New 1,2-dithioether based 2D copper(I) coordination polymer: from synthesis to catalytic application in A3-coupling reaction

Article abstract of DOI:10.1080/00958972.2019.1627339

A new 2D copper(I) coordination polymeric complex has been synthesized from CuI and 1-(1-{4-chlorophenylthio}propan-2-ylthio)-4-chlorobenzene ([(CuI)₂{ArSCH₂CH(CH₃)SAr}₂]_n, Ar = 4-ClC₆H

Full text of DOI:10.1080/00958972.2019.1627339

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
New 1,2-dithioether based 2D copper(I)
coordination polymer: from synthesis to catalytic
3
application in A -coupling reaction
Sankar Saha, Kinkar Biswas, Pranab Ghosh & Basudeb Basu
To cite this article: Sankar Saha, Kinkar Biswas, Pranab Ghosh & Basudeb Basu (2019): New 1,2-
3
dithioether based 2D copper(I) coordination polymer: from synthesis to catalytic application in A -
coupling reaction, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2019.1627339
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2019.1627339
New 1,2-dithioether based 2D copper(I) coordination
polymer: from synthesis to catalytic application in
3
A -coupling reaction
a
b
a
a,b
Sankar Saha , Kinkar Biswas , Pranab Ghosh and Basudeb Basu
a
b
Department of Chemistry, North Bengal University, Darjeeling, India; Department of Chemistry,
Raiganj University, Raiganj, India
ABSTRACT
ARTICLE HISTORY
A new 2D copper(I) coordination polymeric complex has been
synthesized from CuI and 1-(1-f4-chlorophenylthiogpropan-2-
Received 12 February 2019
Accepted 21 May 2019
ylthio)-4-chlorobenzene ([(CuI)
2
fArSCH
2
CH(CH
3 2 n
)SArg ] , Ar ¼ 4-
KEYWORDS
ClC
6 4
H ) and characterized by high resolution mass spectrometry
Coordination polymer; 2D-
copper(I) complex; solvent-
(HRMS) and single crystal X-ray diffraction techniques. The com-
plex has been employed as a suitable catalyst for a solvent-free,
3
free; A -coupling;
3
one-pot, three-component A -coupling reaction. A variety of aro-
propargyl amine
matic and aliphatic aldehydes, terminal alkynes and aliphatic cyc-
lic secondary amines have been used to prepare a library of
propargylamines using the 2D-Cu complex at significantly low
concentration (0.2 mol%).
1. Introduction
Coordination polymers of copper halides with infinite network structures composed
with organic ligands are widely reported due to the presence of their enthralling phys-
ical and chemical properties [1]. For example, Cu(I) halide-based compounds have
been widely explored due to their attractive structural characteristics and possible
applications in luminescence-based sensors, photophysical phenomena, and biological
probes [2]. They also find catalytic applications in various organic transformations
[3–8]. N- and P-based ligands and Cu complexes are employed in catalytic applications
CONTACT Basudeb Basu
basu_nbu@hotmail.com
Supplemental data for this article can be accessed https://doi.org/10.1080/00958972.2019.1627339.
ß 2019 Informa UK Limited, trading as Taylor & Francis Group

2
S. SAHA ET AL.
[4–9]. Interestingly, metal complexes with 1,2-dithioether ligands are rarely synthesized
and used as catalysts except for one recent report that describes the synthesis of a 1,2-
dithioether and Cu(I) halide-based 2D complex and its catalytic application in aminome-
thylation of phenylacetylene. They have shown one example of catalytic use of the com-
plex in the synthesis of propargylamine but the catalyst loading was high (5 mol%) [10].
Propargylamines are versatile building blocks for the preparation of various N-containing
heterocyclic compounds as well as key intermediates for the synthesis of pharmaceuticals
and natural products [11–13]. They also act as key intermediates for the construction of
biologically active compounds such as b-lactams, oxotremorine substrates, conformation-
ally restricted peptides, and therapeutic drug molecules [14]. Because of their importance,
many synthetic methods have been developed [15–18].
The classical methodologies are less attractive due to their low tolerance of functional
groups, harsh reaction conditions, and operational difficulty [19, 20]. However, the most
direct and efficient method for the preparation of propargylamines can be achieved
through transition-metal catalyzed three-component coupling between an aldehyde, an
3
amine and a terminal alkyne, which is commonly known as an A -coupling reaction [21].
3
Among various synthetic methods, the copper-catalyzed A -coupling is the most common
due to its easy availability, low cost, low toxicity, and high reactivity [22, 23].
Trivalent phosphorus ligands have been used to control the metal center that lead to
metal catalysts with improved reactivity and stability. Garcia et al. reported a diallylphos-
3
phine-tetrameric copper(I) complex catalyzed A -coupling reaction for preparing propar-
gylamine [4]. Apart from the phosphorous ligands, nitrogen-based Cu(I) compounds have
3
also been used for A -coupling reaction. For example, a nitrogen-based 1-D Cu(I)-coordin-
ation polymer [5], a benzotriazole-based homogeneous and air-stable Cu-coordination
compounds [6], and a dicopper (I) complex based on 2-picolyliminomethyl ligand [7] have
3
been used in A -coupling reactions. A thioether-based Schiff base Cu(I) complex has been
3
used as the catalyst for an asymmetric type A -coupling reaction [24]. Since the use of
only CuI as catalyst requires prolonged times to complete the reaction, the presence of a
3
co-catalyst or microwave irradiation is mandatory for facile A -coupling reactions [9, 25].
Interestingly, though the S-based copper complexes are widely known, their catalytic
applications are quite limited as compared to the corresponding N- and P-based copper
complexes. We report herein the synthesis of a new coordination polymer of CuI attached
to the bidentate 1,2-dithioether [1-(1-(4-chlorophenylthio)propan-2-ylthio)-4-chloroben-
zene] and characterize it by single crystal X-ray diffraction. The 2-D Cu(I)-1,2-dithioether
3
coordination polymer catalyst works efficiently in A -coupling reactions under solvent-free
ꢀ
condition at 80 C to afford propargylamines in good to excellent yields. A summary of
3
the previous catalytic A -coupling reactions along with the present work has been sche-
matically presented in Scheme 1. This clearly shows the catalytic application of various
3
Cu(I) monomeric and polymeric complexes based on P- and N-ligands in A -coupling reac-
tions. However, to the best of our knowledge, there is no example of a polymeric 2D
Cu(I) complex with 1,2-SS-based bidentate ligands used as the catalyst for the synthesis of
3
propargylamines via A -coupling reaction. The present work thus demonstrates not only a
new CuI-based complex as the catalyst for three-component reaction, but also shows the
potentiality of using 1,2-dithioethers as the chelating ligands for making metal complexes
and their catalytic applications in organic reactions.

JOURNAL OF COORDINATION CHEMISTRY
3
Copper complex (0.1 to 10
mol%)
Ref. 22, 23
o
(
Solvent, temp 80-100 C
ic
r
e
time= 5-48 h)
m
o
on
M
2 2
Cu (pip) , 0.4 mol%
toluene, 100 oC, 2h
yield = 81-98%
c
ri
e
Ref. 7
Ref. 4
im
D
SS ligand based 2D-CP
(CuI) {ArSCH CH(CH )SAr}
Ar = 4-Cl-C
mg (0.2 mol%)
[
2
2
3
2 n
]
3
6
H
4
A reaction
Cu-phosphine
1
N
H
+
N
Tetrameric 0.5 mol%
Catalyst
Solvent, temp.
Present work
Neat, 80 oC, 4h
yield = 82-96%
O
R1
Neat, 50 oC, 6 h,
yield = 15-99%
R1
time
R2
H
R2
Polymeric
P
1D-Cu CP with
o
ly
N-based ligand, 5 mol%
P
m
o
eri
Ref. 5
l
Neat, RT, 6 h,
y
c
m
e
yield = 89-94%
r
i
c
only aliphatic aldehyde used
N-based Cu(II)-CPs
2
mol%
Ref. 6
i
PrOH, 90 oC, 12h
yield = 57-100%
3
Scheme 1. Various copper complexes used as catalysts in A -coupling reaction.
2. Experimental
2.1. Materials and methods
Phenylacetylene, p-bromophenylacetylene, and cyclohexylcarboxaldehyde were purchased
from Sigma ꢁ Aldrich and used directly as obtained. Benzaldehyde and salicylaldehyde
were purchased from Merck and used without purification. All other aldehydes were pur-
chased from SD Fine Chemical Limited, India. Morpholine, piperidine, and pyrrolidine were
purchased from Lancaster and used after distillation. The solvents were purchased from
Thomas Baker (Chemicals) Pvt. Ltd., India and used after distillation. All the products were
purified by column chromatography on 60–120 mesh silica gels (SRL, India). For TLC,
Merck plates coated with silica gel 60, F254 were used. The catalyst was weighed by using
a Mettler-Toledo digital balance (0.1 mg sensitivity). FT-IR spectra were recorded with a
FT-IR-8300 SHIMADZU spectrophotometer using a KBr pellet for solid compounds and
1
13
neat for semi-solid or liquid compounds. H and C NMR spectra were recorded at
00 MHz and 75 MHz, respectively, on a Bruker AV 300 spectrometer in CDCl . Splitting
3
3
patterns of protons were described as s (singlet), d (doublet), t (triplet), bs (broad singlet),
dd (doublet of doublet), and m (multiplet). Chemical shifts (d) were reported in parts per
million (ppm) relative to TMS as internal standard. J values (coupling constant) were
13
reported in Hz (Hertz). C NMR spectra were recorded with complete proton decoupling
CDCl : d 77.0 ppm). HRMS was performed by a Micromass Q-TOF Spectrometer under ESI
(
3
(positive mode) at the Indian Association for the Cultivation of Science.
2.2. Crystal structure determination
Suitable crystals of the compound were obtained by slow evaporation of its saturated
solution using the diffusion method. Single-crystal diffraction studies were carried out
using a Bruker D8 Quest CMOS diffractometer with a Mo Ka (l ¼ 0.71073 Å) sealed
tube. The data frames were obtained using the program APEX3 and processed using
the program SAINT in APEX3 [26]. The structures were solved by direct methods and

4
S. SAHA ET AL.
refined using the SHELXTL-2014/7 program [27]. The structures were refined by full-
2
matrix least-squares (SHELXL2014-7) on F [28]. Non-hydrogen atoms were refined
with anisotropic displacement parameters. All hydrogens were positioned at their
idealized positions using a riding model. The molecular structure figures were pre-
pared using DIAMOND version 3.2 [29]. Table 1 provides the data collection and struc-
ture solving parameters for the compound. Selected bond distances and angles for
the compound are given in Tables 2 and 3.
2.3. General procedure of preparing CuI-L (1,2-bis(4-chlorophenylthio)-
propane)-coordination complex (1) Catena-poly [di-l-iodido-bis[(1,2-bis(4-
chlorophenylthio)-propane)-copper (I)]]
The dithioether ligand (L) was synthesized according to our previously reported pro-
cedure [30]. L (329 mg, 1.0 mmol) and CuI (95 mg, 0.5 mmol) in acetonitrile (2 mL) were
Table 1. Crystal data, data collection, and structure refinement for the complex.
Formula
15 2 2
C H14Cl CuIS
Formula weight
Temperature/K
Description
Color
519.73
296(2)
Block
White
Crystal system
Space group
a/Å
b/Å
c/Å
Cell angle (a)
Cell angle (b)
Cell angle (c) 3
Cell volume/Å
Cell formula units Z
Density (calculated) g/cm
Orthorhombic
Pbca
10.0087(5)
15.4384(10)
23.6978(14)
ꢀ
90
90
90
ꢀ
ꢀ
3661.7(4)
8
3
1.886
h Range for data collection/deg
F(000)
Crystal size/mm
Absorption co-efficient (l)
Index ranges
2.42–27.48
2016
0.216, 0.284, 0.320
3.389
ꢁ12 ꢂ h ꢂ 13
ꢁ
20 ꢂ k ꢂ 20
ꢁ
30 ꢂ l ꢂ 30
Reflections collected
Independent reflections
Refinement method
R-equivalents
62648
4182
2
Full-matrix least-squares on F
0.0285
0.0119
Sigma I/net I
Table 2. Selected bond lengths.
Bond
Length
I3–Cu1
I3–Cu1
Cu1–S2
Cu1–S1
Cu1–I3
Cu1–Cu1
S1–C4
2.6119(4)
2.6182(4)
2.3539(7)
2.3990(7)
2.6182(4)
2.8979(8)
1.779(2)
S1–C1
1.828(2)
S1–Cu1
2.3990(7)

JOURNAL OF COORDINATION CHEMISTRY
5
Table 3. Selected bond angles.
Bond
Angle
Cu1–I3–Cu1
S2–Cu1–S1
S2–Cu1–I3
S1–Cu1–I3
S2–Cu1–I3
S1–Cu1–I3
I3–Cu1–I3
67.296(15)
96.07(2)
123.28(2)
110.344(19)
102.56(2)
110.42(2)
112.705(15)
taken in a 25 mL round-bottomed flask. The mixture was stirred at room temperature
for 4 h and then refluxed for 24 h. After cooling to room temperature, petroleum ether
was added dropwise to the solution and the solution kept in a refrigerator. After two
days, shining white crystals of the complex were separated by simple filtration, fol-
lowed by washing with dry petroleum ether (2 ꢃ 5 mL), and finally dried in a vacuum
desiccator. The 2-D polymeric complex compound (1) from CuI and 1,2-dithioether
was found in 74% yield (384 mg).
3
2
.4. General procedure for A -coupling reaction
A mixture of aldehyde (1.0 mmol), secondary amine (1.0 mmol), terminal acetylene
ꢀ
(
1.1 mmol), and the polymer catalyst (ꢄ1.0 mg) was magnetically stirred at 80 C in
an open reaction vessel for hours. The progress of the reaction was monitored by
TLC. After completion of the reaction (disappearance of the alkyne spot on TLC),
the reaction mixture was cooled to room temperature, dichloromethane (5 mL) was
added, concentrated, and adsorbed on silica gel. The dry silica-adsorbed material
was passed through a bed of silica gel in a column and elution with a light petrole-
um:ethyl acetate solvent mixture (in varying proportions) afforded the desired
propargylamine.
3
. Results and discussion
.1. Characterization of the complex
The CuI-1,2-dithioether 2-D polymeric complex (1) was characterized by H NMR,
3
1
13
C
NMR spectroscopy, HRMS spectrometry (Supplementary Materials) and by single crystal
X-ray diffraction (XRD) techniques. The d values of proton and carbon in complex (1)
1
13
were shifted downfield compared to the ligand (L) in both H NMR and C NMR spec-
tra, indicating the formation of the complex. Single crystal XRD analysis (Table 1)
revealed that 1 crystallizes in the orthorhombic Pbca space group and shows a poly-
meric propagation in the form of the [(CuI) fArSCH CH(CH )SArg ] (Ar ¼ 4-ClC H )
2
2
3
2 n
6 4
metallopolymer (Figure 1) [31–33]. The ORTEP diagram of the complex is given in
Figure 1(a). The 2D-network is built up of dimeric Cu I units which are interconnected
2
2
via dithioether ligands. Within the cluster core, the Cu–I bond lengths range between
.6119(4) and 2.6182(4) Å. The interatomic distance between two Cu within the Cu2I2
cluster is 2.8979(8) Å, significantly larger than the sum of the van der Waals radius (2.
0 Å) [34]. The mean Cu–S bond length, range between 2.3539(7) and 2.3990(7) Å, is a
2
8

6
S. SAHA ET AL.
Figure 1. (a) ORTEP diagram of the ([(CuI) fArSCH CH(CH )SArg ] , Ar ¼ 4-ClC H ) complex, 1. (b)
2
2
3
2 n
6 4
Two-dimensional framework of complex 1.
little in excess of that seen in [fCu(l-I) Cug fl-PhS(CH ) SPhg ] (2.3465 Å) and
2
2
2 3
2 n
(
[(CuI) fArS(CH ) SArg ] , Ar ¼ 4-FC H ); range between 2.3339(11) and 2.3551(12)
2
2 3
2 n
6 4
ꢀ
Å) [31, 35]. The angle Cu … I … Cu is 67.296(15) and the angle I … Cu … I is 112.
7
ꢀ
05(15) in the metallocluster. The polymeric framework of 1 is formed by the con-
nection of Cu I unit and four 1,2-dithioether linkers L. Each 1,2-dithioether coordi-
2
2
nates via its S-donor atoms to two Cu I units, while each Cu I unit connects with
2
2
2 2
four 1,2-dithioether ligands (L). This gives a 2-D shaped network matrix topology
Figure 1(b)). The crystal data, data collection, and structure refinement of the poly-
(
meric complex are given in Table 1. Selected bond lengths and angles of the com-
plex are also given in the Tables 2 and 3, respectively. The refined bond length
and angles are given in the Supplementary Materials (Tables S1 and S2, respect-
ively, under 2.2).

JOURNAL OF COORDINATION CHEMISTRY
7
3.2. The catalytic activity of copper complex 1
3
The catalytic activity of the complex towards A -coupling reactions was optimized in a
model reaction of phenyl acetylene, benzaldehyde, and morpholine under varying
catalyst loading, different temperatures and solvents (Table 4). Initially, the reaction of
phenylacetylene (1.1 mmol), benzaldehyde (1.0 mmol), and morpholine (1.0 mmol) was
ꢀ
performed in acetonitrile at 60 C for 8 h using 5 mg of the complex as catalyst. A
trace amount of conversion was achieved (entry 1). Raising the temperature of the
ꢀ
medium from 60 to 80 C gave 40% yield of the product (entry 2). Using polar hydrox-
ylic solvents e.g. ethanol and water, the yield of the product was ꢄ50% (entries 3 and
4
). In a binary solvent mixture (acetonitrile:water ¼ 1:1), the conversion was increased
to 65% (entry 5). When the reaction was studied under neat conditions, the yield of
the product was significantly increased to 91% (entry 6). Decreasing the amount of
the catalyst from 5.0 mg to 3.0 and 1.0 mg (±0.1 mg) (approx. 0.2 mol%), respectively,
did not affect the overall yield of the product (90% yield in both cases; entries 7 and
8). Reducing the reaction time did not show any significant drop in the yield of the
desired product (entries 9 and 10). A reaction performed without any catalyst did not
produce any desired product after 24 h (entry 11). On the other hand, conducting the
experiment at room temperature showed traces of product after 24 h (entry 12). We
also performed the reaction using CuI as the catalyst under similar reaction conditions
affording the product in relatively lower yield (55%; entry 13). Among the different
conditions attempted, the best condition was optimized as the presence of 1 mg
3
Table 4. Optimization of reaction conditions for the 2-D Cu(I)-polymeric complex catalyzed A -
coupling reaction.
O
H
O
[(CuI) {ArSCH(CH )CH SAr} ]
2
3
2
2 n
H
N
Ar = 4-Cl-C H
N
6
4
x mg
Solvent/Neat, Temperature
O
ꢀ
a
Entry
Solvent
Cu-catalyst (mg)
Temp. ( C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
Acetonitrile
Acetonitrile
Ethanol
Water
Acetonitrile:water
5
5
5
5
5
5
3
1
60
80
80
80
80
80
80
80
80
80
80
RT
80
8
8
8
8
8
8
8
8
6
Traces
40
52
50
65
91
90
90
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
1
88
88
b
1
1
1
1
0
1
2
1 ± 0.1 ~ 1
4
–
1
1
24
24
4
No reaction
Traces
55
c
3
Reaction conditions: phenyl acetylene (1.1 mmol), benzaldehyde (1.0 mmol) and morpholine (1.0 mmol), Cu-complex
5 mg to 1 mg), Neat.
(
a
Isolated yield after purification through column chromatography over silica gel.
Error in the measurement of the catalyst is ±0.1 mg.
b
c
CuI was used as catalyst.
The bold values refer to the optimized reaction conditions used for the reaction.

8
S. SAHA ET AL.
(
8
±0.1 mg) (approx. 0.2 mol%) catalyst under solvent-free and aerobic conditions at
0 C (entry 10).
ꢀ
In order to explore the generality of the optimized reaction conditions, different
types of substrates such as secondary amines with different types of aldehydes were
allowed to react with terminal acetylenes. Very good to excellent isolated yields of the
products have been achieved under this protocol (Table 5). In Table 5, it is clearly evi-
dent that various aldehydes including electron releasing or withdrawing groups such
as OMe, OH, Br, Cl as well as benzaldehyde reacted smoothly with terminal alkynes
(
phenyl acetylene and 4-bromophenyl acetylene) and cyclic secondary amines (mor-
pholine, piperidine and pyrrolidine). Furthermore, the reaction of an alicyclic aldehyde
cyclohexanecarboxaldehyde) and straight-chain aliphatic aldehyde (n-heptanal) with
(
morpholine and phenylacetylene were performed efficiently and afforded the desired
products in brilliant yields (entries 9 and 10).
3.3. Probable mechanism
3
The most possible mechanism of the A -coupling reaction is believed to proceed via
the activation of the C –H bond of the terminal alkyne by the copper catalyst (here
sp
the new coordination 2D polymer complex derived from CuI and 1,2-dithioether). The
resulting four-coordinate alkynyl–Cu intermediate (3), formed by the dissociation of
one thioether ligand, then reacts with the iminium ion generated in situ from alde-
hyde and secondary amine to produce the corresponding propargylamine product.
The proposed mechanism is outlined in Scheme 2.
3
Table 5. Catalytic activities of the 2-D Cu(I)-polymeric complex catalyzed A -coupling reaction.
[
(CuI) {ArSCH(CH )CH SAr} ]
2
3
2
2 n
H
X
H
Ar = 4-Cl-C6H4
1
+_ 0.1 mg (approx. 0.2 mol%)
X
n
n
R1
N
O
HN
o
Neat, 80 C, 3-4 h
R2
R1
X = O, CH
n = 1, 2
2
R2
o
a
Sl No.
Aldehyde
2 Amine
Alkyne
Ph
Ph
Ph
Ph
Ph
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
4 ꢁ OMeꢁC6H4CHO
4 ꢁ BrꢁC6H4CHO
4 ꢁ C1ꢁC6H4CHO
2 ꢁ C1ꢁC6H4CHO
C6H5CHO
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Piperidine
4
4
4
4
4
4
4
3
3.5
3.5
4
3
4
3
4
87
92
96
88
88
95
92
85
91
86
93
90
82
92
91
3; 5ꢁBrꢁC6H3CHO
4ꢁOMeꢁC6H4CHO
2ꢁOHꢁC6H4CHO
Cy ꢁ CHO
Ph
4ꢁBrꢁC
4ꢁBrꢁC
Ph
6
H
H
4
6
4
10
11
12
13
14
15
nꢁC6H13 ꢁ CHO
4ꢁOMeꢁC6H4CHO
2ꢁOHꢁC6H4CHO
4ꢁOMeꢁC6H4CHO
2ꢁOHꢁC6H4CHO
4ꢁOMeꢁC6H4CHO
Ph
Ph
Ph
Ph
Piperidine
Pyrrolidine
Pyrrolidine
Pyrrolidine
Ph
4ꢁBrꢁC H
6 4
Reaction conditions: phenyl acetylene/4-bromo phenyl acetylene (1.1 mmol), aldehyde (1.0 mmol) and morpholine/
piperidine/pyrrolidine (1.0 mmol), Cu-complex (1 ± 0.1 mg, approx. 0.2 mol%) in neat condition.
Isolated yield after purification through column chromatography by silica gel.
a

JOURNAL OF COORDINATION CHEMISTRY
9
H
SH
S
S
I
S
S
Cu Cu
I
2)
R1
(
S
I
S
S
R CHO+ H N
Cu Cu
I
H
3
A -Coupling
(
3)
R1
Catalytic cycle
R1
R C N
H
(
4) iminium ion
S
I
S
N
R
Cu Cu
I
(
R1
S
S
SH
1)
Propargyl amine
2-D polymeric
complex
3
Scheme 2. A probable mechanism of Cu(I)-complex catalyzed A -coupling reaction.
4. Conclusion
We have demonstrated the synthesis and characterization of a new 2D-Cu(I) coordin-
ation polymer of 1,2-dithioether ligands (SS, bidentate) and its catalytic application in
3
A -coupling reactions for the synthesis of various propargylamine derivatives under
solvent-free conditions. Easy preparation of the copper complex, low catalyst loading
(0.2 mol%), mild catalytic conditions and wider applicability to different reacting part-
ners are notable features. The catalyst however performs better in the case of cyclic
secondary amines. As the dithioether-based chelating ligands and corresponding cop-
per complexes are less known in catalysis, we expect that the present work would
encourage newer S,S-based copper complexes for catalytic applications. The choice of
chloro-substituted ligands, however, does not carry any specific significance except
physical parameters, easy characterization, etc.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the Science and Engineering Research Board of India under Grant
Number EMR/2015/000549.
References
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