1
668
V. S. Borude et al.
and aryl halide gave good yields of product. The reaction was
of carried out in ethanolamine as it acts as a base, ligand, and
solvent at 90 °C. The PS–Cu–NHC complex and EA were
recycled up to three consecutive cycles with no loss of
activity. Further efforts to extend the application of this
system to other chemical transformations are underway.
NHC complex. To measure the amount of Cu loaded on it,
3
20 mg of PS–Cu–NHC was treated with 5 cm of a mixture
of hydrochloric acid and nitric acid (1:1, v/v) at room
temperature for 2 h. The orange-colored solution was fil-
tered and the polymer support was washed with distilled
3
water (2 9 5 cm ). The filtrate and washing solutions were
combined to detect the amount of copper using AAS.
Experimental
Synthesis of diphenylacetylene derivatives
All the solvents and chemicals were procured from S.
D. Fine Chemicals (India) and were used without any
further purification. Merrifield polymer (4.3 mmol Cl/g
resin and 2 % cross-linked with divinylbenzene) was pro-
cured from Fluka Pvt. Ltd. The reactions were monitored
by TLC using 0.25 mm E-Merck silica gel 60 F254 pre-
A two-necked round-bottom flask containing a magnetic
bar under a nitrogen atmosphere was charged with aryl
3
halide (1.3 mmol), 2 cm ethanolamine, catalyst (15 %
w/w), and aryl acetylene (1 mmol). The mixture was
heated and stirred at 90 °C for 3 h and then cooled to room
temperature. Catalyst settled at the bottom of the flask and
the reaction mass was decanted by adding diethyl ether
1
coated plates, which were visualized with UV light. The H
1
3
3
NMR and C NMR spectra were recorded at 300 MHz
and 75 MHz, respectively, on a Varian Mercury Plus
spectrometer (VARIAN, USA). Chemical shifts are
expressed in d (ppm) using TMS as an internal standard.
FT-IR spectra were recorded on Shimadzu 8400S FT-IR
spectrophotometer. Thermogravimetric analysis (TGA)
was performed using a DTG-60H instrument (Shimadzu) in
nitrogen atmosphere between 25 and 500 °C with a heating
rate of 10 °C/min. The copper content in the polymer-
supported catalyst was determined by atomic absorption
spectroscopy (AAS) (model GBC 932 plus, Australia).
Inductively coupled plasma atomic emission spectroscopy
(2 9 5 cm ). The organic layer was separated and washed
with water. The organic extracts were dried with sodium
sulfate and evaporated under reduced pressure. The residue
was purified by column chromatography using 100–200
mesh silica with 2 % ethyl acetate in n-hexane as eluent
and afforded products 3a–3f, which were identified by
comparison of their spectra with literature data (see Sup-
plementary Material).
Recyclability of PS–Cu–NHC catalyst
and ethanolamine
(
ICP-AES) was performed on an ARCOS system from M/s.
After completion of the reaction, the catalyst was separated
by decanting the reaction mass. The separated catalyst was
washed with water, dried at 60 °C for 1 h, and used again
for the coupling reaction. The decanted reaction mixture
contained ethanolamine, salt, product, and reactants. The
reactant and product were extracted with diethyl ether and
the layer was separated (solubility of ethanolamine in
diethyl ether is 1.4 % at 25 °C). Ethanolamine was
recovered after addition of potassium carbonate to neu-
tralize the ammonium salt formed during the reaction. It
was washed with diethyl ether. Recovered ethanolamine
was dried in a rotary evaporator at 60 °C for 1 h. Recycled
ethanolamine was directly used for the coupling reaction
between aryl halide and phenylacetylene for three con-
secutive cycles.
Spectro, Germany.
Preparation of polymer-supported ionic liquids (SIL)
A round-bottom flask under a nitrogen atmosphere was
charged with 1 g polystyrene resin and 0.423 g 1-methyl-
3
imidazole (5.16 mmol) in 10 cm toluene and refluxed for
2
4 h. The reaction mass was cooled to room temperature,
filtered, and washed with toluene, 0.1 M HCl, water, and
ethanol. The residue was then dried under reduced pressure
to afford the supported ionic liquid (SIL) (1.32 g).
Preparation of polymer-supported Cu–NHC complexes
(
PS–Cu–NHC)
Acknowledgments The authors are grateful to the University
Grants Commission, New Delhi for fellowship to VSB and RVS.
A mixture of 1 g SIL (2.95 mmol/g) and 0.251 g
3
CuCl Á2H O (1.47 mmol) was suspended in 5 cm DMF.
2
2
To this suspension was added a solution of 0.625 g
3
Na CO (5.90 mmol) in 5 cm water. The mixture was
2
3
References
stirred at room temperature for 2 h. After filtration, the
polymer support was washed thoroughly with water
1
. Doucet H, Hierso JC (2007) Angew Chem Int Ed 46:834
2. Chinchilla R, Najera C (2011) Chem Soc Rev 40:5084
. Chinchilla R, Najera C (2007) Chem Rev 107:874
3
2 9 10 cm ), then with methanol (2 9 10 cm ), and dried
3
(
3
under reduced pressure to give polymer-supported Cu–
1
23