Magnetic nanoparticle-tethered Schiff base–palladium(II): Highly active and reusable heterogeneous catalyst for Suzuki–Miyaura cross-coupling and reduction of nitroarenes in aqueous medium at room temperature

Article abstract of DOI:10.1002/aoc.4266

As a continuation of our efforts to develop new heterogeneous nanomagnetic catalysts for greener reactions, we identified a Schiff base–palladium(II) complex anchored on magnetic nanoparticles (SB-Pd@MNPs) as a highly active nanomagnetic catalyst for Suzuki–Miyaura cross-coupling reactions between phenylboronic acid and aryl halides and for the reduction of nitroarenes using sodium borohydride in an aqueous medium at room temperature. The SB-Pd@MNPs nanomagnetic catalyst shows notable advantages such as simplicity of operation, excellent yields, short reaction times, heterogeneous nature, easy magnetic work up and recyclability. Characterization of the synthesized SB-Pd@MNPs nanomagnetic catalyst was performed with various physicochemical methods such as attenuated total reflectance infrared spectroscopy, UV–visible spectroscopy, inductively coupled plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, powder X-ray powder diffraction, thermogravimetric analysis and Brunauer–Emmett–Teller surface area analysis.

Full text of DOI:10.1002/aoc.4266

Received: 2 November 2017
DOI: 10.1002/aoc.4266
Revised: 13 December 2017
Accepted: 14 December 2017
F U L L P A P E R
Magnetic nanoparticle‐tethered Schiff base–palladium(II):
Highly active and reusable heterogeneous catalyst for
Suzuki–Miyaura cross‐coupling and reduction of
nitroarenes in aqueous medium at room temperature
K. Manjunatha1 | Tuhin S. Koley1 | Vishal Kandathil1 | Ramesh B. Dateer1 |
Geetha Balakrishna1 | B. S. Sasidhar2 | Shivaputra A. Patil3 | Siddappa A. Patil1
1 Centre for Nano and Material Sciences,
As a continuation of our efforts to develop new heterogeneous nanomagnetic
catalysts for greener reactions, we identified a Schiff base–palladium(II)
complex anchored on magnetic nanoparticles (SB‐Pd@MNPs) as a highly
active nanomagnetic catalyst for Suzuki–Miyaura cross‐coupling reactions
between phenylboronic acid and aryl halides and for the reduction of
nitroarenes using sodium borohydride in an aqueous medium at room temper-
ature. The SB‐Pd@MNPs nanomagnetic catalyst shows notable advantages
such as simplicity of operation, excellent yields, short reaction times, heteroge-
neous nature, easy magnetic work up and recyclability. Characterization of the
synthesized SB‐Pd@MNPs nanomagnetic catalyst was performed with various
physicochemical methods such as attenuated total reflectance infrared
spectroscopy, UV–visible spectroscopy, inductively coupled plasma atomic
emission spectroscopy, energy‐dispersive X‐ray spectroscopy, field‐emission
scanning electron microscopy, transmission electron microscopy, powder X‐ray
powder diffraction, thermogravimetric analysis and Brunauer–Emmett–Teller
surface area analysis.
Jain University, Jain Global Campus,
Kanakapura, Ramanagaram, Bangalore
562112, India
2 Organic Chemistry Section, Chemical
Sciences and Technology Division,
National Institute for Interdisciplinary
Science and Technology (CSIR),
Thiruvananthapuram 695019 Kerala,
India
3 Pharmaceutical Sciences Department,
College of Pharmacy, Rosalind Franklin
University of Medicine and Science, 3333
Green Bay Road, North Chicago, IL 60064,
U.S.A.
Correspondence
Siddappa A. Patil, Centre for Nano and
Material Sciences, Jain University, Jain
Global Campus, Kanakapura,
Ramanagaram, Bangalore 562112, India.
Email: p.siddappa@jainuniversity.ac.in
KEYWORDS
Funding information
DST‐SERB, India, Grant/Award Number:
YSS/2015/000010; DST‐Nanomission, India,
Grant/Award Number: SR/NM/NS‐20/2014
magnetic nanoparticle, nanomagnetic catalyst, reduction of nitroarenes, Schiff base–palladium(II),
Suzuki–Miyaura cross‐coupling
1 | INTRODUCTION
base–transition metal complexes have exhibited superior
catalytic activities and several homogeneous catalysts
The Suzuki–Miyaura cross‐coupling reactions are some of
the most extensively used C‐C bond forming reactions in
synthetic chemistry and have been utilized as an efficient
method to obtain pharmaceutical drugs, complex natural
products, engineering materials such as liquid crystals,
molecular wires and conducting polymers.[1–9] Numerous
catalysts have been developed for Suzuki–Miyaura
cross‐coupling reactions.[10–19] Among these, Schiff
have been developed.[20–23] Various organic amines have
been used for the synthesis of numerous chemicals such
as pesticides, agrochemicals, polymers, surfactants and
dyestuffs.[24] The traditional methods for the synthesis
of amines are based on the amination of functional
groups such as H, F, Cl, Br, I, OH, etc. through the
corresponding diazonium salts or the reduction of nitro
compounds with homogeneous catalysts.[25–29] However,
Appl Organometal Chem. 2018;e4266.
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https://doi.org/10.1002/aoc.4266

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MANJUNATHA ET AL.
a 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. Hence, huge efforts
have been made for the design and development of
various heterogeneous catalysts for Suzuki–Miyaura
cross‐coupling reactions and the reduction of
nitroarenes. Numerous examples of heterogenization
of Schiff base–transition metal complexes by immo-
bilization onto various supports, such as zeolites,[30,31]
polymers[32–34] and clays,[35] have been reported.
Inorganic matrices show some advantages over organic
supports, such as high thermal, chemical and mechanical
stability.
The increasing demand for environment‐friendly
(greener) chemical processes has stimulated many
researchers across the globe to develop heterogeneous
catalysts, which can be recovered easily and reused effec-
tively. Additionally, our efforts are targeted towards
utilizing these catalysts to develop greener reactions,
avoiding the use of organic solvents and high tempera-
tures. Recently developed magnetically recyclable cata-
lysts have proved to be promising, combining the
advantages of high activities and facile recovery in hetero-
geneous catalytic processes.[36–38] In a continuation of our
recent investigation of the application of magnetically
recyclable catalysts in cross‐coupling reactions,[39,40]
herein we report the synthesis and characterization of a
new nanomagnetic catalyst, a Schiff base–palladium(II)
2 | EXPERIMENTAL
2.1 | 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 glass-
ware with magnetic stirring. FeCl3⋅6H2O, FeCl2⋅4H2O,
ammonium hydroxide, 2‐hydroxy‐1‐naphthaldehyde,
3‐aminopropyltriethoxysilane, palladium(II) acetate, aryl
halides, bases and phenylboronic acid were purchased
from Sigma‐Aldrich and were used without further purifi-
cation. Heating was accomplished by either a heating
mantle or silicone oil bath. Column chromatography
was conducted with silica gel 230–400 mesh (Merck)
and preparative TLC 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 dia-
phragm pump (10–15 mmHg) followed by pumping to a
constant weight with an oil pump (<300 mTorr). All
organic products were known and identified by compari-
son of their physical and spectral data with those of
authentic samples.
2.2 | Instrumentation and Analyses
Attenuated total reflectance infrared (ATR‐IR) spectra
were recorded with a Bruker Alpha Eco‐ATR spectrome-
ter. UV–visible spectrophotometry was carried out
with a Shimadzu UV‐1800 A11454907691. Brunauer–
Emmett–Teller (BET) surface areas were obtained by
physisorption of nitrogen using a Microtrac BELSORP
MAX instrument. The elemental palladium content of
the nanomagnetic catalyst was determined with a Thermo
Electron IRIS INTREPID II XSP DUO inductively coupled
plasma atomic emission spectroscopy (ICP‐AES) instru-
ment. Transmission electron microscopy (TEM) images
were obtained using a Jeol/JEM 2100 microscope.
Field‐emission scanning electron microscopy (FESEM)
along with energy‐dispersive X‐ray spectroscopy (ESX)
to observe morphology and determine elemental
distributions, respectively, were conducted with a JEOL
model JSM7100F. Thermogravimetric analysis (TGA)
was carried out with a PerkinElmer Diamond TG/DTA
with a heating rate of 10.0 °C min−1. Powder X‐ray dif-
fraction (XRD) patterns were obtained using a Bruker
AXS D8 Advance. 1H NMR spectra were recorded at
400 MHz, and are reported relative to deuterated
complex
anchored
on
magnetic
nanoparticles
(SB‐Pd@MNPs), for Suzuki–Miyaura cross‐coupling
of various aryl halides with phenylboronic acid and for
the reduction of nitroarenes. The SB‐Pd@MNPs
nanomagnetic catalyst was structurally investigated using
a combination of spectroscopic and microscopic tech-
niques. Furthermore, the SB‐Pd@MNPs nanomagnetic
catalyst is shown to exhibit high catalytic activity in
Suzuki–Miyaura cross‐coupling reactions and in the
reduction of nitroarenes in aqueous medium at
room temperature. Additionally, the SB‐Pd@MNPs
nanomagnetic catalyst could be effortlessly separated
from a reaction system using an external magnet, and
could be reused in the next reaction cycle without signif-
icant loss of activity. The use of environmentally benign
solvent water and reusable SB‐Pd@MNPs nanomagnetic
catalyst at ambient temperature makes our reaction pro-
cedure more fascinating for cross‐coupling and reduction
reactions. Thus, our research efforts have identified the
perfect greener conditions to achieve high yields for
Suzuki–Miyaura cross‐coupling reactions as well as for
reduction of nitroarenes. We hope our research findings
will add great value to the catalysis and green chemistry
research field.
1
chloroform (CDCl3; δ = 7.27 ppm). H NMR coupling
constants (J) are reported in hertz (Hz) and multiplicities
are indicated as follows: s (singlet), d (doublet), t (triplet),

MANJUNATHA ET AL.
3 of 21
m (multiplet). Liquid chromatography–mass spectra
were recorded with an Agilent Technologies quadrupole
LC‐MS system.
reaction mixture was cooled to room temperature. The
resulting SB‐Pd@MNPs as a dark brown solid was
separated by magnetic decantation, washed with water
(3 × 20 ml) followed by ethanol (3 × 20 ml) and
dried at 45 °C for 12 h. The obtained yield of
SB‐Pd@MNPs nanaomagnetic catalyst was 3.81 g. In
addition, the purity of the SB‐Pd@MNPs nanaomagnetic
catalyst was confirmed using various physicochemical
methods.
2.3 | Synthesis of Hydroxyl‐Substituted
Magnetic Nanoparticles (MNPs) (1)
MNPs (1) were synthesized from chemical co‐
precipitation of Fe3+ and Fe2+ ions with a molar ratio of
2:1. A mixture of FeCl3⋅6H2O (4.70 g, 17.38 mmol) and
FeCl2⋅4H2O (1.73 g, 8.70 mmol) was dissolved in
deionized water (80 ml) and the resultant solution was
stirred for 30 min at 85 °C. Subsequently, ammonium
hydroxide (15 ml) solution was added slowly with
vigorous stirring at 85 °C to produce a black‐coloured
precipitate and stirring was continued for an additional
30 min. The obtained black‐coloured MNPs were
collected by magnetic decantation, washed repeatedly
with deionized water until neutrality, further washed
with ethanol (6 × 30 ml) and dried at 80 °C for 12 h.
2.7 | General Procedure for SB‐Pd@MNPs‐
Catalysed Suzuki–Miyaura Cross‐Coupling
Reactions
To a mixture of aryl halide (0.27 mmol), phenylboronic
acid (0.036 g, 0.30 mmol), SB‐Pd@MNPs nanomagnetic
catalyst (0.15 mol% Pd) and trisodium phosphate
(0.098 g, 0.60 mmol) in an oven‐dried round‐bottomed
flask was added EtOH–H2O (1:1, 10 ml) and the reaction
mixture was stirred at room temperature for the required
time. The progress of the reaction was monitored by TLC.
After completion of the reaction, the SB‐Pd@MNPs
nanomagnetic catalyst was separated using a permanent
magnet and dichloromethane (20 ml) was added. The
dichloromethane layer was separated from the water layer
using a separating funnel and dried with anhydrous mag-
nesium sulfate. The dried dichloromethane layer was con-
centrated in vacuum, and the crude cross‐coupled product
was purified through column chromatography over silica
gel using n‐hexane and ethyl acetate as eluting solvents
to obtain the desired purity. All the cross‐coupled
products were known molecules and were confirmed by
comparing the melting point and 1H NMR and mass spec-
troscopic data (see supporting information) with those of
authentic samples.
2.4 | Synthesis of Amine‐Functionalized
Magnetic Nanoparticles (AFMNPs) (3)
Nanoparticles 1 (4.0 g) were suspended in an EtOH–H2O
(2:1) mixture (140 ml) with ultrasonicating for 10 min.
3‐Aminopropyltriethoxysilane (2; 16.43 g, 74.22 mmol)
was added to the suspension and stirred at 40 °C for
20 h. Then the reaction mixture was cooled to room
temperature. The obtained dark brown AFMNPs (3) were
collected using a magnetic separator, washed with deion-
ized water (2 × 20 ml) followed by ethanol (2 × 20 ml) and
dried at 45 °C for 12 h.
2.5 | Synthesis of Magnetic Nanoparticle‐
Tethered Schiff Base (SB@MNPs) (5)
2.8 | General Procedure for Reduction of
Nitroarenes
Nanoparticles 3 (4.0 g) were dispersed in toluene (60 ml)
by ultrasonicating for 10 min. 2‐Hydroxynapthaldehyde
(4; 4.0 g, 23.23 mmol) was added in one portion to the
reaction mixture and stirred at 110 °C for 24 h. Then
the reaction mixture was cooled to room temperature.
The obtained dark brown SB@MNPs was collected using
an external magnetic field, washed with methanol (3 ×
20 ml) and dried at 45 °C for 12 h.
In a typical reduction reaction, nitroarene (0.05 g) was
mixed with the SB‐Pd@MNPs nanomagnetic catalyst
(0.05 mol% Pd) in water (10 ml) and the reaction mixture
was stirred for 1 min at room temperature. Subsequently,
NaBH4 (3.0 mol) was added to the flask and the reaction
mixture was vigorously stirred at room temperature for
the required time. The progress of the reaction was
checked through TLC. After completion of the reaction,
the SB‐Pd@MNPs nanomagnetic catalyst was separated
2.6 | Synthesis of Magnetic Nanoparticle‐
Supported Schiff Base–Palladium(II)
Complex (SB‐Pd@MNPs) (6)
using
a permanent magnet and dichloromethane
(20 ml) was added. The dichloromethane layer was sepa-
rated from the water layer using a separating funnel and
dried with anhydrous magnesium sulfate. The dried
dichloromethane layer was concentrated in vacuum,
To a solution of palladium(II) acetate (0.8 g,3.56 mmol)
in ethanol (40 ml) was added 5 (3.5 g) and the
reaction mixture was stirred at 78 °C for 12 h. Then the

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MANJUNATHA ET AL.
and the crude reduced product was purified through
column chromatography over silica gel using n‐hexane
and ethyl acetate as eluting solvents to afford the
pure product. All the reduced products were known
molecules and were confirmed by comparing the
melting point and H NMR and mass spectroscopic data
(see supporting information) with those of authentic
samples.
3 | RESULTS AND DISCUSSION
3.1 | Synthesis of SB‐Pd@MNPs
Nanomagnetic Catalyst
In continuation of our studies of the applications of palla-
dium complexes immobilized on MNPs in organic
transformations,[39,40] herein we report a simple and effi-
cient green 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 catalytic
amounts of SB‐Pd@MNPs nanomagnetic catalyst.
The synthetic pathway for the SB‐Pd@MNPs
nanomagnetic catalyst described in this work is outlined
in Scheme 1. Initially, 1 was prepared via chemical co‐pre-
cipitation from a 2:1 molar ratio of Fe3+ and Fe2+ with
ammonium hydroxide as base. Then, 3 was prepared by
the functionalization of 1 with 2 in EtOH–H2O mixture
at 40 °C. In the next step, 5 was synthesized from the reac-
tion between 4 and 3 in toluene at 110 °C. Finally, 5 was
1
2.9 | Procedure for Recovery of SB‐
Pd@MNPs Nanomagnetic Catalyst
After
reaction
completion,
the
SB‐Pd@MNPs
nanomagnetic catalyst was separated using a permanent
magnet. The separated SB‐Pd@MNPs nanomagnetic cata-
lyst was then washed with water (2 × 10 ml) followed by
ethanol (2 × 10 ml) and dried at 45 °C for 12 h. The dried
SB‐Pd@MNPs nanomagnetic catalyst was used for the
next reaction run without further purification.
SCHEME 1 Synthetic route to (a)
MNPs (1) and (b) SB‐Pd@MNPs
nanomagnetic catalyst (6)

MANJUNATHA ET AL.
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treated with palladium(II) acetate in ethanol at 78 °C
to afford the desired SB‐Pd@MNPs nanomagnetic
catalyst (6).
3.2 | Spectroscopic and Microscopic
Characterization
3.2.1 | ATR‐IR spectroscopy
All the synthesized compounds were structurally charac-
terized using the ATR‐IR spectroscopic technique.
Figure 1 displays ATR‐IR spectra of MNPs, AFMNPs,
SB@MNPs and SB‐Pd@MNPs nanomagnetic catalyst.
The strong absorption peak at 556 cm−1 is attributed to
Fe‐O bond stretching and the broad peak at around
3000–3500 cm−1 represents the O‐H stretching vibrations
of MNPs (Figure 1a).[39,40] The ATR‐IR spectrum of
AFMNPs (Figure 1b) displays a characteristic peak of
Si‐‐O at 1007 cm−1 and stretching vibrations of aliphatic
C‐H bonds at 2901 cm−1
, which confirms that
3‐aminopropyltriethoxysilane is successfully grafted on
the surface of MNPs.[39,40] In the ATR‐IR spectrum of
SB@MNPs, a new band is observed at1630 cm−1 due to
the C=N stretch of the imine group and another new
band at around 1405 cm−1 is assigned to the aromatic
C=C stretch (Figure 1c). These bands demonstrate that
2‐hydroxynaphthaldehyde has been successfully grafted
onto the AFMNPs.[41,42] The ATR‐IR spectrum of the
SB‐Pd@MNPs nanomagnetic catalyst reveals typical
bands at 2906, 1437, 1009 and 558 cm−1 attributed to
aliphatic C‐H stretching, aromatic C=C stretching, Si‐‐O
stretching and O‐‐H stretching vibrations (Figure 1
d).[39,40] The band due to (C=N) in the SB@MNPs spec-
trum is observed at 1630 cm−1 and is shifted to lower
wavenumber of 1619 cm−1 in the SB‐Pd@MNPs spectrum
indicating coordination of SB@MNPs through imine
nitrogen to palladium (Figure 1d).[41,42] Figure 2(b,c)
shows the ATR‐IR spectra of five‐times‐recycled
SB‐Pd@MNPs nanomagnetic catalyst from Suzuki–
Miyaura cross‐coupling reaction and ten‐times‐recycled
SB‐Pd@MNPs nanomagnetic catalyst from reduction of
nitroarenes. Results show that recycled SB‐Pd@MNPs
nanomagnetic catalyst from both reactions is intact except
for some slight shift in the peak positions.
3.2.2 | Thermogravimetric analysis
The thermal stability of MNPs and the SB‐Pd@MNPs
nanomagnetic catalyst was investigated using TGA under
nitrogen atmosphere from 40 to 740 °C at a rate of 10 °C
min−1. Figure 3(a) shows a weight loss of 3% at
40–110 °C which corresponds to removal of hydroxyl
groups present on the surface of the MNPs. On the other
FIGURE 1 ATR‐IR spectra of (a) MNPs, (b) AFMNPs, (c) SB‐
MNPs and (d) SB‐Pd@MNPs nanomagnetic catalyst

6 of 21
MANJUNATHA ET AL.
allows the usage of this SB‐Pd@MNPs nanocatalyst in
reactions carried out at temperatures up to 200 °C.
3.2.3 | BET surface area analysis
The surface functionalization of MNPs and the SB‐
Pd@MNPs nanomagnetic catalyst was investigated using
BET surface area analysis. The nitrogen adsorption and
desorption isotherms for MNPs and the SB‐Pd@MNPs
nanomagnetic catalyst are shown in Figure 4. The SB‐
Pd@MNPs nanomagnetic catalyst exhibited a type‐II iso-
therm. The amount of nitrogen adsorbed on MNPs is high
compared to that on the SB‐Pd@MNPs nanomagnetic cat-
alyst. The surface area of bare MNPs is 77.47 m2 g−1
which is decreased to 48.18 m2 g−1 upon the formation
of the SB‐Pd@MNPs nanomagnetic catalyst. The decrease
in surface area reveals the successful functionalization of
FIGURE 2 ATR‐IR spectra of SB‐Pd@MNPs nanomagnetic
catalyst: (a) freshly prepared, (b) recycled after Suzuki–Miyaura
reaction and (c) recycled after reduction reaction
FIGURE 3 TGA curves of (a) MNPs and (b) SB‐Pd@MNPs
nanomagnetic catalyst
hand, the SB‐Pd@MNPs nanomagnetic catalyst shows
weight loss in two stages (Figure 3(b)). In the first stage,
a weight loss of up to 3% is observed in the range
40–110 °C which is due to hydroxyl groups and physically
adsorbed solvent molecules present on the surface of
MNPs. A weight loss of up to 7% is found in the second
stage at 110–600 °C which is due to the thermal decompo-
sition of organic moieties anchored on the surface of
MNPs. Therefore, on the basis of the TGA results,
attachment of the Schiff base–palladium(II) complex on
the surface of MNPs is confirmed.[43,44] In addition, from
the TGA results, it is clear that the SB‐Pd@MNPs
nanomagnetic catalyst is stable up to 220 °C which in turn
FIGURE 4 Nitrogen adsorption–desorption curves for (a) MNPs
and (b) SB‐Pd@MNPs nanomagnetic catalyst

MANJUNATHA ET AL.
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MNPs with the Schiff base–palladium(II) complex, which
is evident from the BET data.[39,40,45]
3.2.4 | TEM analysis
TEM was used to obtain direct information regarding the
morphology and structure of the synthesized nanoparti-
cles. TEM images of MNPs, SB‐Pd@MNPs nanomagnetic
catalyst and recycled SB‐Pd@MNPs nanomagnetic catalyst
are shown in Figure 5. MNPs are spherical in nature and
the size of the nanoparticles varies from 7 to 10 nm
(Figure 5a). After immobilization of the Schiff base–
palladium(II) complex on the surface of MNPs, the size
increases to 10–20 nm with quasi‐spherical morphology
(Figure 5b). In addition, dark magnetic core present inside
the SB‐Pd@MNPs nanomagnetic catalyst particles can be
clearly seen in the TEM image. Furthermore, the recycled
SB‐Pd@MNPs nanomagnetic catalyst did not show much
change in morphology after being reused five times in
Suzuki–Miyaura cross‐coupling reaction (Figure 5c).[46–48]
Moreover, the selected area electron diffraction (SAED)
pattern (Figure 5d) of the SB‐Pd@MNPs nanomagnetic
catalyst reveals the material is polycrystalline in nature.
3.2.5 | FESEM analysis
To obtain more information about the surface morphology
of freshly prepared SB‐Pd@MNPs nanomagnetic catalyst
and recycled SB‐Pd@MNPs nanomagnetic catalyst after
use in Suzuki–Miyaura cross‐coupling reaction, FESEM
analysis was carried out. FESEM images are shown in
Figure 6. The FESEM image of freshly prepared SB‐
Pd@MNPs (Figure 6a) shows that nanoparticles are dis-
tributed uniformly and of nanometre size with spherical
morphology.[49–51] After five recycles in Suzuki–Miyaura
cross‐coupling reaction, the surface morphology of the
SB‐Pd@MNPs nanomagnetic catalyst remains almost
same as that of fresh freshly prepared SB‐Pd@MNPs
nanomagnetic catalyst as shown in Figure 6(b).
3.2.6 | EDX analysis
In order to confirm the existence of each element present
in the newly synthesized SB‐Pd@MNPs nanomagnetic
catalyst, EDX was employed. The EDX spectrum
(Figure 7) of the SB‐Pd@MNPs nanomagnetic catalyst
shows characteristic signals corresponding to C, N, O, Si,
Fe and Pd atoms which evidence the attachment of Schiff
base–palladium(II) complex on the surface of MNPs.[52]
Elemental mapping of the SB‐Pd@MNPs nanomagnetic
catalyst was carried out to understand the distribution of
elements as shown in Figure 8. From elemental mapping
data it is clear that all the elements are distributed evenly.
FIGURE
5
TEM images of (a) MNPs, (b) SB‐Pd@MNPs
nanomagnetic catalyst and (c) five‐times‐recycled SB‐Pd@MNPs
nanomagnetic catalyst in Suzuki–Miyaura cross‐coupling reaction.
(d) SAED pattern of SB‐Pd@MNPs nanomagnetic catalyst

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MANJUNATHA ET AL.
11.43% (w/w) of palladium on the SB‐Pd@MNPs
nanomagnetic catalyst.
3.2.8 | XRD analysis
The crystalline structure of MNPs and the SB‐Pd@MNPs
nanomagnetic catalyst was determined using the powder
XRD technique. The diffraction patterns of MNPs and
SB‐Pd@MNPs nanomagnetic catalyst are shown in
Figure 9. The XRD pattern of bare MNPs (Figure 9a)
shows diffraction peaks at 2θ 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. Figure 9(b)
depicts the XRD pattern of the SB‐Pd@MNPs
nanomagnetic catalyst which shows that the phase
remains unaltered even after the functionalization of
MNPs which is in good agreement with the TEM images.
Diffraction peaks at 2θ of 39.99° and 43.14° corresponding
to the crystal planes of (111) and (200) show the presence
of palladium in the SB‐Pd@MNPs nanomagnetic
catalyst.[53,54]
3.2.9 | UV–visible spectroscopy
The UV–visible spectra of MNPs and the SB‐Pd@MNPs
nanomagnetic catalyst in water are shown in Figure 10.
The spectra of MNPs and the SB‐Pd@MNPs
nanomagnetic catalyst display bands at 386 and 322 nm.
The band shift from 386 to 322 nm suggests the successful
surface functionalization of MNPs.[55,56]
FIGURE 6 FESEM images of (a) SB‐Pd@MNPs nanomagnetic
catalyst and (b) five‐times‐recycled SB‐Pd@MNPs nanomagnetic
catalyst in Suzuki–Miyaura cross‐coupling reaction
3.3 | Catalytic Activity of SB‐Pd@MNPs in
Suzuki–Miyaura Cross‐Coupling Reactions
After full characterization of the synthesized SB‐
Pd@MNPs nanomagnetic catalyst with spectroscopic
and microscopic methods, its catalytic potential was
investigated as a magnetically separable nanomagnetic
catalyst in Suzuki–Miyaura cross‐coupling reactions. The
Suzuki–Miyaura cross‐coupling reaction is one of the
most important methods for C‐C bond formation in
organic transformations. The Suzuki–Miyaura cross‐
coupling reaction is used in various organic reactions
and therefore it now belongs to an essential set of palla-
dium‐catalysed cross‐coupling reactions. Thus, the
catalytic potential of the synthesized SB‐Pd@MNPs
nanomagnetic catalyst was explored in Suzuki–Miyaura
cross‐coupling reactions. The reaction conditions were
optimized for a model Suzuki–Miyaura cross‐coupling
reaction of 4‐bromobenzonitrile with phenylboronic acid
as shown in Scheme 2.
FIGURE 7 EDX spectrum of SB‐Pd@MNPs nanomagnetic
catalyst
3.2.7 | ICP‐AES analysis
In addition, the exact quantity of palladium loaded on the
SB‐Pd@MNPs nanomagnetic catalyst was determined
using ICP‐AES analysis. This analysis shows a loading of

MANJUNATHA ET AL.
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FIGURE 8 Elemental mapping of SB‐Pd@MNPs nanomagnetic catalyst
FIGURE 10 UV–visible spectra of (a) MNPs and (b) SB‐
Pd@MNPs nanomagnetic catalyst
FIGURE 9 XRD patterns of (a) MNPs and (b) SB‐Pd@MNPs
nanomagnetic catalyst
catalyst as presented in Table 1. The preliminary outcome
revealed that using Na3PO4⋅12H2O base, EtOH–H2O (1:1)
solvent and 0.15 mol% Pd of SB‐Pd@MNPs nanomagnetic
catalyst at room temperature for 4 h resulted in the
highest yield (Table 1, entry 7). The catalytic potential of
the SB‐Pd@MNPs nanomagnetic catalyst with varying
base, solvent, temperature, time and catalyst ratio was
also studied for the model reaction, with the results pre-
sented in Tables 2–6, respectively.
Recently, worldwide significant research efforts have
been devoted to the replacement of organic solvents
(flammable, non‐biodegradable and toxic) in chemical
reactions by green solvents (non‐toxic, cheap, bio‐renew-
able and non‐flammable). Thus, ethanol and water were
given high priority as solvents during process optimiza-
tion. The reaction conditions were optimized for model
reaction in the presence of SB‐Pd@MNPs nanomagnetic

10 of 21
MANJUNATHA ET AL.
SCHEME 2 Suzuki–Miyaura cross‐
coupling reaction of 4‐bromobenzonitrile
with phenylboronic acid
TABLE 1 Optimization of conditions for Suzuki–Miyaura cross‐coupling model reaction in presence of SB‐Pd@MNPs nanomagnetic
catalysta
Entry
Base
K2CO3
Solvent
EtOH
Temperature (°C)
Time (h)
Yield (%)b
1
RT
3.0
45
2
Na2CO3
EtOH
EtOH–H2O (1:1)
EtOH
RT
RT
RT
RT
RT
RT
RT
40
3.0
3.0
10.0
7.5
3.0
4.0
5.0
4.0
4.0
4.0
62
75
45
65
—
94
94
90
92
92
3
Na2CO3
4
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
5
H2O
6
DMF
7
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
8
9
10
11
50
70
aReaction conditions: 4‐bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol), SB‐Pd@MNPs nanomagnetic catalyst (0.15 mol% Pd with respect to aryl
halide), base (2.2 mmol) and solvent (10 ml) in air.
bIsolated yield after separation by column chromatography; average of two runs.
TABLE 2 Suzuki–Miyaura cross‐coupling model reaction using SB‐Pd@MNPs nanomagnetic catalyst with various basesa
Entry
Base
Na2CO3
Solvent
Temperature (°C)
Time (h)
Yield (%)b
1
EtOH–H2O (1:1)
RT
4.0
80
2
3
4
5
6
7
8
K2CO3
NaOH
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
RT
RT
RT
RT
RT
RT
RT
4.0
4.0
4.0
4.0
4.0
4.0
4.0
85
37
30
94
32
85
59
KOH
Na3PO4⋅12H2O
KF
Cs2CO3
Triethylamine
aReaction conditions: 4‐bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol), SB‐Pd@MNPs nanomagnetic catalyst (0.15 mol% Pd with respect to aryl
halide), base (2.2 mmol) and solvent (10 ml) in air.
bIsolated yield after separation by column chromatography; average of two runs.
3.4 | Effect of Base on Suzuki–Miyaura
Cross‐Coupling Reaction
3.5 | Effect of Solvent on Suzuki–Miyaura
Cross‐Coupling Reaction
The catalytic potential of the SB‐Pd@MNPs
nanomagnetic catalyst was studied in the model reaction
using various bases: Na2CO3, K2CO3, NaOH, KOH,
Na3PO4⋅12H2O, KF, Cs2CO3 and triethylamine (Table 2;
Figure 11a). Among the bases employed, Na3PO4⋅12H2O
showed good conversion rate (Table 2, entry 5) and bases
Na2CO3, K2CO3, NaOH, KOH, KF, Cs2CO3 and
trimethylamine resulted in lesser conversion (Table 2,
entries 1–4 and 6–8).
The catalytic activity of the SB‐Pd@MNPs nanomagnetic
catalyst in the model reaction was investigated
using various solvents, namely H2O, EtOH, MeOH,
dimethylformamide (DMF), tetrahydrofuran (THF),
toluene, acetone, acetonitrile (CH3CN), dichloromethane
(DCM), isopropyl alcohol (IPA) and EtOH–H2O (1:1)
mixture. The results are presented in Table 3 and
Figure 11(b). It is clear that the SB‐Pd@MNPs
nanomagnetic catalyst worked well with polar solvents

MANJUNATHA ET AL.
11 of 21
TABLE 3 Suzuki–Miyaura cross‐coupling model reaction in presence of SB‐Pd@MNPs nanomagnetic catalyst with various solventsa
Entry
Base
Solvent
Temperature (°C)
Time (h)
Yield (%)b
1
Na3PO4⋅12H2O
MeOH
RT
4.0
60
2
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
EtOH
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
70
30
—
—
—
26
—
—
—
94
3
H2O
4
CH3CN
Acetone
THF
5
6
7
Toluene
DCM
8
9
DMF
10
11
IPA
EtOH–H2O (1:1)
aReaction conditions: 4‐bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol), SB‐Pd@MNPs nanomagnetic catalyst (0.15 mol% Pd with respect to aryl
halide), base (2.2 mmol) and solvent (10 ml) in air.
bIsolated yield after separation by column chromatography; average of two runs.
TABLE 4 Suzuki–Miyaura cross‐coupling model reaction using SB‐Pd@MNPs nanomagnetic catalyst at various temperaturesa
Entry
Base
Solvent
Temperature (°C)
Time (h)
Yield (%)b
1
Na3PO4⋅12H2O
EtOH–H2O (1:1)
0
4.0
30
2
3
4
5
6
7
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
15
RT
40
50
60
70
4.0
4.0
4.0
4.0
4.0
4.0
40
94
90
92
92
92
aReaction conditions: 4‐bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol), SB‐Pd@MNPs nanomagnetic catalyst (0.15 mol% Pd with respect to aryl
halide), base (2.2 mmol) and solvent (10 ml) in air.
bIsolated yield after separation by column chromatography; average of two runs.
TABLE 5 Suzuki–Miyaura cross‐coupling model reaction using SB‐Pd@MNPs nanomagnetic catalyst at various time intervalsa
Entry
Base
Solvent
Temperature (°C)
Time (h)
Yield (%)b
1
Na3PO4⋅12H2O
EtOH–H2O (1:1)
RT
1.0
73
2
3
4
5
6
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O(1:1)
EtOH–H2O (1:1)
RT
RT
RT
RT
RT
2.0
3.0
4.0
5.0
6.0
81
87
94
94
93
aReaction conditions: 4‐bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol), SB‐Pd@MNPs nanomagnetic catalyst(0.15 mol% Pd with respect to aryl
halide), base (2.2 mmol) and solvent (10 ml) in air.
bIsolated yield after separation by column chromatography; average of two runs.

12 of 21
MANJUNATHA ET AL.
TABLE 6 Suzuki–Miyaura cross‐coupling model reaction using various SB‐Pd@MNPs nanomagnetic catalyst ratiosa
Entry
Base
Solvent
Temperature (°C)
Pd (mol%)
Yield (%)b
1
Na3PO4⋅12H2O
EtOH–H2O (1:1)
RT
0.025
50
2
3
4
5
6
7
8
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
RT
RT
RT
RT
RT
RT
RT
0.05
75
80
85
88
94
94
94
0.075
0.10
0.125
0.15
0.175
0.20
aReaction conditions: 4‐bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol), base (2.2 mmol) and solvent (10 ml) in air.
bIsolated yield after separation by column chromatography; average of two runs.
FIGURE 11 Plots depicting yields of Suzuki–Miyaura cross‐coupling products against varying (a) base, (b) solvent, (c) temperature, (d) time
and (e) catalyst ratio
like MeOH, EtOH, H2O and EtOH–H2O mixture (Table 3,
entries 1–3 and 11). Furthermore, the model reaction in
EtOH–H2O (1:1) mixture gave the highest yield (Table 3,
3.6 | Effect of Temperature on Suzuki–
Miyaura Cross‐Coupling Reaction
To explore the catalytic activity of our new SB‐Pd@MNPs
entry 11).
nanomagnetic catalyst at varying temperatures, the model

MANJUNATHA ET AL.
13 of 21
TABLE 7 Suzuki–Miyaura cross‐coupling reactions between aryl halides and phenylboronic acid catalysed by SB‐Pd@MNPs nanomagnetic
catalysta
Entry
Aryl halide
Product
Time (h)
Yield (%)b
1
4
94
2
3
3
3
71
81
4
5
15
15
75
72
6
22
84
7
8
9
2.5
0.5
0.5
89
43
56
10
11
12
1
88
85
87
0.5
22
(Continues)

14 of 21
MANJUNATHA ET AL.
TABLE 7 (Continued)
Entry
Aryl halide
Product
Time (h)
Yield (%)b
13
1
22
14
22.5
81
15
16
0.5
74
60
22.5
17
17
68
18
19
20
23
24
0.5
Trace
Trace
95
aReaction conditions: aryl halide (1.0 mmol), phenylboronic acid (1.1 mmol), SB‐Pd@MNPs nanomagnetic catalyst (0.15 mol% Pd), base (2.2 mmol) and EtOH–
H2O (10 ml) in air.
bIsolated yield after separation by column chromatography; average of two runs.
reaction was carried out at different temperatures as pre-
sented in Table 4 (Figure 11c). Results show high catalytic
activity at room temperature (Table 4, entry 3) and above
(Table 4, entries 4–7); hence the preferred reaction tem-
perature for the model reaction is room temperature
(Table 4, entry 3). On the other hand, below room temper-
ature the yields were less (Table 4, entries 1 and 2).
period of 4 h (Table5, entries 5 and 6). Therefore, 4 h is
the optimum time period required for the maximum yield
(Table 5, entry 4).
3.8 | Effect of Catalyst Ratio on Suzuki–
Miyaura Cross‐Coupling Reaction
Catalyst ratio plays an important role in the Suzuki–
Miyaura cross‐coupling reaction. In order to investigate
the effect of the quantity of catalyst, various catalyst ratios
of 0.025, 0.05, 0.075, 0.10, 0.125, 0.15, 0.175 and 0.20 mol%
of Pd were used in the model reaction (Table 6; Figure 11
e). Increase in catalyst ratio resulted in increased yield up
to 0.15 mol% of Pd (Table 6, entries 1–6) and further
increase in the catalyst ratio did not increase the yield
(Table 6, entries 7 and 8). Hence, 0.15 mol% of Pd is the
3.7 | Effect of Time on Suzuki–Miyaura
Cross‐Coupling Reaction
To understand the effect of time, the model reaction was
conducted for various time intervals with the SB‐
Pd@MNPs nanomagnetic catalyst (Table 5; Figure 11d).
It is clear from the results obtained that the yield
increased with increasing time (Table 5, entries 1–4) and
further yield improvement was not observed after a time

MANJUNATHA ET AL.
15 of 21
best catalyst ratio required for the maximum yield
(Table 6, entry 6).
was confirmed by the presence of a negligible amount of
the homocoupled product obtained. For additional clarifi-
cation on selectivity, Suzuki–Miyaura cross‐coupling reac-
tions were carried out without aryl halides under
optimized conditions. The biphenyl homocoupled prod-
uct obtained was in a trace amount, which indicated that
the SB‐Pd@MNPs nanomagnetic catalyst is highly selec-
tive.[57,58] A plausible mechanism for our newly investi-
gated SB‐Pd@MNPs nanomagnetic catalyst is illustrated
in Scheme 3 which delivers the C‐C coupling products
via possible mechanistic intermediates (I–III).[13]
3.9 | Suzuki–Miyaura Cross‐Coupling
Reactions of Aryl Halides
To explore the scope of the Suzuki–Miyaura cross‐
coupling reaction, various aryl halides were reacted
with phenylboronic acid catalysed by SB‐Pd@MNPs
nanomagnetic catalyst using the aforementioned opti-
mized conditions and the results are presented in
Table 7. The obtained results reveal that variously
substituted aryl bromides, aryl chlorides and aryl iodide
are converted into the corresponding products in good to
excellent yields. Aryl halides with both electron‐
withdrawing and electron‐donating groups were sub-
jected to the reaction. The results show that all aryl
halides gave good to excellent yields, but the steric effect
played an important role in conversion of aryl halide to
product. Nevertheless, aryl chloride (Table 7, entries
16–18) reacted more slowly than aryl bromide (Table 7,
entries 1–5, 7–11, 13 and 15) and aryl iodide (Table 7,
entry 20) derivatives. Overall, these results confirmed that
the SB‐Pd@MNPs nanomagnetic catalyst is highly active
towards Suzuki–Miyaura cross‐coupling reactions. Also,
the selectivity of the SB‐Pd@MNPs nanomagnetic catalyst
3.10 | Catalyst Recyclability and Leaching
in Suzuki–Miyaura Cross‐Coupling
Reactions
Catalyst recycling is important from industrial, economic
and environmental points of view. Hence, the
SB‐Pd@MNPs nanomagnetic catalyst was studied in the
model reaction. We successfully recovered the
SB‐Pd@MNPs nanomagnetic catalyst after cross‐coupling
reaction by applying an external magnetic field, washing
with ethanol and water and drying. The recovered
SB‐Pd@MNPs nanomagnetic catalyst can be reused for
up to five cycles without loss of catalytic activity
(Table 8). After five recycles, a decrease in catalytic activ-
ity was observed (Figure 12; Table 8). The ATR‐IR spec-
trum (Figure 2b), TEM image (Figure 5c) and FESEM
image (Figure 6b) of five‐times‐recycled SB‐Pd@MNPs
nanomagnetic catalyst were obtained. No change in the
morphology was observed through the TEM image after
recycling up to five tomes which is further confirmed by
the FESEM image. Furthermore, the ATR‐IR spectrum
shows that the SB‐Pd@MNPs nanomagnetic catalyst is
intact after recycling.
Leaching of palladium is a serious problem for sup-
ported palladium catalysts, and prevents catalyst separa-
tion and recycling. Hence, leaching study was done for
magnetic separation of the SB‐Pd@MNPs nanomagnetic
SCHEME 3 Proposed mechanism of Suzuki–Miyaura reaction
TABLE 8 Recyclability of the SB‐Pd@MNPs nanomagnetic catalyst in model reactiona
Entry
1
Base
Solvent
Temperature (°C)
RT
Catalyst run
Fresh
Yield (%)b
94
Na3PO4⋅12H2O
EtOH–H2O (1:1)
2
3
4
5
6
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
Na3PO4⋅12H2O
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
EtOH–H2O (1:1)
RT
RT
RT
RT
RT
1st recycle
2nd recycle
3rd recycle
4th recycle
5th recycle
94
93
92
92
90
aReaction conditions: 4‐bromobenzonitrile (1.0 mmol), phenylboronic acid (1.1 mmol), SB‐Pd@MNPs nanomagnetic catalyst (0.15 mol% Pd), base (2.2 mmol)
and solvent in air.
bIsolated yield after separation by column chromatography.

16 of 21
MANJUNATHA ET AL.
Suzuki–Miyaura cross‐coupling reactions.[59–70] Some of
the main benefits of the SB‐Pd@MNPs nanomagnetic
catalyst are: (i) use of green solvents, (ii) short reaction
times, (iii) mild reaction conditions, (iv) excellent selec-
tivity, (v) ability to easily remove the catalyst from reac-
tion mixture and (vi) reusability for subsequent
reactions. In addition, the SB‐Pd@MNPs nanomagnetic
catalyst can be prepared using inexpensive chemicals
under aerobic conditions, which do not require a
sophisticated setup.
3.12 | Activity of SB‐Pd@MNPs
Nanomagnetic Catalyst in Reduction of
Nitroarenes
FIGURE 12 Recycling efficiency of SB‐Pd@MNPs nanomagnetic
catalyst in Suzuki–Miyaura cross‐coupling reaction of 4‐
bromobenzonitrile and phenylboronic acid
In continuation of our investigation of the catalytic
activity and application of the newly synthesized SB‐
Pd@MNPs nanomagnetic catalyst, we next studied its cat-
alytic effect in the reduction of nitroarenes. To optimize
the reaction conditions, reduction of nitrobenzene to
amine was used as a model reaction (Scheme 4). Condi-
tions such as catalyst ratio, amount of reducing agent
(NaBH4), solvent, temperature and time were investi-
gated. As expected, target product could not be detected
in the absence of the SB‐Pd@MNPs nanomagnetic cata-
lyst. The best results were achieved by carrying out the
reaction with 3.0 equivalents of reducing agent, water as
solvent (10 ml) and 0.05 mol% Pd of SB‐Pd@MNPs
catalyst after 30 min of reaction time, and the same reac-
tion was additionally continued for more than 4 h and
was observed through TLC. Further conversion was not
observed and the isolated yield was around 65%. This
proved that leaching of the SB‐Pd@MNPsnanomagnetic
catalyst did not occur perhaps because of the specific
nature of the designed catalyst.
3.11 | Comparison of Catalysts
Table 9 presents a comparison of results for the SB‐
Pd@MNPs nanomagnetic catalyst with those for other
catalysts for the Suzuki–Miyaura cross‐coupling reaction.
Comparison of the results demonstrates a better catalytic
activity of SB‐Pd@MNPs nanomagnetic catalyst at room
temperature in aqueous medium (EtOH–H2O (1:1)) for
SCHEME 4 Catalytic activity of SB‐Pd@MNPs nanomagnetic
catalyst in reduction of nitrobenzene
TABLE 9 Comparison of results for SB‐Pd@MNPs nanomagnetic catalyst with those for other catalysts in model reaction
Entry
Catalyst
Solvent
Temp. (°C)
Time (h)
Yield (%)
Ref.
[59]
1
Fe3O4/SiO2‐NH2/SA/Pd
Toluene
100
1
76
[60]
[61]
[62]
[63]
[64]
[65]
[66]
[67]
[68]
[69]
[70]
2
Pd/Fe3O4@charocoal
Iron oxide–Pd complex
Palladacycle adduct catalyst
Pd/CoFe2O4
DMF–H2O (4:1)
DMF
100
50
4
99
77
93
99
99
95
92
99
91
97
81
94
3
12
12
1
4
Dioxane
100
100
85
5
DMF
6
C/Co@PNIPAM
Toluene–H2O (2:1)
THF–H2O (2:5)
THF–H2O (1:2)
DMF
16
14
12
1
7
Pd/phosphine catalyst (6‐G0)
Co/C‐ROMP gel Pd
MUA‐Pd
60
8
65
9
90
10
11
12
13
Catalyst‐C4
CH3CN
80
16
3
Pd‐SB@MWCNTs
Pd‐Fe3O4 NCS
DMF–H2O (1:1)
DME–H2O (3:1)
EtOH–H2O (1:1)
60
Reflux
RT
24
4
SB‐Pd@MNPs
Present work

MANJUNATHA ET AL.
17 of 21
TABLE 10 Optimization f conditions for reduction reaction of nitrobenzene with sodium borohydride in presence of SB‐Pd@MNPs
nanomagnetic catalysta
Entry
Solvent
NaBH4 (mol)
Pd (mol%)
Temperature (°C)
Time (h)
Yield (%)b
1
H2O
2
—
RT
4.0
—
2
3
4
5
6
7
8
9
H2O
2
2
4
4
3
3
3
3
0.1
0.1
—
RT
50
2.5
25
—
—
75
86
72
92
92
THF–H2O
THF–H2O
THF–H2O
THF–H2O
THF–H2O
H2O
1.0
RT
RT
RT
RT
RT
RT
24.0
0.16
0.16
0.33
0.033
0.033
0.1
0.1
0.05
0.1
0.05
H2O
aReaction conditions: nitrobenzene (1.0 mmol) and solvent (10 ml).
bIsolated yield after separation by column chromatography; average of two runs.
TABLE 11 Nitroarene reduction catalysed by SB‐Pd@MNPs nanomagnetic catalysta
Entry
Nitroarene
Product
Time (h)
Yield (%)b
1
0.03
92
2
3
0.03
68
67
0.03
4
5
2.5
Trace
88
0.03
6
7
0.03
18
86
62
8
9
7
Trace
31
0.03
10
0.03
92
aReaction conditions: nitroarene (1.0 mmol), NaBH4 (3.0 mmol), SB‐Pd@MNPs nanomagnetic catalyst (0.05 mol% Pd), and water (10 ml).
bIsolated yield after separation by column chromatography; average of two runs.

18 of 21
MANJUNATHA ET AL.
SCHEME 5 Proposed mechanism for
reduction of nitroarene using NaBH4
catalysed by SB‐Pd@MNPs nanomagentic
catalyst
TABLE 12 Recyclability of SB‐Pd@MNPs nanomagnetic catalyst in nitrobenzene reductiona
Entry
1
Solvent
H2O
Catalyst (mol%)
0.05
Time (h)
0.033
Temp. (°C)
RT
Catalyst run
Fresh
Yield (%)b
92
2
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
1st recycle
2nd recycle
3rd recycle
4th recycle
5th recycle
6th recycle
7th recycle
8th recycle
9th recycle
10th recycle
92
92
92
92
92
92
91
91
91
91
3
4
5
6
7
8
9
10
11
aReaction conditions: nitrobenzene (1.0 mmol), NaBH4 (3.0 mmol), SB‐Pd@MNPs nanomagnetic catalyst (0.05 mol% Pd), and water.
bIsolated yield after separation by column chromatography; average of two runs.
nanomagnetic catalyst at room temperature in 2 min. The
results are presented in Table 10.
catalyst through possible mechanistic intermediates
(I–IV) is given in Scheme 5.[71]
3.13 | Reduction of Various Nitroarenes
Using the aforementioned optimized reaction conditions,
next we examined the utility of the SB‐Pd@MNPs
nanomagnetic catalyst for reaction of nitroarenes contain-
ing both electron‐withdrawing and electron‐releasing
groups. As evident from Table 11, our method is reason-
ably good and can be applied to several types of
nitroarenes. In all cases, this procedure gives the desired
products in good to excellent conversion rate and yield.
Reduction of nitrobenzene to aniline shows 100% conver-
sion in 2 min (Table 11, entry 1). Additionally, steric hin-
drance of the substituent influenced the product yield
(Table 11, entries 2, 3, 7 and 9). These results confirm that
the synthesized SB‐Pd@MNPs nanomagnetic catalyst can
act as an excellent catalyst in reduction of nitroarenes. A
proposed mechanism for the reduction of nitroarene
using NaBH4 catalysed by SB‐Pd@MNPs nanomagentic
FIGURE 13 Recycling efficiency of SB‐Pd@MNPs nanomagnetic
catalyst in nitroarene reduction reaction

MANJUNATHA ET AL.
19 of 21
TABLE 13 Comparison of results for SB‐Pd@MNPs nanomagnetic catalyst with those of other catalysts in nitroarene reduction reaction
Entry
Catalyst
Solvent
Temp. (°C)
Time (h)
Yield (%)b
Ref.
[72]
1
Pd catalyst
THF–H2O
RT
3.0
85
[73]
[74]
[75]
[76]
[77]
[78]
[29]
2
3
4
5
6
7
8
9
NaBH4/Ni(OAc)2.4H2O
PMHS/Ni(acac)2
Pd complex
CH3CN–H2O
Dioxane
MeOH
RT
100
50
0.33
3.0
92
84
95
97
85
96
83
92
12.0
0.083
0.166
16.0
3.0
Pd/C, NH2NH2.H2O
Pd/C
MeOH
80
EtOAc
80
RuCl2(PPh3)
Dioxane
MeOH
60
1,1‐Dioctyl‐4,4‐BPDB
SB‐Pd@MNPs
RT
RT
H2O
0.033
Present work
reactions and reduction of nitroarenes using this new
SB‐Pd@MNPs nanomagnetic catalyst. Notably, the SB‐
Pd@MNPs nanomagnetic catalyst shows good to excellent
catalytic activity in both Suzuki–Miyaura cross‐coupling
reactions and reduction of nitroarenes in aqueous
medium at room temperature. The main advantages of
the SB‐Pd@MNPs nanomagnetic catalyst are simplicity,
selectivity, eco‐friendliness and ease of recovery using an
external magnetic field. The recovered catalyst can be
reused for a minimum of five recycles without significant
loss of catalytic activity in Suzuki–Miyaura cross‐coupling
and ten recycles in the case of nitroarene reduction. Thus,
novel Schiff base–palladium complexes can be prepared
and immobilized on magnetic nanoparticles following
the above discussed protocol for the development of
greener methodologies for various organic transforma-
tions such as Mizoroki–Heck reaction, Sonogashira–
Hagihara coupling reaction and oxidation reactions in
addition to Suzuki–Miyaura cross‐coupling reactions and
nitroarene reduction.
3.14 | Catalyst Recyclability in Nitroarene
Reduction
One of the most important factors in catalysis is catalyst
recovery and recycling. The newly synthesized SB‐
Pd@MNPs nanomagnetic catalyst was successfully recov-
ered by applying an external magnetic field, washing with
ethanol and distilled water and drying at 45 °C for 12 h.
Further, the recovered catalyst was reused for reduction
of nitrobenzene to aniline under the optimized condi-
tions, and it was observed that there was no change in cat-
alytic activity up to 10 recycles in the reduction of
nitrobenzene with NaBH4 (Table 12; Figure 13). Recycled
SB‐Pd@MNPs nanomagnetic catalyst was characterized
using ATR‐IR analysis, and the spectrum shows that the
SB‐Pd@MNPs nanomagnetic catalyst is intact after
recycling (Figure 2c).
3.15 | Comparison of Catalysts
In comparison with other catalysts used for nitroarene
reduction,
the
as‐synthesized
SB‐Pd@MNPs
ACKNOWLEDGEMENTS
nanomagnetic catalyst is more efficient (Table 13). Reac-
tion solvent, temperature, time and yield are the impor-
tant factors in view of efficiency. As is evident from
Table 13, the reported catalysts require various organic
solvents, high temperature, longer reaction time and low
yield for nitroarene reduction.[29,72–78]
The authors thank DST‐Nanomission, India (SR/NM/NS‐
20/2014), DST‐SERB, India (YSS/201S/000010) and Jain
University, India for financial support.
ORCID
Siddappa A. Patil http://orcid.org/0000-0002-2855-5302
4 | CONCLUSIONS AND FUTURE
SCOPE
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