Immobilizing Pd nanoparticles on the ternary hybrid system of graphene oxide, Fe3O4 nanoparticles, and PAMAM dendrimer as an efficient support for catalyzing sonogashira coupling reaction

Article abstract of DOI:10.1002/aoc.5203

An alternative approach to develop a Pd catalyst based on dendrimer-functionalized graphene oxide for C-C cross-coupling reactions is reported. Pd@MGO-D-NH₂ has been synthesized by incipient wet impregnation method. The structure of the catalyst was thoroughly characterized by a set of analytical techniques such as TEM, BET, SEM/EDS, FTIR, and elemental mapping analysis. Then, the catalytic activity of the catalyst was scrutinized for promoting sonogashira C-C coupling reaction. The results manifested that Pd@MGO-D-NH₂ was able to catalyze the coupling reaction to obtain high coupling yields in short reaction time. The results of present work are hoped to aid the development of new class of heterogeneous catalysts as the high performance candidate for industrial applications.

Full text of DOI:10.1002/aoc.5203

Received: 22 January 2019
DOI: 10.1002/aoc.5203
Revised: 1 August 2019
Accepted: 1 August 2019
F U L L P A P E R
Immobilizing Pd nanoparticles on the ternary hybrid
system of graphene oxide, Fe3O4 nanoparticles, and PAMAM
dendrimer as an efficient support for catalyzing sonogashira
coupling reaction
Mehrasa Tarahomi1 | Heshmatollah Alinezhad1
| Behrooz Maleki2
1 Faculty of Chemistry, University of
An alternative approach to develop a Pd catalyst based on dendrimer‐
functionalized graphene oxide for C‐C cross‐coupling reactions is reported.
Pd@MGO‐D‐NH2 has been synthesized by incipient wet impregnation
method. The structure of the catalyst was thoroughly characterized by a set
of analytical techniques such as TEM, BET, SEM/EDS, FTIR, and elemental
mapping analysis. Then, the catalytic activity of the catalyst was scrutinized
for promoting sonogashira C‐C coupling reaction. The results manifested that
Pd@MGO‐D‐NH2 was able to catalyze the coupling reaction to obtain high
coupling yields in short reaction time. The results of present work are hoped
to aid the development of new class of heterogeneous catalysts as the high per-
formance candidate for industrial applications.
Mazandaran, P.O. Box 47416‐95447,
Babolsar, Iran
2 Department of Chemistry, Faculty of
Sciences, Hakim Sabzevari University,
96179‐76487 Sabzevar, Iran
Correspondence
Heshmatollah Alinezhad, Faculty of
Chemistry, University of Mazandaran,
P.O. Box 47416‐95447, Babolsar, Iran.
Email: heshmat@umz.ac.ir
Behrooz Maleki, Department of
Chemistry, Faculty of Sciences, Hakim
Sabzevari University, 96179‐76487,
Sabzevar, Iran.
Email: b.maleki@hsu.ac.ir
KEYWORDS
dendrimer, graphene oxide, Pd nanoparticles, Sonogashira coupling reaction
Funding information
Hakim Sabzevari University; Research
Council of University of Mazandaran
1 | INTRODUCTION
herbicides, the synthesis of natural products, and drug
industry.[4,6–8]
The Sonogashira reaction is a cross‐coupling reaction
which used to form carbon–carbon bonds between a ter-
minal alkyne and an aryl or vinyl halide and it employs
a palladium catalyst. Palladium‐based catalyst is one of
the most promising agent for a classic C‐C bond forma-
tion in organic chemistry.[1–4]
Palladium‐catalyzed cross‐coupling reactions which
employ the formation of biphenyl compounds have
become one of the most important and powerful syn-
thetic procedures.[5] Among various coupling reactions,
one of the most widely used reaction to form a new C‐C
bond is the palladium catalyzed Sonogashira coupling
reaction. Due to the importance of palladium‐catalyzed
coupling reaction, it has been applied in many different
areas of science, including pharmacological agents,
Graphene oxide as a chemically modified and highly
oxidized form of graphene with a giant aromatic macro-
molecule and a large number of oxygen functionalities on
their basal plant, can simply disperse in organic solvents,
water, and different matrixes. The popularity of graphene
oxide (GO) promotes extensively, due to its unique physi-
cochemical properties such as thermal and electrical con-
ductivity, superior dispersibility, facile modification, and
etc.[9–13] Combining the GO with polymer or ceramic
matrixes can enhance their mechanical and electrical
properties. Up to now, the utility of graphene based com-
posite for energy research,[14–16] catalysis,[17,18] and elec-
trochemical analysis[19] has also been widely confirmed.
Dendrimers are an important class of organic com-
pounds due to their defined hyperbranched
Appl Organometal Chem. 2019;e5203.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5203

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TARAHOMI ET AL.
1
nanoarchitecture, monodispersity, abundance of func-
tional groups at the periphery and biocompatibility,[20–22]
So, it is visualized that the interface of graphene oxide with
dendrimer would provide physico chemical advantages
such as a solution/dispersion state.[23] So, developing a
multicomponent graphene‐based nanocarriers for organic
transformation can be very important.
properties of the synthesized catalyst. H and 13C NMR
spectra were recorded on a Bruker DRX‐400 AVANCE
(MA, USA) spectrometer at 400.13 and 100.61 MHz,
respectively. Mass spectra were determined on
Finnigan‐Matt 8430 (Waltham, USA) mass spectrometer
operating at an ionization potential of 70 eV.
a
The combination of activity and high reaction rates
can be attained when Pd is supported on an appropriate
material. Then, research on novel Pd‐based catalyst has
received much attention.[24–29]
2.2 | Preparation of GO/Fe3O4 (MGO)
GO was prepared by oxidizing graphite with a modified
Hummers method.[41,42] To synthesize magnetic
graphene oxide nanocomposite (MGO‐NCs) an effective
chemical precipitation method was used. To form a
well‐distributed suspension, 30 mg GO was sonicated in
10 ml distilled water for 20 minutes. It was heated to
50 °C, followed by purging with N2 to remove O2 in the
solution. After that, 80 mg FeCl2·4H2O and 216 mg
FeCl3·6H2O were added to the suspension and
ultrasonicated for 30 min. One ml solution of NH3·H2O
was dropwise added to the mixture with vigorous
mechanical agitation and kept on reacting for 40 min at
50 °C protected by N2. When it was cooled to room tem-
perature, the obtained composites were magnetically
separated by a supermagnet and washed with double‐
distilled water for several times. The resulting product
was dispersed in 20 ml water, and the homogeneous
product of the magnetic nanoparticles was obtained.
In the last decades, several Pd‐based catalyst with dif-
ferent supports have been reported in cross‐coupling
reactions such as graphene‐supported Pd/Fe3O4 nanopar-
ticles,[30] dendrimer‐stabilized Pd nanoparticles,[31] palla-
dium catalysts deposited over donor‐functionalized silica
gel,[32] polymer‐supported palladium/N‐heterocyclic
carbene complex,[33] active palladium nanoparticles
discharged from multilayer films,[34] palladium
nanoparticle‐graphene hybrids,[35] Pd@MTiO2,
palla-
[36]
dium anchored to SBA‐15 functionalized with
melamine‐pyridine groups,[37] Pd‐Ni bimetallic synergis-
tic catalyst on ZIF‐8,[38] Pd immobilized on dendrimer
decorated halloysite clay,[39] and etc.
According to our interest to graphene‐based nano-
structured system,[40] in the present study, we describe
the design, synthesis and evaluation of novel Pd sup-
ported on the dendrimer‐functionalized graphene oxide
to develop cross coupling reaction.
2 | EXPERIMENTAL SECTION
2.1 | Materials and instruments
2.3 | Functionalization of MGO‐NCs with
a modified PAMAM dendrimer (MGO‐D‐
NH2)
All chemicals were purchased from Merck and Aldrich.
Solvents were purified by conventional methods. The
structure of Pd@MGO‐D‐NH2 was characterized by
TEM, BET, SEM/EDS, FTIR, and elemental mapping
measurements. The progress of the reaction was checked
with thin layer chromatography (TLC) using commercial
plates coated with silica gel 60 F254.
Fourier transform infrared (FT‐IR) spectra of the cata-
lyst and the synthesized compounds were recorded on a
TENSOR BRUKER 27 spectrometer in the frequency
range of 400–4000 cm−1 using KBr pellets. The
SEM/EDX analysis were recorded with MIRA3 XMU
instrument in which the specimens were sputter‐coated
with a thin layer of gold. The applied transmission elec-
tron microscope (TEM) images were recorded on a
Philips CM30 transmission electron microscope. Nitrogen
adsorption–desorption isotherms were performed on a
BELSORP Mini II apparatus to characterize the textural
The modified PAMAM dendrimer was synthesized
according to previous work.[22,40,43] The second genera-
tion dendrimer which contains 10‐NH2 terminal groups
(G2) as pale yellow oil was obtained. The main steps of
the experimental procedure are described in details
below. MGO (0.3 g) was dispersed in 200 ml of deion-
ized water by sonication for 30 min. Then, 1‐ethyl‐
3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride
(EDC.HCl) of 0.052
g
and N‐hydroxysuccinimide
(NHS) of 0.015 g were added to the solution and stirred
for 10 min to activate the carbonyl group on MGO.
Finally, modified PAMAM dendrimer (3 ml) was added
dropwise to the system, and the reaction was allowed to
proceed at 25 ̊C for 1 day. The precipitate was collected
by an external magnetic field, washed with deionized
water and ethanol 3 times, and finally dried in a vac-
uum at 343(k). The resulting dark‐brown precipitates
of modified G2 PAMAM‐MGO were ready to use.

TARAHOMI ET AL.
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NMR (100.6 MHz, DMSO‐d6), δ: 160.15, 133.58, 132.30,
129.60, 128.79, 128.32, 124.03, 115.88, 89.95, 88.22,
55.08 ppm. IR (KBr)/ (cm−1); 2231, 1592, 1241, 1169,
1142, 830, 758, 698. MS (EI, 70 eV) m/z (%): 208 [M+],
193, 177, 76.
2.4 | Immobilization of Pd nanoparticles
on MGO‐D‐NH2 (Pd@MGO‐D‐NH2)
Pd supported on dendrimer‐functionalized graphene
oxide‐based catalyst (MGO‐D‐NH2) was obtained by incip-
ient wet impregnation method. In this procedure, the dried
support (0.5 g) was impregnated with dried dichlorometh-
ane solution (15 ml) of PdCl2 (0.02 g, Aldrich 99%), and
2.6.3 | 1‐nitro‐4‐(phenylethynyl)benzene
(entry 5)
then stirred at 25 ̊C overnight. The chemical reduction pro-
cess reduced Pd (II) to Pd nanoparticles. In this procedure,
a solution of sodium borohydride in methanol (10 ml,
0.2 M) was prepared. Then the prepared solution was
added dropwise to the suspension under vigorous stirring
for 4 hr to complete the reduction process. As a final point,
the resulting precipitate was filtered and three times
washed with methanol, and then dried in oven vaccum at
343 (k) for 24 hr to obtain Pd@MGO‐D‐NH2.
1H NMR (400.13 MHz, DMSO‐d6), δ: 8.18–8.30 (m, 2H),
7.60–7.83 (m, 2H), 7.50 (dt, J = 5.5, 2.1 Hz, 2H), 7.23–
7.31 (m, 3H). 13C NMR (100.6 MHz, DMSO‐d6), δ: 146.8,
132.5, 132.2, 130.8, 129.5, 128.4, 123.2, 122.2, 94.4, 87.3.
IR (KBr) /ν (cm−1); 2942, 2220, 1585, 1522, 1368, 850.
MS (EI, 70 eV) m/z (%): 223 [M+], 193, 177, 165,151, 76.
2.6.4 | 4‐(phenylethynyl)benzaldehyde
(entry 7)
2.5 | Typical procedure for the catalytic
Sonogashira cross‐coupling reaction
1H NMR (400.13 MHz, DMSO‐d6), δ: 10.14 (s, 1 H), 7.78
(d, J = 8.4 Hz, 2H), 7.72 (d, J = 8.2 Hz, 2 H), 7.48–7.69
2 H), 7.32–7.49 (m, 3
H) ppm. 13C NMR
Pd@MGO‐D‐NH2 (20 mg) and K2CO3 (4.0 mmol) were
added to reaction mixture of H2O: EtOH (1:1, v:v),
followed by 1 mmol of phenylacetylene and 1 mmol of
Aryl halide. The reaction mixture was refluxed at
100 °C, stirred vigorously, and monitored using TLC in
n‐hexane as eluent until the start is completely disap-
peared. After completion of the reaction, the catalyst
was removed from the reaction mixture via an external
magnetic field, and then the mixture was allowed to cool
down to room temperature. The product was purified by
column chromatography over deactivated silica gel using
pure n‐hexane as eluent to furnish a crude product.
(m,
(100.6 MHz, DMSO‐d6), δ: 192.22, 192.16, 136.21, 132.78,
132.59, 130.39, 130.30, 129.68, 129.15, 123.24, 94.32,
89.02 ppm. IR (KBr)/ν (cm−1); 3058, 2854, 2216, 1700,
1600. MS (EI, 70 eV) m/z (%): 206 [M+], 177, 76.
2.7 | Recyclability evaluation of
Pd@MGO‐D‐NH2
The catalyst was recovered from the reaction mixture
after completion of the reaction using an external mag-
netic, and then it was washed with hot ethanol 3 times
and vacuum‐dried at 333 k overnight.
2.6 | Selected spectral data
3 | RESULTS AND DISCUSSION
2.6.1 | 1,2‐diphenylethyne (entry 1)
With respect to our interest in the design, synthesis and
characterization of novel heterogeneous nanocata-
lysts,[22,40,44] we report a novel experimental protocol for
preparation of Pd@MGO‐D‐NH2. As illustrated in
scheme 1, the catalyst was prepared using an approach
which includes several steps. In the first step, GO and
MGO was prepared. The following step was the covalent
attachment of modified PAMAM dendrimer (G. 2) with
MGO using EDC/NHS.[40] In the final step, Pd NPs were
immobilized on the dendrimer‐functionalized graphene
oxide through graft interactions between free chelating
amino groups of dendrimer and Pd precursor. Then, the
catalyst was characterized by FT‐IR analysis, SEM‐EDS,
elemental mapping analysis, BET, and TEM.
1H NMR (400.13 MHz, DMSO‐d6), δ: 7.52 (ddd, J = 6.4,
4.0, 2.8 Hz, 4H), 7.28–7.40 (m, 6H). 13C NMR
(100.6 MHz, DMSO‐d6), δ: 131.2, 128.6, 127.2, 122.1,
89.1. IR (KBr) /νcm−1); 3061, 2930, 1580, 1489, 1450,
1284, 1072, 762, 677. MS (EI, 70 eV) m/z (%): 178 [M+],
152, 126, 76.
2.6.2 | 1‐methoxy‐4‐(phenylethynyl)ben-
zene (entry 4)
1H NMR (400.13 MHz, DMSO‐d6), δ: 7.50 (dd, J = 8.1,
1.5 Hz, 2 H), 7.42 (d, J = 8.9 Hz, 2 H), 7.30–7.42 (m, 3
H), 6.92 (d, J = 8.9 Hz, 2 H), 3.63 (s, 3 H) ppm. 13C

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TARAHOMI ET AL.
SCHEME 1 The synthetic procedure for the preparation of pd@MGO‐D‐NH2.
analysis was implemented to elucidate the composition
of the catalyst, Figure 1.
3.1 | Catalyst characterization
The characterization of Pd@MGO‐D‐NH2 was performed
using various kinds of techniques including SEM‐EDS,
elemental mapping, BET, TEM, and FT‐IR. To character-
ize the structure of the catalyst, a detailed SEM‐EDS
The SEM‐EDS images of the catalyst Figure 1, showing
the distribution of the N, Fe, O, C, N and Pd elements.
Therefore the immobilization of Pd(0) nanoparticles was
confirmed. The presence of N atoms in the EDS pattern,

TARAHOMI ET AL.
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FIGURE 1 The SEM‐EDS of
Pd@MGO‐D‐NH2
can be ascribed to the incorporation of polyamidoamine
on the catalyst (Figure 1). Also the percentage of ele-
ments in proved our claim (Table 1). However, the struc-
ture of the catalyst cannot be confirmed solely by SEM‐
EDS, other measurement techniques have been
employed. Further, the elemental mapping analysis of
Pd@MGO‐D‐NH2 (Figure 2) demonstrates the uniform
distribution of N, C, Fe, O and Pd elements which is con-
firmed by the TEM observation, Figure 3.
TABLE 1 The percentage of elements with EDS‐analysis
Elt
C
N
O
Fe
Pd
W%
A%
13.66
28.68
2.48
4.47
26.55
41.86
53.09
23.98
4.22
1:00
Also, the catalyst was evaluated by an inductively –
optical emission spectrometry (ICP‐OES) to measure the
accurate content of Pd. The content of pd was calculated

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TARAHOMI ET AL.
FIGURE 2 The elemental mapping of Pd@MGO‐D‐NH2
to be 5.57 %W (1.04 mol%) which is another proof for the
fact that palladium nanoparticles was be immobilized
onto the Pd@MGO‐D‐NH2 catalyst.
proves the existence of the nitrogen‐containing functional
groups.[40,45]
The BET surface area (SBET), average pore diameter
and total pore volume of the catalysts was determined
via nitrogen adsorption/desorption isotherms, Figure 5.
As indicated in Table 2, the measured SBET of the MGO‐
D‐NH2 and Pd@MGO‐D‐NH2 were 86.4 m2 g−1 and
77.9 m2 g−1. It is possible to deduce that upon decoration
of PAMAM dendrimer and incorporation of palladium
NPs, the SBET of the catalyst was decreased, Table 2.
Moreover, it can be concluded that the total pore
volumes and average pore diameter of the catalysts
decreased in the order of MGO‐D‐NH2 > Pd@MGO‐D‐
NH2, which confirmed that the inner cavity of PAMAM
dendrimer and graphene oxide could be occupied by Pd
NPs.
TGA can evaluate the thermal stability and bond for-
mation of materials. The TGA results of MGO, MGO‐D‐
NH2, and Pd@MGO‐D‐NH2 is indicated in Figure 6. A
slow weight loss at low temperature (<100 °C) can be
observed, which can be assigned to the loss of adsorbed
water. Then the stage of weight reduction occurred
around 200 °C, indicating the decomposition and vapori-
zation of various oxygen‐containing functional groups at
In order to characterize the morphology of the
Pd@MGO‐D‐NH2 catalyst, TEM images of catalyst were
acquired, Figure 3a & b. According to TEM images of
the catalyst (Figure 3.), the layered morphology of the
GO was preserved upon decoration of PAMAM dendri-
mer and incorporation of palladium NPs. Moreover, the
small spots on GO sheet, on the surface of the dendrimer
and in the dendritic cavity in the TEM images can be
ascribed to the Pd NPs. According to the results of
TEM images, it can be concluded that MGO‐D‐NH2 cat-
alyst was effective in suppression the aggregation of the
Pd NPs. Additionally, the Pd particle size distribution
was determined based on TEM characterization,
Figure 3c.
In the FT‐IR pattern of MGO‐D‐NH2 (Figure 4a) the
bands at 2923 and 2863 cm−1 are assigned to alkyl
group(C‐H stretch) in the Modified polyamidoamine.
The characteristic peaks of MGO‐D‐NH2 at 1639, 1547
and 1434 cm−1 were attributed to NH deformation vibra-
tion of primary amine, the coupling of N–H bending and
C–N stretching of amide. Also, the peak 3435 cm−1

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FIGURE 3 The TEM image of Pd@MGO‐D‐NH2
different positions on the surface of the MGO. The TGA
curve of MGO‐D‐NH2 (4b) indicates a weight loss
between 200 and 600 °C is assigned to modified PAMAM
dendrimer.[40] Also, same weight‐loss profile is achievable
for Pd@MGO‐D‐NH2.
The TGA curve of the Pd@MGO‐D‐NH2 reveals an ini-
tial ascending behavior, unlike MGO and MGO‐D‐NH2,
due to the buoyancy effect of the instrument in which
the differences in heat capacity and thermal conductivity
of the purging gas can lead to initial weight gain for the
sample and platinum pan.
3.2 | Activity assessment of Pd@MGO‐D‐
NH2 catalyst
The activity, recovery and reuse of the catalyst is highly
preferable due to the importance of expanding eco‐
FIGURE 4 The FTIR spectrum of prepared a) MGO‐D‐NH2 and
b) Pd@MGO‐D‐NH2

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TARAHOMI ET AL.
FIGURE
6
The TGA curves of MGO, MGO‐D‐NH2 and
Pd@MGO‐D‐NH2
phenylacetylene(1 mmol) was chosen as a model reaction
to evaluate the catalytic activity of Pd@MGO‐D‐NH2
(scheme 2).
According to the section 2.4. (experimental section)
the catalyst was prepared with different loading, Table 3
Then, the reaction parameters, such as different cata-
.
lysts, bases, solvents, duration, temperature, and catalyst
loading were investigated and optimized to gain the opti-
mal reaction parameters. The optimized reaction condi-
tions were applied to cross‐coupling reaction and the
results are summarized in Table 4.
As tabulated in Table 4, solvent screening demon-
strated that the mixture of water/ethanol (1:1, v/v) was
the best choice in the reaction. Also, among the screened
bases (KOH, NaOH, K2CO3, DABCO and KO‐tBu), K2CO3
proved to be the best and was thus chosen as the base in
the coupling reaction. Also, the optimal amount of the
Pd@MGO‐D‐NH2 catalyst was 20 mg (A, 0.52 mmol/g,
1.04 mol%) at reflux and water/ethanol (1:1, v/v)
conditions.
As can be seen in the Table 4, the doping of trace pal-
ladium into MGO‐D‐NH2 can amazingly increase the
yield of the desired reaction products (Table 4, entry 8).
In an attempt to confirm the utility of this catalyst, the
coupling reaction of phenylacetylene and a broad variety
FIGURE 5 A: Nitrogen adsorption/desorption isotherms (a) and
BJH‐plot (b) of the MGO‐D‐NH2. B: Nitrogenadsorption/desorption
isotherms (c) and BJH‐plot (d) of the pd@MGO‐D‐NH2
TABLE 2 Textural properties of the MGO‐D‐NH2 and Pd@MGO‐
D‐NH2
SBET
Total pore volume Average pore
Catalyst
(m2 g−1) (cm3 g−1
)
diameter (nm)
SCHEME
Diphenylacetylene derivatives.
2
Pd@MGO‐D‐NH2–catalyzed
synthesis
of
MGO‐D‐NH2 86.4
0.34
0.23
15.79
11.83
Pd@MGO‐D‐ 77.9
NH2
TABLE 3 Preparation of Pd@MGO‐D‐NH2 with different
amount of PdCl2
friendly procedures for Sonogashira coupling reaction.
Also, the catalytic activity of Pd@MGO‐D‐NH2 was scru-
tinized. The reaction of iodobenzene (1 mmol) with
Entry
A
B
C
D
E
Amount of PdCl2 (mg)
20
10
5
2
1

TARAHOMI ET AL.
9 of 13
TABLE 4 Optimization of reaction conditionsa
Time
(h)
Yield
(%)
Entry
Reaction condition
1
GO (30 mg), K2CO3, water/ethanol (1:1, v/v), reflux
10
trace
trace
20
2
MGO (30 mg), K2CO3,water/ethanol (1:1, v/v), reflux
8
3
MGO‐D‐NH2 (30 mg), K2CO3,water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (A, 30 mg), K2CO3, water/ethanol (1:1, v/v), 25 °C
Pd@MGO‐D‐NH2 (A, 30 mg), K2CO3, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (A, 30 mg), K2CO3, water/ethanol (1:4, v/v), reflux
Pd@MGO‐D‐NH2 (A, 20 mg), K2CO3,water/ethanol (1:1, v/v), 25 °C
Pd@MGO‐D‐NH2 (A, 20 mg), K2CO3, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (B, 20 mg), K2CO3, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (C, 20 mg), K2CO3, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (D, 20 mg), K2CO3, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (E, 20 mg), K2CO3, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (A, 20 mg), K2CO3, water, reflux
5
4
2:15
60
5
1
95
6
1
95
7
2:30
1
55
8
95
9
1
92
10
11
12
13
14
15
16
17
18
19
20
21
1
90
1
85
1
82
2
60
Pd@MGO‐D‐NH2 (A, 20 mg), K2CO3, ethanol, reflux
1
85
Pd@MGO‐D‐NH2 (A, 20 mg), K2CO3, water, 25 °C
3
45
Pd@MGO‐D‐NH2 (A, 20 mg), K2CO3, CHCl3, reflux
1:30
2
60
Pd@MGO‐D‐NH2 (A, 20 mg), K2CO3, Toluene, reflux
65
Pd@MGO‐D‐NH2 (A, 20 mg), KOH, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (A, 20 mg), NaOH, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (A, 20 mg), DABCO, water/ethanol (1:1, v/v), reflux
Pd@MGO‐D‐NH2 (A, 20 mg), KO‐tBu, water/ethanol (1:1, v/v), reflux
2
50
2
45
2
30
2
50
aiodobenzene(1 mmol), phenylacetylene(1 mmol).
of halobenzene with different electronic and steric prop-
erties were investigated to the synthesis of desired prod-
ucts, Table 5.
Hence, it can be deduced from the Table 5, that a wide
range of halobenzenes can be used for this purpose.
Moreover, it has also been demonstrated, within the
TABLE 5 Effect of Pd@MGO‐D‐NH2 catalyst for Sonogashira reaction
Entry
Aryl halide
product
Time (h)
Yield (%)
Melting point
1
1
95
58–60[46]
2
3
4
5
6
7
2
1:45
2
85
88
70
90
90
95
58–60[46]
112–114[46]
61–63[46]
1:45
1:15
00:40
112–114[46]
97–99[47]
101–103[46]
8
00:50
90
101–103[46]

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TARAHOMI ET AL.
TABLE 6 Comparison of catalytic activity of Pd@MGO‐D‐NH2 with some reported catalysts in the Sonogashira coupling reactiona
Time
(h)
Yield
(%)
Entry
Reaction condition
1
2
3
4
5
6
Pd(0)/MCoS‐1, Et3N,H2O,90 °C[48]
Nanopolymer‐supported palladium (II) complex, Et3N, TBAB, H2O, 70 °C[49]
PdNPs@EDACs, K2CO3, CuI, H2O,80 °C[50]
6
6
94
94
98
93
95
95
7
Fe3O4@SiO2/Schiff base/Pd (II), K2CO3, DMF, 90 °C[51]
Pd@Hal‐P‐CD, H2O:EtOH (1:1), 60 °C[52]
1
1:15
1
Pd@MGO‐D‐NH2, K2CO3, H2O:EtOH (1:1), reflux (This work)
aiodobenzene(1 mmol), phenylacetylene(1 mmol).
SCHEME 3 The plausible mechanism of the sonogashira coupling reaction.
halobenzene series, iodobenzenes exhibited the higher
yields and shorter reaction times due to their more
reactivity.
According to Table 5, using of the catalyst Pd@MGO‐
D‐NH2 produced the desired products in higher yields
and shorter reaction times, compared to several reported
protocols. Additionally, this procedure avoids hazardous
material and can be used as a promising alternative to
the existing procedures. Also the reactions proceeded
under mild reaction conditions. Remarkably, Compared
to homogeneous catalysts traditionally applied in organic
transformation, the heterogeneous Pd@MGO‐D‐NH2 cat-
alyst can be recovered and reused for subsequent reac-
FIGURE 7 Recycling of Pd@MGO‐D‐NH2. Reaction conditions:
phenylacetylene (1 mmol), Aryl halide (1mmol), K2CO3
(4.0 mmol), Pd@MGO‐D‐NH2 (20 mg) with water/ethanol (1:1, v/v)
at reflux 100 °C.
tions without significant loss in its activity.
Moreover, the efficiency of Pd@MGO‐D‐NH2 catalyst
was confirmed with comparing the yield of the model

TARAHOMI ET AL.
11 of 13
reaction under Pd@MGO‐D‐NH2 catalyst and other
reported catalysts, Table 6. As presented in Table 6,
Pd@MGO‐D‐NH2 illustrated the best catalytic perfor-
mance in comparison to the other counterparts according
to the values of time and yield.
According to the reaction procedure, initially the
Pd@MGO‐D‐NH2 catalyst activates the terminal C‐H of
phenyl acetylene. Then, terminal C‐H of phenyl acetylene
can be deprotonated by K2CO3 to form potassium
acetylide. Also Pd@MGO‐D‐NH2 catalyst activates ArX
and forms arylpalladium halide complex (ArPdX). For
the next step, the halide can be displaced to form
A plausible mechanism for the Pd@MGO‐D‐NH2‐cata-
lyzed coupling reaction is illustrated in Scheme 3.
FIGURE 8 The TEM images of
Pd@MGO‐D‐NH2 a) before use and b)
after four runs

12 of 13
TARAHOMI ET AL.
TABLE 7 Textural properties of the Pd@MGO‐D‐NH2 a) before
use b) after 4 runs
4 | CONCLUSIONS
In summary, we have reported an efficient approach for
immobilizing Pd nanoparticles on the ternary hybrid sys-
tem of graphene oxide, Fe3O4 nanoparticles, and
PAMAM dendrimer as an efficient support for catalyzing
sonogashira coupling reaction in H2O:EtOH (1:1) at
reflux. The activity, recovery and reuse of the catalyst is
highly preferable due to the importance of expanding
eco‐friendly procedures for Sonogashira coupling
reaction.
SBET
Total pore
Average pore
Catalyst
(m2 g−1) volume (cm3 g−1) diameter (nm)
Pd@MGO‐D‐
77.9
77.6
0.23
0.20
11.83
11.79
a
NH2
Pd@MGO‐D‐
b
NH2
arylpalladium acetylide. In the last step, the desired cou-
pling product can be produced by reductive elimination.
The advantages of the present procedure are based on
the high yields of products, simple operation, easy cata-
lyst separation, and absence of any toxic solvents.
3.3 | Recycling of catalyst and leaching
test
ACKNOWLEDGMENTS
We gratefully acknowledge financial support from the
Research Council of University of Mazandaran and par-
tial support from the Hakim Sabzevari University.
Further, we investigated the possibility of recycling of the
Pd@MGO‐D‐NH2 catalyst. To evaluate the recyclability
of the catalyst, the reaction of iodobenzene and
phenylacetylene in a 1:1 mole ratio was used as a model
reaction for Sonogashira reaction. Upon completion the
reaction in each run, the catalyst was recovered via a
magnet, and then washed with hot ethanol. So, it was
ready to be used for the next batch reaction under the
same conditions.
ORCID
Heshmatollah Alinezhad
https://orcid.org/0000-0002-
7189-2961
Behrooz Maleki https://orcid.org/0000-0002-0322-6991
The recyclability of the catalyst was investigated and
the results are presented in Figure 7. Recycling tests show
that the catalyst could be recycled up to four times with
virtually no loss in catalytic activity.
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