Recyclable hydrophobic copper (II) phthalocyanine catalyzed N-arylation of imidazoles in dimethylsulfoxide

Article abstract of DOI:10.1016/S1872-2067(14)60148-0

Copper (II) phthalocyanine (CuPc) was used as a catalyst for the N-arylation of imidazoles with aryl iodides or bromides. The catalyst showed high activity and could be reused 3 times without any significant loss in activity. The catalyst was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible spectroscopy.

Full text of DOI:10.1016/S1872-2067(14)60148-0

Chinese Journal of Catalysis 35 (2014) 1818–1824
ava i l a b l e a t w w w. s c i e n c ed i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e /c h n j c
Article
Recyclable hydrophobic copper (II) phthalocyanine catalyzed
N‐arylation of imidazoles in dimethylsulfoxide
Qiang Huang, Limei Zhou*, Xiaohui Jiang, Xiaolong Qi, Zhonghua Wang, Wencheng Lang
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637002, Sichuan, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Copper (II) phthalocyanine (CuPc) was used as a catalyst for the N‐arylation of imidazoles with aryl
iodides or bromides. The catalyst showed high activity and could be reused 3 times without any
significant loss in activity. The catalyst was characterized by Fourier transform infrared spectros‐
copy, X‐ray photoelectron spectroscopy, and ultraviolet‐visible spectroscopy.
© 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 11 April 2014
Accepted 12 May 2014
Published 20 November 2014
Published by Elsevier B.V. All rights reserved.
Keywords:
Copper (II) phthalocyanine
N‐arylation
Aryl halide
Recyclable catalyst
1. Introduction
is also difficult leading to recycling problems.
N‐arylated azoles (e.g., arylpyrroles, arylpyrazoles, arylim‐
Phthalocyanine transition metal complexes are important
industrial pigments and are considered to be potential oxida‐
tion catalysts because of their cheap and facile preparation on
large scale and in particular their chemical and thermal stabil‐
ity [1–3]. For example, Rezaeifard and coworkers [1] used
copper (II) phthalocyanine (CuPc) for the aqueous heteroge‐
neous oxygenation of hydrocarbons. However, few reports
exist about other reactions by metal phthalocyanine [3,4]. Shi‐
nu and coworkers [3] reported a novel highly stereoselective
multi‐component synthesis of N‐substituted‐β‐amino ketone
derivatives using CuPc as a reusable catalyst. However, the low
solubility of metallophthalocyanines is perhaps the most seri‐
ous limitation in their application as catalysts although it may
be overcome by sulfonation and carboxylation at the periphery
of the molecule to give water‐soluble derivatives [5]. Unfortu‐
nately, the separation of water‐soluble catalysts from solutions
idazoles, aryltriazoles, arylindoles, arylcarbazoles, etc.) have
important applications in the medicinal and material fields
[6–8]. The transition‐metal‐catalyzed cross‐coupling of aryl
halides with amines, amides, and N‐heterocyclic nucleophiles
has become a powerful strategy for these reactions [9–12].
Some homogeneous and heterogeneous catalysts for the cata‐
lytic N‐arylation coupling reaction have been reported
[10,13–15]. However, not much research has been done on the
N‐arylation reaction catalyzed by metal phthalocyanines.
We thus report the first efficient CuPc system for the
N‐arylation of imidazoles with aryl halides. Although homoge‐
neous catalysis under mild reaction conditions is characterized
by higher catalytic activity than heterogeneous catalysis, ho‐
mogenous catalysts are difficult to separate and recycle.
Therefore, the use of homogeneous catalysts in industrial pro‐
duction is limited [16,17]. CuPc is soluble in dimethylsulfoxide
* Corresponding author. Tel: +86‐817‐2568081; Fax: +86‐817‐2568081; E‐mail: cwnuzhoulimei@163.com
This work was supported by the National Natural Science Foundation of China (21303139), the Educational Department of Sichuan Province
(11ZA035), and the Open Project of Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province (CSPC2010‐3).
DOI: 10.1016/S1872‐2067(14)60148‐0 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 35, No. 11, November 2014

Qiang Huang et al. / Chinese Journal of Catalysis 35 (2014) 1818–1824
1819
(DMSO) but not in water. Therefore, in our experiment, DMSO
was used as the solvent and was involved in the reaction. CuPc
played a homogeneous role in the reaction process because of
its excellent solubility in DMSO, which had the remarkable ad‐
vantage of homogeneous catalysis under mild conditions. Addi‐
tionally, this material was precipitated by adding water to the
reaction system, and isolated by simple centrifugation. There‐
fore, this reaction has the advantages of both heterogeneous
and homogeneous catalysis.
(a)
(b)
2. Experimental
Fig. 2. Dispersity of CuPc in different solvents. (a) A mixture of DMSO
and water (VDMSO:VH2O = 1:2); (b) DMSO.
2.1. Materials and characterization
3
Results and discussion
CuPc was synthesized according to the literature [18]. The
structure of the CuPc catalyst is shown in Fig. 1. All reagents
were purchased from commercial suppliers and used without
further purification. The catalyst was characterized by Fourier
transform infrared spectroscopy (FT‐IR, Nicolet 6700 FT‐IR,
USA), X‐ray photoelectron spectroscopy (XPS, Kratos
XSAM‐800, UK) and ultraviolet‐visible spectroscopy (UV‐Vis,
Shimadzu UV‐2550, JP).
3.1. Characterization of the catalyst
The effective dispersity of the CuPc catalyst in the solvent
seems to be the most important factor that affects its catalytic
performance in this reaction. First, the dispersibility of the cat‐
alyst was investigated in different solvents, as shown in Fig. 2.
The result indicated that the CuPc catalyst was insoluble and
hydrophobic in a mixture of DMSO and water (VDMSO:VH2O
=
2.2. General procedure for the N‐arylation of imidazoles with
aryl halides
1:2), whereas it was uniformly dispersed in DMSO. Therefore,
the reaction could be carried out in a homogeneous system
using CuPc as the catalyst. After the completion of each reaction
we reused the CuPc catalyst after centrifugation. Therefore, the
reaction has the advantages of both heterogeneous and homo‐
geneous catalysis.
Figure 3 shows FT‐IR spectrum of the CuPc catalyst. The
as‐fabricated CuPc sample has several absorption peaks around
724, 901, 1091, 1120, and 1636 cm–1, which can be assigned to
the phthalocyanine skeletal and metal‐ligand vibrations, re‐
spectively [19]. This is consistent with structure of a typical
CuPc material.
To further confirm the valence state of the copper complex,
an XPS spectrum of the catalyst was obtained and is shown in
Fig. 4. The characteristic Cu 2p peak and the satellite peaks are
very typical of a stable CuPc layer. The XPS spectrum shows a
single Cu 2p3/2 peak at 934.8 eV, which can be assigned to Cu2+
[20–22]. Therefore, divalent copper was immobilized in the
CuPc material without other valence states being present.
In a typical experiment, imidazole (1.2 mmol), aryl halide
(1.0 mmol), catalyst, and base (2.0 mmol) were added to a hy‐
drothermal reactor (20 mL). The mixture was heated to the
desired temperature with stirring. After the completion of the
reaction and cooling to room temperature, the reaction mixture
was diluted with water and extracted with ethyl acetate (3 × 15
mL). The combined organic extracts were dried with anhy‐
drous Na2SO4 and the obtained product was purified by column
chromatography on silica gel using dichloromethane: methanol
(100:1, v/v) as the eluent.
2.3. Recycling experiment
The recyclability of the synthesized catalyst was investigat‐
ed using the coupling reaction between iodobenzene and imid‐
azole. After the completion of each reaction the material was
precipitated by adding water to the reaction system and the
CuPc composite was removed by centrifuging and washing
with 3 mL ethyl acetate. The collected catalyst was dried under
vacuum at 70 °C, and reused for a subsequent reaction.
901
2854
1636
2923
1420
1510
1091
1120
1333
N
724
N
N
N
N
3446
Cu
N
N
N
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm1)
Fig. 3. FT‐IR spectrum of the CuPc catalyst.
Fig. 1. Structure of the CuPc catalyst.

1820
Qiang Huang et al. / Chinese Journal of Catalysis 35 (2014) 1818–1824
temperature was determined to be 90 °C. Finally, the reaction
Cu 2p
time was also found to be an important factor as is shown by a
comparison between entries 9, 11, and 12 in Table 1. The most
appropriate reaction time was found to be 24 h. Therefore, the
optimum conditions were: CuPc catalyst (10 mol%), KOH as
base (2.0 mmol), and DMSO as solvent at 90 °C for 24 h.
934.8
To determine the scope of the practical use of the CuPc cat‐
alyst, N‐arylations of various substituted aryl halides were car‐
ried out under optimal conditions (Table 2). As shown in Table
2, it is clear that the activity of the aryl halides in this reaction
Table 2
CuPc catalyzed N‐arylation of imidazole with different substituted aryl
halides.
970 965 960 955 950 945 940 935 930 925
Binding energy (eV)
X
CuPc
N
N
Fig. 4. XPS spectrum of the CuPc catalyst.
R
N
NH
R
KOH, DMSO
X = I, Br, Cl
3.2. N‐arylation catalyzed by the CuPc catalyst
Isolated yield
(%)
Entry
1
ArX
Product
A series of experiments were initially conducted using im‐
idazole and iodobenzene as model substrates to evaluate and
optimize the most efficient catalytic system (Table 1). Poor
conversion was achieved in the reaction in the absence of the
catalyst (Table 1, entry 1). In the presence of the catalyst, the
yield of product increased significantly. Different bases were
then evaluated using the model reaction, and the best result
was achieved when using KOH as the alkali (Table 1, entries
2–5). We then investigated the effect of catalyst amount on this
reaction (Table 1, entries 5–8). When the amount of CuPc was
increased from 5 to 15 mol%, the product yield increased. A
nearly equivalent conversion ratio was achieved using 10 and
15 mol% of the catalyst. Therefore, from an economic point of
view the 10 mol% catalyst loading is most appropriate. The
effect of reaction temperature on the catalytic activity of the
CuPc catalyst was also investigated (Table 1, entries 6, 8–10).
When the reaction temperature was increased from 90 to 110
°C no significant change in yield was observed. However, a sig‐
nificant decrease in the yield was observed when the tempera‐
ture was decreased to 80 °C. Therefore, the optimal reaction
I
92.6
N
N
N
Br
2
3
31.3
86.5
N
F3C
Br
N
F3C
N
CF3
CF3
Br
N
4
31.8
N
H3CO
H3CO
Cl
5
6
5.5
N
N
N
N
Cl
75.1
Table 1
NO2
Screening reaction conditions for the N‐arylation of imidazole with
NO2
N
iodobenzene.
O2N
Cl
Cl
7
8
77.3
88.3
N
N
O2N
I
N
N
CuPc
N
NH
Base, Solvent
Temperature
(°C)
90
Time
Catalyst
Yield
(%)
4.5
Entry
Base
N
(h)
24
24
24
24
24
24
24
24
24
24
20
16
(mol%)
—
5
O2N
O2N
1
2
3
4
5
6
7
8
KOH
CsCO3
K3PO4
NaOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
O2N
O2N
110
110
110
110
110
110
100
90
16.8
24.0
42.2
75.2
95.5
97.3
93.5
92.6
51.0
75.7
66.9
5
5
5
10
15
10
10
10
10
10
I
I
9
94.4
38.8
N
N
N
N
H3C
10
H3C
9
10
11
12
80
90
90
Reaction conditions: aryl halides 1.0 mmol, imidazole 1.2 mmol, CuPc
10 mol%, KOH 2.0 mmol, DMSO 2 mL, 90 °C, 24 h.

Qiang Huang et al. / Chinese Journal of Catalysis 35 (2014) 1818–1824
1821
0.8
Table 3
CuPc catalyzed N‐arylation of heterocycles with iodobenzene.
CuPc, 90 o
C
N-Het
I
(1)
Het-NH
0.6
0.4
0.2
0.0
KOH, DMSO
(2)
Entry
1
Isolated yield
(%)
Het‐NH
Product
H
N
53.8
N
N
N
N
N
2
3
92.6
71.9
500
600
700
800
N
NH
/nm
Fig. 5. UV‐Vis spectra of fresh (1) and after 5 runs (2) CuPc in DMSO.
H
N
times CuPc catalyst by UV‐Vis spectroscopy (Fig. 5).
CH3
N
Generally, the aggregation of CuPc is the main factor that
caused catalyst deactivation [23]. As shown in Fig. 5, typical
dimer absorption peak was observed at 630 nm, and the broad
absorption around 730 nm in the near‐infrared region is be‐
lieved to originate from the Q‐band of the benzene ring struc‐
ture [24]. However, we found that the amount of dimer did not
evidently increase before and after the reaction, which indi‐
cates that CuPc was stabilized in DMSO. Therefore, the aggrega‐
tion of CuPc did not lead to low catalytic activity. However,
Q‐band of the used catalyst moved toward the long‐
er‐wavelength side. Therefore, a new species might be gener‐
ated via an interaction between CuPc and imidazole.
Furthermore, the conditions of this CuPc catalyzed
N‐arylation reaction are mild compared with the systems listed
in Table 5. High product yields were achieved at 90 °C in 24 h,
which is better than that of the other heterogeneous catalysts.
A salen‐Cu(II) complex has also shown good catalytic perfor‐
mance during N‐arylation reactions but this catalyst could not
be recycled from the homogeneous system [26]. In our previ‐
ous research, the Cu+‐MMT catalyst gave good performance but
a high temperature was still required in this system [27]. The
catalyst thus has an obvious advantage in terms of its out‐
standing performance and utilization value.
N
CH3
N
Reaction conditions: iodobenzene 1.0 mmol, azoles 1.2 mmol, CuPc 10
mol%, KOH 2.0 mmol, DMSO 2 mL, 90 °C, 24 h.
increase as follows: iodobenzene > bromobenzene > chloro‐
benzene (Table 2, entries 1, 2, 5). Furthermore, the elec‐
tron‐deficient aryl halides afforded the corresponding N‐aryl
imidazole products in better yields than the electron‐rich aryl
halides (Table 2, entries 3, 4, 9, 10). Interestingly, steric hin‐
drance had little impact on the outcome of the reaction (Table
2, entries 6–8).
To further evaluate the scope of the catalytic system, the
N‐arylation of iodobenzene was investigated with a variety of
nitrogen‐containing heterocycles (Table 3). It is clear that ben‐
zimidazole and 2‐methylimidazole were successfully coupled
with iodobenzene to give the corresponding N‐arylated prod‐
ucts in satisfactory yields (Table 3, entries 1 and 3). These re‐
sults thus show the versatility of the current catalytic system.
3.3. Recycling the catalyst
A series of experiments were also carried out to evaluate the
recyclability of the catalyst. The results are listed in Table 4.
The catalyst was recovered by centrifugation and reused 3
times without significant loss of activity. The yield was lower in
the fourth recycle but we obtained a yield of 90.3% when pro‐
longing the reaction time. To explain the reasons for this de‐
crease in catalyst activity, we characterized fresh and used 5
4. Conclusions
In conclusion, we used hydrophobic divalent CuPc as a cat‐
alyst for the N‐arylation reaction. Good yields were achieved
when using CuPc under mild conditions. The CuPc catalyst was
Table 5
Comparison of the activity of different heterogeneous catalysts in the
N‐arylation of imidazole with iodobenzene.
Table 4
CuPc catalyst recycling for the N‐arylation of imidazole and iodoben‐
zene.
Isolated
yield (%)
Catalyst
Reaction conditions
Ref.
Run
1
2
3
4
Yield (%)
93.1
89.3
88.7
75.3
CuI
CuI/PEG
Cu2O
10 mol%, 120°C, DMSO, NaH, 24 h
10 mol%, 110°C, K2CO3, 24 h
10 mol%, 120°C, KOH, DMSO, 24 h
95
91
92
98
[9]
[10]
[25]
[26]
Salen‐Cu(II) 10 mol%, 100°C, DMSO, NaOH, 12 h
complex
Cu+‐MMT
CuPc
5*
90.3
0.2 mol%, 110°C, DMSO, KOH, 24 h
10 mol%, 90°C, DMSO, KOH, 24 h
92
93
[27]
this study
Reaction conditions: iodobenzene 2.0 mmol, imidazole 2.4 mmol, CuPc
10 mol%, KOH 4.0 mmol, DMSO 3 mL, 90 °C, 24 h (*30 h).

1822
Qiang Huang et al. / Chinese Journal of Catalysis 35 (2014) 1818–1824
Graphical Abstract
Chin. J. Catal., 2014, 35: 1818–1824 doi: 10.1016/S1872‐2067(14)60148‐0
Recyclable hydrophobic copper (II) phthalocyanine catalyzed N‐arylation
X
of imidazoles in dimethylsulfoxide
R
Qiang Huang, Limei Zhou*, Xiaohui Jiang, Xiaolong Qi, Zhonghua Wang,
Wencheng Lang
China West Normal University
H O
2
N
N
NH
N
N
N
N
o
N
DMSO, 90
C
N
Cu
N
N
The copper (II) phthalocyanine (CuPc) catalyst catalyzed the N‐arylation of im‐
idazoles with aryl iodides or bromides under mild conditions and was reused 3
times without any significant loss in activity.
N
R
Recovery
CuPc
[14] Mondal P, Sinha A, Salam N, Roy A S, Jana N R, Islam S M. RSC Adv,
2013, 3: 5615
[15] Altman R A, Buchwald S L. Org Lett, 2006, 8: 2779
[16] Sehlotho N, Nyokon T. J Mol Catal A, 2004, 209: 51
[17] Ghorbani‐Vaghei R, Hemmati S, Veisi H. Tetrahedron Lett, 2013,
54: 7095
used 3 times without significant loss of activity. This catalytic
system has the advantages of homogeneous and heterogeneous
catalysis, which could be potentially useful in industrial appli‐
cations. Work is in progress to further broaden the scope of this
catalytic system and the results will be reported in due course.
[18] Shaabani A. J Chem Res, Synop, 1998: 672
[19] Guo Z C, Chen B, Mu J B, Zhang M Y, Zhang P, Zhang Z Y, Wang J F,
Zhang X, Sun Y Y, Shao C L, Liu Y C. J Hazard Mater, 2012, 219‐220:
156
[20] Peisert H, Knupfer M, Schwieger T, Auerhammer J M, Golden M S,
Fink J. J Appl Phys, 2002, 91: 4872
[21] Krzywiecki M, Grządziel L, Ottaviano L, Parisse P, Santucci S,
Szuber J. Mater Sci‐Poland, 2008, 26: 287
[22] Ottaviano L, Lozzi L, Rispoli F, Santucci S. Surf Sci, 1998, 402‐404:
518
References
[1] Rezaeifard A, Jafarpour M, Naeimi A, Mohammadi K. J Mol Catal A,
2012, 357: 141
[2] Grootboom N, Nyokong T. J Mol Catal A, 2002, 179: 113
[3] Shinu V S, Pramitha P, Bahulayan D. Tetrahedron Lett, 2011, 52:
3110
[4] Sadek S A, Solyman S M, Abdel‐Samad H S, Hassan S A. Int J
Polymer Mater, 2010, 59: 353
[5] Sorokin A B, Kudrik E V. Catal Today, 2011, 159: 37
[6] Kison C, Opatz T. Chem Eur J, 2009, 15: 843
[7] Kantam M L, Yadav J, Laha S, Sreedhar B, Jha S. Adv Synth Catal,
2007, 349: 1938
[8] Chen C X, Shang G N, Zhou J J, Yu Y H, Li B, Peng J S. Org Lett, 2014,
16: 1872
[9] Yang Q C, Wang Y F, Zhang B J, Zhang M J. Chin J Chem, 2012, 30:
2389
[10] Zhang Q, Luo J, Wei Y Y. Synth Commun, 2012, 42: 114
[11] Boswell M G, Yeung F G, Wolf C. Synlett, 2012, 23: 1240
[12] Jin M, Zhao D, He G Z, Tong Y, Han S Q. Chin J Catal, 2013, 34:
1651
[23] Koifman O I, Hanack M, Syrbu S A, Lyubimtsev A V. Russ Chem Bull,
2013, 62: 896
[24] Zhang L, Wang L. Poly Plast Technol Eng, 2012, 51: 6
[25] Huang Y Z, Miao H, Zhang Q H, Chen C, Xu J. Catal Lett, 2008, 122:
344
[26] Liu Y, Zhang Q, Ma X W, Liu P, Xie J W, Dai B, Liu Z Y. Int J Org
Chem, 2013, 3: 185
[27] Qi X L, Zhou L M, Jiang X H, Fan H W, Fu H Y, Chen H. Chin J Catal,
2012, 33: 1877
Page numbers refer to the contents in the print version, which include
both the English and Chinese versions of the paper. The online version
only has the English version. The pages with the Chinese version are only
available in the print version.
[13] Sreedhar B, Arundhathi R, Reddy P L, Reddy M A, Kantam M L.
Synthesis, 2009: 2517