An efficient and recyclable chitosan supported copper(II) heterogeneous catalyst for C-N cross coupling between aryl halides and aliphatic diamines

Article abstract of DOI:10.1016/j.tetlet.2014.11.120

A useful and convenient methodology has been developed for synthesis of mono N-arylated aliphatic 1,2- and 1,3-diamines and amino alcohols. A highly efficient and renewable heterogeneous chitosan supported copper(II) catalyst has been employed for the C-N cross coupling between aryl halides and aliphatic diamines/amino alcohols. The main advantages of this reaction are the high yields of the products, reduced reaction time, convenient work up procedure, renewability of the catalyst, and less metal contamination of the products. All these factors make the present C-N cross coupling reaction economical, green, and sustainable.

Full text of DOI:10.1016/j.tetlet.2014.11.120

Accepted Manuscript
An efficient and recyclable chitosan supported copper(II) heterogeneous cata-
lyst for C-N cross coupling between aryl halides and aliphatic diamines
Chandan Bodhak, Ashis Kundu, Animesh Pramanik
PII:
S0040-4039(14)02034-6
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.11.120
TETL 45504
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
8 September 2014
25 November 2014
26 November 2014
Please cite this article as: Bodhak, C., Kundu, A., Pramanik, A., An efficient and recyclable chitosan supported
copper(II) heterogeneous catalyst for C-N cross coupling between aryl halides and aliphatic diamines, Tetrahedron
Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.11.120
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An efficient and recyclable chitosan supported copper(II)
heterogeneous catalyst for C-N cross coupling between aryl halides
and aliphatic diamines
Chandan Bodhak, Ashis Kundu and Animesh Pramanik*
Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata-700 009, India;
Fax: +91-33-2351-9755; Tel: +91-33-2484-1647.
E-mail: animesh_in2001@yahoo.co.in
Abstract: A useful and convenient methodology has been developed for synthesis of mono
N-arylated aliphatic 1,2- and 1,3-diamines and amino alcohols. A highly efficient and renewable
heterogeneous chitosan supported copper(II) catalyst has been employed for the C-N cross coupling
between aryl halides and aliphatic diamines/amino alcohols. The main advantages of this reaction
are the high yield of the products, reduced reaction time, convenient work up procedure,
renewability of the catalyst and less metal contamination of the products. All these factors make the
present C-N cross coupling reaction economical, green and sustainable.
Keywords: Aryl halides, 1,2- and 1,3- diamines/amino alcohols, chitosan@copper catalyst,
chelation pathway.
1
Nitrogen-containing compounds are ubiquitous among biologically active molecules. The
development of efficient methodologies for generating C–N bonds are of great importance due to
2
their wide applicability in pharmaceutical as well as agrochemical research. The C-N bond forming
1

reactions also produce N-arylated amino moieties which are essential components of many bio-
3
active compounds, such as oxcarbazepine and imatinib. Moreover many polyamines are used in
coordination and biological chemistry, cellular growth, and ribonucleic acid transcription activity as
4
,5
well as in protein synthesis and regulation of immune responses.
6
Many C-N coupling reactions such as Ullmann reaction, Chan-Lam coupling reaction,
7
8
and Buchwald-Hartwig amination reactions are reported in the literature. In all these reactions
9
,10
11,12
various metal catalysts such as palladium, nickel
and copper
are employed along with
1
different coordinating ligands such as bisamines, amino acids, DPPF, phosphoramidites, and
3
14
15
16
1
7
oxime-phosphine oxides. Although these catalysts and ligands are used in low loadings they are
very expensive and the toxicity caused by the presence of metals in the products is a serious
1
disadvantage of these reactions. Previously Han et al. reported N-arylation of amines/amino
8
19
alcohols with aryl halides using free CuCl as catalyst which causes high metal contamination of the
20
final products and also the reaction takes longer time (~ 8 h). Aguiar et al. reported the use of
Cu O and CuO nanoparticles (NPs) as catalysts in N-arylation reactions which demand N
2
2
atmosphere and prolonged reaction times (~12-48 h). Therefore development of new methodologies
taking into consideration of reduction of reaction time, minimum metal contamination of products,
simple reaction conditions, easy isolation of products and catalysts, and renewability of catalyst is
highly desirable. In this regards applications of environment-friendly polymer supported metal
2
catalysts are very promising due to low cost and less toxicity. Chitin is a linear polysaccharide
1
22
composed of randomly distributed β-(1-4)-linked D-glucosamine (acetylated unit), which is the
principal component of protective cuticles of crustaceans such as crabs, shrimps, prawns, lobsters
2
and cell walls of some fungi such as aspergillus and mucor. Generally chitosan which possesses
3
both free amino and alcoholic groups is prepared by alkaline deacetylation of chitin. In the present
2

paper we wish to report a new strategy for C-N cross coupling between aryl halides and aliphatic
diamines/amino alcohols using an efficient and ecofriendly chitosan scaffold based copper(II)
catalyst (chitosan@copper). The chitosan@copper catalyst was prepared following a simple
2
4,25
procedure where the copper sulfate was immobilized over the chitosan scaffold (Scheme 1).
OH
OH
OH
OH
O
O
O
O
O
O
O
O
NH2
HO
NH2
NH
HO
2
NH2
OH
HO
HO
OH
OH
H N
2
H N
2
H N
2
OH
H N
2
O
O
O
O
O
O
O
O
HO
HO
HO
HO
H O
2
CuSO4
Stirring,
hr
3
OH
OH
OH
OH
O
O
O
O
O
O
O
O
NH2
NH2
NH2
HO
NH2
HO
HO
HO
Cu2+
Cu2+
Cu2+
Cu2+
OH
OH
OH
OH H N
H N
2
H N
2
2
H N
2
O
O
O
O
O
O
O
O
HO
HO
HO
HO
Scheme 1. Schematic representation of preparation of chitosan embedded copper catalyst
In order to find out the appropriate reaction conditions for the C-N coupling, initially we
have carried out an optimization study for N-arylation reaction employing iodobenzene 1a and
ethylenediamine 2a in a ratio of 1:2 equiv using different catalysts, reactions time and solvent
3
systems (Table 1). When the reaction was carried out in different solvents such as THF, CH CN
and EtOH without using any catalyst, the reaction did not proceed at all even after prolonged
refluxing (Table 1, entries 1-3). Then the reaction was performed with 5 mol% CuI as catalyst in
3

THF under refluxing condition which afforded product 3a in good yield, ~ 60% (entry 4). When
the amount of CuI in the above reaction was reduced from 5 to 1 mol% the yield of 3a decreased
to some extent, ~52% (entry 5). Subsequently the reaction was performed in CH
mol% CuI as catalyst which produced a better yield of 3a (~ 75%) under refluxing condition
entry 6). When the reaction was carried out in THF and CH CN with 10 mol% CuCl catalyst,
CN is much better, ~ 91% compared to that of in THF (entries 7 and 8).
as catalysts gives better yield in CH CN than in THF, but
overall the yield is much less compared to CuCl catalyst (entries 9 and 10). The use of nano
Cu O and CuO catalysts under N atmosphere in CH CN and THF produced 3a in 46-82% yield
after prolonged refluxing (entries 11-14). Furthermore, other copper catalyst such as Cu(OAc)
CuSO and Cu(acac) were also employed for the reaction in THF and CH CN and the yield of
a obtained around 50-72% (entries 15-20). Use of EtOH as solvent in the reaction with
Cu(acac) catalyst produced poor yield of 3a, ~ 35% (entry 21). Therefore CH CN is found to be
3
CN using
1
(
3
the yield of 3a in CH
3
The same reaction with 5 mol% CuCl
2
3
2
2
3
2
,
4
2
3
3
2
3
the best solvent for this type of coupling reaction. Since in all the above reactions free copper
catalysts have been used the possibility of metal contamination of product is high. Therefore we
became interested to use chitosan@copper as heterogeneous catalyst in the reaction where
copper(II) is coordinated in the matrix of chitosan polymer. Employing 100 mg chitosan@copper
as catalyst in THF the reaction produced 68% yield of 3a where as EtOH as solvent afforded
only 38% yield (entries 22 and 23). The maximum yield of 3a (~94%) was achieved when the
3
reaction was carried out in CH CN under reflux for a period of 3 h employing 100 mg of
chitosan@copper catalyst (entry 24). However, reduction of the amount of chitosan@copper
catalyst in the above reaction caused less yield of 3a, ~ 62% (entry 25). When the reaction was
carried out with other metal catalysts such as chitosan@nickel and chitosan@cobalt in place of
4

chitosan@copper, no product was formed even after prolonged refluxing (Table 1, entries 26,
7).
2
After optimization of the reaction conditions (Table 1, entry 24), the scope and generality
of the reaction was assessed by employing various aryl halides (1) and 1, 2- and 1,3-diamines
and amino alcohols (2). The results are summarized in Table 2 which shows that aryl bromide
and iodide and various 1, 2- and 1,3-diamines and amino alcohols are suitable for this
2
N-arylation reaction (Table 2, entries 1-10). All the N-arylated products 3a-e were isolated as
6
1 13
gummy liquid and characterized by HRMS, H NMR and C NMR spectroscopy. Interestingly
1
,4-diaminobutane and pentane 1,3-diamine do not participate in this coupling reaction (Table 2,
entries 11 and 12). Moreover, aromatic amines and aliphatic mono amines do not undergo
N-arylation by this coupling reaction. All these information provide valuable insights about the
mechanism of the reaction.
1
Table 1 Optimization study for the synthesis of N -phenyl-1, 2-diaminoethane 3a
[a]
NH2
I
HN
NH2
Catalyst
Solvent
+
H N
2
1a
2a
3a
[
b]
Entry
Solvent
THF
Catalyst
__
Catalyst load
Time (h)
Yield (%)
1
2
3
4
5
__
__
12
10
10
10
10
__
__
__
60
52
CH
3
CN
__
EtOH
THF
THF
__
__
CuI
CuI
5 mol%
1 mol%
5

6
7
8
9
CH
3
3
CN
CN
CuI
1 mol%
10 mol %
10 mol%
5 mol%
5 mol%
1 mol %
1 mol %
1 mol %
1 mol %
5 mol %
5 mol %
10 mol%
10 mol%
5 mol %
5 mol %
5 mol %
100 mg
100 mg
100 mg
50 mg
6
10
10
8
75
91
61
56
75
68
46
82
48
69
51
72
59
72
53
35
68
38
94
62
__
__
CH
CuCl
CuCl
THF
THF
CuCl
2
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
CH
3
3
CN
CN
CuCl
2
8
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
CH
NPs Cu
NPs Cu
2
2
O (N
2
2
)
)
14
18
8
THF
O (N
CH
3
CN
NPs CuO (N
2
)
THF
NPs CuO (N
2
)
8
CH
3
CN
Cu(OAc)
Cu(OAc)
2
2
8
THF
12
8
CH
3
CN
CuSO
4
4
THF
CuSO
12
6
CH
3
CN
Cu(acac)
Cu(acac)
Cu(acac)
2
2
2
THF
EtOH
THF
EtOH
6
6
Chitosan@copper
Chitosan@copper
Chitosan@copper
Chitosan@copper
Chitosan@nickel
Chitosan@cobalt
14
12
3
CH
3
CN
CH
CH
CH
3
3
3
CN
10
8
CN
CN
100 mg
100 mg
8
6

[
a]
Optimization of the reaction of iodobenzene (1a) with ethylene diamine (2a) in different
[b]
solvents, and catalysts under heating at reflux for the indicated times. Isolated Yield.
Table 2 Reaction yields of chitosan@copper-catalyzed C–N cross-couplings between 1 equiv of
aryl halides and 2 equiv of diamines/amino alcohol in acetonitrile
R
X
HN
R
+
Chitosan@copper
H N
2
CH CN, Reflux
3
1
2
3
Entry
Aryl
halide (1)
Diamines/amino
alcohol (2)
Product
Catalyst Reaction
Yield
a]
(%)
[
load
mg)
time
(h)
(
3)
(
NH2
HN
NH2
I
H N
2
1
2
100
3
5
4
5
94
88
90
86
3
a
NH2
3a
120
Br
H N
2
HN
NH2
1
20
I
H N
2
NH2
3
4
5
3
3
b
b
150
120
Br H2N
NH2
OH
HN
OH
I
H N
2
4
88
3
c
7

OH
6
3c
150
120
6
5
87
Br
H N
2
NH2
*
HN
NH2
3d
92
(3d:3d'=1:1)
I
*
[b]
H N
2
7
NH2
*
HN
3
d'
NH2
*
Br H2N
8
9
3d and 3d'
150
120
6
5
90
3d:3d'=1:1)
[b]
(
H N
2
NH
I
92
H N
2
H N
2
3
e
H N
2
1
0
Br
3
e
100
100
120
6
6
6
89
__
__
H N
2
NH2
1
1
2
I
__
__
H N
2
NH2
1
I
H N
2
[a]
[b]
Isolated Yield; Percentage determined from NMR
8

Characterization of the prepared chitosan@copper catalyst was carried out by scanning
electron microscopy (SEM), TGA, powder XRD and IR studies. SEM study at an accelerating
voltage of 15kV is employed to know the morphology and size of the prepared chitosan
embedded copper catalyst. The SEM images of the catalyst taken before (Figure 1a) and after 5
times of application in the reaction (Figure 1b) shows no significant change in the morphology
indicating substantial retention of the catalytic activity after recycling. Powder XRD study was
carried out to confirm the crystalline nature of as-synthesized chitosan@copper catalyst. The
XRD pattern of chitosan@copper catalyst and chitosan itself are displayed in Figure 2. The
signals pertaining to copper metal was not detected by XRD of chitosan@copper, presumably
2
7
due to complexation of copper with chitosan or low percentage of copper. The formation of
chitosan@copper catalyst was further confirmed by IR and TGA studies (Supporting
Information).
(a)
(b)
Figure 1. SEM images of chitosan@copper catalyst
a) before reaction; (b) after 5 times application in reaction
(
9

B
A
10
20
30
40
50
60
70
80
2
θ(Degree)
Figure 2. X-ray diffraction pattern of (A) chitosan and (B)
chitosan@copper catalyst
A plausible mechanism for the formation of 3 involving chitosan embedded copper (II)
catalyst is depicted in Scheme 2. In the chitosan@copper catalyst A, Cu(II) ions are encapsulated
in the polymer supported matrix of chitosan through the amino and hydroxyl groups. The
2
diamine 2 coordinates with Cu(II) by expelling two H O molecules from the coordination sphere
to generate intermediate B. It is interesting to note that during the reaction the color of the
reaction mixture changes from light blue to light green indicating oxidation of Cu(II) to transient
2
8,29
Cu(III) ions.
The formation of intermediate C from B is responsible for this color change.
Intermediate C is formed through the oxidative addition of aryl halide 1 and temporary
detachment of one chitosan polymeric unit from the coordination sphere of B. Furthermore the
conversion of C to D is facilitated by the reductive elimination of N-aryl amine 3 which is
accompanied by the conversion of Cu(III) to Cu(II) in the polymer scaffolds and also
simultaneous regeneration of the chitosan@copper catalyst A. Chelation of 1,2- and 1,3-
diamines 2 with copper as shown in B and C is important for the reaction. Since 1,4-diamino
butane cannot form stable chelate with copper it fails to react with aryl halides (Table 2, entry
1
1). Sterically crowded pentane 1,3-diamine also does not participate in the reaction since it
10

cannot form stable chelate with copper due to steric reason (Table 2, entry 12). The monoamines
also cannot form N-arylated products in this method due to absence of chelate formation.
OH
OH
O
O
O
O
NH
2
NH
2
2
H N
n
NH2
N
O
2
+
2
O
H
2
O
Cu
OH
2
2+
Cu
O
-2H O
2
H
2
O
H
2
N
H
2
N
2
H N
n
O
O
O
O
HO
A
HO
B
X
NH
2
-
H O
2
HN
Oxidative
addition
n
1
OH
OH
O
3
O
O
O
NH
2
O
NH
2
2+
H
2
O
H
Cu
OH
2
O
Reductive
elimination
Cu3+
X
2
O
H
2
N
NH
2
O
2
H N
n
O
O
C
D
HO
Scheme 2. Plausible mechanism for the formation of 3
Furthermore, we have carried out the recovering and reusability test of chitosan@copper
catalyst for the formation of compound 3a employing iodobenzene 1a and ethylenediamine 2a.
After the completion of the reaction the desired product 3a was isolated by extracting with ethyl
acetate. The solid chitosan@copper catalyst was recovered by simple filtration and reused five
11

times after through washig with ethylacetate each time. The yield of the product 3a varied from
4% to 84%, indicating little loss of reactivity of chitosan@copper catalyst even after repeated
applications (Figure 3).
9
1
00
80
60
40
20
0
1
2
3
4
5
Number of cycles
Figure 3. Reusability study of chitosan@copper catalyst
Conclusions
In conclusion, chitosan@copper has been found to be a polymer based, highly active
reusable heterogeneous green catalyst for the C-N cross coupling reaction to achieve mono
N-arylated 1,2- and 1,3-diamines and amino alcohols. Most importantly these N-arylated
products are readily prepared from inexpensive starting materials in moderate to high yield under
a straight forward, efficient and highly economical reaction conditions in shorter reaction time.
Another interesting aspect is the use of inexpensive, biodegradable, nontoxic and renewable
12

chitosan polymer unit for the preparation of effective catalytic system which can reduce the
metal contamination of products significantly.
Acknowledgments
C. B. and A.K. thanks the University Grant Commission (UGC) for offering Junior Research
Fellowship (JRF) and Senior Research Fellowship (SRF) respectively. The financial assistance
of CSIR, New Delhi is gratefully acknowledged [Major Research Project, No.
0
2(0007)/11/EMR-II]. We also acknowledge University of Calcutta and Centre for Research in
Nanoscience and Nanotechnology (CRNN), University of Calcutta for instrumental facilities.
Supporting Information
1 13
Supplementary data ( H, C, DEPT-135, HRMS, data of compounds 3a-e and FT-IR spectra of
chitosan@copper catalyst) associated with this article can be found in the online version at
……………….
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4
5. Experimental procedure for synthesis of the chitosan@copper catalyst:
Chitosan (5.0 g, medium molecular weight) was suspended in 100 ml of water. To this
suspension, 1.0 g of CuSO ·5H O was added and the mixture was stirred continuously for 3 h at
4
2
room temperature. The prepared catalyst was separated by centrifugation (5000 rpm 5 min) and
dried under vacuum at 50 °C. The catalyst was characterized by SEM, TGA, powder X-ray
diffraction and IR studies.
15

2
6. General synthetic procedure for the preparation of 3a-e:
Aryl halide (1.0 equiv) and aliphatic diamines/amino alcohol (2.0 equiv) were taken in a 100 ml
round bottom flask along with 100-150 mg of the chitosan@copper catalyst in CH CN (15 ml)
solvent. The resultant mixture was heated at reflux for 3-6 h. After completion of the reaction
the complete consumption of starting materials was confirmed by TLC) the reaction mixture
3
(
was extracted with ethylacetate. The separated organic phase was concentrated to get the gummy
liquid product 3. The chitosan@copper catalyst was collected by simple decanting off the
reaction mixture. The recovered catalyst was then washed thoroughly with ethylacetate 2-3
times, dried under vacuum at 50 °C and used for another run.
1
1
N -phenyl-propane-1, 2-diamine (3b): Yellowish brown liquid (435 mg, 90%). H NMR (300
MHz, CDCl ): δ 7.35 (m, 2H), 6.78 (t, J = 7.5 Hz, 1H), 6.6 (d, J = 8.1 Hz, 2H), 3.15 (t, J = 6.9
Hz, 2H), 2.80 (t, J = 6.9 Hz, 2H), 1.74 (m, 2H); C NMR (75 MHz, CDCl
3
1
3
3
): δ 30.1, 39.3, 41.3,
+
1
13.0, 117.2, 129.1, 148.3; ESI-MS m/z 151.0 [M +H].
-phenylamino-1-ethanol (3c): Yellowish brown liquid (420 mg, 88%). H NMR (300 MHz,
): δ 7.18 (t, J = 7.6 Hz, 2H), 6.73 (t, J = 7.5 Hz, 1H), 6.65 (d, J = 7.5 Hz, 2H), 3.80 (t, J =
1
2
CDCl
3
1
3
5
1
3
.4 Hz, 2H), 3.28 (d, J = 5.4 Hz, 2H), 2.79 (brs, 1H); C NMR (75 MHz, CDCl ): δ 46.1, 61.2,
+
13.2, 117.9, 129.3, 148.1; ESI-MS m/z 138.1 [M +H].
2
2
7. Baig, R. B. N.; Varma, R.S. Green Chem., 2013, 15, 1839.
8. Zhang, Y.; Yang, X.; Yao, Q.; Ma, D. Org. Lett. 2012, 14, 3057.
2
9. Sperotto, E.; van Klink, G.P.M.; van Koten, G.; Johannes G. de Vries. Dalton Trans. 2010,
9, 10338.
3
16

Graphical Abstract
An efficient and recyclable chitosan supported copper(II)
heterogeneous catalyst for C-N cross coupling between aryl halides
and aliphatic diamines
Chandan Bodhak, Ashis Kundu and Animesh Pramanik*
R
X
HN
R
Chitosan@copper
+
H N
2
CH CN, Reflux
3
X= I, Br
R= -(CH ) NH , -(CH ) NH , -(CH ) OH, -CH CH(CH )NH ,
2
2
2
2 3
2
2 2
2
3
2
H N
2
-
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17