1-D copper(I) coordination polymer based on bidentate 1,3-dithioether ligand: Novel catalyst for azide-alkyne-cycloaddition (AAC) reaction

Article abstract of DOI:10.1016/j.tetlet.2018.05.040

A novel 1,3-bis(4-fluorophenylthio)-propane ligand based CuI 1-D polymeric coordination complex having formula ([(CuI)₂{ArS(CH₂)₃SAr}₂]_n, Ar = 4-F-C₆H₄) has been synthesized and characterized by ¹H NMR, ¹³C NMR and single crystal XRD techniques. This complex has been employed for the first time as suitable catalyst for base-free one-pot three-component regioselective azide-alkyne cycloaddition (AAC) reaction. A novel 1,2,3-triazole compound with sulfur functionalized pendant arms has also been prepared using our catalytic system in a multicomponent manner via one-pot two-step reaction.

Full text of DOI:10.1016/j.tetlet.2018.05.040

Accepted Manuscript
1
-D Copper(I) coordination polymer based on bidentate 1,3-dithioether ligand:
Novel catalyst for azide-alkyne-cycloaddition (AAC) reaction
Sankar Saha, Kinkar Biswas, Basudeb Basu
PII:
S0040-4039(18)30653-1
https://doi.org/10.1016/j.tetlet.2018.05.040
TETL 49987
DOI:
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
6 April 2018
14 May 2018
16 May 2018
Please cite this article as: Saha, S., Biswas, K., Basu, B., 1-D Copper(I) coordination polymer based on bidentate
1
,3-dithioether ligand: Novel catalyst for azide-alkyne-cycloaddition (AAC) reaction, Tetrahedron Letters (2018),
doi: https://doi.org/10.1016/j.tetlet.2018.05.040
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1
-D Copper(I) coordination polymer based
Leave this area blank for abstract info.
on bidentate 1,3-dithioether ligand: Novel
catalyst for azide-alkyne-cycloaddition
(
AAC) reaction
a
b,
a,
Sankar Saha , Kinkar Biswas *, Basudeb Basu *

1
Tetrahedron Letters
1
-D Copper(I) coordination polymer based on bidentate 1,3-dithioether ligand: Novel
catalyst for azide-alkyne-cycloaddition (AAC) reaction
a
b,
a,
Sankar Saha , Kinkar Biswas *, Basudeb Basu *
a
Department of Chemistry, North Bengal University, Darjeeling 734013, India
Department of Chemistry, Raiganj University, Raiganj 733134, India
b
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A novel 1,3-bis(4-fluorophenylthio)-propane ligand based CuI 1–D polymeric coordination
complex having formula ([(CuI) {ArS(CH SAr} , Ar = 4-F-C ) has been synthesized and
2
2
)
3
2
]
n
6 4
H
1
13
characterized by H-NMR, C-NMR and single crystal XRD techniques. This complex has
been employed for the first time as suitable catalyst for base-free one–pot three-component
regioselective azide-alkyne cycloaddition (AAC) reaction. A novel 1,2,3–triazole compound
with sulfur functionalized pendant arms has also been prepared using our catalytic system in a
multicomponent manner via one–pot two–step reaction.
Available online
Keywords:
Click reaction
2
009 Elsevier Ltd. All rights reserved.
1
1
1
-D Cu Coordination complex
,3-Dithioether
,2,3-Triazole
Introduction
catalyst met with the problems of undesired alkyne-alkyne
14
homocoupling reaction.
The 1,2,3-triazoles are known to be an important heterocyclic
scaffolds from biological and pharmaceutical viewpoints; such as
Hor et al reported the synthesis of novel pyridyl and thioether
hybridised 1,2,3-triazole ligands based Cu(I) coordination
polymers and its application in azide-alkyne cycloaddition
1
2
3
anti-allergic, anti-bacterial, and anti-HIV activity, and selective
4
β3-adrenergic receptor agonism. The atom-efficient 1,3-dipolar
15
Huisgen cycloaddition reaction between alkynes and organyl
azides (commonly known as AAC) is one of the mos5t
straightforward methods for the synthesis of 1,2,3-triazoles.
While AAC reaction gives a mixture of 1,4- and 1,5-disubstituted
reactions. It opened a new dimension for the polymeric
coordination complex catalyzed AAC reactions. Due to strong
coordination power of sulfur atoms, sulfur containing ligands are
generally used for the preparation of Cu(I)-coordination
1
6
1,2,3-triazoles, the use of Cu(I) catalysts under mild conditions
polymer. Knorr et al illustrated the coordination mode of
16
selectively forms the 1,4-disubstituted 1,2,3-triazoles in excellent
yields and this is commonly known as 'click reaction'. The
simplest example of Cu(I) catalyzed click triazole synthesis was
2 n
aromatic dithioether ligands of the type PhS(CH ) SPh. Apart
from the structural and photophysical properties, the catalytic
activity of these types of dithioether based copper complexes in
the AAC reaction has not been reported yet. Herein we report the
synthesis, characterization of a new type of 1,3-dithioether based
CuI coordination polymer and find its application to one pot
azide-alkyne cycloaddition reaction in a multicomponent fashion.
Our 1,3-bis(4-fluorophenylthio)-propane ligand based CuI
coordination polymeric complex having molecular formula,
4
effectively achieved by excess of CuSO and sodium ascorbate,
where sodium ascorbate reduces the Cu(II) to Cu(I) and inhibits
6
the aerobic oxidation of Cu(II) species. For well-defined Cu(I)
catalytic systems, various ligands like PPh
3
, NHC, S- and N-
based molecules have been used so far, though P-based ligands
6-9
afford unwanted Staudinger reaction.
The coordination
(
[(CuI)
2
{ArS(CH
2
)
SAr} ]
3 2 n
,
Ar
=
4-F-C
6
H
4
)
was first
chemistry of sulfur ligands has been studied extensively and their
copper complexes are attractive due to the reducing power of
sulfur group as well as prevent further oxidation of Cu(I) to
synthesized and characterized by NMR and single crystal X-ray
diffraction pattern. The catalyst works efficiently in AAC
reaction under base-free condition in water/acetonitrile solvent
10
Cu(II) in the absence of any base. This promoted the synthesis
and application of Copper(I)-thioamide catalytic complex in
o
mixture at 50 C to afford selectively 1,4-disubstituted 1,2,3-
11
AAC reaction. Mononuclear complexes like [CuX
2
(SNS)] (X =
triazole products. In scheme 1, the AAC reaction performed by
various Cu(I) complexes with S, NS and SNS ligand is presented.
NN- and SNS-based polymeric Cu(I) complexes have been found
as catalyzing the AAC reaction but interestingly, polymeric Cu(I)
complex with SS-based bidentate ligands, used as AAC reaction
is not found in literature.
Cl, Br), [Cu(OTf)
polymer, [Cu (SNS)]
the AAC reaction.
2
(H
2
O)(SNS)] and 1-D Cu(I)-coordination
have been used as effective catalyst for
Hybrid nitrogen-sulfur (NS) ligands
2
I
2
n
1
2
supported Cu(I)/ Cu(II) complexes have also been used for AAC
13
reaction. But in some cases, the hybrid SNS-based Cu(I)

2
Tetrahedron Letters
S-based Cu-catalyst (5.7 mol%)
Ref. 11
H O, EtOH, RT
2
c
4 h, 91% yield
i
r
s
e
e
NS-based Cu-complex (2.0 mol%)
m
x
o
le
c
Ref. 13
i
r
n
p
s
o
o
M
e
m
m
e
CH OH:H O (1:1), 35 C
3
2
o
x
c
o
le
n
p
15 h
o
m
M
o
96% GC-MS conversion
c
SNS-based
Cu-complex
(5.0 mol%)
R1
R2
H
N
Cu-Complex
Both Monomeric &
Polymeric complexes
R1
Ref. 12
X + NaN +
N
3
R2
MeCN:H O (2:1)
Solvent, Temperature
2
N
or H O, RT
2
1
h, 92% yield
P
c
o
o
l
y
m
Ref. 16
P
m
e
c
o
p
o
l
l
r
i
y
e
m
p
x
m
c
NN-based Cu-complex (0.5 mol%)
e
s
e
Ref. 15
l
e
r
o
i
x
c
MeOH:H O (1:1), 50 C
2
SS-ligand based
2
4 h, Near quantitative yield
polymeric Cu-complexes
are known for
Photoluminescent and
other phtophysical
properties
[
(CuI) {ArS(CH ) SAr} ]
2
2 3
2 n
0.5 mg (0.1 mol%)
Present Work
o
Acetonitrile:H O (1:1), 50 C
2
3
h, 96% yield
Ar = 4-F-C H -
6
4
First time used in AAC reaction in our protocol
Scheme 1: Various ligand based copper complex catalyzed AAC reaction.
[
(CuI)
network is built up upon dimeric Cu
interconnected via dithioether ligands. The framework consists of
Cu (μ-I) prismatic part connected with the dithioether ligands.
2
{ArS(CH
2
)
3
SAr}
2
]
n
metallopolymer (Fig 1). The 1D-
Results and discussion
2 2
I
units which are
Synthesis of the copper complex
2
2
The 1,3-bis(4-fluorophenylthio)-propane ligand (L) was
Within the cluster core, the Cu─I bond lengths range between
2.5867 (5) and 2.6443 (12) Å. The Cu…..Cu distance between
the two Cu (I) centers, 2.7812 (10) Å falls significantly below the
sum of the vander Waals radius (2.8 Å). The mean Cu─S bond
length of range between 2.3339 (11) to 2.3551 (12) Å similar to
17
synthesized according to our previously reported procedure.
1
13
This compound was characterized by H- and C-NMR
spectroscopy. This ligand has been reacted with CuI in 1:2 metal
to ligand ratio in acetonitrile solvent to obtain the desired 1-D
polymeric CuI-1,3-dithioether complex. The as-synthesized Cu-
16a
[{Cu(μ-I)
2
Cu}
2
{μ-PhS(CH
2
)
3
SPh}
]
2 n
(2.3465 Å).
The angle
1
13
°
°
complex was characterized by H-NMR, C-NMR and single
crystal XRD techniques. The NMR spectra of bare ligand and
copper(I) complex are given in Supporting Information.
between Cu…I…Cu is 64.23 and I…Cu…I 115.77 in the
metallocluster. The crystal data, data collection and structure
refinement for the polymeric complex is given in the Supporting
Information.
This complex crystallizes in the monoclinic space group P 21/c
,
and shows polymeric propagation in the form of
a
2 2
Figure 1. View of (a) monomeric picture of the complex and (b) infinite 1-D chain of the complex incorporating dinuclear Cu(μ -I) Cu motifs along ‘b’ axis.
with 5 mg of the complex. After 5 hours, 84% of the product was
isolated under this condition (entry 1). When methanol was used
as solvent relatively less conversion was achieved compared to
the neat condition (70%, entry 2). Similarly the reactions in
acetonitrile and water gave 87% and 80% yield of the product
respectively (entry 3 & 4). A binary solvent mixture of
acetonitrile and water (1:1) resulted excellent yield of the desired
triazole product with lesser time (entry 5). The same experiment
The catalytic activity of the copper complex
The catalytic activity of the complex towards one-pot
multicomponent AAC reaction under base-free conditions was
optimized by the model reaction of benzyl bromide, NaN and
3
phenylacetylene with varying catalyst loading under different
temperature and solvent conditions (Table 1). The reaction was
first studied at neat condition and higher temperature (60 °C)

3
on microwave reactor yielded lesser amount of yield than
conventional thermal heating (entry 6). Decreasing the
temperature to 50 C also gave excellent yield (97%) in 3 hours
catalytic activity has been found to be very effective with only
0.5 mg of the complex catalyst for this reaction (entry 11). While
using CuI as the catalyst, the product was obtained in relatively
lower yield (entry 12). Performing the reaction by doubling the
reactants and keeping the catalyst quantity same (0.5 mg) also
afforded the desired product in poor yield (entry 13).
o
(entry 7). The product conversion was dropped when the reaction
was carried out at room temperature (entry 8). The catalyst
loading was also performed from entry 8 to entry 10 and the
Table 1
Optimization of reaction conditions for the Cu(I)–complex catalyzed one–pot three–component AAC reaction.
[
(CuI) {ArS(CH ) SAr} ]
2
2 3
2 n
Ar = 4-F-C H
6
4
N
+
NaN3
+
x mg
N
Br
Solvent, Temperature
N
o
a
Entry
Solvent
Neat
Complex/CuI in (mg)
Temp. ( C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
5
60
60
60
60
60
60
50
RT
50
50
50
50
50
5
84
70
87
80
97
Methanol
5
5
Acetonitrile
5
5
Water
5
8
Acetonitrile: water
Acetonitrile: water
Acetonitrile: water
Acetonitrile: water
Acetonitrile: water
Acetonitrile: water
Acetonitrile: water
Acetonitrile: water
Acetonitrile: water
5
3
b
5
0.5
3
92
5
97
85
97
96
96
79
65
5
5
3
3
1
1
1
1
0
1
2
3
1
3
0.5
0.5
0.5
3
c
3
d
4
3
Reaction conditions: Phenyl acetylene (1 mmol), NaN (1.2 mmol) and benzyl bromide (1.1 mmol),
2
Cu–complex [5.0 mg (1.0 mol%) to 0.5 mg (0.1 mol%)], Acetonitrile:H O (1:1, 2 mL).
a
Isolated yield after purification through column chromatography by silica gel.
b
Reaction tried on focused microwave reactor.
c
CuI was used as catalyst.
d
Phenyl acetylene (2 mmol), NaN
3
(2.4 mmol) and benzyl bromide (2.2 mmol).
The complex is air stable and can tolerate a range of benzyl,
and 7). Benzyl chlorides have been found to be reactive as benzyl
bromides (entry 8 and 9). But the same reaction when carried out
with diphenyl acetylene (internal alkyne) no reaction occurred
even after 12 hours (entry 10). This methodology has been also
applied for cinnamyl chlorides (entry 11 and 12). n-Octyl iodide,
an aliphatic halide also responded well to this cycloaddition
reaction (entry 15). All the reactions proceeded without any
difficulty and the products were isolated in good to excellent
yields in high purity through column chromatography.
allyl, cinnamyl and alkyl halides under mild reaction conditions
Table 2). The terminal alkynes have participated in this reaction
very smoothly (Table 2). Phenyl acetylene, 4-ethynyl toluene and
-bromo phenyl acetylene gave excellent yield (entry 1 to 3). 4-
nitro-phenyl acetylene also gave excellent yield but slightly
lesser than the previous entries (entry 4). Apart from aromatic
alkynes, alphatic alkynes responded also to this reaction
smoothly (entries 5, 13 and 14). Allyl bromide was found to be
very reactive as a coupling partner in this AAC reaction (entry 6
Table 2
(
2
Catalytic activities of the Cu(I)–complex catalyzed one-pot three–component AAC reaction.
[
(CuI) {ArS(CH ) SAr} ]
2
2 3
2 n
R1
(
Ar = 4-F-C H )
6 4
R1
+
+
R2
N
X
NaN3
H
0.5 mg (0.1 mol%)
N
R2
Acetonitrile:water (1:1)
N
o
5
0 C

4
Tetrahedron Letters
1
Entry
1
R2
a
R CH X
H
Time (h)
3
Yield (%)
2
Product
N
PhCH Br
Ph
97
96
96
2
Ph
Ph
N
N
[
2a]
p-Tol
PhCH Br
2
3
2
3
4
Ph
Ph
N
N
p-Tol
N
[
2b]
N
PhCH Br
o-Br-Ph
o-Br-Ph
2
N
N
[
2c]
Ph
Ph
N
N
p-NO -Ph
2
4
5
6
PhCH Br
2
p-O N-Ph
4
4
4
2
91
90
N
[
2d]
N
N
Ph
PhCH Br
2
Ph
OH
N
OH
[
2e]
Br
Ph
N
N
Ph
81
N
[
2f]
N
N
Br
p-Tol
7
8
p-Tol
4
83
95
N
[
2g]
Ph
Ph
N
N
Ph
PhCH Cl
Ph
2
3.5
N
[
2a]
N
N
PhCH Cl
p-Tol
3.5
p-Tol
94
9
2
N
[
2b]
1
0
PhCH Br
Ph
Ph
12
4
NR
2
Ph
N
Ph
N
84
1
1
Ph
Ph
Cl
Cl
Ph
N
[
2h]
Ph
Ph
N
N
1
2
3
p-Tol
4
4
4
p-Tol
8
5
N
[2i]
O
N
N
O
O
1
PhCH Br
72
81
2
O
N
[
2j]
N
1
4
PhCH Br
Cl
I
Ph
2
N N
Cl
[2k]
N
N
Ph
6
Ph
1
5
4
76
N
[
2l]
(1.2 mmol) and benzyl/allyl/cinnamyl/alkyl halide (1.1 mmol),
O (1:1, 2 mL).
Reaction conditions: Teminal alkynes (1 mmol), NaN
Cu–complex (0.5 mg, 0.1 mol%), Acetonitrile:H
3
2

5
a
Isolated yield after purification through column chromatography by silica gel.
benzyl/allyl/cinnamyl/alkyl azide was formed in-situ by the
substitution reaction between benzyl/allyl/cinnamyl/alkyl halide
and sodium azide. The polymeric copper acetylide moiety
reacted with benzyl/allyl/cinnamyl/alkyl azide via cycloaddition
fashion followed by elimination of the complex catalyst give rise
to 1,4–disubstituted 1,2,3–triazoles as the main product.
Mechanism
A probable mechanism for this multicomponent azide-alkyne-
cycloaddition reaction was proposed in Scheme 2. It was
presumed that the reaction was initiated by the metalation of
phenylacetylene in the presence of the 1D-CuI dithioether
polymeric complex giving copper acetylide. In the next step,
Scheme 2. A plausible mechanistic path for the Cu(I)–complex catalyzed one–pot three–component AAC reaction.
propargyl bromide (1 mmol) in presence of triethyl amine (2
mmol) in water at room temperature. After 2 hours, benzyl
Synthesis of sulfur functionalized 1,2,3–triazole
bromide (1.1 mmol) and sodium azide (1.2 mmol) and Cu(I)-
1
,2,3–triazoles containing diverse functional groups have
complex (0.5 mg, 0.1 mol%) were added to the reaction mixture.
The progress of the reaction was monitored by TLC and finally
the desired product was isolated in column chromatography (82%
yield). The preparation methodology is presented in Scheme 3.
strong potential as steel corrosion inhibitors or suitable ligands
18
for transition–metal chemistry. We have prepared sulfur
functionalized pendant arms of 1,2,3–triazole compounds in a
multicomponent approach via one–pot two–step reaction using
our catalyst. Benzenethiol (1.1 mmol) was first reacted with
SH
Et N
Water
N
N
3
Br
and NaN3
N
S
S
Br
+
RT, 2 h, Stirring
[
(CuI) {ArS(CH ) SAr} ]
2
2 3
2 n
[3a]
(
Ar = 4-F-C H )
6 4
0
.5 mg (0.1 mol%)
o
Acetonitrile:water (1:1), 50 C
Scheme 3. One–pot two–step synthesis of sulfur functionalized 1,2,3–triazole derivative.
Acknowledgements
Conclusion
This work was supported by Science and Engineering
Research Board of India (Grant No. EMR/2015/000549).
In conclusion, we have synthesized a suitably designed Cu(I)
coordination polymer based on dithioether ligands (SS,
bidentate), which can be used as efficient catalyst for AAC
reaction. The polymeric complex has been well characterized and
applied in variety of substrates and the desired 1,4–disubstituted
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1
temperature and low catalyst loading for the reaction are
noteworthy besides demonstrating the catalytic activity of S,S-
based Cu(I) coordination polymer. Further application of the
polymeric complex is under active pursuits.
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1

7
Highlights
1-D Copper(I) coordination polymer based
on bidentate 1,3-dithioether ligand: Novel
catalyst for azide-alkyne-cycloaddition
(
AAC) reaction
Sankar saha, Kinkar Biswas,* Baudeb Basu
Department of Chemistry, North Bengal University,
Darjeeling 734013, India

New Cu complex from CuI and 1,3-
Dithioether, characterized by single crystal
X-ray



Acts as a catalyst in AAC at low
concentration and ambient temperature
First example of SS-based Cu complex used
as catalyst in AAC
Extended to the synthesis of S-
functionalized pendent arms of 1,2,3-
triazole
—
——

Corresponding author. Tel.: +91-353-2776-381; fax: +91-353-
2
699-001; e-mail: basu_nbu@hotmail.com (B. Basu).