Synthesis and development of Chitosan anchored copper(II) Schiff base complexes as heterogeneous catalysts for N-arylation of amines

Article abstract of DOI:10.1016/j.tetlet.2015.05.049

Abstract The Chitosan anchored Cu(II) Schiff base complexes (C₁-C₃) have been synthesized and characterized by FTIR, UV, FE-SEM, EDAX, TGA, AAS and elemental analysis. These complexes have been found to be efficient and recyclable heterogeneous catalysts for the Chan-Lam C-N coupling reaction of various aromatic/aliphatic amines with arylboronic acid under mild reaction conditions. These complexes can be easily filtered out from the reaction medium and reused up to five times without significant loss of catalytic activity.

Full text of DOI:10.1016/j.tetlet.2015.05.049

Accepted Manuscript
Synthesis and development of Chitosan anchored Copper(II) Schiff base com-
plexes as heterogeneous catalysts for N-arylation of amines
Anuradha, Shweta Kumari, Devendra D. Pathak
PII:
S0040-4039(15)00858-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.05.049
TETL 46321
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
14 April 2015
13 May 2015
14 May 2015
Please cite this article as: Anuradha, Kumari, S., Pathak, D.D., Synthesis and development of Chitosan anchored
Copper(II) Schiff base complexes as heterogeneous catalysts for N-arylation of amines, Tetrahedron Letters (2015),
doi: http://dx.doi.org/10.1016/j.tetlet.2015.05.049
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Synthesis and development of Chitosan
anchored Copper(II) Schiff base complexes
as heterogeneous catalysts for N-arylation of
amines
Anuradha, Shweta Kumari and Devendra D. Pathak*

1
Tetrahedron Letters
journal homepage: www.els evier.com
Synthesis and development of Chitosan anchored Copper(II) Schiff base
complexes as heterogeneous catalysts for N-arylation of amines
Anuradha, Shweta Kumari and Devendra D. Pathak*
Department of Applied Chemistry, Indian School of Mines, Dhanbad-826004, India
*Email: ddpathak@yahoo.com
Phone number: +91 9431126250
ARTICLE INFO
ABSTRACT
Article history:
Received
The Chitosan anchored Cu(II) Schiff base complexes (C1 to C3) have been synthesized
and characterized by FTIR, UV, FE-SEM, EDAX, TGA, AAS and elemental analysis.
These complexes have been found to be efficient and recyclable heterogeneous
catalysts for Chan-Lam C-N coupling reaction of various aromatic/aliphatic amines
with arylboronic acid under mild reaction conditions. These complexes can be easily
filtered out from the reaction medium and reused up to five times without significant
loss of catalytic activity.
Received in revised form
Accepted
Available online
Keywords:
Chan-Lam coupling
Chitosan
Amines
2009 Elsevier Ltd. All rights reserved.
Arylboronic acid
for C-N bond formation by the arylation of amines with
arylboronic acid at room temperature in the presence of Cu(II)
Introduction
source.12,13 This protocol has several advantages over the classical
Ullmann coupling reaction and Pd-catalyzed Buchwald-Hartwig
amination. It involves mild reaction conditions and use of weak
bases. The low toxicity, high thermal stability and structural
diversity of arylboronic acid were found to be inherent
advantages over the use of aryl halides. The protocol did not
require any ligands. Later on, the protocol has been modified by
the use of various additives, such as TEMPO, pyridine-N-oxide
and molecular oxygen.14 Recently, Bora and co-workers
developed a Cu(II)-Salen type complex for the N-arylation of
anilines and imidazole with arylboronic acids at room
temperature.15 However, these protocols are homogeneous in
nature, where an efficient separation and subsequent recycling of
the homogeneous catalyst remains a challenge and an economic
concern. Heterogeneous catalysis is of importance in the
chemical industries due to easy separable and reuse upto several
times.16 Here in, our interest lies in the development of novel
heterogeneous catalyst for C-N coupling reactions of amines with
arylboronic acid under milder reaction conditions.
The N-arylation of amines is currently an active area of research
in organic synthesis due to its applications in the synthesis of a
variety of biologically active compounds, agrochemicals, HIV-1
protease inhibitors and in material science.1-2 Due to wide range
of applications of these compounds, several protocols for C-N
bond formation have emerged over the years. Mainly, three
important protocols for C-N coupling reactions have been
reported to-date namely, Ullmann coupling reaction3, Buchwald-
Hartwig amination4 and Chan-Lam couping5 (Scheme 1).
Ullmann-type protocol involves the coupling of amines with aryl
halides in the presence of Cu(I) source.6 However, this protocol
suffers from certain disadvantages, such as harsh reaction
conditions, high temperature (~150-200 C̊ ), moderate yield, use
of stochiometric amount of copper reagent and formation of by-
products. In order to circumvent these drawbacks, use of
copper(I) salts with several ligands such as 1,10-phenanthroline7,
L-proline8, ( )-trans-1,2-cyclohexyldiamine9 etc were introduced.
However, none of the modifications could address the problems
of high temperature and prolong reaction time.10 Considering the
drawbacks of this reaction, Buchwald and Hartwig, in 1994,
devised a new protocol for the coupling of amines with aryl
halides for C-N bond formation in the presence of catalytic
amount of Pd(II).11Although palladium compounds were used
with spectacular success as catalysts for C-N bond formation4,
these catalysts were unable to catalyze the coupling reaction of
an electron rich or o-substituted aryl halides with aromatic
amines. However, spectacular success has been achieved using
very small loading of Pd (ca 0.01 mol%) in Buchwald-Hartwig
amination reaction. Therefore, it mitigates the cost factor.
Subsequently, in 1998, Chan and Lam reported a new protocol
Recently, Chitosan has emerged as a novel support for
anchoring transition metal complexes. It is the second most
abundant natural co-polymer, obtained by alkaline deacetylation
of chitin.17 The renaissance of interest in the Chitosan arises
mainly due to the presence of free amino group, which can easily
be subjected to variety of chemical modifications such as
carboxymethylation, acylation, sulfation, enzymatic substitution,
metal chelation, cyanoethylation, nitration, phosporylation and
Schiff’s base formation.18-21 Chitosan anchored metal Schiff base

2
Tetrahedron
complexes have been reported as good catalysts for
(Scheme 3a). Schiff base Ligands (L1, L2, and L3) were
prepared by reacting salicyaldehyde and substituted aniline
under reflux (Scheme 3b). The Chitosan anchored Cu(II)
Schiff base complexes (C1, C2, C3) were prepared by the
reaction of Schiff base of Chitosan (L) with Cu(OAc).H2O
and Schiff base (L1 or L2 or L3) in ethanol under reflux for
12-15hr (Scheme 3c). The structural features of Chitosan, its
Schiff base (L) and complexes were elucidated by FTIR,
UV, FE-SEM, EDAX, TGA, AAS and elemental analyses.
cyclopropanation22, olefin oxidation23 and C–C coupling
reactions.24 Importantly, the Chitosan anchored Metal Schiff base
complexes have been found to be more potent than the Chitosan
metal complexes only.25 Prompted by these reports, we herein,
describe the synthesis and development of Chitosan anchored
Copper(II) Schiff base complexes as heterogeneous catalysts for
Chan-Lam coupling reactions (Scheme 2).
NH2
X
X
NH2
H
N
Cu(I)-source
high temperature
[A]
Pd(II)-source
[B]
The FTIR data of Chitosan, its Schiff base (L), Schiff base
ligands (L1 to L3) and complexes (C1 to C3) are given in Table 1.
The representative FTIR spectra of Chitosan, its Schiff base (L),
complex (C3) and Schiff base (L3) are shown in Figure 1. A
comparison of IR spectra of Chitosan and its Schiff base (L),
indicates the absence of -NH2 band and presence of two
additional bands at 1632 cm-1and 1212 cm-1, which were assigned
to the stretching modes of azomethine (C=N) group and phenolic
(C-O) groups, respectively. The FTIR studies indicate the
formation of Schiff base of Chitosan (L). The FTIR spectra of
free Schiff base (L3), indicates peaks at 1622 cm-1 and 1520 cm-1
characteristics of azomethine (C=N) group and aromatic –NO2
group, respectively, and confirm the formation of Schiff base
(L3). However, the IR spectra of complex (C3) indicate the
presence of few additional bands at 1614 cm-1 and 1523 cm-1.
The shifting of Ʋ (C=N) to lower wave number (ca.~10-15 cm-1)
confirms the coordination of Cu(II) metal ion with azomethine
nitrogen atom of the Schiff’s base. 26
+
+
X= Cl, Br
X= Cl, Br
[C]
NH2
B(OH)2
+
Scheme 1. Schematic representation of [A] Ullmann coupling
reaction, [B] Buchwald-Hartwig amination reaction, and [C]
Chan-Lam coupling reaction.
NH2
B(OH)2
H
N
,
Complexes (C1, C2, C3)
+
CH3CN, K2CO3 (2 equiv)
X
Y
X
Y
X= -H, -Cl, -NO2, -OH
Y= -H, -Cl, -CH3
Scheme 2. Chan-Lam coupling of N-aryl/alkyl amines with
different arylboronic acids in presence of a base and catalyst.
Table 1. Selected FTIR data of Chitosan, its Schiff base (L),
Schiff base ligands (L1 to L3) and complexes (C1 to C3).
OH
O
OH
O
CHO
OH
,
Ethanol
30 h
CO MP O UN DS
Ʋ ( NH2 )
Ʋ( OH)
Ʋ (C =N)
Ʋ (C-
O)
Ʋ(M -
O
HO
O
HO
*
*
+
*
*
n
n
N)
-
NH2
HC
N
CH I T OS A N
1 65 3
31 6 3
34 2 8
34 2 6
33 2 0
31 4 8
34 4 2
34 4 0
-
-
OH
(L )
L1
-
-
-
-
-
-
1 6 3 2
1 6 3 5
1 6 3 0
1 6 2 2
1 6 2 2
1 6 2 2
1 21 2
1 26 2
1 21 5
1 26 7
-
-
-
-
L2
(3a) Schiff base of Chitosan (L)
L3
-
C1
C2
43 9
43 8
CHO
NH2
-
OH
C
H
N
,
Ethanol
5-6h
C3
-
31 5 5
1 6 1 4
-
45 5
Y
+
OH
Y
Y= H, L1
70
Y= p-OCH3, L2
Y= m-NO2, L3
CHITOSAN
60
50
40
30
20
10
(3b) Schiff base Ligands (L1, L2, L3)
1622
L
1520
3
1614
1523
OH
OH
C
O
3
O
HO
O
*
n
*
O
HO
,
Ethanol
*
n
*
C
H
N
+
Cu(OAc).H2O +
12-15 h
HC
N
HC
N
Y
1632
O
Cu
OH
OH
L
O
N=CH
1212
Y= H, C1
Y
Y= p-OCH3, C2
Y= m-NO2, C3
(3c) Complexes (C1, C2, C3)
758
4000
3500
3000
2500
2000
1500
1000
500
Wavelength (cm)-1
Scheme 3. General procedure: (a) Schiff base of Chitosan (L),
(b) Schiff base Ligand (L1, L2, L3), and (c) Chitosan anchored
Cu(II) Schiff base complexes (C1, C2, C3)
Figure1. FT-IR spectra of (a) Chitosan, (b) L, (c) C3, (d) L3
Results and Discussion
Schiff base of Chitosan (L) was prepared by the reaction
of Chitosan and salicyaldehyde in ethanol under reflux
The UV-Visible spectra of the Schiff base of Chitosan (L)
and its complex (C3) are depicted in Figure 2. The observed λmax

3
value from electronic spectra of the complexes is used to predict
the geometry around the central metal ion. The electronic spectra
of (L) show two significant bands below 400 nm. This might be
due to n-π* and π-π* transition of azomethine C=N group and
aromatic C=C group of benzene ring, respectively. The electronic
spectra of complexes observed slight shift in the position and
intensity of these bands. This might be due to coordination of
metal ion with ligand. The charge transfer transition from metal
to ligand may also contribute to these absorption bands below
400 nm in the complexes.27 The electronic spectra of the
complexes show an additional band between 500-600 nm, which
is the characteristic band, arises from d-d transitions. The
electronic spectra of the complex (C3) show only one broad band
~535 nm, which suggest the square planar geometry of the
Figure 3. FE-SEM micrographs of (a) Chitosan, (b) Schiff base
of Chitosan (L), (c)Complex (C1), (d) Complex (C2) and (e)
Complex (C3)
complex. Generally, Copper(II) square planar complexes are
2
expected to show three spin allowed transitions namely, B1g
→
2
2
2
2
2A1g (dx2-y2 → dz2), B1g → B2g (dx2-y2 → dxy) and B1g → Eg
(dx2-y2 → dxz, dyz) and dx2-y2 in a ground state.28 These three
bands may overlap inside the broad band appeared in complexes
due to similar energy of these transitions.
4
3
Figure 4. EDAX analysis of (a) Chitosan, (b) Schiff base of
Chitosan (L), (c) Complex (C1), (d) Complex (C2) and (e)
Complex (C3)
L
2
C
3
The TGA study is used to explain the thermal stability
and mode of decomposition of ligand and complexes. The
TGA thermogram of (L) and complexes (C1 to C3) are
depicted in Figure 5. The TGA thermogram of L shows two
1
0
300
400
500
600
700
800
Wavelength (nm)
mass loss stages. The initial mass loss (~13%) up to 100 ̊C
may be due to hygroscopic nature of the Chitosan unit. The
maximum and significant second mass loss (~49%) occurs
at higher temperature (325-350oC) and can be attributed to
the dehydration, depolymerisation along with decomposition
of acetylated and deacetylated unit of Chitosan.30 However,
the TGA thermogram of complexes (C1 to C3) display first
Figure 2. UV- Visible spectra of Schiff base of Chitosan (L) and
Complex (C3)
The FE-SEM micrographs of Chitosan, its Schiff base
(L) and complexes (C1 to C3) are depicted in Figure 3. FE-
SEM image of Chitosan displays the smooth and even
surface. However, the FE-SEM micrograph of (L) indicates
the rough surface and this might be due to the chemical
modification of Chitosan through the condensation of
salicyaldehyde with free amino group of Chitosan. The FE-
SEM micrograph of complexes (C1 to C3) also indicates the
rough surface and this might be due to the imprinting of
metal ion on the modified Chitosan.29 Energy dispersive X-
ray spectroscopy (EDAX) analysis data for the Chitosan, its
Schiff base ligand (L) and complexes (C1 to C3) are given in
Figure 4. The EDAX spectra of complexes show the
presence of copper in the complex.
mass loss (~8%), (~12%) and (~5%), respectively, ~100
is due to physically absorbed water. The second mass loss
(~34%), (~44%) and (~29%), respectively, occur at (260-
280oC), (300-330oC) and (280-300
C), respectively. This
̊C
̊
might be due to the introduction of a metal ion on polymer
matrix, which obstructs the chain packing and cause
loosening of the packed structure. Thus (L) decomposes at
higher temperature and thermally more stable than the
complexes (C1 to C3).
10 0
C
3
9 0
L
8 0
7 0
C
6 0
5 0
4 0
1
C
2
100
200
300
T em p era tu re(oC )
400
500
60 0
Figure 5. TGA thermogram of Schiff base of Chitosan (L) and
Complexes (C1 to C3)

4
Tetrahedron
The elemental analysis data of Chitosan and its Schiff
Table 3. Optimization of the catalysts (C1, C2, C3) for Chan-Lam
coupling reaction of aniline (1mmol) and phenylboronic acid
(2mmol) in acetonitrile using K2CO3 as a base.
base (L) are used to calculate the degree of substitution (DS)
in Chitosan. It is apparent from the elemental analysis
(Table 2) that the observed micro analytical data (C, H and
N) of the compounds are closely comparable to the
theoretical data. The DS of Schiff base Ligand (L) to –NH2
group on Chitosan was estimated by the equation, proposed
by Inukai et al.31
Entry
Catalyst
Catalyst
Load
(mol%)
-
Time
(h)
Temp
(oC)
Yield
(%)a
1
2
-
48
48
48
36
36
36
36
24
24
24
09
10
rt
-
-
-
Chitosan
Chitosan
Chitosan
Chitosan
C1
-
50
reflux
rt
a(C/N)m- (C/N)o
3
-
DS =
n
4
5
50
reflux
rt
-
-
100
100
3.5
Where (C/N)m is the C/N ratio of modified Chitosan,
(C/N)o is the ratio of original Chitosan and ‘a’ and ‘n’ are
the number of nitrogen and carbon introduced after Schiff
base modification, respectively. C/N ratio of Chitosan and
its Schiff base Ligand (L) are calculated as 5.22 and 11.81,
respectively. The calculated DS for Chitosan is 0.65.
6
reflux
rt
-
7
-
8
C1
C2
3.5
3.5
reflux
reflux
reflux
reflux
reflux
63
54
71
85
83
9
10
11
12
C3
3.5
C3
08
Table 2. Elemental analysis data of Chitosan, Schiff base ligand
(L) and complexes (C1 to C3).
C3
12
aIsolated yield after work up
C AL C UL A T E D
(% )
In order to find out the best solvent for the reaction
(Table 4, entry 1-5), the reaction was conducted in a number of
solvents, e.g. H2O, CH3CN, CH3COOC2H5, CH3OH and
C2H5OH. Out of these solvents, H2O was found to be the worst
solvent (Table 4, entry 1). On the other hand, CH3CN was found
to be the best solvent (Table 4, entry 2). The other solvent such
as, CH3COOC2H5, CH3OH and C2H5OH gave poor yields of
53%, 35% and 38%, respectively (Table 4, entries 3-5).
CO MP O UN D
( F O U N D )
(% )
C
4 4. 72
( 4 4. 80 )
5 8. 86
H
6. 38
(6. 32 )
5. 70
N
8. 69
(8. 54 )
5. 28
C U
-
C HI TO S AN
L
-
( 5 8. 89 )
6 2. 22
( 6 1. 35 )
6 1. 12
(5. 21 )
5. 40
( 5. 38 )
5. 46
( 4. 93 )
4. 89
(4. 23 )
4. 60
C 1
C 2
C 3
1 0 .9 7
(1 0 .3 6)
1 0 .4 3
Table 4. Study of solvent effect on the coupling reaction of
aniline (1mmol) with phenylboronic acid (2mmol) in presence of
optimized catalyst (C3) (8 mol%).
( 6 0. 99 )
5 9. 59
( 5 9. 16 )
(5. 19 )
5. 35
( 5. 21 )
( 4. 38 )
4. 62
(4. 80 )
(1 0 .3 1)
1 0 .7 9
(1 0 .6 5)
Entry
Solvent
H2O
CH3CN
CH3COOC2H5
CH3OH
CH3CH2OH
Time (h)
Yield (%)a
Based upon AAS analysis, the copper content are found to
be (21 mg), (23 mg) & (24 mg) per litre for C1, C2 & C3
complexes, respectively, against calculated value of (26
mg), (27 mg) & (30 mg), respectively.
1
2
3
4
5
48
09
19
36
36
-
85
53
35
38
aIsolated yield after work up
After full characterization of the complexes, the
catalytic activity of the complexes (C1 to C3) was explored for
Chan-Lam C-N coupling reaction of amines with arylboronic
acid. In order to optimize conditions, the reaction of aniline
(1mmol) and phenylboronic acid (2mmol) was chosen as a model
reaction in acetonitrile using K2CO3 as a base. When the reaction
was carried out without catalyst at room temperature for 48 hr
(Table 3, entry 1), no product was isolated. The same reaction
under reflux also did not afford any product (Table 3, entry 2).
The reaction was also performed in the presence of neat Chitosan
(50 mol% and 100 mol%) in acetonitrile at room temperature and
under reflux. No trace of product could be isolated from the
reaction mixture (Table 3, entries 3-6). It clearly indicates that
Chitosan itself does not catalyze the reaction. The reaction was
performed in the presence of the complex (C1) at room
temperature (Table 3, entry 7), no product was isolated.
Subsequently, the reaction was performed in presence of 3.5
mol% of the complex (C1, C2, C3), respectively, under reflux, to
afford the desired products in 63%, 54% and 71% yield,
respectively (Table 3, entries 8-10). Among the three complexes
(C1 to C3), C3 afforded good yield product under the reflux. To
optimize the catalyst loading, the reaction was carried out in the
presence of 8 mol% of the complex (C3) instead of 3.5 mol%, the
yield of the product was increased from 71 to 85% (Table 3,
entry 11). However, when the catalyst load was increased to 12
mol%, no significant improvement in the yield was observed
(Table 3, entry 12).
In order to find out the best base, the reaction was carried
out with different bases such as K2CO3, Na2CO3, NaHCO3 and
Cs2CO3 (Table 5, entry 1-7). The best yield (85%) was obtained
in case of 2 equivalent of K2CO3 (Table 5, entry 2). The reaction
did not afford any product in the absence of base (Table 5, entry
1). The reaction was also carried out with 1.0 and 1.5 equiv of
K2CO3, to afford 61% and 73% yields, respectively (Table 5,
entry 6-7). However, NaHCO3 gave only trace mount of product
(Table 5, entry 4). On the other hand, Cs2CO3 gave only 45%
(Table 5, entry 5) within 24 h. Therefore, K2CO3 was found to be
the best base for the reaction.
Table 5. Screening of base for the coupling reaction of aniline
(1mmol) with phenylboronic acid (2mmol).
Entry
Base ( equiv)
Time
(h)
30
09
36
36
22
19
15
Yield
(%)a
-
85
29
Trace
45
61
1
2
3
4
5
6
7
Without base
K2CO3 (2)
Na2CO3 (2)
NaHCO3 (2)
Cs2CO3 (2)
K2CO3 (1.0)
K2CO3 (1.5 )
73
aIsolated yield after work up

5
NH2
B(OH)2
H
N
6
7
12
24
82
66
OH
With the optimized conditions in our hand, we further
extend the scope of the reaction to various aromatic and aliphatic
amines with phenylboronic acid bearing either electron-donating
group (EDG) or electron-withdrawing group (EWG). The results
obtained, are summarized in (Table 6, entry 1-15). The products
were obtained as colourless/yellow oil to colourless/yellow/red
crystalline solids, soluble in common organic solvents such as
CHCl3, CH3OH and C2H5OH and were fully characterized by 1H
NMR and Mass spectra. The data were in close agreement with
the literature values.32
OH
1f
2a
3f
H2N
H
N
B(OH)2
H3C
H3C
1g
3g
2a
B(OH)2
H2N
H
N
8
9
24
11
69
84
H3C
CH3
Aliphatic amines were found to be comparatively less
reactive and took longer reaction time than aromatic amines
(Table 6, entries 7, 8). The aromatic amines bearing EWG such
as -NO2, and -Cl, afforded corresponding diaryl amines in high
isolated yields (72 - 85%, Table 6, entries 3-5). The meta-
position of EWG in amine (Table 6, entry 5) gave higher yield
than corresponding ortho- and para-positions (Table 6, entries 3,
4). However, the aromatic amines bearing –OH afforded
corresponding product in high yield (Table 6, entry 6).
Benzylamine, cyclohexylamine and morpholine gave yields
(71%, 72% and 84%), respectively (Table 6, entries 2, 9 and 10).
Electron rich and electron withdrawing group at meta and para-
position of the phenylboronic acid were also tested. The electron
donating group enhanced the yield while low yields were
obtained with electron withdrawing group (Table 6, entry 11-
15). The plausible reason for such substituents effect is that the
oxidation of Cu(II) complexes, bearing electron withdrawing
substituent, to Cu(III) is less facile as compared to electron
donating substituents. The presence of electron withdrawing
groups either on aryl boronic acids or amines retards the
formation of putative Cu(III)-intermediate and hence influence
3h
1h
2a
B(OH)2
O
N
O
N
H
3i
1i
NH2
2a
B(OH)2
H
N
10
11
11
18
72
77
3j
1j
NH2
2a
B(OH)2
H
N
Cl
3k
3l
Cl
1k
2b
B(OH)2
NH2
H
N
12
14
14
81
80
CH3
1l
CH3
2c
B(OH)2
H
N
NH2
13
the yield of the products12,33
.
Table 6. The reaction of various aromatic and aliphatic amines
with phenylboronic acid under optimized reaction conditions
OCH3
CH3
3m
OCH3
1m
2d
B(OH)2
NH2
H
N
14
15
13
13
78
74
NH2
X
B(OH)2
H
N
CH3
3n
3o
Complex (C3)(8 mol%)
1n
NH2
2e
B(OH)2
+
,
,
K2CO3 (2 equiv)
CH3CN
H
N
X
Y
Y
X= -H, -Cl, -NO2, -OH
Y= -H, -Cl, -CH3
F
F
1o
Ent
-ry
Amines
Aryl
boronic
acid
Productsa
Time
(h)
Yeild
(%)b
2f
a Purity determined by TLC & 1H NMR
b Isolated yield after work up
NH2
B(OH)2
H
N
1
9
85
Furthermore, the recyclability of Complex (C3) was checked
by choosing the reaction of aniline and phenylboronic acid as a
model reaction. After completion of reaction, the catalyst could
easily be separated out by filtration from the aqueous layer, and
then washed with diethyl ether for the subsequent batch reaction.
It is apparent from Figure 6 that the complex (C3) could be re-
used up to five cycles with no significant loss of catalytic
activity.
1a
NH2
2a
B(OH)2
3a
NH
2
3
12
18
71
72
2a
3b
1b
NH2
Cl
B(OH)2
H
N
Cl
B(OH)2
NH2
1c
2a
3c
NH2
H
N
B(OH)2
4
5
18
15
74
82
+
First recycle
Second recycle
Third recycle
85%
83%
82%
Cl
3d
Cl
2a
Complex (C3)
1d
NH2
CH3CN, K2CO3
reflux
B(OH)2
H
N
Fourth recycle
Fifth recycle
80%
77%
H
N
NO2
NO2
2a
1e
3e

6
Tetrahedron
Figure 6. Recyclability of the catalyst
Winters, M. P.; Chan, D. M. T.; Combs, A. Tetrahedron
Lett. 1998, 39, 2941-2944; (c) Lam, P. Y. S.; Vincent,
G.; Bonne, D.; Clark, C. G. Tetrahedron Lett. 2003, 44,
4927; (d) Evans, D. A.; Katz, J. L.; West, T. R.
Tetrahedron Lett. 1998, 39, 2937-2940; (e) Singh, K.
N.; Raghuvanshi, D. S.; Gupta, A. K. Org. Lett. 2012,
14 (17), 4326-4329.
Conclusion
In summary, Schiff base of Chitosan (L), Schiff base ligands
(L1, L2, and L3) and the resultant Chitosan anchored Copper(II)
Schiff base complexes (C1, C2, and C3) have been synthesized
and characterized by various spectroscopic and instrumental
techniques. All the three complexes (C1 to C3) were found to be
good heterogeneous catalyst for Chan-Lam C-N coupling
reactions. However, the best results were obtained with complex
C3. The complex C3 contains an electron withdrawing NO2 group
which presumably enhances the Lewis acidity of the complex.
The novelty of the work is that the catalyst can be easily filtered
out and reused at least for five times with no significant loss of
the catalytic activity.
6. Ullmann, F.; Illgen, E. Ber. Dtsch. Chem. Ges. 1914,
47, 380–383
7. Tang, B.; Guo, S.; Zhang, M.; Li, J. Synthesis 2008,
1707- 1716.
8. Chouhan, G.; Wang, D.; Alper, H. Chem. Commun.
2007, 4809–4811.
Acknowledgments
We are thankful to the Central Instrumentation Facility of
ISM for providing help in the analysis of the samples.
Anuradha and S. Kumari acknowledge the receipt of ISM
fellowship.
9. Antilla, J. C.; Klapars, A.; Buchwald, S. L. J. Am.
Chem. Soc. 2002, 124, 11684–11688.
10. Rao, R. K.; Naidu, A. B.; Jaseer, E. A.; Sekar, G.
Tetrahedron 2009, 65, 4619-4624.
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 Three new Chitosan anchored Copper(II) Schiff base complexes (C1 to C3) have been
synthesized.
 The complexes were found to be efficient heterogeneous catalyst for Chan-Lam coupling
reaction.
 The catalyst can be easily filtered out and reused at least for five times.