Synthesis and structural characterization for novel mixed-donor ligand palladium (II) based on graphene and oxime: its application as a highly stable and efficient recyclable catalyst

Article abstract of DOI:10.1007/s13738-018-1427-7

In this article, the palladium (II) mixed-ligand complex synthesized with reduced graphene oxides containing tetraethoxysilane and menthone oxime was used as an efficient solid catalyst for the Heck coupling reaction. To maintain stability and catalytic activity in the C–C bond reaction, graphene was considered due to the available surface as the solid support. Then, the structure of new heterogeneous catalyst was investigated by FT-IR, UV–Vis DRS, FE-SEM, EDX, AFM, XRD, ICP-OES, Raman, and TGA. The newly synthesized nanocatalyst have beneficial properties, including product’s easy separation, the shorter time to react, purity products (yield 79–99%), and easier work-up procedure. Furthermore, the catalyst was reused six times without significant degradation in catalytic activity and performance.

Full text of DOI:10.1007/s13738-018-1427-7

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-018-1427-7
ORIGINAL PAPER
Synthesis and structural characterization for novel mixed-donor
ligand palladium (II) based on graphene and oxime: its application
as a highly stable and efficient recyclable catalyst
Samira Ashiri1 · Ebrahim Mehdipour1
Received: 9 January 2018 / Accepted: 31 May 2018
© Iranian Chemical Society 2018
Abstract
In this article, the palladium (II) mixed-ligand complex synthesized with reduced graphene oxides containing tetraethox-
ysilane and menthone oxime was used as an efficient solid catalyst for the Heck coupling reaction. To maintain stability and
catalytic activity in the C–C bond reaction, graphene was considered due to the available surface as the solid support. Then,
the structure of new heterogeneous catalyst was investigated by FT-IR, UV–Vis DRS, FE-SEM, EDX, AFM, XRD, ICP-OES,
Raman, and TGA. The newly synthesized nanocatalyst have beneficial properties, including product’s easy separation, the
shorter time to react, purity products (yield 79–99%), and easier work-up procedure. Furthermore, the catalyst was reused
six times without significant degradation in catalytic activity and performance.
Keywords Heterogeneous catalyst · Mixed-ligand palladium complex · Graphene oxides · Heck reaction · Solid support ·
Oxime
Introduction
processes [6, 7]. Considering the importance of palladium
complex, many homogeneous catalytic processes have sig-
nificant disadvantages. These disadvantages include low
catalyst stability [8–10], inability in catalyst recovery, and
probabilistic toxicity due to remaining metal species [11],
preventing their proper use in the reaction. On the other hand,
homogeneous Pd catalysts lose their catalytic activity through
accumulation and sedimentation, while with the emergence
of heterogeneous catalysis, less product contamination and
reusability of the precious catalysts can be achieved [12, 13].
Over the past decades, researchers have intensively stud-
ied the subject of dendritic catalysts proven on solid sup-
ports [14, 15]. In most cases, the dendritic catalyst has more
positive effects than their non-dendritic analogs such as the
improved catalytic activity of the heterogeneous dendritic
catalysts. Several types of N-heterocyclic carbenes [16, 17]
and nitrogen-based ligands [18] have been spread by prov-
ing them on solid supports. The most common solid support
includes zeolite [19], metal oxides [20], silica starch [21],
polymers [22], carbon nanotubes (CNTs) [23], clay [24],
montmorillonite [25], and carbon derivatives [26], which
are used to immobilize metal catalysts. Alternatively, these
substrates are known to facilitate the catalyst recovery and
recycling [27]. Functionalization of solid supports with
showing chelating ligands appears to be a viable method
Palladium (Pd) noble metal is a stable catalyst playing an
indispensable role in organic synthesis due to its outstand-
ing versatility and high activity. Palladium complexes have
been considered as really useful and efficient choices for C–C
coupling reactions. Pd-catalyzed coupling of aryl or vinyl
halides and olefins, called as the Heck reaction, was one of
the most effective ways to create a new C–C bond in various
organic transformations [1–3]. The Heck coupling reaction
provided a true path to assemble important vinylated olefins
and arylated, and an extensive range of functional groups
tolerance on both reactants allowed the appropriate usage in
the final stage of total synthesis without protecting groups
[4, 5]. In the past four decades, particular attention is paid to
the use of palladium-catalyzed Heck cross-coupling reaction
for organic and industrial synthesis such as natural products
synthesis, active pharmaceutical intermediates, biologically
active molecules, and modern chemical organic materials
* Ebrahim Mehdipour
mehdipour.e@lu.ac.ir
1
Department of Chemistry, Faculty of Science, Lorestan
University, Khoramabad, Iran
Vol.:(0123456789)
1 3

Journal of the Iranian Chemical Society
to adjust their catalytic efficiencies and stabilize the metal
complexes [28].
purification. The completion of reactions was monitored
by the thin-layer chromatography (TLC) (hexane/EtOAc,
80:20). The FTIR spectrum of the products was recorded
in a Bruker-Tensor320 spectrometer. In the range of
450–4000 cm−1. The samples IR spectra were obtained using
KBr tablet (weight ratio of 5/200 mg for samples: KBr).
The catalysts structure were examined using patterns XRD.
These patterns were recorded through a powder diffractom-
eter, Holland Philips Xpert with Cu Kα radiation at a scan-
ning op 2°/min from 10° to 90° (2θ). Surface structure and
morphology of samples were studied using an LEO 440i
scanning electron microscope at an operating voltage of
10 kV and under vacuum. Before measurements, the sam-
ples were coated by sputtering with a thin layer of gold.
Absorption spectra UV–DRS of the sample were obtained
using a Shimadzu UV–DRS 1650. TGA analyses were per-
formed by a STA 409 apparatus (Linei) at a temperature
from 0 to 800 °C with a 10 °C/min heating rate under nitro-
gen gas. The Pd content in the heterogeneous catalyst was
determined using inductively coupled plasma optical emis-
sion spectroscopy (ICP-OES) conducted on a Perkin-Elmer
7300DV (Made in USA) model spectrometer. Elemental
analysis was performed using an instrument model Flash
EA 1112 Elemental Analyzer. Raman spectroscopy analy-
ses were recorded on dispersive Raman Microscope with
Lately, applications of graphene oxide (GO) and graphene
(rGO) have been widely investigated by the development of
metal-free carbon catalysts and the progress in graphene mate-
rials [29]. Graphene oxide nanosheet (GONS) is a flat mon-
olayer two-dimensional sp2-hybridized carbon material pro-
viding large surface area for interaction with other compounds
[30]. It has attracted considerable attention during the past
years due to their high thermal and mechanical stability as
well as electrical conductivity and environmental friendliness.
Functional groups on the GO sheets, according to availability,
allow them to react to a wide range of compounds. This prop-
erty of GO has highlighted it for potential applications in solid
support catalysis [31]. These properties of GO led to its intro-
duction as an efficient platform to load metals. These oxygen-
containing groups on GO sheets had strong interactions with
the organosilane to form functionalized GO. In this context,
[3-(2 amino-ethylamino) propyl] triethoxysilanes (AATPES)
were the most suitable molecules, which could behave as a
linker in attaching PdCl2(oxime)2 complex to GO (Scheme 1).
Experimental
Materials and methods
ʎ
exc =785 nm and high spatial and spectral resolution at the
position of the sample.
All organic substrates and solvents purchased with purity
98% from Aldrich and Merck were used without further
Scheme 1 Schematic illustration to prepare rGO-AATPES-Pd(oxime)2 complex
1 3

Journal of the Iranian Chemical Society
Synthetic procedures
Synthesis of GO-AATPS
at 40 °C (Scheme 1). The loading of palladium in the hetero-
geneous catalyst was determined using ICP-OES and EDX
analyses. The concentration of palladium was 12.75 wt%,
which was determined by ICP-OES. CHNs; C%: 56.67, N%:
7.38, H%: 6.85.
The GO was prepared from pure graphite using the Hum-
mer’s method. 2.0 g of GO powder was dispersed in 20 mL
of toluene and sonicated for 10 min. The reaction was car-
ried out with adding 3-chloropropyltriethoxysilane (CPETS:
4 mL) to suspension. The resulting mixture was stirred under
reflux conditions for 24 h and then washed with toluene and
ethanol (3×). The sample was dried at the temperature of
70 °C for 8 h. To prepare final GO-AATPES (AATPES:
[amino-ethylamino]-propyltrimethoxysilane) on the surface
of graphene oxide, 1.0 g of GO-CPTES was sonicated in
100 mL n-butanol and was added dropwise to 20 mL of eth-
ylenediamine; the mixture of reaction was stirred at 85 °C
for 10 h. After the performance of the reaction, the solid
precipitate was washed several times with ethanol and then
dried in a vacuum oven at 60 °C for a full day. CHNs: C%:
60.78, N%: 9.34, H%: 4.67.
General procedure for Heck reactions
rGO-AATPES-Pd(oxime)2 complex (0.15 mol%), aryl halide
(1 mmol), olefin (2.2 mmol), and K2CO3 (1.5 mmol) in DMF
(2 mL) were added to a flask armed with a magnetic stirring
bar and the mixture stirred for the appropriate time until the
reaction was complete. Progression of the reaction mixture
was monitored by TLC (hexane/EtOAc, 80:20) at 110 °C.
After completing the reaction, the catalyst was separated by
filtration and then the solution diluted with EtOAc: water
(15:15 mL). Then the organic layer was removed by a sepa-
ratory funnel and dried in a rotavap (Scheme 2). Finally, the
catalyst was reused for the same reaction. This process was
repeated for six runs. The amount of catalyst leached was
determined using inductively coupled plasma (ICP-OES).
Synthesis of menthone oxime
Results and discussion
Menthone (2.15 mL, 1.314 mmol) was added to methanol
(10 mL) containing sodium bicarbonate (1.5 g, 5.700 mmol)
and hydroxylamine (1.12 g, 3.600 mmol). To the reaction
mixture was added 1.25 mL water and refluxed for 3 h. Solu-
tion was diluted with water (12.5 mL) until all solids were
dissolved. The organic layer was separated by adding hex-
ane (25 mL) and this step was repeated three times, and the
white crystals were formed after evaporation of the solvent.
m.p: 55–56.5 °C, CHNs; C%: 71.37, N%: 8.61, H%: 11.23.
The catalytic activity rGO-AATPES-Pd(oxime)2 was stud-
ied in the heck reaction on a laboratory scale. The catalyst
preparation procedure is shown in Scheme 1. This process
was characterized by UV–Vis, FT-IR, SEM, XRD, AFM,
EDS, TGA, and Raman spectroscopy.
Structural characterization of the catalyst
All synthesized products were characterized by FT-IR analy-
sis. Figure 1a shows the FT-IR spectrum of pure graphite.
The graphene oxide FT-IR spectrum shows strong absorp-
tion bands at 3438, 2929, 1730, and 1642 cm−1, which was
related to –OH, C–H, C=O in –COOH group and non-oxi-
dized carbon skeletal domains (C=C aromatic), respectively
(Fig. 1b). In Fig. 1c, the bands at 722 and 556 cm−1 are
relevant to the asymmetric and symmetric stretching vibra-
tions of the C–Cl group. In addition, the stretching band at
2856 and 2927 cm−1 related to C–H sp2 and C–H sp3 groups
the (CH2)3 propyl chains in the GO-CTPES. Also, the peaks
at 1027 and 700 cm−1 correspond to O–Si stretching modes
Synthesis of palladium complex with menthone oxime
[PdCl2(oxime)2]
To prepare PdCl2 (oxime)2 complex, menthone oxime
(0.156 g, 0.922 mmol) was added to methanol (7.3 mL).
K2PdCl4 aqueous solution (50 mL) was then added dropwise
and the suspension stirred whilst flask was covered with a
lid. After, the mixture solvent was evaporated on rotavap for
18 h. The brown solid product was dissolved in acetone and
dried in a vacuum. m.p: 59–60 °C, CHNs; C%: 46.32, N%:
5.36, H%: 7.216.
Synthesis of rGO-AATPES-Pd (oxime)2 complex
In a two-neck flask, 0.5 g of GO-AATPES was dispersed in
20.5 mL of ethanol. Then 0.21 g of PdCl2(oxime)2 dissolved
in 5 mL of methanol and gradually added to the mixture
and stirred for 8 h under reflux conditions. The precipitate
obtained was washed with water and ethanol. The solution
was filtered and the precipitate was dried in a vacuum for 4 h
R1
rGO-AATPES-Pd(Oxime)2 R2
R1
R2
+
X
Base/110°C
Scheme 2 Schematic illustration the heck reaction catalyzed by rGO-
AATPES-Pd(oxime)2 complex under mild conditions
1 3

Journal of the Iranian Chemical Society
Fig. 1 FT-IR spectra for a
graphite, b graphite oxide, c
GO-CPTES, d GO-AATPES,
e (s)-Menthone, f Menthone
oxime, g PdCl2(oxime)2, and h
rGO-AAPTES-Pd(oxime)2
of GO-CTPES [32]. The characteristic peaks of the GO-
AATPES in IR spectra are as followed: a sharp band at
3412–3440 cm−1 resulted from the stretching vibrations
of NH2 and N–H groups. These peaks at 2923–2849 and
1122–1278 cm−1 in Fig. 1d are relevant to the C–H and C–N
stretching modes of GO-AATPES, respectively. Figure 1e, f
shows the IR spectra of pure menthone and menthone oxime,
respectively. The disappearance of the carbonyl group
absorbance band at 1710 cm−1 and the appearance of oxime
group absorbance band at 3320 cm−1 could be confirmed the
synthesis of menthone oxime. Also, the peaks at 1668 cm−1
correspond to C=N stretching modes of menthone oxime.
The PdCl2(oxime)2 FT-IR spectrum (Fig. 1g) shows that
hydroxyl functional groups of menthone oxime were shifted
1 3

Journal of the Iranian Chemical Society
has shown a strong absorption peak with a shoulder at
240 and 329 nm (curve a), which corresponds to π–π*
transition in the aromatic C=C bond and n–π* transition
in the C=O groups [34]. However, the absorption peak at
240 nm redshifted to 261 nm which could be attributed to
the reduced GO [35]. The first and second curves showed
no change compared with the third curve during the reac-
tion. Furthermore, the bands at around 240 and 329 nm in
GO-AARPES spectra disappeared, which shows graphene
oxide was indeed reduced by palladium complex [36].
The graphite XRD pattern shown in Fig. 3a diffraction
peak at 2θ=43.11 was corresponding to the (100) plane of
the honeycomb structure of carbon and very strong diffrac-
tion peak at 2θ = 26 which is relevant to the (002) plane
of graphite. Also as shown in Fig. 3b after oxidation, the
diffraction peak has appeared at 2θ = 11.71 [with 0.8 nm
interlayer spacing related to the (001) reflection], which indi-
cates that GO has been fully oxidized. The XRD patterns of
the rGO-AAPTES-Pd(oxime)2 (Fig. 3c) showed peak cor-
responds to graphene. The diffraction peaks at 2θ=11.71°
were disappeared and one new peak appeared at 2θ=26.8
assigned to (002) reflections of rGO, indicating the reduction
of GO in the presence of PdCl2(oxime)2 [36].
Fig. 2 UV–Vis DRS spectra of GO, GO-CPTES, GO-AATPES, and
rGO-AATPES-Pd(oxime)2
The morphology of GO and rGO-AAPTES-Pd(oxime)2
complex was characterized by AFM, as shown in Fig. 4.
AFM images revealed morphological variations between
GO and rGO-AAPTES-Pd(oxime)2 complex. Graphene
oxide presented a nanosheet structure with several hundred
nanometers large and 1.05 nm in thickness (Fig. 4a). While
coated GO with complex (Fig. 4b) showed a thickness of
56.82 nm. The increased thickness of GO indicated the pres-
ence of a complex coating on GO surfaces.
One of the most useful tools for proving the structural
characteristics and properties of graphene-based materials is
Raman spectroscopy. Thus, it was used to study the changes
that occurred in the crystal structure of the GO and rGO-
AAPTES-Pd(oxime)2 (Fig. 5). In Fig. 5a, Raman spectra
of GO samples display two prominent peaks at 1343 and
1596 cm−1, which is relevant to the D band and G band,
respectively. The G band has corresponded to the first scat-
tering of the E2g phonon of sp2-bonded carbon atoms in a
2D lattice. The D band suggests the presence of sp3 defects
(arising from a breathing mode of the aromatic rings). The
spectral shifts which observed during reaction steps could be
attributed to the derangement of the GO structure caused by
the chemical interactions between functional groups of GO
and other reactants. In Fig. 5b, G band of rGO-AAPTES-
Pd(oxime)2 complex (1587 cm−1) shows redshifted com-
pared with of GO (1596 cm−1), which can be related to the
interactions between GO and AATPES. To evaluate the
quality of the graphite structure and to measure defects in
the base graphene materials, the ID/IG (intensity ratio D
band to G band) is used. The intensity ratio of the D and G
Fig. 3 XRD pattern of a graphite, b graphene oxide, and c rGO-
AAPTES-Pd(oxime)2 complex
to higher frequencies (3386 cm−1) and peaks at 1650 cm−1
correspond to C=N [33]. Amin functional groups (–NH) of
GO-AATPES were shifted to lower (3396 cm−1). That, this
transfer can be assigned to their more effective interactions
with the palladium complex (Fig. 1h).
The formation of rGO-AATPS-Pd(oxime)2 was inves-
tigated using UV–Vis diffuse reflectance spectroscopy
(DRS) analysis. Figure 2 shows UV–Vis DRS of GO, GO-
CPTES, GO-AATPES, and rGO-AATPS-Pd(oxime)2. GO
1 3

Journal of the Iranian Chemical Society
Fig. 4 The two- and three-
dimensional AFM topography
images, and corresponding
height profiles of a GO and
b rGO-AAPTES Pd(oxime)2
complex
bands (ID/IG) improved from GO (0.957) to rGO-AAPTES-
Pd(oxime)2 (1.18). This increase is due to the decrease of the
sp2 in-plane domain induced by the introduction of defects
and disorder of the sp2 domain. Furthermore, the presence
of Pd complex seems to cause structural defects and disor-
der of the GO sheets. These structural defects could play a
significant effect in increasing the catalytic activity of the
rGO-AAPTES-Pd(oxime)2 catalyst [37, 38].
removing the interaction between sheets due to the pres-
ence of carboxylic, epoxy, and hydroxyl functional groups
(Fig. 6c). Compared to the GO, GO-AAPTES showed more
wrinkles and distance due to the presence of ethylenedi-
amine (Fig. 6d). As observed from Fig. 6e, complex particles
were attached to the edges and surface of graphene sheets.
Information about the chemical composition of the cata-
lyst and the mass ratios of elements are measured by Energy
Dispersive Spectroscopy (EDS). The EDX elemental anal-
ysis of the PdCl2(oxime)2 and rGO-AAPTES-Pd(oxime)2
complex is shown in Fig. 7. The results further confirmed
that PdCl2(oxime)2 was composed of carbon, nitrogen, oxy-
gen, chlorine, and palladium (Fig. 7a) with mass ratios of
66.78, 9.84, 9.29, 8.98%, and 5.11 wt%, respectively. The
ratio of chlorine, oxygen, and nitrogen is approximately
Scanning electron microscopy (SEM) was used for sur-
vey surface morphology and microstructures of modified
graphene oxide. Figure 6a shows the uniform distribution of
Pd(II) complex. SEM image in Fig. 6b showed the structure
and morphology of natural graphite layers that were bonded
by van der Waals forces. After oxidation, GO nanosheets
were relatively exfoliated and wrinkled, that resulted in
1 3

Journal of the Iranian Chemical Society
equal, but the proportion of palladium to each of the ele-
ments (O, N, Cl) is almost 1:2 ratio, that was confirmed to
the synthesis of the compound PdCl2(oxime)2.
Also, the results further confirmed that the catalyst rGO-
AAPTES-Pd(oxime)2 was composed of carbon, nitrogen,
oxygen, silicon, and palladium (Fig. 7c) with mass ratios
of 48.24, 14.50, 17.80, 8.55%, and 10.91 wt%, respectively.
The Si/Pd ratio (1:0.78) was higher than 1: 1 due to chemical
reaction with edges and surface of graphene oxide during
sample preparation. Furthermore, the element distribution
maps (Fig. 7d) showed that the GO-AATPES sheets were
densely functionalized with PdCl2(oxime)2 complex, reflect-
ing the uniformity of the modification.
Both powdery samples GO and rGO-AAPTES-
Pd(oxime)2 are analyzed using TGA by heating the com-
pounds from 0 to 800 °C at a heating rate of 10 °C min−1
under a nitrogen atmosphere (Fig. 8). As clearly seen from
the graph in Fig. 8a, the GO at 100 °C exhibits about 12%
weight loss and more than 42.3% loss between 110 and 210
resulting from the evaporation of water molecules that are
trapped between the layers of GO and the decomposition
of the labile oxygen-containing functional groups such as
epoxy or hydroxyl groups, respectively. The third stage
has shown 14.68% weight loss, which occurred at higher
Fig. 5 Raman spectroscopy of a GO and b rGO-AATPES-Pd(oxime)2
Fig. 6 FE-SEM images a PdCl2(oxime)2 complexes, b graphite, c graphene oxide (GO), d GO-AATPES, and e rG-AAPTES-Pd(oxime)2 com-
plex
1 3

Journal of the Iranian Chemical Society
Fig. 7 The EDS spectrum of a
PdCl2(oxime)2 and c rGO-
AAPTES-Pd(oxime)2 complex,
elemental distribution maps in
the b PdCl2(oxime)2 and d rGO-
AAPTES-Pd(oxime)2 complex
region shown by EDX
Table 1 Optimization of the reaction conditions for Heck reaction
catalyzed by rGO-AAPTES-Pd(oxime)2 complex
Entry Solvent Base
Cat. (mol%) T (°C)
Yield (%)
1
2
3
4
5
6
7
9
MeCN
PhMe
THF
NEt3
NEt3
NaHCO3 0.04
t-BuOK
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
0.01
0.02
80
90
21
34
Reflux 40
Reflux 45
100
120
120
110
110
THF
0.06
0.08
0.1
0.12
0.15
0.18
DMF
DMF
DMF
DMF
DMF
85
75
90
95
91
11
Reaction conditions: rGO-AATPES-Pd(oxime)2 complex (0.15 mol
%), aryl halide (1 mmol), olefin (2.2 mmol) ,and K2CO3 (1.5 mmol)
in DMF (2 mL) at 110 °C
Fig. 8 TGA thermograms of a GO and b rGO-AATPES-Pd(oxime)2
1 3

Journal of the Iranian Chemical Society
temperature is due to the combustion of carbon skeleton in
the GO [39]. In contrast, rGO-AAPTES-Pd(oxime)2 has
shown a higher thermal stability with a much lower mass
loss up to 800 °C. The first mass loss in rGO-AAPTES-
Pd(oxime)2 (10%) which occurred at 100–110 °C and 15%
at 220–300 °C was because of decomposition of the oxime
and functional groups on graphene sheets and remains some
oxygen functional groups on the surface rGO, respectively.
The final mass loss which occurred at around 800 °C (35%)
is due to the destruction of ring carbon. Also, it can be sug-
gested that increasing the thermal stability of the catalyst is
due to the presence of palladium on the rGO sheets.
showed that the polar aprotic solvent such as DMF obtained
better results than other solvents. Hence, DMF solvent was
preferred for further study. To investigate the effect of tem-
perature on reaction, different temperatures were studied.
The increase of reaction temperature in DMF solvent up to
110 °C led to high yield (Table 1, entry 5–11). Among all the
investigated bases, the increase of the catalytic activity and
high yields in the presence of K2CO3 were shown (Table 1,
entry 11). After obtaining the optimum conditions for reac-
tion, to investigate the scope and generality of this protocol,
wide range aryl halides and olefins were used as substrates
in the heck reaction. The results are shown in Table 2. In
the Heck reaction, various substituents on olefins and aryl
halides can influence on the rate of reaction. Electron-rich
substituents (such as NH2) on aryl halides cause to decrease
the reaction rate, and conversely, electron-withdrawing sub-
stituents on aryl halides increase the reaction rate (Table 2,
entries 3 and 9).
Screening of reaction conditions
The efficiency of the Heck reaction depends on a variety of
parameters, such as the solvent, temperature, base, structure
of catalyst, and substrate nature. For optimizing the reac-
tion conditions, different parameters were investigated on
the synthesis of compound 3d that was selected as a model
reaction. Initially, to evaluate the effect of the catalyst, dif-
ferent amounts of rGO-AAPTES-Pd(oxime)2 complex were
examined. As shown in Table 1, it was found that the highest
yield was obtained using 0.15 g of the catalyst. There was
no significant improvement in the yield by increasing the
amount of catalyst (Table 1, entries 11).
Also, the results from Table 2 show that aryl iodides pro-
duce the desired products in a shorter time than the aryl
bromides and aryl chlorides. The reason is the difference
in the carbon–halogen band that the increase in the length
of the bond in the ariel iodide causes easier metal penetra-
tion and break the band. In the study of catalytic systems
in coupling reactions, we find that aryl chloride is usually
inactive in the reaction of the Heck with palladium, and only
the iodine and brome react. Fortunately, the study of rGO-
AATPES-Pd(oxime)2 complex reveals appropriate results
for aryl chlorides with proper yields.
Next, the effect of various solvents such as polar protic,
aprotic solvents, and non-polar solvents such as MeCN,
THF, DMF, and Toluene on the improvement of reaction
was tested. The screening results presented in Table 1
Table 2 Heck cross-coupling reaction of aryl halides and olefins using catalyst rGO-AAPTES-Pd(oxime)2
Product
No.
R1
X
Candition
R2
R1
R2
+
Entry
Olefin
Styrene
X
R1
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
I
I
I
I
H
H
30
35
45
40
30
65
40
35
35
60
75
80
3a
3b
3c
3d
3e
3f
3g
3h
3i
98
96
92
95
99
95
97
95
90
93
85
79
Methyl acrylate
Methyl acrylate
Methyl methacrylate
Acrylonitrile
Methyl methacrylate
Styrene
Acrylonitrile
Acrylonitrile
Methyl acrylate
Styrene
Methyl methacrylate
NH2
H
I
H
H
H
H
Br
Br
Br
Br
Br
Cl
Cl
9
NH2
H
10
11
12
3j
3k
3l
H
H
Reaction conditions: rGO-AATPES-Pd(oxime)2 complex (0.15 mol%), aryl halide (1 mmol), olefin (2.2 mmol), and K2CO3 (1.5 mmol) in DMF
(2 mL) at 110 °C
1 3

Journal of the Iranian Chemical Society
Fig. 9 a FT-IR. b FE-SEM. c Reusability of the catalyst for the synthesis of 3d (rGO-AATPES-Pd(oxime)2 complex (0.01 mol%), aryl halide
(1 mmol), olefin (2.2 mmol), and K2CO3 (1.5 mmol) in DMF (2 mL) at 110 °C
Table 3 Catalytic performance of different catalysts in the coupling reaction of iodobenzene, chlorobenzene, and bromobenzene with olefins
Entry Catalyst
Conditions
X
Time (h)
Yield (%) References
1
2
3
4
5
6
7
8
PdLn@β-CD
Pd/WO3
1-(9-Anthracenylmethyl)imidazole/PdCl2(MeCN)2
Fe3O4@OA–Pd
Pd[(PhCH2NH)(pC6H4OMe)PS2]2
Pd/CoBDC
K2CO3, H2O, reflux
Na2CO3, 120 °C
NMP, KOH, 160 °C
n-Pr3N, solvent free
DMF, K2CO3, 100 °C Br,I
Et3N, DMA, 90 °C
Li2CO3, PEG, 80 °C Br, I
Br, I
Br, I
Cl, Br, I
Cl, Br
12, 4
5
5
12, 7
8
9
5
90, 95
85, 96
79, 95, 99 [16]
81, 96
86, 73
92
[41]
[42]
[43]
[7]
[44]
[11]
I
Co–NHC@MWCNTs
rGO-AATPES-Pd(oxime)2 complex K2CO3, DMF, 110 °C
77, 85
Cl, Br, I 1.25, 0.66, 0.5 85, 97, 98 This study
The aryl halides react with a variety of aliphatic and
Reusability is one of the notable features environmen-
tally and economically. Thereupon, reusability and recy-
cling performance of the rGO-AATPS-Pd(oxime)2 nano-
catalyst were investigated under optimal conditions. The
rGO-AATPS-Pd(oxime)2 as a heterogeneous catalyst was
recovered for six runs without significant loss of its activ-
ity. After the catalytic reaction, the catalyst was isolated
aromatic olefins with electron-withdrawing and donating
group and giving the coupling products in good to excel-
lent yields. It was observed that olefins with electron-with-
drawing groups exhibit higher activity and reaction times
of less relative to those bearing electron-donating groups
on the olefin in the Heck reactions [40].
1 3

Journal of the Iranian Chemical Society
9. K.R. More, R. Mali, Tetrahedron 72, 7496 (2016)
10. J.L. Pratihar, P. Mandal, C.-H. Lin, C.-K. Lai, D. Mal, Polyhedron
135, 224 (2017)
by the filtration of the reaction mixture and washed with
EtOH, and dried under vacuum at 80 °C for 2 h. The FT-IR
and FE-SEM analyses of the catalyst after six periods indi-
cated no detectable changes in the catalyst during the reac-
tion of the recovery steps (Fig. 9). These results clearly
indicate that the catalyst has high stability.
11. A.R. Hajipour, Z. Khorsandi, Catal. Commun. 77, 1 (2016)
12. S.S. Shendage, A.S. Singh, J.M. Nagarkar, Tetrahedron Lett. 55,
857 (2014)
13. D. Sahu, C. Sarmah, P. Das, Tetrahedron Lett. 55, 3422 (2014)
14. A. Guarnizo, I. Angurell, G. Muller, J. Llorca, M. Seco, O. Ros-
sell, M. Rossell, RSC Adv. 6, 68675 (2016)
To get more information about the leaching of palladium
in reaction, the reaction of iodobenzene with Methyl meth-
acrylate as a model reaction was studied. After completion
of the reaction and the workup for the first run, the amount
of leaching was determined by ICP-OES analysis to be
12.75 wt%. The amount of Pd leaching after the six run was
also determined by ICP-OES analysis to be only 9.85%, which
indicates the stability of the catalyst during the reaction.
The comparison of the activity of the catalyst presented
with various catalyst Pd in the Heck coupling reaction
published in Table 3.
15. S. Verma, D. Verma, A.K. Sinha, S.L. Jain, Appl. Catal. A 489,
17 (2015)
16. X.-D. Xiao, Y.-L. Bai, J.-Q. Liu, J.-W. Wang, Tetrahedron Lett.
57, 3385 (2016)
17. T. Taira, T. Yanagimoto, K. Sakai, H. Sakai, A. Endo, T. Imura,
Tetrahedron 7(2), 4117 (2016)
18. C.J. Madadrang, H.Y. Kim, G. Gao, N. Wang, J. Zhu, H. Feng,
M. Gorring, M.L. Kasner, S. Hou, ACS Appl Mater Interfaces 4,
1186 (2012)
19. J. Gou, Q. Ma, X. Deng, Y. Cui, H. Zhang, X. Cheng, X. Li, M.
Xie, Q. Cheng, Chem. Eng. J. 308, 818 (2017)
20. Y. Zhao, C. Tao, G. Xiao, G. Wei, L. Li, C. Liu, H. Su, Nanoscale
8, 5313 (2016)
21. W. Puthai, M. Kanezashi, H. Nagasawa, T. Tsuru, J. Membr. Sci.
524, 700 (2017)
Conclusions
22. J.C. Pessoa, M.R. Maurya, Inorg. Chim. Acta 455, 415 (2017)
23. D. Bonduel, S. Bredeau, M. Alexandre. F. Monteverde, P. Dubois,
J. Mater. Chem. 17, 2359 (2007)
In summary, mixed-ligand rGO-AAPTES-Pd(oxime)2 com-
plex was successfully prepared and characterized through
various analyses. The functionalized graphene complex was
synthesized simply by reacting covalently to a reactive sur-
factant. Hence, this study highlighted that rGO had higher
performance compared to other catalysts, since it is highly
efficient and economical, and show increased activity at
shorter reaction times and higher yields of products. The
high stability and catalytic activity of this solid catalyst were
related to Pd complexes. This method was efficient and sim-
ple, and is expected to be a useful synthetic protocol for syn-
thesis of a wide range of novel chemical organic materials.
24. C. Ruiz-García, J. Pérez-Carvajal, A. Berenguer-Murcia, M.
Darder, P. Aranda, D. Cazorla-Amorós, E. Ruiz-Hitzky, Phys.
Chem. Chem. Phys. 15, 18635 (2013)
25. Z. Zhang, B. Liu, K. Lv, J. Sun, K. Deng, Green Chem. 16, 2762
(2014)
26. N. Mansor, T.S. Miller, I. Dedigama, A.B. Jorge, J. Jia, V. Bráz-
dová, C. Mattevi, C. Gibbs, D. Hodgson, P.R. Shearing, Electro-
chimica Acta 222, 44 (2016)
27. S.M. Sarkar, M.L. Rahman, M.M. Yusoff, New J. Chem. 39, 3564
(2015)
28. M. Amini, M. Bagherzadeh, Z. Moradi-Shoeili, D.M. Boghaei,
RSC Adv. 2, 12091 (2012)
29. M. Heidarizadeh, E. Doustkhah, S. Rostamnia, P.F. Rezaei, F.D.
Harzevili, B. Zeynizadeh, Int. J. Biol. Macromol. 101, 696 (2017)
30. H. Li, X. Zhu, H. Sitinamaluwa, K. Wasalathilake, L. Xu, S.
Zhang, C. Yan, J. Alloy. Compd. 714, 425 (2017)
31. R.H. Fath, S.J. Hoseini, H.G. Khozestan, J. Organomet. Chem.
842, 1 (2017)
Acknowledgements The authors thank the Lorestan University
Research Council for the support of this work.
32. J. Safari, S. Gandomi-Ravandi, S. Ashiri, New J. Chem. 40, 512
(2016)
33. G.C. Dickmu, L. Stahl, I.P. Smoliakova, J. Organomet. Chem. 756,
27 (2014)
References
34. K.A. Kumar, L. Chandana, P. Ghosal, C. Subrahmanyam, Mol.
Catal. 451, 87 (2017)
1. M.R. dos Santos, R. Coriolano, M.N. Godoi, A.L. Monteiro, H.C.
de Oliveira, M.N. Eberlin, B.A. Neto, New J. Chem. 38, 2958
(2014)
35. S. Mahalingam, J. Ramasamy, Y.-H. Ahn, J. Taiwan Inst. Chem.
Eng. 80, 276 (2017)
36. G. Yang, L. Li, R.K. Rana, J.-J. Zhu, Carbon 61, 357 (2013)
37. J.Y. Park, S. Kim, Int. J. Hydrog. Energy 38, 6275 (2013)
38. G. Wu, X. Wang, N. Guan, L. Li, Appl. Catal. B 136, 177 (2013)
39. A.R. Siamaki, S.K. Abd El Rahman, V. Abdelsayed, M.S. El-
Shall, B.F. Gupton, J. Catal. 279, 1 (2011)
2. Y. Zhu, J. Bai, J. Wang, C. Li, RSC Adv. 6, 29437 (2016)
3. K.R. Balinge, P.R. Bhagat, Comptes Rendus Chimie 20, 773
(2017)
4. R.P. Jumde, M. Marelli, N. Scotti, A. Mandoli, R. Psaro, C. Evan-
gelisti, J. Mol. Catal. A Chem. 414, 55 (2016)
5. E. Mohammadi, B. Movassagh, J. Mol. Catal. A Chem. 418, 158
(2016)
40. F.R. Fortea-Pérez, M. Julve, E.V. Dikarev, A.S. Filatov, S.-E.
Stiriba, Inorganica Chimica Acta (2017)
41. S.D. Dindulkar, D. Jeong, H. Kim, S. Jung, Carbohydr. Res. 430,
85 (2016)
6. H.-P. Gong, Z.-J. Quan, X.-C. Wang, Tetrahedron 72, 2018 (2016)
7. K. Gholivand, R. Salami, K. Farshadfar, R.J. Butcher, Polyhedron
119, 267 (2016)
42. M. Amini, D.B. Heydarloo, M. Rahimi, M.G. Kim, S. Gautam,
K.H. Chae, Mater. Res. Bull. 83, 179 (2016)
8. M.E. Martínez-Klimov, P. Hernandez-Hipólito, T.E. Klimova,
D.A. Solís-Casados, M. Martínez-García, J. Catal. 342, 138
(2016)
43. E. Rafiee, M. Kahrizi, J. Mol. Liq. 218, 625 (2016)
44. F. Ashouri, M. Zare, M. Bagherzadeh, C. R. Chim. 20, 107 (2017)
1 3