SiO2-functionalized melamine-pyridine group–supported Cu(OAc)2 as an efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions

Article abstract of DOI:10.1016/j.crci.2018.03.002

This study reports a convenient approach to prepare SiO₂/CCPy/Cu(OAc)₂ as a novel nanocatalyst, in which melamine-bearing pyridine groups have functionalized SiO₂ and can act as a capping agent to stabilize Cu(II) species.

Full text of DOI:10.1016/j.crci.2018.03.002

C. R. Chimie xxx (2018) 1e10
Contents lists available at ScienceDirect
Comptes Rendus Chimie
www.sciencedirect.com
ꢀ
Full paper/Memoire
SiO2-functionalized melamine-pyridine groupesupported
Cu(OAc)2 as an efficient heterogeneous and recyclable
nanocatalyst for the N-arylation of amines through Ullmann
coupling reactions
,
, *
Saba Hemmati a *, Akram Naderi b, Mohammad Ghadermazi b, Hojat Veisi a
a Department of Chemistry, Payame Noor University, 19395-4697 Tehran, Iran
b Department of Chemistry, Faculty of Science, University of Kurdistan, 66177-15175 Sanandaj, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
This study reports a convenient approach to prepare SiO2/CCPy/Cu(OAc)2 as a novel nano-
catalyst, in which melamine-bearing pyridine groups have functionalized SiO2 and can act as
a capping agent to stabilize Cu(II) species. The catalyst is characterized through Fourier
transform infrared, transmission electron microscopy, field emission scanning electron mi-
croscopy (FESEM), BrunauereEmmetteTeller (BET), thermogravimetric analysis, inductivity
coupled plasma (ICP), and energy dispersive X-ray (EDX) techniques. Furthermore, its cat-
alytic behavior is evaluated in the N-arylation of indole, imidazole, and aniline during
Ullmann-type CeN coupling reactions. Moreover, it has been proved that the heterogeneous
nanocatalyst can be feasibly recovered by filtration and reused in five consecutive reaction
cycles without any noticeable loss of its catalytic activity. The results clarified that the
devised method is advantageous from several perspectives, that is, low catalyst loading, high
product yield, experimental simplicity, broad substrate scope, and short reaction time.
© 2018 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Received 22 October 2017
Accepted 12 March 2018
Available online xxxx
Keywords:
Silica
Ullmann
Heterogeneous nanocatalyst
Copper
Indole
Imidazole
1. Introduction
Therefore, synthetic chemists have attempted to focus on
Cu-based catalysts and introduce milder methods for the
Transition metalebased catalysis of CeN bond forma-
tion through cross-coupling reactions is a powerful method
for preparing important compounds that are highly
demanded in pharmaceutical, material, and chemical in-
dustries [1e4]. For this reason the development of conve-
nient and effective catalyst synthesis methods has attracted
much attention. Some studies have reported successful
CeN coupling of nucleophilic aromatic groups with aryl
halides by using catalysts based on palladium [2,4], nickel
[3], and copper [5]. Lower cost of Cu-based catalysts has
motivated their large-scale industrial applications.
synthesis of Cu-containing catalysts. One of the simplest
and cheapest solutions of producing N-aryl nitrogen het-
erocycles is using the Ullmann-type coupling of aryl halides
with nitrogen heterocycles [6e8]. Cu-based catalysts can
catalyze Ullmann reactions, meantime their efficiencies can
be promoted if their copper sources, ligands, bases, and
other additives be selected, correctly.
Recently, several mild and efficient methods have been
adopted for N-arylation of heterocyclic amines, for
example, Refs. [9e11]. Although these reported methods of
Cu-catalyzed N-arylation of amines are highly efficient,
they rely on homogeneous catalysis and restrict separation
of the catalysts from the reaction mixture. This issue can be
overcome by developing recyclable and efficient hetero-
geneous catalysts through immobilization of catalytically
* Corresponding authors.
E-mail addresses: hojatveisi@yahoo.com, s_organo2005@yahoo.com
(H. Veisi).
https://doi.org/10.1016/j.crci.2018.03.002
1631-0748/© 2018 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

2
S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
active species, for example, organometallic complexes, on a
solid support [12]. In this respect, many heterogeneous Cu-
based catalytic systems have been proposed to perform
cross-coupling reactions. Some notable examples include
Merrifield resinesupported phenanthroline copper(I)
complex [13], Cu immobilized on organiceinorganic hybrid
materials [14], Cu immobilized on MCM-41 [15], Cu ferrite
and preparation of an SBA-15/CCPy/Pd(II) nanocatalyst by
grafting melamine-bearing pyridine groups on SBA-15 and
depositing Pd NPs for stable catalysis of SuzukieMiyaura
reactions and N-arylation of indoles [[30], 4h]. Because
the results of our previous works on synthetic application
of nanocatalysts [31] were encouraging, herein we report a
novel heterogeneous catalytic system based on Cu(OAc)2
immobilization on melamine-bearing pyridine-modified
SiO2 particles (Scheme 1). This novel catalyst is air stable,
can be reused, and shows excellent catalytic performance
for CeN coupling in Ullmann reactions.
nanoparticles (NPs) [16], [Cu30I16(mtpmt)12(m10-S4)] [17],
Al2O3esupported Cu(II) catalyst [18], glycerol ingrained Cu
[19], CuO nanocatalyst [20], and polymer-supported Cu(II)
catalyst [21].
This study aims to prepare a silica-supported Cu cata-
lyst. The major concern is that making silica-based hybrid
materials with a high portion of organic functional groups
is difficult because of the heterogenous distribution of
active sites on silica particles. To achieve a homogeneous
distribution of organic functional groups on silica-hybrid
materials, several approaches, such as surface patterning,
surface functionalization with dendrimers, and molecular/
ion imprinting, have been reported [22e29]. As an alter-
native approach, our research group reported the design
2. Experimental section
2.1. Preparation of SiO2/CCPy
Thirty milliliters of anhydrous toluene, 1.0 g of SiO2, and
0.36 g (3.0 mmol) of 3-aminoropropyl trimethoxysilanewere
added to a 100-mL round-bottom flask. The solution was
refluxed under an inert atmosphere for 24 h, filtered, washed
subsequently with toluene, dichloromethane, and methanol,
Scheme 1. Schematic diagram of SiO2/CCPy/Cu(OAc)2 fabrications.
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
3
Fig. 1. FTIR spectra of (a) SiO2/CCPy, and (b) SiO2/CCPy/Cu(OAc)2.
and dried under reduced pressure at 80 ꢀC for 10 h. In another
100-mLround-bottomflask, a solutionof 1 gof aminopropyl-
functionalized SiO2 in 35 mLTHF was prepared and 0.5 mL of
diisopropylethylamine was added to it. Then, 0.46 g (3 mmol)
of cyanuric chloride (CC) was added to the functionalized
SiO2 solution, at 0 ꢀC. After 2 h, the solutionwas decanted and
washed two times with 25 mL of THF. Then, 25 mL of
acetonitrile and 1 mL of diisopropylethylamine were added
to the residual solid. Next, 7 mmol dipyridylamine was
added, the mixture was stirred for 2 h at room temperature
and the resultant solution was refluxed for 12 h. After
completion of the reaction, the solid product was filtered,
washed with deionized water and then acetone, and dried at
80 ꢀC for 12 h. In this way, dipyridylamine clung on triazine-
functionalized SiO2 (SiO2/CCPy) was obtained.
dried under vacuum at 80 ꢀC for 24 h to give SiO2/CCPy/
Cu(OAc)2. Elemental analysis of the SiO2/CCPy/Cu(OAc)2
product by inductively coupled plasma-atomic emission
spectrometry (ICP-AES) determined 0.32 mmol/g Cu
loading.
2.2. Heterogenization of Cu(OAc)2 on the surface of SiO2/CCPy
Cu(OAc)2 (1.5 mmol) was dissolved in 50 mL of H2O and
stirred for 0.5 h. Then, 1.0 g of the prepared SiO2/CCPy solid
was added and stirred at room temperature for 24 h. After
completion of the reaction, the blue solid product was
filtered, washed with water, acetone, and ethanol, and
Fig. 2. TEM image of SiO2/CCPy/Cu(OAc)2.
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

4
S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
Fig. 3. EDX spectrum of SiO2/CCPy/Cu(OAc)2.
2.3. N-Arylation of amines in the presence of SiO2/CCPy/
Cu(OAc)2
was recovered by centrifugation and washed with ethanol
and ethyl acetate. The combined organic layer was dried
over anhydrous sodium sulfate and evaporated in a rotary
evaporator under reduced pressure. The resultant material
was purified by silica gelebased preparative TLC to sepa-
rate the desired product.
In a 25-mL round-bottom flask, the synthesized catalyst
(25 mg; 0.7 mol %), aryl halides (1 mmol), CH3CN (3 mL),
amines (1 mmol), and Et3N (2 mmol) were mixed. Then, the
mixture was stirred for the desired time at 50 ꢀC. The re-
action progress was observed by thin-layer chromatog-
raphy (TLC). After completion of the reaction, the reaction
mixture was cooled to room temperature and the catalyst
2.4. Procedure for reusing the catalyst
At any specific reaction time, 5 mL of ethyl acetate was
added to the reaction mixture and stirred for 5 min. After
this time, the catalyst was separated by centrifugation. In
the next step, the recovered solid was washed using
ethanol and dried under vacuum. Then, the recovered
catalyst was used in another catalytic run.
Fig. 4. FESEM image of SiO2/CCPy/Cu(OAc)2.
Fig. 5. TGA diagram of the catalyst.
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
5
2.5. Large-scale N-arylation of indole in the presence of SiO2/
3. Results and discussion
CCPy/Cu(OAc)2
3.1. Catalyst preparation and characterization
In a 250-mL round-bottom flask, the catalyst (0.5 g;
0.7 mol %), iodobenzene (20 mmol), CH3CN (60 mL), indole
(20 mmol), and Et3N (40 mmol) were mixed. Then, the
mixture was stirred for the desired time at 50 ꢀC. The re-
action was observed by TLC. After completion of the reac-
tion, the reaction mixture was cooled to room temperature
and the catalyst was separated by simple filtration and
washed with ethanol and ethyl acetate. The combined
organic layer was dried over anhydrous sodium sulfate and
evaporated in a rotary evaporator under reduced pressure.
The resultant material was purified by silica gelebased
preparative TLC to obtain N-phenylindole with 95% yield.
The proposed catalyst was prepared by following the
steps that are described in Scheme 1. In this synthesis pro-
cess, first, SiO2 was chosen as the support material. Then,
silica was reacted with 3-aminopropyltriethoxysilane to
produce functionalized silica. In the next step, CC was
immobilized on the surface of the functionalized SiO2 par-
ticles covalently while the temperature was under control.
Then, the other two chloride functional groups of CC were
replaced with 2 equiv of dipyridylamine through the for-
mation of CeN bonds between the triazine ring and the
amine moieties. In the final step, the SiO2/CCPy/Cu(OAc)2
Fig. 6. (a) N2 adsorption isotherm, (b) pore size distribution of SiO2/CCPy/Cu(OAc)2.
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

6
S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
Fig. 7. Wide-angle XRD pattern of SiO2/CCPy/Cu(OAc)2.
nanocatalyst was synthesized by reacting Cu(OAc)2 with
SiO2/CCPy in water. According to ICP measurements, Cu
loading of the prepared catalyst was about 0.32 mmol/g of
the catalyst.
support after functionalization. Furthermore, the TEM re-
sults demonstrate a nearly uniform size distribution for the
SiO2/CCPy/Cu(OAc)2 particles and clarify that the silica NPs
with 10e15 nm dimension are self-aggregated throughout
the sample. Also, some randomly distributed micropores,
that is, the white spots, are clearly visible in each porous
silica NP.
The EDX spectrum of the catalyst approved successful
functionalization of the silica particles and outlined the
existence of C, N, and Cu elements in addition to Si and O
(Fig. 3). Moreover, scanning electron microscopy (SEM) of
the silica NPs was performed. In the obtained microgram
(Fig. 4), the observed particles are mostly spherical. Also,
self-aggregation of the particles is evident throughout the
sample. Therefore, it can be stated that the self-aggregation
nature of the silica NPs is conserved even after modification
of their surfaces with organic functional groups.
Fourier transform infrared (FTIR) spectroscopy was used
to assure about incorporation of pyridine groups and
melamine-based dendrimers in the silica framework. Fig. 1
shows the FTIR spectra of SiO2/CCPy and SiO2/CCPy/
Cu(OAc)2. The typical 453, 794, and 1086 cmꢁ1 bands of
SieOeSi are present in both samples and are attributed to
the condensed silica network [32]. Also, the strong ab-
sorption band at about 3422 cmꢁ1 (curves a and b) corre-
sponds to the eOH stretching vibrations of the silanol
groups [33]. The stretching frequencies of 2880 and
2950 cmꢁ1 are associated with the asymmetric and sym-
metric CeH stretching in the propyl chain, respectively. The
new bands that have appeared at 1455 and 1561 cmꢁ1
(curve a) belong to the aromatic triazine rings in the SiO2/
CCPy sample and confirm formation of melamine-based
dendrimers [27,34]. Also, availability of pyridine groups
was verified by the 3050 cmꢁ1 (CeH aromatic stretching)
and 1657 cmꢁ1 (C]N stretching) bands. These results
approved successful functionalization of SiO2 by amino-
propyl and melamine-bearing pyridine groups. The peak
located at 1657 cmꢁ1, in curve a, refers to metaleligand
coordination [35]. If this peak of curve a be compared
with the most relevant peak in curve b, then it will be
noticed that this peak has shifted to a lower frequency
(from 1657 to 1648 cmꢁ1). Therefore, the peaks of curves a
and b approve successful linkage of organic pyridine li-
gands and coordination of Cu2þ ions to the hybrid silica
support.
Formation of a bond between the silica NPs and the Cu
catalyst can be inferred from thermogravimetric analysis
(TGA) (Fig. 5). TGA curve of the SiO2/CCPy/Cu(OAc)2 catalyst
displays two steps of weight loss above 220 ꢀC. The weight
loss observed at temperatures less than 200 ꢀC is attributed
Particle size and the spherical structure of the silica NPs
were revealed by transmission electron microscopy (TEM)
(Fig. 2). The TEM image of SiO2/CCPy/Cu(OAc)2 shows that
particle size of the synthesized catalyst is in the nanometer
range and the catalyst retains the morphology of the silica
Fig. 8. EPR spectrum of SiO2/CCPy/Cu(OAc)2.
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
7
Table 2
SiO2/CCPy/Cu(OAc)2 catalyzed coupling of aryl halides and amines.a
Entry Aryl halides Amines
Time (h) Yield (%)b Reference
1
2
3
4
5
6
7
8
Ph-I
Ph-Br
Ph-Cl
4-Me-Ph-I
4-Me-Ph-Br Indole
4-Me-Ph-Cl Indole
Ph-I
Ph-Br
Ph-Cl
Ph-I
Ph-Br
Ph-Cl
Ph-I
Ph-Br
Ph-I
Ph-Br
Ph-Cl
Ph-I
Ph-Br
Ph-Cl
Ph-I
Indole
Indole
Indole
Indole
0.5
1
96
96
75
94
92
70
96
80
65
92
85
60
90
80
98
96
90
96
90
75
90
80
[39]
[39]
[39]
[39]
[39]
[39]
[40]
[40]
[40]
[41]
[41]
[41]
[4d]
[4d]
[41]
[41]
[41]
[40]
[40]
[40]
[42]
[42]
12
0.5
1.5
12
1
1H-Imidazole
1H-Imidazole
1H-Imidazole 12
1H-Pyrazole
1H-Pyrazole
1H-Pyrazole
Benzimidazole
Benzimidazole
Benzyl amine 0.5
Benzyl amine 0.5
Benzyl amine
Aniline
Aniline
Aniline
4
9
10
11
12
13
14
15
16
17
18
19
20
21
22
2
4
24
3
5
Scheme 2. SiO2/CCPy/Cu(OAc)2 catalyzed N-arylation of amines.
4
1
2
12
2
to desorption of physisorbed solvent molecules and surface
hydroxyl groups. One the other hand, the organic groups
desorb at temperatures greater than 230 ꢀC. Therefore, the
observed weight loss, that is, about 11.3% from 230 to
500 ꢀC, has resulted from decomposition of the organic
spacer grafted on the silica surface.
Morpholine
Morpholine
Ph-Br
3
a
Reactions were carried out under aerobic conditions in 3 mL of CH3CN,
1.1 mmol aryl halides, 1.0 mmol amines, and 2 mmol Et3N in the presence
of the Cu(II) nanocatalyst (20 mg, 0.7 mol %) at 50 ꢀC.
Nitrogen adsorption isotherms of the as-synthesized
SiO2/CCPy/Cu(OAc)2 catalyst were evaluated to calculate
its porosity and specific surface area, which suggested that
the sample is mostly microporous (Fig. 6a). The obtained
adsorption/desorption isotherms can be related to type I
microporous materials [36]. Moreover, at a relatively low
pressure of nitrogen gas, the slopes of the curves are very
small, which indicate existence of micropores. However,
upon increase in relative pressure, the slopes of the curves
increase dramatically. Also, some loops can be seen in the
curves, which indicate the presence of interparticle meso-
pores [37]. On the basis of the results, surface area and pore
volume of SiO2/CCPy/Cu(OAc)2 are 302.31 m2 gꢁ1 and
b
Isolated yield.
The crystallite structure of the catalyst was investigated
by X-ray diffraction (XRD) spectroscopy. No crystalline
impurity was detected in the wide-angle XRD spectra
(Fig. 7). The broad XRD peaks belong to the silica matrix. In
addition, electron paramagnetic resonance (EPR) spec-
troscopy was used to probe the heterogeneous copper
catalyst. When conducting EPR evaluation on SiO2/CCPy/
Cu(OAc)2, a strong EPR signal was observed (Fig. 8), which
is consistent with the literature [38]. This result implies
that single electrons exists in the catalyst, which means
that the Cu sites are in their Cu(II) status.
0.7 cm3 ꢁ1, respectively, and the catalyst presents a wide
g
distribution of pore size peaking around ca. 100 Å (Fig. 6b).
After structural characterization of SiO2/CCPy/Cu(OAc)2,
as a novel nanocatalyst, its catalytic activity was evaluated
in the Ullmann coupling reaction of amines with aryl ha-
lides under aerobic conditions (Scheme 2). To optimize the
reaction conditions, the reaction between bromobenzene
and indole was chosen as a model reaction (Table 1). Then,
the effects of different parameters on this model reaction
Table 1
Optimization of reaction condition for the N-arylation of indole with
bromobenzene.a
Entry
Catalyst
(mol %)
Base
Solvent
T (ꢀC)
t (h)
Yield
(%)b
1
2
3
4
5
6
7
8
0.5
0.5
0.5
0.5
0.5
0.5
0.3
0.7
0.7
e
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
e
CH3CN
EtOH
Toluene
H2O
CH2Cl2
DMF
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
50
50
50
50
50
50
50
50
50
50
50
50
50
50
25
80
60
4
6
6
6
6
5
5
1
24
24
2
2
2
2
2
1
1
90
55
75
20
35
88
60
96
Trace
0
60
55
75
60
35
96
96
9
10
11
12
13
14
15
16
17
Et3N
K2CO3
Na2CO3
KOH
NaHCO3
Et3N
Et3N
Et3N
0.7
0.7
0.7
0.7
0.7
0.7
0.8
a
Reaction conditions: indole (1.0 mmol), bromobenzene (1.1 mmol),
catalyst, base (2.0 mmol), solvent (3.0 mL).
b
Isolated yield.
Fig. 9. The recycling of the SiO2/CCPy/Cu(OAc)2.
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

8
S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
Fig. 10. SEM (a), TEM (b), and EDX (b) images of recovered SiO2/CCPy/Cu(OAc)2.
were considered to get the best possible combination of
various effects imposed by the solvent, reaction tempera-
ture, base, catalyst loading, and reaction period.
negatively (entry 15, Table 1), meantime temperature in-
creases to 80 ꢀC make no difference (entry 16, Table 1).
In addition, the effect of a catalyst amount was investigated
and increasing its amount from 0.7 to 0.8 mol % afforded
an excellent yield (entry 17; 96%) whereas using 0.3 mol %
of the catalyst decreased reaction yield to 60% (entries
6e8, Table 1). Moreover, it should be emphasized that
N-arylation of indole did not occur in the absence of the
Cu(II) catalyst (entry 10, Table 1). Consequently, it was
decided to continue the catalytic studies using CH3CN sol-
vent, Et3N base, and 0.7 mol % SiO2/CCPy/Cu(OAc)2 at 50 ꢀC
under aerobic conditions, as the optimal conditions (entry 8,
Table 1).
As the first factor, solvent effect was examined by using
toluene, CH3CN, H2O, DMF, CH2Cl2, and ethanol in the pres-
ence of 0.7 mol % Cu(II) and 2 equiv Et3N, at 50 ꢀC (Table 1).
The reaction was considerably influenced by the nature of
the solvent (entries 1e6, Table 1) and the highest yield was
acquired in CH3CN (entry 1; 90%). Then, the impacts of Et3N,
KOH, Na2CO3, NaHCO3, and K2CO3 bases were explored. Et3N
resulted in the highest product yield (entries 1 and 11e14,
Table 1). Furthermore, it was found that the presence of a
baseisnecessarybecausea low yieldcan beobtained without
applying any base (entry 9, Table 1). Also, variation in the
reaction temperature posed a major influence on the model
reaction (entries 8,15, and 16, Table 1). Accordingly, reducing
temperature from 50 to 25 ꢀC impacts product yield
The optimum conditions were set and the catalyst was
applied to a broader range of aryl halides and indole. In
general, the conducted Ullmann coupling reactions be-
tween aryl iodides/bromides and indole were clean and
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
9
gave high yields (entries 1e5, Table 2). However, lower
yields were gained when chloride was used as the leaving
group (entries 3 and 6, Table 2). On the basis of the results,
the following order of reactivity rules this catalytic reac-
tion: ReI > ReBr > ReCl.
experimental simplicity, broad substrate scope, and short
reaction time.
Acknowledgments
To explore activity of the proposed catalyst in a broader
scope, Ullmann-type CeN coupling reaction of other
amines, including imidazole, pyrazole, benzimidazole,
benzyl amine, aniline, and morpholine, with aryl halides
was investigated (entries 7e22, Table 2). The target prod-
ucts were achieved in moderate to high yields. The most
important observation was that the reaction is very selec-
tive and gives N-arylated products, only. However, C-ary-
lation of the amines was never observed.
To determine if the entire SiO2/CCPy/Cu(OAc)2 complex
acts as the catalyst or the Cu(II) complex separates from the
support during the reaction, acts as a homogeneous cata-
lyst, and returns to the support in the end, the reaction
between bromobenzene and indole was terminated after
0.5 h at 60% conversion. Then, the catalyst was filtered and
the reaction was continued with the filtrate for an addi-
tional 0.5 h. After this hot filtration process, the reaction
yield remained constant. Therefore, it can be inferred that
the Cu(II) catalyst has not detached from the SiO2/CCPy
support, at 50 ꢀC, and the reaction process is of heteroge-
neous nature.
Reusability of heterogeneous catalysts is an important
issue, specifically in commercial applications. As a conse-
quence, recyclability of SiO2/CCPy/Cu(OAc)2 was investi-
gated by considering the reaction of bromobenzene with
indole under the optimum reaction conditions. After
completion of the reaction, the reaction mixture was
cooled down to room temperature. Then, EtOAc was added
to the solution and the catalyst mixture was centrifuged,
washed with ethanol and warm water, and reused several
times. The obtained data are displayed in Fig. 9 and imply
that the catalyst can be reused up to five times with
negligible loss of its catalytic activity. Reusability and high
stability of SiO2/CCPy/Cu(OAc)2 should be due to the
chelated pyridine groups on Cu(II) and porosity of the
SiO2support.
We are thankful to Payame Noor University (PNU) and
Kurdistan University of Iran for financial supports.
References
[1] M. Negwer, in: Organic Chemical Drugs and Their Synonyms: An
International Survey, 7th ed., Akademie Verlag, Berlin, 1994.
[2] T. Balle, J. Perregaard, T.M. Ramirez, K.A. Larsen, K.K. Soby,
T. Liljefors, K. Andersen, J. Med. Chem. 46 (2003) 265e283.
[3] (a) J. Arnt, T. Skarsfeldt, Neuropsychopharmacology 18 (1998)
63e101;
(b) K. Sonogashira, in: B.M. Trost (Ed.), Comprehensive Organic
Synthesis, vol. 3, Pergamon Press, New York, NY, USA, 1991.
[4] (a) D.-W. Tan, J.-B. Xie, Q. Li, H.-X. Li, J.-C. Li, H.-Y. Li, J.-P. Lang,
Dalton Trans. 43 (2014) 14061e14071;
(b) D.-W. Tan, H.-X. Li, D.J. Young, J.-P. Lang, Tetrahedron 72 (2016)
4169e4176;
(c) J.-Y. Xue, J.-C. Li, H.-X. Li, H.-Y. Li, J.-P. Lang, Tetrahedron 72
(2016) 7014e7020;
(d) Z.-L. Xu, H.-X. Li, Z.-G. Ren, W.-Y. Du, W.-C. Xu, J.-P. Lang, Tet-
rahedron 67 (2011) 5282e5288;
(e) J. Gao, Z.-G. Ren, J.-P. Lang, Chin. Chem. Lett. 28 (2017)
1087e1092;
(f) J. Shi, F.-L. Li, H.-X. Li, F. Wang, H. Yu, Z.-G. Ren, W.-H. Zhang, J.-
P. Lang, Inorg. Chem. Commun. 46 (2014) 159e162.
[5] (a) F. Monnier, M. Taillefer, Angew. Chem., Int. Ed. 48 (2009)
6954e6971;
(b) M.G. Boswell, F.G. Yeung, C. Wolf, Synlett 23 (2012) 1240e1244;
(c) Y.-C. Teo, F.-F. Yong, G.S. Lim, Tetrahedron Lett. 52 (2011)
7171e7174.
[6] F. Ullmann, Ber. Dtsch. Chem. Ges. 37 (1904) 853e854.
[7] P.C. Unangst, D.T. Connor, S.R. Stabler, R.J. Weikert, J. Heterocycl.
Chem. 24 (1987) 811e816.
[8] Y. Kato, M.M. Conn, J. Rebek, J. Am. Chem. Soc. 116 (1994)
3279e3284.
[9] I.P. Beletskaya, A.V. Cheprakov, Coord. Chem. Rev. 248 (2004)
2337e2364.
[10] J.-P. Corbet, G. Mignani, Chem. Rev. 106 (2006) 2651e2710.
[11] S.V. Ley, A.W. Thomas, Angew. Chem., Int. Ed. 42 (2003) 5400e5449.
[12] R. Xiao, H. Zhao, M. Cai, Tetrahedron 69 (2013) 5444e5450.
[13] J. Yang, P. Li, L. Wang, Tetrahedron 67 (2011) 5543e5549.
[14] T. Miao, L. Wang, Tetrahedron Lett. 48 (2007) 95e98.
[15] R. Xiao, R. Yao, M. Cai, Eur. J. Org Chem. (2012) 4178e4184.
[16] N. Panda, A.K. Jena, S. Mohapatra, S.R. Rout, Tetrahedron Lett. 52
(2011) 1924e1927.
[17] H.-X. Li, W. Zhao, H.-Y. Li, Z.-L. Xu, W.-X. Wang, J.-P. Lang, Chem.
Commun. 49 (2013) 4259e4261.
[18] D. Kundu, S. Bhadra, N. Mukherjee, B. Sreedhar, B.C. Ranu, Chem. Eur
J. 19 (2013) 15759e15768.
[19] P.K. Khatri, S.L. Jain, Tetrahedron Lett. 54 (2013) 2740e2743.
[20] K.H.V. Reddy, G. Satish, K. Ramesh, K. Karnakar, Y.V.D. Nageswar,
Tetrahedron Lett. 53 (2012) 3061e3065.
[21] S.M. Islam, S. Mondal, P. Mondal, A.S. Roy, K. Tuhina, N. Salam,
M. Mobarak, J. Organomet. Chem. 696 (2012) 4264e4274.
[22] J.C. Hicks, C.W. Jones, Langmuir 22 (2006) 2676.
[23] H. Li, J. Lü, Z. Zheng, R. Cao, J. Colloid Interface Sci. 353 (2011) 149.
[24] M. Bhagiyalakshmi, S.D. Park, W.S. Cha, H.T. Jang, Appl. Surf. Sci. 256
(2010) 6660.
[25] A. Shahbazi, H. Younesi, A. Badiei, Chem. Eng. J. 168 (2011) 505.
[26] E.J. Acosta, C.S. Carr, E.E. Simanek, D.F. Shantz, Adv. Mater. 16 (12)
(2004) 985e989.
[27] S. Yoo, J.D. Lunn, S. Gonzalez, J.A. Ristich, E.E. Simanek, D.F. Shantz,
Chem. Mater. 18 (2006) 2935e2942.
[28] S. Yoo, S. Yeu, R.L. Sherman, E.E. Simanek, D.F. Shantz, D.M. Ford, J.
Membr. Sci. 334 (2009) 16e22.
[29] Q. Wang, V.V. Guerrero, A. Ghosh, S. Yeu, J.D. Lunn, D.L.F. Shantz, J.
Catal. 269 (2010) 15e25.
Again, TEM, SEM, and EDX measurements were per-
formed on the SiO2/CCPy/Cu(OAc)2 nanocatalyst, which
was reused five times, to verify that its nanostructure has
not altered. The results demonstrated that the size of the
catalyst is the same as the fresh catalyst and its morphology
and composition have not changed (Fig. 10).
4. Conclusions
This study introduces and prepares a modified silica
supported copper catalyst for efficient N-arylation of N(H)-
heterocycles, aniline, and benzyl amine by aryl halides,
under mild conditions. TEM, FESEM, EDX, TGA, XRD, BET,
and ICP characterization techniques confirmed the struc-
ture of the SiO2/CCPy/Cu(OAc)2 nanocatalyst. Also, the re-
sults revealed that the catalyst can be conveniently
separated by filtration and reused for several more reaction
cycles without any significant changes in its activity. The
results demonstrated the advantages of the synthesized
catalyst, that is, low catalyst loading, high product yield,
[30] H. Veisi, M. Hamelian, S. Hemmati, J. Mol. Catal. A Chem. 395 (2014)
25.
[31] (a) H. Veisi, S. Taheri, S. Hemmati, Green Chem. 18 (2016) 6337;
(b) F. Bonyasi, M. Hekmati, H. Veisi, J. Colloid Interface Sci. 496
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002

10
S. Hemmati et al. / C. R. Chimie xxx (2018) 1e10
(2017) 177;
[32] G. Socrates, Infrared and Raman Characteristic Group Frequencies:
Tables and Charts, 3rd ed., John Wiley & Sons, 2004.
[33] Y. Jiang, Q. Gao, H. Yu, Y. Chen, F. Deng, Microporous Mesoporous
Mater. 103 (2007) 316.
[34] Z. Liang, B. Fadhel, C.J. Schneider, A.L. Chaffee, Microporous Meso-
porous Mater. 111 (2008) 536.
[35] J. Guerra, M.A. Herrero, Nanoscale 2 (2010) 1390.
[36] M. Sasidharan, A. Bhaumik, Phys. Chem. Chem. Phys. 13 (2011)
16282e16294.
(c) M. Pirhayati, H. Veisi, A. Kakanejadifard, RSC Adv. 6 (2016)
27252;
(d) B. Abbas Khakiani, K. Pourshamsian, H. Veisi, Appl. Organomet.
Chem. 29 (2015) 259;
(e) H. Veisi, A. Sedrpoushan, S. Hemmati, Appl. Organomet. Chem.
29 (2015) 825;
(f) H. Veisi, A. Rashtiani, V. Barjasteh, Appl. Organomet. Chem. 30
(2016) 231;
(g) B. Maleki, D. Azarifar, R. Ghorbani-Vaghei, H. Veisi, S.F. Hojati,
M. Gholizadeh, H. Salehabadi, M. Khodaverdian Moghadam, Mon-
atsh. Chem. 140 (2009) 1485;
(h) H. Veisi, A.R. Faraji, S. Hemmati, A. Gil, Appl. Organomet. Chem.
29 (2015) 517;
(i) R. Ghorbani-Vaghei, M. Chegini, H. Veisi, M. Karimi-Tabar, Tet-
rahedron Lett. 50 (2009) 1861;
(j) S. Lebaschi, M. Hekmati, H. Veisi, J. Colloid Interface Sci. 485
(2017) 223;
[37] J. Yuan, T. Zhou, H. Pu, J. Phys. Chem. Solids 71 (2010) 1013e1019.
[38] J. Mondal, A. Modak, A. Dutta, S. Basu, S.N. Jha, D. Bhattacharyya,
A. Bhaumik, Chem. Commun. 48 (2012) 8000e8002.
[39] Y.X. Xie, S.F. Pi, J. Wang, D.L. Yin, J.H. Li, J. Org. Chem. 71 (2006) 8324.
[40] Y.-Z. Huang, J. Gao, H. Ma, H. Miao, J. Xu, Tetrahedron Lett. 49 (2008)
948.
[41] M.L. Kantam, M. Roy, S. Roy, B. Sreedhar, R.L. De, Catal. Commun. 9
(2008) 2226.
[42] C. Zhang, Z. Zhan, M. Lei, L. Hu, Tetrahedron 70 (2014) 8817.
(k) H. Veisi, D. Kordestani, S. Sajjadifar, M. Hamelian, Iran. Chem.
Commun. 2 (2014) 27.
Please cite this article in press as: S. Hemmati, et al., SiO2-functionalized melamine-pyridine groupesupported Cu(OAc)2 as an
efficient heterogeneous and recyclable nanocatalyst for the N-arylation of amines through Ullmann coupling reactions, Comptes
Rendus Chimie (2018), https://doi.org/10.1016/j.crci.2018.03.002