Effect of addition of iron on morphology and catalytic activity of PdCu nanoalloy thin film as catalyst in Sonogashira coupling reaction

Article abstract of DOI:10.1002/aoc.3675

Palladium-supported catalysts are complex assemblies with a challenging preparation. Minor changes in their preparation conditions can affect the activity, selectivity and lifetime of these catalysts. PdCuFe nanoparticle (NP) thin films were supported on

Full text of DOI:10.1002/aoc.3675

Received: 29 August 2016
DOI 10.1002/aoc.3675
Revised: 30 September 2016
Accepted: 4 October 2016
F U L L PA P E R
Effect of addition of iron on morphology and catalytic activity of
PdCu nanoalloy thin film as catalyst in Sonogashira coupling
reaction
S. Jafar Hoseini | Nahal Aramesh | Mehrangiz Bahrami
Department of Chemistry, Faculty of Sciences,
Palladium‐supported catalysts are complex assemblies with a challenging prepara-
Yasouj University, Yasouj 7591874831, Iran
tion. Minor changes in their preparation conditions can affect the activity, selectivity
Correspondence
S. Jafar Hoseini, Department of Chemistry, Faculty
and lifetime of these catalysts. PdCuFe nanoparticle (NP) thin films were supported
on reduced graphene oxide (RGO) by the reduction of the organometallic complex
[PdCl2 (cod)] (cod = cis,cis‐1,5‐cyclooctadiene), and [Cu(acac)2] and [Fe(acac)3]
of Sciences, Yasouj University, Yasouj
7591874831, Iran.
Email: jhosseini@yu.ac.ir; sjhoseini54@yahoo.
com
(acac = acetylacetonate) complexes at a toluene–water interface. We have investi-
gated the application of the liquid–liquid interface method for preparing ultrathin
films of catalysts and have evaluated the catalytic activity of the prepared NPs for
the Sonogashira coupling reaction in micelle media. Also, we have investigated the
effect of the addition of iron on the morphology, size and catalytic activity of
PdCu/RGO NPs. Our study shows that both of the prepared catalysts (PdCu/RGO
and PdCuFe/RGO) are efficient and recoverable catalysts for the Sonogashira car-
bon–carbon coupling reaction. This method has advantages compared to other routes,
such as short reaction times, high to excellent yields, facile and low‐cost method for
the preparation of the catalysts, and easy separation and reusability of the catalysts.
KEYWORDS
carbon–carbon coupling, graphene oxide, palladium/copper nanoalloys, Sonogashira
reaction, thin film
1
|
INTRODUCTION
heterogeneous ones. In this case, palladium is stabilized on
a
solid support such as activated carbon,[7,8] metal
oxides,[9–11] zeolites,[12] clays[13] and so on. In this manner,
the heterogeneous catalysts can be separated after the reac-
tion and can be reused in a few catalytic cycles. There are
some reports of solid‐supported palladium catalysts showing
higher activities than homogeneous ones due to their higher
stability.[14]
Palladium‐supported catalysts are complex assemblies
and their preparation is a challenging task. Minor changes
in their preparation conditions can affect the activity,
selectivity and lifetime of these catalysts. Palladium cata-
lysts can be stabilized on the supports using various
methods such as wet or dry impregnation,[15] deposition–
precipitation,[16] deposition–reduction,[17] ion exchange
methods,[18] sol–gel processes[19] and liquid–liquid inter-
face self‐assembly.[20–22]
Homogeneous palladium catalysis has attracted much interest
for C─C coupling reactions such as Suzuki–Miyaura,
Sonogashira, Heck and Stille reactions. This methodology
has some advantages such as high reaction rate, turnover
number, selectivity and yield. Also, some products can be
synthesized in this way for the first time.[1] The properties
of these catalysts are dependent on ligand type such as
amines[2] and phosphines[3] that are expensive. Recent inves-
tigations of ligand‐free palladium‐based catalysts have shown
them as promising alternatives to ligand‐assisted
methods.[4,5] Homogeneous palladium catalysts have some
disadvantages: recycling problem for reusing the catalysts
that leads to loss of expensive metal and ligands and produces
impurities in products.[6] Such problems have to be overcome
by replacing homogeneous palladium catalysts with
Appl Organometal Chem 2016; 1–9
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
1

2
HOSEINI ET AL.
In recent years, the interface between two immiscible
patterns were obtained using a Bruker AXS (D8 Advance)
instrument employing the reflection Bragg–Brentano geome-
try with Cu Kα radiation (λ = 1.54184 Å). Energy‐dispersive
analysis of X‐rays (EDAX) was carried out using a Philips
XL30 instrument with an accelerating voltage of 20 kV.
Transmission electron microscopy (TEM) images were
obtained with a Philips CM‐10 microscope operated at
100 kV. The loading amount of palladium was determined
using an inductively coupled plasma (ICP) analyser (Varian
solutions has been studied as it plays a key role for the
assembly of nanostructures and a large variety of solid
particles.[23–25] In this strategy, reducing the surface tension
between the fluid phases can lead to stable structures at the
liquid–liquid interface formed by solid particles.[26–30] In
contrast to many synthetic processes, the liquid–liquid inter-
face strategy does not need a calcination process. Also, this
assembly method can be applied for the in situ synthesis of
materials, template preformed structures and alloys.
1
Vista‐Pro). H NMR spectra were obtained with a Bruker
Nanoalloys of transition metals exhibit superior activity
over their monometallic counterparts in many organic trans-
formations [31–33] due to the strong synergy between the
metals that leads to a higher catalytic performance. Graphene
oxide (GO) can be used as a stabilizer with oxygen‐contain-
ing surface groups to enhance the interaction with a metal
at a liquid–liquid interface. These structures exhibit a wide
variety of applications especially in catalysis.[34–36] Previ-
ously, some platinum‐ and palladium‐based nanostructures
were synthesized at a liquid–liquid interface from organome-
tallic precursors and their applications were investigated in
p‐nitrophenol reduction reaction, methanol oxidation in fuel
cells and Suzuki–Miyaura reactions.[20–22,37–42]
In this paper, we report a synthesis of trimetallic PdCuFe
nanoalloy thin film supported on GO from the organometallic
precursor [PdCl2(cod)] (cod = cis,cis‐1,5‐cyclooctadiene),
and an investigation of the effect of the addition of iron on
the morphology and catalytic activity of PdCu/reduced
graphene oxide (RGO) nanostructures. These nanoalloys were
applied as an efficient catalyst in the Sonogashira coupling
reaction (reaction of alkynes with aryl or vinyl halides for
the formation of C(sp2)─C(sp) bonds) under mild reaction
conditions and in an environmentally friendly aqueous
medium to investigate the effect of the addition of Fe on
PdCu/RGO bimetallic alloy. In this study, we adopted a strat-
egy using ligand‐free palladium‐based catalysts that show
interesting catalytic activity with low palladium loading.
There are some reports of palladium‐based catalysts such as
Pd/C that was first investigated by Guzman and co‐
workers,[43] but PdCuFe/RGO catalyst produces a higher yield
compared to Pd/C catalyst in the Sonogashira reaction.[43]
Also, Pd/C–PPh3–CuI mixture exhibited very interesting cata-
lytic activity in this case in which two cooperative catalytic
cycles of palladium and copper were accepted as a plausible
mechanism,[44] but our strategy involves the synthesis of
ligand‐free catalyst that has lower cost and lower toxicity.
400 MHz Ultra‐shield spectrometer using CDCl3 as the
solvent. Products were characterized by comparison of their
spectral and physical data with those of known samples
(supporting information). All yields refer to isolated
products.
2.1 | Preparation of PdCu/RGO and PdCuFe/RGO
Thin films at toluene–water interface
GO was prepared from graphite powder in accordance with
the modified Hummers–Offeman method.[40] GO was first
exfoliated by dispersing GO (10 mg) in double‐distilled water
(25 ml) with sonication for 10 min. To prepare PdCuFe/RGO
thin film, an equimolar solution of [PdCl2 (cod)], [Cu(acac)2]
and [Fe(acac)3] (0.33 M, 25 ml) in toluene was sonicated for
5 min to prepare an orange‐coloured solution. This solution
was placed in contact with the solution of GO in a beaker
(100 ml). Once the two layers were stabilized, a freshly pre-
pared aqueous solution of NaBH4 (15 ml, 0.1 M) was
injected into the aqueous layer using a syringe with minimal
disturbance to the toluene layer. The onset of reduction was
marked by a coloration of the liquid–liquid interface. With
the passage of time, a thin film formed at the liquid–liquid
interface. A similar procedure was applied for the synthesis
of PdCu/RGO nanoparticle (NP) thin films. The catalyst
was obtained from the liquid–liquid interface as follows: (i)
the toluene top phase was removed using a syringe; (ii) etha-
nol was added to the mixture and centrifuged after 30 min;
(iii) precipitates were washed with ethanol two times; and
(iv) a drying procedure was performed under nitrogen.
2.2 | General procedure for Sonogashira coupling
reaction
Phenylacetylene (1.0 mmol) was added to a flask containing
catalyst and KOH (2 mmol) in
4 ml of H2O–
cetyltrimethylammonium bromide (CTAB) with a critical
micelle concentration of 1 (1 CMC). This mixture was placed
in an oil bath at 60 °C. Once the mixture reached this temper-
ature, the reaction was initiated by the addition of aryl halide
(1.0 mmol). After completion of the reaction (monitored
using TLC), the reaction mixture was cooled to room temper-
ature and then dichloromethane (3 × 5 ml) was added to the
reaction vessel. The organic phase was separated and dried
over anhydrous MgSO4. Subsequently, the solution was
2
| EXPERIMENTAL
PdCl2, phenylacetylene and bromobenzene were purchased
from Merck Company. [PdCl2 (cod)] and [Fe(acac)3] (acac
= acetylacetonate) complexes were prepared according to
reported procedures[45,46] and the [Cu(acac)2] complex was
purchased from Merck. Powder X‐ray diffraction (XRD)

HOSEINI ET AL.
3
evaporated and the resulting compound was washed with
cool hexane to afford the desired pure product. The catalyst
was recovered from the reaction mixture by decantation of
the solution and remained at the bottom of the round‐bottom
flask. Finally, the catalyst was washed with dichloromethane,
water and diethyl ether and dried with nitrogen.
3
| RESULTS AND DISCUSSION
The liquid–liquid interface strategy was used for the synthesis
of PdCu/RGO and PdCuFe/RGO. GO was used as a stabilizer
with oxygen‐containing surface groups, thus enhancing the
interaction with the metal. Reduction of GO sheets was started
after the addition of the reducing agent of NaBH4 and they
moved to the interface from the bottom phase due to the
decrease of the hydrophilicity of the GO and decrease in the
polar functionality on the surface of the sheets (Figure 1b).
Also, metallic precursors started to reduce and moved from
the top phase to the interface (Figure 1b). The effect of the
addition of Fe on the morphology of the nanoalloy was inves-
tigated. Also, these catalysts were applied in the Sonogashira
coupling reaction to evaluate their catalytic activity. These
coupling reactions were performed in a water and CTAB
medium. Figure 1 shows the reaction steps.
3.1 | PdCu/RGO and PdCuFe/RGO characterizations
FIGURE 2 XRD patterns of (a) PdCu/RGO NP thin film [22] and (b)
The crystal structure and composition of the PdCu/RGO [22]
and PdCuFe/RGO thin films were confirmed using XRD. In
the XRD pattern of PdCu/RGO thin film (Figure 2a), five main
diffraction peaks at 2θ = 40.2°, 47°, 67°, 82.6° and 87° can be
assigned as the (111), (200), (220), (311) and (222) planes cor-
responding to the face‐centred cubic Pd structure.[40] The
other diffraction peaks at 2θ = 45.2°, 52.08° and 75.6° corre-
spond to the (111), (200) and (220) planes of Cu (0) lattice.[47]
PdCuFe/RGO NP thin film deposited on glass
RGO shows a broad and weak diffraction peak at 2θ = 25.25°
that can be assigned as the (002) plane.[40]
Figure 2(b) shows the XRD pattern of PdCuFe/RGO NP
thin film. In addition to the five main diffraction peaks of
face‐centred cubic Pd, the weak and broad peak of RGO
and three peaks that belong to Cu(0), weak diffraction peaks
are observed at 2θ = 44°, 65.1° and 84° corresponding to the
(110), (200) and (221) planes of Fe(0).[41] Relative to the
same reflections for Pd, the diffraction peaks of these thin
films are shifted to higher 2θ values, revealing decreased lat-
tice parameters and a high level of alloying.[48]
As shown in Figure 3(a,b), TEM images of the PdCu/
RGO NPs exhibit spherical structures with an average diam-
eter of 8.8 nm (Figure 3c). Figure 4(a–c) shows TEM images
of the PdCuFe/RGO NP thin film. The average diameter of
the thin‐film particles is approximately 7.2 nm (Figure 4(d)).
The chemical composition of the PdCuFe/RGO thin film
was characterized using EDAX, confirming the presence of
Pd, Cu, Fe and C elements (Figure 5).
FIGURE 1 Schematic of PdCuFe/RGO trimetallic thin film formation at
toluene–water interface. (a) Stabilized mixture of [PdCl2 (cod)], [Cu(acac)2]
and [Fe(acac)3] in toluene (orange) and GO in water (brown) followed by
dropwise addition of NaBH4 to the stabilized mixture. (b) Thin film of
PdCuFe/RGO nanoalloy appeared at the toluene–water interface after
adding NaBH4. (c) Sonogashira C─C coupling reaction in H2O–CTAB
medium
3.2 | Investigating effect of addition of Fe on
morphology of PdCu/RGO thin film
One of our main purposes in the work reported was in fact to
improve the catalytic performance of the thin films and

4
HOSEINI ET AL.
FIGURE 3 (a, b) TEM images of PdCu/RGO NP thin film with (c) an
average diameter of 8.8 nm [22]
reduce the usage of precious and expensive metals for com-
mercialization of the catalysts by developing a suitable route
for the synthesis of alloy nanostructures having well‐defined
shapes (Table 1).
From the TEM images (Figures 3 and 4), it is obvious
that the addition of Fe to the PdCu/RGO nanoalloy thin film
not only prevents particle aggregation, but also decreases the
size of NPs having a very good dispersion.
FIGURE 4 (a–c) TEM images of PdCuFe/RGO NP thin film and (d)
histogram of particle size distribution

HOSEINI ET AL.
5
TABLE 2 Sonogashira coupling reaction of bromobenzene with
phenylacetylene (1:1 mmol) in various solvents and in the presence of
K2CO3 as base at 80 °C in 20 min
PdCu/RGO
PdCuFe/RGO
Entry
Solvent
DMF
(mol%)a; yield (%)b
(mol%)a; yield (%)b
1
2
3
4
5
6
0.006; 50
0.006; 5
0.001; 20
0.001; 5
THF
Toluene
0.006; trace
0.006; 85
0.006; 75
0.006; 90
0.001; 30
0.001; 40
0.001; 35
0.001; 90
H2O
H2O–EtOH (1:1)
H2O–CTAB
aPd mol%.
bIsolated yield.
FIGURE 5 EDAX spectrum of PdCuFe/RGO thin film
TABLE 1 Effect of alloying on morphology of thin films
Entry
Thin film
Morphology
Size (nm)
Ref.
TABLE 3 Sonogashira coupling reaction of bromobenzene with
phenylacetylene at various temperatures in micellar system of CTAB and in
the presence of K2CO3 as base for 20 min
[20]
1
2
3
Pd/RGO
Spherical NPs
Spherical NPs
Spherical NPs
7
PdCu/RGO
PdCuFe/RGO
8.8
7.2
This work
This work
PdCu/RGO (mol%)a;
yield (%)b
PdCuFe/RGO (mol%)a;
yield (%)b
Entry
Temp. (°C)
1
2
3
4
80
60
50
40
0.006; 90
0.006; 90
0.006; 50
0.006; 20
0.001; 90
0.001; 90
0.001; 75
0.001; 60
3.3 | Investigating effect of addition of Fe on catalytic
activity of PdCu/RGO thin film using Sonogashira C─C
coupling reaction
aPd mol%.
Synthesis of Pd(0) NPs from Pd(II) at a GO support can be
advantageous due to the generation of species with a higher
catalytic activity.[1] In this study, the catalytic activity of
PdCu/RGO and the effect of the addition of Fe to the thin
film were investigated for the Sonogashira coupling reaction.
The PdCu/RGO and PdCuFe/RGO nanoalloy thin films
were used as suitable and recoverable catalysts in the
Sonogashira coupling reaction. We initiated our investigation
by optimizing the reaction conditions. Phenylacetylene and
bromobenzene were used in a model C─C coupling reaction.
The solvent has an important effect on the reactivity of this
type of coupling reaction. Therefore, the reaction of
bromobenzene with phenylacetylene was performed in the
presence of the nanoalloy thin films using various solvents.
The results of the catalytic reactions are summarized in
Table 2. Among the various solvents tested, the best conver-
sion is observed for H2O–CTAB (1 CMC) (Table 2, entry 6).
The product is detected in a lower yield when the reaction is
carried out with other solvents (Table 2).
Also, the Sonogashira coupling reaction of
bromobenzene with phenylacetylene at various temperatures
was investigated. According to the results summarized in
Table 3, we choose 60 °C as the reaction temperature in aque-
ous solutions (Table 3, entry 2).
In the next step, the reaction of bromobenzene with
phenylacetylene was performed in the presence of the
nanoalloy thin films. Kotschy and co‐workers used
diisopropylamine as an alternative to K2CO3, but the yields
bIsolated yield.
were not very high.[49] We used KOH as an efficient base
with the best yield for this type of coupling reaction (Table 4,
entry 4).
Finally, various amounts of catalysts were studied. The
reaction yields a trace amount of product (below 5%)
without catalyst after 24 h; it proceeds catalytically upon
the addition of the NP thin films. The optimal amounts of
the catalysts were determined from the reaction of
bromobenzene with phenylacetylene at 60 °C in micellar
system of CTAB (1 CMC). PdCuFe/RGO (0.001 mol%)
and PdCu/RGO (0.006 mol%) give the best results in the
Sonogashira coupling reaction.
TABLE 4 Variation of bases for Sonogashira coupling reaction of
bromobenzene with phenylacetylene at 60 °C in micellar system of CTAB for
20 min
PdCu/RGO (mol%)a;
yield (%)b
PdCuFe/RGO (mol%)a;
yield (%)b
Entry
Base
1
2
3
4
5
K2CO3
Na2CO3
NEt3
0.006; 90
0.006; 90
0.006; 60
0.006; 95
0.006; 60
0.001; 90
0.001; 85
0.001; 40
0.001; 95
0.001; 80
KOH
NaOH
aPd mol%.
bIsolated yield.

6
HOSEINI ET AL.
Bromobenzene (1 mmol) was treated with
3. Size of the crystallites. According to TEM images, the
size of PdCuFe/RGO nanostructures is smaller than that
of PdCu/RGO nanostructures. Therefore, the PdCuFe/
RGO nanostructure thin film exhibits a better catalytic
activity.
phenylacetylene (1 mmol) and KOH (2 mmol) in the pres-
ence of the PdCuFe/RGO catalyst (0.001 mol%) and the
PdCu/RGO catalyst (0.006 mol%) at 60 °C and after 20 min
a quantitative yield was obtained (Table 5, entry 2). To inves-
tigate the scope of the reaction, the optimized conditions
were utilized for the Sonogashira couplings of various aryl
halides with phenylacetylene. The results for related investi-
gations are summarized in Table 5. Different aryl halides
bearing electron‐withdrawing and electron‐donating groups
can react in short reaction times with good reaction yields
(70–95%). The activity of aryl halides usually decreases in
the order I > Br > Cl due to the stronger C(sp2)─Cl bond
than the C(sp2)─Br and C(sp2)─I bonds. Aryl iodide is found
to be more reactive than aryl chloride and bromide (Table 5,
entries 1–3). We also investigated some aryl chlorides in the
Sonogashira cross‐coupling reaction, and products are found
in good yields (Table 5, entry 5). These results clearly show
that PdCu/RGO and PdCuFe/RGO are efficient catalysts for
the Sonogashira coupling reaction.
4. Oxidation state of Pd. Synthesis of Pd(0) NPs from
Pd(II) at the GO support can be advantageous due to
the generation of species with a higher catalytic activ-
ity.[1] Both PdCu/RGO and PdCuFe/RGO catalysts con-
tain Pd(0) and have higher catalytic activity than
catalysts containing Pd(II) under similar conditions.[1]
5. Conditions of catalyst preparation. PdCu/RGO and
PdCuFe/RGO catalysts are nanostructures prepared at a
toluene–water interface. Therefore, all the atoms are on
the surface of the catalyst that can lead to a higher cata-
lytic activity.
6. Turnover frequency (TOF) and turnover number
(TON) calculations. The TON (moles of product per
mole of catalyst) and TOF (= TON per time (h)) were
calculated. The TOF and TON, which are measures of
the efficiency of a catalyst, totally depend on the Pd con-
centration. Kohler and co‐workers reported that the Pd/
C‐catalysed Sonogashira reaction of iodobenzene with
phenylacetylene without the addition of CuI or PPh3
gives TOF = 1184 h−1 and TON =592.[50] Gholinejad
and Ahmadi reported that the Sonogashira reaction over
Also, the efficacy of the present catalysts was compared
with that of previously reported catalysts in the coupling of
aryl iodides with phenylacetylene. The results are summa-
rized in Table 6.
To compare the catalytic activity of PdCu/RGO with
PdCuFe/RGO thin film we should consider the following
important points that affect catalytic activity:
Pd–CuFe2O4/SiO2 catalyst gives TOF = 10.97 h−1 [51]
.
Under similar conditions, Basu and co‐workers,[52]
Metin and co‐workers[53] and Gao and co‐workers[54]
reported the Sonogashira reaction with Pd/Cu‐ARF(II)
1. Surface area. Dispersion of nanostructures on the GO
support in the form of thin films can increase the surface
area. PdCu/RGO and PdCuFe/RGO thin films exhibit
higher catalytic activity compared to other catalysts
according to Table 6. Furthermore, in the presence of
PdCu/RGO and PdCuFe/RGO, the Sonogashira reaction
progresses under milder conditions. Also, PdCuFe/RGO
exhibits a better catalytic activity than PdCu/RGO due to
the smaller particle size.
(TOF = 43.43 h−1), Cu48Pd52/RGO (TOF = 145.26 h−1
and MMT/Pd‐Cu (TOF
)
= ) catalysts,
6.06 h−1
respectively. In the present study, PdCu/RGO and
PdCuFe/RGO catalysts show higher TOF (68 839 and
593 750 h−1, respectively) and TON (15 833 and 95
000, respectively) for the Sonogashira reaction of
phenylacetylene with iodobenzene.
2. Dispersion of metal atoms on the support. TEM
images show a better dispersion of nanostructures on
the RGO surface for PdCuFe/RGO and confirm its better
catalytic activity.
The size of PdCu/RGO (8.8 nm) and PdCuFe/RGO
(7.2 nm) is very nearly equal. So the doping of Fe has
changed the PdCuFe/RGO particles. The results show that
TABLE 5 Sonogashira cross‐coupling reaction between aryl halides and phenylacetylene in the presence of NP thin films under optimized reaction conditionsa
PdCu/RGO: time
(min); yield (%)b
PdCu/RGO: TON;
TOF (h−1
PdCuFe/RGO: time
(min); yield (%)b
PdCuFe/RGO: TON;
TOF (h−1
Entry
Substrate
)
)
1
2
3
4
5
6
7
PhI
14; 95
20; 95
90; 88
80; 90
80; 80
18; 70
120; 70
15 833; 68 839
15 833; 47 979
14 667; 9778
10; 95
20; 95
70; 91
35; 93
55; 86
15; 75
80; 70
95 000; 593 750
95 000; 287 879
91 000; 78 448
93 000; 159 520
86 000; 93 886
75 000; 300 000
70 000; 52 632
PhBr
PhCl
4‐MeC6H4Br
4‐NO2C6H4Cl
4‐NO2C6H4Br
C5H4NCl
15 000; 11 278
13 333; 10 025
11 666; 38 887
11 666; 5833
aReaction conditions: 60 °C, H2O–CTAB and KOH as base.
bIsolated yield.

HOSEINI ET AL.
7
TABLE 6 Study of efficacy of the present catalysts compared with previously reported catalysts
Entry
Catalyst
Pd/C
Catalyst (mol%)
Solvent
Base
Temp. (°C)
Time (min)
Yield (%)
Ref.
[50]
[50]
[1]
1
2
3
4
5
6
7
8
9
0.5
0.125
0.5
Piperidine
DMAa
Piperidine
100
100
100
50
360
360
360
1440
360
60
61
77
80
80
85
93
97d
95
95
Pd/C
Pyrrolidine
Pd/C
Pyrrolidine
DMA
Pyrrolidine
[51]
[52]
[53]
[54]
Pd‐CuFe2O4/SiO2
Pd/Cu‐ARF(II)b
Cu48Pd52/RGO
MMTc/Pd‐Cu
PdCu/RGO
PdCuFe/RGO
0.3
1,4‐Diazabicyclo[2.2.2]octane
Not reported
0.63
CH3CN
K2CO3
KOH
80
DMF
120
65
1
Ethanol
K2CO3
KOH
960
14
0.006
0.001
H2O–CTAB
H2O–CTAB
60
This work
This work
KOH
60
10
aDMA: dimethylacetamide.
bARF(II): Amberlite resins with formate, under N2 condition.
cMMT: montmorillonite.
dIn the presence of 2 mol% PPh3.
with increasing Fe amount in the NPs with nearly the same
size, the efficiency of the reaction is increased.
metals such as Cu and Fe to the Pd thin film is reduces the
amount of expensive Pd content of the catalyst and improves
the catalytic activity due to the synergistic effect of Cu and Fe
that accelerates the reductive elimination reaction. Moreover,
theoretical studies demonstrated that metals such as Cu can
modify the Pd valence state via injection of charge into the
sp subband.[57] Due to electronic modification in the Pd–Cu
alloys, it improves the catalytic activity of the alloy systems.
ICP analysis shows no Pd leaching, but it has been accepted
that most heterogeneous Pd catalysts catalyse via a homoge-
neous method (dissolved as colloids or complexes by
leaching from the supported Pd) by leached Pd species, and
can re‐deposited on reaction completion.[1]
There are some reports of the Sonogashira reaction in the
absence of palladium and using other transition metals such
as iron [55] and copper.[56] In most of these reports, results
are limited to the use of aryl iodides and activated bromides
under high reaction temperature (130 °C) and high loading
of catalysts. Therefore, there are few reports about the reac-
tion in the presence of aryl chlorides, but the PdCu/RGO
and PdCuFe/RGO thin films can react with aryl chlorides to
give high yields of products.
One of the major advantages of the system under investi-
gation is the easy separation of the catalyst from the reaction
mixture for recovery and reuse. The reusability of the cata-
lysts was investigated in the reaction of bromobenzene with
phenylacetylene at 60 °C under optimized reaction condi-
tions. When the reaction was completed, the catalyst could
be easily separated and then it was washed with water and
diethyl ether. The recovered catalyst was dried and can be
reused successfully. As evident from Table 7, the catalytic
activity of the alloy catalysts remains and they retain a good
performance after four recycles.
4
| CONCLUSIONS
Palladium‐based alloys exhibit promising catalytic activity in
various organic transformations. Homogeneous Pd catalysts
in C─C Sonogashira reactions exhibit some disadvantages
such as the high cost of Pd, they cannot be recycled and
reused and are difficult to extract from the reaction mixture
that can cause a severe problems for pharmaceutical indus-
tries and limiting their application. Heterogeneous systems
have high catalyst stability, and the catalysts are easily
extracted from the reaction mixture by simple filtration and
can be reused for several subsequent reactions. In this study,
PdCuFe NPs supported on RGO thin films were prepared via
a simple liquid–liquid interface self‐assembly method as a
heterogeneous catalyst (insoluble catalyst in the reaction
medium and catalyst recovery is achieved by solvent
decantation). In most cases of Sonogashira coupling
catalysed by Pd/C, the presence of CuI and PPh3 as ligands
is necessary. There are few reports of the use of Pd/C cata-
lysts for Sonogashira coupling reactions being successful in
the absence of phosphine ligands. Also, cross‐coupling reac-
tions catalysed by supported Pd can be carried out in organic
solvents or organic solvent–water mixtures. In this study we
In general, C─C coupling reactions catalysed by sup-
ported palladium follow the usual reaction mechanism with
three main steps: (i) oxidative addition, (ii) transmetallation
and (iii) reductive elimination. Addition of non‐precious
TABLE 7 Recycling results of PdCu/RGO and PdCuFe/RGO NP thin films
as catalyst at 60 °C for coupling reaction of phenylacetylene with
bromobenzenea
Cycle
PdCu/RGO: yield (%)b
PdCuFe/RGO: yield (%)b
Fresh catalyst
First recycle
95
95
90
80
80
95
95
95
90
85
Second recycle
Third recycle
Fourth recycle
aReaction conditions: 60 °C, H2O–CTAB and KOH as base.
bIsolated yield.

8
HOSEINI ET AL.
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How to cite this article: Hoseini, S. J., Aramesh, N.,
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