Synergetic catalytic effect of rGO, Pd, Fe3O4 and PPy as a magnetically separable and recyclable nanocomposite for coupling reactions in green media

Article abstract of DOI:10.1002/aoc.4439

In this paper, rGO/Pd–Fe₃O₄@PPy as an efficient stable nanocomposite was synthesized. To understand the synergetic effects of rGO, Pd, Fe₃O₄ and PolyPyrrole, the performance of rGO/Pd–Fe₃O₄@PPy as a heterogeneous recyclable nanocatalyst in the green synthesis of C-C and C-O coupling products, as well as different conditions are studied. Synthesized rGO/Pd–Fe₃O₄@PPy was characterized by FT-IR, XRD, FE-SEM, EDS, TGA and AFM analysis. Best results are obtained under sonication in H₂O for C-C coupling and by ball-milling for C-O coupling. The benefits of this method include: green solvents and conditions, absence of external base, low reaction times with high yield and easy work-up method.

Full text of DOI:10.1002/aoc.4439

Received: 1 March 2018
DOI: 10.1002/aoc.4439
Revised: 26 April 2018
Accepted: 27 April 2018
F U L L P A P E R
Synergetic catalytic effect of rGO, Pd, Fe3O4 and PPy as a
magnetically separable and recyclable nanocomposite for
coupling reactions in green media
Atefeh Emami | Hossein Ghafuri
Catalysts and Organic Synthesis Research
In this paper, rGO/Pd–Fe3O4@PPy as an efficient stable nanocomposite was
Laboratory, Department of Chemistry,
Iran University of Science and
synthesized. To understand the synergetic effects of rGO, Pd, Fe3O4 and Poly-
Technology, P.O. Box 16846‐13114,
Tehran, I. R, Iran
Pyrrole, the performance of rGO/Pd–Fe3O4@PPy as a heterogeneous recyclable
nanocatalyst in the green synthesis of C‐C and C‐O coupling products, as well
Correspondence
Hossein Ghafuri, Catalysts and Organic
as different conditions are studied. Synthesized rGO/Pd–Fe3O4@PPy was char-
acterized by FT‐IR, XRD, FE‐SEM, EDS, TGA and AFM analysis. Best results
Synthesis Research Laboratory,
Department of Chemistry, Iran University
of Science and Technology, P.O. Box
16846‐13114 Tehran, I. R. Iran.
Email: ghafuri@iust.ac.ir
are obtained under sonication in H2O for C‐C coupling and by ball‐milling
for C‐O coupling. The benefits of this method include: green solvents and con-
ditions, absence of external base, low reaction times with high yield and easy
work‐up method.
KEYWORDS
rGO/Pd–Fe3O4@PPy, coupling reactions, sonochemical condition, ball‐mill
1 | INTRODUCTION
make it an extraordinary support material for the catalytic
application. Most ordinarily used form of graphene for cat-
Increasing attention has been paid to nanocomposites in
recent years due to their abundant potential applications
in different categories especially in catalysis science. The
synergetic catalytic effect in nanocomposites which is col-
laborations or interactions between certain catalytic com-
ponents and the support can improved catalytic activity
and reduced side effects to achieve more environmental‐
friendly performance. The catalytic performance in nano-
composite is fundamentally dependent on the structure of
components, so selecting proper components are the
determining stage in the synthesis of these compounds.[1]
Graphene, new charming member of carbonaceous
materials, discovered and isolated as a single atomic layer
of carbon in 2004 which lead to Nobel Prize in Physics in
2010. This world's first two‐dimensional substance may
be the most adaptable material accessible to researchers.
Hummers and Offeman advanced Hummers' method to
synthesize Graphene and is still used commonly.[2] The fas-
cinating tough, strong and thin character of graphene,
alytic application is reduced graphene oxide (rGO). rGO
interacts with metals simply, so despite the difficulty in for-
mation of nanocomposite with inorganic materials, nano-
composite of rGO with metal can be synthesized
effectively without any noteworthy problems.[2,3] The main
problem in metal nanoparticle applications include nano-
particle agglomeration, this can decrease the catalytic abil-
ity as nanocatalyst. Metal particles must be produced with
ultrafine sizes with a high surface area which increase their
catalytic ability. Particularly, rGO are a promising material
in order to disperse metal nanoparticles since loading metal
nanoparticles on rGO surface can avoid aggregation.[4–11]
The foundations of many natural products and phar-
maceuticals contain substituted aromatic structures,
biaryls and diaryl ethers. Palladium complexes can carry
out various kinds of C‐X (C, O and N) coupling reactions
starting from aryl and heteroaryl halides. An important
C‐C coupling reaction is Suzuki reaction that's because of
that in 2010, Heck, Negishi and Suzuki were awarded the
Appl Organometal Chem. 2018;e4439.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4439

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EMAMI AND GHAFURI
Nobel Prize in Chemistry. Due to air‐ and moisture‐stabil-
ity of organoboranes, Suzuki–Miyaura cross‐coupling is
the most effective approach for the synthesis of C‐C bond-
ing and biaryl compounds. This cross coupling reaction
has many advantages over other coupling methods for cre-
ating C‐C bonding containing steadiness of its reagents and
raw materials, mild conditions and the ease of handling.[12]
The Suzuki reaction has been used broadly in the synthetic
organic chemistry, synthesis of natural products and phar-
maceuticals.[13] Another important coupling reaction is C‐
O coupling. Several compounds have C‐O bond in their
structures such as: ethers, epoxides, lactones and carbon-
ate derivatives. A synthetic challenge was shaped to form
aryl‐oxygen linkage under mild condition owing to the
importance of aryl ethers. One solution could be raised to
this challenge: Pd‐catalyzed system. There is some litera-
tures using Pd for C‐O coupling with excellent results.[14]
In chemical reactions, big quantities of organic sol-
vents are used to gain final products. Eco‐friendly media
and solvent free reactions are effective steps to reduce
the toxic solvent effects. In the field of green coupling
reactions, solvent and media selection for waste manage-
ment are based on economic and safety considerations.
Around sustainable development and sustainability, pre-
senting an easy applicable method simplifies the access
way to green chemistry.[15]
Here, due to palladium applications in coupling reac-
tions,[16–19] and together to benefit of the abundant chem-
ical properties of graphene, we decided to use Pd‐GO
nanocomposite to use in coupling reactions. To improve
the dispersity of Pd nanoparticles and to avoid agglomer-
ation of nanoparticles, polypyrrole as a special reducing
agent was selected to synthesize efficient nanocomposite.
In addition of this, to take advantageous of easy separat-
ing method and reusability of Fe3O4, Fe3O4/rGO supports
was prepared to load Pd nanoparticles.[4] Synergistic
effect of rGO, Pd, Fe3O4 and PPy was led to well‐defined
and high impact nanocomposite.
Suzuki C‐C coupling reaction under sonication in H2O and
second in C‐O coupling reaction by ball‐milling. To the best
of our Knowledge, there is no report about using the het-
erogeneous rGO/Pd–Fe3O4@PPy nanocomposite for
catalysing the Suzuki C‐C and C‐O coupling reactions. It
is necessary to mention that there have been a few reports
for coupling reactions in the absence of external base.
Moreover, this method has other advantages such as green
solvents and conditions, low reaction times with high
yields, good catalytic activity, magnetically separable and
reusable catalyst, and easy work‐up method (Scheme 1).
2 | EXPERIMENTAL
All chemicals and solvents were purchased from Merck
and Aldrich. The ultrasonic reactions are carried out in
an Elmasonic S 60 H (220–240 v) with a frequency of
37 kHz, ultrasonic power effective of 150 W and power con-
sumption total of 550 W, and ball‐mill device was Retsch
Mixer Mill MM 400. Field emission scanning electron
microscopy (FE‐SEM) images were recorded by Sigma
Zeiss, energy dispersive X‐ray (EDX) spectra were taken
on a Numerix DXP‐X10P, the FT‐IR spectroscopy were
recorded by Shimadzu IR‐470 spectrometer, NMR spectra
were recorded by Bruker DRX‐500 Avance spectrometer,
X‐ray diffraction (XRD) measurements were taken on a
JEOL JDX‐8030, Atomic force microscopy (AFM) analysis
were recorded by DUALSCOPETM DS 95 series, TGA anal-
ysis was recorded by Netzsch ‐ TGA 209 F1 and melting
points were checked out by Electrothermal 9100 apparatus.
2.1 | Preparation of the rGO/Pd–
Fe3O4@PPy nanocomposite
GO was prepared using Hummer's method.[21] For the
synthesis of rGO/Pd–Fe3O4@PPy, 0.5 g of GO was dis-
persed in 30 ml of water for 30 min, 1 ml of pyrrole was
added into it and stirred for 30 min. To this mixture,
10 ml solution of 0.035 g PdCl2 and 0.4 g of FeCl3·6H2O
was added and stirred for 5.0 h. 0.1 g of FeCl2·4H2O
and 10 ml of NH3·H2O were added to above mixture
under N2 atmosphere at room temperature for 2.0 h.
The synthesized products were isolated and washed with
ethanol and dried by vacuum.[4]
Previously, other graphene‐based catalysts have been
reported to have had very good results for coupling reac-
tion,[20] so we decided to study this reaction with rGO/
Pd–Fe3O4@PPy nanocomposite. To use synergistic effect
of rGO, Pd, Fe3O4 and PPy, rGO/Pd–Fe3O4@PPy nano-
composite was synthesized successfully[4] and the catalytic
property of synthesized nanocomposite was studied first in
SCHEME 1 Suzuki and C‐O coupling
catalyzed by rGO/Pd–Fe3O4@PPy

EMAMI AND GHAFURI
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beaker containing 5 ml of ethanol. The catalyst was easily
separated with an external magnet. The products were
obtained by filtration and washing with hexane. The iso-
lated products were analyzed by their melting points and
some of them were analyzed by NMR spectroscopy.
2.2 | General procedure for the C‐C
coupling reaction
In a typical reaction, 2 mmol of aryl halide, 2 mmol of
phenylboronic acid and the 30 mg of rGO/Pd–Fe3O4@PPy
were sonicated together in 5 ml of H2O at 70 °C (Table 1).
The catalyst was easily separated with an external magnet.
Then, the products were extract with ethyl acetate. The
products in the form of crystals were obtained by filtration
and washing with n‐hexane. Other products were obtained
by chromatography with n‐hexane: EtOAc ‐ 9:1. The iso-
lated products were analyzed by their melting points and
some of them were analyzed by NMR spectroscopy.
2.4 | Selected spectral data
2.4.1 | [1,1′:3′,1”‐Terphenyl]‐2′‐ol (3d)
65% yield. White solid. M.p.: 103–105 °C. 1H NMR
(500 MHz, CDCl3) 7.63–7.65 (m, 4H), 7.54–7.57 (m, 4H),
7.45–7.48 (tt, J = 4.2 Hz, J = 1.3 Hz, 2H), 7.36–7.37
(d, J = 7.6 Hz, 2H), 7. 13‐7.16 (dd, J = 7.6 Hz, 1H), 5.50
(s, 1H, OH).
2.3 | General procedure for the C‐O
coupling reaction
2.4.2 | Benzophenone (3e)
Vibrational frequency of ball‐milling device was 50 Hz, its
grinding jars were stainless steel and the size of each of
them was 10 ml. Two balls for ball‐milling were used
and size of milling balls are 10 mm. In a typical reaction,
2 mmol of substituted phenols, 2 mmol of 2‐chloro‐5‐
nitropyridine and the 30 mg of catalyst were milled in
30.0 Hz and the completion of the reaction was moni-
tored by TLC (Table 2). After completion of the reaction,
the contents of ball mill vessel were transferred to a 10 ml
60% yield. White solid. M.p.: 50–51 °C. 1H NMR
(500 MHz, CDCl3) 7.81–7.83 (m, 4H), 7.57–7.61 (m, 2H),
7.47–7.50 (m, 4H).
2.4.3 | 5‐Nitro‐2‐phenoxypyridine (6a)
92% yield. Yellow solid. M.p.: 8 6‐87°C. 1H‐NMR
(500 MHz, CDCl3) 9.09 (d, J = 2.7 Hz, 1H, Py‐6‐H),
TABLE 1 Suzuki cross‐coupling catalyzed by rGO/Pd–Fe3O4@PPya
Entry
R1
X
Y
Product
Time (min)
Yieldb (%)
1
H
I
H
30
95
3a
2
3
4
5
6
7
4‐CH3
4‐OCH3
4‐OCH3
H
I
H
H
H
H
H
Cl
60
91
93
88
85
50
65
3b
3c
3c
I
45
Br
Br
Cl
Cl
70
60
3a
3a
H
180
180
4‐OH
3d
8
H
COCl
H
150
60
3e
arGO/Pd–Fe3O4@PPy catalyst, 70 °C, under sonication, H2O as solvent,
bisolated yield.

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EMAMI AND GHAFURI
TABLE 2 C‐O‐coupling catalyzed by rGO/Pd–Fe3O4@PPya
Entry
R1
Product
Time (min)
Yieldb (%)
1
H
90
92
6a
6b
6c
2
3
4
5
6
7
8
2‐NO2
2‐CH3
120
75
80
85
87
90
82
88
90
2, 5‐CH3
4‐OCH3
4‐NO2
4‐NH2
4‐CH3
60
6d
60
6e
120
90
6f
6g
75
6h
arGO/Pd–Fe3O4@PPy catalyst, ball‐milling, room temperature,
bisolated yield.
8.51–8.53 (dd, J = 9.0 Hz, J = 2.7 Hz, 1H, Py‐4‐H),
7.50–7.52 (m, 2H, Ph‐2‐H, Ph‐6‐H), 7.3 4‐7.37 (m, 1H,
Ph‐4‐H), 7. 20‐7.22 (m, 2H, Ph‐3‐H, Ph‐5‐H), 7.08 (d,
1H, J = 9.0 Hz, Py‐3‐H).
In the synthesis of rGO/Pd–Fe3O4@PPy nanocompos-
ite, the reduction of GO, the polymerization of the pyr-
role, the synthesis of Pd and Fe3O4 nanoparticles and
the reduction of GO were completed in one stage. PdCl2
and FeCl3·6H2O were used as the initiator for the pyrrole
polymerization. The Pd2+ were reduced to Pd nanoparti-
cles and Fe3+ ions were reduced to Fe2+ ions during the
polymerization process. By NH3 and under basic condi-
tion, Fe3O4 nanoparticles were prepared and together
2.4.4 | 4‐(5‐Nitropyridin‐2‐yl‐amino) phe-
nol (6 g)
Yield: 88%. Brown solid. 1H NMR (500 MHz, CDCl3) 9.09
(d, J = 2.7 Hz, 1H, Py‐6‐H), 8. 22‐8.24 (dd, J = 9.1 Hz,
J = 2.7 Hz, 1H, Py‐4‐H), 7. 24‐7.25 (dd, J = 6.5 Hz,
J = 2.1 Hz, 2H, Ph‐2‐H, Ph‐6‐H), 7.07 (br, NH2), 6.91–
6.93 (dd, J = 6.5 Hz, J = 2.2 Hz, 2H, Ph‐3‐H, Ph‐5‐H),
6.61 (d, J = 9.3 Hz, 1H, Py‐3‐H).
3 | RESULTS AND DISCUSSION
3.1 | Characterization of the rGO/Pd–
Fe3O4@PPy catalyst
Driving force for the assembly of Pd, PPy and Fe3O4
nanoparticles are the electrostatic force, π– π* interac-
tions, and also based on ionic interactions and depends
on the negative charges of the carboxylic and hydroxyl
groups and positive charges of Pd2+ and Fe3+
.
FIGURE 1 FE‐SEM image of rGO/Pd–Fe3O4@PPy

EMAMI AND GHAFURI
5 of 10
with Pd were deposited on the GO and covered by the
PPy layer. By polymer and NH3.H2O, GO nanosheet were
converted to rGO nanosheet.
From FE‐SEM image of rGO/Pd–Fe3O4@PPy in
Figure 1, we have realized that the Pd and Fe3O4
nanoparticles deposited on the graphene surface and
covered with polypyrrole. So, nanaoparticles are not
observed in FE‐SEM image. Also, no aggregation
appears outside of the GO nanosheet and nanoparticles
uniformly occupy the GO surface. As well, it indicates
a
complete perfect combination of GO and the
nanoparticles.
From EDX spectra in Figure 2, we can identify what is
synthesized rGO/Pd–Fe3O4@PPy nanocomposite particu-
lar elements are and their relative proportions. X‐ray
energies are used to identify and quantify the elements
present in a nanocomposite. From its peaks positions,
existence of C (43.6%), Fe (30.8%), O (12.9%), N (11%)
and Pd (1.8%) in this nanocomposite can be confirmed.
Fourier‐transform infrared (FT‐IR) spectrum was
shown in Figure 3. The stretching mode of the C=C in
the graphene ring was observed at 1560 cm−1, the peak
at 1178 cm−1 is related to the vibrations of C‐H, the band
at 1035 cm−1 is assigned to the C‐H bending mode and
the band at around 557 cm−1 corresponds to the
stretching mode of Fe‐O. Also the characteristic peak at
912 cm−1 is attributed to pyrrole‐ring deformation.
X‐ray diffraction (XRD) pattern of rGO/Pd–
Fe3O4@PPy was shown in Figure 4. Six sharp diffraction
peaks appear at 2θ = 30.00, 34.75, 42.48, 53.36, 56.53,
and 61.88, which are respectively indexed to (220),
FIGURE 2 EDX image of rGO/Pd–Fe3O4@PPy
FIGURE 3 FT‐IR spectra of rGO/Pd–
Fe3O4@PPy
FIGURE 4 XRD pattern of rGO/Pd–
Fe3O4@PPy

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EMAMI AND GHAFURI
(311), (400), (422), (511), and (440) and confirmed the
face‐centered cubic lattice of Fe3O4 nanoparticles (JCPDS
no. 19‐0629). As well, for rGO, the peak at around
2θ = 9.8 for GO has noticeably less sharpness than pure
GO, and a new peak appears at 2θ = 26.04 owing to the
reduction of intercalated oxygen functionalities of GO.
Due to the synchronous addition of FeCl3, FeCl2 and
Pd, Pd was placed between the crystalline layers of
Fe3O4. The atomic radius of palladium is larger than iron,
so according to Bragg's law which is 2dSinθ = nλ, inser-
tion of Pd in structure cause to increase in d and decrease
in θ. This cause the shift to smaller degree in XRD
pattern.
The surface of rGO/Pd–Fe3O4@PPy nanocomposite
was shown in AFM images in Figure 5. As can be seen,
the thickness of rGO/Pd–Fe3O4@PPy is about 0.8 nm
FIGURE 5 AFM analysis of rGO/Pd–
Fe3O4@PPy
FIGURE 6 TGA analysis of rGO/Pd–Fe3O4@PPy

EMAMI AND GHAFURI
7 of 10
which completely in agreement with reported single layer
GO. Studying AFM analysis also was done using the
height distribution histograms which was about 2 nm.
In TGA analysis, the weight loss of sample mass is
measured over increasing in temperature. From Figure 6,
weight loss observed below 120 °C is because of the loss
of moisture and the evaporation of water (−3.49%). In
the temperature between 120‐240 °C, the observed weight
loss is due to the decomposition of the oxygen species
present on the substrate surface which have not been
reduced during synthesis (−8.79%). Between 240‐400 °C,
layers of PPy was decomposed on rGO surface
(−33.58%). This analysis was carried out in air, so com-
plete decomposition of nanocomposite is up to 660 °C.
TABLE 3 Optimizing condition for Suzuki cross‐coupling catalyzed by rGO/Pd–Fe3O4@PPya
Entry
Catalyst
Loading (mg)
Solvent
Condition/Temp. (°C)
Time (min)
Yieldb (%)
1
‐
‐
EtOH
EtOH
H2O
reflux
180
180
180
180
180
180
180
180
180
30
No product
2
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
40
40
40
40
40
40
40
40
40
30
20
reflux
40
55
45
30
20
60
60
75
95
95
70
3
reflux
4
Solvent‐free
H2O
100
5
60
6
H2O
25
7
Solvent‐free
H2O
Ball milling
Ultrasonic/25
Ultrasonic/50
Ultrasonic/70
Ultrasonic/70
Ultrasonic/70
8
9
H2O
10
11
12
H2O
H2O
30
H2O
180
arGO/Pd–Fe3O4@PPy catalyst, Aryl halide and phenylboronic acid,
bisolated yield.
TABLE 4 Optimizing condition for C‐O‐coupling catalyzed by rGO/Pd–Fe3O4@PPya
Entry
Catalyst
Loading (mg)
Solvent
Condition/Temp.(°C)
Time (min)
Yieldb (%)
1
‐
‐
EtOH
reflux
reflux
180
180
180
180
180
180
180
180
180
90
No product
2
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
rGO@Pd,Fe3O4,PPy
40
40
40
40
40
40
40
40
40
30
20
EtOH
50
60
40
45
25
40
55
70
92
92
80
3
H2O
reflux
4
Solvent free
H2O
100
5
60
6
H2O
25
7
H2O
Ultrasonic/25
Ultrasonic/50
Ultrasonic/70
Ball‐mill
Ball‐mill
Ball‐mill
8
H2O
9
H2O
10
11
12
Solvent‐free
Solvent‐free
Solvent‐free
90
240
arGO/Pd–Fe3O4@PPy catalyst, substituted phenols and 2‐chloro‐5‐nitropyridine,
bisolated yield.

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EMAMI AND GHAFURI
SCHEME 2 Proposed mechanism for Suzuki reaction
Furthermore, higher yield was obtained in H2O under
sonication with 30 mg of catalyst in shorter reaction time.
It was observed that more than 30 mg, there is no notice-
able change in the yield of product (Table 3).
Studying the catalytic effect in C‐O coupling was per-
formed in various conditions. In the absence of catalyst,
the product was not produced in 180 min and reflux.
3.2 | Investigation of the catalytic ability
of the rGO/Pd–Fe3O4@PPy nanocatalyst for
C‐C and C‐O coupling reactions
After characterization of the catalyst, the catalytic ability of
rGO/Pd–Fe3O4@PPy was investigated in C‐C coupling reac-
tion over a systematic study. Hence, the reaction of 2 mmol
Aryl iodide and 2 mmol phenylboronic acid was studied as
the model reaction. The reaction conditions were optimized
to determine appropriate solvent, temperature, amount of
catalyst and device for the synthesis of desired product.
To analyze the various conditions for the C‐C cou-
pling reaction, in the no‐catalyst condition in EtOH and
reflux, no product obtained in 180 min. But the reaction
in 180 min and in the presence of rGO/Pd–Fe3O4@PPy
in reflux had 40% and 55% yield of product in EtOH
and H2O, respectively. Also had 45% yield in solvent free
condition and 100 °C. So H2O was selected as a reaction
media. Also the reaction was studied by ultrasonic and
ball‐milling technique that ultrasonic showed better
results in 70 °C (30 min, 95%). To optimize the amount
of catalyst, after addition of 20 mg of the catalyst, the
yield of the desired product was about 70% in 180 min.
FIGURE 7 Recycling result of the Suzuki coupling reaction

EMAMI AND GHAFURI
9 of 10
TABLE 5 Study of the efficiency of the rGO/Pd–Fe3O4@PPy nanocatalyst compared with previous reportsa
Entry Catalyst
Base
Solvent Temperature (°C) Time (min) Yieldb (%) Ref.
[22]
1
2
3
4
5
Pd‐slGO‐60
K2CO3 EtOH
25
60
30
60
240
30
44
94
95
98
92
[23]
[24]
[25]
f‐GO [Pd (C^N) Cl (dmso)]nanohybride K2CO3 Toluene 25
Pd@AGu@MGO
K2CO3 H2O
NaOH H2O
25
80
70
Sr/Alg/CMC/GO/Au composites
rGO/Pd‐Fe3O4@PPy
‐
H2O
This work
aAryl halide and phenylboronic acid for Suzuki coupling,
bisolated yield.
The yield of the reaction in the presence of rGO/Pd–
Fe3O4@PPy in the same condition is 50% in 180 min.
to study the solvent effect, between EtOH, H2O and solvent
free condition, H2O had the yield of 60% in 180 min which
was the best among them. But by using ball‐mill as a sol-
vent free device, best yield (90 min, 92%) was gained com-
pared to sonication and reflux (Table 4).
superior to the others: absence of base as co‐catalyst, low
reaction times with high yield in mild reaction conditions
and easy work‐up method.
4 | CONCLUSION
In summary, we have developed an efficient method for
coupling reactions using rGO/Pd–Fe3O4@PPy nanocom-
posite with a very stable character of catalyst and high
yield of products. These graphene‐based nanocomposite
exhibit great catalytic activity and stability for loading
Pd nanoparticles. Coupling reactions has been setup and
several functional groups studied, representing the high
adaptability of the method. High yields and short reaction
times have been gained in the absence of external base in
this green procedure for C‐C and C‐O couplings in H2O
and ball‐mill, respectively. Also this catalyst can be
recycled easily from reaction media by external magnet.
Catalytic activity of this nanocomposite was attributed
to the synergetic effect of rGO, Pd, Fe3O4 and PPy.
To study the scope of these methods for C‐C and C‐O
couplings, the optimized reaction conditions were
established to other derivatives and the results have been
reported in Table (3, 4). After monitoring the reaction by
TLC and completion of the reaction, the catalyst was iso-
lated by external magnet from the reaction mixture and
the product was filtrated by chromatography. Good to
high yields of the desired products were obtained under
the optimized conditions in reasonable reaction times.
Both electron‐withdrawing and electron‐donating groups
involved in the optimized reaction conditions to gain
desired products. In general, the nature of the aryl sub-
stituents has an important impact on the reaction rate.
The proposed mechanism starts with addition of the
organohalide to the Pd(0) to oxidized and form a Pd (II)
complex which followed by participation of basic group of
PPy. By this action, driving force for next action is supplied.
By adding the catalyst to organoborane, this compound by
nucleophilic addition is added to gain compound 3. Because
of H2O media and after addition of H2O to organoborane
compound, acid boric as byproduct is formed and catalyst
is returned to catalytic cycle. By transmetallation process,
compound 4 is formed (Scheme 2).
ORCID
Hossein Ghafuri http://orcid.org/0000-0001-6778-985X
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How to cite this article: Emami A, Ghafuri H.
Synergetic catalytic effect of rGO, Pd, Fe3O4 and
PPy as a magnetically separable and recyclable
nanocomposite for coupling reactions in green
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