Fe3O4@mesoporouspolyaniline: A highly efficient and magnetically separable catalyst for cross-coupling of aryl chlorides and phenols

Article abstract of DOI:10.1002/adsc.201000977

A high surface, magnetic Fe₃O₄@mesoporouspolyaniline core-shell nanocomposite was synthesized from magnetic iron oxide (Fe ₃O₄) nanoparticles and mesoporouspolyaniline (mPANI). The novel porous magnetic Fe₃O₄ was obtained by solvothermal method under sealed pressure reactor at high temperature to achieve high surface area. The mesoporouspolyaniline shell was synthesized by in situ surface polymerization onto porous magnetic Fe₃O₄ in the presence of polyvinylpyrrolidone (PVP) and sodium dodecylbenzenesulfonate (SDBS), as a linker and structure-directing agent, through 'blackberry nanostructures' assembly. The material composition, stoichiometric ratio and reaction conditions play vital roles in the synthesis of these nanostructures as confirmed by variety of characterization techniques. The role of the mesoporouspolyaniline shell is to stabilize the porous magnetic Fe₃O₄ nanoparticles, and provide direct access to the core Fe₃O₄ nanoparticles. The catalytic activity of magnetic Fe₃O ₄@mesoporousPANI nanocomposite was evaluated in the cross-coupling of aryl chlorides and phenols. Copyright

Full text of DOI:10.1002/adsc.201000977

FULL PAPERS
DOI: 10.1002/adsc.201000977
Fe O @mesoporouspolyaniline: A Highly Efficient and
3
4
Magnetically Separable Catalyst for Cross-Coupling of Aryl
Chlorides and Phenols
a
a
a,
a
R. Arundhathi, D. Damodara, Pravin R. Likhar, * M. Lakshmi Kantam,
b
c
c
P. Saravanan, Travis Magdaleno, and Sun Hee Kwon
Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad – 500007, India
Fax : (+91)-40-2716-0921; phone: (+91)-40-2719-3510; e-mail: plikhar@iict.res.in
Defence Research and Development Organization, Hyderabad, India
Department of Chemistry and Biochemistry, Rowan University, Ames, 201, Mullica Hill Road, Glassboro, NJ 08028, USA
a
b
c
Received: December 29, 2010; Revised: March 2, 2011; Published online: May 23, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000977.
Abstract:
A
high
surface,
magnetic The material composition, stoichiometric ratio and
Fe O @mesoporouspolyaniline core-shell nanocom- reaction conditions play vital roles in the synthesis of
3
4
posite was synthesized from magnetic iron oxide these nanostructures as confirmed by variety of char-
(
(
Fe O ) nanoparticles and mesoporouspolyaniline acterization techniques. The role of the mesoporous-
3 4
mPANI). The novel porous magnetic Fe O was ob- polyaniline shell is to stabilize the porous magnetic
3
4
tained by solvothermal method under sealed pres- Fe O nanoparticles, and provide direct access to the
3
4
sure reactor at high temperature to achieve high sur- core Fe O nanoparticles. The catalytic activity of
3
4
face area. The mesoporouspolyaniline shell was syn- magnetic Fe O @mesoporousPANI nanocomposite
3
4
thesized by in situ surface polymerization onto was evaluated in the cross-coupling of aryl chlorides
porous magnetic Fe O in the presence of polyvinyl- and phenols.
3
4
pyrrolidone (PVP) and sodium dodecylbenzenesulfo-
nate (SDBS), as a linker and structure-directing Keywords: O-arylation; aryl chlorides; mesoporous
agent, through ꢀblackberry nanostructuresꢁ assembly. polyaniline; phenols; porous magnetic Fe O4
3
Introduction
prevent the aggregation. Nevertheless, these organic
capping reagents can decompose at high temperature
Mesoporous materials, with a variety of desired prop- and the metal nanoparticles can deform and aggre-
erties, are extensively used as absorbents, catalysts, gate. Alternatively, core-shell nanostructured compo-
[
9]
and supports in the chemical and petrochemical in- site materials have attracted increasing interest due
dustries due to their high surface area and tunable to their unique physicochemical stability. These spe-
pore size which can be controlled by the preparation cific core- shell types of bifunctional micro or sub-
[1]
protocol.
Recently, magnetic nanoparticles have micro sized hollow spheres, whereby nanoparticles
been the subject of intensive research for their wide are encaged in the channels of the mesoporous mate-
[
1–7]
spectrum of potential applications.
However, the rials is of considerable technological importance for
thermal and chemical stability of these magnetic improving the accessibility, lifetime and the reusabili-
[10]
nanomaterials (diameter ~10 nm) are notoriously dif- ty of the catalyst in the field of molecular catalysis,
ficult as they tend to deform and aggregate during the controlled drug release, chromatography separation,
[
11]
chemical reactions. Controlling the size distribution coatings, photonic, and electronic devices. Especial-
and achieving thermal as well as chemical stability are ly, superparamagnetic microspheres coated with vari-
therefore among the pivotal concerns in an applica- ous polymers, biopolymers and inorganic materials
tion point of view of these materials. Though they can have unique importance due to their magnetic separa-
[
12]
be achieved effectively by the surface modification of tion properties. In this context recently Deng et al.
[
8]
magnetic nanoparticles using appropriate organic and Leung et al. have reported the preparation of
[
13,14]
capping agents, such as polymers or surfactants to polyaniline (PANI)/Fe O .
Though the applica-
3
4
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Scheme 1. Step-wise preparation of the porous Fe O nanoparticles@mesoporous (mPANI) core-shell nanocomposite.
3
4
tions of Fe O magnetic particles have been explored cross-coupling of phenols and aryl iodides by combi-
3
4
in several areas, their usage in catalysis is largely ex- nation of FeCl and 2,2,6,6-tetramethyl-3,5-heptane-
3
[
15,16]
[26]
ploited for immobilization and support.
To the dione (TMHD) as a catalytic system.
Similarly,
best of our knowledge, there are very few reports de- Yuan and Bolm have also recently reported a mixture
scribing the direct use of Fe O magnetic particles as of dimethyl sulphoxide and potassium hydroxide as a
3
4
[17]
catalysts
and no reports on the use of super base for the cross-coupling of aryl iodides with
[27]
Fe O @mesoporousPANI as a heterogeneous catalyst phenols. In most of the above methodologies, aryl
3
4
for organic cross-coupling reactions.
iodides and bromides are used as a coupling part-
[28]
In continuation of our studies on the applications ner,
require additional ligand and high reaction
of environmentally benign catalysts for the develop- temperature and are homogeneous in nature where
ment of useful new synthetic methodologies with recyclability of the catalyst could not be achieved.
[18]
PANI, we focused our attention on the preparation
Magnetite Fe O nanoparticles, like other nanopar-
3 4
of porous Fe O nanoparticles encaged in mesopor- ticles, have high surface energy, which may result in
3
4
ouspolyaniline microspheres, Fe O @mPANI, its char- the agglomeration of particles when they are dis-
3
4
acterization and its catalytic application in the synthe- persed in organic solvents. We envisaged the catalytic
sis of diaryl ethers from aryl chlorides and phenols. activity of porous magnetic Fe O in the cross-cou-
3
4
The thermal and chemical stability of Fe O @mPANI pling of aryl chloride and phenol. However, it has
3
4
could enable activation of the CÀCl bond of aryl been observed that the catalytic activity of Fe O in
3
4
chlorides in the cross-coupling without deforming or the next successive cycle was diminished due to defor-
aggregating the Fe O nanoparticles, which was not mation or aggregation of magnetite particles. One of
3
4
possible with bare magnetic Fe O nanoparticles. The the most promising solutions to overcome this prob-
3
4
synergistic effects of metal-support interfaces may be lem is surface modification of magnetic nanoparticles
maximized where such interfaces are important in cat- using appropriate organic capping agents, such as
alytic performance.
polymers or surfactants to prevent the aggregation.
Diaryl ethers are important class of organic com- We have modified the preparation of the
pounds and constitute many natural cyclopeptides Fe O @mPANI composite using porous magnetite
3
4
[
19]
such as the antibiotic vancomycin and the anti-HIV Fe O and mesoporouspolyaniline in three steps
3
4
[
20]
agents chloropeptins, exhibit remarkable physiolog- (Scheme 1).
ical activities. The major methods to the synthesis of
diaryl ethers relay on the cross-couplings catalyzed by
[21]
[22]
palladium
or copper. The success of examples Results and Discussion
are highly dependent on the use of ligands such as
[
23,24]
N,N or N,O-bidentate compounds,
ylglycine and l-proline gave poor conversions.
However, despite the efficiency of these protocols, Fe O @mPANI nanocomposite is prepared in three
while N-meth- Preparation of Fe O @mesoporousPANI
3 4
[25]
3
4
the development of less expensive and environmen- steps: (i) porous magnetite Fe O nanoparticles were
3
4
tally more benign catalyst is a major goal for organic synthesized by the solvo-thermal approach in the
synthesis. In this respect, Bolm et al. recently reported presence of sodium acetate and ethylene glycol in a
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Fe O @mesoporouspolyaniline: A Highly Efficient and Magnetically Separable Catalyst
3
4
Figure 1. XRD pictures of [A] Fe O nanoparticles, and [B] Fe O @mesoporousPANI.
3
4
3
4
sealed teflon-lined stainless-steel autoclave at 2008C;
ii) chemical modification/functionalization of Fe O
The XRD patterns of magnetic Fe O nanoparticles
3 4
reveal that the crystal structure is indexed as face cen-
(
3
4
nanoparticles was achieved by 3-aminopropyltrime- tered cubic (fcc) (JCPDS card No. 19-629) (Figure 1).
thoxysilane (APTMS). The APTMS acts as an organic No other characteristic peaks due to the impurities of
spacer, which may induce a steric repulsion between hematite or hydroxide were detected. The XRD pat-
the Fe O through its ÀNH end group, and also re- terns of the Fe O @mPANI nanocomposite (Figure 1
3
4
2
3
4
stricts the crystal growth of magnetic nanoparticles [B]) are similar to those of magnetite Fe O particles
3
4
(
cluster formation). (iii) Fe O @mPANI nanocompo- (Figure 1[A]), which indicates that the crystal struc-
3 4
sites were prepared by an in situ surface polymeri- ture of Fe O is well-maintained during the shell for-
3
4
[
29]
zation method in the presence of PVP+SDBS. Simi- mation process under acidic conditions.
The pres-
larly, the thickness of the mesoporousPANI layers for ence of an additional diffraction peak at low angle
the Fe O @mPANI microsphere core/shell structure area (2.58) in the Figure 1 [B] clearly suggests the
3
4
was tuned by changing the relative concentrations of mesoporous behaviour of polyaniline.
the Fe O @polyvinylpyrrolidone (PVP)+sodium do- The modified preparative method for magnetite
decylbenzenesulfonate (SDBS) particles and aniline/ Fe O indicates that the formed Fe O nanoparticles
3
4
3
4
3
4
HCl concentrations in the solution. The parameters are of a porous nature (Figure 2).The porous nature
such as reaction temperature and stirring speed play of the catalyst was confirmed by the Barrett–Joyner–
an important role in maintaining the thickness of the Halenda (BJH) method. Hystersis found was to be of
mesostructures of PANI microspheres. The synthe- type-IV, and clearly displays two peaks of the pore
sized catalyst was well characterized by XRD, FTIR, size centered at about 2.5 nm and 5.5 nm, respectively,
SEM-EDX, TEM and XPS (see Supporting Informa- for two types of mesopores (Figure 2). The porosity
tion).
of magnetite Fe O nanoparticles increases the active
3 4
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volume of the Fe O @mPANI nanocomposite are cal-
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4
2
À1
3
À1
culated as 445 m g and 0.29 cm g , respectively.
Thus, the increase in surface area and decrease in
pore volume suggest that active sites are reasonably
increased due to porosity of magnetic Fe O nanopar-
3
4
ticles and the thickness of the mesoporousPANI
layers decreased.
TEM images for porous magnetic Fe O4 and
3
Fe O @mPANI nanocomposite are shown in Figure 3.
3
4
The TEM images of Fe O particles reveal that the
3
4
average diameter of porous Fe O particles is around
3
4
6
nm and the presence of white patches on the surface
of magnetic Fe O is due to the porous nature of the
3
4
materials which was confirmed by BET analysis. We
also studied the TEM images of the step-wise forma-
tion of functionalized Fe O particles and the subse-
3
4
quent formation of interesting ꢀblackberryꢁ morpholo-
Figure 2. Pore volume and pore size distribution of gy around Fe O particles in which PVP and SDBS
3
4
Fe O @mesoporousPANI.
serve as a linker and structure-directing agent, respec-
3
4
tively (Figure 3, [D–G]). The Fe O @mPANI nano-
3
4
composite was produced by an in situ surface poly-
site. This was further studied by BET analysis of ni- merization method as a single-crystal magnetite core-
trogen adsorption/desorption isotherms for the shell nanocomposite with an average diameter 20 nm
Fe O @mPANI nanocomposite. The BET surface (Figure 3, [H–L]).
3
4
area and pore volume of the mesoporousPANI layers
FT-IR analysis reveals that Fe O @mPANI nano-
3 4
2
À1
3
À1
(
mPANI) are calculated as 190 m g and 0.78 cm g , composites have characteristics peaks at around at
À1
respectively. The narrow pore size calculated from the 3215, 2924, 1644, 1502, 1288, 1125, 1040, 831 cm for
adsorption branch of the isotherms is at the mean PANI. These could be attributed to the characteristic
value of 2.1 nm. The BET surface area and total pore NÀH, CÀN stretching modes of benzenoid and qui-
Figure 3. TEM pictures of [A–C] Fe O nanoparticles, [D–G] Fe O @PVP+SDBS and [H–L] Fe O @mesoporousPANI.
3
4
3
4
3
4
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Fe O @mesoporouspolyaniline: A Highly Efficient and Magnetically Separable Catalyst
3
4
[
30]
noid ring forms of polyaniline,
1
The peaks at dimethyl formamide (DMF) and K CO was the most
2 3
À1
125 cm are due to the CÀN bond stretching vibra- effective solvent and base pair furnishing the desired
tion, respectively (see Figure 4 in Supporting Informa- product in 97% yield using Fe O @mPANI nanocom-
3
4
tion). The relatively high intensity of a band at posite as a catalyst (Table 1, entry 8).
À1
5
96 cm (FeÀO stretching of Fe O ) indicates the low
On the basis of the optimized reaction conditions,
3
4
content of PANI in the Fe O @PANI nanocompo- we explored the efficiency of this catalyst in the O-ar-
3
4
[31]
site.
ylation of phenol with various functionalized chloro-
The magnetic nature of Fe O @mPANI nanocom- benzenes and the results are summarized in Table 2.
3
4
posite was analyzed by a superconducting quantum In the cross-coupling reactions of substituted chloro-
interference device magnetometer, the saturated mag- benzenes with phenol, the corresponding diaryl ethers
netization value of Fe O @mPANI nanocomposite is are obtained in good to excellent yields (Table 2, en-
3
4
À1
5
3.86 emug at 300 K (for magnetic Fe O particles,
3 4
À1
the saturated magnetization value is 61.0 emug at
00 K) with zero coercivity and the reversible hystere-
sis behaviour indicate the superparamagnetic nature
Table 2. Fe O @mPANI nanocomposite catalyzed O-aryla-
3
4
3
[a]
tion of phenol with aryl chlorides.
[
30]
of the nanocomposite
(see Figure 5 in Supporting
Information). This feature provides an easy and effi-
cient avenue for separating the Fe O @mPANI core/
3
4
shell nanocomposite from a reaction mixture under
an external magnetic field. The iron content in the
catalyst was analyzed using atomic absorption spec-
troscopy (AAS) and was found to be 4.69 atm%.
In our preliminary studies to find the best catalyst
for the coupling reaction, we chose the coupling reac-
tion of 4-chloroanisole and phenol in N,N-dimethyl-
formamide to give the ether 1-(4-methoxyphenoxy)-
benzene as the model reaction. It was observed that
Table 1. Optimization of O-arylation reaction of 4-chloro-
ACHTUNGTRENNUNGa nisole and phenol catalyzed by Fe O @mPANI nanocom-
3 4
[a]
posite.
[
a]
Reaction conditions: 4-chloroanisole (1 mmol), phenol
[
a]
(
(
1.2 mmol), base (1.5 mmol), solvent 2 mL, catalyst
Reaction conditions: aryl chloride (1 mmol), phenol
25 mg, Fe, 4.69 atm%), 1108C for 12 h. n.r=no reaction.
(1.2 mmol), K CO (1.5 mmol), DMF 2 mL, catalyst
2
3
[
[
b]
c]
th
Isolated yield after 5 cycle.
Yield obtained at room temperature. np=nanoparticles.
(25 mg, Fe, 4.69 atm%), 1108C for 12 h.
[b]
th
Isolated yield after 5 cycle.
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tries 1–11). The reaction conditions were attuned with Table 3. Fe
O @mPANI nanocomposite catalyzed O-aryla-
4
tion of substituted phenols with chlorobenzene.
3
[a]
a variety of functionalized aryl chlorides, including
those bearing electron-donating and electron-with-
drawing groups (Table 2, entries 2–11). The order of
reactivity was also studied with Br, Cl and F substitu-
ents on the aryl chloride and as expected, 1-bromo-4-
chlorobenzene afforded the highest yield of the corre-
sponding coupling products (Table 2, entries 4, 5 and
6). The deactivated aryl chlorides afforded a slight de-
crease in the yields of the product when compared to
activated aryl chlorides (Table 2, entries 9–11). The
rate of reaction was slow for the coupling of sterically
hindered aryl chlorides (Table 2, entries 3, 9 and 11).
Encouraged by the efficiency of the cross-coupling
protocol described above, the scope of the substrate
was investigated with substituted phenols (Table 3,
entries 1–10). A variety of substituted phenols was
tested under the optimized reaction conditions using
chlorobenzene as the arylating agent. Electron-defi-
cient phenols provided the coupling products in
slightly lower yields (Table 3, entries 2–4). Nitro-sub-
stituted phenol which is generally considered as the
challenging substrate also yielded the O-arylated
product in good yields (Table 3, entry 4). On the
other hand, several electron-rich phenols afforded O-
arylation products in excellent yields (Table 3, en-
tries 5–10).
To further explore the scope of Fe O @mPANI-cat-
3
4
alyzed O-arylation reaction, benzyl alcohol (Table 4,
entry 1), cyclohexanol (Table 4, entries 2 and 3), phe-
nols (Table 4, entries 4–6), 4-hydroxyacetophenone
(
Table 4, entry 7), 4-phenylphenol (Table 4, entry 8)
and naphthol (Table 4, entry 9) were used as coupling
partners with various substituted aryl chlorides. The
reaction of para-nitrochlorobenzene with benzyl alco-
hol afforded an excellent product yield (Table 4,
entry 1). However, the reaction with cyclohexanol af-
forded a slightly lower yield (Table 4, entry 3). The
decrease in the yield can be ascribed to enhanced
steric hindrance at the substrates. To further test
more versatility of this catalyst, we studied the reac-
tion between cyclohexanol and para-chloroanisole
[a]
Reaction conditions: phenol (1.0 mmol), chlorobenzene
(1.2 mmol), K CO (1.5 mmol), DMF 2 mL, catalyst
2
3
(25 mg, Fe, 4.69 atm%), 1108C for 12 h.
since the para-substituted electron-rich aryl halides Reusability of the Catalyst
are difficult substrates for the corresponding transfor-
mations (Table 4, entry 2). We also noticed that in the Magnetic separation is an attractive alternative to fil-
reaction of para-chloroanisole, the yield was slightly tration or centrifugation as it prevents loss of the cat-
lower than that with para-nitrochlorobenzene alyst and increases the reusability of the catalyst. The
(
Table 4, entries 2 and 3). Electron-donating substitu- magnetite Fe O particles are known for their para-
3 4
ents on aryl chlorides and electron-withdrawing sub- magnetic property and as we mentioned above in the
stituents on phenols also afforded the corresponding magnetization results, the Fe O @mPANI nanocom-
3
4
coupling products in excellent (Table 4, entry 6) albeit posites are superparamagnetic in nature which makes
lower yields. The reaction of chlorobenzene with them amenable for magnetic separation. Therefore,
para-phenylphenol and 1-naphthol also afforded ex- the separation of these Fe O @mPANI nanocompo-
3
4
cellent yields of the corresponding product (Table 4, sites from the reaction mixture is very easy and effi-
entries 8 and 9). Overall, the results show that this cient. The catalyst was recovered by simple decanta-
catalytic system is relatively insensitive to electronic tion of the reaction in the presence of an external
effects on coupling partners.
magnet as depicted in Figure 4. The catalyst was then
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Fe O @mesoporouspolyaniline: A Highly Efficient and Magnetically Separable Catalyst
3
4
Table 4. Fe O @mPANI nanocomposite catalyzed O-arylation of substituted alco-
3
4
[a]
hols with substituted chlorobenzenes.
[a]
Reaction conditions: alcohol (1.0 mmol), aryl chloride (1.2 mmol), base
1.5 mmol), DMF 2 mL, catalyst (25 mg, Fe, 4.69 atm%), 1108C for 12 h.
(
washed with ethyl acetate, dried in an oven and used phenol in the presence of the filtrate, which was ob-
directly for the next cycle of the reaction without fur- tained after removal of the solid catalyst at the same
ther purification. The recoverability and reusability reaction temperature. After 12 h of reaction, no cor-
was performed by the reaction of O-arylation of 4- responding product could be identified. This result
chloroanisole with 1.2 equivalents of phenol and the confirms the heterogeneous nature of catalysis by the
results are summarized in Table 5. We have also veri- core magnetic nanoparticles. The present catalytic
fied the activity of the catalyst by scaling up the O-ar- system is far more facile than previously reported cat-
[
19–23]
ylation reaction of 4-chloroanisole (1 mL, 8.14 mmol) alysts
as it circumvents high temperatures, ligands
with 1.2 equivalents of phenol in DMF in presence of and high catalyst loading. This enhanced catalytic ac-
K CO at 1108C using the set of optimized reaction tivity of mesoporousPANI over different supported
2
3
conditions and obtained a 96% isolated yield, albeit metal catalysts screened as well as its homogeneous
the time taken for the reaction was 14 h. analogue can be explained by the high basicity and
To confirm that the catalytic activity originated dual role of PANI as support as well as a macro
from the core Fe O and not from temporarily leach- ligand which facilitates the reaction similar to other
3
4
ed Fe O , a control experiment was performed by car- nitrogen-containing ligands as reported in litera-
3
4
[
32]
rying out the reaction of 4-chloronitrobenzene with ture.
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undergo reaction with aryl chloride to give intermedi-
ate a. In the next step, the approach of nucleophile
(
phenol) to a in the presence of base may result in
the formation of intermediate b. The catalytic cycle
can be completed by a reductive elimination step via
[
33]
generation of the cross-coupled product.
Conclusions
In summary, we have developed a high surface mag-
netite Fe O @mPANI core-shell nanocomposite from
3
4
porous Fe O particles and mesoporousPANI using
3
4
cheap and easily accessible reagents. These magnetic
nanocomposites have very high surface area, a large
pore volume, and uniform pore size. Their thermal
and chemical stability was confirmed by various char-
acterization techniques. Applications of these magnet-
ite Fe O @mPANI nanocomposites were demonstrat-
Figure 4. [A] Fe O @mesoporousPANI dispersed in DMF
3
4
during the reaction. [B] Separation of Fe O @meso-
3
4
3
4
ACHTUNGTRENNUNGp orousPANI using a strong external magnet.
ed in the activation of CÀCl bonds in cross-coupling
with phenols. The superparamagnetic nature of
Table 5. Recycling of Fe O @mPANI nanocomposites cata- Fe O @mPANI allows for easy separation and re-dis-
3
4
3
4
[a]
lyzed O-arylation of 4-chloroanisole with phenol.
persion of the catalyst for its reuse.
Experimental Section
[
[
a]
b]
Reaction conditions: 4-chloroanisole (1.0 mmol), phenol
General Remarks
(
1.2 mmol), K CO (1.5 mmol), catalyst (25 mg, Fe,
2 3
Ferric chloride hexahydrate (FeCl ·6H O), sodium acetate
4
.69 atm%) and DMF 2 mL stirred at 1108C for 12 h.
3
2
(
CH COONa), ethylene glycol, 3-aminopropyltrimethoxysi-
Yield of O-arylated product.
3
lane (APTMS), absolute ethanol (95 wt%), sodium dodecyl-
benzenesulfonate (SDBS), ammonium peroxodisulfate
[(NH ) S O ; APS], and poly(vinylpyrrolidone) (PVP;
Proposed Catalytic Mechanism
4
2
2
8
3
0 kDa, 95 wt%) were purchased from Sigma Aldrich, USA.
The possible mechanism for O-arylation is outlined in All chemicals were of analytical grade and used without fur-
ther purification. Aniline was obtained from AVRA Synthe-
Scheme 2. As we investigated, one of the important
sis Pvt. and was distilled at a reduced pressure before use.
roles of mesoporouspolyaniline in the Fe O @mPANI
3
4
Doubly deionized water was used through all the processes.
The particle size and external morphology of the samples
were observed on a Philips TECNAI F12 FEI transmission
electron microscope (TEM). SEM-EDX was performed on
a Hitachi SEM S-520, An EDX-Oxford Link ISIS-300 in-
strument was used to determine the iron content in the
sample. BET surface areas were recorded on a Micromerit-
ics ASAP 2020 Surface Area and Pore Analyzer instrument.
Prior to surface area analysis all the samples were degassed
nanocomposite is to provide direct access to the
Fe O nanoparticles through mesoporouspolyaniline.
The highly surfaced porous Fe O nanoparticles may
3
4
3
4
1
13
at 1008C. H and C NMR spectra were recorded on
1
Bruker 200, Inova 500 and Avance 300 (300 MHz H and
1
3
C) spectrometers in CDCl using TMS as internal standard.
3
ACME silica gel (100–200 mesh) was used for column chro-
matography purposes and thin layer chromatography was
performed on Merck precoated silica gel 60-F254 plates.
Preparation of the Catalyst
Synthesis and chemical modification of Fe O particles: The
3
4
Scheme 2. The proposed reaction mechanism for O-aryla-
tion of aryl chlorides in the presence of porous
Fe O @mesoporouspolyaniline.
magnetic Fe O particles were prepared through a solvo-
3 4
thermal reaction. FeCl ·6H O (1.35 g) and sodium acetate
3
2
(3.6 g) were dissolved in ethylene glycol (40 mL) under mag-
3
4
1598
asc.wiley-vch.de
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 1591 – 1600

Fe O @mesoporouspolyaniline: A Highly Efficient and Magnetically Separable Catalyst
3
4
netic stirring. The obtained homogeneous yellow solution
was transferred to a Teflon-lined stainless-steel autoclave
and sealed for heating at 2008C. After a reaction time of
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h, the autoclave was cooled to room temperature. The ob-
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tained black magnetite particles were washed with ethanol
six times and then dried in vacuum at 608C for 12 h. Subse-
quently, the Fe O4 particles were chemically modified by
using APTMS. Typically, porous Fe O microspheres (0.1 g)
and APTMS (2 mL) were dissolved in anhydrous ethanol to
give a mixed solution (50 mL). The mixture was refluxed for
1
Fe O particles were separated with the help of a magnet
and then washed with ethanol. Finally, the product was
3
3
4
2 h under dry nitrogen. The resulting modified porous
3
4
dried in vacuum at 608C for 24 h to obtain the amine func-
tionalized Fe O particles (NH -Fe O ).
Lett. 2004, 4, 187.
3
4
2
3
4
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3
4
Fe O @mPANI microspheres were prepared by an in situ
3
4
surface polymerization method in the presence of PVP+
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2
006, 25, 5105; c) J. Ye, W. Chen, D. Wang, Dalton
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2
3
4
then ultrasonically dispersed, and a solution of aniline
20 mL) in HCl (0.1 mL) was added into the mixture with
(
vigorous stirring. Afterwards, the mixture was mechanically
stirred for 30 min at 208C. Then an aqueous solution
[
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[
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2
01.
instantly to start the oxidative polymerization. The reaction
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nol several times. Finally, the product was dried in vacuum
at 608C for 24 h to obtain of the desired Fe O @mPANI
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nanocomposite as a black powder.
General Procedure for O-Arylation of Aryl Chlorides
with Phenols
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The reaction vessel was charged with aryl chlorides
(
1 mmol), phenol (1.2 mmol), K CO (1.5 mmol) and the
2 3
catalyst (Fe O @mPANI) (25 mg, 4.69 atm%) in N,N-dime-
3
4
thylformamide (2 mL). The reaction mixture was stirred at
108C for the given reaction time and the progress of reac-
1
tion was monitored by TLC. At the end of the reaction, the
reaction mixture was cooled to room temperature the cata-
lyst was removed using a simple magnet, the reaction mix-
ture was then subjected to column chromatography on silica
gel using ethyl acetate and hexane to afford the O-arylated
product in high purity.
1
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Acknowledgements
[
[
R.A. thanks DST (GAP-0152) and D. D. thanks UGC, India
for their fellowships. The authors thank Prof. B. Viswana-
than, (HOD, NCCR-IITM, India) for scientific discussions.
2
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Adv. Synth. Catal. 2011, 353, 1591 – 1600