A highly stable and active magnetically separable Pd nanocatalyst in aqueous phase heterogeneously catalyzed couplings

Article abstract of DOI:10.1039/c3gc40421h

An active and stable magnetically separable Pd nanocatalyst was prepared and characterized. The nanocatalyst exhibited excellent activities and reusabilities in aqueous phase processes including the O-arylation of phenols and Sonogashira cross-coupling reactions. The proposed protocol features mild reaction conditions and an extraordinary simplicity and efficiency using NaOH as base in water.

Full text of DOI:10.1039/c3gc40421h

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ISSN 1463-9262
COMMUNICATION
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Luque, Varma and Baruwati
Dumesic et al.
Magnetically seperable organocatalyst Catalytic conversion of biomass
for homocoupling of arylboronic acids to biofuels
1463-9262(2010)12:9;1-U
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A highly stable and active magnetically separable Pd nanocatalyst
in aqueous phase heterogeneously catalyzed couplings
a
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Mohammad Ali Zolfigol, * Vahid Khakyzadeh, Ahmad Reza Moosavi-Zare, Abed Rostami,
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Abdolkarim Zare, Nasser Iranpoor and Mohammad Hassan Beyzavi , Rafael Luque *
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Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran. 6517838683.
b
Department of Chemistry, College of Science, Shiraz University, Shiraz 71454, Iran.
c
Department of Chemistry, Payame Noor University, PO BOX 19395-4697 Tehran, Iran.
d
Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany.
e
Departamento de Quimica Organica, Universidad de Córdoba, Edif. Marie Curie, Ctra Nnal IV-A, Km 396,
E14014, Córdoba (Spain).
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E-mail: mzolfigol@yahoo.com , q62alsor@uco.es
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Abstract
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An active and stable magnetically separable Pd nanocatalyst was prepared and characterized. The
nanocatalyst exhibited excellent activities and reusabilities in aqueous phase processes including the
O-arylation of phenols and Sonogashira cross-coupling reactions. The proposed protocol features
mild reaction conditions and an extraordinary simplicity and efficiency using NaOH as base in water.
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Keywords: Magnetite nanoparticles, Palladium, Sonogashira cross-coupling reaction, O-arylation of
phenol, Water.
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Introduction
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The design of novel magnetically separable systems has attracted a great deal of attention in
recent times as an interesting alternative to improve the efficient separation of heterogeneous
(nano)catalysts from solutions upon reaction completion by applying a simple magnet, providing
improved reusability in the designed systems as well as enhanced properties depending on the
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selected approach. The combination of this concept with that of nanocatalysis holds a significant
potential in the development of innovative systems with improved activities and selectivities in
different chemistries due to the inherent advantages of nanocatalysts. Nanomaterial-based catalysts
can indeed provide high specific surface area to volume ratio which enhances the contact between
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reactants and catalyst support and consequently increases the catalytic activity. Although their
higher surface area affords more active sites, their large surface energies make them unstable, with
a significant tendency to agglomerate. In this regard, magnetic nanoparticles (MAGNPs) can offer
very promising properties as catalyst supports due to their large specific surface areas and magnetic
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properties, which facilitate the separation of the catalyst upon reaction completion. MAGNPs have
been designed and widely employed as novel magnetically separated catalysts in traditional metal
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catalyzed reactions, organocatalysis, and enzymatic catalysis. MAGNPs of Fe O are particularly
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robust, chemically stable as well as readily available with an inherent low toxicity and cost. Their
preparation is also generally very simple, making them an efficient and important alternative to
conventional heterogeneous catalyst supports (e.g. silica, alumina). Most importantly,
MAGNPs-supported catalyst can be conveniently separated from the final reaction mixture upon
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completion by using an external magnet without filtration. The subsequent functionalisation of
MAGNPs with a range of different chemical entities including metal complexes, functional groups
and metal nanoparticles (e.g. Pd) has allowed the design of highly active and selective systems in a
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variety of catalytic applications.
The Sonogashira reaction is probably one of the most straightforward and powerful
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transformations for the construction of C(sp )–C(sp) bonds which can lead to conjugated acetylenic
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compounds, an important class of molecules that have found applications in areas including natural
products, pharmaceuticals, biologically active molecules, liquid crystalline materials, conducting
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polymers and molecular organic materials in nanomaterials. The most commonly utilized catalytic
systems for this reaction comprised palladium homogeneous catalysts including PdCl (PPh ) ,
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[Pd(allyl)Cl] /PPh , PdCl /PPh , or Pd(PPh ) together with CuI as the co-catalyst and large amounts of
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amines as solvents or co-solvents. However, the presence of CuI can result in the formation of
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diyne side products (via oxidative homocoupling of in situ generated Cu(I) acetylides) and can also
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decrease the efficiency to cross-coupling products.
Furthermore, only limited success has to date
been reported in the Sonogashira cross-coupling of alkynes with aryl chlorides. For these reasons,
this field is still challenging and the development novel and greener protocols for the Sonogashira
cross-coupling reaction are desirable. A range of homogeneous and heterogeneously catalyzed
systems have been reported in past years with different results being obtained for a wide variety of
conditions, catalysts and compounds. For more details, readers are kindly referred to recent
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literature reviews on the topic of the development of Sonogashira couplings in recent years.
On the other hand, transition metal catalyzed coupling reactions of aryl halides and phenols
(Ullman type reactions) are the most straightforward methods for the preparations of diaryl
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ethers. Diaryl ethers are commonly found in a variety of important compounds including a number
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of pharmaceuticals, agrochemicals and polymers. This linkage also appears in biologically active
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natural products such as mammalian hormone thyroxine and antibiotics. In recent years, much
progress has been achieved in Cu/Pd-catalyzed synthesis of diaryl ethers using aryl bromides and
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aryl iodides as aryl donors to couple with phenols providing excellent yields under mild conditions.
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Additionally, other organometalloids such as organobismuth, organotrifluoroborate reagents and
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arylboronic acids have extended this challenging field of research. However, in some cases the
requirements of stoichiometric or greater quantities of copper at high temperatures (125-300 ºC) in
polar solvents (typically pyridine or DMF) compromised the environmentally soundness of the
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protocol and often rendered it unsuitable for the construction of complex molecules. Examples for
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the coupling of aryl chlorides with phenols have also been rarely reported in the literature but
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there are some relevant examples of the use of magnetically separable Pd catalysts and a Cu-free
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system based on a charcoal supported Pd material.
In this work, we present our approach based on the design of a water tolerant novel
Pd-containing magnetically separable system for C-O and C-C coupling reactions including the
Sonogashira coupling and the O-arylation of phenols in aqueous environments (Scheme 1).
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Scheme 1. O-Arylation of phenols and copper and amine-free Sonogashira reaction.
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Results and discussion
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Fe O particles (I) were prepared according to a previous report by Qu et al. and subsequently
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coated with a layer of silica upon reaction with tetraethyl orthosilicate (TEOS). MAGNPS-Silica
core-shell materials (II) were then sonicated in toluene. Chlorodiphenylphosphine was immediately
added to the dispersed MAGNPS-Silica core-shell materials (II) under nitrogen atmosphere and the
intermediate material III was obtained. Finally, III was reacted with PdCl in DMF as solvent and
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heated at 140ºC to yield the final catalyst. A pictorial representation of the current synthesis has
been illustrated in Figure 1.
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Figure 1. Stepwise preparation of the magnetically separable system
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Transmission electron microscopy (TEM) images of the synthesized catalyst were recorded and
depicted in Figure 2a and 2b. According to these images, the catalyst was approximately 50 nm in
size (Figure 2a). EDX from the obtained nanomaterials (Figure 2a) provided the presence of the
expected elements in the structure of the catalyst, namely iron, oxygen, silicon, phosphorus, carbon
and palladium (Figure 2c).
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The phase and purity of the different stepwise synthesized materials in this work (from magnetite
{Fe O } to final catalyst {Fe O @SiO @PPh @Pd(0)}) have been determined by XRD patterns (shown
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in Figure 2). XRD pattern of Fe O exhibited peaks at 2θ= 18.3, 30.2, 35.6, 43.3, 53.6, 57.3, 62.8 and
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74.2 corresponding to diffraction lines (111), (220), (311), (400), (422), (511) and (440), respectively.
The diffraction peaks in this pattern can be well indexed to the cubic spinel phase of Fe O , in good
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agreement with literature data (JCPDS 01-1111) (Figure 3a). Silica coated magnetite particles
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{Fe O @SiO } exhibited an XRD broadened pattern due to its non-crystalline nature at 2θ= 20-29
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and also 30.2, 35.6, 43.3, 53.6, 57.3, 62.8 and 74.2 which corresponded to a Fe O structure (Figure
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3b). Upon addition of the phosphorus ligands to Fe O @SiO , a much broadened diffraction pattern
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to that of Fe O @SiO was observed (Figure 3c). Finally, the addition of palladium to
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Fe O @SiO @PPh gave rise to lines at 2θ= 39.9, 46.4, 67.7, 81.6 and 86.1 oriented along (111),
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(200), (220), (311), and (222) diffraction lines, respectively. No peaks due to impurities were
detected, indicating the high purity of the catalyst (Figure 3d). The lattice constant measured for the
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sample is a= 3.907 A . The miller-indices and lattice constant of the catalyst
{Fe O @SiO @PPh @Pd(0)}) were found to be in agreement with values reported in the
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JCPDS 87-0643 card.
b)
a)
c)
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Figure 2. (a) Core-shell structure of the catalyst (b) Transmission electron microscopy (TEM) of the catalyst (c)
Energy-dispersive X-ray spectroscopy (EDX) of the catalyst
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(a)
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Figure 3. XRD patterns of (a) Fe O (b) Fe O @SiO (c) Fe O @SiO @PPh (d) Fe O @SiO @PPh @Pd(0)
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The average crystallite size D for the designed {Fe O @SiO @PPh @Pd(0)} catalyst was calculated
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using the Debye–Sherrer formula D = Kλ /(ßCos ɵ), with λ being the X-ray wavelength, K is the
Scherrer constant, ß the peak width of half-maximum, and ɵ is the Bragg diffraction angle.
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The average size of the catalyst thus obtained from this equation was found to be ca. 52 nm, in good
agreement to that observed in the transmission electron micrograph (TEM) studies. ICP/MS analysis
of the catalyst showed that the Pd content was ca. 1.5 wt% Pd in the systems.
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UV-DRS studies within the range of 200–850 nm were subsequently conducted to visualise the
presence of Pd(0) in the materials. Figure 4 depicts the two curves obtained for materials III
(phosporus layer) and IV (supported Pd material). The final nanocatalyst {Fe O @SiO @PPh @Pd(0)}
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exhibited a broad band which could be attributed to Pd(0) in the structure, in good agreement with
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previous studies. These findings were also corroborated in XPS investigations (Figure 5) in which
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two peaks could be observed related to Pd 3d and Pd 3d of Pd(0) at 335.2 and 340.2 eV.
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Figure 4. UV-DRS spectra of the third layer (Blue) and fourth layer (Pd(0), Black) in the magnetite
catalyst.
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Figure 5. XPS spectra of the catalyst.
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Figure 6 shows the magnetic properties of the catalyst in comparison with Fe O that were
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investigated at room temperature using a vibrating sample magnetometer (VSM). Based on
magnetization curves, the magnetization is saturated up to 4 emu/g at an applied field of 7000 Oe,
with an almost insignificant coercivity. The insert figures in the right image indicate the magnetic
properties of the catalyst allow a facile separation from the reaction mixture and subsequent
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redispersion into solution without any appreciable aggregation in successive reaction runs.
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Figure 6. The vibrating sample magnetometer (VSM) of the catalyst in comparison with Fe O .
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The activity of the catalyst was subsequently investigated upon characterisation in the
Sonogashira reaction as well as in the O-arylation of phenols with less activated aryl halides
(X = Cl, Br). Starting with the Sonogashira coupling, the reaction of phenylacetylene with
bromobenzene was studied as test process for optimisation. Blank runs provided negligible activity
to the cross-coupling product in the absence of catalyst. The effect of catalyst loading in the reaction
was firstly investigated and different quantities of catalyst ranging from 0.002 to 0.010 g were
tested. The best results were obtained using 0.005 g catalyst (ESI). No significant improvement in
reaction results was observed by further increasing the quantity of catalyst in the reactions. A series
of bases including NaOH, K CO , Cs CO and Et N were then screened, with optimum results
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obtained using aqueous NaOH (up to 93% isolated yield at 80 ºC, Table 1). No homocoupling product
was observed under the investigated conditions. Additionally, to study the effect of solvents in the
reaction, we examined a range of solvents in comparison with water (e.g. EtOH, DMF, DMSO, PEG
and toluene) for the model reaction. Gratifyingly, results obtained with alternative solvents to water
did not provide any improved yields under the investigated conditions (Table 2).
Table 1. Effect of different bases in the catalytic activity of {Fe O @SiO @PPh @Pd(0)} in the
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[a]
Sonogashira reaction at 80 C
Entry
Base
Amount of the Catalyst [g]
Time (min)
Isolated yield [%]
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NaOH
0.005
0.005
0.005
0.005
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43
93
89
K
2
CO
CO
Et
NaOH
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Cs
2
3
35
93
3
N
120
240
Trace
---
[
a] Reaction conditions: Bromobenzene (1mmol), Phenylacetylene (1 mmol), Water (5 ml) and 1.5 eq
Base.
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The scope of the reaction was subsequently expanded to several substrates including a range of
more challenging aryl chlorides (Table 3). Results summarized in Table 3 clearly demonstrate that
the protocol was amenable to various substrates (bromo- and chloro-derivatives) and substituents,
providing very good to excellent yields to products even in the case of less activated substrates (e.g.
1-chloro-4-methoxybenzene), with relatively short times of reaction in the range of 0.5 - 6 h.
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Table 2. Effect of different solvents in the catalytic activity of {Fe O @SiO @PPh @Pd(0)} in the
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[a]
Sonogashira reaction at 80 C
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Entry
Solvent
Temp [ C]
t [min]
Isolated yield [%]
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2
3
4
5
6
H
2
O
80
80
80
80
80
80
33
40
93
90
81
83
69
40
EtOH
DMF
60
DMSO
PEG
60
80
Toluene
120
[
a] Reaction conditions: Catalyst (0.005 g), Bromobenzene (1mmol), Phenylacetylene (1 mmol),1.5 mmol
NaOH and Solvent (5 ml).
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The magnetically separable catalyst was subsequently tested in the O-arylation of phenols. The
reaction of bromobenzene with phenol was chosen as model reaction. Blank runs gave no
conversion to products in the absence of catalyst. Aqueous NaOH media was also found to be the
best choice (Table 4), selected as optimum, as poor activities were obtained in other solvents
(Table 5). Catalyst loading studies were also conducted (see ESI for full details). Under optimized
conditions (2 hours, 0.005 g of catalyst, 80 °C), quantitative conversion of bromobenzene to target
product was obtained, with a 90 % of isolated yield. Similarly to the Sonogashira reaction, the
versatility of the protocol was clearly proved when a range of aryl halides were succesfully converted
to target products in very good yields in times of reaction in the 1.5-15 h range. Naphthols could also
be conveniently coupled to bromobenzene and chlorobenzene in good yields.
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To investigate the truly heterogeneous nature of the protocols and thus any potential palladium
leaching, ICP/MS results proved no detected any palladium leaching in the filtrate (<0.05 ppm) upon
reaction completion, which indicates the high stability of the prepared catalyst. In order to know
whether the reaction takes place at the surface of solid Pd as a truly heterogeneous reaction or any
Pd-leached species act as homogeneous catalyst, the hot filtration test was conducted at 80ºC in a
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similar way to that previously recommended and reported.
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Table 3. Investigations of the scope of substrates in the Pd-catalyzed Sonogashira cross-coupling
reaction
[
a]
[b]
Entry
1
Aryl Halide
Product
t [min]
Yield (%)
4a
15
91
93
85
2
3
4
4b
4c
4d
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55
180
95
77
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4e
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360
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90
88
4g
90
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4h
4i
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90
93
90
1
0
4j
250
35
70
[
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1
4b
>90
[
a] Reaction conditions: Aryl Halide (1 mmol), phenylacetylene (1 mmol), water (5 mL), NaOH (1.5 mmol)
−4
and catalyst (0.005 g, containing 17 × 10 g, 0.015 mmol of Pd)
[
[
b] Yields of purified products.
c] Hot filtration test (run corresponding to fresh substrates added to the recovered catalyst from entry 2 in
a new reaction under identical conditions at 80ºC).
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[
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Table 4. Effect of different bases in Pd-catalyzed O-arylation of phenols
Entry
Base
Amount of the Catalyst [g]
t [h]
Isolated yield [%]
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2
3
4
5
NaOH
0.005
0.005
0.005
0.005
---
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3
90
90
K
2
CO
CO
Et
NaOH
3
Cs
2
3
2.5
4
90
3
N
Trace
---
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[
a] Reaction conditions: Bromobenzene (1mmol), Phenol (1 mmol), Water (5 ml) and 1.5eq Base,
0ºC.
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1
90
91
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1
2
2
2
2
92
93
94
95
96
97
98
99
00
01
02
03
In the light of these premises, the Sonogashira cross-coupling reaction for bromobenzene and
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phenylacetylene in the presence of the catalyst in H O at 80 C was performed for 5 min and
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then the catalyst was immediately removed from the reaction mixture with a magnet. In this
step, isolated yield of reaction product showed a 28% conversion to product. In the next step,
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the reaction mixture (without the catalyst) was further reacted under stirring at 80 C for 12
hours. After this time, the reaction did not progress any further (conversion ca. 30%).
Comparatively, the isolated catalyst from the hot filtration reaction provided >90% isolated
yield after 33 min when fresh reagents were added in a new reaction run (Table 3, entry 11).
These findings indicate that the reaction has mainly been catalyzed by the heterogeneous
system. A similar result was obtained in the case of the O-arylation of phenols (Table 6, entry
11).
[a]
Table 5. Effect of Different Solvents in the Pd- catalyzed O-arylation of phenols
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Entry
Solvent
Temp [ C]
t [h]
Isolated yield [%]
1
2
3
4
5
6
H
EtOH
DMF
DMSO
PEG
Toluene
2
O
80
80
80
80
80
80
2
2.5
3
3
4
90
88
85
83
75
30
5
[
a] Reaction conditions: Catalyst (0.005 g), Bromobenzene (1mmol), Phenol (1 mmol),1.5 mmol NaOH
and Solvent (5 mL).
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Table 6. Palladium-supported onto phosphorus silica magnetite catalyzed O-arylation of phenols.
[
a]
[b]
Entry
1
Aryl Halide
Ar-OH
Product
t [h]
Yield [%]
Phenol
1a
1.5
93
2
3
4
Phenol
Phenol
Phenol
1b
1c
1d
2
90
83
88
3.5
1.5
5
6
Phenol
Phenol
1e
1f
5
7
90
80
7
8
9
1-Naphthol
1-Naphthol
2-Naphthol
2-Naphthol
Phenol
2a
2b
3a
3b
1b
9
7
72
70
10
15
2
60
1
0
60
[
c]
1
1
>90
[
a] Reaction condition: Aryl Halide (1mmol), Ar-OH (1mmol),water (5 mL), NaOH (1.5 mmol) and
−4
catalyst (0.005 g, containing 17 × 10 g, 0.015 mmol of Pd), 80ºC.
b] Yields of purified products.
[
[
c] Hot filtration test (run corresponding to fresh substrates added to the recovered catalyst from entry 2
in a new reaction under identical conditions at 80ºC).
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Apart from the magnetic isolation and separation of the catalyst upon reaction completion, the
additional possibility to reuse the catalyst several cycles was also studied. Results depicted in Figure
7 confirm that the magnetically separable Pd catalyst could be recycled and reused several times (up
to 6 uses) without any appreciable loss of its initial catalytic activity regardless of the type of
coupling.
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A schematic representation of the proposed catalytic routes for both types of couplings has been
summarized in Scheme 2. In a first step, the active palladium catalyst reacts with the aryl halide in an
II
oxidative addition to produce Pd intermediate (complex A) in both couplings. Such intermediate
could react with phenylacetylene (Sonogashira reaction) or phenol (O-arylation) in the presence of
NaOH as a base to render intermediates B or C. Finally, these complexes undergo reductive
elimination to afford the expected products, regenerating the catalyst at the same time, which can
be further used in another cycle.
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Figure 7. The catalytic activity and reusability of the Pd-magnetically separable catalyst
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Scheme 2. Proposed reaction mechanisms for the Pd-catalysed Sonogashira reaction (bottom part of the
mechanism) and O-arylation of phenols (top part of the mechanism).
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Conclusions
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A novel and efficient Pd-containing phosphorus silica magnetite [Fe O @ SiO @ PPh @ Pd (0)] has
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been developed as highly active and stable nanocatalyst for aqueous phase coupling reactions,
namely the O-arylation of phenols with aryl halides [ArX (X= Cl, Br and I)] and the Sonogashira
coupling reaction under mild conditions. The salient features of the proposed methodology include
high efficiency, generality and simplicity which lead to high yields, a cleaner reaction profile and easy
recyclability of the highly stable heterogeneous catalyst by a simple magnet. The applicability of the
current systems is currently under investigation in related chemistries which will be reported in due
course.
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Experimental
Characterization methods
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The structure of the magnetite nanocatalyst was characterized by FT-IR, UV-VIS (DRS), XRD, XPS,
EDAX, TEM and VSM analysis. NMR spectra were recorded with a Bruker Avance 250 spectrometer
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( HNMR 250 MHz and CNMR 62.9 MHz) in pure deuterated chloroform with tetramethylsilane
(TMS) as the internal standard. Transmission electron microscope, TEM (ZEISS EM900) was also used
to obtain TEM images. The crystallographic structure of synthesized materials was determined by an
X-ray diffractometer ITAL STRUCTURES model APD2000 with applying Cu Kα radiation wavelength
(0.15405 nm), and at 2θ range of 10° to 90°. XPS spectrum was acquired by VG and consisted of a
twin anode XR3E2 x-ray source. Magnetic measurements were carried out in a vibrating sample
magnetometer (VSM - 4 inch, Daghigh Meghnatis Kashan Co., Kashan, Iran) at room temperature.
The elemental analysis of the catalyst using energy-dispersive X-ray spectroscopy technique (EDAX,
Röntec QX2) was calculated to obtain direct data for the elemental composition of the layers and
elementals. Infrared spectrum of layers is recorded by Perkin Elmer PE-1600-FTIR. Ultraviolet diffuse
reflectance spectroscopy (UV-DRS, V-670, JASCO spectrometer) of the catalyst was recorded within
the range of 200–900 nm. The metal content in the materials was determined using Inductively
Coupled Plasma (ICP) in a Philips PU 70000 secuential spectrometer equipped with an Echelle
monochromator (0.0075 nm resolution) couple with mass spectrometry. Samples were digested in
HNO and subsequently analysed by ICP at the SCAI in Universidad de Cordoba.
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Catalyst preparation
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Initially, Fe O (magnetite phase) was prepared by adding 3 mL FeCl (2 mol L dissolved in 2 mol L
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HCl) to 10.33 mL double distilled water followed by a dropwise addition of 2 mL Na SO (1 mol L ) in
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1 min under magnetic stirring. Upon solution color changing from red to light yellow, 80 mL NH .H O
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solution (0.85 mol L ) were added under vigorous stirring. After 15 min, the magnetite precipitate (I)
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was washed to pH<7.5 by distilled water and separated with a magnet.
To a mixture containing
1 g of Fe O (I) 20 mL water, 80 mL ethanol, 3 mL ammonia and 3 ml tetraethyl orthosilicate (TEOS)
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were added under reflux to obtain MAGNPS-Silica core-shell materials (II). 1 g of prepared particles
(II) were sonicated in 5 mL toluene and then 2 mL of ClPPh was added under nitrogen atmosphere
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(to remove the produced HCl) for 4 hours to give III. The amount of active phase of phosphorus
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layer, measured according to a previously reported method, was 4 mmol per gram of material.
Finally, 1 g of compound III was reacted with 0.727 g of PdCl (4.2 mmol) in 8 mL DMF at 140 ºC for
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12 hours to give the final catalyst IV as a black powder.
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General procedure for the Sonogashira cross-coupling reaction
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A round-bottomed flask (10 mL) was charged with aryl halide derivatives (1 mmol) and
phenylacetylene (1 mmol) in water (5 mL). NaOH (1.5 mmol) and the catalyst (0.005 g, containing 17
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× 10 g, 0.015 mmol of Pd) were then added and the final mixture connected to a reflux condenser.
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The reaction mixture was stirred for the required period of time at 80 C to reaction completion, as
monitored by TLC. The final reaction mixture was then cooled at room temperature, the catalyst
easily collected by means of a magnet to be reused in subsequent reactions and the residue of the
reaction extracted with Et O (3mL × 5mL). The ethereal solution was evaporated to afford the
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desired product in an almost pure state. For further purification, has been performed by using
column chromatography over silica gel that eluted with n-hexane/ethyl acetate (10:1) to give the
pure biphenyl compounds.
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General procedure for the O-arylation of phenols
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A round-bottomed flask (10 mL) was charged with phenol derivatives (1 mmol) and aryl halides
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(1 mmol) in water (5 mL). NaOH (1.5 mmol) and the catalyst (0.005 g, containing 17 × 10 g, 0.015
mmol of Pd) were then added and the final mixture connected to a reflux condenser. The reaction
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mixture was stirred for 1.5-15 hours at 80 C to reaction completion, as monitored by TLC, and then
cooled at room temperature; the catalyst was removed from the solution using a magnet and the
final residue of the reaction subsequently purified by column chromatography over silica gel using
n-hexane/ethyl acetate (13:1).
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Acknowledgements
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The authors gratefully acknowledge partial support of this work by the Research Affairs Office of Bu-
Ali Sina University (Grant number 32-1716 entitled development of chemical methods, reagents and
molecules), and Center of Excellence in Development of Chemical Method (CEDCM), Hamedan, I.R.
Iran. Rafael Luque gratefully acknowledges MICINN for the concession of a Ramon y Cajal Contract
(ref. RYC-2009-04199) and funding from projects CTQ2011-28954-C02-02 (MEC) and P10-FQM-6711
(Consejeria de Ciencia e Innovacion, Junta de Andalucia).
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References
1 (a) E. Rafiee, S. Eavani, Green Chem. 2011, 13, 2116-2122; (b) C.Ó. Dálaigh, S.A. Corr, Y. Gun’ko,
S. J. Connon, Angew. Chem. Int. Ed. 2007, 46, 4329-4332; (c) D. M. Lai, L. Deng, J. Li, B. Liao, Q. X.
Guo, Y. Fu, Chem. Sus. Chem.2011, 4, 55-58; (d) Y. Zhang, C. G. Xia, Appl.Catal. A. 2009, 366, 141-
147; (e) X. X. Zheng, S. Z. Luo, L. Zhang, J. P.Cheng, Green Chem. 2009, 11, 455-458.
2 V. Polshettiwar, R. S. Varma, Green Chem. 2012, 12, 743-754.
3 (a) A.-H. Lu, E. L. Salabas, F. Schüth, Angew. Chem. Int. Ed. 2007, 46, 1222-1244; (b) Y. Zhu, L. P.
Stubbs, F. Ho, R. Liu, C. P. Ship, J. A. Maguire, N. S. Hosmane, Chem. Cat. Chem. 2010, 2, 365-374.
4 V. Polshettiwar, R. S. Varma, Org. Biomol. Chem. 2009, 7, 37-40.
5 (a) R. Abu-Reziq, H. Alper, D. S. Wang, M. L. Post, J. Am. Chem.Soc. 2006, 128, 5279-5282; (b) G.
Chouhan, D. S.Wang, H. Alper, Chem.Commun. 2007, 4809-4811; (c) T. Hara, T. Kaneta, K. Mori, T.
Mitsudome, T. Mizugaki, K. Ebitani, K. Kaneda, Green Chem. 2007, 9, 1246-1251; (d) M. J. Jin, D.
1
9

View Article Online
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
H. Lee, Angew. Chem., Int. Ed. 2010, 49, 1119-1122; (e) H. Q. Yang, Y. Wang, Y. Qin, Y. Chong, Q.
Yang, G. Li, L. Zhang, W. Li, Green Chem. 2011, 13, 1352-1361; (f) S. E. Garca-Garrido, J. Francos,
V. Cadierno, J-M. Basset, V. Polshettiwar, Chem.Sus.Chem, 2011, 4, 104-111.
6 (a) X. Wang, P. P. Dou, P. Zhao, C. M. Zhao, Y. Ding, P. Xu, Chem. Sus. Chem. 2009, 2, 947-950; (b)
J. Lee, Y. Lee, J. K. Youn, H. B. Na, T. Yu, H. Kim, S. M. Lee, Y. M. Koo, J. H. Kwak, H.G. Park, H.N.
Chang, M. Hwang, J. G. Park, J. Kim, T. Hyeon, Small. 2008, 4, 143-152.
7 (a) S. Wu, A. Sun, F. Zhai, J. Wang, W. Xu, Q. Zhang, A. A. Volinsky, Materials Letters. 2011, 65,
1882–1884; (b) K. S. Lee, M. H. Woo, H. S. Kim, E. Y. Lee, I. S. Lee, Chem. Commun. 2009, 25,
3780-3782; (c) V. Polshettiwar, Á. Molnár, Tetrahedron. 2007, 63, 6949-6976; (d) L. M. Rossi, I. M.
Nangoi, N. J. S. Costa, Inorg. Chem. 2009, 48, 4640-4642.
8 (a) S. B. Kim, C. Cai, J. Kim, S. Sun, D. A. Sweigart, Organometallics. 2009, 28, 5341–5348; (b) H.
Zhang, G. Zhu, Appl. Surf. Sci. 2012, 258, 4952–4959; (c) M. Ma, Q. Zhang, D. Yin, J. Dou, H. Zhang,
H. Xu, Catal. Commun. 2012, 17, 168-172; (d) N. Koukabi, E. Kolvari, A. Khazaei, M. A. Zolfigol, B.
Shirmardi-Shaghasemi, H. R. Khavasi, Chem. Commun. 2011, 47, 9230-9232.
9 (a) S. Qu, H. Yang, D. Ren, S. Kan, G. Zou, D. Li, M. Li, J. Colloid Interface Sci. 1999, 215, 190-192;
(b) V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara, J. -M. Basset, Chem. Rev. 2011, 111,
3036-3075.
10 (a) D. Alberico, M.E. Scott, M. Lautens, Chem. Rev. 2007, 107, 174-238; (b) R. Chinchilla, C. Najera,
Chem. Rev. 2007, 107, 874-922; (c) E. M. Beccalli, G. Broggini, M. Martinelli, S. Sottocornola,
Chem. Rev. 2007, 107, 5318-5365; (d) J. Zhang, M. Dakovic, Z. Popovic, H. Wu, Y. Liu, Catal.
Commun. 2012, 17, 160-163.
11 (a) K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. 1975, 16, 4467-4470; (b) H. A. Dieck,
F. R. Heck, J. Organomet. Chem. 1975, 93, 259-263; (c) L. Cassar, J. Organomet.Chem. 1975, 93,
253-257.
2
0

View Article Online
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
12 (a) M. Kotora, T. Takahashi In Handbook of OrganopalladiumChemistry for Organic Synthesis, (Ed:
E.-i. Negishi), John Wiley & Sons, Inc., New York, USA, 2003; (b) P. Siemsen, R.C. Livingston, F.
Diederich, Angew. Chem., Int. Ed. 2000, 39, 2632-2657.
13 (a) D. Gelman, S. L. Buchwald, Angew.Chem. Int. Ed. 2003, 42, 5993-5996; (b) J. Liu, J. Chen, C. Xia,
J. Catal. 2008, 253, 50-56; (c) A. Corma, H. García, A.Primo, J. Catal. 2006, 241, 123-131; (d) A.
Corma, H. García, A. Leyva, J. Catal. 2006, 240, 87-99.
14 (a) H. Huang, H. Liu, H. Jiang, K. Chen, J. Org. Chem. 2008, 73, 6037-6040; (b) Y. Liang, Y. -X. Xie, J.
-H. Li, J. Org. Chem. 2006, 71, 379-381.
15 (a) M. Pagliaro, V. Pandarus, R. Ciriminna, F. Beland, P. D. Cara, Chem.Cat.Chem. 2012, 4, 432-
435; (b) M. Schilz, H. Plenio, J. Org. Chem. 2012, 77, 2798-2807; (c) R. Chinchilla, C. Najera, Chem.
Soc. Rev. 2011, 40, 5084–5121; (d) R. Chinchilla, C. Najera, Chem. Rev. 2007, 107, 874-922.
16 F. Ullmann, Ber. Dtsch. Chem. Ges. 1904, 37, 853–854.
17 (a) F. Theil, Angew. Chem., Int. Ed. 1999, 38, 2345–2347; (b) J. S. Sawyer, Tetrahedron. 2000, 56,
5045–5065; (c) A. W. Thomas, S. V. Ley, Angew. Chem., Int. Ed. 2003, 42, 5400–5449.
18 (a) E. S. Tan, M. Miyakawa, J. R. Bunzow, D. K. Grandy, T. S. Scanlan, J. Med. Chem. 2007, 50,
2787–2798; (b) K. C. Nicolaou, C. N. C. Boddy, S. Brase, N. Winssinger, Angew. Chem., Int. Ed.
1999, 38, 2097–2152.
19 (a) J. -F. Marcoux, S. Doye, S. L. Buchwald, J. Am. Chem. Soc. 1997, 119, 10539–10540; (b) P. J.
Fagan, E. Hauptman, R. Shapiro, A. Casalnuovo, J. Am. Chem. Soc. 2000, 122, 5043–5051; (c) R. K.
Gujadhur, C. G. Bates, D. Venkataraman, Org. Lett. 2001, 3, 4315–4317; (d) E. Buck, Z. J. Song, D.
Tschaen, P. G. Dormer, R. P. Volante, P. J. Reider, Org. Lett. 2002, 4, 1623–1626; (e) D. Ma, Q. Cai,
H. Zhang, Org. Lett. 2003, 5, 3799–3802; (f) A. Ouali, J. -F. Spindler, H. -J. Cristau, M. Taillefer, Adv.
Synth. Catal. 2006, 348, 499–505; (g) Q. Cai, B. Zou, D. Ma, Angew. Chem., Int. Ed. 2006, 45,
1276–1279; (h) H. J. Cristau, P. P. Cellier, S. Hamada, J. F. Spindler, M. Tailefer, Org. Lett. 2004, 6,
913–916; (i) X. Lv, W. Bao, J. Org.Chem. 2007, 72, 3863–3867; (j) Y. Chen, H. Chen, Org. Lett.
2
1

View Article Online
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
2006, 8, 5609–5612; (k) J. Niu, H. Zhou, Z. Li, J. Xu, S. Hu, J. Org. Chem. 2008, 73, 7814–7817; (l) A.
B. Naidu, E. A. Jaseer, G. Sekar, J. Org. Chem. 2009, 74, 3675–3679.
20 J. -P. Finet, A. Y. Fedorov, S. Combes, G. Boyer, Curr. Org. Chem. 2002, 6, 597-626.
21 T. D. Quach, R. A. Batey, Org. Lett. 2003, 5, 1381-1384.
22 P. Y. S. Lam, C. G. Clark, S. Saubern, J. Adams, M. P. Winters, D. M. T. Chan, A. Combs,
Tetrahedron Lett. 1998, 39, 2941-2944.
23 a) S. V. Ley, A. W. Thomas, Angew. Chem., Int. Ed. 2003, 42, 5400–5449; b) R. Frlan, D. Kikelj,
Synthesis. 2006, 2271–2285; c) J. S. Sawyer, Tetrahedron. 2000, 56, 5045–5065; d) G. Evano, N.
Blanchard, M. Toumi, Chem. Rev. 2008, 108, 3054–3131; e) I. P. Beletskaya, A. V. Cheprakov,
Coord. Chem. Rev. 2004, 248, 2337–2364; f) J. Lindley, Tetrahedron. 1984, 40, 1433–1456.
24 a) N. Xia, M. Taillefer, Chem. Eur. J. 2008, 14, 6037–6039; b) H. Rao, Y. Jin, H. Fu, Y. Jiang, Y. Zhao,
Chem.Eur. J. 2006, 12, 3636–3646; c) J. Zhang, Z. Zhang, Y. Wang, X. Zheng, Z. Wang, Eur.J.
Org.Chem. 2008, 5112–5116.
25 a) M.-J. Jin, P.-H. Lee, Angew. Chem. Int. Ed. 2010, 49, 1119-1122; b) P. Li, L. Wang, L. Zhang, G.W.
Wang, Adv. Synth. Catal. 2012, 354, 1307-1318; c) R. Arundhathi, D. Damodara, Pravin R. Likhar,
M. Lakshmi Kantam, P. Saravanan, T. Magdaleno, S.H. Kwon, Adv. Synth. Catal. 2011, 353,
1591-1600.
26 A. Komaromi, Z. Novak, Chem. Comm. 2008, 4968-4970.
27 M. Dams, L. Drijkoningen, B. Pauwels, G. Van Tendeloo, D. E. De Vos, P. A. Jacobs, J. Catal. 2002,
209, 225-236.
28 A. Khalafi-Nezhad, F. Panahi, Green. Chem. 2011, 13, 2408-2415.
29 L. Yin, J. Liebscher, Chem. Rev. 2007, 107, 133-173.
30 Y.- H. Deng, C.-C. Wang, J.-H. Hu, W.-L. Yang, S.-K. Fu, Colloid Surface A. 2005, 262, 87-93.
31 N. Iranpoor, H. Firouzabadi, S. Motevalli, J. Mol. Catal. A: Chem. 2012, 355, 69-74.
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