A simple, efficient and recyclable phosphine-free catalytic system for Suzuki-Miyaura reaction of aryl bromides

Article abstract of DOI:10.1016/j.molcata.2011.01.014

The Suzuki-Miyaura reaction of aryl bromides using 3-(2-aminoethylamino) propyl-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-2N-Pd(II)] as an efficient heterogeneous catalyst is described. Developed catalytic system is found to be effective for the Suzuki-Miyaura reaction of aryl bromides with arylboronic acids providing good to excellent yield of the desired products. This heterogeneous palladium catalyst can be reused at least 10 times without any decrease in activity. Our system not only avoids the use of phosphine ligands, but also solves the basic problem of palladium catalyst recovery and reuse.

Full text of DOI:10.1016/j.molcata.2011.01.014

Journal of Molecular Catalysis A: Chemical 337 (2011) 56–60
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
A simple, efficient and recyclable phosphine-free catalytic system for
Suzuki–Miyaura reaction of aryl bromides
Hong Zhaoa, Jian Pengb, Ruian Xiaob, Mingzhong Caib,∗
a School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University, Guangzhou 510006, PR China
b Department of Chemistry, Jiangxi Normal University, Nanchang, Jiangxi Province 330022, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The Suzuki–Miyaura reaction of aryl bromides using 3-(2-aminoethylamino)propyl-functionalized MCM-
41-immobilized palladium(II) complex [MCM-41-2N-Pd(II)] as an efficient heterogeneous catalyst is
described. Developed catalytic system is found to be effective for the Suzuki–Miyaura reaction of aryl
bromides with arylboronic acids providing good to excellent yield of the desired products. This hetero-
geneous palladium catalyst can be reused at least 10 times without any decrease in activity. Our system
not only avoids the use of phosphine ligands, but also solves the basic problem of palladium catalyst
recovery and reuse.
Received 16 November 2010
Received in revised form 3 January 2011
Accepted 7 January 2011
Available online 21 January 2011
Keywords:
Supported palladium catalyst
Suzuki–Miyaura reaction
Functionalized MCM-41
Biaryl
© 2011 Elsevier B.V. All rights reserved.
Heterogeneous catalysis
1. Introduction
contamination of products by palladium is prevented. Despite the
general use of the Suzuki reaction in organic synthesis, polymer-
The importance of biaryl units as molecular components in
pharmaceuticals, herbicides and natural products, as well as in
engineering materials such as conducting polymers, molecular
wires and liquid crystals, has attracted enormous interest [1,2]. The
Suzuki reaction is proving to be increasingly popular method for the
construction of unsymmetrical biaryl compounds as it represents
an attractive alternative over other methods using organometallics
because organoboranes are air- and moisture-stable with rela-
tively low toxicity [3,4]. However, catalysts used in the Suzuki
reaction have been traditionally based on homogeneous palla-
dium complexes such as Pd(PPh3)4, Pd(PPh3)2Cl2, which are rarely
recoverable without elaborate and wasteful procedures that are
commercially unacceptable [5]. In contrast, heterogeneous cata-
lysts can be easily separated from the reaction mixture by simple
filtration and reused in successive reactions provided that the
active sites have not become deactivated. Heterogeneous catalysis
also helps to minimize wastes derived from reaction workup, con-
tributing to the development of green chemical processes [6–9].
From the standpoint of environmentally benign organic synthesis,
development of immobilized palladium catalysts is challenging and
important [10–12]. In an ideal system, they can be recovered from
the reaction mixture by simple filtration and re-used infinitely, and
supported palladium catalysts have not been widely used for this
reaction yet [13–19]. Study of new types of polymer-supported pal-
ladium catalysts which might be suitable for the Suzuki reaction
has theoretical and practical significance. In the past, some of these
studies have been related to polymer-supported phosphine palla-
dium catalysts [13–16]. It is known that the catalysts containing
phosphine ligands at higher temperatures are unstable [20–22].
Furthermore, the procedure for preparing the polymer-supported
phosphine palladium complexes is rather complicated since the
synthesis of the phosphine ligands requires multi-step sequences.
Therefore, the development of phosphine-free heterogeneous pal-
ladium catalysts having a high activity and good stability is a topic
of enormous importance.
Our approach was guided by three imperatives: the polymeric
ligand should be easily accessible (1), starting from readily available
and cheap reagents (2). The polymeric palladium catalyst should
be air stable at room temperature, which should allow its stor-
age in normal bottles with unlimited shelf life (3). Developments
on the mesoporous material MCM-41 provided a new possible
candidate for a solid support for immobilization of homogeneous
catalysts [23]. MCM-41 has a regular pore diameter of ca. 5 nm and
a specific surface area >700 m2 g−1 [24]. Its large pore size allows
passage of large molecules such as organic reactants and metal
complexes through the pores to reach to the surface of the channel
[25–27]. It is generally believed that high surface area of heteroge-
neous catalyst results in high catalytic activity. Very recently, Yang
∗
Corresponding author. Tel.: +86 791 8120388; fax: +86 791 8120388.
E-mail address: caimingz@tom.com (M. Cai).
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.01.014

H. Zhao et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 56–60
57
Scheme 1. Preparation of the MCM-41-2N-Pd(II).
et al. have reported that palladium–guanidine complex immobi-
2.2. Preparation of MCM-41-2N-Pd(II)
lized on mesoporous materials [28,29] and N-heterocyclic carbene
palladium complex supported on ionic liquid-modified SBA-16 [30]
are highly active and recyclable catalysts for the Suzuki coupling.
Considering the fact that the MCM-41 support has an extremely
high surface area and the catalytic palladium species is anchored
on the inner surface of the mesopore of MCM-41 support, we
expect that MCM-41-supported palladium catalyst will exhibit
high activity and good reusability. To date, a few palladium com-
plexes on functionalized MCM-41 support have been prepared
and used in organic reactions [31–34]. In continuing our efforts
to develop greener synthetic pathways for organic transforma-
tions, our new approach, described in this paper, was to design and
In a small Schlenk tube, 2.03 g of the above-functionalized MCM-
41 (MCM-41-2N) was mixed with 0.137 g (0.61 mmol) of Pd(OAc)2
in 50 ml of dry acetone. The mixture was refluxed for 72 h under
an argon atmosphere. The solid product was filtered by suction,
washed with acetone, distilled water and acetone successively and
dried at 70 ◦C/26.7 Pa under Ar for 5 h to give 2.12 g of a yellow pal-
ladium complex [MCM-41-2N-Pd(II)]. The nitrogen and palladium
content was found to be 1.68 mmol/g and 0.27 mmol/g, respec-
tively.
2.3. General procedure for Suzuki reaction of aryl bromides with
arylboronic acids
synthesize
a new 3-(2-aminoethylamino)propyl-functionalized
MCM-41-immobilized palladium(II) complex, which was used as
an effective palladium catalyst for the Suzuki–Miyaura reaction of
aryl bromides with arylboronic acids.
A
mixture of aryl bromide (1.0 mmol), arylboronic acid
(1.5 mmol), potassium carbonate (2.0 mmol), xylene (3 ml) and the
MCM-41-2N-Pd(II) complex (7 mg, 0.002 mmol of Pd) was stirred
under Ar in an oil bath at 90 ◦C for 2–10 h. The mixture was cooled
and filtered. The MCM-41-2N-Pd(II) complex was washed with dis-
tilled water (2× 10 ml), dioxane (2 × 10 ml) and Et2O (2× 10 ml)
and reused in the next run. The filtrate was poured into a saturated
aqueous NaCl solution (50 ml) and extracted with methylene chlo-
ride (2× 50 ml). The extracts were washed with water (3× 30 ml)
and dried over MgSO4. After removal of the solvent, the residue was
purified by column chromatography on silica gel.
2. Experimental
All chemicals were reagent grade and used as purchased. The
mesoporous material MCM-41 was prepared according to a liter-
ature procedure [35]. All reactions were performed under an inert
atmosphere of dry argon using distilled dried solvents. All coupling
products were characterized by comparison of their spectra and
physical data with authentic samples. IR spectra were determined
on a Perkin-Elmer 683 instrument. 1H NMR spectra were recorded
on a Bruker AC-P400 (400 MHz) spectrometer with TMS as an inter-
nal standard in CDCl3 as solvent. 13C NMR spectra were recorded on
a Bruker AC-P400 (100 MHz) spectrometer in CDCl3 as solvent. Pal-
ladium content was determined with inductively coupled plasma
atom emission Atomscan16 (ICP-AES, TJA Corporation). X-ray pow-
der diffraction patterns were obtained on Damx-rA (Rigaka). X-ray
photoelectron spectra were recorded on XSAM 800 (Kratos).
3. Results and discussion
Although the phosphine ligands stabilize palladium and influ-
ence its reactivity, the simplest and cheapest palladium catalysts
are of course the phosphine-free systems, specifically when used in
low loading. A novel 3-(2-aminoethylamino)propyl-functionalized
MCM-41-immobilized palladium(II) complex [MCM-41-2N-Pd(II)]
was very conveniently synthesized from commercially avail-
able and cheap 3-(2-aminoethylamino)propyltrimethoxysilane via
immobilization on MCM-41, followed by reacting with palladium
acetate (Scheme 1). X-ray powder diffraction (XRD) patterns of the
parent MCM-41 and the modified material MCM-41-2N-Pd(II) are
displayed in Fig. 1. Small angle X-ray powder diffraction of the par-
ent MCM-41 gave the peaks corresponding to hexagonally ordered
mesoporous phases. For MCM-41-2N-Pd(II), the (1 0 0) reflection of
the parent MCM-41 with decreased intensity was remained after
functionalization, while the (1 1 0) and (2 0 0) reflections became
weak and diffuse, which could be due to contrast matching between
the silicate framework and organic moieties which are located
inside the channels of MCM-41. These results indicated that the
basic structure of the parent MCM-41 was not damaged in the
whole process of catalyst preparation.
2.1. Preparation of MCM-41-2N
Asolutionof 1.54 g of3-(2-aminoethylamino)propyltrimethoxy-
silane in 18 ml of dry chloroform was added to a suspension of
2.2 g of the MCM-41 in 180 ml of dry toluene. The mixture was
stirred for 24 h at 100 ◦C. Then the solid was filtered and washed
by CHCl3 (2× 20 ml), and dried in vacuum at 160 ◦C for 5 h. The
dried white solid was then soaked in a solution of 3.1 g of Me3SiCl
in 100 ml of dry toluene at room temperature under stirring for
24 h. Then the solid was filtered, washed with acetone (3× 20 ml)
and diethyl ether (3× 20 ml), and dried in vacuum at 120 ◦C for
5 h to obtain 3.49 g of hybrid material MCM-41-2N. The nitrogen
content was found to be 1.84 mmol/g by elemental analysis.

58
H. Zhao et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 56–60
Table 2
Coupling reaction of 4-bromoanisole with phenylboronic acid in the presence of
several bases and solvents.a
Entry
Base
Solvent
MCM-41-2N-
Pd(II)
Time (h)
Yieldb (%)
(100)
1
2
(mol%)
1
2
3
4
5
6
7
8
9
K3PO4
K3PO4
K3PO4
Na2CO3
Na2CO3
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Xylene
DMF
Dioxane
Xylene
DMF
Dioxane
Xylene
DMF
Dioxane
Xylene
Xylene
Xylene
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.1
0.05
0.5
10
79
75
76
92
84
88
95
86
91
94
91
95
10
10
8
9
8
6
8
7
(110)
(200)
10
11
12
14
24
3
1
2
3
4
5
6
a
All reactions were performed using 1.0 mmol of 4-bromoanisole, 1.5 mmol of
phenylboronic acid, 2.0 mmol of base in 3.0 ml of solvent at 90 ◦C under Ar.
2θ (degrees)
b
Isolated yield based on the 4-bromoanisole used.
Fig. 1. XRD patterns of the parent MCM-41 (1) and MCM-41-2N-Pd(II) (2).
0.2 mol%MCM-41-2N-Pd(II)
K2CO3, xylene, 90-110 oC
Elemental analyses and X-ray photoelectron spectroscopy (XPS)
were used to characterize the 3-(2-aminoethylamino)propyl-
functionalized MCM-41-immobilized palladium(II) complex. The
N:Pd mole ratio of the MCM-41-2N-Pd(II) was determined to be
6.22. The XPS data for MCM-41-2N-Pd(II), MCM-41-2N, Pd(OAc)2
and metal Pd are listed in Table 1. It can be seen that the binding
energies of Si2p and O1s of MCM-41-2N-Pd(II) are similar to those
of MCM-41-2N. However the difference of N1s binding energies
between MCM-41-2N-Pd(II) and MCM-41-2N is 1.2 eV. The bind-
ing energy of Pd3d5/2 in MCM-41-2N-Pd(II) is 0.7 eV less than that
in Pd(OAc)2, but 2.1 eV larger than that in metal Pd. These results
show that a coordination bond between N and Pd is formed in
MCM-41-2N-Pd(II).
The Suzuki–Miyaura cross-coupling reaction of phenylboronic
acid (1.5 equiv.) with 4-bromoanisole was chosen as a model reac-
tion, and the influences of various reaction parameters such as
base, solvent, and palladium catalyst quantity on the reaction were
tested. The results are summarized in Table 2. For the bases evalu-
ated [K3PO4, Na2CO3, and K2CO3], K2CO3 was found to be the most
effective. Other bases such as Na2CO3 and K3PO4 were substan-
tially less effective. We then turned our attention to investigate
the effect of solvents on the Suzuki–Miyaura cross-coupling reac-
tion. Among the solvents used [DMF, dioxane, and xylene], xylene
was the best choice. Increasing the amount of palladium catalyst
could shorten the reaction time, but did not increase the yield of
4-methoxybiphenyl (entry 12). The low palladium concentration
usually led to a long period of reaction, which was consistent with
our experimental results (entries 10 and 11). Taken together, excel-
lent result was obtained when the coupling reaction was carried out
with 0.2 mol% of the catalyst using K2CO3 as base in xylene at 90 ◦C
(entry 7).
Ar1 B(OH)2
Ar
Ar1
Ar
3
Br
+
2
1
Scheme 2. Suzuki reaction of aryl bromides with arylboronic acids catalyzed by
MCM-41-2N-Pd(II).
(Scheme 2) and the results are outlined in Table 3. As shown in
Table 3, the Suzuki–Miyaura coupling reactions of a variety of sub-
stituted bromobenzene with phenylboronic acid proceeded very
smoothly at 90 ◦C to afford the corresponding coupled products in
excellent isolated yields (entries 1–4). The reactions of sterically
hindered 2-methylbromobenzene and bulky 1-bromonaphthalene
with phenylboronic acid also provided good yields of the desired
biaryls 3e and 3f under the optimized reaction conditions, respec-
Table 3
Heterogeneous Suzuki–Miyaura reaction of aryl bromides with arylboronic acids
catalyzed by MCM-41-2N-Pd(II).a
Entry Ar
Ar1
Temp. (◦C) Time (h) Product Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Ph
Ph
90
90
90
90
100
90
90
90
90
90
100
90
90
90
90
90
90
90
90
90
90
4
6
2
4
8
5
3
3
6
3
8
3
3
5
3
3
6
3
3
4
3
7
5
10
10
10
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
93
95
92
93
85
83
86
89
94
97
83
93
96
86
84
93
91
95
92
85
94
84
85
68
71
75
4-CH3OC6H4
4-O2NC6H4
4-PhC6H4
Ph
Ph
Ph
2-CH3C6H4
1-Naphthyl
2-Thienyl
2-Pyridyl
Ph
Ph
Ph
Ph
4-CH3OC6H4
4-CH3COC6H4
2-CH3C6H4
3-O2NC6H4
4-PhC6H4
1-Naphthyl
2-Thienyl
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
To examine the scope for this heterogeneous Suzuki–Miyaura
cross-coupling reaction, we have investigated the reactions using
a variety of arylboronic acids and a wide range of aryl bro-
mides as the substrates under the optimized reaction conditions
4-CH3OC6H4
4-CHOC6H4
4-CH3OCOC6H4 4-CH3C6H4
3s
3t
Table 1
2-Pyridyl
4-CH3C6H4
4-CH3C6H4
XPS data for MCM-41-2N-Pd(II), MCM-41-2N, Pd(OAc)2 and metal Pd.a
3-CNC6H4
2-CH3C6H4
1-Naphthyl
3-CH3C6H4
4-CH3C6H4
3-CNC6H4
3u
3v
3w
3x
3y
3z
4-CH3C6H4 100
4-CH3C6H4 90
2-CH3C6H4 110
2-CF3C6H4 110
2-CH3C6H4 110
Sample
Pd3d5/2
337.5
N1s
Si2p
O1s
MCM-41-2N-Pd(II)
MCM-41-2N
Pd(OAc)2
400.8
399.6
103.3
103.2
533.1
533.2
338.2
335.4
Metal Pd
a
Reactions were carried out with 1 mmol of aryl bromide, 1.5 mmol of arylboronic
acid, 0.002 mmol of palladium catalyst, 2 mmol of K2CO3 in 3.0 ml of xylene.
a
The binding energies are referenced to C1s (284.6 eV) and the energy differences
were determined with an accuracy of 0.2 eV.
b
Yield of isolated product 3 based on the aryl bromide.

H. Zhao et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 56–60
59
Table 4
Suzuki cross-coupling reaction of 4-bromoanisole with phenylboronic acid catalyzed by recycled catalyst.
0.02 mmol MCM-41-2N-Pd(II)
(1st-10th use)
+
MeO
10 mmol
Br
PhB(OH)2
15 mmol
MeO
Ph
K2CO3, xylene, 90 oC, 6 h
3b
.
Entry
Catalyst cycle
Time (h)
Isolated yield (%)
TON
1
2
3
4
5
6
7
8
9
1st
6
6
6
6
6
6
6
6
6
6
95
94
95
94
94
93
94
94
475
470
475
470
470
465
470
470
465
465
2nd
3rd
4th
5th
6th
7th
8th
9th
10th
93
93
Av. 94
10
11
1st to 10th consecutive
Total of 4700
tively (entries
5
and 6). The Suzuki–Miyaura cross-coupling
bromoanisole with phenylboronic acid. In general, the continuous
recycle of resin-supported palladium catalysts is difficult owing
to leaching of the palladium species from the polymer supports,
which often reduces their activity within a five-recycle run. How-
ever, when the reaction of 4-bromoanisole with phenylboronic acid
was performed even with 0.2 mol% of MCM-41-2N-Pd(II), the cat-
alyst could be recycled 10 times without any loss of activity. The
reaction promoted by the 10th recycled catalyst gave 3b in 93%
yield (Table 4, entry 10). The average yield of 3b in consecutive reac-
tions promoted by the 1st through the 10th recycled catalyst was
94% (entry 11). The palladium content of the reused catalyst was
determined by ICP to be 0.26 mmol/g after ten consecutive runs,
only 3.7% of palladium had been lost from the MCM-41 support.
The high stability and excellent reusability of the catalyst should
result from the chelating action of bidentate 2-aminoethylamino
ligand on palladium and the mesoporous structure of the MCM-
41 support. The result is important from a practical point of view.
The high catalytic activity, excellent reusability and the easy acces-
sibility of the MCM-41-2N-Pd(II) make them a highly attractive
heterogeneous palladium catalyst for the parallel solution phase
synthesis of diverse libraries of compounds.
reactions of heteroaryl bromides such as 2-bromothiophene and
2-bromopyridine with phenylboronic acid gave the corresponding
coupled products 3g and 3h in 86% and 89% yields, respectively
(entries 7 and 8).
The optimized reaction conditions were also applied to the
Suzuki–Miyaura cross-coupling of substituted phenylboronic acids
such as 4-methylphenylboronic acid and 4-chlorophenylboronic
acid with a variety of aryl bromides, the results are also summarized
in Table 3. Various electron-donating and electron-withdrawing
groups such as –CH3, –OCH3, –Ph, –Cl, –CN, –NO2, –CF3, –COCH3,
–CHO, and –CO2CH3 on both aryl bromides and arylboronic acids
were well tolerated to give the desired unsymmetrical biaryls
in good to excellent yields (entries 9–23). A favorable effect
of electron-withdrawing substituents is normally observed in
palladium-catalyzed reactions [36]. With our catalyst however,
electron-withdrawing groups in aryl bromides have relatively little
effect on the Suzuki coupling reaction. Substituted chlorobenzenes
are inert under the same conditions giving traces of cross-coupling
products. To further illustrate that chloroarenes are inert in
the reaction system, 4-chloro-4ꢀ-methylbiphenyl was selectively
produced in the coupling reaction of (4-methylphenyl)boronic
acid with 1-bromo-4-chlorobenzene (Table 3, entry 16). The
Suzuki–Miyaura cross-coupling reactions of sterically hindered
arylboronic acids with aryl bromides could also proceed smoothly
at 110 ◦C, affording the desired coupled products 3x–3z in good
yields after 10 h (entries 24–26). The present method provides a
quite general route for the synthesis of unsymmetrical biaryls hav-
ing various functionalities.
In order to determine whether the catalysis was due to the
MCM-41-2N-Pd(II) complex or to a homogeneous palladium com-
plex that comes off the support during the reaction and then returns
to the support at the end, we performed the hot filtration test
[37]. We focused on the coupling reaction of bromobenzene with
phenylboronic acid (1.5 equiv.). We filtered off the MCM-41-2N-
Pd(II) complex after 30 min of reaction time and allowed the filtrate
to react further. The catalyst filtration was performed at the reac-
tion temperature (90 ◦C) in order to avoid possible re-coordination
or precipitation of soluble palladium upon cooling. We found that,
after this hot filtration, no further reaction was observed and no
palladium could be detected in the hot filtered solution by atomic
absorption spectroscopy (AAS). This result suggests that the pal-
ladium catalyst remains on the support at elevated temperatures
during the reaction.
4. Conclusion
We have developed a novel, phosphine-free, practical and
economic catalyst system for the Suzuki–Miyaura cross-coupling
reaction of aryl bromides with arylboronic acids by using 3-(2-
aminoethylamino)propyl-functionalized
MCM-41-immobilized
palladium(II) complex [MCM-41-2N-Pd(II)] as catalyst. This novel
heterogeneous palladium catalyst can be conveniently prepared
by a simple two-step procedure from commercially available
and cheap reagents and can be reused at least 10 times without
any decreases in activity. The Suzuki–Miyaura cross-coupling
reaction of aryl bromides with arylboronic acids catalyzed by
MCM-41-2N-Pd(II) provides a better and practical procedure for
the synthesis of unsymmetrical biaryls.
Acknowledgement
We gratefully acknowledge the financial support of this work
by the National Natural Science Foundation of China (Project No.
20862008).
References
This heterogeneous palladium catalyst can be easily recovered
by simple filtration. We also investigated the possibility to reuse
the catalyst by using the Suzuki cross-coupling reaction of 4-
[1] S.P. Stanforth, Tetrahedron 54 (1998) 263.
[2] S. Paul, J.H. Clark, Green Chem. 5 (2003) 635.

60
H. Zhao et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 56–60
[3] N. Miyaura, T. Yanagi, A. Suzuki, Synth. Commun. 11 (1981) 513.
[4] N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457.
[23] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992)
710.
[5] E.B. Mubofu, J.H. Clark, D.J. Macquarrie, Green Chem. 3 (2001) 23.
[6] M. Poliakoff, J.M. Fitzpatrick, T.R. Farren, P.T. Anastas, Science 297 (2002) 807.
[7] A. Kirschnig, H. Monenschein, R. Wittenberg, Angew. Chem. Int. Ed. 40 (2001)
650.
[8] N.E. Leadbeater, M. Marco, Chem. Rev. 102 (2002) 3217.
[9] L. Yin, J. Liebscher, Chem. Rev. 107 (2007) 133.
[10] Y.R. de Miguel, J. Chem. Soc. Perkin Trans. 1 (2000) 4213.
[11] S.J. Shuttleworth, S.M. Allin, R.D. Wilson, D. Nasturica, Synthesis (2000) 1035.
[12] J.A. Loch, R.H. Crabtree, Pure Appl. Chem. 73 (2001) 119.
[13] Y.M.A. Yamada, K. Takeda, H. Takahashi, S. Ikegami, Org. Lett. 4 (2002) 3371.
[14] S.-B. Jang, Tetrahedron Lett. 38 (1997) 1793.
[15] F. Koc, F. Michalek, L. Rumi, W. Bannwarth, R. Haag, Synthesis (2005) 3362.
[16] M. Cai, J. Sha, Q. Xu, J. Mol. Catal. A: Chem. 268 (2007) 82.
[17] C. Baleizao, A. Corma, H. Garcia, A. Leyva, Chem. Commun. (2003) 606.
[18] S. Paul, J.H. Clark, J. Mol. Catal. A: Chem. 215 (2004) 107.
[19] A. Gomann, J.A. Deverell, K.F. Munting, R.M. Guijt, Tetrahedron 65 (2009) 1450.
[20] N.P. Holy, Chemtech (1980) 366.
[24] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.-
W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J.
Am. Chem. Soc. 114 (1992) 10834.
[25] W. Zhou, J.M. Thomas, D.S. Shephard, B.F.G. Johnson, D. Ozkaya, T. Maschmeyer,
R.G. Bell, Q. Ge, Science 280 (1998) 705.
[26] T. Maschmeyer, F. Rey, G. Sankar, J.M. Thomas, Nature 378 (1995) 159.
[27] C.-J. Liu, S.-G. Li, W.-Q. Pang, C.-M. Che, Chem. Commun. (1997) 65.
[28] H. Yang, X. Han, Z. Ma, R. Wang, J. Liu, X. Ji, Green Chem. 12 (2010) 441.
[29] H. Yang, Z. Ma, Y. Qing, G. Xie, J. Gao, L. Zhang, L. Du, Appl. Catal. A: Gen. 382
(2010) 312.
[30] H. Yang, X. Han, G. Li, Y. Wang, Green Chem. 11 (2009) 1184.
[31] P.C. Mehnert, D.W. Weaver, J.Y. Ying, J. Am. Chem. Soc. 120 (1998) 12289.
[32] K. Mukhopadhyay, B.R. Sarkar, R.V. Chaudhari, J. Am. Chem. Soc. 124 (2002)
9692.
[33] C. Baleizao, A. Corma, H. Garcia, A. Leyva, J. Org. Chem. 69 (2004) 439.
[34] M. Cai, G. Zheng, G. Ding, Green Chem. 11 (2009) 1687.
[35] M.H. Lim, A. Stein, Chem. Mater. 11 (1999) 3285.
[36] V.V. Grushin, H. Alper, Chem. Rev. 94 (1994) 1047.
[37] H.E.B. Lempers, R.A. Sheldon, J. Catal. 175 (1998) 62.
[21] J. Masllorens, M. Moreno-Manas, A. Pla-Quintana, A. Roglans, Org. Lett. 5 (2003)
1559.
[22] K. Shimizu, S. Koizumi, T. Hatamachi, H. Yoshida, S. Komai, T. Kodama, Y.
Kitayama, J. Catal. 228 (2004) 141.