Palladium–cadmium sulfide nanopowder at oil–water interface as an effective catalyst for Suzuki–Miyaura reactions

Article abstract of DOI:10.1002/aoc.3718

A simple and effective strategy is described for the synthesis of Pd–CdS nanopowder by the reduction of an organopalladium(II) complex, [PdCl₂(cod)] (cod = cis,cis-1,5-cyclooctadiene), in the presence of CdS quantum dots (QDs) at a toluene–water interface. We investigated the impact of addition of CdS QDs on catalytic activity of Pd nanoparticles (NPs). The Pd–CdS nanopowder functions as an efficient catalyst for Suzuki–Miyaura reactions for the formation of carbon–carbon bonds. There is a high electron density on Pd NPs and due to their high electron affinity they behave as an electron scavenger from CdS increasing the rate of oxidative addition, which is the rate-determining step of the catalytic cycle, and, just as we expect, the C─C coupling reaction with the Pd–CdS nanopowder is faster and occurs in less time than that with Pd nanocatalysts. Compared to classical reactions, this method consistently has the advantages of short reaction times, high yields in a green solvent, reusability of the catalyst without considerable loss of catalytic activity and low cost, and is a facile method for the preparation of the catalyst.

Full text of DOI:10.1002/aoc.3718

Received: 9 September 2016
DOI 10.1002/aoc.3718
Revised: 22 November 2016
Accepted: 25 November 2016
F U L L PA P E R
Palladium–cadmium sulfide nanopowder at oil–water interface as
an effective catalyst for Suzuki–Miyaura reactions
S. Jafar Hoseini | Elham Jahanshahi | Roghayeh Hashemi Fath
Department of Chemistry, Faculty of Sciences,
A simple and effective strategy is described for the synthesis of Pd–CdS nanopowder
Yasouj University, Yasouj 7591874831, Iran
by the reduction of an organopalladium(II) complex, [PdCl (cod)] (cod = cis,cis‐
1,5‐cyclooctadiene), in the presence of CdS quantum dots (QDs) at a toluene–water
Correspondence
S. Jafar Hoseini, Department of Chemistry, Faculty
of Sciences, Yasouj University, Yasouj
2
interface. We investigated the impact of addition of CdS QDs on catalytic activity of
Pd nanoparticles (NPs). The Pd–CdS nanopowder functions as an efficient catalyst
for Suzuki–Miyaura reactions for the formation of carbon–carbon bonds. There is
a high electron density on Pd NPs and due to their high electron affinity they behave
as an electron scavenger from CdS increasing the rate of oxidative addition, which is
the rate‐determining step of the catalytic cycle, and, just as we expect, the C─C cou-
pling reaction with the Pd–CdS nanopowder is faster and occurs in less time than
that with Pd nanocatalysts. Compared to classical reactions, this method consistently
has the advantages of short reaction times, high yields in a green solvent, reusability
of the catalyst without considerable loss of catalytic activity and low cost, and is a
facile method for the preparation of the catalyst.
7
591874831, Iran.
Email: jhosseini@yu.ac.ir; sjhoseini54@yahoo.com
KEYWORDS
oil–water interface, organopalladium complex, quantum dot, Suzuki–Miyaura reaction
[
7]
1
|
INTRODUCTION
labelling, etc. Cadmium sulfide (CdS), in the form of semi-
conductor QDs, has a direct band gap (2.63 eV) and thus it
becomes sensitive towards visible light. Among various mod-
ification strategies, coupling semiconductors with metal ions
with a suitable work function has proven to be effective for
enhancing the performance of catalysts. For example, Pd
has a high work function value, which is very suitable for tak-
Palladium‐catalysed Suzuki–Miyaura cross‐coupling (SMC)
reactions are a powerful tool for the formation of new car-
bon–carbon bonds and are routinely used in fine chemicals
research and development and in pharmaceutical discovery
[
1]
laboratories. Approaches for significantly improving het-
erogeneous Pd‐based nanoparticle (NP) catalysts are still rare
at the moment, as electron density within the metal could pre-
[
8]
ing up electrons from the conduction band of CdS NPs.
Herein, we demonstrate a novel, facile, simple and cost‐
effective method for the synthesis of Pd–CdS nanopowder.
Our synthetic method is advantageous in the following
respects. (1) It is a simple and less expensive synthesis of
Pd–CdS nanopowder, only a beaker and syringe being
required to produce a high‐quality nanopowder of Pd–CdS
in a short time. To the best of our knowledge, there is no
report concerning fabrication of metal loading on QDs at a
liquid–liquid interface. (2) So far various methods have been
[2]
viously not be easily modified on that scale. We are inter-
ested in enhancing the activity of heterogeneous Pd‐based
NP catalysts by increasing their electron density via support
effects. Solar light absorption is a convenient and sustainable
method for generating electronically excited states of
[
3,2]
photocatalysts.
In recent years, colloidal II–VI semiconductor nanostruc-
[
4]
tures, often known as quantum dots (QDs), have been com-
monly investigated because of their special optical properties
including broad absorption, excellent photostability and
[
8,9]
employed for the synthesis of Pd–CdS.
Using the organo-
metallic precursor in the present work, i.e. [PdCl (cod)] (cod
2
[5]
narrow emission, which in light‐emitting diodes enable
= cis,cis‐1,5‐cyclooctadiene), being able to decompose in the
[6]
their potential applications in solar cells,
biomedical
presence of NaBH as a reducing agent, it appears as a
4
Appl Organometal Chem 2017;e3718.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 8
https://doi.org/10.1002/aoc.3718

2
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JAFAR HOSEINI ET AL.
valuable alternative for the synthesis of Pd–CdS nanopowder.
In recent years, application of organometallic complexes has
appeared as an important alternative route for the synthesis
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 toluene–water interface. With
the passage of time, the colour became more vivid, finally
resulting in a film at the toluene–water interface. The organic
and aqueous layers above and below the film were, however,
transparent. The ICP analysis results for the amounts of Pd
and Cd in the powder were 8.4 and 2.21%, respectively.
[
10]
of nanomaterials.
In the study reported here, we prepared Pd–CdS
nanopowder via a facile method, utilizing CdS as the semi-
conductor to absorb visible light and Pd as the electron
scavenger. The Pd–CdS nanopowder was characterized using
transmission electron microscopy (TEM), X‐ray diffraction
(XRD), and Fourier transform infrared (FT‐IR) and
2
.3 | General Procedure for SMC Reaction
UV–visible spectroscopies. The Pd–CdS nanopowder exhib-
ited a high catalytic activity in the SMC reaction in water as
solvent. This composite was shown to act as an efficient
semi‐heterogeneous catalyst for the SMC reaction in aqueous
solution under aerobic conditions and could be efficiently
reused whilst retaining its inherent catalytic activity.
In a typical reaction, 5.00 ml of water, 1.00 mmol of K CO ,
2
3
0
.50 mmol of aryl halide, 0.75 mmol of phenylboronic acid
or 2‐methylphenylboronic acid, and Pd–CdS nanopowder
were mixed. Catalyst containing a certain amount of Pd
(0.00004–0.012 mmol; for Pd–CdS nanopowder catalyst con-
taining 8.4 wt% Pd, corresponding to 0.051–15.4 mg of cat-
alyst) was added to the mixture. ICP analysis indicated that
the ratio of Pd to Cd was 3.8:1. If the total amount of the cat-
alyst used was less than 1.0 mg, a water dispersion of the cat-
alyst with a concentration less than 1.0 mg ml− was first
prepared and then a small amount of the dispersion was taken
and used as the catalyst. The mixture was stirred at room tem-
perature. After completion of the reaction (monitored by
TLC), the catalyst was separated from the reaction mixture
by filtration, and then dichloromethane (3 × 5 ml) was added
to the reaction mixture. The organic phase was separated and
2
| EXPERIMENTAL
1
All of the chemical compounds were purchased from Merck
or Sigma‐Aldrich. The [PdCl (cod)] complex was synthe-
2
[11]
sized using a reported procedure.
obtained with a Philips CM‐10 microscope operated at
00 kV. XRD patterns were obtained using a Bruker AXS
D8 Advance) instrument employing the reflection
TEM images were
1
(
Bragg–Brentano geometry with Cu Kα radiation. UV–visible
studies were carried out using a PerkinElmer Lambda
dried over anhydrous MgSO . Evaporation of the solvent
4
2
5 spectrophotometer. FT‐IR spectra were recorded using a
gave the pure desired product which was then characterized
1
1
JASCO FT/IR‐680 Plus spectrometer. H NMR spectra were
obtained with a Bruker 400 MHz Ultra‐shield spectrometer
by comparing H NMR and FT‐IR spectra with those of
authentic samples (details are given in the supporting infor-
mation). The turnover number (TON; moles of product per
mole of catalyst) and the turnover frequency (TOF; TON
per time) were calculated on the basis of the amount of biaryl
product formed. Also, a similar procedure was applied for the
experiment in the dark.
using CDCl as the solvent. The loading amounts of Pd and
3
Cd were determined using an inductively coupled plasma
(ICP) analyser (Varian Vista‐Pro).
2
.1 | Preparation of CdS QDs
Firstly, an aqueous solution of mercaptosuccinic acid (MSA;
.525 g, 5 ml) was added to CdCl solution (0.01 M, 50 ml).
0
2
3 | RESULTS AND DISCUSSION
The reaction mixture was bubbled with nitrogen gas for
0 min to remove oxygen. Secondly, under the protection of
nitrogen gas, the reaction mixture was heated under reflux
at 110 °C. After the pH was adjusted to 11 with NaOH
3
3
.1 | Physicochemical Characterization of Catalyst
CdS QDs were prepared using a one‐step route with MSA,
CdCl and Na S as precursors in water. Here MSA and
(
1.0 M), 5.5 ml of Na S (0.1 M) was added to the solution
2
2
2
Na S act as the capping agent and the sulfur source, respec-
tively. A facile route for the synthesis of Pd–CdS nanopowder
via a simple chemical reduction of [PdCl (cod) ] complex at
the oil–water interface with NaBH at room temperature is
and the reaction mixture was heated under reflux for 4 h.
Finally, the reaction mixture was cooled to room temperature,
and ethanol was added, precipitating a yellow product.
2
2
2
4
demonstrated. The [PdCl (cod) ] complex was selected as
2
2
2
.2 | Preparation of Pd–CdS Nanopowder at Toluene–
Water Interface
PdCl (cod) ] complex (1 mM) in toluene (25 ml) was soni-
the Pd precursor due to its solubility in organic solvents and
easy reduction to Pd(0) in the presence of reducing agents
such as NaBH4.
[
2
2
cated for 15 min to prepare a yellow‐coloured solution. This
solution was stood in contact with distilled water (25 ml) con-
taining CdS QDs (1 mM) in a beaker (100 ml). Once the two
The FTIR spectra of MSA and CdS QDs are shown in
Figure 1. For MSA, absorption bands appear at 2643 and
−
1
2564 cm , which are attributed to CH ; a stronger absorp-
2
−
1
layers were stabilized, 10 ml of aqueous NaBH (0.1 M) was
tion band appears at 1697 cm , which is assigned to C═O;
4

JAFAR HOSEINI ET AL.
3 of 8
FIGURE 3 UV–visible spectra of (a) CdS and (b) Pd–CdS nanopowder
[
12]
band gap of 2.63 eV.
When the Pd NPs are introduced, a
red shift is observed in the maximum absorption,
likely because the presence of metallic Pd NPs
contributes to enhanced absorption in the visible light region
[
12]
(
Figure 3b). As a result, the effective band gap of Pd–CdS
decreases (2.06 eV). This distinct absorption in the visible
light region suggests that the Pd–CdS nanopowder is more
efficient at utilizing visible light, in the solar spectrum, a
potential advantage to the photoelectrocatalytic efficiency
for the catalytic SMC reaction.
The crystal structures of the compounds were investigated
using XRD. Figure 4(a) shows the XRD pattern recorded for
the CdS QDs. The four main diffraction peaks can be assigned
as the (111), (220), (311) and (331) crystalline planes of CdS
[
13]
QDs.
Figure 4(b) shows the XRD pattern of the Pd–CdS
nanopowder catalyst. The five main diffraction peaks can be
FIGURE 1 FT‐IR spectra of (a) MSA and (b) CdS QDs
assigned as the (111), (200), (220), (311) and (222) indices
of face‐centred cubic Pd(0), and the diffraction peaks con-
firm the presence of CdS QDs (Figure 4b). Relative to the
same reflections for Pd(0) and CdS QDs, the diffraction peaks
of the Pd–CdS nanopowder are shifted, revealing decreased
lattice parameters and a high level of alloying.
−
1
[14]
an absorption band appears at 1423 cm , which is assigned
to C─O; and absorption bands of OH and SH appear around
the 3200 cm− (Figure 1a). The FT‐IR spectrum of CdS QDs
is shown in Figure 1(b). The characteristic peaks of the S─H
and O─H stretching disappear, the peak of C═O shifts from
1
−
1
−1
1
697 to 1552 cm (145 cm ) and the peak of C─O remains
Recently, we have reported the formation of Pd(0) NPs
almost unchanged. The disappearance of the O─H peak and
shifting of the C═O peak are due to deprotonation of the car-
boxyl group of MSA. As shown in Figure 2, the disappear-
ance of the S─H peak is not due to the deprotonation of the
sulfhydryl group of MSA which suggests that there must be
a coordination interaction between Cd metal ion and MSA.
UV–visible spectra were used to analyse the optical prop-
erties of CdS and Pd–CdS nanopowder (Figure 3). The UV–
visible spectrum (Figure 3a) shows the maximum absorption
at ca 430 nm, revealing the CdS semiconductor QDs with
from reduction of [PdCl (cod)] complex at a toluene–water
2
interface, the NPs having a mean diameter of approximately
[
14]
4 nm.
Figure 5(a) and (b) shows TEM images of the
Pd–CdS nanopowder, indicating spherical structures with
mean diameter of approximately 5 nm that can obviously
confirm Pd–CdS nanopowder formation.
2
+
3
.2 | Catalytic Activity
To investigate the catalytic efficiency of Pd–CdS
nanopowder, we began with SMC reaction of phenylboronic
acid with bromobenzene as the model substrates (Table 1).
K CO was used as the base to optimize the conditions of
2
3
the reaction. The semi‐heterogeneous catalyst was used in
the present project. The Pd loading of the catalyst, which
was obtained using ICP, was 4.2 μg in 0.051 mg of catalyst.
The optimum amount of the catalyst is found to be
0.00004 mmol of Pd for Pd–CdS nanopowder catalyst, the
FIGURE 2 Schematic representation of formation of CdS QDs

4
of 8
JAFAR HOSEINI ET AL.
9
{
4% yield under mild conditions (room temperature)
#,32] (Table 1, entry 1). Further, when the same reaction
is carried out in a H O–EtOH (1:1) solvent mixture at
2
8
0 °C, the desired product is obtained in 83% yield (Table 1,
entry 3). Other solvents, such as ethanol, H O–sodium
2
dodecylsulfate
(SDS),
H O–cetyltrimethylammonium
2
bromide (CTAB), dimethylsulfoxide (DMSO) and tetrahy-
drofuran (THF), also afford low yields of the coupling
product (Table 1, entries 2 and 4–7).
We investigated the impact of addition of CdS semicon-
ductor QDs on the catalytic activity of the Pd NPs in the
SMC reaction. For the coupling reaction of phenylboronic
acid and bromobenzene, the reaction does not occur when
using only pure CdS as catalyst. However, the Pd–CdS
nanopowder catalyst shows excellent catalytic activity under
the given conditions. The experimental results demonstrate
the marked catalytic activity of Pd–CdS nanopowder with
TON of 11 750 and TOF of 11 750 h− (0.008 mol% Pd–
CdS nanopowder, 94% yield at room temperature for 1 h)
for SMC reaction of bromobenzene and phenylboronic acid.
The catalytic activity of Pd–CdS nanopowder is much higher
than that for the same SMC reaction catalysed by the Pd NP
catalyst (0.8 mol% Pd NPs, 90% yield at 80 °C for 1.5 h,
FIGURE 4 XRD patterns of (a) CdS QDs and (b) Pd–CdS nanopowder
1
−
1 [14]
TON =112.5, TOF = 75 h ). Also, for the same Pd load-
ing (0.8 mol% Pd NPs), Pd NPs exhibit only 51% yield after
1
h. Thus, it may be concluded that Pd NPs deposited on the
surface of CdS actually accelerate the rate of SMC reaction
+
by stabilizing holes (hVB ) in the valence band (VB) of
CdS. As the work functions of Pd and CdS are 5.12 and
[
8]
4
.2 eV, a built‐in potential of 0.92 eV can form between
FIGURE 5 (a, b) TEM images Pd–CdS nanopowder and (c) histogram of
particle size distribution
Pd and CdS. The potential forces electrons to transfer from
CdS to Pd NPs and results in electron‐rich Pd NPs. Also,
[
8]
Pd is very much prone to electron capture due to its high
electron affinity, and thus can scavenge the photogenerated
electrons from the CdS NPs. The electron‐rich Pd NPs can
activate bromobenzene and produce Pd‐adsorbed aryl. Mean-
while, the photogenerated holes on the CdS surface can assist
in activating phenylboronic acid molecules by cleaving the
carbon–boron bond. Finally, the redox‐activated species meet
to couple to the final products. A schematic mechanism on
the SMC reaction is illustrated in Figure 6.
TABLE 1 Effects of solvent and temperature on SMC reaction of
bromobenzene with phenylboronic acid
a
b
Entry
Solvent
Temp. (°C)
Yield (%)
1
2
3
4
5
6
7
H
2
O
r.t.
r.t.
80
80
80
r.t.
r.t.
94
70
EtOH
EtOH–H
2
O (1:1)
83
H
H
2
O–CTAB
O–SDS
60
2
40
DMSO
THF
Trace
Trace
a
Reaction conditions: 0.50 mmol of bromobenzene, 0.75 mmol of phenylboronic
acid, 1.00 mmol of K CO , 5.0 ml of solvent, sunlight irradiation, the amount of
2
3
supported Pd used is 0.00004 mmol, reaction time 1 h.
b
Isolated yield.
yield of biaryl being markedly is reduced when less catalyst
is used. The reaction proceeds in the presence of Pd–CdS
nanopowder in water and the desired product is obtained in
FIGURE
6
Proposed mechanism for SMC reaction on Pd–CdS
nanopowder catalyst

JAFAR HOSEINI ET AL.
5 of 8
We then planned to evaluate the mechanism of the
photocatalysis of Pd–CdS nanopowder in the SMC reaction.
For this, we carried out the reaction of phenylboronic acid
with bromobenzene in the presence of Pd–CdS nanopowder
in water without irradiation (dark reaction). The irradiation
of sunlight is necessary for reaction. These studies suggest
the suppression of electron transfer from CdS to Pd NPs in
the absence of sunlight. Furthermore, without irradiation of
sunlight, only trace yield is observed which highlights the
importance of irradiation to the catalytic activity of the
system.
For example, when Pd–CdS nanopowder was used as
catalyst, the SMC reactions of deactivated aryl chloride
including chlorobenzene, 1‐chloro‐4‐nitrobenzene and
The SMC reaction of various aryl halides, even aryl
chloride derivatives, was examined under optimal reaction
conditions to show the high catalytic activity of the Pd–CdS
nanohybrid. The results are summarized in Table 2. To
avoid the homo‐coupling product, we used different aromatic
rings for halide and boronic acid (Table 2 entries 4–11).
FIGURE 7 Recycling result for coupling reaction of bromobenzene with
phenylboronic acid in the presence of Pd–CdS nanopowder
TABLE 2 SMC reaction of aryl halides with phenylboronic acid or 2‐methylphenylboronic acid catalysed by Pd–CdS nanopowder under sunlight irradiation
a
b
−1 b
Entry
Substrate
ArB(OH)
2
Product
Time (h); yield (%)
TON
TOF (h )
1
0.35, 96
12 000
11 750
10 250
10 000
34 286
11 750
5 125
2
3
4
1, 94
2, 82
1.5, 80
6 667
5
6
7
1.33, 76
1.4, 79
2.5, 73
9 500
9 875
9 125
7 143
7 054
3 650
8
9
9, 80
10 000
10 250
1 111
5 694
1.8, 82
1
0
1
2.37, 80
1.28, 79
10 000
9 875
4 219
7 715
1
a
Isolated yield.
b
See Section 1.3 for the calculation of TONs and TOFs.

6
of 8
JAFAR HOSEINI ET AL.
2‐chloropyridine proceed with high yields of 82, 76 and 80%,
respectively (Table 2, entries 3, 5 and 8). The SMC reactions
of activated aryl chlorides with different substituents also
give good yields (Table 2, entries 6, 7 and 9–11). The results
unambiguously indicate that aryl iodides and aryl bromides
are involved in the fast steps of the catalytic cycle of the
SMC reaction (Table 2, entries 1, 2 and 4). Sterically hin-
dered aryl chlorides and arylboronic acids are effective as
substrates (Table 2, entries 7 and 10). Generally, the catalytic
cycle of the SMC reaction includes three steps: (1) oxidative
addition, (2) transmetalation, and (3) reductive elimina-
[
14]
tion.
Normally, the activity of aryl halides decreases in
the order of I > Br > Cl and electron‐deficient aryl halides
are usually more active than electron‐rich ones. Thus, the
oxidative addition step is generally considered as the
rate‐determining step. In the oxidative addition step, Pd(0)
acts as a nucleophile and preferentially attacks the most
electron‐deficient position. It should be noted that the
Pd–CdS nanopowder behaves as a very good catalyst in the
SMC reaction. The Pd–CdS nanopowder catalyst, compared
to Pd NP catalyst due to the presence of CdS groups, exhibits
FIGURE 8 TEM image of Pd–CdS nanopowder after seven catalytic cycles
TABLE 3 Catalytic performance of various Pd‐based catalysts in the coupling of chlorobenzene and 1‐chloro‐4‐nitrobenzene with phenylboronic acid
Entry
G
Catalyst
Solvent
Base
Temp. (°C)
Time (h)
Yield (%)
Ref.
a
1
2
3
4
5
6
7
8
9
H
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
.(1f)
2
H
H
H
2
2
2
O–EtOH (3:2)
O–EtOH (3:2)
O
K
K
2
2
CO
3
80
80
48
10
5 min
2–6
7
33
73
45
65
53
75
80
70
80
85
82
67
90
90
78
70
74
76
[16]
[16]
b
d
H
.(1 g)
2
CO
3
c
H
Na
2
CO
3
150–170
130
65
[17]
H
NAP–Mg–Pd(0)
Pd(II)–MWCNTs
DMA
K
K
K
K
K
K
K
K
K
3
2
2
2
2
2
2
2
2
PO
4
[18]
e
H
H
H
H
2
2
2
O–DMF (1:1)
CO
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
3
[19]
f
H
Pd FS
O
O
80
4
[14]
g
H
Pd/RGO
80
3
[14]
h
H
PdZn
EtOH–H
2
O (1:1)
80
8
[14]
i
H
PdPtZn
H
H
H
H
H
2
2
2
2
2
O–CTAB
80
2
[14]
j
10
11
12
13
14
15
16
17
18
H
Pd/Fe
Pd–dS
Pd(OAc)
Na [PdCl
3
O
4
/RGO
O
80
2.5
2
[14]
H
O
r.t.
This work
[16]
a
2
NO
NO
NO
NO
NO
NO
NO
2
2
2
2
2
2
2
2
.(1f)
O–EtOH (3:2)
O–DMSO
r.t.
10
18
2–6
1.5
2.5
1.5
1.33
k
2
4
]
KF, K
3
PO
4
80
[20]
d
NAP–Mg–Pd(0)
DMA
K
K
K
K
K
3
2
2
2
2
PO
CO
CO
CO
CO
4
130
80
[18]
j
Pd/Fe
3
O
4
/RGO
H
H
H
H
2
O
2
O
2
O
2
O
3
3
3
3
[14]
f
Pd FS
80
[14]
g
Pd/RGO
80
[14]
Pd–CdS
r.t.
This work
a
Pd(OAc)
2
.(1f)
.(1 g)
(0.4 mol%).
2
(2 mol%) (1f = 1,1,3,3‐tetramethyl‐2‐n‐butylguanidine).
b
Pd(OAc)
2
2
(2 mol%) (1 g = 1,1,3,3‐tetramethyl‐2‐sec‐butylguanidine); TBAB (0.1 equiv.) as additive.
c
Pd(OAc)
2
d
NAP–Mg–Pd(0) (3 mol%).
e
Pd–Schiff base@MWCNTs (0.2 mol%).
f
Pd FS NP (0.8 mol%).
g
h
i
Pd/RGO NP (0.48 mol%).
PdZn NP (1.5 mol%).
PdPtZn NP (1 mol%).
j
Pd/Fe
3
O
4
/RGO nanohybrid (0.36 mol%).
k
Na
2
[PdCl ] (0.5 mol%).
4

JAFAR HOSEINI ET AL.
7 of 8
a faster oxidative addition. As mentioned, in the Pd–CdS
nanopowder donation of electrons from CdS to Pd NPs
improves the reactivity of the catalyst compared to Pd NPs.
Good recyclability is the main advantage of heteroge-
neous or semi‐heterogeneous catalysts. From an industrial
point of view, the reusability of a catalyst is important for
large‐scale operation. To test the recyclability of the Pd–CdS
nanopowder catalyst in the C─C coupling of bromobenzene
and phenylboronic acid, the catalyst was reused for seven
times after filtering and drying, without noticeably losing
activity (Figure 7). The recovered catalyst was dried and
observed using TEM analysis. The particles of the Pd–CdS
nanopowder remain the same size, and no considerable
aggregation phenomenon is observed after seven cycles from
TEM imaging (Figure 8). Also, the used catalyst was
analysed using ICP and no discernible leaching of Pd is
observed.
micelle medium, (ii) the catalyst leaching was calculated
from ICP analysis and no discernible leaching of Pd was
observed (this is the most important point) and (iii) catalyst
recovery is done by solvent decantation. The catalyst can be
handled easily as it is very stable in air and can be easily
removed from the reaction mixture by filtration. By
employing this novel heterogeneous photocatalyst, the SMC
reaction can proceed at room temperature under the irradia-
tion of natural sunlight. The present work will inspire the fur-
ther exploitation of semiconductor‐supported metal NPs as
photocatalysts for a wide range of organic transformations
driven by visible light, even natural sunlight.
ACKNOWLEDGMENTS
We thank the Yasouj University Research Council and the
Iranian Nanotechnology Initiative Council for their support.
TON and TOF, which are measures of the efficiency of
a catalyst, totally depend on the Pd concentration. Guo and
co‐workers reported that the SMC reaction over a Mott–
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| CONCLUSIONS
The study presented shows that Pd–CdS nanopowder catalyst
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