Palladium Nanoparticles Immobilized with Polymer Containing Nitrogen-Based Ligand: A Highly Efficient Catalyst for Suzuki–Miyaura and Mizoroki–Heck Coupling Reactions

Article abstract of DOI:10.1007/s10562-019-02981-7

Abstract: An outstanding heterogeneous catalyst was successfully prepared by immobilization of palladium nanoparticles (Pd NPs) with polymer containing 4′‐(4‐hydroxyphenyl)‐2,2′:6′,2″‐terpyridine (HPTPy) ligand. The polymer cross‐linked with trimethylolpropane triacrylate (TMPTA) units was synthesized by polymerization of itaconic acid-HPTPy (ITC-HPTPy) monomer (so-called cross‐linked poly (ITC- HPTPy)). The cross‐linked poly (ITC-HPTPy) can stabilize the Pd NPs effectively against aggregation, thereby improving the catalytic efficiency of Pd NPs. The presence of Pd NPs on the polymer was confirmed by various physicochemical techniques. The resulting cross‐linked poly (ITC-HPTPy)-Pd was applied as a highly effective recyclable catalyst in Suzuki–Miyaura and Mizoroki–Heck coupling reactions under low Pd-loading conditions and straightforward methods, and provided the corresponding products with excellent yields (up to 98%), high catalytic activities (TOF up to 213?h^?1). The catalyst can be separated from the reaction mixture by centrifugation and can be reused consecutive six times with slight reduction in catalytic activity. Graphic Abstract: Pd NPs immobilized with polymer containing terpyridine ligand are highly active heterogeneous catalysts for Suzuki–Miyaura and Mizoroki–Heck coupling reactions.[Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02981-7

Catalysis Letters
https://doi.org/10.1007/s10562-019-02981-7
Palladium Nanoparticles Immobilized with Polymer Containing
Nitrogen‑Based Ligand: A Highly Efcient Catalyst for Suzuki–Miyaura
and Mizoroki–Heck Coupling Reactions
Homa Targhan1 · Alireza Hassanpour2 · Samira Sohrabnezhad3 · Kiumars Bahrami1,4
Received: 9 July 2019 / Accepted: 19 September 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
An outstanding heterogeneous catalyst was successfully prepared by immobilization of palladium nanoparticles (Pd NPs)
with polymer containing 4′‐(4‐hydroxyphenyl)‐2,2′:6′,2″‐terpyridine (HPTPy) ligand. The polymer cross‐linked with trimeth-
ylolpropane triacrylate (TMPTA) units was synthesized by polymerization of itaconic acid-HPTPy (ITC-HPTPy) monomer
(so-called cross‐linked poly (ITC- HPTPy)). The cross‐linked poly (ITC-HPTPy) can stabilize the Pd NPs efectively against
aggregation, thereby improving the catalytic efciency of Pd NPs. The presence of Pd NPs on the polymer was confrmed
by various physicochemical techniques. The resulting cross‐linked poly (ITC-HPTPy)-Pd was applied as a highly efective
recyclable catalyst in Suzuki–Miyaura and Mizoroki–Heck coupling reactions under low Pd-loading conditions and straight-
forward methods, and provided the corresponding products with excellent yields (up to 98%), high catalytic activities (TOF
up to 213 h−1). The catalyst can be separated from the reaction mixture by centrifugation and can be reused consecutive six
times with slight reduction in catalytic activity.
Graphic Abstract
Pd NPs immobilized with polymer containing terpyridine ligand are highly active heterogeneous catalysts for Suzuki–
Miyaura and Mizoroki–Heck coupling reactions.
Keywords Polymer-stabilized nanoparticles · Palladium nanocatalyst · Terpyridine ligand · Suzuki–Miyaura reactions ·
Mizoroki–Heck reactions
* Kiumars Bahrami
kbahrami2@hotmail.com; k.bahrami@razi.ac.ir
Extended author information available on the last page of the article
Vol.:(0123456789)
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H. Targhan et al.
Since the early 1970s, functionalized polymers ofer a
broad range of applications in areas such as catalysis, ultra-
fltration, separation methods, membrane technologies, med-
icine, pharmacy and others [11]. Use of polymer-immobi-
lized MNPs as catalyst provides essential technique whereby
classical organic synthetic process can shift towards green
chemistry. In addition to the aspect of simplicity of catalyst
recovery and recycling, it is even possible to apply the poly-
meric catalysts to the continuous fow system which can lead
to an economical automation system [12–14].
1 Introduction
Cross-coupling reactions have been identifed as outstand-
ing tools to available to synthetic chemists to create or
manipulate intricate organic molecules. Interestingly, the
cross-coupling reactions provide straightforward possibili-
ties for joining two organic fragments via carbon–carbon
bond-forming reactions [1]. The cross-coupling reactions
have been used as key steps in the synthesis of many medi-
cines, natural products and valuable starting materials [2,
3]. Therefore, development of these reactions provides
access to a diverse range of intricate organic scafolds.
Since the heterogeneous nanocatalysts have the poten-
tial to develop more environmentally-friendly and eco-
nomical catalytic processes, one of the most signifcant
aspects of chemistry investigation has been the develop-
ment of efcient, selective, stable and recyclable nano-
catalysts. Palladium (Pd)-based nanocatalysts have found
widespread use for catalytic applications, especially in
carbon–carbon coupling reactions due to their superior
catalytic performance [1]. As are well known, small metal
nanoparticles (MNPs) have high surface energies and large
surface area, which these properties could often lead to
aggregation of the naked MNPs and decreasing of catalytic
activity [4]. In particular, highly active palladium nano-
particles are prone to aggregate easily to form larger par-
ticles [5]. Recently, many stabilizing methods have been
developed to make Pd-based nanocatalysts with small size,
high thermodynamically stability and catalytic efciency.
In the case of noble metals such as palladium, the common
stabilizing methods to prevent nanoparticles aggregation
are to use polymers or ligands [6]. The use of various
organic‐ligand stabilizers such as amines, phosphines, and
thiols has been extensively developed [7]. It is interesting
to note that dispersion and stability of the MNPs can be
obtained employing tridentate nitrogen ligands due to the
strong interaction metal-nitrogen and the formation of two
fve-membered metallacycles [8–10].
Various methods, including chemical methods and elec-
trochemical methods, have been developed to prepare the
polymers containing MNPs. In most of the chemical tech-
niques, monomer or polymer plays the role of reducing agent
for the metal species. The chemical techniques include the
following methods: polymerization of the monomer in the
presence of the MNPs, in situ reduction of metal ions from
their salt solution in the presence of the polymer, simultane-
ous formation of MNPs and polymerization of the monomer
[15].
Our early interest in the use of noble metal nanoparti-
cles as catalyst for organic transformations prompted us to
examine various methods for the immobilization these nano-
particles [10, 17]. As part of our continuing investigations
and considering potential advantages of using polymers to
immobilize MNPs, herein, we report the synthesis of a new
polymer containing HPTPy ligand for the stabilization of
Pd NPs (cross‐linked poly (ITC-HPTPy)-Pd). The catalytic
activity of the cross‐linked poly (ITC-HPTPy)-Pd was evalu-
ated in the Suzuki–Miyaura and Mizoroki‐Heck coupling
reactions (Scheme 1).
2 Experimental
2.1 Materials and Methods
The materials were purchased from Merck and Fluka and
were used without any additional purification. Melting
Cross-linked poly (ITC-HPTPy)-Pd
R2
K2CO3
+
X
B(OH)2
R2
R1
R1
EtOH/H2O, 80 °C
12 Examples (95-98% yields)
Cross-linked poly (ITC-HPTPy)-Pd
Et3N
+
X
R1
R1
solvent free, 100 °C
7 Examples (92-98% yields)
Scheme 1 The cross‐linked poly (ITC-HPTPy)-Pd catalyzed Suzuki–Miyaura and Mizoroki‐Heck coupling reactions
1 3

Palladium Nanoparticles Immobilized with Polymer Containing Nitrogen-Based Ligand: A Highly…
points were determined using a Stuart Scientific SMP2
apparatus. FT‐IR spectra were determined with a Perkin
Elmer 683 instrument. Thermogravimetric analysis (TGA)
was carried out with a STA PT- 1000 Linseis instrument
(Germany) under air atmosphere at a heating rate of 10 °C
min−1. SEM and energy‐dispersive X‐ray (EDX) measure-
ments were performed using a TESCAN‐ MIRA3 operated
at 26 kV with the electron gun flament: tungsten. TEM
observations were carried out with a Zeiss‐EM10C (Ger-
many) operating at 100 kV with samples on formvar carbon‐
coated Cu grid (mesh 300). The elemental palladium content
of nanocatalyst was determined by Perkin Elmer Optima
7300D inductively coupled plasma (ICP). X‐rays difrac-
tion (XRD) patterns were obtained using STOE STADI-P
difractometer (Cu K-α radiation λ=1.54060 Å). N2 adsorp-
tion study of nanocatalyst was done using BET (BELSORP
Mini, Microtrac Bel Corp). The chemical compositions of
the catalysts were performed using XPS a Kratos Axis Ultra
DLS spectrometer with an Al Kα as a source.
palladium loaded on the 0.1 g of cross‐linked poly (ITC-
HPTPy)-Pd (2.48 wt%).
2.5 General Procedure for the Suzuki–Miyaura
Cross‐Coupling Reactions
ArX (1.2 mmol), ArB(OH)2 (1 mmol) and K2CO3
(1.5 mmol) were added into a fask containing cross‐linked
poly (ITC-HPTPy)-Pd (0.01 g, 0.23 mol%) and EtOH/H2O
(2/1). The mixture was then stirred in an 80 °C oil bath for
an appropriate reaction time (Table 2). The progress of the
reaction was monitored by TLC. After completion of the
reaction, ethyl acetate (10 mL) was added into the reaction
mixture, the catalyst was separated by using centrifugation
and the organic solvent was evaporated to obtain biaryl
products in excellent yields.
2.6 General Procedure for the Mizoroki–Heck Cross‐
Coupling Reactions
2.2 Preparation of HPTPy‑ ITC
A mixture of aryl halide (1 mmol), styrene (1.2 mmol),
Et3N (3 mmol) and the cross‐linked poly (ITC-HPTPy)-Pd
(0.012 g, 0.27 mol%) was stirred at 100 °C (oil bath tem-
perature) under solvent-free conditions. After completion
of the reaction, which was monitored by TLC, ethylacetate
(10 mL) was added to the reaction mixture. The catalyst
was separated using centrifugation. Water (3 × 15 mL)
was added to the ethylacetate phase and decanted. After
evaporation of the solvent, the resulting crude products
were purifed from n-hexane/ethylacetate giving the pure
products in high to excellent yields (Table 4).
First, HPTPy was prepared according to recipes investigated
in the literature [16, 17], then a mixture of HPTPy (0.325 g,
1 mmol) and ITC (0.065 g, 0.5 mmol) in DMSO (4 mL) was
stirred at 100 °C for 48 h. After this time, EtOH (10 mL) and
H2O (5 mL) were added into the reaction mixture, and the
precipitate collected by fltration and dried at 70 °C.
2.3 Preparation of Cross‐Linked Poly (ITC‑HPTPy)
Briefy, HPTPy- ITC (0.033 g) and TMPTA (0.9 mL) were
added to a 40:60 mixture of MeOH/CH3CN (5 mL) and the
mixture was sonicated for 2 min then 0.06 g of 2,2-azobi-
sisobutyronitrile (AIBN) was added. The fnal volume is
adjusted with MeOH/CH3CN (40:60) to 35 mL. The mix-
ture was sonicated for 2 min and then purged with nitro-
gen to remove dissolved oxygen. The resulting mixture was
refuxed at 60–70 °C for 24 h. Finally, after air cooling, the
mixture was centrifuged and the solid obtained was dried in
vacuum at 50 °C.
3 Results and Discussion
3.1 Synthesis and Characterization of Cross‐linked
poly (ITC‑HPTPy)‑Pd
The steps of synthesis of cross‐linked poly (ITC-HPTPy)-
Pd are summarized in Scheme 2. HPTPy-ITC was initially
prepared via esterifcation reaction of ITC and HPTPy.
Then, polymerization of HPTPy-ITC as a monomer and
TMPTA as a cross-linker was achieved in the presence
of AIBN as an initiator in a mixture of MeOH/CH3CN
afording the fnal polymer. The cross‐linked poly (ITC-
HPTPy)-Pd was obtained by interaction of PdCl2 with
cross‐linked poly (ITC-HPTPy) in EtOH as a solvent and
green reducing agent (Scheme 2). Moreover, Pd NPs can
be successfully prepared and stabilized on Polymer-TPy
2.4 Preparation of Cross‐Linked Poly
(ITC‑HPTPy)‑Pd
0.1 g of the cross‐linked poly (ITC-HPTPy) was soni-
cated in 5 mL EtOH for 10 min. To the resulting mixture
PdCl2 (0.005 g, 0.028 mmol) was added and refuxed for
24 h. Then, the mixture was fltered and the solid catalyst
was washed with EtOH to remove the excess of PdCl2 and
dried under vacuum for 24 h. ICP showed 0.023 mmol of
1 3

H. Targhan et al.
N
N
N
N
N
O
O
DMSO
O
OH
+
HO
N
N
HO
100 °C, 48h
O
O
O
N
N
ITC
HPTPy
ITC-HPTPy
O
O
N
HPTPy- ITC
TMPTA
AIBN
Pd
PdCl2
N
O
O
O
EtOH
MeOH/CH3CN (40:60)
60-70 °C for 24 h
N
O
O
reflux, 24 h
O
O
O
N
N
N
cross-linked poly (ITC-HPTPy)-Pd
Pd
O
O
O
O
TMPTA =
O
O
Scheme 2 Synthetic steps for the preparation of cross‐linked poly (ITC-HPTPy)-Pd
without the addition of external reducing agents because
HPTPy ligands serve also as a reducing agent due to its
nitrogen atoms [18, 19].
cross-linker in the polymer structure leads to increase of the
pores number and decrease of their size [20].
In previous studies, EtOH has been suggested as a green
reducing agent in the synthesis of Pd NPs [18]. Moreover,
the nitrogen-based ligands have been employed to work as
both reducing and stabilizing reagent in the reaction for prep-
aration of Pd NPs [19]. UV–Visible spectroscopic technique
is used to investigate the reduction of Pd(II) ions to Pd NPs
(Fig. 2). The UV–visible spectrum of a solution of PdCl2 in
EtOH at room temperature showed a distinct peak approxi-
mately at 425 nm, which is related to the existence of Pd(II)
ion [21]. During the formation of Pd NPs on the polymer
containing HPTPy ligand, the peak was removed indicating
reduction of Pd(II) ions to Pd NPs.
The cross‐linked poly (ITC-HPTPy)-Pd was extensively
analyzed by several characterization techniques including,
FT-IR, TEM, SEM, BET, TGA, EDX, XRD, XPS, UV–Vis
and ICP.
At outset, infuence of cross-linker concentration, on the
resulting polymer porosity was investigated. For this pur-
pose, two of polymeric samples using diferent TMPTA con-
centrations and the same degree of ITC-HPTPy dilution have
been prepared under the same conditions. Porous properties
of the polymeric samples were investigated by BET. The
N2 adsorption/desorption isotherms of the polymers declare
typical type IV isotherms (Fig. 1a and c). Furthermore, it is
found that porosity, pore volume, surface area and mean pore
diameter are greatly infuenced by varying the concentra-
tion of cross-linker (Table 1) and using higher concentration
of cross-linker (0.9 mL of TMPTA) has provided a better
result (Table 1, entry 1). These fndings are consistent with
the literature results which confrm increasing amount of
The immobilization of Pd NPs on cross‐linked poly (ITC-
HPTPy) was also confrmed by the color changes of the pol-
ymer from white into dark grey during the preparation of the
catalyst in EtOH within 24 h (Fig. 3). The color changes are
due to reduction of Pd(II) to Pd(0) [22] and immobilization
of Pd NPs on cross‐linked poly (ITC-HPTPy).
1 3

Palladium Nanoparticles Immobilized with Polymer Containing Nitrogen-Based Ligand: A Highly…
Fig. 1 BET adsorption/desorption isotherms of the polymeric samples using 0.6 and 0.9 mL TMPTA (a and c respectively), BJH pore size dis-
tributions for the polymeric samples using 0.6 and 0.9 mL TMPTA (b and d respectively)
Table 1 The infuence of the
cross-linker concentration on
the total pore volume, mean
pore diameter and surface area
of the polymers
Entry
ITC-HPTPy (g)
TMPTA (mL)
Total pore vol-
Mean pore
diameter (nm) g−1
)
Surface area (m2
ume (cm3 g−1
)
BET
Langmuir
1
2
0.033
0.033
0.6
0.9
0.012
0.026
7.92
4.94
6.34
21.14
9.23
31.10
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H. Targhan et al.
Grafting of the HPTPy ligand to the ITC monomer and
the synthesis of cross‐linked poly (ITC-HPTPy)-Pd was
further confrmed through FT-IR spectra (Fig. 4). In the
FT-IR spectrum of HPTPy (Fig. 4a), the following func-
tional groups were identified: OH stretching vibration
(3386 cm−1), sp2 C–H stretching vibration (3036 cm−1),
and C=N stretching frequency (1595 cm−1). In the case of
HPTPy-ITC (Fig. 4b), the band at 1740 cm−1 corresponds to
C=O stretching of ester groups. The weak absorption peak
at 2856 cm−1 and 2926 cm−1 are attributed to the sp3 C–H
stretching vibrations. The bands observed at 1592 cm−1 and
3055 cm−1 can be attributed to the C=N stretching frequency
and C–H aromatic (pyridine rings) stretching vibration,
respectively. The C=N bands of complex TPy‐Pd in cross‐
linked poly (ITC-HPTPy)-Pd is shifted to a lower frequency
(1583 cm−1) in the FT‐IR spectrum compared to that of TPy
(1595 cm−1). The lowering in frequency of the C=N peak is
indicative of the interaction of TPy with Pd (Fig. 4c).
Fig. 2 UV-Vis spectrum of the Pd NPs and PdCl2 solution in EtOH
Figure 5a and b display SEM images of cross‐linked poly
(ITC-HPTPy)-Pd with diferent magnifcations. The size of
the Pd NPs produced on the polymer was analysed by TEM.
The image in Fig. 5c indicates the presence of uniform and
small sized Pd NPs on the cross‐linked poly (ITC-HPTPy)-
Pd. The particle size distribution of Pd NPs on the polymer
was evaluated using TEM and showed that the maximum
numbers of Pd NPs were around 9 nm in diameter (Fig. 5d).
The thermal behaviour of the prepared polymer was
investigated by TGA in oxidative environment (air). TGA
thermogram for the cross‐linked poly (ITC-HPTPy) is
shown in Fig. 6. The TGA result can prove that the poly-
mer has excellent thermal stabilities up to 320 °C in air.
Fig. 3 The color change of the polymer, cross‐linked poly (ITC-
HPTPy) (a), preparation of Pd catalyst after 1 min (b), after 2 h (c)
and after separating using centrifugation (d)
Fig. 4 FT‐IR spectra of HPTPy
(a), HPTPy-ITC (b) and cross‐
linked poly (ITC-HPTPy)-Pd
(c)
1 3

Palladium Nanoparticles Immobilized with Polymer Containing Nitrogen-Based Ligand: A Highly…
Fig. 5 a and b SEM images and c TEM image of cross‐linked poly (ITC-HPTPy)-Pd, d particle size distribution histogram of Pd NPs on the
polymer from TEM images
Maximum weight loss occurred between 350 and 470 °C
and above 600 °C, virtually no mass remains.
The cross‐linked poly (ITC-HPTPy)-Pd was also stud-
ied by XPS, the observed characteristic peaks in XPS are
attributed to C 1 s, O 1 s and Pd 3d (Fig. 9a). Furthermore,
high resolution XPS results confrmed the presence of Pd (0)
and Pd (II) on the catalyst (Fig. 9b). The peaks at 335.5 eV
(Pd 3d5/2) and 340.5 eV (Pd 3d3/2) regard to Pd (0), whereas
peaks at 336.5 eV (Pd 3d5/2) and 341.5 eV (Pd 3d3/2) are
assigned for Pd (II) species present on the polymer [25, 26].
The XPS results also allow us to determine the percentage
of the respective oxidation states of Pd by measuring the
area under the peaks: 41% as Pd(0) and 59% as Pd(II) in
the sample.
Figure 7 presents XRD pattern of the MP-TPy/Pd. The
difraction peaks at the Bragg angles of 40.10°, 46.66°, and
68.14° correspond to the 111, 200, and 220 facets of elemen-
tal palladium in the cross‐linked poly (ITC-HPTPy)-Pd [23,
24].
A sample of the cross‐linked poly (ITC-HPTPy)-Pd was
studied using EDX technique for precise elemental analy-
sis, and successful synthesis of the cross‐linked poly (ITC-
HPTPy)-Pd was inferred from this technique. EDX spectra
show the presence of C, O, N and Pd in the cross‐linked poly
(ITC-HPTPy)-Pd (Fig. 8).
1 3

H. Targhan et al.
Fig. 6 TGA thermogram of the
polymer
Fig. 7 XRD pattern of the
cross‐linked poly (ITC-
HPTPy)-Pd
(ITC-HPTPy)-Pd catalyst was studied in different tem-
peratures, solvents, bases, and in the presence of vari-
ous mol% of the cross‐linked poly (ITC-HPTPy)-Pd
for 2 h. As the first parameter of these set, the role of
cross‐linked poly (ITC-HPTPy)-Pd as a catalyst was
investigated. In the absence of any catalyst and only in
the presence of K2CO3 (1.5 mmol) at 80 °C, the product
was not formed (Table 2, entry 1). However, the use of a
3.2 Catalytic Studies
The performance of cross‐linked poly (ITC-HPTPy)-
Pd catalyst was initially tested for the Suzuki–Miyaura
coupling reaction. Phenyl boronic acid and iodobenzene
were selected as a model substrate for optimization of
the Suzuki C‐C coupling reaction (Table 2). As shown
in the Table, the catalytic activity of cross‐linked poly
1 3

Palladium Nanoparticles Immobilized with Polymer Containing Nitrogen-Based Ligand: A Highly…
afford the corresponding biaryl products in excellent
yields. The aryl iodides, bromides and chlorides are effec-
tively treated as substrates with this procedure, though,
the reaction of aryl chlorides required longer reaction
times.
As an extension to use of the catalyst, we also inves-
tigated the catalytic activities of the cross‐linked poly
(ITC-HPTPy)-Pd for the Mizoroki–Heck coupling reac-
tion. The iodobenzene and styrene were selected as sub-
strates to optimization of condition in the presence of
different mol% of the cross‐linked poly (ITC-HPTPy)-
Pd and various bases and solvents at 100 °C (Table 4).
As can be seen from the Table 4, the best result was
obtained in 98% yield by carrying out the reaction with
aryl iodide (1 mmol), styrene (1.2 mmol) in the presence
of 0.27 mol% of cross‐linked poly (ITC-HPTPy)-Pd and
Et3N (3 mmol) as base, under solvent-free condition at
100 °C (Table 4, entry 4).
Fig. 8 EDX pattern of the cross‐linked poly (ITC-HPTPy)-Pd
small amount (0.12, 0.16 and 0.23 mol%) of cross‐linked
poly (ITC-HPTPy)-Pd gave the desired product in good
(65%) to excellent (98%) yields (Table 2, entries 2-4).
It was found that applying 0.01 g of cross‐linked poly
(ITC-HPTPy)-Pd (0.23 mol%) and 1.5 mmol of K2CO3
as base at 80 °C for 2 h in a mixture of EtOH/H2O (2/1)
as solvent, is the best conditions for the reaction of iodo-
benzene (1 mmol) with phenylboronic acid (1.2 mmol)
(Table 2, entry 4).
Using the optimized reaction conditions, in a simple
experimental procedure, several trans-stilbene compounds
were prepared and the results are presented in Table 5. As
the table shows electronic efect of the substituents was not
generally observed and donor- and acceptor substituted aryl
iodides have been reacted with styrene in excellent yields.
However, when iodobenzene was replaced by bromoben-
zene, the reactions require longer reaction times. However,
the scope of this methodology was found not to be efective
to chlorobenzene (Table 5, entry 7).
The generality and scope of this approach were illus-
trated in the reaction of commercially available aryl hal-
ides with arylboronic acids (Table 3). The cross‐linked
poly (ITC-HPTPy)-Pd effectively catalyzed the coupling
reaction between aryl halides with arylboronic acids to
The performance of the present catalyst has been com-
pared with some Pd-based nanocatalysts. Table 6 shows the
comparison between cross‐linked poly (ITC-HPTPy)-Pd as
Fig. 9 XPS survey spectrum (a) and high-resolution XPS scan spectrum over Pd 3d peak of the cross‐linked poly (ITC-HPTPy)-Pd
1 3

H. Targhan et al.
Table 2 Optimization of conditions in the Suzuki‐Miyaura coupling reaction
+
I
B(OH)2
Entry
Cat.(mol%)
Base
Solvent
T (°C)
Yield (%)a
1
2
3
4
5
6
7
8
9
0
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Et3N
K2CO3
KOH
K2CO3
EtOH/H2O (2/1)
EtOH/H2O (2/1)
EtOH/H2O (2/1)
EtOH/H2O (2/1)
EtOH/H2O (2/1)
EtOH/H2O (2/1)
H2O
80
80
80
80
80
80
80
80
r.t
0
0.12
0.16
0.23
0.23
0.23
0.23
0.23
0.23
65
85
98
87
65
23
15
46
H2O
EtOH/H2O (2/1)
Reaction conditions: Iodobenzene (1 mmol), phenylboronic acid (1.2 mmol), base (1.5 mmol), solvent (3 mL), under air atmosphere, 2 h
aIsolated yields
Table 3 Suzuki–Miyaura coupling reactions of aryl halides with phenylboronic acid
Cross-linked poly (ITC-HPTPy)-Pd
R2
K2CO3
X
B(OH)2
+
R2
R1
R1
EtOH/H2O, 80 °C
Entry
X
R1
H
4-NO2
H
4-NO2
H
H
H
4-Me
H
H
4-NO2
H
R2
Time (h)
Yield (%)a
TOF (h−1
)
Mp [Refs.]
1
2
3
4
5
6
7
8
I
I
I
I
Br
Br
Br
Br
Cl
Cl
Cl
Cl
H
H
2
98
97
98
97
98
97
96
96
96
95
95
95
213
210
213
210
106
105
104
104
41
65-68 [27]
110–116 [28]
43–45 [28]
185–188 [29]
65–67 [27]
83–88 [27]
75–78 [27]
46 [28]
63–68 [27]
47 [28]
112-116 [28]
75–79 [27]
2
4-Me
3-NO2
H
4-OMe
4-F
H
H
4-Me
H
2
2
4
4
4
4
10
10
10
10
9
10
11
12
41
41
41
4-F
Reaction conditions: Aryl halide (1 mmol), phenylboronic acid (1.2 mmol), catalyst (0.23 mol%), K2CO3 (1.5 mmol), EtOH/H2O (3 mL), under
air atmosphere
aIsolated yields
a catalyst for Suzuki coupling of iodobenzene and phenylbo-
ronic acid with some Pd-based nanocatalysts in terms of
mol% of Pd, reaction time, and yields of the product. The
results of comparison show that this catalyst is superior to
some previously reported nanocatalysts in terms of mol% of
Pd used, product yield and reaction time.
Reusability is important characteristic of the heterogene-
ous catalyst to be used for industrial applications, due to the
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Palladium Nanoparticles Immobilized with Polymer Containing Nitrogen-Based Ligand: A Highly…
Table 4 Optimization
tions
of
reaction
condi-
reducing production cost and environmental pollution sub-
stantially. We investigated recyclability of the cross-linked
poly (ITC-HPTPy)-Pd by using the reaction of iodobenzene
and phenylboronic acid. This heterogeneous catalyst easily
separated from the reagents and products, and washed with
ethanol and followed by water, dried for the next run. It is
interesting to note that, recycling experiments confrmed
the chemical stability and reusability of the catalyst and the
recovered catalyst can be used during fve runs (Fig. 10).
To confrm this further, leaching of palladium during the
course of the catalytic reactions was exactly evaluated by
ICP analysis. ICP of the recovered catalyst after six catalytic
cycles indicated that 26% of palladium was leached into the
reaction medium (0.1 g of the manufactured catalyst and the
+
I
Entry Cat. (mol%) Base
Solvent
T (°C) Yield (%)a
1
2
3
4
5
6
7
0
NEt3
NEt3
NEt3
NEt3
NEt3
No solvent 100
No solvent 100
No solvent 100
No solvent 100
No solvent r.t
0
0.16
0.23
0.27
0.27
0.27
0.27
45
87
98
18
96
15
K2CO3 DMF
K2CO3 H2O
100
100
Reaction conditions: Iodobenzene (1 mmol), styrene (1.2 mmol), base
(3 mmol), solvent (3 mL), under air atmosphere, 5 h
aIsolated yields
Table 5 Coupling reactions of aryl halides with styrene
Cross-linked poly (ITC-HPTPy)-Pd
Et3N, solvent free, 100 °C
X
+
R
R
Entry
X
R
Time (h)
Yield (%)a
TOF (h−1
)
Mp [Refs.]
1
2
3
4
5
6
7
I
I
I
Br
Br
Br
Cl
H
5
5
5
7
7
7
24
98
96
97
93
92
92
Trace
72
71
71
49
48
48
–
117–121 [30]
150–153 [30]
113–117 [31]
118–120 [30]
152–154 [30]
115–117 [31]
4-NO2
4-Me
H
4-NO2
4-Me
H
Reaction conditions: Aryl halide (1 mmol), styrene (1.2 mmol), the catalyst (0.27 mol%), NEt3 (3 mmol), under solvent-free, 100 °C
aIsolated yields
Table 6 Catalytic performances
Entry Conditions
Pd (mol%) Time
Yield(%) Refs.
of some Pd-based nanocatalysts
for Suzuki coupling of
iodobenzene and phenylboronic
acid
1
2
3
4
5
6
7
8
GO/NHC-Pd, Na3PO4.12H2O, H2O, 100 °C
Pd–HoMOF, KOH, DMF, 100 °C
(Pd (II)–NHCs)n@nSiO2, K2CO3, DMF/H2O (2:1), 60 °C 0.27
Pd NPs on polymer, K2CO3, H2O, 25-100 °C
Pd(II)-NiFe2O4, K2CO3, EtOH/H2O, 80 °C
GO‐CPTMS@Pd‐TKHPP, K2CO3, EtOH/H2O, 80 °C
Pd–IPG, NaOH, EtOH/H2O, 60 °C
1
0.4
6 h
1 h
91.6
99
[32]
[33]
[34]
[22]
[35]
[36]
[37]
[17]
6 min 97
5 h
3 h
0.08
0.5
83
96
10
0.1
1.38
15 min 99
1 h
3 h
99
95
(1,4‐C6H4)(GO‐CPTMS@HPTPy‐Pd‐TPy)2, K2CO3,
H2O/EtOH, 80 °C
9
This work
0.23
2 h
98
1 3

H. Targhan et al.
catalyst after 6th run, contained 0.023 and 0.017 mmol of
Pd, respectively).
The EDX spectrum of the recovered nanocatalyst is
presented in Fig. 11, atoms such as C, O, N and Pd related
to the catalyst structure, are seen in the spectrum. How-
ever the EDX spectra shows little leaching of Pd species
into reaction solutions over multiple uses according to
relative peak surfaces. Furthermore, The SEM images of
the recovered catalyst after sixth run (Fig. 12) prove the
stability of the nanocatalyst after several uses.
4 Conclusion
In summary, cross‐linked poly (ITC-HPTPy)-Pd has been
prepared and fully characterized. As expected, cross‐linked
poly (ITC-HPTPy)-Pd exhibited excellent activity in
Suzuki–Miyaura and Mizoroki–Heck cross-coupling reac-
tions under low palladium loading conditions, and provided
the corresponding products with excellent yields (up to 98%)
and high catalytic activities (TOF up to 213 h−1). It is note-
worthy that the Pd NPs were prepared by the in situ reduc-
tion of the PdCl2 precursor in the presence of cross‐linked
poly (ITC-HPTPy) in ethanol as a green reducing agent.
Furthermore the terpyridine-based ligands existing in the
polymer structure can be considered as agent to stabilize
Pd NPs. Ultimately we believe that this work ofers several
advantages including simplicity of product workup and sepa-
ration of the catalyst. In addition, nanocatalyst was reused
consecutive six times with small drop in catalytic activity,
considering the high cost of palladium, reuse of the catalysts
could lead to economical automation system.
Fig. 10 Recycling of the catalyst for the reaction of iodobenzene and
phenylboronic acid
Fig. 11 EDX pattern of recovered catalyst after 6th run
Fig. 12 SEM images of recovered catalyst after 6th run
1 3

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Compliance with Ethical Standards
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Conflict of interest The authors declare that they have no confict of
interest.
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Publisher’s Note Springer Nature remains neutral with regard to
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Afliations
Homa Targhan1 · Alireza Hassanpour2 · Samira Sohrabnezhad3 · Kiumars Bahrami1,4
1
3
Department of Organic Chemistry, Faculty of Chemistry,
Razi University, Kermanshah, Iran
Department of Chemistry, Faculty of Science, Lorestan
University, Khoramabad, Iran
2
4
Department of Analytical Chemistry, Faculty of Chemistry,
Razi University, Kermanshah, Iran
Nanoscience and Nanotechnology Research Center (NNRC),
Razi University, Kermanshah, Iran
1 3