Alkyne-azide cycloaddition catalyzed by Fe-Cu nanoparticles

Article abstract of DOI:10.2174/157017812800167457

1,2,3-triazoles were synthesized using several alkynes and azides as starting materials in the presence of catalytic amounts of Cu-Fe nanoparticles. The process represents many advantages because it does not require additional bases or reductants, and thi

Full text of DOI:10.2174/157017812800167457

160
Letters in Organic Chemistry, 2012, 9, 160-164
Alkyne-Azide Cycloaddition Catalyzed by Fe-Cu Nanoparticles
Ángel García-Muñoz, Jaime González, Jessica Trujillo-Reyes, Raul A. Morales-Luckie,
Víctor Sánchez-Mendieta, Carlos González, Aydeé Fuentes and Erick Cuevas-Yañez*
Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM, Carretera Toluca-Atlacomulco Km 14.5,
Toluca, Estado de México, 52000, Mexico
Received July 01, 2011: Revised November 07, 2011: Accepted December 15, 2011
Abstract: 1,2,3-triazoles were synthesized using several alkynes and azides as starting materials in the presence of
catalytic amounts of Cu-Fe nanoparticles. The process represents many advantages because it does not require additional
bases or reductants, and this is carried out under ambient pressure and temperature with good yields.
Keywords: 1,2,3-triazoles, alkynes, azides, nanoparticles.
INDTRODUCTION
CuSO4.5H2O aqueous mixture [10, 11]. This last reduction
provides convenient method to prepare Fe-Cu
a
Copper-catalyzed Alkyne-azide cycloaddition (CuAAC)
has become one of the most important potent ligation
methods developed in the 21st century [1, 2]. In addition,
this reaction represents the main route to 1,2,3-triazoles
which have demonstrated interesting biological activities [3].
One of the advantages of this reaction is the combination of
mild conditions with high yields and regioselectivities joined
to high efficiency in terms of atom economy, which makes
CuAAC the most used “click” reaction.
nanoparticles with a grain size larger than 10 nm (average
size: 10.47 nm, Fig. 2), which are suitable for catalysis. Figs.
(1 and 2) show HRTEM images of quasi-spherical
nanoparticles, as well as the unimodal particle size
distribution for the synthesized nanoparticles, in agreement
with other studies [11].
Thus, Fe-Cu nanoparticles were tested as catalysts in
CuAAC reaction in several solvents. The reaction yields are
presented in Table 1, and based on these results; methanol
was selected as work solvent.
Currently, there are two important protocols to perform
these reactions, developed initially by the Meldal [4] and
Sharpless-Fokin [5] groups. Although both procedures are
widespread in application, research and developing in new
copper catalysts is quite desirable, where the use of reducing
agents or bases could be avoided.
On the other hand, the field of nanoparticles offers a new
group of catalysts with many applications in chemical reac-
tions [6]. In this regard, copper nanoparticles have been suc-
cessfully used in CuAAC to synthesize 1,2,3-triazoles [7-9].
In connection with other studies, the group of Sanchez-
Mendieta has developed a novel class of iron-copper
nanoparticles which was initially used in waste water
treatment [10]. In order to explore the catalytic ability of
these compounds; we attempted to extend the use of the Fe-
Cu nanoparticles to copper-catalyzed alkyne-azide
cycloaddition. Herein is described a summary of our recent
endeavors in this area.
Fig. (1). TEM Micrograph of Fe-Cu nanoparticles, scale bar: 10
nm.
In a model study, benzyl azide 1, which in turn was
prepared from benzyl bromide and sodium azide, was
reacted with phenylacetylene 2 at room temperature using
catalytic amounts of Cu-Fe nanoparticles in different
On the other hand, the use of base (sodium carbonate)
[12] temperature and catalyst ratio in CuAAC was studied,
and these results are presented in Table 2. Optimal
conditions were obtained when the reaction is carried out at
room temperature using 10 mg/mmol of catalyst and sodium
carbonate was not used as additive. Other catalytic systems
were tested, such as CuSO4-sodium ascorbate in tBuOH-
water [5], CuI-DIPEA [4] and CuI-Et3N [13] (entries 7-9,
Table 2). The results suggest that Cu-Fe nanoparticles are
effective catalysts in these kind of processes.
solvents to afford 1-benzyl-4-phenyl-1,2,3-triazole
(Scheme 1). The Cu-Fe nanoparticles catalysts were obtained
from sodium borohydride reduction of FeSO4.7H2O and
3
*Address correspondence to this author at the Centro Conjunto de
Investigación en Química Sustentable UAEM-UNAM, Carretera Toluca-
Atlacomulco Km 14.5, Toluca, Estado de México, 52000, Mexico; Tel: +52
722 276 66 10 ext. 7734; Fax: +52 722 217 51 09;
E-mail: ecuevasy@uaemex.mx
1875-6255/12 $58.00+.00
© 2012 Bentham Science Publishers

Alkyne-Azide Cycloaddition Catalyzed by Fe-Cu Nanoparticles
Letters in Organic Chemistry, 2012, Vol. 9, No. 3
161
which is unique in this kind of materials [11]. Some
nanoparticles with similar properties have been used by other
groups to design new catalytic systems [14-15], and in our
case, we decide to investigate the feasibility to use these
nanoparticles as recoverable heterogeneous catalysts in the
synthesis of triazole 3. The recycling experiments were
carried out by applying an external magnet to the reaction
flask. A separation of Fe-Cu nanoparticles was achieved and
the supernatant containing the product can be decanted. The
catalyst was re-dispersed in methanol and the magnetic
decantation was repeated again. These nano-materials could
be reused for the next cycle without further activation. The
results (Table 4) suggest a progressive lost of efficiency in
the yield which is consistent with other studies. Thus, Fe-Cu
nanoparticles represent a new class of catalysts that can be
easily separated for reuse.
In conclusion, the appropriately constituted alkynes and
azides are efficiently converted into 1,2,3-triazoles through a
simple and mild method, using Cu-Fe nanoparticles as
catalysts. In addition, the procedure is economic and
environmentally benign. These elements suggest that this
route will enjoy widespread application.
Fig. (2). TEM Micrograph of Fe-Cu nanoparticles, scale bar: 5nm.
N3
N
Fe-Cunano
solvent
EXPERIMENTAL
N
N
+
The starting materials were purchased from Aldrich
Chemical Co. and were used without further purification.
The organic azides were prepared according to the literature
[16, 17]. Solvents were distilled before use. Silica plates of
0.20 mm thickness were used for thin layer chromatography.
Melting points were determined with a Fisher-Johns melting
1
2
3
Scheme 1. Reaction between benzyl azide and phenylacetylene
using Fe-Cu nanoparticles.
1
point apparatus and they are uncorrected. H and 13C NMR
spectra were recorded using a Bruker AVANCE 300, the
chemical shifts (ꢀ) are given in ppm relative to TMS as
internal standard (0.00). For analytical purposes the mass
spectra were recorded on a JEOL JMS-5X 10217 in the EI
mode, 70 eV, 200oC via direct inlet probe. Only the
molecular and parent ions (m/z) are reported. IR spectra
were recorded on a Nicolet Magna 55-X FT instrument.
TEM studies were performed on a JEM-100CX transmission
electron microscope, operated at accelerating voltage of 200
kV.
Table 1. Solvent Effect in CuAAC Using Cu-Fe Nanoparticles
Catalysts
Solvent
% Yield
methanol
Acetone
82
32
42
18
15
10
4
Ethyl acetate
Tetrahydrofuran
water
The iron-copper nanoparticles were provided by the
Advanced Materials Laboratory from Universidad
Autónoma del Estado de Mexico and they were prepared
using the method described by Sanchez-Mendieta and
coworkers [10, 11].
Acetonitrile
dichloromethane
Preparation of Iron-Copper Nanoparticles
In order to explore the reaction scope, several alkynes
and azides were reacted under similar conditions (see Table
3). In general, the results showed that 1,2,3-triazoles were
the only products, and starting materials were recovered after
24 h when yields were moderated. The use of Cu-Fe
nanoparticles catalysts represents many advantages in this
process, because bases or reducing agents were not required
and the reactions are performed in mild conditions (room
pressure and temperature).
According to the method described by Sanchez-Mendieta
and coworkers [10, 11], a solution of FeSO4.7H2O (2.30 g;
7.5 mmol) in H2O (750 mL) was added to the solution of
CuSO4.5H2O (0.69 g; 2.5 mmol) in H2O (250 mL). The
resulting mixture was stirred with mechanical stirring (300
rpm) at room temperature. A solution of 0.5 M NaOH was
added dropwise to pH=7. When pH was adjusted, a solution
of NaBH4 (0.757 g; 20 mmol) in H2O (100 mL) was added, a
vigorous evolution of hydrogen occurred, and the resulting
dark mixture was stirred at room temperature for 15 min.
The mixture was filtered, and the precipitate was washed
The Fe-Cu nanoparticles obtained in this work exhibit a
paramagnetic behavior (average magnetic field: 40.57 T)

162 Letters in Organic Chemistry, 2012, Vol. 9, No. 3
García-Muñoz et al.
Table 2. Dependence of Temperature, Catalyst Ratio and Base in CuAAC
Entry
Temperature (°C)
Catalytic System
Reaction Time (h)
Base
% Yield
Catalyst ratio
(mg/mmol)
1
2
3
4
5
6
7
8
9
R. T.
60
Cu-Fe nanoparticle
Cu-Fe nanoparticle
Cu-Fe nanoparticle
Cu-Fe nanoparticle
Cu-Fe nanoparticle
Cu-Fe nanoparticle
CuSO4 Na ascorbate
CuI-DIPEA
10
10
10
20
5
12
12
12
3
Na2CO3
Na2CO3
No base
No base
No base
No base
No base
DIPEA
Et3N
43
44
53
81
82
82
75
85
80
60
R. T.
R. T.
R.T.
R.T.
R.T.
R.T.
48
12
12
12
12
10
10
10
10
CuI-Et3N
Table 3. 1,2,3-Triazoles Obtained from Alkyne-Azide Cycloaddition Catalyzed by Cu-Fe Nanoparticles
Triazole
Triazole
Entry
% Yield
Entry
% Yield
O
O
N
H
N
N
N
1
N
N
82
6
64
N
ꢀ
ꢀ
O
H
O
Cl
O
N
N
Cl
N
N
2
69
7
66
N
N
ꢀ
ꢀ
O
Cl
N
N
NO2
3
56
8
34
N
N
N
N
ꢀ
ꢀ
O
CH3
N
N
4
75
9
58
N
N
N
N
Cl
ꢀ
OCH3
Cl
ꢀ
O
N
N
5
79
N

Alkyne-Azide Cycloaddition Catalyzed by Fe-Cu Nanoparticles
Letters in Organic Chemistry, 2012, Vol. 9, No. 3
163
Table 4. Recycling of Cu-Fe Nanoparticles in the Synthesis of
Triazole 3
1-Benzyl-4-(4´-chlorophenoxymethyl)-1,2,3-triazole (Entry
3)
56% yield m.p. 85°C (MeOH). IR (KBr, cm-1) 1599,
1491, 1241. 1H-NMR (CDCl3, 300 MHz) ꢀ 5.12 (s, 2H), 5.50
(s, 2H), 6.87 (d, 2H, J=8.2 Hz), 7.19 (d, 2H, J=8.2 Hz), 7.30
(m, 5H), 7.50 (s, 1H). 13C-NMR (CDCl3, 75 MHz) ꢀ. 55.6,
62.3, 115.1, 122.9, 128.0, 128.9, 129.1, 130.3, 134.3, 143.5,
153.1. MS [EI+] m/z (%) 301 [M +2]+ (5) 299 [M]+ (15),
144 [M – C6H4ClN2O]+ (50), 91 [C6H5CH2]+ (100). HRMS
(EI+): for C16H14ClN3O calcd. 299.0825, found 299.0827.
Cycle
Conversion (%)
Yield (%)
Purity (%)
1
2
3
95
87
75
82
73
64
98
98
98
successively with water and acetone. The nanoparticles were
dried in vacuo at room temperature for 24 h.
1-Benzyl-4-(4-tolyloxymethyl)-1,2,3-triazole (Entry 4)
75% yield m.p. 76°C (MeOH).18 IR (KBr, cm-1) 1572,
1475, 1276. H-NMR (CDCl3, 300 MHz) ꢀ 2.26 (s, 3H),
1
Synthesis of Benzyl Azide
5.11(s, 2H), 5.45(s, 2H), 6.84 (d, 2H, J=8.5Hz), 7.03 (d, 2H,
J=8.5Hz), 7.22- 7.32(m, 5H), 7.47(s, 1H). 13C-NMR (CDCl3,
75 MHz) ꢀ 20.51, 55.9, 62.2, 114.7, 122.6, 128.1, 128.7,
129.1, 129.9, 134.6, 144.8, 156.1. MS [EI+] m/z (%) 279
[M]+ (40), 144 [M – C7H7N2O]+ (70), 91 [C6H5CH2]+ (100).
HRMS (EI+): for C17H17N3O calcd. 279.1372, found
279.1377.
A solution of benzyl bromide (2.8 g; 16.5 mmol) in DMF
(6mL) was added dropwise to a suspension of dry sodium
azide (4.9 g, 75.3 mmol) in DMF (6 mL). The resulting
mixture was stirred at 30 ° C under a nitrogen atmosphere
for 12 h. Water (50mL) was added and the phases were
separated, the aqueous phase was extracted with CH2Cl2 (3
X 50mL). The organic layers were joined and dried over
Na2CO3 and the solvent was removed in vacuo to yield a
colorless oil (1.8 g, 80%) which was used without
1-Benzyl-4-[(4-methoxyphenoxy)methyl]-1,2,3-triazole
(Entry 5)
1
purification. IR (KBr, cm-1) 2098, 1453. H NMR (CDCl3,
79% yield m.p. 78°C (MeOH). IR (KBr, cm-1) 1508,
1458, 1228. 1H-NMR (CDCl3, 300 MHz) ꢀ 3.76 (s, 3H), 5.10
(s, 2H), 5.47 (s, 2H), 6.78 (d, 2H, J=8.5Hz), 6.89 (d, 2H,
J=8.5Hz), 7.33(m, 5H), 7.49 (s, 1H). 13C-NMR (CDCl3, 75
MHz) ꢀ 55.5, 56.5, 62.8, 114.6, 115.9, 116.15, 122.6, 128.0,
128.7, 129.1, 134.5, 144.8, 154.2, 154.5. MS [EI+] m/z
(%)MS [EI+] m/z (%) 295 [M]+ (20), 144 [M – C7H7N2O2]+
(35), 123 [M – C9H8N3]+ (100), 91 [C6H5CH2]+ (50).
HRMS (EI+): for C17H17N3O2 calcd. 295.1321, found
295.1327.
300 MHz) ꢀ 4.31 (s, 2H), 7.25-7.43 (m, 5H). 13C NMR
(CDCl3, 75 MHz) ꢀ. 54.7, 128.2, 128.3, 129.3, 135.5 MS
[EI+] m/z (%) 133 [M]+ (44), 91 [C6H5CH2]+ (100).
Synthesis of 1,2,3-triazoles
Typical Procedure
To a stirring solution of benzyl azide (0.6g, 4.5 mmol)
and Fe-Cu nanoparticles powder (45 mg) in anhydrous
methanol (5 mL) at room temperature a solution of alkyne
(4.7 mmol) was added dropwise, in methanol (2 mL). The
resulting mixture was stirred at room temperature for 12 h
and the solvent was removed in vacuo. Water (10 mL) and
10% EDTA (4 mL) were added and the mixture was stirred
for additional 0.5 h. the product was filtered and purified by
crystallization.
(1-Benzyl-1,2,3-triazol-4-yl)methyl butylcarbamate (Entry
6)
64% yield m.p. 82°C (MeOH). IR (KBr, cm-1) 1710,
1610, 1536. 1H-NMR (CDCl3, 300 MHz) ꢀ 1.25 (t, 3H), 2.57
(m, 4H), 3.31 (d, 2H), 5.26 (s, 2H), 5.54 (s, 2H), 7.26 (s,
2H), 7.28-7.37 (m, 5H), 7.56 (s, 1H). 13C-NMR (CDCl3, 75
MHz) ꢀ 13.9, 17.5, 31.3, 54.33, 55.6, 62.2, 115.2, 128.1,
128.9, 129.1, 134.28, 143.62, 163.13. MS [EI+] m/z (%) 288
[M]+ (10), 144 [M – C5H10N3O2]+ (20), 91 [C6H5CH2]+
(100). HRMS (EI+): for C15H20N4O2 calcd. 288.1586, found
288.1583.
1-Benzyl-4-phenyl-1,2,3-triazole (Entry 1)
82% yield m.p. 130°C (MeOH, lit. 130-130.9ºC).13 IR
(KBr, cm-1) 1636, 1459, 1071. 1H NMR (CDCl3, 300 MHz)
ꢀ 5.58 (s, 2H), 7.33-7.41 (m, 8H), 7.68 (s, 1H), 7.80 (m, 2H).
13C NMR (CDCl3, 75 MHz) ꢀ 54.2, 119.5, 125.7, 128.0,
128.1, 128.2, 128.8, 128.8, 129.1, 130.5, 134.7, 148.2. MS
[EI+] m/z (%) 235 [M]+ (20), 206 [M -HN2]+ (50), 116 [M -
C7H7N2]+ (100), 91 [C6H5CH2]+ (85).
(1-Benzyl-4-[(3,4-dichlorophenoxy)methyl]-1,2,3-triazole
(Entry 7)
66% yield m.p. 81°C (MeOH). IR (KBr, cm-1) 1635,
1465, 1250. 1H-NMR (CDCl3, 300 MHz) ꢀ 5.22 (s, 2H), 5.53
(s, 2H), 6.98 (m, 1H), 7.27-7.26 (m, 7H), 7.53 (s, 1H). 13C-
NMR (CDCl3, 75 MHz) ꢀ 55.9, 62.4, 114.5, 115.7, 116.2,
122.6, 128.0, 128.7, 129.1, 129.3, 134.3, 144.5, 154.5. MS
[EI+] m/z (%) 377 [M+4]+ (3), 335 [M+2]+ (9), 333 [M]+
(15), 144 [M – C6H4ClN2O]+ (30), 91 [C6H5CH2]+ (100).
HRMS (EI+): for C16H13Cl2N4O calcd. 233.0436, found
233.0433.
4-(1-Benzyl[1,2,3]triazol-4-ylmethoxy)benzaldehyde (Entry
2)
69% yield m.p. 80°C (MeOH) [18]. IR (KBr, cm-1) 1680,
1508, 1252. 1H-NMR (CDCl3, 300 MHz) ꢀ 5.25 (s, 2H), 5.53
(s, 2H), 7.08(d, 2H, J= 8 Hz), 7.36 (m, 3H), 7.58(s, 1H), 7.80
(m, 2H), 7.83 (s, 2H, J= 8 Hz), 9.89(s, 1H). 13C-NMR
(CDCl3, 75 MHz) ꢀ 55.9, 62.1, 115.1, 122.9,128.0, 128.9,
129.1, 130.3, 134.3, 143.5, 163.1, 163.14, 190.7. MS [EI+]
m/z (%) 293 [M]+ (10), 172 [M - C7H9N2]+ (75), 144 [M –
C7H7N2O]+ (80), 91 [C6H5CH2]+ (100). ). HRMS (EI+): for
C17H15N3O2 calcd. 293.1164, found 299.1169.
1-(2-Nitrophenyl)-4-phenyl-1,2,3-triazole (Entry 8)
34% yield m.p. 80°C (MeOH). IR (KBr, cm-1) 1634,
1
1430, 1350. H-NMR (CDCl3, 300 MHz) ꢀ 7.38 (m, 1H),

164 Letters in Organic Chemistry, 2012, Vol. 9, No. 3
García-Muñoz et al.
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7.46 (m, 2H), 7.70 (m, 2H), 7.83 (m, 1H), 7.92 (m, 2H), 8.09
(s, 1H), 8.12 (m, 1H). 13C-NMR (CDCl3, 75 MHz) ꢀ 120.9,
125.6, 126.0, 128.6, 129.2, 130.3, 130.7, 133.8, 144.4, 148.4.
MS [EI+] m/z (%) 266 [M]+ (100). HRMS (EI+): for
C14H10N4O2 calcd. 266.0804, found 266.0809.
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1-(3,4-Dichlorophenyl)-4-phenyl-1,2,3-triazole (Entry 9)
58% yield m.p. 79°C (MeOH). IR (KBr, cm-1) 1640,
1
1420, 1150. H-NMR (CDCl3, 300 MHz) ꢀ 7.35 (m, 1H),
7.46 (m, 2H), 7.62 (m, 1H), 7.68 (s, 2H), 7.89 (m, 2H),
8.17(s, 1H). 13C-NMR (CDCl3, 75 MHz) ꢀ 112.4, 115.8,
122.0, 123.9, 128.7, 129.1, 129,8, 133.2, 133.8, 135.6, 136.8,
146.7. MS [EI+] m/z (%) 293 [M +4]+ (10), 291 [M +2]+
(65), 289 [M]+ (100). HRMS (EI+): for C14H9Cl2N3 calcd.
289.0174, found 289.0176.
[9]
[10]
[11]
ACKNOWLEDGEMENTS
Financial support from SIEA-UAEMEX (project No.
2692-2008U) is gratefully acknowledged. The authors would
like to thank Signa, S.A. de C.V. for some graciously
donated solvents and reagents, and M. C. Nieves Zavala for
the technical support.
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CONFLICT OF INTEREST
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Declared none.
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