A PdCl2-ionic liquid brush assembly: An efficient and reusable catalyst for Mizoroki-Heck reaction in neat water

Article abstract of DOI:10.1002/aoc.1857

An efficient and reusable heterogeneous catalytic assembly of PdCl ₂ held in ionic liquid brushes has been synthesized and an environmentally-friendly procedure was developed for coupling aryl iodides with acrylic acid. These reactions were conducted in water under aerobic conditions with water-insoluble or even solid aryl iodides and they proceeded smoothly and cleanly without any organic co-solvent or other additives. A 0.5 mol% (based on Pd atom) dose of the catalyst was found to be sufficient for Mizoroki-Heck reaction. The catalyst is easily recovered post reaction, via simple filtration, and reused at least eight times without a noticeable loss of activity. The protocol has the advantages of excellent yield, environmental friendliness, and catalyst recyclability. Copyright

Full text of DOI:10.1002/aoc.1857

Full Paper
Received: 2 September 2011
Revised: 24 October 2011
Accepted: 24 October 2011
Published online in Wiley Online Library: 20 December 2011
(wileyonlinelibrary.com) DOI 10.1002/aoc.1857
A PdCl2–ionic liquid brush assembly: an
efficient and reusable catalyst for Mizoroki–
Heck reaction in neat water
Xianying Shi,* Xiaoyan Han, Wenjuan Ma, Juan Fan and Junfa Wei
An efficient and reusable heterogeneous catalytic assembly of PdCl2 held in ionic liquid brushes has been synthesized and an
environmentally-friendly procedure was developed for coupling aryl iodides with acrylic acid. These reactions were conducted
in water under aerobic conditions with water-insoluble or even solid aryl iodides and they proceeded smoothly and cleanly
without any organic co-solvent or other additives. A 0.5 mol% (based on Pd atom) dose of the catalyst was found to be
sufficient for Mizoroki–Heck reaction. The catalyst is easily recovered post reaction, via simple filtration, and reused at least
eight times without a noticeable loss of activity. The protocol has the advantages of excellent yield, environmental friendliness,
and catalyst recyclability. Copyright © 2011 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: ionic liquid brush; Heck reaction; heterogeneous catalysis; organic solvent-free
need for complicated and/or toxic ligands (e.g. phosphine); and
Introduction
the lack of reusability or poor lifespan.[42,43] In past decades, many
Palladium-catalyzed arylation or vinylation of olefins, known as
the Mizoroki–Heck (M-H) reaction, is one of the most important
reactions for the formation of C–C bonds in organic synthesis,
from both the research and industrial points of view.[1–3] Because
of its tolerance to different functional groups, a variety of applica-
tions in the synthesis of pharmaceuticals, fine chemicals,
polymers and natural compounds have been worked out.[4] Many
palladium catalysts with excellent catalytic activities have been
developed, such as phosphine ligand catalysts,[5–7] palladacycle
catalysts,[8–11] N-heterocyclic carbene (NHC) ligand catalysts[12–14]
and phosphine-free catalysts.[15,16]
However, in both homogeneous or heterogeneous catalytic
systems, in order to overcome the incompatibility of lipo-
philic substrates and inorganic base, these M-H reactions are
often conducted in polar aprotic solvents, such as DMF,[17–20]
N,N-dimethylacetamide (DMA)[21–24] and N-methylpyrrolidone
(NMP).[25–28] Organic solvents not only enhance the reaction rate
but also bring about environmental pollution because many polar
solvents are toxic. In view of economic and environmental prob-
lems, the use of a clean and environmentally friendly reaction
medium to replace the traditional organic solvent is an important
research topic to realize a green M-H reaction. Among green
solvents, water as a medium for organic reactions has attracted
much attention owing to its low cost and safety to industrial pro-
cesses and to the environment.[29–32] However, water is still not
commonly used as sole solvent in the M-H reaction. Most of the
so-called water phase reactions were actually performed in a
water–organic mixed solvent other than in neat water, such as
DMF–H2O,[33–35] NMP–H2O,[36] CH3CN–H2O,[37] or EtOH–H2O.[38]
Although there are a few reports of the M-H reaction in neat
water, these catalytic systems usually suffer from at least one of
the following shortcomings: the use of surfactants or phase transfer
catalyst to improve solvation of the organic substrate;[39–41] the
efforts have been made to solve these problems through the devel-
opment of active, reusable catalysts and more facile and benign
procedures, but satisfactory solutions are still a challenge.
Consequently, the development of reusable and highly efficient
alternatives and environment-friendly procedures with water as
the reaction medium is highly desirable.
Our group have recently designed and synthesized a series of
SiO2-supported multi-imidazolium ionic liquid brush catalysts,
which have demonstrated high efficiency and excellent reusability
in several organic transformations with water as a sole solvent.[44,45]
Encouraged by our previous research,[44,45] we have herein devel-
oped a novel heterogeneous catalytic assembly of dianion PdCl42ꢀ
held in bis-layer ionic liquid brush-modified silica (Fig. 1). We
envisioned that this catalytic assembly of ionic liquid brushes, with
PdCl24ꢀ as the active species, could work well as a green and reus-
able catalyst in the M-H reaction using H2O as solvent. More impor-
tantly, as a supported bi-positively charged organic salt, our
bis-layer ionic liquid brushes, bearing two imidazolium cations on
each of its side chains, would associate tightly with the PdCl24ꢀ dia-
nions via a strong electrostatic interaction. Therefore, the loss of
active components or the contamination of metal ions in the
product should be minimized significantly or even eliminated.
Herein, we present our study on a Pd-in-brush catalytic assembly
for the M-H reaction of aryl halide with acrylic acid in neat water.
*
Correspondence to: Xianying Shi, Key Laboratory for Macromolecular
Science of Shaanxi Province, School of Chemistry and Chemical Engineering,
Shaanxi Normal University, Xi’an, 710062, People’s Republic of China. E-mail:
shixy@snnu.edu.cn
Key Laboratory for Macromolecular Science of Shaanxi Province, School of
Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an710062,
People’s Republic of China
Appl. Organometal. Chem. 2012, 26, 16–20
Copyright © 2011 John Wiley & Sons, Ltd.

A PdCl2–ionic liquid brush assembly for Mizoroki–Heck reaction
iodobenzene (1.53 g, 7.5 mmol), acrylic acid (0.648 g, 9 mmol)
and Na2CO3 (1.908 g, 18 mmol) were added successively. The
reaction mixture was magnetically stirred and refluxed at
100 ꢁC. After completion of the reaction, the reaction mixture
was cooled to room temperature. The catalyst was separated by
filtration under reduced pressure and washed with hot water.
The filtrate was acidified with 3 mol lꢀ1 HCl aqueous solution
and cooled at 0 ꢁC. The precipitate was filtered, recrystallized
and dried under vacuum at 40 ꢁC to give trans-cinnamic acid.
1
The products were confirmed by H NMR. The selectivity of the
trans product was ~100% and no cis product was observed.
The reaction of iodobenzene with acrylic acid as a model
reaction was carried out to examine the recyclability of the
catalyst. The reactions were carried out under optimal conditions
and post-processing was the same as above. The catalyst was
recovered by simple filtration, washed with EtOH, dried under
vacuum and reused for the next cycle.
Results and Discussion
Synthesis of Catalysis
The catalyst of Pd–ionic liquid brushes assembly was prepared
via coordination linkage between immobilized ionic liquid
brushes with PdCl2 using cheap SiO2 as supporter, as shown in
Scheme 1. Elemental analysis revealed that the material contains
1.02 mmol imidazolium gꢀ1. In the catalyst, parts of Clꢀ coordinated
with PdCl2 to form complexes; thus the catalytic active center of the
metal Pd was transferred to the heterogeneous catalyst. Meanwhile,
the ionic liquid formed from unreacted Clꢀ and imidazolium cation
can play the trait of the homogeneous reaction of the ionic liquid in
the M-H reaction.
Figure 1. The ionic liquid brush catalytic assembly and its possible
working principle.
Experimental
General Information
Unless otherwise stated, all reagents were purchased from
commercial sources and used without purification. The Pd
loading of the catalyst was determined by inductively coupled
plasma mass spectrometry (ICP-MS), using an X series Π mass
spectrometer. The BET surface areas of materials were measured
by nitrogen adsorption using a Peking Pioneer-2002 ST-03A. C, H
and N elemental analysis was performed on a PerkinElmer 2400
CHN elemental analyzer. Infrared (IR) spectra were recorded
separately on a Bruker Equinox-55 spectrophotometer (KBr pellets
in the range 400–4000 cmꢀ1).
Catalytic Activity of Catalyst in the M-H Coupling Reaction
Initially, we employed the M-H reaction of iodobenzene with
acrylic acid as a prototypical reaction for discovery of suitable
reaction conditions and examination of activity of the catalyst
in neat water. All of the reactions were carried out by stirring a
mixture of iodobenzene, acrylic acid, Na2CO3 and catalyst in neat
water using different ratios of catalyst and various temperatures
under aerobic conditions. No other organic co-solvent, phosphine
ligand, phase transfer catalyst or other additives were employed.
The results are listed in Table 1 (entries 1–9).
As can be seen, the present brush catalyst is efficient for the
M-H reaction of iodobenzene with acrylic acid in water alone. A
catalyst:iodobenzene molar ratio of 0.5:100 is recommended
because 0.5 mol% of the catalyst was sufficient, giving the
desired coupled product in the highest yield without detectable
unwanted self-coupling product (entry 4). If the ratio of the
catalyst was reduced to 0.1 mol%, the yield of cinnamic acid
was significantly reduced to 81.3% (entry 1). Although the yield
of cinnamic acid improved with the increasing amount of the
catalyst, 1 mol% of the catalyst gave the desired product in a
yield (91.6%) that was lower than that of 0.5 mol% catalyst (entry
5). This result may be rationalized by the byproduct of undesired
self-coupling product. Furthermore, the yield of cinnamic acid
was enhanced with increasing reaction time. Therefore, in order
to obtain a higher yield, the reaction time should not be less than
24 h. In view of the fact that the yield of cinnamic acid increased
slightly from 24 h to 48 h (entries 4, 9), the reaction mixture
usually refluxed for 24 h in subsequent experiments.
Preparation of the Catalyst
The bis-layered ionic liquid brushes SiO2–BisILs were synthesized
via a three-step route according to the procedure we previously
reported.[44,45] The catalyst SiO2–BisILs[PdCl24ꢀ] was synthesized
using the following procedure. The mixture of PdCl2 (0.9mmol,
0.17 g) and SiO2–BisILs (1g) in 10 ml CH3CN was vigorously
stirred under refluxed condition for 24 h. After the reaction, the
material obtained was washed by Soxhlet extraction with CH3CN
as solvent and dried under vacuum. The catalyst is insensitive
against air and moisture, and stable at room temperature.
Elemental analysis: found C, 13.58; H, 2.39; N, 2.85%, revealing
that the catalyst contains 1.02 mmol imidazolium gꢀ1. IR (KBr disk):
3168, 3120cmꢀ1 n(C&bond;H, aromatic), 2958, 2933, 2860cmꢀ1
(C–H, aliphatic), 1564, 1522, 1452 cmꢀ1 n(C&dbond;N). SBET = 227
m2 gꢀ1. The loading amount of metal Pd was 0.241 mmolgꢀ1
n
.
General Procedures for M-H Reaction and
Recycling Experiment
In a typical experimental procedure, the catalyst and 25 ml water
were stirred at room temperature for about 10 min. Then,
Appl. Organometal. Chem. 2012, 26, 16–20
Copyright © 2011 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

X. Shi et al.
Scheme 1. Preparation of peroxotungstate–ionic liquid brush assembly.
Table 1. Scope of the M-H reaction with PdCl2–ionic liquid brusha
Entry
Aryl halide
C6H5I
Product
Catalyst (eq.)
Time (h)
Yield (%)b
1
C6H5CH¼CHCOOH
0.001
0.002
0.003
0.005
0.010
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
24
24
24
24
24
2
81.3
86.0
91.5
93.6
91.6
30.8
80.3
88.6
96.7
82.0
66.5
85.0
83.5
94.9
92.3
94.6
96.4
93.0
94.5
2
3
4
5
6
7
12
16
48
24
24
24
24
24
24
24
24
24
24
8
9
10
11
12
13
14
15
16
17
18
19
4-MeC6H4I
4-MeC6H4CH¼CHCOOH
2-MeC6H4CH¼CHCOOH
4-MeOC6H4CH¼CHCOOH
2-MeOC6H4CH¼CHCOOH
4-COOHC6H4CH¼CHCOOH
2-COOHC6H4CH¼CHCOOH
3-NO2C6H4CH¼CHCOOH
4-NO2C6H4CH¼CHCOOH
4-BrC6H4CH¼CHCOOH
2-MeC6H4I
4-MeOC6H4I
2-MeOC6H4I
4-COOHC6H4I
2-COOHC6H4I
3-NO2C6H4I
4-NO2C6H4I
4-BrC6H4I
20
21
4-NO2C6H4Br
C6H5Br
4-NO2C6H4CH¼CHCOOH
C6H5CH¼CHCOOH
0.005
0.005
48
48
49.5
~0
aReaction conditions: aryl halide (7.5 mmol), acrylic acid (9 mmol), Na2CO3 (18 mmol), catalyst (based on content of Pd) and H2O (25 ml) were stirred
and refluxed at 100 ꢁC.
bIsolated yields (average of two runs).
To verify the effectiveness and generality of this procedure, the
reactions of various aryl halides with acrylic acid were examined
under the optimized reaction conditions (Table 1, entries 10–22).
All of the present reactions were carried out in neat water without
the need for phase transfer catalyst and protection from
air, showing that the methodology has distinct advantages.
Furthermore, water-insoluble aryl halides were efficiently
transformed to the desired products in excellent yield without
the aid of organic co-solvent owing to the solvent power of the
immobilized ionic liquid.
Aryl iodides, which are electron poor, electron rich, or very
sterically hindered, were easily converted to the corresponding
wileyonlinelibrary.com/journal/aoc
Copyright © 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 16–20

A PdCl2–ionic liquid brush assembly for Mizoroki–Heck reaction
Table 2. Recycling of catalyst in the coupling reaction of iodobenzene and acrylic acida
Cycle
1
2
3
4
5
6
7
8
Yield (%)b
94.6
94.1
93.7
92.8
90.9
92.3
91.9
90.8
aReaction conditions: the mixture of iodobenzene, acrylic acid, Na2CO3 and catalyst in a molar ratio of 1:1.2:2.4:0.005 in H2O were stirred and refluxed
at 100 ꢁC for 24 h.
bIsolated yields (average of two runs).
products in satisfactory yields, while under the same reaction
conditions the coupling of bromobenzene and acrylic acid failed
to provide the target product (entries 20, 21). This observation
coincides with previous findings that aryl iodides are more active
than aryl bromides. The reason may be that cleavage of the
C&bond;I bond is easier than that of C&bond;Br. In addition,
another reason for the low reactivity of bromobenzene may lie
in the polymerization of acrylic acid. The rate of M-H reaction of
bromobenzene with acrylic acid under the established conditions
is far less than that of polymerization of acrylic acid, which is
subjected to polymerization at high temperature and high
concentration. Thus, there is no coupling product in the reaction.
Electronic effects have a great effect on the yield of coupling
product. Although electron-withdrawing and electron-donating
substituents on the aryl halide did not have a detrimental effect
on the ability of the catalyst to promote this reaction to
completion, aryl halides with electron-withdrawing groups gave
higher yields than those with electron-donating substituents,
which is similar to the M-H reaction reported previously (entries
10–12, 13 vs. 14–18). This could also be confirmed by the
observation that although it was difficult for bromobenzene to
dissolved Pd may be the main active species that catalyzes the
reaction. In order to check for leaching of metal Pd from catalyst
into the reaction medium during the M-H reaction, two separate
experiments was carried out in selected systems. (i) The mixture
of iodobenzene, acrylic acid, Na2CO3 and catalyst in a molar ratio
of 1:1.2:2.4:0.005 was refluxed for 2 h. After dealing with the
reaction mixture, a cinnamic acid yield of 30.8% was obtained.
(ii) The mixture of iodobenzene, acrylic acid, Na2CO3 and catalyst
in a molar ratio of 1:1.2:2.4:0.005 was refluxed for 2 h. The catalyst
was then separated from the reaction mixture. The filtrate
continued to reflux for 10 h. After dealing with the reaction
mixture, a cinnamic acid yield of 31.9% was obtained. There
was a tiny difference of 1.1% in the two cases, which confirmed
that the reaction almost did not proceed on the removal of the
catalyst and hence the reaction was heterogeneous in nature.
In addition to this, the filtrate was tested by ICP-MS for the
presence of any leached metallic Pd. As we expected, no
significant leaching of metal was observed because ICP-MS
analysis showed that after filtration of the catalyst the reaction
stream contained only 0.40 mg Lꢀ1 Pd.
give a coupling product, a considerable improvement in yield in Conclusion
the case of 4-bromonitrobenzene was obtained due to the pres-
In summary, a ’real’ on-water procedure and an environmentally
ence of strong electron-withdrawing substituent NO2 on the
phenyl ring (entry 20). As for the different aryl iodides with the
same substituents, the yields of ortho-substituted products are
slightly lower than that of para-substituted products (entries 10
vs. 11, 12 vs. 13, 14 vs. 15). This may be due to the steric influence.
benign catalyst for the M-H reaction in neat water without any
organic co-solvent or other additives have been developed. The
reaction gives the desired products in excellent yield. The air-
stable catalyst showed high activity in the M-H reaction and
could be easily recovered and reused at least eight times without
significant loss of activity. Because of its recyclability and the use
of neat water as the reaction medium, it is distinguished by both
green and economic advantages from other palladium-based
catalysts. In addition to those features, this catalytic system has
the advantage of avoiding the need for inert gas and an organic
co-solvent for water-insoluble aryl halides. The high efficiency,
simplicity of product isolation, outstanding recyclability, and or-
ganic solvent-free and water-alone conditions make the process
very cheap and highly valuable for environmental concerns.
Test for Recyclability and Heterogeneity of the Reaction
Convenient recyclability and a prolonged retention of catalytic
activity are two very important features for the practical and
efficient application of catalytic processes. The reusability of our
catalyst was established by carrying out repeated M-H reactions
of iodobenzene, acrylic acid, and Na2CO3 with each successive
catalyst recovery, under optimum conditions. It is worth pointing
out that the use of water as solvent allows easy recycling of the
catalyst, since the catalyst can be recovered by simple filtration.
After the first use, the catalyst separated was washed with EtOH,
dried under vacuum and subjected to another cycle with a fresh
reaction mixture, under the same reaction conditions. It was
pleasing to found that eight consecutive preparations of
cinnamic acid led to no appreciable loss in yield (Table 2), which
suggested that the metal complex is intact, with the supported
ionic liquid brushes and catalytic activity of the catalyst not
changing significantly, as compared with fresh catalyst. The high
recyclability of this catalytic system allows for a more economic
and environmentally friendly process.
SUPPORTING INFORMATION
Supporting information may be found in the online version of
this article.
Acknowledgments
The authors are grateful to the National Foundation of Natural
Science (Grant No. 20906059 and 21072123), the Natural Science
Foundation of Shaanxi Province (Grant No. 2009JQ2007), the
Foundation of Science and Technology Planning Project of Xi’an
City (Grant No. CXY1121) and the Innovation Foundation of
Postgraduate Cultivation of Shaanxi Normal University (Grant
No. 2011CXS038) for providing financial support for this research.
It is a matter of debate whether the reactions are homoge-
neously or heterogeneously catalyzed in the presence of
supported catalyst. Some conclusions can be drawn from the
Pd level passed into the solvent during the reaction, because
Appl. Organometal. Chem. 2012, 26, 16–20
Copyright © 2011 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

X. Shi et al.
[21] Q. W. Yao, E. P. Kinney, Z. Yang, J. Org. Chem. 2003, 68, 7528.
References
[22] D. E. Bergbreiter, S. Furyk, Green Chem. 2004, 6, 280.
[23] S. A. Patel, K. N. Patel, S. Sinha, B. V. Kamath, A. V. Bedekar, J. Mol.
Catal. A 2010, 332, 70.
[24] J. Demel, J. Čejka, P. Štěpnička, J. Mol. Catal. A 2010, 329, 13.
[25] Y. C. Cui, L. Zhang, J. Mol. Catal. A 2005, 237, 120.
[26] T. Chakraborty, K. Srivastava, H. B. Singh, R. J. Butcher, Appl.
Organometal. Chem. 2011, 696, 2559.
[1] I. P. Beletskaya, A. V. Cheprakov, Chem. Rev. 2000, 100, 3009.
[2] M. A. K. Vogel, C. B. W. Stark, I. M. Lyapkalo, Adv. Synth. Catal. 2007,
349, 1019.
[3] L. Yin, J. Liebscher, Chem. Rev. 2007, 107, 133.
[4] K. C. Nicolaou, P. G. Bulger, D. Sarlah, Angew. Chem. Int. Ed Engl.
2005, 44, 4442.
[5] F. Berthiol, H. Doucet, M. Santelli, Appl. Organometal. Chem. 2006,
20, 855.
[6] S. S. Pawar, D. V. Dekhane, M. S. Shingare, S. N. Thore, Tetrahedron
Lett. 2008, 49, 4252.
[27] M. Z. Cai, J. C. Sha, Catal. Commun. 2007, 8, 1691.
[28] J. Zhu, J. H. Zhou, T. J. Zhao, X. G. Zhou, D. Chen, W. K. Yuan, Appl.
Catal. A 2009, 352, 243.
[29] S. Narayan, J. Muldoon, M. G. Finn, V. V. Fokin, H. C. Kolb, K. B. Sharpless,
[7] A. R. Hajipour, K. Karami, G. Tavakoli, Appl. Organometal. Chem. 2010,
24, 798.
Angew. Chem. Int. Ed. 2005, 44, 3275.
[30] C. J. Li, Chem. Rev. 2005, 105, 3095.
[8] R. B. Bedford, Chem. Commun. 2003, 1787.
[9] W. A. Herrmann, K. Öfele, D. von Preysing, S. K. Schneider, J. Organo-
met. Chem. 2003, 687, 229.
[10] J. G. de Vries, Dalton Trans. 2006, 421.
[11] A. D. Zotto, F. I. Prat, W. Baratta, E. Zangrando, P. Rigo, Inorg. Chim.
Acta 2009, 362, 97.
[12] A. C. Hillier, G. A. Grasa, M. S. Viciu, H. M. Lee, C. Yang, S. P. Nolan,
J. Organomet. Chem. 2002, 653, 69.
[13] E. Peris, R. H. Crabtree, Coord. Chem. Rev. 2004, 248, 2239.
[14] E. A. B. Kantchev, C. J. O’Brien, M. G. Organ, Angew. Chem. Int. Ed.
2007, 46, 2768.
[15] B. R. Buckley, S. P. Neary, Tetrahedron 2010, 66, 7988.
[16] T. Mino, H. Shindo, T. Kaneda, T. Koizumi, Y. Kasashima, M. Sakamoto,
T. Fujita, Tetrahedron Lett. 2009, 50, 5358.
[17] Y. X. Liu, Z. W. Ma, J. Jia, C. C. Wang, M. L. Huang, J. C. Tao, Appl.
Organometal. Chem. 2010, 24, 646.
[31] A. Chanda, V. V. Fokin, Chem. Rev. 2009, 109, 725.
[32] R. A. Sheldon, Green Chem. 2005, 7, 267.
[33] J. Tian, K. D. Moeller, Org. Lett. 2005, 7, 5381.
[34] S. Demir, I. Özdemir, B. Çetinkaya, Appl. Organometal. Chem. 2006,
20, 254.
[35] Y. J. Shang, J. W. Wu, C. L. Fan, J. S. Hu, B. Y. Lu, J. Organomet. Chem.
2008, 693, 2963.
[36] F. Y. Zhao, M. Shirai, M. Arai, J. Mol. Catal. A 2000, 154, 39.
[37] Z. F. Wang, B. Shen, A. H. Zou, N. Y. He, Chem. Eng. J. 2005, 113, 27.
[38] R. N. Ram, V. Singh, Tetrahedron Lett. 2006, 47, 7625.
[39] G. P. Lu, C. Cai, Colloid Surface A 2010, 355, 193.
[40] T. Dwars, E. Paetzold, G. Oehme, Angew. Chem. Int. Ed. 2005, 44,
7174.
[41] R. K. Arvela, N. E. Leadbeater, J. Org. Chem. 2005, 70, 1786.
[42] K. Qiao, R. Sugimura, Q. X. Bao, D. Tomida, C. Yokoyama, Catal.
Commun. 2008, 9, 2470.
[18] S. Nadri, M. Joshaghani, E. Rafiee, Applied Catalysis A: Gen. 2009,
362, 163.
[19] A. M. Zawisza, J. Muzart, Catal. Commun. 2011, 12, 1015.
[20] E. Mieczyńska, A. Gniewek, I. Pryjomska-Ray, A. M. Trzeciak,
H. Grabowska, M. Zawadzki, Appl. Catal. A 2011, 393, 195.
[43] L. Botella, C. Nájera, J. Org. Chem. 2005, 70, 4360.
[44] J. F. Wei, J. Jiao, J. J. Feng, J. Lv, X. R. Zhang, X. Y. Shi, Z. G. Chen,
J. Org. Chem. 2009, 74, 6283.
[45] J. Li, J. J. Cao, J. F. Wei, X. Y. Shi, L. H. Zhang, J. J. Feng, Z. G. Chen, Eur.
J. Org. Chem. 2011, 229.
wileyonlinelibrary.com/journal/aoc
Copyright © 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 16–20