Biogenic synthesis of cellulose supported Pd(0) nanoparticles using hearth wood extract of Artocarpus lakoocha Roxb - A green, efficient and versatile catalyst for Suzuki and Heck coupling in water under microwave heating

Article abstract of DOI:10.1016/j.catcom.2015.09.011

A simple, convenient and green protocol has been developed for the synthesis of cellulose supported Pd(0) nanoparticles (NPs) using hearth wood extract of Artocarpus lakoocha Roxb-as a bioreductant. Novel one-step method for the isolation of active bioreductant oxyresveratrol (2, 3′, 4, 5′-tetrahydroxy-trans-stilbene) present in the hearth wood extract of A. lakoocha Roxb is also disclosed. Synthesized cellulose supported Pd(0) NPs have been used as an efficient catalyst for Suzuki and Heck coupling reactions in water under microwave irradiation. The prepared Pd(0) NPs were characterized by Ultraviolet-visible (UV-vis), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The catalyst can be recycled up-to ten times without losing its activity significantly.

Full text of DOI:10.1016/j.catcom.2015.09.011

Catalysis Communications 72 (2015) 73–80
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Biogenic synthesis of cellulose supported Pd(0) nanoparticles using
hearth wood extract of Artocarpus lakoocha Roxb — A green, efficient and
versatile catalyst for Suzuki and Heck coupling in water under
microwave heating
Diganta Baruah a, Ram Nath Das a, Swapnali Hazarika b, Dilip Konwar a,
⁎
a
Synthetic Organic Chemistry Division, CSIR-North East Institute of Science and Technology, Jorhat 785006, Assam, India
b
Chemical Engineering Division, CSIR-North East Institute of Science and Technology, Jorhat 785006, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 August 2015
Received in revised form 15 September 2015
Accepted 17 September 2015
Available online 21 September 2015
A simple, convenient and green protocol has been developed for the synthesis of cellulose supported Pd(0) nano-
particles (NPs) using hearth wood extract of Artocarpus lakoocha Roxb-as a bioreductant. Novel one-step method
for the isolation of active bioreductant oxyresveratrol (2, 3′, 4, 5′-tetrahydroxy-trans-stilbene) present in the
hearth wood extract of A. lakoocha Roxb is also disclosed. Synthesized cellulose supported Pd(0) NPs have
been used as an efficient catalyst for Suzuki and Heck coupling reactions in water under microwave irradiation.
The prepared Pd(0) NPs were characterized by Ultraviolet–visible (UV–vis), Fourier transform-infrared spectros-
copy (FT-IR), X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The catalyst can be recycled
up-to ten times without losing its activity significantly.
Keywords:
Cellulose
Oxyresveratrol
Biogenic
© 2015 Elsevier B.V. All rights reserved.
Suzuki–Heck
Green
1. Introduction
and non-biodegradable chemical reagents (N2H4·H2O, NaBH4, DMF, etc.)
as well as high temperature and pressures. Hence economically viable, en-
Palladium nanoparticles (NPs) have diverse applications in the field of
both homogeneous and heterogeneous catalysis [1]. Suzuki and Heck reac-
tions are the most important coupling reactions in the synthesis of great va-
riety of simple to complex molecules which have tremendous application in
the field of drugs, pharmaceuticals, agrochemicals and advanced materials
[2]. Homogeneous Pd catalysts always exhibit better reaction rate, activity
and selectivity but heterogeneous catalysts have many advantages over
their homogeneous counterparts such as recycling, cost effectiveness and
ease of catalyst/product separation [1–2]. Nowadays, much attention have
been paid to investigate biocompatible solid support to provide thermo
and air stable metal NPs as the synthetic solid support (carbon [3], zeolites
[4], metal oxides [5], sol–gel [6], clays [7], dendrimers [8], polymers [9]) or
the stabilizing ligands (phosphine, etc. [10]) are expensive, toxic, and in
large-scale applications they may become more tedious for solid waste
disposals.
vironmentally safer plant based biogenic synthetic protocols for NPs syn-
thesis are more advantageous [11–13]. Numerous metal NPs such as Au,
Ag, Pd, Pt, Cu and bimetallic Ag–Au, Au–Pd, and Cu–Au can successfully
be synthesized by different plant extracts [14]. These NPs have potential ap-
plication in the field of catalysis [15]. In this research work, we report the
successful isolation of oxyresveratrol, the active bio-reductant present in
the hearth wood extract of Artocarpus lakoocha Roxb, a medicinal plant
available in NE region of India in the synthesis of Pd(0) NPs. To enhance
the surface area per volume, the NPs should be anchored on a suitable
solid support so as to increase the catalyst robustness as well as reusability
of the catalyst. In this endeavour, in continuation of our earlier works
[16–20], we used microgranullar cellulose as a sustainable solid support
for Pd(0) NPs to make the catalyst more stable and recyclable in the
study on Suzuki and Heck coupling reaction in aqueous media under mi-
crowave heating. Cellulose consists of anhydroglucose units joined by β-
1–4 glycosidic linkage to form a molecular chain. The intra-chain hydrogen
bonding between hydroxyl groups and oxygens of the adjoining ring mol-
ecules stabilizes the linkage and results in the linear configuration of the
cellulose chain. Cellulose contains microfibrils up to 30 nm width that are
three dimensionally connected to each other. The metal NPs can be stabi-
lized in these cavities via oxygen–metal electrostatic interaction. Depend-
ing upon the pore size of cellulose microfibrils the size of the metal NPs
also varies. That is how cellulose can act as a solid support for the metal
In recent years, biogenic synthesis of metal NPs using different plant ex-
tracts received much attention both from environment and economy
points of view. It was assumed that different flavonoids and polyphenols
present in these plant extracts act as bio-reductant and stabilizing agent
in NPs' synthesis. Biogenic synthesis eliminates the use of toxic, expensive
⁎
Corresponding author.
E-mail address: dkonwar@yahoo.co.uk (D. Konwar).
http://dx.doi.org/10.1016/j.catcom.2015.09.011
1566-7367/© 2015 Elsevier B.V. All rights reserved.

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D. Baruah et al. / Catalysis Communications 72 (2015) 73–80
NPs' synthesis [21]. Biogenic synthesis of cellulose supported Pd(0) NPs
using hearth wood extract of A. lakoocha Roxb and their application as a
versatile and efficient catalyst in Suzuki and Heck coupling is the first pro-
tocol that we depicted herein (Scheme 1). We performed all the reactions
under microwave heating. As being energy efficient, microwaves can en-
hance the rate of reactions and improve product yields [22].
extract of A. lakoocha Roxb. The hearth wood extract of A. lakoocha Roxb
was prepared by grinding the dry heart wood of A. lakoocha Roxb and
extracted with water. The mixture was stirred for 30 min at room tem-
perature and then warmed (50 °C) for 15 min until the light brown so-
lution turned into black colour. No further colour change was observed
after 15 min. The black precipitate was filtered, washed, vacuum dried,
and finally stored under N2 atmosphere in a dessicator. The synthesized
Pd NPs were characterized by UV–visible spectroscopy, FT-IR spectros-
copy, XRD and TEM analysis.
2. Experimental section
2.1. General remarks
2.2.2. Isolation of active bio-reductant present in hearth wood extract of A.
lakoocha Roxb
Cellulose (CAS: 9004-34-6, microcrystalline, 20 μm, pH: 5–7), PdCl2
(99.9%), all arylbromides, all phenylboronic acids, methyl acrylate, acryloni-
trile, bases, and all solvents were purchased from Sigma Aldrich, USA and
were used without any further purification. X-ray diffraction (XRD) analysis
was performed with a scanning rate of 3° min−1 and two theta values rang-
ing from 5 to 100° using a Rigaku X-ray diffractometer (model: ULTIMA IV,
Rigaku, Japan) with a Cu Kα X-ray source (λ = 1.54056 Å) at a generator
voltage of 40 kV and a generator current of 40 mA. Transmission electron
microscopy (TEM) and high-resolution transmission electron microscopy
(HRTEM) images were recorded on a JEM-2100 electron microscope
(Transmission Electron Microscope, NEHU, Shillong, India) operated at an
accelerating voltage of 60–200 kV. UV–visible spectra were recorded
using Specord 200 and Spectrum 100 FTIR-Spectrometer (resolution:
4 cm−1) was used for recording IR data. All microwave (MW) reactions
were carried out in CEM, Discover microwave reactor. All NMR (1H, 13C)
spectra were recorded on a Bruker Avance DPX 500 MHz spectrometer.
Chemical shifts were reported on the δ scale (ppm) downfield from TMS
(δ = 0.0 ppm) using the residual solvent signal at δ = 7.26 ppm (1H) or
δ = 77 ppm (13C) as an internal standard. All products were purified by col-
umn chromatography using silica gel (200–300 mesh) and petroleum ether
(60–90 °C).
2.2.2.1. Method A. 10 g of dried and ground hearth wood of A. lakoocha
Roxb was treated with 100 mL petroleum ether (40–60 °C) and kept
overnight for removing fatty materials. After filtration, these wood ma-
terials were taken in 100 mL water, refluxed for 6 h, filtered off at hot
condition, concentrated to one fourth of the volume under reduced
pressure, and kept in a refrigerator for overnight. Separated deep
brown solid materials were filtered, washed with cool water (50 mL)
and vacuum dried. These solid materials are identified as oxyresveratrol
(2, 3′, 4, 5′-tetrahydroxy-trans-stilbene), yield: 500 mg (5%), melting
point: 200 °C, (Lit. Mp 201 °C [23–25]).
2.2.2.2. Method B. 10 g of dry and powdered wood material was taken in
100 mL acidic water solution (pH = 4) and 20 mL accelerase enzyme
[Aldrich] was added to the solution. The mixture was heated for 5 h at
40 °C, hot filtered, extracted with ethyl acetate (3 × 50 mL), the organic
layer washed with 5% NaHCO3 solution and dried over anhydrous so-
dium sulphate for 5 h. The solvent was distilled off under reduced pres-
sure to give deep brown solid oxyresveratrol (2, 3′, 4, 5′-tetrahydroxy-
trans-stilbene), yield: 600 mg, (6%). The compound was analysed and
found as above.
2.2. General procedures
2.2.3. Reaction of arylbromides with phenylboronic acids using Pd
(0) NPs@cellulose under microwave heating [Suzuki coupling]
In a 10 mL microwave glass vial 0.5 mol% (0.028 g) Pd(0) NPs@cellu-
lose, 0.5 mmol arylbromides, 0.75 mmol phenylboronic acid and
1.5 mmol K2CO3 were mixed in 5 mL water. The mixture was stirred at
2.2.1. Synthesis of Pd(0) NPs on cellulose [Pd(0) NPs@cellulose] using
hearth wood extract of A. lakoocha Roxb
200 mg nanoporous cellulose and 10 mg palladium(II) chloride were
added to a 250 mL round bottom flask containing 100 mL hearth wood
Scheme 1. Schematic diagram of fabrication of Pd(0) NPs on cellulose by biogenic method and its catalytic activity towards Suzuki and Heck coupling reaction.

D. Baruah et al. / Catalysis Communications 72 (2015) 73–80
75
Scheme 2. Photograph of (A) hearth wood extract of A. lakoocha Roxb in water; (B) solution A with cellulose; (C) Solution B with PdCl2; (D) Solution C after 15 min warming in heating
bath at 60 °C; (E) solid recyclable Pd(0) NPs@cellulose.
80 °C for the stipulated time in a microwave. After completion of the re-
action [monitored by TLC], the catalyst was filtered off and washed with
acetone and stored for further reactions. The filtrate was concentrated
and then extracted with ethyl acetate (2 × 20 mL). The organic layer
was washed with water (2 × 10 mL), brine (15 mL), dried over anhy-
drous Na2SO4, concentrated, and purified by column chromatography.
3. Results and discussions
3.1. Isolation of oxyresveratrol
Oxyresveratrol was isolated from the hearth wood of A. lakoocha
Roxb available in North-East part of India. The isolation methods
(methods A & B) are disclosed. These two methods eliminate multi-
step chemical synthesis [23] and long tedious separation and purifica-
tion processes [24]. It was found that method B for the isolation of
oxyresveratrol gave better yield than method A. In spite of using longer
synthetic process, this eco-friendly protocol will be highly beneficial for
industrial purposes as our protocol do not require the use of expensive
chemicals [25].
2.2.4. Reaction of arylbromides with alkenes using Pd(0) NPs@cellulose un-
der microwave heating [Heck coupling]
0.5 mol% (0.028 g) Pd(0) NPs@cellulose, 0.5 mmol arylbromides,
1.0 mmol alkene (e.g. methyl acrylate) and 1.5 mmol K2CO3 were
mixed in 5 mL water in a 10 mL microwave glass vial and heated
under microwave for a stipulated time period. Progress of the reaction
was monitored by TLC. After completion of the reaction, the catalyst
was filtered off and washed with acetone. The filtrate was concentrated
and then extracted with ethyl acetate (2 × 20 mL). The organic layer
was washed with water (2 × 10 mL), brine (15 mL), dried over anhy-
drous Na2SO4, concentrated, and purified by column chromatography.
3.2. Characterization of Pd(0) NPs@cellulose
Synthesis of Pd(0) NPs@cellulose using hearth wood extract of A.
lakoocha Roxb was initially assumed from the colour changes. A light
Fig. 1. A comparative UV–visible spectra of PdCl2, cellulose, oxyresveratrol and Pd(0) NPs@cellulose.

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D. Baruah et al. / Catalysis Communications 72 (2015) 73–80
Fig. 2. Comparative FT-IR spectra of pure cellulose and Pd(0) NPs@cellulose. (For interpretation of the references to colour in this figure, the reader is referred to the web version of this
article.)
brown colour of aqueous solution of oxyresveratrol, PdCl2 and cellulose,
C gradually changed to black colour, D. The black solid deposited on the
bottom of the test tube E is solid Pd(0) NPs@cellulose (Scheme 2).
UV–visible study of the synthesized nanocomposites revealed the
formation of Pd(0) NPs (Fig. 1). The UV–visible spectrum of PdCl2 ex-
hibits an absorption maximum in the range of 400–430 nm, due to
the absorption of Pd(II) ions. As this peak completely disappeared and
replaced by a broad and continuous absorption band in the UV–visible
spectrum of black solid Pd/cellulose matrix, this indicates the formation
of Pd(0) NPs@cellulose [26].
Comparative FTIR spectra of cellulose and cellulose supported Pd are
shown in Fig. 2. The red line indicates the FTIR of cellulose supported Pd
and the blue line indicates the FTIR of pure cellulose. Strong absorption
peak at 3349.6 cm−1 corresponds to the O–H stretching intramolecular
Fig. 3. Powder XRD spectra of Pd(0) NPs@cellulose.

D. Baruah et al. / Catalysis Communications 72 (2015) 73–80
77
Fig. 4. TEM images of Pd(0) NPs@cellulose: (A) dispersion of nanoparticles in cellulose; (B), (C) Size of the Pd(0) NPs with HRTEM image (inset); (D) Selected Area Electron Diffraction
(SAED) of Pd(0) NPs [31,32].
hydrogen bonds for cellulose. Peak at 2903 cm−1 is due to the C–H
stretching vibration. Peak at 1650 cm−1 is because of O–H bending vi-
bration, 1430 cm−1 (CH2 scissoring motion), 1384 cm−1(C-H bending),
1336 cm−1 (O–H in plane bending), 1317 cm−1 (CH2 wagging),
1053 cm−1 (C–O–C pyranose ring stretching vibration) and peak at
897 cm−1 is associated with the cellulosic β-glycosidic linkages [27]. A
decrease in intensity at 3346 cm−1 of the cellulose supported Pd as
compared to 3349.6 cm−1 indicates the formation of Pd(0)–oxygen
linkage, i.e. palladium metals are stabilized by the –OH groups of the cel-
lulose moiety by metal–ligand interactions. Due to these interactions
weaker absorption peaks were observed in the FTIR spectra of cellulose
supported Pd. This results demonstrate that the –OH groups on micro-
crystalline cellulose acts as a stabilizing agent of metal nanoparticles,
i.e. formation of Pd(0) NPs inside the cavities. Shifting of peaks in FTIR
of cellulose supported Pd as compared to FTIR of pure cellulose is also
an indication of the formation of Pd(0) NPs inside the cavities of cellu-
lose template [28].
Powder X-ray diffraction study (XRD) (Fig. 3) showed that in combi-
nation with three cellulose peaks at 2θ values of 14.8°, 16.4°, and 22.9°
corresponding to the Braggs planes (101), (101′) and (002), there
were five peaks at 2θ values of 40.2°, 46.5°, 67.9°, 81.7° and 85.7 corre-
sponding to (111), (200), (220), (311) and (222) planes representing
Pd(0) NPs on cellulose [29–30]. No peaks corresponding to any other
impurity were observed. The intense reflection at 40.2° (111) in com-
parison with four other peaks may indicate the preferred growth direc-
tion of the nanocrystals [2].
Table 1
Optimization of the reaction conditions for the Suzuki cross-coupling reaction of 2-
bromobenzaldehyde with phenylboronic acid.a
The TEM images (Fig. 4, A–D) of synthesized nanocomposites
showed that Pd(0) NPs were dispersed in the nanopores of cellulose
matrix. The supported Pd(0) NPs were spherical in shape with sizes in
the range of 10–30 nm. The HRTEM image (Fig. 4C, inset) of a single
Pd(0) NPs showed the reticular lattice planes inside the nanoparticles
indicating the crystalline nature. The selected area electron diffraction
(SAED) image shows the Braggs planes.
Entry
Catalyst
Loading of
catalyst
Base
(1.5 mmol)
Temp (°C)/time
(min)
Yield %b
1
2
3
4
5
6
7
8
9
..........
PdCl2
............
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
NaOH
Et3N
100/10
100/15
80/5
100/5
100/15
140/15
100/5
100/5
100/5
100/5
0
25
94
82
94
94
20
40
20
68
0.05 mmol
0.5 mol%
0.3 mol%
1.0 mol%
0.5 mol%
0.5 mol%
0.5 mol%
0.5 mol%
0.5 mol%
Pd(0)NPs
Pd(0)NPs
Pd(0)NPs
Pd(0)NPs
Pd(0)NPs
Pd(0)NPs
Pd(0)NPs
Pd(0)NPs
3.3. Catalytic activity of Pd(0) NPs@cellulose under microwave heating
Cellulose supported Pd(0) NPs were tested as a catalyst in the Suzuki
cross/homo coupling and Heck reactions under microwave heating. Ini-
tially, we have chosen the coupling reaction of 2-bromobenzaldehyde
(0.5 mmol) and phenylboronic acid (0.75 mmol) as model substrates
for the development of optimized conditions under microwave heating
taking water as a solvent. Several bases such as Et3N, NaOH, NaOAc,
Cs2CO3, K2CO3, etc. were used in order to find the optimized reaction
condition (Table 1). Study with different bases indicates that they
NaOAc
Cs2CO3
10
aReaction conditions: 2-bromobenzaldehyde (0.5 mmol), phenylboronic acid (0.75
mmol), Pd(0) NPs@cellulose (0.5 mol%), K2CO3(1.5 mmol), H2O (5 mL), 80 °C, microwave.
The reaction was monitored by TLC.
bIsolated yield.

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D. Baruah et al. / Catalysis Communications 72 (2015) 73–80
Table 3
have remarkable effect on the yields of the product. Among the tested
bases, K2CO3 (entry 3, Table 1) gave the highest yield of 1a, (94%) as
compared to all other bases (entries 7–10, Table 1). These results
imply that K2CO3, among the bases under study, was the most effective
for activating this catalytic system in the Suzuki cross coupling reaction.
Next we studied the catalytic behaviour of Pd(0) NPs@cellulose as well
as loading of the catalyst in this coupling reaction. Control experiments
showed that no product formation took place in the absence of Pd
(0) NPs@cellulose in aqueous medium under microwave irradiation
(entry 1, Table 1). However, addition of the catalyst to this mixture
has rapidly increased the formation of product in high yields. Taking
PdCl2 salt as a catalyst for this coupling reaction under the same reaction
condition gave disappointing result (entry 2, yield 30%, Table 1) as
compared to Pd(0) NPs@cellulose which showed more than 90% prod-
uct yield. A decrease in the catalyst loading from 0.5 mol% to 0.3 mol%
lowered the product yield (entry 4, Table 1). On the other hand, increas-
ing the catalyst loading did not improve the yield of the product signif-
icantly (entry 5, Table 1). 0.5 mol% of the catalyst was found to be
optimal for the coupling reaction (entry 3, Table 1). The optimum tem-
perature for the reaction is 80 °C and only 5–10 min time is required to
complete the reaction under microwave heating. The best result was
obtained with 0.5 mmol of 2-bromobenzaldehyde, 0.75 mmol of
phenylboronic acid, 0.5 mol% (0.028 g) of catalyst, 1.5 mmol of K2CO3
and 5 mL of H2O at 80 °C, which gave the product an excellent yield. Fur-
thermore two comparative cross coupling reactions were performed
using the same substrates, one in microwave heating and the other in
conventional heating using oil bath at 100 °C to find the best reaction
condition. It was observed that reactions performed under microwave
heating require shorter time and afforded maximum yield as compared
to the conventional heating. Taking water as a solvent we got very high
yield of products, therefore, studies of the reactions in other solvents
was excluded.
Pd(0) mediated Suzuki homocoupling reaction of phenyl boronic acids.a
aReaction conditions: arylbromide (1.0 mmol), Pd(0) NPs@cellulose (0.5 mol%), K2CO3
(1.5 mmol), H2O (5 mL), 60 °C, microwave. The reactions were monitored by TLC.
bIsolated yield.
After optimization of reaction conditions, we explored the scope and
limitations of this protocol towards the coupling reactions. As illustrated
in Table 2, it was subsequently extended to a wide range of substituted
aryl bromides and phenylboronic acids as substrates for Suzuki cross
coupling reaction. In general, all the reactions gave excellent yields of
coupling product under microwave heating. However, arylbromides
containing electron withdrawing groups as substrates gave slightly
more yields (1a, 1c) as compared to the electron donating counterparts.
This protocol was found to be well tolerated towards the hetero aryl
bromides (1e, 1i) and ortho substituted aryl bromide (1a, 1g, 1h, 1j,
1k) as substrates. Overall, steric and electronic factors of the substrates
do not affect significantly the yield of the products because of the high
catalytic activity of Pd(0) NPs@cellulose system.
Next, we tried to study the homocoupling reactions of arylboronic
acids, Table 3. It was observed that Pd(0) NPs@cellulose system effi-
ciently catalyses the homocoupling reaction with high yield percentage
of desired product regardless of the nature of boronic acids under mi-
crowave heating (2a–2d). In homocoupling reaction the requirement
of time as well as temperature is somewhat less than the cross coupling
reactions. All the products were well characterized by the comparison of
their physical characteristics (TLC Rf value and melting point) and spec-
tral data (1H & 13C NMR) with those of the authentic samples.
Table 2
Suzuki cross-coupling reaction between phenylboronic acid and substituted arylbromides
under microwave heating.a
We investigated the catalytic activity of Pd(0) NPs@cellulose to-
wards the Heck reaction (Table 4). 15–20 min time is required for suc-
cessful completion of all Heck reactions under study. To find the
optimized reaction condition we used iodobenzene (0.5 mmol) and
methyl acrylate (1.0 mmol) as substrates. Regardless of the substituents
present in arylbenzenes and alkenes (3a–3d, Table 4), the catalyst
Table 4
Heck reaction of aryl halides and olefins under microwave heating catalysed by Pd(0)
NPs@cellulose.a
aReaction conditions: arylhalides (0.5 mmol), alkene (0.75 mmol), Pd(0) NPs@cellulose
(0.5 mol%), K2CO3(1.5 mmol), H2O (5 mL), 80 °C, microwave. The reactions were moni-
tored by TLC.
bIsolated yield.
aReaction conditions: arylbromides (0.5 mmol), phenylboronic acid (0.75 mmol), Pd
(0) NPs@cellulose (0.5 mol%), K2CO3(1.5 mmol), H2O (5 mL), 80 °C, microwave. The reac-
tions were monitored by TLC.
cReaction time is 15 min.
dReaction time is 20 min.
eIodobenzene as a substrate.
fSubstituted bromobenzene as a substrate.
bIsolated yield.

D. Baruah et al. / Catalysis Communications 72 (2015) 73–80
79
Table 5
The recovered catalyst (after the 5th run) was further investigated
by powder XRD and TEM studies (Fig. 5). The appearance of low inten-
sity peaks as compared to the fresh one may indicate the aggregation
and leaching of Pd(0) NPs in the surface of cellulose. Due to these com-
bined effects of aggregation and leaching reduction of catalytic activity
was observed after multiple runs. The catalyst can also be reusable in
Heck reactions.
Reusability of Pd(0) NPs@cellulose in the Suzuki cross-coupling reaction of 2-
bromobenzaldehyde and phenyl boronic acid under microwave heating.a
4. Conclusion
In summary, we have demonstrated a green biogenic approach
for the synthesis of Pd(0) NPs@cellulose using the hearth wood ex-
tract of A. lakoocha Roxb. We have also depicted a novel one step
approach for the isolation of active bioreductant oxyresveratrol
from the hearth wood extract of A. lakoocha Roxb. This novel proce-
dure for isolation of oxyresveratrol will be highly beneficial for in-
dustrial production of potent therapeutic agents in human health,
e.g. tyrosinase inhibitor, antioxidant, antiglycation, free radical
scavenger, and neuroprotection [23–25]. This eco-friendly protocol
for the synthesis of metal NPs provides thermo and air stable crys-
talline spherical shaped NPs without requiring harmful reducing
agents, toxic nitrogenous ligands, solid waste disposals, etc. Pd
(0) NPs@cellulose exhibit versatile catalytic activity towards the
Suzuki and Heck reactions in water under microwave heating
with very high product yield. The main advantages of this environ-
mentally benign protocol are such as ease of catalyst preparation,
ease of work up procedure, high catalytic activity, stability, reus-
ability up-to ten times without measurable Pd leaching, etc. Pd
(0) NPs@cellulose may be regarded as a very effective alternative
for Suzuki and Heck reaction considering the green chemistry
point of view.
aReaction conditions: arylbromides (0.5 mmol), phenylboronic acid (0.75 mmol), Pd
(0) NPs@cellulose (0.5 mol%), K2CO3(1.5 mmol), H2O (5 mL), 80 °C, microwave.
bIsolated yield.
effectively catalysed the Heck coupling reactions with excellent yields in
aqueous media under microwave heating.
3.4. Reusability of Pd(0) NPs@ cellulose
The reusability of Pd(0) NPs@cellulose catalyst was investigated by
using the Suzuki cross-coupling reaction between phenyl boronic acid
and 2-bromobenzaldehyde under the abovementioned optimized con-
ditions in microwave heating. After completion of the reaction the cata-
lyst was separated from the mixture by simple filtration, washing it
with H2O and acetone alternatively and finally vacuum dried. Then it
was reused directly for the next cycle without any further treatment.
This experiment showed that our catalyst can be recycled up to ten
times without major loss of yield of product. At the end of the 5th and
10th runs we were able to collect 89% and 71% yield of the product re-
spectively (Table 5).
Acknowledgements
This research work was financially supported by the CSIR, New
Delhi, through the grants CSC0125 and MLP3000/03. The authors
thank the Director, CSIR-NEIST. The authors also acknowledge
the Materials Science Division for recording XRD data and Analy-
tical Chemistry Division, CSIR-NEIST for recording NMR data. The au-
thors are very thankful to Mr. O. P. Sahu, Analytical Chemistry
Division for recording FT-IR and UV–visible spectroscopy data. TEM
analysis was done in SAIF, North Eastern Hilly University [NEHU],
Shillong, Meghalaya, India.
Fig. 5. The powder XRD pattern and TEM image of recovered catalyst.

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D. Baruah et al. / Catalysis Communications 72 (2015) 73–80
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