Iron-containing mesoporous aluminosilicate: A highly active and reusable heterogeneous catalyst for hydroarylation of styrenes

Article abstract of DOI:10.1021/jo100803y

Hydroarylation of various styrene derivatives has been successfully carried out in excellent yield using Fe-Al-MCM-41 catalyst. The C-H functionalization using solid heterogeneous catalyst provides a straightforward access to a series of important 1,1-diarylalkane products. The catalyst can be recovered and reused at least three times without any significant loss in its catalytic activity.

Full text of DOI:10.1021/jo100803y

pubs.acs.org/joc
or acyl halides, there are lacunas in the product selectivity and its
Iron-Containing Mesoporous Aluminosilicate: A
Highly Active and Reusable Heterogeneous Catalyst
for Hydroarylation of Styrenes
widespread applicability. Recent development involves the uti-
lization of esters, aldehydes, olefins, or alkynes as the alkylating
reagent.4 However, the use of aromatic olefins has been found to
be very useful and practical as the resulting diarylalkane block
represents an important part in biologically active compounds
and pharmaceuticals substrates such as dimetindene, haplopap-
pin, phenprocoumone, papaverine, or afenopin (Figure 1). In
addition, diarylmethanes are utilized for the preparation of
fluorenyl-based electroactive and photoactive oligomers and
polymers.5
Satyajit Haldar and Subratanath Koner*
Department of Chemistry, Jadavpur University,
Kolkata 700 032, India
snkoner@chemistry.jdvu.ac.in
Received April 24, 2010
FIGURE 1. Biologically active compounds and pharmaceutical
substrates.
Hydroarylation of various styrene derivatives has been
successfully carried out in excellent yield using Fe-Al-
MCM-41 catalyst. The C-H functionalization using
solid heterogeneous catalyst provides a straightforward
access to a series of important 1,1-diarylalkane products.
The catalyst can be recovered and reused at least three
times without any significant loss in its catalytic activity.
Reactions being carried out in homogeneous media using
FeCl3, these methods, while useful, suffer from serious limita-
tions including high catalyst loading, difficulty in recovery,
reusability of the catalyst, and tedious workup procedures.
Therefore, development of highly active and recoverable hetero-
geneous catalysts for such C-C coupling reactions is still an
open challenge.
In the last few decades, mesoporous materials have received
much attention in the field of catalysis, especially for their use as
solid supports.6 Supported catalysts have attracted increased
attention in organic transformation due to their easy separation
from the reaction mixture and possible reuse. Toward this end,
mesoporous aluminosilicates (Al-MCM-41) have been employed
in different organic reactions.7 Although Al-MCM-41 has been
successfully employed in heterogeneous C-C coupling reactions,
most of the reactions have involved alkyl or acyl halides,8 whereas
The modified and tailored arenes and heteroarenes have
attracted a considerable attention for its synthetic application
in the field of pharmaceutical, agricultural, and fine chemical
industries. Traditionally, Friedel-Crafts alkylation and acyla-
tion is one of the most powerful methods for such carbon-
carbon bond-forming reactions.1 These reactions are performed
using strong Lewis acids such as TiCl4, BF3 OEt2, and AlCl3
3
€
and Bronsted acids such as HF and H2SO4. There are ongoing
(4) For example, see: (a) Okumura, K.; Yamashita, K.; Hirano, M.;
Niwa, M. J. Catal. 2005, 234, 300–307. (b) Jovel, I.; Mertins, K.; Kischel, J.;
Zapf, A.; Beller, M. Angew. Chem., Int. Ed. 2005, 44, 3913–3917. (c) Zhan, Z.-
P.; Cui, Y.-Y.; Liu., H.-J. Tetrahedron Lett. 2006, 47, 9143–9146. (d) Kischel,
J.; Jovel, I.; Mertins, K.; Zapf, A.; Beller, M. Org. Lett. 2006, 8, 19–22. (e) Li,
R.; Wang, S. R.; Lu, W. Org. Lett. 2007, 9, 2219–2222. (f) Li, Z.; Duan, Z.;
Kang, J.; Wang, H.; Yu, L.; Wu, Y. Tetrahedron 2008, 64, 1942–1930.
(g) Siffert, S.; Gaillard, L.; Su, B.-L. J. Mol. Catal. A: Chem. 2000, 153, 267–279.
(5) (a) Skabara, P. J.; Serebryako, I. M.; Perepichka, I. F. Synth. Met.
1999, 102, 1336–1337. (b) Khan, M. S.; Al-Mandhary, M. R. A.; Al-Suti,
M. K.; Ahrens, B.; Mahon, M. F.; Male, L.; Raithby, P. R.; Boothby, C. E.;
Kohler, A. J. Chem. Soc., Dalton Trans. 2003, 74–84. (c) Jacob, J.; Oldridge,
L.; Zhang, J. Y.; Gaal, M.; List, E. J. W.; Grimsdale, A. C.; Mullen, K. Curr.
Appl. Phys. 2004, 4, 339–342.
investigation programs to identify catalysts that address pro-
blems like high catalyst loading, low selectivity, overalkylation,
formation of byproducts (salt), and sensitivity toward moisture
and strong acid medium.
During the past decade, studies of iron-catalyzed C-C
coupling reactions grew immensely.2 “Iron-exploited cata-
lysts” have been proven to be the most effective and green
system in modern organic synthesis because of their lower
toxicity and easy accessibility.3
Though the use of FeCl3 as Lewis acid catalyst in car-
bon-carbon coupling reactions has been studied using alkyl
(6) (a) Wight, A. P.; Davis, M. E. Chem. Rev. 2002, 102, 3589–3614.
(b) Corma, A.; Garcia, H. Chem. Rev. 2002, 102, 3837–3892. (c) Mallat, T.;
Baiker, A. Chem. Rev. 2004, 104, 3037–3058.
(1) (a) Olah, G. A. In Friedel-Crafts Chemistry; Wiley: New York, 1973.
(b) Olah, G. A.; Krishnamurti, R.; Prakash, G. K. S. In Comprehensive
Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford,
1991; Vol. 3, p 293. (c) Bandini, M.; Melloni, A.; Ronchi, A. U. Angew.
Chem., Int. Ed. 2004, 43, 550–556.
(7) (a) Corma, A.; Fornes, V.; Navarro, M. T.; Perezpariente, J. J. Catal.
1994, 148, 569–574. (b) Corma, A. Chem. Rev. 1997, 97, 2373–2420. (c) De
Vos, D. E.; Dams, M.; Sels, B. F.; Jacobs, P. A. Chem. Rev. 2002, 102, 3615–
3640. (d) Iwanami, K.; Choi, J.-C.; Lu, B.; Sakakura, T.; Yasuda, H. Chem.
Commun. 2008, 8, 1002–1004.
ꢀ
(2) Czaplik, W. M.; Mayer, M.; Cvengros, J.; von Wangelin, A. J.
(8) (a) Hu, X.; Chuah, G. K.; Jaenicke, S. Appl. Catal. A: Gen. 2001, 217,
1–9. (b) Choudhary, V. R.; Jana, S. K.; Mamman, A. S. Microporous
Mesoporous Mater. 2002, 56, 65–71. (c) Sartori, G.; Maggi, R. Chem. Rev.
2006, 106, 1077–1104.
ChemSusChem 2009, 2, 396–417.
(3) Bolm, C.; Legros, J.; Paih, J. L.; Zani, L. Chem. Rev. 2004, 104, 6217–
6254.
DOI: 10.1021/jo100803y
r
Published on Web 08/02/2010
J. Org. Chem. 2010, 75, 6005–6008 6005
2010 American Chemical Society

Haldar and Koner
JOCNote
the use of olefins as the alkylating reagent is mainly restricted
to the homogeneous system.4d However, there are examples
for the synthesis of alkylbenzene using heterogeneous cata-
lysts.4g Further, the catalytic activity of such aluminosili-
cates can be increased via incorporation of metal ions such as
CuII, ZnII, FeIII, etc., which causes the generation of highly
active Lewis acid sites.9 The combination of such active
TABLE 1. Fe-Al-MCM-41-Catalyzed Reaction of Styrene and Phenola
entry T (°C)
solvent
time (h) conversionb (%) yieldc (%)
€
Lewis acid site along with the available Bronsted acid site
1
2
3
4
5
6
7
8
9
80
80
40
80
80
70
rt
CH3CN
THF
CH2Cl2
CH3NO2
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
4
4
4
4
3
6
8
0
0
0
75
95
93
0
in metal-exchanged Al-MCM-41 together with their high
surface area are known to facilitate reactions by localizing
the reactants in their pore surfaces and providing high local
concentration.7c,10
In the course of our continuing investigation of different
organic reactions using ordered mesoporous silica materials as
heterogeneous catalytic support we have found that the hybrid
organic-inorganic material demonstrates desirable catalytic
efficacy.11 Herein, we report a facile and reusable heterogeneous
catalyst, which is not sensitive to moisture, for the synthesis of
diarylethane through C-H functionalization. The catalyst de-
monstrates high yield of products with good selectivity under
mild conditions in a short reaction time.
90
82
100
55
2
4
24
24
24
60
40
9
5
0
0
aReaction conditions: 0.5 mmol of styrene, 2 mmol of phenol, 65 mg
of catalyst, 5 mL of solvent. bGC conversion of styrene. GC yield of
arylated products.
c
TABLE 2. Reactions of Phenol with Styrenea
MCM-41 and Al-MCM- 41 were prepared following the
method described in a previous report.12 The BET surface area
and the BJH pore diameter of Fe-Al-MCM-41 were 917 m2
g-1 and 3.3 nm, respectively. The hexagonal pore structures of
MCM-41 and Al-MCM-41 were confirmed from the XRD
pattern.12 FeIII was immobilized into Al-MCM-41 by the con-
ventional ion-exchange method.13 The catalyst is hereinafter
abbreviated as Fe-Al-MCM-41. The aluminum and iron con-
tent of the Fe-Al-MCM-41 was 5 wt % and 0.75 wt %, respec-
tively, as estimated by atomic absorption spectrometer. Initial
experiments focused on optimizing the solvent and temperature
for the reaction of styrene with phenol using Fe-Al-MCM-41
(Table 1). The reaction was monitored by GC analysis. Con-
siderable solvent dependence was revealed for this reaction
(Table 1, entry 1-5). While the reaction yielded no product in
acetonitrile or tetrahydrofuran, a rapid conversion of styrene
was observed in dichloromethane. However, no arylated pro-
duct of phenol is produced in dichloromethane. The yield of
desired product in nitromethane was relatively less. Almost
complete conversion of styrene to its desired product was ob-
served in cyclohexane within a remarkably short reaction time
(Table 1, entry 5). The optimum temperature of the reaction
was 80 °C. On reduction of the reaction temperature, the yield is
also reduced. For example,when the temperature was reduced to
70 °C, the yield of diarylethane was only 55% in 4 h (Table 1,
entry 6). Notably, the coupling reaction did not take place below
60 °C in 24 h (Table 1, entry 7-9).
time
(h)
conversionb
(%)
yieldc
(%)
entry
catalyst
1e
2e
3
4
5
6
7
8
HCl (10 mol %)
FeCl3 6H2O (10 mol %)
HY
MCM-41
20
20
24
24
24
24
24
8
94
3
1
4
2
0
88
0
0
0
0
0
0
95
3
Al-MCM-41
basic alumina
Acidic alumina
Neutral alumina
Fe-Al-MCM-41
5
1
24
3
9
100
(a) <1
(b) 3
10f
FeCl3 6H2O
(0.008 mmol)
(a) 3
(b) 20
(a) <1
(b) <3
3
aReaction conditions: 0.5 mmol of styrene, 2 mmol of phenol, 65 mg
of catalyst, 5 mL of cyclohexane, 80 °C. bGC conversion of styrene. cGC
yield of arylated products. e10 mmol % of catalyst, ref 4d. fCatalyst: 2.32
mg of FeCl3 6H2O (0.008 mmol)
3
carried out using a variety of other prospective catalysts, like
microporous, mesoporous, and amorphous silica and alumina in
cyclohexane at 80 °C (Table 2). The well-known solid acid
catalyst, HY zeolite could not activate the substrates (Table 2,
entry 3). An analogous result was obtained using a strong
€
In order to understand the role of the iron center in Fe-
Al-MCM-41, the coupling reaction of phenol and styrene was
mineral (Bronsted) acid like HCl (Table 2, entry 1). Similarly,
mesoporous silica MCM-41 also does not catalyze the reaction
(Table 2, entry 4). This is, however, expected as there is no acid
site in silicious MCM-41. Mesoporous aluminosilicates are
known for their catalytic efficiency for a number of reactions.8
Catalytic activity normally originates owing to the presence of
(9) Luan, Z.; Hatmann, M.; Zhao, D.; Zhou, W.; Kevan, L. Chem. Mater.
1999, 11, 1621–1627.
€
(10) Taguchi, A.; Schuth, F. Microporous Mesoporous Mater. 2005, 77,
1–45.
€
mild Bronsted acid centers as well as Lewis acid centers in alu-
(11) (a) Jana, S.; Dutta, B.; Bera, R.; Koner, S. Langmuir 2007, 23, 2492–
2496. (b) Jana, S.; Dutta, B.; Bera, R.; Koner, S. Inorg. Chem. 2008, 47, 5512–
5520. (c) Jana, S.; Haldar, S; Koner, S. Tetrahedron Lett. 2009, 50, 4820–
4823.
minosilicates. Notably, when Al-MCM-41 was used in this reac-
tion no conversion was observed (Table 2, entry 5). To under-
stand the role of aluminum, reactions were performed using
different amorphous alumina (Table 2, entries 6-8). The three
types of alumina (acidic, basic, and neutral) were catalytically
inactive in this reaction. However, Fe-Al-MCM-41 demon-
strates remarkable performance showing a high yield of products
€
(12) (a) Grun, M.; Unger, K. K.; Matsumoto, A.; Tsutsumi, K. Micro-
porous Mesoporous Mater. 1999, 27, 207–216. (b) Selvaraj, M.; Sinha, P. K.;
Pandurangan, A. Microporous Mesoporous Mater. 2004, 70, 81–91.
(13) Cardin, D. J.; Constantine, S. P.; Gilbert, A.; Lay, A. K.; Alvaro, M.;
Galletero, M. S.; Garcia, H.; Marquez, F. J. Am. Chem. Soc. 2001, 123, 3141–
3142.
6006 J. Org. Chem. Vol. 75, No. 17, 2010

Haldar and Koner
JOCNote
with good selectivity within a very short time (Table 2, entry 9).
These results indicate that the mesoporous aluminosilicate itself
does not catalyze the reaction. Nevertheless, its catalytic activity
was remarkably enhanced when FeIII was immobilized into it. In
fact, only 65 mg of Fe-Al-MCM-41 was enough to complete
the reaction at 3 h. Thus, the catalytic efficacy of mesoporous
catalyst Fe-Al-MCM-41 was found to be much higher than the
TABLE 3. Reactions of Arenes with Styrenea
corresponding homogeneous FeCl3 6H2O catalyst under the
3
same conditions (Table 2, entry 10). Notably, iron-doped
commercially available silica remained virtually inactive in this
reaction14 and so also did iron-doped microporous aluminosili-
cates (see Table S2,Supporting Information).
To explore the scope and limitation of the reaction, the
optimized conditions were subsequently applied to several
other substituted phenols (Table 3). The reactions proceeded
smoothly, and the desired products were obtained in high
yields within 2.5-7.5 h. Analysis reveals that the substituted
phenols with electron-donating groups quickly reacted to
afford full conversion of the styrene, and the corresponding
diarylethanes were obtained in high yield. The catalyst was
active enough in the C-C coupling reactions of electron
deficient arenes like p-chlorophenol and p-nitrophenol with
styrene. However, salicylaldehyde was totally inactive to-
ward this reaction under the reaction condition.
Further, to explore the general applicability of the reac-
tion, different methyl-substituted styrenes were examined
(Table 4). 4-Methylstyrene reacted adequately with phenol
and p-cresol with a complete conversion with a shorter time
period (Table 4, entries 3 and 4). In the case of 3-methylstyr-
ene, 81% and 91% arylated products were obtained with
phenol and p-cresol, respectively. Thus, both styrene and the
substituted styrene reacted smoothly with different arenes to
produce the Markownikoff adduct in high conversion and
selectivity in a reasonable time frame.
To test the recycling of the catalyst, the C-C coupling
reaction of phenol and styrene was performed using the recov-
ered catalyst (Table 5). After each cycle, the reaction mixture
was allowed to cool to room temperature, and catalyst was
separated by filtration. Recovered catalyst was then washed with
cyclohexane and methanol followed by dichloromethane and
dried at 80 °C for 1 h. The catalyst was then reused without any
further treatment. The recycled catalyst exhibited 100% conver-
sion in 3-4 h (Table 5). Fe-Al-MCM-41 also demonstrates
good mechanical stability (see Table S1 and Figure S4 in the
Supporting Information).
aReaction condition: 0.5 mmol of styrene, 2 mmol of arene, 5 mL of
In order to confirm the true heterogeneity of the catalyst, the
“hot filtration method” was employed as described by Lempers
and Sheldon.15 Catalyst was separated from the reaction mix-
ture by filtration when approximately 22% conversion had
taken place (after around 1 h) in a coupling reaction of styrene
and phenol. The “catalyst-free” filtrate was then kept under the
reaction conditions. Analysis of the filtrate showed no further
progress of reaction even after 24 h. Catalyst was filtered off at
the reaction temperature (80 °C) in order to avoid readsorption
of leached iron on the catalyst surface on cooling. Leaching of
c
cyclohexane, 65 mg of Fe-Al-MCM-41, 80 °C. bMain product. GC
e
conversion of styrene. dGC yield of arylated products. Main product:
other isomers. fYield after column chromatography.
the metal from the catalyst during reaction was examined by
AAS analysis. Upon completion of the coupling reaction
catalyzed by Fe-Al-MCM-41, the reaction mixture was filtered
through a dried Celite pad under the reaction temperature
(80 °C) to remove the solid catalyst. The AAS analysis of the
clear filtrate did not show any leached iron.
(14) Reaction of phenol and styrene using different iron doped silica
(reaction conditions: 0.5 mmol of styrene, 2 mmol of phenol, 65 mg of
modified silica, 5 mL of cyclohexane, 80 °C): Fe-silica gel 60-120 mesh,
24 h, 1% conversion (based on GC conversion of styrene), 0% yield (based
on GC yield of arylated products); Fe-silica gel 230-400 mesh, 24 h, 2%
conversion (based on GC conversion of styrene), 0% yield (based on GC
yield of arylated products).
In conclusion, we have succeeded in preparing a heteroge-
neous solid catalyst, Fe-Al-MCM-41, for hydroarylation of
styrenes. The catalyst has shown notable activity in the carbon-
carbon coupling reaction toward a variety of substituted phenols
and olefins in an extraordinarily short time. Thus, the Fe-
Al-MCM-41 offered an effective and facile catalytic method
(15) Lempers, H. E. B.; Sheldon, R. A. J. Catal. 1998, 175, 62–69.
J. Org. Chem. Vol. 75, No. 17, 2010 6007

Haldar and Koner
JOCNote
TABLE 4. Reaction of Phenol and p-Cresol with Styrene Derivativesa
TABLE 5. Recycling of Fe-Al-MCM-41 Catalyst for the Reaction of
Phenol with Styrene
cycle
1
2
3
4
conversion (%)a
time (h)
100
3
95
100
3.5
96
100
4
93
100
3.5
91
yield (%)b
aGC conversion of styrene. bGC yield of arylated products.
with active sites present on the solid surface inside the ordered
mesopore.
Experimental Section
Typical Procedure for Catalytic Reaction. The coupling reac-
tion was carried out in a glass batch reactor. Styrene (0.5 mmol)
was added to a mixture of phenol (2 mmol) and Fe-Al-MCM-
41 (0.065 g) in 5 mL of cyclohexane. The mixture was stirred at
80 °C in an oil bath. To study the progress of the reaction, the
products were collected at different time intervals and identified
and quantified by gas chromatograph. After completion of the
reaction, the solution was cooled, and the catalyst was removed
by filtration. The resulting crude mixture was gently evaporated
under vacuo and purified by column chromatography on silica
gel using an appropriate solvent.
2-(1-Phenylethyl)phenol (1a): 1H NMR (300 MHz, CDCl3) δ
7.34 -7.19 (m, 6H, CH), 7.17 -7.11 (m, 1H, CH), 6.98 -6.93 (m,
1H, CH), 6.78 -6.75 (m, 1H, CH), 4.69 (s, 1H, OH), 4.39 (q, J
(H,H) = 7.2 Hz, 1H, CHCH3), 1.64 (d, J (H,H) = 7.2 Hz, 3H,
CH3CH); 13C NMR (75 MHz, CDCl3) δ 152.7, 144.8, 131.4,
128.1, 127.4, 126.9, 125.9, 120.3, 115.4, 38.2, 20.4.
Synthesis of the Catalyst (Fe-Al-MCM-41). Iron was incor-
porated into the mesoporous aluminosilicate (Al-MCM-41) by
the ion-exchange method. Al-MCM-41 (0.5 g) was added to 100
mL of a 0.001 M methanolic solution of FeCl3 6H2O and stirred
3
vigorously for 12 h. The resultant solid was then filtered. To
remove the excess FeCl3, the isolated solid was washed with
Soxhlet extraction using methanol. The resulting solid was dried
in oven at 80 °C and characterized. The catalyst then used
directly in reactions without any further activation.
aReaction conditions: 0.5 mmol of 4/3-methylstyrene or styrene, 2
mmol of arene, 5 mL of cyclohexane, 65 mg of Fe-Al-MCM-41, 80 °C.
bMain product. cGC conversion of 4/3-methyl styrene or styrene. dGC
yield of arylated products. eMain product: other isomers.
Acknowledgment. S.H. thanks CSIR, New Delhi, for the
award of fellowships. Mr. S. K. Maity is thanked for general
discussions. We acknowledge the Department of Science and
Technology (DST), Government of India, for funding a
project (to S.K.) (SR/S1/IC-01/2009).
for the synthesis of a wide variety of diarylethanes. The catalyst
can be recovered by filtration and reused several times without
any loss of activity. The catalytic reaction can be performed
under “open-flask” conditions. The enhanced efficacy of Fe-
Al-MCM-41 in the catalytic C-C coupling reaction is attribu-
ted to the high internal surface area of the nanoporous catalyst
that provides enough space for organic substrate to interact
Supporting Information Available: Experimental procedures
and compound characterization data of all unknown compounds
as well as known compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
6008 J. Org. Chem. Vol. 75, No. 17, 2010