A reusable polymer supported copper(I) complex for the C-N bond cross-coupling reaction

Article abstract of DOI:10.1016/j.inoche.2011.05.019

The Ullmann coupling of amines with aryl iodide as well as arylboronic acids and N(H)-heterocycles with arylboronic acids has been carried out efficiently using PS-LCu(I) catalyst. The copper complex has been prepared and characterized by using scanning electron microscope (SEM), elemental analysis, atomic absorption spectroscopy (AAS), Thermo gravimetric analysis and spectrometric methods like Fourier transform infrared spectroscopy (FTIR). The effects of various parameters such as temperature, solvent and base on the reaction system were studied. The reusability experiments show that the catalyst can be used five times without much loss in the catalytic activity.

Full text of DOI:10.1016/j.inoche.2011.05.019

Inorganic Chemistry Communications 14 (2011) 1352–1357
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A reusable polymer supported copper(I) complex for the C–N bond
cross-coupling reaction
a
a
a
b
a
S.M. Islam a, , Sanchita Mondal , Paramita Mondal , Anupam Singha Roy , Kazi Tuhina , Manir Mobarok
⁎
a
Dept. of Chemistry, University of Kalyani, Kalyani, Nadia, 741235, W.B., India
Dept. of Chemistry, B.S. College, S-24 PGS, 743329, W.B., India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The Ullmann coupling of amines with aryl iodide as well as arylboronic acids and N(H)-heterocycles with
arylboronic acids has been carried out efficiently using PS-LCu(I) catalyst. The copper complex has been
prepared and characterized by using scanning electron microscope (SEM), elemental analysis, atomic
absorption spectroscopy (AAS), Thermo gravimetric analysis and spectrometric methods like Fourier
transform infrared spectroscopy (FTIR). The effects of various parameters such as temperature, solvent and
base on the reaction system were studied. The reusability experiments show that the catalyst can be used five
times without much loss in the catalytic activity.
Received 27 April 2011
Accepted 19 May 2011
Available online 27 May 2011
Keywords:
PS-LCu(I) catalyst
N-arylation
© 2011 Elsevier B.V. All rights reserved.
Amination
Reusable catalyst
The synthesis of N-aryl amines and N-aryl heterocycles is an active
area in organic synthesis due to their occurrence in biologically
important natural products, pharmaceuticals and their applications in
materials research [1,2]. Among the various strategies developed to
date, the copper-catalyzed Ullmann reaction has proven to be the
most convenient synthetic route for installing an N-aryl functionality
[3,4]. In addition, Buchwald [5] and Hartwig [6,7] have reported on Pd
mediated C–N bond formation. However, the cost of reagents and
removal trace palladium from late stage synthetic intermediate are
the major drawbacks of this method. Copper mediated amination and
N-arylation is another choice of reaction for the production of these
compounds due to cheap price and environmental friendly nature.
However, copper-mediated couplings are still the reaction of choice
for large and industrial scale formation of C–N bonds. The reaction
system mostly employs an in situ generated catalyst from a copper
source and highly efficient N/P-containing ligands such as amino
acids, [8] diamines, [9] diimines, [10] pyridine, [11] oximephosphine
oxides [12] and phosphoramidite [13]. In spite of the significant
advances in this area, very few reports employing a structurally well
defined and stable copper complex as a catalyst have been reported
[14–16]. Chan and Lam established an efficient approach to N-
arylimidazoles via Cu(OAc)2-mediated coupling of imidazoles with
readily available arylboronic acids [17]. Later, Collman and coworkers
reported using Cu(II) complexes with nitrogen-chelating bidentate
ligands in the coupling of imidazoles at room temperature [18]. Very
recently, Xie and coworkers have shown the simple copper salt
catalyzed coupling of imidazoles with arylboronic acids in protic
solvent without any base [19]. Recently, calcium hydroxyapatite has
been used as a heterogeneous support for transition metals, and the
supported hydroxyapatite is used for organic transformations [20].
Nowadays solid-phase technique has gained much importance in
this cross-coupling reaction. Homogeneous catalysts have some
disadvantages, such as they may easily be destroyed during the
course of the reaction and they cannot be easily recovered after the
reaction for reuse. These disadvantages can be overcome by anchoring
metal on suitable supports. There are many examples of heteroge-
neous catalysts for C–N coupling reactions and they are prepared by
different approaches like encapsulation or immobilization of a
catalytically active metal complex on solid supports [21].
In this present work, N-arylation reactions of various N(H)-
heterocycles with arylboronic acids were carried out in methanol
with PS-LCu(I) catalyst, without the need of any organic co-solvent,
base or additives such as phase transfer catalysts. This catalyst was
also effective in amination reactions of primary amines with various
aryl halides as well as arylboronic acids. The experimental results
reveal that the anchoring of the complex on a solid support not only
exhibits improved catalyst activity, stability and selectivity of the
product but also enables easy recovery and reuse of the catalyst.
The synthesis of the immobilized PS-LCu(I) catalyst illustrated in
Scheme 1. It was readily prepared through a two-step procedure. Firstly
the 0.2 g of chloromethylated polystyrene copolymer (2) treated with
0.979 g of β-alanine (1) to produce the corresponding polymer
supported ligand (PS-L) in the presence of sodium carbonate
(0.490 g) in N,N-dimethylformamide (DMF) to obtained a light brown
polymer. The polymer was washed thoroughly with DMF to remove
excess β-alanine and then with 1 M HCl to remove excess base. Finally, it
⁎
Corresponding author at: Department of Chemistry, University of Kalyani, Kalyani,
Nadia, 741235, W.B., India. Tel.: + 91 33 2582 8750; fax: +91 33 2582 8282.
E-mail address: manir65@rediffmail.com (S.M. Islam).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.05.019

S.M. Islam et al. / Inorganic Chemistry Communications 14 (2011) 1352–1357
1353
P
O
C
O
C
CH2
CH3
CH2
CH2
NH2
DMF/ Na2CO3
P
100 0C/
NH2
48 h
HO
CH2
O
P
(PS-L)
(1)
CH2Cl
(2)
MeOH
CuI
Reflux
O
C
O
CH2
CH2
NH
P
CH2
P
Cu
I
PS-LCu(I) catalyst
Polymer supported copper catalyst
Scheme 1. Synthesis of the PS-LCu(I) catalyst.
was washed with double distilled water, dried and stored at room
temperature for further use. Then the polymer anchored β-alanine
ligand (1 g) in methanol (20 mL) was treated with 5 mL 1% (w/v)
methanolic solution of copper iodide over a period of nearly 30 min
under constant stirring. Then the reaction mixture was refluxed for 24 h.
The green color copper complex thus formed was filtered and washed
thoroughly with ethanol and dried in room temperature under vacuum.
The outline for the preparation of PS-LCu(I) catalyst is given in
Scheme 1.
Due to insolubilities of the PS-LCu(I) catalyst in all common organic
solvents, its structural investigation was limited to its physicochemical
properties, chemical analysis, SEM, TGA and IR spectroscopic data.
Table 1 provides the data of elemental analysis of different functiona-
lized polymer and the complexes. Copper content in the catalysts
determined by AAS suggests 0.83 wt.% Cu in the catalyst. The band at
676 cm−1 for –C–Cl stretching had disappeared in the polymer
anchored ligand. A few new bands appeared, e.g. those at 3422 cm−1
along with bands at 1641 cm−1 showed the presence of free –NH2
groups in the ligand. On complexation with copper, the frequency of
free –NH2 groups is reduced in intensity. In addition, the bands at
528 cm−1 may be assigned to the Cu–N [22] stretching vibration. The
scanning electron micrographs of the PS-L and PS-LCu(I) catalyst clearly
show the morphological change which occurred on the surface of
polystyrene after loading of metal on it(Fig. 1A and B). Energy dispersive
spectroscopy analysis of X-rays (EDAX) data for the PS-L and PS-LCu(I)
catalyst is given in Fig. 2A and B. The EDX data also inform that the
attachment of copper metal on the surface of the polymer matrix.
Thermal stability of the complex was investigated using TGA-DTA at a
heating rate of 10 °C /min in air over a temperature range of 30–600 °C.
Table 1
Chemical composition of various compounds and PS-LCu(I) catalyst.
Compound
Color
C %
H %
Cl %
N %
Cu %
(1)
(2)
(PS-L)
PS-LCu(I)
White
White
White
Green
40.45
70.82
70.24
47.29
7.87
5.90
7.32
4.60
–
15.73
–
–
23.28
–
–
6.83
4.60
–
–
0.83
0.82a
a
Used catalyst.
Fig. 1. FE SEM image of PS-L (1A) and PS-LCu(I) catalyst (1B).

1354
S.M. Islam et al. / Inorganic Chemistry Communications 14 (2011) 1352–1357
Fig. 2. EDAX data of PS-L (2A) and PS-LCu(I) catalyst (2B).
TGA–DTA curves of the PS-L and PS-LCu(I) catalyst are shown in Fig. 3.
The complex is stable up to 200 °C and above this temperature it
decomposes. Thermo gravimetric study suggests that the PS-LCu(I)
catalyst degrades at considerably higher temperature.
as solvent in absence of any base and with a limited range of substrates,
it is likely that our catalyst should be applicable to other substituted
arylboronic acid systems. To check the generality and scope of the
catalyst, we tried the N-arylation of N–H heterocycles with several other
arylboronic acids in MeOH without using any base under this
experimental condition [23] and the results are summarized in
Table 2. The reaction of imidazole with phenylboronic acid is completed
within 12 h at lower temperature (40 °C). Imidazole is successfully
applied to couple electron rich arylboronic acids with in high yields
(Table 2, entries 2–5). Electron withdrawingarylboronic acids reacted at
a slower rate with moderate to good yields (entries 6–9). The coupling
of 3-nitroboronic acid which is a difficult substrate also proceeded
smoothly under the present conditions (Table 2, entry 7). A similar
observation is made when benzimidazole is used in place of imidazole to
obtain the corresponding N-arylbenzimidazoles, but the reactions took
longer time compared to that in the reactions of imidazole (Table 2,
entries 10–12). In an endeavor to expand the scope of the above
methodology, the catalytic system was also applied to amides and
sulfonamides. Such coupling of benzamide wasfound togive the desired
N-arylation products in good yields, as shown in Table 2, entry 13, but
for sulfonamide, which afforded the corresponding products in lower
yield (Table 2, entry 14). Phenylboronic acid and 4-methylphenylboro-
nic acid (Table 2, entries 15 and 16) were coupled with phthalimide
under the generalized reaction conditions to afford the corresponding
products in excellent yields.
Catalytic activity of the PS-LCu(I) catalyst
Although the current catalyst is performed in the N-arylation
reaction of N(H)-heterocycles with phenylboronic acid using methanol
After achieving excellent results with N(H)-heterocycles, we
further applied this catalytic system for the amination of aromatic
amines. Preliminary experiments are carried out by taking phenyl-
boronic acid as a test molecule for the amination of aniline. In order to
determine the best reaction medium, we tested different solvents
Fig. 3. Thermogravimetric weight loss plots for the PS-L and PS-LCu(I) catalyst.

S.M. Islam et al. / Inorganic Chemistry Communications 14 (2011) 1352–1357
1355
Table 2
N-arylation of N–H heterocycle with various arylboronic acidsa.
B(OH)2
methanol , 400C
N-H heterocycles
Aryl-N-heterocycles
R
R= H, Me, OMe, Cl, F, CF3, NO2
Entry
N–H heterocycle
Aryl halides
Products
Time (h)
Isolated yieldb(%)
1.
2.
3.
4.
5.
6.
7.
8.
Imidazole
Imidazole
Imidazole
Imidazole
Imidazole
Imidazole
Imidazole
Imidazole
C6H5–B(OH)2
N-Phenylimidazole
10 h
10 h
10 h
15 h
15 h
18 h
18 h
18 h
18 h
14 h
16 h
16 h
14 h
14 h
14 h
14 h
96
95
92
80
73
82
83
79
60
94
91
90
90
38
94
92
4-Me–C6H4B(OH)2
4-MeO–C6H4B(OH)2
2-Me–C6H4B(OH)2
3,4-MeO–C6H3B(OH)2
4-Cl–C6H4B(OH)2
4-F–C6H4B(OH)2
3-NO2–C6H4B(OH)2
4-CF3–C6H4B(OH)2
C6H5–B(OH)2
4-Me–C6H4B(OH)2
4-MeO–C6H4B(OH)2
C6H5–B(OH)2
C6H5–B(OH)2
C6H5–B(OH)2
N-(4-Methylphenyl)imidazole
N-(4-Methoxyphenyl)imidazole
N-(2-Methylphenyl)imidazole
N-(3,4-dimethoxyphenyl)imidazole
N-(4-Chlorophenyl)imidazole
N-(4-Fluorophenyl)imidazole
N-(3-nitrophenyl)imidazole
N-(4-Trifluoromethylphenyl)imidazole
N-phenylbenzimidazole
N-(4-Methylphenyl)benzimidazole
N-(4-Methoxyphenyl)benzimidazole
N-Phenylbenzamide
N-phenylbenzenesulfonamide
N-phenylphalimide
9.
Imidazole
10.
11
12
13
14
15
16
Benzimidazole
Benzimidazole
Benzimidazole
Benzamide
Sulfonamide
Phalimide
Phalimide
4-Me–C6H4B(OH)2
N-(4-Methylphenyl)phalimide
a
Reaction conditions: PS-LCu(I) catalyst (0.05 g, 0.0065 mmol), 1 mmol of arylboronic acid, 1.2 mmol of N–H heterocycle, MeOH (10 ml), 40 °C, N2 atm.
Isolated yield after column chromatography.
b
such as MeOH, ACN, toluene, DMF and DMSO for the amination
different arylboronic acids are carried out under these optimized
conditions [24] and results are summarized in Table 4. It is clear from
Table 4 that amination proceeds very effectively and affords the
corresponding products in good to excellent yields under our reaction
conditions. No spectacular electronic effects are observed in the
amination of aniline; only a slight decrease in the reaction rate is
noted with the 3-nitrophenylboronic acid. Benzyl amine gives 85%
yield of the desired product when reacted with phenylboronic acid.
After achieving excellent results with arylboronic acids, we further
applied this catalytic system for the amination reaction of aromatic
amines with aryl halides. To optimize the conditions for the amination
reaction, we have chosen the reaction between iodobenzene and
aniline as a model reaction and various solvents and bases were
screened. The results are shown in Table 5. The amount of copper
catalyst (0.05 g) was the same for all experiments and was not further
optimized. The solvents also play an important role in the amination
reaction and best results were obtained with toluene as a solvent
reaction of aniline with phenylboronic acid (Table 3). MeOH is found
to be the best solvent for the amination of aniline (Table 3, entry 1).
On the other hand, reaction in other solvents gives low to moderate
coupled product (Table 3, entries 2–5). Further experiments with
Table 3
Effect of solvent on the amination reaction of aniline with phenylboronic acidsa.
Entry
Solvent
Temperature
Time (h)
Yieldb (%)
1.
2.
3.
4.
5.
MeOH
ACN
DMSO
DMF
40 °C
40 °C
130 °C
140 °C
90 °C
14
14
16
20
16
90
76
81
77
64
Toluene
a
Reaction conditions: PS-LCu(I) catalyst (0.05 g, 0.0065 mmol), 1.5 mmol of
phenylboronic acid, 1.2 mmol of aniline, solvent (10 ml), 140 °C, N2 atm.
b
Yield determined by GC and GCMS analysis.
Table 4
Amination reaction of aniline with various arylboronic acidsa.
B(OH)2
NH2
H
N
MeOH , 40 0
C
R
R
R= H, Me, OMe, Cl, NO2.
Entry
Arylboronic acids
Aryl amines
Products
Time (h)
Isolated yieldb (%)
1.
2.
3.
4.
5.
6.
C6H5–B(OH)2
C6H5NH2
C6H5NH2
C6H5NH2
C6H5NH2
C6H5NH2
C6H5CH2NH2
N-(Phenyl)aniline
14
15
15
16
20
17
90
94
91
70
65
85
4-Me–C6H4B(OH)2
4-MeO–C6H4B(OH)2
4-Cl–C6H4B(OH)2
3-NO2–C6H4B(OH)2
C6H5–B(OH)2
N-(4-Methylphenyl)aniline
N-(4-Methoxyphenyl)aniline
N-(4-Chlorophenyl)aniline
N-(3-nitrophenyl) aniline
N-Phenylbenzylamine
a
Reaction conditions: PS-LCu(I) catalyst (0.05 g, 0.0065 mmol), 1.5 mmol of arylboronic acid, 1.2 mmol of aniline, MeOH (10 ml), 40 °C, N2 atm.
Isolated yield after column chromatography.
b

1356
S.M. Islam et al. / Inorganic Chemistry Communications 14 (2011) 1352–1357
Table 5
iodobenzene gave triphenylamine selectively in 94% yield (entry 1). A
variety of functional groups including methyl, methoxy and bromo
were well tolerated.
Effect of solvent, base, temperature, reaction time on the amination reaction of aniline
with iodobenzenea.
Entry
Base
Solvent
Temperature
Time (h)
Yieldb(%)
Table 7 provides a comparison of the results obtained for our
present catalytic system with those reported in the literature. From
Table 7, it is seen that present catalyst exhibited higher conversions
and yields compared to the other reported system [11,21,26].
To determine whether the catalyst is actually functioning in a
heterogeneous manner, a hot-filtration test was performed in the N-
arylation reaction of imidazole with phenylboronic acid, the solid
catalyst was filtered out after the reaction proceeded for 4 h and the
determined yield was 72%. The liquid phase of the reaction mixture is
collected at the reaction temperature. Atomic absorption spectromet-
ric analysis of the liquid phase of the reaction mixtures thus collected
by filtration confirms that Cu is absent in the reaction mixture. The
obtained filtrate was continually stirred under the reaction condi-
tions. After 4 h the conversion was determined to still be 72%. This
result indicated that the catalytic reaction was caused by the solid
catalyst. Cu is also not detected in the liquid phase of the reaction
mixture after the completion of the reaction. It is noteworthy that the
methanol remains completely colorless on addition of copper catalyst.
These results suggest that the Cu is not being leached out from the
catalyst during N-arylation reactions.
The best advantage of the heterogeneous catalysis was the
possibility of recovering and reusing the catalyst during the reaction.
The capability of recycling of the catalyst was confirmed after five
consecutive N-arylation reactions of imidazole with phenylboronic
acid in MeOH medium, amination reaction of aniline with phenyl-
boronic acid in DMSO medium and amination of aniline with
iodobenzene in DMSO medium. After first run, the catalyst was
separated by filtration, washed, dried under vacuum and then
subjected to the second run under the optimized reaction conditions.
The catalytic run was repeated with further addition of substrates in
appropriate amount under optimum reaction conditions and the
nature and yield of the final products were comparable to that of the
original one. The results for the N-arylation reaction of imidazole with
phenylboronic acid summarized in Fig. 4, demonstrate that there was
almost no change in catalytic activity even after fifth recycle. Metal
content of the recycled catalyst remained almost unaltered indicating
no leaching of the metal from the polymer support.
1.
2.
3.
4.
5.
6.
7.
8.
KOt-Bu
KOt-Bu
KOt-Bu
KOt-Bu
KOt-Bu
KOt-Bu
KOH
NaOMe
K3PO4
K2CO3
Toluene
1, 4 dioxane
ACN
DMSO
DMF
120 °C
80 °C
40 °C
12
14
12
16
12
14
12
12
14
14
16
95
89
90
71
65
79
65
51
75
72
69
130 °C
120 °C
140 °C
120 °C
120 °C
120 °C
120 °C
120 °C
NMP
Toluene
Toluene
Toluene
Toluene
Toluene
9.
10.
11.
Cs2CO3
a
Reactionconditions: PS-LCu(I)catalyst (0.05 g, 0.0065 mmol), 2 mmol of iodobenzene,
1 mmol of aniline, 1 mmol base, solvent (10 ml), N2 atm.
b
Yield determined by GC and GCMS analysis.
(Table 5, entry 1). Low yields of triphenylamine (TPA) were obtained
with polar solvents like DMF and THF (Table 5, entries 2–3). Moderate
to good yields were obtained for the solvents like 1,4-dioxane and
acetonitrile (Table 5, entries 4–5). Very poor yields were obtained
using polar solvent like NMP (Table 5, entry 6). The influence of bases
on the yields of TPA in the presence of copper catalyst was
investigated to find that potassium tertiary butoxide (KOt-Bu) was
the most effective base (Table 5, entry 1). With KOH and NaOMe as a
base very poor activity was obtained (Table 5, entries 7–8). Using
milder bases such as K3PO4, K2CO3, and Cs2CO3 significantly resulted
in lower yields (Table 5, entries 9–11). This reaction using polymer
supported Cu(I) catalyst was also performed at higher temperature
(120 °C) and higher reaction time (12 h). From the above discussions,
it can be seen that the best yield was obtained in the amination
reaction of aniline with iodobenzene by using KOt-Bu in toluene
solvent at 120 °C for 12 h. The scope of this methodology was further
extended for coupling of primary amines with aryl iodides under this
experimental condition [25] (Table 6, entries 1–6). 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
Table 6
Amination reaction of primary amines with various arylhalidesa.
Entry
Aryl halides
Aryl amines
Products
Time (h)
Isolated yieldb (%)
1.
2.
3.
4.
5.
6.
7.
8.
9.
C6H5I
C6H5NH2
C6H5NH2
C6H5NH2
4-Me–C6H5NH2
4-MeO–C6H5NH2
4-BrC6H5NH2
4-Me–C6H5NH2
4-MeO–C6H5NH2
C6H5NH2
N-(Phenyl)aniline
12
14
14
14
14
16
12
12
16
95
72
70
65
61
57
76
75
62
4-Me–C6H4I
4-MeO–C6H4I
C6H5I
C6H5I
C6H5I
4-Me–C6H4I
4-MeO–C6H4I
2-Me–C6H4I
N-(4-Methylphenyl)aniline
N-(4-Methoxyphenyl)aniline
N-(4-Methylphenyl)aniline
N-(4-Methoxyphenyl)aniline
N-(4-Methoxyphenyl)aniline
N-(4,4-Methylphenyl)aniline
N-(4,4-Methoxyphenyl)aniline
N-(2-Methylphenyl)aniline
a
Reaction conditions: PS-LCu(I) catalyst (0.05 g, 0.0065 mmol), 2 mmol of aryl halide, 1 mmol of aromatic amine, 1 mmol KOt-Bu, Toluene (10 ml), 120 °C, N2 atm.
Isolated yield after column chromatography.
b

S.M. Islam et al. / Inorganic Chemistry Communications 14 (2011) 1352–1357
1357
Table 7
Comparison of activity of different catalysts in the N-arylation and amination reaction.
Reaction
Catalyst
Reaction conditions
Yield (%)
Reference
N-Arylation
(imidazole +phenylboronic acid)
Amination (aniline+ phenylboronic acid)
PS-LCu(I)
Cu-FAP
PS-LCu(I)
Cu-FAP
Cu(OAc)2
PS-LCu(I)
CuI
MeOH, 40 °C, 10 h
MeOH, 5 h, rt.
MeOH, 40 °C, 14 h
MeOH, 3 h, rt.
DCM, Et3N/Py, rt, 2 h
Toluene, KOt-Bu, 120 °C, 12 h
Toluene, KOt-Bu, 2,2′-bipyridine, 115 °C, 3.5 h
96
88
90
90
71
95
95
This study
21
This study
21
26
Amination (aniline+ iodobenzene)
This study
11
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[19] J.B. Lan, L. Chen, X.Q. Yu, J.S. You, R.G. Xie, Chem. Commun. 2 (2004) 188–189.
[20] K. Mori, K. Yamaguchi, T. Hara, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem. Soc.
124 (2002) 11572–11573.
100
80
60
40
20
0
1
2
3
4
5
No. of cycles
Fig. 4. Recycling activity of the PS-LCu(I) catalyst. Reaction conditions: 1 mmol of
phenylboronic acid, 1.2 mmol of imidazole, MeOH (10 ml), 40 °C, 10 h, N2 atm.
[21] M.L. Kantam, G.T. Venkanna, C. Sridhar, B. Sreedhar, B.M. Choudary, J. Org. Chem.
71 (2006) 9522–9524.
[22] S.S. Kandil, G.B. EL-hefnawy, Transit. Met. Chem. 28 (2003) 168–175.
[23] General procedure for N-arylation of N–H heterocycles with arylboronic acids: In
a 100 mL RB flask, PS-LCu(I) catalyst (50 mg, 0.0065 mmol), 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 intervals and identified by GCMS 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 resulting
residue was purified by column chromatography on silica gel to provide the
desired product.
[24] General procedure for amination of aromatic amines with aryl boronic acids: In a
100 mL RB flask, PS-LCu(I) catalyst (50 mg, 0.0065 mmol), aryl boronic acid
(1.5 mmol), aromatic amines (1.2 mmol) and 10 ml MeOH were stirred under
nitrogen atmosphere, at 40 °C. The reaction mixtures were collected at different
time intervals and identified by GCMS 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 resulting
residue was purified by column chromatography on silica gel to provide the
desired product.
[25] General procedure for amination of aromatic amines with aryl halides: In a
100 mL RB flask, PS-LCu(I) catalyst (50 mg, 0.0065 mmol), aryl halide (4 mmol),
aromatic amines (2 mmol), KOt-Bu (1 mmol) and 10 ml toluene were stirred
under nitrogen atmosphere, at 120 °C. The reaction mixtures were collected at
different time intervals and identified by GCMS 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 resulting
residue was purified by column chromatography on silica gel to provide the
desired product.
Conclusions
In conclusion, a new PS-LCu(I) catalyst have been synthesized and
the structure of this catalyst was confirmed by means of elemental
analysis, FTIR, SEM picture, EDAX spectra and TGA spectra. A detailed
investigation of N-arylation reaction of N–H heterocycles with
arylboronic acids and aromatic amines with aryl iodides as well as
arylboronic acids were carried out using this catalyst under
heterogeneous conditions. The methodology was successfully applied
to a wide variety of substrates. Further work is in progress to broaden
the scope of this catalytic system especially for aryl chlorides and to
understand the reaction mechanism.
Acknowledgements
We thank the Department of Chemistry, University of Calcutta, for
providing us the instrumental support. We also thank Dr. D.K. Maiti,
University of Calcutta, for his various help for this work. We gratefully
acknowledge DST, New Delhi, for award of grant under its FIST
program to the Department of Chemistry, University of Kalyani. SMI
acknowledge the following agencies for funding: DST, CSIR and UGC,
New Delhi, India.
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