Synthesis of new Copper Catalyst with Pyrazole Based Tridentate Ligand and Study of Its Activity for Azide Alkyne Coupling

Article abstract of DOI:10.1016/j.jorganchem.2020.121627

Synthesis of new copper catalyst with pyrazole based tridentate ligand and study of its activity for azide alkyne coupling were investigated by researchers. To a solution of acetyl acetone (2.002 g, 20 mmol), 2- nitrophenylhydrazine in ethanol was added five drops of con. HCl and heated at 50° for 1 hour. After confirming the formation of 3, 5-dimethyl-1-(2-nitrophenyl)- 1H-pyrazole by TLC, ice cooled water was added in to the reaction mixture. The precipitate was filtered, washed with water and then hexane. The product formed as yellow precipitate, that precipitate had been filtered by normal filter paper. The product was recrystallized in ethanol. For synthesis, was suspended in 6 mL of deionized and stirred for 4 h until a clear solution was obtained in 50 ml round bottom flask Cu(OAc) ₂. The reaction mixture was diluted with water, filtered, washed sequentially with water, methanol and n-hexane. Then dark greenish blue color crystal were formed and used for the reactions. The solid was crystallized in CH₂Cl₂ to get crystal whose structure was confirmed by single crystal XRD.

Full text of DOI:10.1016/j.jorganchem.2020.121627

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Synthesis of new Copper Catalyst with Pyrazole Based Tridentate
Ligand and Study of Its Activity for Azide Alkyne Coupling
Panneer Selvam Rajeswari , Rajendran Nagarajan , Sujith K P ,
Lourdusamy Emmanuvel
PII:
S0022-328X(20)30530-1
DOI:
Reference:
https://doi.org/10.1016/j.jorganchem.2020.121627
JOM 121627
To appear in:
Journal of Organometallic Chemistry
Received date:
Revised date:
Accepted date:
4 June 2020
15 October 2020
17 November 2020
Please cite this article as: Panneer Selvam Rajeswari , Rajendran Nagarajan , Sujith K P ,
Lourdusamy Emmanuvel , Synthesis of new Copper Catalyst with Pyrazole Based Tridentate Ligand
and Study of Its Activity for Azide Alkyne Coupling, Journal of Organometallic Chemistry (2020), doi:
https://doi.org/10.1016/j.jorganchem.2020.121627
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Highlights:
1) Here we synthesized pyrazole based tridentate ligand and its copper(II) catalyst in
simple route.
2) We have also studied the efficiency of the catalyst for the azide-alkyne cycloaddition
and azide reduction reactions.
3) The ligand as well as the catalyst were well studied with spectroscopic techniques and
single crystal XRD.

Synthesis of new Copper Catalyst with Pyrazole Based Tridentate Ligand
and Study of Its Activity for Azide Alkyne Coupling
Panneer Selvam Rajeswaria,1, Rajendran Nagarajanb,1, Sujith K Pa, Lourdusamy
Emmanuvela*
a Department of Applied Chemistry, Karunya Institute of Technology and Sciences, Karunya
Nagar, Coimbatore, 641114, India
b Department of Chemistry, Kongju National University, Gongju, Chungnam 32588, Republic
of Korea
1Panneer Selvam Rajeswari and Rajendran Nagarajan have contributed equally to this work
E-mail:emmanuvel@karunya.edu Fax: 0422-2615615 Ph: +919042678370
Keywords: Tridentate ligand, copper catalyst, Click reaction, azide reduction, pyrazole
1. Introduction
Transition metal complexes have emerged as one of the important members of
catalyst for organic reactions in the last few decades [1]. More specifically, copper complexes
have received more attention due to their redox behaviour, ability to form stable complex
readily with several ligands, easy accessibility and economic reasons [2]. Copper(II) is also
an essential trace element in all living system which has so many important biological role
like oxygen transport and redox reactions [3]. In the recent past, several research groups have
studied the anticancer activity of Copper(II) complexes which contain derivatives of sevevral
heterocycles [4]. They have also been studied for biological activities such as cytotoxicity
against cancer cells, anticancer activity, antiviral activity and DNA and protein cleavage
activity [5]. In particular, copper(II) complexes containing pyrazole derivative show
antitumor activity similar to that of cisplatin [6]. Also, this pyrazole moiety in copper(II)
complexes has some promising pharmacological, agrochemical and analytical applications
[7].
Copper complexes are widely used in the organic transformation including
asymmetric synthesis, [3+2] cycloaddition between azide and alkyne, popularly known as
click reaction [8], cyclopropanation of diazo compounds via carbenoid [9], aldol-type
reaction, Mannich reaction [10], Diels-Alder reaction [11] are a few to be highlighted. The

most common types of ligands for copper include bisoxazoline, Phenanthroline, salen, imine
and amine based ligands (Fig.1)
Fig.1: Common types of ligands for Copper
The copper(II)-catalysed Huisgen [3+2] dipolar Cycloaddition (CuAAC) [12] between
terminal alkynes and organic azide has arguably become the most popular ligation reaction to
give 1,4-disubstituted 1,2,3-triazoles and exhibits remarkably broad scope and exquisite
selectivity. Thus obtained 1,2,3-triazole derivatives have been utilized as dyes, photo
stabilizers, agrochemicals, and biochemical polymer, drug discovery, advanced material
science, etc [13].
More attention has been paid to the development of copper(I) catalytic
systems for CuAAC reactions, a direct method for the preparation of a extensive range of
five-membered ring heterocycles [14]. Most of the described catalytic system generate Cu(I)
via in situ reduction of Cu(II) by sodium ascorbate, oxidation of Cu(0) to Cu(I) via oxidation
or Cu(II)/Cu(I) comproportionation reactions. Copper(I) salts are least used because of their
common thermodynamic instablility [15], except copper(I) iodide.
2. Experimental Section
2.1. Synthesis of 3,5-dimethyl-1-(2-nitrophenyl)-1H-pyrazole (C).
To a solution of acetyl acetone (2.002 g, 20 mmol), 2-nitrophenylhydrazine (3.369 g, 22
mmol), in ethanol (60 ml) was added five drops of con. HCl and heated at 50 oC for 1 h. After
confirming the formation of 3, 5-dimethyl-1-(2-nitrophenyl)-1H-pyrazole by TLC, ice cooled
water is added in to the reaction mixture. The precipitate was filtered, washed with water and
then hexane. The product will form as yellow precipitate, that precipitate has been filtered by
normal filter paper. The product was recrystallized in ethanol. Brown solid, 95% (4.1265 g),

m.p 78 oC, IR (ν, cm-1): 3444, 2923, 2104, 1612, 1527, 1359, 1118, 785. 1H NMR (400 MHz,
CDCl3): δ 7.99 (d, 1H, J = 8 Hz), 7.72 (t, 1H, J = 8 Hz), 7.59 (t, 1H, J = 8 Hz), 7.50 (d, 1H, J
= 8 Hz), 6.03 (s, 1H), 2.25 (s, 3H), 2.19 (s, 3H). 13CNMR (75 MHz, CDCl3): δ 150.52,
146.43, 141.01, 133.23, 133.17, 129.54, 129.28, 125.12, 106.87, 13.50, 11.36. HRMS (ESI):
m/z [M + H]+ calcd for: C11H11N3O2 Calculated=217.2239, found= 217.2238.
2.2. Synthesis of 2-(3,5-dimethyl-1H-pyrazol-1-yl)aniline (D)
To a solution of 3, 5-dimethyl-1-(2-nitrophenyl)-1H-pyrazole (3.8 g, 17.49 mmol) in ethanol
o
(50 ml) at 0 C was added SnCl2 (17.165 g, 76.07 mmol) portion wise over a period of 10
min. After complete addition of SnCl2, the reaction mixture was slowly brought to room
temperature and then refluxed for 4 h. After completion of the reaction, ice-cold water was
added to the reaction mixture and neutralized with 20% NaOH. The compound was extracted
with ethyl acetate, dried over anhydrous sodium sulphate concentrated under reduced
pressure to get light brown powder. The product was pure enough and used as such in the
next reaction without column chromatographic purification. Light brownish solid, 78%,
o
1
(2.5548 g) m.p 79 C, IR (ν, cm-1): 3419, 2916, 1629, 1506, 1029, 746. H NMR (400 MHz,
13
CDCl3):δ 8.41 (m, 4H, J = 4, 4 Hz), 7.25 (s, 1H), 5.42 (s, 2H), 3.54 (s, 3H), 3.40 (s, 3H). C
NMR (75 MHz, CDCl3): δ 153.75, 148.64, 145.39, 134.13, 132.24, 129.94, 122.15, 121.26,
110.35, 18.42, 16.23. HRMS (ESI): m/z [M + H]+ calcd for: C11H13N3 Calculated=187.2410,
found= 187.2411.
2.3. Synthesis
of
tridentate
ligand
[(E)-1-(((2-(3,5-dimethyl-1H-pyrazol-1-
yl)phenyl)imino)methyl)naphthalen-2-ol]
A pressure tube was charged with 2-(3, 5-dimethyl-1H-pyrazol-1-yl) aniline (187.24 mg, 1
mmol), 2-hyroxy-1-naphthaldehyde (172.18 mg, 1 mmol), NH4OAc (77. 08 mg, 1 mmol) and
o
ethanol (3 ml) and was heated at 75 C for 12 h. After confirming the formation of pyrazole
derivative by TLC, ice cooled water was added in to the reaction mixture and was extracted
with ethyl acetate, dried over anhydrous sodium sulphate concentrated under reduced
pressure to get reddish brown semi solid as crude which was purified by column
chromatography (silica gel) using pet.ether/ethyl acetate (80:20) to get pure compound.
Reddish brown gummy compound, 94% (319 mg), m.p 72 oC, IR (ν, cm-1): 3425, 2916, 1618,
1550, 1165, 746. 1H NMR (400 MHz, CDCl3): δ 14.55 (s, 1H), 9.15 (s, 1H), 8.02 (t, 1H, J =
8, 8 Hz), 7.81 (t, 1H, J = 12, 8 Hz), 7.73 (t, 1H, J = 8, 8 Hz), 7.57 (m, 3H, J = 8, 4 Hz), 7.42

(m, 2H, J = 8, 12 Hz), 7.19 (t, 1H, J = 8, 8 Hz ) 7.07 (t, 1H, J = 12, 8 Hz), 2.32 (s, 3H), 2.09
(s, 3H). 13C NMR (75 MHz, CDCl3): δ 167.40, 158.05, 143.33, 140.78, 136.30, 132.99,
132.51, 130.02, 129.20, 127.96, 127.32, 126.68, 123.56, 121.08, 120.43, 119.22, 117.63,
116.46, 109.20, 106.04, 13.57, 11.24. HRMS (ESI): m/z [M + H]+ calcd for: C22H19N3O
Calculated=341.4058, found= 341.4060.
2.4. Synthesis of catalyst F
In 50 ml round bottom flask Cu(OAc)2 (074.42 mg, 0.3315 mmol) was suspended in 6 mL of
deionized water and stirred for 4 h until a clear solution was obtained. To this solution (E)-1-
(((2-(3,5-dimethyl-1H-pyrazol-1-yl)phenyl)imino)methyl)naphthalen-2-ol
(230.44 mg,
0.675 mmol) in methanol (3 mL) was added drop wise and stirred for another 24 h. The
reaction mixture was diluted with water, filtered, washed sequentially with water, methanol
and n-hexane. Then dark greenish blue color crystal were formed and used for the reactions.
The solid was crystallized in CH2Cl2 to get crystal whose structure was confirmed by single
crystal XRD.
2.5. General experimental procedure for the preparation of triazole via azide alkyne
coupling
To a solution of alkene (3 mmol) and azide (3 mmol) in 12 mL of a 1:1 water/tert-butanol
mixture. Sodium ascorbate (0.3 mmol) was added, followed by copper ligand catalyst (0.03
o
mmol, 1 mol %). The reaction mixture was stirred vigorously at 80 C for 5h. After the
completion of the reaction as indicated by TLC, the reaction mixture was diluted with ethyl
acetate and water and extracted three times with EtOAc. The combined organic layer was
dried over anhydrous sodium sulphate and evaporated under reduced pressure to get the
colorless solid which was further purified by column chromatography using silica gel and
ethyl acetate: petroleum ether (1:9) as eluent gave the pure tri azole. The common triazole
compounds were confirmed by comparing melting points and retention time in HPLC with
authentic sample.
5-phenyl-1-tosyl-1H-1,2,3-triazole – Compound (3a)
White solid 90% yield. mp: 170 o C 1H NMR (400 MHz, CDCl3): δ = 2.36(s, 3H), 7.12 –
7.14 (m, 2H), 7.34 (s, 1H), 7.36-7.50 (m, J=7.0 HZ 4H), 7.86-7.88 (d, 2H) 8.35 (s,1H). 13C
NMR (100 MHz, CDCl3): δ = 21.2, 125.9, 126.0, 127.6, 128.6, 129.4, 130.7, 138.3, 145.6,
146.0.
5-phenyl-1-(phenylsulfonyl)-1H-1,2,3-triazole – Compound (3b)

o
White solid 79% yield. mp: 138 C 1H NMR (400 MHz, CDCl3): δ = 7.12 – 7.14 (m, 2H),
7.34 (s, 1H), 7.36-7.50 (m, J=7.0 HZ 4H), 7.86-7.88 (d, 2H) 8.35 (s,1H). 13C NMR (100
MHz, CDCl3): δ = 21.2, 125.9, 126.0, 127.6, 128.6, 129.4, 130.7, 138.3, 145.6, 146.0.
3-(Toluene-4-sulfonyl)-3H-[1,2,3]triazol-4-yl]-methanol Compound (3c)
Milk white solid 80% yield. 1H NMR (400 MHz, CDCl3): δ=2.44 (s, 3H), 3.86 (s, 2H) 4.81
(s, 1 H) 7.33 – 7.35 (t, 3 H), 7.93 – 7.96 (d, 1H). 13C NMR (100 MHz, CDCl3): δ = 22.1,
57.9, 126. 3, 128.7, 130, 130.1, 135.3, 138.3, 145.
5-phenyl-1-(p-tolyl)-1H-1,2,3-triazole – Compound (3d)
white solid (yield 85%). mp: 84oC. 1H NMR (400 MHz, CDCl3): δ= 2.26(s, 3H), 7.25-
7.47(m, 7H), 7.92(t, J=4.4 Hz, 2H), 7.96(s, 1H).13C NMR (100 MHz, CDCl3): δ= 17.8,
121.0, 125.7, 125.8, 126.7, 128.2, 128.8, 129.8, 130.3, 131.4, 133.6, 136.4, 147.5
1,5-diphenyl-1H-1,2,3-triazole – Compound (3e)
white solid (yield 98%). mp: 185-186oC. 1H NMR (400 MHz, CDCl3): δ= 7.36(t, J=7.4 Hz,
1H) 7.43-7.48(m, 3H), 7.52-7.56(m, 2H), 7.80(t, J=4.6 Hz, 2H), 7.92(d, J=7.2 Hz, 2H),
7.92(d, J=7.2 Hz, 2H), 8.20(s, 1H), 13C NMR (100 MHz, DMSO): δ=119.5, 119.9, 125.3,
128.1, 128.6, 128.3, 129.8, 130.2, 136.6, 147.2.
1-(2-chlorophenyl)-4-phenyl-1H-1, 2, 3-triazole – Compound (3f)
brown solid (yield 98%). mp: 130 0C. 1H NMR (400 MHz, CDCl3): δ= 7.35(t, J=7.4 Hz,
1H), 7.42-7.46(m, 4H), 7.55-7.58(m, 1H), 7.62-7.65(m, 1H), 7.92(t, J=4.2 Hz, 2H), 8.19(s,
1H).13C NMR (100 MHz, CDCl3): δ= 121.5, 125.7, 127.6, 127.8, 128.2, 128.4, 128.8,
130.0, 130.6, 134.7, 147.4
2.6. General procedure for the Azide reduction
A 50ml round bottom flask was charged with Azide (3 mmol), sodium ascorbate (3.3mmol)
and tBuOH : H2O in 3:1 ratio (8mL) at room temperature. To this mixture copper catalyst
o
(1mol%) was added. Then the reaction mixture was stirred vigorously for 6 hours at 80 C.
After the completion (monitored by TLC), the reaction mixtures were taken to separating
funnel and the organic layer was extracted with EtOAc. Following evaporation of the solvent
under reduced pressure, the residue was purified by column chromatography on a silica gel
column eluted with petroleum ether/EtOAc.
Benzenesulfonamide – Compound (4a)

Yield is 92%, m.p = 150 0C; IR (ν, cm-1): 3340, 3240, 1550, 1440, 1330, 1150, 1090, 900; 1H
13
NMR (400 MHz, (CD3)2SO): δ 7.84 – 7.82 (m, 2H), 7.59 (m, 1H), 7.36 (m, 2H) C NMR
(100 MHz, (CD3)2SO): δ 144.60, 132.27, 129.41, 126.04, 39.06
4-methylbenzenesulfonamide – Compound (4b)
0
Yield is 95%, m.p = 135 C; IR (ν, cm-1): 3390, 3310, 3250, 3110, 1555, 1460, 1320, 1155;
1H NMR (400 MHz, (CD3)2SO): δ 12.47 – 12.40 (m, 1H), 12.09 (d, J = 7.8 Hz, 1H), 12.00 (s,
1H), 8.08 (s, 4H), 7.26 – 7.20 (m, 1H), 7.10 (s, 2H); 13C NMR (100 MHz, (CD3)2SO): δ
142.36, 141.83, 129.78, 126.09, 21.37
4-nitrobenzenesulfonamide – Compound (4c)
Yield is 95%, m.p = 179 0C; IR (ν, cm-1): 3340, 3250, 1610, 1520, 1350, 1260, 850; 1H NMR
(400 MHz, (CD3)2SO): δ 8.21 (d, 2H, J = 8 Hz), 7.84 (d, 2H, J = 8 Hz), 7.05 (s, 2H);13C
NMR (100 MHz, (CD3)2SO): δ 154.53, 147.79, 127.39, 123.86
4-aminobenzenesulfonamide – Compound (4d)
0
1
Yield is 98%, m.p = 165.5 C, IR (ν, cm-1): 3450, 3360, 1352, 1172; H NMR (400 MHz,
13
(CD3)2SO): δ 7.46 (d, 2H, J = 8 Hz), 6.89 (s, 2H), 6.59 (d, 2H, J = 8 Hz), 5.8 (s, 2H); C
NMR (100 MHz, (CD3)2SO): δ 152.38, 130.48, 127.9, 112.93
Benzyl amine – (Compound 4e) and Aniline – (Compound 4f) were confirmed by
comparing with authentic sample
3. Results and discussion
In continuation of our research interest, [16] we attempted the synthesis of α-diazo
hydrazones B by reacting nitro phenyl hydrazine and acetyl acetone followed by diazo
transfer reaction. 2, 4-dinitrophenyl hydrazine reacted readily to give the corresponding
hydrazone A in excellent yield while 2-nitrophenyl hydrazine gave pyrazole derivative C via
Knorr pyrazole synthesis (Scheme-1). The difference in reactivity can be ascribed to the
nucleophilicity of the nitrogen atoms in the two reactants. In 2, 4-dinitrophenyl hydrazine the
two electron withdrawing NO2 groups reduce the nucleophilicity of nitrogen via resonance.
But, in the case of 2-nitrophenyl hydrazine the nitrogen is nucleophilic enough to undergo
cyclization to give pyrazole in spite of presence of one NO2.

Scheme 1
Even though we got disappointed with the unwanted product, we envisaged that the
pyrazole deivative C with suitable substituent could serve as scaffold to obtain a novel class
of atropisomerism based ligand in which the chiral axis passes through N-N bond.
Accordingly, the nitro group in C was reduced with SnCl2 in EtOH at reflux to get the
corresponding amine in 78% yield. Treatment of amine with 2-hydroxy naphthaldehyde gave
the tridentate ligand E in quantitative yields. [17]
Scheme 2: Synthesis of Tridentate ligand and catalyst
The tridentate ligand E was thoroughly characterized by the spectral data and single
crystal X-ray technique. We were delighted to observe the pyrazole and phenyl rings to be in
different planes and the angle of inclination of the two rings is more than 45o. This is highly

encouraging and by introducing more bulky substituent it would be possible to isolate
atropisomers in pure form.
As the phenyl ring and pyrazole were in different planes, we assumed that the ligand
might not act as tridentate ligand. To our surprise, reaction of the ligand with copper acetate
resulted in the metal complexes which was readily crystallized in CH2Cl2. The single crystal
X-ray diffraction shows that the complexes crystalizes with two molecule of CH2Cl2 and the
ligand coordinate the metal through pyrazole N, imine nitrogen and phenoxide ion. The
pyrazole and phenyl ring attain nearly planarity to coordinate to metal. The geometry of Cu2+
is not exactly tetrahedral or square planar
Fig.3: ORTEP diagram of the Tridentate
Fig.4: ORTEP diagram of the catalyst F
ligand E
After successfully achieving the synthesis of new copper complex with tridentate
ligand, we undertook the study of the application of the catalyst in organic tranformations.
We have chosen the very well-known Cu(I) catalysed azide-alkyne cyclization to get triazole
derivatives. Our attention was more on the [3+2] cycloaddition between alkyne and sulfonyl
azide instead of aryl and alkyl azide since only a few reports are available on this
cycloaddition.
Accordingly when toluene sulfonyl azide was treated with phenyl acetylene, sodium
ascorbate in the presence of catalyst F (1 mol%) in solvent (t-BuOH:H2O, 1:1), we obtained
the corresponding triazoles in good yield. Surprisingly a small quantity of p-toluene
sulfonamide was also obtained in the reaction. As expected benzyl azide and phenyl azide
also gave the corresponding 1, 4-disubstituted triazoles derivative (Table -1). Even though
Cu(II) is employed as the catalyst, Cu(I) is the reactive species in the reaction. Cu(II) is in-

situ reduced by sodium ascorbate to give Cu(I) species which promotes the azide alkyne
coupling. [18]
Table 1 : Substrate Screening for Azide – Alkyne Cyclization a
Entry
Azide (R2)
4-CH3-C6H4SO2-N3
C6H5SO2-N3
Alkyne (R1)
Ph-
Yield b
90
a
b
c
d
e
f
Ph-
79
4-CH3-C6H4SO2-N3
4-CH3-C6H4-N3
C6H5-N3
-CH2OH
Ph-
80
85
Ph-
98
4-Cl-C6H4-N3
Ph-
98
a
Reaction condition: alkyne (3 mmol), azide (3 mmol), Sod.Ascorbate (0.3 mmol), cat.
F (1 mol%), tBuOH : H2O (1:1), 80 oC, 5 h. b Isolated yield by column chromatography
During the study of substrate scope, we also found the reaction to follow different
pathway to give sulphonamide instead of azide – alkyne cycloaddition product. Azide
reduction is the most widely used route to introduce amine functionality in the total synthesis
[19]. Expecting our catalyst to serve as new protocol for azide reduction, we undertook the
study of the catalyst to reduce azide to give the corresponding amide or amine. Accordingly,
o
sulfonyl azide were heated at 80 C with sodium ascorbate (1 equivalent) and the catalyst (1
mol%) in t-BuOH and H2O as solvent. The corresponding sulphonamide were obtained in
excellent yield with complete conversion (Table- 2). Since water is more acidic than tBuOH,
we believe that the hydrogens for reduction are obtained from the water. Even though
excellent yields were obtained for sulfonyl azide, this methodology furnished poor yields
with aryl azide and alkyl azides (Entry e and f, Table 2).
In order to get insight into the mechanism, control experiments were carried out with
p-toluene sulfonyl azide in the absence of catalyst and obtained the corresponding
sulfonamide in considerably less yield (23%). Further, we also checked the possibility for

thermal decomposition under the reaction temperature, by heating the azide in the absence of
catalyst and ascorbate. We found the compound to be stable under the reaction condition
o
(solvent : tBuOH and H2O, temperature: 80 C) and no sulphonamide was observed. So we
conclude that the formation of sulphonamide is not via the thermal decomposition of sulfonyl
azide and there is role of catalyst in the reduction.
Table 2: Substrate Screening for Azide Reduction a
Entry
Azide (R2)
C6H5SO2-
Yield b (%)
95 (40)c
92 (23)d
95
a
b
c
d
e
f
4-CH3C6H4SO2-
4-NO2C6H4SO2-
4-NH2 C6H4SO2-
C6H5CH2-
98
23
C6H5-
15
a Reaction condition: azide (3 mmol), Sod. Ascorbate (3.3 mmol), cat.
F (1 mol%), tBuOH : H2O (3:1, 6 mL : 2 mL), 80 oC, b Isolated yield
by column chromatography, c Yield at 60 oC, d yield without catalyst
Based on the control experiments and experimental observations, we propose the following
mechanism. Mechanistically, it is well proven that sodium ascorbate can reduce Cu(II) to
Cu(I) by transferring one electron. We presume that Copper(I) gives one electron to the azide
to furnish the intermediate X which can eliminate nitrogen via six member transition state to
give the sulphonamide (Fig.2). Since we obtained poor yield of sulphonamide in the absence
of copper catalyst, we believe that the transfer of electron from Cu(I) to azide is more facile
than from sodium ascorbate to azide. Since the reduction of sulphonamide gave quantitative
yield of the sulfonamide, we presume the sulfonyl group to facilitate the reduction via N2
elimination.

Fig.2: Plausible Mechanism
4. Conclusion
In conclusion, we have synthesized pyrazole based tridentate ligand and its copper(II)
catalyst via a simple and efficient route. The ligand as well as the catalyst were well studied
with spectroscopic techniques and single crystal XRD. We have also studied the efficiency of
the catalyst for the azide-alkyne cycloaddition and azide reduction reactions. The ligand with
suitable substituents will be separated into its enantiomers and the possibility to give chiral
induction will be studied.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The author thank DST-SERB for the financial support to carry out this research work. The
authors are also thankful to the management, Karunya Institute of Technology and Sciences
for their constant support.
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Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.