A highly water-dispersible/magnetically separable palladium catalyst based on a Fe3O4@SiO2 anchored TEG-imidazolium ionic liquid for the Suzuki-Miyaura coupling reaction in water

Article abstract of DOI:10.1039/c3gc42311e

A novel ionic liquid functionalized magnetic nanoparticle was prepared by anchoring an imidazolium ionic liquid bearing triethylene glycol moieties on the surface of silica-coated iron oxide nanoparticles. The material proved to be an effective host for the immobilization of a Pd catalyst through a subsequent simple ion-exchange process giving a highly water dispersible, active and yet magnetically recoverable Pd catalyst (Mag-IL-Pd) in the Suzuki-Miyaura coupling reaction in water. The as-prepared catalyst displayed remarkable activity toward challenging substrates such as heteroaryl halides and ortho-substituted aryl halides as well as aryl chlorides using very low Pd loading in excellent yields and demonstrating high TONs. Since the catalyst exhibited extremely low solubility in organic solvent, the recovered aqueous phase containing the catalyst can be simply and efficiently used in ten consecutive runs without significant decrease in activity and at the end of the process can be easily separated from the aqueous phase by applying an external magnetic field. This novel double-separation strategy with negligible leaching makes Mag-IL-Pd an eco-friendly and economical catalyst to perform this transformation. the Partner Organisations 2014.

Full text of DOI:10.1039/c3gc42311e

Green Chemistry
View Article Online
View Journal
PAPER
A highly water-dispersible/magnetically separable
palladium catalyst based on a Fe3O4@SiO2
anchored TEG-imidazolium ionic liquid for the
Suzuki–Miyaura coupling reaction in water†
Cite this: DOI: 10.1039/c3gc42311e
Babak Karimi,*a Fariborz Mansouria and Hojatollah Valib
A novel ionic liquid functionalized magnetic nanoparticle was prepared by anchoring an imidazolium
ionic liquid bearing triethylene glycol moieties on the surface of silica-coated iron oxide nanoparticles.
The material proved to be an effective host for the immobilization of a Pd catalyst through a subsequent
simple ion-exchange process giving a highly water dispersible, active and yet magnetically recoverable Pd
catalyst (Mag-IL-Pd) in the Suzuki–Miyaura coupling reaction in water. The as-prepared catalyst displayed
remarkable activity toward challenging substrates such as heteroaryl halides and ortho-substituted aryl
halides as well as aryl chlorides using very low Pd loading in excellent yields and demonstrating high TONs.
Since the catalyst exhibited extremely low solubility in organic solvent, the recovered aqueous phase con-
taining the catalyst can be simply and efficiently used in ten consecutive runs without significant decrease
in activity and at the end of the process can be easily separated from the aqueous phase by applying an
external magnetic field. This novel double-separation strategy with negligible leaching makes Mag-IL-Pd
an eco-friendly and economical catalyst to perform this transformation.
Received 9th November 2013,
Accepted 29th January 2014
DOI: 10.1039/c3gc42311e
www.rsc.org/greenchem
catalyst loading, deactivation of catalyst through the agglo-
meration of Pd particles, and product contamination which is a
Introduction
Palladium-catalyzed cross-coupling of aryl halides and triflates serious problem in the pharmaceutical industry. Considering
with arylboronic acids, universally called the “Suzuki–Miyaura this intrinsic limitation of homogeneous catalysts, in addition
reaction”, is one of the most important and versatile trans- to environmental and economical (Pd is an expensive metal)
formations in biaryl synthesis from both academic and indus- concerns, many attempts have been directed toward the devel-
trial points of view.1 This is because the resulting biaryls are opment of new strategies to immobilize the homogeneous Pd
multipurpose building blocks in the field of liquid crystals, catalysts onto various solid supports in the form of either
pharmaceuticals, conducting polymers, herbicides, natural metal complex or metal nanoparticles in order to improve
products, functional materials and ligands for catalysis.2 The their recovery and recycling properties.7 In this context,
great significance of the palladium-catalyzed Suzuki–Miyaura numerous solid supports such as mesoporous and amorphous
reaction has been documented by awarding the 2010 Nobel silica,8 polymers,9 zeolites,10 metal oxides11 and carbon
Prize in Chemistry to Professor Akira Suzuki.3 Whereas the material12 have been adopted for heterogeneous Pd-catalyzed
Suzuki reaction has been conventionally performed using Suzuki reaction. The key factor of these protocols is decreasing
homogeneous palladium catalysts in the presence of phos- the energy and time used for achieving chemical transform-
phine ligands4 and N-heterocyclic carbenes5 or palladacycle ations and separations.
complexes,6 they suffer from some drawbacks such as catalyst
In recent decades, magnetic nanoparticles that have been
separation from the reaction mixture, catalyst recycling, high studied extensively for various biological and medical appli-
cations13 have emerged as smart and promising supports for
immobilization of catalysts because magnetic-supported cata-
aDepartment of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS),
P.O. Box 45137-66731, Gava Zang, Zanjan, Iran. E-mail: karimi@iasbs.ac.ir;
Fax: (+98)-241-4214949
bAnatomy and Cell Biology and Facility for Electron Microscopy Research,
McGill University, 3450 University St, Montreal, Quebec H3A 2A7, Canada
†Electronic supplementary information (ESI) available: Characterization data for
the catalyst and Suzuki products. See DOI: 10.1039/c3gc42311e
lysts can be easily separated from the reaction medium using
an external permanent magnet, which provides a simple separ-
ation of the catalyst without the need for filtration, centrifu-
gation or other tedious workup processes.14 Notably, this
separation technique has great significance for nano-sized
catalyst supports in which the conventional filtration method
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
results in the loss of catalyst particles and product contami- TEG tags of functionalized magnetic nanoparticles result in a
nations. Besides the easy separation, an interesting feature of hydrophilic character for the catalyst and provide superior dis-
magnetic nanoparticles is their convenient surface modifi- persion of catalyst particles in water. In addition, supported IL
cation that provides a wide range of magnetic-functionalized not only stabilizes the Pd nanoparticles during the reaction
catalysts showing identical and sometimes even higher activity but also creates an ionic liquid based nano-environment
than their homogeneous counterparts in organic transform- on the surface of magnetic nanoparticles to enhance their
ations. In recent years, magnetic nanoparticles as catalysts or interaction with aryl halides, thus improving the reaction
catalyst supports have been extensively used in a variety of efficiency.
important organic reactions including C–C couplings,15 C–X
couplings,16 reductions,17 oxidations18 and multicomponent
reactions19 with a high level of activity. Despite the consider-
Experimental
able success achieved in the field of magnetically separable
General information
nanocatalysts, the application of these systems in water as a
All chemicals and solvents were purchased from commercial
suppliers. Liquid NMR was obtained on a DMX-250 and
DMX-400 MHz Bruker Avance instrument using CDCl3 as a
solvent and TMS as an internal standard. Thermogravimetric
analysis was conducted from room temperature to 800 °C in
an oxygen flow using a NETZSCH STA 409 PC/PG instrument.
The structure of the prepared materials were observed by
transmission electron microscopy (Philips CM-200 and Titan
Krios TEM) and were verified further by the nitrogen sorption
analysis (Belsorp, BELMAX, Japan). The content of palladium
in the catalyst was determined using atomic absorption spec-
trometry (Varian). FT-IR spectra were recorded using a Bruker
Vector 22 instrument after mixing the samples with KBr. The
magnetic properties of the prepared materials were measured
using a homemade vibrating sample magnetometer (Meghna-
tis Daghigh Kavir Company, Iran) at room temperature from
−10 000 to +10 000 Oe. Gas chromatography analyses were per-
formed on a Varian CP-3800 using a flame ionization detector
(FID).
green solvent has still remained a great challenge and has not
been addressed properly, especially for Suzuki reaction in
which water-soluble boronic acids fall off to the homocoupling
reaction or hydrolytic deboronation as side reactions. Thanks
to their nano-metric sizes, although magnetic nanoparticles
are well-dispersed in many solvents, they cannot provide a suit-
able exposure of their catalytically active centers in the proxi-
mity of organic substrates when water is used as the reaction
medium. To the best of our knowledge, there are only a few
reports on the application of magnetically separable Pd-cata-
lyzed Suzuki reaction in neat water;20 however, many of them
were necessarily conducted in the presence of large amounts
of ionic liquids or n-Bu4NBr (TBAB) as a phase transfer
reagent. Therefore, it seems that there is still much room to
make novel magnetically recyclable catalysts displaying
improved catalytic performance in pure water. Very recently,
we have introduced a novel water-soluble N-heterocyclic palla-
dium polymer with triethylene glycol (TEG) legs as a highly
recyclable catalyst in the Suzuki–Miyaura coupling of aryl
halides in neat water.21 Furthermore, it was found that this
water-soluble catalyst exhibited much better catalytic activity
Synthesis of silica-coated Fe3O4 magnetic nanoparticles
and yet superior reusability in comparison with its previously Magnetite/silica core/shell nanoparticles were prepared by
developed water-insoluble analog.22 However, despite the using a micro-emulsion method in the presence of sodium
excellent reusability, recycling of this catalyst system requires a dodecylbenzenesulfonate as a surfactant. 1.75 g of sodium
time consuming dialysis technique. Therefore, we were very dodecylbenzenesulfonate was dissolved in 15 mL of xylene by
much interested in designing and preparing a novel catalyst sonication for 30 min to prepare a microemulsion. On the
system by emphasizing controlling its high solubility (dis- other hand, an aqueous solution of iron salts was prepared by
persion) in water while avoiding time consuming recycling dissolving 0.75 mmol of FeCl2·4H2O and 1.5 mmol of Fe-
stages. We hypothesized that incorporating TEG functional- (NO3)3·9H2O in 0.75 mL deionized water (DW). Under vigorous
ities into a magnetically-based supported catalyst should not stirring the iron salts solution was added to the microemulsion
only result in superior water-dispersible character but also it and the mixture was stirred at room temperature for about
may lead to higher catalytic performance and faster recycling. 12 h. After 12 h, the reverse-micelle solution was gradually
Taking cues from these criteria, herein we wish to report on heated to 90 °C under a continuous flow of argon gas for 1 h.
the preparation of a highly water-dispersible/magnetically When the temperature reached to 90 °C, 1 mL of hydrazine
separable Pd catalyst for Suzuki reaction based on a TEG sub- (34 wt% aqueous solution) was injected dropwise into the solu-
stituted imidazolium ionic liquid. To do this, we first prepared tion (formation of a black precipitate was observed) and the
relatively monodispersed Fe3O4@SiO2 core–shell magnetic mixture was stirred at 90 °C for 3 h under a flow of argon gas
nanoparticles using a reverse-micelle template protocol accord- (5 mL min−1). After 3 h, the temperature was cooled down to
ing to a reported procedure with slight modifications.23 The 40 °C within an hour and at this temperature 2 mL of TEOS
resulting silica-coated iron oxide magnetic nanoparticles were was added dropwise into the mixture under vigorous stirring.
then modified with TEG-functionalized IL and subsequent Then the solution was stirred for another 15 h to achieve
2−
simple ion exchange with PdCl4 provides the corresponding formation of silica shells on the surface of the magnetite
magnetic catalyst which is denoted Mag-IL-Pd. In this system, nanoparticles. Finally, the prepared Fe3O4@SiO2 magnetic
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
nanoparticles were collected with the aid of a magnetic bar Immobilization of TEG-IL onto silica-coated Fe3O4 magnetic
and repeatedly washed with DW and EtOH to complete nanoparticles
removal of the surfactant and then dried overnight in an oven
at 80 °C. At the end, a reddish brown powder was obtained.
50 mL toluene by sonication for 30 min, and then a solution
1 g of Fe3O4@SiO2 magnetic nanoparticles was dispersed in
containing 1.65 g TEG-IL in 20 mL toluene was added to it.
Synthesis of 1-(2-(2-methoxyethoxy)ethoxy)-2-bromoethane
(TEG-Br)
The mixture was stirred in refluxing temperature of toluene for
24 h under an argon atmosphere. After 24 h, the nanoparticles
were separated using an external magnet and washed repeat-
edly with MeOH, EtOH and CH2Cl2. Finally, drying under an
air oven for 24 h at 80 °C afforded the Fe3O4@SiO2 supported
IL (Mag-IL). The loading of IL was determined by thermal
analysis.
TEG-Br was prepared according to the Apple reaction.24 In a
typical experiment, triethylene glycol monomethyl ether
(1.64 g, 10 mmol) was added to 50 mL dry CH2Cl2 in a well
dried flask under an argon atmosphere. Then, 4 g (12 mmol)
carbon tetrabromide was added to this solution under stirring
and the reaction mixture was cooled to 0 °C. At 0 °C, a solution
of 3.9 g (15 mmol) triphenyl phosphine in 10 mL dichloro-
methane was added dropwise to the reaction mixture. After
stirring for 5 h the solvent from the reaction mixture was eva-
porated out. 25 mL diethyl ether was added to the reaction
mixture, kept for 5 min and filtered. The same process
(addition of ether and filtration) was repeated thrice. The
residue was subjected to flash column chromatography to
obtain the pure TEG-Br in 84% yield. The spectral data for
Preparation of Mag-IL-Pd catalyst
Synthesis of Mag-IL-Pd catalyst was carried out via a simple
ion-exchange of chloride with Pd salt. In a typical procedure,
500 mg of Mag-IL nanoparticles was sonicated in 20 mL
acetone (Merck) for 30 min. 15.1 mg of Na2PdCl4·3H2O was
dissolved in 3 mL acetone and added to Mag-IL nanoparticles
under stirring under an Ar atmosphere (dropwise and for
10 min). The mixture was stirred for 12 h at room temperature,
and then nanoparticles were collected with a magnet and
washed with acetone and EtOH and finally dried at 80 °C for
5 h. The content of Pd was estimated to be 0.084 mmol g−1
based on AAS.
1
TEG-Br are as follows: H-NMR (250 MHz, CDCl3, 25 °C, TMS):
δ = 3.34 (s, 3H), 3.43 (t, 2H, J = 6.4 Hz), 3.50–3.52 (m, 2H),
3.60–3.66 (m, 6H), 3.77 (t, 2H, J = 6.4 Hz); 13C-NMR (250 MHz,
CDCl3, 25 °C, TMS): δ = 30.32, 59.00, 70.48, 70.56, 70.57, 71.15,
71.89 (C7H15BrO3).
General procedure for the Suzuki coupling reaction using
Mag-IL-Pd catalyst
Synthesis of 1-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-3-(3-
(trimethoxysilyl)propyl)-1H-imidazol-3-ium chloride (TEG-IL)
The Suzuki reaction was performed in a 10 mL round-
bottomed flask, aryl halide (0.5 mmol), arylboronic acid
(0.6 mmol), K2CO3 (0.75 mmol), Mag-IL-Pd (0.025–0.5 mol%
with respect to aryl halide) and water (3 mL) were charged and
stirred at r.t. to 120 °C under an argon atmosphere. The reac-
tion progress was monitored by GC. After completion of the
reaction, the mixture was allowed to cool to room temperature.
The product was extracted with addition of 3 mL n-hexane
while the Mag-IL-Pd catalyst was remaining in aqueous phase.
The organic layer was dried with MgSO4 and the solvent was
then removed under reduced pressure to get the crude
product. Pure products were obtained after recrystallization or
by isolation of the residue by column chromatography on
silica using the n-hexane and ethyl acetate mixture as
For the preparation of TEG-IL all reactions were performed
under a dry argon atmosphere and all solvents were dried in
the presence of suitable reagents and freshly distilled prior to
use. In a typical experiment, a suspension of sodium imidazo-
lide in dry THF was prepared from the reaction between dried
imidazole (20 mmol) and NaH 95% (0.77 g) in a dried two
neck flask containing dry THF (40 mL) under an argon atmos-
phere. Then, 20 mmol TEG-Br was added to the solution of
sodium imidazolide and the mixture was heated to reflux for
24 h and then cooled to room temperature. After removal of
THF under reduced pressure, a solution containing 20 mmol
(4.4 g) 3-chloropropyltrimethoxysilane (98%, Merck) in 40 mL
absolute toluene was added to the mixture. Again, the reaction
mixture was heated to refluxing temperature of toluene for
48 h, and after cooling to room temperature, maintained over-
night for phase separation. Then, the upper phase of the
mixture (toluene) was removed with a pipette. Subsequently,
1
an eluent. All the products were characterized by H NMR and
13C NMR.
Procedure for the reusability test of Mag-IL-Pd catalyst
the residual oil was washed with absolute toluene (3 times) 4-Bromoanisole (1 mmol), phenylboronic acid (1.2 mmol),
and CH2Cl2 to remove unreacted substrates and precipitated K2CO3 (1.5 mmol) and the Mag-IL-Pd catalyst (0.025 mol% Pd)
NaCl from the reaction mixture. Finally, after removing the were added to 3 mL distilled water and heated under an argon
solvent under vacuum at room temperature, a highly viscose atmosphere in an oil bath at 80 °C. After completion of the
yellow IL was obtained (TEG-IL) in 89% yield. 1H NMR reaction, the product was extracted with hexane and the
(250 MHz, CDCl3, 25 °C, TMS): δ = 10.10 (s, 1H), 7.64–7.77 aqueous phase containing the Mag-IL-Pd catalyst was loaded
(m, 2H), 4.53–4.59 (m, 2H), 4.26–4.35 (m, 2H), 3.87 (m, 2H), with the reactants and base for the next run. The catalyst in
3.35–3.65 (m, 17H), 3.34 (s, 3H), 1.96–2.13 (m, 2H), water could be reused for 10 subsequent runs without any loss
0.60–0.68 (m, 2H).
of activity and no need for washing and purification of the
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
catalyst after each run. After 10 runs reusing the catalyst by
this technique, the catalyst was separated from water by using
an external magnet.
Results and discussion
To prepare the catalyst, initially magnetite/silica core/shell
nanoparticles were prepared using a Fe+2/Fe+3 mixture via a
micro-emulsion method in the presence of sodium dodecyl-
benzenesulfonate (SDBS) as a surfactant (Scheme 1). In this
method, SDBS provides an emulsion in xylene/H2O solvent
which is a platform for nucleation and limited growth and
silica-coating of iron oxide magnetic nanoparticles providing
precise control of the size, shape and core–shell structure of
nanoparticles.
Then, the imidazolium based ionic liquid (TEG-IL) that has
TEG functionality on one side and a trimethoxysilyl moiety on
the other side was synthesized and subsequently grafted to the
surface of silica-coated iron oxide magnetic nanoparticles in
refluxing toluene for 24 h. Finally, treatment of IL-function-
alized magnetic nanoparticles with Na2PdCl4·3H2O in acetone
Fig. 1 FT-IR spectra for Fe3O4@SiO2 (a), Mag-IL (b) and Mag-IL-Pd
catalysts (c).
at room temperature for 12 h provides the Mag-IL-Pd catalyst
simple ion-exchange of Cl− with PdCl4
2−
through
a
(Scheme 1).
The structure of prepared materials was characterized by
various techniques including TEM, TGA, FT-IR, VSM, AAS and
N2 adsorption–desorption analysis. FT-IR spectra of
Fe3O4@SiO2 magnetic nanoparticles showed characterization
peaks for Fe–O–Fe, Si–O–Si and O–H groups (Fig. 1a), which
indicates the presence of iron oxide and silica phases. For IL-
functionalized Fe3O4@SiO2 (Mag-IL) and Mag-IL-Pd catalysts,
additional peaks were observed for CvC, CvN, aromatic C–H
and aliphatic C–H, which confirms successful immobilization
Fig. 2 TG analysis of Fe3O4@SiO2 (a), Mag-IL (b), Mag-IL-Pd catalyst
(c) and recycled Mag-IL-Pd catalyst after 10 cycles (d).
of TEG-IL on the surface of magnetic nanoparticles (Fig. 1b
and 1c). Also, the presence of TEG-IL on the surface of magnetic
nanoparticles was proved by TG analysis. While the TG curve
of Fe3O4@SiO2 has no weight loss after 300 °C, for Mag-IL and
Mag-IL-Pd catalysts a sharp decrease in weight was observed at
300 °C–700 °C (Fig. 2).
In addition, TG analysis indicated that the prepared Mag-
IL-Pd catalyst has high thermal stability and negligible IL
leaching up to about 300 °C. Based on TG analysis the amount
of loaded IL on the surface of magnetic nanoparticles was
1.3 mmol IL g−1. The prepared material showed typically type
IV N2 adsorption–desorption isotherm with H3 hysteresis
loops according to the IUPAC classification (Fig. S1–S3†). Also,
the Brunauer–Emmett–Teller (BET) surface areas for
Fe3O4@SiO2, Mag-IL and Mag-IL-Pd catalysts were 312, 47.5
and 35 m2 g−1, respectively. The large surface area of
Fe3O4@SiO2 magnetic nanoparticles was related to the
small particle size of this material as could be observed
in TEM images. After immobilization of IL the surface area
Scheme 1 General route for the synthesis of Fe3O4@SiO2 magnetic
nanoparticles and Mag-IL-Pd catalyst.
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
Fig. 4 Good dispersion and solubility of Mag-IL-Pd catalyst in water (a),
distribution of Mag-IL-Pd catalyst in
a biphasic water/n-hexane
system (b), and easy separation of Mag-IL-Pd catalyst using an external
magnet (c).
analysis in order to measure the zeta potential and possibly
quantify the stability of colloidal dispersion of our catalyst in
water. It is generally accepted that zeta potentials greater than
30 mV (or more negative than −30 mV for negatively charged
particles) are generally considered as a value to prove the stabi-
lity of colloidal dispersion.25 We have obtained an initial value
of 45.9 mV at 25 °C after mixing of the colloidal solution for
5 min before analysis (ESI, Fig. S8†). This value certainly high-
lights the notion that our catalyst affords a stable colloidal
mixture in water. The formation of stable colloidal dispersion
of the present catalyst system was further confirmed by per-
forming zeta potential analysis of the above mixture after two
days which gave a value of 41.1 mV (ESI, Fig. S9†). This clearly
demonstrates that our catalyst system provided a consistently
stable dispersion in pure water.
Fig. 3 TEM images of Fe3O4@SiO2 (a, b), Mag-IL (c) and Mag-IL-Pd
catalyst (d).
dramatically decreased to 47.5 m2 g−1 because the IL occupied
the surface of nanoparticles and filled completely the inter-
particles spaces. Furthermore, a small decrease in the surface
area from Mag-IL to Mag-IL-Pd catalyst (47.5 to 35 m2 g−1) con-
firmed that the ion-exchange of Cl− with PdCl4 was carried
2−
The magnetic properties of the Fe3O4@SiO2, Mag-IL and
Mag-IL-Pd catalysts were investigated using a vibrating sample
magnetometer at room temperature. As illustrated in Fig. 5,
the magnetization curves of the prepared materials exhibit no
hysteresis loop which demonstrates its superparamagnetic
characteristics. Moreover, the strong magnetic properties of
the prepared catalyst were revealed by complete and easy
out effectively. In addition, AAS analysis indicates the presence
of Pd in the catalyst and the content of Pd was estimated to be
0.084 mmol Pd g−1. The structure of the prepared materials
was further verified using transmission electron microscopy
(TEM) images. As can be clearly seen, Fe3O4@SiO2 nanoparti-
cles have a well-defined core–shell structure with relatively
narrow size distribution (Fig. 3a). A magnified TEM image of a
single Fe3O4@SiO2 nanoparticle indicated that the diameter of
the iron oxide core and the thickness of silica shell are about
10 and 5–7 nm, respectively (Fig. 3b). After functionalization
with TEG-IL and the subsequent ion-exchange process the
nanoparticles kept their core–shell structure as shown in the
edge of their TEM images (Fig. 3c and 3d).
All of these observations confirmed the successful immobil-
ization of TEG-IL onto the Fe3O4@SiO2 nanoparticles. It is also
worth mentioning that although the TEM image of the Mag-
IL-Pd catalyst showed a little agglomeration of magnetic nano-
particles, no aggregation of Pd nanoclusters had occurred or
was detected in the sample either before or after catalysis (vide
infra). As shown in Fig. 4a the nanoparticles provide a homo-
geneous and stable suspension after dispersing in water due
to the presence of a hydrophilic ionic liquid in their surfaces.
Interestingly, this suspension is even stable for several days at
room temperature without any precipitation. To further shed
light on this issue, we prepared a sample of our catalyst in
water according to its actual concentration in the described
Fig. 5 The VSM curves of Fe3O4@SiO2 (A), Mag-IL (B), Mag-IL-Pd cata-
protocol. We then performed a dynamic light scattering (DLS) lysts (C) using a KAVIR magnetometer.
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
attraction using an external magnet (Fig. 4c). The saturation
magnetization of the Fe3O4@SiO2 magnetic nanoparticles was
found to be 8.64 emu g−1 as measured using a homemade
vibrating sample magnetometer (Meghnatis Daghigh Kavir
Table 1 Optimization of the Suzuki coupling reaction of 4-bromoani-
sole and phenyl boronic acid in the presence of Mag-IL-Pd
Company, Iran). As expected, after functionalization with
2−
TEG-IL and subsequent ion-exchange with PdCl4
it was
reduced to 5.74 emu g−1 and 5.58 emu g−1, respectively.
It is believed that the immobilization of TEG-IL on the
surface of magnetic nanoparticles could provide a good distri-
bution of catalytically active Pd species on the support and
stabilizes the Pd nanoparticles during the chemical reaction,
and also protects the Pd nanoparticles from aggregation. In
addition, the hydrophilic character of supported IL provides a
means of good dispersion of magnetic nanoparticles in
aqueous medium for developing this system as a semi-homo-
geneous Pd catalyst for organic reactions in neat water as a
safe and green solvent.
The catalytic activity of the prepared Mag-IL-Pd catalyst was
evaluated in Suzuki cross-coupling reaction in water. Although
the boronic acids are water-soluble, as mentioned above,
usually the efficiency of Suzuki reaction in neat water is ham-
pered by side reactions of boronic acids themselves such as
homo-coupling reaction or hydrolytic deboronation. In
addition, the major drawback associated with magnetic sup-
ported Pd catalysts when water is the reaction solvent is the
poor interaction of active Pd with organic substrates. To over-
come this drawback, typically a mixture of organic solvents
and water is used as the reaction medium for magnetic sup-
ported Pd-catalyzed Suzuki reaction.26 It is supposed that this
magnetic Pd catalyst with its functionalized hydrophilic ionic
liquid provides a good interaction between the water-soluble
boronic acids and hydrophobic aryl halides and improves the
efficiency of Suzuki reaction in neat water.
The reaction of 4-bromoanisole and phenyl boronic acid
was used for initial studies and after optimization of time and
temperature (Table S1†) the best result was obtained after 12 h
at 60 °C using 0.1 mol% of Mag-IL-Pd catalyst and K2CO3 as a
base. We next investigated the impact of a number of organic
as well as inorganic bases under similar reaction conditions in
a more systematic manner (Table 1). Under the described con-
ditions at 60 °C in neat water the best catalytic performance
was obtained using K2CO3 (Table 1, entry 2).
Having optimized the reaction conditions, we next pro-
ceeded to examine the scope and limitation of this Mag-IL-Pd
catalyst in the Suzuki cross-coupling reaction of various types
of iodo-, bromo-, and chloroaryl derivatives and arylboronic
acids (Table 2). In general, all of the coupling products were
obtained in good to excellent yields with high TONs using as
low as 0.025–0.5 mol% of Mag-IL-Pd (Pd mol%) and K2CO3 as
a base during the 4–24 h in neat water. As expected, aryl
iodides were rapidly converted to the respective products using
only 0.025 mol% of catalyst for 4–6 h at 60 °C (Table 2, entries
1–6). Moreover, bromobenzene and aryl bromides bearing the
electron-withdrawing group at the para position were reacted
with boronic acids in high yields for 6–7.5 h again using
0.025 mol% of the catalyst (Table 2, entries 8–13). It is worth
Entry
T (°C)
t (h)
Base
Yielda (%)
1
2
3
4
5
6
7
8
60
60
60
60
60
60
60
60
6
12
12
12
12
12
12
12
K2CO3
K2CO3
52
96
63
52
63
41
51
39
Cs2CO3
tBuOK
Na2CO3
NaOAc·3H2O
Et3N
K3PO4
a Reaction conditions: 4-bromoanisole (0.5 mmol), phenyl boronic acid
(0.6 mmol), base (0.75 mmol), and H2O (3 mL), under an argon
atmosphere, GC yield.
mentioning that the Suzuki reactions of iodo and bromo
arenes with phenyl boronic acid effectively proceeded even
at room temperature with good yields but longer reaction
times were required to allow satisfactory conversion (Table 2,
entries 7 and 11). Also, electron-rich aryl bromides such as
those bearing OMe, OH or NH2 groups at the para or meta
position, which are classified as highly challenging coupling
partners, selectively furnished the corresponding products
after 12 h at 80 °C using 0.025 or 0.05 mol% of the catalyst
(Table 2, entries 14–18). Remarkably, no product arising from
the homocoupling of aryl boronic acids or cross-coupling with
OH and NH2 functional groups were detected in this sub-
strates. Then, we focused our investigation on the Suzuki reac-
tion of sterically hindered aryl bromides and boronic acids
and interestingly it was found that the system was effective for
the synthesis of mono or di-ortho substituted biaryl com-
pounds using as low as 0.025–0.5 mol% of the catalyst at
60–80 °C as exemplified by entries 19–24 in Table 2.
Since heteroaromatic compounds are very important frag-
ments in most of the drugs, the cross-coupling reactions of
these compounds are in high demand, but deactivation of
the transition metal catalysts with the heteroatoms such as
nitrogen or sulfur usually hampers the efficiency of these types
of coupling reactions.27 Thus, we examined the efficiency of
our system for Suzuki reaction of heteroaryl bromides or
iodides with boronic acids. As can be seen in entries 25–30 of
Table 2, using 0.05 or 0.1 mol% of the Mag-IL-Pd catalyst at
60 °C or 80 °C was quite effective for cross-coupling reaction of
heteroaryl compounds with boronic acids in excellent yields.
However, when heteroatom-containing boronic acid was used
as a coupling partner, moderate yields were obtained (Table 2,
entry 31). Encouraged by these results, we next turned our
attention to the use of more challenging chloroarenes for this
reaction. Our preliminary investigations showed that appli-
cation of the optimized coupling protocol for the Suzuki reac-
tion of aryl chlorides in water at 80 °C was inefficient and gave
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
Table 2 The Suzuki reaction of various aryl halides and boronic acids in the presence of Mag-IL-Pd catalyst
Entry
Ar1
Ar2
X
T (°C)
t (h)
x (mol%)
Yielda (%)
TON/TOF (h−1
)
1
2
3
4
5
6
7
8
Ph
Ph
Ph
I
I
I
I
I
I
I
60
60
60
60
60
60
r.t.
60
60
60
r.t.
60
60
80
80
80
80
80
80
60
80
80
80
80
60
80
80
80
80
80
80
80
120
120
6
6
4
4
6
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.05
0.05
0.05
0.025
0.025
0.1
0.1
0.1
0.5
0.05
0.1
0.1
0.05
0.1
0.1
0.05
0.2
95
>99
99
93
100
95
72
82
97
100
100
100
100
100
90
3800/633.3
4000/666.7
3960/990
3720/930
4000/666.7
3800/633.3
2880/120
3280/437.3
3880/517.3
4000/666.7
4000/166.7
4000/666.7
4000/666.7
4000/333.3
3600/300
2000/166.7
1940/161.7
2000/166.7
4000/333.3
4000/500
1000/83.3
950/63.3
4-Me–C6H4
Ph
4-Me–C6H4
Ph
4-Me–C6H4
Ph
Ph
4-Me–C6H4
Ph
Ph
4-Me–C6H4
Ph
Ph
4-NO2–C6H4
4-NO2–C6H4
4-OMe–C6H4
4-OMe–C6H4
Ph
Ph
Ph
6
24
7.5
7.5
6
24
6
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
I
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
4-CHO–C6H4
4-CHO–C6H4
4-CHO–C6H4
4-CO2H–C6H4
4-OMe–C6H4
4-OMe–C6H4
4-OH–C6H4
4-NH2–C6H4
3-OH–C6H4
2-CHO–C6H4
4-CHO–C6H4
2-CHO–C6H4
2-Me–C6H4
2-Et–C6H4
2,6-Me–C6H3
2-Thiophenyl
5-Pyrimidinyl
2-Thiophenyl
3-Pyridyl
6
12
12
12
12
12
12
8
12
15
15
20
12
12
12
15
15
15
24
24
24
24
4-Me–C6H4
Ph
Ph
Ph
100
97
100
100
100
100
95b
89b
87b
>99
100
100
97
Ph
2-Me–C6H4
2-Me–C6H4
2-Me–C6H4
2-Me–C6H4
Ph
Ph
Ph
Ph
Ph
Ph
Ph
3-Pyridyl
Ph
890/59.3
174/8.7
2000/166.7
1000/83.3
1000/83.3
1940/129.3
1000/66.7
1000/66.7
1020/42.5
185/7.8
3-Thiophenyl
2-Pyridyl
Ph
4-NO2–C6H4
4-NO2–C6H4
4-NO2–C6H4
100b
100b
51
37b,c
96b,d
85b,d
Ph
0.2
0.2
480/20
425/17.7
4-Me–C6H4
a Reaction conditions: aryl halide (0.5 mmol), boronic acid (0.6 mmol), K2CO3 (0.75 mmol), and 3 mL H2O, under an argon atmosphere, GC
yields. b 0.5 eq. TBAB was added. c H2O–t-BuOH (1 : 1) was used as a solvent. d H2O–DMF (1 : 1) was used as a solvent.
a considerable amount of the products arising from the homo- 12 h. But our separation technique was different from other
coupling of the employed boronic acid. However, we found conventional magnetic supported catalysts. The presence of a
that by changing the solvent to t-BuOH–H2O (1 : 1), and hydrophilic ionic liquid in the surface of magnetic nanoparti-
increasing the catalyst loading to 0.2 mol% at 80 °C, the coup- cles provides a means of complete dispersion of the catalyst
ling reaction of aryl chlorides bearing electron-withdrawing into the aqueous phase, and as far as we examined, the catalyst
groups went to completion within 24 h, affording the corres- had no affinity to the organic phase. Considering this property,
ponding cross-coupled products in moderated yields (Table 2, after the first use of the catalyst in the above mentioned
entry 32).We found that by changing the reaction solvent to Suzuki reaction, the product was simply extracted with
H2O–DMF (1 : 1) and increasing the reaction temperature to n-hexane while the Mag-IL-Pd catalyst remained in the aqueous
120 °C resulted in excellent yields of the Suzuki coupling pro- phase (Fig. 4b). In the next stage, the aqueous phase contain-
ducts (Table 2, entries 33 and 34), but due to the environ- ing the Mag-IL-Pd catalyst was recharged with fresh coupling
28
mental impact of DMF we decided not to continue this partners and K2CO3 for the next run without any washing
protocol for the rest of the aryl chlorides in the present form.
and purification of the catalyst. The results indicated that this
The recycling and recovery of the supported catalysts are a simple separation method could be repeated for 10 consecu-
very important issue from both the practical and environment tive runs and the recovered aqueous phase containing the
points of view. Since the primary target of this study was to Mag-IL-Pd catalyst showed remarkably constant catalytic
develop a highly dispersible as well as easily recoverable cata- activity in all the 10 cycles (Fig. 6). Finally, the magnetic sup-
lyst, we further explored the reusability of the catalyst in the ported catalyst was easily and completely separated from the
model reaction between 4-bromoanisole and phenylboronic aqueous phase using an external magnetic field (Fig. 4c).
acid in the presence of 0.025 mol% of catalyst at 80 °C for However, it is worth mentioning that the complete magnetic
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
Fig. 6 Recycling of the Mag-IL-Pd catalyst in the Suzuki reaction of
4-bromoanisole and phenylboronic acid.
separation of this catalyst from the water consumes more time
(after five minutes) in comparison to other magnetic materials
due to its high water-dispersity. Moreover, owing to the highly
water-dispersible feature of the designed catalyst we developed
a novel double-separation technique (strategy) for complete and
easy recycling of the catalyst for the first time. Since we also
recycled n-hexane in each reaction cycle, we were able to
perform all of the 10 consecutive runs by employing as low as
50 mL of n-hexane for the extraction of coupling products,
giving high TON of 39 760. It is also worth mentioning that the
amount of leached Pd species into the aqueous phase in the
selected runs of recycling test (runs 2, 10) and also into the
final extracted n-hexane phase was negligible (less than detec-
tion limit) as measured by ICP-AES analysis. The recycled cata-
lyst after the 10th run was analyzed with ICP-AES, TEM and
TGA. ICP-AES indicated no decrease in Pd content of the cata-
lyst after 10 cycles. The Pd content of the catalyst after 10 runs
was the same as the fresh catalyst (0.084 mmol Pd g−1). TEM
image of the recovered catalyst after the 10th reaction run also
indicated that the Mag-IL-Pd catalyst maintained its core–shell
structure after using in 10 consecutive Suzuki reactions
(Fig. 7). However, as can be seen it is very difficult (actually
impossible in this system) to discriminate between the mag-
netic nanoparticles and the Pd nanoparticles possibly gener-
ated in the catalyst matrix. Therefore, in order to assess
whether the Mag-IL-Pd catalyst system could be a source of
in situ generation of Pd nanoparticles in the course of reaction,
the kinetics of the Suzuki reaction between bromobenzene
and phenylboronic acid in the presence of 0.025 mol% of Mag-
IL-Pd have been investigated in the presence of an excess of
Hg(0) (Pd–Hg; 1 : 400) following the condition demonstrated in
Table 2, entry 8.22 This new control experiment led to a
remarkable decrease in the catalytic activity upon addition of
Hg(0), giving the respective biaryl in 18% conversion after 8 h
at 60 °C, which is a clear indication that Mag-IL-Pd might
Fig. 7 TEM image of the recycled catalyst after 10th reaction runs.
the reaction pathway (ESI Fig. S12†). Therefore, although we
were not capable to see any Pd nanoparticles in the TEM
images of the recovered Mag-IL-Pd, based on both the
observed induction period and also positive Hg poisoning
experiments, it would be impossible to exclude the generation
of Pd nanoparticles.22 Therefore, we believe that the Pd nano-
particles are most likely in sub-nanometer sizes and are highly
dispersed on the magnetic support thus estimating their size
distribution is technically impossible at this stage.
On the other hand, TG analysis of recovered catalyst
showed that the amount of supported IL was slightly less than
the fresh catalyst (Fig. 2d). The fact that Pd content of the final
magnetically recycled catalyst has not reduced and that the
catalyst has operated in a homogeneous pathway (as expected
from its high dispersible behaviour in water), provides at least
a noticeable feature concerning the present catalyst system.
We believe that in the present catalytic system while Mag-IL-Pd
is acting as a semi-homogeneous or even as a reservoir for
highly active and soluble Pd species in water, the imidazolium
functionalities on the surface of magnetic nanoparticles may
also create a nano-ionic liquid environment to continuously
re-capture the palladium nanoparticles, thus resulting in sig-
nificant Pd preservation at the end of the process.
Conclusions
We demonstrated the preparation of a novel ionic liquid func-
tionalized magnetic nanoparticle by anchoring an imidazo-
indeed be a source of generation of Pd nanoparticles (ESI lium ionic liquid bearing triethylene glycol moieties on the
Fig. S10 and S11†). It is also worth noting that the existence of
surface of silica-coated iron oxide nanoparticles as a new
an induction period of about 15 min can be also considered as
highly water-dispersible/magnetically separable support for cata-
a strong evidence for the generation of Pd nanocluster during lysis of organic reaction in aqueous medium. A simple ion
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
exchange reaction of Cl− by PdCl4 provides a high perform-
ance magnetically separable Pd catalyst that has remarkable
efficiency and reusability for the Suzuki coupling reaction of a
wide range of activated and deactivated aryl halides with
boronic acids in water. Interestingly, the prepared catalyst
showed improved activity in the Suzuki coupling reaction of
highly challenging substrates such as heteroaryl- and ortho-
substituted aryl halides using very low Pd loading, affording
the corresponding cross-coupled products in excellent yields
and TONs. It is believed that the presence of a hydrophilic
ionic liquid on the structure of the catalyst not only provides a
good distribution of Pd nanoparticles on the surface of the
support and its stability during the reaction but also generates
a stable dispersion (solubility) of the catalyst in water as the
reaction medium and exposes the active Pd sites to substrates
like homogeneous systems. Since the catalyst exhibited extre-
mely low solubility in organic solvent, the recovered aqueous
phase containing the catalyst can be simply and efficiently
used in ten consecutive runs without a significant decrease in
activity and at the end of the process can be easily separated
from the aqueous phase by applying an external magnetic
field. This novel double-separation strategy with negligible
leaching makes the Mag-IL-Pd an eco-friendly and economic
catalyst to perform this transformation. Altogether, the possi-
5 E. A. B. Kantchev, C. J. O’Brien and M. G. Organ, Angew.
Chem., Int. Ed., 2007, 46, 2768; W. A. Herrmann, Angew.
Chem., Int. Ed., 2002, 41, 1290; O. Navarro, R. A. Kelly and
S. P. Nolan, J. Am. Chem. Soc., 2003, 125, 16194;
G. Altenhoff, R. Goddard, C. W. Lehmann and F. Glorius,
J. Am. Chem. Soc., 2004, 126, 15195.
6 L. Botella and C. Najera, Angew. Chem., Int. Ed., 2002, 41,
179; R. B. Bedford, C. S. J. Cazin and S. L. Hazelwood,
Angew. Chem., Int. Ed., 2002, 41, 4120.
2−
7 A. Molnar, Chem. Rev., 2011, 111, 2251.
8 V. Polshettiwar, C. Len and A. Fihri, Coord. Chem. Rev.,
2009, 253, 2599; M. Cai, Q. Xu and Y. Huang, J. Mol. Catal.
A: Chem., 2007, 271, 93; S. M. Lee, H. J. Yoon, J. H. Kim,
W. J. Chung and Y. S. Lee, Pure Appl. Chem., 2007, 79, 1553;
B. Karimi, D. Elhamifar, J. H. Clark and A. J. Hunt,
Chem.–Eur. J., 2010, 16, 8047; B. Karimi and A. Zamani,
Org. Biomol. Chem., 2012, 10, 4531; L. Li, J. L. Shi and
J. N. Yan, Chem. Commun., 2004, 1990; K. Shimizu,
S. Koizumi, T. Hatamachi, H. Yoshida, S. Komai,
T. Kodama and Y. Kitayama, J. Catal., 2004, 228, 141.
9 S. Schweizer, J. M. Becht and C. L. Drian, Tetrahedron,
2010, 66, 765; E. Sin, S. S. Yi and Y. S. Lee, J. Mol. Catal. A:
Chem., 2010, 315, 99; A. Primo, M. Liebel and F. Quignard,
Chem. Mater., 2009, 21, 621.
bility to perform the reaction in water, and at the same time 10 L. Artok and H. Bulut, Tetrahedron Lett., 2004, 45, 3881;
the easy and rapid recycling protocol via the described double-
A. Corma, H. Garcia and A. Leyva, Appl. Catal., A, 2002, 236,
separation technique, makes this protocol a valid candidate
179.
towards the goal of green chemistry. We speculate that this 11 K. Gude and R. Narayanan, J. Phys. Chem. C, 2011, 115,
catalyst system would open a new challenging area in the 12716.
design of new types of water dispersible/magnetically separ- 12 T. Maegawa, Y. Kitamura, S. Sako, T. Udzu, A. Sakurai,
able catalyst systems in other important industrial as well as
synthetic transformations.
A. Tanaka, Y. Kobayashi, K. Endo, U. Bora, T. Kurita,
A. Kozaki, Y. Monguchi and H. Sajiki, Chem.–Eur. J., 2007,
13, 5937; G. Marck, A. Villiger and R. Buchecker, Tetrahe-
dron Lett., 1994, 35, 3277; F. X. Felpin, T. Ayad and S. Mitra,
Eur. J. Org. Chem., 2006, 2679.
References
13 Q. A. Pankhurst, J. Connolly, S. K. Jones and J. Dobson,
J. Phys. D: Appl. Phys., 2003, 36, R167, and references cited
therein; Z. M. Saiyed, S. D. Telang and C. N. Ramchand,
Biomagn. Res. Technol., 2003, 1, 2; S. K. Sahoo and
V. Labhasetwar, Drug Discovery Today, 2003, 8, 1112.
14 For a recent review on the field of magnetically recyclable
catalysts see: V. Polshettiwar, R. Luque, A. Fihri, H. Zhu,
M. Bouhrara and J.-M. Basset, Chem. Rev., 2011, 111,
3036.
1 Metal-Catalyzed Cross-Coupling Reaction, ed. F. Diederich
and A. de Meijere, Wiley-VCH, Weinheim, 2004,
pp. 41–109; J.-P. Corbet and G. Mignani, Chem. Rev., 2006,
106, 2651; L. Yin and J. Liebscher, Chem. Rev., 2007, 107,
133.
2 G. Bringmann, S. Rudenauer, T. Bruhn, L. Benson and
R. Brun, Tetrahedron, 2008, 64, 5563; Y. D. Wang, M. Dutia,
M. B. Floyd, A. S. Prashad, D. Berger and M. Lin, Tetra-
hedron, 2009, 65, 57; F. Bellina, S. Cauteruccio, A. Di Fiore, 15 P. D. Stevens, G. Li, J. Fan, M. Yen and Y. Gao,
C. Marchetti and R. Rossi, Tetrahedron, 2008, 64, 6060;
Y. Fang, R. Karisch and M. Lautens, J. Org. Chem., 2007, 72,
1341; X. Yang, X. Dou and K. Mullen, Chem.–Asian J., 2008,
3, 759; J. Kim and T. M. Swager, Nature, 2001, 411, 1030;
J. Hassan, M. Sevignon, C. Gozzi, E. Schulz and
M. Lemaire, Chem. Rev., 2002, 102, 1359.
Chem. Commun., 2005, 4435; P. Li, L. Wang, L. Zhang and
G. W. Wang, Adv. Synth. Catal., 2012, 354, 1307;
S. Wittmann, A. Schatz, R. N. Grass, W. J. Stark and
O. Reiser, Angew. Chem., Int. Ed., 2010, 49, 1867;
B. Kaboudin, R. Mostafalu and T. Yokomatsu, Green Chem.,
2013, 15, 2266.
3 A. Suzuki, Angew. Chem., Int. Ed., 2011, 50, 6723.
4 A. F. Littke and G. C. Fu, Angew. Chem., Int. Ed., 2002, 41,
4176; P. Lloyd-William and E. Giralt, Chem. Soc. Rev., 2001,
3, 145; L. Pu, Chem. Rev., 1998, 98, 2405; N. Miyaura, Top.
Curr. Chem., 2002, 219, 11.
16 C. Park, H. J. Lee, H. S. Jung, M. Kim, H. J. Kim, K. H. Park
and H. Song, ChemCatChem, 2011, 3, 755; R. Arundhathi,
D. Damodara, P. R. Likhar, M. L. Kantam, P. Saravanan,
T. Magdaleno and S. H. Kwon, Adv. Synth. Catal., 2011, 353,
1591; A. Saha, J. Leazer and R. S. Varma, Green Chem.,
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Paper
Green Chemistry
2012, 14, 67; R. B. Nasir Baig and R. S. Varma, Chem. 23 J. Lee, Y. Lee, J. K. Youn, H. B. Na, T. Yu, H. Kim, S. M. Lee,
Commun., 2012, 48, 2582.
Y. M. Koo, J. H. Kwak, H. G. Park, H. N. Chang, M. Hwang,
17 Y. Wang and J. K. Lee, J. Mol. Catal. A: Chem., 2007, 263,
J. G. Park, J. Kim and T. Hyeon, Small, 2008, 4, 143.
163; L. M. Rossi, F. P. Silva, L. L. R. Vono, P. K. Kiyohara, 24 R. Appel, Angew. Chem., Int. Ed. Engl., 1975, 14, 801.
E. L. Duarte, R. Itri, R. Landersc and G. Machadod, 25 D. Li, M. B. Müller, S. Gilge, R. B. Kaner and G. G. Wallace,
Green Chem., 2007, 9, 379; A. H. Lu, W. Schmidt,
N. Matoussevitch, H. Bonnemann, B. Spliethoff, B. Tesche,
E. Bill, W. Kiefer and F. Schueth, Angew. Chem., Int. Ed.,
Nat. Nanotechnol., 2008, 3, 101; Ultrasound for Characteriz-
ing Colloids, Particle Sizing, Zeta Potential, Rheology, ed.
A. S. Dukhin and P. J. Goetz, Elsevier Science, 1st edn, 2002.
2004, 43, 4303; D. K. Yi, S. S. Lee and J. Y. Ying, Chem. 26 S. Zhou, M. Johnson and J. G. C. Veinot, Chem. Commun.,
Mater., 2006, 18, 2459.
2010, 46, 2411; S. Li, W. Zhang, M. H. So, C. M. Che,
R. Wang and R. Chen, J. Mol. Catal. A: Chem., 2012, 359,
81; Z. Gao, Y. Feng, F. Cui, Z. Hua, J. Zhou, Y. Zhu and
J. Shi, J. Mol. Catal. A: Chem., 2011, 336, 51; K. Mori,
Y. Kondo and H. Yamashita, Phys. Chem. Chem. Phys., 2009,
11, 8949; S. Xuan, W. Jiang and X. Gong, Dalton Trans.,
2011, 40, 7827; J. F. Hu, Y. P. Wang, M. Han, Y. M. Zhou,
P. P. Sun and X. Q. Jiang, Catal. Sci. Technol., 2012, 2, 2332;
M. Zeltner, A. Schatz, M. L. Hefti and W. J. Stark, J. Mater.
Chem., 2011, 21, 2991; V. Polshettiwar, M. N. Nadagouda
and R. S. Varma, Chem. Commun., 2008, 6318; A. Schätz,
T. R. Long, R. N. Grass, W. J. Stark, P. R. Hanson and
O. Reiser, Adv. Funct. Mater., 2010, 20, 4323; Q. Zhang,
H. Su, J. Luo and Y. Wei, Catal. Sci. Technol., 2013, 3, 235;
M. Keller, V. Colliere, O. Reiser, A.-M. Caminade,
J.-P. Majoral and A. Ouali, Angew. Chem., Int. Ed., 2013, 52,
3626.
18 V. Polshettiwar and R. S. Varma, Org. Biomol. Chem., 2009,
7, 37; L. Aschwanden, B. Panella, P. Rossbach, B. Keller and
A. Baiker, ChemCatChem, 2009, 1, 111; R. L. Oliveira,
P. K. Kiyohara and L. M. Rossi, Green Chem., 2010, 12, 144;
B. Karimi and E. Farhangi, Chem.–Eur. J., 2011, 17, 6056;
A. Schätz, R. N. Grass, W. J. Stark and O. Reiser, Chem.–Eur.
J., 2008, 14, 8262; A. K. Tucker-Schwartz and R. L. Garrell,
Chem.–Eur. J., 2010, 16, 12718.
19 T. Zeng, L. Yang, R. Hudson, G. Song, A. R. Moores and
C. J. Li, Org. Lett., 2011, 13, 442; B. Karimi and E. Farhangi,
Adv. Synth. Catal., 2013, 355, 508.
20 M. J. Jin and D. H. Lee, Angew. Chem., Int. Ed., 2010, 49,
1119; J. Y. Jung, J. B. Kim, A. Taher and M.-J. Jin, Bull.
Korean Chem. Soc., 2009, 30, 3082; A. Taher, J. B. Kim,
J. Y. Jung, W. S. Ahn and M. J. Jin, Synlett, 2009, 2477;
Z. Yinghuai, S. C. Peng, A. Emi, S. Zhenshun, M. Lisa and
R. A. Kemp, Adv. Synth. Catal., 2007, 349, 1917.
27 V. F. Slagt, A. H. M. de Vries, J. G. de Vries and
R. M. Kellogg, Org. Process Res. Dev., 2010, 14, 30;
C. A. Fleckenstein and H. Plenio, Chem.–Eur. J., 2008, 14,
4267 and the references cited therein.
21 B. Karimi and P. F. Akhavan, Chem. Commun., 2011, 47,
7686.
22 B. Karimi and P. F. Akhavan, Chem. Commun., 2009, 3750;
B. Karimi and P. F. Akhavan, Inorg. Chem., 2011, 50, 28 The amount of base needed in each run was estimated by
6063.
pH analysis of the recovered aqueous reaction phase.
Green Chem.
This journal is © The Royal Society of Chemistry 2014