Nano copper(i) oxide/zinc oxide catalyzed N-arylation of nitrogen-containing heterocycles with aryl halides and arylboronic acids in air

Article abstract of DOI:10.1039/c3ra46548a

The synergistic effect of zinc and copper in Cu₂O/ZnO nanoflake as a heterogeneous catalyst for the N-arylation of heterocycles with aryl halides and arylboronic acids in the absence of additional ligand in air were demonstrated. The catalyst was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area measurement, and FT-IR spectroscopy. The Royal Society of Chemistry 2014.

Full text of DOI:10.1039/c3ra46548a

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Nano copper(I) oxide/zinc oxide catalyzed
N-arylation of nitrogen-containing heterocycles
Cite this: RSC Adv., 2014, 4, 7321
with aryl halides and arylboronic acids in air
Mona Hosseini-Sarvari* and Fatemeh Moeini
2
The synergistic effect of zinc and copper in Cu O/ZnO nanoflake as a heterogeneous catalyst for the N-
Received 10th November 2013
Accepted 6th January 2014
arylation of heterocycles with aryl halides and arylboronic acids in the absence of additional ligand in air
were demonstrated. The catalyst was characterized by powder X-ray diffraction (XRD), scanning electron
microscopy (SEM), transmission electron microscopy (TEM), BET surface area measurement, and FT-IR
spectroscopy.
DOI: 10.1039/c3ra46548a
www.rsc.org/advances
1
9
20
tris(hydroxymethyl)ethane, thiophenecarboxylate, pyridine
Introduction
21
22
23
N-oxides, phosphorus dendrimers, and tricarbene. These
N-aryl heterocycles, are ubiquitous in biochemical, biological, ligands play an important role in controlling the concentration
1
and medicinal structures and functions, and have been of active catalytic species, but they may contaminate the nal
2
24
exploited as precursors of versatile N-heterocyclic carbenes,
product. Using a catalyst in the absence of any additional
3
and efficient ligands for synthesis of transition-metal catalysts
ligands could be a good alternative to avoid the inconvenience
or ionic liquids. Traditionally, these compounds have usually of ligand removal from the reaction mixture.
4
been prepared by Ullmann-type coupling reactions. However,
2
In recent years, several CuI/Cu O-catalyzed ‘ligand-free’
9
c,25
these reactions were conducted under harsh conditions, catalytic systems have emerged.
However, these catalytic
ꢀ
25a,b,j
including high temperature (around 200 C) for extended systems oen require excess substrates
or high catalyst
25c–f
periods of time, stoichiometric amount of copper reagents, and loadings.
Although there are some reports on the amination
selective halide substrate, which is problematic for industrial of aryl halides with amines promoted by Cu(II) salts without
use due to high cost and waste disposal. To overcome these using organic ligands, they oen suffer from one or more
26
drawbacks, great progresses have been made recently to develop limitations, such as high reaction temperature and/or pro-
26e–h
new catalytic systems. In some instances catalytic amounts of longed reaction time.
In addition, some of these methods
copper agent and arylboronic acids in place of aryl halides have require large amounts of catalyst, which raised the cost of the
26a–d
26h
been employed, but this protocol is not general due to the reaction
and some of the catalyst are air sensitive. Thus, a
relative instability of boronic acids and the tedious purication need to develop a ligand-free, environmentally friendly, less
5
1b,6
1d,7
procedure. Buchwald
and Hartwig
independently repor- expensive and easily separable catalytic system for such
ted the applicability of Pd catalysts for N-arylation of amines coupling reactions is substantial.
with aryl halides. However, industrial use of these procedures is
Herein, for the rst time, we report the efficient catalytic
2
problematic in many cases due to their air and moisture activity of Cu O/ZnO nanoparticles toward the N-arylation of
sensitivity, as well as the higher costs of palladium catalysts and various N-heterocycles with aryl halides and arylboronic acid
the ligands. Thus, Cu-based catalysts have continued to provide under ‘ligand-free’ conditions (Scheme 1).
the most effective system for the N-arylation of nitrogen-con-
In comparison with the current methods of the C–N bond
8
9
taining heterocycles. Indeed, Buchwald and Taillefer reported, formation, our approach has several distinguishing features
respectively, that copper-catalyzed cross-coupling of N–H that are worth mentioning: (i) the coupling yield is excellent,
heterocycles with aryl halides could be improved with the
addition of diamines or oxime/imine derivatives as additives.
Other groups have also utilized various ligands, such as b-
1
0
8b,11
12
13
diketones, 1,2-diamines,
phenanthrolines, bipyridines,
14
15
9a
16
a-aminoacids, phosphines, Schiff bases, ethylene glycol,
diethyl salicylamide,
17
18
per-6-amino-b-cyclodextrin,
1,1,1-
Department of Chemistry, Shiraz University, Shiraz 71454, I. R. Iran. E-mail:
hossaini@shirazu.ac.ir; Fax: +0098 711 6460788; Tel: +0098 711 6137169
Scheme 1 Synthesis of N-aryl heterocycles in air catalyzed by Cu
ZnO nanoflake.
2
O/
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and the reaction tolerates both electron-donating and electron-
withdrawing substituents in ortho-, meta-, or para-positions of
the aryl halide. (ii) The approach offers experimental simplicity
and can be performed without the need for protection from air
or moisture; (iii) this procedure can be performed in the
absence of any additional ligand at lower cost, safely and is
environmentally benign on a large, or industrial scale.
Furthermore, this approach is not only efficient for aryl halides
but also it is convenient for arylboronic acids.
Results and discussion
Characterization of Cu
2
O/ZnO nanoake
The Cu O/ZnO nanoake catalyst was prepared by a simple
2
method from cheap and commercial sources. The preparation Fig. 2 The XRD pattern of Cu
2
O/ZnO nanoflake.
process involved combing of the zinc oxide (ZnO) and the
copper sulfate (CuSO
4
) as copper source, centrifuged and
washed with deionized water and absolute ethanol to dispose of diffraction peak was selected to calculate the average grain size
2
+
free Cu ions, and nally reducing by hydrazine hydrate of Cu
N H $H O).
Cu O along the (200) direction and ZnO along the (002) direc-
In order to evaluate the Cu and Zn contents of the catalyst, it tion in a Cu O/ZnO nanoake is about 21 nm and 30 nm
was treated with concentrated HCl to digest the metal complex respectively.
2
O by using the Scherrer formula. The average grain size of
(
2
2
4
2
2
and then analyzed by inductively coupled plasma (ICP) analysis.
The results revealed that the contents of Cu and Zn were 47.01% Cu
The scanning electron micrograph (SEM) of the synthesized
O/ZnO particles is shown in Fig. 3. It demonstrates that a well
O/ZnO nanoake has been formed. The
size and morphology of Cu O/ZnO nanoparticles analyzed by
2
(
w/w) and 21.77% (w/w) respectively (see Experimental section dened and discrete Cu
2
for details).
2
The FT-IR spectrum of the catalyst in the region of 400–950 TEM is represented in Fig. 4. This image reveals that the product
ꢁ
1
ꢁ1
cm is shown in Fig. 1. The peak at 624 cm corresponds to consists of ake particles with the average size of 32 nm.
27
ꢁ1
the Cu–O bond, and a weak absorption at about 455 cm is
The data obtained by BET measurements of nano Cu
powder are shown in Table 1. The BET surface area of nano
O/ZnO
2
28
attributed to the characteristic absorption band of Zn–O.
The crystal structure and composition of the obtained Cu
sample were analyzed by X-ray diffraction. Fig. 2 displays the BJH adsorption surface area of pores was 13.08 m g . The
2
ꢁ1
2
O/ZnO powder was found to be 14.74 m g , whereas the
2
ꢁ1
ꢁ1
3
XRD pattern of the sample. The XRD pattern of the Cu
nanoake can be indexed with ve Cu O diffraction peaks at the cumulative adsorption pore volume was 0.06 cm g . The
2
O/ZnO single point total pore volume was found to be 0.07 cm g , and
3
ꢁ1
2
ꢀ ꢀ ꢀ ꢀ ꢀ
2
9.5 (110), 36.4 (111), 42.3 (200), 61.6 (220), 73.8 (311) and pore size distribution was found to be 2.41 nm and the mean
ꢀ
ꢀ
ꢀ
six ZnO diffraction peaks at 31.8 (100), 34.5 (002), 36.4 (101), pore diameter was 19.54 nm.
ꢀ
ꢀ
ꢀ
4
7.8 (102), 56.7 (110), 63.0 (103) (JCPDS 78-2076 and 89-1397),
which suggests the presence of Cu O and ZnO phases in the Catalytic activity of the nano Cu O/ZnO for N-arylation of
sample. Considering the overlapping of a ZnO (101) diffraction nitrogen heterocycles
2
2
2 2
peak with a Cu O (111) diffraction peak, the Cu O (200)
In order to establish the optimum conditions, for our initial
screening experiment, the catalytic activity of a few zinc and
Fig. 1 FT-IR spectrum of Cu
2
O/ZnO nanoflake.
2
Fig. 3 The SEM image of Cu O/ZnO nanoflake.
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entries 2 and 4). However, no product was formed when the
reaction was run in the presences of nano or bulk ZnO indi-
vidually (Table 2, entries 3 and 5). This may be because of
increasing the reactivity of Cu O aer interacting with ZnO.
2
With respect to the catalyst loading, 0.010 g of nano Cu
2
O/ZnO
was found to be optimal. When 0.005 g of nano Cu O/ZnO was
2
used, the reaction did not go to completion, and good yield of
the product was obtained as the reaction time prolonged (Table
2, entry 6). However, no signicant improvement was observed
with 0.020 g and 0.040 g of nano Cu O/ZnO (Table 2, entries 7
2
and 8). In addition, performing the experiment in the absence
of nano Cu O/ZnO did not lead to any product even aer 48 h
2
(Table 2, entry 9). In addition, we further investigated the N-
Fig. 4 TEM image of Cu
2
O/ZnO nanoflake.
arylation reaction between imidazole (1a) and iodobenzene (2a)
by adding some nitrogen-containing ligands such as 1,10-phe-
nanthroline and ethylenediamine (Table 2, entries 10 and 11).
O/ZnO However, surprisingly it was found that the effect of the ligand
is negligible as compared to the reactions without additional
Table 1 Results of BET surface area measurements for Cu
nanoflake
2
ligand.
2
ꢁ1
Surface area
Pore volume
BET surface area (m g )
14.74
13.08
Encouraged by this result, then we examined the effect of
BJH adsorption cumulative
surface area of pores (m g
Single point adsorption total
pore volume of pores (cm g
2
ꢁ1
)
different solvents and bases on the coupling reaction (Table 3).
0.07 Among the solvents used, DMSO was found to be the best one
for such reaction (Table 3, entry 1), while other solvents such as
DMF, PEG, and MeCN gave comparatively lower yields (Table 3,
entries 2–4). Toluene and water did not afford any product
2.41 (Table 3, entries 5 and 6). For a variety of bases (e.g., KOH,
3
ꢁ1
)
BJH adsorption cumulative
0.06
3
ꢁ1
volume of pores (cm g
)
Pore size
Mean pore diameter (nm)
Pore size distribution (nm)
19.54
a
Table 3 The optimization of solvent and base
copper metal oxides were examined in a model reaction
between imidazole (1a) and iodobenzene (2a) in DMSO at 100 C Entry
b
ꢀ
Solvent/base
Time (h)
Yield (%)
(
Table 2). Nano Cu O/ZnO was found to be the most effective
2
1
2
3
4
5
6
7
8
9
10
DMSO/KOH
DMF/KOH
PEG (300)/KOH
Acetonitrile/KOH
2
4
4
4
4
4
4
4
4
4
4
95
40
35
20
0
catalyst in terms of reaction rate, and isolated yield of the cor-
responding products without observing any other products
(
Table 2, entry 1). Both nano and bulk Cu O afforded the
2
H
2
O/KOH
Toluene/KOH
DMSO/Cs CO
CO
PO
desired products in 60 and 48% yields, respectively (Table 2,
0
2
3
45
35
30
10
0
DMSO/K
DMSO/K
2
3
3
4
Table 2 Investigation of a few zinc and copper metal oxides in N-
arylation of imidazole with iodobenzene
a
DMSO/NaOAc
DMSO/NEt
11
3
b
Entry
Catalyst (g)
Time (h)
Yield (%)
a
Reaction conditions: imidazole (1.2 mmol), iodobenzene (1 mmol),
base (2 mmol), and Cu
100 C. Isolated yield.
2
O/ZnO nanoake (0.010 g) in solvent (2 mL) at
ꢀ
b
1
2
3
4
5
6
7
8
9
Nano Cu
Nano Cu
Nano ZnO (0.01)
Bulky Cu
Bulky ZnO (0.01)
2
O/ZnO (0.01)
2
24
24
24
24
3
2
2
48
2
2
95
60
0
48
0
70
95
95
0
95
95
c
2
O (0.01)
c
d
2
O (0.01)
d
a
Table 4 The optimization of temperature
Nano Cu
Nano Cu
Nano Cu
None
2
2
2
O/ZnO (0.005)
O/ZnO (0.02)
O/ZnO(0.04)
ꢀ
b
Entry
Temperature ( C)
Time (h)
Yield (%)
e
1
2
3
4
5
25
50
80
100
120
6
6
6
2
2
0
30
45
95
96
1
1
0
1
Nano Cu
Nano Cu
2
O/ZnO (0.01)
O/ZnO (0.01)
f
2
a
Reaction conditions: imidazole (1.2 mmol), iodobenzene (1 mmol),
ꢁ2
KOH (2 mmol), and catalyst (0.010 g, 7.3 ꢂ 10 mmol Cu) in DMSO
ꢀ
b
c
(
2 mL) at 100 C. Isolated yield. Nano Cu
2
O and ZnO individually,
d
a
were prepared according to the Experimental section. Cu
2
O and ZnO
Reaction conditions: imidazole (1.2 mmol), iodobenzene (1 mmol),
e
ꢁ2
were purchased from Merck. 1,10-Phenanthroline (7.3 ꢂ 10 mmol) KOH (2 mmol), and Cu
2
O/ZnO nanoake (0.010 g) in DMSO (2 mL).
f
ꢁ2
b
as ligand. Ethylenediamine (7.3 ꢂ 10 mmol) as ligand.
Isolated yield.
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a
Table 5 N-Arylation of imidazole with aryl halide or arylboronic acid
b
Entry
ArX
Product
Time (h)
15
Yield (%)
Ref.
1
90
90
90
25c
2
3
3
25c
4.25
33
4
3
85
34
5
6
10
2
90
95
25c
25c
7
3
90
35
8
9
2
95
95
92
90
25c
25c
33
1.25
4.66
15
1
0
1
1
25c
1
2
4.83
90
36
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Table 5 (Contd.)
b
Entry
ArX
Product
Time (h)
6
Yield (%)
Ref.
33
13
14
15
80
90
95
4.66
1.25
1.33
33
25c
37
1
6
7
90
90
1
2.25
3.5
33
c
1
8
95
25c
a
b
ꢀ
Reaction conditions: imidazole (1.2 mmol), aryl halide or arylboronic acid (1 mmol), KOH (2 mmol), and catalyst (0.010 g) in DMSO (2 mL) at 100 C.
Isolated yield. Large scale test.
c
K
2 3 3 4 2 3 3
CO , K PO , Cs CO , NaOAc, and NEt ), KOH was selected as imidazole with sterically hindered aryl halides were found in
8c
the best one for this reaction in DMSO (Table 3, entry 1). NEt
an organic base was ineffective (Table 3, entry 11) and moderate to iodobenzene (2h) was slower with a lower conversion of
yield was afforded by using Cs CO (Table 3, entry 7) and poor starting materials, even aer extending the reaction time (Table
result was observed by using NaOAc (Table 3, entry 10). 5, entry 5). Coupling reaction of imidazole 1 with chlorobenzene
3
as the literatures. The reaction with bromobenzene (2e) relative
2
3
Furthermore, during our optimization studies, the effect of (2a) was also investigated, and the chloride showed lower
temperature utilizing nano Cu O/ZnO (0.010 g), was also reactivity compared with bromide and iodide (Table 5, entry 1).
2
examined and it was found that the reaction temperature exerts Independently on the aryl halide used the reactions were never
great impact on this reaction (Table 4). Finally, the optimized accompanied by the formation of biaryl homocoupling by
reaction conditions were found to be 0.010 g of nano Cu
KOH (as the base) and DMSO (as a solvent) at 100 C.
2
O/ZnO, products.
To our delight, our system could promote almost exclu-
ꢀ
With the optimized reaction conditions in hand, a variety of sively the selective N-arylation of 4-iodoaniline to afford the
substituted aryl halides derivatives were chosen as the corresponding N-arylimidazole (3f) in high yield, avoiding the
substrates in this cross-coupling reaction. As shown in Table 5, competition from the formation of diarylamine (Table 5,
the coupling reactions were performed well for all the entry 11). It is noteworthy that the reaction was highly che-
substrates examined, and the desired products were isolated in moselective, for example, reaction between 1-bromo-4-
moderate to excellent yields. Notably, the present catalyst chlorobenzene, 1-bromo-4-uorobenzene and imidazole gave
system could facilitate the N-arylation of imidazole with ortho- 1-(4-chlorophenyl)-1H-imidazole and 1-(4-uorophenyl)-1H-
substituted aryl iodide and chloride. For example, the reaction imidazole as the only products respectively (Table 5, entries
of imidazole with 2-nitrochlorobenzene and 4-methyl-2-nitro- 13 and 14). To explore further the applicability of nano Cu
iodobenzene, afforded the corresponding coupling products in ZnO catalyst for C–N coupling reactions, we tested the N-
5 and 90% yields, respectively (Table 5, entries 4 and 12). arylation of imidazole with various arylboronic acids bearing
2
O/
8
Generally, the Ullmann-type condensations are sensitive to electron-donating and withdrawing groups; and the desired
steric hindrance near the halogen atom, and only a few exam- products were isolated in high yields (Table 5, entries 15–17).
ples concerning with the copper-catalyzed arylation of To check the feasibility of this procedure on a preparative
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scale, we carried out the N-arylation of imidazole (1a) with pyrrole, underwent coupling with iodobenzene under the opti-
iodobenzene (2a) on a 50 mmol scale in the presence of nano mized experimental conditions and provided their corre-
Cu O/ZnO catalyst. As expected, the reaction proceeded sponding products in 50–85% yield (Table 6, entries 1–4).
2
similarly to the experiment on a smaller scale, except that a
In order to show the merit of this catalytic method, we
slight increase in the reaction time was observed (3.5 h) compared our obtained results with similar data published by
(Table 5, entry 18).
other groups which used other catalysts. For this purpose, the
The catalytic activity of nano Cu
2
O/ZnO in N-arylation reac- reactions of imidazole and iodobenzene were chosen as a model
tions of other nitrogen-containing heterocycles was also inves- reaction and comparison was carried out on the basis of reac-
tigated. 2-Methyl-1H-imidazole, indole, 1H-1,2,4-triazole, and tion conditions, time, and percentage yields (Table 7).
a
Table 6 N-Arylation of various nitrogen heterocycles
b
Entry
Amine
Product
Time (h)
12
Yield (%)
Ref.
18
1
75
c
2
3
5
3
50
25c
25c
85
80
4
5
25c
a
ꢀ
b
Reaction conditions: Het-NH (1.2 mmol), iodobenzene (1 mmol), KOH (2 mmol), and catalyst (0.010 g) in DMSO (2 mL) at 100 C. Isolated yield.
The yield was not improved event aer 12 h.
c
Table 7 Comparison of activity of different copper catalysts in the N-arylation reaction of iodobenzene and imidazole
Entry
Catalyst, ligand
$H O (1 mol%)
Reaction conditions
Time (h)/yield (%)
Ref.
ꢀ
1
2
3
Cu(OAc)
Cu(0) (2 equiv.)
Cu O (0.05 mol%), 4,7-dimethoxy-1,10-phenanthroline
0.075 mol%)
MnF (30 mol%), CuI (10 mol%), trans-1,2-
diaminocyclohexane (20 mol%)
Cu(OAc) $H O (20 mol%), hippuric acid (20 mol%)
Silica tethered copper complexes (5 mol%)
Cu O (10 mol%), ninhydrin (20 mol%)
CuI (0.05 mmol), tetrazole-1-acetic (0.1 mmol)
Nano Cu O/ZnO (0.010 g)
2
2
DMF, 110 C
24/98
12/95
24–48/95
26g
25f
8c
MeCN, reux
Butyronitrile, Ar or N
ꢀ
2
2
, 110 C
(
ꢀ
4
2
H
2
O, 100 C
24/63
29
ꢀ
5
6
7
8
9
2
2
DMF, Ar, 140 C
30/87
8/89
24/92
12/84
2/95
30
31
32
38
ꢀ
Toluene, N
DMSO, Ar, 90 C
DMSO, 110 C
DMSO, 100 C
2
, 100–135 C
ꢀ
2
ꢀ
ꢀ
2
This study
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suspension until lots of red-brown precipitates were produced.
Aer constant temperature water bath for 30 min under stir-
Conclusions
In conclusion, for the rst time, we have demonstrated the ring, products were collected by ltration, washed with deion-
application of Cu
2
O/ZnO nanoake for ‘ligand free’ N-arylation ized water and absolute ethanol several times, and nally dried
ꢀ
of various N-heterocycles from differently substituted aryl in air at 60 C for 3 h. According to the ICP analysis, the Cu and
halides (X ¼ I, Br, Cl) and arylboronic acids. The low cost and Zn content in the catalyst was determined to be 47% (w/w) and
readily available Cu and Zn salts, mild reaction conditions, and 21.77% (w/w) respectively. Therefore, each gram of catalyst
the operational simplicity render this transformation as an includes 7.3 mmol of copper and 3.3 mmol of zinc.
attractive alternative for the assembly of N-arylated products
and make it viable for use both in laboratory research and in
larger industrial scales.
General procedure for the synthesis of nano Cu
2
O
CuSO (1 g, 6.26 mmol) was dissolved in 50 mL distilled water to
4
obtain a solutions. Aer stirring, the solution was subsequently
ꢀ
Experimental section
heated to 70 C in a water bath for 5 min under stirring. Then
1
ꢁ
1
mol L N H $H O was slowly added into the suspension until
2 4 2
1
NMR spectra were recorded on a Bruker Avance DPX-250 ( H
lots of red-brown precipitates were produced. Aer constant
temperature water bath for 30 min under stirring, products
were collected by ltration, washed with deionized water and
1
3
NMR 250 MHz and C NMR 62.9 MHz) in pure deuterated
solvents with tetramethylsilane (TMS) as internal standards.
Scanning electron micrographs were obtained by SEM instru-
mentation (SEM, XL-30 FEG SEM, Philips, at 20 kV). A trans-
mission electron microscopy TEM was also used for TEM
ꢀ
absolute ethanol several times, and nally dried in air at 60 C
for 3 h.
(
Philips CM10) image. Spectroscopic methods including X-ray
General procedure for the synthesis of nano ZnO
diffraction (XRD, D8, Advance, Bruker, axs) and FT-IR spec-
troscopy (Shimadzu FT-IR 8300 spectrophotometer) were First, Zn(OAc) $2H O (as Zn source, 1 g) and PEG 2000 (0.30
2 2
2
+
employed for characterization of the heterogeneous catalyst. g) were dissolved in water (140 mL) and then by drop wise
Surface area measurements were conducted according to the addition of NH OH (1.5 mL, 25%) at reux condition aer 6 h,
were formed. With the presence of a water-soluble
4
2
ꢁ
Brunauer–Emmett–Teller (BET) gas (nitrogen) adsorption Zn(OH)
4
method. The porous structural parameter used in this paper linear polymer (PEG 2000), ZnO crystals form at the interface
was taken from Barret–Joyner–Halenda (BJH) data. Metal between substrate and solution by the dehydration of
2
ꢁ
contents were obtained by an ICP analyzer (Varian, vista-pro). Zn(OH)
. Aer that, the product was centrifuged and washed
4
Mass spectra were determined on a Shimadzu GCMS-QP 1000 with deionized water and absolute ethanol. Then 90 mL
EX instrument at 70 or 20 eV. Melting points determined in deionized water was added and the mixture was reuxed for 8
open capillary tubes in a B u¨ chi-535 circulating oil melting point h. It was cooled by cold water, centrifuged and washed. Finally,
ꢀ
apparatus. The purity determination of the substrates and the nano-rods ZnO powders are dried at 100 C in an oven to
reaction monitoring were accomplished by TLC on silica gel give 0.65 g powder.
PolyGram SILG/UV254 plates or by a Shimadzu Gas Chro-
matograph (GC-10A) instrument with a ame ionization
detector using a column of 15% carbowax 20 M chromosorb-w
acid washed 60–80 mesh. Column chromatography was carried
out on short columns of silica gel 60 (70–230 mesh) in glass
columns (2–3 cm diameter) using 15–30 grams of silica gel per
one gram of crude mixture. Chemical materials were purchased
from Fluka, Aldrich, Alfa Aesar, and Merck Companies.
General procedure for the catalytic N-arylation of nitrogen-
containing heterocycles with aryl halides and arylboronic acid
To a mixture of imidazole (1.2 mmol), Cu
2
O/ZnO nanoake
(
0.01 g), KOH (2 mmol), in DMSO (2 mL), aryl halide or aryl-
ꢀ
boronic acid (1 mmol) was added and stirred at 100 C until
complete consumption of starting material as monitored by
TLC. The reaction mixture was centrifuged to separate the
catalyst. Aer that ethyl acetate was poured into the mixture,
and then washed with water. The organic layer was separated,
General procedure for the synthesis of Cu O/ZnO nanoake
2
2 4
dried over Na SO and the solvent was removed under reduced
pressure to get the crude product. The crude product was
puried by column chromatography (hexane/ethyl acetate, 70/
CuSO (1 g, 6.26 mmol), was dissolved in 50 mL distilled water
to obtain a certain concentration solutions. Commercially ZnO
4
(0.51 g, 6.26 mmol) was then dispersed in the above solution
30) to afford the pure product. The known compounds were
and sonicated to obtain a uniform suspension. The suspension
was vigorously stirred at room temperature for 50 min to ensure
characterized by comparison of their physical and spectroscopic
18,25c,33–37
2
+
data with the already described in the literature.
enough Cu ion adsorbed on the surface of ZnO. Aer stirring,
2
+
in order to dispose of free Cu ions, the mixtures were centri-
fuged and washed by deionized water and absolute ethanol
alternately for three times. Then the mixture was added into 30
Acknowledgements
mL deionized water to obtain suspension. The suspension was We gratefully acknowledge the support of this work by the
ꢀ
subsequently heated to 70 C in a water bath for 5 min under Shiraz University. We are also grateful to Mr H. Sajedian Fard
ꢁ1
stirring. Then 1 mol L
2 4 2
N H $H O was slowly added into the and Mr M. S. Darvish Tafvizi for helpful cooperation.
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