CuI-functionalized halloysite nanoclay as an efficient heterogeneous catalyst for promoting click reactions: Combination of experimental and computational chemistry

Article abstract of DOI:10.1002/aoc.4283

Amine-functionalized halloysite nanotubes (HNTs-2?N) were prepared and further modified by introduction of salicylaldehyde and formation of imine functionality (HNTs-2?N-Sal). The latter was subsequently used for immobilization of CuI and formation of CuI@HNTs-2?N-Sal, which could effectively promote click reactions of terminal alkynes, sodium azide and α-haloketones or alkyl halides in aqueous media and under mild reaction conditions to afford 1,2,3-triazoles in relatively short reaction times. Notably, the catalyst could be recycled in up to six reaction runs with negligible loss of catalytic activity and CuI leaching. Also, the geometry of CuI adsorption on the modified HNTs surface was explored by molecular simulation with density functional theory. Furthermore, topographic steric maps of possible coordination modes were obtained using the recently released SambVca2 web application tool. Based on obtained results, a catalytic site with superior performance was suggested.

Full text of DOI:10.1002/aoc.4283

Received: 16 November 2017
DOI: 10.1002/aoc.4283
Revised: 21 December 2017
Accepted: 24 December 2017
F U L L P A P E R
CuI‐functionalized halloysite nanoclay as an efficient
heterogeneous catalyst for promoting click reactions:
Combination of experimental and computational chemistry
Naeimeh Bahri‐Laleh1 | Samaheh Sadjadi2
| Majid M. Heravi3
| Masoumeh Malmir3
1 Polymerization Engineering Department,
Amine‐functionalized halloysite nanotubes (HNTs‐2 N) were prepared and fur-
ther modified by introduction of salicylaldehyde and formation of imine func-
tionality (HNTs‐2 N‐Sal). The latter was subsequently used for
immobilization of CuI and formation of CuI@HNTs‐2 N‐Sal, which could
effectively promote click reactions of terminal alkynes, sodium azide and
α‐haloketones or alkyl halides in aqueous media and under mild reaction con-
ditions to afford 1,2,3‐triazoles in relatively short reaction times. Notably, the
catalyst could be recycled in up to six reaction runs with negligible loss of cat-
alytic activity and CuI leaching. Also, the geometry of CuI adsorption on the
modified HNTs surface was explored by molecular simulation with density
functional theory. Furthermore, topographic steric maps of possible coordina-
tion modes were obtained using the recently released SambVca2 web applica-
tion tool. Based on obtained results, a catalytic site with superior performance
was suggested.
Iran Polymer and Petrochemical Institute,
PO Box 14965/115, Tehran, Iran
2 Gas Conversion Department, Faculty of
Petrochemicals, Iran Polymer and
Petrochemical Institute, PO Box
14975‐112, Tehran, Iran
3 Department of Chemistry, School of
Science, Alzahra University, Box
1993891176, Vanak, Tehran, Iran
Correspondence
Samaheh Sadjadi, Gas Conversion
Department, Faculty of Petrochemicals,
Iran Polymer and Petrochemical Institute,
PO Box 14975‐112, Tehran, Iran.
Email: s.sadjadi@ippi.ac.ir
KEYWORDS
click reaction, DFT simulation, halloysite nanotubes, heterogeneous catalyst
1 | INTRODUCTION
range of applications[13] such as energy storage, drug
delivery,[14–17] removal of pollutants from water,[18] mem-
Halloysite nanotubes (HNTs) are dioctahedral 1:1 layered
aluminosilicates with the general formula of
Al2(OH)4Si2O5⋅2H2O.[1–3] They are composed of tetrahe-
dral siloxanes on the exterior and aluminols on the inte-
rior surface.[4] Water molecules are also located in
interlayer spaces of HNTs. HNTs possess high surface
area. The lengths of HNTs range between ca 100 and
4000 nm.[5] Their cavities are relatively large (the external
and internal diameters of HNTs vary in the ranges 30–190
and 10–100 nm, respectively.[6] Besides their unique phys-
ical properties, HNTs are chemically inert and biocompat-
ible.[1,7] Moreover, the surface chemistry of HNTs can be
tuned by introducing various functionalities[8–10] on both
inner and outer surfaces.[6,11,12] These features of HNTs
render them promising candidates for use in a diverse
branes for gas separation[19] and catalysis.[20] Recently,
the use of functionalized HNTs for catalysis has received
growing attention and many research groups have devel-
oped various heterogeneous catalysts by immobilization
of a variety of catalytic species on such functionalized
HNTs.[2,21–28]
The concept of click chemistry, initially introduced by
Sharpless and co‐workers in 2001, refers to one of the
most popular reactions, which is performed with high
selectivity under mild reaction conditions. Click chemis-
try has been used in a diverse range of scientific areas[29]
such as bio‐conjugation, drug discovery and polymer
and supermolecular chemistry.[30,31] Among the click
chemistry transformations, the most renowned example
is Huisgen 1,3‐dipolar cycloaddition, in which terminal
Appl Organometal Chem. 2018;e4283.
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https://doi.org/10.1002/aoc.4283

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BAHRI‐LALEH ET AL.
alkynes and organic azides are combined to give 1,4‐
disubstituted 1,2,3‐triazoles. The 1,2,3‐triazole family is
an important heterocyclic category of organic compounds
with a wide range of applications and biological activi-
ties.[32,33] Recently, various heterogeneous and homoge-
neous catalysts have been developed for promoting the
click reactions and synthesis of 1,2,3‐triazoles.[34]
inductively couple plasma atomic emission spectroscopy
(ICP‐AES), X‐ray diffraction (XRD), scanning electron
microscopy (SEM), energy dispersive X‐ray spectroscopy
(EDS), thermogravimetric analysis (TGA) and Fourier
transform infrared (FT‐IR) spectroscopy. To record SEM‐
EDS images, a Tescan instrument, using Au‐coated sam-
ples and an acceleration voltage of 20 kV, was applied.
TGA of CuI@HNTs‐2 N‐Sal was performed using a
Mettler Toledo thermogravimetric analyser with a heating
rate of 10 °C min−1 from 50 to 700 °C under nitrogen
atmosphere. To carry out the BET analyses, a BELSORP
Mini II apparatus was used. Prior to analyses, degassing
was accomplished by heating the samples at 423 K for
4 h. A PerkinElmer Spectrum 65 instrument was
employed for performing FT‐IR spectroscopy. XRD analy-
sis was carried out using a Siemens D5000 with Cu Kα
radiation from a sealed tube. The progress of click reac-
tions was monitored by TLC using commercial alumin-
ium‐backed plates of silica gel 60 F254, visualized using
ultraviolet light. As all click products were known mate-
rials, they were validated by comparing their melting
points, determined in open capillaries using an Electro-
thermal 9100 without further corrections, and FT‐IR spec-
tra with those of authentic samples. For further
Following our attempt to investigate the utility of
novel heterogeneous catalysts for promoting chemical
transformations,[35–38] recently we have focused on the
utility of HNTs as an efficient support for immobilization
of various catalytic active species. Exploiting both experi-
mental and computational chemistry, we tried to shed
light on the chemistry of HNT‐based catalysts.[28,39–41] In
this line, here we report a novel heterogeneous catalyst
based on imine‐functionalization of HNTs through intro-
duction of aminosilanes followed by condensation with
salicylaldehyde. The resulting functionalized HNTs
(HNTs‐2 N‐Sal) were applied for the immobilization of
CuI to afford CuI@HNTs‐2 N‐Sal. The latter was then
used for promoting click reactions of terminal alkynes,
sodium azide and α‐haloketones or alkyl halides in aque-
ous media and under mild reaction conditions to afford
1,2,3‐triazoles in relatively short reaction times
(Scheme 1). The recyclability of the catalyst as well as
CuI leaching were also studied. Then, molecular simula-
tion was employed in order to obtain a deeper insight
into: (i) the various coordination modes of CuI adsorption
on HNTs‐2 N‐Sal; (ii) the interaction energy between CuI
and 2 N‐Sal‐functionalized HNTs in gas and solution
phases; and (iii) the free volume around Cu catalyst in
suggested coordination sites.
1
identification, H NMR and 13C NMR spectra of some
selected samples were also recorded with a Bruker DRX‐
400 spectrometer at 400 and 100 MHz, respectively.
2.2 | Functionalization of HNTs: Synthesis
of HNTs‐2 N
To introduce amine functionality to HNTs, HNTs (1.0 g)
were dispersed in 50 ml of dry toluene. Then, a solution
of AEAPTMS (4 ml) in 20 ml of dry toluene was added
dropwise. The resulting mixture was subsequently
refluxed at 112 °C overnight. After that, the product
(1; Figure 1) was separated by simple filtration and then
washed several times with dry toluene and dried at
90 °C overnight.
2 | EXPERIMENTAL
2.1 | Materials and Instrumentation
The catalyst was synthesized using the following
chemicals: halloysite nanoclay, salicylaldehyde, N‐
[3(trimethoxysilyl)propyl]ethylenediamine (AEAPTMS),
toluene, MeOH and CuI, all purchased from Sigma‐
Aldrich and used with no purification. To perform click
reactions, α‐haloketones, alkyl halides, terminal alkynes
and sodium azide were used. These chemicals were of
analytical grade and obtained from Sigma‐Aldrich.
2.3 | Imine Functionalization of HNTs:
Synthesis of HNTs‐2 N‐Sal
Salicylaldehyde (5 ml) was added to a suspension of
HNTs‐2 N (1 g) in MeOH (50 ml) and refluxed for 18 h.
Upon completion of the reaction, the yellow solid product
Characterization of CuI@HNTs‐2 N‐Sal was
achieved using Brunauer–Emmett–Teller (BET) analysis,
SCHEME 1 Model click reaction of
sodium azide, halides and acetylenes

BAHRI‐LALEH ET AL.
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FIGURE 1 Procedure for synthesis of CuI@HNTs‐2 N‐Sal
(2; Figure 1) was obtained by simple filtration, washing
with MeOH three times and drying at 100 °C overnight.
(0.48 mol%) was added and the reaction mixture was mag-
netically stirred for the appropriate time. The progress of
the reaction was monitored by TLC (n‐hexane–ethyl ace-
tate; 8:2). Upon completion of the reaction, the catalyst
was filtered. The filtrate was washed with ethyl acetate
(410 ml). Then, the organic extract was washed with hot
EtOH and dried over Na2SO4. The removal of solvent
under vacuum furnished the corresponding 1,2,3‐triazole,
which did not require further purification.
To recycle the catalyst, the recovered catalyst was
washed with toluene (2 × 10 ml), dried in an oven and
stored for use in subsequent reaction runs under the same
conditions.
2.4 | Introduction of CuI: Synthesis of
CuI@HNTs‐2 N‐Sal
To incorporate copper iodide, CuI (0.190 g, 1.0 mmol) was
added to a suspension of HNTs‐2 N‐Sal (1.0 g) in dry tol-
uene (50 ml) and stirred overnight. Upon completion of
the reaction, the reaction mixture was filtered off and
the residue was washed three times with toluene and then
dried at 80 °C overnight. The resulting CuI@HNTs‐2 N‐
Sal catalyst (3; Figure 1) was characterized using XRD,
SEM‐EDS, ICP‐AES, elemental mapping, TGA, differen-
tial TGA and FT‐IR techniques.
2.6 | Computational Details
All molecular simulations were performed with the Gauss-
ian 09 package program[42] using the M06 suite of density
functional which comprises the hybrid meta generalized
gradient approximation developed by Zhao and Truhlar.[43]
Electronic configuration of the molecular systems was
described by the standard split valence double‐ζ basis
2.5 | General Procedure for Synthesis of 1‐
Benzyl‐4‐phenyl‐1H‐1,2,3‐triazole (4a)
α‐Haloketone (1 mmol) or alkyl halide (1 mmol), terminal
alkyne (1 mmol) and sodium azide (1.3 mmol) were
mixed in water (10 ml). Then, CuI@HNTs‐2 N‐Sal

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BAHRI‐LALEH ET AL.
set[44] plus diffuse and polarization functions. This method
was included as 3‐21 + G(d,p) keyword in Gaussian.
Harmonic oscillator model of aromaticity (HOMA)
and nucleus‐independent chemical shift (NICS) aromatic-
ity values were calculated at the same level of theory. The
GIAO method of Wolinski and co‐workers[45] was
employed to perform [NICS(0)] calculations, i.e. NICS at
the ring centre. This technique was conducted using the
non‐weighted mean of the heavy atom coordinates.
To estimate the solvent effects, the polarizable solva-
tion model was employed using acetonitrile, ethanol,
dimethylformamide (DMF) and toluene as solvents.
The buried volumes, VBur, were calculated using the
SambVca package developed by Cavallo and co‐
workers.[46,47] VBur provides us with counter steric maps
around the transition metal. A modified version of the
SambVca package, i.e. SambVca2,[46] was used to evaluate
steric maps of the catalyst isomers with different
geometries.
together to form aggregates. Compared to the tubular
morphology of pure HNTs (Figure S1 in supporting infor-
mation), CuI@HNTs‐2 N‐Sal exhibited a distinguished
morphology, which is more compact than that of pure
HNTs. This observation can be attributed to the presence
of functionalities on the surface of HNTs and the possibil-
ity of electrostatic interactions among the tubes. This may
bring the tubes closer and facilitate formation of
aggregates.
The EDS analysis of the catalyst is presented in
Figure 2. The observation of Si, Al and O in the EDS trace
of CuI@HNTs‐2 N‐Sal can be indicative of HNT structure,
while the presence of Cu and I can be representative of
CuI and confirm its incorporation in the structure of the
catalyst. Notably, the functionalization of HNTs with
salicylaldehyde and organosilane can be proved by
observing signals of C, O, N and Si atoms.
The elemental mapping analysis of CuI@Sal‐HNT
(Figure 3) establishes high dispersion of Cu and I atoms,
indicating that CuI catalytic species are dispersed well
on the surface of the functionalized HNTs.
The FT‐IR spectrum of CuI@HNTs‐2 N‐Sal is depicted
in Figure 4. The characteristic bands of HNTs, which are
the bands at 3689 and 3619 cm−1 (vibration of ―OH on
interior surface),[27] the bands at 532 cm−1 (Al―O―Si
vibration) and 1024 cm−1 (Si―O stretching), can be
3 | RESULTS AND DISCUSSION
3.1 | Catalyst Characterization
The SEM images of CuI@HNTs‐2 N‐Sal are shown in
Figure 2. As depicted, the short tubes of HNTs closed
FIGURE 2 SEM images and EDS analysis of CuI@HNTs‐2 N‐Sal

BAHRI‐LALEH ET AL.
5 of 13
FIGURE 3 Elemental mapping analysis of CuI@HNTs‐2 N‐Sal
observed in this spectrum. The characteristic bands of
AEAPTMS, i.e. the bands at 2904 cm−1 (―CH2) and
1024 cm−1 (Si―O stretching), mostly overlap with those
of HNTs. However, other analyses, such as EDS, con-
firmed the conjugation of this functionality. According
to the literature,[48] the band at 746 cm−1 can be assigned
to CuI. Moreover, the band observed at 1646 cm−1 is
indicative of the formation of ―C¼N bond.
The catalyst was also characterized using XRD
analysis (Figure 5). The obtained XRD pattern was
compared with that of pure HNTs (Figure 5). Compar-
ing the two XRD patterns, it can be concluded that
the XRD pattern of CuI@HNTs‐2 N‐Sal exhibits the
characteristic bands of pure HNTs, the peaks observed
at 2θ = 8°, 13°, 23°, 28°, 31°, 58° and 67° (JCPDS
no. 29‐1487, labelled as H),[6,49] indicating that, upon
functionalization and CuI incorporation, the native
structure of HNTs did not collapse. The sharp
peaks, labelled as C, match well with JCPDS card
no. 01‐076‐0207, and can be assigned to cubic CuI.[48]
FIGURE 4 FT‐IR spectrum of CuI@HNTs‐2 N‐Sal

6 of 13
BAHRI‐LALEH ET AL.
thermograms of HNTs‐2 N‐Sal and CuI@HNTs‐2 N‐Sal
showed that incorporation of CuI can alter the thermo-
gram slightly. This can be due to degradation of copper
iodide.
To study the textural properties of CuI@HNTs‐2 N‐Sal,
the nitrogen adsorption–desorption isotherm of the cata-
lyst was recorded (Figure 7). The obtained isotherm,
which was of the nitrogen type II with H3 hysteresis
loops,[6] confirmed the porous structure of CuI@HNTs‐
2 N‐Sal and was similar to that of pure HNT (Figure S2,
supporting information). This observation indicates that,
upon functionalization of HNTs and incorporation of
CuI, the porous structure of CuI@HNTs‐2 N‐Sal was pre-
served. A comparison of the specific surface area of pure
HNTs and CuI@HNTs‐2 N‐Sal implied that upon
functionalization, the specific surface of area of pure
FIGURE 5 XRD patterns of (a) pure HNTs and (b) CuI@HNTs‐
2 N‐Sal
HNTs (51 cm3 g−1) reduced to ca 13 cm3 g−1
.
To further characterize the catalyst, the content of CuI
was measured using ICP‐AES analysis. To prepare sam-
ples for ICP‐AES analysis, CuI@HNTs‐2 N‐Sal was
digested in a concentrated acidic solution of HCl and
HNO3. The filtrate was then subjected to ICP‐AES analy-
sis. Using this protocol, the content of CuI was calculated
to be about 10 wt%.
In the next step, the thermal stability of CuI@HNTs‐
2 N‐Sal and the content of functionality on the HNTs were
studied using TGA. The thermograms of HNT, HNT‐2 N,
HNT‐2 N‐Sal and CuI@HNTs‐2 N‐Sal are depicted in
Figure 6. HNT exhibited two weight losses: the first one,
around 150 °C, is as a result of losing water and the second
one, around 500 °C, is due to the dehydroxylation of the
HNT matrix.[50,51] To estimate the content of the
organosilane (2 N) on the surface of HNTs, the thermo-
gram of HNT‐2 N was obtained and compared with that
of HNT (Figure 6). The results showed that the content
of 2 N was about 2 wt%. Next, to estimate the content of
Sal on the catalyst, the thermogram of HNTs‐2 N‐Sal
was recorded. Using this thermogram the content of Sal
was calculated to be about 14 wt%. A comparison of the
3.2 | Catalytic Activity
In the next step, the catalytic activity of CuI@HNTs‐
2 N‐Sal was studied. Considering the importance of the
click reaction and the utility of 1,2,3‐triazoles for the
synthesis of more complicated heterocycles and biologi-
cally active compounds, the click reaction of α‐
haloketone or alkyl halide, terminal alkyne and sodium
azide was targeted. Initially, the reaction of benzyl bro-
mide, phenylacetylene and sodium azide was selected
as a model reaction and performed in the presence of
various solvents as well as under solvent‐free conditions
(Table 1). Gratifyingly, comparison of the yields of the
model products obtained using various solvents demon-
strated that use of water as solvent led to the highest
FIGURE 6 TGA of pure HNT, HNT‐2 N, HNT‐2 N‐Sal,
CuI@HNTs‐2 N‐Sal and recycled CuI@HNTs‐2 N‐Sal
FIGURE
CuI@HNTs‐2 N‐Sal
7
Nitrogen adsorption–desorption isotherm of

BAHRI‐LALEH ET AL.
7 of 13
TABLE 1 Optimization of reaction conditions in click reaction of phenyl acetylene, benzyl bromide and sodium azidea
Entry
Loading of catalyst (mg)
Condition (solvent/temperature (°C))
Time (min)
Yield (%)b
1
15
15
15
25
5
H2O/r.t.
12
12
12
12
12
60
20
25
30
60
60
12
98
95
96
95
80
25
80
70
55
45
40
75
2
H2O/100
3
H2O/50
4
H2O/r.t.
5
H2O/r.t.
6
None
15
15
15
15
15
15
H2O/r.t.
7
H2O–EtOH (1:1)/r.t.
EtOH/r.t.
8
9
CHCl3/r.t.
Toluene/r.t.
CH3CN/r.t.
Solvent free/r.t.
10
11
12
aReactions were run in 5 ml solvent with phenylacetylene (1.0 equiv.), benzyl bromide (1.0 equiv.) and sodium azide (1.3 equiv.). bIsolated yield.
yield of the desired product. Next, other reaction vari-
ables, namely reaction temperature and catalyst amount,
were optimized by performing the model reaction in the
presence of various amounts of the catalyst at different
temperatures (Table 1). The results indicated that the
highest yield of the model product was achieved at
room temperature in the presence of 0.48 mol% catalyst.
The generality of the protocol was then studied. For
this purpose, a range of substrates with different electron
densities were used and various 1,2,3‐triazoles were syn-
thesized (Table 2). The results confirmed that
CuI@HNTs‐2 N‐Sal could catalyse the reactions of all
applied substrates to afford the corresponding 1,2,3‐
triazoles in high yields and short reaction times. The
results also showed that use of α‐haloketones led to
slightly lower yields and longer reaction times compared
to alkyl halides.
Finally, the efficiency of CuI@HNTs‐2 N‐Sal for the
above‐mentioned click reaction was compared with that
of some previously reported catalysts under various reac-
tion conditions (Table 3).[48,52–69] Comparing the proto-
cols, it can be concluded that use of CuI@HNTs‐2 N‐Sal
led to higher or comparable yield of the desired product
in shorter short reaction time. Moreover, use of aqueous
media, low reaction temperature as well as the recyclabil-
ity of the catalyst render this protocol eco‐friendly.
It is worth mentioning that there are some reports in
which high yields of products were achieved by using a
TABLE 2 Synthesis of three‐component reaction of derivatives of acetylene, halides and sodium azide catalysed by CuI@HNTs‐2 N‐Sala
R1
R2
R3
X
Product
Time (min)
Yield (%)b
M.p., obs. (°C)
M.p., lit. (°C)
1a: C6H5
H
H
Br
Cl
Br
Cl
Br
Br
Br
Br
Br
Br
Br
4a
4b
4c
4d
4e
4f
12
15
15
20
20
22
25
30
30
35
45
98
94
90
91
88
92
90
95
94
89
93
127−129
126−128
78−80
127−128[52]
127−128[52]
77−79[52]
1a
H
H
1b: CH2OH
H
H
1b
1a
1a
1a
1a
1b
1b
1b
H
H
76−78
77−79[52]
¼O
¼O
¼O
¼O
¼O
¼O
¼O
H
168−170
116−118
102−104
156−158
110−112
156−158
180−182
169−171[52]
115−118[52]
102−104[52]
157−159[52]
111−113[52]
156−158[52]
180−183[52]
Br
Cl
Me
H
4g
4h
4i
Br
Me
4j
4k
aReaction conditions: alkynes 1a,b (1.0 equiv.), halides 2a,b (1.0 equiv.) and sodium azide 3 (1.3 equiv.), H2O (5 ml) and CuI@HNTs‐2 N‐Sal (15 mg) under
stirring at room temperature. bIsolated yield.

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BAHRI‐LALEH ET AL.
TABLE 3 Comparison of catalytic activity of CuI@HNTs‐2 N‐Sal with that other recently reported catalysts in click reaction
Reaction
conditions
Yield
(%)b
Time
(h:min)
Entry
Catalyst
Catalyst amount
Ref.
[52]
1
MNP@PILCu
0.7 mol%
5 mg
H2O/Na ascorbate/50 °C
H2O/r.t.
95
99
93
99
91
98
93
94
98
96
95
99
98
94
95
96
3
[53]
[54]
[55]
[56]
[57]
[58]
[48]
2
MNPs@BiimCu(I)
Cu NPs
0:30
8
3
4.3 mol%
0.6 mol%
2 mg
CH3CN/r.t.
4
PS‐C22‐CuI
H2O/r.t.
15
5
Au‐TiO2
H2O/r.t.
0:30
3
6
Cu NPs/C
0.5 mol%
20 mg
H2O/70 °C
7
Fe3O4@TiO2/Cu2O
Cell‐CuI
H2O/reflux
0:15
6
8
3.5 mol%
0.48 mol%
0.3 mol%
10 mg
H2O/70 °C
9
CuI@HNTs‐2 N‐Sal
MNP@PDMA‐Cu
Nano‐Fe3O4@Cellulose‐NH2‐CuI
MNP@SPAAm/Cu
CuI‐MMT
H2O/r.t.
0:12
2
This work
[59]
10
11
12
13
14
15
16
H2O/Na ascorbate/50 °C
H2O/reflux
[60]
[61]
[62]
[63]
[64]
[65]
0:20
1
0.5 mol%
5 mg
H2O/Na ascorbate/50 °C
H2O/r.t.
2
γ‐Fe2O3@TiO2‐EG‐CuII
4 mol%
1 mol%
0.05 mol%
H2O/70 °C
0:05
12
POSS–SAL–Cu
H2O/70 °C
Corn‐cob cellulose‐supported
Na ascorbate/70 °C
2:30
poly(hydroxamic) copper complex
[65]
[65]
[65]
17
18
19
Corn‐cob cellulose‐supported
poly(hydroxamic) copper complex
0.005 mol%
Na ascorbate/90 °C
Na ascorbate/70 °C
Na ascorbate/70 °C
94
91
93
2:30
6
Corn‐cob cellulose‐supported
poly(hydroxamic) copper complex
0.005 mol%
Corn‐cob cellulose‐supported
0.1 mg = 50 mol ppm
20
poly(hydroxamic) copper complex
aReaction conditions: phenylactylene, benzyl bromide and sodium azide reacted under different conditions. bIsolated yield.
low amount of catalyst loading. Notably, in the present
case, we focus on the utility of functionalized HNTs for
incorporation of CuI and shedding light on the interac-
tions of CuI with the support using density functional the-
ory (DFT) studies. To establish the activity of the catalyst,
we investigated its catalytic activity for click reactions. It
is not claimed that CuI@HNTs‐2 N‐Sal is the best catalyst
for click reactions. However, from the results it can be
concluded that the catalytic activity and reusability of
CuI@HNTs‐2 N‐Sal are good and it can be considered as
an efficient (and not the best) catalyst.
diyne. Finally, the desired 1,2,3‐triazole is achieved
through CuI‐catalysed cycloaddition.
3.4 | Catalyst Recycling
Recyclability is an important feature of catalysts that
makes them economically promising. Regarding hetero-
geneous catalysts, which benefit from facile recovery,
the importance of high recyclability can be more pro-
nounced. To investigate whether CuI@HNTs‐2 N‐Sal is
recyclable, the catalyst used for the synthesis of the model
product was recovered from reaction media (see
Section 1), and after washing and drying was subjected
to subsequent reaction runs. The results (Figure 8)
established that recycling of the catalyst for up to six reac-
tion runs can be successfully achieved and upon each
recycling only a slight loss of catalytic activity (1–3%)
was observed. This observation confirmed the recyclabil-
ity of CuI@HNTs‐2 N‐Sal.
3.3 | Reaction Mechanism
Based on previous reports,[48] a potential mechanistic
pathway for the CuI@HNTs‐2 N‐Sal‐catalysed three‐com-
ponent click reaction can be suggested, as depicted in
Scheme 2. As illustrated, initially, benzyl azide was
achieved by nucleophilic substitution of azide on benzyl
halides. Simultaneously, terminal alkyne is activated by
the catalyst and tolerates homocoupling to furnish a
Next, the leaching of CuI species was investigated
using ICP‐AES analysis. The results confirmed negligible

BAHRI‐LALEH ET AL.
9 of 13
SCHEME 2 Possible mechanism for
click reaction[48]
FIGURE 9 FT‐IR spectra of (a) fresh CuI@HNTs‐2 N‐Sal and (b)
FIGURE 8 Recyclability of CuI@HNTs‐2 N‐Sal catalyst in click
after six uses
reaction
possibility of deposition of organic substrates on the cata-
lyst. This fact as well as the slight leaching of CuI can jus-
tify the observed loss of the catalytic activity upon
recycling.
The effect of the recovery and recycling of the catalyst
on its morphology was also studied by comparing SEM
images of the fresh and recycled catalyst. As depicted in
Figure 10, both SEM images are similar and no significant
agglomeration was observed. This indicates that the
recycling of the catalyst did not induce any significant
change in the morphology.
leaching of CuI (0.01 wt%), indicating the heterogeneous
nature of the catalysis as well as the efficiency of HNTs‐
2 N‐Sal for anchoring CuI and preventing it from
leaching.
To shed light on the effect of recycling on the structure
of CuI@HNTs‐2 N‐Sal, the FT‐IR spectrum of recycled
catalyst was obtained and compared with that of the fresh
one. As shown in Figure 9, both spectra exhibited similar
characteristic bands, indicating that the recycled catalyst
preserved its structure upon recycling.
To elucidate whether upon recovery and recycling the
reagents could deposit on the catalyst, TGA of recycled
catalyst was performed and compared with that of fresh
catalyst (Figure 6). The results established that the reused
catalyst showed slightly higher weight loss, indicating the
3.5 | Molecular Simulation Results
An attempt was made to shed light on the possible
geometries of CuI adsorption on the
2
N‐Sal‐

10 of 13
BAHRI‐LALEH ET AL.
FIGURE 10 SEM images of (A) fresh CuI@HNTs‐2 N‐Sal and
(B) and after several runs
FIGURE 11 Optimized structures of CuI@HNTs‐2 N‐Sal
compound in (a) bidentate and (b) tridentate modes
functionalized HNTs by employing molecular model-
ling at the M06/3‐21(G,d) level of theory. The choice
of this method was based on our recent studies
which showed that hybrid functionals give accurate
data on the simulation of transition metal‐containing
systems.[70–74] A cluster containing three aluminium
and two silicon units was utilized as HNT model.
During optimizations, in the presence of surface OH
groups, extra transformation of the corner atoms
was observed due to the strong interaction between
surface OH and the ligand. To avoid such alteration,
most of the surface ―OH groups were replaced with
―CH3 unit.
TABLE 4 EAd (in kcal mol−1) related to CuI physisorption on
HNTs‐2 N‐Sal in solution and gas phases
Interaction via
EAd
NO
Gas phase
−131.9
NNO
Gas phase
Acetonitrile
DMF
−179.1
−174.0
−173.5
−176.4
−174.1
Toluene
Ethanol

BAHRI‐LALEH ET AL.
11 of 13
The energy of CuI adsorption was calculated accord-
ing to the following formula:
ΔEAd ¼ ECuI@HNTs‐2N‐Sal−ECuI−EHNTs‐2N‐Sal
In this formula, ECuI@HNTs‐2N‐Sal is the energy of
CuI@HNTs‐2 N‐Sal, while ECuI and EHNTs‐2N‐Sal are the
energies of bare CuI and HNTs‐2 N‐Sal, respectively.
The geometry of CuI adsorption on 2 N‐Sal‐function-
alized HNTs was then studied. As can be seen in
Figure 11, CuI@HNTs‐2 N‐Sal can adopt two geometries.
The first one corresponds to the CuI epitactically adsorbed
via phenolic OH and C¼N―C groups in bidentate form.
In the second geometry, CuI bonded to the HNTs‐2 N‐
Sal via not only the adsorptions sites available in the first
form, but also via C―NH―C group, introducing HNTs‐
2 N‐Sal as a tridentate ligand. These forms are indicated in
Table 4 as NO and NNO, respectively. Considering the
adsorption energy of different forms, coordination of CuI
in tridentate configuration, with EAd of −179.1 kcal mol−1
(Figure 11b) was markedly favoured relative to its coordi-
nation via bidentate configuration (Figure 11a) with Ead
of only −131.9 kcal mol−1. In fact, the structure of
Figure 11(b) was 47.1 kcal mol−1 more stable than the cor-
responding bidentate form.
EAd was calculated for the most probable CuI@HNTs‐
2 N‐Sal form, i.e. adsorption via NNO, using ethanol,
DMF, toluene and acetonitrile solvents as well. It is worth
mentioning that catalyst leaching is an unwanted phe-
nomenon which degrades the catalytic performance in
the reaction medium. The aim of studying EAd energies
in different media was to find an appropriate solvent to
reach a catalyst composition with lower leaching. Com-
paring EAd energies in the gas and solution phases it
was deduced that CuI physisorption was favourable in
the gas phase. Among the studied solvents, toluene exhib-
ited much higher performance since EAd was lower in this
case. Considering EAd energies in different media, toluene
was selected as an appropriate solvent in the catalyst syn-
thesis procedure.
FIGURE 12 Topographic steric maps of CuI adsorption on
HNTs‐2 N‐Sal in (a) bidentate and (b) tridentate modes. The
isocontour curves are given in Å
indicates that besides lower catalyst leaching in NNO
form, this configuration has less bulkiness which
increases Cu availability in catalytic reactions. This is
beneficial for the catalysis of ongoing reaction.
It was assumed that electron delocalization of the
phenyl ring can be altered differently by CuI coordination
in bi‐ and tridentate forms. The local aromaticity of C6
ring in the ligand structure was determined quantitatively
Steric hindrance around the Cu active centre in both
bidentate and tridentate morphologies was analysed using
the SambVca2 Web application.[46] This extracts simple
two‐dimensional isocontours, i.e. topographic maps.
Using this application, buried volume percent (%VBur
)
was calculated in the single quadrants around the metal
centre. These values were obtained by analysing the steric
bulk of the HNTs‐2 N‐Sal ligand in the DFT optimized
structures of the model complexes (Figure 12). Values of
%VBur of 53.0 and 27.5% in NO and NNO configurations,
respectively, highlighted a difference in steric bulkiness
between these two modes, with the NNO clearly less
bulky than the NO. The result of this analysis clearly
TABLE 5 HOMA and NICS values (in ppm) for phenyl ring of
2 N‐Sal ligand in different bidentate and tridentate CuI coordination
modes
HOMA
NICS
NO (Figure 11a)
0.949
0.993
9.05
9.79
NNO (Figure 11b)

12 of 13
BAHRI‐LALEH ET AL.
through the use of the HOMA and NICS methods.[75,76] In
these calculations, the higher the HOMA and NICS
values, the more aromatic the ring. The data presented in
Table 5 emphasized that the phenyl ring in the tridentate
form has higher aromaticity than it does in the bidentate
configuration. This behaviour definitely would affect cat-
alytic performance of Cu metal. The type of this affect is
unclear to us and needs further investigation.
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134, 1853.
In summary, a novel heterogeneous catalyst, CuI@HNTs‐
2 N‐Sal, was designed and prepared through amine
functionalization of HNTs followed by reaction with
salicylaldehyde and formation of imine functionality and
incorporation of CuI. The catalyst was successfully used
for promoting click reactions of α‐haloketone or alkyl
halide, terminal alkyne and sodium azide in aqueous media
and under mild reaction conditions for the synthesis of 1,2,3‐
triazoles. Notably, the results confirmed the good recyclabil-
ity of the catalyst and low leaching of CuI species. Moreover,
the characterization of the recycled catalyst proved that the
catalyst preserved its morphology and structure upon
recycling. A study of the possible adsorption sites of HNTs‐
2 N‐Sal by molecular simulation revealed that CuI coordina-
tion in tridentate configuration via NNO atoms is preferred
to bidentate coordination via only NO centres. Besides
higher adsorption energy, the former site has a smaller
%VBur value. It increases the availability of Cu catalyst which
is beneficial to the progress of the desired reaction.
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ACKNOWLEDGEMENTS
[19] R. S. Murali, M. Padaki, T. Matsuura, M. S. Abdullah, A. F.
Naeimeh Bahri‐Laleh thanks MOLNAC (www.molnac.
unisa.it) for its computer facilities. Samahe Sadjadi and
Naeimeh Bahri‐Laleh are grateful to the Iran Polymer
and Petrochemical Institute for partial financial support.
M. M. Heravi appreciates support from Alzahra
University.
Ismail, Sep. Purif. Technol. 2014, 132, 187.
[20] Y. Zhang, X. He, J. Ouyang, H. Yang, Sci. Rep. 2013, 3, 2948.
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J. Nanosci. Nanotechnol. 2017, 17, 5310.
[22] V. A. Vinokurov, A. V. Stavitskaya, Y. A. Chudakov, E. V.
Ivanov, L. K. Shrestha, K. Ariga, Y. A. Darrat, Y. M. Lvov, Sci.
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ORCID
[23] T. Yang, M. Du, M. Zhang, H. Zhu, P. Wang, M. Zou,
Nanomater. Nanotechnol. 2015, 5, 1.
Samaheh Sadjadi http://orcid.org/0000-0002-6884-4328
Majid M. Heravi http://orcid.org/0000-0003-2978-1157
[24] M. Massaro, C. G. Colletti, G. Lazzara, S. Milioto, R. Noto, S.
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How to cite this article: Bahri‐Laleh N, Sadjadi S,
Heravi MM, Malmir M. CuI‐functionalized
halloysite nanoclay as an efficient heterogeneous
catalyst for promoting click reactions: Combination
of experimental and computational chemistry. Appl
Organometal Chem. 2018;e4283. https://doi.org/
10.1002/aoc.4283
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