Bioinspired Palladium Nanoparticles Supported on Soil-Derived Humic Acid Coated Iron-Oxide Nanoparticles as Catalyst for C–C Cross-Coupling and Reduction Reactions

Article abstract of DOI:10.1007/s10562-019-02703-z

Abstract: Pd nanoparticles supported on humic acid-coated nanoferrites as magnetically-recoverable catalyst was expediently prepared from inexpensive precursors and characterized by techniques such as SEM, TEM, XPS, FT-IR, XRD, ICP-AES, EDX. The as made catalyst displayed an admirable catalytic activity towards the Suzuki–Miyaura cross-coupling reaction of aryl halides (or) aryl diazonium salts with aryl boronic acid in non-toxic solvent EtOH/water under mild conditions. The same catalyst showed high efficiency for the Heck reaction of aryl halides with styrene was carried out with high efficiency offering good yields under ligand-free conditions. Additionally, the reduction of olefins using molecular hydrogen was also achieved using the same catalyst under ambient and base-free conditions affording the products in good to excellent yields. The magnetic activity of nano-Fe₃O₄ allowed the effortless recovery of the catalyst and demonstrated subsequent recyclability up to 5 cycles without a significant loss in the activity. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02703-z

Catalysis Letters
https://doi.org/10.1007/s10562-019-02703-z
Bioinspired Palladium Nanoparticles Supported on Soil-Derived
Humic Acid Coated Iron-Oxide Nanoparticles as Catalyst for C–C Cross-
Coupling and Reduction Reactions
1
1
1
Anurag N. Chinchole · Abhishek V. Dubey · A. Vijay Kumar
Received: 29 October 2018 / Accepted: 4 February 2019
©
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Pd nanoparticles supported on humic acid-coated nanoferrites as magnetically-recoverable catalyst was expediently prepared
from inexpensive precursors and characterized by techniques such as SEM, TEM, XPS, FT-IR, XRD, ICP-AES, EDX. The as
made catalyst displayed an admirable catalytic activity towards the Suzuki–Miyaura cross-coupling reaction of aryl halides
(
or) aryl diazonium salts with aryl boronic acid in non-toxic solvent EtOH/water under mild conditions. The same catalyst
showed high efficiency for the Heck reaction of aryl halides with styrene was carried out with high efficiency offering good
yields under ligand-free conditions. Additionally, the reduction of olefins using molecular hydrogen was also achieved using
the same catalyst under ambient and base-free conditions affording the products in good to excellent yields. The magnetic
activity of nano-Fe O allowed the effortless recovery of the catalyst and demonstrated subsequent recyclability up to 5
3
4
cycles without a significant loss in the activity.
Anurag N. Chinchole and Abhishek V. Dubey have contributed
equally.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02703-z) contains
supplementary material, which is available to authorized users.
*
A. Vijay Kumar
vijayakki@gmail.com
1
Department of Chemistry, Institute of Chemical
Technology, Nathalal Parekh Marg, Matunga, Mumbai,
Maharashtra 400019, India
Vol.:(0
1
123456789)
3

A. N. Chinchole et al.
Graphical Abstract
B(OH)2
X
R
R'
X = I, Br, Cl (or)
N BF
7
examples
2
4
R
8
5-51% yield
H2
Pd
R'
R
Pd
2
6 examples
5-51% yield
9
Humic Acid
Pd
Pd
Pd
R
6 examples
5-85% yield
9
Fe O
♦Magnetically recyclable catalyst
3
4
♦
♦
♦
Recyclable upto 5 cycles
Humic acid as benign support
Eco-friendly solvents
Keywords Cross-coupling · Heterogeneous · Humic acid · Magnetic nanoparticles · Palladium
1
Introduction
substantial research and are exemplar of “green chemistry
[
12–18].”
Transition-metal catalysts have played a major role in C–C
1] and C–hetero [2] bond forming reactions which have
Owing to their nano-size, separation of nanocatalysts
[
through filtration or centrifugation becomes laborious. To
tackle these challenges, the development of magnetically-
recoverable nanoparticles (MNPs) has proved invaluable.
Among the myriad of available magnetically-recoverable
nanomaterials, iron oxide has flourished tremendously
chiefly because it is biocompatible, nontoxic, inexpensive
and exhibits superparamagnetism [19]. However, the nano-
particles have a strong tendency to aggregate. This issue
is overcome by using suitable stabilizing agents such as
dopamine derivatives [20–24], silica [25–28], dendrimers
[29–32], ionic liquids [33–37], graphene [38–43], natural
polymers [44–48] which also have reactive sites that cova-
lently or non-covalently bind to the catalytic units and thus
can display numerous synthetic applications. Commonly,
synthesis of these capped iron oxide nanoparticles requires
harsh conditions, toxic precursors, inert conditions. Most
essentially, they suffer from the need of sophisticated syn-
thetic procedures for capping and stabilizing the nano-
particles [49–51]. Therefore, the development of robust
catalysts which are environmentally-benign, versatile,
not only benefitted the chemical [3], pharmaceutical [4],
polymer [5], and other allied industries for manufacturing
a wide range of products, but also laboratory-scale organic
synthesis [6–8]. Amongst all the Transition-metal cataly-
sis, palladium based reactions i.e. Heck, Suzuki–Miyaura
and other ancillary cross-coupling reactions are graded the
most versatile transformations in organic synthesis owing
to the efficiency and diversity [9–12]. These reactions have
allowed construction of biphenyls and stilbenoids which
are present in many natural products, drug molecules
and biologically-active molecules (Scheme 1). Although
these homogeneous catalysts demonstrate high activity and
selectivity, the proclivity towards heterogeneous catalysts
is rising primarily due to their ease of separation from
products and reusability in successive reactions. Immo-
bilization of active molecules or metal nanoparticles on a
solid support to fabricate a heterogeneous catalytic system
has gained significant importance in the past decades [10,
1
1]. These heterogeneous nanocatalysts are a subject of
1
3

Bioinspired Palladium Nanoparticles Supported on Soil-Derived Humic Acid Coated Iron-Oxide…
Scheme 1 Some natural
O
OH
OH
OH
products and drug molecules
OH
O
containing biphenyl and stilbene
HO
HO
moieties
OH
Resveratrol
OH
Piceatannol
Acuparin
COOH
HN N
O
N
N
N
H
O
N
N
O
N
N
Valsartan
Telmisartan
inexpensive and expediently prepared from nontoxic pre-
cursors is vital.
and heated to 90 °C. The pH of the solution was regulated by
adding 30% ammonia solution (25 mL) followed by addition
of sodium salt of humic acid (1 g). The solution was stirred
using an overhead stirrer for 40 min and then cooled to room
temperature. The particles were recovered using an external
magnet followed by washing with ethanol and de-ionized
water. Later, the particles were dried in a vacuum oven.
In light of these facts, we focused our attention towards
naturally available polyphenolic substances from soil. Humic
acid (HA) is one such substance found abundantly in soil along
with Humic substances (HS), fulvic acid (FA) and humin [52].
Humic acid possesses multiple hydroxyl and carboxylic groups
which exhibit exceptional binding capability to metal oxide
nanoparticles especially iron oxides and can significantly alter
their physicochemical and sorption behavior [53–55]. Besides
this, due to its planar structure, humic acid shows good interac-
tion with organic compounds especially aromatic molecules
by providing large surface area. Moreover, substantial research
on humic acid for sequestering heavy-metal ions and polyaro-
matic hydrocarbons from aquatic sources is ongoing [56–61].
Considering the sequestering capability of humic acid
towards late transition metal ions, we envisaged that humic
acid can act as an excellent capping agent for iron oxide
nanoparticles which can capture Pd(II) ions and further be
reduced to Pd(0) NPs. Therefore, extending the methodology
for magnetically-recoverable nanocatalyst, we herein present
an environmentally-benign humic acid coated nanoferrites
2.2 Preparation of HA@Pd/Fe O
3
4
The Fe O coated with humic acid (HA@Fe O ) MNPs were
3
4
3
4
obtained from the previously reported method. In a 1000 mL
beaker, 1 g of HA@Fe O MNPs were added to 400 mL of
3
4
de-ionized water and sonicated for 30 min. Meanwhile, in
a 15 mL round-bottom flask, 80 mg of PdCl and 90 mg
2
of NaCl were dissolved in 6 mL of de-ionized water and
heated to 60 °C with constant stirring till homogeneity and
then, cooled to room temperature. This solution was added
to the sonicated mixture of HA@Fe O MNPs and stirred
3
4
on an overhead stirrer at room temperature. Further, NaBH
4
solution (76 mg of NaBH in 25 mL) was added to it portion-
4
wise over a period of 30 min and stirred for 15 h. The result-
ant wet paste was recovered using an external magnet from
the solution and washed with de-ionized water (50 mL×3)
and acetone (25 mL×3). The catalyst was dried in a vacuum
oven at room temperature.
[
62] supported by Palladium nanoparticles for C–C cross-
coupling reactions (Suzuki and Heck reaction) and reduction
of olefins using molecular hydrogen to confront the chal-
lenges of recoverability, reusability, and benign support.
2
.3 General Procedure for Suzuki Cross‑Coupling
2
Experimental Section
Between Aryl Boronic Acid and Aryl Halide
2
.1 Synthesis of HA@Fe O
A 15 mL round bottom flask (back-filled with N ) was
3
4
2
loaded with HA@Pd/Fe O (50 mg). Aryl halide (1 equiv.),
3
4
8
.5 g of FeSO .7H O and 12.3 g of FeCl .6H O were dis-
aryl boronic acid (1.1 equiv.) and potassium carbonate (2.0
4
2
3
2
solved in 200 mL of de-ionized water in a 1000 mL beaker
equiv.) were added to the flask followed by 1:1 mixture of
1
3

A. N. Chinchole et al.
ethanol and water (4 mL). The resultant mixture was stirred
at 50 °C for 4 h under nitrogen atmosphere. With the aid
of an external magnet, the catalyst was recovered and the
product was extracted using ethyl acetate (5 mL× 3). The
organic layer was separated and dried over Na SO followed
mixture was purified using column chromatography on silica
gel (Petroleum ether/Ethyl acetate).
3 Results and Discussion
2
4
by evaporation under reduced pressure and the mixture was
purified using column chromatography on silica gel (Petro-
leum ether/Ethyl acetate).
Initially, humic acid capped Fe O NPs were prepared and
3
4
were used to immobilize palladium nanoparticles on them.
The as synthesized material was fully characterized by
Scanning Electron Microscopy (SEM), Transmission Elec-
tron Microscopy (TEM), X-Ray Diffraction (XRD), X-Ray
Photoelectron Spectroscopy (XPS), Energy Dispersive
Spectroscopy (EDS), Fourier Transformed Infrared Spec-
troscopy (FT-IR), and Inductively Coupled Plasma Atomic
Emission Spectroscopy (ICP-AES) analysis. The humic acid
coating is indistinguishable from SEM images (Fig. 1). For
a detailed knowledge on the surface morphology, Trans-
mission Electron Microscopy (TEM) and High-Resolution
TEM (HR-TEM) of HA@Pd/Fe O was done (Fig. 2). It was
2
.4 General Procedure for Suzuki Cross‑Coupling
Between Aryl Diazonium Tetrafluoroborate
and Aryl Boronic Acid
A 15 mL round bottom flask was loaded with HA@Pd/Fe O
3
4
(
50 mg). Aryl diazonium tetrafluoroborate (1 equiv.), aryl
boronic acid (1.1 equiv.) were added to the flask followed
by methanol (4 mL). The resultant mixture was stirred at
room temperature for 12 h in air. With the aid of an exter-
nal magnet, the catalyst was recovered and the product was
extracted using ethyl acetate (10 mL×3). The organic layer
was separated and dried over Na SO followed by evapora-
3
4
observed that humic acid is uniformly coated along with
evenly distributed Pd NPs of size less than 10 nm on the
catalyst. Energy Dispersive X-Ray (EDX) mapping provided
the elemental composition of HA@Pd/Fe O (Fig. 6a). The
2
4
tion under reduced pressure and the mixture was purified
using column chromatography on silica gel (Petroleum
ether/Ethyl acetate).
3
4
presence of palladium and carbon peaks in the spectrum
confirmed the humic acid coating as well as supported palla-
dium on the catalyst. Upon ICP-AES analysis, it was discov-
ered that 7.98 wt% of Pd was loaded. X-ray Photoelectron
Spectroscopy (XPS) was carried out for native as well as
recycled HA@Pd/Fe O to identify the chemical state of Pd
2.5 General Procedure for the Heck Reaction
To a solution of aryl halide (1 equiv.), styrene (2 equiv.) and
HA@Pd/Fe O (50 mg) in DMF (4 mL), potassium carbon-
3
4
3
4
ate (2.5 equiv.) was added. The resultant mixture was stirred
supported on the catalyst. XPS analysis of the native cata-
under O atmosphere at 140 °C for 24 h. With the aid of
lyst in Pd 3d region (Fig. 7) indicates that BE of Pd 3d at
2
5/2
an external magnet, the catalyst was recovered and water
335.4 eV and 3d at 340.6 eV, which is a characteristic
3
/2
(5 mL) was added to the reaction mixture. Further, the prod-
emissions from metallic Pd (0). The XPS data for recycled
catalyst showed that the peaks did not shift, thus suggesting
the unaffected chemical state of Pd after the reaction. X-ray
Diffraction is a valuable technique to understand the lattice
structure of a material. The XRD pattern of the obtained HA,
HA@Fe O , HA@Pd/Fe O ative and recycled) are shown
uct mixture was extracted using ethyl acetate (5 mL×3). To
remove traces of DMF, the organic layer was washed with
water (4 mL×2) and then the organic layer was dried over
Na SO . The solvent was evaporated under reduced pressure
2
4
and the mixture was purified using column chromatography
3
4
3
4
on silica gel (Petroleum ether/Ethyl acetate).
(Figs. 3, 8). The peaks in the XRD pattern of HA were not
as prominent as the native catalyst peaks. Native HA@Pd/
Fe O shows characteristic broad and weak (1 1 1) reflection
2
.6 General Procedure for Olefin Reduction Using
3
4
Molecular Hydrogen
peak centered at 2θ=39.5° indicate the presence of metal-
lic Pd (0). This peak was visible in recycled HA@Pd/Fe O
3
4
In a 25 mL round bottom flask equipped with Teflon coated
magnetic needle, olefin (1 equiv.) was dissolved in 4 mL of
hinting towards the presence of Pd NPs even after the 5th
cycle. FT-IR of HA@Pd/Fe O was recorded (Fig. S1, sup-
3
4
methanol. Then, H was introduced in the flask followed
porting information) to ascertain the functional groups in
2
by flushing it twice and the resulting mixture was stirred at
the support. The spectrum shows a strong and broad peak
−
1
room temperature under H atmosphere for 15 h. The sol-
at 3400 cm which is indicative of H-bonded hydroxyl
2
−
1
vent was then evaporated under reduced pressure and water
groups whereas the 1720 cm shoulder peak corresponds
to the presence of ketonic or aldehydic C=O group. This was
(
5 mL) was added to the residue to dissolve inorganic impu-
−
−1
rities. The product was then extracted using ethyl acetate
3×5 mL). The organic layer was dried over sodium sulphate
and the solvent was evaporated under reduced pressure. The
confirmed by the characteristic COO peaks at 1600 cm
−
1
−1
(
and 1390 cm . The band near 1600 cm could be due to
C=C aromatic vibrations and H-bonded C=O quinones. The
1
3

Bioinspired Palladium Nanoparticles Supported on Soil-Derived Humic Acid Coated Iron-Oxide…
Fig. 1 SEM images of native HA@Pd/Fe O (a) yellow bar shown is 1 µm length (b) yellow bar shown is 100 nm length
3
4
Fig. 2 HR-TEM images (a, c) and TEM images (b, d) of native HA@Pd/Fe O and TEM images (e, f) of recycled HA@Pd/Fe O
4
3
4
3
strong peak at 530 cm−1 is characteristic of Fe–O stretch-
ing which confirms the interaction between iron oxide and
humic acid [63]. All these characterization techniques con-
clusively authenticated the immobilization of Pd on the sup-
port. To investigate the catalytic activity of HA@Pd/Fe O ,
the reaction between 4-iodoanisole and phenylboronic acid
as a model reaction.
Several parameters such as solvent, bases and temperature
of the reaction were varied to obtain the best yields. The
combination of 1:1 of ethanol: water mixture with K CO
3
4
2
3
we attempted Suzuki–Miyaura cross-coupling reaction. In
as base at 50 °C afforded the cross-coupled product in 94%
order to determine optimized reaction conditions, we chose
yield (Table 1, entry 7). The identity of the product was
1
3

A. N. Chinchole et al.
2
-iodothiophene also gave excellent yields of 89% and 85%
respectively (Tables 2, 1l and 1i).
We further extended the substrate scope by reacting
substituted bromoarenes with phenylboronic acid. Differ-
ent aryl bromides bearing electron-donating and electron-
withdrawing groups also successfully afforded the products
in 90–85% yield. The polyaromatic aryl products viz.,1-
pyrenyl (Table 2, 1k) and 2-naphthyl (Table 2, 1f) obtained
from the corresponding arylboronic acids and 4-iodoanisole
were obtained in 94% and 92% yield respectively whereas
the reaction of the same boronic acids with 4-bromoani-
sole formed products in 88% and 89% yield respectively.
As anticipated the aryl halides possessing electron-donating
substituents were less reactive in contrast to electron-with-
drawing counterparts. For the same reason, the reaction of
4-chloroanisole with phenylboronic acid, was found to be
sluggish even at higher temperature providing unsatisfactory
yield of 32%. (Table 2, 1c).
Fig. 3 XRD pattern of HA, Fe O , HA@Fe O , and HA@Pd/Fe O
4
3
4
3
4
3
(
Native)
It is noteworthy to mention that, the challenging reactions
of aryl bromide, that too the ones with electron-donating
substituents despite their low reactivity underwent conver-
sion to afford products in good to excellent yields vouches
the efficiency of the catalyst. Additionally, reactant/products
bearing oxidation or hydrolysis-prone substituents such as
cyano or ester groups were unaffected under these conditions
and hence, no such side products formation was observed.
Proficiency and mildness of the developed protocol can be
advocated due to the conservation of sensitive groups and
improved activation of substrates. To further examine the
usefulness of the catalyst, we decided to employ it another
cross-coupling reaction which is relatively unexploited with
heterogeneous Pd catalysts. We carried out Suzuki–Miyaura
reaction of aryldiazonium tetrafluoroborate and arylboronic
acid using this catalytic system. Initially, 4-methoxyphenyl-
diazonium tetrafluoroborate and phenylboronic acid were
chosen as model substrates for the optimization of the reac-
tion. Parameters affecting the reaction such as solvent and
temperature were varied to obtain the optimum yield of the
products. The reaction when carried out in methanol as reac-
tion solvent at 30 °C afforded the maximum yield of 88% of
the biaryl product (Table 3).
Table 1 Screening of different bases, solvents and temperatures for
Suzuki cross-coupling of 4-iodoanisole and phenylboronic acid under
reaction condition
Reaction condition: 4-iodoanisole (0.5 mmol), phenylboronic acid
(
0.55 mmol), base (1 mmol), catalyst (50 mg), solvent (4 mL), N
2
atmosphere, 4 h
a
Isolated yield
To broaden the substrate scope, diverse aryldiazonium
tetrafluoroborates and aylboronic acids were assessed for
their conversion. Electron-withdrawing and electron-donat-
ing groups on both aryldiazonium tetrafluoroborates and
arylboronic acids were well-tolerated offering yields rang-
ing from 93 to 83% (Table 4). Only in case of 4-methoxy-
phenyldiazonium tetrafluoroborate and 4-nitrophenylboronic
acid, the corresponding product was obtained in poor yield
of 26% which shows sluggishness of the substrates to react
via oxidative coupling mechanism (Table 4, 2e).
1
13
confirmed by H and C NMR spectroscopy. The turnover
number and turnover frequency of the synthesized PdNPs
−
3 −1
are found to be 14.329 and 1.0023×10
s
respectively.
With the optimized conditions in hand, several substrates
were screened for their conversion. The reaction of phenylb-
oronic acid with aryl iodides possessing electron-withdraw-
ing and electron-donating groups such as nitro, methoxy
and cyano, afforded the products in good yields (95–89%).
The aromatic heterocyclic iodides viz. 2-pyridyl iodide and
The Heck reaction is typically found to be difficult to
accomplish using a supported palladium catalyst. Therefore,
1
3

Bioinspired Palladium Nanoparticles Supported on Soil-Derived Humic Acid Coated Iron-Oxide…
Table 2 Suzuki cross-coupling
reactions between various
aryl halides with arylboronic
acids with HA@Pd/Fe O
3
4
nanocatalyst
Reaction condition: arylhalide (0.5 mmol), aryl/heteroarylboronic acid (0.55 mmol), K CO (1 mmol),
2
3
HA@Pd/Fe O (50 mg,), 4 h/6 h/ 24 h, solvent (4 mL), N atmosphere
3
4
2
Table 3 Screening of different
solvents and temperatures for
Suzuki cross-coupling between
aryldiazonium tetrafluoroborate
and arylboronic acid under
reaction conditions
Reaction condition: 4-methoxyphenyldiazonium tetrafluoroborate (0.5 mmol) and phenylboronic acid
(
0.55 mmol), solvent (4 mL), 12 h
Isolated yield
a
1
3

A. N. Chinchole et al.
Table 4 Suzuki reaction of
various arylboronic acids with
aryldiazonium tetrafluoroborate
using HA@Pd/Fe O
3
4
a
nanocatalyst
Reaction condition: 4-methoxyphenyldiazonium tetrafluoroborate (0.5 mmol) and phenylboronic acid
(
0.55 mmol), solvent (4 mL), 12 h
Isolated yield
a
Table 5 Screening different
solvents, bases and temperature
for the Heck reaction between
4
-iodoanisole and styrene under
reaction condition
Reaction condition: 4-iodoanisole (0.5 mmol), styrene (1 mmol), base (1.25 mmol), solvent (3 mL), cat-
alyst (50 mg), O atmosphere
2
a
Isolated yield
b
Reaction carried out in sealed tube
1
3

Bioinspired Palladium Nanoparticles Supported on Soil-Derived Humic Acid Coated Iron-Oxide…
Table 6 Heck reaction of
different aryl halides with
a
styrene with HA@Pd/Fe O
3
4
Reaction condition: aryl halide (0.5 mmol), styrene (1 mmol), K CO (1.25 mmol), DMF (3 mL), cata-
2
3
lyst (50 mg), O atmosphere, 24 h
Isolated yield
2
a
Table 7 Screening of
different solvent and different
temperatures for reduction
of olefins using molecular
hydrogen
Reaction conditions: (E)-stilbene (0.5 mmol), catalyst (50 mg), solvent (4 mL), 12 h
a
Isolated yield
we decided to investigate the robustness of this catalytic
system towards the Heck reaction of aryl halides namely,
aryl iodides and aryl bromides. The optimized conditions
were determined by taking 4-iodoanisole and styrene as the
model substrates and varying the factors affecting the reac-
tion such as solvent, base and temperature. The optimum
yield of product was obtained when DMF was taken as the
reaction solvent using K CO as base at 140 °C under O
Table 8 Olefin reduction using molecular hydrogen of different stil-
a
benes with Pd/Fe O under reaction condition
3
4
2
3
2
atmosphere (Table 5).
The products were obtained in the range of 85–51%
depending on the nature of aryl halide. As expected, a trend
was observed with electron rich aryl halides which are less
reactive than the electron deficient counterparts. The aryl
bromides being less reactive, required longer reaction times
and afforded only moderate yields of products (Table 6).
However, the reaction did not proceed in the case of aryl
chlorides.
Reaction conditions: olefin (0.5 mmol), catalyst (50 mg), methanol
(
4 mL),12 h
a
Isolated yield
1
3

A. N. Chinchole et al.
Recyclability
9
9
99
98
9
7
96
1
00
94
9
2
8
9
88
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
84
1
2
3
4
5
Cycles
Yield(%)
Recovery(%)
Fig. 4 Recyclability of HA@Pd/Fe O nanocatalyst
3
4
Nowadays, versatile multi-modal catalysts are highly
desirable due to increasing demand in sustainable chem-
istry leveraging the principle “one catalyst-many jobs [47,
Fig. 6 EDX images of native (a) and recycled (b) catalyst
4
8].” In this context, we evaluated the versatility of HA@
Pd/Fe O catalyst for the reduction of olefins using molecu-
3
4
lar hydrogen and trans-stilbene as the model substrate. In
order to optimize the reaction conditions, parameters such
as solvent and temperature were varied. The best outcome
was observed when the reaction was carried out in methanol
at room temperature in 12 h (Table 7).
an inseparable mixture of products was observed, possibly
due to lack of selectivity towards C=C and nitro group lead-
ing to the formation of saturated and unsaturated amines
(Table 8).
For heterogeneous catalytic systems, the level of reusabil-
ity and the lifetime of a catalyst are very crucial. Therefore,
we probed the recyclability of the catalyst (Fig. 4) for Suzuki
cross-coupling between 4-iodoanisole and phenylboronic
acid by recovering the catalyst particles and reuse them in
the next cycle. The recovery of the catalyst was effortless
owing to the magnetic property exhibited by iron oxide nan-
oparticles. Unlike the conventional laborious methods such
as filtration or centrifugation, the catalyst was recovered by
means of an external magnet. The nanoferrite-supported
Applying these optimized conditions, effectiveness of this
catalyst towards diverse substrates was assessed. Substituted
(
E)-stilbene derivatives were employed in order to carry out
this the task and it was found that good to excellent yields of
products ranging from 96 to 85% were obtained. Remark-
ably, the reaction proceeded smoothly without the use of a
base and under mild conditions. Electron-donating as well as
electron-withdrawing substituents on the stilbene were well-
tolerated. When reduction of 4-nitrostilbene was carried out,
Fig. 5 SEM images of recycled HA@Pd/Fe O (a) yellow bar shown is 1 µm length (b) yellow bar shown is 100 nm length
3
4
1
3

Bioinspired Palladium Nanoparticles Supported on Soil-Derived Humic Acid Coated Iron-Oxide…
2
h executed 62% yield of desired coupled product, later the
catalyst was removed/separated magnetically. The obtained
filtrate was taken in a separate reaction flask and reaction
continued at 50 °C for next 24 h, shows no increase in the
coupled product yield. Another hot filtration test was carried
out in the same optimized condition (reaction conversion
after 2 h~61%) but now catalyst filtered by centrifugation
(
3000 rpm) to prevent the back deposition of leached if any
Pd species. This showed a no further increase in yield the
and hence endorse catalyst’s heterogeneous property. In
order to find out the amount of Palladium reamined intact on
the support after the five cycles Pd was deliberately leached
from the recycled HA@Pd/Fe O catalyst and was found to
3
4
be 7.93%, which shows no significant leaching occur during
catalytic processes.
SEM analysis was done for the recycled catalyst which
revealed that morphology of the catalyst was unchanged
(
Fig. 5). Moreover, EDX analysis of the recycled catalyst
Fig. 7 XPS image of native and recycled HA@Pd/Fe O
3
4
showed that the ratios of the peaks were very close compared
to the native catalyst indicating that the elemental composi-
tion is intact (Fig. 6b). When XPS data of the catalyst after
5
cycles was examined, it revealed that Pd 3d region showed
two peaks at BE 340.9 eV and at BE 335.7 eV corresponding
to 3d and 3d respectively (Fig. 7). It can be inferred that
3/2
5/2
since no other peaks were detected, the oxidation state of Pd
is constant. The integrity of the lattice structure of the recy-
cled catalyst was evaluated by XRD pattern. It was found
that the lattice structure of the core nanoferrite and also Pd
NPs is undamaged after 5 cycles (Fig. 8). The catalytic effi-
ciency of various catalysts with respect to their product yield
and other application in organic transformation, including
this work is shown in Table 9 for comparison.
4
Conclusions
Fig. 8 XRD Pattern of native and recycled HA@Pd/Fe O
3
4
In conclusion, a novel and versatile Pd nanoparticles sup-
ported on humic acid stabilized nano-Fe O (HA@Pd/
3
4
Fe O ) was prepared in a straightforward manner using non-
palladium catalyst showed excellent efficiency and recov-
erability till the fifth cycle without any loss of activity.
With the completion of recyclability study, we examined
the change in surface morphology the catalyst after the 5th
cycle as it poses a significant difficulty in heterogeneous
catalytic systems. To gain more insights of heterogeneity
of the catalyst, how palladium is operating in the reaction
under the optimised reaction conditions, we performed a hot
filtration test. For this the cross-coupling reaction between
3
4
toxic precursors. The catalyst displayed excellent catalytic
activity towards Suzuki–Miyaura and Heck cross-coupling
reactions by well-tolerating electron-donating and electron-
withdrawing substituents on aryl iodides and bromides.
Reduction of olefins was rendered possible at room tempera-
ture in nontoxic solvent and under base-free condition mak-
ing it a highly sustainable methodology. Other advantages of
this catalyst were facile recovery and extensive reusability.
Moreover, humic acid played a major role in stabilizing the
Fe O as well as Pd nanoparticles.
4
-iodoanisole and phenylboronic acid was carried out for
3
4
1
3

A. N. Chinchole et al.
Table 9 Catalytic performance of different catalysts in Suzuki–Miyaura cross-coupling and other reactios
Entry Catalyst
Conditions
X
Time (h)
Yield (%) Reactions
References
1
Pd-NPs@Oak Gum (0.3)
K CO , H O, 80 °C
I,Br,Cl 1.0, 2.0, 18.0 96,92,70 Suzuki–Miyaura cross-
coupling and reduction of
[14]
2
3
2
Nitroarenes
2
Fe O @TA/Pd (0.21)
K CO EtOH/H O,25 °C I,Br,Cl 1.5, 3.0, 24.0 98, 96, 45 Suzuki–Miyaura cross-
[18]
3
4
2 3 2
coupling and reduction of
Nitrophenol
3
4
Pd/Fe O @PDA (0.46)
K CO EtOH/H O,80 °C I,Br
6.0, 8.0
0.5, 1.5
98, 88
96, 96
Suzuki–Miyaura cross-
[20]
[28]
3
4
2
3
2
coupling
Fe O @SiO /isoniazide/
K CO , H O/EtOH, r.t
I, Br
Suzuki–Miyaura cross-
coupling and reduction of
Nitrophenol
3
4
2
2
3
2
Pd (0.2)
5
6
7
8
Fe O /IL/Pd (0.20)
EtOH/H O, K CO , rt
I,Br,Cl 0.25, 1.0, 18.0 96, 95, 75 Suzuki–Miyaura cross-
[39]
3
4
2
2
3
coupling
Pd@PS-Met (0.1)
K CO , H O, 80 °C
I,Br
2.0, 4.0
0.5, 0.7
96, 96
Suzuki–Miyaura cross-
coupling
Mizoroki–Heck coupling
[52]
2
3
2
Pd-isatin Schiff base-γ-
Fe O (0.5, 1.5)
Et N, Solvent-free,100 °C I, Br
95, 90
[64]
3
2
3
HA@Pd/Fe3O4 (0.65)
EtOH/H2O, K CO , 50 °C I,Br,Cl 4, 6, 24
94,90,32
This work
2
3
Acknowledgements AVD is grateful to University Grants Commision
18. Veisi H, Pirhayati M, Kakanejadifard A et al ChemistrySelect
(2018) 3:1820
(
UGC) for the research fellowship. AVK is grateful to DST, Govt. of
India, for research funding, DST-SERB (YSS/2015/002064) and the
Department of Pharmaceutical Science and Technology, ICT, for NMR
analysis. We are also thankful to Sophisticated Analytical Instruments
Facility (SAIF) at the Indian Institute of Technology, Mumbai (IITB)
for providing the characterization data for the analysis of the catalyst.
19. Karimi B, Mansouri F, Mirzaei HM, ChemCatChem (2015)
7:1736
20. Dubey AV, Kumar AV, Adv RSC (2016) 6:46864
21. Farzad E, Veisi H (2018) J Ind Eng Chem 60:114
22. Baig RBN, Varma RS (2012) Chem Commun 48:2582
2
3. Nasir Baig RB, Leazer J, Varma RS, Clean Technol Environ
Policy (2015), 17:2073
2
2
4. Dam B, Patil RA, Ma YR, Pal AK (2017) New J Chem 41:6553
5. Jha A, Patil CR, Garade AC, Rode CV (2013) Ind Eng Chem Res
References
5
2:9803
1
2
3
4
.
.
.
.
Molnár (2011) Á Chem Rev 111:2251
26. Yi DK, Lee SS, Ying JY (2006) Chem Mater 18:2459
27. Sharma RK, Yadav M, Gawande MB (2016) In: Eds.: Sharma
VK, Doong R, Kim H, Varma RS, Dionysiou DD ACS Symp Ser.
American Chemical Society, Washington, DC, pp 1–38
28. Heidari F, Hekmati M, Veisi H (2017) J Colloid Interface Sci
501:175
Hartwig JF Nature (2008) 455: 314
Blaser HU, Catal Today (2000) 60:161
Busacca CA, Fandrick DR, Song JJ, Senanayake CH (2011) Adv
Synt Catal 353:1825
5
.
Vandenberg EJ (1992) Catalysis in polymer synthesis. American
Chemical Society, Washington, DC, pp 2–23
Feng J, Holmes M, Krische MJ (2017) Chem Rev 117:12564
Trost BM (1995) Angew Chem Int Ed 34:259
Fumagalli G, Stanton S, Bower J (2017) F, Chem Rev 117:9404
Chen X, Engle KM, Wang DH, Yu JQ (2009) Ang Chem Int Ed
29. Rehm TH, Bogdan A, Hofmann C, Löb P, Shifrina ZB, Morgan
DG, Bronstein LM (2015) ACS Appl Mater Interfaces 7:27254
30. Deraedt C, Wang D, Salmon L, Etienne L, Labrugère C, Ruiz J,
Astruc D, ChemCatChem (2015) 7:303
6
7
8
9
.
.
.
.
31. Asadi B, Mohammadpoor-Baltork I, Tangestaninejad S, Mogh-
adam M, Mirkhani V, Landarani-Isfahani A (2016) New J Chem
40:6171
4
8:5094
1
0. Polshettiwar V, Luque R, Fihri A, Zhu H, Bouhrara M, Basset J-M
(
2011) Chem Rev 111:3036
32. Paez JI, Froimowicz P, Landfester K, Brunetti V, Strumia M
(2014) J Polym Sci Part A 52:3185
1
1
1. Wang D, Astruc D (2017) Chem Soc Rev 46:816
2. Zhang S, Nguyen L, Zhu Y, Zhan S, Tsung CK, Tao F (2013) Acc
Chem Res 46:1731
33. Safaei S, Mohammadpoor-Baltork I, Khosropour AR, Moghadam
M, Tangestaninejad S, Mirkhani V, Kia R (2012) RSC Adv 2:5610
34. Zheng X, Luo S, Zhang L, Cheng JP (2009) Green Chem 11:455
35. Otokesh S, Kolvari E, Amoozadeh A, Koukabi N, RSC Adv
(2015) 5:53749
1
1
1
1
1
3. Fihri A, Bouhrara M, Nekoueishahraki B, Basset JM, Polshettiwar
V (2011) Chem Soc Rev 40:5181
4. Veisi H, Nasrabadi NH, Mohammadi P (2016) Appl Organomet
Chem 30:890
36. Zhang Q, Su H, Luo J, Wei Y (2012) Green Chem 14:201
37. Mandal P, Chattopadhyay AP, Dalton Trans (2015), 44:11444
38. Jamatia R, Gupta A, Pal AK (2017) ACS Sustain Chem Eng
5:7604
5. Lebaschi S, Hekmati M, Veisi HJ (2017) Colloid Interface Sci
4
85:223
6. Veisi H, Faraji AR, Hemmati S, Gil A (2015) Appl Organomet
Chem 29:517
39. Veisi H, Pirhayati M, Kakanejadifard A (2017) Tetrahedron Lett
58:4269
7. Das SK, Parandhaman T, Pentela N et al (2014) J Phys Chem C
1
18:24623
1
3

Bioinspired Palladium Nanoparticles Supported on Soil-Derived Humic Acid Coated Iron-Oxide…
4
4
0. Zhang M, Liu YH, Shang ZR, Hu HC, Zhang ZH, Catal Commun
54. Hu JD, Zevi Y, Kou XM, Xiao J, Wang XJ, Jin Y (2010) Sci Total
Environ 408:3477
(
2017) 88:39
1. Patil MR, Kapdi AR, Vijay Kumar A (2018) ACS Sustain Chem
Eng 6:3264
55. Ni L, Su L, Li S, Wang P, Li D, Ye X, Li Y, Li Y, Li Y, Wang C
(2017) Environ Toxicol Chem 36:1856
4
4
2. Ko S, Jang J (2006) Angew Chem Int Ed 45:7564
3. Jawale DV, Gravel E, Boudet C et al (2015) Catal Sci Technol
56. Lippold H, Gottschalch U, Kupsch H (2008) Chemosphere
70:1979
5
:2388
57. Liu S, Zhu Y, Liu L, He Z, Giesy JP, Bai Y, Sun F, Wu F (2018)
Environ Pollut 234:726
4
4
4. Reddy LH, Arias JL, Nicolas J, Couvreur P (2012) Chem Rev
1
12:5818
58. Tan L, Wang X, Tan X, Mei H, Chen C, Hayat T, Alsaedi A, Wen
T, Lu S, Wang X (2017) Chem Geol 464:91
5. Korneva G, Ye H, Gogotsi Y, Halverson D, Friedman G, Bradley
JC, Kornev KG (2005) Nano Lett 5:879
59. Tang Z, Zhao X, Zhao T, Wang H, Wang P, Wu F, Giesy JP (2016)
Environ Sci Technol 50:8640
4
4
6. Veisi H, Mirzaee N (2018) Appl Organomet Chem 32:e4067
7. Yang S, Zong P, Ren X, Wang Q, Wang X (2012) ACS Appl Mater
Interfaces 4:6891
60. Liu J, Zhao Z, Jiang G (2008) Environ Sci Technol 42:6949
61. Stevenson FJ, Goh KM (1971) Geochim Cosmochim Acta 35:471
62. García-Suárez EJ, Balu AM, Tristany M, García AB, Philippot K,
Luque R (2012) Green Chem 14:1434
4
8. Veisi H, Mohammadi Biabri P, Falahi H (2017) Tetrahedron Lett
5
8:3482
4
5
9. Wang D, Liu W, Bian F, Yu W (2015) New J Chem 39:2052
0. Parandhaman T, Pentela N, Ramalingam B et al (2017) ACS Sus-
tain Chem Eng 5:489
63. García CS, Uberman PM, Martín SE, Beilstein (2017) J Org Chem
13:1717
64. Sobhani S, Zarifi F, Chinese J, Catal (2015), 36:555
5
5
1. Veisi H, Najafi S, Hemmati S (2018) Int J Biol Macromol 113:186
2. Veisi H, Mirshokraie SA, Ahmadian H (2018) Int J Biol Macro-
mol 108:419
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
5
3. Kharisov BI, Kharissova OV, Dias HVR (2014) Nanomaterials
for environmental protection. Wiley, Hoboken, pp 483–501
1
3