Palladium nanoparticles deposited on a graphene–benzimidazole support as an efficient and recyclable catalyst for aqueous-phase Suzuki–Miyaura coupling reaction

Article abstract of DOI:10.1002/aoc.3667

Graphene oxide was functionalized with benzimidazole for palladium immobilization. The resultant graphene–benzimidazole-supported palladium composite (G-BI-Pd) was characterized using infrared and Raman spectroscopies, transmission electron microscopy and

Full text of DOI:10.1002/aoc.3667

Received: 18 July 2016
DOI 10.1002/aoc.3667
Revised: 16 September 2016
Accepted: 26 September 2016
F U L L PA P E R
Palladium nanoparticles deposited on a graphene–benzimidazole
support as an efficient and recyclable catalyst for aqueous‐phase
Suzuki–Miyaura coupling reaction
Mosayeb Sarvestani | Roya Azadi
Chemistry Department, College of Science, Shahid
Graphene oxide was functionalized with benzimidazole for palladium immobiliza-
tion. The resultant graphene–benzimidazole‐supported palladium composite
(G‐BI‐Pd) was characterized using infrared and Raman spectroscopies, transmission
electron microscopy and energy‐dispersive X‐ray spectroscopy. G‐BI‐Pd showed
excellent catalytic activity and fast reaction kinetics in the aqueous‐phase Suzuki–
Miyaura reaction of aryl iodides and bromides with phenylboronic acid under
relatively mild conditions (5–25 min, 80 °C). The catalyst can be used several times
without any significant loss of its catalytic activity.
Chamran University of Ahvaz, Ahvaz 61357‐
3169, Iran
4
Correspondence
Roya Azadi, Chemistry Department, College of
Science, Shahid Chamran University of Ahvaz,
Ahvaz 61357‐43169, Iran.
Email: razadi@scu.ac.ir
KEYWORDS
C─C coupling reaction, graphene, heterogeneous catalyst, palladium nanoparticles,
Suzuki–Miyaura reaction
1
|
INTRODUCTION
mean graphene is a promising candidate for immobilized
catalytically active species for heterogeneous catalysis.
[
12]
Biaryl compounds are versatile building blocks in the field of
pharmaceuticals, herbicides, polymers, liquid crystals, natu-
ral products, ligands for catalysis and advanced materials.
The Suzuki–Miyaura cross‐coupling reaction of aryl halides
with arylboronic acids catalysed by palladium complexes is
one of the most important methods for the preparation of
Up to this point, a few quality papers have reported using
graphene or graphene oxide (GO) or functionalized
graphene‐based materials serving as solid supports for palla-
dium nanoparticle catalysts for carbon–carbon cross‐coupling
[
13–15]
reactions.
However, it was found that the catalytic
activity of the heterogeneous catalysts gradually decreased
during the progress of the reactions when applied several
times. This may be attributed to the low binding affinity of
GO or functionalized graphene with palladium ions or nano-
particles and the aggregation of the nanoparticles. Therefore,
the development and introduction of GO‐based heteroge-
neous catalysts, which have stability in terms of sustained
activity and recyclability in cross‐coupling reactions, are of
practical concern and still in demand.
[1–4]
biaryls in organic synthesis.
Usually, the cross‐coupling
reactions are performed in a homogeneous situation using a
[
5]
soluble palladium organic complex as the catalyst.
However, the high cost, low yield in separation and reusabil-
ity of homogeneous transition metal catalysts remain
scientific challenges. In this regard, heterogeneous catalysis
appears particularly well suited since a palladium catalyst
immobilized on a support could be easily separated from
the product without losing catalytic activity. Activated
[
6]
[7]
[8]
[9]
[10]
carbon, zeolites, silica, polymer and ionic liquids
have been utilized as supports for heterogeneous palladium
catalysts. Recently, graphene as an innovative and interesting
carbon material has greatly attracted the attention of scientists
since its discovery in 2004. Large surface area, fast charge
mobility, unique physical, chemical and mechanical proper-
ties, excellent chemical stability and low manufacturing cost
2 | RESULTS AND DISCUSSION
Continuing our interest in exploring an efficient catalyst for
[11]
[16]
C─C coupling reactions,
in this paper, we demonstrate
graphene functionalized with benzimidazole and its complex
with palladium chloride (G‐BI‐Pd) for the aqueous‐phase
Appl Organometal Chem 2016; e3667;
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
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DOI 10.1002/aoc.3667

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SARVESTANI AND AZADI
Suzuki–Miyaura cross‐coupling reaction. The structure of G‐
BI‐Pd was characterized using various analytical methods,
and its catalytic activity and reusability were investigated in
the Suzuki–Miyaura reaction of various aryl iodides,
bromides and chlorides with phenylboronic acid.
stretching modes of C═N and C‐N, respectively, from the
benzimidazole heterocycle.
Next, PdCl was immobilized at the imidazolium region
2
of G‐BI through the formation of an N–Pd complex
(Scheme 1). Having added PdCl to an ethanol solution of
2
The process of the preparation of the G‐BI‐Pd nanocom-
posite is shown in Scheme 1. As is clear, GO‐BI was
synthesized by treating GO with excess amount of o‐
phenylenediamine (OPD) in the presence of polyphosphoric
G‐BI, the reaction mixture was stirred for 24 h at room tem-
perature in order to create the complete G‐BI‐Pd complex.
The structure of G‐BI‐Pd was analysed using several spectro-
scopic methods. In the FT‐IR spectrum of G‐BI‐Pd, the
[17]
−1
acid (PPA) as a condensing agent and catalyst.
Subse-
vibrational mode of N‐Pd appears at 510 cm (Figure 1).
quent reduction of the functionalized GO by hydrazine
resulted in the benzimidazole‐grafted graphene compound
Raman spectroscopy was also employed to confirm the
structure of benzimidazole–Pd grafted onto the graphene
sheets. Figure 2 presents the Raman spectra of GO and
(G‐BI). After washing and drying G‐BI, its structure was
−
1
analysed using Fourier transform infrared (FT‐IR) spectros-
G‐BI‐Pd. The two bands at about 1368 and 1606 cm corre-
3
copy. Figure 1 clearly shows the most characteristic adsorp-
spond to the vibration of carbon atom with sp electronic
−
1
tion band of GO at 1730 cm corresponding to the C═O
configuration of disordered graphene (D band) and the in‐
2
stretching mode of carboxyl groups on the GO sheets. How-
phase vibration of sp ‐bonded carbon atom (G band). The
ever, after its functionalization and reduction, the peak at
1
I /I ratio of G‐BI‐Pd (1.46) was found to be higher than that
D
G
730 cm− disappears. In the spectrum of G‐BI, the skeletal
1
of initial GO (1.18), revealing a substantial reduction of sp ‐
[18]
3
vibration modes of the benzene ring appear at 1596 and
bonded carbon atoms and oxidized molecular defects.
In
−
1
1
512 cm . Two other typical peaks at 1670 and 1350 cm
addition, such an enhancement has also been observed in
examples of GO and carbon nanotubes decorated with metal
nanoparticles, indicating a probable chemical interaction or
bond between the metal nanoparticles and graphene due to
carbon vacancies and defects that resulted from the chemical
−
1
are also observed, which can be attributed to the
[
19–21]
reduction of GO.
Moreover, the G band of G‐BI‐Pd
−
1
(
(
1606 cm ) is shifted to lower frequency compared to GO
1629 cm ), which can probably be explained by the disrup-
−
1
tion to the alternating pattern of single and double carbon
2
[22]
bonds within sp carbon ribbons during the reaction.
SCHEME 1 Synthesis of G‐BI‐Pd
FIGURE 1 FT‐IR spectra of GO, G‐BI and G‐BI‐Pd
FIGURE 2 Raman spectra of GO and G‐BI‐Pd

SARVESTANI AND AZADI
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Figure 3 shows transmission electron microscopy (TEM)
images of fresh G‐BI‐Pd catalyst and recycled G‐BI‐Pd after
five runs. The TEM image of fresh G‐BI‐Pd catalyst
aggregation. Further, it is also clear from Figure 3(c) that the
sizes of Pd nanoparticles are 3 nm. Figure 3(b) shows a TEM
image of the recycled G‐BI‐Pd after five cycles of Suzuki
reaction. As shown in Figure 3(b), well distributed Pd nano-
particles on the G‐BI sheets can still be observed. It is also
clear from Figure 3(d) that the Pd nanoparticles of the
recycled catalyst are larger than those of the fresh catalyst
due to slight agglomeration and leaching of the Pd nanopar-
(Figure 3a) indicates that Pd nanoparticles are well dispersed
on the surface of the G‐BI sheets with no significant particle
[
23]
ticles during the chemical reaction.
The results indicate
that benzimidazole plays an important role in improving
the dispersibility of Pd nanoparticles and preventing the
aggregation of Pd nanoparticles on the graphene sheets.
Highly dispersed metal nanoparticles on supports with small
diameter are known to have high catalytic activity due to the
advantages of increased low coordination numbers in Pd
nanoparticles and large surface area, resulting in large
[
24]
number of active sites.
The amount of Pd in the catalyst
(
(
G‐BI‐Pd) measured using atomic adsorption spectrometry
AAS) is 16 wt%.
Moreover, the presence of a large number of Pd nanopar-
ticles on graphene is also confirmed using energy‐dispersive
X‐ray spectroscopy (EDS; Figure 4). This analysis clearly
shows the presence of Pd and Cl in the sample and that the
sample consists mainly of carbon with an insignificant
amount of oxygen probably due to the presence of some
unreduced oxygen functional groups. It also shows the pres-
ence of nitrogen indicating the existence of benzimidazole
in the G‐BI‐Pd composite. The amounts of elements detected
by EDS analysis are summarized in Table 1.
The amount of benzimidazole grafted onto the graphene
[
25]
was calculated through the following equation,
nitrogen content of G‐BI‐Pd from EDS analysis:
using the
À
Á
½ðW ×100Þ=Xꢀ×½100=ð100−W ×100=XÞꢀ
Amount mol g−1
t
t
¼
Y
FIGURE 4 EDS analysis of G‐BI‐Pd
TABLE 1 Elemental composition of G‐BI‐Pd determined by EDS analysis
Element (wt%)
FIGURE 3 TEM images of (a) fresh G‐BI‐Pd catalyst and (b) recycled G‐
BI‐Pd after five runs. Histograms of particle size distribution of (c) fresh
G‐BI‐Pd catalyst and (d) recycled G‐BI‐Pd after five runs
Material
C
O
N
Cl
Pd
G‐BI‐Pd
42.83
12.88
9.12
5.15
30.20

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SARVESTANI AND AZADI
a
TABLE 2 Suzuki reaction in various solvents
where W is the weight percent of the element measured, X is
t
b
the theoretical weight percent of the element in the molecule
and Y is the theoretical molecular weight of the molecule.
Benzimidazole has carbon, hydrogen and nitrogen contents
Entry
Solvent
Yield (%)
1
2
3
4
5
H
2
O
88
90
98
30
45
EtOH
O–EtOH
−
1
of 71.18, 5.08 and 23.72 wt% with M of 118 g mol . Based
w
H
2
on this equation, the amount of benzimidazole detected from
Toluene
DMF
−
1
the nitrogen content is 0.53 mol g .
The catalytic performance of the prepared catalyst was
systematically examined through the Suzuki–Miyaura cou-
pling reaction. The reaction of bromobenzene and
phenylboronic acid was chosen initially as a model reaction.
To determine the best solvent, the coupling reaction of
bromobenzene and phenylboronic acid was carried out in N,
N‐dimethylformamide (DMF), toluene, water and ethanol.
According to the results summarized in Table 2, the biphenyl
product is detected in a low yield when the reaction is
conducted in DMF and toluene (Table 2, entries 4 and 5).
a
Reaction carried out with 1 mmol of bromobenzene, 1.2 mmol of phenylboronic
acid, 1.5 mmol of K
for 35 min.
2
CO
3
, 4 mg (0.6 mol%) of G‐BI‐Pd and 6 ml solvent at 80 °C
b
Isolated yield.
a
TABLE 3 Influence of amount of catalyst (G‐BI‐Pd) on Suzuki reaction
Entry
Amount of catalyst (mg)
Pd content (mol%)
Yield (%)b
1
2
3
4
1
2
3
4
0.15
0.3
52
70
98
98
The best conversion of biphenyl is observed for H O–EtOH
2
0.45
0.6
(1:1) in the presence of G‐BI‐Pd (4 mg, 0.6 mol% Pd)
(
Table 2, entry 3). K CO (1.5 mmol) was used as a base
2
3
a
for optimizing the conditions of the reaction.
Reaction carried out with 1 mmol of bromobenzene, 1.2 mmol of phenylboronic
acid, 1.5 mmol of K
2
CO
3
and 6 ml of H
2
O–EtOH (1:1) at 80 °C for 60 min.
The optimum amount of the catalyst was then
determined. The results are summarized in Table 3. Based
b
Isolated yield.
a
TABLE 4 Suzuki–Miyaura reaction of aryl halides with phenylboronic acid catalysed by G‐BI‐Pd
Entry
4
X
R
5
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9
4a
4b
4c
Br
I
—
5a
5a
5b
5c
5d
5e
5f
10
5
98
98
89
90
85
82
88
98
95
90
98
98
95
—
Br
Br
Br
Br
Br
Br
Br
Br
Br
I
CO
CN
2
H
20
10
10
15
15
20
20
25
25
5
4d
4e
COCH
NO
COH
CH
3
4f
2
4 g
4 h
4i
3
5 g
5 h
5i
OH
NH
10
11
12
13
4j
2
4 k
4 l
OCH
OCH
3
3
5j
5j
20
1
4
15
90
1
5
6
4o
4p
Cl
Cl
COH
CN
5f
60
60
35
30
1
5c
a
Reaction conditions: aryl halides (1.0 mmol), phenylboronic acid (1.2 mmol), K
2
CO
3
(1.5 mmol), G‐BI‐Pd (3 mg, 0.45 mol% Pd) and EtOH–H
2
O (1:1) (6 ml) at 80 °C.
b
Isolated yield.

SARVESTANI AND AZADI
5 of 7
on the results presented, the best conversion of biphenyl is
observed for 3 mg of G‐BI‐Pd catalyst (0.45 mol% Pd) in
only 10 min at 80 °C (Table 3, entry 3).
reaction mixture was first cooled to room temperature and
then filtered and washed sufficiently with ethanol and
acetone. Finally, the reuse of G‐BI‐Pd was investigated in
the Suzuki reaction of bromobenzene with phenylboronic
acid. It is evident from Table 5 that the G‐BI‐Pd catalyst
could be recycled five times with a little loss of its catalytic
activity in the reaction of bromobenzene. This clearly
indicates the high catalytic activity and stability of G‐BI‐Pd.
It is also confirmed by the TEM image of the recycled
catalyst after five runs (Figure 3(b)).
The efficiency of the G‐BI‐Pd nanocomposite (time,
yield, reaction conditions) is compared with some reported
heterogeneous palladium catalyst in the Suzuki reaction in
Table 6. It is clear from Table 6 that our method is more
efficient and less time consuming for the Suzuki reaction.
The high catalytic activity was attributed to the small size
and uniform dispersion of Pd nanoparticles on the G‐BI
sheets.
To generalize the application of the G‐BI‐Pd catalyst, the
coupling reactions of various substituted aryl halides with
phenylboronic acid were performed in the presence of
K CO , using H O–EtOH (1:1) as an environmentally benign
2
3
2
solvent. The findings show that the Suzuki reaction proceeds
in good yields with most substrates (Table 4). It is evident
from Table 4 that for most of the aryl bromides having either
electron‐donating groups or electron‐withdrawing groups, the
reaction can be completed in short reaction times
(10–25 min) with excellent yields. It is also noted that the
reaction kinetics of this catalyst in the Suzuki reaction of aryl
iodides and bromides are much faster than those previously
[15,26]
reported for GO‐based catalyst.
The reactions of
electron‐rich aryl bromides (entries 8–11) need a longer time
than those of the electron‐deficient ones (entries 3–7). This
observed fact is presumably because the oxidative addition
process is the rate‐determining step. Unfortunately, the
catalytic system is less effective for the reaction of aryl
chlorides (entries 15 and 16).
To show the role and performance of benzimidazole in
the G‐BI‐Pd catalyst, G‐Pd was fabricated according to the
same procedure as for G‐BI‐Pd except that 50 mg of G‐BI
was replaced by 50 mg of G. It was also investigated in the
Suzuki reaction. The reaction of bromobenzene in the pres-
ence of G‐Pd proceeded with a longer reaction time than
the reaction using the G‐BI‐Pd catalyst. The metal loadings
of G‐BI‐Pd and G‐Pd are different. Actually, the weight
percent of metal in G‐BI‐Pd is approximately 16%, while that
in G‐Pd is just 3% (measured using AAS).
3
| CONCLUSIONS
In summary, we successfully developed a new and practical
graphene‐supported Pd complex catalyst. This novel hetero-
geneous catalyst is easy to prepare and handle as it is stable
in air. The catalytic activity of this catalyst was investigated
in the aqueous‐phase Suzuki–Miyaura reaction. A series of
biaryl derivatives were obtained in moderate to excellent
yields under mild conditions from the reaction of
phenylboronic acid with aryl iodide and bromide derivatives
in short reaction times. The catalyst exhibited high stability
and reusability up to five cycles.
The recyclability of the catalyst was investigated because
recycling of heterogeneous catalysts is desirable in practical
applications. Having completed each catalytic cycle, the
4
4
|
EXPERIMENTAL
.1 | Materials and methods
TABLE 5 Reusability of catalyst in Suzuki reaction of bromobenzene with
a
phenylboronic acid
Graphite powder, sulfuric acid (H SO ), potassium perman-
2
4
Run
1
2
3
4
5
ganate (KMnO ), hydrogen peroxide (H O ), PPA, OPD,
4 2 2
b
various aryl halides, phenylboronic acid, potassium carbon-
ate (K CO ) and palladium(II) chloride were purchased from
Merck Chemical Company (USA), without further purifica-
tion. Double‐distilled water was used throughout the
experiments.
Conversion (%)
100
98
95
97
90
a
2
3
Reaction conditions: bromobenzene (1.0 mmol), phenylboronic acid (1.2 mmol),
CO (1.5 mmol), G‐BI‐Pd (3 mg, 0.45 mol% Pd) and EtOH–H O (1:1) (6 ml)
K
2
3
2
at 80 °C.
b
GC yield; n‐octane used as internal standard.
TABLE 6 Comparison of efficiency of G‐BI‐Pd with other heterogeneous palladium catalyst in Suzuki reaction of bromobenzene with phenylboronic acid
Catalyst
Solvent
Base
Temp. (°C)
Yield (%)
Time
G‐BI‐Pd (0.45 mol%) (this work)
H
H
H
H
H
H
H
2
2
2
2
2
2
2
O–EtOH
O–EtOH
O–DMF
O
K
K
2
2
CO
3
3
80
60
80
90
80
80
80
98
92
10 min
2.5 h
1 h
[
15]
NHC‐Pd/GO (0.1 mol%)
CO
[
15]
GO‐NHC‐Pd (1 mol%)
PCA‐GNS‐Pd (0.2 mol%)
Cs
2
CO
3
87
[
15]
Na
2
2
CO
3
3
97
2 h
2
+
[25a]
Pd ‐GO (0.25 mol%)
O–EtOH
O–EtOH
O
Na
CO
100
88
4 h
[
15]
GO‐PdP
Pd/Fe
2
(0.5 mol%)
/r‐GO (0.36 mol%)
K
K
2
CO
3
3
2 h
[
27]
3
O
4
2
CO
97
25 min

6
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SARVESTANI AND AZADI
FT‐IR spectra were recorded in KBr pellets using a Spec-
trum One FT‐IR spectrometer (PerkinElmer). High‐field
several times, the obtained product was re‐dispersed into
methanol (120 ml) by sonication for 30 min. Then hydrazine
hydrate (1.4 ml) was added and refluxed at 65 °C for 24 h.
The obtained G‐BI was filtered and washed with methanol
several times, and then air‐dried.
NMR spectra were obtained with a Bruker 250 MHz Avance
1
[13]
Ultrashield instrument. H NMR and
C NMR chemical
shifts are quoted relative to solvent resonance(s) as internal
standard. Raman spectra were obtained with an Almega
Thermo Nicolet dispersive Raman spectrometer. The laser
excitation was provided by the second harmonic of a Nd:
YLF laser operating at 532 nm. TEM images were acquired
with a Zeiss‐EM10C transmission electron microscope with
an acceleration voltage of 80 kV. Samples were prepared by
dispersing the GO‐BI‐Pd in water via ultrasonication. One
drop of the suspension was applied to a formvar carbon‐
coated grid Cu mesh 300 and left dry in air. An Analytik Jena
4.4 | Synthesis of G‐BI‐Pd
For the preparation of G‐BI‐Pd, G‐BI (50 mg) was dispersed
in 20 ml of ethanol. Subsequently, PdCl2 (0.25 mmol,
4
4.3 mg) was added and the mixture was subjected to sonica-
tion for 5 min, then stirred for 24 h at room temperature. After
the reaction, the compound G‐BI‐Pd was isolated by centrifu-
gation and washed five times with distilled water. The
obtained catalyst was air‐dried.
(
Germany) flame AAS instrument was used for determina-
tion of Pd. Additionally, investigations by means of scanning
electron microscopy were carried out by applying an EDS
detector. The measurements were conducted using a Rontec
scanning electron microscope (Bruker, Germany).
4
.5 | General procedure for Suzuki–Miyaura cross‐
coupling reaction (synthesis of compounds 5a–5 l)
In a 25 ml round‐bottom flask, 3 mg (0.45 mol% Pd) of the
as‐prepared catalyst (G‐BI‐Pd) was dispersed in 6 ml of
4
.2 | Synthesis of GO
GO was synthesized from graphite using a modified Hum-
H O–EtOH (1:1, v/v) by sonication for 20 min at room tem-
2
[
28]
mers method.
50 μm) and 1 g of sodium nitrate were added into 50 ml
of concentrated H SO (95%) under stirring in an ice bath,
Graphite powder (2 g, particle size
perature. To this suspension, aryl halides 4a–4p (1 mmol),
<
phenylboronic acid (1.2 mmol, 0.15 g) and K CO (1.5 mmol,
2
3
0.21 g) were added and the reaction mixture was stirred at
80 °C for the required time. After completion of the reaction
(monitored by TLC), the reaction mixture was cooled to
room temperature, filtered and then dichloromethane
(3 × 10 ml) was added to the reaction vessel. The organic
phase was separated and dried over anhydrous Na SO and
2
4
and then KMnO (8 g) was slowly added to the suspension
4
to keep the reaction temperature lower than 20 °C. Then the
ice bath was removed and the mixture was stirred at 35 °C
for 12 h. Subsequently, deionized water (400 ml) was slowly
added under vigorous stirring. The diluted suspension was
further stirred at 90 °C for 30 min. Finally the mixture was
further treated with 8 ml of 30% H O solution to convert
the unreacted permanganate and manganese dioxide into sol-
uble sulfate. The vibrant yellow mixture was then filtered and
the precipitate washed with an aqueous HCl solution (5%,
2
4
the crude product was purified by column chromatography
(n‐hexane–ethyl acetate). Evaporation of the solvent gave
the pure desired products 5a–5 l. Products 5a–5 l are known
compounds, and their NMR spectra are in accordance with
2
2
[
15]
those reported in the literature.
Biphenyl (5a). M.p. 70–71 °C (lit. 69–70 °C).
[15]
2
00 ml) and then centrifuged and washed with deionized
Yield
1
water several times, and finally by filtration and air drying,
graphite oxide was obtained. For using in reactions, the
graphite oxide aqueous suspension was ultrasonicated for
150.90 mg, 98%. H NMR (250 MHz, CDCl , δ, ppm):
3
7.62 (4H, d, J = 7.5 Hz), 7.49–7.44 (4H, t, J = 7.3 Hz),
7.37 (2H, t, J = 7.4 Hz).
30 min to form GO.
4‐Acetylbiphenyl (5d). M.p. 119–120 °C (lit. 120–
[
15]
1
1
21 °C).
Yield 166.60 mg, 85%. H NMR (250 MHz,
CDCl , δ, ppm): 8.04 (2H, d, J = 7.8 Hz), 7.69 (2H, d,
J = 8.2 Hz), 7.63 (2H, d, J = 7.5 Hz), 7.46 (3H, m),
2.665 (3H, s).
3
4
.3 | Synthesis of G‐BI
G‐BI was synthesized using a PPA‐catalysed cyclization
reaction. Detailed synthesis of G‐BI was followed from the
reported work of Ai et al.
4‐Nitrobiphenyl (5e). M.p. 111–114 °C (lit. 114–
[17]
[15]
1
In summary, first a suspension
115 °C).
Yield 163.18 mg, 82%. H NMR (250 MHz,
was obtained by ultrasonic exfoliation of graphite oxide
CDCl , δ, ppm): 8.29 (2H, d, J = 7.7 Hz), 7.73 (2H, d,
3
(
(
160 mg) in deionized water (80 ml) for 30 min. OPD
700 mg) was added into the solution and sonicated for
J = 8.2 Hz), 7.63 (2H, d, J = 7.7 Hz), 7.47–7.25 (3H, m).
[
13]
C NMR (62.9 MHz, CDCl , δ, ppm): 147.6, 147.05,
3
another 5 min. Then PPA (1 ml) was added dropwise under
vigorous stirring, and the solution was refluxed at 80 °C in
darkness for 24 h. The product was gathered by filtration,
subsequently re‐dissolved in 1:2 HCl by sonication and then
collected by filtration. After washing with deionized water
138.73, 129.16, 128.93, 127.78, 127.38, 124.09.
4‐Methylbiphenyl (5 g). M.p. 45–48 °C (lit. 47–
[
15]
1
48 °C).
Yield 164.64 mg, 98%. H NMR (250 MHz,
CDCl , δ, ppm): 7.50 (2H, d, J = 7.2 Hz), 7.40 (2H, d,
3
J = 7.4 Hz), 7.34 (2H, t, J = 7.4 Hz), 7.27 (1H, d,

SARVESTANI AND AZADI
7 of 7
[
13]
J = 7.2 Hz), 7.15–7.23 (2H, m), 2.31 (3H, s).
C NMR
[14] a) L. Rumi, G. M. Scheuermann, R. Mülhaupt, W. Bannwarth, Helv.
Chim. Acta 2011, 94, 966. b) M. Gómez‐Martínez, E. Buxaderas, I. M.
Pastor, D. A. Alonso, J. Mol. Catal. A 2015, 404, 1.
(
62.9 MHz, CDCl , δ, ppm): 129.48, 128.71, 126.98, 21.11.
‐Aminobiphenyl (5i). M.p. 51–53 °C (lit. 52–54 °C).
Yield 152.10 mg, 90%. H NMR (250 MHz, CDCl , δ, ppm):
.56 (2H, m), 7.44–7.37 (4H, m), 7.26 (1H, m), 6.76 (2H, d,
C NMR (62.9 MHz, CDCl3,
δ, ppm): 128.65, 128.01, 126.39, 126.24, 115.38.
3
[
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ACKNOWLEDGMENTS
693, 2469.
We thank Shahid Chamran University of Ahvaz Research
Council, Ahvaz, for financial support of this investigation
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How to cite this article: Sarvestani M, Azadi R.
Palladium nanoparticles deposited on a graphene–
benzimidazole support as an efficient and recyclable
catalyst for aqueous‐phase Suzuki–Miyaura coupling
reaction. Appl Organometal Chem. 2016;e3667. doi:
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0.1002/aoc.3667