Multi-functionalized ionic liquid with in situ-generated palladium nanoparticles for Suzuki, Heck coupling reaction: a comparison with deep eutectic solvents

Article abstract of DOI:10.1007/s13738-018-1503-z

Abstract: A new catalytic system for Suzuki and Heck coupling has been developed from multi-functionalized task specific ionic liquid (TSIL) and in situ formed palladium nanoparticles (PdNps). The generated PdNPs were characterized by UV–Visible spectroscopy and transmission electron microscopy (TEM) analysis. These PdNPs have found size below 10?nm and exhibited a excellent catalytic activity in the cross-coupling of aryl halide without using external phosphine ligand. Along with electron deficient olefins, electron rich olefins were also undergo smooth reaction giving excellent yield. The results obtained in ionic liquid are compared with results obtained in deep eutectic solvents. Progress of reaction was found very smooth in ionic liquid rather than in deep eutectic solvents. The aqueous system containing ionic liquid along with PdNPs was recycled for seven times, without any significant loss. Graphical abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s13738-018-1503-z

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-018-1503-z
ORIGINAL PAPER
Multi-functionalized ionic liquid with in situ-generated palladium
nanoparticles for Suzuki, Heck coupling reaction: a comparison
with deep eutectic solvents
D. S. Gaikwad1 · K. A. Undale1 · D. B. Patil1 · D. M. Pore2
Received: 23 April 2018 / Accepted: 19 September 2018
© Iranian Chemical Society 2018
Abstract
A new catalytic system for Suzuki and Heck coupling has been developed from multi-functionalized task specific ionic
liquid (TSIL) and in situ formed palladium nanoparticles (PdNps). The generated PdNPs were characterized by UV–Vis-
ible spectroscopy and transmission electron microscopy (TEM) analysis. These PdNPs have found size below 10 nm and
exhibited a excellent catalytic activity in the cross-coupling of aryl halide without using external phosphine ligand. Along
with electron deficient olefins, electron rich olefins were also undergo smooth reaction giving excellent yield. The results
obtained in ionic liquid are compared with results obtained in deep eutectic solvents. Progress of reaction was found very
smooth in ionic liquid rather than in deep eutectic solvents. The aqueous system containing ionic liquid along with PdNPs
was recycled for seven times, without any significant loss.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-018-1503-z) contains
supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
Graphical abstract
Keywords Multi-functionalized ionic liquid · Suzuki–Miyaura · Heck-Mizoroki · Palladium nanoparticles · Deep eutectic
solvents · Transmission electron microscopy
in addition ILs possesses several distinctive properties, such
as negligible vapor pressure, no miscibility with non-polar
solvents, and reasonable thermal and chemical stability with
excellent electrical conductivity [17–20]. Owing to these
exceptional properties, more attention has been focused on
the synthesis of new ILs with functional groups, so-called
TSILs which will act as reducing as well as stabilizing agent
for MNPs.
Introduction
The utilization of metal nanoparticles (MNPs) is of gigantic
significance in the diverse field including energy conversion
and storage, chemical manufacturing, biological applica-
tions, and environmental technology [1–4]. Looking in to
these diverse applications of MNPs, we can state that it has
a very potential and intense future. Coming towards its effi-
ciency in organic reactions as a catalyst, recently scientific
experts are having significant interest in the terms of green
chemistry because of their tender character, effortlessness of
preparation and availability of large surface area [5–7]. Pres-
ently many active scientists are working on immobilization
MNPs in ionic liquids to prove its synergetic activity in case
of hydrogenation, oxidation, acetylation, and C–C coupling
reactions under both single-phase and multiphase conditions
[8–11]. Alongside this there are some interesting reviews of
MNPs considering its preparation, characterization, and use
as catalyst (soluble or insoluble MNPs) in ILs [12–14]. In
the many of the synthesis of MNPs in ionic liquids, the func-
tionalized ionic liquids which are also called as task specific
ionic liquids (TSILs) used as both ligands and supporting for
immobilization and recycling of MNPs [15, 16]. The reason
is because functionalized ILs can provide stronger stabiliza-
tion for the MNPs without losing their catalytic properties;
In all above discussion ILs are used as recyclable
medium, besides this recently Deep Eutectic Solvents (DES)
are also entering in this era. These DES plays a similar role
as like that of ILs [21, 22]. These can also be recycled
many times without losing its activity and main advantage
of using is their biodegradable nature. Some of the ILs are
not biodegradable but most of the DES has biodegradabil-
ity nature [23–25]. So research communities are focusing
to continue the research in the same. The use of DES in
the field of coupling reactions is still under primary level
because of stability of palladium catalyst used during the
reaction. There are few research articles which they have
focused in using DES only as a reaction medium for the
palladium catalyzed reactions [26–28]. Some of research
group have utilized carbohydrate based DES as a reaction
medium, e.g., D-mannose-urea, L-Carnitine-urea [29, 30].
But these all earlier reports possess drawbacks such as use
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Journal of the Iranian Chemical Society
of external ligand, external reducing agent, and external
base and long reaction time to carry out very effective cou-
pling reaction. Research articles also failed to reproduce the
results obtained with traditional Palladium catalysts and not
stated effective recycling method. Hence here ILs provides
all the solution to these questions. In the present manuscript
we have designed such IL which will act as reducing, stabi-
lizing agent and also act as a base for palladium catalyzed
Suzuki, Heck coupling reaction.
Literature investigation reveals that the hydroxyl-function-
alized ILs possess high solvent polarities, high dielectric
constants than non-functionalized ILs, higher hydrogen-
bond acidity which increases the hydrophilicity of the ILs
[33–35]. The Dyson group [36] reported that, hydroxyl-
functionalized ILs act as reducing agent and formed highly
stable, small PdNPs with a narrow size distribution. Hence
due to these advantages of the hydroxyl group we targeted to
synthesis such ionic liquid which will fulfill all requirements
for carrying out coupling reaction smoothly. The formation
of IL was confirmed by characterizing its 1H and 13C NMR,
and we delighted that spectra confirmed the formation of
desired multifunctional IL.
In continuation with our earlier work in the field of IL,
[31, 32] herein we disclose a novel protocol for the Suzuki
and Heck coupling reaction using synthesized multi-func-
tionalized ionic liquid in aqueous conditions. The desired
carbon–carbon bond formation proceeded under mild condi-
tions with high efficiency and good functional group toler-
ance. Results obtained in different ILs are also compared
with the results obtained of reaction in DES.
Suzuki–Miyaura coupling
As we all know, water is cheap, readily available, nontoxic,
non-flammable and environment friendly solvent. Further-
more, water can provide several other advantages, such as
inertness against oxidation and reduction, high polarity and
high solution ability [37, 38]. In the present study we have
used water as a solvent and different ILs for carrying out
Suzuki coupling reaction. We explored effect of synthesized
ILs with model reaction of 4-iodo anisole, phenyl boronic
acid, and different palladium sources in water (Scheme 2).
When reaction was carried out at room temperature after
prolonged time we observed inferior results, but when the
same carried out at 80 °C giving very promising results. To
Results and discussion
Initially we have synthesized a multi-functionalized ionic
liquid. In the first step quaternisation of 4-amino pyridine
and 3-chloro-1,2-propanediol in acetone at reflux tempera-
ture was carried out and increased the basicity of the ionic
liquid by incorporating OH− on reaction with potassium
hydroxide (Scheme 1). The introduction of diol functional-
ity has some added advantages over other non hydroxyl ILs.
Scheme 1 Synthesis of multi-
,12h
Cl
OH
N+
functionalized ionic liquid
H2N
Cl
H2N
N
+
Acetone
OH
3
HO
OH
1
2
KOH, RT
24h
DCM:MeOH
(1:1)
OH-
N+
H2N
HO
OH
4
[ADPPy] [OH]
Scheme 2 Typical Suzuki–
Miyaura coupling
I
'Pd' catalyst
+
IL, H2O
RT/
O
(HO)2B
O
6
5
7
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Journal of the Iranian Chemical Society
Table 1 Optimization of the
Entry
Catalyst (2 mol%)
Base (mol %)
Temp. (oC)
Time (h)
Yield (%)a
reaction conditions
1
2
3
4
5
6
7
8
Pd(PPh3)4
Pd(PPh3)4
Pd2(dba)3
Pd/C
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
[ADPPy][OH] (20)
[ADPPy][OH] (20)
[ADPPy][OH] (20)
[ADPPy][OH] (20)
[ADPPy][OH] (20)
[ADPPy][OH] (20)
[ADPPy][OH] (30)
[ADPPy][OH] (30)
IL 2 (20)
IL 1 (20)
IL 3 (20)
IL 4 (20)
IL 5 (20)
RT
80
80
80
RT
80
80
80
80
80
80
80
80
80
7
5
7
8
4
1
1
1
8
1.5
1
2
5
20
60
40
10
45
99
99
90
35
60
89
75
30
85
9
10
11
12
13
14
IL 6 (20)
1
Reaction conditions: 4-iodoanisole (1 mmol), phenylboronic acid (1.1 mmol), water (5 mL)
aIsolated yields
Cl-
N+
OH
N
H2N
N+
N
S
N
O
Cl-
H2N
+
Cl-
H2N
+
COO-
HO
OH
NH2
NH2
O
N
H
OH
OH
IL 1
IL 2
DES 1
DES 2
O
N
N
N+
OH-
O
N+
N
O
Cl-
+
NH2
N
H2N
NH2
OH
3-
PO4
OH
HO
NH
OH
O
IL 3
IL 4
O
O
DES 3
DES 4
N+
N+
Cl-
NH2
N
O
Fig. 2 Different deep eutectic solvents used
OH-
IL 5
IL 6
out organic reactions than ILs. So we focused to carry out
reaction in these with similar model reactants. As discussed
earlier we didn’t observe any promising results with DES.
All results are summarized in Table 2. To all these reactions
require external phosphine ligand and base for completion of
reaction. So here our synthesized IL looks to be better than
DES. The DES used during this study are synthesized using
earlier reported procedures [44, 45].
Fig. 1 Different ionic liquids (ILs) studied
carry out reaction with ILs other than [ADPPy][OH] we
have to use external base or any stabilizing agent for cata-
lyst. But only a mixture of IL [ADPPy][OH] and water gave
us excellent results. Achievements of all these preliminary
survey are shown in Table 1.
When we used Pd(OAc)2 (2 mol%), IL [ADPPy][OH]
(20 mol%), and heating at 80 °C, got 99% of desired
product (Entry 6, Table 1). Having these optimized reac-
tion conditions in hand, we next proceeded to exam-
ine the scope and limitation of catalytic system in the
Suzuki cross-coupling reaction of various types of iodo-,
bromo-, and chloro aryl derivatives and aryl boronic acids
(Table 3). In general, all of the coupling products were
Reaction with other ILs also studied, ILs containing basic
functionality got us excellent results. All results are summa-
rized in Table 1. All the ILs are synthesized (Fig. 1) using
earlier reported procedures [39–43]. Achieving success in
IL: water medium we carried out similar reaction in diverse
Deep Eutectic Solvents (DES) (Fig. 2). Nowadays these DES
are considered as excellent reaction medium for carrying
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Journal of the Iranian Chemical Society
Table 2 Suzuki coupling
Sr. No. Catalyst (2 mol%) Base (2 mmol) Ligand (5 mol%)
Solvent Temp. Time in h Yield %a
reaction in deep eutectic solvent
1
2
3
4
5
6
7
8
9
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
NaOH
NaOH
Na2CO3
Triethyl amine Xanthphos
Triethyl amine Xphos
–
DES 1 RT
6
3
3
3
3
55
80
75
79
76
95
92
94
50
Triphenyl phosphine DES 1 RT
Triphenyl phosphine DES 1 RT
DES 1 RT
DES 1 RT
Triethyl amine Triphenyl phosphine DES 1 80 °C 1.5
Triethyl amine Triphenyl phosphine DES 2 80 °C
Triethyl amine Triphenyl phosphine DES 3 80 °C
Triethyl amine Triphenyl phosphine DES 4 80 °C
2
2
5
Reaction conditions: 4-Iodoanisole (1 mmol), phenylboronic acid (1.1 mmol), water (5 mL)
aIsolated yields
Table 3 Reactions of aryl halides and phenyl boronic acids under the optimized reaction conditions
X
Pd(OAc)2
R2
R2
R1
+
[ADPPy]OH
H2O, 80 oC
(HO)2B
R1
8
9
10
X=Br, I, Cl
Entry
Aryl halide (8)
Boronic acid (9)
Time, h
Yield (%)a
TON
TOF
10a
10b
10c
10d
10e
10f
10g
10h
10i
R1 =H, X=I
R2 =H
1
2
1
1
1.5
1.5
1
1.5
2
1.5
1
2
96
80
95
92
89
88
85
84
87
90
87
80
48
40
47.5
46
44.5
44
42.5
42
43.5
45
43.5
40
48
20
R1 =H, X=Cl
R2 =4-OMe
R2 =4-Me
R2 =H
R1 =H, X=Br
47.5
46
29.66
29.33
42.5
28
21.75
30
43.5
20
R1 =4-Me, X=Br
R1 =4-Me, X=I
R1 =4-OMe, X=I
R1 =4-OMe, X=I
R1 =4-CN, X=Br
R1 =4-NO2, X=I
R1 =4-COMe, X=Br
R1 =4-OMe, X=Br
1-Naphthyl Iodie
R2 =4-OMe
R2 =H
R2 =4-OMe
R2 =H
R2 =H
10j
10k
10l
R2 =H
R2 =4-Me
R2 =H
Reaction conditions: aryl halide (1 mmol), boronic acid (1.1 mmol), Pd(OAc)2 (2 mol%), [ADPPy][OH] (20 mol%), Water (5 mL) at 80 °C
aIsolated yield
obtained in good to excellent yields. A variety of elec-
tron donating, electron withdrawing aryl halides, differ-
ent substituted phenyl boronic acids were then explored
as substrates and the results are listed in Table 3. We
found that aryl bromides and iodides reacted with phe-
nyl boronic acid efficiently, giving the good to excellent
yields. Remarkably, no product arising from the homo-
coupling of aryl boronic acids or product from hydro-
lytic deboronation was detected in these substrates. The
turnover frequency and turnover number of the reaction
(TON = Mole of product/IL mole; TOF = TON/time in h)
also calculated and we delight to report here reaction fits
well in these calculations.
During the progress of the reaction we observed change
in color of reaction from yellow to dark brownish black.
Hence there might be formation of Pd-NPs in situ during the
completion of reaction. After the completion of reaction, we
extracted the reaction mixture by diethyl ether to separate
the synthesized biaryls. Then the aqueous phase have been
analyzed by recording UV–Vis spectrum in acetone medium
and compared the same with that of Pd(OAc)2 (Fig. 3a). The
absorption at 405 nm due to Pd(OAc)2 disappeared from
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Journal of the Iranian Chemical Society
Fig. 3 a UV–Vis spectra of
reaction mixture after comple-
tion of reaction. b, c TEM
analysis of separated Pd-NPs
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
Pd(OAc)2
IL+R
IL
230
280
330
380
430
480
Wavelength(nm)
(a)
(b)
(c)
regarding hydroxyl functionality of the ionic liquid, it acts
as reducing agent for formation of Pd-NPs in situ. The -NH2
group from cation act as well stabilizing agent for formed
nanoparticles.
To verify the formation of Pd-NPs and successful com-
pletion of reaction, we performed the mercury poisoning
test [46] with Hg(0) based on the deactivation of metal via
amalgam formation. The addition of Hg(0) to the Suzuki
reaction with Pd-NPs showed a complete inhibition of the
catalytic activity.
Fig. 4 Varsatility of ionic liquid
Heck‑Mizoroki coupling
the reaction mixture due to the formation of Pd-NPs. These
obtained Pd-NPs is characterized by transmission electron
microscopy (TEM) analysis as shown in Fig. 3b, c, and it
was found that there is formation of Pd-NPs of around size
10 nm.
After initial success in Suzuki–Miyaura coupling, we next
focused our attention to carry out Heck coupling under the
similar optimized reaction conditions (Scheme 3). We are
delighted to report here that the same catalytic system is
very much effective in Heck-Mizoroki coupling with aryl
halide and electron deficient olefins to absolutely giving
E-isomer as a major product (Table 4). The formation of
The ionic liquid used during the advancement of reaction
performs many roles (Fig. 4). The anion OH− acts as a base
required for Suzuki coupling reaction. As discussed above
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Journal of the Iranian Chemical Society
donating olefins viz ethyl vinyl ether with aryl halides
(Entry 13 m, 13n Table 4) under optimized reaction con-
ditions (Scheme 4). After hydrolysis, we observed for-
mation of corresponding arylmethylketones with 100%
α-regioselectivity and the product was characterized by
1H NMR and 13C NMR.
R'
Pd(OAc)2
X
R
R
+
ADPPy[OH]; H2O
80 oC
R'
13
11
12
R' = Ph,
COOMe,
COOBu, CN
It is one of the principal of Green chemistry, that cata-
lyst used should be reused to carry out number of reactions
with excellent efficiency. Hence in this standpoint, recy-
cling of catalyst is highly warranted. We carried out the
recyclability study of ionic liquid-PdNps catalytic system
for the model reaction. For reusability study we choose
to study reaction between 4-iodo anisole and phenylbo-
ronic acid under the optimized reaction conditions. Grati-
fyingly, it was observed that the catalytic system can be
reused effectively for 7 times without any significant loss
of activity providing excellent yields of products (Fig. 5).
After 7th run we analyzed the Pd-NPs and we found some
aggregation of Pd-NPs (Fig. 6).
Scheme 3 Heck–Mizoroki coupling
E-isomer was confirmed by 1H NMR analysis of the product
as it shows coupling constant above 8 Hz. Reaction worked
well with both electron donating as well as electron with-
drawing aryl halides. All the products are isolated from reac-
tion mixture by column chromatography using silica (mesh
size 100:200) as stationary phase and ethyl acetate:hexane
(1:9) as mobile phase.
Reaction progressed much better with electron defi-
cient olefins hence we tried the Heck arylation of electron
Table 4 Reactions of aryl
Entry
Aryl halide
Olefin
(12)
Time Yielda*
TON
TOF
halides and olefins under the
optimized reaction conditions
(11)
h
2
3
%
98
95
13a
13b
R = H, X = Br
R = 4-COMe, X =
Br
R’ = Ph
R’ = Ph
49
24.5
47.5
15.83
13c
13d
13e
13f
R = 4-NO2, X = I
R = 4-NO2, X = I
R = H, X = Cl
R’ = Ph
3
4
8
8
92
90
75
70
46
45
15.33
11.25
4.68
R’ = COOMe
R’ = COOMe
37.5
35
R = 4-COMe, X = R’ = COOMe
Cl
4.37
13g
13h
R = 4-OMe, X = I R’ = COOMe
3
3
87
86
43.5
43
14.5
R = 1-Naphthyl,
X = I
R’ = COOMe
R’ = CN
14.33
13i
R = 4-COMe, X =
9
65
32.5
3.61
Cl
13j
13k
13l
R = H, X = Cl
R’ = CN
8
3
2
4
70
90
35
45
4.37
15
R 4-CN, X = Br
R = H, X = I
R’ = COOBu
R’ = COOBu
95
80a
47.5
40
23.75
10
O
13m
O
I
78a
39
9.75
O
13n
4
I
Reaction conditions: Aryl halide (1 mmol), styrene/acrylate/acrylonitrile (1.1 mmol), Pd(OAc)2
a
(2 mol %), ADPPy[OH] (20 mol%), temp.: 100 °C; :100% regioselectivity (isolated yields), *Iso-
lated Yield
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Journal of the Iranian Chemical Society
Scheme 4 Heck arylation of
ethylvinylether with aryl halides
I
2 mol% Pd(OAc)2
O
R'
+
R'
O
ADPPy[OH], H2O
1000C, 4-5h
14
15
R= OMe, Me
Hydrolysis
O
R'
16
employing an IL-PdNPs catalytic system. In situ genera-
tion of PdNPs is assisted by multi-functionalized ionic liq-
uid which also reduces and stabilizes them. The catalytic
system can be reused at least for 7 times without any sig-
nificant loss in catalytic activity which is one of the green
aspects of method. Novelty of the protocol is exploration
of novel efficient catalytic system for coupling reaction
along with additional features viz. operational simplicity,
reusability of the catalytic system, shorter reaction time,
avoidance of conventional volatile organic solvents, 100%
atom economy, easy work up procedure, etc. Thus we
believe that our findings indicate significant gains toward
achieving ideal transformations.
Fig. 5 Reusability of catalytic system (ionic liquid and Pd-NPs)
Acknowledgements One of authors DSG gratefully acknowledges
DST New Delhi for financial assistance under Start-up research grant
[No. SB/FT/CS-145/2014].
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Affiliations
D. S. Gaikwad1 · K. A. Undale1 · D. B. Patil1 · D. M. Pore2
2
* D. S. Gaikwad
Department of Chemistry, Shivaji University, Kolhapur,
dgchemistry@gmail.com
Maharashtra 416004, India
1
Department of Chemistry, Vivekanand College, Kolhapur,
Maharashtra 416003, India
1 3