Synthesis, characterization, and comparison of two new copper(II)complexes containing Schiff-base and diazo ligands as new catalysts in CuAAC reaction

Article abstract of DOI:10.1016/j.ica.2019.04.036

Two copper(II)complexes were synthesized through the reaction of Cu(OAc)₂·H₂O with a Schiff-base ligand (1-(((3,4-dichlorophenyl)imino)methyl)naphthalen-2-ol)and a diazo ligand (1-((3,4-dichlorophenyl)diazenyl)naphthalen-2-ol)in methanol. The complexes and ligands were characterized employing elemental analysis and electronic spectra. In addition, the ligands were fully characterized by using several 1D and 2D NMR techniques. Single crystal X-ray crystallography was also used for the characterization of some of these materials. Due to finding out the effect of Schiff-base and diazo ligands nature on the catalytic activity, the complexes were catalytically compared in one-pot azide-alkyne cycloaddition reaction in water. Furthermore, computational studies were performed on ligands and complexes for further understanding of the relationship between structure, bonding, and reactivity of these new materials.

Full text of DOI:10.1016/j.ica.2019.04.036

Accepted Manuscript
Research paper
Synthesis, Characterization, and Comparison of Two New Copper(II) Com-
plexes Containing Schiff-base and Diazo Ligands as New Catalysts in CuAAC
Reaction
Mojtaba Bagherzadeh, Hamed Mahmoudi, Saeed Ataie, Mohammad Hafezi-
Kahnamouei, Saeed Shahrokhian, Gianfranco Bellachioma, Luigi Vaccaro
PII:
S0020-1693(19)30060-X
https://doi.org/10.1016/j.ica.2019.04.036
ICA 18881
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
12 January 2019
18 April 2019
18 April 2019
Please cite this article as: M. Bagherzadeh, H. Mahmoudi, S. Ataie, M. Hafezi-Kahnamouei, S. Shahrokhian, G.
Bellachioma, L. Vaccaro, Synthesis, Characterization, and Comparison of Two New Copper(II) Complexes
Containing Schiff-base and Diazo Ligands as New Catalysts in CuAAC Reaction, Inorganica Chimica Acta (2019),
doi: https://doi.org/10.1016/j.ica.2019.04.036
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Synthesis, Characterization, and Comparison of Two New
Copper(II) Complexes Containing Schiff-base and Diazo Ligands
as New Catalysts in CuAAC Reaction
Mojtaba Bagherzadeh,a* Hamed Mahmoudi,a† Saeed Ataie,a† Mohammad Hafezi-
Kahnamouei,a Saeed Shahrokhian,a Gianfranco Bellachioma,b and Luigi Vaccarob
a
Chemistry Department, Sharif University of Technology, Tehran, P.O. Box 11155-3615, Iran;
bagherzadeh@sharif.edu
b Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto, 8, I-06123
Perugia, Italy
†Both authors contributed equally to this work
___________________________________________________________________________
Abstract: Two copper(II) complexes were synthesized through the reaction of Cu(OAc)2.H2O
with a Schiff-base ligand (1-(((3,4-dichlorophenyl)imino)methyl)naphthalen-2-ol) and a diazo
ligand (1-((3,4-dichlorophenyl)diazenyl)naphthalen-2-ol) in methanol. The complexes and
ligands were characterized employing elemental analysis and electronic spectra. In addition,
the ligands were fully characterized by using several 1D and 2D NMR techniques. Single
crystal X-ray crystallography was also used for the characterization of some of these materials.
Due to finding out the effect of Schiff-base and diazo ligands nature on the catalytic activity,
the complexes were catalytically compared in one-pot azide-alkyne cycloaddition reaction in
water. Furthermore, computational studies were performed on ligands and complexes for
further understanding of the relationship between structure, bonding, and reactivity of these
new materials.
Keywords: Copper Schiff-base complex, Copper diazo complex, AAC reaction, triazole
compounds, click chemistry
___________________________________________________________________________
1. Introduction
In the past two decades, click chemistry was introduced by Sharpless as a conceptual
framework for the highly efficient assembly of molecules [1]. This term was first introduced
in 1999 [2], and in 2001 Sharpless and his coworkers already applied click chemistry-type
reactions, as a selective, powerful and reliable method for the synthesis of new useful materials
[3]. More generally, click chemistry is not limited to a specific chemical reaction, but it
describes those synthetic methods featuring modularity and a wide substrate scope, using

simple reaction conditions that starting from easily available materials and benign solvents,
allow the access of pure products in high yields. [4].
Among the click reactions, the Copper catalyzed Azide-Alkyne Cycloaddition (CuAAC)
reaction has attracted the most attention [5], as it allows the totally selective preparation of
high-value 1,2,3-triazoles that find applications in several different fields such as
pharmaceutical, polymer, biochemistry, and agrochemicals [6]. CuAAC has also the additional
merit of furnishing an effective and selective alternative to thermal azide-alkyne 1,3-dipolar
cycloaddition developed a long time ago by Huisgen [7].
The main issue of the thermal Huisgen protocol is in fact related to the need for high
temperature, and also to the lack of control of regioselectivity leading to a mixture of 1,4- and
1,5-disubstituted 1,2,3-triazole regioisomers [8]. On the contrary CuAAC reaction only
produces 1,4- regioisomer, without any solvent sensitivity and being 107 times faster [9].
Moreover, according to the viewpoint of green chemistry, one of the remarkable points about
CuAAC reaction is using water as a green solvent [10].
Since its discovery, theories describing CuAAC reaction, have been controversial. At first,
there was a belief that the CuAAC reaction can be catalyzed only by Cu(I) complexes and in
this regard, it has been described to use Cu(I) salts, or ion alternative Cu(II) salts combined
with reducing agents to reduce Cu(II) to the active type Cu(I). But lately, variant works have
been published in click chemistry reaction area using Cu(II) complexes as catalysts with no
reducing agents, in one step without any side products [11]. Due to the nature of circulating
electrons in the structure of the applied ligands, π-conjugation, used ligands definitely
“impress” the catalytic system [12]. In CuAAC reaction using Cu(II) as a catalyst, ligands can
help the system to maintain the copper metal center in its active state, Cu(I), which is able to
promote more efficiently the reaction [13].
Schiff base and diazo groups (C=N and N=N) can establish π-conjugation chain with aromatic
rings, and these systems provide two different environments around central metal and straightly
affect catalytic potential [14].
In this regard, in this contribution we report our results in the synthesis of two copper(II)
complexes containing Schiff-base (1-(((3,4-dichlorophenyl)imino)methyl)naphthalen-2-ol)
and diazo (1-((3,4-dichlorophenyl)diazenyl)naphthalen-2-ol) ligands with the same
geometries. The complexes have been employed as catalysts in CuAAC reaction in water
without using additional reducing agents. Different parameters such as temperature, time,
various media and the amount of catalyst were studied for the definition of the optimum

conditions for each catalyst. Finally, the optimum conditions of both catalysts were compared
together.
2. Results and discussion
2.1. Synthesis and characterization
Complexes 3 and 4 were prepared in good yield by addition of Cu(OAc)2.H2O to a methanolic
solution of 1 or 2 (For details, refer to supporting information) (Scheme1). Complex [Cu(L1)2)]
3 was formed as light brown solid and showed insolubility in water and only very little solubility
in methanol, acetonitrile, acetone, 1,2-dichloroethane, ethanol, or chloroform. On the other
hand, the complex was quite soluble in DMF, DMA, or DMSO. The complex 4 had a dark
brown appearance and was insoluble in water, methanol, ethanol, acetonitrile, acetone, 1,2-
dichloroethane but also poorly soluble in chloroform, DMSO, DMA, or DMF.
1
Structure of Schiff base ligand 1 was confirmed by H NMR (Fig. S2 in supporting
3
information). In fact, its spectrum features a resonance at δ=15.30 ppm (d, 1H, JHH=2.9 Hz)
which corresponds to the keto–amine form (H7 in Fig. S1a), this signal is correlated with the
other one at δ=9.70 ppm (d, 1H, J=2.4 Hz) according to 1H-1H COSY NMR spectrum (Fig. S4
and S5) and therefore this peak can be assigned to aldimine hydrogen (H11, Fig. S1a). This
correlation also indicates that in solution the keto-enol tautomerization equilibrium the keto-
amine form is more stable than the enol-imine form, and this observation is in accordance with
previously published results [15] (see section 2.3 for the results of DFT calculations on the
stability of keto-amine form). In the aromatic area, three sets of resonance appeared in δ=7.61,
7.71 and 8.06 ppm and they correlate altogether and are assigned to H8, H9 and H10 (Fig. S1a),
1
respectively. In the H-1H COSY NMR spectrum the resonance of hydrogens H1-6, that
correlate to each other, appeared in δ=7.82, 7.38, 7.58, 8.55, 7.97 and 7.07 ppm, respectively.
Similarly, for the ligand 2, the 1H NMR (Fig. S8) shows a singlet resonance at δ=15.35 ppm
which was assigned to H7 (Fig. S1b). Similar tautomerization between azo and hydrazone form
was also observed in this compound and in solution, it appears that the hydrazone form is more
stable than the azo form [16]. In addition, three other sets of peaks had a resonance at δ=7.87,
7.77 and 8.16 ppm which are assigned to H8, H9 and H10 (Fig. S1b), respectively. These three
1
peaks were correlated together according to the H-1H COSY NMR spectrum (Fig. S10 and
S11). Finally, the resonance of hydrogens 1-6 were appeared in δ=7.77, 7.48, 7.62, 8.54, 7.97

1
1
and 6.89 ppm, respectively. Furthermore, 13C NMR, H-13C HSQC, and H-13C HMBC
analyses were performed to confirm these assignments (Fig. S3, S6, S7, S9, S12, and S13).
Both complexes were characterized by elemental analysis. CHN analysis shows that 58.80%
Carbon, 2.91% Hydrogen and 3.95% Nitrogen was found in complex 3 As well as, the copper
content of this complex was determined by using ICP-AES instrument and the result showed
9.17% w/w Cu in the structure of this complex. The elemental analysis demonstrated that the
molar ratios of N/Cu, C/Cu and H/Cu were 1.97, 34.19 and 20.31 respectively, which
complies with the molecular formula of this complex (C34H20Cl4CuN2O2). And also, about
complex 4, we found 55.12% C; 2.55% H; 8.18% N and 9.10 Cu. As well as, Elemental analysis
showed that the molar ratios of N/Cu, C/Cu and H/Cu were 4.08, 32.05 and 17.80
respectively, that complies with the molecular formula of this complex (C32H18Cl4CuN4O2).
These results confirmed that two ligands are coordinated to central Copper (II) in each case.
As well as, all structures were characterized by UV-Vis spectroscopy. The modest changes in
the complexes' spectra, compared to the ligands' spectra, can be considered as a sign of
complexation (Fig. S35 and S36).
2.2. Single crystal X-ray structure analysis
Crystals of ligand 1 and complex 3, suitable for X-ray diffraction, were obtained as described
in the Synthesis and Characterization part of supporting information (Scheme 1). The ORTEP
diagrams of the structures 1 and 3 are shown in Fig. 1.
Selected bond lengths, angles, structural parameters and refinements for the ligand 1 and
complex 3 are given in the supporting information.
2.3. DFT studies
Full geometry optimization was performed for both ligands and both complexes. After
optimization, the vibrational frequency illustrates that all structures were in the minimum
energy level. Optimized structures of 1-4 are illustrated in Fig. S24. (Details of optimized
bonds lengths and angles are alleged in table S24-S31 in supporting information).
For both ligands, a tautomeric equivalency between enol and keto forms exists (Fig. 2). The
energy comparison for the ligands show the keto form is stable form and the energy gap
between enol and keto form is 3.80 and 8.06 kJ.mol-1 for ligand 1 and 2 respectively. This
calculation shows activation energy for this tautomerization is 12.94 and 17.26 kJ.mol-1 for 1
and 2, respectively.

The contour plot of frontier molecular orbitals of 1 and 2 are shown in Fig S25 and S26.
Analysis of frontier molecular orbitals, confirms that both ligands have a closed-shell structure,
and also the large energy gap between HOMO and LUMO (3.30 eV for 1 and 2.99 eV for 2)
illustrates the kinetic stability and low chemical activity of these structures [17]. Also, the
molecular orbital analysis showed that an acceptable percentage of HOMO was found on
Nitrogen and Oxygen fragment, which is a good reason for the ability of these structures to
form a complex with any metals (Table S20 and S21 and Fig. S31 and S32 in supporting
information).
The conditions for the complexes 3 and 4 are different and the type of electronic system is
open-shell. There are two series of alpha and beta orbital existed in the system, these orbitals
are demonstrated in Fig. S27-30. The HOMO orbitals were made by the large contribution of
ligand orbitals. In contrast, a large contribution of β-LUMO orbitals in both complexes was
located on the copper ion, which emphasizes the basic role of copper in the reactivity of these
complexes. The energy and contribution of frontier molecular orbitals 3 and 4 are shown in
table S22 and S23, respectively.
The main reason for conducting theoretical studies was the recognition of the structure and
bonding in the synthesized compounds. Understanding the structure and bonding relationship
can help us to find the relationship between structure and reactivity. Natural Bond Orbitals
(NBOs) calculations were carried out to understand the Lewis-like molecular bonding pattern
of electron pairs in an optimally compact form. In other words, NBOs are a set of occupancy
orbitals which give the accurate Lewis description of the total electron. NBO analysis of
complexes 3 and 4 have been performed in DFT B3LYP level with 6-31g* basis set for all
ligands’ atoms and SDD basis set for Copper centers. Summary of Natural Population Analysis
(NPA) for a selected atom of complexes 3 and 4 are listed in table S32 and S33. According to
the table S32 and S33, the natural electron configuration of Cu in complexes 3 and 4 is:
[core]4s0.033d9.994p0.384d0.025d0.01 and [core]4s0.033d9.994p0.404d0.025d0.01, respectively. These
calculations showed that the natural charge of the copper center is almost the same in both
complexes (1.75216 in complex 3 and 1.75260 in complex 4). In comparison, the natural
charge on chelating nitrogens in complex 4 is more positive than complex 3 (natural charge of
N28 and N60 in complex 3 is -0.66930 and -0.70284 respectively and natural charge of N26
and N56 in complex 4 is -0.51334 and -0.42495 respectively) and regarding to the same value
of natural charge in the copper center of both complexes, it can be said that the Cu-N bond in
the complex 4 is weaker than the similar bond in complex 3. These observations are consistent

with the results of the calculated bond length, as the calculated nitrogen-copper bond length in
complex 4 is slightly longer than the length of the same bond in complex 3 (Table S28 and
S30).
2.5. Electrochemical studies
In order to the electrochemical study on the two prepared complexes, CV’s of complex 3/GCE
and complex 4/GCE were conducted in phosphate buffer solution (pH=7.0) at a scan rate 50
mV.s-1 as presented in Fig. 3. As can been seen, the corresponding CV’s demonstrated a
cathodic (c) and two anodic (a1, a2) peaks for both complexes at different peak potentials. For
complex 3, cathodic peak (c) was observed at -0.92 V and in the reverse sweep, two anodic
peaks (a1) and (a2) appeared at 0.53 V and 0.75 V, respectively (Fig. 3A). While for complex
4, cathodic peak (c) was at -0.57 V and two anodic peaks (a1) and (a2) were appeared at -0.21
V and 0.05 V, respectively (Fig. 3B). The cathodic peak (c) can be considered as a two-electron
reduction process of the Cu(ΙΙ) to Cu(Ι), and also, anodic peaks were related to oxidation of
Cu(0) to Cu(Ι) (a1) and Cu(Ι) to Cu(ΙΙ) (a2). In comparison with complex 4, the oxidation peak
for complex 3 is appeared in more positive potentials and consequently, its reduction in more
negative potential. The results revealed more thermodynamic stability for complex 3, relative
to complex 4. The difference between reduction and oxidation potentials in two complexes
were originated from different ligands, which affect the stability of the central metal, and
therefore the catalytic behavior of complexes. the origin of the difference in thermodynamic
stability is related to the difference in the stabilization of ligands.
2.6. Catalytic activity
To evaluate the catalytic potential of complexes 3 and 4, they were utilized in AAC reaction.
First, a blank reaction with no catalyst was considered between phenylacetylene (put always
the number of the structures in bold, in parenthesis if it is the actual IUPAC name otherwise
not) and benzyl chloride in the presence of sodium azide in water (Table 1, entry 1). As
expected no conversion to the product was observed. In order to compare the catalytic activity
of complexes 3 and 4 in AAC reaction, each of the complexes was studied separately to reach
the optimum reaction condition and then compared together. To optimize the reaction condition
for complex 3, phenylacetylene (0.5 mmol) and benzyl chloride (0.55 mmol) with sodium azide
(0.55 mmol) were chosen as starting stoichiometric ratios. According to the previously
o
published work [18], the temperature 70 C and water (2 mL) were chosen as starting non-
optimized parameters. When catalyst 3 was used as 0.28 mol%, the yield obtained was 58%

(entry 2). By increasing the amount of catalyst 3 step by step from 0.28 to 1.15 mol%, the yield
increased to 97% (entry 5). As it is shown in Table 1, entries 6 and 7, by using catalyst amounts
larger than 1.15 mol%, no progress was obtained in the yield. In a quite similar procedure, the
optimal amount of catalyst 4 resulted to be 0.86 mol% with a 76% yield (entry 10) and also, in
this case, using more amount of catalyst no significant increase was obtained in terms of yield
(entries 11-13). Furthermore, different temperatures were applied while using the optimal
amounts of catalysts 3 and 4. For catalyst 3, at room temperature, only 18% yield was obtained
(entry 14). By increasing the temperature to 50 °C, the product was obtained in 96% yield, and
from 60 to 100 °C, no remarkable improvement was observed in the isolated yield (entries 17-
19). Also, in the same manner for the catalyst 4, the best temperature was found to be 70 °C
where a yield of 76% could be obtained (entry 10) and no relevant improvement could be
observed at higher temperatures (entries 24 and 25).
In order to find out the active species of copper in the catalytic cycle, two reactions were
designed with the ratio 2:1 of Sodium ascorbate:catalyst (Sodium ascorbate used as a mild
reducing agent) in the catalytic system and the results were included in Table 1, entries 27 and
28. These results show no remarkable progress was detected by adding a reducing agent.
In this regard, professor Lei Zhu and his coworkers have done a wide study on this issue, and
they monitored the reduction of Cu(II) to Cu(I) during the catalytic reaction employing EPR
and UV analysis [19],and also they have found that the active state of copper during catalytic
reaction is Cu(I), which means when a source of Cu(II) is used as a catalyst of azide-alkyne
cycloaddition, it must be reduced to Cu(I) and then the catalytic reaction cycle starts. In the
absence of reducing agent, the mechanistic studies indicated that the real catalytic Cu(I) species
were generated in a short induction period via reducing Cu(II) salts by alcohol oxidation,
homocoupling of terminal alkyne [5c, 20] or sodium azide [21], and in the present case, due to
lack of alcoholic solvents, Cu(II) is reduced through homocoupling of terminal alkyne or by
sodium azide.
At the end of the optimization process, three catalytic reactions were performed to illustrate
the capabilities of synthesized catalysts 3 and 4. In two of the reactions, the ligands 1 or 2 were
used as a catalyst and after 14h no conversion to the product was observed (Table 1, entries 29
and 30). And also, another reaction was performed by using copper acetate monohydrate as a
catalyst and after 14 h, 67% of the product was obtained (Table 1, entry 31). This observation,
emphasizes that complexes 3 and 4 are good catalysts and show perfect catalytic ability in
comparison with ligand-free copper (II) ion.

In the next step, various solvents were tested as reaction media for both catalysts under the
optimized reaction condition. Among different solvents such as DMSO, acetone, ethanol, 1,2-
dichloroethane, chloroform, acetonitrile and water (Table 2, entries 1-6 and 8), the highest yield
was obtained in water for both catalysts (entry 8). Anyway, due to the low solubility of sodium
azide in organic solvents, negligible yields were achieved for both catalysts. Accordingly, a
mixture solvent including water and DMSO (1:1) was evaluated for both catalysts in their
optimized reaction conditions (entry 7). Nevertheless, the best yields were obtained in aqueous
media for both catalysts.
Additionally, for both catalysts, several reactions were conducted by increasing the reaction
time from 1 to 18 hours using optimal reaction conditions and evaluating the yields obtained
for the corresponding isolated product. The results are illustrated in Fig. 4. For catalyst 3, the
reactions proceeded in 6 h and the highest yields reported were obtained. For catalyst 4 the
reaction proceeded more slowly and the highest yield could be achieved only after 14 h and
after which time stayed constant.
In order to further study both catalysts, they were utilized in AAC reaction with different
halides and alkynes (Table 3). The presence of a group (electron withdrawing or electron
donating) on the ortho position of benzyl chloride (entries 2 and 4) leads the reaction to lower
yield in comparison with the presence of a group on para position. This can be due to the higher
steric hindrance for ortho position. By changing phenylacetylene to propargyl alcohol or 2-
methyl-3-butyn-2-ol small decrease is resulted in outputs and this decrease is more
considerable for 2-methyl-3-butyn-2-ol according to higher steric hindrance. The products 1H
NMR spectra are depicted in Fig. S14-S21 respectively (In supplementary material). Even
though in the optimized reaction condition for catalyst 4, the temperature and time are higher,
but catalyst 3 treated obviously much more efficient than catalyst 4 in their optimized reaction
conditions. Also, for the same amount of both catalysts, higher turnover number and yield have
been obtained for the catalyst 3 (Table 1, entries 4 and 10). As shown in Table 2, in all used
solvents, catalyst 3 exhibited higher activity than catalyst 4. And finally, for all different used
substrates, catalyst 3 presented higher activity than catalyst 4.
Overall, this comparison between two complexes containing Schiff-base and diazo ligands can
confirm that the Schiff-base ligand helps the copper to be more active in AAC reaction. As
mentioned in some published literature [20b, 20d] when the Cu(I) is generated and the catalytic
process is begun, the ligand nature can stabilize the +1 state of copper, and help the reaction to
be progressed efficiently. In this study, it is clear that Schiff-base ligand is more potentiated to
stabilize the Cu(I) in comparison with the diazo ligand. Also, according to the literature [19,

20b], the product of the reaction can act as a ligand in the system, and product inhibition does
not occur and it can be the reason for the difference in the performance of progress in two
catalytic systems.
Due to the insolubility of both complexes in water, and also with regard to the better results of
3 compared to 4 in Azide-Alkyne cycloaddition, complex 3 was selected to perform catalyst
recycling tests. The amounts of the reactants and the catalysts increased by five times, and the
test was carried out under the previous reaction conditions (For details, refer to supporting
information). When the reaction was complete, ethanol was added to the system to dissolve the
product. Then the catalyst was filtrate and wash with ethanol and dry in air and subjected to a
new cycle of the reaction. The results indicated that the used material was also active as a
catalyst for four runs without a dramatic loss of catalytic activity (Fig. 5).
Finally, we performed a comparison between present catalysts, introduced in this work, and
some other previously published catalytic systems, and the results were demonstrated in Table
4. This comparison clearly shows the efficiency of the present catalysts.
3. Conclusions
In summary, we have successfully synthesized and characterized two new Cu(II) complexes
containing Schiff-base and diazo ligands. Both complexes were utilized in AAC reaction as
new catalysts. By comparing the catalytic activity of them in the same procedure, it was
understood that the complex with Schiff-base ligand is able to progress the AAC reaction much
more efficient than the complex with a diazo ligand. In addition to higher yields, the reaction
condition was milder for Schiff-base complex in comparison with the diazo complex. All the
observations confirmed that the nature of Schiff-base ligand is more powerful in maintaining
the copper catalyst in its active form progressing the reaction.
4. Acknowledgments
M.B. acknowledges the research council of the Sharif University of Technology for the
research funding of this work. The Università degli Studi di Perugia and MIUR are also
acknowledged for financial support to the project AMIS, through the program “Dipartimenti
di Eccellenza - 2018-2022”.
Supporting Information
Experimental details, full characterization data, and Additional data for the computational
study are available in the electronic supporting information. CCDC 1859484 and CCDC

1859485 contains the supplementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailed
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre,
12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033..
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Table 1. Evaluation of temperature and amount of the catalysts on the cycloaddition of benzyl
chloride with phenylacetylene in the presence of sodium azide.a
Entry
1
Cat. (mol %)
-
Temp. (oC)
70
Yield (%)b
0
TON
-
2
3
4
5
6
7
8
9
3(0.28)
3(0.57)
3(0.86)
3(1.15)
3(1.44)
3(1.73)
4(0.28)
4(0.57)
4(0.86)
4(1.14)
4(1.44)
4(1.73)
3(1.15)
3(1.15)
3(1.15)
3(1.15)
3(1.15)
3(1.15)
4(0.86)
4(0.86)
4(0.86)
4(0.86)
4(0.86)
4(0.86)
4(1.14)
3(1.15)
4(0.86)
1(1.15)
2(1.15)
Cu(OAc)2.H2O(1.15)
70
70
70
70
70
70
70
70
70
70
70
70
r.t.
40
50
60
90
58
63
83
97
96
97
51
64
76
78
75
78
18
80
96
96
98
98
6
39
64
71
77
76
78
95
77
0
201
109
96
84
66
56
178
111
88
67
52
45
15
69
83
83
85
85
6
45
74
82
89
88
68
83
89
0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27b
28b
29
30
31
100
r.t.
40
50
60
90
100
100
50
70
70
70
70
0
67
0
58
a; Reaction conditions: 0.5 mmol of phenylacetylene, 0.55 mmol of benzyl chloride, 0.55 mmol of sodium azide, 2 mL of H2O,
Time = 6 h for the catalyst 3 and 14 h for the catalyst 4. bIsolated yields.
b; The reactions were performed by adding sodium ascorbate as a reductant with a molar ratio of 2:1 of sodium ascorbate to
the catalyst.

Table 2. The effect of solvent on the cycloaddition of benzyl chloride with phenylacetylene in
the presence of sodium azide.a
Entry
Solvent
Yield (%)b
(3)
54
~0
37
12
~0
9
(4)
38
~0
24
5
1
2
3
4
5
6
7
8
DMSO
Acetone
Ethanol
1,2-Dichloroethane
Chloroform
Acetonitrile
DMSO/Water (1:1)
Water
~0
5
83
61
96
76
a Reaction conditions: 0.5 mmol of phenylacetylene, 0.55 mmol of benzyl chloride, 0.55 mmol of sodium azide,
solvent 2 mL, (50˚C, 6 h and 1.15 mol% for catalyst 3) and (70˚C, 14 h and 0.86 mol% for catalyst 4). b Isolated
yields.

Table 3. CuAAC in the presence of catalysts 3 or 4 and NaN3 under the optimized reaction
conditions.a
Yield (%)b
Entry
Aliphatic halide
Alkyne
(3)
(4)
1
96
76
2
3
91
97
69
73
4
5
89
94
64
73
6
7
90
82
65
46
8
85
49
a Reaction conditions: 0.5 mmol of a terminal alkyne, 0.55 mmol of alkyl halide, 0.55 mmol of sodium azide, 2
b
mL of H2O, (50˚C, 6 h and 1.15 mol% for the catalyst 3) and (70˚C, 14 h and 0.86 mol% for the catalyst 4).
Isolated yields.

Table 4. A comparative study of present catalysts with the previously published catalysts in
the azide-alkyne cycloaddition reaction
Entry
Catalyst
[Cu(tzol)2]
[Cu(dppo)2]
C3H7COOCu(PPh3)2
Cu NPs/silica
coated maghemite
3
Condition
Yield (%)
Ref.
[11c]
[6a]
Catalyst (2.4 mol%)/H2O/12 h/70°C
Catalyst (2.0 mol%)/H2O/8 h/RT
Catalyst (1.0 mol%)/CH2Cl2/5 h/r.t.
96
86
98
1
2
3
[22]
Catalyst (4.3 mol%)/H2O/2 h/70°C
83
[23]
4
5
6
Catalyst (1.15 mol%)/H2O/6 h/50°C
Catalyst (0.86 mol%)/H2O/14 h/70°C
96
76
This work
This work
4

Scheme 1. Synthesis of complexes 3 and 4.

1
3
Figure 1. ORTEP diagram of the structures 1 and 3

30
25
20
15
10
5
0
1.5
1
0.5
0
-0.5
-1
-1.5
Reaction Coordinate
30
25
20
15
10
5
0
1.5
1
0.5
0
-0.5
-1
-1.5
Reaction Coordinate
Figure 2. Energy profiles for enol-keto tautomerization of a) ligand 1 and b) ligand 2

Figure. 3. (A) CV of complex 3 and (B) CV of complex 4 in phosphate buffer solution (pH=
7.0) and scan rate was 50 mV.s-1.

100
90
80
70
60
50
40
30
20
10
0
0
2
4
6
8
10
Time (h)
12
14
16
18
Catayst (3)
Catalyst (4)
Figure 4. Reaction profile for the cycloaddition of benzyl chloride with phenylacetylene in the
presence of azide under optimal conditions (Table 1, entry 16 for catalyst 3 and entry 10 for
the catalyst 4).

Figure 5. Reusability studies of the complex 3 as a catalyst in the azide-alkyne cycloaddition
reaction.

Graphical Abstract- Synopsis
Synthesis, Characterization, and Comparison of Two New Copper(II)
Complexes Containing Schiff-base and Diazo Ligands as New Catalysts in
CuAAC Reaction.
Two Cu(II) complexes were synthesized including Schiff-Base and diazo ligands with the same
geometry. The catalytic potential of the complexes was compared together in one-pot azide-alkyne
cycloaddition reaction due to realize the effect of Schiff-Base and diazo ligands nature on the catalytic
system. Finally, it was understood that the Schiff-base complex behaved much more efficient than the
diazo complex.