Pd@GO/Fe3O4/PAA/DCA: a novel magnetic heterogeneous catalyst for promoting the Sonogashira cross-coupling reaction

Article abstract of DOI:10.1080/00958972.2019.1640360

A hybrid system involving graphene oxide (GO), magnetic oxide (Fe₃O₄), acrylamide and dicyandiamide was prepared via amine functionalization of GO/Fe₃O₄ by means of covalent bonding with acrylamide and subsequent reaction with dicyandiamide to provide a multinitrogen containing polymer on the surface of GO. This hybrid system was utilized as a heterogeneous catalyst support for immobilizing Pd nanoparticles to provide the hybrid, Pd@GO/Fe₃O₄/PAA/DCA. This nano-Pd composite was characterized using Fourier transform infrared, transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometer, thermogravimetric analysis, X-ray diffraction, and ICP techniques and used for promoting Sonogashira cross-coupling under mild reaction conditions. This heterogeneous and magnetic catalyst was easily separated by external magnet and was reused in a model reaction, efficiently up to six times with slight loss of catalytic activity and Pd leaching, showing the suitability of GO/Fe₃O₄/PAA/DCA for embedding Pd nanoparticles. To check the effect of the number of surface nitrogens of the polymeric chain on the catalytic performance, the activity of the catalyst was compared with Pd@GO/Fe₃O₄/PAA; increased number of the surface nitrogens on the chain polymer leads to higher loading of Pd and lower the Pd leaching.

Full text of DOI:10.1080/00958972.2019.1640360

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Pd@GO/Fe3O4/PAA/DCA: a novel magnetic
heterogeneous catalyst for promoting the
Sonogashira cross-coupling reaction
Mansoureh Daraie, Majid M. Heravi & Shaghayegh Sadat Kazemi
To cite this article: Mansoureh Daraie, Majid M. Heravi & Shaghayegh Sadat Kazemi (2019):
Pd@GO/Fe3O4/PAA/DCA: a novel magnetic heterogeneous catalyst for promoting the Sonogashira
cross-coupling reaction, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2019.1640360
To link to this article: https://doi.org/10.1080/00958972.2019.1640360
View supplementary material
Published online: 18 Jul 2019.
Submit your article to this journal
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2019.1640360
Pd@GO/Fe3O4/PAA/DCA: a novel magnetic heterogeneous
catalyst for promoting the Sonogashira cross-
coupling reaction
Mansoureh Daraie, Majid M. Heravi and Shaghayegh Sadat Kazemi
Department of Chemistry, School of Science, Alzahra University, Vanak, Tehran, Iran
ABSTRACT
ARTICLE HISTORY
Received 20 April 2019
Accepted 21 June 2019
A hybrid system involving graphene oxide (GO), magnetic oxide
(Fe3O4), acrylamide and dicyandiamide was prepared via amine
functionalization of GO/Fe3O4 by means of covalent bonding with
acrylamide and subsequent reaction with dicyandiamide to pro-
vide a multinitrogen containing polymer on the surface of GO.
This hybrid system was utilized as a heterogeneous catalyst sup-
port for immobilizing Pd nanoparticles to provide the hybrid,
Pd@GO/Fe3O4/PAA/DCA. This nano-Pd composite was character-
ized using Fourier transform infrared, transmission electron
microscopy, scanning electron microscopy, vibrating sample mag-
netometer, thermogravimetric analysis, X-ray diffraction, and ICP
techniques and used for promoting Sonogashira cross-coupling
under mild reaction conditions. This heterogeneous and magnetic
catalyst was easily separated by external magnet and was reused
in a model reaction, efficiently up to six times with slight loss of
catalytic activity and Pd leaching, showing the suitability of GO/
Fe3O4/PAA/DCA for embedding Pd nanoparticles. To check the
effect of the number of surface nitrogens of the polymeric chain
on the catalytic performance, the activity of the catalyst was com-
pared with Pd@GO/Fe3O4/PAA; increased number of the surface
nitrogens on the chain polymer leads to higher loading of Pd and
lower the Pd leaching.
KEYWORDS
GO; Fe3O4; acrylamide;
dicyandiamide; Pd
nanoparticles; copper and
ligand-free; Sonogashira
cross-coupling reaction
CONTACT Majid M. Heravi
mmh1331@yahoo.com
ß 2019 Informa UK Limited, trading as Taylor & Francis Group

2
M. DARAIE ET AL.
1. Introduction
Organic chemistry is responsible for numerous fascinating natural phenomena. By
studying organic chemistry man has learnt how to augment nature’s chemistry, how
to build carbon-based functional molecules: drugs, plastics, and other high-technical
materials [1]. Therefore, the art of carbon–carbon bond formation and especially cross-
coupling CC bond formation are important for synthetic organic chemists [2].
Pd-catalyzed cross-coupling reactions are numerous and the design of new homo-
geneous and heterogeneous palladium-based catalysts has attracted much attention
[3–5]. Importance of this field has been proven by the Nobel Prize in Chemistry in
2010 to Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki for their outstanding work
on applications of palladium-catalyzed cross-coupling reactions [6]. Sonogashira reac-
tion is another important Pd-catalyzed cross-coupling reaction; the alkynylation reac-
tion of aryl halides using aromatic acetylenes was reported in 1975 in three
independent contributions by Cassar [7], Dieck and Heck [8], as well as
Sonogashira [9].
Sonogashira reaction is one of the most important and powerful methods for CC
bond formation involving the cross coupling between terminal sp hybridized carbon
of an alkyne with a sp2 carbon of an aryl or vinyl halide (or triflate) [9]. The classic Pd-
catalyzed Sonogashira cross reaction involves the reaction of a halide and a terminal
alkyne in the presence of Pd(II) salts such as chloride or acetate and ligands such as
phosphines and phosphates, copper salt (as co-catalyst) and an amine to form an aryl
acetylene under anaerobic conditions [10, 11]. The products obtained from this reac-
tion can be used for the synthesis of substituted alkynes [7] in the total synthesis of
several natural products [12], pharmaceutical complex molecules [13], polymeric and
optical materials [14].
Bearing in mind, the high price of palladium salts and ever-growing concerns to
protect the environment that demand green chemistry be considered for designing
and conducting organic transformations for the synthesis of target molecules. A facile,
efficient and eco-friendly strategy for the preparation of the stable palladium species
has attracted much attention. In particular low loading Pd-catalyzed Sonogashira
cross-coupling reaction has been catalyzed under copper and amine-free reaction con-
dition at atmospheric pressure [15–17].
In spite of superiority and merits of Pd-catalyzed, reactions, the palladium-catalyzed
C C bond formation, suffers from some drawbacks. To circumvent some of these
problems, Pd species has been immobilized to various solid supports in order to pre-
pare heterogeneous catalysts with advantages such as easy separation leading to its
possible reusability, making it being cost-effective as well as conducted under green
conditions [18].
In addition, use of Pd-nano particles (Pd NPs), immobilized onto suitable supports
such as silica, polymers or carbon is even more favorable. Such immobilization makes
these expensive catalysts recoverable and reusable [1, 19, 20]. Because of good cata-
lytic activity, Pd NP is of great interest with potential to be used as heterogeneous cat-
alysts with unparalleled properties [21, 22]. However, dispersion of the chosen
catalytic material on suitable support is still investigated [23].

JOURNAL OF COORDINATION CHEMISTRY
3
In a nanocatalyst, surface to volume ratio implies a large number of active sites
which participate in reactions [24]. Such nanoparticle-based catalysts are generally
attached to solid materials such as graphene [25, 26], graphene oxide (GO) [27, 28],
carbon nanotubes [29], activated carbon [30], zeolites [31], silica, or polymeric materi-
als [32] for easy separation. Among these, GO is a promising supporting material for
Pd catalysts. GO is a resistant two-dimensional molecule, with the thickness of a car-
bon atom, but with high strength due to the d-type bonds and the resonance charac-
teristics in the p-type bonds of the carbons with sp2 hybridization [33]. GO also has
high stability and properties of a low annular tension aromatic polycycle [34].
Furthermore, structural defects in GO can be useful as they make it possible to achieve
new surface functionalities which enhance the interactions with the anchored metal
nanoparticles [35].
GO is usually synthesized by exfoliation of graphite oxide obtained by oxidation of
natural graphite powder with various oxidants in acidic media [36]. Introducing oxy-
genated groups destroyed the conjugated structure of graphite. Therefore, a heavily
oxidized GO is a nonconductor. The oxygen functionalities have been identified as
mostly in the form of hydroxyl and epoxy groups on the basal plane and smaller
amounts of carboxyl, carbonyl, phenol, lactone, and quinone at the sheet edges, which
renders it a good candidate for immobilization of a large number of substances
including metals such as Pd, Cu, Pt, etc. [37]. The association of NPs immobilized on
GO can be prevented and the catalytic activity of NPs-GO can be modified owing to
the synergistic interaction between both components. Magnetic nanoparticles sup-
ported on various materials have provided new ways to develop recyclable catalyst
[38]. Fe3O4 nanoparticles are easily synthesized and functionalized by metal and orga-
nocatalysts and can be easily separated from the reaction mixture by external mag-
netic field and reused [39].
In continuation of our study of the preparation of nano metal particles [40–42] and
their immobilization on supports especially, GO and magnetic Fe3O4 [43–47] as well as
our interest in the Sonogashira cross-coupling reaction [48, 49], we introduce a simple,
fast and effective strategy for preparation and characterization of palladium(II) immobi-
lized on GO/Fe3O4 NPs coated with decorated polyacrylamide and dicyandiamide
(Pd@GO/Fe3O4/PAA/DCA) as a new magnetic heterogeneous catalyst and its application
in Sonogashira CC cross-coupling reaction as an efficient, green and reusable catalyst.
2. Experimental
2.1. Materials and measurements
The chemicals used for preparation of Pd@GO/Fe3O4/PAA/DCA and studying its cata-
lytic activity included graphite powder, iron(III) chloride hexahydrate FeCl3ꢀ6H2O,
iron(II) chloride tetrahydrate FeCl2ꢀ4H2O, 3-(trimethoxysilyl)propyl methacrylate
(MAPTMS), acrylamide, potassium peroxydisulfate (KPS), Dicyandiamide (DCA), triethyl-
amine, toluene, Pd(OAc)2, Stevia,halobenzenes, phenylacetylene, propargyl alcohol,
K2CO3, Cs2CO3, KOH, NaOH, distilled water, and EtOH, all provided from Sigma-Aldrich
and used as received. All other chemicals and reagents used in the study were analyt-
ical grade. The progress of CC coupling reactions was monitored by using thin layer

4
M. DARAIE ET AL.
chromatography (TLC) on commercial aluminum-backed plates of silica gel 60 F254,
visualized using ultraviolet light.
The formation of Pd@GO/Fe3O4/PAA/DCA was confirmed by characterization techni-
ques, including Fourier transform infrared (FT-IR, Perkin Elmer Spectrum 65 instrument)
spectroscopy, X-ray diffraction (XRD, Siemens D5000 with Cu Ka radiation from a
sealed tube), scanning electron microscopy (SEM), transmission electron microscopy
(TEM), thermogravimetric analysis (TGA, Mettler Toledo instrument with a heating rate
of 10 ꢁC minꢂ1, under nitrogen) and vibrating sample magnetometer (VSM, ꢂ10,000 to
þ10,000 Oe at room temperature). The amount of Pd species supported on GO/Fe3O4/
PAA/DCA was also measured by applying an ICP analyzer (Varian, Vista-pro).
2.2. Synthesis of GO and GO/Fe3O4 composite
GO was synthesized from graphite powder as described previously [50]. To synthesize
the GO/Fe3O4 composite, 0.5 g of synthesized GO was poured in 200 mL of distilled
water under stirring for 30 min. After that, 3.5 g of FeCl3ꢀ6H2O was added into the mix-
ture under vigorous stirring and purging of N2 gas for 30 min. Then, 0.65 g of
FeCl2ꢀ4H2O was added into the mixture under N2 atmosphere. Finally, to this mixture
an ammonia solution (25%, 120 mL) was added, diluted by addition of 200 mL water
and the suspension was refluxed for 2 h. The GO/Fe3O4 composite was dried at 50 ꢁC
under vacuum overnight.
2.3. Functionalization of GO/Fe3O4 with 3-(trimethoxysilyl)propyl methacrylate
(MAPTMS): Synthesis of GO/Fe3O4/MAPTMS
To prepare the catalyst, GO/Fe3O4 was first functionalized with 3-(trimethoxysilyl)-
propyl methacrylate; 1 g of GO/Fe3O4 and 1 mL (5 mmol) of MAPTMS were stirred in
25 mL dry toluene under N2 gas at ambient temperature overnight. After that, the
resulting product was magnetically collected and washed several times with toluene
and dried at 35 ꢁC overnight in an oven.
2.4. Polymerization and synthesis of GO/Fe3O4/PAA nanocomposite
GO/Fe3O4/MAPTMS (1.2 g) was suspended in distilled water and sonicated under ultra-
sonic irradiation (100 W) for 30 min. Subsequently, acrylamide (1.2 g) and KPS (0.6 mg) as
the polymerization initiator were added to the reaction mixture and kept at 60ꢁC for 12h
to complete the polymerization. Finally, the precipitate was filtered and washed with H2O
repeatedly. GO/Fe3O4/PAA was achieved after drying for 12 h at 70 ꢁC.
2.5. Conjugation of DCA to GO/Fe3O4/PAA: Synthesis of GO/Fe3O4/PAA/DCA
GO/Fe3O4/PAA/DCA was synthesized by reaction of DCA (0.5 g), triethylamine (0.5 mL),
and GO/Fe3O4/PAA (1 g) under reflux in H2O (25 mL) for 24 h. After completion of the
reaction, the precipitate was filtered, washed with distilled water several times and
dried in an oven for 24 h at 70 ꢁC.

JOURNAL OF COORDINATION CHEMISTRY
5
2.6. Immobilization of Pd nanoparticles on GO/Fe3O4/PAA/DCA by using Stevia
as a reducing agent: Pd@GO/Fe3O4/PAA/DCA
To incorporate Pd nanoparticles on GO/Fe3O4/PAA/DCA, GO/Fe3O4/PAA/DCA (1.2 g)
was suspended in distilled water (15 mL) containing Pd(OAc)2 (0.02 g) and then stirred
at ambient temperature for 12 h. Then, a solution of Stevia in methanol (10 mL) was
added to the reaction mixture and stirred for five more hours. The final product
(Pd@GO/Fe3O4/PAA/DCA) was obtained by an external magnet, washing (three times
with methanol) and drying in the oven at 60 ꢁC overnight (Scheme 1).
Scheme 1. The schematic route for preparation of Pd@GO/Fe3O4/PAA/DCA.

6
M. DARAIE ET AL.
Scheme 2. Sonogashira reaction in the presence of Pd@GO/Fe3O4/PAA/DCA.
2.7. Typical procedure for Sonogashira reaction
Pd@GO/Fe3O4/PAA/DCA (10 mol%) and K2CO3 (3 mmol) were added to a mixture of
halobenzene (1 mmol) and acetylene (1.2 mmol) in water:EtOH (2:1) as the solvent
(Scheme 2). The reaction mixture was then refluxed for appropriate reaction time.
The progress of the reaction was monitored by TLC. At the end of the reaction,
the catalyst was filtered by an external magnet. After that, the organic layer was
extracted with diethyl ether and purified by column chromatography over silica gel
by using hexane/ethyl acetate (4:1) as eluent to furnish the corresponding product.
Upon completion of the coupling reaction, to recycle the catalyst, the recovered
catalyst was washed with EtOH two times and dried in the oven at
90 ꢁC overnight.
3. Results and discussion
The goal of this study was developing a new GO support decorated with acrylamide,
dicyandiamide, and Fe3O4 for immobilization of Pd(0). Using Fe3O4 leads to easy separ-
ation of the catalyst from the reaction medium with an external magnet after comple-
tion of the reaction. At first, GO was prepared from graphene using Hummer’s method
[50]. Then, graphene magnesium oxide was obtained by using FeCl2ꢀ4H2O and
FeCl3ꢀ6H2O salts. The surface of magnetic GO was modified using MAPTMS, leading to
formation of C[dbond]C bonds on GO. Subsequently, acrylamide and dicyandiamide
were used to produce the polymeric network. Pd(ii) salt was then added to GO/
Fe3O4/PAA/DCA, reduced by Stevia and finally Pd@GO/Fe3O4/PAA/DCA was obtained.
3.1. Catalyst characterization
FTIR spectroscopy was employed to establish the structure of Pd@GO/Fe3O4/PAA/
DCA (Figure 1). FTIR spectra of GO/Fe3O4, GO/Fe3O4/MAPTMS, GO/Fe3O4/PAA and
GO/Fe3O4/PAA/DCA were also recorded and compared with that of GO/Fe3O4/PAA/
DCA. In the FTIR spectrum of GO/Fe3O4, the bands at 3393, 1617, 1047, and
587 cmꢂ1 indicate –OH group vibration, C ¼ O stretching vibration of carbonyl, C – O
stretching group of alkoxy and Fe–O stretching vibration, respectively.
In GO/Fe3O4/MAPTMS (Figure 1(b)), bands as a broad peak between 1050 and
1116 cmꢂ1 indicate vibration of Si–O–Si. The presence of the vibration bands at 2924,
1715, 1633, and 1166 cmꢂ1 which can be assigned, respectively, to CH2, C[dbond]O,
C[dbond]C, and CO stretching can prove functionalization of MAPTM to the surface
of GO/Fe3O4. After the polymerization step, bands at 1634 cmꢂ1 and 3250–3450 cmꢂ1
are due to CONH2 and NH, respectively (Figure 1).

JOURNAL OF COORDINATION CHEMISTRY
7
Figure 1. The FTIR spectra of (a) GO/Fe3O4, (b) GO/Fe3O4/MAPTMS, (c) GO/Fe3O4/PAA, (d) GO/
Fe3O4/PAA/DCA, and (e) Pd@GO/Fe3O4/PAA/DCA.
Figure 2. SEM images of (a) GO and (b) Pd@GO/Fe3O4/PAA/DCA.
The FT-IR spectrum of GO/Fe3O4/PAA/DCA (Figure 1) also possesses the characteris-
tic bands of GO/Fe3O4, implying that the structure of GO/Fe3O4 is preserved upon
chemical functionalization with PAA and DCA. Moreover, additionally, the non-observa-
tion of the CN peak in 2230 represents connection of DCA to GO/Fe3O4/PAA.
The morphology of Pd@GO/Fe3O4/PAA/DCA was studied by recording the SEM
images of the catalyst (Figure 2). As depicted, upon decoration of polyacrylamide and
incorporation of DCA and Pd nanoparticles, the morphology of GO is preserved.
Compared to GO, Pd@GO/Fe3O4/PAA/DCA showed more compact morphology, which
can stem from intertwining of the polymeric chain.

8
M. DARAIE ET AL.
TEM image of Pd@GO/Fe3O4/PAA/DCA (Figure 3) shows that Fe3O4 and Pd nanopar-
ticles were distributed between the GO layers.
The Pd@GO/Fe3O4/PAA/DCA catalyst was also studied using EDX analysis (Figure 4).
As can be seen, EDX analysis illustrates presence of all the elements (O, C, N, Fe, Si
and Pd) onto the GO sheets.
XRD analysis, as a method for studying the structure of the catalyst, was also
employed to characterize the Pd@GO/Fe3O4/PAA/DCA (Figure 5). XRD patterns of GO/
Fe3O4 and Pd@GO/Fe3O4/PAA/DCA were obtained. Peaks at 2h ¼ 30.10ꢁ (220), 35.10ꢁ
(311), 43.4ꢁ (400), 51.70ꢁ (422), 57.40ꢁ (511), and 62.61ꢁ (440) can be attributed to the
structure of Fe3O4. Comparing the XRD patterns of the catalyst and GO/Fe3O4 reveals
some additional peaks at 2h ¼ 40.10 (110), 46.521 (200), and 68.25 (220), confirming
the presence of palladium.
Figure 3. TEM images of Pd@GO/Fe3O4/PAA/DCA.
Figure 4. EDX analysis of Pd@GO/Fe3O4/PAA/DCA.

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 5. The XRD patterns of Pd@GO/Fe3O4/PAA/DCA.
Figure 6. Room-temperature magnetization curve of Pd@GO/Fe3O4/PAA/DCA.
The magnetic properties of the Pd@GO/Fe3O4/PAA/DCA catalyst were determined
with a vibrating sample magnetometer (VSM) from ꢂ10,000 to þ10,000 Oe at room
temperature. The magnetization hysteresis loop of the composite was an S-like curve,
indicating that the composite was superparamagnetic (Figure 6). The saturation mag-
netization character of Pd@GO/Fe3O4/PAA/DCA was sufficient to ensure the easy and
quick separation of the compound from solutions.
The content of Pd nanoparticles in Pd@GO/Fe3O4/PAA/DCA was measured by using
ICP-AES analysis. To prepare the sample for analysis, Pd@GO/Fe3O4/PAA/DCA was fully
digested in concentrated hydrochloric and nitric acids mixture. Then, the extract was
subjected to the ICP-AES analysis. Using this method, the content of Pd in Pd@GO/
Fe3O4/PAA/DCA was calculated to be 2.47 w/w%.
Thermal stability of Pd@GO/Fe3O4/PAA/DCA was also investigated by using TGA
analysis (Figure 7). The thermogram of Pd@GO/Fe3O4/PAA/DCA exhibited several
weight losses. Thermogravimetric analysis (TGA) of GO/Fe3O4 (a) and Pd@GO/Fe3O4/
PAA/DCA nanocomposite (b) was further used to study the composition of the nano-
composite. The TGA of both materials show three main weight losses. In the thermo-
gram of GO/Fe3O4, these three steps observed at 100 ꢁC, 160–240 ꢁC, and 380–440 ꢁC
are attributed to the loss of water, dehydration of surface oxygen and hydroxyl groups
in GO decomposition of graphene structure, respectively.

10
M. DARAIE ET AL.
Figure 7. The TGA analysis of (a) GO/Fe3O4 and (b) Pd@GO/Fe3O4/PAA/DCA.
Figure 8. Reusability of the Pd@GO/Fe3O4/PAA/DCA.
In the thermogram of Pd/GO/Fe3O4/PAA/DCA, the first weight loss at 100 ꢁC was
attributed to desorption of water. The second weight loss from 200 ꢁC to 300 ꢁC is due
to dehydration of surface oxygen and hydroxyl groups in GO. The final weight loss
around 400–450 ꢁC indicates decomposition of the graphene structure. (Figure 7 The
comparison of the thermograms exhibits that the content of organosilane and poly-
mer were about 5.6 and 23.57 w/w%, respectively.
3.2. Catalytic activity
Catalytic activity of Pd@GO/Fe3O4/PAA/DCA was investigated for Sonogashira C C
coupling for synthesis of alkyne derivatives from the reaction of halobenzene and
acetylene in the absence of copper co-catalyst and ligand. The reaction of phenylace-
tylene and iodobenzene was selected as a model reaction and used for optimization
of the reaction variables such as solvent, temperature, base and catalyst amount
(Table 1). Comparing the yields of the model product in the presence of various

JOURNAL OF COORDINATION CHEMISTRY
11
Table 1. Optimization of reaction conditions for Sonogashira coupling reaction of iodobenzene
with phenylacetylene.
Entry
Reaction conditiona
Time (h)
Catalyst amount (mol %)
Base
Yield (%)b
1
2
3
4
5
6
7
8
H2O/ r.t
2.2
2.5
2
2
2
10
10
10
10
10
10
10
10
10
10
10
10
15
5
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
KOH
71
68
80
82
94
90
83
87
80
81
90
97
95
82
80
82
EtOH/ r.t
H2O/ 50 ꢁC
EtOH/ 50 ꢁC
H2O/ 96 ꢁC
EtOH/ 87 ꢁC
2
CH3OH/ 60 ꢁC
CH3CN/ 83 ꢁC
CHCl3/ 61 ꢁC
2.5
2.2
2.5
2.5
2
1.8
1.8
2.2
1.8
2.5
9
10
11
12
13
14
15
16
Toluene
H2O–EtOH (1:1)/ 72
H2O–EtOH (2:1)/ 86
H2O–EtOH (2:1)/ 86
H2O–EtOH (2:1)/ 86
H2O–EtOH (2:1)/ 86
H2O–EtOH (2:1)/ 86
10
10
NaOH
aReaction were run in 5 mL of solvent with 1 mmol of iodobenzene, 1.2 mmol of phenylacetylene, and 3 mmol
of base.
bIsolated yield.
solvents such as acetonitrile, toluene, water, chloroform, and H2O/EtOH showed that
the mixture of water and ethanol is the best choice for this reaction.
Eventually, use of K2CO3 as the base, H2O:EtOH (2:1) as the solvent, and 10 mol% of
the catalyst at 86 ꢁC led to high yield of the model product.
We report a highly selective method for preparation of various derivatives of diary-
lethynes by using of Pd@GO/Fe3O4/PAA/DCA in a modified Sonogashira reaction. In
contrast to the original Sonogashira method, very little Glaser Coupling product was
formed. Also, this method reduces the need to use excess arylethyne to promote the
cross-coupling efficiency.
In the following, the effect of the number of surface nitrogens on the catalytic
activity of the final catalyst was investigated. To this purpose, another catalyst,
Pd@GO/Fe3O4/PAA, was prepared and its catalytic efficiency in the synthesis of the
model product was checked.
The results showed that the order of the yield of the desired product in the pres-
ence of various catalysts varied in the following order: Pd@GO/Fe3O4/PAA/DCA (97%)
> Pd@GO/Fe3O4/PAA (60%) (Table 2). The difference of catalytic activity can be attrib-
uted to the different loading of Pd nanoparticle on the catalyst. To verify this assump-
tion and estimate the loading of Pd, two prepared catalysts were subjected to ICP
analysis. Loading of Pd in Pd@GO/Fe3O4/PAA/DCA was the highest (2.47 w/w%) while
Pd@GO/Fe3O4/PAA showed lower Pd content (0.10 w/w%), showing the role of the
number of surface nitrogens in anchoring Pd nanoparticles. Having the optimized
reaction conditions, the generality of this methodology was confirmed by applying dif-
ferent alkynes and aryl halides with electron-withdrawing and electron-donat-
ing groups.
Finally, catalytic activity of this system was used in Sonogashira cross coupling and
the result compared with those of some previously reported catalysts (Table 3). The
new palladium complex as a magnetic catalyst takes advantage of both magnetic and
functionalized surface. Recoverability, reusability, and easy separation of magnetic

12
M. DARAIE ET AL.
Table 2. Pd@GO/Fe3O4/PAA/DCA catalyzed Sonogashira reaction of various halides with ter-
minal alkynes.a
Entry
1
Aryl halide
Terminal alkyne
Product
Time (h)
1.8
Yieldb (%)
97
2
3
4
5
2
95
91
94
85
2.2
1.8
3.5
6
2.8
1.8
3.2
2.8
3.5
91
94
87
89
85
7
8
9
10
11
12
4
82
80
4.5
aReaction condition: aryl halide (1.0 mmol), terminal alkyne (1.2 mmol), Pd/GO/Fe3O4/PAA/DCA (10 mol%) and K2CO3
(3.0 mmol) in H2O:EtOH (2:1) at 86 ꢁC.
bIsolated yield.
nanocatalyst, and performing the reaction in a benign solvent are among the remark-
able advantages of the proposed synthetic method.
Comparison of the catalytic activity of Pd@GO/Fe3O4/PAA/DCA with other catalysts
showed the comparative catalytic activity of our catalyst. This catalyst also could pro-
mote the model reaction in the presence of cost-effective and nontoxic K2CO3 as base
in EtOH:H2O as green solvent while some of the tabulated catalysts required expensive
(Table 3, entry 1) or toxic bases (Table 3, entry 11) and/or solvents (Table 3, entries 2,
3, 5, 7, and 9–11). Furthermore, the reaction time and temperature required for com-
pletion of this reaction in the presence of Pd@GO/Fe3O4/PAA/DCA catalysis were lower
or comparative to the catalysts tabulated in Table 3 (entries 2, 3, 4, 5, and 7–12).
The properties which make our research better than previous procedures are mild
reaction conditions, environmentally benign, simple recycle of the nanocatalyst by an

JOURNAL OF COORDINATION CHEMISTRY
13
Table 3. Comparison of Pd@GO/Fe3O4/PAA/DCA with heterogeneous catalysts.
Entry
Catalyst
Time (h)Temp. (ꢁC)Yield (%) Solvent
Base
Ref.
1
2
3
4
5
6
7
8
9
[Pd(dppe)(OTf)2]
[(P^C)PdCl2]a
[(C^C)PdCl2]b
NiCl2.6H2O
24
6
4.5
2
48
2
3
48
6
3
24
2
60
130
130
120
135
80
120
125
145
135
140
90
70 CH3OH
81 DMF
87 DMF
86 EG
99 Toluene
95 EtOH
Cs2CO3[51]
K2CO3 [52]
K2CO3 [52]
NaOH [53
K3PO4 [54]
K2CO3 [55]
FeCl3.PPh3
PdCl2fC(N(H)-NPh2)@N(H)Cyg(C,,NCy)
[(Pdfk2-C,N)-(3-(dimethylaminomethyl)indole)gm-OAc)2]
85 DMF/H2O K2CO3 [56]
Et2Zn/DMEDA
CuI/Lc
54 Dioxane
90 DMF
55 DMF
65 Et3N
95 EtOH
93 H2O:acetoneNaOH [62]
97 EtOH:H2O K2CO3 This work
K3PO4 [57]
K2CO3 [58]
K2CO3 [59]
Et3N [60]
K2CO3 [61]
10 [N-benzyl DABCO]þ[Cu4Cl5]–
11 Cu(OAc)2
12 Pd@Hal-2N-TCT-EDA
13 [PdCl2(NH2CH2COOH)2
13 Pd@GO/Fe3O4/PAA/DCA
2
1.8
60
80
Reaction of iodobenzene with phenylacetylene.
aFive-membered palladacycle.
bSeven-membered analogs.
cN,N`-dibenzyl BINAM.
Scheme 3. Plausible reaction mechanism.
external magnet and reusability of the catalyst without considerable loss of cata-
lytic activity.
3.3. Reusability of the catalyst
Considering the importance of simple recovery and recyclability of heterogeneous cat-
alysts, the recyclability of Pd@GO/Fe3O4/PAA/DCA for catalyzing the model reaction
was investigated. After completion of each cycle, the catalyst was separated easily by
an external magnet. The catalyst was recovered, washed with EtOH, and recycled for
six reaction runs and the yields of the model product in the presence of the fresh and
recycled Pd@GO/Fe3O4/PAA/DCA were compared. Results showed no significant loss in
activity of catalyst after six reaction runs (about 0.008).
A plausible reaction mechanism is proposed in Scheme 3. In accordance with this
suggested mechanistic pathway, initially [Pd(0)L2] is oxidatively added to the aryl or
vinyl halide. Then, a reversible coordination of the alkyne occurs, generating an
alkyne–Pd(II) complex where the acetylenic proton is removed by the base along with

14
M. DARAIE ET AL.
coordination of the acetylene ligand to the metal. This [Pd(II)R1(C[tbond]CR2)L2] com-
plex releases the cross-coupled product by reductive elimination regenerating the
catalyst species [Pd(0)L2].
4. Conclusion
A hybrid catalyst, Pd@GO/Fe3O4/PAA/DCA, has been prepared by reacting functional-
ized GO/Fe3O4 with acrylamide and dicyandiamide, followed by immobilization of
Pd(0) nanoparticles. Pd@GO/Fe3O4/PAA/DCA catalyzed Sonogashira coupling in the
absence of copper and ligand under mild reaction conditions. To study the effect of
nitrogen atoms on the surface of GO, Pd@GO/Fe3O4/PAA was synthesized and com-
pared with Pd@GO/Fe3O4/PAA/DCA. The results show that Pd@GO/Fe3O4/PAA/DCA has
better performance due to the higher number of nitrogen atoms on GO.
Acknowledgments
The authors gratefully recognize partial financial support from Alzahra, University
research council.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
[1] N.Y. Baran. J. Mol. Struct., 1176, 266 (2019).
[2] B.H. Lipshutz, T. Butler, E. Swift. Org. Lett., 10, 697 (2008).
[3] F.-S. Han. Chem. Soc. Rev., 42, 5270 (2013).
[4] A.O. King, N. Okukado, E.-i. Negishi. J. Chem. Soc. Chem. Commun., 683 (1977).
[5] I.P. Beletskaya, A.V. Cheprakov. Chem. Rev., 100, 3009 (2000).
[6] T.J. Colacot. Platin. Met. Rev., 55, 84 (2011).
[7] L. Cassar. J. Organomet. Chem., 93, 253 (1975).
[8] H. Dieck, F. Heck. J. Organomet. Chem., 93, 259 (1975).
[9] K. Sonogashira, Y. Tohda, N. Hagihara. Tetrahedron Lett., 16, 4467 (1975).
ꢀ
[10] R. Chinchilla, C. Najera. Chem. Soc. Rev., 40, 5084 (2011).
[11] M.M. Heravi, S. Sadjadi. Tetrahedron, 37, 7761 (2009).
[12] K. Nicolaou, W.M. Dai. Angew. Chem. Int. Ed. Engl., 30, 1387 (1991).
[13] N.D. Cosford, L. Tehrani, J. Roppe, E. Schweiger, N.D. Smith, J. Anderson, L. Bristow, J.
Brodkin, X. Jiang, I. McDonald. J. Med. Chem., 46, 204 (2003).
€
[14] V. Francke, T. Mangel, K. Mullen. Macromolecules, 31, 2447 (1998).
[15] M. Esmaeilpour, A.R. Sardarian, H. Firouzabadi. J. Organomet. Chem., 873, 22 (2018).
[16] M. Khajehzadeh, M. Moghadam, S. Jamehbozorgi. Inorg. Chim. Acta, 485, 173 (2019).
[17] F. Zhu, P. Zhao, Q. Li, D. Yang. J. Organomet. Chem., 859, 92 (2018).
[18] X. Liu, D. Astruc. Adv. Synth. Catal., 360, 3426 (2018).
[19] S. Sadjadi, M. Malmir, M.M. Heravi, F.G. Kahangi. Int. J. Biol. Macromol., 118, 1903 (2018).
[20] M. Renuka, V. Gayathri. J. Organomet. Chem., 874, 26 (2018).
[21] Q. Wang, X. Jing, J. Han, L. Yu, Q. Xu. Mater. Lett., 215, 65 (2018).
[22] E. Ghonchepour, M.R. Islami, A.M. Tikdari. J. Organomet. Chem., 883, 1 (2019).
€
[23] R.Y. Parapat, O.H. Saputra, A.P. Ang, M. Schwarze, R. Schomacker. RSC Adv., 4, 50955
(2014).

JOURNAL OF COORDINATION CHEMISTRY
15
[24] G. Zhan. Chem. Eng. J., 355, 320 (2019).
[25] Y. Yang, A.C. Reber, S.E. Gilliland, C.E. Castano, B.F. Gupton, S.N. Khanna. J. Catal., 360, 20
(2018).
[26] T. Revathy, S. Dhanavel, T. Sivaranjani, V. Narayanan, T. Maiyalagan, A. Stephen. Appl. Surf.
Sci., 449, 764 (2018).
[27] J.C. Ng, C.Y. Tan, B.H. Ong, A. Matsuda, W.J. Basirun, W.K. Tan, R. Singh, B.K. Yap. Mater.
Res. Bull., 112, 213 (2019).
[28] N. Shang, C. Feng, H. Zhang, S. Gao, R. Tang, C. Wang, Z. Wang. Catal. Commun., 40, 111
(2013).
[29] M. Feng, Z.-H. Luo, R.-Q. Chen, S. Yi, H. Lu, G.-P. Cao, C. Lu, S.-Y. Feng, C.-Y. Li. Appl. Catal.
A, 570, 329 (2019).
[30] J. Zhou, Z. Lou, J. Xu, X. Zhou, K. Yang, X. Gao, Y. Zhang, X. Xu. Chem. Eng. J., 358, 1176
(2019).
[31] X. Jia, D. Jiang, D.C. Tsang, J. Choi, A.C. Yip. Microporous Mesoporous Mater., 276, 147
(2019).
[32] Z.-W. Ye, W.-B. Yi. J. Fluorine Chem., 129, 1124 (2008).
[33] K. Kelly, W. Billups. Acc. Chem. Res., 46, 4 (2012).
[34] D.C. Marcano, D.V. Kosynkin, J.M. Berlin, A. Sinitskii, Z. Sun, A. Slesarev, L.B. Alemany, W.
Lu, J.M. Tour. ACS Nano., 4, 4806 (2010).
[35] S. Kumar, S. Chinnathambi, N. Munichandraiah. New J. Chem., 39, 7066 (2015).
ꢀ
ꢀ
[36] A. Moreno-Barcenas, J.F. Perez-Robles, Y.V. Vorobiev, I.E. Pech-Pech , A. Garcıa. Int. J.
Electrochem. Sci., 13, 3171 (2018).
[37] C. Huang, C. Li, G. Shi. Energy Environ. Sci., 5, 8848 (2012).
[38] S. Guo, G. Zhang, Y. Guo, J.C. Yu. Carbon, 60, 437 (2013).
[39] S. Schweizer, J.-M. Becht, C. Le Drian. Tetrahedron, 66, 765 (2010).
[40] R. Sedghi, S. Asadi, B. Heidari, M.M. Heravi. Mater. Res. Bull., 92, 65 (2017).
[41] S. Sadjadi, M.M. Heravi, M. Malmir, F. Noritajer. Mater. Chem. Phys., 223, 380 (2019).
[42] S. Sadjadi, S. Samadi, M. Samadi. Res. Chem. Intermed., 45, 2441 (2019).
[43] S. Asadi, R. Sedghi, M.M. Heravi. Catal. Lett., 147, 2045 (2017).
[44] B. Heidari, M.M. Heravi, M.R. Nabid, R. Sedghi, S.E. Hooshmand. Appl. Organomet. Chem.,
33, e4632 (2019).
[45] S. Sadjadi, M.M. Heravi, M. Raja. Int. J. Biol. Macromol., 122, 228 (2019).
[46] S. Sadjadi, M. Malmir, M.M. Heravi. Appl. Clay Sci., 168, 184 (2019).
[47] S. Sadjadi, M. Malmir, M.M. Heravi, F.G. Kahangi. Inorg. Chim. Acta, 488, 62 (2019).
[48] S. Sadjadi, M. Malmir, M.M. Heravi, M. Raja. Int. J. Biol. Macromol , 128, 638 (2019).
ꢀ
[49] S. Sadjadi, M. Akbari, B. Leger, E. Monflier, M.M. Heravi. ACS Sustain. Chem. Eng.,7, 6720
(2019).
[50] W.S. Hummers Jr., R.E. Offeman. J. Am. Chem. Soc., 80, 1339 (1958).
ꢀ
ꢀ
[51] A. Komaromi, G.L. Tolnai, Z. Novak. Tetrahedron Lett., 49, 7294 (2008).
[52] B. Ghanbari, L. Shahhoseini, H. Hosseini, M. Bagherzadeh, A. Owczarzak, M. Kubicki. J.
Organomet. Chem., 866, 72 (2018).
[53] M. Bakherad, A. Keivanloo, S. Samangooei. Chin. J. Catal., 35, 324 (2014).
[54] D.N. Sawant, P.J. Tambade, Y.S. Wagh, B.M. Bhanage. Tetrahedron Lett., 51, 2758 (2010).
[55] S.J. Sabounchei, M. Ahmadi. Catal. Commun., 37, 114 (2013).
[56] N. Nowrouzi, M. Zarei. Tetrahedron, 71, 7847 (2015).
[57] K. Thakur, E. Jaseer, A.B. Naidu, G. Sekar. Tetrahedron Lett., 50, 2865 (2009).
[58] S.J. Sabounchei, M. Ahmadi, Z. Nasri, E. Shams, M. Panahimehr. Tetrahedron Lett., 54, 4656
(2013).
[59] K. Karami, N.H. Naeini. Turk. J. Chem., 39, 1199 (2015).
[60] R.N. Prabhu, S. Pal. Tetrahedron Lett., 56, 5252 (2015).
[61] S. Sadjadi, M.M. Heravi, B. Masoumi, S.S. Kazemi. J. Coord. Chem., 72, 119 (2019).
[62] M.-P. Guo, S.-W. Liu, S.-B. Chen, Y.-J. Wen, H. Liang, M.-Y. Lv. Synth. Commun., 45, 767
(2015).