Two new copper(II) complexes with chelating N,O-type bidentate ligands: Synthesis, characterization, crystal structure and catalytic activity in azide–alkyne cycloaddition reaction

Article abstract of DOI:10.1016/j.ica.2017.06.046

Tetra-coordinated copper(II) complexes, [CuL₂] and [Cu(phox)₂], were synthesized by reaction of 1-((4-bromophenylimino)methyl)naphthalen-2-ol, HL, and 2-(2′-hydroxyphenyl)-2-oxazoline, Hphox, ligands with copper acetate, respectively. The complexes were characterized using FT-IR spectroscopy, elemental analyses, and their solid state structures were confirmed by single crystal X-ray diffraction. The catalytic activity of the complexes was evaluated in one-pot azide–alkyne cycloaddition (AAC) click reaction in water without need of any additional agent. The [CuL₂] complex showed high catalytic activity in this reaction??? and 1,2,3-triazole derivatives were produced in moderate to good yields.

Full text of DOI:10.1016/j.ica.2017.06.046

Accepted Manuscript
Research paper
Two new Copper(II) complexeswith chelating N,O-type bidentate ligands: Syn-
thesis, characterization, crystal structure and catalytic activity in azide-alkyne
cycloaddition reaction
Mojtaba Bagherzadeh, Arshad Bayrami, Reza Kia, Mojtaba Amini, Laurence J.
Kershaw Cook, Paul R. Raithby
PII:
S0020-1693(17)30335-3
http://dx.doi.org/10.1016/j.ica.2017.06.046
ICA 17695
DOI:
Reference:
Inorganica Chimica Acta
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Received Date:
Revised Date:
Accepted Date:
5 March 2017
19 June 2017
20 June 2017
Please cite this article as: M. Bagherzadeh, A. Bayrami, R. Kia, M. Amini, J.K. Cook, P.R. Raithby, Two new
Copper(II) complexeswith chelating N,O-type bidentate ligands: Synthesis, characterization, crystal structure and
catalytic activity in azide-alkyne cycloaddition reaction, Inorganica Chimica Acta (2017), doi: http://dx.doi.org/
10.1016/j.ica.2017.06.046
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Two new Copper(II) complexes with chelating N,O-type bidentate ligands:
Synthesis, characterization, crystal structure and catalytic activity in azide-
alkyne cycloaddition reaction
Mojtaba Bagherzadeha*, Arshad Bayramia, Reza Kiaa, Mojtaba Aminib, Laurence J. Kershaw
Cookc, Paul R. Raithbyc
a Chemistry Department, Sharif University of Technology, P.O. Box 11155-3615, Tehran, Iran;
bagherzadeh@sharif.edu
b Chemistry Department, Faculty of Science, University of Maragheh, P.O. Box 55181-83111, Maragheh,
Iran
c Department of Chemistry, University of Bath, BA2 7AY, Bath, UK
Abstract
Tetra-coordinated copper(II) complexes, [CuL2] and [Cu(phox)2], were synthesized by reaction
of 1-((4-bromophenylimino)methyl)naphthalen-2-ol, HL, and 2-(2′-hydroxyphenyl)-2-oxazoline,
Hphox, ligands with copper acetate, respectively. The complexes were characterized using FT-IR
spectroscopy, elemental analyses, and their solid state structures were confirmed by single
crystal X-ray diffraction. The catalytic activity of the complexes was evaluated in one-pot azide–
alkyne cycloaddition (AAC) click reaction in water without need of any additional agent. The
[CuL2] complex showed high catalytic activity in this reaction and 1,2,3-triazole derivatives were
produced in moderate to good yields.
Keywords: copper; azide–alkyne cycloaddition; 1, 2, 3-triazoles; N,O-bidentate ligands
Introduction
Huisgen 1,3-dipolar cycloaddition is a valuable and powerful method for synthesis of aromatic
five-membered heterocycles containing nitrogen atoms specially 1,2,3-triazoles [1]. A very wide
variety of applications that have been reported for 1,2,3-triazoles in diverse research fields
including synthesis of organic compounds and inorganic complexes [2–5], surface science [6,7],
polymer [8–10] and material chemistry [11,12], reveal the importance of this reaction.

Furthermore, these type of compounds exhibit various biological activities like HIV-1 inhibition
[13], anticancer [14], anti-tubercular [15], antiviral [16], antifungal [17] and antibacterial agents
[18]. These unique properties and impressive applications justify improvement of old procedures
and development of new and efficient methods for the one-pot synthesis of 1,2,3-triazoles in
mild reaction condition. The most important modification for the uncatalyzed Huisgen 1,3-
dipolar cycloaddition reaction was conducted by Sharpless and Meldal in 2002 [19,20]. They
were successfully able to catalyze this non-selective reaction by copper salts and produce 1,4-
disubstituted 1,2,3-triazoles selectively. Cu-catalyzed alkyne–azide cycloaddition (CuAAC) is
the premier example of the click reactions which its concept is introduced by Sharpless group for
the first time [21]. In situ reduction of inexpensive copper(II) sources (mostly CuSO4) in the
presence of reducing agent (e.g. sodium ascorbate) is the most common reaction condition that
has been used in the subsequent reports. The drawback of this methods is the instability of
organic azides and the potential risk of explosion of these components [22]. To avoid this
problem in developed procedures, organic azides are generated in situ by reacting of organic
halides or aryl boronic acids with sodium azide. Recently, the catalytic system including Cu(II)
sources in homogeneous and heterogeneous form have been reported where the reaction occurs
in the absence of reducing agents and also organic azides are generated in situ from organic
halides or aryl boronic acids and NaN3 [23–32]. Among these catalytic systems, the special
attention is devoted to which are active in water and the isolation of the azide intermediates is
not required. Moreover, water is a green solvent that makes purification of products easier and in
situ generated organic azides are immediately consumed in the next step of the reaction.
In this work, we describe the synthesis of two new water insoluble Cu(II) complexes with 1-((4-
bromophenylimino) methyl) naphthalen-2-ol and 2-(2′-hydroxyphenyl)-2-oxazoline ligands, and
the use of these complexes as catalysts in the one-pot azide-alkyne cycloaddition (AAC)
reaction in the presence of water as a solvent without any additional reducing agents or bases.
2. Experimental

2.1. Materials and general methods. All chemicals used were analytical reagent grade. All
solvents purchased from Merck were reagent grade and were used without further purification.
IR spectra in the region of 4000-400 cm-1 were recorded in KBr pellets with a Unicam Matson
1000 FT-IR spectrophotometer. The elemental analyses (CHN) of compounds were done using a
Carlo ERBA Model EA 1108 elemental analyzer. The 1HNMR spectra of the free ligands were
obtained using a Bruker FT-NMR 500 MHZ spectrometer in DMSO-d6. Melting points were
taken on a Gallenkamp melting point apparatus. 2-(2′-Hydroxyphenyl)-2-oxazoline, Hphox, was
prepared according to the reported procedure [33]. Single crystals of 1 and 2 suitable for X-ray
diffraction analysis, were grown by slow evaporation of the solvent from the ethyl acetate and
dimethylformamide solution of 1 & 2, respectively. X-ray intensity data were collected using the
full sphere routine by φ and ω scans strategy on the Agilent SuperNova dual wavelength EoS S2
diffractometer with mirror monochromated Mo Kα radiation (λ = 0.71073 Ǻ) for 1 and Cu Kα (λ
= 1.54184 Ǻ) for 2, respectively. For all data collections the crystals were cooled to 150 K using
an Oxford diffraction Cryojet low-temperature attachment. The data reduction, including an
empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK
scaling algorithm [34], was performed using the CrysAlisPro software package for 1 and 2 [35].
The crystal structures of 1 and 2 were solved by direct methods using the online version of
AutoChem 2.0 in conjunction with OLEX2 suite of programs implemented in the CrysAlis
software and then refined by full-matrix least-squares (SHELXL-97) on F2 [36,37]. The non-
hydrogen atoms were refined anisotropically. All of the hydrogen atoms were positioned
geometrically in idealized positions and refined with the riding model approximation, with
Uiso(H) = 1.2 or 1.5 Ueq(C). For the molecular graphics the program SHELXTL was used [38].
All geometric calculations were carried out using the PLATON software [39]. The difference
Fourier map of crystal 1 shows a high peak (2.2 e.Ǻ-3) with almost 10% occupancy. It was
assigned to oxygen atom of water molecule but it was not possible to locate its hydrogen atoms
because of the very low occupancy. The crystal of 2 was seriously twinned with a refined BASF
ration of 0.986(1)/0.014(1).
2.2. 1-((4-bromophenylimino) methyl) naphthalen-2-ol (HL).

The Schiff base ligand (HL) was synthesized via a condensation reaction of 2-hydroxy-1-
naphthaldehyde and 4-bromoaniline. 4-Bromoaniline (0.516 g, 3 mmol) in ethanol (10 mL) was
added slowly to a stirred solution of 2-hydroxy-1-naphthaldehyde (0.516 g, 3mmol) in hot
ethanol (10 mL), then the solution was refluxed for 4 h. The reaction was allowed to cool down
gradually to room temperature, the chilled ethanol solution gave yellow microcrystals. The
obtained yellow crystalline solid was collected by filtration, washed twice with ethanol and
recrystallized by methanol. Yield 78 %, M.p. 163 °C. Calcd. C, 62.60; H, 3.71; N, 4.29 %.
Found: C, 62.51; H, 3.71; N, 4.32 %. Selected IR frequency (KBr disk, cm-1): 1603 (νC=N). 1H
NMR (500 MHz, DMSO-d6): δ 15.55 (s, 1H, NH), 9.67 (s, 1H, ═CH─NH─), 8.51 (d, 1H, ring
H), 7.96 (d, 1H, arom. H), 7.81 (d, 1H, arom. H), 7.55-7.69 (m, 5H, arom. H), 7.37 (t, 1H, arom.
H), 7.04 (d, 1H, ring H).
2.3. Synthesis of [Cu(phox)2] (1). A methanolic solution (15 mL) of Cu(OAc)2.H2O (0.2 g, 1
mmol) was mixed with a methanolic solution (10 mL) of the ligand, 2-(2′-hydroxyphenyl)-2-
oxazoline, (0.326 g, 2 mmol). The resultant mixture was refluxed for 4 h and the resulting
greenish product was recovered by filtration, washed with methanol and dried in air. M.p. 248
°C. Anal. Calc. for C18H16CuN2O4: C, 55.74; H, 4.16; N, 7.22; Found: C, 55.62; H, 4.08; N, 7.30.
Selected IR frequency (KBr disk, cm-1): 1625 (νC=N).
2.4. Synthesis of [CuL2] (2). To a solution of Cu(OAc)2.H2O (0.2 g, 1 mmol) in 15 mL of
ethanol, a solution of ligand, 1-((4-bromophenylimino) methyl) naphthalen-2-ol (0.652 g, 2
mmol) in 15 mL of hot ethanol was added. The mixture was refluxed for 5 h to produce a brown
precipitate which was filtered, washed with hot ethanol and dried under vacuum. M.p. 304 °C
(dec.). Anal. Calc. for C34H22Br2CuN2O2: C, 57.20; H, 3.11; N, 3.92; Found: C, 57.08; H, 3.10;
N, 3.81. Selected IR frequency (KBr disk, cm-1): 1615 (νC=N).
2.5. General procedure for CuAAC reaction
To a reactor containing alkyne (0.5 mmol), the organic halide (0.55 mmol), NaN3 (0.55 mmol)
and H2O (2 mL), complexes (1) and (2) separately as a catalyst were added. The reaction mixture
was stirred at 70 °C for 8-12 h and completion of the reaction was judged by thin layer
chromatography (TLC). Water (5 mL) was added to the resulting mixture and the product was
extracted with ethyl acetate (2 x 10 mL) from the aqueous phase. The organic layer was dried
with anhydrous Na2SO4 and the solvent was removed under reduced pressure to give the

corresponding 1,2,3-triazoles. Further purification needs to be done in the case of complex 1 due
to its low solubility in ethyl acetate. To obtain the pure products, after extraction with
ethylacetate the reaction mixture was filtered and the residue was subjected to column
chromatography (eluent, 30% EtOAc in n-hexane).
3. Results and discussion
3.1. Characterization
The complex [Cu(phox)2] was obtained by the reaction of the Hphox ligand (2 equiv.) and
Cu(OAc)2.H2O (1 equiv.) in methanol at reflux conditions. The fast color change from bluish-
green to the pale green solution during the synthetic procedure indicated the coordination of
ligand to CuII center. Complex 1 is soluble in CH2Cl2, CHCl3, DMF, DMSO, low soluble in
EtOAc and insoluble in water. The complex [CuL2] was obtained by treatment of copper(II)
acetate mono-hydrate with HL in a 1:2 ratio in ethanol at reflux conditions. Complex 2 was
obtained as brown solid, insoluble in common organic solvents but soluble in DMF, DMSO and
insoluble in water. The reaction pathways are shown in scheme 1. The complexes 1 and 2 were
characterized by FT-IR spectroscopy and elemental analyses. The elemental analyses data in
each complex are consistent with the formulations of bis(ligand)metal species. Moreover, the
molecular structures of these complexes were confirmed by single crystal X-ray crystallography.
Both complexes are insensitive to oxygen or moisture and can be handled in air. Enol–imine and
keto–amine are tautomeric forms that could be existed for the HL ligand, where the aldehyde that
Schiff base is derived from, playing a decisive role in the relative stabilities of the tautomeric
forms [40]. The 1H NMR spectrum of HL showed the signals corresponding to NH and
═CH─NH─ at 15.55 and 9.67 ppm, respectively. Therefore, NMR spectroscopy only can detect
the keto form of HL [41], whereas in its solid state structure which was determined before, both
forms have been reported [42]. Comparison of the FT-IR spectra of Cu(II) complexes with that
of the free ligands revealed that the νC=N vibrations in the free ligand Hphox were shifted to the
lower frequencies from 1641 to 1625 cm-1 in 1 and another ligand HL shifted to the higher
frequencies from 1603 to 1615 cm-1 in 2. This shift in νC=N vibrations clearly indicating that the
imine nitrogen of the Hphox and the azomethine nitrogen of the HL are strongly coordinated to
the metal center [43–45].
3.2. Single crystal X-ray structure analysis

The solid state structures of complexes 1 and 2 were determined by X-ray crystallography and
are shown with their atom labelling scheme in Fig. 1 and 2. Details of data collection and
refinement parameters are given in Table 1. Selected bond lengths and angles of 1 and 2 are
listed in Table 2. Both complexes crystallize in monoclinic system with space group P21/c. The
asymmetric unit of both complexes comprises half of the molecule. The geometry around Cu
atom in both complexes is almost a square planar with N2O2 donor atoms of the ligands. The
bite angle of Hphox and HL ligands is 88.41(10) and 89.1(2)°, respectively. The crystal packing
of 1 shows extended one-dimensional chain running parallel to ac-plane and further connected
through intermolecular π…π interactions with centroid to centroid distances 3.3833(16)–
3.9221(2) Ǻ [Cg1...Cg2 = 3.3833(16), Cg1...Cg3 = 3.3833(16), Cg1...Cg4 = 3.8910(17),
Cg2...Cg2 = 3.9221(2), Cg2...Cg3 = 3.9221(2), Cg3...Cg3 = 3.9220(2) Ǻ; Cg1 =
O7/C8/N9/C10/C11, Cg2 = Cu13/O12/C1A/C2A/C8A/N9A, Cg3 = Cu13/N9/C8/C2/C1/O12A,
and Cg4 = C1–C6]. The crystal packing of 2 is stabilized by the intermolecular C8…Br [3.427(8)
Ǻ], short contact parallel to ac-plane which are further forming a column by the intermolecular
π…π interactions down the b-axis.
3.3. Catalytic Activity
In order to evaluate the catalytic properties of the complexes in the AAC, the reaction of benzyl
chloride, sodium azide, and phenyl acetylene was chosen as a model one. The reaction
conditions were optimized with respect to the solvent, quantity of catalyst, reaction time and the
reaction temperature. The optimization results for catalysts are shown in Tables 3 and 4. First,
the AAC reaction was examined without catalyst and no product was obtained after 12 h (entries
1, Table 3). When the catalyst loading was increased from 0.52 to 2.58 mol%, and from 0.28 to
1.40 mol%, respectively for 1 and 2, isolated yield increased sharply from 29 to 75% for 1 and
77 to 95% for 2. A further increase in the quantity of catalyst to 5.16 and 2.80 mol% for 1 and 2,
respectively, shows no substantial effect on the yield (entries 7 and 13, Table 3). Different
solvents such as water, ethanol, acetone, toluene, and chloroform, were employed to assess the
effect of the solvent for this cycloaddition reaction and results showed that poor yields are
obtained in organic solvents. Interestingly, water was found to be the most effective solvent for
this reaction (Table 4). High reactivity was observed by both of the catalysts when the reaction
mixture was warmed to 70 °C (entries 14-21, Table 3). The reaction is completed at 12 h and an

effective improvement in yield of triazole was observed with increasing reaction time from 8 to
12 h (entries 22 and 23, Table 3). Next, the AAC reaction between diversely substituted phenyl
acetylenes and benzyl halides were carried out under the optimal conditions to produce the
corresponding 1,2,3-triazoles (Table 5). The existence of electron withdrawing and electron
donating groups on the benzyl halides and the phenyl acetylenes have a low effect on the
resulting yields (entries 2-6). The reaction yield could be affected by some factors such as steric
hindrance and coordination ability of substrates to Cu center. The o-methyl benzyl chloride was
less reactive than the p-methyl benzyl chloride due to higher steric hindrance (entries 2 and 3).
The obtained results for both catalysts indicated that benzyl chloride is slightly more reactive
than benzyl bromide (entries 9–13). When propargyl alcohol or 2-methyl-3-butyn-2-ol was used
as a terminal alkyne, the reaction proceeded smoothly to give the corresponding products in
moderate yields (entries 7, 8, 12 and 13). The lower reaction yields are probably due to the
complexation of copper by alcoholic hydroxy groups [46]. Furthermore, 2-methyl-3-butyn-2-ol
gave lower yields compared to the propargyl alcohol owing to the high steric hindrance.
Also, we investigated the reusability of catalyst 2. For this purpose, according to insolubility of
complex 2 in water and ethyl acetate after each recycle this complex was separated from the
reaction mixture by filtration and then washed twice with distilled water and ethyl acetate, dried
at 45 °C for 30 min, and reused for AAC reaction of benzyl chloride, phenyl acetylene, and NaN3
at 70 °C for 12 h (Fig. 3). After three uses the reaction yield is reduced to 41% and this decrease
in the catalytic activity is mainly attributed to structural changes of the complex 2, this change in
the structure is confirmed by comparison of the IR data for the fresh and recycled catalyst (Fig.
4). As it is clear from Figures 3 and 4 the results suggest that the catalyst 2 has poor recyclability
due to structural changes and decomposition of the complex.
Finally, we compared the catalytic reactivity of catalyst 2 with recently reported catalytic
systems in the AAC reaction. Although, the presence of sodium ascorbate and inert atmosphere
are vital in some catalytic systems (entries 3 and 4, Table 6). Our catalytic system works without
needing to an inert atmosphere and any additional reducing agents. Furthermore, the previously
reported systems often required much amount of catalyst (entries 1, 2, 3, 5 and 6), high
temperature (entry 3) and long reaction times (entries 1, 2 and 4) for more progress of the
reaction. Other advantages of the present catalytic systems are, in situ generation of organic

azides, simple catalyst preparation, easy and quick isolation of products and use of water as a
green solvent.
Conclusions
Two copper(II) complexes were synthesized by reactions of copper(II) acetate monohydrate with
2-(2′-hydroxyphenyl)-2-oxazoline and 1-((4-bromophenylimino) methyl) naphthalen-2-ol
ligands. Both complexes exhibited a quasi-planer coordination environment at the copper(II)
centers. The X-ray diffraction studies revealed the coordination of these ligands to the metal
center in a chelate way via N- and O-donor atoms. The catalytic behavior of the 1 and 2
complexes was investigated in the one-pot protocol for the synthesis of 1,4-disubstituted 1,2,3-
triazoles. Complex 2 was found to be an efficient catalyst for the AAC reaction that has been
active in water.
Acknowledgments
MB and RK thank the Research Council of the Sharif University of Technology for financially
support of this work. RK also thanks Prof. Paul R. Raithby and Bath University for visiting
research scientist position and support. PRR is grateful to the Engineering and Physical Sciences
Research Council (EPSRC) for continued funding (EP/K004956/1).
Appendix A. Supplementary material
CCDC Nos. 1533524-1533525 contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be
found, in the online version.
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Scheme 1. Synthesis of complexes 1 and 2.
Figure 1. The ORTEP of 1 with atoms labelling and ellipsoids probability of 40%. The A suffix
is for symmetry code, -x + 2, -y + 1, -z + 2.

Figure 2. The ORTEP of 1 with atoms labelling and ellipsoids probability of 40%. The A suffix
is for symmetry code, -x + 1, -y, -z + 1.

Table 1. Crystal data and refinement parameters for 1 and 2
Complex
1
2
Empirical formula
Formula mass
Crystal size (mm)
Colour
Crystal system
Space group
C18H16CuN2O4
387.87
0.10 × 0.15 × 0.25 0.10 × 0.18 × 0.35
C34H22Br2CuN2O2
713.89
dark green
monoclinic
P21/n
brown
monoclinic
P21/n
30
θmax (°)
26
a (Å)
b (Å)
c (Å)
5.5259(2)
19.4152(8)
7.4422(3)
102.882(4)
778.35(6)
2
1.655
1.430
398
17.2389(5)
3.87926(13)
19.2704(6)
93.123(3)
1286.78(7)
2
1.843
5.144
710
-21 ≤ h ≤21
-4 ≤ k ≤4
-19 ≤ l ≤23
2782
β (°)
V (Å3)
Z
Dcalc (Mg/m3)
µ (mm−1)
F (000)
Index ranges
-6 ≤ h ≤6
-24 ≤ k ≤24
-9 ≤ l ≤9
No. of measured reflns. 20190
No. of independent
reflns./Rint
1584/0.0451
2539/0.2243
No. of observed
reflns. I > 2σ(I)
No. of parameters
1531
122
2360
182
Goodness-of-fit (GOF) 1.244
R1 (observed data)
wR2 (all data)
1.183
0.0740
0.1659
0.0447
0.1032
Table 2. Selected bond lengths and angles for 1 and 2
Bond lengths (Ǻ)
Cu(13)–O(12)
Cu(13)–N(9)
N(9)–C(8)
O(7)–C(8)
1
Bond lengths
Cu(2)–O(1)
Cu(2)–N(3)
O(1)–C(5)
N(3)–C(11)
N(3)–C(14)
C(6)–C(14)
2
1.901(2)
1.958(2)
1.290(4)
1.350(4)
1.452(4)
1.290(4)
1.913(6)
2.005(7)
1.313(9)
1.417(10)
1.300(10)
1.426(10)
O(7)–C(11)
N(9)–C(102)
Bond angles (°)
O(12)–Cu(13)–N(9)
O(12)–Cu(13)–O(12A)a
O(12)–Cu(13)–N(9A)a
C(8)–O(7)–C(11)
Cu(1)–N(9)–C(8)
Bond angles (°)
88.41(10)
180.00
91.59(10)
107.6(2)
126.0(2)
O(1)–Cu(2)–N(3)
O(1)–Cu(2)–O(1A)b
O(1)–Cu(2)–N(3A)b
Cu(2)–O(1)–C(5)
Cu(2)–N(3)–C(11)
89.1(2)
180.00
91.0(2)
123.9(5)
122.9(5)
a and b are for -x + 2, -y + 1, -z + 2 and -x + 1, -y, -z + 1 symmetry codes, respectively.

Table 3. The effect of time, temperature and the amount of catalyst on the cycloaddition of
benzyl chloride with phenyl acetylene in the presence of sodium azide.a
Entry
1
Cat. loading (mol %)
-
Temp. (oC)
70
Time (h)
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
8
Yield (%)b
0
2
1(0.52)
1(1.03)
1(1.55)
1(2.07)
1(2.58)
1(5.16)
2(0.28)
2(0.56)
2(0.84)
2(1.12)
2(1.40)
2(2.80)
1(2.58)
1(2.58)
1(2.58)
1(2.58)
2(1.40)
2(1.40)
2(1.40)
2(1.40)
1(2.58)
2(1.40)
70
29
3
70
53
4
70
55
5
70
63
6
70
75
7
70
76
8
70
77
9
70
79
10
11
12
13
14
15
16
17
18
19
20
21
22
23
70
82
70
90
70
95
70
95
r.t.
40
12
15
50
20
60
52
r.t.
40
21
25
50
73
60
86
70
47
70
8
78
a Reaction conditions: 0.5 mmol of phenylacetylene, 0.55 mmol of benzyl chloride, 0.55 mmol of
sodium azide, 2 mL of H2O. b Isolated yields.

Table 4. Effect of solvent on the cycloaddition of benzyl chloride with phenyl acetylene and
sodium azide.a
Entry
Solvent
Yield (%)b
[Cu(phox)2]
[CuL2]
12
1
2
3
4
5
acetone
ethanol
chloroform
toluene
water
17
23
10
5
31
12
13
75
95
a Reaction conditions: 0.5 mmol of phenylacetylene, 0.55 mmol of benzyl chloride, 0.55 mmol of
sodium azide, solvent 2 mL, 70˚C, 12h. b Isolated yields.

Table 5. Cycloaddition of alkyl halides with terminal alkynes in the presence of Cu(II) catalysts
and NaN3 under the optimized reaction conditions.a
Entry
1
Aliphatic halide
Alkyne
Yield (%)b
[Cu(phox)2]
75
[CuL2]
95
2
74
91
3
4
68
64
82
89
5
6
7
8
73
75
46
41
96
93
63
58
9
70
87

10
11
12
13
75
69
44
42
91
85
59
46
a Reaction conditions: 0.5 mmol of terminal alkyne, 0.55 mmol of alkyl halide, 0.55 mmol of
sodium azide, 2 mL of H2O. b Isolated yields.

Table 6. Recently reported catalytic systems for AAC in the presence of Cu(II) complexes.
Entry
1
Catalyst
Conditions
Yield (%)
77
Ref.
[47]
Cu(OAc)2·H2O
Catalyst (20 mol%) / H2O /20 h / r.t.
2
Cu(NO3)2·3H2O
Catalyst (20 mol%) / H2O /20 h / r.t.
13
[47]
3
4
5
6
7
CuSO4-sodium
ascorbate
CuSO4-sodium ascorbate (10 mol %
each)/acetone: water (1:1)/8.5 h/80 °C
89
99
86
96
95
[48]
[49]
[30]
[32]
[Cu(Npy2pz)]2(PF6)2
[Cu(dppo)2]
[Cu(tzol)2]
Catalyst (0.2mol%), sodiumL-ascorbate (1
mol%)/MeOH/16 h/ /25 °C/N2
Catalyst (2 mol%)/DMF/8 h/ r.t.
Catalyst (2.4 mol%)/H2O/12 h/70°C
Catalyst (1.40 mol%)/H2O/12 h/70°C
[CuL2]
Present
work

Figure 3. Recyclability and reusability study of complex 2 in the AAC reaction.
Figure 4. IR spectrum of (a) fresh and (b) reused catalyst [CuL2 ].

Graphical Abstract
Highlights
• The copper (II) complexes were prepared with chelating N,O-type bidentate ligands.
• Crystal structure of the both complexes was discussed.
• The catalytic activity of the complexes was investigated in one-pot azide–alkyne
cycloaddition reaction that completed in water.
•
Moderate to good yields have been achieved at mild reaction condition.