Metallosurfactant based Pd-Ni alloy nanoparticles as a proficient catalyst in the Mizoroki Heck coupling reaction

Article abstract of DOI:10.1039/c7gc03877a

A highly efficient, operationally simple and green catalytic approach involving Pd-Ni alloy nanoparticles (NPs) has been developed using microwaves (MWs) as an energy source and water-ethanol as a solvent system. Metallosurfactants were synthesized and used as precursors to fabricate Pd-Ni alloy NPs with a good control over the size and morphology. Surfactant capped zerovalent Pd-Ni alloy NPs were fabricated in the metallomicellar cores by a two-phase reduction method. The synthesized NPs exhibited the highest catalytic efficiency for the stereoselective Mizoroki Heck coupling featuring short reaction time, mild reaction conditions, wide substrate scope, preclusion of toxic organic solvents, easy recovery and recyclability of the catalyst.

Full text of DOI:10.1039/c7gc03877a

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Metallosurfactant based Pd-Ni Alloy Nanoparticles as proficient catalyst in Mizoroki Heck
Coupling Reaction
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Navneet Kaur1, Gurpreet Kaur1, Aman Bhalla1, Jaspreet S. Dhau2 and Ganga Ram Chaudhary1, *
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1Department of Chemistry & Centre for Advanced Studies in Chemistry, Panjab University,
Chandigarhꢀ160014, India
2Florida Polytechnic University, Lakelandꢀ33805, Florida, USA
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*Corresponding author.
Tel.: +91ꢀ172 2534406; Fax: +91ꢀ172ꢀ2545074
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Eꢀmail address: grc22@pu.ac.in (Ganga Ram Chaudhary)
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Abstract
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A highly efficient, operationally simple and green catalytic approach involving PdꢀNi alloy
nanoparticles (NPs) has been developed using microwaves (MW) as an energy source and waterꢀ
ethanol as a solvent system. Metallosurfactants were synthesized and used as precursors to
fabricate PdꢀNi alloy NPs with a good control over the size and morphology. Surfactant capped
zerovalent PdꢀNi alloy NPs were fabricated in the metallomicellar cores by a twoꢀphase
reduction method. The synthesized NPs exhibited the highest catalytic efficiency for the
stereoselective Mizoroki Heck coupling featuring short reaction time, mild reaction conditions,
wide substrate scope, preclusion of toxic organic solvents, easy recovery and recyclability of the
catalyst.
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Keywords: PdꢀNi alloy nanoparticles, Mizoroki Heck coupling, Microwave, Green chemistry
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1. Introduction
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Catalysis is a useful tool in the area of synthetic chemistry for performing classical
reactions under milder conditions with dramatically enhanced yields in lesser reaction times.1 In
the present era, where every catalytic approach is critically examined in terms of activity and
selectivity, the environmentꢀfriendly aspect is much more emphasized due to global
environmental concerns.2 Thus, the quest for a cleaner, simpler and greener approach has
underscored the need for developing sustainable and environmentꢀfriendly strategies.3 The
search for such catalytic systems has led to the advent of nanocatalysts, which amalgamate the
superior selectivity of homogeneous catalysts with the recyclability of heterogeneous catalysts.4ꢀ6
The distinct properties exhibited by nanoparticles (NPs) over their bulk analogues are mainly
attributed to quantum effects and surface effects, i.e. smaller particle size leads to a larger surface
area to volume ratios providing more number of active atoms on the surface.7ꢀ9 Out of various
classes of nanomaterials, bimetallic NPs owing to their diverse applications have attracted many
scientists as they not only promise bifunctional performance of the two constituting metals but
also impart additional properties such as strength, functionality, and stability.10ꢀ14 These smartly
engineered nanomaterials with a remarkable catalytic activity empower synthetic chemists to
switch from previously existing protocols to achieve desired goals while addressing economic
and environmental challenges.15ꢀ16
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The catalytic significance of a cheaper transition metal elements in a number of organic
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syntheses
has prompted scientists to develop costꢀeffective systems that combine their
excellent catalytic properties with another noble metals, such as palladium (Pd), for applications
in sensor design,19 fuel cells,20 catalysis,21 and electrocatalysis.22 Owing to its higher efficiency
and selectivity as a catalyst, Pd is majorly known for its utility in organic syntheses particularly
in CꢀC bond formations, e.g. Mizoroki Heck Coupling and SuzukiꢀMiyaura Coupling reactions,23
which received acknowledgment as Noble Prize award (2010) in chemistry. The earlier reports
for Pdꢀbased homogeneous catalysis 24ꢀ26 suffered from a number of drawbacks such as toxicity,
high cost, and product contamination. These drawbacks paved the way to the application of Pdꢀ
based NPs as they performed equally well in environmentꢀfriendly constraints with no significant
metal leaching.27ꢀ30 Bimetallic NPs are of great significance among all the Pdꢀbased catalysts as
they account for high catalytic activity with lesser Pd content.31ꢀ34
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Keeping in view the industrial significance of Mizoroki Heck coupling, the present work
was intended to develop a new catalytic system comprising of PdꢀNi alloy NPs that not only
ensure the synergistic effect of two constituting metals but also redresses the economic and
environmental issues. The asꢀfabricated catalytic system addresses all the challenges of current
solution based coꢀreduction methods of synthesis, i.e. size and growth control etc. Instead of
using simple metal salts as precursors and surfactants, PdꢀNi alloy NPs have been synthesized
following twoꢀphase reduction of mixed reverse metallomicelles formed from Pd and Ni
metallosurfactants (complex 1 and 2) which resulted in NPs with good control over size and
morphology. The asꢀsynthesized catalyst was critically screened for its efficiency in conditions
fitting the Green Chemistry frame. The green chemistry principles primarily account for the
promotion of aqueous reaction media, preclusion of toxic conventional organic solvents and
incorporation of efficient energy input sources.35ꢀ39 The efficiency of MW over traditional oilꢀ
bath heating40 prompted us to perform the wellꢀexploited Mizoroki Heck coupling reaction with
PdꢀNi NPs as catalysts under microwave (MW) conditions in the environmentally benign
aqueous solvent system (water/ethanol) and to the best of our knowledge, no report has been
listed in the literature using PdꢀNi alloy NPs under the aforementioned conditions for Mizoroki
Heck coupling.
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2. Experimental Section
2.1.
Chemicals
Palladium(II) Chloride (99%), dodecylamine (98.6%), nickel(II) chloride (99%), sodium
borohydride, NaBH4 (99%) and haloarenes (99%) were purchased from SigmaꢀAldrich. Styrene
(99%) was purchased from TCI and absolute ethanol (99.9%) was purchased from Changshu
Yuang. Dimethylformamide (DMF) was dried with matrix molecular sieves 5 Å, 30−40 mesh
supplied by SigmaꢀAldrich. Dichloromethane (DCM), potassium carbonate (K2CO3), sodium
carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium bicarbonate (KHCO3), sodium
hydroxide (NaOH) and potassium hydroxide (KOH) were purchased from Fischer Scientific and
all the aqueous solutions were prepared with double distilled water.
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2.2.
Instrumentation
The Xꢀray diffraction (XRD) spectra were recorded on a Panalytical X’Pert Pro Xꢀray
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diffractometer equipped with CuꢀKα radiation (1.5406 Å) operating at 40 kV, with a scanning
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speed of 8°/min to examine the crystalline phase of NPs. UVꢀVisible spectra were recorded with
Evolution 160 UVꢀVis operated in the range 200ꢀ800 nm using quartz cuvettes of path length 1
cm. Infrared (IR) spectroscopic studies were carried out using Perkin ElmerꢀFTIR Spectrumꢀ100
operated in spectral domain of 400 to 4000 cmꢀ1. High resolution transmission electron
microscopy (HRTEM) studies were performed on FP 5022/22ꢀTecnai G2 20 SꢀTWIN operated
at an accelerating voltage of 200 kV. Field emission scanning electron microscopy (FESEM) was
executed on Hitachi (SU8010) operated at an accelerating voltage of 15.0 kV. The chemical
composition of the synthesized NPs was confirmed by energy dispersive Xꢀray spectroscopy
(EDX) along with mapping using Philips XL 30 EDS unit. Xꢀray photoelectron spectroscopy
(XPS) was performed on ESCA+, (omicron nanotechnology, Oxford Instrument Germany)
equipped with monochromator aluminum source (Al kα radiation hν = 1486.7 eV). The
instrument was operated at 15 kV and 20mA. Samples in powder form were deposited on Cu
tape and degassed for overnight in XPS FEL chamber to minimize the air contamination at
sample surface as well as in the main chamber. To overcome the charging problem a charge
neutralizer of 2 keV was applied and binding energy of C1s core (284.6eV) was taken as
reference. The atomic weight % of Pd in the optimized catalytic dose was assessed by ICPꢀAES
analysis performed on ICPꢀOES Varian 720ꢀES. ICPꢀMS analyses were done on ICPꢀMS
Agilent 7800 to know the leached Pd concentration. The Mizoroki Heck coupling reactions were
performed on the commercial microwave, Multiwave Pro by Anton Paar equipped with infrared
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temperature control system in sealed tubes. H and 13C NMR spectra were measured on a model
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advance II (Bruker) instrument with a frequency 400 MHz for H NMR and a frequency of 100
MHz frequency for 13C NMR using TMS as the internal standard and chloroform (CDCl3) as the
solvent.
2.3.
Synthesis of Pd and Ni precursors
Metallosurfactants, bisdodecylamine palladium (II) chloride (complex 1) and bisdodecylamine
nickel (II) chloride (complex 2) were used as precursors of Pd and Ni (NPs), respectively and
were synthesized by ligand insertion method as per the synthesis earlier reported by our group.42ꢀ
43 For complex 1, palladium chloride salt and the ligand, dodecylamine (C12H25NH2) were taken
o
in 1:2 ratio and heated at 60 C using dry N,Nꢀdimethylformamide (DMF) as a solvent under
vigorous stirring for 3 h. The double chained metallosurfactant (complex 1) thus formed was
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recrystallized using ethanol (EtOH) and vacuum dried before further use. Similarly, complex 2
was synthesized using nickel chloride salt under aboveꢀmentioned conditions (Scheme 1, ESI).
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2.4.
Synthesis of Pd-Ni NPs
Equimolar solutions (0.4 mM) of each of Pd and Ni precursors were prepared separately in a
given volume (10 mL) of dichloromethane (DCM) and were mixed well by stirring to give a
uniform solution (S). The metallosurfactant solutions were prepared above their critical micelle
concentration (CMC). This ensured the formation of reverse micelles in the presence of an
organic medium in which metal heads were present in the micellar core in +2 oxidation state.
These metal ions were then reduced by following a twoꢀphase redox methodology. An aqueous
solution of sodium borohydride (40 mM, 40 mL) was freshly prepared and added instantaneously
to the solution, S. High reductant to the metallosurfactant molar ratio (20:1) resulted in an
immediate reduction of metal ions in +2 oxidation state to a zerovalent metallic state. The black
coloured NPs thus formed in the organic phase was separated using a separatory funnel and
vacuumꢀdried further.
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2.5.
Catalytic application of Pd-Ni NPs in Mizoroki Heck coupling reaction
In a typical experiment, styrene (1 mmol), haloarene (1 mmol), base (1.5 mmol), solvent (2 mL)
and catalyst (10 mg, 0.35 mol% Pd) were sealed in a tube and subjected to MW at 300 W (120
⁰C) (Scheme 1). The different batch experiments were performed in sealed tubes for fixed run
time and progress of the reaction in each batch was monitored by thin layer chromatography
(TLC). The comparison of TLC plates of reaction mixture for each run time gave idea about the
time of reaction completion. It is to be noted that the runꢀtime for each batch reaction includes
the heat up and hold times in MW after which the MW are shut off and the reaction cooled to
room temperature from same target temperature in all the runs. Once the reaction was over, the
catalyst was separated from the reaction mixture by centrifugation followed by dilution of
remaining solution with water. The product was extracted with diethyl ether and dried over
sodium sulfate (Na2SO4). After ether evaporation, recrystallization of product was done in
ethanol. The reaction conditions were optimized by varying different factors such as solvent,
base and catalyst amount to find out the best combination that leads to faster reaction with good
product yield.
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X
Pd-Ni NPs,
120 oC , K2CO3
+
H2O/EtOH
R
R
1
2
3
Scheme 1: Mizoroki Heck coupling reaction between styrene and haloarenes under MW
conditions (300 W, 120 ⁰C).
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3. Results and Discussion
3.1. Synthesis and characterization of Pd-Ni NPs
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The complex 1 and 2 which are double chained metallosurfactants of Pd and Ni form reverse
micelles in DCM. The strong solvophilic interactions between hydrocarbon tails of
metallosurfactant and organic solvent push the metal heads in core whereas the hydrocarbon tails
are present as shell.41ꢀ42 The metal ions present in the core of micelles were subsequently reduced
to form zerovalent metal atoms by using NaBH4 as a reducing agent. The use of a strong
reducing agent causes instantaneous reduction of both metal ions present in the micellar core. It
is proposed that both metals nucleate in a restricted core size where one metal diffuses into the
lattice of another forming an alloy structure. The growth of nuclei, thus formed, is controlled by
the surfactant chains (dodecylamine), present in precursor molecules, which subsequently get
physically adsorbed on the NPs surface (Fig. S1, ESI).
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The alloy structure was elucidated by characterization of asꢀsynthesized PdꢀNi NPs.
The UVꢀVis spectra of complex 1, 2 and PdꢀNi NPs (recorded in DCM) are given in Fig. S2(a)
(ESI). It can be seen that the characteristic absorption peaks of complex 1 and 2 were completely
absent in the broad continuous absorption spectrum of PdꢀNi NPs confirming a complete
reduction of bivalent metal ions to zerovalent nanoalloys.41ꢀ42
TEM reveals well dispersed PdꢀNi NPs of spherical shape with average 5 nm (Fig. 1(a)).
The different contrast in HRTEM image confirmed the formation of bimetallic NPs. The dꢀ
spacing between lattice planes is found to be 2.11 Å, which is consistent with the alloy structure
of PdꢀNi NPs (Fig. S2(b), ESI).43 XRD pattern of PdꢀNi NPs shows a broad peak at 2θ = 41.8⁰,
which is placed in between the peaks corresponding to (111) plane of pure Pd (40.1⁰) and Ni
(44.4⁰). The shift in peak position suggested that Ni has entered the lattice structure of Pd (Fig.
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1(b)) thereby confirming the formation PdꢀNi alloy NPs. The only prominent diffraction peak
corresponding to (111) suggests anisotropic growth of NPs along (111) direction.44 The EDX
spectrum of the sample showed that the synthesized NPs contained Pd and Ni in almost 1:1
atomic ratio and were free of impurities (Fig. S2(c), ESI). FESEM was performed to gain insight
into the morphology of the synthesized NPs. The image, (Fig. 1(c)), reveals a nearly spherical
morphology of NPs with a slight agglomeration with a particle size in the range of 10ꢀ15 nm.
Elemental maps of the region selected from FESEM images, highlighting Pd and Ni metals with
different colours, indicate the homogeneous distribution of metals thereby supporting the alloy
nature of the synthesized NPs (Fig. S3, ESI).
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Further, stabilization of NPs by surfactant, dodecylamine, was confirmed by FTIR
spectroscopy. FTIR spectrum of surfactant stabilized NPs shows a significant shift in ꢀNH
stretching frequencies as compared to that of a pure dodecylamine (Fig. 1(d)). Compared to pure
dodecylamine, the NH asymmetric stretching vibrations in dodecylamine stabilized NPs show a
frequency shift of 21 cmꢀ1 and are observed at 3317 cmꢀ1. The NH symmetric stretching band
also shifts from 3182 cmꢀ1 to 3084 cmꢀ1. This is attributed to the surface adsorption of
dodecylamine on NPs through –NH2 group resulting in shift of stretching bands to lower
frequencies.
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Fig. 1: (a) TEM image (b) XRD pattern (c) FESEM image and (d) FTIR spectrum of PdꢀNi NPs
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To further know the surface electronic structure, XPS analysis was done for asꢀ
synthesized NPs. The spectra exhibit signals corresponding to binding energies (BE) of Pd, Ni, N
and C marking their presence on NP surface. Narrow Pd 3d region shows two peaks at 335.8 eV
and 341.2 eV for Pd 3d5/2 and 3d3/2, respectively (Fig. 2(a)). These signals for Pd in PdꢀNi alloy
NPs are found to be shifted to higher BE values as compared to pure Pd signals (335.2 eV and
340.5 eV) indicating the modified electronic structure of Pd in alloyed state. Alloying of Pd and
Ni causes the down shift of Pd’s dꢀband centre with respect to Fermi level causing higher BE
values. The two peaks observed at 853.3 eV and 870.4 eV correspond to Ni 2p3/2 and 2p1/2 states,
respectively (Fig. 2(b)).45 The small satellite peaks (at ~6 eV and 3eV) may be due to small % of
surface oxidized Ni.46 The BE peaks at 399.5 eV and 285.0 eV (Fig. 2(c) and 2(d)) correspond to
N 1s and C 1s present in dodecylamine moieties attached to surface of NPs.47
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Fig. 2 XPS regions for (a) Pd (b) Ni (c) N (d) C.
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3.2.
Catalytic application of Pd-Ni NPs in Mizoroki Heck coupling reaction
The model reaction between styrene and iodobenzene was performed with different solvents
using K2CO3 as a model base. Figure 3(a) shows results from the aforementioned reaction
performed in different solvents (H2O, EtOH, EtOHꢀH2O mixture, DMF, DCM) and solventꢀfree
condition. Solvent screening showed that in MW conditions waterꢀethanol solvent mixture is as
competent as the organic solvent DMF. Despite the low solubility of substrates in water, the
exceptional performance of this greener water based solvent mixture can be attributed to its
microwave absorption efficiency together with EtOH as a coꢀsolvent that resolves the solubility
issues of substrates. The waterꢀEtOH mixture having a higher microwave absorptivity (measured
as tan δ value) in combination, leads to an efficient conversion of MW into heat.48 Apart from
the environmentꢀfriendly aspect of waterꢀEtOH solvent mixture, the ease of product separation
from the solvent mixture at ambient temperature advocates the use of waterꢀEtOH mixture over
conventional organic solvents such as DMF.
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The ionic nature of a base in a solvent system adds to the MW absorbing capacity of the
system. Therefore, we tried Mizoroki Heck coupling reaction in a waterꢀEtOH solvent system
and in the presence of different bases (K2CO3, Na2CO3, NaHCO3, KHCO3, NaOH and KOH). It
was found that K2CO3 works best in terms of both yield and cost effectiveness (Fig. 3(b)).
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Reaction conditions: Styrene (1 mmol), Iodobenzene (1 mmol), catalyst (10 mg, 0.35 mol% Pd), Microwave
(300 W), Temperature 120 oC, 10 mins.
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Fig. 3: Effect of (a) solvent in presence of K2CO3 (1.5 mmol) as base (b) base in Water/EtOH 6:4
(2 ml) as solvent on coupling reaction between styrene and iodobenzene.
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On the basis of aboveꢀoptimized conditions, the coupling reaction performed with MW,
was analyzed for reaction time and catalyst dose optimization (Fig. 4). Figure 4(a) shows the
effect of reaction time on % yield of the product in subsequent experiments under MW
conditions. It is to be noted that separate experiments were performed for fixed times and as
monitored by TLC, the reaction was complete in 8 minutes with 87% yield, with no significant
increase in the yield on increasing the reaction time. The catalyst amount was optimized by
performing the reaction with different amount of catalyst. No reaction occurred in the absence
of catalyst, however, the product yield increased significantly with increase in the amount of
catalyst till 8 mg (Fig. 4(b)). A further increase in the catalyst amount did not show any
significant change in the product yield. Hence, the optimum amount of the synthesized catalyst
(PdꢀNi NPs) was fixed at 8 mg (7.76 wt% and 0.28 mol% Pd). The performance of the catalyst
was also assessed using conventional heating source under sealed conditions and the results, in
terms of % yield of product, are depicted in Fig. 5.
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Reaction conditions: Styrene (1 mmol), Iodobenzene (1 mmol), K2CO3 (1.5 mmol), Water/EtOH 6:4 (2 ml),
MW, sealed tubes, Temperature 120 oC.
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Fig. 4: Effect of (a) different run times of reaction at fixed catalyst dose (10 mg) and (b)
catalyst amount on % yield of coupling product.
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Reaction conditions: Styrene (1 mmol), Iodobenzene (1 mmol), K2CO3 (1.5 mmol), Water/EtOH 6:4 (2 ml),
conventional oil bath heating conditions, sealed tubes, 120 oC.
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Fig. 5: % Yield of coupling product for different run times under sealed tube conditions with
conventional heating source.
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It is not possible to clearly compare the catalysts’ performance under two energy sources since
the temperature profile and reaction conditions achieved in either case were not exactly
identical. The reason for such difference in temperature profiles of reaction performed under
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conventional heating and MW lies in the mechanisms of heat transfer. While the reaction
system achieves the desired temperature through conductionꢀconvection mechanism in
conventional heating source, the heat transfer mechanism in MW is based on radiative losses on
account of rotationalꢀvibrational motion of molecules. It is noteworthy that NPs also add to the
microwave absorbing capacity of the catalytic system which is evident through the temperature
profiles of blank solvent system and system containing NPs (Fig. S4, ESI) that in presence of
NPs, the temperature is achieved faster. The superficially heated catalytic surfaces add to
efficiency of heterogeneous catalytic system49 comprising of NPs when employed in
concomitance with MW, which is an operationally easier method to achieve desired temperature
conditions in shorter times.
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Next, we checked the catalytic system for its substrate scope. Table 1 shows the % yield
of the crossꢀcoupled products of alkene sources (styrene and ethyl acrylate) with various
substituted aryl halides (scheme 2).
X
Pd-Ni NPs,
Z
MW
+
Z
H2O/EtOH
R
R
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X= I, Br, Cl ; R = H, 4ꢀOCH2, 4ꢀNO2, 4ꢀCN, 4ꢀCOCH3 ; Z = Ph (styrene), COOCH2CH3 (ethyl acrylate)
Scheme 2: Mizoroki Heck coupling between alkenes and substituted aryl halides
Table 1: Mizoroki Heck crossꢀcoupling reaction between alkene and different substituted aryl
halides. *
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S. No.
Z
X
R
Yield
(%)a
88
85
85
86
84
82
83
1.
2.
3.
4.
5.
6.
7.
8.
Ph
Ph
Ph
Ph
Ph
Ph
Ph
I
H
H
Br
Br
Br
Br
Cl
Cl
Cl
I
pꢀOCH3
pꢀNO2
pꢀCN
H
pꢀNO2
pꢀCOCH3
H
Ph
81
87
COOCH2CH3
9.
COOCH2CH3
COOCH2CH3
COOCH2CH3
COOCH2CH3
10.
11.
12.
13.
Br
Br
Br
Br
H
86
84
85
85
pꢀOCH3
pꢀNO2
pꢀCN
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COOCH2CH3
COOCH2CH3
COOCH2CH3
14.
15.
16.
Cl
Cl
Cl
H
pꢀNO2
pꢀCOCH3
82
83
80
1
2
*Reaction conditions: Styrene/ Ethyl acrylate (1 mmol), aryl halide (1 mmol), K2CO3 (1.5 mmol), Water/EtOH 6:4
(2 ml), Microwave (300 W), Temperature 120 oC, 10 mins, a Yield of isolated product
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Further, the catalyst (PdꢀNi NPs) was checked for its recyclability by recovering it
through centrifugation. The recovered catalyst was washed with ether followed by drying in air.
The catalytic performance in the coupling reaction between styrene and different aryl halides viz
iodobenzene, bromobenzene and chlorobenzene, was checked for five consecutive cycles. It is
clearly visible from fig. 6 that the catalyst maintains its activity in all the cases and gave fairly
good product yields for five consecutive cycles.
5
6
7
8
9
10
11
Fig. 6: Catalytic efficiency of PdꢀNi NPs after four consecutive cycles.
12
13
14
15
16
17
18
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20
21
22
The excellent recyclability of the PdꢀNi catalyst was attributed to its chemical stability as
demonstrated through leaching experiments. ICPꢀMS analysis of the reaction mixture showed
minimal leaching of active Pd species from catalyst (3.38 ppb). Since there is no significant loss
of active species from NPs, the chemical structure and activity is maintained in subsequent
cycles. This is affirmed by XRD analysis of NPs recovered after the fourth cycle (Fig. S5, ESI)
which does not show any significant change.
In order to further rule out the possibility of catalysis by leached Pd, hot filtration test was
performed. In a typical experiment, reaction mixture containing styrene (1 mmol) and
iodobenzene (1 mmol) in presence of K2CO3 (1.5 mmol) was subjected to MW for 8 mins till the
reaction completion after which the hot reaction mixture was filtered to remove any solid
catalyst. The filtrate devoid of any solid catalyst (having leached Pd) was charged again with 1
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mmol each of styrene and iodobenzene along with K2CO3 (1.5 mmol) and was subjected to MW
under similar reaction conditions. The addition of reactants to the system in the absence of PdꢀNi
NPs did not show any conversion to the product. We also carried out the reaction in the solvent
recovered after complete extraction of the products from the previous batch and no product
formation was observed. These results suggest that the achieved catalytic performance is not due
to leached Pd but is purely attributed to the presence of PdꢀNi NPs.
3
4
5
6
7
3.3.
Regio and stereoselectivity
8
The plausible mechanism of the reaction between the reactants on NP surface is general heck
type mechanism. The catalytic system facilitates the regioselective intramolecular arylation of
electron deficient olefin by different substituted aryl halides (scheme 3) to give exclusive
stereoselective product i.e. trans- substituted alkenes (verified through the coupling constants
data, section S1, ESI). The electronic and stearic factors govern the 2, 1ꢀinsertion of olefin (step
C, Fig. S6, ESI) resulting in the stereoꢀ and regioselectivity of the products which is in
accordance with the literature reports.50ꢀ51 The remarkable catalytic behaviour of the bimetallic
system could be attributed to two facts. First, the synergistic effect of two metals, Ni and Pd
belonging to the same group. The intermetallic interactions of Ni having higher oxidation
potential (+0.25V) with Pd (ꢀ0.915V) increase the nucleophilicity at Pd sites of NP that
accelerated the oxidative addition. Second, apart from the wellꢀestablished active Pd(0) sites in
NP, Ni(0) sites can also actively add aryl halide oxidizing to Ni(+2) in a similar way in coꢀ
operation with Pd sites which is well documented in literature.52
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
3.4.
Role of surfactant coating in catalytic activity of NPs
It is noteworthy that surfactant coating on NPs plays a significant role in their catalytic activity in
Mizoroki Heck coupling reaction. In order to establish the assertion, the model coupling reaction
between styrene and iodobenzene was performed with PdꢀNi NPs without surfactant. The
surfactant coating on the NPs was removed by calcination at 150 ⁰C for 2 hours. The IR
spectrum of the calcined NPs showed no signal corresponding to dodecylamine affirming that
the NPs were devoid of surfactant coating (Fig. S7(a), ESI). It was observed that without
surfactant coating, the catalytic activity was decreased (60% yield) in comparison to surfactant
capped NPs (86% yield). This decrease in catalytic activity on the removal of surfactant coating
is attributed to the aggregation of NPs in the absence of surfactant coating which decreases the
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overall active surface area for the reaction to take place (Fig. S7(b), ESI). It is also noteworthy
that removal of surfactant leads to oxidation of Ni present on the surface. The presence of oxide
layer (Ni) is evidenced from XRD and EDS patterns of calcined NPs (without surfactant coating
(Fig. S7(c) and (d), ESI). Also, the leaching experiments showed comparatively greater loss of
active Pd species during the reaction in case of calcined NPs (3.31 ppm) as compared to NPs
having surfactant coating (<1 ppm). These observations suggest that the alkyl chains of
surfactant, provides chemical stability to NPs apart from ensuring facile diffusion of
hydrophobic reactants from water based reaction medium to active metallic sites of NPs.
9
3.5.
Comparison of present catalytic system with literature reports
10
To check the superiority of the present catalytic system, we tested the Mizoroki Heck
11 coupling reaction with different Pd sources that were reported in the literature and also with
12 monometallic Pd and Ni NPs synthesized via same protocol as PdꢀNi alloy NPs. The results have
13 been summarized in Table 2 and it is clearly evident that the present catalytic system is a better
14 approach for Mizoroki Heck coupling in terms of catalyst fabrication, energyꢀtime consumption,
15 environmentꢀfriendly and economic aspect as PdꢀNi alloy NPs carrying lesser content of noble Pd
16 element as compared to pure monometallic Pd NPs, performed comparably well.
17
Table 2: Comparison of present catalytic system with literature
S. No.
1.
Catalyst
Energy
source
Solvent
DMF
DMF
DMF
H2O
Time Yield (%) Reference
PdꢀNi (1:1) NPs Conventional
heating
PdꢀFe3O4 NPs
24 hr
24 hr
20 hr
6 hr
82
91
96
92
95
22
91
[43]
[53]
[54]
[55]
[56]
[57]
[57]
Conventional
heating
Conventional
heating
2.
PdꢀCuO NPs
3.
PdꢀMesoporous Conventional
Organic Polymer
PdꢀZnO NPs
4.
heating
Conventional
heating
H2O
17 hr
18 hr
18 hr
20 min
5.
PdꢀNi (1:1) NPs Conventional
heating
PdꢀCu (4:1) NPs Conventional
heating
Pd thin films
Pd NPs
MeOH
MeOH
DMF
6.
7.
MW
MW
MW
80
86
76
[58]
8.
9.
10.
Water/EtOH 12 min
Water/EtOH 40 min
Present work
Present work
Ni NPs
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11.
Pd-Ni (1:1) NPs
Conclusion
MW
Water/EtOH 8 min
88
Present work
1
2
3
4
4.
5
In conclusion, a facile solutionꢀbased oneꢀpot method has been successfully developed for
6
the synthesis of PdꢀNi alloy NPs ensuring control over growth and size of nanoparticles by using
metallosurfactants. The asꢀsynthesized NPs have been found to show remarkable catalytic
activity in Mizoroki Heck coupling reaction under MW conditions and waterꢀEtOH as the green
solvent system. Role of surfactant capping has been established and is found to impart stability to
the catalyst to show sustained and enhanced activity over repeated catalytic cycles. Factors such
as simple synthetic procedure, wide substrate scope, easy recovery of final products, milder
reaction conditions, regio/stereoselectivity, preclusion of toxic reagents advocate for the
applicability of present catalytic system in CꢀC coupling reactions as an efficient, economic and
environmentꢀfriendly process. The developed protocol for the synthesis of alloy nanoparticles
can be further extended in future for the synthesis of various nanoalloys with varied metal ratios,
shapes and morphologies to get desired applications viz. hydrogenation reactions, electrocatalysis
which are characteristics of metal catalysts.
7
8
9
10
11
12
13
14
15
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19
20
21
22
23
24
Acknowledgements
Ganga Ram Chaudhary and Jaspreet Dhau would like to acknowledge the support of UGC, India
under INDOꢀUS 21st Century Knowledge Initiative project [F.No. 194ꢀ2/2016 (IC)]. Gurpreet
Kaur is thankful to DST for Inspire Faculty award (IFAꢀ12ꢀCHꢀ41) and Navneet Kaur is thankful
to UGC, Delhi for the fellowships. This work is also supported by PURSE II grant.
5.
References
25 [1] C. W. Lim and I. S. Lee, Nano Today, 2010, 5, 412.
26 [2] Z. Li and R. J. Tong, J. Org. Chem., 2016, 81, 4847.
27 [3] M. L. Kantam, and K. S. R. Rao, Catalysis for sustainable development, J. Chem. Sci.,
28
2014, 126, 309.
17

Green Chemistry
Page 18 of 21
View Article Online
DOI: 10.1039/C7GC03877A
1
2
[4] R. Kardanpour, R. S. Tangestaninejad, V. Mirkhani, M. Moghadam, I. Mohammadpoorꢀ
Baltork, A.R. Khosropour and F. Zadehahmadi, J. Organomet. Chem., 2014, 761, 127.
[5] G. R. Chaudhary, P. Bansal and S. K. Mehta, Chem. Engg. J., 2014, 247, 217.
[6] P. Bansal, G. R. Chaudhary and S. K. Mehta, Chem. Engg. J., 2015, 280, 475.
[7] M. A. ElꢀSayed, Acc. Chem. Res., 2004, 37, 326.
3
4
5
6
[8] Z. D. Fu, Y. S. Cui, S. Y. Zhang, J. Chen, D. P. Yu, S. L. Zhang, L. Niu and J. Z. Jiang,
Appl. Phys. Lett., 2007, 90, 263113.
7
8
[9] E. Roduner, Chem. Soc. Rev., 2006, 35, 583.
9
[10] F. Saleem, Z. C. Zhang, B. Xu, X. B. Xu, P. L. He and X. Wang, J. Am. Chem. Soc., 2013,
135, 18304.
10
11 [11] S. Wang, M. Meng, A. Das, T. Li, Y. Song, T. Cao, X. Zhu, M. Zhu and R. Jin, Angew.
12 Chem. Int. Ed., 2014, 53, 2376.
13 [12] W. Chen, R. Yu, L. L. Li, A. N. Wang, Q. Peng and Y. D. Li, Angew. Chem. Int. Ed., 2010,
14 49, 2917.
15 [13] Y. Lu and W. Chen, ACS Catal., 2012, 2, 84.
16 [14] Y. Wu, S. Cai, D. Wang, W. He and Y. Li, J. Am. Chem. Soc., 2012, 134, 8975.
17 [15] C. J. Li and L. Chen, Chem. Soc. Rev., 2006, 35 (1), 68ꢀ82
18 [16] J. Shi, C. Long and A. Li, Chem. Engg. J., 2016, 286, 408.
19 [17] F. Alonso, P. Riente and M. Yus, Eur. J. Org. Chem., 2009, 34, 6034.
20 [18] W. Zhang, H. Qi, L. Li, X. Wang, J. Chen, K. Peng and Z. Wang, Green Chem., 2009,
21
22 [19] R. R. J. Maier, J. S. Barton, J. D. C. Jones, S. McCulloch, B. J. S. Jones and G. Burnell,
23 Meas. Sci. Technol., 2006, 17, 1118ꢀ1123.
24 [20] N. V. Long, C. M. Thi, Y. Yong, M. Nogami, and M. Ohtaki, J. Nanosci. Nanotechnol.,
25 2013, 13, 4799.
11(8), 1194.
26 [21] M. PerezꢀLorenzo, J. Phys. Chem. Lett., 2012, 3, 167.
27 [22] X. Zhang, J. Zhu, C. S. Tiwari, Z. Ma, H. Huang, J. Zhang, Z. Lu, W. Huang and Y. Wu,
28
ACS Appl. Mater. Interfaces, 2016, 8, 10858.
29 [23] L. Yin and J. Liebscher, Chem. Rev., 2007, 107, 133.
30 [24] A. Zapf and M. Beller, Topics in Catalysis, 2002, 19, 101.
31 [25] R. B. Bedford, C. S. J. Cazin and D. Holder, Coord. Chem. Rev., 2004, 248, 2283.
18

Page 19 of 21
Green Chemistry
View Article Online
DOI: 10.1039/C7GC03877A
1
2
3
4
5
6
7
8
9
[26] D.H. Valentine and J.H. Hillhouse, Synthesis, 2003, 2437.
[27] A. Balanta, C. Godard and C. Claver, Chem. Soc. Rev., 2011, 40, 4973.
[28] V. L. Budarin, J. H. Clark, R. Luque, D. J. Macquarrie and R. J. White, Green Chem.,
2008, 10, 382.
[29] A. V. Martínez, F. Invernizzi, A. LealꢀDuaso, J. A. Mayoral and J. I. García, RSC Adv.,
2015, 5, 10102.
[30] A. V. Martínez, A. LealꢀDuaso, J. I. García and J. A. Mayoral, RSC Adv., 2015, 5, 59983.
[31] N. Moghimi, M. Mohapatra and K. T. Leung, Anal. Chem., 2015, 87, 5546.
[32] W. T. Yu, M. G. Porosoff and J. G. Chen, Chem. Rev., 2012, 112, 5780.
10 [33] P. X. Xi, Y. Cao, F. C. Yang, C. Ma, F. J. Chen, S. Yu, S. Wang, Z. Z. Zeng and X. Zhang,
11 Nanoscale, 2013, 5, 6124.
12 [34] S. W. Kang, Y. W. Lee, Y. Park, B. S. Choi, J. W. Hong, K. H. Park and S. W. Han, ACS
13 Nano, 2013, 7, 7945.
14 [35] R. A. Sheldon, Green Chem., 2017, 19, 18.
15 [36] M. O. Simon and C. J. Li, Chem. Soc. Rev., 2012, 41 (4), 1415.
16 [37] J. Kothandaraman, A. Goeppert, M. Czaun, G. A. Olah and G. K. Surya Prakash, Green
17
Chem., 2016, 18, 5831.
18 [38] M. Francavilla, S. Intini, L. Luchetti and R. Luque, Green Chem., 2016, 18, 5971.
19 [39] A. H. Motagamwala, W. Won, C. T. Maraveliasa and J. A. Dumesic, Green Chem., 2016,
20
18, 5756.
21 [40] D. Gangrade, S. D. Lad and A. L. Mehta, Int. J. Res. Pharm. Sci., 2015, 5(2) , 37.
22 [41] G. R. Chaudhary, P. Singh, G. Kaur, S. K. Mehta, S. Kumar and N. Dilbaghi, Inorg.
23
24 [42] G. Kaur, P. Singh, S. K. Mehta, S. Kumar, N. Dilbaghi and G. R. Chaudhary, Appl. Surf.
25 Sci., 2017, 404, 254.
26 [43] L. Feng, H. Chong, P. Li, J. Xiang, F. Fu, S. Yang, H. Yu, H. Sheng and M. Zhu, J. Phys.
27 Chem. C, 2015, 119, 11511.
Chem., 2015, 54, 9002.
28 [44] G. De and C. N. R. Rao, J. Phys. Chem. B, 2003, 107, 13597.
29 [45] L. Chen, L. Lu, H. Zhu, Y. Chen, Y. Huang, Y. Li and L. Wang, Nature communications,
30
2017, 8.
19

Green Chemistry
Page 20 of 21
View Article Online
DOI: 10.1039/C7GC03877A
1
2
3
4
5
6
7
8
9
[46] L. T. M. Nguyen, H. Park, M. Banu, J. Y. Kim, D. H. Youn, G. Magesh, W. Y. Kim and J.
S. Lee, RSC Adv., 2015, 5, 105560.
[47] C. D. Wagner, A. V. Naumkin, A. KrautꢀVass, J.W. Allison, C. J. Powell and J. R. Jr.
Rumble, NIST Standard Reference Database 20, Version 3.4 (web version)
(http:/srdata.nist.gov/xps/) 2003.
[48] C. Gabriel, S. Gabriel, E. H. Grant, B. S. J. Halstead and D. M. P. Mingos, Chem. Soc.
Rev., 1998, 27, 213.
[49] A. F. Lee, P. J. Ellis, I. J. S. Fairlamb and K. Wilson, Dalton Trans., 2010, 39, 10473.
[50] A. Jutand, John Wiley & Sons, ISBN: 978ꢀ0ꢀ470ꢀ03394ꢀ4.
10 [51] K. Gheoghegan, Springer Theses, DOI 10.1007/978ꢀ3ꢀ319ꢀ10338ꢀ9_2.
11 [52] N. Nowrouzi and M. Zarei, Tetrahedron, 2015, 71, 7847.
12 [53] J. Chung, J. Kim, Y. Jang, S. Byun, T. Hyeon and B. M. Kim, Tetrahedron Lett., 2013, 54,
13
14 [54] M. Nasrollahzadeh, S. M. Sajadi, A. RostamiꢀVartooni and A. Azarian, Mater. Res. Bull.,
15 2015, 68, 150.
5192.
16 [55] J. Mondal, A. Modak and A. Bhaumik, J. Mol. Catal. A: Chem., 2011, 350, 40.
17 [56] M. HosseiniꢀSarvari, Z. Razmi and M. M. Doroodmand, Appl. Catal. A: Gen., 2014, 475,
18
477.
19 [57] F. Heshmatpour, R. Abazari and S. Balalaie, Tetrahedron, 2012, 68, 3001.
20 [58] G. Shore, S. Morin and M. G. Organ, Angew. Chem., 2006, 118, 2827.
21
22
20

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Graphical abstract