Cu-grafted mesoporous organic polymer: A new recyclable nanocatalyst for multi-component, N-arylation and S-arylation reactions

Article abstract of DOI:10.1039/c3cy00600j

A new mesoporous Cu-MPTA-1 nanocatalyst has been synthesized via a simple and facile in situ radical polymerization of triallylamine in the presence of an organic-organic self-assembly of anionic surfactant SDS, followed by grafting of Cu(ii) at room temperature under an inert atmosphere. This nanomaterial has been characterized by elemental analysis, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA), N₂ adsorption-desorption studies, X-ray photoelectron spectroscopy (XPS) and EPR spectroscopy. Cu-MPTA-1 acts as an efficient heterogeneous nanocatalyst exhibiting a high catalytic activity for N-arylation and S-arylation reactions using water as a green solvent and also exhibits an excellent catalytic activity for the one-pot synthesis of propargylamines via a three component coupling of an alkyne, an amine and an aldehyde at room temperature. Moreover, the catalyst is easily recoverable and can be reused six times without an appreciable loss of catalytic activity in the three component coupling reaction. The highly dispersed Cu(ii) sites in the Cu-grafted mesoporous polymer could be responsible for the observed high activities of the Cu-MPTA-1 catalyst in the coupling reactions. No evidence of leached Cu from the catalyst during the course of the reaction has been observed, suggesting true heterogeneity in the catalytic process. The Royal Society of Chemistry.

Full text of DOI:10.1039/c3cy00600j

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Cu-grafted mesoporous organic polymer: A new recyclable nanocatalyst
for multi-component, N-arylation and S-arylation reactions
Noor Salam,a Sudipta K. Kundu,b Anupam Singha Roy,a Paramita Mondal,a
Susmita Roy, a Asim Bhaumikb,* and Sk. Manirul Islama,*
aDepartment of Chemistry, University of Kalyani, Kalyani, Nadia, 741235, W.B., India.
bDepartment of Material Science, Indian Association for the Cultivation of Science,
Kolkata - 700032, India
Abstract
A new mesoporous CuꢀMPTAꢀ1 nanocatalyst has been synthesized via simple and
facile inꢀsitu radical polymerization of triallylamine in the presence of organic–organic
selfꢀassembly of anionic surfactant SDS, followed by grafting of Cu(II) at room
temperature under inert atmosphere. This nanomaterial has been characterized by
elemental analysis, powder Xꢀray diffraction (XRD), transmission electron microscopy
(TEM), Fourier transform infrared spectroscopy (FTꢀIR), UVꢀvis diffuse reflectance
spectroscopy (DRS), thermogravimetric analysis (TGA), N2 adsorption–desorption
studies, Xꢀray photoelectron spectroscopy (XPS) and EPR spectroscopy. The CuꢀMPTAꢀ1
act as an efficient heterogeneous nanocatalyst exhibiting high catalytic activity for the Nꢀ
arylation and Sꢀarylation reactions using water as green solvent and also exhibited
excellent catalytic activity for the oneꢀpot synthesis of propargylamines via a three
component coupling of an alkyne, an amine and an aldehyde at room temperature.
Moreover, the catalyst is easily recoverable and can be reused for six times without
appreciable loss of catalytic activity in the three component coupling reaction. So, the
highly dispersed Cu(II) sites in the Cuꢀgrafted mesoporous polymer could be responsible
for the observed high activities of the CuꢀMPTAꢀ1 catalyst in the coupling reactions. No
1

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evidence of leached Cu from the catalyst during the course of reaction has been observed,
suggesting true heterogeneity in the catalytic process.
Keywords: Mesoporous material, polyꢀtriallylamine, Cuꢀgrafting, Nꢀarylation, Sꢀarylation,
propargylamines.
*Authors to whom correspondence should be addressed.
Dr. Sk. Manirul Islam, Department of Chemistry, University of Kalyani, Kalyani, Nadia,
741235, W.B., India. Phone: +91ꢀ33ꢀ2582ꢀ8750, Fax: +91ꢀ33ꢀ2582ꢀ8282, eꢀmail:
manir65@rediffmail.com
Prof. Asim Bhaumik, Department of Material Science, Indian Association for the
Cultivation of Science, Kolkataꢀ700032, India, Phone: +91ꢀ33ꢀ2473ꢀ4971; Fax: +91ꢀ33ꢀ
2473ꢀ2805, eꢀmail: msab@iacs.res.in
Introduction
Catalyst plays a significant role for the efficient synthesis of several value added
fine chemicals. In this context it is pertinent to mention that nanomaterials have huge
potential to be employed as catalyst for improving efficiency, selectivity and yield of the
catalytic processes. Over a decade of extensive research, nanomaterials have emerged as
one of the most promising catalysts because of their unique surface properties, which
are largely different from their corresponding bulk materials.1ꢀ2 Due to their huge
difference with bulk, nanomaterials have found extensive utility in numerous frontline
areas such as electronic, optical, catalytic, coating, medical, sensor applications, etc.3 The
higher surface to volume ratio in the nanocatalyst signifies large number of active sites
participating in the reaction. Further, different types of organic transformations catalyzed
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by selfꢀassembled nanoparticles are gaining increasing importance in recent times.4
Currently Cuꢀnanoparticles have attracted a considerable awareness in the field of
catalysis5ꢀ6 and as well as in the energy conversions.7 From the past one decade it is
believed that copper, in the nanoform provides fascinating catalytic activity in various
organic transformations. Due to the low cost of Cu compared to Au, Ag, Pd, Pt, Ru and
Rh, it has attracted particular attention as catalyst for various organic reactions.8ꢀ9 In this
context, mesoporous organic polymers carrying the reactive functional groups at the
surface of the mesopores10ꢀ14 can provide an ideal tethering agent for the active metals to
bind at its surface strongly. Due to extensive crossꢀlinking, polymeric materials are highly
desirable material for long term stabilization of the entrapped metal centres, which reduces
the possibility of leaching of the metal under reaction conditions.15 Furthermore, Cuꢀ
grafted functionalized heterogeneous catalysts provide the advantages of simplified
isolation of the product, easy recovery, enhanced stability and recyclability of the
catalysts, which is highly desirable to address the industrial and environmental concerns
over their respective homogeneous counterpart.
Multiꢀcomponent reactions in oneꢀpot syntheses play a significant role in modern
synthetic chemistry. Threeꢀcomponent coupling of an aldehyde, amine and alkyne (A3ꢀ
coupling) is one of the best examples and has received much attention in recent years.
There are several reports on highly efficient threeꢀcomponent couplings of aldehyde,
alkyne, and amine (A3ꢀcoupling) in organic media, ionic liquid, or under solventꢀfree
condition catalyzed by metallic copper, silver, gold, iron, nickel, iridium and other
catalysts via catalytic C–H activation to afford various propargylamines.16 The resultant
propargylamines are versatile intermediates for organic synthesis17 and important
structural elements of natural products, making agrochemicals and potential drug
molecules.18
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In this context it is also pertinent to mention that the transition metal/metal
complex catalyzed formation of carbon–carbon and carbonꢀheteroatom bonds has emerged
as a versatile and powerful tool in chemical synthesis. In particular, the Nꢀarylation of
nitrogen nucleophiles with aryl halides and the Sꢀarylation of thiols with aryl halides have
witnessed considerable importance due to the versatility of the products, which are
prevalent in compounds of biological, pharmaceutical, chemical and materials interest.
Since its discovery, the copperꢀmediated Ullmann coupling reaction19 is still the straight
forward method to prepare the requisite carbon–heteroatom bonds. Ullmann
condensations have proven to be a convenient efficient and recyclable catalytic method for
the syntheses of Nꢀ and Sꢀ arylated compounds. Heterogeneous Cuꢀcatalysts that have
been used for Nꢀarylation and Sꢀ arylation in different organic solvents would be
environmentally acceptable if the reaction can be carried out in water. Today a
considerable effort has been devoted to perform organic reactions in aqueous medium
replacing the hazardous organic solvents, because of its environmental acceptability,
abundance and low cost.20–21
Very recently we have reported the synthesis of a mesoporous polyꢀtriallylamine
(MPTAꢀ1) using an anionic surfactant sodium lauryl sulfate as template.22 Surface of this
mesoporous polymer contains Nꢀdonor sites, which can tether with Cuꢀsites strongly.
Herein we report, the strategy for the synthesis of a new Cuꢀgrafted nanomaterial Cu–
MPTAꢀ1 and its excellent catalytic activity in threeꢀcomponent couplings of aldehyde,
alkyne and amine (A3 coupling), Nꢀarylation reaction of aryl halides with imidazole and
also Sꢀarylation reaction of aryl halides with aryl thiols in aqueous medium.
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Experimental Section
Materials
Triallylamine (TAA) was obtained from Sigma Aldrich. N,N,N’,N’ꢀ
tetramethylenediamine (TEMED) and ammonium persulfate (APS) were obtained from
Loba Chemie, India. Sodium lauryl sulfate (SDS) was purchased from Loba Chemie
and used as structureꢀdirecting agent. Cupric sulphate pentahydrate (CuSO4.5H2O),
NaOH and hydrazine hydrate (N2H4.H2O) was purchased from Merck, India. All other
reagents and substrates were also purchased from Merck, India.
Physical measurements
Powder Xꢀray diffraction (XRD) patterns of different samples were analyzed with
a Bruker D8 Advance Xꢀray diffractometer using Ni–filtered Cu Kα (λ=0.15406 nm)
radiation. Transmission electron microscopy (TEM) images of the mesoporous polymer
were obtained using a JEOL JEM 2010 transmission electron microscope operating at
200 kV. Thermogravimetric analysis (TGA) was carried out using a Mettler Toledo
TGA/DTA 851e. UVꢀVis spectra were taken using a Shimadzu UVꢀ2401PC doubled
beam spectrophotometer having an integrating sphere attachment for solid samples.
Nitrogen adsorption–desorption experiments were carried out using a Bel Japan Inc.
BelsorpꢀHP surface area analyzer at 77 K. Prior to gas adsorption, the sample was
degassed for 4 h at 393 K under high vacuum conditions. X−ray photoluminescence
spectroscopy (XPS) measurements were performed on a Omicron nanotech operated at
15 kV and 20 mA current using monochromatic Al Kα X−ray source. EPR
measurement was performed on a Bruker EMX EPR spectrometer at Xꢀband frequency
(9.46 GHz) at liquid nitrogen temperature (77 K). The reaction products were
quantified by using a Varian 3400 gas chromatographic instrument equipped with a
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30m CPꢀSIL8CB capillary column and a flame ionization detector and identified by
Trace DSQ II GCꢀMS equipped with a 60m TRꢀ50MS capillary column.
Preparation of the catalyst
Synthesis of mesoporous polytriallylamine MPTA-1
MPTAꢀ1 was synthesized through the aqueousꢀphase polymerization of
triallylamine under hydrothermal condition by using APS as initiator (Scheme 1).22 In a
typical synthesis 2.35 g (0.00814 mol) of SDS was dissolved in 40 ml of water with
constant stirring followed by the addition of 2.23 g (0.01628 mol) of TAA. Then 0.94 g
(0.00814 mol) of TEMED was added in this mixture and conc. HCl (12N) was also
added dropwise to obtain a clear solution. This helps the protonation of the Nꢀatoms of
the triallylamine molecules, which facilitates the ionic interaction with the sulfonate
group of the SDS molecules. The pH of the gel was maintained at ca 7.0. Finally, 7.42
g (0.03256 mol) of APS dissolved in 10 ml of water was added quickly into the
solution with vigorous stirring and a white precipitated appeared immediately. The
resultant slurry was stirred for another 1 h and then autoclaved at 348 K for 3 days
without stirring. Final pH of the synthesis gel was ca 4.0ꢀ5.0. The resultant precipitate
was filtered and washed with deionized water, yielding mesoporous polymer MPTAꢀ1.
Scheme 1. Schematic diagram showing the formation of mesoporous polymer MPTAꢀ1
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Synthesis of Cu-MPTA-1 nanocatalyst
In typical synthesis, 250 mg mesoporous polytriallylamine MPTAꢀ1 was dissolved 10
ml double distilled water with stirred for 2 h in 100 ml RB flask. In aqueous solution of
MPTAꢀ1 0.2 mmol CuSO4 was added and again stirred for 2 h. It was followed by the dropꢀ
wise addition of NaOH solution (1.0 M, 1.0 ml) with constant stirring till the solution attained
the desired pH. A deep blue solution appeared. One interesting observation to note here is
that as the pH was increased, the colour of the solution changed from greenish blue to dark
blue. Then, 4 mmol N2H4.H2O in 6 ml H2O was added dropꢀwise with constant stirring under
the nitrogen atmosphere. In the presence of nitrogen atmosphere, the resulting solution was
allowed to stir for overnight at room temperature and then heated at 80 0C for 3 h and formed
brick red colour solution which indicated the grafting Cuꢀspecies at the surface of the porous
polymer. Then the precipitates were collected by centrifugation and washed with double
distilled water for several times, yielding mesoporous CuꢀMPTAꢀ1 nanocatalyst.
One-pot synthesis of propargylamines catalyzed by Cu-MPTA-1 nanocatalyst
In a 50 ml RB flask, cyclohexanecarboxaldehyde (0.112 g, 1.0 mmol ), phenyl
acetylene (0.112 g, 1.1 mmol ), piperidine (0.094 g, 1.1 mmol ) was taken in CH2Cl2 (10 ml)
was added. In this mixture 0.05 g CuꢀMPTAꢀ1 catalyst was added under stirring. Then the
reaction was continued under stirring at room temperature for 24 h. The reaction mixtures
were collected at different time intervals and identified by GCꢀMS and quantified by GC.
After the completion of the reaction, the catalyst was filtered off and washed with water
followed by acetone and dried in oven. The filtrate was extracted three times with ethyl
acetate (3 x 20 ml) and the combined organic layers were dried with anhydrous Na2SO4 by
vacuum. The filtrate was concentrated and the resulting residue was purified by column
chromatography on silica gel to provide the desired product
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General Procedure for N-arylation of N–H heterocycles with aryl halides catalyzed by
Cu-MPTA-1 nanocatalyst
In an oven dried 50 ml RB flask, CuꢀMPTAꢀ1 catalyst (0.05 g), aryl halide (1 mmol),
imidazole (1.2 mmol), KOH (2 mmol), and 10 ml water were stirred under nitrogen
0
atmosphere at 120 C. The reaction mixtures were collected at different time interval and
identified by GCꢀMS and quantified by GC analysis. After the completion of the reaction, the
catalyst was filtered off and washed with water followed by acetone and dried in oven. The
filtrate was extracted three times with ethyl acetate (3 x 20 ml) and the combined organic
layers were dried with anhydrous Na2SO4 by vacuum. The filtrate was concentrated and the
resulting residue was purified by column chromatography on silica gel to provide the desired
product
General procedure for aryl-sulfur coupling reaction of thiophenol with aryl halides
catalyzed by Cu-MPTA-1 nanocatalyst
Cuꢀgrafted mesoporous polymer CuꢀMPTAꢀ1 was used as a catalyst for the arylꢀ
sulfur coupling of thiophenol with aryl halides. To a solution of halides (1 mmol) and
thiophenol (121 mg, 1.1 mmol) in 3 ml of H2O, K2CO3 (276 mg, 2 mmol) and Cuꢀgrafted
catalyst (0.05 g) were added. At the end of specified time, the reaction mixture was filtered
and the filtrate was analyzed by using a Varian 3400 gas chromatograph equipped with a 30
m CPꢀSIL8CB capillary column and a flame ionization detector. Identification of the
products was also confirmed using GCꢀMS. After the completion of the reaction, the catalyst
was filtered off and washed with water followed by acetone and dried in oven. The filtrate
was extracted three times with ethyl acetate (3 x 20 ml) and the combined organic layers were
dried with anhydrous Na2SO4 by vacuum. The filtrate was concentrated and the resulting
residue was purified by column chromatography on silica gel to provide the desired product
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Results and discussion
Characterization of Cu-MPTA-1 material
X-ray diffraction: Small angle powder XRD pattern of the sample CuꢀMPTAꢀ1 is shown in
Figure 1. For the sample a single and broad diffraction peak is obtained in the small angle 2θ
value of 2.5 degree, corresponding to the presence of a disordered mesostructure in the
material and absence of long range ordering in the material. This result agrees well with the
small angle powder XRD pattern of the parent MPTAꢀ1.22 The d spacing for the CuꢀMPTAꢀ1
sample was 3.53 nm, moderately decreased from parent MPTAꢀ1 due to Cuꢀgrafting.
Figure 1. Small angle Powder XRD patterns of CuꢀMPTAꢀ1 material
Electron microscopy analysis: In Figure 2 TEM images of the CuꢀMPTAꢀ1 samples are
shown. In this Figure dark spots could be attributed to the presence of grafted Cu+2 sites and
from these images it is clear that these Cuꢀnanoclusters are uniformly distributed throughout
the specimen grid. The FFT diffractogram of a selected area of the grid is shown in the inset
of the Figure 2C. Diffraction spots in this FFT pattern suggested crystalline feature of the
copper species23 bound at the surface of CuꢀMPTAꢀ1.
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Figure 2. TEM images of the CuꢀMPTAꢀ1 material
UV-visible spectroscopic study: The UVꢀVis absorption spectrum of the CuꢀMPTAꢀ1
displayed absorption peak maxima at 236 nm and a shoulder at ca. 700 nm (Figure 3).
Former peak could be attributed due to the chromophoric organic functionality of the
polymer matrix whereas, weak absorption at 700 nm could be assigned to the d-d transition,
which is a characteristic absorption band of Cu(II) in metal complexes.24ꢀ25
2.0
1.5
1.0
0.5
0.0
200 300 400 500 600 700 800 900
Wavelength (nm)
Figure 3. DRSꢀUVꢀvisible absorption spectra of CuꢀMPTAꢀ1 material.
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Thermal analysis: The quantitative determination of the organic content and the framework
stability of the CuꢀMPTAꢀ1 samples are obtained from the thermogravimetric (TG) and
differential thermal analysis (DTA) under N2 flow. TGAꢀDTA curve of CuꢀMPTAꢀ1
materials are shown in Figure 4. The TGA of this material showed the first weight loss below
0
100 C due to desorption of physisorbed water. This was followed by a gradual decrease in
the weight after 200 0C. Thus this thermal analysis data suggested that CuꢀMPTAꢀ1 sample is
stable up to 200 0C.
100
80
60
40
20
0
60
50
40
30
20
10
0
TGA
DTA
-10
-20
100
200
300
400
500
600
Temperature (0C)
Figure 4. TGA plot and (b) DTA plot of CuꢀMPTAꢀ1 material.
N2 adsorption/desorption: The surface area and porosity of CuꢀMPTAꢀ1 material is
determined by N2 adsorption/desorption at 77 K. N2 adsorption/desorption isotherm is shown
in Figure 5. This isotherm shows the type IV adsorption isotherm having hysteresis
characteristics of mesoporous materials.26 The BET surface areas of templateꢀfree MPTAꢀ1
and CuꢀMPTAꢀ1 are 134 m2gꢀ1 and 35 m2gꢀ1. The total pore volume of CuꢀMPTAꢀ1 material
is 0.0427 ccgꢀ1. The pore size distribution of the sample has been estimated from these
isotherms by using the nonꢀlocal density functional theory (NLDFT) and this is shown in the
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inset of the Figure 5. As seen from the plot that the maximum in the pore widths are centred
at 1.43 nm and 4.16 nm. Peak at 4.16 nm could be attributed to interparticle pores, whereas
considerable decrease in the mesopore size to 1.43 nm and surface area to 35 m2gꢀ1 in Cuꢀ
MPTAꢀ1 visꢀàꢀvis MPTAꢀ1 suggests that Cuꢀsites are anchored in the inner surface of the
pores.
Figure 5. N2 adsorption/desorption isotherm of CuꢀMPTAꢀ1 and pore size distribution curve
is shown in the inset.
XPS analysis: In Figure 6 the XPS profile of CuꢀMPTAꢀ1 material is shown. The XPS data
shows peak centred at 937.6, 530.0 and 287.0 eV. These binding energies correspond to
Cu2p3/2, O1s and C1s, respectively.27 In Figure 2, there is only one peak for O1s. The peak at
529.7 eV has been assigned in the literature for the O2ꢀ bonded to metal in the oxide
frameworks.27a Further, the single peak confirms that there are no free surface hydroxyl
groups on the catalyst. Figure shows the XPS spectrum of the Cu2p region for the resultant
Cuꢀnanocatalyst. The binding energy of the Cu2p3/2 peak at 937.6 eV and indicates that
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copper species are only present as Cu(II) state in the form of Cuꢀnanoclusters in mesoporous
CuꢀMPTATꢀ1.27bꢀ27d
.
Figure 6. XPS data of CuꢀMPTAꢀ1
Electron paramagnetic resonance study: In Figure 7 the EPR spectrum of the CuꢀMPTAꢀ1
in solid state at room temperature (300 K) is shown. It provides information on the nature of
the metal ion environment in the Cuꢀgrafted mesoporous polymer. It shows strong axially
symmetric signal,28 which could be attributed to the highly dispersed or isolated Cu(II)
species interacting with the porous polymeric support. In the low field region parallel
component due to hyperfine interaction between unpaired electron and nuclear spin of copper
(I= 3/2) is observed, whereas in high field region perpendicular component (g┴ = 1.99)
remains unresolved. Further, the EPR spectrum of CuꢀMPTAꢀ1 reveals the following
parameters: g║ = 2.24 and A║ = 0.018 cmꢀ1
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Figure 7. EPR spectrum of CuꢀMPTAꢀ1 material.
Catalytic activity
Since metal ions supported over mesoporous systems exhibit high catalytic activity in
a wide range of the industrially important catalytic reactions and these are extensively
studied, we decided to investigate the catalytic activity of the mesoporous polymer Cuꢀ
MPTAꢀ1 in the CꢀN and CꢀS coupling reaction in water as solvent and A3 coupling reaction
at room temperature.
N-arylation reaction of imidazole with aryl halides catalyzed by Cu-MPTA-1
The N ꢀarylation reaction is a convenient method for the C–N bond formation between N–H
heterocycles with aryl halides. To test the applicability of the copper catalyst, we examined the Nꢀ
arylation reaction between N–H heterocycles with various aryl halides and imidazole in water as
solvent using KOH at 1200 C as model reaction (Scheme 2).
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X
N
N
CuꢀMPTAꢀ1
N
H2O, KOH, 120oC
N
H
R1
R1
X=I, Br; R1 = H, Me, OMe, COMe, NO2
Scheme 2. NꢀArylation of imidazoles with different aryl halides.
Several bases were screened using the copper catalyst for the Nꢀarylation of imidazole with
0
iodobenzene in water as solvent at 120 C, and the results are summarized in Table 1. A
variety of bases (i.e., K2CO3, K3PO4, Cs2CO3, LiOH, NaOH, and KOH) was screened. As
seen in Table 1, we noticed that the base was necessary in this coupling reaction, and no
product was obtained in the absence of the base (Table 1, entry 7). Among the various bases,
obviously, strong bases exhibited higher catalytic ability than carbonate (Table 1, entries 1–
6). The organic base like Et3N was almost inactive (entry 6). Longer reaction time would
bring some byꢀproducts. Nevertheless, we have got little product when the coupling reaction
was performed at 80 0C for 12 h (Table 1, entry 8). From the above discussions, it can be seen
that the best yield was obtained in the Nꢀarylation reaction of imidazole with iodobenzene by
using KOH in water at 120 0C for 12 h.
Table 1. N-arylation reaction using mesoporous Cu-MPTA-1 nanocatalyst at various
bases a
Entry
Base
Solvent
H2O
Yield (%)b
1
2
3
KOH
K2CO3
K2PO4
91
50
58
H2O
H2O
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4
NaOH
Cs2CO3
Et3N
ꢀ
H2O
H2O
H2O
H2O
H2O
80
42
12
0
5
6
7
8c
KOH
trace
aReaction conditions: Cuꢀcatalyst (0.05 g), 1 mmol of iodobenzene, 1.2 mmol of imidazole,
b
2 mmol base, water (10 ml), N2 atm. Yield determined by GC and GCMS analysis. c At 80
0C for 12 h.
With optimized conditions now in hand, we explored the scope of this process with
respect to aryl iodide structure, and the results are summarized in Table 2. To our delight, the
Nꢀarylation of imidazole is smoothly performed with the extensive pool of aryl iodides to
afford the corresponding products in good to excellent yields. It was observed that iodoarenes
with electronꢀwithdrawing groups (Table 2, entries 4, 5) reacted at a faster rate than iodoꢀ
arenes with electronꢀdonating groups (Table 2, entries 2, 3). Sterically hindered 2ꢀiodotoluene
took longer duration to afford a good yield (Table 2, entry 6). Extension of this arylation
process with aryl bromides yielded interesting results. The use of bromobenzene in place of
iodobenzene afforded lower conversion with 70% yield (entry 7) with longer reaction time.
Bromobenzene with an electronꢀdonating group gave lower yield (entry 8), whereas
bromobenzene with an electronꢀwithdrawing group gave excellent yield of product (entry 9).
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Table 2: N-Arylation of imidazoles with different aryl halides using mesoporous Cu-
MPTA-1 nanocatalysta
Entry
Aryl halides Productsb
Time (h)
Yield
(%)c
91
N
I
1
12
N
H
N
N
I
2
3
15
18
80
78
N
N
Me
Me
I
OMe
OMe
I
N
N
4
5
12
12
92
93
N
N
COMe
COMe
I
NO2
NO2
I
N
N
6
7
15
18
60
70
Me
Me
N
N
Br
H
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N
Br
8
9
20
30
73
N
OMe
Me
Br
N
18
N
NO2
NO2
aReaction conditions: CuꢀMPTAꢀ1 nanocatalyst (0.05 g), aryl halide (1 mmol), imidazole (1.2
0
b
mmol), KOH (2 mmol), H2O (10 ml), 120 C, N2 atm. Products were identified by
comparison of their 1HꢀNMR spectral data those reported in the literature. cIsolated yield
Aryl-sulfur coupling reaction of Thiophenol with Aryl iodide catalyzed by Cu-MPTA-1
Diaryl sulfides formed via C–S crossꢀcoupling reaction from aryl halides bearing
different nucleophilic phenyl rings have significant roles in biological, pharmaceutical,
and material research. Here, we have explored the catalytic efficiency of the CuꢀMPTAꢀ1
nanocatalyst in C–S crossꢀcoupling reactions of thiophenol with aryl iodide in green
solvent water using K2CO3 as a mild base at 80 0C (Scheme 3).
I
SH
S
H2O, K2CO3
CuꢀMPTAꢀ1, 80oC
R1
R2
R1
R2
R1= H, CH3, OCH3, NO2, Br, Cl
R2= H, OMe, Cl
Scheme 3. General procedure for arylꢀsulfur coupling reaction of Thiophenol with Aryl
iodide
18

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To optimize the reaction conditions, a series of bases K2CO3, Cs2CO3, KOH, Et3N
and pyridine were screened on the C–S crossꢀcoupling reaction (Table 3). In a
comparison of the efficiency of a variety of inorganic (Table 3, entries 1–3) and organic
bases (entries 4 and 5) were used to afford aryl sulfides. Potassium hydroxide was
found to act as an poor base, whereas Cs2CO3 was effective to some extent and other
bases were not at all effective. Despite that the respective sulfide could be detected
employing the related bases screened, K2CO3 showed the best performance, furnishing
the desired product in quantitative yield (entry 1). Noteworthy is that in the absence of
a base no formation of product was observed (Table 3, entry 7). In view of the extreme
moistureꢀsensitivity and expense of Cs2CO3, cheap and stable K2CO3 was the preferred
base for use in the CuꢀMPTAꢀ1 catalyzed coupling reaction. As a result, K2CO3 was
selected as the optimum base.
Table 3. The effect of base on the mesoporous Cu-MPTA-1 catalyzed C–S coupling reactions a
.
Entry
Base
Yield (%)b
1
2
3
4
5
6
K2CO3
Cs2CO3
KOH
95
76
52
40
10
0
Et3N
Pyridine
None
aReaction conditions: iodobenzene (1 mmol), thiophenol (1.1 mmol) , water (3 ml), base (2
b
mmol), Cuꢀ MPTAꢀ1 (0.05g), temperature (800C), Time (12h). Yields were determined by
GC and GCMS analysis.
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Using the optimized conditions, the present reaction was further expanded to a
broader range of aryl thiols and aryl iodides in order to evaluate the scope and limitations of
the method, as outlined in Table 4. In general, the reactions are very clean and high yielding.
Aryl iodides with an electron withdrawing group were more reactive in comparison to those
with an electron donating group. Thus, the reaction of aryl iodides with methyl and methoxy
substituents gave the corresponding C–S crossꢀcoupled products in 72ꢀ80% yield, while the
reaction of aryl iodides with nitro substituent completed in 87% yield. The effect of different
halogen substituents in the coupling of thiophenol is also shown in the Table 4.The order of
reactivity of different halobenzenes are iodobenzene > bromobenzene > chlorobenzene,
which is observed in our case.
Table 4. C–S coupling reactions catalyzed by mesoporous Cu-MPTA-1 nanocatalysta.
Entry
ArI
ArSH
Productsb
Yield (%)c
I
SH
S
1
95
I
SH
S
2
3
80
72
H3C
CH3
I
S
SH
H3CO
OCH3
I
SH
S
4
87
O2N
NO2
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I
SH
S
5
6
90
43
Br
Cl
Br
I
SH
S
Cl
I
SH
SH
SH
SH
SH
NH2
7
85
71
56
23
69
S
S
NH2
I
8
N
N
Br
S
S
S
9
Cl
11
12
I
OMe
OMe
SH
I
S
13
55
Cl
Cl
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aReaction conditions: aryl iodides (1 mmol), thiophenol (1.1 mmol) , water (3 ml), K2CO3 (2
0
b
mmol) and Cuꢀ nanocatalyst (0.05g), temperature (80 C), Time (12 h). Products were
1
identified by comparison of their HꢀNMR spectral data those reported in the literature.
cIsolated yield
Catalytic activity of mesoporous Cu-MPTA-1 nanocatalyst for ‘one-pot’ A3 coupling
reaction
Herein, we have explored the catalytic efficiency of the CuꢀMPTAꢀ1 nanocatalyst in
the synthesis of propargylamines by the oneꢀpot threeꢀcomponent coupling reaction of
aldehydes, amines and alkynes (A3ꢀcoupling) at room temperature. Propargylicamines,
products of the A3ꢀcoupling, are important synthetic intermediates for potential therapeutic
agents and natural products. As a comparison, we used CuꢀMPTAꢀ1 as a nanocatalyst to test
the catalytic performance of this nanomaterial for A3ꢀcoupling reaction. The effect of
mesoporous CuꢀMPTAꢀ1 nanocatalyst on their catalytic activity for the A3ꢀcoupling reaction
was investigated using cyclohexanecarboxaldehyde, phenylacetylene and piperidine as a
model reaction (Scheme 4).
CHO
CuꢀMPTAꢀ1
Ph
N
H
CH2Cl2, RT
N
H
Ph
Scheme 4. Synthesis of A3ꢀcoupling reaction
In order to optimize the conditions of the A3 reaction, the effect of solvent was surveyed
(Table 5, entries 4 – 10). Among the solvents tested in Table 5, CH2Cl2, CH3CN, DMF, THF
and solventꢀfree conditions all gave excellent yields of 75 – 93% (Table 5, entries 1ꢀ4 and 9).
However, solvents such as CH3OH, toluene, H2O and AcOEt were not suitable for the
22

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reaction and no satisfactory yields were obtained (Table 5, entries 5 – 8). When the amount of
the catalyst loading was increased to 0.5 mol%, there was no obvious increase in the yield of
the reaction (Table 5, entry 10), and the reaction did not occur under catalystꢀfree conditions
(Table 5, entry 11). Thus, the optimized conditions for the A3 reaction are 0.1 mo l% catalyst
and CH2Cl2 as solvent at room temperature. It noteworthy that the high yields of the A3
reaction obtained only with a catalyst loading of 0.1 mo l% are very competitive to other
catalyst systems.
Table 5. The effects of various variables in the three-component coupling of cyclohexane
carbaldehyde, piperidine and phenylacetylene catalyzed by the mesoporous Cu-MPTA-
1 nanocatalysta
Entry
Catalyst loading Solvent
(%)
Yield (%)b
1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.5
ꢀ
CH2Cl2
CH3CN
DMF
93
85
80
81
10
58
50
60
75
93
ꢀ
2
3
4
THF
5
CH3OH
Toluene
H2O
6
7
8
AcOEt
Neat
9
10
11
CH2Cl2
CH2Cl2
aReaction conditions : cyclohexanecarboxaldehyde (1.0 mmol ), phenylacetylene (1.1 mmol),
piperidine (1.1 mmol ), nanocatalyst, CH2Cl2(1 mL), room temperature for 24 h. bGC yield
based on cyclohexanecarboxaldehyde.
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To expand the scope of this A3ꢀcoupling, various aldehydes, alkynes and amines were
used as substrates under the optimized reaction conditions. The results are summarized in
Table 6. From these results we found that the conditions were equally applicable to the
coupling a variety of aromatic aldehydes including heterocyclic aldehydes with either
piperidine, morpholine or pyrrolidine utilizing phenylacetylene, giving the corresponding
propargylamines in high yields in room temperature.
Under
the
optimized
conditions,
aliphatic
aldehydes
such
as
cyclohexanecarboxaldehyde, isoꢀbutyraldehyde, 2ꢀethylbutanal, formaldehyde and heptanal
all give both higher conversions and greater yields at room temperature within 12ꢀ24 h (Table
6, entries 1ꢀ6). However, aromatic aldehydes were less reactive than aliphatic aldehydes, and
0
the reaction could proceed at 60 C in yields of 59 – 65% (Table 6, entries 7ꢀ9). We also
found that a variety of terminal aromatic alkynes with substituted groups in para ꢀ and meta ꢀ
positions could be effectively reacted with cyclohexanecarboxaldehyde and piperidine under
the present reaction conditions (Table 6, entries 12ꢀ15). Note that the reactions proceeded
smoothly to give the corresponding propargylamines in a good yield. The presence of
electronꢀrich groups on the benzene ring (entries 12ꢀ14) increased the reactivities of the
alkynes whereas electronꢀwithdrawing groups (Table 6, entry 15) on the benzene decreased
the yield.
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Table 6. The three-component (A3) coupling reaction catalyzed by the mesoporous Cu-
MPTA-1nanocatalysta
R2
R3
CuꢀMPTAꢀ1
CH2Cl2, RT
N
R1CHO
R2R3NH
R4
H
R1
R4
Entry Aldehyde
Amine
Alkyne
Temperature Time Yield
(oC)
(h)
(%)b
CHO
1
RT
24
93
N
H
2
RT
RT
RT
RT
RT
60
12
12
12
12
24
24
85
70
91
71
79
65
CHO
N
H
CHO
3
4
5
6
7
N
H
HCHO
N
H
CHO
4
N
H
CHO
N
H
CHO
N
H
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8
60
60
RT
24
24
12
54
61
91
MeO
Cl
CHO
N
H
9
CHO
N
H
CHO
CHO
10
N
H
O
11
RT
24
78
N
H
CHO
CHO
CHO
CHO
12
13
14
15
RT
RT
RT
RT
24
24
24
24
92
88
82
65
Me
N
H
MeO
MeO
N
H
N
H
Cl
N
H
aReaction conditions: aldehyde (1.0 mmol ), alkyne (1.1 mmol ), amine (1.1 mmol ),
nanocatalyst (0.1 mol%), CH2Cl2(1 mL), room temperature. bIsolated yield. Products were
identified by comparison of their 1HꢀNMR spectral data those reported in the literature.
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Comparison with other reported system
Oneꢀpot A3ꢀcoupling reactions via various aldehydes, alkynes and amines and also
Nꢀarylation of iodobenzene with imidazole, Sꢀarylation of iodobenzene with thiophenol
under heterogeneous conditions over a variety of catalysts has been studied (Table 7). Table 7
provides a comparison of the results obtained for our present catalytic system with those
reported in the literature.29ꢀ31 From Table 7, it is seen that present catalyst exhibited higher
yields compared to the other reported system.29ꢀ31 Reactions conducted at room temperature
or at moderately low temperature for shorter reaction time. Most importantly most of the
coupling reactions occurred in water over our Cuꢀnanocatalyst.
Table 7 Comparison of catalytic activity of the present catalyst in the N-arylation,
S-arylation and A3 coupling reactions with other reported systems
Entry Copper Source
N-arylation
reaction
S-arylation
reaction
Synthesis
propargylamines
of Ref.
Yield (%)
Yield (%)
Yield (%)
1
Cat2 (Mesoporous 89
ꢀ
ꢀ
29
Silica Supported
Copper catalyst)
2
3
4
Cu(II)ꢀDAꢀ30ꢀA
Cu/NCNTs
ꢀ
99
ꢀ
ꢀ
30
31
ꢀ
85
93
CuꢀMPTAꢀ1
91
95
This
study
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Recycling of Catalyst
For a heterogeneous catalyst, it is important to examine its ease of separation,
recoverability and reusability. The reusability of the mesoporous CuꢀMPTAꢀ1 nanocatalyst
was
investigated
in
Nꢀarylation,
Sꢀarylation
and
A3ꢀcoupling
reactions
(cyclohexanecarboxaldehyde, phenyl acetylene and piperidine). After each run, ethyl acetate
was added to dilute the reaction mixture and the organic layer was dried with anhydrous
Na2SO4 by vacuum. The filtrate was concentrated and the resulting residue was purified.
After a simple wash using ethyl acetate and dried, the catalyst was reused for the next run and
almost consistent activity was observed for next six consecutive cycles (Figure 8). As seen
from the figure that the catalyst can be efficiently recycled and reused for repeating
cycles without appreciable decrease in product yield. TEM image (Figure S1 in the
supporting information) of the reused catalyst did not show any substantial change compared
with the fresh catalyst.
Figure 8. Recycling efficiency for the Nꢀarylation, Sꢀarylation and A3 Coupling reactions.
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Heterogeneity Test
Hot Filtration Test
To examine whether copper was being leached out from the solid support to the
solution, experiment has been carried out in the CꢀS coupling reaction with our supported Cuꢀ
MPTAꢀ1 nanocatalyst. A typical hot filtration test was performed in the Sꢀarylation to
investigate whether the reaction proceeded in a heterogeneous or a homogeneous fashion.
For the rigorous proof of heterogeneity, a test was carried out by filtering catalyst from the
0
reaction mixture at 80 C after 4 h and the filtrate was allowed to react up to the completion
of the reaction (6 h). In this case no change in conversion was observed, which suggests that
the catalyst is heterogeneous in nature. No evidence for leaching of copper or decomposition
of the complex catalyst was observed during the catalytic reaction. It was noticed that after
filtration of the catalyst from the reactor at the reaction temperature, coupling reactions do
not proceed further. Atomic absorption spectrometric analysis of the supernatant solution of
the reaction mixture thus collected by filtration also confirmed the absence of copper ions in
the liquid phase. Thus, results of the hot filtration test suggested that Cu was not being
leached out from the solid catalyst during the crossꢀcoupling reactions.
Conclusions
From our experimental observations we can conclude that a new Cuꢀnanocatalyst has
been developed by grafting of Cu(II) at the surface of mesoporous polymer MPTAꢀ1. This
Cuꢀnanocatalyst has been successfully used as a heterogeneous catalyst for the Nꢀarylation
reaction of imidazole with aryl halides and Sꢀarylation reaction of thiophenol with aryl
halides in water as green solvent and one pot A3 coupling reaction at room temperature with
excellent yields. Thus the catalytic process is green and it offers a number of advantages,
such as easy workꢀup and separation of the catalyst from the reaction mixture by filtration,
29