Immobilization of copper ions onto α-amidotriazole-functionalized magnetic nanoparticles and their application in the synthesis of triazole derivatives in water

Article abstract of DOI:10.1002/aoc.3460

A new heterogeneous copper catalyst was synthesized by immobilization of copper ions onto magnetic nanoparticles with a new ligand based on triazole. The catalyst was characterized using scanning and transmission electron microscopies, atomic absorption a

Full text of DOI:10.1002/aoc.3460

Full paper
Received: 18 November 2015
Revised: 9 January 2016
Accepted: 25 January 2016
Published online in Wiley Online Library: 17 March 2016
(wileyonlinelibrary.com) DOI 10.1002/aoc.3460
Immobilization of copper ions onto α-
amidotriazole-functionalized magnetic
nanoparticles and their application in the
synthesis of triazole derivatives in water
Firouz Matloubi Moghaddam*, Seyed Ebrahim Ayati, Hamid Reza Firouzi
and Fereshte Ghorbani
A new heterogeneous copper catalyst was synthesized by immobilization of copper ions onto magnetic nanoparticles with a new
ligand based on triazole. The catalyst was characterized using scanning and transmission electron microscopies, atomic absorption
and Fourier transform infrared spectroscopies, and thermogravimetric, elemental and energy-dispersive X-ray analyses. The results
confirmed that a good level of organic groups was immobilized on the magnetic nanoparticles. Huisgen cycloaddition reaction was
chosen as a model reaction for the investigation of catalyst activity under green conditions. Phenylacetylene and benzyl bromide
derivatives were used for the synthesis of triazoles. The reaction proceeded with good to excellent yields for various alkynes
and alkyl halides. To investigate catalyst activity for inactive alkynes, aliphatic alkynes were used in the model reaction.
The corresponding triazoles were obtained in good to excellent yields and a high regioselectivity for products was obtained.
The catalyst was easily separated using an external magnetic field and subsequently reused in ten reaction cycles without any loss
of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: magnetic nanoparticle; copper catalyst; Huisgen cycloaddition reaction; green chemistry; water
require solvent mixtures and tedious work-ups leading to maximi-
Introduction
zation of product wastes during catalyst separation and their dis-
posal which is regulated by green chemistry principles.[14,15]
With the growing concern over environmental protection, a
great deal of attention has been devoted to green synthesis
methodologies.[1] In this context, the click chemistry concept
has emerged as a means to couple three or more components
in one single step which is a selective, efficient, fast and power-
ful method for the preparation of wide range of molecules.[2]
One of the notable reactions within the click chemistry concept
is copper-catalysed azide–alkyne cycloaddition (CuAAC) which
was pioneered by Sharpless and Meldal in 2001 and is more regio-
selective in comparison with the former Huisgen method.[3–5] The
former Huisgen method is thermodynamically favourable but a
high kinetic barrier causes a low yield of products at room
temperature.[6,7] 1,2,3-Triazoles have a wide range of applications
including in material science as well as in pharmaceutical
chemistry[8] and also they have been used in combinatorial
chemistry, optical brighteners, dyes, agrochemicals, the synthesis
of macromolecular architectures[9] and biological chemistry.[10]
To date, several homogeneous catalysts based on Cu(I) salts or
complexes,[11] Cu(II)/Cu(0) comprotonation systems[12] and direct
reduction of Cu(II) in the reaction medium[13] have been used for
the click synthesis of terminal alkynes and azides with high catalytic
activity and high yields of products. However, recovery and recycla-
bility of these catalysts are difficult and also the residual amount of
copper could contaminate the final product which is a point of con-
cern in the pharmaceutical industry. Moreover, these systems
In order to overcome the separation problem of homogeneous
catalysts, the concept of heterogenization of homogeneous cata-
lysts has emerged. In this catalytic system, homogeneous catalysts
are immobilized on an insoluble solid support. Following this
concept, various catalysts have been developed by immobilization
(covalent and non-covalent) of copper onto a variety of supports like
TentaGel resin,[16] alumina,[17] charcoal,[18] polymer,[19] silica[20] and
titanium oxide for CuAAC.[21] These catalysts are efficient; however,
they encounter some issues like small amounts of metal loading,
long reaction times, harsh reaction conditions, metal leaching and
difficulties in the recovery process. With regard to these problems,
the introduction of an effective heterogeneous copper-loaded cata-
lyst with high stability and easy recovery is still necessary. The use
of magnetic nanoparticles (MNPs) as a support with their magnetic
properties could facilitate catalyst separation without the need for
any filtration process.[22,23] Low toxicity, high stability, high surface
*
Correspondence to:Firouz Matloubi Moghaddam, Department of Chemistry,
Laboratory of Organic Synthesis and Natural Products, Sharif University of
Technology, Azadi Street, PO Box 111559516, Tehran, Iran. E-mail:
matloubi@sharif.edu
Department of Chemistry, Laboratory of Organic Synthesis and Natural Products,
Sharif University of Technology, Azadi Street, PO Box 111559516, Tehran, Iran
Appl. Organometal. Chem. 2016, 30, 488–493
Copyright © 2016 John Wiley & Sons, Ltd.

Immobilization of copper ions onto α-amidotriazole-functionalized MNPs
area to volume ratio and easy access to the catalytically active sites of
the MNPs are reasons that they have been used in recent years as a
versatile support for a variety of heterogeneous catalysts for di-
verse classes of organic transformations.[24]
Herein, we report a novel MNP catalyst functionalized with triazole
as an excellent ligand for immobilization of copper on MNPs.
The catalyst was used in Huisgen reaction under green conditions.
The reaction proceeds with good to excellent yields for various
alkynes and alkyl halides. A high regioselectivity for products is
obtained. The methods for the preparation and characterization
of the catalyst are described.
Results and Discussion
The catalyst was synthesized according to a procedure reported
elsewhere.[25] After preparation of Fe3O4 using a co-precipitation
method, in order to increase of surface and activity, the Fe3O4 MNPs
were coated with SiO2 using hydrolysis of tetraethyl orthosilicate
(TEOS) under alkaline conditions. To incorporate copper species
on the surface of the MNPs (Fe3O4@SiO2), (3-aminopropyl)
triethoxysilane (APTS) was immobilized on Fe3O4@SiO2 and
then functionalized using ethyl-2-(4-phenyl-1H-1,2,3-triazol-1-yl) ace-
tate. The catalyst was then dispersed in a solution of CuCl2 and stirred
for 24 h (Scheme 1). The catalyst was named [MNPs@APTA][Cl2].
To verify the immobilization of functionalized APTS, Fourier trans-
form infrared (FT-IR) spectra of Fe3O4, Fe3O4@SiO2, [MNPs@APTA]
and [MNPs@APTA][Cl2] were obtained (Fig. 1) to confirm the pro-
posed catalyst. The sharp peaks at 1100 and 560 cmꢀ1 are attributed
to stretching vibrations of Si ;O and Fe ;O bonds, respectively. The
peaks appearing at 2930–2950 cmꢀ1 are ascribed to C ;H stretching
vibration. These results confirm the good immobilization of function-
alized APTS onto the MNPs (Figs 1(c) and (d)).
Figure 1. FTIR spectra of (a) Fe3O4, (b) Fe3O4@SiO2, (c) [MNPs@APTA] and
(d) [MNPs@APTA][Cl2].
An analysis of the surface morphology of the catalyst using the
scanning electron microscopy (SEM) technique supports the
nanospherical nature of the particles of the catalyst (Fig. 2(a)). On
the basis of transmission electron microscopy (TEM) analysis, we
find that the catalyst has a narrow particle size dispersion in the
range 10–20 nm (Fig. 2(b)).
Figure 2. (a) SEM image, (b) TEM image and (c) EDX analysis of
[MNPs@APTA][Cl2].
The results of energy-dispersive X-ray (EDX) analysis clearly sup-
port the presence of iron and a good loading of copper onto the
catalyst matrix (Fig. 2(c)). To verify the immobilization of modified
APTS, CHN elemental analysis of the catalyst was conducted. The re-
sult confirms (C, 13.2%; N, 3.24%; H, 1.62%) a large amount
(0.85 mmol gꢀ1) of organic groups was loaded onto the
Fe3O4@SiO2. To incorporate copper species on the surface of MNPs,
[MNPs@APTA] was dispersed in a solution of copper chloride
([MNPs@APTA][Cl2]). The atomic absorption spectroscopy (AAS)
technique was used to prove and determine the amount of copper
loaded onto the surface of [MNPs@APTA]. A good loading level of
copper (0.65 mg molꢀ1) onto the [MNPs@APTA] prompted us to ex-
ploit the catalyst in a known reaction: the Huisgen reaction. Investi-
gation of the thermogravimetric analysis (TGA) curve of the catalyst
indicates organic degradation of the catalyst at 240 °C and the
Scheme 1. Immobilization and functionalization of (3-aminopropyl)
triethoxysilane (APTS) on Fe3O4@SiO2.
Appl. Organometal. Chem. 2016, 30, 488–493
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

F. M. Moghaddam et al.
complete decomposition continues up to 600 °C. Calculation of the
organic phase (26.6% content) of the catalyst with TGA gives a pow-
erful indication that a high level (0.92 mmol gꢀ1) of triazole groups
had been immobilized on the MNPs (Fig. 3).
The catalyst activity was investigated using the 1,3-dipolar reac-
tion of sodium azide, benzyl bromide and phenylacetylene under
various conditions. Since the solvent of a reaction is the main factor
of the optimization, the effects of various solvents on the reaction
were studied. Initially, water was selected as a safe and green
medium for the reaction (Table 1, entry 4). An excellent yield of
corresponding triazole is obtained after 4 h. For comparison of
the catalyst activity in various solvents, CH2Cl2, EtOH, toluene,
CH3CN, t-BuOH and H2O–t-BuOH (3/1) (entries 5–10, respectively)
were used as media. Of the seven solvents tested, water (entry 4)
was chosen as the best solvent for the reaction. To study the
catalytic effect, the reaction was followed in the absence of catalyst
(entries 1 and 2), with [MNPs@APTA] (entry 3) and in the presence
of various amounts of catalyst (entries 10 and 11). As can be seen,
in the absence of any catalyst or using only [MNPs@APTA], a trace
of corresponding triazole is obtained at 60 °C even after 24 h. It is
demonstrated that using 0.5 mol% of catalyst can effectively catal-
yse the reaction in a short time with a reasonable yield (entry 11). To
investigate the effect of anion, various anions, namely Brꢀ, NO3ꢀ,
OAcꢀ and SO24ꢀ, were examined and the results are presented in
Table 1 (entries 12–15). To investigate the effect of temperature,
the model reaction was conducted at room temperature and 40,
60, 70, 90 and 100 °C (Table 1, entries 16–21).
According to these results, the conditions of entry 11 of Table 1
were chosen as the best for this reaction. Having identified the op-
timum reaction conditions, the substrate scope was investigated
using a variety of crude materials (alkynes, alkyl halides and alkyl
Figure 3. TGA of [MNPs@APTA][Cl2].
Table 1. Control experiment for synthesis of 1,3,5-triazole catalysed by copper-supported [MNPs@APTA][Cl2]a
Entry
Catalyst
Catalyst loading (mol%)
Solvent
T (°C)
Time (h)
Yield (%)b
1
2
—
—
—
10 mgd
1
H2O
H2O
r.t
60
60
55
55
55
55
55
55
55
55
55
55
55
55
r.t
24
24
24
1.5
1.5
1.5
1.5
1.5
1.5
1.5
3
<1c
<3c
<15c
98
—
3
[MNPs@APTA]
H2O
4
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Br2]
[MNPs@APTA][(NO3)2]
[MNPs@APTA][OAc]
[MNPs@APTA][SO4]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
[MNPs@APTA][Cl2]
H2O
5
1
CH2Cl2
EtOH
Toluene
CH3CN
t-BuOH
H2O–t-BuOHe
H2O
45
6
1
75
7
1
40
8
1
85
9
1
80
10
11
12
13
14
15
16
17
18
19
20
21
1
97
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
97
94
H2O
3
H2O
3
90
H2O
3
93
H2O
3
94
H2O
3
40
H2O
40
60
70
90
100
3
78
H2O
3
97
H2O
3
98
H2O
3
98
98f
H2O
3
aReaction condition: phenylacetylene (0.5 mmol), benzyl bromide (0.5 mmol), sodium azide (0.5 mmol), sodium ascorbate (10 mol%), solvent (3 ml).
bIsolated yield.
cMainly recovery of the starting materials.
dMagnetic catalyst without Cu(II).
eRatio of H2O to t-BuOH =3/1.
fMixture of regioisomers.
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 488–493

Immobilization of copper ions onto α-amidotriazole-functionalized MNPs
tosylates) in the presence of sodium ascorbate and sodium azide.
According to the results in Table 2, various leaving groups such as
bromide, tosylate and chloride lead to excellent to good yields of
corresponding triazole in the same times (Table 2, entries 1–3).
The electron donor or acceptor of aromatic alkynes do not
have any effect on the reaction yields and reaction times, with
p-methoxyphenylacetylene and p-nitrophenylacetylene with
some alkyl halides being used for this reaction (Table 2, entries
4–6). According to the results, there is no significant loss in yield or
regioselctivity of products. Also, it can be concluded from Table 2 that
increasing the steric hindrance on the alkyl halide component causes
lower reaction rates as can be realized by comparing entries 1 and 18;
9 and 13; and 28 and 30. As is well known, aliphatic alkynes are more
inactive than aromatic alkynes, and the corresponding triazoles are
obtained in the presence of the catalyst with good yield in longer
times as compared with aromatic alkynes (Table 2, entries 21–27,
29, 32, 33). In the case of 1,2-dibromoethane as the alkyl halide,
the reaction proceeds from both sides of the chain and both Br
atoms participate in the reaction (Table 2, entry 19).
According to the results in Table 2, all the reactions proceed with
high regioselectivity and in all cases only the 1,4-regioisomers
are obtained, comparing with the results reported elsewhere.[26]
To investigate the reusability of the catalyst, the reaction of
phenylacetylene, benzyl bromide and sodium azide was performed
under the aforementioned optimized reaction conditions (Scheme 1).
After the first run the catalyst was collected using an external mag-
netic field and, after washing with ethanol, it was used for
the next run. This process was repeated 10 times and each time
the isolated yield was calculated exactly. As shown in Fig. 4, no
significant decrease in reaction yield is observed after repeated
Table 2. Huisgen 1,3-dipolar cycloaddition catalysed by [MNPs@APTA][Cl2]a
Entry
R
R′
Product
Time (h)
Yield (%)b
1
Ph
Ph
PhCH2
PhCH2
3a
3a
3a
3b
3c
3d
3e
3f
3 (X = Br)
3 (X = Cl)
3 (X = OTs)
4 (X = Br)
5 (X = Br)
4.5 (X = Br)
2.5 (X = Br)
2 (X = Br)
4 (X = Br)
5 (X = Br)
7 (X = Cl)
3 (X = Br)
3 (X = Br)
3.5 (X = Br)
4 (X = OTs)
6 (X = Cl)
4.5 (X = Br)
7 (X = Cl)
8 (X = Br)
5 (X = Br)
4 (X = Br)
4.5 (X = OTs)
4 (X = Br)
5.5 (X = Br)
4 (X = Br)
4.5 (X = OTs)
7 (X = Cl)
2 (X = Br)
5 (X = Br)
3.5 (X = Br)
4 (X = OTs)
4 (X = Br)
6 (X = OTs)
97
94
96
93
91
93
96
98
96
93
90
97
97
91
92
90
96
93
82
88
93
94
92
91
91
90
90
93
89
90
93
91
90
2
3
Ph
PhCH2
4
4-MeOPh
4-NO2Ph
2-NO2PhOCH2
Ph
PhCH2
5
PhCH2
6
PhCH2
7
4-BrPhCH2
4-BrPhCOCH2
C2H5OCOCH2
C7H15
8
Ph
9
Ph
3g
3h
3i
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Ph
Ph
C7H15
Ph
PhCOCH2
CH3OCOC2H4
Allyl
3j
Ph
3k
3l
Ph
Ph
Allyl
3l
Ph
Allyl
3l
Ph
NH2COCH2
1-Naphthyl–CH2
C2H4
3m
3n
3o
3p
3q
3q
3r
Ph
Ph
Ph
(CH3)2C¼CHCH2
PhCH2
C5H11
C5H11
C5H11
C5H11
C5H11
C5H11
C5H11
Ph
PhCH2
4-BrPhCH2
PhCOCH2
Allyl
3s
3t
Allyl
3t
1-Naphthyl–CH2
Ethyl
3u
3v
3w
3x
3x
3y
3y
C5H11
Ph
Ethyl
C6H13
Ph
C6H13
C5H11
C5H11
C6H13
C6H13
aReaction condition: alkyne (0.5 mmol), alkyl halide (0.5 mmol), NaN3 (0.5 mmol), sodium ascorbate (10 mol%), Cu (0.5 mol%), solvent (H2O, 3 ml), 55 °C.
bIsolated yield.
Appl. Organometal. Chem. 2016, 30, 488–493
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

F. M. Moghaddam et al.
using an external magnet and washed with deionized water
(30 ml) and ethanol (3 × 30 ml). The resulting Fe3O4 nanoparti-
cles were dispersed in ethanol (80 ml) using ultrasound for
20 min (ultrasonic power: 100 W).
These MNPs were used to synthesize silica-coated Fe3O4 nano-
particles through the following procedure. In a round-bottom flask,
3 ml of TEOS was slowly added to the solution. Then, 3 ml of ammo-
nium hydroxide (28% v/v) was added to the mixture during a
15 min period while the solution was mechanically stirred. The mix-
ture was stirred for 12 h at 40 °C. Finally, the MNPs coated with silica
(Fe3O4@SiO2) were collected using an external magnet, washed
three times with ethanol (30 ml) and dried under reduced pressure
using a rotary evaporator.
Figure 4. Reuse of [MNPs@APTA][Cl2] in the Huisgen cycloaddition.
cycles of the reaction. AAS analysis of the catalyst after 10 runs
shows that there is no significant metal leaching of the catalyst.
These findings indicate that the proposed catalyst not only cataly-
ses the cycloaddition of phenylacetylene to azides, but can also
be easily separated and reused several times without any signifi-
cant loss of activity.
Immobilization of APTS on Fe3O4@SiO2
Fe3O4@SiO2 (2 g), produced as described above, was added to
10 ml of toluene and sonicated for 30 min. Then 11.32 mmol
(2.5 ml) of APTS was added to the mixture while stirring. The
resulting mixture was refluxed for 48 h. The final product was
washed with methanol (3 × 30 ml) and dried under reduced pres-
sure using a rotary evaporator.
Conclusions
Synthesis of [MNPs@APTA][Cl2]
The synthesis of [MNPs@APTA][Cl2] and application of this catalyst
in the synthesis of triazole were investigated. Good coordination
of triazole ligands to copper causes good stability of the catalyst
under high temperature and in various solvents. According to the
results, the catalyst has excellent activity and leads to regioselec-
tivity in favour of 1,4-regioisomer under mild conditions in water.
Good stability and dispersal of the catalyst in water and high level
of copper loading on the catalyst are advantages for the use of
the catalyst in pharmaceutical and drug synthesis. Furthermore,
due to its magnetic characteristics, the catalyst can be easy re-
moved from the reaction medium using an external magnetic field
and reused in further runs.
To a round-bottom flask containing a mixture of t-BuOH and water
(20/80) with a magnetic stirring bar were added sodium azide
(22.7 mmol, 1.5 g), copper(II) chloride (0.74 mmol, 0.1 g),
phenylacetylene (18.2 mmol, 2 ml), ethyl bromoacetate (18 mmol,
2 ml) and sodium ascorbate (0.76 mmol, 0.15 g). The reaction
mixture was heated at 55 °C for 4 h. After completion, the syn-
thesized triazole was purified by recrystallization. In a round-
bottom flask, 0.5 g of the synthesized triazole was dissolved in
15 ml of tetrahydrofuran (THF), into which was dispersed 1 g
of MNPs functionalized with APTS. The mixture was heated for
48 h at 60 °C. The synthesized catalyst was extracted using an
external magnet, washed with methanol (3 × 20 ml) and dried
under reduced pressure.
Experimental
General Procedure for Synthesis of Triazole
General
To a glass tube was added ascorbic acid (10 mg) followed by
phenylacetylene (0.5 mmol, 55 mg), benzyl bromide (0.5 mmol,
85 mg), sodium azide (0.5 mmol, 33 mg), sodium hydroxide
(3 mg), catalyst (10 mg) and water (2.5 ml) which were dispersed
using ultrasound for 1 min. The mixture was left stirring at 55 °C
for 4 h. After TLC analysis (EtOAc–hexane, 25:75) had shown com-
plete conversion of the starting materials, the product was worked
up and purified according to the following procedure. The mixture
was diluted with EtOAc and water, and then the organic layer
was extracted using a separator funnel. The organic layer was
dried over MgSO4. Concentration under reduced pressure, using
a rotary evaporator, gave the desired target structure. The resi-
due was purified by recrystallization from EtOAc–n-hexane. In
order to reuse the catalyst for the next run, the nanomagnetic
copper catalyst was fixed using an external magnet, washed
with methanol and dried overnight.
All the materials used were commercially available and were pur-
chased from Merck and used without any additional purification.
1H NMR and 13C NMR spectra were recorded with a Bruker (Avance
DRX-500) spectrometer using CDCl3 as the solvent at room temper-
ature. Chemical shifts were measured in ppm relative to
tetramethylsilane as an internal standard. FT-IR spectra of the sam-
ples were taken using an ABB Bomem MB-100 FT-IR spectropho-
tometer. The morphology of the catalyst was observed with SEM
using a Philips XL30 scanning electron microscope. TEM images
were obtained using a Philips CM30 electron microscope. TGA
was conducted under a nitrogen atmosphere with a TGA Q 50 ther-
mogravimetric analyser. CHN analysis was done with a LECO
TruSpec analyser.
Synthesis of Silica-Coated Fe3O4 Nanoparticles
A solution of FeCl3 (66.58 mmol, 10.8 g) and FeCl2 (31.56 mmol,
4 g) was prepared and diluted with deionized water (50 ml) in a
three-necked flask. Then ammonium hydroxide (28% v/v) was
added dropwise to the solution (for pH = 10) under an inert at-
mosphere of argon and the resulting mixture was mechanically
stirred at room temperature for 20 min. The MNPs were collected
Acknowledgment
We gratefully acknowledge the funding support received for this
project from the Iran National Science Foundation (INSF), Islamic
Republic of Iran.
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Appl. Organometal. Chem. 2016, 30, 488–493

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