Synthesis of Water-Dispersible Pd Nanoparticles Using a Novel Oxacalixarene Derivative and their Catalytic Application in C–C Coupling Reactions

Article abstract of DOI:10.1007/s10562-016-1781-y

A novel 5,17-di(hydrazinecarbonyl) tetranitrooxacalix[4]arene (DHOC) derivative has been synthesized and characterized using various spectroscopic techniques. This DHOC derivative has been used to produce water-dispersible catalytically active Pd nanoparticles (PdNps). In the nanoparticle synthesis, DHOC serves as both a reducing and a stabilizing agent, thus simplifying the preparation of the PdNps because no separate reagents are required to reduce and stabilize the nanoparticles. These PdNps were characterized by a number of techniques such as Transmission Electron Microscopy and UV–Visible spectroscopy. The water-dispersible PdNps were 5?±?2?nm in size and showed high catalytic activity in numerous C–C coupling reactions such as the Sonogashira, Suzuki-Miyuara and Heck reactions. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1781-y

Catal Lett
DOI 10.1007/s10562-016-1781-y
Synthesis of Water-Dispersible Pd Nanoparticles Using a Novel
Oxacalixarene Derivative and their Catalytic Application in C–C
Coupling Reactions
Viren Mehta1 Manthan Panchal1 Anita Kongor1 Urvi Panchal1
V. K. Jain1
•
•
•
•
Received: 15 May 2016 / Accepted: 6 June 2016
Ó Springer Science+Business Media New York 2016
Abstract A novel 5,17-di(hydrazinecarbonyl) tetrani-
trooxacalix[4]arene (DHOC) derivative has been synthe-
sized and characterized using various spectroscopic
techniques. This DHOC derivative has been used to pro-
duce water-dispersible catalytically active Pd nanoparticles
(PdNps). In the nanoparticle synthesis, DHOC serves as
both a reducing and a stabilizing agent, thus simplifying
the preparation of the PdNps because no separate reagents
are required to reduce and stabilize the nanoparticles.
These PdNps were characterized by a number of tech-
niques such as Transmission Electron Microscopy and
UV–Visible spectroscopy. The water-dispersible PdNps
were 5 2 nm in size and showed high catalytic activity
in numerous C–C coupling reactions such as the Sono-
gashira, Suzuki-Miyuara and Heck reactions.
Graphical Abstract
Keywords Oxacalix[4]arene Á PdNps Á Catalysis Á C–C
coupling reactions
1 Introduction
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-016-1781-y) contains supplementary
material, which is available to authorized users.
Nanoscience is considered an innovative and interdisci-
plinary science with applications in catalysis, electro
analysis, biology and medicine, among other fields [1–3].
The synthesis of metal nanoparticles of diverse sizes,
controlled mono-dispersity and varied chemical composi-
tions has become an important area of research in
& V. K. Jain
drvkjain@hotmail.com
1
Department of Chemistry, Gujarat University, Navrangpura,
Ahmedabad 380009, India
123

V. Mehta et al.
nanotechnology [4]. The small size of the nanoparticles is
favorable for several catalytic reactions [5]. As catalysis
takes place on the metal surface, the reactivity of metal
nanoparticles is higher than their particulate metal coun-
terparts due to the nanoparticles’ high surface to volume
ratio. These nanoparticles have found practical application
in many fields [6, 7]. Metal nanoparticles are predomi-
nantly synthesized from metals such as silver (Ag), plat-
inum(Pt), gold(Au) and palladium (Pd) [8]. Due to their
applications in catalysis, palladium nanoparticles (PdNps)
have gained great significance in synthesis [9].
coupling reactions. Therefore, these nanoparticles were
further used as catalysts for the Sonogashira, Suzuki-
Miyuara and Heck coupling reactions.
2 Experimental Section
2.1 Chemicals and Reagents
All the chemicals used were of the highest purity, were
procured from Sigma-Aldrich and used without further
purification. Water used in the experiments was obtained
from a Millipore system (resistivity, 18 MXcm at 25 °C,
Millipore Systems). All of the solvents employed for syn-
thesis were commercially available and were used as
received without further purification. The purity of the
compounds and the progress of the reactions were moni-
tored by TLC on pre-coated silica gel-aluminum plates
(Type 60 F254, Merck, Darmstadt, Germany) and were
visualized by exposure to UV-light (254 nm) or I2 vapor.
Because of their unique properties, the study of cat-
alytically active palladium nanoparticles has gained sub-
stantial prominence as they have come to play an important
role in organic synthetic chemistry [10]. Many organic
reactions with industrial applications, such as the Sono-
gashira [11], Suzuki-Miyuara [12], Stille [13], Heck
[14, 15], Hiyama [16], and hydrogenation reactions
[17, 18] can be progressed, and numerous complex organic
compounds are usually synthesized in non-aqueous/aque-
ous media by using catalytically active palladium com-
plexes [19]. A number of carbon–carbon and carbon-
heteroatom coupling reactions can be catalyzed by palla-
dium complexes such as (PPh3)4Pd [20]. However, these
complexes are sensitive to air, are toxic and are difficult to
separate from the reaction products.
2.2 Instrumentation
A VEEGO (Model No: VMP-DS) melting point apparatus
(Mumbai, India) was used to measure the melting points
(uncorrected) in a single capillary tube. Centrifugation of
the colloidal solutions was done using a Remi, Model No.
C-24BL laboratory centrifuge. 1H NMR and 13C NMR
spectra were obtained on a Bruker AV-(III)-400 MHz
spectrometer using a BBFO probe. ESI-Mass spectra were
taken on a micromassQuarter2 mass spectrometer (Utah,
USA) with a capillary voltage of 3000 V and source tem-
perature of 120 °C. The absorption spectra were recorded
using a Jasco V-570 UV–Vis recording spectrophotometer
(Tokyo, Japan) in the range of 200–800 nm. Transmission
Electron Microscopy(TEM) images and Selective Area
Electron Diffraction (SAED) pattern were recorded on a
JEOL model, JEM 2100 microscope using an accelerated
voltage of 200 kV. The zeta potential and particle size
were obtained by the Malvern Zeta sizer (Model;
ZEN3600) as such without dilution. Inductively Coupled
Plasma-Atomic Emission Spectrophotometer (ICP-AES)
JY 2000-2 model was used to check the absence of Pd in
supernatant liquid collected after centrifugation.
The preparation of metal nanoparticles often requires the
use of chemical reduction methods in which a reducing
agent and a number of stabilizers are used to prevent the
accumulation of metal nanoparticles [21, 22] and the
leaching of the activity of the Catalyst [21]. Intriguingly,
supramolecules such as Cyclodextrins [23], Porphyrin [24],
and Calixarenes [25, 26] have been used as both reducing
and stabilizing agents in the preparation of many types of
nanoparticles. In contrast, the use of oxacalixarenes in the
field of nanoscience has not been explored much because
they are still in the synthetic stage [27, 28]. Hence, the use
of oxacalixarenes to synthesize nanoparticles is anticipated
to show their significance in the field of nanoscience and
nanotechnology.
Therefore, 5,17-di(hydrazinecarbonyl) tetranitrooxa-
calix [4] arene (DHOC) has been synthesized, character-
ized and used as both a reducing and a stabilizing agent for
the formation of DHOC-PdNps. We report the use of
DHOC to synthesize Pd nanoparticles in water because the
preparation and stabilization of nanoparticles in an aqueous
medium have a number of significant benefits such as
avoidance of organic solvent, lower cost and potential for
the use of these nanoparticles in biological applications.
Metal nanoparticles with a size of 1–5 nm [10] display
great catalytic activity and also regulate the catalyst
selectivity [29]; as a result, DHOC-PdNps with a size of
3 Synthesis
3.1 Synthesis of 5,17-Di(ethoxycarbonyl)
Tetranitrooxacalix[4]arene (DEOC) (4)
3,5-dihydroxy ethyl benzoate (2) was prepared from 3,5-
dihydroxybenzoic acid (1), as per the reported procedure
5
2 nm can very effectively catalyze various C–C
123

Synthesis of Water-Dispersible Pd Nanoparticles Using a Novel Oxacalixarene Derivative and…
3.3 Synthesis of DHOC Stabilized Palladium
Nanoparticles
[30]. Compound (2) (4 gm, 21.9 mmol), compound (3),
1,5-difluoro-2,4-dinitrobenzene (21.9 mmol) and finely
ground anhydrous K2CO3 (54.9 mmol) were stirred in
DMSO (80 mL) in a 250 mL round bottom flask at room
temperature for 30 min. The reaction was monitored by
TLC. The reaction mixture was added drop wise to 1 M
HCl (400 mL). The aqueous layer was extracted with
EtOAc (500 mL 9 2). The combined organic layers were
washed with brine (500 mL), dried over anhydrous Na2-
SO4, filtered, and concentrated in vacuo. The DEOC (4,
Scheme 1) was purified using 30 % ethyl acetate in hexane
as the eluent, with a yield of 80 %.
Mass ESI (?); m/z = 692.7 (M ? 1); 1H NMR
(400 MHz, CDCl3) d 1.36 (t, J = 7.0 Hz, 3H), 4.35 (q,
J = 7.1 Hz, 2H), 7.17 (s, 1H), 7.49 (t, J = 2.2 Hz, 1H),
7.63 (d, J = 2.3 Hz, 2H), 8.86 (s, 1H); 13C NMR
(125 MHz, CDCl3) d 67.5, 100.1, 101.6, 116.2, 118.8,
122.0, 123.0, 125.6, 131.7, 134.6, 151.4, 151.8, 153.5,
158.4, 160.2, 169.5.; M.P.:190 °C.
First, 100 mL of a solution of palladium acetate (0.022 g)
in double distilled water was heated to 60 °C. To this
heated solution, DHOC (0.066 g) in 100 mL water was
added, and the mixture was kept under vigorous stirring
with heating for 6 h. The complete reduction of the pal-
ladium salt was confirmed by the color change from
brownish yellow to blackish brown. The formation of
DHOC-PdNps was confirmed by TEM, and UV–Vis
spectroscopy. Because DHOC is water soluble, the content
of DHOC in the DHOC-PdNps was 66.0 mg and the Pd
loading in the DHOC-PdNps was 10.4 mg. The final yield
of DHOC-PdNps collected by centrifugation was 76.4 mg.
After centrifugation at 3000 rpm for 15 min, the super-
natant liquid was confirmed for the absence of DHOC and
any unreacted Pd by UV–Visible spectrophotometry and
ICP-AES, respectively. Thus, this procedure for the
preparation of PdNps is a simple one-pot process in the
presence of an ecologically friendly solvent, i.e., water
(Table 1).
3.2 Synthesis of 5,17-Di(hydrazinecarbonyl)
Tetranitrooxacalix[4]arene (DHOC) (5)
A mixture of DEOC(3 gm, 4.3 mmol) and hydrazine
hydrate (10.8 mmol) in 30 mL of THF was refluxed for
24 h and the reaction mixture was concentrated in vacuo.
The DHOC (5, Scheme 1) was purified using 80 % ethyl
acetate in hexane as the eluent, with a yield of 65 %.
Mass ESI (?); m/z = 665.62 (M ? 1); 1H NMR
(400 MHz, CDCl3) d 4.77 (S, 2H), 6.44 (t, J = 2.2 Hz,
2H), 6.82 (d, J = 2.2 Hz, 2H), 7.19 (s, 1H),9.33 (s,
1H),9.65 (s, 1H); 13C NMR (125 MHz, CDCl3) d 90.7,
104.8, 106.9, 122.3, 128.4, 131.5, 149.4, 158.4, 166.2;
M.P.: 250 °C.
4 DHOC-PdNps Catalyzed Various C–C Coupling
Reactions
4.1 Suzuki Reaction of Aryl Halides
To a mixture of phenyl boronic acid (0.5 gm, 4.1 mmol),
aryl halide (4.5 mmol) and Na2CO3 (4.5 mmol) in
DMF:Water (1:1), the DHOC-PdNps (0.0077 mmol) were
added. The reaction mixture was then stirred at 50 °C
(Table 2). The reaction was monitored by TLC, and after
completion of the reaction, the reaction mixture was cooled
Scheme 1 Synthetic route for 5,17-di(hydrazinecarbonyl) tetranitrooxacalix[4]arene (DHOC)
123

V. Mehta et al.
Table 1 Optimization of reaction conditions for Suzuki reaction
Entry
Solvent
Catalyst amount (mmol)
Base
Temperature (°C)
Time (min)
Yieldd (%)
1
Acetone/water
THF/water
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.006a
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Potassium carbonate
Triethylamine
50
50
50
50
50
50
50
50
50
50
50
50
50
50
25
40
50
60
70
80
50
50
60
80
120
50
70
20
45
40
45
60
50
60
35
30
40
45
20
22
21
20
60
120
88
85
65
89
79
92
88
85
80
65
63
72
88
92
88
89
92
90
91
91
80
83
2
3
DCM/water
1,4-dioxane/water
Toluene/water
DMF/water
Ethanol/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
DMF/water
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Sodium acetate
Potassium hydroxide
Sodium bicarbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
Sodium carbonate
0.110a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077a
0.0077b
0.0077c
Reaction conditions: phenyl boronic acid (0.5 gm, 4.1 mmol), aryl halide (4.5 mmol), base (4.5 mmol), catalyst (0.0077 mmol), water:solvent
(1:1) (10 mL), temperature (°C) in air
a
For catalyst, PdNps, Palladium acetate, Tetrakis(triphenylphosphine)-palladium(0), Isolated yield after drying the product
b
c
d
Table 2 DHOC-PdNps-catalyzed Suzuki coupling reaction of dif-
ferent aryl halides
to room temperature. Then, the reaction mixture was
extracted with ethyl acetate (50 mL 9 2) and washed with
water (50 mL). The organic phase was washed with brine
(25 mL), dried over Na2SO4, filtered and concentrated in
vacuo. The products were purified using 10 % ethyl acetate
in hexane as the eluent.
Entry Aryl halide
Product
Time
(min)
Yielda
(%)
4.2 Sonogashira Reaction of Aryl Halides
1
2
3
20
22
20
90
92
89
To a mixture of phenyl acetylene (0.5 gm, 4.9 mmol), aryl
halide (5.4 mmol) and Na2CO3 (5.4 mmol) in N-methyl
2-pyrrolidone (NMP):Water, the DHOC-PdNps (0.0077
mmol) were added. The reaction mixture was then stirred
at 60 °C (Table 3). The reaction was monitored by TLC,
and after completion of the reaction, the reaction mixture
was cooled to room temperature. Then, the reaction mix-
ture was extracted with ethyl acetate (60 mL 9 2) and
washed with water (60 mL). The organic phase was
washed with brine (50 mL), dried over Na2SO4, filtered
Reaction conditions: phenyl boronic acid (0.5 gm, 4.1 mmol), aryl
halide (4.5 mmol), base (4.5 mmol), PdNps (0.0077 mmol),
Water:DMF (1:1) (10 mL), temperature (50 °C)
a
Isolated yield after drying the product
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Synthesis of Water-Dispersible Pd Nanoparticles Using a Novel Oxacalixarene Derivative and…
Table 3 DHOC-PdNps catalyzed Sonogashira coupling reaction of
different aryl halides
Table 4 DHOC-PdNps catalyzed Heck coupling reaction of different
aryl halides
Entry Aryl halide
Product
Time Yielda
(min) (%)
1
55
83
Entry Aryl halides
Product
Time Yielda
(h)
(%)
2
3
60
63
85
90
1
1.5
95
I
Reaction conditions: phenyl acetylene (0.5 gm, 4.9 mmol), aryl halide
(5.4 mmol), base (5.4 mmol), PdNPs (0.0077 mmol), NMP:Water
(1:1) (10 mL), temperature (60 °C)
2
2
92
87
I
a
Isolated yield after drying the product
3
1.5
N
O2
O2N
and concentrated in vacuo. The products were purified
using 5 % ethyl acetate in hexane as the eluent.
Cl
Reaction conditions: alkene (Styrene) (0.5 gm, 4.8 mmol), aryl halide
(5.3 mmol), base (5.3 mmol), PdNps (0.0077 mmol), NMP: Water
(1:1) (10 mL), temperature (50 °C)
4.3 Heck Reaction of Aryl Halides
a
To a mixture of alkene (0.5, 4.8 mmol), aryl halides
(5.3 mmol) and Na2CO3 (5.3 mmol) in NMP:Water, the
DHOC-PdNps (0.0077 mmol) were added. The reaction
mixture was then stirred at 40 °C (Table 4). The reaction
was monitored by TLC, and after completion of the reac-
tion, the reaction mixture was cooled to room temperature.
Then, the reaction mixture was extracted with ether
(30 mL 9 2) and washed with water (30 mL). The organic
phase was washed with brine (30 mL), dried over Na2SO4,
filtered and concentrated in vacuo. The products were
purified using 2 % ethyl acetate in hexane as the eluent.
Isolated yield after drying the product
be avoided. It is believed that the hydrazide part of oxa-
calixarene provide electrons for reduction to the metal ions
and its inherent echoing cavity and web-type structure
[26, 36–40] offer stability to the nanoparticles. Hence, the
facile formation of PdNps was achieved using aqueous
solutions of Pd(OAc)2 and DHOC, without any external
reductant/stabilizer. The formation of DHOC-PdNps has
also been confirmed through TEM, and UV–Visible
spectroscopy.
The UV–Visible spectroscopy study was carried out to
confirm the formation of DHOC-PdNps. Unlike Gold and
Silver nanoparticles, PdNps has no explicit Surface Plas-
mon Resonance (SPR) band; hence, the disappearance of
the band at 400 nm attributed to Pd(OAc)2 (Fig. 1), along
with a distinctive color change from brownish yellow to
blackish brown (Fig. 2), confirms the formation of DHOC-
PdNps [41].
5 Results and Discussion
Reetz demonstrated palladium nanoparticle-catalyzed
coupling reactions and used surfactants as stabilizers
[31, 32]. For aryl iodides, EI-Sayed et al. described the
significance of Pd nanoparticles stabilized by PVP [33]. Pd
nanoparticles are primarily synthesized by numerous sta-
bilizers such as dendrimer [34] and polymers [35]. Nev-
ertheless, the preparation of nanoparticles with use of the
calix system is more efficient due to its combined reducing
and stabilizing properties [36–38]. Hence, we introduce a
dihydrazide derivative of oxacalixarene which works as a
suitable reductant and stabilizer for preparing PdNps. This
procedure is very advantageous for the synthesis of PdNps
as the use of separate reducing and stabilizing agents can
The PdNps have zeta potential values of -30.8 mV
(Fig. 3), which are consistent with reported values for
nanoparticles with good stability [42]. The poly-dispersity
of the particles was ascertained by TEM analysis (Figure).
The lattice spacing value was found to be 0.224 nm in the
high-resolution transmission electron microscopy image
(Fig. 4). The PdNps were approximately spherical, as well
as the narrow size distribution had an average diameter of
123

V. Mehta et al.
5.1 Suzuki Reaction
The effects of temperature, solvents and bases on the yield
of the model reaction were studied using a 1:1 mixture of
water and various organic solvents. Dimethylformamide
(DMF) proved to be a better co-solvent than acetone, THF,
DCM, 1,4-dioxane, toluene and ethanol (Table 1: Entries
1–7), and Na2CO3was a better base than were Triethy-
lamine, K2CO3, NaHCO3 and CH3COONa (Table 1:
Entries 8–12, 17). It was also observed that increasing the
temperature does not increase the yield (Table 1: Entries
17–20). Therefore, a temperature of 50 °C was selected as
the optimum temperature for the model reaction. The effect
of the amount of catalyst (Table 1: Entries 13, 14) on the
percent yield was also studied. An amount of 0.0077 mmol
of PdNps was found to be optimum. Moreover, the opti-
mized reaction conditions for DHOC-PdNps were com-
pared to those of conventional low-yield Pd catalysts such
as palladium acetate and Tetrakis (triphenylphosphine)-
palladium(0) (Table 1: Entries 21, 22). Therefore, the
optimized reaction conditions of the model reaction [sol-
vent, Water:DMF (1:1); base, Na2CO3;temperature,
50 °C;amount of PdNps,0.0077 mmol] were used in all
Suzuki cross-coupling reactions. As shown in Table 2, all
of the aryl halides gave the desired cross-coupled products
with a good to excellent yield.
Fig. 1 UV-Visible spectra of DHOC-PdNps shows the absence of the
broad peak at 400 nm
5.2 Sonogashira Reaction
Sonogashira reactions are very useful in the synthesis of
natural products such as enediyne antibiotics. Although
copper (I) has been most commonly used as the co-catalyst,
a few Cu-free preparations have been successively devel-
oped. These preparations, however, require the use of
ultrasound or microwave irradiation techniques. Our cata-
lyst alone is sufficient for the Sonogashira reaction. The
same optimization procedure as described for the Suzuki
reaction was adopted for the Sonogashira reaction. Like-
wise, the use of a mixture of NMP:Water (1:1) and Na2CO3
proved to be superior to the other solvents and bases.
Consequently, the optimized reaction conditions of the
model reaction [solvent, NMP:Water (1:1); base, Na2CO3;
temperature, 60 °C and amount of PdNps (0.0077 mmol)]
were used in the Sonogashira reactions. As shown in
Table 3, all of the aryl halides gave the preferred products
with a good to excellent yield.
Fig. 2 Photograph showing a palladium acetate and b DHOC-PdNps
5
2 nm (Fig. 5). Also, Crystalline nature of palladium
nanoparticles is confirmed by the SAED pattern, which
exhibits four diffused rings which are assigned to (111),
(200), (220) and (311) reflections of fcc Pd (Fig. 6) [43].
The DHOC-PdNps was isolated in the solid state for
Powder X-ray Diffraction (PXRD) analysis (Fig. 7). The as
prepared nanoparticles were confirmed to be metallic giv-
ing the expected fcc Pd pattern. The peaks were assigned to
diffraction from the (111), (200) and (220) planes of fcc
palladium (0) lattice respectively [44]. After obtaining
proper characteristics for PdNps, we show its utility for
different catalytic reactions such as Suzuki, Heck and
Sonogashira in the present study.
5.3 Heck Reaction
The vinylation of aryl halides is known as the Heck reac-
tion. As described for the Suzuki and Sonogashira reac-
tions, the conditions for the Heck reaction were also
optimized, and as observed for the Suzuki and Sonogashira
123

Synthesis of Water-Dispersible Pd Nanoparticles Using a Novel Oxacalixarene Derivative and…
Fig. 3 Zeta potential of
DHOC-PdNps
Fig. 4 TEM (5 nm Scale-bar)
and HRTEM (1 nm Scale-bar)
of synthesized DHOC-PdNps
Fig. 5 Histogram showing particle size distribution
Fig. 6 SAED pattern of crystalline PdNps
123

V. Mehta et al.
reactions, the mixture of NMP:Water (1:1) and Na2CO3
yielded better results than did other solvents and bases.
Therefore, the optimized reaction conditions of the model
reaction [solvent, NMP:Water (1:1);base, Na2CO3;tem-
perature, 60 °C and amount of PdNps (0.0077 mmol)]
were used in the Heck reactions. As shown in Table 4, all
of the aryl halides gave the preferred products with a good
to excellent yield.
6 Recyclability
The recyclability of the prepared PdNps was assessed for
all C–C coupling reactions under optimized reaction con-
ditions. The reaction mixture was centrifuged for 15 min at
3000 rpm. The separated DHOC-PdNps were washed with
the appropriate mixture of organic solvents and water and
the recovered catalyst was dried overnight at 60 °C. The
Fig. 7 PXRD pattern of DHOC-PdNps
Fig. 8 Recyclability of PdNps in all C–C reactions
123

Synthesis of Water-Dispersible Pd Nanoparticles Using a Novel Oxacalixarene Derivative and…
9. Narayanan R, El-Sayed MA (2005) FTIR study of the mode of
binding of the reactants on the Pd nanoparticle surface during the
catalyst was used without any further activation for five
cycles, with only a minor loss of effectiveness (Fig. 8).
Thus, the DHOC-PdNps can be reused efficiently in all C–
C coupling reactions for at least five cycles. The reaction
mixture was subjected to ICP-AES to check the leaching of
PdNps from the catalyst with the successful result indi-
cating the absence of leaching from the catalyst.
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7 Conclusion
We have synthesized a novel dihydrazide derivative of
oxacalixarene and have successfully shown that the DHOC
derivative can be employed to prepare DHOC-PdNps in
water. DHOC worked as both a reducing and a stabilizing
agent, thus making it more efficient than other methods.
TEM analysis showed the nanoparticles to be 5 2 nm.
Furthermore, the particles showed good stability and
demonstrated astonishing catalytic activities for various C–
C coupling reactions of aryl halides such as the Suzuki,
Heck and Sonogashira reactions.
16. Nasrollahzadeh
M et al (2015) Preparation of palladium
We are presently looking forward to exploiting the
utility of these nanoparticles in biological applications.
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Acknowledgments The authors thank the financial assistance pro-
vided by DRDO (New Delhi) and University Grant Commission-
Basic Scientific Research (UGC-BSR) New Delhi. The authors also
acknowledge Gujarat Forensic Science University, Gandhinagar
(GFSU), Central Salt and Marine Chemicals Research Institute,
Bhavnagar (CSMCRI), Central University of Gujarat-Gandhinagar
(CUG), National Facility for Drug Centre Discovery-Rajkot (NFDD),
Oxygen Healthcare-Ahmedabad (O2 h) for providing instrumental
facilities, and UGC-Info net & INFLIBNET for e-journals.
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