl halides in the absence of solvent for all reactions (solvent-free
conditions) (Table 7, entry 1).
Then, after optimizing the amount of catalyst and solvent, we ex-
plored the effects of bases on the model reaction in solvent-free
conditions in order to find the appropriate base. Various inorganic
and organic bases including Et3N, Na2CO3, K2CO3 and KOH were ex-
amined (Table 7, entries 9–12). As evident from Table 7, the reaction
was performed in neat conditions in terms of short reaction time
and high yield (Table 7, entry 1).
With the optimized reaction conditions in hand, a series of vari-
ous electron-rich and electron-poor aryl iodides or bromides were
reacted with aqueous ammonia to synthesize the corresponding
aniline derivatives. The findings are summarized in Table 8.
Figure 6. Reusability of Pd-MPA@MCM-41.
In order to show the activity of the catalyst on a large scale for in-
dustrial applications, the coupling of iodobenzene (10 g, 49 mmol)
with PhB(OH)2 (6 g, 49 mmol) under optimized condition was per-
formed. A yield of 96% of biphenyl is obtained in 135 min. Also,
in order to examine the reusability of catalyst on a large scale, after
completion of reaction, the catalyst was recovered and reused
again. In this stage 94% of product is obtained after 145 min, which
clearly demonstrates the practical recyclability of this catalyst on a
large scale.
Reusability of Catalyst
From practical and industrial points of view, catalyst recyclability is
highly desirable. To investigate this issue, catalytic reusability of
Pd-MPA@MCM-41 was examined under the optimized reaction
conditions in the model reaction (Fig. 6). After completion of the
reaction, the catalyst was collected by centrifugation and washed
with acetonitrile several times. Then, the catalyst was dried at
50 °C and reused for the next run. After the eighth reaction run,
the yield of product is decreased from 95 to 88%. This decrease
in the product yield may be due to the weight loss of catalyst in
the operation for recovery and/or deactivation of the catalyst.
Therefore, the Pd-MPA@MCM-41 catalyst shows excellent reusabil-
ity, and no significant loss of selectivity and activity is found even
after eight subsequent runs.
Conclusions
In this work, briefly, we have prepared a palladium complex sup-
ported on MCM-41 and carefully characterized its structure using
FT-IR, SEM, EDS, TEM, XRD, ICP and TGA techniques. Pd-MPA@-
MCM-41 has been used for the cross-coupling reaction of aryl ha-
lides with phenylating agents and alkenes; also amination of aryl
halides was performed in the presence of this catalyst. This simple
reported procedure offers several significant advantages such as
isolation of highly pure products in excellent yields, good reaction
times, simple product separation procedure, reusability of the
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Appl. Organometal. Chem. (2016)

Synthesis of Pd-MPA@MCM-41 for C–C and C–N bond formation
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Acknowledgement
This work was supported by the research facilities of Ilam University,
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