Direct use of nanoparticles as a heterogeneous catalyst: Pd0-doped CoFe2O4 magnetic nanoparticles for Sonogashira coupling reaction

Article abstract of DOI:10.1007/s11164-014-1699-1

A magnetically separable nanocatalyst prepared by incorporating Pd nanoparticles onto CoFe₂O₄ magnetic nanoparticles was found to be very effective in catalyzing Sonogashira cross-coupling reactions. In this green synthetic process, it is not necessary to use an external linker to support the palladium nanoparticles onto the cobalt ferrite matrix. The catalyst is effective without the use of any ligand or copper additive. The reaction works smoothly in ethanol at 70 °C with both aryl iodides and bromides to produce corresponding product in high yield. After completion of the reaction, the catalyst could be easily separated using an external magnet and reused up to five catalytic cycles with sustained catalytic activity.

Full text of DOI:10.1007/s11164-014-1699-1

Res Chem Intermed
DOI 10.1007/s11164-014-1699-1
Direct use of nanoparticles as a heterogeneous catalyst:
Pd0-doped CoFe2O4 magnetic nanoparticles
for Sonogashira coupling reaction
•
Subhasish Roy Kula Kamal Senapati
Prodeep Phukan
•
Received: 9 March 2014 / Accepted: 2 May 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract A magnetically separable nanocatalyst prepared by incorporating Pd
nanoparticles onto CoFe2O4 magnetic nanoparticles was found to be very effective
in catalyzing Sonogashira cross-coupling reactions. In this green synthetic process,
it is not necessary to use an external linker to support the palladium nanoparticles
onto the cobalt ferrite matrix. The catalyst is effective without the use of any ligand
or copper additive. The reaction works smoothly in ethanol at 70 °C with both aryl
iodides and bromides to produce corresponding product in high yield. After com-
pletion of the reaction, the catalyst could be easily separated using an external
magnet and reused up to five catalytic cycles with sustained catalytic activity.
Keywords Magnetic nanoparticle Á Nano-catalyst Á Pd-CoFe2O4 Á
Sonogashira Á Aryl halide Á Alkyne
Introduction
In the recent past, magnetic nanoparticles (MNPs) have been extensively employed
as alternative catalyst supports for a variety of organic transformations [1, 2]. The
key advantage of magnetic nano-catalysts is their high surface area, which results in
high catalyst loading capacity, high dispersion, and outstanding stability. Moreover,
these catalysts have the green advantage of convenient and effective recycling, due
to the ease of separation with the help of a magnet. Catalyst supported on super
MNP has been found to catalyze many organic reactions quite effectively [1–3].
Electronic supplementary material The online version of this article (doi:10.1007/s11164-014-1699-1)
contains supplementary material, which is available to authorized users.
S. Roy Á K. K. Senapati Á P. Phukan (&)
Department of Chemistry, Gauhati University, Guwahati 781014, India
e-mail: pphukan@yahoo.com
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S. Roy et al.
Because of the sustained catalytic activity of palladium salts, several MNP-
supported Pd-catalysts have been developed for promoting different organic
reactions [4–10].
The Sonogashira coupling reaction is the most commonly used method for the
selective sp2–sp carbon–carbon bond formation reaction in organic synthesis and the
products have found many applications in the area of natural products and the
pharmaceutical industry [11–13]. In general, palladium along with copper (as a co-
catalyst) is used for the Sonogashira cross-coupling reaction [14–16]. The addition
of Cu salts assist the reaction but this has some serious drawbacks because of the
formation of the self-coupling alkyne side product by Glaser oxidation reaction [17,
18]. Fewer reports on Cu-free Sonogashira reactions are also reported in the
literature but they often require microwave activation or ultrasonic irradiation [19–
23]. There are several reports on homogeneous Pd-catalyzed Sonogashira coupling
reactions [24–38]. However, isolation of the costly and toxic Pd catalyst from the
reaction mixtures is still a challenging task for the chemist. Therefore, heteroge-
neous palladium catalysts have been developed for this particular reaction [39–58].
However, the use of MNPs as support or a catalyst has distinct advantages over
other heterogeneous catalysts [1, 2]. Le et al. [5] reported Sonogashira coupling
reaction using Pd Schiff’s base complex supported on functionalized cobalt ferrite
MNPs as a catalyst using DMF as a solvent. A major disadvantage in most of the
earlier reports is that it is very much necessary to use a linker to support the
catalytically active metals onto the magnetic nano-support. We have recently
reported a water-dispersible cobalt ferrite catalyst for various organic transforma-
tions [6, 7, 59–62]. We also developed a palladium-supported magnetic nanocatalyst
for Suzuki coupling reactions [7]. In continuation of our work on green chemical
synthesis using magnetic nanocatalysts, we wish to report herein a green catalytic
route for ligand- and copper-free Sonogashira reactions using Pd nanoparticle-
supported cobalt ferrite MNPs as a catalyst. The significance of our method is the
direct use of MNP as a catalyst. Unlike other reports, we used no linker to support
the palladium nanoparticles. The catalyst was found to be well dispersed in ethanol
and can be separated easily form the ethanolic dispersion with the help of an
external magnet.
Experimental
Synthesis of Pd nanoparticle-supported cobalt ferrite MNPs
Palladium nanoparticle-supported CoFe2O4 magnetic nano-catalyst was synthesized
using our previously reported ultrasonic-aided co-precipitation technique without
using any surface stabilizers or surface-coating agent [7]. Initially, the Pd
nanoparticles were synthesized taking Pd(OAc)2 and PEG-400 as raw materials
by a reported procedure [63]. Then, CoFe2O4 MNPs were synthesized. For this, two
aqueous solutions of FeCl3 (1.5 g, 9.3 mmol, 50 ml) and CoCl2Á6H2O (1 g,
4.2 mmol, 50 ml) in distilled de-ionized water were mixed in a 200-ml flat-bottom
flask and placed in an ultrasonic bath. An aqueous KOH solution (3 M, 25 ml) was
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Direct use of nanoparticles as a heterogeneous catalyst
added drop-wise under a nitrogen atmosphere with continuous ultrasonic irradiation
(frequency 40 kHz and power of 40 kW). Prior to mixing, all three of these
solutions were sonicated for 30 min to remove dissolved oxygen. The temperature
of the sonicator bath was raised to 60 °C and the mixture was further sonicated for
30 min in air atmosphere. Finally, Pd NPs, which was already synthesized, was
dispersed in ethanol and added drop-wise over the CoFe2O4 reaction mixture and
the reaction temperature was slowly brought to 80 °C and kept under sonication for
an hour. The reaction mixture was slowly cooled down to room temperature. Black
precipitate of Pd-incorporated CoFe2O4 was observed, which was further separated
by centrifugation at 15,000 rpm for 15 min, washed several times with both distilled
de-ionized water and ethanol and kept overnight in an incubator at 60 °C for ageing.
The precipitate was then further dried in an oven at 100 °C for an hour and
subsequently kept in a highly evacuated environment (10-2 bar) for another hour.
The residual water in the product (Pd nanoparticle-doped CoFe2O4) was then
removed by heating the product at 200 °C for 6 h and kept in a desiccator for further
applications.
Characterization of Pd-incorporated CoFe2O4
The as-synthesized Pd nanoparticle-supported CoFe2O4 magnetic nanocatalyst were
completely characterized by FT-IR (Shimadzu 1800 FT-IR Spectrometer), field-
P
emission scanning electron microscopy (FESEM, Carl Zeiss, IGMA), electron
dispersive X-ray (EDX, Oxford INCA X-ray microanalysis), transmission electron
microscopy (TEM, JEOLJEM 2,100–200 kV), X-ray diffraction measurement XRD
(Philips-X pert Pro X-ray diffractometer with Cu-K a radiation having
k = 1.5418 A), BET single point surface area analysis (Micromeritics chemisorb
2720), VSM analysis (Lakeshore 7410 vibrating sample magnetometer).
Sonogashira reaction using PdCoFe2O4 nanoparticle as a catalyst
In a typical coupling reaction, halobenzene (1 mmol), alkyne (1.1 mmol), K2CO3
(2 mmol), and Pd-CoFe2O4 MNPs (5 mol% by its weight, 17 mg) were taken in dry
ethanol (5 ml) in a Schlenk tube under nitrogen atmosphere. The reaction mixture
was heated at 70 °C for the appropriate time. The reaction was monitored using
TLC. After completion of the reaction, the catalyst was separated using a magnet.
The ethanol part was evaporated under vacuum to get the crude product. The crude
product was further purified by column chromatography in 230–400 silica mesh
using ethyl acetate and petroleum ether (0–2 %) as eluent. Separated magnetic
catalyst was dried in an oven at 100 °C and kept in a desiccator for further use.
1-Methyl-4-(2-phenylethynyl) benzene (1a)
1H NMR (CDCl3, 300 MHz): d 7.56–7.54 (m, 2H), 7.45 (d, J = 9 Hz, 2H),
7.36–7.35 (m, 3H), 7.17 (d, J = 9 Hz, 2H), 2.39 (s, 3H); 13C NMR (CDCl3,
75 MHz): d 138.3, 131.5, 131.4, 129.1, 128.3, 128, 123.4, 120.1, 89.5, 88.7, 21.5.
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S. Roy et al.
Fig. 1 FT-IR of Pd-CoFe2O4 MNPs
1, 2-Diphenylethyne (1b)
1H NMR (CDCl3, 300 MHz): d 7.58–7.55 (m, 4H), 7.38–7.36 (m, 6H); 13C NMR
(CDCl3, 75 MHz): d 131.6, 128.3, 128.2, 123.2, 89.3.
1-Methyl-4-(oct-1-yn-1-yl)benzene (1c)
1H NMR (CDCl3, 300 MHz): d 7.31 (d, J = 9 Hz, 2H), 7.1 (d, J = 6 Hz, 2H), 2.41
(t, J = 6 Hz, 2H), 2.34 (s, 3H), 1.75–1.18 (m, 8H), 1.05–0.85 (m, 3H); 13C NMR
(CDCl3, 75 MHz): d 137.2, 131.2, 128.8, 120.9, 89.5, 80.4, 31.2, 28.7, 28.5, 22.4,
21.2, 19.3, 13.9.
Oct-1-yn-1-ylbenzene (1d)
1H NMR (CDCl3, 300 MHz) d: 7.5–7.36 (m, 2H), 7.35–7.2 (m, 3H), 2.41 (t,
J = 6 Hz, 2H), 1.75–1.15 (m, 8H), 1.02–0.75 (m, 3H); 13C NMR (CDCl3,
75 MHz): d 131.4, 128.0, 127.3, 124.0, 90.3, 80.4, 31.2, 28.6, 28.5, 22.4, 19.3, 13.9.
1-Methyl-3-(oct-1-yn-1-yl)benzene (1e)
1H NMR (CDCl3, 300 MHz): d 7.38–7.05 (m, 4H), 2.43–2.38 (m, 2H), 2.32 (s, 3H),
1.63–1.33 (m, 8H), 0.92–0.90 (m, 3H); 13C NMR (CDCl3, 75 MHz) : d 137.6,
132.0, 128.4, 128.2, 127.9, 123.7, 89.9, 80.5, 31.2, 28.6, 28.5, 22.4, 21.0, 19.3, 13.9.
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Direct use of nanoparticles as a heterogeneous catalyst
Fig. 2 a FESEM, b TEM image, c SAED pattern, and d HRTEM image of Pd-CoFe2O4 MNPs
1-Methyl-3-(non-1-ynyl)benzene (1f)
1H NMR (CDCl3, 300 MHz): d 7.25–7.1 (m, 4H), 2.41–2.39 (m, 2H), 2.33 (s, 3H),
1.65–1.28 (m, 10H), 0.92–0.9 (m, 3H); 13C NMR (CDCl3, 75 MHz): d 137.7, 132.1,
128.5, 128.128.3, 128.0, 123.9, 90.0, 80.6, 31.7, 29.7, 28.9, 22.6, 21.1, 19.4, 14.0.
1-Methyl-4-(non-1-yn-1-yl)benzene (1g)
1H NMR (CDCl3, 300 MHz): d 7.31(d, J = 6 Hz, 2H), 7.10 (d, J = 6 Hz, 2H), 2.41
(t, J = 6 Hz, 2H), 2.35 (s, 3H), 1.88–1.20 (m, 12H), 0.80 (m, 3H); 13C NMR
(CDCl3, 75 MHz): d 137.2, 131.3, 128.8, 120.9, 89.5, 80.4, 31.6, 29.6, 28.8, 28.7,
22.5, 21.2, 19.3, 13.9.
1-Nitro-2-(phenylethynyl)benzene (1h)
1H NMR (CDCl3, 300 MHz): d 8.08 (d, J = 9 Hz, 1H), 7.72 (d, J = 6 Hz, 1H),
7.62–7.60 (m, 3H), 7.49–7.39 (m, 4H); 13C NMR (CDCl3, 75 MHz): d 149.5, 134.5,
132.8, 132.0, 129.2, 128.5, 128.4, 124.7, 97.1, 84.7.
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S. Roy et al.
Fig. 3 EDX spectra of the Pd–CoFe2O4 MNPs
Fig. 4 Powered XRD pattern of Pd-CoFe2O4 MNPs (CFT stands for cobalt ferrite)
1-Methyl-4-(2-(2-nitrophenyl)ethynyl)benzene (1i)
1H NMR (CDCl3, 300 MHz): d 8.07 (t, J = 6 Hz, 1H), 7.71–7.68 (d, J = 9 Hz,
1H), 7.60–7.43 (m, 4H), 7.18 (d, J = 9 Hz, 2H), 2.38 (s, 3H); 13C NMR (CDCl3,
75 MHz): d 149.4, 139.5, 134.4, 132.7, 132.3, 131.9, 131.5, 129.1, 128.2, 124.6,
119.2, 118.9, 97.5, 84.2, 21.6.
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Direct use of nanoparticles as a heterogeneous catalyst
Fig. 5 M–H loop in VSM measurement of Pd-CoFe2O4 MNPs at room temperature
X
Pd-CoFe2O4 , Ethanol
R1
+
Y
Y
K2CO3 , 70 oC, 4-18 h
R2
Scheme 1 Sonogashira reaction using Pd nanoparticles-supported CoFe2O4 MNPs
1-tert-Butyl-4-(2-phenylethynyl)benzene (1j)
1H NMR (CDCl3, 300 MHz): d 7.61–7.53 (m, 4H), 7.44–7.37 (m, 5H), 1.39 (s, 9H);
13C NMR (CDCl3, 75 MHz): d 151.4, 131.5, 131.3, 128.3, 128.0, 125.3, 123.5,
120.2, 89.5, 88.7, 34.7, 31.1.
1-Fluoro-4-(2-phenylethylyn)benzene (1k)
1H NMR (CDCl3, 300 MHz): d 7.55–7.51 (m, 4H), 7.38–7.35 (m, 3H), 7.06 (t,
J = 9 Hz, 2H); 13C NMR (CDCl3, 75 MHz): d 164.1, 160.8, 133.5, 131.5, 128.3,
123.0, 119.3, 115.4, 88.9, 88.2.
1-tert-Butyl-4-(2-(2-nitrophenyl) ethynyl) benzene (1l)
1H NMR (CDCl3, 400 MHz): d 8.08 (d, J = 6 Hz, 1H), 7.71 (d, J = 9 Hz, 1H),
7.59–7.53 (m, 3H), 7.48–7.39 (m, 3H), 7.4 (d, J = 9 Hz, 2H), 1.34 (s, 9H); 13C
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S. Roy et al.
Table 1 Sonogashira reaction between iodobenzene and phenylacetylene using PdCoFe2O4
nanoparticles
Entry
Catalyst
concentration
(mol%)
Solvent
Base
Temperature
(°C)
Time
(h)
Yielda
(%)
1
2
3
4
5
6
7
8
9
1
3
5
5
5
5
5
5
5
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethylene glycol
DMF
K2CO3
K2CO3
K2CO3
Na2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
Cs2CO3
70
24
12
6
25
50
90
70
40
80
80
84
77
70
70
70
8
RT
80
36
12
12
12
12
110
110
90
DMF
Dioxane
Reaction condition: iodobenzene (1 mmol), phenylacetylene (1.1 mmol), base (2 mmol), solvent (5 ml)
a
Isolated yield after column chromatography
NMR (CDCl3, 75 MHz): d 152.6, 149.5, 134.5, 132.7, 131.8, 128.2, 125.4, 124.7,
119.3, 119.0, 97.5, 84.2, 31.1.
1-Methoxy-4-(phenylethynyl)benzene (1m)
1H NMR (CDCl3, 300 MHz): d 7.54–7.47 (m, 4H), 7.35–7.34 (m, 3H), 6.89 (d,
J = 9 Hz, 2H), 3.84 (s, 3H); 13C NMR (CDCl3, 75 MHz): d 159.6, 133.0, 131.4,
128.3, 127.9, 123.5, 115.3, 113.9, 89.3, 88.0, 55.2.
1-Nitro-4-(phenylethynyl)benzene (1n)
1H NMR (CDCl3, 300 MHz): d 8.22 (d, J = 9 Hz, 2H), 7.66 (d, J = 9 Hz, 2H),
7.58–7.57 (m, 2H), 7.41–7.39 (m, 3H); 13C NMR (CDCl3, 75 MHz): d 146.9, 132.2,
131.8, 130.2, 129.2, 128.5, 123.6, 122.0, 94.6, 87.5.
4-Methyl-2-(phenylethynyl)aniline (1o)
1H NMR (CDCl3, 300 MHz): d 7.64–7.48 (m, 2H), 7.45–7.3 (m, 3H), 7.22(s, 1H),
6.98 (d, J = 6 Hz, 1H), 6.67 (d, J = 6 Hz, 1H), 3.81 (s, 2H), 2.26 (s, 3H); 13C NMR
(CDCl3, 75 MHz): d 145.3, 132.1, 131.3, 130.5, 128.2, 128.0, 127.1, 123.3, 114.4,
107.8, 94.3, 85.1, 20.1.
1,2-Dip-tolyl-ethyne (1p)
1H NMR (CDCl3, 300 MHz): d 7.42 (d, J = 9 Hz, 4H), 7.15 (d, J = 9 Hz, 4H),
2.37 (s, 6H); 13C NMR (CDCl3, 75 MHz): d 138.1, 131.4, 129, 120.3, 88.8, 21.5.
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Direct use of nanoparticles as a heterogeneous catalyst
Table 2 Sonogashira coupling reaction of aryl iodides using Pd-CoFe2O4 MNPs
Entry Aryl halide
Alkyne
Products
Time (h) Yield (%)a
I
1
10
6
80
90
66
1a
I
2
1b
I
C6H13
C6H13
3
12
1c
I
C6H13
C6H13
C7H15
C6H13
4
12
16
15
77
61
65
1d
I
5
C6H13
1e
I
6
C7H15
1f
I
C7H15
C7H15
7
18
10
60
67
1g
NO2
8
I
1h
NO2
O2N
9
5
95
I
1i
NO2
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S. Roy et al.
Table 2 continued
Entry Aryl halide
Alkyne
Products
Time (h) Yield (%)a
I
10
6
90
1a
I
11
8
89
1j
I
F
12
7
7
4
91
88
94
1k
F
NO2
13
I
1l
NO2
I
OMe
14
1m
OMe
Reaction condition: Aryl bromide (1 mmol), alkyne (1.1 mmol), Pd-CoFe2O4 (5 mol%) and K2CO3
a
(2 mmol), ethanol (5 ml), 70 °C; Isolated yield after column chromatography
Results and discussion
Synthesis and characterization of Pd-CoFe2O4 MNPs
The CoFe2O4 MNPs were synthesized by a combined sonochemical and co-
precipitation technique in aqueous medium without any surfactant or organic
capping agent [7, 64]. After confirming the formation of cobalt ferrite MNPs using
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Direct use of nanoparticles as a heterogeneous catalyst
Table 3 Sonogashira coupling reaction of aryl bromide using Pd-incorporated CoFe2O4 MNPs
Entry
1
Aryl halide
Alkyne
Products
Time(h) Yield(%)a
Br
12
14
65
67
1a
Br
Br
2
3
1b
O2N
8
90
60
1n
NO2
Br
C6H13
C6H13
4
16
1c
Br
Br
C6H13
5
6
18
14
60
60
C6H13
1e
H2N
NH2
1o
Br
7
10
80
1p
Reaction condition: Aryl bromide (1 mmol), alkyne (1.1 mmol), Pd-CoFe2O4 (5 mol%) and K2CO3
a
(2 mmol), ethanol (5 ml), 70 °C; Isolated yield after column chromatography
EDX analysis, the presynthesized palladium nanoparticles were added to the cobalt
ferrite MNPs. The entire process was carried out under ultrasonic irradiation. Two
broad absorption peaks centered around 3,400 and 1,563 cm-1 along with other
characteristic peaks of spinel ferrite was found in the IR spectrum (Fig. 1) [65, 66].
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S. Roy et al.
Fig. 6 Reusability of Pd-CoFe2O4 MNPs
These two peaks are due to excessive hydroxyl ions trapped in the surface of
CoFe2O4 NPs, which gives its surface polarity and stability. The IR spectrum also
exhibits another strong absorption peak at 590 cm-1, which is due to the presence of
an Fe–O bond. The nanocatalyst was further characterized using FESEM and TEM
(Fig. 2a–d). The SEM picture indicates the spherical morphology of the nanopar-
ticles. The image shows that the particles are almost homogeneously distributed
throughout the sample. The elemental composition (weight percentage) of Pd-
CoFe2O4 MNPs was determined using EDX analysis (Fig. 3) and found to be:
Co = 20.18 %, Fe = 42.15 %, Pd = 3.81 %, and O = 33.86 %.
Powered XRD (Fig. 4) of the CoFe2O4 indicates the presence of all characteristic
peaks of the cubic spinel structure (JCPDS–data cards 3–864 and 22–1086) [65–68].
Weak signals for Pd species in the XRD pattern were observed, which is due to the
low percentage of palladium in the sample. From the XRD pattern of the Pd-
CoFe2O4, average crystalline size of the nanoparticles was measured using
Scherer’s equations [69] and was found be 30 nm. The particle size determined
from the XRD pattern was almost consistent with the SEM and HRTEM analysis.
Surface area of the Pd-incorporated CoFe2O4 was measured from BET single-
point surface area determination, which was found to be 122 m2 g-1. To study the
ferromagnetic property, VSM measurement of the Pd-CoFe2O4 nanocatalyst was
undertaken. From the M–H loop (Fig. 5) taken at room temperature with a
maximum applied field of 2 T, both saturation magnetization (Ms) and coercivity
values (Hc) were extracted. Coercivity, Hc was found to be 1,164 Oe with the
corresponding Ms value of 40.0 emu g-1 which indicates the ferromagnetic nature
of the nanostructure material.
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Direct use of nanoparticles as a heterogeneous catalyst
Sonogashira coupling reaction using Pd-CoFe2O4 MNPs
The as-synthesized Pd-incorporated CoFe2O4 nanoparticles were utilized as a
magnetically separable catalyst for the Sonogashira coupling reaction (Scheme 1).
Initial experiments to evaluate the catalytic performance of the nanocatalyst were
carried out between iodobenzene and phenylacetylene. For standardization of the
reaction condition, a series of reactions using different combinations of solvent,
base, and catalyst concentration were carried out (Table 1).
During our investigation, we found that the catalyst can be dispersed very well in
water or alcohol. Hence, initial experiments were carried out in ethanol as a solvent.
The reaction was carried out by heating iodobenzene (1 mmol), phenylacetylene
(1.1 mmol), and K2CO3 (2 mmol) at 70 °C (bath temperature) in the presence of
1 mol% of Pd-CoFe2O4 catalyst. The yield of the reaction was found to be 25 %
after 24 h of reaction. Hence, the amount of catalyst was increased gradually up to
5 mol%. Finally, the use of 5 mol% of catalyst could produce the desired product in
90 % yield after 6 h of reaction. The reaction was further examined using different
solvents as well as base. After performing several experiments, we found ethanol
and K2CO3 to be the best possible combinations of solvent and base, respectively,
for this reaction.
After optimization, the method was extended to a variety of iodobenzenes and
alkynes. The results are presented in Table 2. In general, the catalyst works well for
this reaction. It was observed that both aromatic as well as aliphatic alkynes react
efficiently under the reaction condition. However, the reaction takes a much longer
time in the case of aliphatic alkynes.
Having had success in promoting Sonogashira coupling for aryl iodides, the
reaction was tested for aryl bromides. Results are presented in Table 3. In case of
aryl bromides, the reaction takes a longer time compared to that for aryl iodides.
However, for aryl chloride the reaction does not work well, showing only a trace
amount of the coupling products.
Reusability of the catalyst was tested for the reaction of iodobenzene and
phenylacetylene. To reuse, the catalyst was separated by magnetic decantation after
completion of the reaction, dried at 100 °C for 6 h, and kept in a desiccator
overnight before reuse. The reaction was performed under the same conditions that
were used for the fresh experiment. It was observed that the catalyst could be reused
for five catalytic cycles without an appreciable loss in activity (Fig. 6).
Conclusions
In conclusion, we have developed a green process for Sonogashira coupling reaction
using Pd0-doped CoFe2O4 MNP as a catalyst. The catalyst was found to be very
effective in ethanol at 70 °C under ligand- and Cu-free conditions. Both aliphatic
and aromatic alkynes could be coupled with aryl iodides and aryl bromides using
our catalytic route. The catalyst could be recycled up to five catalytic cycles with
sustained catalytic activity. Easy recovery of the catalyst with the help of a magnet
makes it highly important for green and sustainable chemistry.
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S. Roy et al.
Acknowledgments Financial support from DST, India (Grant No. SR/NM/NS-18/2011) is gratefully
acknowledged. SR thanks UGC for a research fellowship. The authors would also like to acknowledge the
support from SAIF-GU, SAIF-NEHU, and CIF of IIT Guwahati for analytical facilities during the course
of investigations.
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