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HAJIPOUR AND JAJARMI
metal and replaced it with copper metal in our catalytic
system. Compared to the frequently used costly palladium
catalysts, copper‐based catalysts have an economic
advantage, and, therefore, remain noteworthy for indus-
trial‐scale preparations.
64% (entry 13). A low copper concentration gave a
decreased yield (entry 14). Thus for the optimum reac-
tion
conditions,
Cu(I)‐PANI@MWCNT
complex
(10 mol%) as the catalyst, KOH (2.0 equiv.) as the base
and DMF (4 ml) as the solvent were used at 135 °C
under nitrogen atmosphere. We examined the reaction
of bromobenzene with phenylacetylene under these opti-
mized conditions, and found that it was not efficient.
However, by changing the reaction time to 4 h,
bromobenzene could be smoothly coupled with
2 | RESULTS AND DISCUSSION
Polyaniline‐functionalized MWCNTs (PANI@MWCNT)
were synthesized by in situ oxidative polymerization.[29]
Then, Cu(I)‐PANI@MWCNT was prepared by reaction
of CuI and PANI@MWCNT in a tetrahydrofuran
(THF)–water mixture.
phenylacetylene resulting in
a
yield of 60% of
diphenylacetylene (Table 1, entry 11).
With the optimum conditions in hand, Cu(I)‐
PANI@MWCNT nanocatalyst was used for coupling of
phenylacetylene with aryl iodides including those con-
taining electron‐donating or electron‐withdrawing
groups. Electron‐rich, electron‐poor or electron‐neutral
aryl iodides were reacted with phenylacetylene to produce
the corresponding products in high yields under the
optimized reaction conditions (Table 2, entries 1–10).
We next investigated the coupling of various aryl
bromides with phenylacetylene. Unsurprisingly, aryl
bromides were less reactive than aryl iodides, and the sub-
stituent effects in aryl bromides appeared to be more
important than in aryl iodides. Nevertheless, as evident
from Table 2, high catalytic activity was observed in the
coupling of phenylacetylene with activated aryl bromides
such as p‐nitrobromobenzene, m‐nitrobromobenzene,
p‐chlorobromobenzene, o‐acetoxybromobenzene and
p‐methylbenzoate (entries 12, 13, 16, 19 and 20), whereas
unactivated aryl bromides such as p‐bromoanisole
(entry 17) and p‐bromotoluene (entry 18) indicated
lower activity. It should be mentioned that the
coupling reactions of aryl chlorides (entries 21–23)
were not efficient.
A very important consideration of catalysts is their
reusability. Hence, we investigated the recycling and reus-
ability of this nanocatalyst utilizing the reaction of
iodobenzene with phenylacetylene as a model reaction.
After completion of the reaction, ethyl acetate was added
to the reaction solution, and it was separated using centri-
fugation. The acquired solid materials were washed with
water, ethanol and ethyl acetate and dried under vacuum
for 10 h. Then we reused our recovered catalyst in six
subsequent reactions under the same conditions. This
heterogeneous nanocatalyst exhibited a good reusability
(Table 3), which was confirmed from the XPS spectrum
of the recycled nanocatalyst after the sixth run. Based on
this analysis, the structure of CuI particles in the catalyst
had not been destroyed after six consecutive runs
(Figure 3).
Successful synthesis of Cu(I)‐PANI@MWCNT
complex was confirmed using Fourier transform infrared
(FT‐IR) spectroscopy, transition electron microscopy
(TEM), inductively coupled plasma (ICP) analysis,
energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffrac-
tion (XRD) and X‐ray photoelectron spectroscopy (XPS).
The FT‐IR spectrum of PANI@MWCNT in compari-
son with that of bare MWCNTs showed C═N and C═C
stretching vibration bands at 1478 and 1574 cm−1 and
C═N stretching vibration bands at 1243 and 1286 cm−1
(supporting information, Figure S1), confirming the
formation of polyaniline in the emeraldine form. TEM
observations confirmed the immobilization of copper
nanoparticles on PANI@MWCNT (Figure 1). Also, a his-
togram of the size distribution of the catalyst indicated
the size of Cu particles as between 1 and 6 nm and most
particles were 3.2 nm (Figure S2). ICP analysis was used
to determine the amount of copper loading of the Cu(I)‐
PANI@MWCNT complex as 6.1% (0.98 mmol g−1). Also,
the EDX analysis confirmed the presence of copper in
the complex (Figure S3). As shown in Figure 2, the XRD
pattern of Cu(I)‐PANI@MWCNT composite indicated
diffractions of CuI complexes, containing some peaks that
are clearly visible and all of them can be indexed to
crystalline CuI complexes. The peak positions are in agree-
ment with those for CuI complexes reported previously.[22]
Also, XPS analysis of recycled catalyst clearly indicated
peaks corresponding to carbon, nitrogen, iodide and Cu+
ion (Figure 3).
We investigated efficiency of Cu(I)‐PANI@MWCNT
in the Sonogashira reaction using iodobenzene with
phenylacetylene as a model reaction, under various
conditions with nitrogen atmosphere (Table 1). As is
evident, among the screened bases, KOH showed the
best result, and the corresponding coupling product was
obtained in 96% yield (Table 1, entry 5). Effect of temper-
ature on the activity of Cu(I)‐PANI@MWCNT complex
was also investigated. As the temperature decreased from
135 to 120 °C, the yield of product decreased from 96 to
To determine if metal is leached out into the solu-
tion during the reaction, the catalyst was collected from