Open air O-arylation reaction of phenols with aryl halides catalyzed by polymer-anchored copper(II) complexes

Article abstract of DOI:10.1007/s11243-010-9426-2

Two copper complexes were synthesized from macroporous chloromethylated polystyrene beads. The first one was prepared by sequential attachment of imidazole and copper acetate with chloromethylated polystyrene-divinyl benzene copolymer, and the second one was prepared from 4-vinylpyridine and copper acetate with chloromethylated polystyrene-divinyl benzene copolymer. These catalysts showed excellent catalytic activity in O-arylation reaction of aryl halides with phenol in dimethylsulfoxide using potassium carbonate at 130 °C under open air conditions to give diaryl ethers in high yields. Less reactive aryl bromides and aryl chlorides have also been shown to react with phenols to give good yields of the diaryl ethers. The effects of various parameters such as solvent, catalyst from different copper salt and base on the reaction system were studied. The reaction is applicable to a wide variety of substituted aryl halides and phenols with different steric and electronic properties. These catalysts were recovered by simple filtration, and the reusability experiments showed that these catalysts can be used five times without much loss in the catalytic activity.

Full text of DOI:10.1007/s11243-010-9426-2

Transition Met Chem (2011) 36:1–11
DOI 10.1007/s11243-010-9426-2
Open air O-arylation reaction of phenols with aryl halides
catalyzed by polymer-anchored copper(II) complexes
•
Manirul Islam Sanchita Mondal Paramita Mondal
•
•
•
Anupam Singha Roy Dildar Hossain
•
Manir Mobarak
Received: 26 August 2010 / Accepted: 17 September 2010 / Published online: 2 November 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Two copper complexes were synthesized from
macroporous chloromethylated polystyrene beads. The first
one was prepared by sequential attachment of imidazole
and copper acetate with chloromethylated polystyrene-
divinyl benzene copolymer, and the second one was
prepared from 4-vinylpyridine and copper acetate with
chloromethylated polystyrene-divinyl benzene copolymer.
These catalysts showed excellent catalytic activity in
O-arylation reaction of aryl halides with phenol in
dimethylsulfoxide using potassium carbonate at 130 °C
under open air conditions to give diaryl ethers in high
yields. Less reactive aryl bromides and aryl chlorides have
also been shown to react with phenols to give good yields
of the diaryl ethers. The effects of various parameters such
as solvent, catalyst from different copper salt and base on
the reaction system were studied. The reaction is applicable
to a wide variety of substituted aryl halides and phenols
with different steric and electronic properties. These cata-
lysts were recovered by simple filtration, and the reus-
ability experiments showed that these catalysts can be used
five times without much loss in the catalytic activity.
reacts with a phenol under basic conditions in the presence
of copper salt catalysts, has been the focus of a number of
recent studies because it provides very direct access to
diaryl ethers [3–8]. Diaryl ethers have also been prepared
from the cross-coupling reaction of aryl halides with phe-
nol (transition-metal catalyzed O-arylation reaction of
phenol) in the presence of palladium compounds as cata-
lysts. Palladium compounds are very active and have high
catalytic activity, but the high costs of Pd compounds have
lowered their popularity, particularly for large-scale reac-
tions [9]. Hartwig et al. and Buchwald et al. have greatly
contributed to novel Pd-catalyzed arylation of phenols [10,
11], but their systems still suffer from the expensive price
of palladium and ligand sources. As a result, much of the
recent literature has focused on the continuing evolution of
Ullmann’s original copper-based diaryl ether formations
[12, 13]. Recent work in Buchwald’s group with copper(II)
triflate catalyst has made it possible to carry out these
reactions under milder conditions with a wider variety of
substrates in good yields [14]. Due to the relatively high
cost of copper triflate and its air sensitivity, it is still
desirable to develop more robust and more cost-effective
processes for this important reaction. Although recent
progress in palladium-catalyzed ether formation reactions
has solved some problems in this area [15, 16], copper
catalysts still hold the advantage of low cost for large-scale
industrial applications.
Introduction
Diaryl ethers are not only important structures in biological
systems, but also common moieties in pharmaceutical
research and materials interest [1, 2]. The Ullmann ether
formation reaction, in which an aryl bromide or iodide
Copper metal has been employed as catalyst for various
organic reactions such as oxidation [17, 18], amination [19,
20], cyanation [21] and Sonogashira [22, 23], etc. The
O-arylation reaction generally proceeds in the presence of
homogeneous copper catalysts that possess high efficiency
and are suitable for the study of the reaction mechanism, but
their higher susceptibility to drastic reaction conditions and
the difficulties associated with their isolation from the
M. Islam (&) ꢀ S. Mondal ꢀ P. Mondal ꢀ
A. S. Roy ꢀ D. Hossain ꢀ M. Mobarak
Department of Chemistry, University of Kalyani, Kalyani,
Nadia 741235, WB, India
e-mail: manir65@rediffmail.com
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Transition Met Chem (2011) 36:1–11
product mixture restrict their reusability. This is a great
disadvantage in this coupling reaction using homogeneous
catalysts. Also, recycling of catalysts is a task of great
economic and environmental importance in the chemical
and pharmaceutical industry, especially when expensive or
toxic heavy metal complexes are employed [24]. These
disadvantages can be overcome by anchoring the metal on
suitable supports. These studies confirm that the anchoring
of a metal on a solid support not only exhibits improved
catalyst activity, stability and selectivity of the product but
also enables easy recovery and reuse of the catalyst. There
are many examples of immobilizers such as Cu- or Pd-
catalytic systems [25–29]. To date, few reports described
reusable copper catalytic systems for this C–O coupling that
allowed the recycling of active metal; nevertheless, only
some reported leaching measurements of metal toxic resi-
dues in final products [30–33]. This feature is of high
importance for purity requirements especially in pharma-
ceutical industries. Therefore, mild, simple and low-cost
reusable methods are highly desirable to avoid toxicity.
Herein, we report the synthesis of polymer-supported
copper catalysts and illustrate their application in a number
of cross-coupling reactions between aryl halides and phe-
nols. Our strategy was to attach a ligand to a polymer
support and then allow it to bind to copper through ligand
exchange. The resulting binding interaction also needs to
be strong enough to prevent the copper from dissociating
from the polymer support under the reaction conditions.
The experimental results reveal that polymer-anchored
copper(II) catalysts can be recycled more than five times
without much loss in the activity.
Result and discussion
Preparation of catalysts
The outline for the preparation of the polymer-anchored
Cu(II) catalysts is given in Scheme 1.
Characterization of the polymer-anchored Cu(II)
catalysts
Elemental analysis
Elemental analysis for polymer-anchored 4-vinylpyridine
ligand, polymer-anchored imidazole ligand, Cat-1 and Cat-2
was carried out, and the data are tabulated in Table 1.
Amount of metal was determined by stripping the bound
metal from the support and analysis by using atomic
absorption spectrophotometer. Copper content in the
Table 1 Chemical composition of polymer-anchored ligands and
complexes
Compound
Color
C%
H%
N%
Cu%
2
Light-orange
White
80
6.76
6.45
4.13
13.39
15.21
7.23
–
4
78.26
55.74
–
Cat-1
Yellowish-green
1.33
1.33a
1.28
1.27a
Cat-2
Greenish-blue
61.59
4.77
10.27
a
Used catalyst
Scheme 1 Synthesis of the
polymer-anchored Cu(II)
catalysts
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Transition Met Chem (2011) 36:1–11
3
catalysts determined by AAS suggests 1.33 wt% Cu in the
Cat-1 and 1.28 wt% Cu in the Cat-2. Copper content
remained almost unchanged even after recycling the catalyst
for five cycles.
of 525–530 nm [43]. The spectrum for Cat-2 exhibits two
bands at ca. 365–375 and 390–410 nm. The UV spectrum
in the 390–410 nm regions has been widely highlighted in
order to identify the imidazole contribution to the coordi-
nation chemistry [44]. The charge transfer spectra for the
interaction between copper(II) and imidazole nitrogen
appeared at 365–375 nm [42]. The expected d–d bands are
not observed in the polymer-anchored copper catalyst.
Possibly low loading of the complex on the polymer matrix
has prevented observation of the d–d band, which is a low-
energy and eventually less-intense band [45].
Infrared spectral studies
The modes of attachment of metals onto the support were
confirmed by comparison of the FTIR spectral bands of the
metal catalyst over the polymer in various steps of its
synthesis. For the Cat-1, infrared spectra of the complex
are identical to those of the polymers in the region
4,000–1,000 cm-1 [34]. The characteristic stretching of
pyridine rings for pure polymer-anchored 4-vinylpyridine
ligand occurs at ca. 1,600 cm-1, which is shifted to
1,616 cm-1 in copper complex (Cat-1), suggesting coor-
dination between the pyridinic nitrogen atoms and the
copper metallic center [35, 36]. In the metal complex, a
medium or weak band is observed at 547 cm-1, which can
be attributed to the metal with pyridine nitrogen mode [37].
Monodentate acetate usually shows two bands at 1,630 and
1,310 cm-1 due to antisymmetric and symmetric stretch-
ing, respectively [38]. In Cat-1, a band observed at
1,313 cm-1 suggests the monodentate coordination of the
acetate groups [39]. The Cat-1 exhibits a single peak at
430 cm-1 (Cu–Oacetate), indicating the presence of the
coordination of acetate group with copper metal [38].
SEM studies
The morphology of the Cat-1 and Cat-2 were studied using
Scanning Electron Microscope. The micrographs of the
polymer-anchored imidazole ligand, 4-vinylpyridine
ligand, Cat-2 and Cat-1 obtained from the scanning elec-
tron microscope are presented in Fig. 1a–d, respectively.
The morphological changes in the polymer-anchored
ligands and immobilized copper(II) complexes are quite
evident from these images and suggest the loading of
copper metal on the surface of the polymer matrix. Energy-
dispersive spectroscopy analysis of X-rays (EDAX) data
for the anchored imidazole ligand, 4-vinylpyridine ligand,
Cat-2 and Cat-1 are given in Fig. 2a–d. The EDX data also
inform the attachment of copper on the surface of the
polymer matrix.
Chloromethylated polystyrene exhibits
a peak at
1,263 cm-1 attributed to –CH2Cl and imidazole shows mN–
H around 3,124 cm-1. The intensity of the first peck was
reduced (m–CH2Cl), and the second peak was not found in
Cat-2, indicating that hydrogen of (N–H) imidazole is lost
consequent to functionalization and it is bonded to the
polymer support through nitrogen [40]. In this metal
Catalytic activity
The polymer-anchored Cat-1 and Cat-2 have been inves-
tigated as catalysts in the O-arylation reaction of aryl
halides with equimolar amount of phenols using tetrabu-
tylammonium bromide (tBu4NBr) at 130 °C for 12 h. The
O-arylation reaction gives diaryl ether as a main product in
yields of up to 96%. The Cat-1 and Cat-2 are comparable in
their activities, but Cat-1 is superior due to its higher metal
loading (Table 1). To optimize the conditions for the
O-arylation reaction, we have chosen the reaction between
iodobenzene and phenol as a model reaction (Scheme 2)
using copper catalysts and various parameters, such as
solvent and base to get maximum product.
complex, a medium or weak band is observed at 542 cm-1
,
which can be attributed to the metal with imidazole
nitrogen mode [37]. Cat-2 exhibits a medium intensity
band at 1,315 cm-1 consistent with monodentate coordi-
nation of the acetate groups [39] and a single peak at
432 cm-1 (Cu–Oacetate), indicating the presence of the
coordination of acetate group with copper metal [38].
UV–vis spectral studies
Our initial screening experiments were carried out by
the polymer-supported copper catalysts using iodobenzene
and phenol. In the presence of K2CO3 in DMSO medium,
the Ullmann diaryl etherification can be catalyzed by either
Cu(I) or Cu(II) in the absence of any palladium. However,
no reaction occurred in the absence of copper catalyst. As
can be seen from Table 2, polymer-anchored Cu(II) cata-
lysts were superior. Among polymer-supported Cu(II)
catalysts, which were prepared from different copper(II)
sources, polymer-supported Cu(II) catalyst from copper(II)
The electronic spectrum of the polymer-anchored Cu(II)
complexes were recorded in diffuse reflectance spectrum
mode as MgCO3/BaSO4 disks due to their solubility limi-
tations in common organic solvents. The spectrum for Cat-
1 exhibits three spectral bands at ca. 325, 360–380 and
525–530 nm. The peak at 325 nm is due to p–p* [41]
transition of the pyridine moiety. The band at the range
360–380 nm is assigned to ligand to metal charge transfer
[42]. The d–d bands were observed for Cat-1 in the range
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Transition Met Chem (2011) 36:1–11
Fig. 1 FE SEM images of the
polymer-anchored imidazole
ligand (a), Cat-2 (b),
4-vinylpyridine ligand (c),
Cat-1 (d)
acetate was found to be the most effective one (entries
7–8). Next, the reaction was carried out with different
amounts of copper catalysts over the range of
0.025–0.065 g, and it was found that 0.05 g of copper
catalyst was the most effective catalytic system (Table 2,
entries 9–14).
were found to be optimal. From the above discussions, it
can be seen that the best yield was obtained by using
K2CO3 (1 mmol) in DMSO solvent at 130 °C for 12 h
under open air. Now the optimized reaction conditions
were used to examine C–O bond formations involving
functionalized coupling partners. Reactivity comparisons
were made by interrupting the reactions after 12 h.
We tested several different bases for the Ullmann cou-
pling reactions catalyzed by the polymer-supported cop-
per(II) catalysts in DMSO. K2CO3 was found to be the
most effective. Other bases such as KOH, Cs2CO3,
Na2CO3, Et3N and K3PO4 were substantially less effective
(Table 3, entries 1–6). Solvents such as dimethyl sulph-
oxide (DMSO), N-methyl pyrrolidinone (NMP), acetoni-
trile (CAN), methanol (MeOH), dimethyl formamide
(DMF), toluene (PhMe) and water were investigated, and it
was found that moderate polar solvents were more favored.
With DMSO, NMP, ACN, DMF, MeOH and water yields
were comparatively good (Table 3, entries 1, 7–11). By
contrast, the catalytic performance was not acceptable
when the non-polar solvent toluene was employed
(Table 3, entry 12). Consequently, DMSO was chosen as
the medium of choice for this coupling reaction. This
arylation was also found to be highly sensitive to the
reaction temperature and time. At lower temperatures
(60 °C) and with lower reaction time (6 h), only low to
moderate yields were obtained (Table 3, entries 13, 14). A
reaction temperature of 130 °C and reaction time of 12 h
On the basis of the above results, the coupling reactions
catalyzed by Cat-1 and Cat-2 were tested with several
different aryl iodides and phenols, and the results are
summarized in Table 4. Both electron-rich and electron-
deficient aryl iodides were suitable substrates for this
reaction to provide the corresponding diaryl ethers in good
to excellent yields. A variety of functional groups of aryl
iodides were known to tolerate this reaction condition,
which include nitro, methyl, ketomethyl and cyano groups.
Phenols with electron-rich and iodobenzene with electron-
deficient groups made very good pairings for this coupling
reaction (entries 5–7). Some tolerance of electron-with-
drawing groups on the phenols was observed, as the reac-
tions with 4-bromophenol (entry 8) gave reasonable to
good yields. Phenols with extremely strong electron-with-
drawing groups do not undergo the desired ether formation
(entry 9). This might be due to the decreased nucleophi-
licity of phenols induced by the nitro group [46]. The steric
hindrance of phenols was slightly disfavored for this
reaction. For example, when 2-methylphenol and
123

Transition Met Chem (2011) 36:1–11
5
Fig. 2 EDAX data for the polymer-anchored imidazole ligand (a), Cat-2 (b), 4-vinylpyridine ligand (c) and Cat-1 (d)
2-methoxyphenol were used as the substrate, the reaction
gave considerably lower yield in comparison with that of
less-hindered phenol (entries 10, 11). However, the steric
hindrance of aryl iodides was highly disfavored for this
reaction (entries 12, 13). As shown in Table 4, the present
catalytic system was also effective for the coupling reac-
tion of aryl bromides and phenols. High yields were
obtained for the aryl bromides with an electron-with-
drawing group such as nitro and cyano groups (entries 15
and 16). The reaction of 4-methylphenyl bromide with
phenol, which was a difficult case for the classical Ullmann
coupling method, gave the coupling product in 56 and 48%
(entry 17) yield for the Cat-1 and Cat-2, respectively.
Furthermore, 1-bromo-4-nitrobenzene successfully coupled
with 4-methoxyphenol with an excellent yield (entry 18).
Because of their low cost and ready availability, aryl
chlorides are much more attractive substrates for the
industrial production and laboratory preparation of diaryl
ethers [47]. We further investigated the potential catalytic
efficiency of the present catalytic system for the coupling
between aryl chlorides and phenols. In some cases, higher
temperature and higher reaction time were used to promote
the reaction. As summarized in Table 4, Cat-1 and Cat-2
successfully promoted the coupling reaction with good or
moderate yields. The electron-deficient aromatic chlorides
tested gave good yields under the catalysis at 160 °C
(Table 4, entries 20–21).
Comparison of activity of different copper catalysts
in the O-arylation reaction
We compared the activity of the Cat-1 and Cat-2 in the
O-arylation reaction with the other reported copper catalysts
(Table 5). The reaction using the present heterogeneous
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6
Transition Met Chem (2011) 36:1–11
Fig. 2 continued
OH
I
Catalyst reuse and stability
O
Catalyst
Solvent
+
>
t
/
Base
The stabilities of the copper complex catalysts were studied
by performing repeated O-arylation reactions using the same
reaction conditions as described earlier. Phenol and iodo-
benzene were used as model substrates. At the end of each
reaction cycle, the catalyst was recovered by filtration and
washed with DMSO and acetone, dried and reused. The yield
(%) was almost identical up to the 5th recycle (Fig. 3).
Copper content of the recycled catalysts remained almost
unaltered, indicating no leaching of the metal from the
polymer-support complexes (Table 1). No evidence for
leaching of copper or decomposition of the complex cata-
lysts were observed during the catalysis reaction, and no
copper could be detected by atomic absorption spectroscopic
NBr
Bu4
130°C/
12 h
open air
Scheme 2 Copper-catalyzed O-arylation of iodobenzene with phenol
Cat-1 and Cat-2 with phenol and iodobenzene in DMSO
medium at 130 °C for 12 h results in 95 and 92% yields,
respectively, while the other reported copper catalysts such
as CuI with N,N-dimethylglycine HCl salt [49], BINAM-
Cu(OTf)2 catalyst [56], Cu(OAc)2.H2O [57] and Cu(b-
py)2BF4 [58] gave yields of only 86, 70, 78 and 85%,
respectively. From Table 5, it can be also seen that the
present catalytic systems work better at shorter reaction time.
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Transition Met Chem (2011) 36:1–11
7
Table 2 Effect of copper
source/amount on the
O-arylation reaction
Entry
Copper source/amount
Yielda (%)
1.
None
No reaction
2.
CuI (0.05 g)
53
67
79
77
82
92
96
66
68
78
81
93
96
3.
CuCl2 (0.05 g)
4.
Cu(OAc)2 (0.05 g)
5.
Polymer-supported Cu(I)b 4-vinylpyridine (0.05 g)
Polymer-supported Cu(II)c 4-vinylpyridine (0.05 g)
Polymer-supported Cu(II)d imidazole (0.05 g)
Polymer-supported Cu(II)d 4-vinylpyridine (0.05 g)
Polymer-supported Cu(II)d imidazole (0.025 g)
Polymer-supported Cu(II)d 4-vinylpyridine (0.025 g)
Polymer-supported Cu(II)d imidazole (0.04 g)
Polymer-supported Cu(II)d 4-vinylpyridine (0.04 g)
Polymer-supported Cu(II)d imidazole (0.065 g)
Polymer-supported Cu(II)d 4-vinylpyridine (0.065 g)
Reaction conditions: 1 mmol of
iodobenzene, 1 mmol of phenol,
1 mmol of K2CO3, 0.1 mmol of
tBu4NBr, DMSO (10 mL),
130 °C, 12 h, open air
6.
7.
8.
a
9.
Yield determined by GC and
GCMS analysis using dihexyl
ether as internal standard
10.
11.
12.
13.
14.
b
Catalyst prepared from CuI
c
Catalyst prepared from CuCl2
d
Catalyst prepared from
Cu(OAc)2
iodobenzene. The solid catalyst was filtered out after the
reaction had proceeded for 6 h and the yield determined by
GC was 65% for the Cat-1 and 61% for the Cat-2. The
liquid phase of the reaction mixture was collected at the
reaction temperature. Atomic absorption spectrometric
analysis of the liquid phase of the reaction mixtures col-
lected by filtration confirmed that Cu was absent from the
reaction mixture. The obtained filtrate was stirred under the
reaction conditions. After 12 h, the yield was determined to
be still 65 and 61% for the Cat-1 and Cat-2, respectively.
This result indicated that the catalytic reaction was caused
by the solid catalyst. Cu was also not detected in the liquid
phase of the reaction mixture after the completion of the
reaction. It is noteworthy that the DMSO remains com-
pletely colorless on addition of the Cu(II) catalysts. These
results also suggested that the Cu was not being leached out
from the catalyst during the O-arylation reactions.
Table 3 Effect of solvent, base, temperature, reaction time on the
O-arylation reaction
Entry Base
Solvent Temperature Time (h) Yielda (%)
( °C)
Cat-1 Cat-2
1
K2CO3 DMSO 130
12
12
12
12
12
12
14
14
14
18
18
14
12
6
96
85
76
79
66
57
81
88
78
56
55
34
72
65
92
82
68
75
60
55
78
83
74
48
51
30
69
61
2
Cs2CO3 DMSO 130
Na2CO3 DMSO 130
3
4
K3PO4
Et3N
DMSO 130
DMSO 130
DMSO 130
5
6
KOH
7
K2CO3 ACN
K2CO3 DMF
K2CO3 NMP
K2CO3 MeOH
K2CO3 Water
80
140
120
70
8
9
10
11
12
13
14
70
K2CO3 Toluene 130
K2CO3 DMSO 60
K2CO3 DMSO 130
Conclusion
Reaction conditions: Cat-1 (0.05 g, 0.0104 mmol) and Cat-2 (0.05 g,
0.0101 mmol), 1 mmol of iodobenzene, 1 mmol of phenol, solvent
The current procedure enhances the utility of copper-cat-
alyzed coupling reactions of phenols with aryl halides. The
reactions are, in general, more efficient with respect to
quantity of catalyst required and the yields obtained and a
much wider range of substrates can be utilized including
electron-rich, electron-deficient and electronically neutral
aryl halides and phenols. We are currently working to
improve the scope and generality of copper-catalyzed
diaryl ether formation. We anticipate that existing diffi-
culties with homogeneous catalyst will be overcome
through the development of new polymer-anchored Cu(II)
catalyst systems.
t
(10 mL), 1 mmol of base, 0.1 mmol of Bu4NBr, open air
a
Yield determined by GC and GCMS analysis using dihexyl ether as
internal standard
measurement of the liquid reaction mixture after each cata-
lytic reaction.
Heterogeneity tests
To determine whether the catalysts were actually func-
tioning in a heterogeneous manner, a hot-filtration test was
performed in the O-arylation reaction of phenol with
In summary, we have developed a cheap and simple way
to carry out the Ullmann diaryl ether synthesis, which is
123

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Transition Met Chem (2011) 36:1–11
Isolated yield (%)
Table 4 Polymer-supported copper(II) catalyzed O-arylation reaction of aryl halides with phenols
Entry
Phenols
Aryl halides
Products
Cat-1
Cat-2
1
C6H5OH
C6H5I
C6H5OH5C6 (4a)
95
96
96
88
97
94
97
88
45
65
68
57
55
88
90
89
56
92
58
77
74
92
94
93
86
94
93
95
85
38
60
65
51
54
85
88
88
48
91
55
76
70
2
C6H5OH
p-NO2C6H4I
p-CNC6H4I
p-MeC6H4I
p-CNC6H4I
p-COMeC6H4I
p-NO2C6H4I
p-NO2C6H4I
C6H5I
p-NO2C6H4OH5C6 (4b)
p-CNC6H4OH5C6 (4c)
p-MeC6H4OH5C6 (4d)
p-OMeC6H4OH4C6CN-p (4e)
p-MeC6H4OH4C6COMe-p (4f)
p-OMeC6H4OH4C6NO2-p (4g)
p-BrC6H4OH4C6NO2-p (4h)
p-NO2C6H4OH5C6 (4b)
o-MeC6H4OH5C6 (4i)
o-OMeC6H4OH5C6 (4j)
o-MeC6H4OH5C6 (4i)
o-OMeC6H4OH5C6 (4j)
C6H5OH5C6 (4a)
3
C6H5OH
4
C6H5OH
5
p-OMeC6H4OH
p-MeC6H4OH
p-OMeC6H4OH
p-BrC6H4OH
p-NO2C6H4OH
o-MeC6H4OH
o-OMeC6H4OH
C6H5OH
6
7
8
9
10
11
12
13
14
15
16
17
18
19a
20a
21a
C6H5I
C6H5I
o-MeC6H4I
o-OMeC6H4I
C6H5Br
C6H5OH
C6H5OH
C6H5OH
p-NO2C6H4Br
p-CNC6H4Br
p-MeC6H4Br
p-NO2C6H4Br
C6H5Cl
p-NO2C6H4OH5C6 (4b)
p-CNC6H4OH5C6 (4c)
p-MeC6H4OH5C6 (4d)
p-OMeC6H4OH4C6NO2-p (4g)
C6H5OH5C6 (4a)
C6H5OH
C6H5OH
p-OMeC6H4OH
C6H5OH
C6H5OH
p-NO2C6H4Cl
p-CNC6H4Cl
p-NO2C6H4OH5C6 (4b)
p-CNC6H4OH5C6 (4c)
C6H5OH
Reaction conditions: Cat-1 (0.05 g, 0.0104 mmol) and Cat-2 (0.05 g, 0.0101 mmol), 1 mmol of aryl halides, 1 mmol of phenols, 1 mmol
t
K2CO3, DMSO (10 mL), 0.1 mmol Bu4NBr, 130 °C, open air, 12 h
Isolated yield after column chromatography
a
Reaction temperature = 160 °C, reaction time = 18 h
Table 5 Comparison of
Entry Catalyst
Reaction conditions
Yield (%) References
activity of different copper
catalysts in the O-arylation
reaction of phenol with
iodobenzene
1
2
Cat-1
Cat-2
DMSO, K2CO3, 130 °C, 12 h
95
92
86
This study
[49]
0.04 mmol of CuI and
0.15 mmol of N,N-dimethylglycine
HCl salt
Dioxane, Cs2CO3, 90 °C, 16 h
3
4
5
BINAM, Cu(OTf)2 catalyst
Cu(OAc)2.H2O
Dioxane, Cs2CO3, 110 °C, 18 h 70
[56]
[57]
[58]
NMP, K3PO4, 180 °C, 22 h
DMF, K3PO4, 90 °C, 24 h
78
Cu(bpy)2BF4
85
applicable to a wide variety of substrates with different
functional groups. The application of this method to the
synthesis of more complex diaryl ethers, as well as
mechanism studies, is in progress. We have developed the
two new polymer-anchored Cu(II) catalysts that can be
successfully applied in a number of cross-coupling reac-
tions and give better results than other reported copper
catalysts. These two catalysts can be recycled up to five
cycles without appreciable loss of activity. The easy
workup procedure provides a method that is well suited
toward the synthesis of parallel libraries based upon this
type of transformation.
Experimental
Analytical-grade reagents and freshly distilled solvents were
used throughout. All reagents and substrates were purchased
from Merck. Liquid substrates were predistilled and dried by
appropriate molecular sieve, and solid substrates were
123

Transition Met Chem (2011) 36:1–11
9
100
Preparation of the polymer-anchored 4-vinylpyridine
copper(II) catalyst (Cat-1)
Cat-1
Cat-2
80
60
40
20
0
Polymer-anchored 4-vinylpyridine ligand (2 g) was added
to acetic acid (20 mL). Copper acetate (50 mg) in acetic
acid (5 mL) was added to the above suspension with
constant stirring and then refluxed for 24 h. After cooling
the reaction mixture to room temperature, the separated
yellowish-green color solid was filtered out, washed thor-
oughly with methanol and dried under vacuum.
Preparation of the polymer-anchored imidazole
copper(II) catalyst (Cat-2)
Polymer-anchored imidazole ligand (2 g) was added to
acetic acid (20 mL). Copper acetate (0.05 g) in acetic acid
(5 mL) was added to the above suspension with constant
stirring and then refluxed for 24 h. After cooling the
reaction mixture to room temperature, the separated green
solid was filtered out, washed thoroughly with methanol
and dried under vacuum.
1
2
3
4
5
No of cycle
Fig. 3 Recycling activity of the Cat-1 and Cat-2 toward the
O-arylation reaction of phenol with iodobenzene. Reaction conditions:
1 mmol of iodobenzene, 1 mmol of phenol, 1 mmol K2CO3, 0.05 g
t
catalyst, DMSO (10 mL), 0.1 mmol Bu4NBr, 130 °C, 12 h, open air
Instrumentation
recrystallized before use. Distillation, purification of the
solvents and substrate were done by standard procedures
[48]. Chloromethylated polystyrene, 200–400 mesh (Art.
No. 63863-50G) and 4-vinyl pyridine were supplied by
Aldrich Chemical Company, U.S.A. Copper acetate and
imidazole were purchased from Merck and used as such
without further purification.
Surface morphology and particle size of the samples were
analyzed by using a scanning electron microscope (SEM)
(ZEISS EVO40, England) equipped with EDX facility. The
FTIR spectra were recorded on a Perkin-Elmer FTIR 783
spectrophotometer using KBr pellets. Diffuse reflectance
UV–vis spectra were taken using a Shimadzu UV-2401PC
double-beam spectrophotometer having an integrating
sphere attachment for solid samples. A Perkin-Elmer
2400C elemental analyzer was used to collect microana-
lytical data (C, H and N). Copper content in the catalyst
was determined using Varian AA240 atomic absorption
spectrophotometer (AAS).
Preparation of the polymer-anchored 4-vinylpyridine
ligand (2)
The monomer was refluxed over solid KOH pellets and
distilled under nitrogen at a pressure of 6 mmHg. POCl3
(3 g) was added to a toluene solution of the monomer
(100 mL, 2 M) and the mixture was stirred for 20 h at
30 °C under nitrogen. Addition of the mixture to a larger
volume of light petroleum produced a pale-yellow precip-
itate that was dried and purified by precipitating several
times from ethanol by light petroleum (b.p. 40–60 °C).
Representative procedure for O-arylation reaction
of phenols with aryl halides
Cu-catalyst (0.05 g) in DMSO (5 mL) was taken in a 100-
mL R.B flask and stirred at room temperature for 10 min.
Then aryl halide (1 mmol), phenol (1 mmol), tetrabutyl-
ammonium bromide (tBu4NBr) (0.1 mmol), K2CO3
(1 mmol), dihexyl ether (5 mL) and DMSO (5 mL) were
added. The final reaction mixture was refluxed for 12 h at
130 °C under an open air condition. The products were
collected at different time intervals and identified by GCMS
and quantified by GC using dihexyl ether as internal stan-
dard. After cooling to room temperature, the reaction was
extracted with ethyl acetate (3 9 20 mL), and the combined
organic layers were dried with anhydrous Na2SO4 by vac-
uum. The filtrate was concentrated by vacuum and the
Preparation of the polymer-anchored imidazole
ligand (4)
Chloromethylated polystyrene (3 g) was stirred with a 1:1
mixture of acetonitrile and toluene for 30 min. Then
imidazole (1.2 g) was added to the above solution of the
polymer, and the mixture was refluxed for 24 h at 60 °C.
The white polymer-anchored ligand (2) was filtered out,
washed thoroughly with methanol and dried under vacuum.
123

10
Transition Met Chem (2011) 36:1–11
1
4-Phenoxybenzonitrile (4c). Oil [51]. H NMR (CDCl3,
resulting residue was purified by column chromatography on
silica gel to provide the desired product. The product was
purified by column chromatography, and its identity con-
firmed by comparison of color and NMR spectra with those
reported in the literature or authentic samples from our
laboratories.
400 MHz) d: 7.57 (d, J = 8.6 Hz, 2H), 7.42 (t,
J = 7.9 Hz, 2H), 7.25 (t, J = 7.6 Hz, 1H), 7.0 (d,
J = 7.9 Hz, 2H), 6.89 (d, J = 8.8 Hz, 2H); 13C NMR
(CDCl3, 100 MHz) d: 160.4, 151.1, 135.8, 131.5, 123.0,
118.4, 116.5, 120.3, 101.5.
1
4-Methyl-diphenylether (4d). Colorless liquid [49]. H
NMR (CDCl3, 400 MHz) d: 2.41 (s, 3H), 7.00 (d,
J = 8.0 Hz, 2H), 7.03–7.3 (m, 2H), 7.10–7.17 (m, 1H),
7.24 (d, J = 8.4 Hz, 2H), 7.35 (t, J = 8.4 Hz, 2H); 13C
NMR (CDCl3, 100 MHz) d: 20.4, 118.3, 119.6, 122.8,
129.8, 130.1, 133.0, 154.2, 157.9.
Characterization of the used catalyst
Characterization of the used catalyst was done by IR and
UV–vis spectroscopic data. The FTIR spectrum of the used
catalyst was identical to that of the original catalyst. Thus,
for the used Cat-1, peaks at 1,618 cm-1 (for pyridine ring),
1,313 cm-1 (vC–O, coordinated), a weak peak at 547 cm-1
(vCu–N) and a Cu–O stretching vibration at 431 cm-1
were all present in the spectrum. In Cat-2, a peak at
1,250 cm-1 (for –CH2Cl), 1,312 cm-1 (vC–O, coordi-
nated), a weak peak at 542 cm-1 (vCu–N) and a Cu–O
stretching vibration at 433 cm-1 were all present in the
spectrum of the used Cat-2. The UV–vis spectra of the used
catalysts were also very similar to those of the original
catalysts. From the spectroscopic data, we conclude that
the structures of the used catalysts are identical with those
of the original.
4-Cyano-4-methoxy-diphenylether (4e). White solid
[52]. 1H NMR (CDCl3, 400 MHz) d: 3.76 (s, 3 H),
6.84–6.87 (m, 4H), 6.91–6.94 (m, 2H), d 7.47–7.51 (m,
2H); 13C NMR (CDCl3, 100 MHz) d: 55.7, 105.4, 115.2,
117.31, 119.15 122, 134.2, 148, 157.2, 162.5.
4’-Methyl-4-phenoxy-phenylacetate (4f). White Solid
1
[53]. H NMR (CDCl3, 400 MHz) d: 8.00–8.04 (2H, d,
J = 8.4), 7.18–7.20 (2H, d, J = 8.3), 6.95–6.96 (4H, m),
3.88 (3H, s) and 2.34 (3H, s); 13C NMR (CDCl3, 100 MHz)
d: 166.7, 162.6, 153.0, 134.0, 131.6, 130.7, 124.5, 120.3,
117.1, 52.0, 21.0.
1-(4-nitrophenoxy)-4-methoxybenzene (4g). Off-white
1
solid [54]. H NMR (CDCl3, 400 MHz) d: 3.84 (s, 3H),
6.91 (d, J = 8.8 Hz, 2H), 7.05 (d, J = 10.3 Hz, 2H), 7.10
(d, J = 8.8 Hz, 2H), 8.16 (d, J = 8.1 Hz, 2H); 13C NMR
(CDCl3, 100 MHz) d: 55.6, 113.3, 117.7, 118.1, 119.0,
139.4, 149.3, 153.8, 163.0.
Characterization of the products
1
All H and 13C NMR spectra were recorded at 400 and
1-(4-nitrophenoxy)-4-bromobenzene (4h). Yellow solid
1
100 MHz, respectively. The characterizations of the prod-
ucts were carried out by 1H NMR spectroscopy using
Bruker DPX-400 in CDCl3 with TMS as internal standard.
Chemical shifts are given as d values with reference to
tetramethylsilane (TMS) as the internal standard. The
reaction products were quantified (GC data) by Varian
3400 gas chromatograph equipped with a 30 m CP-
SIL8CB capillary column and a flame ionization detector
and identified (GC–MS) by Trace DSQ II GC–MS equip-
ped with a 60-m TR-50MS capillary column. Standardi-
zation of the products was done by calibration using
dihexyl ether as internal standard. Color, 1H and 13C NMR
data of all the products are given below.
[54]. H NMR (CDCl3, 400 MHz) d: 6.98 (d, J = 8.9 Hz,
2H), 7.00 (d, J = 9.3 Hz, 2H), 7.51 (d, J = 8.9 Hz, 2H),
8.22 (d, J = 9.1 Hz, 2H); 13C NMR (CDCl3, 100 MHz) d:
113.0, 118.4, 120.1, 121.0, 139.2, 155.4, 163.3.
1
2-Methyl-diphenylether (4i). Colorless liquid [49]. H
NMR (CDCl3, 400 MHz) d: 2.19 (s, 3H), 6.87–6.91 (m, 3H),
6.97–7.07 (m, 2H), 7.12–7.165 (m, 1H), 7.19–7.30 (m, 3H);
13C NMR (CDCl3, 100 MHz) d: 16.1, 117.6, 119.7, 122.0,
124.0, 127.3, 129.6, 130.1, 131. 2, 154.7, 158.0.
1
2-Methoxy-diphenylether (4j). Colorless liquid [55]. H
NMR (CDCl3, 400 MHz) d: 3.77 (s, 3H), 6.81–6.90 (m,
3H), 6.91–6.94 (m, 1H), 6.96–7.02 (m, 2H), 7.03–7.10 (m,
1H), 7.16–7.25 (m, 2H); 13C NMR (CDCl3, 100 MHz) d:
56, 112.9, 117.3, 121.1, 121.2, 122.6, 124.9, 129.6, 145.1,
151.6, 158.
Diphenylether (4a). Colorless liquid [49]. 1H NMR
(CDCl3, 400 MHz) d: 7.07–7.14 (m, 4H), 7.13–7.20 (m,
2H); 7.41–7.45 (m, 4H); 13C NMR (CDCl3, 100 MHz) d:
116, 124.4, 128.7, 157.0.
1
Acknowledgments We thank the Department of chemistry, Uni-
versity of Calcutta, for providing us the instrumental support. We
gratefully acknowledge DST, New Delhi, for award of grant under its
FIST program to the Department of Chemistry, University of Kalyani.
SMI acknowledge the following agencies for funding: DST, CSIR and
UGC, New Delhi, India.
4-Nitro-diphenylether (4b). Yellow solid [50]. H NMR
(CDCl3, 400 MHz) d: 6.98–7.00 (m, 2H), 7.04–7.10 (m,
2H), 7.20–7.28 (m, 1H), 7.41–7.44 (m, 2H), 8.14–8.20 (m,
2H); 13C NMR (CDCl3, 100 MHz) d: 117.4, 121.2, 125.7,
127, 129.4, 142.2, 153.9, 163.2.
123

Transition Met Chem (2011) 36:1–11
11
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