A highly active reusable polymer anchored copper catalyst for C-O, C-N and C-S cross coupling reactions

Article abstract of DOI:10.1016/j.molcata.2014.02.007

A new furfural functionalized polymer-amine grafted with copper catalyst has been designed and employed for the N-arylation, O-arylation and S-arylation reactions under an open air condition to afford the corresponding coupled products in good to excellent yields. This solid supported catalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), UV-vis spectroscopy and scanning electron microscope (SEM). The developed catalyst can be facilely recovered and reused five times without significant decrease in activity and selectivity. This result confirms that the polymer anchored complex was not leached during the reaction, suggesting the true heterogeneous nature of the catalyst.

Full text of DOI:10.1016/j.molcata.2014.02.007

Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
A highly active reusable polymer anchored copper catalyst for C-O,
C-N and C-S cross coupling reactions
Sk.Manirul Islama,b,∗, Noor Salama,b, Paramita Mondala,b, Anupam Singha Roya,b
,
Kajari Ghosha,b, K. Tuhinac,∗
a Department of Chemistry, University of Kalyani, Nadia, 741235, West Bengal, India
b Department of Chemistry, Aliah University, Sector-V, Salt Lake-Kolkata, 700099 West Bengal, India
c Department of Chemistry, B.S. College, S-24 P.G.S., Canning, 743329 West Bengal, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new furfural functionalized polymer-amine grafted with copper catalyst has been designed and
employed for the N-arylation, O-arylation and S-arylation reactions under an open air condition to afford
the corresponding coupled products in good to excellent yields. This solid supported catalyst was char-
acterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), UV–vis
spectroscopy and scanning electron microscope (SEM). The developed catalyst can be facilely recovered
and reused five times without significant decrease in activity and selectivity. This result confirms that
the polymer anchored complex was not leached during the reaction, suggesting the true heterogeneous
nature of the catalyst.
Received 17 September 2013
Accepted 9 February 2014
Available online 17 February 2014
Keywords:
Polymer anchored Cu-catalyst
N-arylation
O-arylation
S-arylation
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
compounds are very active and have high catalytic activity, but the
high costs of Pd-compounds has lowered its popularity, particu-
Transition metals catalyzed C–O, C–S, and C–N cross coupling
reactions are among the most powerful organometallic transforma-
tions employed in organic synthesis for the preparation of various
compounds that are of biological, pharmaceutical and material
interest [1]. Since its discovery, the copper-mediated Ullmann cou-
pling reaction [2] is still the straight forward method to prepare the
requisite carbon–heteroatom bonds. Due to the economic attrac-
tiveness of copper [3] and by using some special ligands such as
N, N- and N, O-bidentate compounds, many CuI-catalyzed C-N
[4], C-O [5], C-S [6], and C-C [7] bond formation reactions have
led to a resurgence of interest in carbon-heteroatom coupling
reactions, and their applications seem to be of more and more
importance [8]. Of the methods used for the preparation of diaryl
ethers, the classic Ullmann ether synthesis is the most impor-
tant, but it is often limited by the need to employ harsh reaction
conditions and stoichiometric amounts of copper [9]. The use of
palladium catalyst for the combination of phenols and aryl halides
or sulfonates is a desirable extension of other recently reported
carbon-heteroatom bond-forming techniques [10]. Palladium
larly for large scale reactions [11]. Hartwig et al. and Buchwald et al.
have greatly contributed to novel Pd-catalyzed arylation of phenols
[11,12] but their systems still suffer from the expensive palladium
and ligand. As a result, much of the recent literature has focused on
the continuing evolution of Ullmann’s original copper-based diaryl
ether formations [13,14]. C-N bond formation via transition metal
based catalysis is currently a subject of great interest and intensive
research is being carried out to ensure useful organic transfor-
mations [15]. In particular, the synthesis of N-arylimidazoles has
attracted significant interest because of the frequent occurrence
of these structural units in biologically active inhibitors [16]. Usu-
ally these compounds were synthesized via SNAr substitution with
aryl halides bearing electron-withdrawing substituent or via the
Ullmann type coupling at high temperatures [17]. After the initial
reports of Chan and Lam, the Cu-catalyzed cross coupling between
N-heterocycles and arylboronic acids has become an important
synthetic methodology in modern organic synthesis [18]. Later the
discovery and development of the catalytic path for N-arylation
of heterocycles by Buchwald with bromo- and iodoarenes using
copper based complex generated greater interest in industry [19].
Afterwards Taillefer et al. reported oxime type and Schiff base lig-
ands [20] and Ma et al. reported ␣- and ␤-amino acids as ligands
for effective N-arylation of N-heterocycles with aryl halides [21]. In
those catalytic reactions mostly Cu(I) and Cu(II) based complexes
∗
Corresponding author at: Corresponding author. Tel.: +91 33 2582 8750;
fax: +91 33 2582 8282.
E-mail address: manir65@rediffmail.com (Sk.Manirul Islam).
http://dx.doi.org/10.1016/j.molcata.2014.02.007
1381-1169/© 2014 Elsevier B.V. All rights reserved.

8
Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
2.2. Physical and spectroscopic measurements
HNO3 + AcOH
50oC, 6h
AcOH
P
NH3Cl
NaOH
P
NO2
P
SnCl2, HCl
The FT-IR spectra of the samples were recorded from 400 to
4000 cm−1 on a Perkin Elmer FT-IR 783 spectrophotometer using
KBr pellets. UV–vis spectra were taken using a Shimadzu UV-
2401PC doubled beam spectrophotometer having an integrating
sphere attachment for solid samples. Thermogravimetric analysis
(TGA) was carried out using a Mettler Toledo TGA/DTA 851e. Sur-
face morphology of the samples was measured using a scanning
electron microscope (SEM) (ZEISS EVO40, England) equipped with
EDX facility. Copper content in the catalyst was determined using
a Varian AA240 atomic absorption spectrophotometer (AAS). The
reaction products were quantified (GC data) by Varian 340 0 gas
chromatograph equipped with a 30 m CP-SIL8CB capillary column
and a flame ionization detector and identified by Trace DSQ II GC-
MS equipped with a 60 m TR-50MS capillary column.
MeOH
P
Toluene
Reflux
HC=N
P
NH2
O
O
Cu(OAC)2 AcOH
P
CHO
Ac
N
O
N
O
Cu
Cu
O
O
Ac
polystyrene framework
P
PS-Cu-Furfural
2.3. Synthesis of Schiff base ligand
P
The synthetic procedure of polymer anchored furfural ligand
is illustrated in Scheme 1. The ligand was prepared in two steps.
Firstly, p-amino-polystyrene was prepared as reported earlier [28].
The suspension of macroporous amino polystyrene (2 g) in toluene
(20 mL) was taken in a round bottom flask. Furfural (0.01 mol) was
added dropwise to the stirring suspension of amino-polystyrene.
The reaction mixture was refluxed for 24 h. After cooling to room
temperature, the polymer-anchored ligands were filtered, washed
thoroughly with toluene followed by methanol and finally dried
under vacuum.
Scheme 1. Synthesis of polymer anchored copper catalyst.
have been used as homogeneous catalyst. Here we have inves-
tigated the polymer supported copper catalyst as heterogeneous
towards the N-arylation and O-arylation reactions. Aryl sulfides are
of great significance to the pharmaceutical industry and are a com-
mon functionality found in numerous drugs in therapeutic areas
such as diabetes and anti-inflammatory drugs, and Alzheimer’s
and Parkinson’s diseases [22] and also important industrially as
the cost and environmental pollution of the process is relatively
low [23]. Aryl-sulfur coupling reactions can be carried out by using
Pd [24], Fe [25], Co, Ni [26] and Cu [27] containing homogeneous
catalysts carrying suitable ligands. Moreover, the efficient palla-
dium catalysts are usually prepared by using organophosphorous
or phosphine ligands, which are difficult to prepare and environ-
mentally unfriendly. A problem arises for the Ni and Co catalysts
since these are toxic in nature and have low turnover numbers
in their respective reactions. On the other hand, Cu-catalysts are
prepared from Cu-salts, which are very cheap and easily available.
So a successful strategy for designing an alternative inexpensive,
non-air sensitive and recyclable heterogeneous catalyst anchored
by Cu-centres on a high surface area material is highly desirable to
address these industrial and environmental concerns.
2.4. Synthesis of polymer supported copper catalyst
This polymer anchored furfural ligand (500 mg) subsequently
reacted with Cu(OAc)2 (25 mg) in methanol (10 mL) and was kept
under the refluxing condition for about 10 h at 80 ◦C. The reaction
mixture was cooled at room temperature and the resulting poly-
mer supported material was filtered through suction with thorough
washing with ethanol. After washing it was dried under vacuum.
The light green coloured polymer supported material was desig-
nated as Cu-supported catalyst (PS-Cu-Furfural).
2.5. General procedure for O-arylation reaction of phenols with
aryl halides
Herein, we report the synthesis of a new furfural functionalized
polymer-amine grafted with copper (Scheme 1) and its excellent
catalytic activity in a number of cross-coupling reactions such as
O-arylation, N-arylation and S-arylation reactions. The material is
thoroughly characterized by using SEM, EDAX, TGA, FT-IR, UV–vis
spectroscopic tools. The experimental results reveal that the poly-
mer anchored copper Schiff base catalyst can be recycled more than
five times without much loss in the activity.
Cu- catalyst (0.05 g) in DMSO (5 mL) was taken in a 100 mL
round bottom flask and stirred at room temperature for 10 min.
Then aryl halide (1 mmol), phenol (1 mmol), tetrabutylammonium
bromide (tBu4NBr) (0.1 mmol), Cs2CO3 (1 mmol) and DMSO (5 mL)
were added to it. The final reaction mixture was heated at 120 ◦C
under an open air condition. The reaction mixtures were collected
at different time intervals and identified by GC–MS and quantified
by GC. After the completion of the reaction, the catalyst was fil-
tered off and washed with water followed by acetone and dried in
oven. The filtrate was extracted with ethyl acetate (3 × 20 mL) and
the combined organic layers were dried with anhydrous Na2SO4 by
vacuum. The filtrate was concentrated by vacuum and the result-
ing residue was purified by column chromatography on silica gel
to provide the desired product.
2. Experimental
2.1. Material
Analytical grade reagents and freshly distilled solvents were
used throughout. All reagents and substrates were purchased
from Merck. Liquid substrates were predistilled and dried by
molecular sieve and solid substrates were recrystallized before
use. Distillation, purification of the solvents and substrate were
done by standard procedures. 5.5% crosslinked chloromethylated
polystyrene was purchased from Aldrich Chemical Company; U.S.A.
Copper acetate was procured from Merck and used without further
purification. The furfural also was purchased from Sisco Research
Laboratories Pvt. Ltd., India.
2.6. General procedure for N-arylation of N–H heterocycles with
arylboronic acids
In a 100 mL round bottom flask, Cu-grafted catalyst (0.05 g), aryl-
boronic acid (1 mmol), N–H heterocycles (1.2 mmol), and 10 mL
methanol were stirred under nitrogen atmosphere, at 40 ◦C. The
reaction mixtures were collected at different time interval and

Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
9
Fig. 1. FE SEM images of polymer anchored Schiff base ligand (A) and polymer anchored Cu-catalyst (B).
identified by GC–MS and quantified by GC analysis. After the com-
pletion of the reaction, the catalyst was filtered off and washed
with water followed by acetone and dried in oven. The filtrate was
extracted with ethyl acetate (3 × 20 mL) and the combined organic
layers were dried with anhydrous Na2SO4 by vacuum. The filtrate
was concentrated by vacuum and the resulting residue was puri-
fied by column chromatography on silica gel to provide the desired
product.
products were compared and matched with the retention times
of authentic samples. Identification of the products was also con-
firmed using GC–MS.
3. Results and discussion
3.1. Characterization of the polymer supported copper catalyst
Due to insolubilities of the polymer supported copper Schiff base
complex in all common organic solvents, its structural investiga-
tions were limited to their physicochemical properties, chemical
analysis, SEM, EDAX, TGA, IR and UV–vis spectral data. The com-
plete incorporation of the organic substructure in the material was
confirmed by elemental analysis (Table S1).
2.7. General procedure for N-arylation of N–H heterocycles with
aryl halides
In an oven dried 100 mL round bottom flask, Cu-grafted catalyst
(0.05 g), aryl halide (1 mmol), N–H heterocycles (1.2 mmol), K2CO3
(2 mmol), and 10 mL DMSO were stirred under nitrogen atmo-
sphere, at 100 ◦C. The reaction mixtures were collected at different
time interval and identified by GC–MS and quantified by GC anal-
ysis.
3.2. Scanning electron micrographs (SEMs) and energy dispersive
X-ray analyses (EDAX)
Field emission-scanning electron micrographs for single beads
of polymer supported Schiff base ligand and complex were
recorded to understand the morphological changes occurred on
the polystyrene beads at various stages of the synthesis. In Fig. 1,
the SEM image of polymer supported Schiff base ligand (A) and
the immobilized copper complex (B) on functionalized polymer are
shown. The pure polystyrene bead has a smooth surface. Introduc-
tion of ligands into polystyrene beads through covalent bonding
causes the light roughening of the top layer of polymer beads. After
metal loading on polymer anchored ligand, changes in morphol-
ogy of the ligand surface was observed by SEM picture. As expected
smooth and flat surface of polymer bead shows slight roughening
on complexation. The EDAX data (Fig. 2) also inform the attachment
of copper metal on the surface of the polymer matrix.
2.8. General procedure for the N-arylation of aromatic amines
with aryl halides
In an oven dried 100 mL round bottom flask, Cu-grafted cat-
alyst (0.05 g), aryl halide (1 mmol), aromatic amines (1.2 mmol),
KOH (1 mmol), and 10 mL DMSO were stirred under nitrogen atmo-
sphere, at 140 ◦C. The reaction mixtures were collected at different
time intervals and identified by GC–MS and quantified by GC.
After the completion of the reaction, the catalyst was filtered off
and washed with water followed by acetone and dried in oven.
The filtrate was extracted with ethyl acetate (3 × 20 mL) and the
combined organic layers were dried with anhydrous Na2SO4 by
vacuum. The filtrate was concentrated by vacuum and the result-
ing residue was purified by column chromatography on silica gel
to provide the desired product.
3.3. TGA studies
2.9. General procedure for aryl-sulphur coupling reaction of
thiophenol with aryl iodide
Thermal stability of complex was investigated using TGA–DTA
at a heating rate of 10 ◦C/min in air over a temperature range of
30–600 ◦C. TGA curves of polymer anchored ligand and copper
complex are shown in Fig. 3. Polymer anchored ligand decom-
posed at temperature 320 ◦C. After complexation of copper on
polymer anchored ligand, thermal stability of the immobilized
complex improved. Polymer anchored copper complex decom-
posed at 360 ◦C. So from the thermal stability, it concludes that
polymer anchored metal complex degraded at considerably higher
temperature.
Cu-grafted furfural functionalized polymer was used as a cata-
lyst for the aryl-sulphur coupling of thiophenol with aryl iodide. To
a solution of iodobenzene (1 mmol) and thiophenol (1.1 mmol) in
3 mL of water, K2CO3 (276 mg) and Cu-grafted catalyst 1 (0.05 g)
were added. At the end of specified time, the reaction mixture
was filtered and the filtrate was analyzed using a Varian 3400 gas
chromatograph equipped with a 30 m CP-SIL8CB capillary column
and a flame ionization detector. Peak position of various reaction

10
Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
Fig. 2. EDX images of polymer anchored Schiff base ligand (A) and polymer anchored Cu-catalyst (B).
ca.1627 cm−1 indicating the C N bond is coordinated to copper
3.4. IR spectral study
through the lone pair of electrons of nitrogen. The two strong
absorption bands at 1552 [29] and 1440 cm−1 [30,31] can be
assigned to the asymmetric and symmetric vibrations, respec-
tively, of the bridging acetate ions and a weak peak at 418 cm−1
is attributed to the Cu–N coordination [32].
The FT IR spectra of the polymer anchored Schiff base (a) and
polymer anchored Cu-complex (b) are shown in Fig. 4, from which
it is evident that the peak at 1658 cm−1 in polymer anchored
ligand is due to C N. For the polymer anchored copper complex
the C N stretching frequency is shifted to lower wavelength at
3.5. DRS-UV spectroscopy
The electronic spectrum of the polymer-supported Cu(II) Schiff
base catalyst was recorded in diffuse reflectance mode as a BaSO4
disk due to its solubility limitations in common organic solvents.
The UV spectra of the extracted (a) and Cu-loaded (b) samples
are given in Fig. 5. In the case of the extracted sample the peak
in between 300 and 400 nm is due to the ␲–␲* transition of the
conjugated system present in the imine ligand. In the case of the
Cu-loaded sample a small hump at around 330-345 nm is present
and a peak that arises around 250–260 nm can be attributed to the
charge transfer band between Cu+2 and the oxygen of the ligand
[33]. In addition to this, a broad absorption band in between 600 and
800 nm is observed. This could be attributed to the d–d transition
of Cu+2 ions in a pseudo-octahedral environment [34].
PS-Furfural
PS-Cu-Furfural
100
200
300
400
500
600
3.6. Catalytic activity of the copper catalyst in O-arylation
reaction
Temperature (0C)
Aryl ethers are an important class of ‘building blocks’ that
are widely employed in organic synthesis, materials science, and
Fig. 3. Thermogravimetric weight loss plots for polymer anchored Schiff base ligand
and polymer anchored Cu-catalyst.

Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
11
Fig. 4. FT-IR spectra of polymer anchored ligand (a) and polymer anchored copper catalyst (b).
pharmaceutical or agrochemical areas. In our initial study towards
the development of this methodology, we have studied the reac-
tion of phenol (1.0 mmol) with iodobenzene in the presence of
Cu-catalyst and Cs2CO3 as a base in DMSO at 120 ◦C (Scheme 2).
The reaction afforded the corresponding cross-coupled product
in 96% yield (entry 1, Table S2). The influence of solvent on the
yield of diaryl ether in the presence of copper catalyst was also
investigated (Table S2). This table clearly shows the superiority
of dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF)
as reaction solvents for this reaction; other dialkylamide solvents
such as N,N-dimethylacetamide (DMA), or N-methylpyrrolidinone
(NMP) performed worse than DMF, whereas in acetonitrile and 1,4-
dioxane the complex was almost inactive (Table S2, entries 1–6).
The influence of different bases such as Cs2CO3, NaOMe, K3PO4,
Et3N, K2CO3 and KOH on the C–O cross-coupling was observed
(Table S2). It was found that Cs2CO3 was the most effective base,
while the use of other bases such as NaOMe, K3PO4, Et3N, K2CO3
and KOH resulted in much lower or no yields. Cesium carbonate
was particularly effective as a base in O-arylation reaction because
cesium phenoxides are indeed more dissociated and more soluble
in organic solvents than their potassium and sodium counterparts.
It was also found that 0.05 g of copper catalyst was the most effec-
tive catalytic system. This arylation was also found to be highly
sensitive to the reaction temperature and time. At lower tem-
peratures (50 ◦C) and with lower reaction time (6 h) only low to
moderate yield was obtained (Table S2, entries 12 and 13). It was
also found that, 0.05 g of copper catalyst, a reaction temperature of
120 ◦C and reaction time of 12 h were found to be optimal. From the
above discussions, it can be seen that the best yield was obtained
by using Cs2CO3 (1 mmol) in DMSO solvent at 120 ◦C for 12 h under
open air.
Under the optimized conditions, the coupling reaction between
phenol and various aryl halides was investigated to know about
the scope of our method (Table 1). There is very little elec-
tronic effect observed when phenol is submitted to coupling with
para-substituted iodobenzene. It is noted that iodobenzene with
electron-donating groups in para position such as methyl and
methoxy groups decrease the yield slightly (entries 2 and 3) and
electron-withdrawing groups in para position such as kitomethyl,
chloro and nitro groups increase the yield compared to electron-
donating groups (entries 4–6). 2-Iodotoluene with hindered aryl
halides, gives lower conversions after 12 h and the arylation reac-
tion required longer reaction times to go to completion (entry 7),
which is usually observed in the literature. After achieving excellent
results with aryl iodides, we further applied this catalytic system
for the O-arylation of aryl bromides (entries 8–12). Significant elec-
tronic effects are observed for substituted aryl bromides. But the
2.0
PS-Cu-Furfural
PS-Furfural
1.5
1.0
0.5
0.0
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 5. DRS-UV–visible absorption spectra of polymer anchored ligand (PS-furfural)
and polymer anchored Cu-catalyst (PS-Cu-furfural).
OH
I
O
Cu-catalyst
Cs2CO3, DMSO
R1
R1
H
H
R1= H, Me, OMe, CoMe, Cl, NO2
Scheme 2. O-arylation reaction of phenols with aryl halides.

12
Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
Table 1
O-arylation reaction of aryl halides with phenol with polymer anchored Cu Schiff base complex catalysta.
Entry
Phenol
Aryl halides
Productsb
Yield (%)c
I
OH
O
1
96
H
I
H
OH
O
2
3
4
5
85
83
89
92
Me
OMe
H
H
H
H
Me
I
OH
O
H
OMe
I
OH
O
COMe
H
COMe
I
OH
O
O
Cl
H
H
H
Cl
I
OH
6
93
NO2
NO2
I
H
OH
Me
O
Me
7d
73
92
H
H
OH
Br
Br
O
O
8
H
OH
9
65
70
NO2
NO2
Br
H
OH
O
10
CN
H
CN

Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
13
Table 1 (Continued)
Entry
Phenol
Aryl halides
Productsb
Yield (%)c
Br
OH
O
11
71
OMe
H
OMe
Br
OH
O
12
40
Me
H
Me
Br
OH
O
13
72
70
NO 2
MeO
MeO
NO2
Br
OMe
OH
O
14
CN
OMe
CN
a
Reaction conditions: 1 mmol of aryl halides, 1 mmol of phenol, 1 mmol Cs2CO3, Cu-cat. (0.05 g), DMSO (10 mL), 0.1 mmol t-Bu4NBr, 120 ◦C, open air, 12 h.
Products were identified by comparison of their GC–MS and 1H NMR data those reported in the literature.
Yields refer to those of purified products characterized by spectroscopic data.
b
c
d
Reaction time 24 h.
reaction of electron-rich bromoarenes was slightly difficult, and
The results are summarized in Table S3. In order to determine
the best reaction medium, we tested different solvents such
as methanol, DMSO, acetonitrile, DMF and toluene (Table S3).
Methanol was found to be the best solvent for the N-arylation
of imidazole (99%). On the other hand, reaction in other solvents
gave trace amount of coupled product under identical conditions.
N-arylation reactions of N-H heterocycles with phenylboronic acid
were carried out in methanol with this copper catalyst, without
the need of any organic co-solvent, base or additives such as phase
transfer catalysts. From the above discussions, it can be seen that
the best yield was obtained in the N-arylation reaction of imidazole
with phenylboronic acid in MeOH solvent at 40 ◦C for 10 h without
any base.
Our method was successfully amenable to a wide range of aryl-
boronic acids, allowing preparation of N-arylimidazoles in high
yield, and the results are shown in Table 2. It was observed that
arylboronic acids with electron-donating groups reacted at a faster
rate and afforded better yields than arylboronic acids with electron-
withdrawing groups (entries 2–7). o- and p-substituted arylboronic
acids were equally effective for the coupling with imidazole (entries
2 and 7).
offered the desired products with low yields (entry 12). As for
bromoarenes, electron-deficient (entries 9 and 10) ones provide
the desired diaryl ethers in moderate yields. But the reaction with
electron-rich bromoarenes is slightly difficult, and lower yield of
the desired product is obtained. For phenols, electron-rich ones
were viable substrates, and offered the desired products in good
to excellent yields. The moderate to good yields were observed in
the reaction of 4-cyanophenyl bromide and 4-nitrophenyl bromide
with 4-methoxyphenol.
3.7. Catalytic activity of the copper catalyst in N-arylation
reaction of imidazole with arylboronic acids
The synthesis of N-arylimidazoles has been recorded in signifi-
cant interest because of the frequent occurrence of these structural
units in biologically active inhibitors. To check the generality and
scope of the catalyst, we tried the N-arylation of various N-H het-
erocycles with several other arylboronic acids in MeOH without
using any base at 40 ◦C (Scheme 3).
B(OH)2
N
3.8. Catalytic activity of the copper catalyst in N-arylation
reaction of imidazole with aryl halides
N
Cu-catalyst
MeOH, 40oC
N
N
H
The N-arylation reaction is a convenient method for the C–N
bond formation between N–H heterocycles with aryl halides and
imidizole. To test the applicability of the copper catalyst, we exam-
ined the N-arylation reaction between N–H heterocycles with
R1
R1
R1= H, Me, OMe, F, CF3, NO2.
Scheme 3. N-arylation of imidazole with various arylboronic acids.

14
Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
Table 2
N-Arylation of imidazole with various arylboronic acids using PS-Cu-furfurala.
Entry
N(H)-heterocycles
Arylboronic acid
Productsb
Time (h)
Yield (%)c
B(OH)2
N
N
N
1
Imidazole
10
99
H
B(OH)2
N
2
3
4
5
Imidazole
Imidazole
Imidazole
Imidazole
15
18
12
10
82
80
96
94
Me
Me
B(OH)2
N
N
N
N
N
OMe
OMe
B(OH)2
F
F
B(OH)2
N
Cl
Cl
N
N
N
B(OH)2
NO2
N
N
N
6
7
Imidazole
Imidazole
12
12
95
70
NO2
B(OH)2
Me
Me
B(OH)2
8
Imidazole
15
76
COMe
COMe
a
Reaction conditions: catalyst (0.05 g), 1.5 mmol of arylboronic acid, 1.2 mmol of imidazole, MeOH (10 mL),40 ◦C, air.
Products were identified by comparison of their GC–MS and 1HNMR data those reported in the literature.
Yields refer to those of purified products characterized by spectroscopic data.
b
c
various aryl halides and imidazole in DMSO using K2CO3 at 120 ◦C
as model reaction (Scheme 4).
several solvents were screened and results are summarized in Table
S4. It was observed that the polar solvents like DMSO, DMF, NMP,
and acetonitrile were effective (Table S4, entries 1, 5–7). THF and
dimethoxyethane (DME) were less effective (entries 8 and 9). Con-
sequently, DMSO was used as a solvent for the rest of the studies.
With optimized conditions now in hand, we explored the scope
of this process with respect to aryl iodide structure, and the results
are summarized in Table 3. To our delight, the N-arylation of imid-
azole is smoothly performed with the extensive pool of aryl iodides
Several bases were screened using the copper catalyst for the N-
arylation of imidazole with iodobenzene in DMSO solvent at 120 ◦C,
and the results are summarized in Table S4. It was observed that
K2CO3 gave the best result (Table S4, entry 1). K3PO4 was also found
to be fairly active (entry 2). But the organic bases like Et3N and
Cs2CO3 were almost inactive (entries 3 and 4). Next, to check the
effect of solvents in the N-arylation of imidazole with iodobenzene,

Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
15
Table 3
N-Arylation of imidazoles with different aryl halides using PS-Cu-furfurala.
Entry
Aryl halides
Productsb
Time (h)
Yield (%)c
I
N
N
1
12
95
82
H
I
N
N
2
15
Me
Me
I
N
N
N
N
3
4
18
12
80
96
OMe
COMe
NO2
OMe
I
COMe
I
N
N
5
12
95
NO2
N
N
I
Me
Me
N
N
6
7
15
12
60
70
Br
H
Br
N
N
N
N
8
15
12
30
80
Me
Me
Br
9
NO2
NO2
a
Reaction conditions: Cu-catalyst (0.05 g), aryl halide (1 mmol), imidazole (1.2 mmol), K2CO3 (2 mmol), DMSO (10 mL), 120 ◦C, N2 atm.
Products were identified by comparison of their GC–MS and 1H NMR data those reported in the literature.
Yields refer to those of purified products characterized by spectroscopic data.
b
c

16
Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
Table 4
N-arylation reaction of primary amines with various arylhalides using PS-Cu-furfurala.
Entry
Aryl halides
Aryl amines
Productsb
Time (h)
12
Yield (%)c
I
NH2
1
N-(Phenyl)aniline
93
H
I
H
NH2
2
3
4
5
N-(4-Methylphenyl)aniline
N-(4-Methoxyphenyl)aniline
N-(4-Methylphenyl)aniline
N-benzylaniline
14
14
14
14
16
81
83
75
70
62
Me
I
H
NH2
OMe
I
H
NH2
H
I
Me
CH2NH2
H
H
NH2
I
Me
6
N-(2-Methylphenyl)aniline
H
a
Reaction conditions: polymer supported Cu-catalyst (0.05 g), aryl halide (4 mmol), aromatic amine (2 mmol), KOH (1 mmol), DMSO (10 mL), 140 ◦C, N2 atm.
Products were identified by comparison of their GC–MS and 1H NMR data those reported in the literature.
Yields refer to those of purified products characterized by spectroscopic data.
b
c
to afford the corresponding products in good to excellent yields. It
3.9. Catalytic activity of the copper catalyst in N-arylation
reaction of primary amines with aryl iodides
was observed that iodoarenes with electron-withdrawing groups
(Table 3, entries 4 and 5) reacted at a faster rate than iodo-arenes
with electron-donating groups (Table 3, entries 2 and 3). Sterically
hindered 2-iodotoluene took longer duration to afford a good yield
(Table 3, entry 6). Extension of this arylation process with aryl bro-
midesyieldedinterestingresults:Theuseof bromobenzenein place
of iodobenzene afforded lower conversion with 70% yield (entry
7) with longer reaction time and longer reaction temperature.
Bromobenzene with an electron-donating group gave lower yield
(entry 8), whereas bromobenzene with an electron-withdrawing
group gave excellent yield of product (entry 9).
The synthesis of N-aryl amines is an active area in organic
synthesis due to their occurrence in biologically important natu-
ral products, pharmaceuticals and their applications in materials
research. The scope of the methodology of N-arylation reaction
was further extended for coupling of primary amines with aryl
iodides under the experimental condition given in Scheme 5, Table
S5, entries 1–9.
The solvents play an important role in the N-arylation reaction.
Polar solvents, such as DMSO, DMA, and DMF were found to be
X
I
NH2
N
H
N
N
Cu-catalyst
Cu-Catalyst
N
DMSO, K2CO3, 120oC
N
H
DMSO, KOH, 140oC
R1
R2
R1
R1
R1
R2
R1= H, Me, OMe; R2= H, Me
X=I, Br; R1 = H, Me, OMe, COMe, NO2.
Scheme 4. N-arylation of imidazoles with different aryl halides.
Scheme 5. N-arylation reaction of primary amines with various arylhalides.

Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
17
Table 5
C–S coupling reactions catalyzed by polymer supported Cu-catalysta.
Entry
ArI
ArSH
Products
Yield (%)b
I
SH
S
1
97
80
I
SH
SH
S
2
H3C
CH3
I
S
3
74
H3CO
OCH3
I
SH
SH
SH
S
4
90
O2N
NO2
I
S
5
94
Br
Br
I
S
6
58
Cl
Cl
SH
SH
SH
I
S
7
8
9
85
65
45
N
N
Br
S
S
Cl

18
Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
Table 5 (Continued)
Entry
ArI
ArSH
Products
Yield (%)b
SH
I
I
S
S
10
65
OMe
OMe
SH
11
60
Cl
Cl
a
Reaction conditions: aryl iodides (1 mmol), thiophenol (1.1 mmol), water (3 mL), K2CO3 (2 mmol) and Cu-catalyst (0.05 g), temperature (80 ◦C), time (12 h).
Yields were determined by GC and GC–MS analysis.
b
I
SH
highly suited for this reaction, while the less polar solvents, such
as toluene, afforded the product only in very poor yields (Table S5,
entries 1–4). The reaction performs better in more polar solvents,
optimum results being observed in dimethylsulfoxide (DMSO).
Although the reaction did proceed in 1,4-dioxane, the yield of reac-
tion product was much lower (Table S5, entry 5). The influence of
bases on the yields of diphenylamine in the presence of copper
catalyst was investigated to find that KOH was the most effec-
tive and using milder bases such as K3PO4, K2CO3, and Cs2CO3
significantly resulted in low yields (Table S5, entries 1, 7–9). N-
methylpyrrolidinone (NMP) also proved to be an effective solvent.
(Table S5, entry 6). This reaction using polymer supported copper
catalyst was also performed at higher temperature (140 ◦C) and
higher reaction time (16 h). From the above discussions, it can be
seen that the best yield was obtained for the N-arylation reaction of
aniline with iodobenzene by using KOH in DMSO solvent at 140 ◦C
for 16 h.
Substrates with varying degrees of substitution on both the
reagents were examined and were found to provide triarylamines
in good to excellent yields. Usually, primary amines give a mixture
of secondary and tertiary amines; however, in the present case the
coupling of aniline with iodobenzene gave triphenylamine in 93%
yield (Table 4, entry 1). A variety of functional groups including
methyl, methoxy and bromo were well tolerated. With optimized
conditions now in hand, we explored the scope of this process with
respect to aryl iodide structure, and the results are summarized in
(Table 4, Scheme 5). Methyl and methoxy groups at the para posi-
tion were tolerated on the aryl iodide component (Table 4, entries 2
and 3). Both p-toluidine (Table 4, entry 4) and benzylamine (Table 4,
entry 5) were also reacted to a considerable extent. The system also
permits the use of sterically hindered amine such as o -toluidine
(Table 4, entry 6), which gave good yield.
S
water, K2CO3
Cu-Catalyst, 80oC
R1
R2
R1
R2
1= H, CH3, OCH3, NO2, Br, Cl.
2= H, OMe, Cl.
Scheme 6. General procedure for aryl-sulfur coupling reaction of thiophenol with
aryl iodide.
a variety of inorganic (Table S6, entries 1–3) and organic bases
(entries 4 and 5) were used to afford aryl sulfides. Potassium
hydroxide was found to act as a poor base, whereas Cs2CO3 was
effective to some extent and other bases were not at all effective.
Despite that the respective sulfide could be detected employing
the related bases screened, K2CO3 showed the best performance,
furnishing the desired product in quantitative yield (entry 1). Note-
worthy is that in the absence of a base no formation of product
was observed (Table S6, entry 7). In view of the extreme moisture-
sensitivity and expense of Cs2CO3, cheap and stable K2CO3 was
the preferred base for use in the PS-Cu-furfural catalyzed coupling
reaction. As a result, K2CO3 was selected as the optimum base.
Using the optimized conditions, the present reaction was fur-
ther expanded to a broader range of aryl thiols and aryl iodides in
order to evaluate the scope and limitations of the method, as out-
lined in Table 5. In general, the reactions are very clean and high
yielding. Aryl iodides with an electron withdrawing group were
more reactive in comparison to those with an electron donating
group. Thus, the reaction of aryl iodides with methyl and methoxy
substituents gave the corresponding C–S cross-coupled products
in 74–80% yield, while the reaction of aryl iodides with nitro sub-
stituent completed in 90% yield. The effect of different halogen
substituents in the coupling of thiophenol is also shown in Table 5.
The observed order of reactivity of different halobenzenes are
iodobenzene > bromobenzene > chlorobenzene.
3.10. Catalytic activity of the copper catalyst in aryl-sulfur
coupling reaction of thiophenol with aryl iodide
Diaryl sulfides formed via C–S cross-coupling reaction from aryl
halides bearing different nucleophilic phenyl rings have significant
roles in biological, pharmaceutical, and material research. In an
effort to evolve a better catalytic system, various parameters were
screened for S-arylation of thiophenol with aryl iodide in water at
80 ◦C (Scheme 6).
To optimize the reaction conditions, a series of bases K2CO3,
Cs2CO3, KOH, Et3N and pyridine were screened on the C–S cross-
coupling reaction (Table S6). In a comparison of the efficiency of
3.11. Heterogeneity test
To check the leaching of metal into the solution during the reac-
tion, hot-filtration test has been carried out in O-arylation reaction
with our supported PS-Cu-furfural catalyst. A typical hot filtra-
tion test was performed in the O-arylation reaction of iodobenzene
with phenol to investigate whether the reaction proceeded in a

Sk.Manirul Islam et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 7–19
19
Acknowledgements
S.M.I. acknowledges Council of Scientific and Industrial Research
(CSIR) and Department of Science and Technology (DST), New Delhi,
India for funding We thank the Department of Chemistry, Univer-
sity of Kalyani, for providing us the instrumental support. P.M. and
A.S.R. are thankful to the CSIR, New Delhi, India and NS is thankful
to the UGC, New Delhi for senior research fellowship.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
2014.02.007.
Fig. 6. Recycling efficiency for the N-arylation reactions of imidazole with phenyl-
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