species have been immobilized onto various supports such
as activated charcoal,9 amine-functionalized polymers,10 and
zeolites.11 However, the immobilized catalysts frequently
suffer from low activity and low product yield and require
additives9 and high reaction temperatures.6,9,11
We report herein a recyclable copper catalyst (Cu/
AlO(OH), (1)) which is composed of copper nanoparticles
in aluminum oxyhydroxide nanofiber. The catalyst 1 is highly
active at room temperature for the Huisgen (3 + 2)
cycloaddition of a wide range of azides and nonactivated
alkynes without requiring additives. The catalyst 1 can be
easily synthesized from readily available reagents by a one-
pot procedure similar to those for our Pd,12b Ru,12e Rh,12f
and Ir catalysts reported previously (Scheme 1).12
covered with Cu2O and CuO.14,15 The surface area, the pore
volume, and the pore size of 1 were estimated to be 360 m2
g-1, 0.65 cm3 g-1, and 3.2 nm, respectively, by BET nitrogen
adsorption analysis. With the ICP data, the copper content
of 1 was calculated to be 4.0 wt %; the copper nanoparticles
entrapped in the aluminum oxyhydroxide matrix corre-
sponded to 98% of the employed cupric chloride.
We compared the activities of 1 and commercial Cu
catalysts in the cycloaddition of phenylacetylene and n-octyl
azide at room temperature (Table 1). The reaction using 1
Table 1. Activities of 1 and Commercial Cu Catalystsa
entry
catalyst (mol %)
T (°C)
time (h)
yieldb (%)
1
2
3
4
5
6
7
8
1 (3)
1 (5)
1 (5) + Et3Nc
Cu2O (3)
Cu2O (100)
CuO (100)
CuO/Al2O3 (6)
CuCl2‚2H2O (100)
25
60
60
25
25
25
25
25
12
3
95
95
94
trace
15
0
Scheme 1. Preparation of Catalyst
0.5
12
12
12
12
12
0
0
a Phenylacetylene (1.0 mmol) and n-octylazide (1.1 mmol) were reacted
in n-hexane (2.0 mL) for 12 h. b Isolated yield of 1-octyl-4-phenyl-1H-
1,2,3-triazole. c Triethylamine (1.0 equiv) was used as an additive.
Copper nanoparticles were generated by heating a mixture
of cupric chloride dihydrate, ethanol, aluminum tri-sec-
butoxide, and pluronic P123 at 160 °C.13 After 3 h, water
was added for gelation. The resulting bluish powder was
filtered, washed with acetone, and dried at 120 °C for 2 h to
give a green powder. The green powder was characterized
by transmission electron microscopy (TEM), X-ray photo-
electron spectroscopy (XPS), inductively coupled plasma
(ICP), and nitrogen isotherm experiment.14 The fibrous
morphology, which is a typical feature of aluminum oxy-
hydroxide, was observed in the low-resolution TEM image
(Figure 1).
(3 mol % of Cu) gave the cyclized product in 95% yield
(entry 1). Heating or using triethylamine as an additive
increased the rate significantly (entries 2 and 3). Cuprous
oxide showed very low activity (entry 4); even with 100 mol
% of Cu the yield was only 15% (entry 5). Pure cupric oxide
and alumina-supported cupric oxide were inactive (entries
6 and 7). The precursor of 1, cupric chloride dihydrate, was
also inactive (entry 8).
The scope of the (3 + 2) cycloaddition using 1 was
investigated with various alkynes and azides at room
temperature (Table 2). n-Octyl azide (2), 4-azidoanisole (3),
and benzyl azide (4) were employed as aliphatic and aromatic
azides and were synthesized by following the reported
literature procedures.16 Various terminal alkynes were readily
reacted with the azides to give the corresponding 1,2,3-
(10) Girard, C.; O¨ nen, E.; Aufort, M.; Beauvie`re, S.; Samson, E.;
Herscovici, J. Org. Lett. 2006, 8, 1689.
(11) Chassing, S.; Kumarraja, M.; Sido, A. S. S.; Pale, P.; Sommer, J.
Org. Lett. 2007, 9, 883.
(12) (a) Kim, N.; Kwon, M. S.; Park, C. M.; Park, J. Tetrahedron Lett.
2004, 45, 7057. (b) Kwon, M. S.; Kim, N.; Park, C. M.; Lee, J. S.; Kang,
K. Y.; Park, J. Org. Lett. 2005, 7, 1077. (c) Kwon, M. S.; Kim, N.; Seo, S.
H.; Park, I. S.; Cheedrala, R. K.; Park, J. Angew. Chem., Int. Ed. 2005, 44,
6913. (d) Park, I. S.; Kwon, M. S.; Kim, N.; Lee, J. S.; Kang, K. Y.; Park,
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Figure 1. TEM images of 1: (a) low-resolution (100 nm bar scale);
(b) high resolution (5 nm bar scale).
(13) Without pluronic P123, copper nanoparticles were aggregated before
gelation.
As expected on the basis of previous reports,15 the XPS
analysis revealed that the surface of the Cu nanoparticles is
(14) See the Supporting Information.
(15) (a) Molteni, G.; Bianchi, C. L.; Marinoni, G.; Santo, N.; Ponti, A.
New. J. Chem. 2006, 30, 1137. (b) Son, S. U.; Park, I. K.; Park, J.; Hyeon,
T. Chem. Commun. 2004, 778. (c) Chusuei, C. C.; Brookshier, M. A.;
Goodman, D. W. Langmuir 1999, 15, 2806.
(7) D´ıez-Gonza´lez, S.; Correa, A.; Cavallo, L.; Nolan, S. P. Chem. Eur.
J. 2006, 12, 7558.
(8) Pacho´n, L. D.; van Maarseveen, J. H.; Rothenberg, G. AdV. Synth.
(16) (a) Alvarez, S. G.; Alvarez, M. T. Synthesis 1997, 413. (b) Zhu,
W.; Ma, D. Chem. Commun. 2004, 888. (c) Andersen, J.; Madsen, U.;
Bjorkling, F.; Liang, X. Synlett 2005, 2209.
Catal. 2005, 347, 811.
(9) Lipshutz, B.; Taft, B. R. Angew. Chem., Int. Ed. 2006, 45, 8235.
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Org. Lett., Vol. 10, No. 3, 2008