Synthesis of palladium nanoparticles using triazolium based ionic liquids: A reusable catalyst for addition of arylboronic acids to nitrostyrenes

Article abstract of DOI:10.1080/00397911.2018.1533971

Formation of stable and small-sized palladium nanoparticles of diameter 9.4 nm was accomplished by a simple heating of Pd(OAc)₂ in 1-octyl-1,2,4-triazolium trifluoroacetate ionic liquid under standard atmospheric hydrogen pressure. Palladium na

Full text of DOI:10.1080/00397911.2018.1533971

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
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ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Synthesis of palladium nanoparticles using
triazolium based ionic liquids: A reusable catalyst
for addition of arylboronic acids to nitrostyrenes
Kavya Sundararaju, VijayaKumar Veeraragavan & Ramesh Kumar
Chidambaram
To cite this article: Kavya Sundararaju, VijayaKumar Veeraragavan & Ramesh Kumar
Chidambaram (2018): Synthesis of palladium nanoparticles using triazolium based ionic liquids: A
reusable catalyst for addition of arylboronic acids to nitrostyrenes, Synthetic Communications, DOI:
10.1080/00397911.2018.1533971
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https://doi.org/10.1080/00397911.2018.1533971
Synthesis of palladium nanoparticles using triazolium
based ionic liquids: A reusable catalyst for addition
of arylboronic acids to nitrostyrenes
Kavya Sundararaju, VijayaKumar Veeraragavan, and Ramesh Kumar Chidambaram
Organic Chemistry Laboratory Department of Chemistry, Vel Tech Rangarajan Dr. Sagunthala R&D
Institute of Science and Technology, Avadi, Chennai, India
ABSTRACT
ARTICLE HISTORY
Received 23 April 2018
Formation of stable and small-sized palladium nanoparticles of diam-
eter 9.4 nm was accomplished by a simple heating of Pd(OAc)2 in 1-
octyl-1,2,4-triazolium trifluoroacetate ionic liquid under standard
atmospheric hydrogen pressure. Palladium nanoparticles were char-
acterized by XRD, SEM, TEM, and EDX analysis techniques. The appli-
cation of an addition reaction of arylboronic acid to nitrostyrenes
provided diaryl-substituted products in high yields. This Pd-NPs are
capable of being recycled by a simple decantation procedure and
reusable up to four times without any effect on its catalytic activity.
KEYWORDS
Addition reaction;
arylboronic acid; ionic
liquids; nitrostyrene; Pd
nanoparticles
GRAPHICAL ABSTRACT
NO2
NO2
B(OH)2
Pd NPs (5 mol%)
MeOH, 40 °C , 3 h
+
R1
R2
R1
R2
16 examples
56-95% Yield
Introduction
Room temperature ionic liquids (RTIL) are environmentally benign solvents; have gen-
erated considerable attention in the direction of organic chemical reactions. The unique
features of ionic liquids (ILs) are their excellent characteristics of negligible vapor pres-
sures, high-ionic conductivity and as high-thermal stability.[1–3] These characteristics
have made them novel and environmentally friendly solvents, used for enzyme-catalyzed
reactions[4] as well as organic transformations. ILs have wide range of applications due
ꢀ
to their low-melting point (as low as –80 C) and high-thermal stability (stable up to
[5]
ꢀ
300 C). For the last few years, the ionic liquid (IL) field is dominated by imidazo-
lium salts, but there are a very few triazolium compounds that can be characterized as
ILs. Fluorine-based anions referred to in literature are very few in number[6,7] for the
CONTACT Ramesh Kumar Chidambaram
nscrameshkumar@gmail.com
Organic Chemistry Laboratory Department
of Chemistry, Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, Avadi, Chennai, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2018 Taylor & Francis Group, LLC

2
K. SUNDARARAJU ET AL.
Scheme 1. Preparation of 1-octyl-1,2,4-triazolium trifluoroacetate ionic liquid.
synthesis of ILs. The parent triazoles and their derivatives found many applications in
medicine and industry.[8–11]
In recent years, ILs are seen as the most advanced solvents for the organic nanopar-
ticle synthesis with unique physical and chemical properties.[12] Among the classes of
ILs, the chemistry of azolium based IL is the subject of in-depth study, particularly imi-
dazolium based ILs.[13–15] The reason is that the imidazolium based ILs are easily tun-
able by means of changing substitution on nitrogen in the ring and also by using
different anions.[16,17] The literature on azolium based ILs has shown the exploration of
a small magnitude for the triazolium based ILs, especially 1,2,4-triazolium based ILs on
their synthesis and applications in organic reactions.[18–21] Commonly used ILs are [C4-
mim]Br (where C4 depicts the butyl group; and mim represents methylimidazole frag-
ment), [C4-mim][PF6], [C6-mim][PF6] and so on.[22] It was reported that the use of the
longer alkyl chain effectively decrease the solubility of the ionic liquid in the aqueous
phase and lead to improved yields.[23] This has created interest in the subject of synthe-
sizing C8-triazolium based ILs using 1,2,4-triazole as the starting material
(Scheme 1).[24]
Among the various metal nanoparticles (NPs), palladium nanoparticles (Pd-NPs) in
ILs have recently gained considerable importance, as this methodology allows simultan-
eous achievement of the advantages of the elimination of highly toxic solvents and the
possibility of recycling the catalyst.[25,26] In addition, it has been widely demonstrated
that ILs can play a greater role than merely solubilizing reagents, as their ability to
affect the nature of the catalytically active species has also been shown to be dependent
on the structure of both cations and anions.[27,28]
Nacci et al. found the possibility of the use of Pd-NPs in tetraalkylammonium-based
ILs, prepared from the reduction of Pd(OAc) in the presence of tetrabutylammonium
[29]
ꢀ
acetate at 90 C, as pre-catalysts for the Suzuki coupling of aryl halides.
Interestingly,
the results showed the use of tetrabutylammonium hydroxide as a base significantly
increased the catalytic efficiency and the reaction could be performed under mild tem-
peratures. The replacement of tetrabutylammonium bromide (TBAB) by tetraheptylam-
monium bromide (THeptAB), which contains longer side chains, led to the
enhancement of the Suzuki reaction, probably due to the stronger stabilization of the
Pd-NPs provided by the long-chain ionic liquids.[30] Mu’s group established a simple
and general method for preparing poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized noble
metal nanoparticles in ILs. These NPs were very stable and showed high-catalytic activ-
ity and stability in the hydrogenation of olefins under mild conditions and reused the
catalyst without any loss of activity.[31] Calo et al. show that the reaction of Pd(OAc)2
with tetrabutylammonium acetate (TBAA), dissolved in (TBAB), leads to the fast forma-
tion of Pd-NPs, which efficiently catalyze the stereospecific reaction of cinnamates with
aryl halides to provide b-aryl-substituted cinnamic esters. The role of TBAA is crucial

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3
in determining the formation of NPs and stereospecificity of the C–C coupling pro-
cess.[32] Prechtl group had given a brief summary in the field of C–C cross-coupling
reactions with Pd-NPs in ILs. Five exemplary model systems using the Pd-NPs/ILs
approach have been presented: Heck, Suzuki, Stille, Sonogashira, and Ullmann reactions,
all of which have the use of ILs as reaction media in common and the use of Pd-NPs as
a reservoir for the catalytically active palladium species.[33]
Venkatesan et al. synthesized Pd(0)-NPs with a simple heating of Pd(OAc)2 in 1-butyr-
onitrile-3-methylimidazolium-N-bis(trifluoromethane sulfonyl)imide ((BCN)MI.NTf2)
under reduced pressure. These NPs were used as catalysts for the hydrogenation of
internal alkynes at 25 ꢀC under 1 bar of hydrogen yields Z-alkenes. Application of
higher hydrogen pressure (4 bar) in these reactions always led to the formation of alka-
nes without the detection of any alkenes.[34] Calo’s group reported that Palladium nano-
colloids supported on chitosan which behaves as a very effective and recyclable
heterogeneous catalysts in Heck reaction of aryl bromides and activated chlorides in
TBAB as solvent and TBAA as a base. The stability of the catalyst allows an extensive
recycle in the coupling of iodoaromatics with butyl acrylate.[35] The Pd-NPs synthesized
by Safavi et al. found the NPs as highly active, recyclable, and stable catalysts for Suzuki
and Heck reactions even under reflex condition. The nanocatalysts are used several
times without deterioration of its catalytic activity.[36] Yang’s group have developed a
highly stable Pd-NPs, protected by an ionic polymer (IP) in a functionalized IL which
was used as an excellent precatalyst for Suzuki, Heck, and Stille coupling reactions. This
NP-IP-IL system is considered to be an alternative to the traditional palladium on car-
bon (Pd/C) precatalyst employing in many C–C coupling reactions under solvent-free
conditions.[37] Cassol’s group disclosed their results concerning the in situ TEM analysis
of Pd-NPs dispersed in (BMI-PF6) ionic liquid, before and after arylation of n-butyl
acrylate, and the Pd leaching from the IL phase to the organic phase at different sub-
strate conversions.[38]
Faria et al. synthesized Pd-NPs supported on a polymeric membrane, CA/Pd(0),
which was found to be a highly efficient “dip catalyst” for Suzuki–Miyaura cross-cou-
pling reactions. The CA/Pd(0) was prepared initially using the synthesis of Pd(0) by
hydrogen decomposition of Pd(acac)2 dissolved in BMI-BF4 IL.[39] Zhao et al. estab-
lished the identification of the Pd-NPs with nitrile-functionalized ILs as the active
catalyst in the Stille reaction under reflux condition.[40] Lee et al. demonstrated single-
walled carbon nanotubes (SWNTs), which serve as a supporting material for Pd nano-
particles generated in situ in IL. Pd nanocatalysts on SWNTs exhibit superior reactivity
for hydrogenation of aryl ketones in IL under mild conditions and were reused about
10 times without any loss of catalytic activity.[41] Heck reactions of aryl chlorides were
catalyzed by the Calo’s group using ligand-free palladium acetate in a molten mixture
of tetraalkylammonium ILs under aerobic conditions. Deactivated electron-rich aryl
chlorides reacted with a wide array of substituted alkenes under these conditions, which
thereby enabled the coupling of combinations of substrates that are generally unreactive
with traditional catalysts.[42] Umpierre et al. prepared Pd-NPs using a simple hydrogen
reduction in Pd(acac)2 dispersed in BMI.PF6IL. The ILs created an external layer around
the metal NPs that controls the access of the reagents to the catalytically active sites as
a function of their solubility in the ionic layer. This catalytic system [Pd-NPs embedded

4
K. SUNDARARAJU ET AL.
Scheme 2. Synthesis of Pd-NPs using triazolium based ILs.
in ILs] is one of the most effective catalysts for performing selective hydrogenation of
1,3-butadiene to 1-butene.[43]
In 2003, Huang’s group summarized their results that Phenanthroline (Phen) ligand-
protected Pd-NPs in [BMIM][PF6] IL is not only used as an active and selective cata-
lytic system but also reused many times without reducing the activity of hydrogenation
of olefins under mild reaction conditions.[44] In 2004, they conducted their first study
of immobilization of Pd-NPs onto a solid surface (molecular sieves) by 1,1,3,3-tetrame-
thylguanidinium lactate (TMGL) IL. The catalytic system was used in solvent-free
hydrogenation reactions and achieved unprecedented activity and stability. The combin-
ation of NPs, IL, and molecular sieves showed excellent synergistic effects in the
enhancement of the activity and durability of the catalyst, and this approach found wide
potential applications in transition-metal nanocatalysed reactions.[45]
In this work, the authors have synthesized Pd-NPs using novel 1-octyl-1,2,4-triazo-
lium trifluoroacetate ionic liquid (3) (Scheme 2). To the best of the authors’ knowledge,
this is the first use of palladium nanoparticles as a catalyst for the addition reaction of
aryl boronic acid to nitrostyrene. The Pd-NPs are very efficient for addition reaction
and the experiments were also carried out for the reuse of the catalyst by a simple
decantation procedure for further reactions. The catalyst did not show any loss in its
activity, even after four runs of repeated addition reaction.
Results and discussion
In the preliminary experiments, Pd-NPs was synthesized and characterized by XRD,
SEM, TEM and EDX analysis.
XRD analysis
X-ray diffraction (XRD) pattern of the Pd-NPs shown in Figure 1 confirmed the crystal-
line feature of the product and the mean diameter was 9.4 nm, as estimated by the
Debye–Scherrer equation. The XRD patterns of the synthesized Pd-NPs clearly men-
tioned the main characteristic peaks, observed at 39.900ꢀ, 46.500ꢀ, 67.590ꢀ, 81.600ꢀ, and
86.720ꢀ which corresponded to the indexed planes of the crystals of Pd(0) (111), (200),
(220), (311), and (222), respectively.[46]
SEM and EDX analysis
The morphology of the Pd-NPs shown in Figure 2 was determined using scanning elec-
tron microscopy (SEM). A thin film of the sample was prepared on a carbon-coated
copper grid by simply dropping a very small amount of the sample on the grid.
Moreover, the presence of F and Pd in the sample arising from Energy Dispersive X-ray
Spectroscopy (EDX) analysis (Fig. 3) provided evidence of the possibility of strong

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Figure 1. X-ray powder diffraction pattern of synthesized Pd-NPs.
Figure 2. Scanning electron microscopy images of the synthesized Pd-NPs.
coordination or absorption from 1-octyl-1,2,4-triazolium trifluoroacetate ionic liquid on
the surface of Pd-NPs even if the samples had gone through the purification procedure.
TEM and SAD analysis
In this study, topology and particle size of the NPs were characterized using transmis-
sion electron microscopy (Model Philips CM 200 instrument). The morphology of the
synthesized Pd-NPs shown in Figure 4a was determined by transmission electron
microscopy (TEM). The solution containing the nanoparticles was diluted and a drop of
it was placed on the copper grid and allowed to dry in a vacuum. The diffraction ring

6
K. SUNDARARAJU ET AL.
Figure 3. Energy dispersive x-ray spectrum of the synthesized Pd-NPs.
Figure 4. Transmission electron microscopy image of the synthesized Pd-NPs. (a) TEM image at
20 nm. (b) Selected area diffraction (SAD) pattern of Pd-NPs.
patterns from selected area diffraction (SAD) shown in Figure 4b confirmed the crystal-
line nature of the particles.
Optimization of the addition reaction
Apart from the synthetic point of view, the diaryl-substituted product of this reaction is
important, in particular, due to the presence of this structural unit in a number of
pharmaceutical intermediates.[47] Nevertheless, nitrostyrenes are the challenging

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Scheme 3. The model reaction for preparation of 1-methoxy-4-(2-nitro-1-phenylethyl)benzene.
Table 1. Screening of palladium catalysts.a
NO2
NO2
B(OH)2
Pd cat.
+
5 mol%
MeO
OMe
6c
5
4
Entry
Catalyst
Yie
1
2
3
4
5
6
Pd(OAc)2
PdCl2
Pd2(dba)3
Pd(TFA)2
Pd blackb
Pd NPs
26
34
47
40
29
95
aReaction conditions: Nitrostyrene (1 mmol), 4-methoxy phenylboronic acid (1.5 mmol) and Pd catalyst (5 mol%) in 3 mL
MeOH at 40 ꢀC for 3 h.
bInstead of ionic liquid methanol is used as a solvent.
substrate for this reaction in addition to boronic acids. Thus, the optimized conditions
were determined by the reaction of simple nitrostyrene with 4-methoxy phenylboronic
acid, which was selected as a model reaction (Scheme 3). The reaction conditions were
optimized on the basis of catalyst study, solvent effect, time, temperature and quantity
of catalyst to be used for the synthesis of 1-methoxy-4-(2-nitro-1-phenylethyl) ben-
zene (6c).
The catalytic activity of various palladium sources, namely, Pd(OAc)2, PdCl2,
Pd2(dba)3, Pd(TFA)2 were screened for the addition reaction of 4-methoxy phenylbor-
onic acid with nitrostyrene to compare the efficiency of the synthesized Pd-NPs. In add-
ition, palladium black was also prepared in the absence of ionic liquid and its catalytic
activity is compared in Table 1. Among the all palladium catalyst screened, Pd-NPs pre-
pared in the presence of ionic liquid (Entry 6) gave 95% yield while using 5 mol% of
ꢀ
the catalyst at 40 C for 3 h, whereas entry 1–5 furnished less than 50% yield under
identical condition. In order to find the role of solvents on the addition reaction, the
model study was carried out using different solvents at various temperatures in the
presence of 5 mol% of Pd-NPs as a catalyst. Among the different solvents studied,
methanol gave excellent yields. It was evident that the reaction diꢀd not progress well at
room temperature. However, a slight increase in temperature (40 C) enhanced the rate
of the reaction. Yields of the almost same quantity were obtained when the temperature
ꢀ
was raised to 80 C. The authors observed a maximum conversion (95%) while using
ꢀ
methanol as a solvent at 40 C for 3 h (Table 2, Entry 17). The time mentioned in the

8
K. SUNDARARAJU ET AL.
Table 2. Optimization of addition reaction.a
NO2
6c
NO2
+
B(OH)2
Pd NPs
5 mol%
MeO
OMe
5
4
Entry
Solvent
Time (h)b
Temperature (°C)
Yield (%)c
1
2
3
4
5
6
7
8
Toluene
Toluene
Toluene
CH3CN
CH3CN
CH3CN
CHCl3
CHCl3
CHCl3
CH2Cl2
CH2Cl2
CH2Cl2
EtOH
EtOH
EtOH
MeOH
MeOH
MeOH
THF
24
24
24
24
24
24
24
16
16
24
16
16
24
6
6
24
3
3
24
6
RT
40
80
RT
40
80
RT
40
80
RT
40
80
RT
40
80
RT
40
80
RT
40
80
NR
57
58
NR
52
49
NR
39
40
NR
23
21
NR
72
72
NR
95
94
NR
79
76
9
10
11
12
13
14
15
16
17
18
19
20
21
THF
THF
6
NR: no reaction; RT: room temperature.
aReaction conditions: Nitrostyrene (1 mmol), 4-methoxy phenylboronic acid (1.5 mmol) and Pd-NPs (5 mol%).
bAfter complete conversion (confirmed by TLC).
cIsolated yields.
Table 3. Effect of quantity of Pd-NPs on addition reaction.a
Entry
Catalyst (mol%)
Yield (%)b
1
2
3
4
5
–
2
3
5
10
NR
70
74
95
96
NR: no reaction.
aReaction conditions: Nitrostyrene (1 mmol) and 4-methoxy phenylboronic acid (1.5 mmol) in 3 mL MeOH at 40 °C
for 3 h.
bIsolated yields.
table was periodically monitored and confirmed by TLC after a complete conversion of
the reaction.
Next, the authors examined the effect of the amount of Pd-NPs to be used on the
model reaction (Scheme 3). The reaction was performed in the presence of various
quantities of Pd-NPs (Table 3) by fixing the solvent, time, and temperature as indicated
in Table 2. The maximum conversion of the product was obtained using 5 mol% of
ꢀ
nanocatalysts in methanol at 40 C (Table 3, Entry 4). There was no significant increase
in the conversion even when the catalyst loading was increased from 5 to 10 mol%
(Table 3, Entries 4 and 5). Accordingly, the condition was optimized using 5 mol% of
Pd-NPs and a study was made of the addition reaction of various nitrostyrene

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9
derivatives with substituted phenylboronic acids in methanol to give the desired prod-
ucts in good to excellent yields. Both electron-withdrawing and electron-donating
groups were seen well tolerated for addition reaction. The results have been summarized
in Table 4. Thus, the overall catalytic activity was proved to be exceptional for the add-
ition reaction of arylboronic acid to nitrostyrene.
Conclusions
In summary, the authors have developed an environmentally benign Pd-NPs using tria-
zolium based room temperature ionic liquids. The thermal treatment of Pd(OAc)2 in
1-octyl-1,2,4-triazolium trifluoroacetate ionic liquids results in the formation of stable
and highly mono-dispersed Pd-NPs. A mild and simple procedure for the addition reac-
tion of arylboronic acid to nitrostyrene has been developed using this Pd-NPs as a cata-
lyst. In view of the mild reaction conditions, simplicity in product separation, catalyst
recovery, and reusability, this methodology could find extensive industrial applications.
Experimental section
Synthesis of ionic liquid
1-octyl-1,2,4-triazole (2): To a solution of 1,2,4-triazole (345 mg, 5 mmol) dissolved in
THF (5 mL) was added 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) (0.75 mL, 5 mmol)
and stirred for 0.5 h. 1-bromooctane (0.87 mL, 5 mmol) was added to this reaction
mixture slowly and allowed to stir at room temperature for 1 h. The reaction was moni-
tored by TLC. After complete conversion, the reaction mixture was washed with water
(2 Â 20 mL) and brine solution. The crude product was purified by column chromatog-
raphy and the compound 2 was obtained.
1 -octyl-1,2,4-triazole (2)
1
Yield 78%, viscous yellow liquid; H NMR: (400 MHz, CDCl3) d (ppm): 8.03 (1 H, s),
7.92 (1 H, s), 4.14 (2 H, t, J = 8 Hz), 1.88–1.84 (2 H, m), 1.25 (10 H, t, J = 8 Hz), 0.85
(3 H, t, J = 8 Hz); 13C NMR: (100 MHz, CDCl3) d (ppm): 151.7, 142.7, 49.7, 31.6, 29.7,
29.0, 28.9, 26.4, 22.5, 14.0; Anal. Calcd. for C10H19N3: C, 66.26; H, 10.56; N, 23.18;
Found: C, 65.06; H, 9.18; N, 22.79.
1-octyl-1,2,4-triazolium trifluoroacetate ionic liquid (3): Trifluoroacetic acid (0.38
mL, 5 mmol) was added slowly to a magnetically stirred solution of 1-octyl-1, 2, 4-tri-
[24]
ꢀ
azole (906 mg, 5 mmol) in toluene (5 mL) and heated to 80 C for 12 h (Scheme 1).
After complete conversion, the solvent waꢀs evaporated in vacuum and the viscous liquid
was washed with hexane and dried at 45 C under vacuum for 2 h to furnish the com-
pound 3.
1 -octyl-1,2,4-triazolium trifluoroacetate ionic liquid (3)
Yield 89%, viscous yellow liquid; IR (KBr, cmÀ1): 3418, 2934, 2856, 1675, 1464, 1197,
1
1134, 803, 719; H NMR: (400 MHz, CDCl3) d (ppm): 8.44 (1 H, t, J = 4 Hz), 8.09 (1 H,

10
K. SUNDARARAJU ET AL.
Table 4. Pd-catalyzed addition reaction of arylboronic acids to nitrostyrenes.a
NO2
NO2
B(OH)2
Pd-NPs (5 mol%)
MeOH , 40 °C , 3 h
+
R1
R2
R1
R2
4
5
6
S.No
1
R1
R2
4-Cl
Product
6(a–o)
Yield (%)b
80
H
H
H
6a
2
3
4-F
6b
6c
56
95
4-OMe
4
5
6
H
H
H
3-OMe
3-Me
6d
6e
6f
83
91
91
3,5-Me
7
8
9
2-Cl
3-Cl
4-Cl
H
H
H
6g
6h
6i
93
63
82
10
11
2-OMe
3-OMe
H
H
6j
87
84
6k
12
4-OMe
H
6l
88
(continued)

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Table 4. Continued.
S.No
13
R1
R2
Product
6(a–o)
Yield (%)b
82
3,4-OMe
H
H
H
H
6m
14
15
16
4-Me
6n
6o
6p
85
87
82
α-naphthyl
2-NO2
17
18
2-NO2
3,5-Me
3,5-Me
6q
6r
90
86
α-naphthyl
aReaction conditions: Nitrostyrene (2 mmol), Phenylboronic acid (3 mmol), and Pd-NPs (5 mol%) in 5 mL MeOH at 40 °C
for 3 h.
bIsolated yields.
s), 4.22 (2 H, t, J = 8 Hz), 1.91 (2 H, t, J = 8 Hz), 1.30–1.25 (10 H, m), 0.87 (3 H, s); 13C
NMR: (100 MHz, CDCl3) d (ppm): 149.3, 142.0, 50.5, 31.6, 29.5, 28.9, 28.8, 26.3, 22.5,
14.0; Anal. Calcd. for C12H20F3N3O2: C, 48.81; H, 6.83; N, 14.23; Found: C, 49.06; H, 6.76;
N, 14.41.
Synthesis and isolation of Pd-NPs
Palladium nanoparticles were prepared by simple hydrogen decomposition (1 atm H2,
constant pressure) of Pd(OAc)2 (450 mg, 2 mmol) dissolved in 3.0 mL of 1-octyl-
ꢀ
1,2,4-triazolium trifluoroacetate ionic liquid at 75 C for 1 h to yield a black suspension.
Acetone (15–20 mL) was added, and centrifugation of this mixture yielded palladium
nanoparticles (79% yield) with a diameter of 9.4 nm. These nanoparticles were washed
with acetone and dried in vacuum under reduced pressure (Scheme 2).[39]
General procedure for the synthesis of 1-chloro-4-(2-nitro-1-
phenylethyl)benzene (6a)
Pd-NPs (10 mg, 5 mol%) in a 25 mL round bottom flask, was taken with MeOH (5
mL). To this suspension, nitrostyrene (298 mg, 2 mmol) and 4-chloro phenylboronic

12
K. SUNDARARAJU ET AL.
Table 5. Reusability of Pd-NPs for addition reaction.a
Entry
No. of runs
Yield (%)b
1
2
3
4
5
Fresh
First
Second
Third
95
94
92
92
90
Fourth
aReaction conditions: Nitrostyrene (1 mmol) and 4-methoxy phenylboronic acid (1.5 mmol) in 3 mL MeOH at 40 °C
for 3 h.
bIsolated yields.
ꢀ
acid (470 mg, 3 mmol) were added. The reaction mixture was stirred at 40 C for 3 h
under air atmosphere. Then it was filtered and the solvent was removed by a rotary
evaporator under reduced pressure to afford a crude adducts, which was purified using
column chromatography on silica gel using 5% ethyl acetate in hexane to give com-
pound 6a.
1 -chloro-4-(2-nitro-1-phenylethyl)benzene (6a)[47,48]
Yield 80%, pale yellow oil; IR (KBr, cmÀ1): 3064, 3027, 2915, 1554, 1491, 1376, 1091,
1
1015, 820, 755; H NMR: (400 MHz, CDCl3) d (ppm): 7.38–7.28 (5 H, m), 7.24–7.19 (4
H, m), 4.98 (2 H, d, J = 8 Hz), 4.91 (1 H, t, J = 8 Hz); 13C NMR: (100 MHz, CDCl3) d
(ppm): 138.7, 137.7, 133.5, 129.2 (2C), 129.1 (2C), 129.0 (2C), 127.8 (2C), 127.5,
79.0, 48.3.
Reusability study
The recycling potential of palladium nanoparticles was studied by the addition reaction
successively in four runs. NPs in this experiment were recycled four times without any
loss of activity. This is shown in Table 5. After complete conversion of the reaction, the
Pd-NPs were separated from the reaction mixture by a simple filtration procedure and
washed with EtOH to remove all organic impurities. The catalyst residue was dried at
ꢀ
45 C under vacuum and the particles were reused for evaluating the performances in
the cycle. The reaction mixture was again filtered for the next use and the crude prod-
uct was purified using column chromatography to furnish a pure adduct.
Acknowledgement
Dr. C. R. K. acknowledges the financial assistance from Science and Engineering Research Board
(SERB), Department of Science and Technology (DST), India, under scheme Fast Track Young
Scientist (SB/FT/CS-086/2013). Authors are grateful to the management of Vel Tech Rangarajan
Dr. Sagunthala R&D Institute of Science and Technology for their infrastructure support to
our laboratory.
Disclosure statement
The authors announce no competing interest.

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References
[1] Arya, S. K.; Saha, S.; Ramirez-Vick, J. E.; Gupta, V.; Bhansali, S.; Singh, S. P. Recent
Advances in ZnO Nanostructures and Thin films for Biosensor Applications: Review.
Analytica. Chimica. Acta. 2012, 737, 1–21. DOI: 10.1016/j.aca.2012.05.048.
[2] Ma, Z.; Yu, J.; Dai, S. Preparation of Inorganic Materials Using Ionic Liquids. Adv. Mater.
2010, 22, 261–285. DOI: 10.1002/adma.200900603.
[3] Torimoto, T.; Tsuda, T.; Okazaki, K.; Kuwabata, S. New Frontiers in Materials Science
Opened by Ionic Liquids. Adv. Mater. 2010, 22, 1196–1221. DOI: 10.1002/
adma.200902184.
[4] Plechkova, N. V.; Seddon, K. R. Applications of Ionic Liquids in the Chemical Industry.
Chem. Soc. Rev. 2008, 37, 123–150. DOI: 10.1039/b006677j.
[5] Parvulescu, V. I.; Hardacre, C. Catalysis in Ionic Liquids. Chem. Rev. 2007, 107,
2615–2665. DOI: 10.1021/cr050948h.
[6] Vestergaard, B.; Bjerrum, N. J.; Petrushina, I.; Hjuler, H. A.; Berg, R. W.; Begtrup, M.
Molten Triazolium Chloride Systems as New Aluminum Battery Electrolytes. J.
Electrochem. Soc. 1993, 140, 3108–3113. DOI: 10.1149/1.2220994.
[7] Astleford, B. A.; Goe, G. L.; Keay, J. G.; Scriven, E. F. V. Synthesis of l-Alkyl-1,2,4-
Triazoles: A New One-Pot Regiospecific Procedure. J. Org. Chem. 1989, 54, 731–732.
DOI: 10.1021/jo00264a048.
[8] Garratt, P. J. Comprehensive Heterocyclic Chemistry II; Elsevier, 1996.
[9] Katritzky, A.; Pozharskii.; Ramsden, C. A.; Joule, J.; Zhdankin, V. Handbook of
Heterocyclic Chemistry, 2nd ed.; Academic Press, Cambridge, Massachusetts, 2000.
[10] Dalvie, D. K.; Kalgutkar, A. S.; Khojasteh-Bakht, S. C.; Obach, R. S.; O’Donnell, J. P.
Biotransformation Reactions of Five-Membered Aromatic Heterocyclic Rings. Chem. Res.
Toxicol. 2002, 15, 269–299. DOI: 10.1021/tx015574b.
[11] Olofson, R. A.; Kendall, R. V. Protection by Acylation in the Selective Alkylation of
Heterocycles. J. Org. Chem. 1970, 35, 2246–2248. DOI: 10.1021/jo00832a031.
[12] Dupont, J.; Scholten, J. D. On the Structural and Surface Properties of Transition-Metal
Nanoparticles in Ionic Liquids. Chem. Soc. Rev. 2010, 39, 1780–1804. DOI: 10.1039/
b822551f.
[13] Wang, R.; Jin, C. M.; Twamley, B.; Shreeve, J. M. Syntheses and Characterization of
Unsymmetric Dicationic Salts Incorporating Imidazolium and Triazolium Functionalities.
Inorg. Chem. 2006, 45, 6396–6403. DOI: 10.1021/ic060822i.
[14] Dupont, J. On the Solid, Liquid and Solution Structural Organization of Imidazolium
Ionic Liquids. J. Braz. Chem. Soc. 2004, 15, 341–350. DOI: 10.1590/s0103-
50532004000300002.
[15] Crosthwaite, J. M.; Aki, S. K. V. K.; Maginn, E. J.; Brennecke, J. F. Liquid Phase Behavior
of Imidazolium-Based Ionic Liquids with Alcohols. J. Phys. Chem. B. 2004, 108,
5113–5119. DOI: 10.1021/jp037774x.
[16] Mirzaei, Y. R.; Twamley, B.; Shreeve, J. M. Syntheses of 1-Alkyl-1,2,4-Triazoles and the
Formation of Quaternary 1-Alkyl-4-Polyfluoroalkyl-1,2,4-Triazolium Salts Leading to Ionic
Liquids. J. Org. Chem. 2002, 67, 9340–9345. DOI: 10.1021/jo026350g.
[17] Seddon, K. R.; Stark, A.; Torres, M.-J. Influence of Chloride, Water, and Organic Solvents
on the Physical Properties of Ionic Liquids. Pure Appl. Chem. 2000, 72, 2275–2287.DOI:
10.1351/pac200072122275.
[18] Daily, L. A.; Miller, K. M. Correlating Structure with Thermal Properties for a Series of 1-
Alkyl4-Methyl-1,2,4-Triazolium Ionic Liquids. J. Org. Chem. 2013, 78, 4196–4201. DOI:
10.1021/jo4003932.
[19] Luo, J.; Hu, J.; Saak, W.; Beckhaus, R.; Wittstock, G.; Vankelecom, I. F. J.; Agert, C.;
Conrad, O. Protic Ionic Liquid and Ionic Melts Prepared from Methanesulfonic Acid and
1H-1,2,4-Triazole as High Temperature PEMFC Electrolytes. J. Mater. Chem. 2011, 21,
10426–10436. DOI: 10.1039/c0jm04306k.

14
K. SUNDARARAJU ET AL.
[20] Gnanamgari, D.; Moores, A.; Rajaseelan, E.; Crabtree, R. H. Transfer Hydrogenation of
Imines and Alkenes and Direct Reductive Amination of Aldehydes Catalyzed by Triazole-
Derived Iridium(I) Carbene Complexes. Organometallics. 2007, 26, 1226–1230. DOI:
10.1021/om060938m.
[21] Xue, H.; Twamley, B.; Shreeve, J. M. The First 1-Alkyl-3-Perfluoroalkyl-4,5-Dimethyl-
1,2,4-Triazolium Salts. J. Org. Chem. 2004, 69, 1397–1400. DOI: 10.1021/jo0356107.
[22] Dzyuba, S. V.; Kollar, K. D.; Sabnis, S. S. Synthesis of Imidazolium Room-Temperature
Ionic Liquids. J. Chem. Educ. 2009, 86, 856–858. DOI: 10.1021/ed086p856.
[23] Williamson, C. L.; Maly, K. E.; MacNeil, S. L. Synthesis of Imidazolium Room-
Temperature Ionic Liquids: A Follow-Up to the Procedure of Dzyuba, Kollar, and Sabnis.
J. Chem. Educ. 2013, 90, 799–801. DOI: 10.1021/ed300369m.
[24] Nagarajan, S.; Kandasamy, E. Reusable 1,2,4-Triazolium Based Brønsted Acidic Room
Temperature Ionic Liquids as Catalyst for Mannich Base Reaction. Catal. Catal. Lett.
2014, 144, 1507–1514. DOI: 10.1007/s10562-014-1312-7.
[25] Wilkes, J. S. Properties of Ionic Liquid Solvents for Catalysis. J. Mol. Catal A: Chem.
2004, 214, 11–17. DOI: 10.1016/j.molcata.2003.11.029.
[26] Welton, T. Ionic Liquids in Catalysis. Coord. Chem. Rev. 2004, 248, 2459–2477. DOI:
10.1016/j.ccr.2004.04.015.
[27] Gu, Y.; Shi, F.; Deng, Y. Ionic Liquid as an Efficient Promoting Medium for Fixation of
CO2: Clean Synthesis of a-Methylene Cyclic Carbonates from CO2 and Propargyl
Alcohols Catalyzed by Metal Salts under Mild Conditions. J. Org. Chem. 2004, 69,
391–394. DOI: 10.1021/jo0351365.
[28] Dupont, J.; Spencer, J. On the Noninnocent Nature of 1,3-Dialkylimidazolium Ionic
Liquids. Angew. Chem. Int. Ed. 2004, 43, 5296–5297. DOI: 10.1002/anie.200460431.
[29] Calo, V.; Nacci, A.; Monopoli, A.; Montingelli, F. Pd Nanoparticles as Efficient Catalysts
for Suzuki and Stille Coupling Reactions of Aryl Halides in Ionic Liquids. J. Org. Chem.
2005, 70, 6040–6044. DOI: 10.1021/jo050801q.
[30] Fihri, A.; Bouhrara, M.; Nekoueishahraki, B.; Basset, J. M.; Polshettiwar, V. Nanocatalysts
for Suzuki Cross-Coupling Reactions. Chem. Soc. Rev. 2011, 40, 5181–5203. DOI: 10.1039/
clcs15079k.
[31] Mu, X. D.; Evans, D. G.; Kou, Y. A General Method for Preparation of PVP-Stabilized
Noble Metal Nanoparticles in Room Temperature Ionic Liquids. Catal. Lett. 2004, 97,
151–154., DOI: 10.1023/b:catl.0000038577.18441.bf.
[32] Calo, V.; Nacci, A.; Monopoli, A.; Laera, S.; Cioffi, N. Pd Nanoparticles Catalyzed
Stereospecific Synthesis of b-Aryl Cinnamic Esters in Ionic Liquids. J. Org. Chem. 2003,
68, 2929–2933. DOI: 10.1021/jo026877t.
[33] Prechtl, M. H. G.; Scholten, J. D.; Dupont, J. Carbon-Carbon Cross Coupling Reactions in
Ionic Liquids Catalysed by Palladium Metal Nanoparticles. Molecules. 2010, 15,
3441–3461. DOI: 10.3390/molecules15053441.
[34] Venkatesan, R.; Prechtl, M. H. G.; Scholten, J. D.; Pezzi, R. P.; Machado, G.; Dupont, J.
Palladium Nanoparticle Catalysts in Ionic Liquids: synthesis, Characterization and
Selective Partial Hydrogenation of Alkynes to Z-Alkenes. J. Mater. Chem. 2011, 21,
3030–3036. DOI: 10.1039/c0jm03557b.
[35] Calo, V.; Nacci, A.; Monopoli, A.; Fornaro, A.; Sabbatini, L.; Cioffi, N.; Ditaranto, N.
Heck Reaction Catalyzed by Nanosized Palladium on Chitosan in Ionic Liquids.
Organometallics. 2004, 23, 5154–5158. DOI: 10.1021/om049586e.
[36] Safavi, A.; Maleki, N.; Iranpoor, N.; Firouzabadi, H.; Banazadeh, A. R.; Azadi, R.;
Sedaghati, F.; Highly, efficient, Stable, Palladium Nanocatalysts Supported on an Ionic
Liquid-Modified Xerogel. Chem. Commun. 2008, 6155–6157. DOI: 10.1039/b814559h.
[37] Yang, X.; Fei, Z.; Zhao, D.; Ang, W. H.; Li, Y.; Dyson, P. J. Palladium Nanoparticles
Stabilized by an Ionic Polymer and Ionic Liquid: A Versatile System for C-C Cross-
Coupling Reactions. Inorg. Chem. 2008, 47, 3292–3297. DOI: 10.1021/ic702305t.

R
SYNTHETIC COMMUNICATIONSV
15
[38] Cassol, C. C.; Umpierre, A. P.; Machado, G.; Wolke, S. I.; Dupont, J. The Role of Pd
Nanoparticles in Ionic Liquid in the Heck Reaction. J. Am. Chem. Soc. 2005, 127,
3298–3299. DOI: 10.1021/ja0430043.
[39] Faria, V. W.; Oliveira, D. G. M.; Kurz, M. H. S.; Goncalves, F. F.; Scheeren, C. W.; Rosa,
G. R. Palladium Nanoparticles Supported in a Polymeric Membrane: an Efficient
Phosphine-Free “Green” Catalyst for Suzuki–Miyaura Reactions in Water. RSC Adv. 2014,
4, 13446–13452. DOI: 10.1039/c4ra01104.
[40] Zhao, D.; Fei, Z.; Geldbach, T. J.; Scopelliti, R.; Dyson, P. J. Nitrile-Functionalized
Pyridinium Ionic Liquids: Synthesis, Characterization, and Their Application in Carbon-
Carbon Coupling Reactions. J. Am. Chem. Soc. 2004, 126, 15876–15882. DOI: 10.1021/
ja0463482.
[41] Lee, J. K.; Kim, M. J. Hydrogenation of Aryl Ketones Using Palladium Nanoparticles on
Single-Walled Carbon Nanotubes in an Ionic Liquid. Tetrahedron Lett. 2011, 52, 499–501.
DOI: 10.1016/j.tetlet.2010.11.081.
[42] Calo, V.; Nacci, A.; Monopoli, A.; Cotugno, P. Heck Reactions with Palladium
Nanoparticles in Ionic Liquids: Coupling of Aryl Chlorides with Deactivated Olefins.
Angew. Chem. Int. Ed. 2009, 48, 6101–6103. DOI: 10.1002/anie.200902337.
[43] Umpierre, A. P.; Machado, G.; Fecher, G. H.; Morais, J.; Dupont, J. Selective
Hydrogenation of 1,3-Butadiene to 1-Butene by Pd(0) Nanoparticles Embedded in
Imidazolium Ionic Liquids. Adv. Synth. Catal. 2005, 347, 1404–1412. DOI: 10.1002/
adsc.200404313.
[44] Huang, J.; Jiang, T.; Han, B.; Gao, H.; Chang, Y.; Zhao, G.; Wu, W. Hydrogenation of
Olefins Using Ligand-Stabilized Palladium Nanoparticles in an Ionic Liquid. Chem.
Commun. 2003, 1654–1655. DOI: 10.1039/b302750c.
[45] Huang, J.; Jiang, T.; Gao, H.; Han, B.; Liu, Z.; Wu, W.; Chang, Y.; Zhao, G. Pd
Nanoparticles Immobilized on Molecular Sieves by Ionic Liquids: Heterogeneous Catalysts
for Solvent-Free Hydrogenation. Angew. Chem. Int. Ed. 2004, 43, 1397–1399. DOI:
10.1002/anie.200352682.
[46] Hu, Y.; Yu, Y.; Hou, Z.; Li, H.; Zhao, X.; Feng, B. Biphasic Hydrogenation of Olefins by
Functionalized Ionic Liquid-Stabilized Palladium Nanoparticles. Adv. Synth. Catal. 2008,
350, 2077–2085. DOI: 10.1002/adsc.200800290.
[47] He, Q.; Xie, F.; Fu, G.; Quan, M.; Shen, C.; Yang, G.; Gridnev, I. D.; Zhang, W.
Palladium-Catalyzed Asymmetric Addition of Arylboronic Acids to Nitrostyrenes. Org.
Lett. 2015, 17, 2250–2253. DOI: 10.1021/acs.orglett.5b00863.
[48] Wang, Z.-Q.; Feng, C.-G.; Zhang, S.-S.; Xu, M.-H.; Lin, G.-Q. Rhodium-Catalyzed
Asymmetric Conjugate Addition of Organoboronic Acids to Nitroalkenes Using Chiral
Bicyclo[3.3.0] Diene Ligands. Angew. Chem. Int. Ed. 2010, 49, 5780–5783. DOI: 10.1002/
anie.201001883.