A new magnetically recyclable heterogeneous palladium(II) as a green catalyst for Suzuki-Miyaura cross-coupling and reduction of nitroarenes in aqueous medium at room temperature

Article abstract of DOI:10.1016/j.ica.2018.04.015

In the current work, a new stable and powerful magnetic nanoparticle supported Schiff base-palladium(II) (MNPs@SB-Pd) nanomagnetic catalyst was synthesized. The structural feature of the MNPs@SB-Pd nanomagnetic catalyst was properly characterized using a combination of attenuated total reflectance infrared spectroscopy (ATR-IR), ultraviolet–visible spectroscopy (UV–Visible), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), energy-dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller surface area analysis (BET). The air- and moisture stable prepared MNPs@SB-Pd nanomagnetic catalyst was applied in C–C bond formation through Suzuki-Miyaura cross-coupling reactions and reduction of nitroarenes. Use of green medium, eco-friendly, waste-free, efficient preparation leading to high yield of products, short reaction time and cost effective catalyst are the major benefits of the method presented. In addition, the MNPs@SB-Pd nanomagnetic catalyst was easily separated from the reaction mixture with the help of an external magnetic field and reused for five consecutive cycles in Suzuki-Miyaura cross-coupling and ten consecutive cycles in reduction of nitroarene reactions with no significant loss of catalytic efficiency.

Full text of DOI:10.1016/j.ica.2018.04.015

Accepted Manuscript
Research paper
A new magnetically recyclable heterogeneous palladium(II) as a green catalyst
for Suzuki-Miyaura cross-coupling and reduction of nitroarenes in aqueous me-
dium at room temperature
Vishal Kandathil, Tuhin S. Koley, K. Manjunatha, Ramesh B. Dateer, Rangappa
S. Keri, B.S. Sasidhar, Shivaputra A. Patil, Siddappa A. Patil
PII:
S0020-1693(17)31746-2
https://doi.org/10.1016/j.ica.2018.04.015
ICA 18206
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
13 November 2017
1 March 2018
10 April 2018
Please cite this article as: V. Kandathil, T.S. Koley, K. Manjunatha, R.B. Dateer, R.S. Keri, B.S. Sasidhar, S.A.
Patil, S.A. Patil, A new magnetically recyclable heterogeneous palladium(II) as a green catalyst for Suzuki-Miyaura
cross-coupling and reduction of nitroarenes in aqueous medium at room temperature, Inorganica Chimica Acta
(
2018), doi: https://doi.org/10.1016/j.ica.2018.04.015
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A new magnetically recyclable heterogeneous palladium(II) as a green catalyst
for Suzuki-Miyaura cross-coupling and reduction of nitroarenes in aqueous
medium at room temperature
a
a
a
a
a
†
†
Vishal Kandathil , Tuhin S. Koley , Manjunatha K , Ramesh B. Dateer , Rangappa S. Keri ,
b
c
a,
Sasidhar B. S. , Shivaputra A. Patil , Siddappa A. Patil *
a
Centre for Nano and Material Sciences, Jain University, Jain Global Campus, Kanakapura,
Ramanagaram, Bangalore 562112, India.
b
Organic Chemistry Section, Chemical Sciences & Technology Division, National Institute for
Interdisciplinary Science and Technology (CSIR), Thiruvananthapuram - 695019, Kerala, India.
c
Pharmaceutical Sciences Department, College of Pharmacy, Rosalind Franklin University of
Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA.
*
Corresponding author: Dr. Siddappa A. Patil
Tel: +91 80 27577254
Fax: +91 80 27577211
E-mail: p.siddappa@jainuniversity.ac.in
†These authors contributed equally.
1

Abstract
In the current work, a new stable and powerful magnetic nanoparticle supported Schiff base-
palladium(II) (MNPs@SB-Pd) nanomagnetic catalyst was synthesized. The structural feature of
the MNPs@SB-Pd nanomagnetic catalyst was properly characterized using a combination of
attenuated total reflectance infrared spectroscopy (ATR-IR), ultraviolet-visible spectroscopy
(UV-Visible), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), energy-
dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscopy (FESEM),
transmission electron microscopy (TEM), X-ray powder diffraction (XRD), thermogravimetric
analysis (TGA) and Brunauer-Emmett-Teller surface area analysis (BET). The air- and moisture
stable prepared MNPs@SB-Pd nanomagnetic catalyst was applied in C-C bond formation
through Suzuki-Miyaura cross-coupling reactions and reduction of nitroarenes. Use of green
medium, eco-friendly, waste-free, efficient preparation leading to high yield of products, short
reaction time and cost effective catalyst are the major benefits of the method presented. In
addition, the MNPs@SB-Pd nanomagnetic catalyst was easily separated from the reaction
mixture with the help of an external magnetic field and reused for five consecutive cycles in
Suzuki–Miyaura cross-coupling and ten consecutive cycles in reduction of nitroarene reactions
with no significant loss of catalytic efficiency.
Keywords: Magnetic nanoparticle; Schiff base-palladium(II); nanomagnetic catalyst; synthesis
and characterization; Suzuki-Miyaura cross-coupling; reduction of nitroarenes
2

1
. Introduction
The palladium catalysed Suzuki-Miyaura cross-coupling reactions are probably among
the most commonly employed approaches of C-C bond formation in organic transformations [1-
]. They have been used for the synthesis of various organic compounds, especially those of
3
pharmaceutical drugs, agrochemicals, supramolecular chemistry, complex natural products, and
engineering materials such as liquid crystals, molecular wires and conducting polymers [4-8].
Hence, many efforts have been made to the development of homogeneous systems for Suzuki-
Miyaura cross-coupling reaction, such as N-heterocyclic carbenes, oxime palladacycles,
diazabutadienes, amines and phosphine ligands [9-12]. On the other hand, complete reduction of
nitroarenes to aromatic amines is very much essential, as they are important intermediates for the
preparation of agriculture products, rubber chemicals, photographic chemicals, pharmaceuticals,
polyureathens and polymers [13-15]. The traditional methods to synthesize amines are based on
the amination of numerous functional groups such as H, F, Cl, Br, I, OH, etc. through the
corresponding diazonium salts [16] or the reduction of nitro compounds with homogeneous
catalysts [17-20]. However, major drawback of homogeneous catalysts is the difficulty of their
recovery from the reaction medium for reuse. This problem is of environmental and economic
concern in large-scale syntheses. Recent past, Schiff base transition metal complexes have been
successfully used as catalyst for various organic reactions [21, 22]. Stable Schiff base transition
metal complexes have been easily synthesized from many transition metal ions with different
oxidation states. In many cases, Schiff base transition metal complexes have been anchored on
different materials, such as dendrimers, polymers, silica, and zeolites [23-26]. However,
3

inorganic matrices show some advantages compared to organic supports such as high thermal,
chemical, and mechanical stability [27-30].
In this regard, magnetic nanoparticles supported catalysts were successfully used as
heterogeneous catalysts. The main benefits of magnetic nanoparticles supported catalyst is that
nanoparticles can be efficiently separated from the reaction mixture by using an external magnet
after completion of the reaction and easily reused for next round [31-35]. In addition, magnetic
nanoparticles supported catalysts also exhibit high dispersion and reactivity with high chemical
stability. These advantages of magnetic nanoparticles make them superior over other supporting
materials for immobilization of many catalysts and ligands on these nanoparticles [36].
Therefore, magnetic nanoparticles supported catalytic systems have been successfully applied as
potent, clean and environment friendly recoverable nanomagnetic catalysts for many organic
reactions.
Our continued interest in this area led us to explore the magnetic nanoparticles supported
Schiff base palladium(II) complex, which can be suitably applied for Suzuki-Miyaura cross-
coupling and reduction of nitroarenes reactions in aqueous (eco-friendly) medium at room
temperature, and then could be easily separated from the product to reuse. Herein, we report the
synthesis and characterization of a new magnetic nanoparticle supported Schiff base-
palladium(II) nanomagnetic catalyst for Suzuki-Miyaura cross-coupling of various aryl
bromides/chlorides/iodides with phenylboronic acid and reduction of nitroarenes reactions. The
MNPs@SB-Pd nanomagnetic catalyst was structurally characterized by the combination of
spectroscopic and microscopic techniques. Furthermore, MNPs@SB-Pd nanomagnetic catalyst is
shown to exhibit high catalytic activity in both Suzuki-Miyaura cross-coupling and reduction of
nitroarenes reactions.
4

2
. Experimental procedures
.1. Materials
All solvents were purified according to standard methods prior to use. Unless otherwise
stated, all reactions were performed under aerobic conditions in oven-dried glassware with
2
.
.
magnetic stirring. FeCl 6H O, FeCl 4H O, ammonium hydroxide, 2-hydroxy-3-
3
2
2
2
methoxybenzaldehyde, 3-aminopropyl triethoxysilane, palladium(II) acetate, aryl halides, bases
and phenylboronic acid were purchased from Sigma-Aldrich chemical company and were used
without further purification. Heating was accomplished by either a heating mantle or silicone oil
bath. Column chromatography was conducted on Silica gel 230-400 mesh (Merck) and
preparative thin-layer chromatography was carried out using 0.25 mm Merck TLC silica gel
plates with UV light as a visualizing agent. Yields refer to chromatographically pure material.
Concentration in vacuo refers to the removal of volatile solvent using a rotary evaporator
attached to a dry diaphragm pump (10-15 mm Hg) followed by pumping to a constant weight
with an oil pump (<300 mTorr). All the organic products were known and identified by
comparison of their physical and spectral data with those of authentic samples.
2
.2. Characterization
Attenuated total reflectance infrared spectra were recorded with Bruker Alpha Eco-ATR
spectrometer. UV-visible spectrophotometry was carried out by SHIMADZU UV-1800
A11454907691. Brunauer-Emmett-Teller surface areas were obtained by physisorption of N2
using Microtrac BELSORP MAX instrument. The elemental palladium content of the
nanomagnetic catalyst was determined by Thermo Electron IRIS INTREPID II XSP DUO
inductively coupled plasma-atomic emission spectroscopy. Transmission electron microscope
5

images were obtained using Jeol/JEM 2100 microscope. FESEM images along with energy
dispersive X-ray spectroscopy to observe morphology and elemental distributions respectively
were obtained with JEOLModel-JSM7100F. Thermogravimetric analysis was carried out by
Perkin Elmer, Diamond TG/DTA with a heating rate of 10.0 °C/min. X-ray powder
1
diffractometer patterns were obtained using Bruker AXS D8 Advance. H NMR spectra were
1
recorded at 400 MHz, and are reported relative to CDCl ( 7.27). H NMR coupling constants
3
(
J) are reported in Hertz (Hz) and multiplicities are indicated as follows: s (singlet), d (doublet), t
triplet), m (multiplet). Liquid chromatography mass spectra (LC-MS) were recorded on Agilent
(
technologies quadrupole LC-MS system.
2
2
.3. Syntheses
.3.1. Synthesis of hydroxyl substituted magnetic nanoparticles (MNPs) (1)
Hydroxyl substituted magnetic nanoparticles (1) were prepared by chemical co-
precipitation of ferric and ferrous salts according to the reported method with slight modification.
.
To a solution of FeCl 6H O (9.4 g, 34.77 mmol) in deionized water (100 mL) was added
3
2
.
FeCl 4H O (3.46 g, 17.40 mmol). The reaction mixture was stirred for 30 minutes at 85 °C.
2
2
Then, ammonium hydroxide (20 mL) solution was added drop wise to the reaction mixture with
vigorous stirring at 85 °C to produce black colored precipitate and stirring was continued for
additional 30 minutes. The black colored precipitate was separated by a permanent magnet and
washed with deionized water until pH neutral. Finally, hydroxyl substituted magnetic
nanoparticles were washed with ethanol (3 x 20 mL) and dried at 45-50 °C for 8 h.
2
.3.2. Synthesis of amine functionalized magnetic nanoparticles (AFMNPs) (3)
Hydroxyl substituted magnetic nanoparticles (1) (4.0 g) were dispersed in ethanol
(
EtOH)-water (H O) (2:1) mixture (140 mL) with ultrasonicating for 10 minutes. (3-
2
6

Aminopropyl)triethoxysilane (2) (15.2 g, 68.6 mmol) was added to the suspension and stirred at
5 °C for 24 h [37, 38]. Subsequently, the reaction mixture was cooled to room temperature. The
4
dark brown amine-functionalized magnetic nanoparticles (3) were collected using magnetic
separator, washed with deionized H O (3 x 20 mL) followed by ethanol (EtOH) (3 x 20 mL) and
2
dried at 45 °C for 12 h.
2
.3.3. Synthesis of magnetic nanoparticle tethered Schiff base (MNPs@SB) (5)
To a suspension of aminofunctionalized magnetic nanoparticles (3) (4.0 g) in EtOH (60
mL) was added 2-hydroxy-3-methoxybenzaldehyde (4) (4.0 g, 26.28 mmol). The reaction
mixture stirred at 70 °C for 24 h and then The dark brown colored
magnetic nanoparticle tethered Schiff base (5) was separated using an external magnetic field
and washed with methanol (MeOH) (3 x 20 mL) and dried at 45 °C for 12 h.
2
.3.4. Synthesis of magnetic nanoparticle tethered Schiff base palladium(II) complex
(MNPs@SB-Pd )nanomagnetic catalyst (6)
Palladium (II) acetate (0.87g, 3.87 mmol) was added to the solution of magnetic
nanoparticle tethered Schiff base (5) (3.5 g) in EtOH (40 mL) and stirred at 70 °C for 12 h.
the reaction mixture The MNPs@SB-Pd nanomagnetic catalyst
6) as dark brown colored solid was isolated by an external magnet, washed with H O (3 x 20
(
2
mL) followed by EtOH (3 x 20 mL) and dried at 70 °C for 6 h.
2
.3.5. General procedure for Suzuki-Miyaura cross-coupling reactions catalyzed by MNPs@SB-
Pd nanomagnetic catalyst
An oven-dried flask was charged with aryl halide (0.27 mmol), phenylboronic acid
0.036 g, 0.30 mmol), MNPs@SB-Pd nanomagnetic catalyst (0.05 mol% Pd) and K CO (0.082
(
2
3
g, 0.60 mmol). EtOH:H O (1:1, 10 mL) was added and the reaction mixture was stirred at room
2
7

temperature for designated time. The progress of the reaction was monitored using TLC. Then
the reaction mixture was allowed to cool to room temperature and quenched by adding
dichloromethane (20 mL) and the MNPs@SB-Pd nanomagnetic catalyst was separated using a
permanent magnet. Dichloromethane layer was separated from water layer through separatory
funnel and dried with anhydrous MgSO . The dried dichloromethane layer was concentrated in
4
vacuum and purified through column chromatography using hexane and ethyl acetate as eluting
solvent to get the corresponding products in excellent yields.
1
1
. 4-Nitrobiphenyl (Table 5, entry 1): Pale yellow crystals. Melting point = 111-114 °C; H NMR
(
2
400 MHz, CDCl ): δ (ppm) = 7.42-7.50 (m, 3H), 7.65 (d, J = 6.0 Hz, 2H), 7.75 (d, J = 6.8 Hz,
H), 8.28 (d, J = 6.8 Hz, 2H). LC-MS for C H NO : m/z = 200.05 [M+H] .
12 9 2
3
+
1
2
. 2-Phenylbenzaldehyde (Table 5, entry 2): Yellow oil. H NMR (400 MHz, CDCl ): δ (ppm) =
3
9
.92 (s, 1H), 7.34-7.32 (m, 3H), 7.39-7.36 (m, 2H), 7.55 (d, J = 7.6 Hz, 2H), 7.71-7.75 (m, 2H).
+
LC-MS for C H O: m/z = 183.03 [M+H] .
1
3
10
1
3
. 4-Phenylbenzaldehyde (Table 5, entry 3): Yellow crystals. Melting point = 57-58 °C; H NMR
(
400 MHz, CDCl ): δ (ppm) = 9.97 (s, 1H), 7.44-7.41 (m, 3H), 7.56 (d, J = 8.0 Hz, 2H), 7.70 (d,
3
+
J = 8.0 Hz, 2H), 7.91 (d, J = 8.0 Hz, 2H). LC-MS for C H O: m/z = 183.07 [M+H] .
1
3
10
1
4
. 4-Acetylbiphenyl (Table 5, entries 4 and 16): White powder. Melting point = 119-121 °C; H
NMR (400 MHz, CDCl ): δ (ppm) = 2.62 (s, 3H), 7.38-7.40 (m, 1H), 7.44-7.47 (m, 2H), 7.62 (d,
3
J = 7.6 Hz, 2H), 7.66 (d, J = 8.8 Hz, 2H), 8.02 (d, J = 8.4 Hz, 2H). LC-MS for C H O: m/z =
1
4
12
+
1
97.15 [M+H] .
1
5
. Biphenyl (Table 5, entries 5 and 17): Colorless crystals. Melting point = 68-71 °C; H NMR
(
400 MHz, CDCl ): δ (ppm) = 7.33 (t, J = 7.6 Hz, 2H), 7.45 (t, J = 7.6 Hz, 4H), 7.54 (d, J = 8.0
3
+
Hz, 4H). LC-MS for C H : m/z = 155.06 [M+H] .
1
2
10
6
. 4-Methylbiphenyl (Table 5, entries 6 and 18): White crystalline solid. Melting point = 45–48
1
°
C; H NMR (400 MHz, CDCl ): δ (ppm) = 2.25 (s, 3H), 7.26-7.30 (m, 2H), 7.35–7.38 (m, 4H),
3
7
.65 (s, 1H), 7.79 (d, J = 7.6 Hz, 2H). LC-MS for C H : m/z = 169.07 [M + H]+.
13 12
1
7
. 4-Aminobiphenyl (Table 5, entry 7): Purple crystals. Melting point = 52-55 °C; H NMR (400
MHz, CDCl ): δ (ppm) =7.51 (d, J = 8.4 Hz, 2H), 7.44-7.41 (m, 4H), 7.28-7.24 (m, 1H), 6.76 (d,
3
+
J = 8.0 Hz, 2H), 3.70 (s, 2H). LC-MS for C H N: m/z = 170.02 [M+H] .
1
2
11
1
8
. 4-Phenylbenzoic acid (Table 5, entry 8): White solid. Melting point = 220–223 °C; H NMR
(
400 MHz, CDCl ): δ (ppm) = 7.35–7.37 (m, 4H), 7.44–7.41 (m, 1H), 7.54–7.51 (m, 3H), 7.65
3
+
(d, J = 7.2 Hz, 1H). LC-MS for C H O : m/z = 199.12 [M + H] .
1
3
10
2
8

1
9
. 3-Phenylbenzoic acid (Table 5, entry 9): Off-white crystals. Melting point = 163–165 °C; H
NMR (400 MHz, CDCl ): δ (ppm) = 7.39–7.36 (m, 2H), 7.47–7.40(m, 1H), 7.62 (d, J = 7.2 Hz,
3
3
H] .
H), 7.74 (d, J = 7.6 Hz, 2H), 7.86 (d, J = 7.2 Hz, 1H). LC-MS for C H O : m/z = 199.07 [M +
13 10 2
+
1
0. 2,4-Difluoro-1,1’-biphenyl (Table 5, entry 10): Pale yellow crystals. Melting point = 61-63
1
°
C; H NMR (400 MHz, CDCl ): δ (ppm) = 7.12-7.14 (m, 4H), 7.35-7.37 (m, 2H), 7.52 (d, J =
3
+
8
.0 Hz, 2H). LC-MS for C H F : m/z = 191.03 [M+H] .
12 8 2
1
1. 4-Hydroxybiphenyl (Table 5, entries 11 and 15): White crystals. Melting point = 164-167 °C;
1
H NMR (400 MHz, CDCl ): δ (ppm) = 4.91 (s, 1H), 6.82 (d, J = 8.0 Hz, 2H), 7.24 (m, 1H), 7.35
3
(
=
d, J = 6.0 Hz, 2H), 7.41 (d, J = 8.0 Hz, 2H), 7.45 (d, J = 8.0 Hz, 2H). LC-MS for C H O: m/z
171.09 [M+H] .
1
2
10
+
1
2.4-Phenylbenzophenone: (Table 5, entry 12): Crystalline powder, Melting point = 102-105 °C;
1
H NMR (400 MHz, CDCl ): δ (ppm) = 7.41-7.66 (m, 8H), 7.70-7.75 (m, 4H), 7.81 (d, J=6.8 Hz,
2
3
+
H), LC-MS for C H O: m/z = 259.23 [M+H] .
19 14
1
1
3.4-Methoxybiphenyl (Table 5, entry 13): White powder. Melting point = 86-89 °C; H NMR
(
7
400 MHz, CDCl ): δ (ppm) = 3.84 (s, 3H), 6.97 (d, J = 8.0 Hz, 2H), 7.29 (t, J = 7.2 Hz, 1H),
.41 (t, J = 7.6 Hz, 2H), 7.51-7.55 (m, 4H). LC-MS for C H O: m/z = 185.10 [M+H] .
13 12
3
+
1
4.4-(tert-butyl)-1,1'-biphenyl: (Table 5, entry 14): Light brown powder, Melting point = 50-53
1
°
C; H NMR (400 MHz, CDCl ): δ (ppm) = 1.35 (s, 9H), 7.41-7.47 (m, 5H), 7.66-7.68 (m,2H),
3
+
7
.82 (d, J=8.4 Hz, 2H), LC-MS for C H : m/z = 211.05 [M+H] .
16 18
1
1
5. 2-Methoxybiphenyl (Table 5, entry 19): White powder. Melting point = 30-33 °C; H NMR
(
7
400 MHz, CDCl ): δ (ppm) = 3.75 (s, 3H), 6.91-6.98 (m, 2H), 7.24-7.27 (m, 3H), 7.34 (t, J =
.8 Hz, 2H), 7.46 (d, J = 6.0 Hz, 2H). LC-MS for C H O: m/z = 185.23 [M+H] .
13 12
3
+
2
.3.6. General procedure for reduction of nitroarene reactions catalyzed by MNPs@SB-Pd
nanomagnetic catalyst
In a round-bottomed flask equipped with nitroarene, MNPs@SB-Pd nanomagnetic
catalyst (0.05 mol% Pd with respect to nitroarene), NaBH (2.0 equiv) and H O (10 mL) were
4
2
added and stirred under air atmosphere at room temperature for designated time. The progress of
the reaction was monitored using TLC. After completion of the reaction, dichloromethane (20
mL) was added and the MNPs@SB-Pd nanomagnetic catalyst was separated using an external
magnet. The organic layer was washed with water (3 × 10 mL) and dried over anhydrous
9

MgSO . The crude reduced product was isolated by column chromatography over silica gel using
4
hexane and ethyl acetate to afford the corresponding pure reduced products in excellent yields.
All the reduced products were known molecules and were confirmed by comparing the melting
1
point, H NMR and mass spectroscopic data with authentic samples.
1
1
. Phenylamine (Table 8, entry1): Colorless liquid; H NMR (400 MHz, CDCl ): δ (ppm) = 3.54
3
(
s, 2H), 6.68 (d, J= 8.8 Hz, 2H), 6.71 (t, J = 7.6 Hz, 1H), 7.18 (d, J= 8.8 Hz, 2H), LC-MS for
+
C H N: m/z = 94.26 [M+H] .
6
7
1
2
. 4-Aminobenzoic acid (Table 8, entry 2): Off-white solid, Melting point = 187-189 °C; H
NMR (400 MHz, CDCl ): δ (ppm) = 5.91 (s, 2H), 7.52 (d, J = 7.2 Hz, 2H), 7.76 (d, J = 7.2 Hz,
3
+
2
H), LC-MS for C H NO : m/z = 138.17 [M+H] .
7 7 2
1
3
. 3-Aminobenzaldehyde (Table 8, entry 3): Pale yellow solid, Melting point = 29-32 °C; H
NMR (400 MHz, CDCl ): δ (ppm) = 4.55 (s, 2H), 6.54 (d, J = 8.4 Hz, 1H), 6.66-6.69 (m,
3
+
2
H),7.47 (t, J = 7.6 Hz,1H), 9.99 (s, 1H), LC-MS for C H NO: m/z = 122.13 [M+H] .
7 7
1
4
. Benzene-1,3-diamine (Table 8, entries 4 and 6): Colorless solid, Melting point = 64-67 °C; H
NMR (400 MHz, CDCl ): δ (ppm) = 3.54 (s, 4H), 6.42-6.45 (m, 2H), 6.98 (s, 1H), 7.32 (t, J =
3
+
7
.6 Hz, 1H), LC-MS for C H N : m/z = 109.19 [M+H] .
6 8 2
5
. 1-(4-aminophenyl)ethanone (Table 8, entry 7): Pale yellow solid, Melting point = 104-108 °C;
1
H NMR (400 MHz, CDCl ): δ (ppm) = 5.65 (s, 2H), 7.12 (d, J = 8.8 Hz, 2H), 7.54 (d, J=8.4 Hz,
2
3
+
H), 9.69 (s, 1H), LC-MS for C H NO: m/z = 136.18 [M+H] .
8 9
1
6
. Benzene-1,4-diamine (Table 8, entry 8): white solid, Melting point =137-142 °C; H NMR
(
[
400 MHz, CDCl ): δ (ppm) = 3.58 (s, 4H), 6.83-6.85 (m, 4H), LC-MS for C H N : m/z = 109.15
M+H] .
3
6
8
2
+
1
7
. 4-Aminobenzaldehyde (Table 8, entry 9): Pale yellow solid, Melting point = 77-79 °C; H
NMR (400 MHz, CDCl ): δ (ppm) = 5.65 (s, 2H), 7.14 (d, J = 8.8 Hz, 2H), 7.52 (d, J=8.4 Hz,
3
+
2
H), 9.67 (s, 1H), LC-MS for C H NO: m/z = 122.13 [M+H] .
7 7
2
.3.7. Procedure for recovery of MNPs@SB-Pd nanomagnetic catalyst
After completion of the reaction, MNPs@SB-Pd nanomagnetic catalyst was separated
using a permanent magnet from the reaction mixture. The separated MNPs@SB-Pd
nanomagnetic catalyst was then washed with water (2 x 10 mL) followed by ethanol (2 x 10 mL)
1
0

and dried at 45 °C for 12 h. Then, dried MNPs@SB-Pd nanomagnetic catalyst was used for next
round of reaction without further purification.
3
. Results and Discussion
3
.1. MNPs@SB-Pd nanomagnetic catalyst preparation
In continuation of our studies on the applications of magnetic nanoparticles tethered
palladium(II) complexes in various organic reactions [39, 40], herein, we report a simple and
efficient greener method for Suzuki-Miyaura cross-coupling between phenylboronic acid and a
range of aryl halides containing iodo, bromo and chloro moieties and also for the reduction of
nitroarenes in the presence of MNPs@SB-Pd nanomagnetic catalyst.
The MNPs@SB-Pd nanomagnetic catalyst was synthesized using a procedure shown in
Scheme 1. Initially, hydroxyl substituted magnetic nanoparticles (1) were synthesized from
.
.
chemical co-precipitation method using FeCl 6H Oand FeCl 4H O in basic solution at 85 °C.
3
2
2
2
Subsequently hydroxyl substituted magnetic nanoparticles were coated with (3-
aminopropyl)triethoxysilane (2) to obtain the amine functionalized magnetic nanoparticles (3).
Afterwards, the reaction of amino groups with 2-hydroxy-3-methoxybenzaldehyde (4) gave the
corresponding magnetic nanoparticle tethered Schiff base (5). Finally, magnetic nanoparticle
tethered Schiff base palladium(II) (6) was prepared through coordination of palladium(II) acetate
with magnetic nanoparticle tethered Schiff base.
1
1

Scheme 1. Synthetic schemes of (a) hydroxyl substituted magnetic nanoparticles (MNPs) and (b)
magnetic nanoparticles supported Schiff base palladium(II) nanomagnetic catalyst.
3
.2. Spectroscopic and microscopic characterization of MNPs@SB-Pd nanomagnetic catalyst
The newly synthesized MNPs@SB-Pd nanomagnetic catalyst was characterized from
attenuated total reflectance infrared spectroscopy, ultraviolet-visible spectroscopy, inductively
coupled plasma-atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, field-
emission scanning electron microscopy, transmission electron microscopy, X-ray powder
1
2

diffraction, thermogravimetric analysis and Brunauer-Emmett-Teller surface area analysis to
know the structure and composition.
3
.2.1. ATR-IR spectroscopy
Successful functionalization of the MNPs can be determined from the ATR-IR
spectroscopic technique. ATR-IR spectra of (a) MNPs, (b) AFMNPs, (c) SB@MNPs and (d)
MNPs@SB-Pd nanomagnetic catalyst are shown in Fig. 1. The ATR-IR spectrum of MNPs (Fig.
-1
1
a) exhibits a strong band at 546 cm assigned to Fe-O bond vibration and a broad band at 3396
-1
cm is attributed to the presence of OH groups on the surface of the MNPs. The bands observed
-1
around 1007 and 2904 cm are ascribed to the Si–O and C–H stretching vibrations of the propyl
-1
group from (3-aminopropyl)triethoxysilane apart from a Fe-O stretching vibration at 567 cm of
AFMNPs (Fig. 1b), which confirms the functionalization of aminopropyltriethoxysilane on the
-1
surface of the MNPs [39, 40]. A new peak observed at 1633 cm attributed to C=N stretching
-1
vibrations of SB@MNPs (Fig. 1c) apart from Si-O stretching vibrations at 1007 cm which
proves the formation of Schiff base on the surface of MNPs [41, 42]. The ATR-IR spectrum of
−
1
MNPs@SB-Pd nanomagnetic catalyst reveals typical bands at 2928, 1452, 1014 and 556cm
attributed to aliphatic C-H stretching, aromatic C=C stretching, Si-O stretching and Fe-O
stretching vibrations (Fig. 1d) [39, 40]. The absorption due to (C=N) in MNPs@SB-Pd is
-1
-1
observed at 1633 cm and has shifted to lower wave number at 1616 cm in MNPs@SB-Pd
indicating coordination of SB@MNPs through imine nitrogen to palladium (Fig. 1d) [41, 42].
Fig 2b and 2c demonstrated the ATR-IR spectra of five times recycled MNPs@SB-Pd
nanomagnetic catalyst from Suzuki-Miyaura cross-coupling reaction and ten time recycled
MNPs@SB-Pd nanomagnetic catalyst from reduction of nitroarene respectively. Results show
1
3

that recycled MNPs@SB-Pd nanomagnetic catalyst from both the reactions is intact except some
slight shift in the peak positions.
a
b
c
d
Fig. 1. ATR-IR spectra of (a) MNPs, (b) AFMNPs, (c) SB@MNPs and (d) MNPs@SB-Pd
nanomagnetic catalyst.
1
4

Fig. 2. ATR-IR spectra for (a) freshly prepared MNPs@SB-Pd nanomagnetic catalyst (b)
Suzuki-Miyaura recycled MNPs@SB-Pd nanomagnetic catalyst and (c) reduction recycled
MNPs@SB-Pd nanomagnetic catalyst.
3
.2.2. UV–visible spectroscopy
The UV-visible spectra are often very helpful in the evaluation of results furnished by
other methods of structural investigation. The UV-visible spectra of MNPs and MNPs@SB-Pd
nanomagnetic catalyst were recorded at room temperature using water as the solvent (Fig. 3).
The λmax observed for MNPs is 371 nm, whereas in the case of MNPs@SB-Pd nanomagnetic
catalyst, the λmax observed is at 389 nm. The shift in λmax from 371 nm to 389 nm could be
attributed to the successful surface functionalization of MNPs [43, 44].
1
5

Fig. 3. UV-visible spectra of (a) MNPs and (b) MNPs@SB-Pd nanomagnetic catalyst.
.2.3. Brunauer-Emmett-Teller surface area analysis
3
The surface functionalization of MNPs was additionally confirmed from analyzing the
surface area by Brunauer-Emmett-Teller surface area analysis (BET). Nitrogen adsorption–
desorption curves for (a) MNPs and (b) MNPs@SB-Pd nanomagnetic catalyst are shown in Fig.
4
a and 4b. The MNPs@SB-Pd nanomagnetic catalyst exhibited a type-II isotherm. The amount
of nitrogen adsorbed on the surface of MNPs is high compared to MNPs@SB-Pd. The surface
2
-1
2 -1
area of bare MNPs is 77.48 m g which was reduced to 71.11 m g upon the formation of
MNPs@SB-Pd nanomagnetic catalyst. The decrease in surface area reveals the successful
functionalization of MNPs with Schiff base palladium(II) complex which is evident from data
obtained from the BET [39, 40, 45].
1
6

Fig. 4. Nitrogen adsorption-desorption curve for (a) MNPs and (b) MNPs@SB-Pd nanomagnetic
catalyst.
3
.2.4. Transmission electron microscopy (TEM)
The size and morphology of MNPs, fresh MNPs@SB-Pd nanomagnetic catalyst and five
time recycled MNPs@SB-Pd nanomagnetic catalyst from Suzuki-Miyaura cross-coupling
reaction were evaluated using transmission electron microscopy. The TEM images of (a) MNPs
(b) MNPs@SB-Pd nanomagnetic catalyst and (c) five time recycled MNPs@SB-Pd
nanomagnetic catalyst are shown in Fig. 5a, 5b and 5c. TEM image confirm the spherical shape
of bare MNPs and size of the nanoparticles varied from 7 to 12 nm (Fig. 5a). On the other hand,
TEM image of MNPs@SB-Pd nanomagnetic catalyst show that the nanoparticles are quite
homogeneous and quasi-spherical with an average diameter of about 12-20 nm (Fig. 5d). In
addition, the recycled MNPs@SB-Pd nanomagnetic catalyst did not show much change in
morphology after being reused up to five times (Fig. 5c) [46-48].
1
7

b
a
c
d
Fig. 5. TEM images of (a) MNPs, (b) MNPs@SB-Pd nanomagnetic catalyst, (c) five time
recycled MNPs@SB-Pd nanomagnetic catalyst and (d) particle size distribution histogram.
3
.2.5. Field emission scanning electron microscopy (FESEM)
In addition to the TEM image, in attempting to confirm the size and morphology of the
freshly synthesized MNPs@SB-Pd nanomagnetic catalyst and five time recycled MNPs@SB-Pd
nanomagnetic catalyst, SEM images were recorded and are shown in Fig. 6a and 6b. It can be
inferred from the SEM images that the size of the freshly synthesized MNPs@SB-Pd
1
8

nanomagnetic catalyst particles is in the nanometer range in good accordance with the TEM
image (Fig. 6a) [49-51]. After five recycles, the surface morphology of recycled MNPs@SB-Pd
nanomagnetic catalyst remained almost same as that of freshly prepared MNPs@SB-Pd
nanomagnetic catalyst as shown in Fig. 6b.
a
b
Fig. 6. FESEM images of (a) MNPs@SB-Pd nanomagnetic catalyst and (b) five time recycled
MNPs@SB-Pd nanomagnetic catalyst.
3
.2.6. EDX analysis
Energy-dispersive X-ray spectroscopy is an analytical technique which is used for the
elemental analysis of the newly synthesized MNPs@SB-Pd nanomagnetic catalyst. EDX spectra
Fig. 7) for MNPs@SB-Pd nanomagnetic catalyst shows different characteristic signals
(
corresponding to C, N, O, Si, Fe and Pd atoms which validate the attachment of Schiff base-
palladium(II) complex on the surface of MNPs [52]. Elemental mapping of MNPs@SB-Pd
nanomagnetic catalyst was carried out to understand the distribution of elements in the
MNPs@SB-Pd nanomagnetic catalyst as shown in Fig. 8. From elemental mapping data it is
clear that all the elements are distributed evenly.
1
9

Fig. 7. EDX spectrum of MNPs@SB-Pd nanomagnetic catalyst.
C
N
O
Si
2
0

Fe
Pd
Fig. 8. Elemental mapping of MNPs@SB-Pd nanomagnetic catalyst.
3
.2.7. ICP-AES analysis
Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was employed to
determine the exact quantity of palladium in the MNPs@SB-Pd nanomagnetic catalyst. From
ICP-AES analysis, the amount of palladium loaded on the MNPs@SB-Pd nanomagnetic catalyst
was found to be 5.43% w/w.
3
.2.8. XRD analysis
The crystalline nature of the synthesized MNPs@SB-Pd nanomagnetic catalyst was
established using XRD. The diffraction pattern for MNPs and MNPs@SB-Pd nanomagnetic
catalyst is shown in Fig. 9a and 9b. XRD pattern of MNPs (Fig. 9a) reveals diffraction peaks at
2
θ of 30.09°, 35.59°, 43.07°, 53.43°, 57.37° and 62.90° corresponding to the crystal planes of
220), (311), (400), (422), (511) and (440) which confirms cubic spinel structure of MNPs. Fig.
b represents XRD pattern for MNPs@SB-Pd nanomagnetic catalyst which shows that the phase
(
9
2
1

remained unaltered even after the functionalization of MNPs which is in good agreement with
the TEM image. Diffraction peaks at 2θ of 40.05° and 47.00° corresponding to the crystal planes
of (111) and (200) shows the presence of palladium in the SB-Pd@MNPs nanomagnetic catalyst
[
53, 54].
Fig. 9. XRD pattern of (a) MNPs and (b) MNPs@SB-Pd nanomagnetic catalyst.
2
2

3
.2.9. Thermogravimetric analysis
The functionalization of MNPs with organic layer and Schiff base-palladium(II) complex
is inferred using TGA. The thermal stability of MNPs and MNPs@SB-Pd nanomagnetic catalyst
was determined through thermogravimetric analysis, which was carried out under an inert
o
o
nitrogen atmosphere between 40 C to 730 C. Fig. 10a showed 4% weight loss in the range of
o
5
0-110 C which is due to the loss of surface hydroxyl groups and moisture present on the
surface of the magnetic nanoparticles. The MNPs@SB-Pd nanomagnetic catalyst (Fig.10b)
o
decomposed in two steps. In first step, it showed the 1.5% weight loss in the range of 50 C to
o
1
10 C correspond to the loss of physically adsorbed solvent and surface hydroxyl groups. In the
o
second step, 6% mass loss in the range of 150-600 C was observed which is due to the complete
loss of covalently attached organic moiety. Therefore, from TGA result it is confirmed that the
MNPs@SB-Pd nanomagnetic catalyst was successfully anchored on magnetic nanoparticles [49,
5
5]. Furthermore, on the basis of TGA results, it is clear that SB-Pd@MNPs nanomagnetic
catalyst is stable up to a temperature of 200 °C which in turn allows the usage of this
MNPs@SB-Pd nanomagnetic catalyst in reactions carried out at higher temperature up to 200
°
C.
2
3

Fig. 10. TGA curves of (a) MNPs and (b) MNPs@SB-Pd nanomagnetic catalyst.
3
.3. Catalytic activity of the MNPs@SB-Pd nanomagnetic catalyst in Suzuki-Miyaura cross-
coupling reaction
MNPs@SB-Pd nanomagnetic catalyst was obtained as an air- and moisture stable
catalyst. After structural characterization of the synthesized MNPs@SB-Pd nanomagnetic
catalyst and in continuation of our work to test the catalytic potential and application of
synthesized MNPs@SB-Pd nanomagnetic catalyst, we next investigated the catalytic effects of
MNPs@SB-Pd nanomagnetic catalyst in Suzuki–Miyaura cross-coupling reaction. Initially,
reaction conditions were optimized on model Suzuki–Miyaura cross-coupling reaction between
4
-bromobenzonitrile and phenylboronic acid as shown in Scheme 2.
Scheme 2. Suzuki–Miyaura cross-coupling reaction between 4-bromobenzonitrile with
phenylboronic acid in the presence of MNPs@SB-Pd nanomagnetic catalyst.
2
4

During the optimization of reaction conditions, environmentally benign solvents were
given highest priority. Therefore, EtOH and H O were given highest priority as green solvent
2
system. The reaction conditions were optimized with a series of Suzuki-Miyaura cross-coupling
reactions of 4-bromobenzonitrile with phenylboronic acid in the presence of MNPs@SB-Pd
nanomagnetic as shown in Table 1.The preliminary outcome revealed that using K CO base,
2
3
EtOH:H O (1:1) solvent mixture, 0.15 mol% Pd of MNPs@SB-Pd nanomagnetic catalyst at
2
room temperature for 6 h resulted in highest yield (Table 1, entry 5). Then catalytic potential of
MNPs@SB-Pd nanomagnetic catalyst for varying base, solvent, temperature, time and catalyst
ratio were also studied for the model reaction.
Table 1
Optimization of conditions for Suzuki-Miyaura cross-coupling reaction of 4-bromobenzonitrile
a
with phenylboronic acid in the presence of MNPs@SB-Pd nanomagnetic catalyst .
o
b
Entry
Base
Solvent
EtOH
Temperature ( C)
Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
K CO
2
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
10
18
9
80
74
78
85
87
59
50
38
35
56
74
80
78
37
58
-
3
3
3
3
K CO
2
MeOH
K CO
2
H O
2
K CO
2
EtOH:H O (2:1)
7
2
K CO
2
EtOH:H O (1:1)
6
3
2
K CO
2
DMF
EtOH
EtOH
5
3
NaOH
KOH
5
7
Na CO
EtOH:H O (1:1)
6
2
3
2
.
1
1
1
1
1
1
1
0
1
2
3
4
5
6
Na PO 12H O
EtOH
MeOH
EtOH
8
3
4
2
K CO
2
18
10
9
3
3
3
3
3
3
K CO
2
K CO
2
H O
2
K CO
2
Acetone
DCM
24
7
K CO
2
K CO
2
CH CN
5
3
2
5

1
1
1
2
7
8
9
0
K CO
Toluene
DMF
RT
RT
RT
RT
10
5
67
59
-
2
3
3
3
3
K CO
2
K CO
2
THF
24
26
K CO
2
2-propanol
31
a
Reaction conditions: 4-bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol),
MNPs@SB-Pd(0.15 mol% palladium with respect to aryl halide),base (2.2 mmol) and solvent
10mL) in air. Isolated yield after separation by column chromatography; average of two runs.
b
(
3
.3.1. Effect of solvent on Suzuki-Miyaura cross-coupling reaction
The efficiency of various solvents such as EtOH, MeOH, H O, acetone, dichloromethane
2
(
DCM), acetonitrile (CH CN), toluene, dimethylformamide (DMF), tetrahydrofuran (THF), 2-
3
propanol and EtOH:H O (1:1) solvent mixture were examined. From the results obtained, it is
2
clear that the reaction proceeded smoothly with high yield in polar solvent like MeOH, EtOH,
H O and EtOH:H O (1:1) solvent mixture (Table 1, entries 11-13 and 5). When DCM, toluene
2
2
and DMF were used, cross-coupled product yield was medium (Table 1, entries 15, 17 and 18).
In case of acetone and 2-propanol, the rate of reaction was slow and cross-coupled product yield
was less (Table 1, entries 14 and 20). On the other hand, in CH CN and THF, reaction did not
3
proceed (Table 1, entries 16 and 19). However, EtOH:H O (1:1) solvent mixture as a green
2
solvent appears to be superior to the others (Table 1, entry 5).
Table 2
Suzuki-Miyaura cross-coupling reactions of 4-bromobenzonitrile with phenylboronic acid using
a
MNPs@SB-Pd nanomagnetic catalyst with varying base and temperature .
b
Entry
Base
Solvent
Temperature(°C)
Time(h)
Yield (%)
1
2
3
4
5
6
Na CO
EtOH:H O (1:1)
RT
RT
RT
RT
RT
RT
6
6
5
7
8
9
35
87
50
38
56
47
2
3
2
K CO
2
EtOH:H O (1:1)
3
2
NaOH
EtOH:H O (1:1)
2
KOH
EtOH:H O (1:1)
2
.
Na PO 12H O EtOH:H O (1:1)
3
4
2
2
KF
EtOH:H O (1:1)
2
2
6

7
8
9
Cs CO
EtOH:H O (1:1)
RT
RT
0
9
8
6
6
6
5
5
5
55
47
30
61
87
82
83
84
2
3
2
NEt3
EtOH:H O (1:1)
2
K CO
EtOH:H O (1:1)
2
3
2
1
0
1
2
3
4
K CO
EtOH:H O (1:1)
15
40
50
60
70
2
3
2
1
1
1
1
K CO
EtOH:H O (1:1)
2
3
3
3
3
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
2
a
Reaction conditions: 4-bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol),
MNPs@SB-Pd (0.15 mol% palladium with respect to aryl halide), base (2.2 mmol) and solvent
10 mL) in air. Isolated yield after separation by column chromatography; average of two runs.
b
(
3
.3.2. Effect of base on Suzuki-Miyaura cross-coupling reaction
The influence of various bases (Na CO , K CO , NaOH, KOH, Na PO 12H O, KF,
.
2
3
2
3
3
4
2
Cs CO and NEt ) at room temperature using EtOH:H O (1:1) solvent system and MNPs@SB-
2
3
3
2
Pd (0.15 mol% Pd with respect to aryl halide) nanomagnetic catalyst was studied in Suzuki-
Miyaura cross-coupling reaction between 4-bromobenzonitrile and phenylboronic acid. Among
.
4
these bases, Na CO , K CO Na PO 12H O and Cs CO were found to be rather effective
2
3
2
3,
3
2
2
3
(Table 2, entries 1, 2, 5 and 7) bases for Suzuki-Miyaura cross-coupling reaction. On the other
hand, bases like NaOH, KOH, KF and NEt showed lower conversion and lesser yields (Table 2,
3
entries 3, 4, 6 and 8). As evident from Table 2, base K CO gave the highest yield (Table 2, entry
2
3
2
).
3
.3.3. Effect of temperature on Suzuki-Miyaura cross-coupling reaction
To discover the catalytic potential of newly synthesized MNPs@SB-Pd nanomagnetic
catalyst towards Suzuki-Miyaura cross-coupling reaction of 4-bromobenzonitrile with
phenylboronic acid at varying temperatures, the model reaction was carried out at different
temperatures as shown in Table 2. Results shown that at higher temperatures (40, 50, 60 and 70
o
C) (Table 2, entries 11-14) the yields were almost same as that of room temperature (Table 2,
2
7

o
entry 2). However, at below room temperature (0 and 15 C), the rate of catalytic activity was
decreased with lower yields (Table 2, entries 9 and 10). Overall, the best yield of the cross-
coupling reaction was observed at room temperature (Table 2, entry 2).
3
.3.4. Effect of time on Suzuki-Miyaura cross-coupling reaction
To know the effect of time, Suzuki-Miyaura cross-coupling reaction of 4-
bromobenzonitrile with phenylboronic acid was exposed at different time intervals with
MNPs@SB-Pd nanomagnetic catalyst as summarized in Table 3. It is clear from the results
obtained that the yield of the Suzuki-Miyaura cross-coupling reaction increased with increase in
time (Table 3, entries 1-6) and further yield improvement was not observed after a time interval
of 6 h (Table 3, entries 6 and 7). Hence, 6 h is the optimum time required for the maximum yield
(Table 3, entry 6).
Table 3
Suzuki-Miyaura cross-coupling reactions of 4-bromobenzonitrile with phenylboronic acid using
a
MNPs@SB-Pd nanomagnetic catalyst at various time intervals .
b
Entry
Base
Solvent
Temperature (°C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
K CO
EtOH:H O (1:1)
RT
RT
RT
RT
RT
RT
RT
1
2
3
4
5
6
7
67
75
80
82
83
87
87
2
3
3
3
3
3
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
3
2
K CO
EtOH:H O (1:1)
2
3
2
a
Reaction conditions: 4-bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol),
MNPs@SB-Pd (0.15 mol% palladium with respect to aryl halide), base (2.2 mmol) and solvent
b
(
5 mL) in air. Isolated yield after separation by column chromatography; average of two runs.
2
8

3.3.5. Effect of catalyst ratio on Suzuki-Miyaura cross-coupling reaction
Catalyst ratio plays an important role in organic transformations. Suzuki-Miyaura cross-
coupling reaction between 4-bromobenzonitrile and phenylboronic acid was carried out with
varying palladium ratio starting from 0.025 mol% to 0.20 mol% (Table 4, entries 1-7). Increase
in catalyst ratio resulted in increased yield up to 0.15 mol% of palladium (Table 4, entries 1-6)
and further increase in the catalyst ratio does not increased the yield (Table 4, entry 7). Hence,
0
6
.15 mol% of palladium is the best catalyst ratio required for the maximum yield (Table 4, entry
) for Suzuki-Miyaura cross-coupling reaction between 4-bromobenzonitrile and phenylboronic
acid.
Table 4
Suzuki-Miyaura cross-coupling reaction of 4-bromobenzonitrile with phenylboronic acid using
a
different ratios of MNPs@SB-Pd nanomagnetic catalyst .
b
Entry
Base
Solvent
Temperature (°C)
Pd (mol%)
0.025
0.050
0.075
0.100
0.125
0.15
Yield (%)
1
2
3
4
5
6
7
K CO
2
EtOH:H O (1:1)
RT
RT
RT
RT
RT
RT
RT
35
59
63
76
82
87
85
3
3
3
3
3
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
2
K CO
2
EtOH:H O (1:1)
3
2
K CO
2
EtOH:H O (1:1)
0.20
3
2
a
Reaction conditions: 4-bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol), base (2.2
b
mmol) and solvent (10 mL) in air. Isolated yield after separation by column chromatography;
average of two runs.
3
.3.6. Suzuki-Miyaura cross-coupling reactions of different aryl halides
After optimization of the reaction conditions, the scope of MNPs@SB-Pd nanomagnetic
catalyst was studied for Suzuki-Miyaura cross-coupling reaction of various aryl halides with
phenylboronic acid and results are tabulated in Table 5. The experimental method is very simple
2
9