Open-air N-arylation of N-H heterocycles with arylboronic acids catalyzed by copper(II) Schiff base complexes

Article abstract of DOI:10.1007/s11243-014-9881-2

Two copper Schiff base complexes, in both homogeneous and heterogeneous forms, were prepared and characterized by using elemental analysis, FTIR, UV-Vis spectroscopy and scanning electron microscopy. The catalytic performances of these complexes were studied in the N-arylation of N-H heterocycles with arylboronic acids in methanol without any added base at 40 °C under open air. The effects of various parameters such as solvent and temperature on the reaction system were studied. The reaction is applicable to a wide variety of N-H heterocycles and arylboronic acids. The heterogeneous catalyst was recovered by simple filtration, and reusability experiments showed that this catalyst can be used five times without much loss in the catalytic activity.

Full text of DOI:10.1007/s11243-014-9881-2

Transition Met Chem (2014) 39:961–969
DOI 10.1007/s11243-014-9881-2
Open-air N-arylation of N–H heterocycles with arylboronic acids
catalyzed by copper(II) Schiff base complexes
•
S. M. Islam Ram Chandra Dey Anupam Singha Roy
•
•
•
Sumantra Paul Sanchita Mondal
Received: 5 June 2014 / Accepted: 5 September 2014 / Published online: 13 September 2014
Ó Springer International Publishing Switzerland 2014
Abstract Two copper Schiff base complexes, in both
homogeneous and heterogeneous forms, were prepared and
characterized by using elemental analysis, FTIR, UV–Vis
spectroscopy and scanning electron microscopy. The cat-
alytic performances of these complexes were studied in the
N-arylation of N–H heterocycles with arylboronic acids in
methanol without any added base at 40 °C under open air.
The effects of various parameters such as solvent and
temperature on the reaction system were studied. The
reaction is applicable to a wide variety of N–H heterocy-
cles and arylboronic acids. The heterogeneous catalyst was
recovered by simple filtration, and reusability experiments
showed that this catalyst can be used five times without
much loss in the catalytic activity.
temperatures, and many functional groups are not tolerated.
In addition, they often require the use of stoichiometric
amounts of copper reagents, which, on scale-up, leads to
problems of waste disposal. To overcome these drawbacks,
several Pd- and Ni-catalyzed protocols have been devel-
oped by Hartwig and Buchwald [8, 9]. Also, Chan et al. [5],
Evans et al. [6], Lam et al. [10] and others [11] have
reported the preparation of arylamines and N-arylhetero-
cycles using boronic acids and cupric acetate under milder
conditions than conventional methods. There are reports
describing arylsiloxanes [12], diaryliodonium salts [13] or
aryllead triacetates [14] as aryl donors using cupric acetate
and a base. Some of these processes include use of stoi-
chiometric quantities of Cu(OAc)2, excess arylboronic acid
or base and extended reaction times. Recently, N-arylation
reactions have been reported using copper salts in the
absence of base in protic solvents [15, 16]. However,
copper-mediated couplings are still the reaction of choice
for large- and industrial-scale formation of C–N bonds.
Chan and Lam established an efficient approach to
N-arylimidazoles via Cu(OAc)2-mediated coupling of
imidazoles with readily available arylboronic acids [10].
Xie et al. [15] have demonstrated the simple copper-cata-
lyzed coupling of imidazoles with arylboronic acids in
protic solvent without added base. Recently, Buchwald
used a diimine as ligand for effective copper-mediated
cross-coupling reactions under mild conditions [17]. Very
recently, Buchwald and others have reported a copper-
based protocol for the formation of N-aryl bonds [18–20].
There are, however, very few reports of N-arylation reac-
tions under open-air conditions [21]. Despite the significant
progress made in the development of copper-catalyzed
coupling reactions of this type, there still exists a need for
new methods that involve cheap and environmentally
benign catalysts.
Introduction
Copper-mediated N-arylation reactions play an important
role in organic synthesis since the products, arylamines and
N-arylheterocyclic compounds are ubiquitous in pharma-
ceuticals, crop protection chemicals and materials science
[1–4]. In 1997, a copper-mediated heteroatom arylation
reaction using arylboronic acids as aryl donors was dis-
covered independently by Chan, Evans and Lam [5, 6].
Ullmann and Goldberg arylation of amines, amides and
anilines with aryl halides using copper catalysts is a pop-
ular methodology for the synthesis of N-arylated products
[7]. These reactions have been carried out at high
S. M. Islam (&) ꢀ R. C. Dey ꢀ A. S. Roy ꢀ S. Paul ꢀ S. Mondal
Department of Chemistry, University of Kalyani,
Kalyani, Nadia 741235, WB, India
e-mail: manir65@rediffmail.com
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Transition Met Chem (2014) 39:961–969
Immobilization of soluble catalysts onto an insoluble
NH
OH
2OHC
matrix can allow for easy separation and recyclability of
the catalyst. In this direction, we have already reported
reusable palladium catalysts for C–C cross-coupling reac-
tions [22, 23]. Many of the disadvantages of homogeneous
catalysts can be overcome by anchoring onto a polymer
[24]. There are many examples of heterogeneous catalysts
for C–N coupling reactions, and they can be prepared by
different approaches such as encapsulation or immobili-
zation of a catalytically active metal complex on a solid
support [25–28].
MeOH
Reflux
A
HO
N
OH
OH
Cu(OAc)2
MeOH
KOH
In this work, we found that N-arylation can be effi-
ciently catalyzed by copper(II) Schiff base complexes
under open-air conditions. Furthermore, a variety of imi-
dazoles, benzimidazoles, amides, imides and sulfonamides
can be reacted with arylboronic acids using this catalytic
system to give the corresponding N-arylation products in
moderate to excellent yields.
N
O
OH
Cu
OAc
B
N
O
Results and discussion
Cu
NH2 OAc
O
H
The synthesis of the copper complexes is outlined in
Scheme 1. These copper complexes were synthesized and
characterized according to our earlier study [29]. The
reaction of 2-aminophenol and salicylaldehyde in methanol
leads to the formation of a Schiff base. Reaction of the
Schiff base with copper acetate in methanol gave a Cu(II)
Schiff base complex which we designate as [Cu(am-
p)(OAc)]. For the heterogeneous catalyst, first, aminopo-
lystyrene was stirred with copper acetate, and then, the
Schiff base ligand was reacted with this metal-loaded
polymer to produce PS–Cu–amp–OAc.
P
Scheme 1 Synthesis of the homogeneous (a) and polymer-anchored
(b) copper(II) Schiff base catalysts
[Cu(amp)(OAc)] catalyst, a medium intensity band at
1,318 cm-1 suggests monodentate coordination of the
acetate groups. The vC=O stretching vibration of the ace-
tate groups is observed at 1,720 cm-1 in copper complex.
The FTIR spectra of poly(4-aminostyrene) and the poly-
mer-supported immobilized complex were also studied.
The intensity of the spectrum of the polymer-supported
metal complex is weak, due to its low concentration in the
polymer matrix. However, it appears to be quite similar to
the neat metal complex. The band at 1,619 cm-1 for the
primary amine in poly(4-aminostyrene) is shifted to
1,590–1,600 cm-1 in the supported complex. The presence
of the Schiff base moiety in the immobilized complex is
indicated by a band at 1,641 cm-1 assigned to the v(C=N)
stretch.
Elemental analysis of the soluble copper complex was
quite comparable to the calculated values. The copper
content of the polymer-supported catalyst was estimated by
atomic absorption spectroscopy as 1.52 %.
The formation of a Schiff base was indicated by an
absorption band at 1,639 cm-1 assigned to the C=N
stretching vibration in the spectrum of Schiff base. In the
spectrum of copper complex, this band is shifted to lower
frequency at 1,606 cm-1, indicating coordination of
the azomethine nitrogen to the metal [30]. The phenolic
(C–O) stretching frequency was observed in the region
of 1,270 cm-1 (free Schiff base), compared with
1,294–1,315 cm-1 for the complex, indicating coordina-
tion through phenolic oxygen [31, 32]. In addition, the
spectrum of the copper complex includes a new feature
around 520–580 cm-1, which is assigned to the Cu–N
bond [33]. The complexation of copper(II) also resulted in
bands around 630–688 cm-1 assigned to the Cu–O bond
[33]. A weak band in the 3,435 cm-1 region indicates the
presence of –OH in copper complex. In spectrum of the
The electronic spectra of the free Schiff base and its
copper complex were measured in acetonitrile (Fig. 1a). In
the UV spectrum of the free Schiff base, absorption bands
at 265 and 348 nm are assigned to the n?p* and p?p*
transition, respectively. The electronic spectrum of the
copper complex exhibits a shoulder around at 430 nm that
is assigned to d$d transitions [34]. A band at 275 nm is
presumably caused by charge transfer. The thermal sta-
bility of heterogeneous copper complex was investigated
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Transition Met Chem (2014) 39:961–969
963
by TGA (heating rate, 10 °C/min in air from 30 to 500 °C,
Fig. 1b). The polymer-supported Cu(II) Schiff base com-
plex decomposes at 230 °C.
Catalytic activity
Initially, we chose imidazole and phenylboronic acid as
model substrates to optimize the catalytic conditions for the
cross-coupling reaction (Scheme 2). Several simple copper
salts were tested as copper sources to promote the coupling
reaction in methanol as solvent. As shown in Table 1, most
of the copper salts that were used gave the desired products
in low to moderate yields (Table 1, entries 2–4). Copper
chloride and copper iodide (entries 2 and 3) were less
reactive than copper(II) acetate and gave a result among
our best attempts with 79 % yield (entry 4). Between the
homogeneous- and polymer-anchored Cu(II) Schiff base
catalysts, the polymer-anchored catalyst obtained from
copper(II) acetate was found to be most effective (entry 7).
Reaction temperature plays a crucial role in such cross-
coupling reactions [35]. It is reported that reaction times
may sometimes be dramatically affected by changing the
reaction temperature. We found that increasing the tem-
perature remarkably accelerated the reaction, and further-
more, yields were also increased (Table 2, entries 1–5). A
high yield was obtained when the reaction was carried out
in methanol at 40 °C within 6 h (entry 3). A still higher
temperature of 60 °C did not much improve the results and
showed a large decrease in reactivity (entry 5). Further-
more, higher temperature was unfavorable as more of the
biphenyl byproduct was obtained.
Field emission SEM for poly(4-aminostyrene) and the
polymer-supported copper complex was recorded to
examine the morphological changes that occur in the
polystyrene beads during various stages of synthesis.
The SEM images of poly(4-aminostyrene) (A) and the
immobilized copper complex (B) are shown in Fig. 2. The
pure poly(4-aminostyrene) bead has a smooth surface.
After metal loading on the polymer, a change in mor-
phology of the polymer surface is observed. The presence
of copper metal along with oxygen and chlorine on
polymer-anchored complex was verified by EDX
(Fig. 2c).
The effect of solvent was also examined (Table 3,
entries 1–8). We first selected toluene and acetonitrile as
reaction solvents (entries 1 and 2). However, low to
moderate yields were obtained with these solvents. Mod-
erate yield of the product was obtained when water was
used as solvent (entry 3). However, when protic solvents
such as methanol and ethanol were employed (entries 4 and
5), the desired products were obtained in high yields.
Reaction in DMF and DMSO gives trace amounts of the
coupled product (entries 6 and 7). Here, methanol is found
to be the best solvent for the N-arylation.
Under the optimized reaction conditions, a wide range
of structurally diverse arylboronic acids were coupled with
imidazole using both the homogeneous and heterogeneous
copper(II) Schiff base catalysts in methanol at 40 °C to
produce the corresponding substituted N-aryl imidazoles in
good to excellent yields. In an endeavor to expand the
scope of this methodology, the catalytic system was
applied to imidazole, benzimidazole, imides, amides and
sulfonamides. N-arylation of imidazole with phenylboronic
acid using the copper(II) catalysts was carried out in the
absence of added base. Our method was successfully
amenable to a wide range of arylboronic acids, allowing
preparation of N-arylimidazoles and N-arylbenzimidazoles
in high yields, as shown in Table 4. Arylboronic acids with
electron-donating groups afforded better yields with
Fig. 1 Electronic spectra of Schiff base, copper(II) Schiff base
complex (a) and thermogravimetric weight loss plot for polymer-
supported Cu(II) complex (b)
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Transition Met Chem (2014) 39:961–969
Fig. 2 FE SEM images of poly(4-aminostyrene) (a), polymer-supported Cu(II) Schiff base complex (b) and EDX plot of polymer-supported
Cu(II) Schiff base complex (c)
Table 1 Effect of copper source on the coupling of imidazole with
phenylboronic acida
B(OH)2
N
Copper(II) Schiff
base complex
N
N
Entry
Copper source
Yield (%)b
methanol 40 0C,
N
H
6 h
,
1
2
3
4
5
6
7
8
a
None
No reaction
CuCl2
48
44
79
92
72
96
74
Scheme 2 Homogeneous copper(II) Schiff base catalyzed N-aryla-
tion of imidazole with phenylboronic acid
CuI
Cu(OAc)2
Homogeneous copper(II)c
Homogeneous copper(II)d
Heterogeneous copper(II)c
Heterogeneous copper(II)d
imidazole than arylboronic acids with electron-withdraw-
ing groups (entries 2–9). The coupling reactions of
2-methylphenylboronic acid, 2-methoxyphenylboronic
acid and 3,4-dimethoxyphenylboronic acid afforded lower
yields, presumably due to steric effects (entries 4–6). The
coupling of 3-nitrophenylboronic acid which is a difficult
substrate also proceeded smoothly under the present con-
ditions (entry 8). Similar observations were made when
benzimidazole was used in place of imidazole to obtain the
corresponding N-arylbenzimidazoles (entries 10–12). A
series of substituted arylboronic acids were coupled with
phthalimide (entries 13–16) and succinimide (entries 17
and 18) under the optimized reaction conditions to afford
the corresponding N-aryl imides in good to excellent
Reaction conditions: phenylboronic acid (0.0182 g, 1.5 mmol),
imidazole (0.082 g, 1.2 mmol), catalyst (1.5 9 10-5 mol), methanol
(10 ml), 40 °C, 6 h, open air
b
Yield refers to GC and GC–MS analysis
c
Catalyst prepared from Cu(OAc)2
d
Catalyst prepared from CuCl2
yields. The reaction of amides and sulfonamides with
phenylboronic acid afforded the corresponding products in
higher and lower yields, respectively, (entries 19 and 20).
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Transition Met Chem (2014) 39:961–969
965
analysis was 46 %. The liquid phase of the reaction mix-
ture was collected at the reaction temperature. Atomic
absorption spectrometric analysis of this liquid phase
confirmed that Cu was absent from the reaction mixture.
The filtrate was then stirred under the reaction conditions.
After 6 h, the yield was determined to be still 46 %. This
result indicated that the reaction was caused by the solid
catalyst and suggested that the Cu was not being leached
out from the catalyst during the N-arylation reactions.
A key advantage of heterogeneous catalysis is the pos-
sibility of recovering and reusing the catalyst. The capa-
bility of recycling of the catalyst was confirmed after five
consecutive N-arylation reactions of imidazole with phen-
ylboronic acid in MeOH medium. After the first run, the
catalyst was separated by filtration, washed, dried under
vacuum and then subjected to further runs under the opti-
mized reaction conditions. The results summarized in
Fig. 3 demonstrate that there was almost no change in
catalytic activity even after the fifth recycle. The metal
content of the recycled catalyst remained unaltered, indi-
cating no leaching of the metal from the polymer support.
Table 2 Effect of temperature on the coupling of imidazole with
phenylboronic acida
Entry
Temperature
(°C)
Time
(h)
Yield (%)b
Cu–amp–OAc/
PS–Cu–amp–OAc
1
3
5
6
7
a
20
48
24
6
83/87
88/90
92/96
92/97
74/78
30
40 °C
50 °C
60 °C
10
24
Reaction conditions: copper(II) catalyst (1.5 9 10-5 mol), phen-
ylboronic acid (0.0182 g, 1.5 mmol), imidazole (0.082 g, 1.2 mmol),
methanol (10 ml), open air
b
Yield refers to GC and GC–MS analysis
A possible reaction mechanism can be outlined for the
copper-catalyzed N-arylation of N–H heterocycles with
arylboronic acid, based on the previously reported mech-
anism [1, 36, 37]. The first step is transmetalation of
arylboronic acid with the copper catalyst. Then, in the
presence of base, coordination of N–H heterocycles to CuII
species causes a decrease in the reduction potential of the
CuIII/CuII couple. Air or oxygen oxidizes CuII–CuIII spe-
cies. Finally, in a reductive elimination pathway, the
product is eliminated, and the CuI species is ready to
continue the catalytic cycle.
Conclusions
In summary, we have successfully prepared homogeneous
and heterogeneous copper(II) Schiff base acetate com-
plexes. These compounds show high catalytic activity in
the N-arylation of various nitrogen-containing compounds,
in methanol under open-air conditions. The catalytic sys-
tems are base-free, economical, easy to handle and do not
need addition of oxygen or nitrogen. The N-arylation
products were generally obtained in moderate to excellent
yields.
Heterogeneity and recycling tests
To determine whether the catalyst was actually functioning
in a heterogeneous manner, a hot-filtration test was per-
formed in the N-arylation of imidazole with phenyl boronic
acid. The solid catalyst was filtered out after the reaction
had proceeded for 2 h, and the yield determined by GC
Experimental
Table 3 Effect of solvent on the coupling of imidazole with phen-
ylboronic acida
Materials
Entry Solvent
Temperature °C Time h Yield (%)b
Cu–amp–OAc/
PS–Cu–amp–OAc
Analytical grade reagents and freshly distilled solvents
were used throughout. All reagents and substrates were
purchased from Merck. Liquid substrates were distilled and
dried with the appropriate molecular sieve. Solid reagents
were recrystallized before use. Copper salts and other
organic reagents were purchased from Merck and used
without further purification.
1
2
3
4
5
6
7
a
PhCH3
CH3CN
H2O
120
50
16
12
12
6
51/53
60/64
75/78
91/94
92/96
45/46
41/45
50
EtOH
MeOH
DMF
40
40
6
140
140
24
24
DMSO
Physical measurements
Reaction conditions: copper(II) catalyst (1.5 9 10-5 mol), phen-
A Perkin-Elmer 2400 C elemental analyzer was used to
collect microanalytical data (C, H and N). The transition
metal contents of the samples were measured with a
ylboronic acid (0.0182 g, 1.5 mmol), imidazole (0.082 g, 1.2 mmol),
solvent (10 ml), open air
b
Yield refers to GC and GC–MS analysis
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Transition Met Chem (2014) 39:961–969
Table 4 N-arylation of N–H
heterocycles using
homogeneous copper(II)
catalyst with various
arylboronic acidsa
Entry
N-H
Arylboronic
Acids
Products
Isolated Yield (%)b
Cu-amp-OAc/PS-
Cu-amp-OAc
heterocycles
B(OH)2
N
1
2
3
Imidazole
Imidazole
Imidazole
92/96
87/90
89/91
N
H
B(OH)2
N
N
Me
Me
B(OH)2
N
N
OMe
OMe
N
N
N
Me
B(OH)2
Me
4
5
6
Imidazole
Imidazole
Imidazole
80/83
82/87
77/78
N
N
OMe
B(OH)2
OMe
B(OH)2
N
OMe
OMe
OMe
OMe
B(OH)2
N
7
Imidazole
88/90
N
Cl
Cl
B(OH)2
N
8
9
Imidazole
Imidazole
82/86
80/84
N
NO2
NO2
B(OH)2
N
N
COMe
COMe
B(OH)2
N
10
11
Benzimidazole
Benzimidazole
93/95
88/93
N
H
B(OH)2
N
N
Me
Me
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Transition Met Chem (2014) 39:961–969
967
Table 4 continued
Entry
N-H
Arylboronic
Acids
Products
Isolated Yield (%)b
Cu-amp-OAc/PS-
Cu-amp-OAc
heterocycles
B(OH)2
N
12
13
Benzimidazole
Phthalimide
87/90
N
OMe
OMe
B(OH)2
O
N
O
90/93
H
O
N
O
B(OH)2
14
15
16
Phthalimide
Phthalimide
Phthalimide
89/92
88/90
86/89
Me
Me
B(OH)2
O
N
O
Cl
Cl
O
N
O
B(OH)2
COMe
COMe
B(OH)2
O
N
O
Succinamide
Succinamide
Benzamide
17
18
19
20
90/92
87/89
93/95
71/76
H
O
N
O
B(OH)2
Me
Me
B(OH)2
CONH
a
Reaction conditions:
copper(II) catalyst (0.005 g,
1.5 9 10-5 mol), 1.5 mmol of
arylboronic acids, 1.2 mmol of
N–H heterocycles, MeOH
(S)
H
B(OH)2
Sulfonamide
SO2NH
(10 ml), 40 °C, 6 h, open air
b
Isolated yield after column
chromatography. All products
were characterized by NMR
(T)
H
Varian AA240 atomic absorption spectrophotometer
(AAS). FTIR spectra were recorded on a Perkin-Elmer
FTIR 783 spectrophotometer using KBr pellets. Electronic
spectra were recorded on a Shimadzu UV/3101 PC
spectrophotometer. NMR spectra were recorded at
400 MHz for 1H NMR and 100 MHz for 13C NMR,
123

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Transition Met Chem (2014) 39:961–969
air, at 40 °C for 6 h. The reaction mixtures were collected
at different time interval and identified by GC–MS and
quantified by GC analysis. 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 9 20 ml), and the
combined organic layers were dried with anhydrous Na2
SO4 by vacuum. The filtrate was concentrated by vacuum,
and the resulting residue was purified by column chroma-
tography on silica gel to provide the desired product.
Fig. 3 Recycling efficiency for the N-arylation of imidazole with
phenylboronic acid by polymer-supported Cu(II) Schiff base complex
respectively. Characterization of the products was carried
1
out by H NMR spectroscopy using Bruker DPX-400 in
Spectroscopic data for selected products
CDCl3 with TMS as internal standard. Chemical shifts are
reported as d values with reference to tetramethylsilane
(TMS) as internal standard. The reaction products were
quantified (GC data) with a Varian 3,400 gas chromato-
graph equipped with a 30 m CP-SIL8CB capillary column
and a flame ionization detector and identified by a Trace
DSQ II GC–MS equipped with a 60 m TR-50MS capil-
lary column.
1-Phenyl-1H-imidazole (Table 4, entry 1)
1H NMR (400 MHz, CDCl3) d: 7.83 (s, 1H), 7.52–7.44 (m,
2H), 7.41–7.34 (m, 3H), 7.28 (bs, 1H), 7.21 (bs, 1H); 13C
NMR (100 MHz, CDCl3) d: 136.0, 134.3, 129.7, 129.5,
127.4, 121.3, 118.0.
1-(4-Methylphenyl)-1H-imidazole (Table 4, entry 2)
Synthesis of the Schiff base and complex
1H NMR (400 MHz, CDCl3) d: 7.77 (s, 1H), 7.24 (m, 4H),
7.20 (bs, 1H), 7.13 (bs, 1H), 2.40 (s, 3H); 13C NMR
(100 MHz, CDCl3) d: 137.4, 134.9, 134.8, 130.5, 130.0,
121.1, 118.3, 20.9.
N-(hydroxyphenyl) salicyldimine was prepared by mixing
2-aminophenol and salicylaldehyde in (1:1) molar ratio
[38]. The copper complex was prepared as follows. To a
solution of the Schiff base (0.01 mol) in methanol (20 ml)-
containing KOH (0.01 mol) was added copper acetate
(0.01 mol). The resultant mixture was stirred for 1 h at
room temperature under air, whereupon a solid precipitated
out. This was filtered off and washed thoroughly with water
and ether and then dried over fused CaCl2
1-(4-(1H-imidazol-1-yl)phenyl)ethanone (Table 4,
entry 9)
1H NMR (400 MHz, CDCl3) d: 8.10 (d, 2H), 7.97 (bs, 1H),
7.49 (d, 2H), 7.34 (bs, 1H), 7.24 (bs, 1H), 2.63 (s, 3H); 13
C
NMR (100 MHz, CDCl3) d: 196.4, 141.1, 135.8, 135.4,
131.2, 130.3, 120.7, 117.7, 26.6.
½CuðampÞðOAcÞꢁ ¼ ½C% 53:9ð53:80Þ; H% 4:0ð3:9Þ;
N% 4:2ð4:2Þꢁ:
Synthesis of the immobilized catalyst
1-Phenyl-1H-benzimidazole (Table 4, entry 10)
1H NMR (400 MHz, CDCl3) d: 8.07 (s, 1H), 7.81–7.86 (m,
1H), 7.44–7.62 (m, 6H), 7.5–7.3 (m, 2H); 13C NMR
(100 MHz, CDCl3) d: 144.0, 142.6, 136.7, 133.6, 130.2,
128.0, 126.0, 124.0, 123.0 (2C), 120.3, 110.1 (2C).
First, poly(4-aminostyrene) was prepared according to the
literature [39]. The poly(4-aminostyrene) was stirred with a
solution of excess copper acetate in methanol for 12 h and
then washed thoroughly with water. The metal-loaded
poly(4-aminostyrene) samples were then reacted with
solutions of Schiff base ligand in methanol to get the
immobilized metal complex (PS–Cu–amp–OAc).
1-(4-Methylphenyl)-1H-benzimidazole (Table 4, entry
11)
1H NMR (400 MHz, CDCl3) d: 8.02 (br s, 1H), 7.77–7.86
(m, 1H), 7.40–7.47 (m, 1H), 7.20–7.33 (m, 6H), 2.41 (s,
3H); 13C NMR (100 MHz, CDCl3) d: 145.0, 142.0, 138.0,
135.0 (2C), 130.6, 124.0, 123.9, 123.0 (2C), 120.3, 110.0
(2C), 21.0.
General procedure for N-arylation reaction
In a 100-ml RB flask, copper catalyst (1.5 9 10-5 mol),
arylboronic acids (1.5 mmol), N–H heterocycles
(1.2 mmol) and 10 ml methanol were stirred under open
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Transition Met Chem (2014) 39:961–969
969
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2-Phenylisoindoline-1,3-dione (Table 4, entry 13)
1H NMR (400 MHz, CDCl3) d: 7.41–7.47 (m, 3H),
7.49–7.56 (m, 2H), 7.79–7.83 (m, 2H), 7.98 (m, 2H).
16. Lan JB, Zhang GL, Yu XQ, You JS, Chen L, Yan M, Xie RG
(2004) Syn Lett 6:1095–1097
17. Surry DS, Buchwald SL (2010) Chem Sci 1:13–31
18. Cristau HJ, Cellier PP, Spindler JF, Taillefer M (2004) Chem Eur
J 10:5607–5622
19. Surry DS, Buchwald SL (2011) Chem Sci 2:27–50
20. Maiti D, Fors BP, Henerson JL, Nakamura Y, Buchwald SL
(2011) Chem Sci 2:57–68
N-Phenylbenzamide (Table 4, entry 19)
1H NMR (400 MHz, CDCl3) d: 7.13–7.16 (m, 1H),
7.36–7.41 (m, 2H), 7.49–7.54 (m, 2H), 7.55–7.57 (m, 1H),
7.64–7.65 (m, 2H), 7.83 (s, 1H), 7.86–7.88 (m, H).
´
21. Joubert N, Basle E, Vaultier M, Pucheault M (2010) Tetrahedron
Lett 51:2994–2997
N-Phenylsulfonamide (Table 4, entry 20)
22. Islam SM, Mondal P, Tuhina K, Roy AS, Mondal S, Hossain D
(2010) J Organomet Chem 695:2284–2295
23. Islam SM, Mondal S, Roy AS, Mondal P, Mobarak M, Hossain
D, Pandit P (2010) Transit Met Chem 35:305–313
24. Islam SM, Mondal P, Roy AS, Tuhina K (2010) Transit Met
Chem 35:491–499
25. Kantam ML, Venkanna GT, Sridhar C, Sreedhar B, Choudary
BM (2006) J Org Chem 71:9522
26. Islam M, Mondal S, Mondal P, Roy AS, Tuhina K, Salam N, Paul
S, Hossain D, Mobarok M (2011) Transit Met Chem 36:447–458
27. Likhar PR, Roy S, Roy M, Kantam ML, De RL (2007) J Mol
Catal A Chem 271:57–62
1H NMR (400 MHz, CDCl3) d: 7.73–7.76 (m, 2H), 7.52
(t, 1H), 7.40 (t, 2H), 7.20 (t, 2H), 7.09–7.06 (m, 4H).
Acknowledgments We thank the Indian Association for the Culti-
vation of Science, Kolkata for providing the instrumental support. MI
acknowledges Department of Science and Technology (DST),
Council of Scientific and Industrial Research (CSIR) and University
Grant Commission (UGC), New Delhi, India for funding.
28. Kantam ML, Roy M, Roy S, Sreedhar B, De RL (2008) Catal
Commun 9:2226–2230
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