Synthesis of a novel 8-hydroxyquinoline functionalized poly (ethylene glycol) bridged dicationic ionic liquid and its application in palladium-catalyzed Heck reaction under solvent-free conditions

Article abstract of DOI:10.1016/j.jorganchem.2013.04.006

A novel 8-hydroxyquinoline functionalized poly (ethylene glycol) bridged dicationic ionic liquid ([HQ-PEG₁₀₀₀-DIL][BF₄]) was synthesized and characterized. It was applied as an efficiently recyclable ligand for Pd-catalyzed Heck reaction under solvent-free conditions. It is noteworthy that the Pd(OAc)₂/[HQ-PEG₁₀₀₀-DIL][BF ₄] catalytic system could be easily recovered and reused without obvious loss of catalytic activity after five recycling runs.

Full text of DOI:10.1016/j.jorganchem.2013.04.006

Journal of Organometallic Chemistry 739 (2013) 1e5
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of a novel 8-hydroxyquinoline functionalized poly (ethylene
glycol) bridged dicationic ionic liquid and its application in palladium-
catalyzed Heck reaction under solvent-free conditions
*
Yinglei Wang, Jun Luo , Zuliang Liu
School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel 8-hydroxyquinoline functionalized poly (ethylene glycol) bridged dicationic ionic liquid ([HQ-
PEG1000-DIL][BF4]) was synthesized and characterized. It was applied as an efficiently recyclable ligand
for Pd-catalyzed Heck reaction under solvent-free conditions. It is noteworthy that the Pd(OAc)2/[HQ-
PEG1000-DIL][BF4] catalytic system could be easily recovered and reused without obvious loss of catalytic
activity after five recycling runs.
Received 26 September 2012
Received in revised form
5 March 2013
Accepted 3 April 2013
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
8-Hydroxyquinoline
Poly (ethylene glycol)
Functionalized ionic liquid
Heck reaction
Solvent-free
1. Introduction
amine, amide, nitrile, ether, alcohol, acid, urea and thiourea, have
been designed and synthesized. Such ionic liquids find application
The palladium-catalyzed Heck reaction is one of the most
important and general methodologies for carbonecarbon bond
formation in organic synthesis [1e4]. In general, the palladium-
catalyzed Heck reaction is performed with phosphine ligands and
base under an inert atmosphere. However, phosphine ligands are
often toxic, expensive, unrecoverable, sensitive to air and moisture,
which limitedthe large-scale application in the industrial chemistry.
On the other hand, recovery or recycling of the expensive palladium
complex is difficult or impossible. It is desirable to develop a robust,
simple and cost-effective non-phosphine ligand for palladium-
catalyzed Heck reaction to make the catalyst recyclable.
Ionic liquids (ILs), which are a special class of molten salts
composed of organic cations and inorganic or organic anions, have
attracted lots of chemists’ attention in the last decades. ILs are
considered as reaction media or catalysts in the organic chemistry
because of their unique properties, such as undetectable vapour
pressure, excellent thermal stability, remarkable solubility, and
ease of recovery and reuse [5e8]. Recently, functionalized ionic
liquids (FILs), so-called task-specific ionic liquids (TSILs), which
incorporate a covalently linked reactive functionality, such as
in a wide range of areas, including catalysis, synthesis, analysis, gas
absorption and new materials [9e11]. Recently, ILs have been re-
ported to be applied in the Heck reaction [12e17]. Hagiwara and co-
workers prepared a novel heterogeneous catalyst by the immobi-
lization of Pd(OAc)2 on the reversed phase silica gel in low con-
centration with the aid of [bmim][PF6] and used for Heck reaction
in water [14]. Sawant and co-workers designed an ester appending
multifunctional ionic liquid for Heck reaction [16].
Poly (ethylene glycol) (PEG) is a linear polymer formed from the
polymerization of ethylene oxide. It has received rising interest as
environmental friendly reaction medium for organic synthesis and
catalytic process because it is cheap, thermally stable, nontoxic,
recoverable, nonvolatile and easily degradable. The commercial
availability of many PEGs and its derivatives with either one or two
terminal hydroxyl groups make it easy to prepare a variety of PEG
supported ligands and catalysts [18e22]. The PEG based function-
alized ionic liquids have proved to display special chemical and
physical properties. Some PEG based functionalized ionic liquids
have been prepared and used as solvents and (or) catalysts in
organic synthesis, such as Heck reaction [23], hydrosilylation re-
action [24], synthesis of peptide [25], Suzuki reaction [26], syn-
thesis of 2-oxazolidinones [27], cycloaddition reaction of CO2 [28].
8-Hydroxyquinoline is a versatile ligand in coordination chem-
istry, which is mainly used for analytical purposes and separation
* Corresponding author. Tel.: þ86 25 84315514; fax: þ86 25 84315030.
E-mail address: luojun@njust.edu.cn (J. Luo).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.04.006

2
Y. Wang et al. / Journal of Organometallic Chemistry 739 (2013) 1e5
techniques [29]. More recently, 8-hydroxyquinoline and its de-
rivatives have been used as an efficient N,O-ligand for the transition-
metal catalyzed reactions, such as Ullmann reaction [30e38],
Sonogashira coupling [39], Suzuki reaction [40,41], hydroxylation
[42], anti-Markovnikov intermolecular hydroalkoxylation [43]. Iyer
and co-workers reported that Heckreaction could be catalyzedbyPd
complex of 8-hydroxyquinoline, however, hazardous organic sol-
vents were used and the catalyst could not be recovered [44].
In our continuous research on synthesis and application of poly
(ethylene glycol) bridged dicationic ionic liquid in synthetic organic
chemistry [45e48], herein, we report a novel 8-hydroxyquinoline
functionalized poly (ethylene glycol) bridged dicationic ionic
liquid ([HQ-PEG1000-DIL][BF4]) (Scheme 1) as an efficient recyclable
ligand for the palladium-catalyzed Heck reaction under solvent-
free conditions. In consideration of the structural feature of [HQ-
PEG1000-DIL][BF4], besides the N-heterocyclic carbene (NHC) donor
derived from the imidazolium skeleton [49], the ether of 8-
hydroxyquinoline could act as an excellent bidentate chelating
ligand (N,O-ligand) for the palladium.
0.055 mol) at ambient temperature. The reaction mixture was
stirred at ambient temperature for 12 h. After completion, the
solvent was evaporated in vacuum. The residue was then dissolved
in ethyl acetate to allow the pyridine hydrochloride to be precipi-
tated and filtered off. After evaporating the solvent, the interme-
diate 1 was obtained and used directly for the next reaction. 1H
NMR (500 MHz, CDCl3, ppm)
(m, 78H).
d
3.77 (t, J ¼ 5.9 Hz, 4H), 3.73e3.60
2.2.2. Synthesis of PEG1000 bridged di-imidazolium compound (2)
Imidazole (8.2 g, 0.12 mol) was melted at around 100 ꢀC and
NaOH (4 g, 0.1 mol) was added. After the solid NaOH thawed,
toluene (50 mL) was added and heated to remove water by azeo-
tropy for 3 h. Then, the toluene was evaporated under reduced
pressure. Subsequently, the solution of intermediate 1 obtained in
CH3CN (80 mL) was added. The mixture was stirred at 70 ꢀC for
another 12 h. After completion, the solvent was removed by
distillation. The residue was dissolved in CH2Cl2 and washed with
deionized water several times to remove inorganic salts and excess
imidazole. After removal of solvent, 20.5 g of the desired compound
2 was obtained, yield 89%. 1H NMR (500 MHz, CDCl3, ppm)
d 7.47 (s,
2. Experimental
2H), 6.96 (d, J ¼ 11.8 Hz, 4H), 4.05 (t, J ¼ 5.2 Hz, 4H), 3.68 (t,
J ¼ 5.2 Hz, 4H), 3.65e3.48 (m, 87H).
2.1. General remarks
2.2.3. Synthesis of 3-chloropropyl PEG1000 bridged di-imidazolium
tetrafluoroborate (3)
All of the reagents and solvents were purchased from com-
mercial suppliers and used without further purification. 1H NMR
and 13C NMR were recorded on Bruker DRX 500 and tetrame-
thylsilane (TMS) was used as internal standard. GC analyses were
performed on an Agilent 7890A instrument. IR spectra were
recorded in KBr disks with a SHIMADZU IRPrestige-21 FT-IR spec-
trometer. The thermogravimetric analysis (TGA) was performed on
a TGA/SDTA851e thermal analyzer (Switzerland-Mettler Toledo).
Samples were loaded into an aluminium oxide crucible and heated
at a rate of 20 ꢀC minꢁ1 from 50 ꢀC to 600 ꢀC under N2. The dif-
ferential scanning calorimetry (DSC) was performed on a DSC823e
(Switzerland-Mettler Toledo), and heated at a rate of 10 ꢀC minꢁ1
from ꢁ50 ꢀC to 300 ꢀC under N2.
Compound
2
(20.5 g) was mixed with 1-bromo-3-
chloropropane (6.5 g, 2.2 equiv) in CH3CN and stirred at 50 ꢀC for
48 h under nitrogen atmosphere. After completion, the solvent was
removed by distillation. The residue was dissolved in deionized
water and washed with ethyl ether several times to remove traces
of starting materials, followed by evaporation under reduced
pressure to yield the yellow oily liquid. Subsequently, NaBF4 (6.7 g,
2.4 equiv) and acetone (60 mL) were added. The reaction mixture
was stirred at room temperature for 48 h. After completion, the
resulting mixture was filtered. With removing solvent of filtrate,
the compound 3 was finally obtained (25.1 g, yield 94%). 1H NMR
(500 MHz, D2O, ppm)
d
8.86 (d, J ¼ 12.5 Hz, 2H), 7.54 (dd, J ¼ 7.4,
5.5 Hz, 4H), 4.42e4.25 (m, 10H), 3.86 (dd, J ¼ 10.3, 5.5 Hz, 6H),
2.2. Synthesis of 8-hydroxyquinoline functionalized poly (ethylene
glycol) bridged dicationic ionic liquid
3.79e3.45 (m, 105H), 2.54e2.27 (m, 4H).
2.2.4. Synthesis of [HQ-PEG1000-DIL][BF4]
2.2.1. Synthesis of PEG1000 dichloride (1)
A mixture of compound 3 (25.1 g), K2CO3 (5.8 g, 2.4 equiv) and 8-
hydroxyquinoline (6.2 g, 2.4 equiv) in acetone (80 mL) was stirred at
50 ꢀC for 72 h. After acetone was removed in vacuum, the residue
was washed repeatedly with ethyl acetate to remove excess 8-
hydroxyquinoline, followed by evaporation under reduced pres-
sure, and the 8-hydroxyquinoline functionalized poly (ethylene
glycol) bridged dicationic ionic liquid was finally obtained (23.5 g,
To a solution of PEG1000 (25 g, 0.025 mol) and pyridine (4.0 mL,
0.05 mol) in CH2Cl2 (150 mL) was dropped SOCl2 (4.0 mL,
yield 81%). 1H NMR (500 MHz, CDCl3, ppm)
d 9.32 (s, 2H), 8.84 (d,
J ¼ 3.4 Hz, 2H), 8.10 (d, J ¼ 8.3 Hz, 2H), 7.61 (s, 2H), 7.51 (s, 2H), 7.42e
7.33 (m, 6H), 7.06 (d, J ¼ 7.3 Hz, 2H), 4.55 (t, J ¼ 6.5 Hz, 4H), 4.38e4.29
(m, 6H), 4.22 (t, J ¼ 5.5 Hz, 4H), 3.82e3.71 (m, 6H), 3.65e3.42 (m,
122H), 2.56e2.45 (m, 4H). 13C NMR (126 MHz, CDCl3, ppm)
d 153.90,
149.16, 140.04, 136.96, 136.18, 129.46, 126.90, 123.18, 122.66, 121.78,
120.41, 109.91, 70.42, 70.23, 70.14, 68.62, 65.39, 49.72, 47.18, 29.44.
IR (KBr, cmꢁ1): 2868, 1568, 1502, 1468, 1375, 1349, 1318, 1257, 1052,
946, 827, 796, 761, 730, 668, 643. ESI-MS, m/z: 612.9 (Mþþ/2, n ¼ 20),
635.0 (Mþþ/2, n ¼ 21), 657.3 (Mþþ/2, n ¼ 22).
2.3. General procedure for Heck reaction and recycling of catalyst
In a typical reaction, aryl halide (1.0 mmol), olefin (1.5 mmol),
Et3N (2 mmol), Pd(OAc)2 (0.01 mmol) and [HQ-PEG1000-DIL][BF4]
(0.1 mmol) were added to a tube and sealed. The reaction mixture
Scheme 1. Synthesis of 8-hydroxyquinoline functionalized poly (ethylene glycol)
bridged dicationic ionic liquid ([HQ-PEG1000-DIL][BF4]).

Y. Wang et al. / Journal of Organometallic Chemistry 739 (2013) 1e5
3
was stirred at 100 ꢀC for a certain time. At the end of the reaction,
2.4.11. (E)-Ethyl 3-(3-methoxyphenyl)acrylate [52]
1H NMR (500 MHz, CDCl3)
J ¼ 7.9 Hz, 1H), 7.13 (d, J ¼ 7.6 Hz, 1H), 7.06 (s, 1H), 6.95 (dd, J ¼ 8.2,
2.5 Hz, 1H), 6.44 (d, J ¼ 16.0 Hz, 1H), 4.28 (q, J ¼ 7.1 Hz, 2H), 3.84 (s,
3H), 1.36 (t, J ¼ 7.1 Hz, 3H).
the final mixture was cooled to room temperature and extracted
with diethyl ether. The combined organic extracts were dried over
anhydrous MgSO4 and concentrated to give the crude product,
which was purified by column chromatography on silica gel (200e
300 mesh) using ethyl acetate/petroleum ether as eluent to afford
the desired product in high purity. Only the trans-products were
selectively obtained and characterized by comparison of 1H NMR
data in the literature.
The catalyst left in the reaction vessel was dried in vacuo for 2 h.
The residue was subjected to a second run by charging the reaction
tube with fresh starting materials without further addition of
Pd(OAc)2 and [HQ-PEG1000-DIL][BF4].
d
7.67 (d, J ¼ 16.0 Hz, 1H), 7.31 (t,
2.4.12. (E)-Ethyl 3-(p-tolyl)acrylate [50,51]
1H NMR (500 MHz, CDCl3)
J ¼ 8.1 Hz, 2H), 7.21 (d, J ¼ 8.0 Hz, 2H), 6.41 (d, J ¼ 16.0 Hz, 1H), 4.28
(q, J ¼ 7.1 Hz, 2H), 2.39 (s, 3H), 1.36 (t, J ¼ 7.1 Hz, 3H).
d
7.68 (d, J ¼ 16.0 Hz, 1H), 7.44 (d,
2.4.13. (E)-Ethyl 3-(4-aminophenyl)acrylate [53]
1H NMR (500 MHz, CDCl3)
d
7.62 (d, J ¼ 15.9 Hz, 1H), 7.37 (d,
J ¼ 8.5 Hz, 2H), 6.67 (d, J ¼ 8.5 Hz, 2H), 6.25 (d, J ¼ 15.9 Hz, 1H), 4.26
2.4. Characterization data of products
(q, J ¼ 7.1 Hz, 2H), 3.95 (s, 2H), 1.34 (t, J ¼ 7.1 Hz, 3H).
2.4.1. (E)-Methyl cinnamate [50,52,54,55]
2.4.14. (E)-Ethyl 3-(4-hydroxyphenyl)acrylate [51,56]
1H NMR (500 MHz, CDCl3)
d
7.72 (d, J ¼ 16.0 Hz, 1H), 7.58e7.52
1H NMR (500 MHz, CDCl3)
d
7.65 (d, J ¼ 16.0 Hz, 1H), 7.45 (d,
(m, 2H), 7.44e7.36 (m, 3H), 6.46 (d, J ¼ 16.0 Hz, 1H), 3.83 (s, 3H).
J ¼ 8.6 Hz, 2H), 6.86 (d, J ¼ 8.6 Hz, 2H), 6.32 (d, J ¼ 16.0 Hz, 1H), 5.24
(s, 1H), 4.28 (q, J ¼ 7.1 Hz, 2H), 1.35 (t, J ¼ 7.1 Hz, 3H).
2.4.2. (E)-Ethyl cinnamate [50e52,54,55]
1H NMR (500 MHz, CDCl3)
d
7.71 (d, J ¼ 16.0 Hz, 1H), 7.54 (dd,
3. Results and discussion
J ¼ 6.7, 2.9 Hz, 2H), 7.40 (dd, J ¼ 6.3, 3.8 Hz, 3H), 6.46 (d, J ¼ 16.0 Hz,
1H), 4.29 (q, J ¼ 7.1 Hz, 2H), 1.36 (t, J ¼ 7.1 Hz, 3H).
The synthetic route of 8-hydroxyquinoline functionalized poly
(ethylene glycol) bridged dicationic ionic liquid is illustrated in
Scheme 1. It was readily prepared through a straightforward four-
step procedure from commercially available starting materials
and reagents in good yields. Firstly, PEG1000 was chlorinated with
thionyl chloride in the presence of pyridine in CH2Cl2 to afford
PEG1000 dichloride 1. Next, the solution of 1 in CH3CN was added
into sodium imidazole, which was prepared from imidazole and
NaOH in toluene, to afford PEG1000 bridged di-imidazolium com-
pound 2. And then, the quaternization of 2 and 1-bromo-3-
chloropropane was conducted in CH3CN, and then bromide was
exchanged with NaBF4 in acetone to afford the 3-chloropropyl
PEG1000 bridged di-imidazolium tetrafluoroborate 3. Finally, ionic
liquid 3 reacted with 8-hydroxyquinoline in the presence of K2CO3
in acetone to afford the target 8-hydroxyquinoline functionalized
2.4.3. (E)-n-Butyl cinnamate [50,55]
1H NMR (500 MHz, CDCl3)
d
7.71 (d, J ¼ 16.0 Hz, 1H), 7.54 (dt,
J ¼ 5.5, 3.5 Hz, 2H), 7.45e7.36 (m, 3H), 6.47 (d, J ¼ 16.0 Hz, 1H), 4.23
(t, J ¼ 6.7 Hz, 2H), 1.71 (tt, J ¼ 15.6, 7.9 Hz, 2H), 1.51e1.40 (m, 2H),
0.99 (t, J ¼ 7.4 Hz, 3H).
2.4.4. (E)-Stilbene [53,55]
1H NMR (500 MHz, CDCl3)
J ¼ 7.7 Hz, 2H), 7.30 (s, 1H), 7.14 (s, 1H).
d
7.54 (d, J ¼ 7.4 Hz, 2H), 7.38 (t,
2.4.5. (E)-Ethyl 3-(4-acetylphenyl)acrylate [54]
1H NMR (500 MHz, CDCl3)
J ¼ 16.0 Hz,1H), 7.63 (d, J ¼ 8.3 Hz, 2H), 6.54 (d, J ¼ 16.0 Hz,1H), 4.30
(d, J ¼ 7.1 Hz, 2H), 2.64 (s, 3H), 1.37 (t, J ¼ 7.1 Hz, 3H).
d
7.99 (d, J ¼ 8.4 Hz, 2H), 7.72 (d,
poly (ethylene glycol) bridged dicationic ionic liquid [HQ-PEG1000
-
DIL][BF4], which was characterized by 1H NMR, 13C NMR, IR, MS.
The thermal property of this dicationic ionic liquid was determined
by thermal gravimetric analysis (TGA) and differential scanning
calorimetry (DSC). TGA results indicates that the [HQ-PEG1000-DIL]
[BF4] have good thermal stability for the high decomposition
temperature (>300 ꢀC) (Fig. 1). As shown in Fig. 2, there was no
melt point for this ionic liquid but had a glass transition tempera-
ture of ꢁ35 ꢀC from differential scanning calorimetry (DSC). In
addition, the solubility of [HQ-PEG1000-DIL][BF4] was determined at
room temperature. In general, it is immiscible with heptane,
cyclohexane, diethyl ether, toluene and water, but miscible with
dichloromethane, acetone, methanol, ethanol, N,N-dime-
thylformamide (DMF) and dimethyl sulfoxide (DMSO).
To optimize the reaction conditions, iodobenzene and ethyl
acrylate were chosen as the substrates for model Heck reaction.
Selected results from our screening experiments are summarized in
Table 1. The amount of catalyst loading was firstly investigated. It
was observed that 1.0 mol% loading amount of Pd(OAc)2 could give
ethyl cinnamate in high yields (Table 1, entries 1e3). However, Pd
2.4.6. (E)-Ethyl 3-(4-bromophenyl)acrylate [51,52]
1H NMR (500 MHz, CDCl3)
d
7.62 (d, J ¼ 16.0 Hz, 1H), 7.53 (d,
J ¼ 8.5 Hz, 2H), 7.39 (d, J ¼ 8.4 Hz, 2H), 6.43 (d, J ¼ 16.0 Hz, 1H), 4.28
(q, J ¼ 7.1 Hz, 2H), 1.35 (t, J ¼ 7.1 Hz, 3H).
2.4.7. (E)-Ethyl 3-(4-cyanophenyl)acrylate [51,52]
1H NMR (500 MHz, CDCl3)
(d, J ¼ 8.3 Hz, 2H), 6.53 (d, J ¼ 16.1 Hz, 1H), 4.30 (d, J ¼ 7.1 Hz, 2H),
1.37 (t, J ¼ 7.1 Hz, 3H).
d
7.69 (dd, J ¼ 12.1, 10.2 Hz, 3H), 7.63
2.4.8. (E)-Ethyl 3-(4-nitrophenyl)acrylate [51,52,54,55]
1H NMR (500 MHz, CDCl3)
d
8.27 (d, J ¼ 8.4 Hz, 2H), 7.71 (dd,
J ¼ 17.7, 12.3 Hz, 3H), 6.58 (d, J ¼ 16.0 Hz, 1H), 4.31 (q, J ¼ 7.1 Hz, 2H),
1.37 (t, J ¼ 7.1 Hz, 3H).
2.4.9. (E)-Ethyl 3-(4-methoxyphenyl)acrylate [50,51,53]
1H NMR (500 MHz, CDCl3)
d
7.66 (d, J ¼ 16.0 Hz, 1H), 7.49 (d,
J ¼ 8.7 Hz, 2H), 6.92 (d, J ¼ 8.7 Hz, 2H), 6.32 (d, J ¼ 16.0 Hz, 1H), 4.27
(q, J ¼ 7.1 Hz, 2H), 3.85 (s, 3H), 1.35 (t, J ¼ 7.1 Hz, 3H).
black precipitated and low yield was obtained if no [HQ-PEG1000
-
DIL][BF4] was added (Table 1, entry 4). When PEG1000 was added in
the reaction, the yield was increased to 58% (Table 1, entry 5). Only
trace of product was detected with 8-hydroxyquinoline as ligand
under solvent-free conditions, but 31% of product was afforded
when the NMP was added as solvent (Table 1, entry 6e7). A high
yield of 72% was obtained in the presence of 3-chloropropyl
2.4.10. (E)-Ethyl 3-(2-methoxyphenyl)acrylate [51]
1H NMR (500 MHz, CDCl3)
d
8.01 (d, J ¼ 16.2 Hz, 1H), 7.52 (dd,
J ¼ 7.7, 1.6 Hz, 1H), 7.40e7.33 (m, 1H), 6.98 (t, J ¼ 7.5 Hz, 1H), 6.93 (d,
J ¼ 8.3 Hz, 1H), 6.55 (d, J ¼ 16.2 Hz, 1H), 4.28 (q, J ¼ 7.1 Hz, 2H), 3.90
(s, 3H), 1.36 (t, J ¼ 7.1 Hz, 3H).

4
Y. Wang et al. / Journal of Organometallic Chemistry 739 (2013) 1e5
Table 1
Optimization of the reaction conditions.a
100
80
60
40
20
0
Entry
Pd(OAc)2
(mol%)
Base
Temperature
(ꢀC)
Time (h)
Yield (%)b
1
2
3
2.0
1.0
0.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
e
100
100
100
100
100
100
100
100
100
100
100
2
2
2
2
2
2
2
2
2
2
2
98
98
53
27
58
Trace
31
72
Trace
48
4c
5d
6e
7f
8g
9
0
100
200
300
400
500
600
10
11
(n-Bu)3N
(i-
Temperature(oC)
93
Pr)2EtN
Pyridine
K2CO3
Et3N
Et3N
Et3N
Fig. 1. The TGA spectrum of [HQ-PEG1000-DIL][BF4].
12
13
14
15
15
1.0
1.0
1.0
1.0
1.0
100
100
90
80
100
2
2
2
2
1
16
0
64
56
72
PEG1000 bridged di-imidazolium tetrafluoroborate 3 (Table 1, entry
8). Base is an important factor to affect the reaction. Only a trace
amount of product was detected in the absence of base (Table 1,
entry 9). Lower yields were obtained when other organic bases
such as (n-Bu)3N, (i-Pr)2EtN or pyridine was used (Table 1, entries
10e12). No desired product was detected when inorganic base
K2CO3 was utilized (Table 1, entry 13). In addition, low temperature
or short time led to lower yields (Table 1, entries 14e15).
To investigate the recyclability of this catalytic system, the
recycle experiments were conducted by model Heck reaction
catalyzed by Pd(OAc)2/[HQ-PEG1000-DIL][BF4]. After completion of
the reaction, the final mixture was cooled to room temperature and
the product was extracted with diethyl ether. The catalyst left in the
reaction vessel was dried under vacuum for 2 h. The resultant
residues were used directly without further treatment for the next
run after being charged with fresh starting materials (iodobenzene,
ethyl acrylate and triethylamine). The results indicated that
Pd(OAc)2/[HQ-PEG1000-DIL][BF4] system could be reused for five
times without apparent loss of catalytic activity (Fig. 3).
a
Reagents: iodobenzene (1.0 mmol), ethyl acrylate (1.5 mmol), base (2.0 mmol),
[HQ-PEG1000-DIL][BF4] (0.1 mmol).
b
GC yield.
c
Without [HQ-PEG1000-DIL][BF4].
With PEG1000 (0.1 mmol).
With 8-hydroxyquinoline (0.1 mmol).
With 8-hydroxyquinoline (0.1 mmol), NMP (2.0 mL).
d
e
f
g
With 3-chloropropyl PEG1000 bridged di-imidazolium tetrafluoroborate
3
(0.1 mmol).
acrylate, ethyl acrylate, n-butyl acrylate and styrene, was firstly
examined to result in high yields (Table 2, entries 1e4). Aryl iodides
with electron-withdrawing groups afforded the corresponding
products in excellent yields (Table 2, entries 5e8). Meanwhile, aryl
iodides with electron-donating groups required prolonged reaction
time to obtain good yields (Table 2, entries 9e14). The aryl iodides
with substituted groups in ortho and meta positions gave lower
yields in comparison with para-isomers due to steric hindrance
(Table 2, entries 9e11). However, the coupling of aryl bromide
bearing strong electron-withdrawing groups, such as 4-
bromonitrobenzene, resulted in lower yield even reacting at
elevated temperature (120 ꢀC) for manifold reaction time (24 h)
with double loading of Pd(OAc)2 (Table 2, entry 15). Unfortunately,
In order to extend the scope of this catalytic system, a variety of
substituted aryl iodides were used to couple with olefins under the
optimized conditions, and the results are presented in Table 2. In
general, all the aryl iodides afforded the corresponding products in
good to excellent yields ranging from 81% to 98%. The scope of this
catalytic system with different vinyl substrates, such as methyl
98
98
97
100
80
60
40
20
0
95
94
16
14
12
10
8
6
4
2
0
-2
-4
1
2
3
4
5
-50
0
50 100 150 200 250 300 350
Temperature(oC)
Run
Fig. 3. Recycling results of model Heck reaction catalyzed by Pd(OAc)2/[HQ-PEG1000
-
Fig. 2. The DSC spectrum of [HQ-PEG1000-DIL][BF4].
DIL][BF4].

Y. Wang et al. / Journal of Organometallic Chemistry 739 (2013) 1e5
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5
Table 2
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Heck reaction of aryl halide with olefin catalyzed by Pd(OAc)2/[HQ-PEG1000-DIL]
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Entry
X
R1
R2
Time (h)
Yield (%)b
1
2
I
I
I
I
I
I
I
I
I
I
I
I
I
I
Br
Cl
H
H
H
H
Me
Et
t-Bu
Ph
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
2
2
2
4
2
2
2
2
4
4
4
4
4
4
24
24
96
94
93
86
93
95
96
98
89
81
83
86
89
84
48
Trace
3
4c
5
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Commun. 12 (2010) 273e276.
p-CH3CO
p-Br
6
7
8
9
10
11
12
13
14
15d
16d
p-CN
p-NO2
p-CH3O
o-CH3O
m-CH3O
p-CH3
p-NH2
p-OH
p-NO2
p-NO2
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6383e6387.
a
Reaction conditions: aryl halide (1.0 mmol), olefin (1.5 mmol), Pd(OAc)2
(0.01 mmol), Et3N (2 mmol), [HQ-PEG1000-DIL][BF4] (0.1 mmol), 100 ꢀC.
b
Isolated yield, all of the products were isolated as trans-isomers.
c
E/Z ¼ 87:13, the ratio of E/Z was determined by GC of the crude reaction mixture.
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519e527.
d
Pd(OAc)2 (0.02 mmol), 120 ꢀC.
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as for the aryl chloride, even bearing strong electron-withdrawing
group such as 4-chloronitrobenzene, only a trace amount of prod-
uct could be detected (Table 2, entry 16).
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4. Conclusions
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In summary, a novel 8-hydroxyquinoline functionalized poly
(ethylene glycol) bridged dicationic ionic liquid was synthesized
and applied to Pd-catalyzed Heck reaction as an efficient ligand
under solvent-free conditions. Using the Pd(OAc)2/[HQ-PEG1000
-
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DIL][BF4] system, a series of substituted aryl iodides coupled with
olefins to afford the corresponding products in good to excellent
yields. Furthermore, this catalytic system could be easily recycled
for five times without obvious deactivation.
Acknowledgements
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978.
This project was financially sponsored and supported by the
National Natural Science Foundation of China (No. 21002050),
Doctoral Fund of Ministry of Education of China for New Teacher
(No. 200802881029), the “Zijin Star Project” and the “Excellence
Initiative Project” of NUST.
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Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.jorganchem.2013.04.006.
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