Regioselective Heck reaction catalyzed by Pd nanoparticles immobilized on DNA-modified MWCNTs

Article abstract of DOI:10.1039/c6ra11737f

This is the first report of regioselective Heck reaction of aryl iodides with 2,3-dihydrofuran using heterogonous nanocatalyst. Herein, palladium nanoparticles is immobilized on DNA-modified multi walled carbon nanotubes and characterized by FT-IR spectroscopy, UV-vis spectroscopy, field emission scanning electron microscopy, X-ray diffraction, transmission electron microscopy, inductively coupled plasma and elemental analysis. DNA as a well-defined structure and biodegradable natural polymer generate the palladium catalyst which showed high activity in common and regioselective Heck reaction in excellent yields and good selectivity under ligand-free and mild reaction conditions. Moreover, the catalyst could be recovered and reused at least nine times without any considerable loss of its catalytic activity.

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Regioselective Heck Reaction catalyzed by Pd nanoparticles
immobilized on DNA-modified MWCNTs
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a
c
Abdol R. Hajipour* Zahra Khorsandi and Hossein Farrokhpour*
DOI: 10.1039/x0xx00000x
This is the first report of regioselective Heck reaction of aryl iodides with 2,3-dihydrofuran using heterogonous
nanocatalyst. Herein, palladium nanoparticles is immobilized on DNA-modified multi walled carbon nanotubes and
characterized by FT-IR spectroscopy, UV-vis spectroscopy, field emission scanning electron microscopy, X-ray
diffraction, transmission electron microscopy, inductively coupled plasma and elemental analysis. DNA as a well-
defined structure and biodegradable natural polymer generate the palladium catalyst which showed high activity in
common and regioselective Heck reaction in excellent yields and good selectivity under ligand-free and mild reaction
conditions. Moreover, the catalyst could be recovered and reused at least nine times without any considerable loss
of its catalytic activity.
www.rsc.org/
workers reported the arylation of DHF with common aryl
bromides and chlorides catalyzed by spiro bisphosphine oxides
as a ligand of Pd catalysts. This method gave a high conversion
and good olefinic ratio but suffer from some limitations such
Introduction
The Heck reaction is one of the most important carbon−carbon
bond forming reactions in organic synthesis and in the
pharmaceutical, agrochemical, and fine chemical industries.
as harsh reaction conditions, long reaction times and using
14
1
-3 expensive ligands. Lauer and co-workers recently reported
conditions for achieving excellent vinyl selectivity in the Heck
coupling of cyclic olefins with aryl bromides using neopentyl
phosphine ligands.
The palladium-catalyzed bond forming reaction between aryl
halides and olefins bearing electron-withdrawing substituents
15
4
EWG, e.g. –COOR, –CN) is well studied. In contrast, the Heck
-8
(
Despite the wide application of these homogeneous palladium
catalysts, their separation is very difficult and their recycling is
almost complicated. Moreover, in concern to toxicity of
palladium residuals, acceptable limits of palladium traces in
pharmaceuticals were set usually as ppm level. Application of
heterogonous catalysts can solve this problem. Furthermore,
due to economical and environmental factors, catalytic
systems without expensive and toxic phosphine ligands are
favourable. Numerous P-free conditions for Heck reaction of
coupling involving an olefin bearing a hydrogen atom in the
allylic position has proved to be a more challenging substrate.
This reaction can be accompanied by migration of the carbon–
9
-18
carbon double bond leading to products mixture.
Reactions
of this type have been intensively investigated in some
variants with respect to the kind of used substrate such as
arylation of dihydrofuran (DHF). Most conventional methods
of palladium-catalyzed Heck reaction were limited to using
phosphine ligands and homogeneous route. These approaches
employing aryl triflate substrate and numerous phosphine
DHF has been reported to obtain selective products through
This
19-24
1
1
Jeffry method which used ionic media in the reaction.
backbone ligands such as amide-based phosphite-oxazolines,
atropisomeric P,O-ligands,
16
P-free catalytic processes in spite of various advantages such
as better commercial and ecological properties in compared to
phosphine/palladium catalysts, exhibited lower selectivity.
Therefore, more convenient selective approaches using a
palladium catalyst are required.
benzylically substituted P,N-
in
1
7
18
ligands,
presenting of palladium salts.
and
diphosphine-oxazoline ferrocenyl
In the typical procedure of Heck arylation of DHF, aryl triflate
was used. However, the main drawback of this substrate is the
easy hydrolysis of triflate, limiting its application in the
presence of water. Thus, aryl halides are cheaper and more
easily available substrates. There are a few reports about
application of aryl halides in the Heck coupling. Zhou and co-
Development of effective and practical catalytic methods,
under more economic and greener conditions, has been a
25-30
topic of great interest during recent years.
Learning from
the nature, employing biomolecules is highly favourable in
chemical transformations. In the past ten years, DNA has also
emerged as a powerful tool for the synthesis of various
3
1-38
biomaterials and biocatalysts.
This molecule has several
a.
Pharmaceutical Research Laboratory, Department of Chemistry, Isfahan
University of Technology, Isfahan, 84156 Iran. E-mail: haji@cc.iut.ac.ir
Department of Neuroscience University of Wisconsin, Medical School Madison,
WI 53706-1532, USA
Department of Chemistry, Isfahan University of Technology, Isfahan, 84156,
Iran. E-mail: h-farrokh@cc.iut.ac.ir
properties that make it a very promising scaffold for designing
a hybrid catalyst, which is chemically stable and commercially
available natural DNA is inexpensive. Furthermore its solubility
and biodegradability make it an attractive material in catalyst
field, giving it green credentials. Transition metal cations, such
b.
c.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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3
9
40
as Ag, Au, Co,
41-42
43 44
Cu, Pt and Pd
45-46
can be chelated via
dative bonding in such defined sites along the DNA lattice and
these metal nanoparticles can be stabilized in the catalytic
system.
In the majority of the DNA-based catalytic transformations
investigated to date, it have been used effectively in some
transformations such as the Diels-Alder, (oxa)-Michael addition
4
7
and Friedel-Crafts alkylation reactions. A notable exception,
however, is the DNA-based catalytic Suzuki reaction using
graphene/Pd hybrid catalyst without using ligand in water and
under aerobic conditions which reported by Qu and co-
4
8
workers. They indicated that a highly charged polyelectrolyte
and the negatively charged phosphate groups on the DNA
backbone can provide DNA-modified materials with high
dispersibility in aqueous solutions. Thus, these properties of
natural DNA make it an ideal mediator to build carbon-based
palladium catalysts. Meanwhile, application of nano-supports
in this case because of high activity and environmental accept-
ability, is preferred.
Scheme 1. Synthesis of the catalyst Pd/DNA@MWCNTs
-1
A sharp band appeared at 2221 cm which can be due to
phosphate group of DNA. Very similar FT-IR spectra to
previously reports have been observed.
6
1
The structural properties of the synthesized catalyst was
analysed by XRD and compared with the pure MWCNTs. The
XRD pattern in Fig. S2 shows characteristic peaks of
amorphous MWCNTs and the appearance of new peaks in
pattern of catalyst attributed to metal Pd species. The nitrogen
content of Pd/DNA@MWCNTs, determined by elemental
In recent years, carbon nanotubes (CNTs) have aroused
significant interests of scientists all over the world since; it
exhibits unique features such as large surface, intrinsic low
mass and easy surface modifications which might be promising
4
9-52
-1
candidates as catalysts or supports.
analysis, was found to be 0.99 mmolg of catalyst. The
reduction of oxidized-MWCNTs and the formation
Pd/DNA@MWCNTs hybrids can be monitored by UV−vis
spectroscopy (Fig. S3). The UV−vis spectrum of oxidized-
MWCNTs contains a strong absorption band at 202 nm, which
is corresponded to C-C π → π* and C-O n → π* transitions.
After reaction, the absorption peaks of Pd/DNA@MWCNTs
composites red shift from 202 to 213 nm, suggesting that the
electronic conjugation within carbon nanotube is restored
after the reaction. The disappearance of the absorption of
Modification of its activity, including immobilization of DNA
and palladium nanoparticles, make a unique and recoverable
catalyst. Based on the fascinating structure of CNTs material,
as well as the large capability of loading organic molecules, we
reason that the CNTs can be used as an efficient support for
DNA allowing for desirable catalytic properties. Single-
stranded salmon testes of DNA (ss-DNA) can be loaded on the
MWCNTs surface via non-covalent and simple route by mixing
them in an aqueous solution, giving the excellent
DNA/MWCNTs catalyst for organic synthesis. In this hybrid, the
aromatic nucleobases in DNA can interact through π−π
2
+
2 4
H PdCl at 378 nm indicated Pd has been reduced to Pd(0)
nanoparticles. The morphology of the surfaces of
Pd/DNA@MWCNTs were studied by field emission scanning
electron microscopy (FE-SEM) and compared it to pure
MWCNTs images (Fig. 1).
5
3-54
stacking with carbon basal surface
and stabilize palladium
nanoparticles. Synthesis and study on the structure of DNA-
modified materials such as MWCNTs, SWCNTs and graphene
have been reported in the literature, and their applications in
drug delivery, biosensors and high-performance modern
5
5
materials have also been investigated. However, it´s catalytic
applications are rare and to the best of our knowledge, olefin
arylation employing immobilized palladium on DNA-modified
MWCNTs, have not been reported previously.
In continuation of our recent investigations on the application
of heterogeneous catalytic systems in cross-coupling
5
6-60
reactions;
In this report, palladium is supported on the ss-
DNA-functionalized MWCNTs materials to give a new and
highly stable palladium catalyst (Pd/DNA@MWCNTs).
Results and Discussion
The catalyst preparation procedure was shown in Scheme 1.
This process were monitored by various analysis.
As shown in FT-IR spectrum depicted in Fig S1 (supplementary
-
material). The characteristic peaks of C–N stretching (1264 cm
-1
, C–H stretching (3014, 2985, 2900 cm ) N-H stretching
1
)
3100-3500 cm ), C=C (1507 cm ) and C=N (1620 cm ) to
-1
-1
-1
(
aromatic nucleobases which assignable to DNA. The peak at
-1
1643 cm is observed due to carbonyl group stretching
vibration.
Figure 1. FE-SEM images of (a) MWCNTs and (b) Pd/DNA@MWCNTs
2
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As can be seen the nanotubes are aggregated and has retained bromides was coupled with olefins to generate the desired
their nanotube nature upon functionalization with DNA and coupling products in 83–96% yields (Table 2). The results
palladium. Further characterization of Pd/DNA@MWCNTs was showed that aryl halides with either electron withdrawing or
performed by transmission electron microscopy (TEM). The electron-donating substituents reacted with olefins rapidly and
TEM images of Pd/DNA@MWCNTs showed well-defined generated the coupled products in excellent yields at mild
spherical Pd particles dispersed as small dots on reaction conditions.
immobilization of DNA which surround around MWCNTs (Fig. Encouraged by the obtained results in the Mizoroki–Heck
2). The size distribution of Pd nanoparticles was about 5-8 nm, cross-coupling,
the
efficiency
of
the
catalyst
indicating that palladium nanoparticles did not aggregate upon (Pd/DNA@MWCNTs) was investigated in the Heck reaction of
immobilization on MWCNTs. All these observations display an electron-reach olefin (DHF) with aryl iodides. Initially, the
that the natural DNA polymer is a good host and ligand for Heck cross-coupling of 4-methoxyiodobenzene with 2,3-
palladium nanoparticles. The palladium content of the dihydrofuran was chosen as a model. The results are
catalyst, measured by ICP, showed a value of 1.27% (0.12 summarized in Table 3.
-
1
mmolg of MWCNTs).
After structure characterization of the catalyst, its catalytic different
The model reaction was first performed in the presence of
solvents such as acetonitrile (MeCN),
activity was investigated in Mizoroki–Heck reaction (Table 1). dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and
In order to obtain the optimum experimental conditions, the tetrahydrofuran (THF), among them THF was found to be the
reaction of 4-bromoacetophenone with styrene was most effective solvent in conversion and selectivity. The
considered as a model reaction.
obvious improvement in the conversion (81 %) and selectivity
The effects of the reaction conditions such as the type of base, was achieved for the reaction at 50 °C, (Table 3, entry 6).
solvent and temperatures were tested. According to the Higher reaction temperature (80 and 110 °C) even though gave
experimental results and the essential goal of green chemistry better yield but resulted lower regioselectivty. Therefore, all
to reduce consumption of energy, the best conditions were reactions were carried out at 50 °C. The effects of the amount
chosen using 4-bromoacetophenone (1 mmol), styrene (1.5 of catalyst in the model reaction were also explored; the best
mmol), KOH (3 mmol) and 5 mg of catalyst in DMF/H
2
O (1:2) at result was obtained using 10 mg of catalyst.
50 ºC (Table 1, entry 11). Using the optimized reaction
conditions, a variety of structurally divergent aryl iodides and
Figure 2. TEM images of Pd/DNA@MWCNTs
a
Table 1. Optimization of the Heck reaction of 4-bromoacetophenone with styrene
Entry
Solvent
Base (equiv.)
T (ºC)
Yield (%)
1
2
3
4
5
6
7
8
9
DMSO
NMP
DMF
MeCN
H2O:EtOH
DMF/H
DMF/H
DMF/H
DMF/H
DMF/H
DMF/H
DMF/H
KOH (3)
KOH (3)
KOH (3)
KOH (3)
KOH (3)
KOH (3)
80
80
80
80
80
80
80
80
80
80
50
r.t
75
87
63
48
50
92
84
79
72
69
2
2
2
2
2
2
2
O (1:2)
O (1:2)
O (1:2)
O (1:2)
O (1:2)
O (1:2)
O (1:2)
K
2
CO
NaOH (3)
Li CO (3)
3
(3)
2
3
1
1
1
0
1
2
KOH (1.5)
KOH (3)
KOH (3)
c
91
40
d
a
Reaction conditions: 1 mmol 4-bromoacetophenon, 1.5 mmol styrene, 2 mL of solvent, for 3 h.
b
GC and isolated yield.
h, 24 h.
c
5
d
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a
Table 2. Heck reaction of aryl halides with olefins
Pd/DNA@MWCNTs
R
R
R'
R'
X
KOH, DMF/H O (1:2), 50 C
°
2
b
Entry
X
RC
H
4-NO
2
4-OMe
H
4-NO
4-Cl
2-Cl
3-Cl
4-OMe
3-Me
4-CN
4-Br
2-Me
1-naphthalene
6
H
4
X
Olefin
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
I
I
I
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Styrene
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
5
5
5
95
93
96
95
89
92
90
93
94
91
96
92
84
87
90
96
87
91
74
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
I
Br
Br
Br
Br
Br
2
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
9
4-COH
H
H
4-COMe
4-COMe
Styrene
Styrene
4-Me-Styrene
1
a
The reaction was carried out with aryhalide (1.0 mmol), olefin (1.5 mmol) and KOH (3 mmol) in DMF/H
2
O (1:2) in the presence of 5 mg of catalyst at 50 ºC.
b
Isolated yield.
and 10 mg of catalyst at 50 °C was selected as the best
Table 3. Optimization conditions of the Heck reaction of 4- conditions. We then examined the generality and versatility of
a
methoxyiodobenzene with 2,3-dihydrofuran
this supported palladium-catalyzed, regioselectivty arylation
OMe
reaction of 2,3-dihydrofuran cross-coupling of aryl iodides. The
results are illustrated in Table 4. Some varieties of aryl iodides
bearing either electron-rich or electron-deficient substitutes
reacted efficiently with 2,3-dihydrofuran and gave the
corresponding products in moderate to good yields and
selectivity. In comparison to the known activity of palladium-
base catalyst designed to obtain selective products (all of them
are homogenous), this catalyst has presented comparable
activity and selectivity. The Heck reactions of 2,3-dihydrofuran
with a number of para-substituted phenyl bromide including 4-
Br, 4-Cl, 4-CN, and 4-COMe were also investigated.
Unfortunately, all of these reactions failed to form the Heck
products.
O
I
3
Pd/DNA@MWCNTs
O
Li CO , solvent, T
°
C
MeO
2
3
OMe
1
2
O
4
b
Entry
Solvent
Tem.
ºC)
Cat. (mg)
Conv.%
(2+3)
86
Ratio
c
3/4
(
1
2
3
4
5
6
7
8
MeCN
DMF
DMSO
MeCN
MeCN
THF
80
80
80
50
110
50
50
50
50
10
10
10
10
10
10
5
47:53
68:32.
49:51
58:42
55:45
87:13
62:38
56:44
-
93
87
78
d
97
92
54
84
d
d
Table 4. Heck reactions of aryl halides with 2,3-dihydrofuran.
THF
THF
THF
d
20
Cat (10 mg)
Ar-I
9
10(Pd/MWCNTs) 14
a
O
THF, 50
°
C, Li
2
CO
3
O
O
Unless otherwise noted, 4-methoxyiodobenzene (0.5 mmol), 2,3-
R
R
dihydrofuran (1 mmol), solvent (3 mL) and Li
Conversion percentages was determined by GC.
The selectivity was measured by GC.
2
CO
3
(2 mmol), 24 h.
1
2
3
4
b
c
18
I
I
I
d
4
I
8 h.
Ar-I:
Cl
MeO
O N
2
The Pd/DNA@MWCNTs hybrid materials could catalyze
arylation reaction of 2,3-dihydrofuran with yields more than
a
b
c
d
Entry
Substrate
Yielda (%)
Ratio 3/4b
77:23
87:13
97:3
79:21
67%, while the palladium supported on MWCNTs
1
2
3
2a
2b
2c
2d
94
92
97
89
(Pd/MWCNTs) displayed a yield of just 14% (Table 3, entry 9).
The high activity of our catalyst can be ascribed to the good
synergistic effects of palladium nanoparticles with DNA which
grafted on MWCNTs. With the optimum trade-off between
activities and selectivity, the conditions of using THF as solvent
4
a
Isolated yield of major isomer.
Determined by GC.
b
18
4
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It was originally proposed that the mechanism of the selective The structure of the catalyst was demonstrated after the last
Heck reaction proceed via a kinetic resolution. As shown in recovery using ICP and CHN analyses (N = 8.51%) and the results
showed that only a very small amount of palladium metal was
removed from the catalyst (ICP
Scheme 2, it seems that the negatively charged phosphate
groups on the DNA backbone as a ligand bind to the olefin
product tightly.
The strong bonding permits for the hydridopalladium species
to undergo reversible insertion/elimination to give the desired
products; while, the previous reports have been emphasized
-
= 0.11 mmolg ); the
1
morphologies of the recovered catalysts were also examined by
TEM (Fig S4), the typical images indicate that Pd nanoparticles
are well dispersed on MWCNTs surfaces after nine cycles and
high conversion is kept at about 84%. Additionally, to explore
the leaching of these catalysts, two similar control experiments
that phosphine ligands with steric hindrance are essential in were performed in each case. To this end, the reaction between
the performance of this regioselective intermolecular Heck 4-bromoacetophenone and styrene was carried out
reaction.
simultaneously in two different vessels under the exactly the
same conditions. In each case, the reaction progress was
monitored using gas chromatography. After 2.5 hours, the
catalyst was separated from one of these vessels using
centrifuge (in 8000 rpm for 6 min), while the other remained
unchanged. Thereafter, both reactions continued under the
same conditions. After another 2.5 hours, both reactions was
stopped and their completion was again examined using GC. The
results showed that the reaction in the absence of the catalyst
did not proceeded any more, while completion of the reaction in
the other vessel was improved. This observation confirmed that
no leaching occurred in the reaction medium during the process.
In addition, the leaching of palladium from the
Pd/DNA@MWCNTs catalyst was measured by ICP-OES, and it
was found that no leaching of palladium occurred during the
reaction. This clearly revealed that the catalyst is stable under
the reaction conditions and can be recovered and reused. All
these results demonstrate that the Pd/DNA@MWCNTs catalyst
exhibits significantly higher catalytic activity and selectivity in
regioselective intermolecular Heck reaction, showing more
environmental and economic advantages over the wide range of
homogenously pervious reported catalysts.
Scheme 2. Possible mechanism for arylation of 2,3-dihydrofuran in the
presence of palladium catalyst
It is noteworthy that the application heterogonous palladium
catalyst in such reactions has not been previously reported.
Furthermore, this method offers several advantages such as high Conclusions
product yields, mild reaction conditions, excellent
regioselectivity, clean reaction profiles and operational
simplicity. Therefore, this synthetic methodology can be
considered as a useful practical achievement in the preparation
of these important heterocyclic compounds.
In summary, this work provides a novel environmental friendly
and economical route for dramatically efficient and
regioselective arylation of dihydrofuran using a DNA-modified
MWCNTs-based Pd hybrid catalyst. In addition, our catalytic
systems show high activity for Heck reaction under mild and
aerobic conditions. To the best of our knowledge, this is the first
report on using heterogonous catalyst for regioselective Heck
reaction of aryl iodides and dihydrofuran.
The separation and reusability of noble metal catalysts are the
trends of the catalysis industry and green chemistry, not only for
lowering costs, but also for avoiding pollution. To gain insight
into this issue, the catalyst reusability experiments in the
Mizoroki–Heck reaction of 4-bromoacetophenone with styrene
were carried out. At the end of each reaction, the catalyst was
separated by centrifugation (in 8000 rpm for 6 min), washed
with acetone and water for several times and dried in vacuum
overnight at 60°C. After that, the catalyst was reused in model
reaction. As reported in Table 5, the catalyst was reused several
times (nine consecutive runs were checked) without significant
loss of activity. Wonderful recyclability of palladium
heterogonous catalyst based on MWCNTs were reported
Experimental Section
1
.1. General
All the reagents and solvents were purchased from Merck
chemical company. Salmon testes DNA was purchased from
Sigma-Aldrich Chem Co. (USA). The state of palladium was
determined by X-ray diffractometer (XRD, Xpert MPD), X-ray
diffractometer using CuKα radiation. The size and morphology of
catalyst were observed using transmission electron microscopy
6
2
before.
Table 5. Reusability of the catalyst
a
a
Run
1
Yield
Run
6
Yield
89
90
89
84
-
(
TEM) EM208S micro-scope with an accelerating voltage of 100
91
KV. The palladium quantity on the carriers was measured by
inductively coupled plasma-atomic emission spectrometry (ICP-
AES, Varian vistampx). Reaction yields were analysed by gas
chromatography (GC, Agilent Technologies). The selectivity was
also investigated using GC. The FT-IR spectra were recorded on a
2
90
7
3
90
8
4
90
9
5
90
-
Jasco-680 (Japan) spectrophotometer in KBr pellets and
reported in cm . UV−vis spectroscopy was carried out with a
JASCO V-550 UV/vis spectrometer. Scanning electron
a
−1
Isolated yield
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micrographs of the support and catalyst were taken on a SEM
EM 3200 instrument. The NMR of the products was recorded on
2
K. C. Nicolaou, P. G. Bulger and D. Sarlah, Angew. Chem., Int.
Ed. 2005, 44, 4442-4489.
a 500 MHz Bruker-avance in CDCl
3
.
3
4
5
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Multi walled carbon nanotubes oxide was synthesized using
2
964;
6
7
M. R. Nabid and Y. Bide. Appl. Catal. A. 2014, 469, 183-190;
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2 4 2 2
SO and H O (0.3 g of the as-received MWCNTs
2
013,
F. Yang, S. Y. Fu, W. Chu, C. Li and D. G. Tong. RSC Adv., 2014,
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3, 21251-21255;
8
9
4
ml round bottom flask equipped with a condenser and
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washed up to neutral pH and the sample was dried in vacuum at
9
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1
1
1
4
prepared using Qu’s strategy follows the steps described in
0°C overnight). The DNA-functionalized MWCNTs have been
2
7
4
8
Scheme 1. The DNA was heated at 95 °C for 1 h to obtain ss-
DNA. The CO H-MWCNTs dispersion was mixed with single-
stranded DNA (10 mL, 2 mg mL ), and NaBH
2
2
−
1
,
4
was added (8 μL,
/ MWCNTs-O); the mixture refluxed at 100 °C for
h. Then, the solution was centrifuged in 8000 rpm for 6 min
1
7
1
5 wt %; NaBH
4
1
1
5 M. G. Lauer, M. K. Thompson and K. H. Shaughnessy. J. Org.
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1
1
1
1
2
2
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4
1.3. General procedure for the Heck reaction of aryl halides
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mmol), olefin (1.5 mmol) and DMF: H O (1:2, 3 mL), followed by
2
adding 5 mg of catalyst. The mixture was then stirred at 50 °C in
an oil bath, and the extent of the reaction was monitored by TLC
2
9
5
(thin-layer chromatography, n-hexane / ethyl acetate, 5:1) and
0 A. A. Sabino, A. H. L. Machado, C. R. D. Correia and M. N.
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mixture was diluted with dichloromethane and water. The
organic layer was washed with brine, dried over anhydrous
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,
2
4
MgSO , and concentrated under reduced pressure. Finally, the
product was isolated by chromatography on a column of silica
gel (n-hexane / ethyl acetate, 5:1) to obtain the corresponding
products in 74–96% yields. The products were characterized by
comparing their physical properties m.p., IR, H, C NMR spectra
with those found in the literatures (Supplemental Data).
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13
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2
2
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3
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,
,
,
8
2
2
.4. General procedure for the Heck reaction of aryl iodide with
,3-dihydrofuran
5
The Pd/DNA@MWCNTs (10 mg) was dispersed in THF (2 mL) by
sonication and then aryl iodide (1 mmol), 2,3-dihydrofuran (1.5
5
7 M. Brovetto, D. Gamenara, P. Saenz, G. Mendez and A.
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8 h. After completion, the reaction mixture was diluted with
hexane (5 mL) and the catalyst was separated by centrifuging
8000 rpm for 6 min). The isomeric ratio of the product was
2 3
CO (1.5 mmol) was added and stirred at 50 ºC for
4
8 K. Fesko and M. G. Khadjawi. Chem Cat Chem. 2013,
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5, 1248–
1
(
determined by GC before purification. In final, the residue was
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2
0 P. Tufvesso, J. L. Ramos, M. Nordblad and J. M. Woodley.
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6
:1) to afford the products. All the products are known and their
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spectral data, compared with literature data (Supplemental
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,
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