Nitro resin supported copper nanoparticles: An effective heterogeneous catalyst for [Formula presented] cross coupling and oxidative [Formula presented] homocoupling

Article abstract of DOI:10.1016/j.molcata.2016.06.009

In the present study, we investigate the synthesis and catalytic activity of copper nanoparticles (CuNPs) stabilized onto a novel nitro functionalized polystyrene resin. The deposited nanoparticles were characterized by various analytical techniques and TEM images, revealed uniformly distributed copper nanoparticles of sizes 3–9?nm. We effectively used the resin impregnated CuNPs for [Formula presented] coupling of various aromatic amines with aryl halides and for the oxidative [Formula presented] homocoupling of phenyacetylene. Further, recycling of the catalyst, leaching of metal ions and post reaction changes in the support were studied and it was concluded that the support acts as oxidant during the homocoupling of phenyl acetylene which is oxidative by nature.

Full text of DOI:10.1016/j.molcata.2016.06.009

Accepted Manuscript
Title: Nitro resin supported Copper Nanoparticles: An
Effective Heterogeneous Catalyst for C-N Cross Coupling and
Oxidative C-C Homocoupling
Author: Nirav Barot Sunil B. Patel Harjinder Kaur
PII:
S1381-1169(16)30222-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.06.009
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Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
13-3-2016
8-6-2016
9-6-2016
Please cite this article as: Nirav Barot, Sunil B.Patel, Harjinder Kaur, Nitro resin
supported Copper Nanoparticles: An Effective Heterogeneous Catalyst for C-N Cross
Coupling and Oxidative C-C Homocoupling, Journal of Molecular Catalysis A:
Chemical http://dx.doi.org/10.1016/j.molcata.2016.06.009
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Nitro resin supported Copper Nanoparticles: An Effective Heterogeneous
Catalyst for C-N Cross Coupling and Oxidative C-C Homocoupling
Nirav Barot, Sunil B. Patel, Harjinder Kaur*
Department of Chemistry, School of Sciences, Gujarat University, Ahmedabad, India
E- mail: hk_ss_in@yahoo.com, Fax: +91 79 26308545; Tel: +91 79 26300969,
Graphical abstract
Highlights of the work
 Work presents a new nitro functionalized support for stabilizing copper nanoparticles.
 CuNPs catalyzed oxidative C-C homocoupling and C-N coupling
 C-N coupling in benign solvent.
 Catalyst regeneration and recycling.
Abstract
In the present study, we investigate the synthesis and catalytic activity of copper nanoparticles
(CuNPs) stabilized onto a novel nitro functionalized polystyrene resin. The deposited
nanoparticles were characterized by various analytical techniques and TEM images, revealed
1

uniformly distributed copper nanoparticles of sizes 3-9 nm. We effectively used the resin
impregnated CuNPs for C-N coupling of various aromatic amines with aryl halides and for the
oxidative C-C homocoupling of phenyacetylene. Further, recycling of the catalyst, leaching of
metal ions and post reaction changes in the support were studied and it was concluded that the
support acts as oxidant during the homocoupling of phenyl acetylene which is oxidative by nature.
KEYWORDS
Copper nanoparticles, N-arylation, oxidative homocoupling of alkynes, nitro resin supported
CuNPs, Oxidative support.
1. Introduction
The catalysis of carbon-carbon and carbon-nitrogen bond formation is central to synthetic
chemistry especially synthesis of pharmaceuticals and functional materials. Burgeoning literature
on nanocatalysis indicates the interest of researchers in metals other than routinely used and
expensive palladium, platinum etc. [1, 2]. Copper (0) at nanoscale, is being widely explored for
such coupling reactions [3-5] as it is not only cheaper but also less toxic compared to palladium.
But due to its reactive nature, stabilization of copper in nanoform and its reuse is difficult. Copper
nanoparticles not only need protection against aggregation but also from atmospheric oxidation or
surface hydroxylation [6]. A good support can fulfil both these aims. Many supports such as SiO2
[7], Al2O3 [8, 9], MgO [10], Y-Zeolite [11], graphene [12], graphene oxide [13], perlite [14], ionic
liquids [15, 16], PVC [17], have been reported for stabilization of copper nanoparticles. Polymer
2

supports are generally more attractive for liquid phase reactions. Recently, John Mondal and co-
workers have developed two new heterogeneous Cu (0) nanocatalysts, where CuNPs were
deposited on carbonaceous matrix and nanoporous polymer DVAC-1, and studied their catalytic
performance for the coupling reactions of aryl iodides and bromides with primary and secondary
aliphatic amines in aqueous solution [18]. Borah and co-workers have stabilized copper onto
montmorillonite while Islam et al have stabilized copper on polyaniline to carry out “click”
reaction between azide and terminal alkynes [19, 20]. Gholinejad have stabilized copper
nanoparticles on Agarose, a bio-organic and degradable polymer, to carry out “click” reaction
between azide and terminal alkynes [21]. Reddy and co-workers synthesized copper nanoparticles
on cellulose support and successfully catalyzed N-arylation of nitrogen heterocycles with aryl
halides and aryl boronic acids [22].
Supporting of nanocatalysts on cross-linked resins is not new and recent development have
shown that synthesis of nanoparticles on resin is easy as the polymer matrix can effectively control
the size of nanoparticles [23-24]. Polystyrene resins functionalized with acidic or basic groups
have been reported to stabilize nanoparticles of Ag, Au, Pd, Ni etc. and successfully used in organic
synthesis [25]. But there are hardly any example of copper nanoparticles being supported on such
resins though, a few cases of bimetallic nanoparticles are there [26].In our lab, we have earlier
synthesized palladium and gold nanoparticles supported on a commercially available
nonfunctional Amberlite XAD-4 resin where, the formation of stable and recyclable catalyst with
excellent activity towards C-C coupling reactions was achieved [27-28]. However, we observed
that copper nanoparticles synthesized in this inert resin were not stable and brown coloured CuNPs
impregnated resin beads quickly changed colour to bluish green on keeping. This was attributed
to surface hydroxylation of copper (0) nanoparticles. Nitrobenzene has been used as a solvent and
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a mild oxidant in the Skraup synthesis of quinolone [29]. It is a polar group and can enhance the
hydrophilicity of extremely hydrophobic polystyrene. To the best of our knowledge nitro
functionalized resin has never been explored for the synthesis of nanoparticles. Prompted by this
information, we functionalized Amberlite XAD-4 resin with nitro group with an assumption that
negatively charged oxygen atoms may co-ordinate with surface atoms of copper nanoparticles
aiding their stabilization. Copper nanoparticles synthesized in this modified resin were found to
be stable and were characterized by various analytical techniques. We studied C-N coupling of
aryl amines aryl halides and oxidative C-C homocoupling of phenyl acetylene. All the reaction
parameters were studied and conditions were optimized for the best reaction yield.
2. Experimental
2.1. Materials and Instruments
All chemicals used were of analytical grade or of the highest purity available. Amberlite XAD-4
(surface area 725 m2g−1 mesh sizes 20–40) and copper acetate were purchased from Aldrich. Aryl
halides, and acetylene derivatives were purchased from Aldrich. Ethyl acetate, methanol, K2CO3
and NaBH4 were purchased from Finar Chemicals. Water used in all experiments was purified by
Millipore-Q system. All glassware was thoroughly cleaned with freshly prepared 3:1 HCl/HNO3
(aqua regia) prior to use. Nitration was carried out by using three different procedures to prepare
nitro functionalized resin with different N-content (See supplementary information).
IR spectra were recorded on Bruker FT-IR spectrophotometer as pellets after mixing
with KBr. The pellet containing 1 mg of sample was scanned within a range of 600 to 4000 cm-1.
The percentage elemental composition was analyzed by C H N Elementar Vario Micro Cube
analyzer. High resolution transmission electron microscopy (HR-TEM) pictures were taken using
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a Hitachi (H-7500) instrument. The swollen resin beads were milled and a drop of alcoholic
suspension was placed into a 200 mesh carbon coated copper grid. It was then dried to evaporate
the solvent and used for microscopy. The powder XRD of the catalyst was recorded on Brucker
D2 Phaser using Cu Kα radiation (λ = 1.54184 Å) and a filter of nickel at 30 kV and 10 mA with
step size 0.03 and count time 0.1s. Scanning electron microscopy (SEM) image of the bead was
taken with a LEO 440i Electron Microscope after coating it with gold. UV–Visible absorption
spectra were acquired on a Jasco V-570 UV–visible spectrophotometer. GC–MS measurements
were carried on Shimadzu-QP 5000/QP 5050 A with DB - 5 MS column, detector temperature 300
˚C, column heating rate 15 ˚C/min upto 300 ˚C, He gas flow rate of 1 ml/min. Atomic absorption
spectroscopy (AAS) measurements were carried out on an Atomic absorption spectrophotometer
SL-243 Elico instrument: Voltage 619 V, nebulizer flow 7 ml/min, wavelength 324.8 nm, slit
width 0.5 nm, current 5.0 mA and air-acetylene flame. 1H NMR spectra were measured in Bruker
AV 400MHz using CDCl3 as solvent and TMS as internal standard. Mass spectra were recorded
by injecting the samples in ESI ionizer of Shimadzu LCMS 2010 with the single quadruple
analyzer. XPS measurements were conducted at an ultrahigh vacuum (UHV) multipurpose surface
analysis system (Specs™ model, Germany) at the SCAI in Universidad de Cordoba (Spain),
operating at pressures <10−14 MPa using a conventional X-Ray source (XR-50, Specs, Mg-Kα,
1253.6 eV) in a “stop-and-go” mode to reduce potential damage due to sample irradiation. The
survey and detailed high-resolution spectra (pass energy 25 and 10 eV, step size 1 and 0.1 eV,
respectively) were recorded at room temperature using a Phoibos 150-MCD energy analyser.
Powdered samples were deposited on a sample holder using double sided adhesive tape and
subsequently evacuated under vacuum (<10−6 Torr) overnight. Eventually, the sample holder
5

containing the degassed sample was transferred to the analysis chamber for XPS studies. Binding
energies were referenced to the C1s line at 284.6 eV from adventitious carbon.
2.2. Preparation of resin supported copper nanoparticles (Resin-CuNPs)
The resin supported copper nanoparticles were synthesized by a simple sorption-reduction method.
Initially, the nitro functionalized Amberlite XAD-4 beads (5.0 g) were washed repeatedly with
water to remove reagents, swollen in methanol and then equilibrated with 100 mL of 5 mmol
solution of copper acetate in methanol. After 24 h, the excess solution was drained off and the
metal was reduced by passing cold aqueous NaBH4 (0.1 mol dm−3 10 – 15 ˚C) solution. Excess
reagent was removed by washing the beads with water and the CuNPs impregnated beads were
stored in dry methanol.
2.3. General procedure for the N-arylation of aryl halides with aryl amines
In a 25 mL round bottom flask a mixture of 4:1 methanol/water, aryl halide (1 mmol), Resin-
CuNPs (0.2 g), K2CO3 (3 mmol) and aryl amine (1.2 mmol) were taken and heated at reflux
temperature for 12 - 24 h in an oil bath under inert conditions. Resin beads were filtered off at the
end of reaction while the solution was still hot. After a work up with dichloromethane and water,
the organic layer was separated, dried over anhydrous Na2SO4. The crude products obtained after
removal of solvent (Scheme 1.) were purified by column chromatography (ethyl acetate: hexane)
and identified by mass or 1H NMR spectroscopy (see ESI).
2.4. Synthesis of 1, 4-diphenylbuta-1,3-diyne by homocoupling of phenyl acetylene
In a 25 mL two necked round bottom flask containing phenyl acetylene (1mmol), base (1
mmol), catalyst (100 mg) and DMSO (3 ml), O2 gas was purged with the help of a balloon. The
flask was heated at 50˚C for 8 h and the progress of the reaction was monitored by TLC. After the
completion of the reaction, the catalyst was separated while the solution was still hot and the
6

reaction quenched by pouring the filtrate in chilled water. The reaction mixture was extracted with
ethyl acetate and a light yellow crude product was isolated after removing the solvent in a rotary
evaporator. The crude after purification was identified by NMR (Scheme 2).
3. Results and discussion
3.1 Synthesis and characterization of CuNPs
Heterogenization of nanoparticles by stabilizing them on different supports and the effect of
support on the catalytic reaction is an important area of research in the field of catalysis. Amberlite
XAD-4 is a commercial polystyrene resin that has many physical attributes such as porosity;
uniform pore size distribution, high surface area, durability and chemical stability towards acids,
bases and oxidizing agents. These make it an attractive material for supporting catalysts.
Functionalization of the resin can enhance their ability to stabilize metal nanocatalysis [30]. It can
also impart excellent hydrophilicity to these otherwise hydrophobic resins. This enhances their
metal sorption capacities as well as swelling properties. The latter enables the reactants to make
better contact with the embedded catalyst [31]. Polystyrene resin was nitrated using different
methods in order to obtain different degree of nitration that was measured by determining their N-
content using CHN analyser. Details of resin nitration are provided in ESI. It was observed that
the metal sorption capacity of resin increased with the increase in functionalization. Copper acetate
was used as metal precursor and the resin beads were impregnated with nanoparticles by simple
sorption reduction technique. IR spectra of the resin taken before and after impregnation showed
that the chemical structure of the resin remained unchanged. The nitrated resin beads, which were
pale to dark yellow in colour became brown on impregnation with copper nanoparticles. No
deterioration in the colour of the resin was observed on storing the nanoparticles in dry methanol
over long period of time. Nitro is not very common co-ordinating group unlike amino and
7

carboxylic groups that are frequently used to cap and stabilize nanoparticles. However, with two
oxygen atoms, there is considerable electron density on this functional group and of late, its
coordinating properties with metals has been established [32]. Schematic stabilization of copper
nanoparticles inside the resin pores is shown in Fig.1.
The XRD pattern of the finely powdered resin beads is shown in Fig. 2. Amorphous polymer resin
showed a broad hump at 2θ value below 30. Some peaks were indicated in the 2θ region of 30° to
50° but they were unresolved. This was attributed to low loading of catalyst and nano size of the
particles. The latter invariably leads to large broadening of the peaks. A catalyst with higher
loading of the metal was prepared using 10 mmol solution of precursor. The peak observed near
2θ = 43.0 (Fig. 2b) was identified as (1 1 1) reflection (JCPDS No. 04-0836) corresponding to the
fcc lattice of copper (0) [33]. Another scan in the range of 40° to 48° with step size 0.02 and count
time of 3s was carried out (Fig. 2c) which clearly showed the peak at 43.1206. This conclusively
proved the presence of Cu (0) in the catalyst. A second peak was observed at 2θ = 36.381 that
corresponds to (1 1 1) reflection of oxide of copper. Thus, it can be concluded that supported
copper (0) nanoparticles were covered with an oxide layer. Same was also indicated by electron
diffraction obtained during TEM analysis.
The shape and size of nanoparticles was studied by HR-TEM. TEM pictures (Fig. 3.) of all the
three CuNPs impregnated resins were studied and it was observed that the number of nanoparticles
increased with increase in nitrogen content and hence metal sorption capacity of the resin. Mostly
spherical but some irregular shaped nanoparticles were also observed. The variation in size of the
8

nanoparticles for resin 3 with copper loading of 0.21 mmol /g was measured between 3 to 9 nm.
This resin was used in all catalytic reactions.
Further studies on X-Ray Photoelectron Spectroscopy (XPS, Figure 4) confirmed the presence of
both Cu2+ and Cu reduced species as clearly visualized in Cu2p XPS experiments. The presence
of a shake-up peak (about 940–945 eV) is characteristic of Cu2+ species, particularly of CuO (in
the absence of Cu2+ species, no shake-up peaks can be visualized) [34], is in good agreement with
XRD results. The presence of lower Cu2p3/2 binding energy peaks (933 eV) indicates the
existence of reduced copper species [35]. However, the distinction between Cu+ and Cu0 species
(that appear at very similar binding energies) is only feasible through examination of the Auger
spectra [36]. O1s spectra also supported the presence of Cu-O bonds with the O1s contribution
(ca. 15%) centered at 529.0 eV, assigned to the presence of metal oxides [37]. The surface copper
content, according to XPS, was ca. 8.1 %, with the additional confirmation of the presence of N in
the materials (N1s spectra, results not shown). Nevertheless, no clear evidences of the coordination
of nitro groups with copper species could be drawn from XPS data.
3.2. C-N cross coupling reaction catalyzed by Resin-CuNPs
Compounds containing aryl amines moieties are widely used as agrochemicals, pharmaceuticals,
dyes, conducting polymers and as intermediates for organic synthesis [38]. The classical Ullmann
reactions carried out using copper as catalyst is tricky for industrial application as it involves high
temperature, stoichiometric amount of metal and high cost of waste disposal [39-41]. So,
development of environmentally benign methods for N-arylation or C-N coupling is an important
task. Transition metal catalyzed cross coupling reactions of aryl amines with aryl halides has been
widely studied. These reactions are catalyzed by palladium or copper salts using a variety of
9

ligands such as diamine, diimines, amino acids, β-ketoesters and 1, 10-phenanthroline derivatives,
ninhydrin, diols, amino arenethiolate, phosphine ligands, hydrazones, N-hydroximides,
hydroxyquinoline etc. [42, 43]. Most of these methods are homogeneous in nature which makes
the recovery of catalyst difficult and the presence of stabilizing ligands further complicates the
catalytic reaction. Performing these reactions under heterogeneous conditions is favorable as it
facilitates work-up, recovery and reusability of the catalyst for multiple reaction cycles [44-46].
One of the highlight of nanoparticle catalysis is their ability to catalyze reactions in the absence of
ligands. Our studies are especially aimed at establishing ligand less green protocols for organic
synthesis in benign solvents.
The reaction between Iodobenzene and aniline was chosen as the standard reaction and
reaction conditions such as optimum ratio of reactants, catalysts, solvents base etc. was established
by carrying out the reaction frequently with changing parameters. A ratio of 1:1.2 between
iodobenzene and aniline was found to be ideal. All the three catalyst were tried (Table 1) and best
yield was observed with 200 mg of catalyst 3. This corresponded to 4.2 mmol % of copper.
Presence of CuNPs was essential for the catalytic reaction as no product formed in the absence of
catalyst.
The effect of other parameters on the reaction was studied and results are tabulated in Table
2. Base played an important role in this reaction and both organic as well as inorganic bases were
investigated. KOH and K2CO3 were found to be equally effective in methanol/water system.
Quantitative yield of diphenyl amine was obtained using NaOtBu in toluene. Tri ethyl amine (TEA)
was ineffective as base. The reaction was studied using a variety of solvents such as acetonitrile,
toluene, DMF, THF, dioxane, methanol and methanol water mixture. Good results can be obtained
in both polar and non-polar type of solvents using appropriate base. However, methanol-water
10

mixture in 4:1 ratio was considered the best choice as it was easy to remove, benign in nature and
no side products were observed on the TLC of the reaction mixture.
The generality and the scope of the catalytic reaction were further explored by carrying out
the reaction with different aryl halides and the results are shown in table 3. All the reported results
are for the reactions carried out in MeOH - H2O though, other solvents like DMSO and Toluene
with sodium tertiary butoxide (NaOtBu) was equally effective. N-arylation of aniline with all the
three aryl halides viz. iodo, bromo and chloro were successful. However, product yield decreased
as we moved from iodobenzene to chlorobenzene (table 3 entries 1, 5, 8). Effect of electron
donating and electron withdrawing groups on the reactivity of aryl halides was also investigated.
Especially noteworthy is the case of 4-nitro aryl halide where 4-nitroanisole was obtained as major
product which indicated ring activation towards methoxylation rather than amination in the
presence of strongly electron withdrawing nitro group. Replacing methanol with acetonitrile as
solvent gave the corresponding amine products (table 3 entries 4, 7, 9). In case of entry 11 where
an electron withdrawing nitro and electron donating methoxy group was attached, major product
was the corresponding diphenyl amine.
3.3. C-C oxidative homocoupling of phenyl acetylene catalyzed by Resin-CuNPs
Being a versatile building block in organic chemistry, 1,3-diynes are important
intermediates in the synthesis of natural products, polymers, pharmaceuticals and in material
science [47, 48]. Synthesis of conjugated diynes has been reported by couplings like Elington,
cadiot-chodkiewikz, sonagashira and hay-glaser etc. Lately, salts of many transition metals like
Ag, Au, Ni, Pd and Cu have been used to catalyze this coupling reaction as homogeneous and
heterogeneous catalysts [49-51]. However, there are only a few reports of nanoparticles as catalysts
11

in this oxidative coupling reaction [52-54]. We have used a nitro resin for stabilization of CuNPs.
Nitrobenzene has been used as a solvent and mild oxidant in the Skraup synthesis of quinoline. It
has been reported as a mild oxidant in the ruthenium catalyzed oxidative coupling of alkynes [55].
These reports prompted us to explore nitro resin stabilized CuNPs for oxidative coupling of phenyl
acetylene and we got excellent conversion and yield. The effect of solvent, base, catalyst
concentration and temperature on the reaction was studied and the results are reported in table 4.
Among the various solvents used best yield was obtained in DMSO with 96 % conversion in 8
hours. Different bases such as K2CO3, Na2CO3, KOH, NaOH, TEA etc. were studied. K2CO3 was
selected as optimum base as it gave high conversion without any undesired products in the reaction
mixture.
The generality and the scope of the catalytic reaction were further explored by carrying out
reaction using different terminal alkynes and the results are shown in table 5. Homocoupling of
aliphatic as well as aromatic terminal alkynes was successfully achieved. Phenyl acetylenes are
activated by electron withdrawing groups. In the present case we obtained excellent yields with
both strong and weak electron donating groups like -OCH3, -OH, and -CH3. Especially noteworthy
is reaction with bromo substituted phenyl acetylene where only one product i.e. 1,4-bis(4-
bromophenyl)buta-1,3-diyne was obtained.
The effect of temperature on the rate of reaction was studied by varying the temperature of
oil bath from 40 to 90 °C. Quantitative conversion was obtained at 50 °C, thereafter, the yield of
isolated product decreased on increasing the temperature (figure 5). The effect of catalyst
concentration was studied by varying the catalyst quantity from 50 to 150 mg and the results are
shown in figure 4.100 mg of catalyst was sufficient to complete the reaction. This amount of
12

catalyst corresponds to 2.1 mol. % of the copper. The effect of time on the progress of reaction
was also investigated. Reaction mixture was withdrawn at regular intervals of time and progress
of reaction was monitored by GCMS. Complete conversion was observed in 8 h. Further increase
in reaction temperature led to decrease in the yield of isolated product.
3.4 Recycling and reusability of the catalyst
Recycling and reusability is the most important aim of catalyst heterogenization. In this
respect usage of polymer resins beads as support is highly useful as they are easy to handle and
can be separated by simple filtration. Resins have tendency to sorb reagents and hence, thorough
washing of beads is necessary. In the present case the catalyst was separated from the reaction
mixture by filtration and washed frequently with appropriate solvents (water/methanol/acetone) to
completely remove the sorbed products. The recyclability of the recovered catalyst was checked
for both the reactions viz. N-arylation of iodo benzene with aniline and homocoupling of phenyl
acetylene. The results are shown in figure 6. It can be seen case of N-arylaiton there is little
decrease in activity. However, in case of oxidative homocoupling reaction the decrease in activity
was substantial after each cycle.
Leaching is an important issue that depletes the activity of heterogeneous catalyst. A hot
filtration test was performed to check leaching of the catalyst during the reactions. In both the
cases reactions were stopped at half the reaction time which was 6 h for N-arylation of aniline and
4 h for homocoupling of phenyl acetylene (Figure 7). The catalyst was filtered off and the filtrate
was heated further to check the progress of reaction. In both the cases no significant change in the
concentration of reactants was observed. Additionally, the filtrate was analyzed for the presence
of copper by Atomic absorption spectrometer (AAS) and the concentration of copper in the filtrate
which was estimated to be 55 ± 10 ppb and 48 ± 10 ppb respectively.
13

As the leaching was very low in oxidative homocoupling, we assumed that the passivation
may be due to the fact that the reaction was carried out in the presence of oxygen which can lead
to the formation of oxide layer on the surface of copper nanoparticles. We passed cold 1 mmol
solution of NaBH4 over the catalyst and retested its activity. Quantitative results were obtained on
recycling. Further, we also checked the effect of reaction parameters on the support. FTIR spectra
of the used and fresh resin were taken (figure 8) and compared. It was observed that there is no
change in the functional groups of the resin during N-arylation. However, after oxidative coupling
the stretching frequencies of nitro group which appeared at 1526 and 1347 cm-1 in fresh resin
changed. The band at 1526 cm-1 shifted to 1512 cm-1 and the intensity of the band at 1347 cm-1
decreased. This indicated the conversion of nitro group to nitroso group. This indicated that the
support was acting as an oxidant in the reaction.
4. Conclusions
In summary, we report that nitro functionalized polystyrene can be used to synthesize
highly stable reusable copper nanoparticles. The loading of copper metal is affected by degree of
nitration This is a new robust support reported for stabilizing copper nanoparticles which is highly
suitable for solution phase reactions. Copper nanoparticles were found to be stable in dry methanol
over a long time and the work may throw new light on the stabilizing mediums used for
nanoparticles. The catalyst was found highly active for homo coupling of phenyl acetylene. Good
recycling of the catalyst, environmentally benign solvents and hardly any leaching of the metal
into reaction mixture make it a promising catalyst for ligand free coupling of aryl halides with aryl
amines. We are studding other applications of this catalyst.
14

Acknowledgements
The authors are grateful to the DST nanomission for the financial support, UGC, New Delhi for
the BSR fellowship to Nirav barot, SAIF, Panjab University, Chandigarh, for the TEM analysis
and NMR, UGC-DAE consortium for scientific research, Indore for XPS inputs., FCIPT
1
Gandhinagar, Gujarat for SEM pictures, O2h Ahmedabad for ESI Mass and H NMR. Authors
gratefully acknowledge suggestions from Prof. Rafael Luque and support for recommended XPS
measurements conducted at Universidad de Cordoba (Spain).
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17

Scheme 1. C-N coupling reactions of aryl halides with aryl amines
Resin-CuNPs, K2CO3
DMSO, 50 oC, 8 h, O2
R
R
R
Scheme 2. Glaser-Hay coupling of terminal alkynes
18

Fig. 1. Stabilization of CuNPs inside nitro functionalized resin
Fig. 2. XRD pattern of resin-CuNPs
19

Fig. 3. TEM image of resin-CuNPs a) catalyst 3 b) Catalyst 2 c) catalyst 1 d) electron diffraction
pattern
20

Fig. 4. a) O1s and b) Cu2p XPS spectra of Resin-CuNPs
Fig. 5. Effect of Catalyst quantity and temperature on the homocoupling reaction
21

Fig.6. Recycling studies of the catalyst for N-arylation and homocoupling of phenyl acetylene
Fig. 7. Hot filteration test
22

Fig. 8. FT-IR spectra of Fresh Resin-CuNPs, recycled resin after C-N coupling, recycles resin after
C-C homocoupling reaction.
Table 1: N-arylation reaction catalyzed by different catalysts
Entry Catalyst
Cu
loaded
mmol
Base
Yield
(%)
1
2
3
4
5
Catalyst 1 0.01
Catalyst 2 0.023 K2CO3 70
Catalyst 3 0.042 K2CO3 99
Catalyst 3 0.042
-
K2CO3 56
-
25
K2CO3 trace
aReaction coditions: Iodobenzene (1 mmol), aniline (1.2 mmol),
0.2 g of resin-CuNPs,K2CO3 (3 mmol), 5 ml (4:1) MeOH: H2O,
reflux temperature, 12 h.
Table 2: Evaluation of the effects of the solvent, base and catalyst on the N-arylation
Entry Base
Solvent
Yield
(%)
1
2
K2CO3 1,4-dioxane
K2CO3 Acetonitrile trace
trace
23

3
4
5
6
7
8
9
10
K2CO3 DMSO
92b
K2CO3 MeOH:H2O 99a
K2CO3 DMF
K2CO3 THF
K2CO3 MeOH
70b
trace
30
KOH
KOH
KOH
DMSO
MeOH
MeOH:H2O 95
(4:1)
98b
40
11
12
13
TEA
TEA
MeOH
DMF
trace
traceb
95
NaOtBu Toluene
aReaction conditions: aryl halide (1 mmol), amine(1.2 mmol),
K2CO3 ( 3 mmol), Catalyst 3 (200 mg), Solvent (5 ml), reflux
temperature, 12 h.b / 120˚ C (for DM
Table 3. Resin-CuNPs catalyzed N-arylation of aryl halides with aryl amines and nitrogen
heterocyclesa
Entry
R1
H
4-CH3
4-OCH3
4-NO2
H
4-OCH3
4-NO2
H
4-NO2
H
X
I
I
I
I
Br
Br
Br
Cl
Cl
I
R2
H
H
H
H
H
H
H
Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
12
12
12
12
12
12
12
12
12
12
12
99
92
80
60b
95
75
50b
85
H
H
4-Cl
55b
96
10
11
4-NO2, 2-OCH3 Cl
H
72
2-Amino
pyrimidine
12
H
I
12
85
a Reaction conditions: 1 mmol aryl halide, 1.2 mmol of amine, 3 mmol of K2CO3,
Catalyst (200 mg), MeOH/H2O (4:1) (5 ml), reflux temperature. bacetonitrile as solvent.
Table 4: Evaluation of the effects of the solvent and base on oxidative C-C homocoupling
Entry
Base
Solvent
Yield
(%)
1
2
Et3N
Et3N
DMSO
MeOH
Trace
15
24

3
4
5
6
7
8
9
10
11
12
13
NaOH
KOH
DMSO
DMSO
DMSO
DMSO
DMSO
MeOH
EtOH
48
58
86
92
96
90
88
80
86
Piperidine
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Acetonitrile
THF
DMF
DMSO
83
Trace*
phenyl acetylene (1mmol), base (1mmol), catalyst (100
mg),solvent (3 mL), 50 °C, 8 h, O2 gas,* in the absence of
catalyst
Table 5. Resin-CuNPs catalyzed homocoupling of terminal alkynes
Yield
(%)
Entry
Substrate
Product
1
2
95
95
3
92
4
5
90
94
6
7
8
92
95
trace
terminal alkyne (1mmol), base (1mmol), catalyst (100 mg), DMSO (3 mL), 50 °C, 8 h, O2 gas
25