Copper(I)-chitin biopolymer based: An efficient and recyclable catalyst for click azide–alkyne cycloaddition reactions in water

Article abstract of DOI:10.1002/aoc.6275

The naturally occurring α-chitin biopolymer was employed for the immobilisation of copper(I) ion, resulting into a new bioconjugate complex, namely, Cu(I)-α-chitin (CuI-CHT) with catalytic efficiency in copper-catalysed azide–alkyne cycloaddition reaction

Full text of DOI:10.1002/aoc.6275

Received: 13 January 2021
DOI: 10.1002/aoc.6275
Revised: 25 March 2021
Accepted: 11 April 2021
F U L L P A P E R
Copper(I)-chitin biopolymer based: An efficient and
recyclable catalyst for click azide–alkyne cycloaddition
reactions in water
1
,2
3
4
Lahoucine Bahsis
| El-Houssaine Ablouh
| Mouhi Eddine Hachim
|
2
5
6
6
Hafid Anane
| Moha Taourirte
| Miguel Julve
| Salah-Eddine Stiriba
1
Laboratoire de Chimie de Coordination et d'Analytique (LCCA), Département de Chimie, Faculté des Sciences d'El Jadida, Université Chouaïb
Doukkali, El Jadida, Morocco
2
Laboratoire de Chimie Analytique et Moléculaire, LCAM, Faculté Polydisciplinaire de Safi, Université Cadi Ayyad, Safi, Morocco
3
Materials Science and Nanoengineering Department (MSN), Mohammed VI Polytechnic University (UM6P), Ben Guerir, Morocco
4
Équipe de Modélisation Moléculaire et de Spectroscopie, Faculté des sciences, Université de Chouaïb Doukkali, El Jadida, Morocco
5
Laboratoire de Chimie Bioorganique et Macromoléculaire, Faculté des Sciences et Techniques de Marrakech, Université Cadi Ayyad, Marrakech,
Morocco
6
Instituto de Ciencia Molecular/ICMol, Universidad de Valencia, Valencia, Spain
Correspondence
Lahoucine Bahsis, Laboratoire de Chimie
The naturally occurring α-chitin biopolymer was employed for the
de Coordination et d'Analytique (LCCA),
immobilisation of copper(I) ion, resulting into a new bioconjugate complex,
Département de Chimie, Faculté des
namely, Cu(I)-α-chitin (CuI-CHT) with catalytic efficiency in copper-catalysed
Sciences d'El Jadida, Université Chouaïb
Doukkali, B.P. 20, 24000 El Jadida,
Morocco.
azide–alkyne cycloaddition reactions (click chemistry, CuAAC). The prepared
catalyst was characterised by using spectroscopic and analytical methods such
as Fourier-transform infrared (FT-IR), scanning electron microscopy (SEM),
energy-dispersive X-ray (EDX), X-ray diffraction (XRD) and inductively
coupled plasma (ICP) analysis. The catalytic activity of CuI-CHT was investi-
gated in the [3 + 2] cycloaddition reactions of alkynes and organic azides for
the regioselective click of 1,4-disubstituted-1,2,3-triazole derivatives in water at
room temperature. The catalytic results indicate that the prepared CuI-CHT
catalyst led to a high yield with a regioselective synthesis of the corresponding
Email: bahsis.l@ucd.ac.ma;
bahsis.lahoucine@gmail.com
El-Houssaine Ablouh, Materials Science
and Nanoengineering Department (MSN),
Mohammed VI Polytechnic University
(
UM6P), Lot 660—Hay Moulay Rachid,
3150 Ben Guerir, Morocco.
4
Email: elhoussaine.ablouh@um6p.ma
Salah-Eddine Stiriba, Instituto de Ciencia
Molecular/ICMol, Universidad de
Valencia, C/Catedr ꢀa tico José Beltr ꢀa n,
1
,4-disubstituted-1,2,3-triazoles under strict click conditions. The reusability
and simple recovery of this catalyst make it a suitable sustainable catalyst for
CuAAC reactions.
46980 Valencia, Spain.
Email: stiriba@uv.es
K E Y W O R D S
Funding information
1
,4-disubstituted-1,2,3-triazoles, click chemistry, DFT calculations, heterogeneous catalysis,
Ministerio Español de Economía y
Competitividad (MINECO), Grant/Award
Numbers: PID2019-109735GB-I00,
CTQ2016-75068P
regioselectivity, α-chitin
Appl Organomet Chem. 2021;e6275.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6275

2
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BAHSIS ET AL.
1
| INTRODUCTION
catalyst was studied in the click of the corresponding
1,4-disubstituted-1,2,3-triazoles in a regioselective man-
1
,2,3-Triazole moieties are an important class of organic
ner. The separation from the reaction mixture through
simple filtration, recovery of reuse of this catalyst has also
been addressed.
[
1]
compounds which have many applications in biology,
[2]
[3]
materials science and medicinal chemistry. As for
their preparation, the most straightforward method
for the formation of 1,2,3-triazole derivatives is the
established click chemistry copper-catalysed azides–
alkynes [3 + 2] cycloaddition (CuAAC) reaction. The
original noncatalysed side of the azide–alkyne [3 + 2]
cycloadditon reaction, known as Huisgen reaction, has
been characterised by its slow rate and low selectivity
due to the high reaction kinetic barrier. The discovery of
CuAAC improved the regioselectivity of the [3 + 2]
cycloaddition reaction of azides and alkynes, by selec-
tively affording 1,4-disubstitued-1,2,3-triazoles in an
efficient way and easy manner from a wide range of azide
2 | EXPERIMENTAL SECTION
2.1 | Materials and methods
[
4]
α-Chitin was obtained from shrimp shells (Parapenaeus
longirostris) following the detailed procedures described
[
22]
previously.
Copper(I) iodide, MgSO and all the other
4
reagents were purchased from Sigma-Aldrich. The
obtained α-chitin and the CuI-CHT supported catalyst
were characterised using several methods. X-ray diffrac-
tion (XRD) patterns were recorded on a diffractometer
(Rigaku SmartLab), which operated at 40 kV and 30 mA
[5,6]
and alkynes substrates.
and heterogeneous catalytic systems for CuAAC reac-
tions has been used for the click of 1,4-disubstitued-
A variety of homogeneous
utilising copper anode (K = 1.5418 Å). The XRD data
α
[7–13]
ꢀ
ꢀ
1
,2,3-triazole derivatives.
In recent years, increasing
were collected in the 2θ range 5 to 70 with a scanning
step size of 0.02 . Scanning electron microscopy (SEM)
ꢀ
efforts have been devoted to the use of eco-friendly
polymer supports for the metal catalysts in view of
obtaining heterogeneous catalysts that can be recovered
observations of the samples surface were performed using
a TESCAN-VEGA3 microscope under an accelerating
voltage of 20 kV. The specific elemental composition was
determined by an energy-dispersive X-ray (EDX) ana-
lyser. The functional groups were identified by using a
[14–16]
and recycled.
In this context, naturally occurring
polysaccharides such as cellulose, chitosan and alginate
biopolymers have been employed as biosupports for the
stabilisation of copper ions followed by their application
for the regioselective synthesis of 1,4-disubstituted-
Bruker VERTEX 70 spectrometer, which was operated at
À1
room temperature at 4 cm
over a range of 4000–
À1
1
,2,3-triazoles under the click chemistry approach
400 cm . A TA–TGA55 Thermogavimetric Analyser was
[17–21]
(Chart 1).
used to evaluate the thermal stabilities of the samples
ꢀ
ꢀ
13
We herein present the use of the α-chitin biopolymer
under a nitrogen flow from 30 C to 600 C with a heating
ꢀ
À1
1
as support for the preparation and characterisation of
copper(I)-chitin-based catalyst (CuI-CHT) and its applica-
tion in the click chemistry reaction between a variety of
alkynes and azides in water as solvent. The obtained
rate of 10 C min
.
H NMR and C NMR were
recorded on a Bruker DRX-300 spectrometer. Inductively
coupled plasma (ICP) (iCAP 6000) analysis was used to
determine the copper loading.
CHART 1 Naturally occurring
polysaccharides

BAHSIS ET AL.
3 of 15
FIGURE 1 Photographs of (a) α-chitin (CHT) and (b) CuI-CHT catalyst and surface scanning electron microscopy (SEM) images of (c,d)
CHT and (e,f) CuI-CHT catalyst at different scales
2
.2 | Preparation of the CuI-CHT
content in the prepared catalyst was estimated to be
6.58% (w/w).
supported catalyst
Natural α-chitin (0.5 g), 0.125 g (0.66 mmol) of copper(I)
3
iodide and 10 cm of acetonitrile were introduced into a
2.3 | General procedure: Synthesis of
1,2,3-triazole from azide and alkyne
3
well-dried 25-cm bottom flask. The mixture was stirred
under stirring for 12 h. The catalyst was filtered, washed
3
with acetonitrile (2 Â 15 cm ) and dried under vacuum
Alkyne (0.5 mmol) and azide (0.6 mmol) were added to a
suspension of CuI-CHT (4 mg, 1 mol% Cu) in H O
overnight. According to the ICP analysis, the copper
2

4
of 15
BAHSIS ET AL.
3
(
3 cm ). The reaction mixture was kept under continuous
stirring until the completion of the reaction. Then, the
mixture was diluted by dichloromethane and the catalyst
was recovered through simple filtration. It was then
washed and dried for its reuse in subsequent runs. The
organic phase was removed under vacuum to isolate
the corresponding pure 1,2,3-triazole derivative.
2
.4 | General procedure for one-pot
synthesis of 1,4-disubstituted-1,2,3-triazoles
Alkyl halide (0.6 mmol), alkyne (0.5 mmol) and NaN3
(
(
0.6 mmol) were added to a suspension of CuI-CHT
3
8 mg, 2 mol% Cu) in H O (5 cm ) and then stirred for
2
2
4 h at room temperature. Further, the product was
extracted by using dichloromethane and then filtered off
to separate the CuI-CHT catalyst. The corresponding
pure 1,4-triazole derivative was obtained after the evapo-
ration of the organic solvent under vacuum.
3
3
| RESULTS AND DISCUSSION
.1 | Characterisation of the CuI-CHT
catalyst
The optical photomicrographs and SEM images of the
α-chitin (CHT) and CuI-CHT catalysts are shown in
Figure 1. After the adsorption process of copper into the
α-chitin surface, there is a change in the colour of the
CHT from white to green as shown in Figure 1a,b. This
change in colour could be due to the significant amount
of copper adsorbed on the CHT surface. In general, the
SEM images show that the adsorption of copper on
the surface of α-chitin is accompanied by a change in the
morphological structures. The SEM images in Figure 1c,d
confirm that CHT presents a flat and regular crystalline
surface and that it is made of flakes of different sizes.
Furthermore, the SEM images of the CuI-CHT surface
show a uniform surface morphology and dense fibrils
and roughness without much porosity. However, the sur-
face appears to be less crystalline (Figure 1e). At the
highest magnification (Figure 1f), the CuI-CHT surface
loses its crystalline appearance, but some attached parti-
cles can still be observed.
FIGURE 2 Energy-dispersive X-ray (EDX) spectra of (a) α-
chitin and (b) CuI-CHT catalyst
(N) confirms that the supported catalyst maintains the
elemental composition of α-Chitin. Furthermore, the
absence of a peak corresponding to the other elements
indicates the absence of any impurity in the sample.
In order to get deeper insights about the spatial distri-
bution of elements on the surface of the CuI-CHT cata-
lyst, the elemental mapping was employed by using EDX
(Figure 3). The copper mapping image (Cu) shows a
homogeneous distribution on the CuI-CHT catalyst sur-
face. Furthermore, the elemental mapping analysis dem-
onstrates that nitrogen (N) and copper (Cu) are almost
completely interloped with each other. This result indi-
cates that the acetamide groups in α-chitin promote the
distribution of copper on the surface, this feature all-
owing to better predict the catalytic activity of the devel-
oped CuI-CHT catalyst.
The differences observed in the morphological sur-
faces of the native α-chitin and the prepared CuI-CHT
catalyst are confirmed by an EDX elemental analysis,
which shows a peak around 0.95 keV corresponding to
the Cu (7.80%) which appears after adsorption (Figure 2).
Furthermore, the presence of major α-chitin element
constituents such as oxygen (O), carbon (C) and nitrogen
XRD was employed to compare α-chitin with α-chitin
loaded copper(I) iodide (Figure 4). As shown in a previ-
[
23]
ous report,
α-chitin monomers undergo strong inter-
molecular hydrogen bonds, enabling α-chitin to exhibit

BAHSIS ET AL.
5 of 15
FIGURE 3 Energy-dispersive X-ray (EDX) mapping of the prepared CuI-CHT catalyst
intensities on the other hand can be explained by the
lowering of the amount of free acetyl groups during the
coordination to copper, which leads to the deformation
of hydrogen bonds and decreases the degree of crystallin-
[
26]
ity of the CuI-CHT.
The thermal stability of the CHT and the prepared
CuI-CHT catalysts was investigated through a ther-
mogravimetric analysis (TGA) under nitrogen flow. This
analysis shows the occurrence of two mass loss stages
ꢀ
(
1
Figure 5). The first stage occurred between 44 C and
ꢀ
20 C, with weight losses for CHT and CuI-CHT of 5.08%
and 3.18%, respectively. This weight loss corresponds to
the evaporation of physically adsorbed water. The second
ꢀ
ꢀ
stage occurred between 260 C and 420 C with a weight
loss of 95.55% for the native α-chitin, which is signifi-
cantly greater than the 85.06% weight loss of the CuI-
CHT catalyst. The decomposition of the α-chitin structure
FIGURE 4 X-ray diffraction patterns of α-chitin (CHT) and
CuI-CHT catalyst
[
23]
chains account for these weight losses.
The decompo-
more crystalline polymorph character compared with
other chitin forms (β-chitin and γ-chitin) because of its
antiparallel compact structure. In this study, the XRD
sition of the developed catalyst did not occur below
250 C. This feature illustrates the potential of the applica-
tion of the α-chitin catalysts because the thermal stability
ꢀ
ꢀ
patterns of CHT showed diffraction peaks at 9.21 ,
of catalysts is needed for several heterogeneous catalytic
ꢀ
ꢀ
ꢀ
[27]
1
9.01 , 23.52 and 26.20 , which are characteristic of the
reactions.
[24]
α-chitin form.
The same peaks are observed in the
A Fourier-transform infrared (FT-IR) analysis was
conducted to assess the purity of the extracted α-chitin
and to observe if there is a structural change after the
copper loading. As shown in the FT-IR spectrum of the -
CuI-CHT catalyst, all the bands are almost the same of
those for the pure α-chitin, which indicates that no chem-
ical modification occurred (Figure 6). An examination of
XRD patterns of the CuI-CHT catalyst, which has lower
peak intensities but similar peak positions. Also, a non-
copper peak was observed. This result can be explained
by the small Cu particles present in α-chitin which do
not form a long-range ordering, preventing the XRD dif-
[25]
fraction from being detected.
The lower peak

6
of 15
BAHSIS ET AL.
FIGURE 5 Thermo
gravimetric analysis (TGA)/
differential thermogravimetry
(
DTG) of the α-chitin (CHT) and
the CuI-CHT catalyst
À1
the FT-IR spectrum of both the α-chitin and the CuI-
2967 cm are assigned to the C H stretchings of the
[
25]
CHT catalysts shows stretching vibrations of hydroxyl
CH and CH groups.
The most prominent change in
2
3
À1 [22,25,28]
groups around 3400 cm
.
Intrachain and
the FT-IR spectrum of CuI-CHT was a slight shift in the
position of the peaks, which can be attributed to
the C O vibration of amide I and amide II to 1660, 1632
interchain hydrogen bonds and the NH stretching of
À1
[29,30]
α-chitin at 3268 and 3109 cm are also present.
The other characteristic bands located at 2890 and
À1
[31]
and 1558 cm , respectively
(Figure 6). The second

BAHSIS ET AL.
7 of 15
FIGURE 6 Fourier-
transform infrared (FT-IR)
spectra of the α-chitin (CHT)
and the CuI-CHT catalyst
difference in the FT-IR spectrum of CuI-CHT compared
with α-chitin is the reduction in the intensities of the
peaks, which is attributed to the anchoring of copper on
the α-chitin surface.
3.2 | Catalytic study
To evaluate the efficiency of the newly synthesised cata-
lyst, it was tested in [3 + 2] cycloaddition reactions

8
of 15
BAHSIS ET AL.
between terminal alkynes and organic azides. In the pre-
sent work, the reaction between phenyl acetylene (1a)
and benzyl azide (2a) in water as solvent was chosen as
the model reaction (Scheme 1). Different reaction condi-
tions, such as different copper sources and the amount of
a catalyst were investigated in the studied reaction, using
the CuI-CHT catalyst (Table 1). The controlled experi-
ments show that the [3 + 2] cycloaddition azide–alkyne
reaction does not take place in the absence of the catalyst
The catalytic activity of CuI-CHT was also tested in
three components [3 + 2] cycloaddition reactions of ter-
minal alkynes, sodium azides and alkyl halides (see
Scheme 2). The results show that the 1,4-triazole product
was formed under a regioselective manner with high
yield at room temperature by using catalyst copper load-
ings of 2 mol% (Table 3). A higher copper loading did not
promote this click reaction whereas a lower amount of
catalyst conducts to a lower yield of 1,4-disubstituted-
1,2,3-triazoles. Further, the reaction scope of this CuAAC
reaction was investigated, and the results show that the
desired products can be obtained in excellent yields
within 24 h (Table 4). The substituted benzyl bromides or
alkynes had not any great significant effect on the cata-
lytic activity of our catalyst in these reactions. Moreover,
the 1,4-regioisomer was the only regioisomer obtained in
these reactions.
(
Entries 1 and 2). The use of copper(I) iodide only leads
to a moderate yield of the corresponding 1,4-triazole (3a)
ꢁ52%). The effect of the oxidation of copper(I/II) was
examined using copper(I) iodide and copper(II) sulphate
Entries 4 and 5), and the results show that the CuI
(
(
supported on naturally occurring chitin achieves signifi-
cant yields compared with CuSO -chitin in water. Inter-
4
estingly, the catalyst loading could be further reduced to
1
1
mol%, leading to a significant yield of 1,4-disubstituted-
,2,3-triazole (84%) within 12 h (Entry 7, Table 1).
After optimising the reaction conditions, several azide
In order to investigate the applicability of CuI-CHT, a
comparative study of the catalyst and other reported cata-
lysts was conducted, the results being compiled in
Table 5. The reaction between phenylacetylene (1a) and
benzyl azide (2a) was chosen as the model reaction. The
results indicate that CuI-CHT is more efficient than the -
Cu(II)-alginate hydrogels, Cu(II)-alginate, Cu(II)-poly
(hydroxamic acid), Cu(II)-polyethylenimine and CuSO4-
PEG-PS catalysts and also that it is similar, in terms of
sustainability and catalytic reactivity, to the Cu(I)-cellu-
lose. However, the prepared catalyst has a lower catalytic
activity compared with those of the Cu(I)-AMPS, Cu(II)-
hydrotalcite and Cu NPs@hydrotalcite catalysts. Indeed,
the highly functionalisation of this polysaccharide makes
and alkyne derivatives were catalysed using the CuI-
chitin catalyst (Table 2). The results indicate that
CuI-CHT can effectively catalyse the regioselective
synthesis of 1,4-disubstituted-1,2,3-triazole derivatives in
a click manner. The electron-donating and electron-
withdrawing substituents do not have a significant
impact on yields or regioselectivity. However, the alkyl-
substituted azide shows a moderate yield (Entry 15). Fur-
thermore, in most cases, the reactions were completed
within 12 h, and the corresponding 1,2,3-triazoles did not
require any further purification.
SCHEME 1 [3 + 2] Cycloaddition azide–
alkyne catalysed by the Cu-CHT catalyst
a
TABLE 1 Optimisation of the
reaction conditions for the click
reaction catalysed by the Cu-CHT
catalyst
Entry
Catalyst
Neat
Loading (mol%)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
-
24
24
24
12
24
12
12
12
0
α-Chitin
CuI
-
0
5
5
5
3
1
0.5
52
96
65
94
90
75
CuI-CHT
4
CuSO -chitin
CuI-CHT
CuI-CHT
CuI-CHT
3
Note: Conditions: benzyl azide (0.6 mmol), phenyl acetylene (0.5 mmol), solvent (3 cm ) and catalyst at
room temperature.
a
Isolated yields.

BAHSIS ET AL.
9 of 15
TABLE 2 Synthesis of the corresponding 1,2,3-triazoles (3a–3j) using the CuI-CHT catalyst
a
Entry
Alkyne
Azide
Product
Yield (%)
1
3a
3b
90
2
3
90
92
3c
3d
4
87
5
6
3e
3f
89
87
7
8
3g
84
89
3h
9
3i
75
(
Continues)

10 of 15
BAHSIS ET AL.
TABLE 2 (Continued)
Entry Alkyne
a
Azide
Product
Yield (%)
1
0
3j
86
1
1
1
1
1
2
3
4
3k
3l
79
86
89
92
3m
3n
1
5
3o
52
3
Note: Reaction conditions: azide (0.6 mmol), alkyne (0.5 mmol), water (3 cm ) and CuI-CHT (1 mol%) at room temperature (12 h).
a
Isolated yields.
SCHEME 2 One-pot synthesis of
,4-disubstituted-1,2,3-triazoles catalysed by
1
CuI-CHT
TABLE 3 Optimisation of the reaction conditions for the one-pot CuAAC reaction using the CuI-CHT catalyst
a
Entry
Catalyst
Neat
Loading (mol %)
Time (h)
Yield (%)
1
2
3
4
5
5
-
24
24
24
24
12
24
0
CuI
5
5
2
2
1
61
98
96
69
56
CuI-CHT
CuI-CHT
CuI-CHT
CuI-CHT
3
Note: Conditions: benzyl bromide (0.6 mmol), phenyl acetylene (0.5 mmol), H
2
O (5 cm ) and catalyst at room temperature.
a
Isolated yields.

BAHSIS ET AL.
11 of 15
TABLE 4 One-pot synthesis of 1,4-disubstituted-1,2,3-triazoles using the CuI-CHT catalyst
a
Entry
Alkyne
Azide
Product
Yield (%)
1
4a
4b
96
2
98
3
4
4c
4d
90
92
5
4e
85
6
7
4f
92
54
4g
3
Note: Conditions: alkyl halides (0.6 mmol), alkyne (0.5 mmol), NaN
3
2
(0.6 mmol), CuI-CHT (2 mol%) and H O (5 cm ) at room temperature (24 h).
a
Isolated yield.
it an excellent polymeric skeleton for the immobilisation
of copper ions, constituting then a very appealing sustain-
able catalytic material. The undemanding preparation
and reaction mixtures, as well as the lack of reducing
agents, make this catalyst easily adaptable and more
sustainable.
3.3 | Mechanistic study
In order to explain the catalytic activity of the proposed
catalyst in azide–alkyne cycloaddition reactions and to
better understand the reaction mechanism,
[
36–44]
density
functional theory (DFT) calculations were conducted at

12 of 15
BAHSIS ET AL.
TABLE 5 A comparison of our protocol with other reported protocols for the click synthesis of 1,4-disubstituted-1,2,3-triazole
derivatives
[
Cu] Loading
Time
(h)
Yield
(%)
Entry Catalyst
(mol%)
Conditions
Ref.
1
2
CuI-CHT
1
2
H
2
2
O, r.t.
O, r.t.
12
48
90
93
This work
Bahsis et al.
[
20]
Cu(II)-alginate
hydrogel
H
3
Cu(II)-alginate
21
H
2
O, r.t.
18
98
Goodrich, and
Winter
[
32]
[
17]
4
5
6
Cu(II)-cellulose
Cu(I)-cellulose
Cu(II)-poly
1.2
H
H
H
2
2
2
O, r.t.
O, r.t.
12
4
96
93
91
Bahsis et al.
0.14
0.1
ꢀ
[33]
O, 50 C
4
Reddy et al.
Mandal et al.
El Ayouchia
(
hydroxamic acid)
Cu(II)-
polyethylenimine
CuSO -PEG-PS
[
34]
7
8
5
H
2
O, r.t.
24
12
98
97
4
5
H
2
O, N
10 mol%)
CH Cl , r.t.
N, r.t.
2
, r.t., sodium ascorbate
[35]
(
et al.
Chetia et al.
Namitharan
[
36]
9
1
CS-Fe
3
O
4
-Cu(II)
1.54
2
2
12
78–89
75–89
a
0
1
Cu NPs@hydrotalcite
10
C
2
H
3
6–12
[37]
et al.
[
18]
1
Cu(I)-AMPS
1
Water, r.t.
1–2
80–98
Bahsis et al.
Abbreviations: AMPS, aminomethyl polystyrene; CS, chitosan; PEG-PS, poly(ethylene glycol)-polystyrene.
a
In milligrams.
SCHEME 3 Proposed mechanism of the CuAAC catalysed by Cu(I)-CHT

BAHSIS ET AL.
13 of 15
the M062X/6-31G(d,p) (LANL2DZ for Cu) level using
water as a solvent in the CPCM model. As illustrated in
Scheme 3, the model complex of the CuI-chitin catalyst
was chosen as the appropriate model for the CuI-CHT
with benzyl azide and phenyl acetylene as the starting
materials for the CuAAC reaction. In fact, the reaction
between the copper(I)-chitin complex and the terminal
alkyne contributes to the formation of the copper-
water at room temperature using optimised reaction con-
ditions was also investigated (Scheme 3). After 12 h, the
reaction mixture was diluted with dichloromethane, and
the catalyst was recovered through simple filtration. It
was then washed, dried and used for the next run. Impor-
tantly, the catalytic activity and selectivity of the catalyst
did not significantly decrease for the next four consecu-
tive runs (Table 6). The structure of the recovered catalyst
was analysed by conducting a SEM and an EDX analysis
(Figures 7 and 8). The SEM analysis shows a smaller sur-
face morphology in both fresh and recycled catalysts,
whereas the EDX data used in the ICP analysis show a
decrease in the copper percentage of the catalyst after
four runs ([Cu] = 4.89%). Moreover, a very low copper
concentration in the final 1,2,3-triazolic products was
revealed by ICP analysis (less than 1 ppm). The simple
structure, catalytic activity and recyclability of the
CuI-CHT catalyst make it more environmentally benign.
[39–47]
acetylide complex (Scheme 3).
This interaction
leads to the formation of the reactive complex
(
RC) intermediate. This step is highly exothermic in
À1
water with 4.24 kcal mol (Figure S1). These interac-
tions lead to the formation of a six-membered copper-
containing intermediate complex (IC). Furthermore, a
reductive elimination step leads to the formation of the
[48–50]
triazolide ring (AT) (Scheme 3).
Finally, the proton-
ation of the triazolide complex results into the formation
of the corresponding 1,4-disubstituted-1,2,3-triazole,
which is in good agreement with the experimentally
[51,52]
observed regioselectivity.
3.4 | Reusability of the catalyst
The reusability of the CuI-CHT catalyst for the AAC reac-
tion of phenylacetylene (1a) and benzyl azide (2a) in
TABLE 6 Recycling of the CuI-CHT catalyst in the CuAAC
reaction
a
Run
Yield (%)
1
2
3
4
82
79
72
68
FIGURE 8 Energy-dispersive X-ray (EDX) spectrum of the
a
Isolated yield after 12 h.
CuI-CHT recycled catalyst
FIGURE 7 Scanning electron microscopy (SEM) analysis of the CuI-CHT recycled catalyst

14 of 15
BAHSIS ET AL.
4
| CONCLUSION
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