Solar energy assisted synthesis of palladium nanoplates and its application in 2-phenoxy-1,1′-biphenyls and N,N-dimethyl-[1,1′-biphenyl] derivatives synthesis

Article abstract of DOI:10.1016/j.molcata.2013.07.012

Present work aims to develop a greener approach for the palladium nanoplates (PdNPs) synthesis and its catalytic applications. The protocol deals with solar energy assisted ionic palladium reduction in the presence of polyvinylpyrrolidone (PVP) and ethylene glycol (EG) with a good shape selectivity. Polyvinylpyrrolidone plays a duel role of capping agent and mild reductant; whereas, ethylene glycol acts as a reductant and solvent. The optimum sunlight concentration is a key factor to the anticipated nanoplate's synthesis. Results show that the most of nanoparticles are hexagonal and triangular nanoplates in the range of 20-50 nm. This is a first report which shows ～70% selectivity to the nanoplates formation using sun light. The study also covers it's catalytic application, wherein; 2-phenoxy-1,1′- biphenyls and N,N-dimethyl-[1,1′-biphenyl] derivatives were synthesized by a simple, ligand free, faster, one pot, ecological and economic protocol in aqueous medium. The catalyst shows better performance than that of conventionally available 10% Pd/C catalyst. The prepared PdNPs showed excellent catalytic performance to the desired products with recyclability.

Full text of DOI:10.1016/j.molcata.2013.07.012

Journal of Molecular Catalysis A: Chemical 379 (2013) 30–37
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Solar energy assisted synthesis of palladium nanoplates
and its application in 2-phenoxy-1,1ꢀ-biphenyls and
N,N-dimethyl-[1,1ꢀ-biphenyl] derivatives synthesis
Aniruddha B. Patil, Bhalchandra M. Bhanage∗
Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai 400019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 June 2013
Received in revised form 20 July 2013
Accepted 22 July 2013
Available online 1 August 2013
Present work aims to develop a greener approach for the palladium nanoplates (PdNPs) synthesis and
its catalytic applications. The protocol deals with solar energy assisted ionic palladium reduction in
the presence of polyvinylpyrrolidone (PVP) and ethylene glycol (EG) with a good shape selectivity.
Polyvinylpyrrolidone plays a duel role of capping agent and mild reductant; whereas, ethylene glycol
acts as a reductant and solvent. The optimum sunlight concentration is a key factor to the antici-
pated nanoplate’s synthesis. Results show that the most of nanoparticles are hexagonal and triangular
nanoplates in the range of 20–50 nm. This is a first report which shows ∼70% selectivity to the nanoplates
formation using sun light. The study also covers it’s catalytic application, wherein; 2-phenoxy-1,1ꢀ-
biphenyls and N,N-dimethyl-[1,1ꢀ-biphenyl] derivatives were synthesized by a simple, ligand free, faster,
one pot, ecological and economic protocol in aqueous medium. The catalyst shows better performance
than that of conventionally available 10% Pd/C catalyst. The prepared PdNPs showed excellent catalytic
performance to the desired products with recyclability.
Keywords:
Solar energy
Palladium nanoplate
Phosphine-free
Biphenyl, Aryl halide
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
routes. However, most of the protocols required harsh reaction
conditions such as longer reaction time, high pressure, toxic
Metal nanoparticle synthesis has been a current research
theme as motivated by their widespread use in electronics,
optoelectronics, optical sensing, biological labelling, imaging, catal-
ysis, photography, photonics, plasmonics and information storage
[1–10]. Size, shape, crystallinity, composition and structure of the
metal nanoparticles determine their properties [11]. Palladium
plays a central role and showing diverse industrial applications
[12–17]. For example, it helps as a catalyst for low-temperature
reduction of automobile pollutants as well as for organic reactions
such as Heck and Suzuki coupling reactions. To enhance the per-
formance, several efforts have been dedicated to the synthesis of
Pd nanostructures in the presence of surfactants or polymers. Till
date, Pd nanoparticles of various morphologies have been prepared
such as cubes, cuboctahedrons, decahedrons, bars, single-crystal
rods, icosahedrons, right bipyramids, fivefold twinned rods, and
thin plates (triangular or hexagonal) using conventional methods
under reflux condensations [18]. In earlier reports nanoparticle
synthesis has been achieved by techniques like thermal, sono-
chemical, microwave, electrochemical and sonoelectrochemical
reagents, harmful by-product formation, poisonous gas production
and requirement of sophisticated equipments with tedious work up
procedures. Hence, the development of non-conventional, environ-
mental benign and inexpensive protocol for efficient synthesis of
nanoparticles is still desirable.
Considering this issue, recent investigation focused towards
available renewable energy sources for nanoparticles synthesis.
Solar energy is one of the non-polluting, carbon free and easily
available energy source. In earlier reports, metal nanoparticles are
synthesized under normal sunlight [19,20]. Most of these reports
relate to the silver and the gold nanoparticle synthesis which
works in the temperature range of 30–50 ◦C. However, many other
metal and metal oxide nanoparticles synthesis requires higher
energy intensity, which is not possible under normal sunlight and
hence the concept of concentrated solar energy has been developed
[21–23].
Present study is focused on the palladium nanoplate’s synthesis
using solar energy. While working with this concept, we specifically
expected at answering the following questions related to the syn-
thesis of nanoplates: (a) the role of EG as a reducing agent and how it
works for the synthesis of nanoplates? (b) How concentrated solar
energy advantageous than that of conventional energy sources?
While answering to these questions, it was observed that polyol
reduction has long been known as a simple and versatile method
∗
Corresponding author. Tel.: +91 22 3361 1111/2222; fax: +91 3361 1020.
E-mail addresses: bm.bhanage@gmail.com, bm.bhanage@ictmumbai.edu.in,
bhalchandra bhanage@yahoo.com (B.M. Bhanage).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.07.012

A.B. Patil, B.M. Bhanage / Journal of Molecular Catalysis A: Chemical 379 (2013) 30–37
31
for producing metal nanoparticles, wherein nanoplates synthesis
2.2. Synthesis of Pd (0) nanoplates
using polyol method has been discussed [24]. Present study is a
continuation of our previous works on multiple twinned parti-
cles (MTPs) synthesis, wherein, the reductant like citric acid was
responsible to blocks the oxidative etching that results in the for-
mation of MTPs. Hence to take the benefit of etching phenomena
for the nanoplates synthesis herein, we used acetaldehyde derived
from EG with PVP as a mild reductant.
In a typical synthesis, 0.017 g of PdCl2 and 0.038 g of PVP
(MW-40,000) were separately dissolved in 3 mL of EG at room
temperature. Meanwhile, 7 mL of ethylene glycol was placed in
a round bottom flask (equipped with air condenser) and heated
under solar radiations concentrated by a ‘Fresnel lens’ for 10 min.
The above solutions of Pd precursor with PVP were added in
a reaction mixture slowly. The reaction mixture was contin-
ued with heating by solar energy for 3 h. Considering the aim
of nanoplates synthesis the concentration ratio of sunlight has
been adjusted in such a way that the temperature of reaction
was in the range of 70 5 ◦C. As the incident solar energy has a
spatial and temporal variation, to minimize temperature varia-
tion all the experiments were conducted from 11 am to 2 pm in
summer days. The Author’s institute is located at Matunga, Mum-
bai (Geographical location: Greater Bombay, Maharashtra, India,
Asia. Geographical Coordinates: 19◦2ꢀ0ꢀꢀ North, 72◦51ꢀ0ꢀꢀ East).
The product was centrifuged at 18000 rpm for 20 min at 25 ◦C
and washed with acetone followed by ethanol to remove addi-
tives.
The PdNPs synthesis is associated with the reduction of Pd
(II) to Pd (0) which requires a higher driving force that is not
achieved under the intensity of natural sunlight. The idea of ‘Fres-
nel lens’ assist to concentrate the solar radiation and to reduce
the ionic palladium to metallic form was used. Though, concen-
trated solar energy helps in the reduction of ionic palladium,
it may hurdle to nanoplates formation as nanoplates synthe-
sis associated with slow reduction kinetics. Hence, the optimum
driving force to the nanoplates formation from solar energy was
obtained by adjusting the concentration ratio of sunlight. This
above discussion helps to answer the second question. Hence, in
continuation of previous work, present study deals with novel,
etchant free, inexpensive and eco-friendly protocol for the syn-
thesis of Pd nanoplates (triangular and Hexagonal) using a polyol
process wherein PVP acts as a mild reducing agent and concen-
trated solar energy as an energy source for the reduction. The result
reveals that the obtained nanoparticles are in the range of 20–50 nm
having ∼70% of triangular and hexagonal nanoplates contribution.
Though the selectivity to the nanoplates formation is up to 70%;
this is the first green approach wherein the concentration ratio of
sunlight helps to the nanoplates synthesis in absence of organic
etchants.
Along with the nanoplates synthesis, its application in the
synthesis of 2-phenoxy-1,1ꢀ-biphenyl’s and N,N-dimethyl-[1,1ꢀ-
biphenyl] derivatives was also studied. In earlier works, such
products were synthesized by different protocols linked with one or
more drawbacks such as the use of complex ligands, multistep syn-
thesis, organic reaction medium, and low yield. To overcome these
limitations, herewith, we report simple one stroke, one pot, ligand
free, heterogeneous, recyclable and fast approach with an excellent
yield to the desired product. The synthesized Pd nanoplates showed
excellent catalytic applications at lowest catalyst loading under
mild reaction conditions. The nanoplates have shown better cat-
alytic performance than that of conventionally available 10% Pd/C
catalyst. The catalyst showing excellent performance up to three
consecutive recycles without significant loss in catalytic activity. To
the best of our knowledge, this is a first report wherein 2-phenoxy-
1,1ꢀ-biphenyl’s and N,N-dimethyl-[1,1ꢀ-biphenyl] derivatives are
synthesized in one pot, one step, greener, faster protocol using Pd
nanoplates as heterogeneous and recyclable catalyst in aqueous
medium.
2.3. Characterization of prepared palladium (0) nanoparticles
The obtained nanoplates were characterized using the UV spec-
trophotometer (Shimadzu 1650) to confirm reduction of Pd (II)
to Pd (0). This was further confirmed by the X-ray Photoelectron
spectroscopy (XPS) analysis using AXIS Ultra ‘DLD’ X-ray photoelec-
tron spectrometer, Transmission electron microscopy (TEM) and
selected area energy dispersion (SAED) was done by Philips model
CM 200, Field Emission Gun-Scanning Electron Microscopy (FEG-
SEM) and Energy dispersive X-ray Spectral analysis EDAX images
were recorded with a JEOL JSM-7600 F.
2.4. Typical procedure for the synthesis of
2-phenoxy-1,1ꢀ-biphenyls and N,N-dimethyl-[1,1ꢀ-biphenyl]
derivatives
In a typical synthesis, sealed tube of 10 mL capacity was
charged with aryl halide (1.0 mmol), (2-phenoxyphenyl) boronic
acid (1.2 mmol)/(3-(dimethylamino)phenyl) boronic acid, KOH
(2.0 mmol), Pd nanoplates solution (50 ␮L, 0.0005 mmol) in aque-
ous medium. The reaction mixture was heated at 100 ◦C for 1 h and
then allowed to cool at room temperature. Conversion of aryl halide
and the formation of product were monitored by gas chromatog-
raphy. The product was extracted with ethyl acetate (3 × 5 mL);
died over Na2SO4 and the solvent was evaporated under vacuum.
The obtained crude product was then purified by column chro-
matography using silica gel, (100–200 mesh size) with petroleum
ether/ethyl acetate (PE–EtOAc, 95:05) as eluent to give pure prod-
uct. All products are confirmed by GC–MS (Shimadzu GC-MS QP
2010). The representative products were characterized by 1H NMR
and 13C NMR (Bruker UXNMR/XWIN-NMR (300 MHz) or Inova Var-
ian VXR Unity (400, 500 MHz) instruments. Chemical shifts (ı) are
reported in ppm downfield from an internal TMS standard. High
resolution MS (HR-MS) data were recorded on a QSTAR XL Hybrid
MS–MS mass spectrometer.
2. Experimental
2.1. Materials and methods
Palladium chloride was purchased from M/s Parekh Platinum
Ltd., Mumbai (PdCl2, 99%); poly vinyl pyrrolidone (PVP, MW-
40000) from M/s CDH and ethylene glycol was purchased from
M/s s.d. Fine-Chem Ltd. The deionized water was distilled by water
purification system (Milli-Q). All chemicals were of highest purity
grade and used without further purification. Considering the low
catalyst loading and highest accuracy the catalyst loading was done
by using PdNPs stock solution, which prepared using 0.0106 g of
PdNPs in 10 mL of DI water. In 2-phenoxy-1,1ꢀ-biphenyls synthe-
sis optimized yields were calculated based on gas chromatography
(GC) using external standard method.
2.5. GC analysis
The reaction progress was analyzed by GC equipped with a flame
ionization detector (FID) and a capillary column (Perkin–Elmer,
Clarus 400, 30 m × 0.32 mm × 0.25 ␮m). The GC parameters were as
follows: Initial temperature 80 ◦C; initial time 1 min; solvent delay
3 min; temperature ramp 10 ◦C/min; final temperature 250 ◦C;

32
A.B. Patil, B.M. Bhanage / Journal of Molecular Catalysis A: Chemical 379 (2013) 30–37
injector port temperature 250 ◦C; detector temperature 250 ◦C and
injection volume 0.6 ␮L.
2H), 6.82–6.79 (m, 1H), 3.03 (s, 6H) ppm. 13C NMR (75 MHz,
CDCl3): 150.96, 148.66, 146.88, 139.67, 129.71, 127.79,
123.81, 115.56, 112.88, 111.10, 40.45, 21.04. GC–MS (EI) m/z
(%): 242(1 0 0) [M]+, 212(6.5), 196(19.2), 195(31.1), 152(23.2),
139(3.9), 98(4.7), 76(6.1), 63(4.4), 39(5.1). HRMS (ESI): m/z
calcd. for C14H15O2N2[M + H]+ = 243.11162, found 243.11280.
2.6. Spectral data of selected products
2.6.1. Spectral data of 2-phenoxy-1,1ꢀ-biphenyls
(1) 2-phenoxy-1,1ꢀ-biphenyl (Table 2, entry 1)1H NMR (400 MHz,
CDCl3): 7. 54 (2H, d, J = 10 Hz), 7.45 (1H, m), 7. 34
(2H, d, J = 10 Hz), 7.3–7.18 (5H, m), 7.02 (2H, t), 6.93
(2H, d, J = 10.4 Hz) ppm; GC–MS (EI) m/z (%): 246(100)
[M]+, 245(29.2), 231(11.8), 229(21.8), 228(12.1), 227(14.1),
217(11.4), 202(10.7), 152(37.0), 151(10.5), 115(13.3).
(2) 2ꢀ-phenoxy-[1,1ꢀ-biphenyl]-4-ol (Table 2, entry 2)GC–MS (EI)
m/z (%): 263(18.7), 262(1 0 0) [M]+, 185(5.7), 168(5.4), 157(5.7),
141(6.6), 139(9.3), 115(12.5), 89(5.7), 77(6.7), 45(13.4),
44(11.6).
3. Results and discussion
3.1. Preparation and characterization PdNPs
We initiated our investigation aiming at the synthesis of pal-
ladium nanoplates using the concept of solar energy. The seeds,
crystallinity and the growth rates of different crystallographic
facets are important in determining the shape of resultant nano-
structures. In case of metal like palladium, synthesis of triangular
or hexagonal nanoplates depends on the reduction kinetics. A shape
evolution is observed during the growth mechanism: in the initial
state the nanoplates have a circular cross section obtained by the
combination of atoms; then it will evolve into hexagonal and then
triangular shapes [25–27].
(3) 4ꢀ-methyl-2-phenoxy-1,1ꢀ-biphenyl (Table 2, entry 3)1H NMR
(400 MHz, CDCl3): 7.43 (3H, d, J = 10.8 Hz), 7.3–7.2 (4H, m), 7.16
(2H, d, J = 10.8 Hz), 7.04–6.92 (4H, m), 2.34 (3H, s) ppm; GC–MS
(EI) m/z (%): 260(1 0 0) [M]+, 245(24.5), 244(7.5), 243(10.8),
217(8.7), 183(8.1), 168(9.8), 165(24.5), 152(21.7), 139(5.1),
115(7.9), 77(6.1).
(4) 4ꢀ-nitro-2-phenoxy-1,1ꢀ-biphenyl (Table 2, entry 4)1H NMR
(400 MHz, CDCl3): 8.2 (2H, d, J = 11.6 Hz), 7.7 (2H, d, J = 11.6 Hz),
7.46 (1H, dd, J = 10), 7.38 (1H, dd, J = 10), 7.3–7.0 (5H, m), 6.9
(2H, d, J = 10.4 Hz) ppm; GC–MS (EI) m/z (%): 291(1 0 0) [M]+,
245(9.1), 244(20.1), 228(10.0), 226(10.1), 218(11.7),215(17.6),
202(13.1), 168(8.9), 152(8.8), 151(10.0), 139(13.0) 77(11.9),
51(8.6).
Cuboctahedrons and multiple twinned particles (MTPs) are the
thermodynamically favourable shapes of Pd nanoparticles. At high
reduction rate the final product will take the thermodynamically
favoured shapes. When the reduction rate retarded, the nuclea-
tion as well as growth will be deviating into kinetic control and
the final product can take a variety of shapes deviated from the
thermodynamic ones. In previous studies, it was found that at ele-
(5) 2-methyl-2ꢀ-phenoxy-1,1ꢀ-biphenyl (Table 2, entry 5)GC–MS
(EI) m/z (%): 260(1 0 0) [M]+, 245(6.7), 182(14.9), 181(25.3),
165(57.8), 151(20.9), 149(33.4), 115(11.5), 91(61.4), 77(8.9),
51(8.0).
vated temperature PdCl4 was added to EG, the rapid reduction
2−
of PdCl42− takes place with EG and produced 10% MTPs and 90% Pd
cubooctahedra of 8–10 nm in size [28].
As development of nanoplates is favourable at slow reduction
process, the selective synthesis of Pd nanoplates has been attained
by careful control of the reduction kinetics, mainly at the seeding
stage. In earlier work, to achieve controlled synthesis of triangu-
lar and hexagonal nanoplates two different approaches have been
reported to retard the reduction rate. In first approach, the reduc-
tion rate was substantially reduced through the introduction of
etchants like Fe(III) species, which competed with the polyol reduc-
tion and altered the reduction kinetics helps to synthesis triangular
or hexagonal nanoplates [29]. In the second approach, a mild reduc-
ing agent like PVP can be used to slow down the reduction [30]. The
mild reducing power of such compound is anticipated for kineti-
cally controlled synthesis of Pd nanoplates.
(6) 2-methoxy-2ꢀ-phenoxy-1,1ꢀ-biphenyl (Table 2, entry 6)1H NMR
(400 MHz, CDCl3): 7. 36 (1H, dd, J = 5.2 Hz), 7.3–7.2 (5H, m),
7.17(1H, t, J = 5.2 Hz), 7–6.9 (5H, m), 6.87 (1H, d, J = 5.6), 3.6 (3H,
s) ppm; GC–MS (EI) m/z (%): 276(1 0 0) [M]+, 215(7.5), 183(7.5),
181(9.7), 169(7.8), 168(48.7), 152(5.0), 139(15.9), 115(4.1),
91(20.5), 77(5.5).
(7) 2ꢀ-phenoxy-[1,1ꢀ-biphenyl]-2-ol(Table 2, entry 7)GC–MS (EI)
m/z (%): 262(1 0 0) [M]+, 170(11.9), 169(95.0), 168(79.1),
141(20.3), 139(24.4), 115(18.5), 77(8.4), 51(8.2), 39(7.8).
(8) 2ꢀ-phenoxy-[1,1ꢀ-biphenyl]-2-amine (Table 2, entry 8)GC–MS
(EI) m/z (%): 261(41.6) [M]+, 169(10.0), 168(69.2), 167(100),
166(10.6), 139(8.2), 115(5.6), 89(9.1), 58(5.5), 45(24.0),
44(18.0), 43(7.6).
On the basis of the above discussion, herein concentrated
solar energy protocol has been used for hexagonal and triangu-
lar nanoplates synthesis using a polyol synthesis protocol with
PVP (MW = 40,000) as a stabilizer cum mild reductant. In case
of Pd nanoparticle synthesis higher driving force is required
for the reduction of ionic palladium species. Concentrated solar
energy has combined effect of the thermal and radiational energy
help to reduce ionic palladium to metallic palladium. Though,
concentrated solar energy executes necessity of the ionic palla-
dium reduction, the high intensity sunlight may create obstacle
for nanoplate synthesis as it required slow reduction kinetics.
Hence, essential energy requirement for nanoplates preparation
was achieved by moving the ‘Fresnel lens’ towards the reactor
(round bottom flask) which allows optimum sunlight concentra-
tion to the nanoplates formation. So here we can demonstrate
that the concentrated solar energy not only helps for the reduc-
tion of ionic palladium but also it could be used for the selective
nanoplate’s formation too. Also, low molecular weight PVP act as a
mild reductant to slow down the reduction process along with its
capping effect [29,30]. In general, glycols can serve as the reduc-
tant source for the PdNPs synthesis [29,31]. In aqueous medium
2.6.2. Spectral data of N,N-dimethyl-[1,1ꢀ-biphenyl] derivatives
(9) N,N-4ꢀ-trimethyl-[1,1ꢀ-biphenyl]-3-amine (Table 3, entry
1)1H NMR (400 MHz, CDCl3): 7.49 (d, J = 8.1 Hz, 2H), 7.23
(t, J = 7.3 Hz, 1H), 7.22 (d, J = 8.1 Hz, 2H), 6.94–6.91 (m, 2H),
6.73–6.71 (m, 1H), 2.99 (s, 6H), 2.38 (s, 3H) ppm. 13C NMR
(75 MHz, CDCl3): 150.90, 142.13, 139.33, 136.70, 129.30,
129.25, 127.10, 115.70, 111.40, 40.64, 21.04. GC–MS (EI) m/z
(%): 211(1 0 0) [M]+, 195(8.1), 168(9.2), 165(11.4), 152(13.6),
105(18.2), 82(5.1), 63(2.7), 39(4.6). HRMS (ESI): m/z calcd. for
C15H18N[M + H]+ = 212.14338, found 212.14261.
(10) 2ꢀ-methoxy-N,N-dimethyl-[1,1ꢀ-biphenyl]-3-amine (Table 3,
entry 2)1H NMR (300 MHz, CDCl3): 7.45–7.16 (m, 3H),
7.02–6.83 (m, 4H), 6.71 (d, J = 8.1 Hz, 1H), 3.77 (s, 3H), 2.94
(s, 6H) ppm. GC–MS (EI) m/z (%): 227(1 0 0) [M]+, 210(26.3),
196(13.3), 183(9.2), 181(9.0), 168(14.2), 152(5.6), 139(9.6),
113(8.1), 108(14.1), 98(10.8), 91(5.9), 78(5.8), 63(3.6), 39(4.8).
(11) N,N-dimethyl-4ꢀ-nitro-[1,1ꢀ-biphenyl]-3-amine (Table 3,
entry 3)1H NMR (300 MHz, CDCl3): 8.26 (d, J = 8.7 Hz, 2H),
7.72 (d, J = 8.7 Hz, 2H), 7.35 (t, J = 7.9 Hz, 2H), 6.95–6.88 (m,

A.B. Patil, B.M. Bhanage / Journal of Molecular Catalysis A: Chemical 379 (2013) 30–37
33
Table 1
Effect of reaction parameters on synthesis of synthesis of 2-phenoxy-1,1ꢀ-biphenylsa
Entry
Catalyst amount (mmol)
Base
Temperature (◦C)
Time (min)
Yield (%)b
Effect of catalyst loading
1
2
3
4
0.001
KOH
KOH
KOH
KOH
100
100
100
100
60
60
60
60
98
98
61
NR
0.0005
0.0002
0.0000
Effect of temperature
5
6
0.0005
0.0005
0.0005
0.0005
KOH
KOH
KOH
KOH
60
80
100
27
60
60
60
71
90
98
34
7
8c
1440
Effect of time
9
10
11
0.0005
0.0005
0.0005
KOH
KOH
KOH
100
100
100
30
45
60
75
92
98
a
Reaction conditions: iodobenzene (1 mmol), (2-phenoxyphenyl) boronic acid (1.2 mmol), water (4 mL). KOH (2 mmol).
GC yield.
Reaction time (24 h).
b
c
Fig. 1). The UV–Visibleabsorptionspectrumof reactionmixturewas
taken before irradiation and after irradiation (Fig. 2). The results
shows the palladium complex before irradiation shown absorption
peak at 294 nm, which disappeared with irradiation time indicates
reduction of ionic palladium and propagation towards the metallic
palladium formation this gives another point to support the syn-
thesis of PdNPs. The oxidation state of reduced material was further
confirmed by the XPS analysis. The XPS of Pd 3d spectrum with the
binding energies of Pd 3d5/2 and Pd 3d3/2 lying at about 335.6 and
341.0 eV, respectively, suggest the presence of the Pd(0) species
(Fig. 3). This result confirms metallic state of Pd and its stability in
aqueous medium. The stable solution of synthesized PdNPs with-
out any aggregation indicates the capping effect of PVP in synthesis.
The TEM and FEG-SEM analysis were used for size and morphologi-
cal investigation. The TEM image shows the maximum contribution
of triangular and hexagonal nanoplates ranging from 20 to 50 nm
(Fig. 4). The SAED pattern illustrates the crystalline nature of the
product (Fig. 4 (inset)). In the synthesized material the nanoplate’s
contribution was observed up to 70%, which is calculated from TEM
images at different locations and using manual calculation tech-
nique for 200 nanoparticles (Fig. 5). However, FEG-SEM gives three
dimensional ideas about nanoplates structure (Fig. 6). The EDAX
analysis shows the presence of elemental palladium along with Cu
which is due to the use of Cu stub for the analysis (Fig. 7). Though
the percentage of nanoplates is up to ∼70%, this is the first exam-
ple wherein the solar energy concept used for the shape selective
Scheme 1. Synthesis of palladium nanoparticles using ethylene glycol under solar
irradiation.
glycols dehydrates to aldehyde, which can reduce metallic ions to
elemental form. Herein, ethylene glycol initially acting as a solvent,
and then it dehydrates to form acetaldehyde that results reduc-
tion of metallic ions [24]. The reaction was schematized as follows
(Reaction Scheme 1):
‘Fresnel lenses’ often used as a solar concentrator helps here
for the shape selective nanoplates (Fig. 1). Under the concentrated
solar energy colour change from pale yellow to dark brown of
reaction mixture was observed and that is a first point of evi-
dence which indicates reduction of Pd (II) ions to Pd (0) (inset
Fig. 1. Schematic representation of reaction setup with reaction progress observed
by colour change (inset).
Fig. 2. UV–vis spectrum showing reaction progress.

34
A.B. Patil, B.M. Bhanage / Journal of Molecular Catalysis A: Chemical 379 (2013) 30–37
Table 2
Pd nanoplates-catalyzed reaction of (2-phenoxyphenyl) boronic acid and aryl iodides and bromidea
R
Pd nano
O
+
base, 100 °C,
water
O
X
B
X= I, Br
HO
OH
.
Entry
Aryl iodide
Aryl boronic acid
Product
Yield (%)b
I
O
B
HO
OH
1
2
97
I
O
B
HO
I
HO
OH
96
91
O
B
CH3
I
HO
OH
3
4
O
B
NO2
HO
OH
93
I
O
B
CH3
I
HO
HO
HO
HO
OH
OH
OH
OH
5
6
7
8
91
90
96
12
O
B
OCH3
O
I
O
OH
B
OH
Br
O
B
NH2
a
Reaction conditions: aryl halide (1 mmol), (2-phenoxyphenyl) boronic acid (1.2 mmol), Pd(0) nanoplates (0.0005 mmol), KOH (2 mmol), water 4 mL, 100 ◦C, 60 min.
GC yield.
b
nanoplates synthesis, which could be a greater opportunity for the
further research.
a bridge between homogeneous and heterogeneous catalysis. In
addition to the nanoplates synthesis this study also associated with
simple and heterogeneous protocol with economic and ecologi-
cal views for the synthesis of 2-phenoxy-1,1ꢀ-biphenyls (Reaction
Scheme 2). In earlier work, such products were synthesized by
different groups and their protocols have limitations due to mul-
tistep synthesis, catalyst separation and reusability, harsh reaction
conditions like high catalyst loading, toxic solvents, expensive and
3.2. Catalytic activity of Pd nanoplates for the
2-phenoxy-1,1ꢀ-biphenyls synthesis
The nanomaterial applications in catalysis overcome variety of
problems that associated with homogeneous catalysis by offering

A.B. Patil, B.M. Bhanage / Journal of Molecular Catalysis A: Chemical 379 (2013) 30–37
35
Fig. 3. XPS spectra of Pd 3d spectrum recorded at 160 eV pass energy and 600 W
X-ray power.
Fig. 6. FEG-SEM image of palladium nanoplates.
Fig. 7. EDAX pattern of synthesized palladium nanoparticles.
The optimum reaction parameter selection was started with cat-
alyst screening wherein, catalyst concentration was varied from
0.001 to 0.0002 mmol (Table 1, entries 1–4). Initially, 0.001 mmol
catalyst loading shows 98% yield however, at half concentration
(0.0005 mmol) it gave same yield 98%. A further decrease in the
loading (0.0002) showing 61% of the desired product. The blank
experiment without catalyst displaying no product formation indi-
cates the necessity of PdNPs for the synthesis. The reaction was
carried at various temperatures ranging from 60 to 120 ◦C (Table 1,
entries 5–8) and 100 ◦C was found to be the optimum tempera-
ture. Followed to this study reaction time was optimized and for
this various reactions in the range of 30–120 min were performed
(Table 1, entries 9–11). It showed that 60 min is the optimum
reaction time. In combine, optimized parameters for the synthe-
sis are: iodobenzene (1 mmol), (2-phenoxyphenyl) boronic acid
(1.2 mmol), Pd nanoplates (0.0005 mmol), KOH (2 mmol), at 100 ◦C
for 1 h in aqueous medium.
Fig. 4. TEM image of palladium nanoplates with SAED pattern (inset).
toxic ligands. Hosseinzadeh et al. reported copper-catalyzed ary-
lation of 1,1ꢀ-biphenyl-2-ol with aryl iodides using KF/Al2O3 as
a suitable base and CuI and 1,3 diphenyl-1,3 propandione as the
catalyst wherein the catalyst and substrate loading is quite high
[32]. Niu et al. reported similar arylation technique by copper
(I)–bipyridyl complex catalyst [33]. Considering the above dis-
cussed issue herein, we are reporting a simple approach of Suzuki
coupling reaction for the synthesis of 2-phenoxy-1,1ꢀ-biphenyl and
derivatives using Pd nanoplates.
These optimized conditions were applied for the synthesis of
various derivatives of 2-phenoxy-1,1ꢀ-biphenyls. The screening
of various electron donating and withdrawing groups like CH3,
Scheme 2. Pd nanoparticles-catalyzed synthesis of 2-phenoxy-1,1ꢀ-biphenyls using
Fig. 5. Particle size distribution of 2 0 0 nanoparticles using TEM images.
(2-phenoxyphenyl) boronic acid and aryl halides.

36
A.B. Patil, B.M. Bhanage / Journal of Molecular Catalysis A: Chemical 379 (2013) 30–37
Scheme 3. Pd nanoplates-catalyzed synthesis of N,N-dimethyl-[1,1ꢀ-biphenyl]
using (3(dimethylamino) phenyl) boronic acid and aryl iodides.
OCH3, OH, NH2 and NO2 on aryl iodide (I, Br) smoothly under-
goes Suzuki coupling reaction with (2-phenoxyphenyl) boronic
acid providing desired products in the presence PdNPs in aqueous
medium (Table 2, entry 1–9).
3.3. Catalytic activity of Pd nanoplates for the
N,N-dimethyl-[1,1ꢀ-biphenyl] and derivatives synthesis
Fig. 8. Recyclability of Pd nanoplates for Suzuki coupling reaction.
Followed to the above discussion and applications the catalytic
activity of the Pd nanoplates was explored for the synthesis of
N,N-dimethyl-[1,1ꢀ-biphenyl] derivatives (Reaction Scheme 3). In
literature, only two reports are available for the synthesis of such
compounds. In 2006, Solodenko et al. reported PVP supported
palladium catalyst in the presence of tetra-n-butylammonium
bromide (TBAB), at 0.25 mmol catalyst loading under 130 ◦C
microwave heating for 3 h [34]. In 2007, Fleckenstein and Ple-
nio reported the synthesis of N,N-dimethyl-[1,1ꢀ-biphenyl], but
the reaction conditions were harsh and it requires the use
of fluorenyl-based phosphine ligand and high catalyst load-
ing [35]. In comparison to the previous reports, herein, we
carrying representative experiments from both the reactions under
the same optimized conditions by using 10% Pd/C (0.0005 mmol Pd)
(Table 4).Table 4 showing comparative data between catalytic per-
formance of PdNPs and 10% Pd/C for the above mentioned reaction.
The TOF values of obtained results were compared and it is noticed
that the Pd nanoparticles shown better performance than that of
Pd/C. The TOF values obtained using PdNPs are 1940 and 1860 h−1
(Table 4, entries 1 and 3) whereas, the same reactions using Pd/C
shown 1680 and 1500 h−1 respectively (Table 4, entries 2 and 4).
The better performance of PdNPs is credited to the well dispersion
and smaller size of the nanoparticles.
are reporting
a simple, one step, faster, green protocol for
the synthesis of the N,N-dimethyl-[1,1ꢀ-biphenyl] in aqueous
medium. The synthesis was carried out under optimized reac-
tion conditions using 1 mmol of aryl halide and 1.2 mmol of
(3-(dimethylamino)phenyl) boronic acid at 0.0005 mmol catalyst
loading (Pd (0) nanoplates) and it gives excellent yield of the desired
product. The catalyst showing excellent activity for the both elec-
tron donating and electrons withdrawing moieties (Table 3 entries
1–3).
3.4. Catalyst recyclability
Considering economic and ecological issues reusability of cata-
lyst is a very important aspect. The catalyst recycles study was done
by scale up of model reaction to 4 mmol wherein, Pd nanoplates
shows excellent performance up to three consecutive recycles to
the reaction of iodobenzene with (2-phenoxyphenyl) boronic acid
(Fig. 8). The nanoparticles was separated and reused by centrifu-
gation at 18000 rpm at 25 ◦C for 20 min with frequent wash with
water followed by ethyl acetate. The reduction of % yield (88%) after
third recycle is may be due to the handling loss of catalyst.
In addition to the above applications to the organic transfor-
mations we compare the catalyst activity with the commercially
available 10% Pd/C catalyst. This comparison study was done by
Table 3
Pd nanoplates-catalyzed synthesis of N,N-dimethyl-[1,1ꢀ-biphenyl] derivatives.a
Entry
Aryl iodide
(3(dimethylamino) phenyl) boronic acid
Product
Yield (%)b
CH
3
I
N
N
N
B(OH)2
B(OH)2
B(OH)2
N
CH3
1
2
93
96
I
N
OCH
3
OCH3
NO
2
I
N
NO2
3
88
a
Reaction conditions: aryl halide (1 mmol), (3(dimethylamino) phenyl) boronic acid (1.2 mmol), Pd(0) nanoplates (0.0005 mmol), KOH (2 mmol), water 4 mL, 100 ◦C,
60 min.
b
GC yield.

A.B. Patil, B.M. Bhanage / Journal of Molecular Catalysis A: Chemical 379 (2013) 30–37
37
Table 4
Activities of Pd [0] nanoparticles catalyst and 10% Pd/C catalyst in terms of TOF valuesa
Entry
Catalyst
Boronic acid derivative
Aryl iodide
Product
Yieldb (%)
TOF (h−1
)
O
I
O
B
CH
CH
HO
OH
3
3
1
PdNPs
97
1940
O
I
O
B
CH
CH
HO
OH
3
3
2
3
10% Pd/C
84
1680
CH
3
I
N
N
B(OH)2
CH3
PdNPs
93
75
1860
1500
CH 3
I
N
B(OH)2
N
CH
3
4
10% Pd/C
a
Reaction conditions: aryl halide (1 mmol), boronic acid derivative (1.2 mmol), Pd catalyst (0.0005 mmol Pd content), KOH (2 mmol), 100 ◦C, 60 min.
GC yield.
b
4. Conclusions
[5] J. Chen, F. Saeki, B.J. Wiley, H. Cang, M.J. Cobb, Z.Y. Li, L. Au, H. Zhang, M.B.
Kimmey, X. Li, Y. Xia, Nano Lett. 5 (2005) 473–477.
[6] X. Zhang, M.A. Young, O. Lyandres, R.P. Van Duyne, J. Am. Chem. Soc. 127 (2005)
4484–4489.
[7] L.N. Lewis, Chem. Rev. 93 (1993) 2693–2730.
[8] X. Teng, D. Black, N.J. Watkins, Y. Gao, H. Yang, Nano Lett. 3 (2003) 261–264.
[9] T.S. Ahmadi, Z.L. Wang, T.C. Green, A. Henglein, M.A. El-Sayed, Science 272
(1996) 1924–1926.
[10] C.B. Murray, S. Sun, H. Doyle, T. Betley, MRS Bull. 26 (2001) 985–991.
[11] B.R. Cuenya, Thin Solid Films 518 (2010) 3127–3150.
[12] Y. Nishihata, J. Mizuki, T. Akao, H. Tanaka, M. Uenishi, M. Kimura, T. Okamoto,
N. Hamada, Nature 418 (2002) 164–167.
[13] M. Ferna’ndez-Garcı’a, A. Martı’nez-Arias, L.N. Salamanca, J.M. Coronado, J.A.
Anderson, J.C. Conesa, J. Soria, J. Catal. 187 (1999) 474–485.
[14] S. Kim, M. Kim, W.Y. Lee, T. Hyeon, J. Am. Chem. Soc. 124 (2002) 7642–7643.
[15] M.T. Reetz, E. Westermann, Angew. Chem. Int. Ed. 39 (2000) 165–168.
[16] S.U. Son, Y. Jang, J. Park, H.B. Na, H.M. Park, H.J. Yun, J. Lee, T. Hyeon, J. Am. Chem.
Soc. 126 (2004) 5026–5027.
In conclusion, we have developed a novel, green and simple
method for the synthesis of well dispersed palladium nanoparticles
with a maximum contribution of nanoplates using ethylene glycol
as a reducing agent and concentrated solar radiations as a renew-
able energy source. The optimum reaction condition for nanoplate’s
formation was attained by adjusting the concentration ratio of
sunlight in presence of PVP as a mild reductant. The obtained
nanoplates showing greater catalytic applicability in the novel and
greener protocol for synthesis of 2-phenoxy-1,1ꢀ-biphenyls and
N,N-dimethyl-[1,1ꢀ-biphenyl] derivatives at mild reaction condi-
tion. The catalyst could be reused for three more consecutive cycles.
[17] Y. Li, X.M. Hong, D.M. Collard, M.A. El-Sayed, Org. Lett. 2 (2000) 2385–2388.
[18] B. Lim, M. Jiang, J. Tao, P. Camargo, Y. Zhu, Y. Xia, Adv. Funct. Mater. 19 (2009)
189–200.
Acknowledgments
[19] Y. Chien, C. Huang, S. Wang, C. Yeh, Green Chem. 13 (2011) 1162–1166.
[20] Y. Yin, G. Jiang, J. Liu, ACS Nano. 6 (2012) 7910–7919.
[21] A.B. Patil, S.R. Lanke, K.M. Deshmukh, A.B. Pandit, B.M. Bhanage, Mater. Lett. 79
(2012) 1–3.
[22] A.B. Patil, D.S. Patil, B.M. Bhanage, Mater. Lett. 86 (2012) 50–53.
[23] A.B. Patil, D.S. Patil, B.M. Bhanage, J. Mol. Catal. A 365 (2012) 146–153.
[24] F. Fievet, J.P. Lagier, M. Figlarz, MRS Bull. 14 (1989) 29–34.
[25] V. Germain, J. Li, D. Ingert, Z.L. Wang, M.P. Pileni, J. Phys. Chem. B 107 (2003)
8717–8720.
[26] Y. Sun, B. Mayers, Y. Xia, Nano Lett. 3 (2003) 675–679.
[27] Y. Sun, Y. Xia, Adv. Mater. 15 (2003) 695–699.
[28] Y. Xiong, J. Chen, B. Wiley, Y. Xia, S. Aloni, Y. Yin, J. Am. Chem. Soc. 127 (2005)
7332–7333.
The authors express their gratitude towards DAE-ICT (Depart-
ment of Atomic Energy and Institute of Chemical Technology,
Mumbai, India) and Department of Science and Technology, Govt. of
India for DST-Nanomission Project SR/NM/NS-1097/2011 for finan-
cial assistance.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
2013.07.012.
[29] Y. Xiong, J.M. McLellan, J. Chen, Y. Yin, Z. Li, Y. Xia, J. Am. Chem. Soc. 127 (2005)
17118–17127.
[30] Y. Xiong, I. Washio, J. Chen, H. Cai, Z. Li, Y. Xia, Langmuir 22 (2006) 8563–8570.
[31] B. Veisz, Z. Kirly, Langmuir 19 (2003) 4817–4824.
[32] R. Hosseinzadeh, M. Tajbakhsh, M. Mohadjerani, P. Rezaei, M. Alikarami, Synth.
Commun. 38 (2008) 3023–3031.
[33] J. Niu, H. Zhou, Z. Li, J. Xu, S. Hu, J. Org. Chem. 73 (2008) 7814–7817.
[34] W. Solodenko, K. Mennecke, C. Vogt, S. Gruhl, A. Kirschning, Synthesis 11 (2006)
1873–1881.
References
[1] S. Chen, Y. Yang, J. Am. Chem. Soc. 124 (2002) 5280–5281.
[2] M.A. El-Sayed, Acc. Chem. Res. 34 (2001) 257–264.
[3] T.A. Taton, C.A. Mirkin, R.L. Letsinger, Science 289 (2000) 1757–1760.
[4] A.G. Tkachenko, H. Xie, D. Coleman, W. Glomm, J. Ryan, M.F. Anderson, S.
Franzen, D.L. Feldheim, J. Am. Chem. Soc. 125 (2003) 4700–4701.
[35] C.A. Fleckenstein, H. Plenio, Chem. Eur. J. 13 (2007) 2701–2716.