Copper(I) Confined in Interlayer Space of Montmorillonite: A Highly Efficient and Recyclable Catalyst for Click Reaction

Article abstract of DOI:10.1007/s10562-015-1625-1

Cu^I-exchanged solid based on montmorillonite material was investigated as catalyst in organic synthesis. The catalytic potential of this material was evaluated in the Huisgen [3 + 2]cycloaddition. This catalytic system has been examined and pro

Full text of DOI:10.1007/s10562-015-1625-1

Catal Lett
DOI 10.1007/s10562-015-1625-1
Copper(I) Confined in Interlayer Space of Montmorillonite:
A Highly Efficient and Recyclable Catalyst for Click Reaction
1
,3
2
1
•
Mohammed El Mehdi Mekhzoum
1
•
Hanane Benzeid
1
•
Abou El Kacem Qaiss
,3
El Mokhtar Essassi
•
Rachid Bouhfid
Received: 3 July 2015 / Accepted: 6 September 2015
Ó Springer Science+Business Media New York 2015
I
Abstract Cu -exchanged solid based on montmorillonite
material was investigated as catalyst in organic synthesis.
The catalytic potential of this material was evaluated in the
Huisgen [3 ? 2]cycloaddition. This catalytic system has
been examined and proved to be an efficient heterogeneous
catalyst for this ‘‘click chemistry’’-type transformation.
The ensuing catalyst can be recycled and reused five times
without dramatic yield loss.
Graphical Abstract
Keywords Click chemistry Á Montmorillonite Á
Heterogeneous catalysis Á Azide Á Triazole
1
Introduction
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-015-1625-1) contains supplementary
material, which is available to authorized users.
1,2,3-Triazoles are an important class of heterocyclic com-
pounds that received a huge attention from many pharma-
ceutical and organic chemists due to its broad spectrum of
their biological and pharmaceutical properties [1]. Although
these compounds are thus use in the making of dyes, cor-
rosion inhibition, photostabilizers, and photographic mate-
rials [2]. Indeed, the main method for the synthesis of 1,2,3-
triazoles is the Huisgen 1,3-dipolar cycloaddition reaction of
azides with alkynes [3], which has been known as one of the
most interesting synthetic tools essentially because of the
convenient and reliable construction of 1,2,3-triazole
derivatives [4]. However, unfortunately, the thermally
induced 1,3-dipolar cycloaddition reaction requires an ele-
vated temperatures and often gives a mixture of 1,4- and 1,5-
&
Rachid Bouhfid
r.bouhfid@mascir.com; gbouhfid@yahoo.fr
1
Moroccan Foundation for Advanced Science, Innovation and
Research (MAScIR), Institute of Nanomaterial and
Nanotechnology (NANOTECH), Rabat Design Center, Rue
Mohamed El Jazouli, Madinat Al Irfane, 10100 Rabat,
Morocco
2
3
Laboratoire de Chimie Analytique, Universit e´ Mohammed V
de Rabat- Facult e´ de M e´ decine et de Pharmacie,
BP 6203, Rabat, Morocco
Laboratoire de Chimie Organique H e´ t e´ rocyclique, Universit e´
Mohammed V de Rabat, Facult e´ des Sciences, Av. Ibn
Battouta, BP 1014, Rabat, Morocco
123

M. E. M. Mekhzoum et al.
triazole stereoisomers (nearly 1:1) when using asymmetric
alkynes [5]. In this respect, the classic 1,3-dipolar cycload-
dition fails as a true click reaction.
Southern Clay Product Inc. (Gonzales, Texas). Na-MMT
consists on fine particle powder with a cationic exchange
capacity CEC = 96 mEq/100 g and an interlayer spacing
d001 = 1.17 nm.
Alternatively, click chemistry represents an ideal set of
near perfect reactions [6]. Historically, the Synthesis of
triazolo conjugated compounds through click chemistry
reaction has attracted attention in many fields and lots of
interest in recent years [7, 8]. The click chemistry has many
applications in synthetic and medicinal chemistry [9], bio-
conjugations [10], material sciences [11], and polymer
chemistry [12], it’s used increasingly in drug discovery
I
2.2 Preparation of Cu -Montmorillonite Catalyst
I
Cu -MMT was prepared from Na-MMT as follows: 2 g of
the Na-MMT was dispersed in 300 ml of 1 M CuI aqueous
solution for 24 h at room temperature under vigorous
stirring. The dispersion was centrifuged at 10,000 rpm and
I
[
13]. Among the number of reactions that fulfill click
washed several time with deionized water. Cu -MMT was
chemistry’s criteria, the copper-I catalyzed version of the
Huisgen 1,3-dipolar cycloaddition between azides and
alkynes is to date the most practical and useful ‘‘click’’
reaction, regioselectively affording 1,4-disubstituted 1,2,3-
dried overnight at 80 °C.
2.3 Preparation of 2-Azidoethanol and
2-Azidopropanol
I
triazoles [14–17]. However, The catalyst could be Cu salt
I
II
or Cu generated in situ by the reduction of Cu salts,
usually in organo-aqueous media. Besides, The use of this
catalytic Copper(I) accelerate the reaction resulting in the
highly regioselective formation of 1,4-disubstituted tria-
zoles [18, 19].
These compounds were prepared as described in the liter-
ature [26, 27] from 2-bromoethanol, 3-bromo-1-propanol
and sodium azide. Caution: special care should be taken to
minimize the possible explosion in the preparation and
handling of the azides compound.
Recent years have witnessed a phenomenal growth in
the use of inorganic solids as reaction media for organic
transformations [20–23], in this case, we propose to
explore the use of copper exchanged montmorillonite for
such catalytic application. Clays and modified clays are
used to catalyze due to their high specific surface [24]
various types of organic reactions such as addition,
Michael addition, carbene addition and insertion, hydro-
genation, allylation, alkylation, acylation, pericyclic reac-
tions, epoxidation and several more [25]. Considering all
these aspects, the objective of this research is to report a
simple and efficient synthesis of a montmorillonite-sup-
ported, recyclable, and inexpensive copper catalyst. This
system catalytic has been used especially in the reaction of
click chemistry of azide with alkyne in aqueous media at
room temperature to obtain 1,4-disubstituted triazole.
2.4 Typical Experimental Procedure
for the Synthesis of 1,2,3-Triazoles
To a glass bottle, was added a mixture of alkyne (1 mmol),
I
Cu -MMT (5 mg) and the appropriate alkyl azide
(1.2 mmol) in water (5 ml), the reaction mixture was stir-
red at room temperature for 2 h. The reaction was moni-
tored by thin layer Chromatography. After completion of
the reaction. Chloroform (25 ml) was added to the whole
reaction mixture. The catalyst was removed by filtration
and washed with CHCl (10 ml), dried in vacuum at 80 °C
3
and then stored in a desiccator before being reused in
subsequent reactions to demonstrate its prolonged activity.
The filtrate was dried over Na SO to remove remaining
2
4
water, conducting in filtration filter paper and the solvent
was removed in vacuum. The products were purified by re-
crystallization or column chromatography and character-
1
13
2
Experimental
ized by standard analytical techniques such as ( H and C)
NMR, FTIR, mass spectroscopy, melting point determi-
nation and all gave satisfactory results (see supporting
information).
2
.1 General Remarks
Unless stated otherwise, all reagents and solvents were
purchased from commercial suppliers and were used
without further purification. Benzyl azide, azidoethanol,
azidopropanol, 1-propargylthiabendazole, 3-phenyl-1-
3 Results and Discussion
I
(
prop-2-yn-1-yl)quinoxalinone and copper(I)-clay catalyst
were prepared in our laboratory. 2-bromoethanol (95 %),
-bromo-1-propanol (97 %) and sodium azide (99 %) are
purchased from Sigma-Aldrich. Natural montmorillonite
trade name of Na-Cloisite Na-MMT) is purchased from
3.1 Preparation and Characterization of MMT-Cu
3
At first, the catalyst was efficiently prepared by cationic
?
exchange of interfoliar cation Na in saturated solution of
(
CuI. The suspension was stirred 24 h at room temperature,
1
23

Copper(I) Confined in Interlayer Space of Montmorillonite: A Highly Efficient and Recyclable…
followed by centrifugation, washed with deionized water,
and finally drying overnight. Once the material was pre-
pared, a systematic analysis was needed in order to correlate
its structural, textural and morphological properties to its
catalytic activity. A thorough characterization of the catalyst
was done using different characterization techniques like
XRD, FTIR, BET and thermal analysis. The X-ray diffrac-
the stretching vibration of structural (octahedral) hydroxyl
3
(O–H) groups linked either to Al or Mg . The bands at
?
2?
-
3370 and 1627 cm is assigned to the hydroxy group of
1
interlayer water molecules. The absorption bands at 1118,
-
1
980 and 925 cm are attributed to the stretching vibration
of Si–O, Si–O-Si and the deformation of hydroxyl linked to
3
either Al or Mg or Fe . On the other hand, as the Cu
?
2?
3?
I
?
is exchanged with Na in MMT, the hydration peak
tion patterns of the Na-MMT and Cu -MMT in the range of
?
2
.5°–10° (2h) were presented in (Fig. 1). The Na-MMT
intensity decreases in consistent with the fact that Na
shows the peak corresponding to the reflexion of the (001)
planes at 2h = 7.24°, the basal spacing of this clay calcu-
lated to be 1.17 nm. After treatment of the parent Na-MMT
coordinates higher amount of water than the exchanged
cation [31–34].
I
The TGA/DTG curves of Na-MMT and Cu -MMT were
I
with CuI the XRD studies of Cu -MMT showed that the
used to measure the thermal stability (Fig. 3). In the case of
Na-MMT, two thermal decomposition steps are observed,
one dehydration stage with the maximum peak at 82 °C in
the range of 25–160 °C and the second stage at 663 °C in
the range of 300–720 °C originate from the dehydroxyla-
tion of montmorillonite. Moreover, the catalyst showed one
dehydration stage over the temperature range of
25–300 °C. The evolution of adsorbed and cation-coordi-
nated water specie from Cu-MMT is represented by a peak
centered at 65 °C and a shoulder at 160 °C, respectively.
Three peaks at 369, 577 and 630 °C in the range of
layered structure is retained and the basal spacing of (d001
)
was estimated to be 1.47 nm. On the other hand, the ionic
I
radius for Cu is 0.96 A which is similar to the Na of 0.95 A;
˚
˚
I
it seemed that Cu entered into the interlayer space of MMT
as hydrated cation or composite cation that made planar
distance increase. The increase in the basal plane distance
I
from XRD may be caused by intercalation of Cu into the
framework or swelling/hydration of the clay. Further, the
incorporation of copper(I) in clays was not much studied due
to its relative instability and the pH-dependent redox phe-
nomena occurring inside the clay, even for copper(II). Clays
that were cation exchanged with other metals were usually
dispersed in aqueous solutions of the metal salt for long
periods of time [28–30]. In our case, We decided to prepare
I
300–870 °C signify the dehydroxylation process of Cu -
MMT [35, 36]. Thus, the Na-MMT showed more absorp-
I
tion of water than Cu -MMT and can be explained by the
exchanged of hydrate metal. Furthermore, many research-
ers agree that for temperatures up to 200 °C, Copper spe-
cies migrate into hexagonal cavities and above 200 °C,
they penetrate the octahedral sheets where they saturate the
charge of the sheet [37–39].
I
Cu -MMT and washed with deionized water several times to
remove the physisorbed copper onto the surface of clay
keeping in mind that the copper salt may only be adsorbed
or partially exchanged.
I
The FT-IR spectrum of both Na-MMT and Cu -MMT
The N adsorption isotherms of Na-MMT and the cat-
2
catalyst are shown in (Fig. 2). Most of the changes in the
spectrum of copper-exchanged montmorillonite were
alyst are displayed in Fig. 4 and Table 1 shows their
respective surface areas, pore volumes and areas. As can be
depicted from Fig. 4, the shape of the isotherm gives a
qualitative assessment of the porous structure of the
materials. For both isotherms, the shape is approximately
-
1
noticed in the 3700–3000 cm region, as the remaining
part of the spectra is almost identical to the Na-MMT.
These spectra present three bands absorption in the region
-
1
-1
4
000–1500 cm . The band at 3625 cm is assigned to
100
3
00
8
6
4
2
0
0
0
0
0
MMT-Na
MMT--Cu(I)
200
100
MMT-Na
MMT-Cu(I)
0
4
000
3000
2000
1000
2
4
6
8
10
-1
2
θ
Wavelenght (cm )
I
Fig. 1 XRD patterns of Na-MMT and Cu -MMT
I
Fig. 2 FTIR spectra of Na-MMT and Cu -MMT
123

M. E. M. Mekhzoum et al.
Fig. 3 TGA and DTG curves of
I
Na-MMT and Cu -MMT
100
0.3
0.2
0.1
0.0
MMT-Na
MMT-Na
MMT-Cu(I)
MMT-Cu(I)
9
8
7
0
0
0
200
400
600
800
200
400
600
800
Temperature (°C)
Temperature (°C)
2
Fig. 4 N adsorption/
desorption isotherm of both
I
Na-MMT and Cu -MMT
Na-MMT
Cu-MMT
2
1
1
0
0
.0
.5
.0
.5
.0
3
2
1
0
0.01
0.1
1
0.01
0.1
1
Relative Pressure (p/p0)
Relative Pressure (p/p0)
I
Table 1 Nitrogen physisorption data of both Na-MMT and Cu -
MMT
as well as 52 % increase in pore volume. This gives first
I
indication of chemical interaction between Cu and MMT.
The insertion of copper cation into MMT reduces the
number of small mesopores and thus, the exchange process
results in significant increase in the surface areas of Cu-
montmorillonite with respect to the Na-montmorillonite.
These findings suggest that the copper ion is introduced
inside the interlayer of the clay mineral not only by cation
exchange at the planar sites, but also through the interac-
tion with the aluminosilicate sheets. The above results
indicate that the exchanged ion affect the surface charac-
teristics of MMT in some manner that appears to be related
to the size and interlayer arrangement of the exchanged ion
in the clay [40].
Surface area
(
BJH total pore
3
volume (cm g
BJH total pore
-1
2
BET) (m g
-1
)
-1
)
2
area (m g
)
Na-MMT
18.9
0.053
0.111
30.92
55.78
I
Cu -MMT 42.6
the same. The isotherm powder shows a significant hys-
teresis pattern but does not show a plateau at high P/Po like
the Type IV isotherm. The adsorption–desorption isotherm
was of type-IIB which reflects predominance of macrop-
ores with a H3 hysteresis pattern indicates presence of slit-
like pores. The isotherm shape indicates that the material
contains fine and larger mesopores, which is responsible
for the hysteresis and macropores, which results in the
absence of the plateau. Furthermore, the strong adsorption
3.2 Preparation and Characterization of 1,4-
Disubstituted Triazoles
at low relative pressures (P/P \ 0.01), characteristic for
After synthesis and characterization of copper(I)-ex-
changed montmorillonite. The model reaction of pheny-
lacetylene and benzyl azide was used to investigate the
o
microporous materials, is, however, very low indicating
that the material has negligible or non-existent micropores.
The surface area and pore volume of Na-MMT was found
I
efficiency of this Cu -modified montmorillonite. Although
2
-1
to be 18 m g and 0.053 nm and that for catalyst was
acetonitrile was often used as solvant for click reaction
(because many early experiments were performed in ace-
tonitrile). First, it should be noted that the reaction without
any catalyst, did not occur in acetonitrile at room
2
-1
found to be 42 m g and 0.111 nm, respectively. The
incorporation of copper into the framework of the MMT is
apparent here, as it leads to 57 % increase in surface area
1
23

Copper(I) Confined in Interlayer Space of Montmorillonite: A Highly Efficient and Recyclable…
temperature, but led to a 1:1 mixture of regioisomers after a
extended reaction time at reflux (36 h; 70 %). At room
temperature, using CuI alone as the catalyst, the reaction
was still very slow but yielded a single regioisomer with
incomplete conversion (36 h, 70 %). In sharp contrast, the
appears at d = 120 ppm, whereas the C-4 signal of 1,5
1
3
appears at d = 133 ppm. In this respect, the C NMR
signal of the 1,4 isomer was more shielded than the 1,5
1
3
isomer. In our case, C NMR spectrum showing the
characteristic signal at *124 ppm assigned to C-5 triazolyl
carbon, which confirm that the 1,4-regiosmers has been
I
modified montmorillonite Cu -MMT had a significant
I
effect on catalytic activity and gave the expected adduct 1a
even at room temperature (12 h; 72 % only the 1,4-adduct
pure was formed and isolated after complete conversion).
obtained exclusively in the presence of Cu -MMT catalyst.
Considering the above result, the best yields were
obtained when the reaction was terminated after 2 h. Pro-
longing the reaction time had no distinguishable effect on
the progress of the reaction. Furthermore, when the click
reaction was conducted at room temperature the increase of
the temperature up to reflux affect slightly the reaction
yield. It has been found that water is the most suitable
solvent for this reaction process. Among the examined
solvents, when water was used alone, the yield increase
until 98 % for 1a. According to a recent DFT calculations
study [43], the coordination of the alkyne to the
Cu(I) species was calculated to be slightly endothermic in
acetonitrile. However, with water, the displacement pro-
cess becomes exothermic. This is in good agreement with
our experimental results that the reaction proceeds much
faster in aqueous solution and does not require an amine
base to form the corresponding triazole products in excel-
lent yields. Moreover, there was no difference in yield and
reaction time when catalyst loading was reduced to 30, 10
and 5 mg. As a result; we decided to use 5 mg of the
catalyst for further studies. On the other hand, using 5 mg
Refluxing acetonitrile, good yield was also obtained (6 h;
I
6 %). Given the above experimental data, the Cu cat-
7
alytic activity is significantly enhanced in the presence of
modified montmorillonite. In order to get the best result
that involves the reaction yield, we started with optimizing
the reaction conditions keeping in mind the greener con-
ditions. Various reaction conditions were examined
namely: catalyst loading, time, and different solvent sys-
tems. Initially, the influence of the solvent nature was first
studied on the synthesis of 1a to adjust the reaction con-
ditions, the model reaction was carried out in ACN, ACN/
water (1:1) and then water at room temperature. In general,
the yields obtained are privileged 80–98 % (Table 2).
More polar solvent such as ethanol and tetrahydrofuran
including the increase of catalyst loading and varying
reaction time provided as well the corresponding com-
pound 1a, the yield was lower than the one in water.
However, the reaction was less clean with detectable for-
mation of byproducts [41] and thus, water proved to be the
best solvent.
I
as the amount of catalyst Cu -MMT afforded the satisfac-
The regioselectivity of this 1,3-dipolar cycloaddition
tory results of 1a. Shabber et al. [44] developed a highly
efficient and economical one-pot protocol for synthesis of
1,4-disubstituted 1,2,3-triazoles at room temperature using
a heterogeneous clay supported CuO nanoparticles which is
recyclable, environmentally friendly. Using others support
catalytic as chitosan [45] or silica [46] based-copper(I), the
authors reported a green and recyclable heterogeneous
catalyst for the Huisgen 1,3-dipolar cycloaddition.
1
3
reaction was confirmed by C NMR spectrum, according
to a recent study release by Creary et al. [42] concerning
the difference between 1,4- and 1,5-disubstituted triazoles,
the 1,4-disubstituted-1H-1,2,3-triazoles can easily be dis-
tinguished from the isomeric 1,5-disubstituted-1H-1,2,3-
triazoles by the large bond C–H coupling constant in the
1
3
gated decoupled C NMR spectrum. Depending on the
substituents within the triazole ring, The C-5 signal of 1,4-
To illustrate the scope of this method, the optimized
reaction condition to azides and other alkynes cyclo addi-
tions were extended to obtain a novel 1,4-disubstituted 1,2,3-
triazole derivatives. As the results indicate, the catalyst gave
good yields for most synthesized triazoles that were isolated
by a simple filtration to separate the catalyst and by solvent
evaporation. The products were isolated in a pure form
Table 2 Screening of catalyst optimization studies for the cycload-
dition of phenylacetylene to benzyl azide
N
N
N
N3
Catalyst
I
Conditions
without traces of copper and thus the Cu -MMT proved to be
1
a
a useful catalyst for [3 ? 2] Huisgen cycloaddition between
azides and alkynes. As show (Table 3) a various compounds
Entry
Solvent
ACN
Yield (%)
1a–i were regioselectively obtained as 1,4-disubstituted-
1
2
3
80
86
98
1,2,3-triazoles in excellent yields.
2
ACN: H O
The recyclability of our catalyst was investigated in the
2
H O
cycloaddition of phenylacetylene and benzyl azide. The
catalyst was recovered by a simple filtration technique after
each experiment. The recovered catalyst was washed with
I
Reaction condition [Cu -MMT] (5 mg); stirred at room temperature;
ACN/H O (1:1); ACN; H O; 2 h
2
2
123

M. E. M. Mekhzoum et al.
Table 3 Scope of the catalytic system
Entry Alkyne
1
Azide
Product
Yield (%)
98
N3
N
N
N
1a
N3
2
94
OH
N
N
N
OH
1
1
b
N3
OH
3
4
94
96
N
N
N
OH
S
c
N
N
N
N
N
N3
S
N
N
N
N
1d
N3
N
S
N
N
N
5
90
OH
S
N
N
N
N
N
HO
1e
1
23

Copper(I) Confined in Interlayer Space of Montmorillonite: A Highly Efficient and Recyclable…
Table 3 continued
N
N
N
N
N3
OH
6
S
88
S
N
N
N
N
N
OH
1
1
f
N
N
7
N3
93
90
N
N
N
N
N
O
O
g
N
N3
N
OH
8
OH
N
N
N
N
O
N
O
1h
OH
9
N3
OH
N
91
N
N
N
N
N
N
O
O
1i
I
2
Reaction conditions 5 mg of Cu -MMT, rt, H O, 2 h
I
Table 4 Recycling of Cu -MMT catalyst
Chloroform, dried in a desiccator and reused directly with
fresh reaction mixture without further purification for the
desired 1,2,3-triazole synthesis up to the 5th run. The
catalyst showed catalytic activity in five consecutive
reactions and it can be stated that in all experiments there
was a small loss in the amounts of catalyst initially intro-
duced in the first reaction. Despite the high activity of
catalyst, there is a slight decrease of its activity after the
recycling experiments that may be related to the decrease
in the amount of copper in the MMT after the recycles. As
the results in (Table 4) indicate, the obtained conversions
for five successive runs are 97, 96, 96, 94 and 92 %
respectively. The reused catalyst was further characterized
by ICP-AES analysis in order to evaluate
N
N
N
N3 MMT-Cu(I)
5mg
1a
No of cycles
Yield
1
2
3
4
5
97
96
96
94
92
Recycling experiments 1.2 mmol of benzyl azide, 1 mmol of pheny-
I
lacetylene, recovered Cu -MMT, H O, rt, 2 h
2
123

M. E. M. Mekhzoum et al.
the catalyst leaching degree in the reaction. The metal
leaching was studied of the catalyst before and after the 5th
reaction cycle. The reuse studies show a slight decrease in
yields from 97 to 92 % which may be due to Cu leaching.
The weight percentage of copper was found to be 28.9
wt.%. After the reaction the Cu concentration was found to
be 27.7 wt.%, and thus we observed that the amount of
copper present in the spent catalyst after 5 reuses is almost
same with that of the fresh catalyst as estimated by ICP-
AES, which further confirms the true heterogeneity of the
catalyst. After 5 recycles, a negligible amount of leached
Cu was detected by ICP-AES (3.9 %). The above results of
the recycle experiments followed by the ICP-AES analysis,
confirmed the feasibility of using montmorillonite as sup-
ports for copper(I) in catalysis, which displayed merits of
the heterogeneous (excellent recyclability) catalysis.
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2
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In summary, we explained the synthesis and characteriza-
tion of Copper(I) modified montmorillonite as a highly
active heterogeneous catalyst, this material was found to
efficiently catalyze the formation of several 1,4-disubsti-
tuted 1,2,3-triazoles from organic azides and various ter-
minal alkynes. Using this catalytic system, with the best
conditions found, specially water as solvent, 1,4-disubsti-
tuted-1,2,3-triazole adducts are mainly obtained, in good to
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Acknowledgments This work was supported by Hassan II Acad-
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