Schiff base complex of palladium immobilized on magnetic nanoparticles: an efficient and recyclable nanocatalyst for C?C coupling reactions

Article abstract of DOI:10.1002/aoc.3531

A Schiff base complex of palladium anchored on Fe₃O₄ magnetic nanoparticles as an efficient and magnetically reusable nanocatalyst is reported for C?C bond formation through Heck and Suzuki reactions. The catalyst was easily recovere

Full text of DOI:10.1002/aoc.3531

Full paper
Received: 28 March 2016
Revised: 28 April 2016
Accepted: 7 May 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3531
Schiff base complex of palladium immobilized
on magnetic nanoparticles: an efficient and
recyclable nanocatalyst for C–C
coupling reactions
Somaieh Rezaei , Arash Ghorbani-Choghamarani * and Rashid Badri
a
b
a
3 4
A Schiff base complex of palladium anchored on Fe O magnetic nanoparticles as an efficient and magnetically reusable
nanocatalyst is reported for C–C bond formation through Heck and Suzuki reactions. The catalyst was easily recovered
and reused several times without significant loss of its catalytic efficiency or palladium leaching. The magnetic nanocatalyst
was characterized using Fourier transform infrared and inductively coupled plasma atomic emission spectroscopies, thermo-
gravimetric analysis, vibrating sample magnetometry, and transmission and scanning electron microscopies. Copyright ©
2
016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: magnetic nanoparticle; C–C coupling; Heck reaction; Suzuki reaction; Schiff base
minimal leaching of palladium species. These cross-coupling
Introduction
reactions are used as a powerful method in modern synthetic
organic chemistry for the preparation of advanced materials,
natural products, liquid crystal materials, agrochemicals, pharma-
ceuticals, biologically active compounds, herbicides, UV screens,
The immobilization of homogeneous catalysts on various support
materials to facilitate catalyst separation and recycling is of great
importance in catalyst science. However, the active sites in classic
heterogeneous catalysts have limited accessibility compared to
homogeneous systems, and thus the activity and selectivity of
[1,2]
[
12–16]
polymers and hydrocarbons.
[3,4]
classical heterogeneous catalysts are usually reduced.
Ideally,
the advantages of homogeneous and heterogeneous catalysts, such
as high activity and selectivity of the former and easy separation and
recycling of the latter, should be combined. These goals can be
achieved by nanocatalysts. Nanocatalysts bridge the gap between
Experimental
3 4
Preparation of Fe O MNPs
[5,6]
homogeneous and heterogeneous catalysts.
This is because
Free Fe MNPs were prepared using chemical precipitation of
3 4
O
3+
2+
when the size of the support is decreased to the nanometre scale,
the surface area is substantially increased and the support can be
Fe and Fe ions with a molar ratio of 2:1. Typically, FeCl
3 2
ꢀ6H O
(5.838 g, 0.0216 mol) and FeCl O (2.147 g, 0.0108 mol) were
2
ꢀ4H
2
[7]
evenly dispersed in solution, forming a homogeneous emulsion.
dissolved in 100 ml of deionized water at 80 °C under nitrogen
atmosphere and vigorous mechanical stirring conditions. Then,
10 ml of 25% NH3(aq) was added to the reaction mixture. After
30 min, the reaction mixture was cooled to room temperature,
However, the nanocatalyst support can be separated from products
by conventional filtration or centrifugation techniques. But, it is
difficult, time consuming and expensive to separate fine particles
[8,9]
from a reaction mixture.
Therefore, to improve the mentioned
3 4
and black MNPs (Fe O ) were washed five times with distilled
limitations, magnetic nanoparticles (MNPs) have been extensively
employed as alternative catalyst supports, which can be easily
water, and each time were decanted with an external magnet
and dried in vacuum.
[10]
removed from a reaction mixture using magnetic separation.
One of the most promising MNP supports is superparamagnetic iron
oxide. The notable advantages of Fe MNPs are simple synthesis,
ready availability, low cost, high surface area and low toxicity.
More importantly, magnetic separation is easier and more effective
than filtration or centrifugation. Therefore, Fe MNPs are
considered as ideal supports for the heterogenization of homoge-
3 4
O
[6,11]
*
Correspondence to: Arash Ghorbani-Choghamarani, Department of Chemistry,
Faculty of Science, Ilam University, PO Box 69315516, Ilam, Iran.
E-mail: arashghch58@yahoo.com
3 4
O
[5]
a Islamic Azad University, Ahvaz Branch, College of Science, Department of
neous catalysts.
We report here the synthesis and characterization of a palladium
Schiff base complex immobilized on Fe MNPs. This reusable
Chemistry, Ahwaz, Iran
3 4
O
b Department of Chemistry, Faculty of Science, Ilam University, PO Box 69315516,
catalyst was applied for the Suzuki and Heck reactions with a
Ilam, Iran
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

S. Rezaei, A. Ghorbani-Choghamarani and R. Badri
Preparation of MNPs Bonded with Schiff Base Complex of
Palladium (Schiff-base-Pd@MNPs)
Results and Discussion
Catalyst Preparation
The obtained Fe
ethanol–water (1:1 v/v) solution by sonication for 30 min, and then
.5 ml of (3-aminopropyl)trimethoxysilane (APTES) was added to
3 4
O MNPs (1.5 g) were dispersed in 100 ml of
In continuation of our studies on the application of metal complexes
[17]
2
immobilized on MNPs in organic reactions, herein we report a
simple and efficient method for the Suzuki and Heck carbon–carbon
reactions through coupling of aryl halides with phenylboronic acid or
butyl acrylate in the presence of catalytic amounts of Schiff-base-
Pd@MNPs as catalyst.
the reaction mixture. The reaction mixture was stirred using a
mechanical stirring under nitrogen atmosphere at 40 °C for 8 h.
Subsequently, nanoparticles were re-dispersed in ethanol via
sonication five times and separated through magnetic decantation.
The nanoparticle product (APTES@Fe O ) was dried at room tem-
The details of the preparation procedure for the supported catalyst
3
4
perature. In order to prepare Schiff-base@MNPs, the APTES@Fe O4
solid (1 g) was refluxed with 1 mmol of 5-bromosalicylaldehyde in
ethanol for 8 h under nitrogen atmosphere. The resulting solid
are presented in Scheme 1. Initially, the core of Fe
prepared by a chemical co-precipitation technique using FeCl
and FeCl O in basic solution at 80 °C. Then, after coating of Fe O
3 4
MNPs with APTES, the reaction of amino groups with 5-
bromosalicylaldehyde led to 5-bromosalicylaldehyde Schiff base
3
O
4
MNPs was
3
ꢀ6H O
3 2
ꢀ6H
2
2
(Schiff-base@MNPs) was separated using magnetic decantation,
washed with ethanol and dried at room temperature. Finally, for
the preparation of Schiff-base-Pd@MNPs, Schiff-base@MNPs (0.5
g) was dispersed in 20 ml of dry ethanol and was mixed with 0.25
mmol of palladium. The mixture was stirred at 80 °C for 20 h. Then,
supported on Fe O MNPs (Schiff-base@MNPs). Finally, Schiff-base-
3 4
Pd@MNPs was prepared via coordination of palladium with Schiff-
base@MNPs and was characterized using transmission electron
microscopy (TEM), scanning electron microscopy (SEM), thermogra-
vimetric analysis (TGA), vibrating sample magnetometry (VSM) and
inductively coupled plasma atomic emission spectroscopy (ICP-OES).
NaBH (0.3 mmol) was added to the reaction mixture and the
4
reaction was continued for 2 h. The Schiff-base-Pd@MNPs solid
product was obtained by magnetic decantation, and washed with
ethanol and dried at 40 °C in air, because one of the advantages
of this catalyst is that it is stable in air and moisture.
Catalyst Characterization
The size of the catalyst was evaluated using SEM and TEM. The SEM
and TEM images of Schiff-base-Pd@MNPs show that the catalyst is
formed of nanometre-sized particles. As shown in Figs 1 and 2,
most of the particles are quite homogeneous and quasi-spherical
with an average diameter of about 10 nm.
General Procedure for C–C Coupling through Suzuki Reaction
A mixture of aryl halide (1 mmol), phenylboronic acid (1 mmol),
K CO (1.5 mmol) and Schiff-base-Pd@MNPs (0.005 g, 0.81 mol%)
2 3
was stirred in poly(ethylene glycol) (PEG)-400 (1 ml) at 60 °C. The
progress of the reaction was monitored by TLC. After completion
of the reaction, the mixture was cooled to room temperature and
the catalyst was separated using an external magnet and washed
with diethyl ether and the organic layer was extracted with water
and diethyl ether to afford pure products. The organic layer was
3 4
The functionalization of Fe O MNPs with organic layers and
Schiff base complex of palladium is inferred using TGA. Figure 3
2 4
dried over Na SO (1.5 g). Then the solvent was evaporated and
pure biphenyl derivatives were obtained in good to excellent yields.
General Procedure for Coupling of Aryl Halides with Butyl
Acrylate through Heck Reaction
A mixture of aryl halide (1 mmol), butyl acrylate (1.2 mmol), K CO3
2
(3 mmol) and Schiff-base-Pd@MNPs (0.016 g, 2.62 mol%) was
stirred in dimethylformamide (DMF) at 120 °C and the progress of
the reaction was monitored by TLC. After completion of the
reaction, the mixture was cooled to room temperature and the
catalyst was separated using an external magnet and washed with
diethyl ether and the organic layer was extracted with water and
diethyl ether to afford pure products. The organic layer was dried
over Na SO (1.5 g). Then the solvent was evaporated and pure
2
4
products were obtained in 88 to 97% yields.
Scheme 1. Synthesis of Schiff-base-Pd@MNPs.
Figure 1. SEM image of Schiff-base-Pd@MNPs.
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

Schiff-base-Pd@MNPs applied as catalyst in C–C bond formation
3 4
Figure 4. Magnetization curves for (black) Fe O MNPs and (green) Schiff-
base-Pd@MNPs.
loss of about 29%. Meanwhile, weight losses of about 2, 5 and
2% occur for Fe O MNPs, APTES@MNPs and Schiff-base@MNPs,
2
3
4
respectively. On the basis of these results, the grafting of Schiff base
complex of palladium on the Fe O surface is verified.
3
4
In order to determine the exact amount of palladium in Schiff-
base-Pd@MNPs, the ICP-OES technique was used. Based on ICP-
OES analysis, the amount of palladium in the catalyst is 1.63 ×
ꢁ
3
ꢁ1
1
0
mol g based on ICP-OES.
The magnetic property of Fe
of Schiff-base-Pd@MNPs using VSM at room temperature. The
3 4
O MNPs was compared with that
Figure 2. TEM images of Schiff-base-Pd@MNPs.
shows the TGA curves for Fe O MNPs, APTES@MNPs, Schiff-base@-
3
4
MNPs and Schiff-base-Pd@MNPs. The TGA curve of Schiff-base-
Pd@MNPs shows the mass loss of the organic functional groups
as it decomposes upon heating. The weight loss at temperatures
below 200 °C is due to the removal of physically adsorbed solvent
and surface hydroxyl groups. In the TGA curve of Schiff-base-Pd@-
MNPs, decomposition of organic groups is evident with a weight
Figure 3. TGA curves of (a) Fe
O
3 4
MNPs, (b) APTES@MNPs, (c) Schiff-
3 4
Figure 5. FT-IR spectra of (a) Fe O MNPs, (b) APTES@MNPs, (c) Schiff-
base@MNPs and (d) Schiff-base-Pd@MNPs.
base@MNPs and (d) Schiff-base-Pd@MNPs (d).
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

S. Rezaei, A. Ghorbani-Choghamarani and R. Badri
In order to optimize Suzuki reaction conditions, we examined the
coupling of iodobenzene with phenylboronic acid as a model
reaction in various solvents, with different bases and in the
presence of various amounts of catalyst at 25–80 °C (Table 1). As
expected, no product is obtained in the absence of catalyst or base,
even after 24 h (Table 1, entries 1 and 2). As evident from Table 1,
the best results are observed in PEG-400 at 60 °C in the presence
of 5 mg (0.81 mol%) of Schiff-base-Pd@MNPs using 1.5 mmol of
K CO (Table 1, entry 12).
2
3
Scheme 2. Schiff-base-Pd@MNPs catalyses C–C coupling through Suzuki
and Heck reactions.
After optimization of the reaction conditions, the coupling of a
variety of aryl halides with phenylboronic acid was investigated to
confirm the generality of this method. All products are obtained
in good to high yields. The results of this study are summarized in
Table 2. A variety of aryl halides, aryl iodides, aryl bromides and aryl
chlorides, were successfully employed to prepare the corres-
ponding biphenyl derivatives in excellent yields.
In the second part of our study of the application of the catalytic
activity of Schiff-base-Pd@MNPs in C–C coupling reactions, we in-
vestigated the applicability of this catalyst to the Heck reaction
using coupling of aryl halides with butyl acrylate. In order to
optimize the reaction conditions, we examined the coupling
of iodobenzene with butyl acrylate as a model reaction
3 4
room temperature magnetization curves of Fe O MNPs and Schiff-
base-Pd@MNPs are shown in Fig. 4. The Ms. value decreases from 77
ꢁ
18]
1
ꢁ1
emu g for Fe
3
O
4
MNPs to 47.29 emu g for Schiff-base-Pd@-
MNPs. On the basis of these results, the good grafting of organic
layers including palladium complex on the Fe is verified.
Successful functionalization of the Fe MNPs can be inferred
from the Fourier transform infrared (FT-IR) technique. Figure 5 shows
FT-IR spectra for Fe MNPs, APTES@MNPs, Schiff-base@MNPs and
Schiff-base-Pd@MNPs. Two strong absorption bands of the Fe–O
[
3 4
O
3 4
O
3 4
O
ꢁ
1
stretching vibration at 560 and 440 cm , symmetric and asymmetric
modes of the O–H bond stretching vibration near 3120 and 3390
(
Table 3). In order to choose the reaction media, various sol-
ꢁ
1
ꢁ1
cm and O–H deformation vibration near 1620 cm are observed
in the FT-IR spectrum of bare Fe MNPs. Modification of Fe
MNPs using APTES is proved with C–H stretching vibrations that ap-
vents (water, DMF, 1,4-dioxane, dimethylsulfoxide (DMSO)
and PEG) and amounts of Schiff-base-Pd@MNPs were exam-
ined. The best results are observed in DMF using 0.016 g
3 4
O
3 4
O
ꢁ
1
pear at 2920 and 2856 cm
appearing as a broad band at 3440 cm . Schiff-base@MNPs exhibits
and also N–H stretching mode
(
2.62 mol%) of catalyst (Table 3, entry 2). Also, the model re-
action was tested using various bases (KOH, K CO , Na CO
and Et N): the best results are observed using 3 mmol of
CO . Also, the effect of temperature was studied and the
ꢁ
1
2
3
2
3
ꢁ
1
a ν(C¼N) stretch at 1620 cm while in the Schiff-base-Pd@MNPs
3
[2]
this peak appears at lower frequency.
K
2
3
best result is obtained at 120 °C.
Catalytic Study
After the optimization of the reaction conditions, various aryl ha-
lides containing several functional groups were reacted under opti-
mum condition and the corresponding products are obtained in
good to excellent yields (Table 4). The experimental procedure is
very simple and convenient, and has the ability to tolerate a variety
of other functional groups.
After characterization of the catalyst, its catalytic activity was
studied in Suzuki and Heck reactions. These C–C coupling
reactions catalysed by Schiff-base-Pd@MNPs are outlined in
Scheme 2.
2
Table 1. Optimization of Suzuki reaction conditions for coupling of iodobenzene with PhB(OH) in the presence of Schiff-base-Pd@MNPs
a
Entry
Catalyst (mg)
Solvent
Base
Amount of
Temperature (°C)
Time (min)
Yield (%)
base (mmol)
1
2
3
4
5
6
7
8
9
—
5
8
5
3
5
5
5
5
5
5
5
5
5
PEG
PEG
K
2
CO
3
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
80
80
80
80
80
80
80
80
80
80
80
60
40
r.t.
24
24
Trace
Trace
96
—
PEG
K
K
K
K
K
K
2
CO
CO
CO
CO
CO
CO
CO
3
40
PEG
2
2
2
2
2
3
50
98
PEG
3
100
60
91
DMF
DMSO
1,4-Dioxane
PEG
3
93
3
85
92
3
70
94
Na
Et
KOH
2
3
90
86
10
11
12
13
14
PEG
3
N
55
93
PEG
120
70
75
PEG
K
2
K
2
K
2
CO
CO
CO
3
96
PEG
3
150
240
82
PEG
3
Trace
a
Isolated yield.
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Appl. Organometal. Chem. (2016)

Schiff-base-Pd@MNPs applied as catalyst in C–C bond formation
Table 2. Catalytic C–C coupling reaction of aryl halides using
phenylboronic acid in the presence of catalytic amount of Schiff-base-
Pd@MNPs (5 mg, 0.81 mol%) in PEG-400 at 60 °C
Table 4. Coupling of aryl halides with butyl acrylate in the presence of
catalytic amounts of Schiff-base-Pd@MNPs (16 mg, 2.62 mol%)
a
Entry
Aryl halide
Iodobenzene
Time (h)
Yield (%)
Entry
Aryl halide
Time (min)
Yield
Melting
point (°C)
a
(%)
1
2
3
4
5
6
7
8
9
6
7
97
96
91
95
94
88
91
89
90
90
[
19]
19]
20]
1
2
3
4
5
6
7
8
9
Iodobenzene
70
75
96
95
94
94
97
96
96
92
93
97
66–68
4-Bromotoluene
2-Iodotoluene
10.5
3.5
6
[
4-Iodoanisole
80–82
[
4-Iodotoluene
80
41–44
[17]
4–Bromonitrobenzene
4–Bromobenzonitrile
4-Bromotoluene
390
240
265
40
111–113
Bromobenzene
5.5
5.5
4
[
20]
85–86
[17]
42–44
4-Bromophenol
[
19]
Bromobenzene
69
1-Bromo-3-(trifluoromethyl)benzene
4.5
8
[
20]
4–Bromochlorobenzene
Chlorobenzene
80
52–54
10
[17]
225
70
67–68
[17]
a
10
4-Chloronitrobenzene
110–113
Isolated yield.
a
Isolated yield.
In order to show the amount of leaching of the catalyst, the
amount of palladium in the catalyst was obtained using ICP-OES af-
ter six re-uses. The amount of palladium in the catalyst is found to
ꢁ
3
ꢁ1
Reusability of Catalyst
be 1.61 × 10 mol g after six cycles based on ICP-OES measure-
ments. Therefore the catalyst can be recovered and recycled with-
out any significant leaching of palladium. Based on ICP-OES
analysis, the amount of palladium in Schiff-base-Pd@MNPs after
Schiff-base-Pd@MNPs as a magnetically reusable nanocatalyst can
be easily recycled for repeated use in the formation of C
C bonds. To investigate this issue, the recyclability of the catalyst
was examined for the coupling of iodobenzene with phenylboronic
acid as a model reaction. We find that this catalyst demonstrates
markedly excellent reusability; after the completion of the reaction,
the catalyst was easily and rapidly separated from the products
using an external magnet, followed by washing with diethyl ether
to remove residual product and decantation of the reaction mixture
ꢁ
3
six runs is comparable to that of fresh catalyst (1.63 × 10 mol
for fresh Schiff-base-Pd@MNPs).
In order to investigate the leaching of palladium during reaction
and heterogeneity of this catalyst, we conducted a hot filtration test
for the coupling of 4-iodotoluene with phenylboronic acid (Table 2,
entry 3). In this experiment, the yield of product was obtained as
ꢁ
1
g
7
6% after half the reaction time (40 min). Then the reaction was re-
(Fig. 6). Then, the reaction vessel was charged with fresh reactants
peated and catalyst was separated after half the reaction time, and
filtrated solution was allowed to continue reacting until 80 min. The
yield of the reaction in this stage was 79%, confirming that the
leaching of palladium in the reaction mixture is negligible.
and subjected to the next run. As shown in Fig. 6, the catalyst was
used over six runs without any significant loss of activity or palla-
dium leaching. The average isolated yield for six runs is 93.5%,
which clearly demonstrates the practical recyclability of this
catalyst.
Comparison of Catalysts
In order to show the efficiency of the described catalytic system, the
results obtained for the coupling of iodobenzene with
Table 3. Optimization of reaction conditions for cross coupling reac-
tion of iodobenzene with butyl acrylate
Entry Catalyst
Solvent Base Temperature Time
Yield
(%)
a
(mg)
(°C)
(h)
1
2
3
4
5
6
7
12
14
16
18
16
16
16
DMF
DMF
DMF
DMF
K
2
K
2
K
2
K
2
K
2
K
2
K
2
CO
CO
CO
CO
CO
CO
CO
3
120
120
120
120
120
120
120
12
77
91
97
97
43
94
38
3
8.6
6
3
3
5.7
2
H O
3
10
7.2
10
DMSO
1,4-
3
3
Dioxane
PEG
8
9
16
16
16
16
16
K
2
CO
3
120
120
120
120
100
9.8
10
10
7.3
10
86
36
55
96
74
DMF
Et
KOH
CO
CO
3
N
1
0
1
2
DMF
1
1
DMF Na
DMF
2
3
K
2
3
a
Isolated yield.
Figure 6. Recycling experiment of Schiff-base-Pd@MNPs in coupling of
iodobenzene with phenylboronic acid.
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

S. Rezaei, A. Ghorbani-Choghamarani and R. Badri
Table 5. Comparison of results for Schiff-base-Pd@MNPs with other catalysts for the coupling of iodobenzene with phenylboronic acid
Entry
Catalyst (mol% of Pd)
Conditions
Time
Yield
(%)
Ref.
a
(
min)
[
[
[
[
[
[
21]
22]
23]
24]
25]
26]
1
2
3
4
5
6
NHC–Pd(II) complex (1.0 mol%)
Pd NPs (1.0 mol%)
Tetrahydrofuran, Cs
2
CO
3
, 80 °C
720
720
120
88
95
94
88
99
97
H
H
2
O, KOH, 100 °C
O, K CO , 100 °C
O, K CO , 80 °C
CO , 100 °C
CO , 100 °C
CA/Pd(0) (0.5–2.0 mol%)
Pd/Au NPs (4.0 mol%)
2
2
3
EtOH–H
DMF, Cs
O, K
2
2
3
1440
1440
180
Pd(II)–NHC complex (1 mol%)
N,N′-bis(2-pyridinecarboxamide)-
2
3
H
2
2
3
1
,2-benzene palladium complex (1 mol%)
[
[
27]
28]
7
8
9
LDH–Pd(0) (0.3 g)
K
K
2
CO
CO
3
, 1,4-dioxane–H
, 1,4-dioxane–H
2
O (5:1), 80 °C
O (1:1), 95 °C
600
240
70
96
91
96
PANI–Pd (2.2 mol%)
2
3
2
Schiff-base-Pd@MNPs (0.81 mol%)
PEG, K
2
CO
3
, 60 °C
This work
a
Isolated yield
[
7] M. Hajjami, A. Ghorbani-Choghamarani, R. Ghafouri-Nejad, B. Tahmasbi,
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phenylboronic acid are compared with previously reported proce-
dures. Comparison of the results shows a better catalytic activity
and shorter reaction time for Schiff-base-Pd@MNPs in the Suzuki
reaction (Table 5).
[
[
2
[
[
[
11] V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara, J. M. Basset,
Chem. Rev. 2011, 111, 3036.
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Conclusions
In summary, Schiff-base-Pd@MNPs was used as a green, efficient,
highly reusable and air- and moisture-stable nanocatalyst for
carbon–carbon bond formation through Suzuki and Heck reactions.
The advantages of these protocols are the use of a commercially
available, eco-friendly, cheap and chemically stabile material.
Product separation and catalyst recycling are easy with the assis-
tance of an external magnet. This catalyst was characterized using
the VSM, TEM, TGA, SEM and ICP-OES techniques. Also, the catalyst
can be reused for up to six runs without any significant loss of its
activity or palladium leaching.
13] S. Pasa, Y. S. Ocak, H. Temel, T. Kilicoglu, Inorg. Chim. Acta 2013, 405,
493.
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Appl. Organometal. Chem. (2016)