Suzuki-Miyaura cross-coupling for efficient synthesis of aryl-substituted N-heteroarenes catalyzed by recyclable N-phenylpiperazine-Palladium(II) complex

Article abstract of DOI:10.1016/j.ica.2018.03.006

Polystyrene supported N-phenylpiperazine-Pd(II) complex D was synthesized and characterized by various techniques, including Fourier transform infrared spectroscopy (FTIR), scanning electronmicroscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and thermal analysis (TG-DTA). This heterogeneous Pd(II) complex showed high catalytic efficiency for the Suzuki-Miyaura coupling of arylboronic acids with aryl bromides, aryl chlorides to give the corresponding 2-arylpyridines and heteroarenes. The coupled products were formed in excellent yields at low catalyst loadings under mild reaction conditions. Further, this heterogeneous catalyst showed excellent recyclability and reused for four cycles with no significant decrease in its activity.

Full text of DOI:10.1016/j.ica.2018.03.006

Accepted Manuscript
Research paper
Suzuki–Miyaura Cross-Coupling for Efficient Synthesis of Aryl-Substituted N-
Heteroarenes Catalyzed by Recyclable N-phenylpiperazine-Palladium(II) com-
plex
Pullaiah C. Perumgani, Kodicherla Balaswamy, Mohan Rao Mandapati, Sai
Prathima Parvathaneni
PII:
S0020-1693(18)30163-4
https://doi.org/10.1016/j.ica.2018.03.006
ICA 18151
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
29 January 2018
6 March 2018
8 March 2018
Please cite this article as: P.C. Perumgani, K. Balaswamy, M. Rao Mandapati, S. Prathima Parvathaneni, Suzuki–
Miyaura Cross-Coupling for Efficient Synthesis of Aryl-Substituted N-Heteroarenes Catalyzed by Recyclable N-
phenylpiperazine-Palladium(II) complex, Inorganica Chimica Acta (2018), doi: https://doi.org/10.1016/j.ica.
2018.03.006
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Suzuki–Miyaura Cross-Coupling for Efficient Synthesis of Aryl-Substituted
N-Heteroarenes Catalyzed by Recyclable N-phenylpiperazine-Palladium(II)
complex
Pullaiah C. Perumgani, Kodicherla Balaswamy, Mohan Rao Mandapati, Sai Prathima
Parvathaneni*
Catalysis Laboratory, Inorganic and Physical Chemistry Division
CSIR-Indian Institute of Chemical Technology (IICT),Tarnaka, Hyderabad –500 607, India,
Fax: +91-040-27160921, Tel: (+) 91 40 27191527
E-mail: saiprathimaiict@gmail.com, saiprathima@iict.res.in
Abstract: Polystyrene supported N-phenylpiperazine–Pd(II) complex D was synthesized and
characterized by various techniques, including Fourier transform infrared spectroscopy (FTIR),
scanning electronmicroscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and thermal
analysis (TG-DTA). This heterogeneous Pd(II) complex showed high catalytic efficiency for the
Suzuki–Miyaura coupling of arylboronic acids with aryl bromides, aryl chlorides to give the
corresponding 2-arylpyridines and heteroarenes. The coupled products were formed in excellent
yields at low catalyst loadings under mild reaction conditions. Further, this heterogeneous
catalyst showed excellent recyclability and reused for four cycles with no significant decrease in
its activity.
Scheme 1
Introduction:
The Suzuki–Miyaura cross-coupling reaction [1-3], in which arylboronates coupled with
arylhalides in presence of palladium catalyst, is the main basis of carbon–carbon bond formation
employed in the pharmaceutical industry [4-5]. This has been used in the synthesis of natural
products such as alkaloids, polymers, ligands, biaryls and agrochemicals, viable industrially for

large-scale processes [6-8]. Arylpyridines are important frameworks entrenched in a large
number of drug molecules such as crizotinib (lung carcinoma), etoricoxib (arthritis), altazanavir
(HIV) and also as ligands in metal-catalyzed reactions [9-13]. Thus the development of efficient
synthetic methods allowing facile access to such heterobiaryls has attracted considerable
attention in the field of synthetic chemistry. Suzuki–Miyaura cross-coupling of (hetero)
arylhalides with arylboronic acids represents as one of the most reliable strategy to synthesize
these frameworks [14]. The scale of the challenge in using pyridine derivatives/N-hetero
arylhalide substrates for the Suzuki reaction is mainly due to the possible coordination of the
nitrogen to the active palladium species [15-16]. Several groups reported ligand-promoted
protocols for N-heteroaryl halide substrates [17-19]. In the past few decades, palladium
complexes with tertiary phosphines, phosphates and phosphine oxides have been widely
employed in Suzuki–Miyaura cross-coupling reactions [20-24]. Therefore a new class of
nitrogen-based ligands has been developed to replace toxic, expensive and sensitive phosphine
ligands. These ligands form Pd complexes with high stability and high catalytic activity for
coupling reactions [25-26].
In an effort to reduce the generation of hazardous substances, and to minimize the environmental
consequences it would be ideal to develop a recyclable catalyst, with water as reaction medium
for Suzuki–Miyaura cross coupling of highly challenging aryl and hetero arylchlorides. Our
research group mainly interested in developing simple recyclable polymer bound metal
complexes, and its applications for C-C bond formation reactions [27]. Recently, we have
reported polystyrene-supported N-phenylpiperazine-Cu(II) complex
E
for KA2 coupling
(figure 1) [28].
Fig. 1 Polymer supported palladium and copper complexes (
D and E)

As part of our ongoing interest in recyclable palladium-catalysis [29-30], we herein report the
Suzuki–Miyaura cross coupling reaction of heteroarylbromides and arylchlorides with
arylboronic acids with stable polystyrene supported N-phenylpiperazine-Palladium(II) complex
D as catalyst in EtOH:water system. The main benefit of the present polymeric palladium (II)
complex D over existing methods is mainly less catalytic loading (0.0045 mmol/Pd), better
recyclability and broad scope with excellent yields (Scheme 1).
Experimental
Material and Instruments
Analytical-grade reagents and freshly distilled solvents were used throughout the experiment.
The reagents were supplied by Sigma-Aldrich Chemicals Company; USA and Merck Co. Liquid
substrates were redistilled and dried with appropriate molecular sieves. Distillation and
purification of the solvents and substrates were done by standard procedures. The starting
materials and reagents were purchased from various commercial sources and used without
further purification. ACME silica gel (60-120 mesh) was used for column chromatography.
Analytical thin-layer chromatography (TLC) was performed on pre-coated TLC plates with silica
1
13
gel 60-F254 plates and visualized by UV-light. H NMR and C NMR spectra were recorded,
using tetramethylsilane (TMS) in the solvent of CDCl3 as the internal standard on a 400, 500
MHz spectrometer (1H NMR: TMS at 0.00 ppm, CDCl3 at 7.26 ppm; 13C NMR: CDCl3 at 77.00
ppm). Chemical shifts (δ) were recorded in ppm with respect to TMS as an internal standard and
coupling constants are quoted in Hertz (Hz). Mass spectra were recorded on a mass spectrometer
by the electron spray ionization (ESI) and the data acquired in positive ionization mode. HRMS
spectra were determined on TOF type mass analyzer. FTIR spectra of the samples were recorded
on a Perkin-Elmer FTIR 783 spectrophotometer using KBr pellets. A EXSTAR TG/DTA7200
instrument was used for the thermogravimetric (TGA) analysis.
Preparation of polymer supported N-phenylpiperazine C: A 250 mL round bottom flask
containing CH3CN (50mL), equipped with a magnetic stirring bar is added with N-
phenylpiperazine A (5 mmol), chloromethylated polystyrene B (1 g, 1.2 mmol g-1 of Cl) and NaI
(0.1 mmol). The reaction mixture was stirred for 48 h at 70 oC and was subsequently filtered and
washed thoroughly with CH3CN, and dried in an oven at 80 oC for 24 h.

Preparation of polystyrene-supported Pd complex D: To the EtOH solution the polystyrene-
supported N-phenylpiperazine ligand C (0.5 g) and a solution of Pd(CH3CN)2Cl2 (0.5 g) in EtOH
(10 mL) were added, and the resulting mixture was allowed to reflux for 12 h. This mixture was
filtered and washed thoroughly with EtOH (3 x 30 mL) and finally dried in a vacuum at 80 oC
for 24 h (Scheme 2).
General procedure for Suzuki coupling reaction catalyzed by Polymer anchored-Pd(II) D:
A dried round bottomed flask equipped with a magnetic stirring bar was charged with 10 mg
Polymer anchored-Pd(II) D catalyst (PS-NPPZ-Pd) (0.0045 mmol/Pd), 2-halopyridine (0.5
mmol), phenylboronic acid (0.6 mmol) and K3PO4 (1.0 mmol) were added to a reaction vessel.
o
The mixture was stirred in 4mL of H2O: EtOH (1:1) at 100 C for 8 h and then cooled to room
temperature. The catalyst was filtered and the filtrate was extracted with ethyl acetate (3 × 10
mL). The combined organic layers were extracted with water, and dried over anhydrous Na2SO4.
The organic layers were evaporated under reduced pressure and the resulting crude product was
purified by column chromatography by using ethyl acetate/hexane (10:90) as eluent to give the
1
13
corresponding coupled products. The products were characterized by H NMR, C NMR and
HRMS analysis.
Results and discussion
Catalytic activity
The synthesis of polymer-supported N-phenylpiperazine derived Pd(II) complex D is
systematically represented in Scheme 2. N-phenylpiperazine functionalized polystyrene resin C
was formed by heating a mixture of chloromethylated polystyrene B and N-phenylpiperazine A
o
in CH3CN at 70 C for 48 h. To the polystyrene-supported N-phenylpiperazine B, EtOH and
Pd(CH3CN)2Cl2 was added in 1:1 molar ratio and was refluxed for 12 h. This resulted in
covalent attachment of palladium to give a functionalized polymer complex D. The polymer
anchored metal complexes exhibit high catalytic efficiency with broad applicability, they have
been extensively studied. In our previous reports we have studied the complete characterisation
and their catalytic activity in the field of coupling reactions [25-26] and carboacylations [27-28].

Now we have investigated the catalytic activity of the PS-NPPZ–Pd D catalyst to prepare 2-
phenylpyridine derivatives via Suzuki coupling reaction.
Scheme 2. Synthesis of polymer-supported N-phenylpiperazine derived Pd(II) complex D.
The two characteristic peaks at 1263 and 670 cm-1 of IR spectrum were due to stretching and
bending vibrations of C–Cl group of chloromethylated polystyrene (Fig. S1(A)). The complete
disappearance of these peaks after the introduction of N-phenylpiperazine, confirms the
formation of polymer-anchored N-phenylpiperazine ligand (Fig. S1(B)). The peak 2330 cm–1 (C
N of CH3CN) is absent in the case of complex compared to the IR spectrum of Pd(CH3CN)2Cl2.
In addition the peak at 3437 cm–1 of polystyrene-supported palladium complex D in the IR
spectrum indicates the formation Pd–N bond and confirms the complex formation by FT-IR
analysis (Fig. S1(C)) (see supporting information). The scanning electron microscopy (SEM)
images of the polymer-anchored N-phenylpiperazine ligand C and polymer supported N-
phenylpiperazine Pd(II) complex D shows notable morphological changes. The SEM image of
the polymeric ligand has rough surface and polymeric Pd(II) complex was found to be composed
of regions of white flake-like appearance (Fig 2 A & B). Energy dispersive X-ray spectroscopy
(EDX) analysis data for the polymer anchored ligand and palladium catalyst are given in Fig.
3(C) and (D). The EDX spectrum clearly shows the presence of palladium metal in the polymer
complex D (Fig 3 D).

Fig. 2 SEM images of the polymer anchored ligand PS-NPPZ (A),
PS-NPPZ–Pd (B) complex.
Fig. 3 EDX images of the polymer anchored ligand PS-NPPZ (C),
polymer anchored complex PS-NPPZ-Pd(D).
Fig. 4 Thermogravimetric analysis of polymer supported
N-phenylpiperazine–Pd (II) complex D

Table 1. Optimization studiesa
Entry
1
Base
Solvent
H2O
Time (h)
12
Yield (%)b
45
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K2CO3
NaOH
Cs2CO3
K3PO4
2
3
4
5
6
7
8
9
1,4-dioxane
EtOH
8
8
54
58
91
48
60
25
69
91
H2O:EtOH
Toluene
8
12
8
H2O:EtOH
H2O:EtOH
H2O:EtOH
H2O:EtOH
12
12
12
10
11
12
13
-
H2O:EtOH
H2O:EtOH
H2O:EtOH
H2O:EtOH
12
12
12
12
_c
_d
K3PO4
K3PO4
K3PO4
35e
64f
aReaction conditions: 1a (0.5 mmol), 2a (0.6 mmol), catalyst (10 mg),
d
base (1.0 mmol) in solvent at 100 oC, bIsolated yield, cNo Base, No Catalyst,
eReaction at 50 oC temperature, fReaction at 80 oC temperature.
.
The thermal stability of the complex was investigated by thermogravimetric analysis of
polymer supported N-phenylpiperazine–Pd (II) complex D (Fig. 4). The complex is stable up to
o
o
350 C and above this temperature it decomposes. The negligible weight loss below 250 C is
due to the physically adsorbed solvent molecules. The amount of palladium incorporated into the
polymer was determined by inductively coupled plasma (ICP), which showed a value of 4.94%
(0.45 mmol/g).
We began our study, to synthesize 2-phenylpyridine derivatives from cross-coupling reaction of
2-bromopyridine (1.0 equiv) with phenylboronic acid (1.2 equiv) in the presence of Catalyst D as
the model reaction to optimize the reaction conditions (Table 1). At first, the solvent effect was
o
examined with water and K3PO4 as base at 100 C (Table 1, entry 1). While other solvents such

as 1,4-dioxane, EtOH and toluene were substantially less effective (Table 1, entries 2, 3 & 5).
Among the solvents examined, H2O:EtOH (1:1) was found to be the best choice (Table 1, entries
4 & 9). Our next studies focused on the effect of base on the Suzuki reaction. To obtain good
yields inorganic bases such as K2CO3, Cs2CO3, NaOH and K3PO4 were used and K3PO4 was the
most effective (Table 1, entry 4), whereas NaOH afforded low yields (Table 1, entry 7), and
bases such as K2CO3, Cs2CO3 gave moderate yields (Table 1, entries 6 & 8), so K3PO4 was
finally selected as the base for the reaction. There is no significant change in yields by
o
increasing the reaction time from 8 h to 12 h at 100 C (entry 9). Finally, the effect of
o
reaction temperature on the model reaction was also investigated and 100 C was found to be
o
o
optimal reaction temperature as 50 C and 80 C furnished low yields (entries 12 & 13). As
expected the desired product was not obtained even in trace amounts in absence of base
and catalyst, Pd complex
D (entries 10-11). Therefore, the optimal catalytic system involved
the use of complex D (0.0045 mmol/Pd), K3PO4 (1.0 equiv) in H2O:EtOH (1:1) at 100 oC for 8 h
(Table 1, entry 4).
Table 2. Substrate Scope of Arylboronic acidsa
Entry
1
R
H
Product
Yield(%)b
91
2
3
4-CH3
3-CH3
85
86
4
4-OEt
82

5
3-OEt
84
6
7
8
4-t-bu
4-vinyl
4-CF3
79
75
79
9
4-COCH3
4-CN
82
72
10
11
12
1-napthyl
88
85
13
4-F
78
aReaction conditions:
1
(0.5 mmol), 2a (0.6 mmol), catalyst (10 mg, 0.0045
mmol/Pd), base (1.0 mmol), 100 oC for 8h, bIsolated yield.
With the optimized conditions in hand, substrate generality of this Pd(II)-catalyzed Suzuki cross
coupling reaction of 2-bromopyridines was surveyed (Table 2). The reactions with
phenylboronic acids bearing electron-donating groups and electron withdrawing substituents at
the aromatic ring proceeded to give the desired products in good to excellent yields. First, the
electronic effect of the substrates was explored by changing the para-substituents of R (Table 2,
entries 2, 4, 6−10 & 13). When the substrates bearing the electron-donating groups (Me,
OC2H5) on the para-position of the phenyl ring were employed, the corresponding products
were obtained in high yields (Table 2, entries 2 & 4). Similarly, the substrates bearing the

electron-donating groups (Me, OC2H5) on the meta-position of the phenyl ring resulted in (3c
)
86%, (3e) 84% yields of the desired products. Moreover the substrates bearing tertiary
butyl, vinyl, acetyl and cyano groups at para-position, coupling products were achieved in
(
3f) 79%, (3g) 75%, (3i) 82% and (3j) 72% (Table 2, entries 6-7 & 9-10). When the strong
electron-withdrawing group ( CF3 & F) are installed on the para-position of R, the Suzuki
reaction could still be carried out smoothly, but a slight decrease in yield was observed (Table 2,
entries 8 & 13). Interestingly, napthyl derived system and substrates bearing methylenedioxy
functional groups were compatible under the reaction conditions (Table 2, entries 11 & 12).
In addition, we also extended the reaction with various substituted heterocycles under the
optimized conditions, and the results are presented in Table 3. 2-phenylpyrimidine 4a, 2-
phenylthiophene 4b, 2-phenylquinoline 4c and 1-phenylisoquinoline 4d coupled products were
formed in good yields (Table 3, entries 1-4). The functional groups including Me and OMe
were well-suited and para, meta, ortho substituted derivatives gave the desired products
in excellent yields (Table 3, entries 5-12).
Table 3 Substrate Scope of 2-bromoheteroarenesa
Entry
1
R-Br
R1-B(OH)2
Product
Yield(%)b
79
2
3
72
81

4
5
79
78
6
7
8
74
69
65
9
69
71
10
11
12
81
80
aReaction conditions:
base (1.0 mmol), 100 oC for 8h, bIsolated yield.
1 (0.5 mmol), 2 (0.6 mmol), catalyst (10 mg, 0.0045 mmol/Pd),

In addition we also tested the reaction with more challenging 2-chloropyridines with
substituted phenylboronic acids, and the results are represented in Table 4. The reaction
with phenylboronic acid bearing electron-donating group 3c (62%) (Table 4, entry 2) gave good
yield compared to electron withdrawing substituents at the aromatic ring 3h (54%), 3i (58%), 3j
(50%) and 3m (49%) (Table 4, entries 3-6)
.
The recyclability of the polymer–anchored Pd (II) complex D was tested in the Suzuki–
Miyaura Cross-Coupling reaction for synthesis of 2-phenylpyridine derivatives. It was found
that the catalyst can be reused for four cycles with only 5% decline of activity after the
4th recycle as shown in Fig 5. The AAS analytical data of used catalyst
any appreciable loss in the palladium metal.
D did not show
100
80
60
40
20
0
1
2
3
4
No of Cycles
Fig 5: Recyclability of Pd(II) catalyst D
Table 4. Substrate Scope of boronic acids with 2-chloropyridinesa
Entry
1
R
Product
Yield(%)b
58
H

2
3-CH3
62
54
3
4
4-CF3
4-COCH3
58
50
5
6
4-CN
4-F
49
aReaction conditions:
1
(0.5 mmol), 2a (0.8 mmol), catalyst (10 mg,
0.0045 mmol/Pd), base (1.0 mmol), 100 oC for 8h, bIsolated yield.
Conclusion
In summary, we have described a user-friendly methodology for the Suzuki–Miyaura reaction
using a simple versatile, active and stable recyclable heterogeneous Pd(II) complex at low
catalyst loading. The reactions were optimized in a 1:1 water/ethanol mixture in the presence of a
mild and inexpensive inorganic base. This system extends the scope of the Suzuki–Miyaura
reaction using a wide range of hetero arylbromides, arylchlorides and boronic acids in good to
excellent yields. Thus this represents as an efficient and economical protocol for the synthesis of
potential phenylpyridines and N-heteroarenes under mild reaction conditions with broad
substrate scope.
Acknowledgements
P. S. P gratefully acknowledge to the financial assistance provided by CSIR-Senior
Research Associateship (Scientist’s Pool Scheme), New Delhi and PCP (UGC-SRF), thanks

for the fellowship provided by UGC, Govt of India. We also acknowledge director IICT for
providing infrastructural facilities.
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HIGHLIGHTS:
Synthesis of Arylpyridines and N-heterocycles
EtOH:water system
Simple polystyrene supported N-phenylpiperazine-Palladium(II)
Recyclability
Low catalytic loading (0.0045 mmol/Pd)
Broad scope with excellent yields.

Graphical Abstract:
Polystyrene supported N-phenylpiperazine–Pd(II) complex D was synthesized and characterized
by various techniques, including Fourier transform infrared spectroscopy (FTIR), scanning
electronmicroscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and thermal analysis
(TG-DTA). This heterogeneous Pd(II) complex showed high catalytic efficiency for the Suzuki–
Miyaura coupling of arylboronic acids with aryl bromides, aryl chlorides to give the
corresponding 2-aryl pyridines and heteroarenes. The coupled products were formed in excellent
yields at low catalyst loadings under mild reaction conditions. Further, this heterogeneous
catalyst showed excellent recyclability and reused for four cycles with no significant decrease in
its activity.