Biogenic synthesis of palladium nanoparticles using Boswellia sarrata and their applications in cross-coupling reactions

Article abstract of DOI:10.1002/aoc.6012

A facile and green route for biogenic synthesis of palladium nanoparticles (PdNPs) using aqueous extract of nontoxic and renewable Boswellia sarrata leaves is reported. The as-synthesized PdNPs were systematically characterized by using ultraviolet (UV)–visible spectroscopy, X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The PdNPs were crystalline and cubic in nature with average particle size of ~6 nm and successfully employed as heterogeneous catalyst in the Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions. The PdNPs could be recycled up to five times with modest change in the catalytic activity.

Full text of DOI:10.1002/aoc.6012

Received: 5 May 2020
DOI: 10.1002/aoc.6012
Revised: 8 August 2020
Accepted: 19 August 2020
F U L L P A P E R
Biogenic synthesis of palladium nanoparticles using
Boswellia sarrata and their applications in cross-coupling
reactions
Satyanarayan M. Arde
Audumbar D. Patil
| Gajanan S. Rashinkar
| Rajashri S. Salunkhe
| Sanjay N. Jadhav
|
Department of Chemistry, Shivaji
University, Kolhapur, India
A facile and green route for biogenic synthesis of palladium nanoparticles
(PdNPs) using aqueous extract of nontoxic and renewable Boswellia sarrata
leaves is reported. The as-synthesized PdNPs were systematically characterized
by using ultraviolet (UV)–visible spectroscopy, X-ray diffraction analysis, scan-
ning electron microscopy, transmission electron microscopy, energy-dispersive
X-ray spectroscopy, and X-ray photoelectron spectroscopy. The PdNPs were
crystalline and cubic in nature with average particle size of ꢀ6 nm and suc-
cessfully employed as heterogeneous catalyst in the Suzuki–Miyaura and
Mizoroki–Heck cross-coupling reactions. The PdNPs could be recycled up to
five times with modest change in the catalytic activity.
Correspondence
Rajashri S. Salunkhe, Department of
Chemistry, Shivaji University, Kolhapur
416004, MS, India.
Email: rss234@rediffmail.com
K E Y W O R D S
Boswellia sarrata, Mizoroki-Heck reaction, palladium nanoparticles, reusability, Suzuki–Miyaura
reaction
1 | INTRODUCTION
Generally, both Suzuki–Miyaura and Mizoroki–Heck reac-
tions are frequently catalyzed by using palladium complexes
Admirable research has been progressed in cross-coupling
reactions, which made great revolution in the organic trans-
formation by developing simple and efficient protocols. Par-
ticularly, the transition metals like rhodium, ruthenium,
nickel, and palladium have been frequently used for the
development of highly efficient and mild protocols in the
construction of carbon–carbon and carbon–heteroatom
bonds.[1–4] Conceivably, the most successful development in
this regard are Stille, Suzuki–Miyaura, Mizoroki–Heck,
Sonogashira, Mukaiyama reactions, and so on. Among
these, Suzuki–Miyaura cross-coupling reaction of aryl
halides with aryl boronic acids is the most powerful
carbon–carbon bond forming methodology for constructing
biaryls in the toolbox of organic chemists. In addition to
this, Mizoroki–Heck reaction is also the most fundamental
palladium catalyzed carbon–carbon bond forming reaction
that is used for the stereoselective synthesis of alkenes.
such as [Pd (OAc)2], [Pd (PPh3)Cl2], and Pd (dppf)Cl2
homogenous catalytic systems.[5,6] Amid various palladium
catalysts for cross-coupling reactions, homogenous catalysts
have been widely investigated, and less expensive heteroge-
neous catalysts have received less attention. However, in
the last few years, the importance of palladium-based het-
erogeneous catalytic systems has received significant atten-
tion because of their facile recovery and reusability.
Precedently, carbon,[7] magnetic materials,[8] silica,[9]
hydroxyapatite,[10] zeolites,[11] Pd/DNA,[12,13] metal organic
frameworks (MOFs),[14] organic polymers,[15] clays,[16] and
bio-supports[17,18] have been employed for as support for
this purpose. In the recent years, palladium nanoparticles
(PdNPs) have garnered tremendous attention in heteroge-
neous catalysis due to their excellent catalytic activity.[19–25]
In this regard, the green synthesis of PdNPs has attracted
the vigil eye of attraction of nanotechnologists and material
Appl Organomet Chem. 2020;e6012.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6012

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ARDE ET AL.
scientists, due to the growing environmental pollution cau-
sed by the conventional chemical methods.[26–31] Among
various green recipes, biogenic synthesis of PdNPs[32–34] has
recently emerged as an active area of research due to sim-
plicity, cost-effectiveness, higher potential of reduction, and
low toxic effect on human health as well as on the environ-
ment. Unfortunately, majority of earlier methods of plant-
based reported catalysts[35a–d] often suffer from limitations
like high reaction temperatures, high catalyst loadings, lim-
ited substrate scopes, and/or used of undesirable organic
solvents as reaction, solid support, greater reaction time,
and so on. Moreover, the biogenic reduction occurs at phys-
iological conditions of temperature and pressure. In addi-
tion, the raw materials are easily available, and therefore,
the reaction can be easily scaled up. Also, the reported
plant-based PdNPs mostly tested for a single catalytic sys-
tem, while their multifunctional potentiality remains largely
underexplored. Thus, the appropriate selection of plant
extract, which can bestow multifunctional role, namely,
bio-reduction of Pd salts, aid in multiple catalytic reactions,
and afford biological activities, is highly desirable. In this
context, we would like to exploit a bio-resource, namely,
Boswellia sarrata L. aqueous leaves extract for the synthesis
of PdNPs. It comes under the family Burseraceae and is an
evergreen middle-sized tree. It is mostly found in tropical
part of Asia and Africa. In India, it is found in dry hilly
woodland of Rajasthan, Madhya Pradesh, Bihar, Assam,
Orissa, Telengana, and western Sahyadri hills of Maharash-
tra. The leaves, bark, and resins of B. sarrata L. contain
strong aroma. The gum resin of this plant has been widely
used in the treatment of cancer, skin disease, and urinary
disorder, as analgesic, anti-inflammatory, and antipyretic
properties.[36]
leaves of Boswellia serrata were collected from “Western
Hill Region” of Maharashtra (India), and the taxonomic
identification was done in Department of Botany, Shivaji
University, Kolhapur (MS, India). The voucher specimen
(SMA 001) was numbered and kept in research laboratory
for further reference. The aqueous extract of B. sarrata
leaves was freshly prepared using double distilled water.
The ultraviolet (UV)–visible spectra were recorded over
200- to 800-nm range with UV-3600 PC UV–VIS NIR Spec-
trophotometer (Shimadzu). X-ray diffraction (XRD) pat-
terns were recorded on Bruker AXS model D-8, (10–70ꢁ
range, scan rate = 1ꢁ min−1) equipped with a monochro-
mator and Ni-filtered Cu Kα radiation. Scanning electron
microscopy (SEM) was performed using a HITACHI S-
4800 instrument to study the morphology of PdNPs. The
transmission electron microscopy (TEM) analysis was per-
formed on a Jeol model JEM 1200 electron microscope
operated at an accelerating voltage of 120 kV. The Energy-
dispersive X-ray spectroscopy (EDS) was carried out on a
DX-700HS spectrometer for elemental analysis. X-ray pho-
toelectron spectroscopy (XPS) data of catalyst were col-
lected on a VG scientific ESCA-3000 spectrometer using a
non-monochromatized Mg K radiation (1,253.6 eV) at a
pressure of about 1 × 10−9 Torr (pass energy of 50 eV, elec-
tron takeoff angle 55ꢁ). Melting points were determined in
1
an open capillary and found to be uncorrected. H NMR
spectra were recorded at 300-MHz Bruker Avon spectrom-
eter using CDCl3 as solvent and TMS as an internal refer-
ence standard. Fourier-transform infrared spectroscopy
(FTIR) spectra were recorded on Thermo Scientific
Neconet 6700 FTIR, in the range 4,000–400 cm−1. Mass
spectra were performed on an Ultima Global spectrometer
with an ESI source.
Considering aforementioned discussion, in present
work, we describe a facile and environmentally friendly
technique for the preparation of PdNPs using an aqueous
extract of B. sarrata L. leaves as a bioreductant. More-
over, the phytomolecules present in B. sarrata L. extract
are not only accountable for the reduction and progres-
sion of nanoparticles, but they were also found to per-
form as stabilizing agents. Furthermore, the green
synthesized metallic PdNPs were used as a catalyst for
Suzuki–Miyaura cross-coupling reaction in aqueous
medium and Mizoroki–Heck reactions in DMF at moder-
ate reaction conditions.
2.2 | Preparation of aqueous extract of
B. sarrata leaves
Air-dried leaves of B. serrata were taken in mortar and
crushed to fine powder. A mixture of fine powder of
B. serrata leaves (5 g) and distilled water (200 mL) was
heated at 90ꢁC for 30 min. The mixture was cooled and
filtered through Whatmann filter paper no. 41. The fil-
trate was diluted to 2 L by adding distilled water and used
for the preparation of PdNPs.
2 | EXPERIMENTAL
2.1 | General information
2.3 | General procedure for the synthesis
of PdNPs
A mixture of an aqueous solution of Pd (OAc)2 (1 mM,
25 mL) and diluted aqueous extract of B. sarrata leaves
(25 mL) was refluxed for 2 h in an oil bath. The resulting
All reagents were purchased from Sigma-Aldrich and used
without further purification. Fresh, green, and mature

ARDE ET AL.
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solution was centrifuged at 10,000 rpm for 20 min. Thus,
obtained brown solid was washed with distilled water
(3 × 10 mL) and dried under vacuum to get the desired
PdNPs dried crystal powder.
2.5 | General procedure for Mizoroki–
Heck coupling reaction
Aryl halide (1.0 mmol), olefin compound (1.1 mmol),
K2CO3 (2 mmol), PdNPs catalyst (0.3 mol %), and DMF
(5 mL) were taken in Schlenk flask, which was equipped
with a magnetic stir bar, septum, and a condenser. The
flask was immersed in a heating bath and reaction mix-
ture stirred at 110ꢁC. Upon complete consumption of
starting materials as determined by TLC analysis (petro-
leum ether:ethyl acetate, 8:2), catalyst was separated out
by centrifugation, and the liquid mixture was extracted
with diethyl ether (3 × 10 mL). The combined organic
layer was collected, dried over anhydrous Na2SO4, and
concentrated. The resulting compound was purified by
column chromatography.
2.4 | General procedure for the Suzuki–
Miyaura cross-coupling reaction
Aryl halide (1.0 mmol), aryl boronic acid (1.1 mmol),
K2CO3 (2 mmol), PdNPs (0.3 mol %), and 5 mL of water
were stirred in Schlenk flask, equipped with a magnetic
stir bar and a condenser at 60ꢁC. Upon complete con-
sumption of starting materials as determined by thin-
layer chromatography (TLC) analysis, water (20 mL) was
added, and the catalyst was separated out by centrifuga-
tion. The filtrate was extracted with diethyl ether
(3 × 10 mL). The combined organic layers were collected,
dried over anhydrous Na2SO4, concentrated in vacuum to
afford desired product, and purified by column
chromatography.
3 | RESULTS AND DISCUSSION
Initially, aqueous solution of Pd (OAc)2 (1 mM) was
treated with aqueous extract of B. sarrata leaves at room
temperature. There was no formation of PdNPs even after
prolonged reaction time of 24 h. Therefore, a series of
experiments were undertaken in which the mixture was
stirred at elevated temperatures. The formation of PdNPs
was observed at and above 70ꢁC with the best results
obtained at reflux conditions (Table 1). The formation of
PdNPs was easily identified by color change from pale
yellow to dark brown and finally confirmed by UV–
visible spectroscopy. The characteristic UV–visible
absorption peak of Pd (OAc)2 at 460 nm disappeared after
color change clearly indicated the formation of PdNPs
(Figure 1).
TABLE 1 Effect of temperature on the synthesis of PdNPs
Sr.
Reaction
Reaction
status
no. Solvent Temperature time
1.
2.
Water
Water
32ꢁC (RT)
50ꢁC
24 h
24 h
No change in
pale yellow
color
No change in
pale yellow
color
3.
4.
5.
Water
Water
Water
70ꢁC
3.5 h
2.5 h
2.0 h
Dark brown
color
80ꢁC
Dark brown
color
After the successful formation of PdNPs in aqueous
extract of B. sarrata leaves, we investigated impact of vari-
ous solvent systems such as acetone, water–acetone, ethyl
alcohol, and water–ethyl alcohol, and the results are
Reflux
Dark brown
color
FIGURE 1 UV–visible spectra of
PdNPs (a) at room temperature (b) at
reflux condition

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TABLE 2 Effect of solvent on the complete reduction of
palladium as PdNPs at room temperature
summarized in Table 2. The formation of PdNPs was
observed in all the investigated solvent systems with the
best results in acetone as a solvent within short reaction
time. We decided to employ water as a solvent for the syn-
thesis of PdNPs as it is a green and ecofriendly solvent.
In all above experiments, plant extract was extracted
in distilled water and kept constant for all reaction condi-
tions. Further detailed characterization of biogenically
synthesized PdNPs, water refluxed product was taken.
After the completion of reaction, brown solution was cen-
trifuged at 10,000 rpm in cooling centrifuge machine and
washed thrice by distilled water and dried in vacuum.
FTIR (Figure 2) measurements were carried out to
identify the possible biomolecules responsible for the
reduction and stabilization of PdNPs synthesized by
aqueous extract of B. sarrata leaves. The peaks at
1,736.53, 1,589.88, 1,365.96, 1,216.97, and 1,043.30 cm−1
show the presence of higher esters of fatty acids, polyol,
polyphenol, flavonoids, and hydroxyflavones like groups.
The peak at 1,589.88 cm−1 was assigned to C C
stretching vibration in aliphatic compounds, which may
be characterized by the presence of high content of terpe-
noids and flavonoids. The peak 1,365.96 cm−1 was due to
deformation of CH2 and CH3 groups in aliphatic com-
pounds.[37] The peaks at 1,216.97 cm−1 arises most proba-
bly from the C–O groups of polyols such as
hydroxyflavones and catechins.[37] The peak near
Color of the reaction
Sr.
Reaction
time
mixture after addition
of plant extract
No. Solvent
1.
Water
24 h
No change in pale yellow
color
2.
Water:
acetone
(95:5)
10 min
Dark brown color
Dark brown color
Dark brown color
Dark brown color
3.
4.
5.
Water:
10 min
10 min
10 min
acetone
(90:10)
Water:
acetone
(85:15)
Water:
acetone
(80:20)
6.
7.
Acetone
08 min
10 h
Dark brown color
Dark brown color
Water:ethyl
alcohol
(95:5)
8.
9.
Water:ethyl
alcohol
(90:10)
10 h
09 h
Dark brown color
Dark brown color
Ethyl alcohol
FIGURE 2 FTIR analysis of aqueous
extract of B. sarrata leaves and PdNPs
suspension
FIGURE 3 (a) XRD pattern of
PdNPs; (3b) SAED pattern of PdNPs

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1,736.53 cm−1 is assigned for higher esters of fatty acids.
The peaks present in 'B. sarrata plant extract graph' at
1,736.53, 1,589.88, 1,365.96, 1,216.97 and 1,043.30 cm−1
are totally disappeared in 'PdNPs suspension graph' indi-
cated that the polyols, hydroxyflavones, and terpenoid
molecules are mainly responsible for the reduction of
Pd++ ions.
Biogenically synthesized PdNPs were characterized
by XRD analysis (Figure 3a). All the high-intensity reflec-
tions were observed at 2θ = 39.524ꢁ, 44.924ꢁ, 66.812ꢁ, and
80.782ꢁ corresponding to 111, 200, 220, and 311 planes.
These are in good agreement with reported values
(JCPDS file no. 00-001-1310). The analysis revealed that
PdNPs are in the form of cubic nanocrystals. The full
width at half maximum (FWHM) values measured for
111 plane of reflection were used with the Debye–
Scherrer's equation d = 0.9 λ/βcosθ. The average size of
PdNPs was calculated as 7 nm, which is in accordance
with the TEM image size (Figure 4c). Moreover, XRD
pattern is in good agreement with the selected area elec-
tron diffraction pattern (SAED) (Figure 3b).
SEM was used for investigating surface morphology
of biogenically synthesized PdNPs. The SEM images
(Figure 4a) of PdNPs displayed less aggregated particles
with spherical shape. The morphology and particle size
of PdNPs were further confirmed by TEM and are dis-
played in Figure 4b,c. The analysis revealed size distribu-
tion with average size diameters of ꢀ6 nm (Figure 4d).
The quantification of elemental palladium in PdNPs
was confirmed by EDS. The PdNPs display an optical
absorption peak at 2.4 KeV, which is typical absorption
of metallic palladium nanocrystallites (Figure 5). The
FIGURE 4 (a) SEM image, (b,c)
TEM image, (d) size distribution graph
of biogenically synthesized PdNPs
FIGURE 5 EDS spectrum
of biogenically synthesized PdNPs

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FIGURE 6 (a) Full survey XPS
analysis; (b) highlighted XPS spectrum
of biogenically synthesized PdNPs
total weight percentage of palladium in PdNPs is found
to be 39.75%.
XPS analysis was conducted to examine the compre-
hensive picture in terms of quantity and chemical state of
biogenically synthesized PdNPs. Full survey XPS analysis
(Figure 6a) displayed peaks at 286.08, 337.08, and
535.08 eV corresponding to C 1s, Pd 3d, and O 1s respec-
tively. Scanning of Pd 3d (Figure 6a) shows (core spectrum)
double peaks with binding energies at 335.95 and
341.27 eV corresponding to two chemical states of the Pd
as Pd 3d5/2 and Pd 3d3/2 indicating Pd0 whereas 338.21 eV
and 343.53 eV values indicating oxidative Pd2+ ions. Quan-
titative comparison in the fitting peak area of Pd0 and Pd2+
indicates that the oxidation degree of Pd is reduced with
decreasing Pd percentage as shown in the Figure 6b.
FIGURE 7 TGA analysis of biogenically synthesized PdNPs
TABLE 3 Screening of bases for Suzuki–Miyaura coupling reactiona
Entry
Base (mmol)
Et3N
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9
85
65
75
60
80
65
55
40
35
62
82
61
78
66
72
92
90
95
NaOAc
n-Pr3N
t-BuOK
Pyridine
DABCO
K3PO4
Na2CO3
K2CO3
aReaction conditions: 4-bromobenzopheneone (1.0 mmol), phenyl boronic acid (1.1 mmol), in the presence of catalytic amount of PdNPs,
base (2.0 mmol), water (5 mL), at 60ꢁC under air.
bIsolated yields.

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7 of 12
TABLE 4 Optimization of catalyst for Suzuki–Miyaura
TABLE 5a TON and TOF values for the Suzuki–Miyaura
reaction
coupling reactiona
Catalyst
Entry (mol %)
Temp.
(ꢁC)
Time
(min)
Yield
(%)b
Sr. no.
Products
TON
317
267
313
300
307
317
313
317
313
TOF (min−1
7.92
)
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
3f
1
2
3
4
5
6
7
8
0.1
0.2
0.3
0.4
0.5
0.3
0.3
0.3
60
60
60
60
60
r.t.
50
80
60
45
35
35
35
70
45
35
60
82
95
95
95
40
82
94
4.45
6.95
4.00
5.11
9.05
3g
3h
3i
4.81
9.05
7.82
aReaction conditions: 4-bromobenzopheneone (1.0 mmol), phenyl
boronic acid (1.1 mmol), PdNPs (mol %), K2CO3 (2.0 mmol), water
(5 mL), at 60ꢁC under air.
Abbreviations: TOF, turnover frequency; TON, turnover number.
bIsolated yields.
TABLE 5 The Suzuki–Miyaura reaction of various aryl bromides and phenyl boronic acidsa with an isolated yieldb
aReaction conditions: arylbromides (1 mmol), arylboronic acids (1.1 mmol), PdNPs (0.3 mol %), K2CO3 (2 mmol), water (5.0 mL), at 60ꢁC in air.
bIsolated yields.

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The thermal profile of biogenically synthesized PdNPs
0.3 mol % increased the yield significantly to 95%
(Table 4, entries 2 and 3). However, further increase in
the catalyst quantity beyond to 0.3 mol % did not have
quantitative effect on the yield of the product (Table 4,
entries 4 and 5). The efficiency of reaction was affected
was investigated by using thermal gravimetric analysis
(TGA) (Figure 7). The thermogram displayed initial
weight loss of 6.03% up to 160ꢁC due to evaporation of
water or moisture. The combined weight loss of 30.04% in
the range 160–400ꢁC and 6.05% in the range 400–780ꢁC is
attributed to the degradation of volatile organic materials
loosely bound on the surface of the PdNPs.
After the successful formation and characterization of
biogenically synthesized PdNPs, we explored their cata-
lytic activity in Suzuki–Miyaura and Mizoroki–Heck
reactions. To begin with, we investigated the catalytic
activity of PdNPs in Suzuki–Miyaura cross-coupling reac-
tion. The cross-coupling between 4-bromo benzophenone
(1 mmol) and phenyl boronic acid (1.1 mmol) in the pres-
ence of PdNPs in water was chosen as a model reaction
for optimization of reaction conditions. Initially, the
influence of nature of bases was investigated by per-
forming model reaction with various organic and inor-
ganic bases in water at 60ꢁC. It was observed that
inorganic bases are more effective (Table 3, entries 7–9)
as compared with organic bases (Table 3, entries 1–6).
The results revealed K2CO3 as a promising base for the
effective cross-coupling (Table 3, entry 9).
TABLE 7 Effect of solvent for Mizoroki–Heck reactiona
Yield
Entry Solvent
Temp. (ꢁC) Time (min) (%)b
1
CH3CN
DMF
110
110
110
110
110
70
35
65
15
70
70
70
70
50
40
70
30
92
35
78
10
Nil
10
30
80
90
Nil
2
3
DCM
4
THF
5
Toluene
6
95% EtOH 30
95% EtOH 50
95% EtOH 70
95% EtOH 90
95% EtOH 110
7
8
9
10
11
Next, we investigated the effect of amount of PdNPs
on the model reaction, and results are summarized in
Table 4. The model reaction afforded 60% of
corresponding product with loading of 0.1 mol % of
PdNPs (Table 4, entry 1). Increasing the quantity to
Water
110
aReaction conditions: 4-nitro bromobenzene (1.0 mmol), methyl
acrylate (1.1 mmol), PdNPs (0.3 mol %), K2CO3 (2.0 mmol), DMF
(5 mL), at 110ꢁC under air.
bIsolated yields.
TABLE 6 Screening of various bases for Mizoroki–Heck reactiona
Entry
Base (mmol)
K3PO4
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9
60
45
35
30
55
70
80
55
40
80
82
92
78
81
79
78
77
90
NaOAc
K2CO3
Et3N
n-Pr3N
t-BuOK
Pyridine
DABCO
Na2CO3
aReaction conditions: 4-nitro bromobenzene (1.0 mmol), methyl acrylate (1.1 mmol), PdNPs (0.3 mol %), base (2.0 mmol), DMF (5 mL), at
110ꢁC under air.
bIsolated yields.

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TABLE 8 Screening of amount of catalyst for Mizoroki–Heck
by temperature, and maximum product yield was noted
at 60ꢁC (Table 4, entries 6–8).
reactiona
After optimization of reaction conditions, the scope
and generality of the protocol were investigated by
reacting various aryl bromides with aryl boronic acids,
and the results are summarized in Table 5. In all the
cases, the reactions proceeded smoothly affording cross-
coupling products in good to excellent yields, which
lighten the generality of the protocol.
Entry
Catalyst (mol %)
Time (min)
Yield (%)b
1
2
3
4
5
0.1
0.2
0.3
0.4
0.5
45
40
35
35
35
60
82
92
92
92
Inspired by success of biogenically synthesized PdNPs
in Suzuki–Miyaura reaction, we decided to extend the
protocol for Mizoroki–Heck reaction. Accordingly, reac-
tion between 4-nitro bromobenzene and methyl acrylate
aReaction conditions: 4-nitro bromobenzene (1.0 mmol), methyl
acrylate (1.1 mmol), PdNPs (mol %), K2CO3 (2.0 mmol), DMF
(5 mL), at 110ꢁC under air.
bIsolated yields.
TABLE 9 The Mizoroki–Heck reaction of various aryl halides and olefinic compounds over PdNPs catalysta with an isolated yieldb
aReaction conditions: 4-nitro bromobenzene (1.0 mmol), methyl acrylate (1.1 mmol), PdNPs (mol %), K2CO3 (2.0 mmol), DMF (5 mL), at 110ꢁC under air.
bIsolated yields.

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using PdNPs in DMF at 110ꢁC was chosen as a model
reaction for optimization of reaction conditions. In order
to evaluate the effects of base, various bases were
screened for model reaction (Table 6). The results rev-
ealed K2CO3 as the best base for the model reaction as
the corresponding product was obtained in quantitative
yield within short reaction time (Table 6, entry 3).
In order to evaluate the effects of solvent, various
protic and aprotic solvents were screened for model reac-
tion (Table 7). The results revealed DMF as the best sol-
vent for the model reaction (Table 7, entry 2) as
corresponding product was obtained in quantitative yield
within short reaction time. To study the effect of temper-
ature, the model reaction was carried out at different
heating conditions. As expected, when the reaction
temperature was increased from 25ꢁC to 110ꢁC, the reac-
tion time was decreased significantly affording excellent
yield of corresponding product (Table 7, entries 6–10),
indicating that temperature is a crucial factor.
Further, the effect of amount of PdNPs was investi-
gated (Table 8). It is observed that with increasing the
amount of PdNPs from 0.1 to 0.3 mol% dramatically
enhanced the yield of corresponding product (Table 8,
entries 1–3). However, further increase from 0.3 to
0.5 mol % did not significantly improved the yield. Thus,
among the different quantity of PdNPs catalyst, 0.3 mol %
proved to be the best affording desired product in 30 min
with 92% yield in DMF at 110ꢁC (Table 8, entry 3).
After optimization of reaction conditions, the scope
and generality of the protocol were investigated by
reacting variety of substituted and nonsubstituted aryl
bromides with olefins under the optimized reaction con-
ditions. In all the cases, Mizoroki–Heck reactions
proceeded effectively furnishing desired products in
excellent yields within 30–80 min (Tables 9 and 10).
For practical applications of heterogeneous systems,
the lifetime of the catalyst and its level of reusability are
important features. The recyclability of PdNPs was
TABLE 10 TON and TOF values for the Mizoroki–Heck
reaction
Sr. no.
Products
6a
TON
TOF (min−1
)
1
300
8.57
2
6b
6c
6d
6e
6f
283
300
307
297
307
283
286
300
270
293
300
4.35
6.00
10.23
7.22
8.77
4.71
4.08
6.00
4.90
3.66
6.00
3
investigated
with
Suzuki–Miyaura
reaction
of
4
4-bromobenzophenone and phenyl boronic acid and
Mizoroki–Heck reaction of 4-nitro bromobenzene with
methyl acrylate. After first cycle, PdNPs were recovered
by centrifugation and extensively washed with water, dic-
hloromethane, and acetone. The PdNPs were dried under
vacuum before performing the reusability test, and the
results are summarized in Table 11 as well as shown in
graph. We were delighted to note that PdNPs could be
effectively reused for five consecutive runs without appre-
ciable decrease in the yield of corresponding products.
The graphical representation of recyclability of PdNPs
5
6
7
6g
6h
6i
8
9
10
11
12
6j
6k
6l
Abbreviations: TOF, turnover frequency; TON, turnover number.
TABLE 11 Recyclability of catalyst in Suzuki–Miyaura and Mizorokii–Heck reactions
Entry
Cycle
Time (min)
Yield (%)
1
1
35
95
2
3
4
5
40
50
65
80
92
90
86
83
2
1
2
3
4
5
35
40
60
90
100
92
88
85
81
78

ARDE ET AL.
11 of 12
biogenically synthesized PdNPs were used as efficient
heterogeneous catalyst in Suzuki–Miyaura and
Mizoroki–Heck reactions. The PdNPs could be recycled
up to five cycles with modest change in catalytic activity.
The developed protocol provides an unprecedented
reactivity pattern, economically attractive and environ-
mentally benign alternative route for the production of
various biaryl and alkene derivatives.
Data availability statement
Data were available on request from the authors.
FIGURE 8 The graphical representation of recyclability of
PdNPs catalyst
AUTHOR CONTRIBUTIONS
Satyanarayan Arde: Conceptualization; data curation;
formal analysis; methodology; resources. Gajanan
Rashinkar: Supervision. Sanjay Jadhav: Data curation;
formal analysis. Audumbar Patil: Formal analysis.
Rajashri Salunkhe: Conceptualization; data curation;
methodology; supervision.
catalyst with respect to Suzuki–Miyaura and Mizoroki–
Heck reactions has given below (Figure 8).
The leaching study revealed that, larger size of cubic
nanocrystals whose size more than 20 nm are more stable
and shows lower leaching property. Whereas, smaller
cubic nanocrystals whose size less than 20 nm shows
greater catalytic activity with greater leaching prop-
erty.[38] To assess the PdNPs leaching from catalyst dur-
ing the reaction, we performed the hot filtration test for
Suzuki–Miyaura reaction of 4-bromo benzophenone and
phenyl boronic acid. The reaction was stopped after
20 min and then the hot filtrate was transferred to
another flask containing base and water at 60ꢁC. Upon
further heating of the catalyst free solution for 3.5 h, no
considerable progress was observed. Moreover, using
AAS, the same reaction solution at the midpoint of com-
pletion indicated that no significant quantities of PdNPs
were lost to the reaction liquors during the process. Also,
the PdNPs catalyst was used for five runs and showed
modest change in catalytic activity with increased time
period with each run. This is due to the smaller size of
PdNPs (ꢀ6 nm).
ORCID
Satyanarayan M. Arde https://orcid.org/0000-0002-
9732-8269
Gajanan S. Rashinkar https://orcid.org/0000-0002-
7200-5260
Sanjay N. Jadhav https://orcid.org/0000-0002-3792-
5889
Audumbar D. Patil https://orcid.org/0000-0002-8299-
9326
Rajashri S. Salunkhe https://orcid.org/0000-0001-9352-
1769
REFERENCES
[1] a) L. Yang, G. Zhang, H. Huang, Adv. Synth. Catal. 2014, 356,
1509; b) O. M. Demchuk, K. M. Pietrusiewicz, Synlett 2009, 7,
1149; c) H. Rao, L. Yang, Q. Shuai, C.-J. Li, Adv. Synth. Catal.
2011, 353, 1701.
[2] B. M. Trost, M. R. Machacek, Z. T. Ball, Org. Lett. 2003, 5, 1895.
[3] a) M. Baghbanzadeh, C. Pilger, C. O. Kappe, J. Org. Chem.
2011, 76, 1507; b) M. Xu, X. Li, Z. Sun, T. Tu, Chem. Commun.
2013, 49, 11539.
4 | CONCLUSION
[4] a) S. N. Jadhav, C. V. Rode, Green Chem. 2017, 19, 5958; b)
S. Jadhav, S. Patil, A. Kumbhar, S. Kamble, R. Salunkhe,
Transition Met. Chem. 2019, 44, 507; c) L. Liang, L. Nie,
M. Jiang, F. Bie, L. Shao, C. Qi, X. M. Zhang, X. Liu, New
J. Chem. 2018, 42, 11023; d) P. R. Boruah, A. A. Ali, B. Saikia,
D. Sarma, Green Chem. 2015, 17, 1442.
In conclusion, we have developed rapid, green, eco-
friendly, and simple strategy for the synthesis of PdNPs
by using aqueous extract of B. sarrata leaves as a
reducingv and stabilizing agent without adding external
reducing agent or surfactant template. The average
particle size of PdNPs was characterized by TEM analysis
and found to be ꢀ6 nm. The crystalline nature of PdNPs
was confirmed by XRD and SAED analysis. XPS results
confirmed the formation of metallic PdNPs. The
[5] A. Migliorini, C. Oliviero, T. Gasperi, M. A. Loreto, Molecules
2012, 17, 4508.
[6] L. A. Adrio, B. N. Nguyen, G. Guilera, A. G. Livingston,
K. K. Hii, Catal. Sci. Technol. 2012, 2, 316.

12 of 12
ARDE ET AL.
[7] J. C. Espinosa, R. C. Contreras, S. Navalon, C. Rivera-
Carcamo, M. Alvaro, B. F. Machado, P. Serp, H. Garcia, Eur.
J. Inorg. Chem. 2019, 14, 1979.
[8] M. Tukhani, F. Panahi, A. Khalafi-Nezhad, ACS Sustainable
Chem. Eng. 2018, 6(1), 1456.
[9] K. Martina, F. Baricco, M. Caporaso, G. Berlier, G. Cravotto,
Chem Cat Chem. 2016, 8, 1176.
[10] A. Bulut, M. Aydemir, F. Durap, M. Gulcan, M. Zahmakiran,
Chemistry Select 2018, 3, 1569.
[11] J. Yao, Y. Yao, Int. J. Hydrogen Energ. 2019, 44, 287.
[12] M. Mart, W. Tylus, A. M. Trzeciak, Catalysts 2018, 8, 552.
[13] V. Kandathil, M. Kempasiddaiah, S. K. Nataraj,
S. B. Somappa, S. A. Patil, Appl Organometal Chem. 2020,
34(3), e5357.
[14] L. Chen, H. Chen, R. Luque, Y. Li, Chem. Sci. 2014, 5, 3708.
[15] a) S. Ding, B. Qu, Y. Li, L. Sun, S. Wu, R. Zeng, M. Xu,
C. Chen, N. Zhang, New J. Chem. 2019, 43, 14674; b) P. Gao,
Y. Xiao, Z. Dong, H. Pan, W. Wang, J. Saudi. Chem. Soc. 2020,
24, 282.
[28] Y. Chen, M. Wang, L. Zhang, Y. Liu, J. Han, RSC Adv. 2017, 7, 47104.
[29] K. S. Siddiqi, A. Husen, Lett. 2016, 11, 482.
[30] V. Kandathil, R. B. Dateer, B. S. Sasidhar, S. A. Patil,
S. A. Patil, Catal. Lett. 2018, 148(6), 1562.
[31] Y. Du, S. Wei, M. Tang, M. Ye, H. Tao, C. Qi, L. Shao, Appl
Organometal Chem. 2020, 34(5), e5619.
[32] S. Hemmati, A. Sedrapoushan, N. Alizadeh, K. Khosravi,
M. Hekmati, Appl Organometal Chem. 2019, 33(10), e5103.
[33] A. Tadjarodi, M. Dehghani, M. Imani, Appl Organometal
Chem. 2018, 32(12), e4594.
[34] R. K. Borah, A. Mahanta, A. Dutta, U. Bora, A. J. Thakur, Appl
Organometal Chem. 2017, 31(11), e3784.
[35] a) M. Hazarika, D. Borah, P. Bora, A. R. Silva, P. Das, PLoS
ONE 2017, 12(9), e0184936; b) X. Yang, Q. Li, H. Wang,
J. Huang, L. Lin, W. Wang, D. Sun, Y. Su, J. B. Opiyo,
L. Hong, Y. Wang, N. He, L. Jia, J. Nanopart. Res. 2010, 12,
1589; c) R. K. Petla, S. Vivekanandhan, M. Misra,
A. K. Mohanty, N. Satyanarayana, J. Biomater Nanobiotechnol
2012, 3, 14; d) L. Jia, Q. Zhang, Q. Li, H. Song, Nanotechnology
2009, 20, 385601. (10pp)
[16] D. Makwana, B. Dakhara, H. C. Bajaj, Int J Res Eng Technol.
2019, 8(11), 65.
[17] I. Hussain, J. Capricho, M. A. Yawer, Adv. Synth. Catal. 2016,
358, 3320.
[36] a) S. Khan, M. L. Gangwal, Int. J. Entomol. Res. 2017, 2(5), 116;
b) H. H. Ahmed, A. A. Abd-Rabou, A. Hassan, S. E. Kotob,
Asian Pac J Cancer Prev. 2015, 16(16), 7179.
[18] P. Zhou, H. Wang, J. Yang, J. Tang, D. Sun, W. Tang, RSC
Adv. 2012, 2, 1759.
[19] M. Khan, M. Kuniyil, M. R. Shaikh, M. Khan, S. F. Adil, A. Al-
Warthan, H. Z. Alkhathan, W. Tremel, M. N. Tahir,
M. R. H. Siddigu, Catalysts 2017, 7(1), 20.
[37] a) G. Rajkumar, A. A. Rahuman, Res. Vet. Sci. 2012, 93, 303; b)
D. Jain, H. K. Daima, S. Kachhwaha, S. L. Kothari, Dig.
J. Nanomaterials 2009, 4(3), 557.
[38] H. Ramezani-Dakhel, P. A. Mirau, R. R. Naik, M. R. Knecht,
H. Heinz, Phys. Chem. Chem. Phys. 2013, 15, 5488.
[20] V. Kozell, T. Giannoni, M. Nocchetti, R. Vivani, O. Piermatti,
L. Vaccaro, Catalysts 2017, 7(6), 186.
[21] S. Jang, T. Kim, K. H. Park, Catalysts 2017, 7(9), 247.
[22] S. Shabbir, S. Lee, M. Lim, H. Lee, H. Ko, Y. Lee, H. Rhee,
J. Organomet. Chem. 2017, 846, 296.
[23] M. E. Martinex-Klimov, P. Hernandez-Hipolito, M. Martinez-
Garcia, T. E. Klimova, Catal. Today 2018, 305, 58.
[24] M. Koohgard, M. Hosseini-Sarvari, Catal. Commun. 2018,
111, 10.
[25] A. Khazaei, S. Rahmati, Z. Hekmatian, S. Saeednia, J Mol
Catal A-Chem. 2013, 372, 160.
[26] V. L. Nguyen, D. C. Nguyen, H. Hirata, M. Ohtaki,
T. Hayakawa, M. Nogami, Adv. Nat. Sci.: Nanosci.
Nanotechnol. 2010, 1, 035012.
[27] I. Saldan, Y. Semenyuk, I. Marchuk, O. Reshetnyak, J. Mater.
Sci. 2015, 50, 2337.
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
How to cite this article: Arde SM, Rashinkar GS,
Jadhav SN, Patil AD, Salunkhe RS. Biogenic
synthesis of palladium nanoparticles using
Boswellia sarrata and their applications in cross-
coupling reactions. Appl Organomet Chem. 2020;
e6012. https://doi.org/10.1002/aoc.6012