Palladium Stabilized by Amino-Vinyl Silica Functionalized Magnetic Carbon Nanotube: Application in Suzuki–Miyaura and Heck–Mizoroki Coupling Reactions

Article abstract of DOI:10.1007/s10562-017-2150-1

Abstract: This study describes an investigation on Suzuki and Heck cross-couplings of aryl electrophiles in the presence of heterogeneous Pd nanoparticles supported on amino-vinyl silica functionalized magnetic carbon nanotube. The core–shell contains CNT@Fe₃O₄@SiO₂-Pd in which the functionalized SiO₂ helps the stabilization of Pd nanoparticles and also responsible for the reduction of Pd(II) to Pd(0) without the need for adding external reducing agents. All of the reactions were done under phosphine-free condition. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-017-2150-1

Catal Lett
DOI 10.1007/s10562-017-2150-1
Palladium Stabilized by Amino-Vinyl Silica Functionalized
Magnetic Carbon Nanotube: Application in Suzuki–Miyaura
and Heck–Mizoroki Coupling Reactions
1
2
1
Dariush Khalili · Ali Reza Banazadeh · Elham Etemadi-Davan
Received: 17 March 2017 / Accepted: 26 July 2017
©
Springer Science+Business Media, LLC 2017
Abstract This study describes an investigation on Suzuki
and Heck cross-couplings of aryl electrophiles in the pres-
ence of heterogeneous Pd nanoparticles supported on
amino-vinyl silica functionalized magnetic carbon nano-
tube. The core–shell contains CNT@Fe O @SiO -Pd in
which the functionalized SiO helps the stabilization of
2
Pd nanoparticles and also responsible for the reduction of
Pd(II) to Pd(0) without the need for adding external reduc-
ing agents. All of the reactions were done under phosphine-
free condition.
3
4
2
Graphical Abstract
B(OH)
2
, [Pd]
'
R, [Pd]
K CO , TBAB
X
CsCO , EtOH, reflux
R
2
3
R
3
R
R'
DMF, 130 °C
X = -I, -Br, -Cl
R' = -Ph, -CO
X = -I, -Br, -Cl, -OTf, -OTs
2
Bu, -hexyl
H
N
OH
HO
Si
H N
2
N
H
Si
O
NH
2
O
O
O
[Pd]=
Si
O
O
Si
O
O
O
O
NH2
H
H
N
Si
HO
N
Si
OH
NH2
=
=
Fe O
3
4
Palladium
Keywords Heterogeneous catalysis · Suzuki reaction ·
C–C coupling · Phosphine-free condition · Carbon
nanotube · Heck reaction
*
Dariush Khalili
khalili@shirazu.ac.ir
1
Introduction
1
2
Department of Chemistry, College of Sciences, Shiraz
University, Shiraz 71454, Iran
Transition-metal nanoparticles mediated C–C bond for-
mation have become one of the most straightforward and
Department of Chemistry and Biochemistry, Texas
Tech. University, Lubbock, TX 79409, USA
Vol.:(0
1
123456789)
3

D. Khalili et al.
important protocols in modern synthetic organic chem-
istry [1]. Among different metal nanocatalysts, palladium
nanoparticles (Pd NPs) have gained much reputation with
numerous review articles published in both heterogeneous
and homogeneous catalysis [2–5]. Palladium nanocata-
lysts have been employed for a large number of different
reactions, namely Suzuki–Miyaura [6], Stille [7, 8], Heck
of CNTs and the separation convenience of MNPs has been
more favorable. Recently, Safavi and Banazadeh research
groups independently demonstrated an efficient route for
the synthesis of deposited Pd NPs on organically modified
silica [39–41]. However, the low surface area was the main
disadvantage of the presented catalysts by these research
groups. Driven by these results, herein, we introduced a
facile strategy for assembling of Pd NPs on amino-vinyl
silica functionalized magnetic carbon nanotube to produce
(CNT-Fe O @(A-V)-silica-Pd) as a heterogeneous catalyst.
[
9], Sonogashira [10] and Negishi [11]. The reactions
between aryl halides and arylboronic acids (the so-called
Suzuki–Miyaura reaction) or activated alkenes (Heck reac-
tion) are the most extensively studied coupling reactions
and provides a powerful tool to access a wide range of
biaryl and stilbene compounds which are frequently present
in medicines and other functional materials [12, 13]. Dur-
ing the past decade, remarkable progress has been achieved
in the area of homogeneous and heterogeneous catalysts for
promoting the transformation [14–31]. Whereas homogene-
ous catalysis has made a great impact on the development
of Suzuki and Heck reactions, their separation and recovery
from the reaction mixture and their troublesome work-up
are still challenging. Considering the inherent drawbacks
of homogeneous catalysts and to overcome these issues,
significant efforts have been performed to introduce new
strategies to immobilize the homogeneous Pd catalysts
onto various solid supports [32–36]. In this regard, carbon
nanotubes (CNTs) has received a great deal of attention as
a promising Pd support in the field of catalysis, due to their
large specific surface area, porous structure and extraordi-
nary chemical and mechanical stability [37, 38]. However,
the separation process of this nanocatalyst from the reaction
mixture is tedious. It is generally known that magnetic nan-
oparticles (MNPs) such as Fe O could be isolated easily
3
4
Introduction of sol–gel monomers containing amine func-
tional groups which have high affinity to coordinate with Pd
ions is of special interest for the stabilization of the metal
NPs in silica matrix [42–44]. However, these monomers
require an external chemical reducing agents or reduction
condition to reduce metal ions. According to the literature
[45, 46] the vinyl groups in the silica matrix appeared to be
the best choice because the vinyl group plays dual role both
to facilitate the reduction process between amine and Pd
ions and stabilizes Pd in zero oxidation state. Then, the new
magnetically recoverable catalyst is successfully applied in
Suzuki–Miyaura and Heck-coupling reactions under phos-
phine-free reaction conditions. In comparison to previous
works,[39, 40] the present nanocatalyst has more surface
2
area (463.1 vs. 181.7 m /g) with higher loading amount of
Pd NPs, which improves the efficiency of the investigated
reactions.
2 Results and Discussion
3
4
by an external magnetic field, therefore, synthesis of hybrid
Our initial investigations were focused on the preparation
of the magnetic nanocatalyst (Scheme 1). The details of
materials (CNTs/Fe O ) combining the unique properties
3
4
Scheme 1 Illustration on the
preparation of CNT@Fe O @
3
4
(
A-V)-silica-Pd MNPs. TEOS
1) HNO , Microwave, 30 min
1) TEOS,H
O-EtOH
2
2) VTEOS, AEAPS, Tolene (dry)
3
tetraethyl orthosilicate, AEAPS
) Fe2+/Fe3+, NH OH
2
4
[
3-(2-aminoethylamino)propyl]
trimethoxysilane, VTEOS vinyl-
triethoxysilane
HO
Si
H
N
HO
Si
N
H
O
NH2
O
NH
2
O
O
PdCl , 80 °C
O
Si
2
O
Si
O
O
O
O
H
H
Si
HO
N
Si
HO
N
NH2
NH2
=
=
Fe O
3
4
Palladium
1
3

Palladium Stabilized by Amino-Vinyl Silica Functionalized Magnetic Carbon Nanotube:…
these procedures and characterization of the catalyst are
explained in Sect. 3.
2
.1 Characterization of Catalyst MCNTs@
A-V)-silica-Pd Nanocomposites
(
The morphology and structure of the prepared MCNTs@
(
A-V)-silica-Pd nanocomposites were characterized by
various techniques including Fourier transform infrared
spectroscopy (FT-IR), X-ray diffraction (XRD), transition
electron microscopy (TEM), thermogravimetric analysis
(
TGA) and vibrating sample magnetometer (VSM) analy-
sis to establish its authenticity.
Figure 1 shows the FT-IR spectra of MCNTs,
Fig. 2 XRD spectrum of MCNTs@(A-V)-silica-Pd nanocomposites
MCNTs@-SiO and MCNTs@(A-V)-silica nanocom-
2
posites, respectively. As depicted in Fig. 1, the bands at
−
1
5
86 and 1725 cm corresponds to the stretching vibra-
tions of Fe–O and C=O bonds of MCNTs. The pres-
ence of characteristic peaks of the Si–OH and Si–O–Si
indices (220), (311), (400), (422), (511), (440) and (533)
of the Fe O MNPs (JCPDS Card No. 89-3854) [48].
3
4
−
1
bond stretching vibration (957 and 1106 cm ) indicates
the formation of silica shells on the surface of MCNTs.
The average crystallinity size of the Fe O MNPs is
3 4
about 3.8 nm which was determined by Debye-Scherrer’s
formula. The peak for the (002) plane of CNTs located at
2θ=26.9° (JCPDS Card No. 75-1621) [49] and the other
three characteristic peaks at 2θ=40.2°, 47.4° and 68.7°
(JCPDS No. 7440-05-3) [50], are related to the formation
of the fcc structure of Pd NPs indicating the presence of
Pd(0) in the prepared nanocatalyst [51]. Also, the broad
peak at 2θ of 15°–23° (JCPDS 27-1402) is in agreement
with the amorphous structure of silica layer [51]. The effi-
−
1
A broad band at 3417 cm is a factor of hydrogen-
bonding of hydroxyl and silanol groups, furthermore the
−
1
C–H stretching of CH vibrations appears at 2932 cm .
2
Besides, the related to the N–H bending vibrations and
C=C stretching demonstrates absorption bands at 1565
−
1
and 1644 cm respectively. Therefore, the formation of
MCNTs@(A-V)-silica nanocomposite is confirmed by
the FT-IR spectra [47].
2
+
A typical XRD pattern of the synthesized supported
Pd nanocatalysts is shown in Fig. 2. The characteris-
tic diffraction peaks at 2θ of 30.7°, 35.8°, 43.7°, 53.6°,
cient reduction of Pd ions to Pd with crystalline struc-
ture was confirmed by XRD. In order to identify the mag-
netic properties of MCNTs, MCNTs@(A-V)-silica, and
MCNTs@(A-V)-silica-Pd nanocomposites, VSM was taken
5
7.5°, 63.8° and 74.8° were related to their corresponding
(Fig. 3).
Fig. 1 FT-IR spectra of MCNT (blue line), MCNTs@SiO (gray
Fig. 3 Magnetization curves of MCNTs (green line), MCNTs@
(A-V)-silica (violet line) and MCNTs@(A-V)-silica-Pd (blue line)
2
line) and MCNTs@(A-V)-silica nanocomposites (red line)
1
3

D. Khalili et al.
Fig. 4 TEM images of CNT
and MCNTs@(A-V)-silica-Pd
and MCNTs@(A-V)-silica
(
inset) nanocomposites
Fig. 5 TGA curves of MCNTs (red line), MCNTs@SiO (blue line)
2
Fig. 6 Nitrogen adsorption–desorption isotherm of MCNTs@(A-V)-
and MCNTs@(A-V)-silica (green line) nanocomposites
silica-Pd
As can be seen, in the presence of the silica shell, the
magnetic strength was reduced. It should be noted that the
prepared nanocomposites still shows strong magnetization
and can be separated easily from the solution by applying
an external permanent magnet.
MCNTs, the thermal stability is improved in the presence
of silica layer.
The main weight loss for the decomposition of
MCNTs@SiO ends at 625 °C, while relatively slow
2
weight loss at elevated temperatures can be related to the
decomposition of the silica shell. Furthermore, the approxi-
mately 6.7% weight loss from 380 to 460 °C in MCNTs@
(A-V)-silica may readily be attributed to the decomposition
of organic groups on the surface of silica layer [52].
The morphological structure of MCNTs@(A-V)-silica-
Pd nanocomposite was investigated by TEM (Fig. 4). It
shows that the spherical iron oxide particles were formed
on the surface of CNTs, with an average size of 4.1 nm. The
average diameter of pristine CNTs is around 10 nm. TEM
observation further reveals increasing in diameter to 66 nm
after coating with mesoporous silica, confirmed 28 nm
thick mesoporous silica layer on the MCNTs. Also, as can
be seen, the Pd NPs on the surface of modified MCNTs are
spherical in shape with an average size of 12.3 nm.
Accordingly, it can be concluded that Pd NPs were
formed on the surface of amino-vinyl silica functionalized
MCNTs. With regard to previous, the presence of vinyl
groups speeds up the reduction between Pd ions and amine
groups both thermodynamically and kinetically without the
need for any external reducing agent [39].
To investigate the thermal stability of the functional-
ized CNTs, TGA analysis was studied (Fig. 5). As it can be
seen, oxidized CNTs decompose slowly with the increasing
of temperature below 600 °C, due to the removal of car-
boxyl groups on the surface of CNTs. Moreover, as a result
of the decomposition of CNTs, significant weight reduction
can be seen in the region of 570–750 °C. For silica coated
Figure 6 displays the N adsorption–desorption iso-
2
therms for MCNTs@(A-V)-silica-Pd catalyst. From nitro-
gen adsorption–desorption analysis, the BET surface area
2
−1
of the catalyst was about 463.1 m g . Moreover the
elemental composition analysis of the catalyst shows that
the amount of Fe, Si and Pd are 18.95, 15.49 and 4.37%
respectively.
1
3

Palladium Stabilized by Amino-Vinyl Silica Functionalized Magnetic Carbon Nanotube:…
Table 1 Optimization of the parameters for Suzuki reaction of bro-
electrophiles in the presence of the nano-palladium cata-
mobenzene
lyst (Table 2). The yields in Table 2 are isolated yields.
The desired biphenyl derivatives were achieved in good
to high yields even from the heterocyclic iodide and bro-
mide. The scope of our catalyst was further explored by
the Heck cross-coupling reaction of bromobenzene with
styrene (Table 3). First, the reaction was performed in
DMF with K CO as a base at 110 °C which delivered only
[
Pd],
base
Br
+
2B
(HO)
solvent, 80 °C
1
a
2a
Entry Solvent Base (mmol) [Pd] (mol%) Time (h) Yield (%)a
1b
2
3
4
5
6
7
8
9
H O
K CO (1.0) 1.5
24
20
24
24
24
24
24
24
10
10
24
10
18
18
43
51
67
59
71
62
43
66
84
92
0
2
2
3
2
3
H O
K CO (1.0) 1.5
22% of 4a. Increasing the temperature to 130 °C, dramati-
cally increased the yield of 4a to 69% (entry 2). Screen-
ing solvents showed that DMF is the most suitable one
(entries 3–6). In order to explore the efficiency of other
bases in DMF, a range of organic and inorganic bases were
employed and K CO proved to be the more effective one
2
2
3
H O
K CO (1.5) 1.5
2
2 3
H O
KOAc (1.5) 1.5
Cs CO (1.5) 1.5
2
H O
2
2
3
H O
KOH (1.5)
1.5
2
Toluene Cs CO (1.5) 1.5
DMF
EG
EtOH
EtOH
EtOH
EtOH
EtOH
2
3
2
3
Cs CO (1.5) 1.5
(Table 3, entries 7–12). Interestingly, the use of TBAB pro-
vided a significance increase in yield of 4a (91%, entry 13).
In addition, the decrease in the amount of the catalyst led to
an inferior yield of 4a and longer reaction time (entry 14).
On the basis of our findings, we then examined the reac-
tion of aryl halides with alkenes in the presence of the Pd
nanocatalyst in DMF as a solvent (Table 4). As the results
in Table 4 showed, aryl halides react smoothly with alk-
ene derivatives. In case of styrene, substrates bearing both
electron-withdrawing and electron-donating substituents
afforded the desired products in high yields, while in case
of steric hindered substrate, reaction occurred slowly giv-
ing lower yields. In addition, the reaction of aryl halides
with butyl acrylate as another coupling partner were also
checked. In this regard, high yields of the products were
obtained which revealed the efficiency of our optimized
condition for acrylate compounds. Furthermore, 1-octene
was also tested and the desired cross-coupling products
were obtained in good yields. Hence, the efficiency of the
catalyst was verified in the Heck cross-coupling and the
desired products were obtained in good yields.
2
3
Cs CO (1.5) 1.5
2
3
1
1
1
1
1
0
Cs CO (1.5) 1.5
2 3
1
2
3
4
Cs CO (1.5) –
2 3
a
Cs CO (1.5) 1.5
80
71
64
2
3
Cs CO (1.5) 1.1
2
3
Cs CO (1.5) 0.75
2
3
Reaction conditions: In all entries, 1a (1.0 mmol), PhB(OH)
2
(
1.3 mmol), [Pd] (1.5 mol%), base (1.5 mmol), and solvent (3.0 mL)
was used unless otherwise noted
a
Isolated yield
The temperature was 60 °C
b
The preliminary experiments for the Suzuki reaction
of aryl halides starts with the reaction of bromobenzene
1.0 mmol) with PhB(OH) (1.3 mmol) in the presence
(
2
of K CO (1.0 mmol) and nano-pd catalyst (1.5 mol%,
2
3
0
.035 g) in H O at 60 °C which delivers the biphenyl (2a)
2
in 43% yield (Table 1, entry 1).
Then, the temperature was increased to 80 °C along
with the increase in the amount of the base which
improves the yield of 2a to 67% (entries 2–3).
As a result, we next decided to test variety of bases in
H O at 80 °C which shows that Cs CO gives the high-
Additionally, a hot filtration test was taken to find out if
any appreciable amounts of the palladium leaches out form
the solid catalyst to the solution during the reaction. There-
fore, the reaction of bromobenzene and phenylboronic acid
was monitored and the catalyst was removed from the reac-
tion mixture with an external magnet under hot condition
after 6 h which provided 2a in 55% yield. Then the filtrate
was further stirred under the optimum condition and no
conversion of bromobenzene to 2a was detected thereafter.
Therefore, it can be concluded that no appreciable leach-
ing of palladium takes place under hot condition from the
catalyst. Moreover, ICP analysis did not show any Pd metal
in the solution which also confirms the hot filtration test
results.
2
2
3
est yield among the screened bases while full conversion
was not achieved (entries 4–6). In order to enhance the
yield of 2a other solvents such as toluene, EtOH, DMF,
EG were investigated, among them EtOH was recognized
to be the ideal one (Table 1, entries 7–10). Besides, the
palladium catalyst is essential for the mentioned trans-
formation since no product was observed in the absence
of the catalyst (entry 11). Decreasing the temperature to
6
0 °C slightly dropped the yield of 2a (entry 12). We also
examined the reaction with lower amounts of the catalyst
and we found that 1.5 mol% of the catalyst leads to higher
yields and shorter reaction times (Table 1, entries 13–14).
Having the optimized conditions in hand, we explored
the scope of the Suzuki–Miyaura cross-coupling of aryl
To gain further insight about homo/heterogeneous
nature of the nanocatalyst, a control experiment was con-
ducted under the identical condition for Suzuki cross-cou-
pling of bromobenzene in the presence of Hg(0) as catalyst
1
3

D. Khalili et al.
Table 2 Suzuki reaction of aryl electrophiles using nano magnetic Pd catalyst
[
Pd] (1.5 mol%)
Cs CO (1.5 mmol)
2
3
X
+
2B
HO)
(
EtOH, reflux
R
1
R
mmol
a-e
1.3 mmol
1
2a-k
H CO
H C
3
3
2
a
2
b
2c
X: -I, 4.5 h, 95%
X: -Br, 10 h, 92%
X: -Cl, 18 h, 81%
X: -I, 8 h, 93%
X:
X:
X:
X:
8
-
-
-
-
I, h, 90%
X: -Br, 15 h, 89%
Br, 15 h, 91%
X:
X:
-
-
Cl,
22
h, 80%
Cl,
OTs,
h,
24 78%
X: -OTf, 4 h, 90%
9
OTf, h, 90%
h,
22 71%
X: -OTs, 13 h, 80%
O N
2
CH3
2
e
2
f
2
d
X: -I, 1.5 h, 92%
X: -Br, 5h, 90%
X: -Cl, 15 h, 84%
X: -I, 13 h, 80%
X: -Br, 17 h, 82%
X: -Cl, 24 h, 73%
X: -I, 15 h, 88%
X: -Br, 20 h, 85%
N
N
O N
2
N
CH3
2
h
2i
X: -I, 15 h, 83%
2
g
X: -I, 2 h, 90%
X: -Br, 12 h, 86%
NC
H N
2
2
k
2
j
X: -I, 1.5 h, 91%
X: -Br, 7 h, 87%
X: -I, 10 h, 82%
poisoning (molar ratio to [Pd] ~300). It was revealed that
the reaction was almost completely inhibited. It can be
concluded that Pd nanocatalyst cannot prompt the Suzuki
reaction since it was poisoned by the scavenger, therefore,
this result proves the heterogeneous nature of the catalyst.
Therefore, it can be concluded that under optimized Suzuki
reaction condition, the intact MCNTs@(A-V)-silica-Pd cat-
alyst promoted the reaction which confirms the palladium
remains in lower oxidation state Pd(0) during the reaction
course. Since the cost of transition metal supported cata-
lysts are often high, the recycling and recovery of them is
a great concern from the practical, economic and environ-
mental points of view. Therefore, the recyclability of the
catalyst was examined for the preparation of 2a starting
with bromobenzene and phenylboronic acid in the presence
of 1.5 mol% of catalyst in ethanol under reflux condition.
For the recycling experiment, the MCNTs@(A-V)-silica-
Pd catalyst was easily recovered from the reaction mixture
with an external magnet (Fig. 7) and then the separated
catalyst was recharged with fresh substrates for the next run
under the same reaction conditions.
Finally, recycling experiments showed that the catalytic
activity remained almost unchanged after being reused for
seven consecutive runs (Fig. 8; Table 5).
In order to investigate the structure of the catalyst the TEM
analysis of the catalyst after the third run was taken (Fig. 9).
TEM image of the recovered catalyst after the 3th reaction
run indicated that the magnetic Pd catalyst maintained its
structure after using in three consecutive Suzuki reaction.
To check the merit of the present work, the catalytic
performances of MCNTs@(A-V)-silica-Pd catalyst were
compared to other reported catalysts used in the synthesis
of biphenyl 2a from starting bromobenzene and PhB(OH)
2
(Table 6).
These comparative results establish the advantage of
MCNTs@(A-V)-silica-Pd catalyst over the some existing
methods (based on yield or reaction condition).
1
3

Palladium Stabilized by Amino-Vinyl Silica Functionalized Magnetic Carbon Nanotube:…
3
Experimental
with CuKα radiation) and transmission electron micros-
copy (TEM-CM10, Philips). The magnetic properties of
supported Pd nanocatalysts were investigated by using
a VSM with an applied field between −110,000 and
110,000 Oe at room temperature (MDKF, Iran). ICPOES
spectrometer (Thermo Scientific, IRIS Intrepid II, USA)
were used for determination the loading amounts of Pd
on the surface of prepared nanocomposites. The specific
surface area of the nanocomposites was obtained by using
gas adsorption analyzer (BELSORP, BELCo., Japan) and
Brunauer–Emmett Teller (BET) method.
3
.1 General Information
All chemicals used in this study were analytical grade,
purchased from commercial suppliers and used without
further purification. All of the products were purified by
column chromatography from appropriate solvents and
1
13
were identified by H NMR, C NMR and elemental
analyses. Progress of the reactions was monitored by TLC
using silica gel polygrams SIL G/UV 254 plates and were
visualized with UV light. FT-IR spectra were recorded
on Shimadzu DR-8001 Spectrometer. NMR spectra were
recorded on a Bruker Avance DPX 250 MHz Instrument
3.2 Synthesis of Magnetic Carbon Nanotubes
in CDCl solvent using TMS as internal standard. Chemi-
In a Teflon bottles, concentrated nitric acid (5 mL) was
added to pristine CNTs (200 mg) and closed which then
placed in a microwave apparatus (Milestone, Japan) oper-
ated at 900 W power and 160 °C operating temperature for
30 min for dispersion by microwave irradiation. Functional-
ization of CNTs with carboxylic groups was occurred. Cen-
trifusion of the dispersion followed by washing with water
until it turned neutral and dried at 50 °C overnight. Sub-
sequently, 150 mL water containing 50 mg of FeCl ·4H O
3
cal shifts were reported in parts per million (ppm, δ), and
coupling constants (J), in hertz (Hz). Elemental analyses
were determined in our department using ThermoFinni-
gan Flash EA 1112 Series.
The structure and morphology of MCNTs and
MCNTs@(A-V)-silica-Pd nanocomposites were char-
acterized by X-ray diffracttion (XRDD8, BRUKER,
employing a scanning rate of 0.05 °/s from 10° to 90°
2
2
Table 3 Optimization of the reaction parameters for the Heck reaction of bromobenzene with styrene
[
Pd], base
solvent, T °C
Br
+
4a2
Entry
Solvent
Base
Temp.
Time (h)
4a (%)a
2
1
2
3
4
5
6
7
8
9
DMF
DMF
–
K CO
110
130
130
130
130
130
130
130
130
130
130
130
130
130
24
24
24
24
24
24
24
24
24
24
24
24
8
22
69
11
9
Trace
37
56
63
54
32
44
55
91
76
2
3
3
3
3
3
3
K CO
2
K CO
2
o-Xylene
PEG 200
Diglyme
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
K CO
2
K CO
2
K CO
2
KOAc
Et N
3
n
Pr N
3
10
11
12
13
14
DABCO
NaOH
K PO ·3H O
3
4
2
b
K CO
2
3
3
b, c
K CO
24
2
Reaction conditions: bromobenzene (1.0 mmol), styrene (1.4 mmol), base (1.5 mmol), [Pd] (1.5 mol%), solvent (3.0 mL)
a
Isolated yield
TABAB (0.5 mmol) was added
b
c[Pd]: 1.0 mol%
1
3

D. Khalili et al.
Table 4 Heck cross-coupling of aryl halides with MCNTs@(A-V)-silica-Pd catalyst
[
Pd] (1.5 mol%)
R'
K CO
2
3
(1.5 mmol)
0.5 mmol)
X
+
R'
TBAB
DMF, 130 °C
(
R
1
3a-c
4
X: -I, -Br, -Cl
R: 4-Me-, 4-OMe-, 4-CN-, 4-NO -, 2-Me-,
2
R': -Ph, -CO Bu,
2
-hexyl
H C
H CO
3
3
NC
4
a(1-3)
4b(1-3)
4c(1-3)
X: -I, 8 h, 91%
X: -I, 9 h, 89%
X: -I, 9.5 h, 86%
4
d(1-2)
X: -I, 6 h, 92%
X: -Br, 24 h, 89%
X: -Cl, 24 h, 71%
X: -Br, 24 h, 89%
X: -Cl, 24 h, 76%
X: -Br, 24 h, 86%
X: -Cl, 24 h, 73%
X: -Br, 24 h, 91%
O
O
O
H C
O (CH CH
2
)
3 3
3CH3
2
CH )
3
(
O N
2
CH3
4h(1-3)
4
e(1-3)
4g(1-3)
X: -I, 5 h, 95%
X: -I, 7.5 h, 88%
X: -I, 9 h, 86%
4
f(1-3)
X: -Br, 24 h, 93%
X: -Cl, 24 h, 77%
X: -Br, 24 h, 88%
X: -Cl, 24 h, 74%
X: -Br, 24 h, 84%
X: -Cl, 24 h, 70%
X: -I, 14 h, 80%
X: -Br, 24 h, 78%
O
O
O
5CH3
2
CH )
(
H CO
3CH3
2
(CH )
3
NC
O
3CH3
2
(CH )
4i(1-3)
4
k(1-3)
X: -I, 9.5 h, 84%
X: -Br, 24 h, 87%
X: -Cl, 24 h, 74%
4
j(1-2)
X: -I, 12 h, 83%
X: -I, 5.5 h, 89%
X: -Br, 24 h, 87%
X:
X:
24 80%
-
-
Br,
Cl,
h,
24 67%
h,
92
92
8
9
89
90
90
91
Run 7 Run 6 Run 5 Run 4 Run 3 Run 2 Run 1
Fig. 8 The recyclability results of MCNTs@(A-V)-silica-Pd catalyst
Fig. 7 Photograph showing the magnetic separation of the catalyst
in the Suzuki reaction of bromobenzene with phenylboronic acid
1
3

Palladium Stabilized by Amino-Vinyl Silica Functionalized Magnetic Carbon Nanotube:…
Table 5 Catalyst reusability
Run
1
2
3
4
5
6
7
study
Yield of 2aa
Time (h)
92
10
92
10
91
10
90
10
90
12
89
12
89
15
Reaction conditions: In all runs, bromobenzene (1.0 mmol), PhB(OH) (1.3 mmol), [Pd] (1.5 mol%),
2
Cs CO (1.5 mmol), and EtOH (3.0 mL) at 80 °C was used
Isolated yield
2
3
a
and 136 mg of FeCl ·6H O was added to 100 mg of puri-
of MCNTs (100 mg), H O (6 mL), and absolute EtOH
3
2
2
fied CNTs. The temperature of the mixture (suspension)
was raised to 50 °C under Ar atmosphere. Then, 300 μL
of ammonia solution (25%) was added slowly and stirred.
After that increasing the temperature to 80 °C was allowed
for 30 min and the suspension was cooled to room tem-
perature. At this moment, an external magnet was used to
separate MCNTs from the solution which then washed with
deionized water and ethanol repeatedly. Finally, the pre-
pared MCNTs were dried at 50 °C in a vacuum oven.
(50 mL) were added to a round-bottom three-neck flask
and ultrasound for 10 min followed by addition of ammo-
nia solution (3 mL, 25%). Meanwhile, tetraethyl orthosili-
cate (TEOS, 1 mL) was injected to a mixture dropwise and
stirred for 12 h. The obtained MCNTs@SiO as a black
2
precipitate was washed with water and EtOH several times.
At this point, a mixture of [3-(2-aminoethylamino)propyl]
trimethoxysilane (AEAPS, 0.5 mL) and vinyltriethoxysi-
lane (VTEOS, 0.5 mL) was added to the black precipitate
in dry toluene (100 mL) and refluxed for 12 h under nitro-
gen atmosphere. The resulting nanocomposite (MCNTs@
3
.3 Synthesis of Supported Palladium Nanocatalysts
(
A-V)-silica) was filtered and washed with toluene and eth-
According to the Stöber method, MCNTs were functional-
ized with amino-vinyl silica. For this purpose, a mixture
anol respectively and dried in oven at 80 °C for 24 h. The
last step in preparation of the MCNTs@(A-V)-silica-Pd cat-
alyst was to disperse the synthesized MCNTs@(A-V)-silica
(
100 mg) in PdCl solution (10 mL of 5 mM PdCl in 1 mM
2
2
H SO ). The mixture was stirred for 20 min at 80 °C and
2
4
the Pd ions were adsorbed and reduced completely. Run-
−
4
ning the ICP analysis demonstrates the 4.3×10 mmol/mg
loading of Pd on prepared nanocomposite.
3
.4 General Procedure for the Suzuki Reaction of Aryl
Electrophiles in the Presence of the Nano-Pd
Catalyst
To a round-bottom flask, aryl electrophile (1.0 mmol), Pd
nanocatalyst (1.5 mol%), Cs CO (1.5 mmol), PhB(OH)
2
3
2
Fig. 9 TEM image of recycled catalyst after third run
Table 6 Comparison with
(
1.3 mmol), and EtOH (3.0 mL) were added, stirred and
heated at 80 °C. The progress of the reaction was checked
Entry
System, condition
Time
Yield (%)
Ref.
previously reported catalytic
systems for the Suzuki–Miyaura
coupling of bromobenzene with
PhB(OH)2
1
2
3
4
5
6
7
8
9
MCNTs@(A-V)-silica-Pd, Phosphine-free, 80 °C, EtOH
Fe O -CNT-Pd, MW, 150 °C, Dioxane-H O
10 h
15 min
25 min
24 h
7.5 h
8 h
3 h
10 h
7
92
89
79
85
82
90
82
95
65
98
90
This work
[53]
[16]
[54]
[55]
[56]
[57]
[58]
[59]
3
4
2
Pd-AAPTMS@G, tripotassium phosphate, 80 °C, H O
2
GO-PdNPs, 80 °C, toluene
Mag-IL-Pd, 60 °C, H O
Pd–pDAB, 90 °C, toluene
2
Pd-BIP-g-Fe O @SiO , 100 °C, DMF
PFG-Pd, 80 °C, H O:EtOH
Ni0.90Pd0.10, r.t., H O:EtOH
2
3
2
2
2
1
1
0
1
PdNPs-starch, r.t., H O
4
12
[60]
[61]
2
PdNPs-TDTAT, 80 °C, H O
2
1
3

D. Khalili et al.
using TLC. After the completion of the reaction, the mix-
ture was cooled down and the catalyst was isolated using
an external magnet. The solvent was evaporated and further
purification was achieved using column chromatography on
silica gel to deliver the desired biphenyl derivatives in high
yields.
H CO
3
1
4-Methoxy-1,1′-biphenyl (2c) [62]. H NMR (250 MHz,
CDCl ) δ (ppm): 7.59 (m, 4H), 7.46 (t, J=7.5 Hz, 2H),
3
3
.5 General Procedure for the Heck Reaction of Aryl
Electrophiles in the Presence of the Nano-Pd
Catalyst
7.49–7.31 (m, 1H), 7.03 (d, J=8.8 Hz, 2H), 3.88 (s, 3H);
1
3
C NMR (62.9 MHz, CDCl ) δ (ppm): 159.3, 141.1,
3
137.1, 134.2, 128.7, 128.1, 126.7, 114.4, 55.6; Anal. Calcd
for C H O: C, 84.75; H, 6.57. Found: C, 84.78; H, 6.50.
1
3
12
Styrene (1.4 mmol) was added to a stirring mixture of aryl
halide (1.0 mmol), K CO (1.5 mmol), nano-pd catalyst
2
3
(
1.5 mol%), TBAB (0.5 mmol) in DMF (3.0 mL) and then
the reaction mixture was heated at 130 °C for the appro-
priate time. The mixture was cooled down to room tem-
perature and the catalyst was isolated using an external
CH3
magnet. Then, the residue was diluted with H O (10.0 mL)
2
and extracted with EtOAc (10×3). The combined organic
phases were combined and dried over anhydrous Na SO .
1
2
4
2-Methyl-1,1′-biphenyl (2d) [62]: H NMR (250 MHz,
Concentration of the mixture and column chromatography
on silica gel afforded the desired cross-coupling products
in high yield.
CDCl ) δ (ppm): 7.38–7.36 (m, 2H), 7.33–7.31 (m, 3H),
3
13
7
.23–7.21 (m, 4H), 2.25 (s, 3H); C NMR (62.9 MHz,
CDCl ) δ (ppm): 141.9, 135.3, 130.2, 129.7, 129.1, 128.0,
3
1
27.2, 126.7, 125.7, 20.5; Anal. Calcd for C H : C, 92.81;
13 12
H, 7.19. Found: C, 92.92; H, 7.08.
3
.6 Product Characterization Data
O N
2
1
1
1
,1′-Biphenyl (2a) [62]. H NMR (250 MHz, CDCl ) δ
3
4-Nitro-1,1′-biphenyl (2e) [63]: H NMR (250 MHz,
1
3
(
ppm): 7.68–7.34 (m, 10H); C NMR (62.9 MHz, CDCl )
3
CDCl ) δ (ppm): 8.26 (d, J=8.8 Hz, 2H), 7.70 (d,
3
δ (ppm): 145.5, 130.3, 127.4, 127.2; Anal. Calcd for
C H : C, 93.46; H, 6.54. Found: C, 93.60; H, 6.40.
J=8.8 Hz, 2H), 7.62–7.58 (m, 2H), 7.50–7.42 (m, 3H);
1
3
1
2
10
C NMR (62.9 MHz, CDCl ) δ (ppm): 147.6, 147.0,
3
1
38.9, 129.1, 128.9, 127.7, 127.3, 124.0; Anal. Calcd for
C H NO : C, 72.35; H, 4.55; N, 7.03. Found: C, 72.35; H,
1
2
9
2
4
.60; N, 7.07.
H C
3
1
4
-Methyl-1,1′-biphenyl (2b) [62]. H NMR (250 MHz,
CDCl )δ (ppm): 7.73 (d, J=8.2 Hz, 2H), 7.60 (d,
3
J=8.1 Hz, 2H), 7.57–7.51 (m, 2H), 7.45 (t, J=8.0 Hz,
1
3
1
H), 7.37 (d, J=7.9 Hz, 2H), 2.51 (s, 3H); C NMR
(
62.9 MHz, CDCl ) δ (ppm): 142.0, 141.3, 135.0, 130.4,
3
1
1
29.3, 128.2, 127.6, 126.4, 20.6; Anal. Calcd for C H : C,
1-Phenylnaphthalene (2f) [62]: H NMR (250 MHz,
1
3
12
9
2.81; H, 7.19. Found: C, 92.75; H, 7.25.
CDCl ) δ (ppm): 7.90–7.79 (m, 3H), 7.45–7.34 (m, 9H);
3
1
3

Palladium Stabilized by Amino-Vinyl Silica Functionalized Magnetic Carbon Nanotube:…
1
3
1
C NMR (62.9 MHz, CDCl ) δ (ppm): 140.7, 140.2,
[1,1′-Biphenyl]-4-amine (2j) [67]: H NMR (250 MHz,
3
1
1
5
33.7, 131.5, 130.0, 128.7, 128.2, 127.5, 127.1, 126.8,
CDCl ) δ (ppm): 7.68–7.20 (m, 7H), 6.66 (d, J=8.25 Hz,
3
1
3
25.9, 125.7, 125.3; Anal. Calcd for C H : C, 94.08; H,
2H), 3.5 (br s, 2H); C NMR (62.9 MHz, CDCl ) δ (ppm):
1
6
12
3
.92. Found: C, 94.16; H, 5.84.
146.1, 141.5, 131.7, 129.0, 128.3, 126.8, 126.5, 115.6;
Anal. Calcd for C H N: C, 85.17; H, 6.55; N, 8.28.
1
2
11
Found: C, 85.10; H, 6.59; N, 8.31.
N
NC
1
3
-Phenylpyridine (2g) [64]: H NMR (250 MHz, CDCl )
3
δ (ppm): 8.88 (s, 1H), 8.61 (s, 1H), 7.90 (d, J=8.3 Hz,
1
[
(
(
1,1′-Biphenyl]-4-carbonitrile (2k) [66]:
H
NMR
1
H), 7.60–7.35 (m, 6H); 13 C NMR (62.9 MHz, CDCl3)
1
3
250 MHz, CDCl ) δ (ppm): 7.73–7.42 (m, 9H); C NMR
3
δ (ppm): 148.0, 147.8, 137.5, 136.3, 134.0, 128.6, 127.8,
62.9 MHz, CDCl ) δ (ppm): 145.5, 139.1, 132.5, 128.9,
3
1
26.9, 123.3; Anal. Calcd for C H N: C, 85.13; H, 5.85;
11 9
1
28.6, 127.5, 127.1, 118.8, 111.0; Anal. Calcd for C H N:
1
3
9
N, 9.02. Found: C, 85.07; H, 5.80; N, 9.13.
C, 87.12; H, 5.06; N, 7.82. Found: C, 87.02; H, 5.18; N,
7
.80.
N
N
1
5
-Phenylpyrimidine (2h) [65]: H NMR (250 MHz,
CDCl ) δ (ppm): 9.16 (d, J=2.4 Hz, 1H), 8.90 (d,
3
1
1
3
(E)-1,2-Diphenylethene (4a) [52]: H NMR (250 MHz,
J=2.6 Hz, 2H), 7.47 (m, 5H); C NMR (62.9 MHz,
CDCl ) δ (ppm): 7.54 (d, J=8.0 Hz, 4H), 7.42–7.34
CDCl ) δ (ppm): 157.4, 154.8, 134.3, 134.2, 129.4, 128.9,
3
3
1
3
(
m, 4H), 7.30–7.24 (m, 2H), 7.13 (s, 2H); C NMR
1
1
26.9; Anal. Calcd for C H N : C, 76.90; H, 5.16; N,
1
0
8
2
(
62.9 MHz, CDCl ) δ (ppm): 136.5, 128.9, 128.8, 127.0,
7.94. Found: C, 76.78; H, 5.21; N, 18.01.
3
1
9
26.2; Anal. Calcd for C H : C, 93.29; H, 6.71. Found: C,
14 12
3.21; H, 6.79.
O N
2
CH3
H C
3
1
2
-Methyl-5-nitro-1,1′-biphenyl (2i) [66]:
H
NMR
(
250 MHz, CDCl ) δ (ppm): 8.14 (d, J=1.9 Hz, 1H),
1
3
(
E)-1-Methyl-4-styrylbenzene (4b) [68]:
H
NMR
8
.08 (dd, J=8.4, 2.3 Hz, 1H), 7.52–7.40 (m, 3H), 7.37 (d,
(
250 MHz, CDCl ) δ (ppm): 7.56 (d, J=8.0 Hz, 2H), 7.49–
3
1
3
J=8.2 Hz, 1H), 7.32–7.29 (m, 2H), 2.35 (s, 3H); C NMR
62.9 MHz, CDCl ) δ (ppm): 148.5, 146.9, 139.7, 137.2,
7
.38 (m, 4H), 7.32 (d, J=7.5 Hz, 1H), 7.22 (d, J=7.5 Hz,
(
13
3
2
H), 7.14 (s, 2H), 2.42 (s, 3H); C NMR (62.9 MHz,
1
30.6, 128.7, 128.4, 127.9, 125.1, 121.0, 20.9; Anal. Calcd
CDCl ) δ (ppm): 137.5, 137.3, 134.6, 129.5, 128.7, 128.7,
3
for C H NO : C, 73.23; H, 5.20; N, 6.57. Found: C,
1
3
11
2
1
27.8, 127.5, 126.5, 126.5, 21.3; Anal. Calcd for C H : C,
15 14
7
3.15; H, 5.35; N, 6.52.
9
2.74; H, 7.26. Found: C, 92.85; H, 7.15.
H N
2
H CO
3
1
3

D. Khalili et al.
1
(
E)-1-Methoxy-4-styrylbenzene (4c) [69]:
H NMR
O
O
(
250 MHz, CDCl ) δ (ppm): 7.39–7.32 (m, 4H), 7.26–7.19
3
(
m, 3H), 7.02 (d, J=15 Hz, 1H), 6.91 (d, J=15 Hz, 1H),
(CH
2
)
3CH
3
1
3
6
.78 (d, J=8.5 Hz, 2H), 3.72 (s, 3H); C NMR (62.9 MHz,
1
CDCl ) δ (ppm): 159.0, 137.5, 132.4, 129.2, 128.7, 128.7,
(E)-3-(Phenyl)acrylic acid butyl ester (4g) [71]: H
3
1
28.1, 126.7, 126.6, 114.2, 55.3; Anal. Calcd for C H O:
NMR (250 MHz, CDCl ) δ (ppm): 7.62 (d, J=16.0 Hz,
1
5
14
3
C, 85.68; H, 6.71. Found: C, 85.65; H, 6.80.
1H), 7.46–7.42 (m, 2H), 7.30–7.28 (m, 3H), 6.37 (d,
J=16.0 Hz, 1H), 4.14 (d, J=6.75 Hz, 2H), 1.67–1.56
1
3
(
m, 2H), 1.44–1.29 (m, 2H), 0.89 (t, J=7.25 Hz, 3H);
C
NMR (62.9 MHz, CDCl ) δ (ppm): 166.5, 142.2, 138.9,
3
NC
132.5, 128.4, 123.1, 118.3, 64.9, 30.7, 19.3, 14.0; Anal.
Calcd for C H O : C, 76.44; H, 7.90. Found: C, 76.57;
1
3
16
2
H, 7.83.
1
(
E)-4-Styrylbenzonitrile (4d) [68]: H NMR (250 MHz,
O
O
CDCl ) δ (ppm): 7.62–7.52 (m, 6H), 7.42–7.31 (m, 3H),
3
1
3
7
.16 (d, J=16.5 Hz, 1H), 7.02 (d, J=16.5 Hz, 1H);
C
H C
3CH3
(CH )
3
2
NMR (62.9 MHz, CDCl ) δ (ppm): 141.6, 136.2, 132.4,
3
1
32.3, 128.8, 128.6, 126.9, 126.8, 126.7, 119.1, 110.7;
Anal. Calcd for C H N: C, 87.77; H, 5.41; N, 6.82.
1
5
11
Found: C, 87.69; H, 5.55; N, 6.76.
1
(
E)-n-butyl 3-(p-tolyl)acrylate (4h) [72]: H NMR
(
250 MHz, CDCl ) δ (ppm): 7.63 (d, J=16.0 Hz, 1H),
3
7
.39 (d, J=8.0 Hz, 2H), 7.16 (d, J=8.0 Hz, 2H), 7.37 (d,
J=16.0 Hz, 1H), 4.18 (t, J=6.7 Hz, 2H), 2.34 (s, 3H),
O N
1.72–1.63 (m, 2H), 1.49–1.36 (m, 2H), 0.96 (t, J=7.2 Hz,
2
1
3
3
H); C NMR (62.9 MHz, CDCl ) δ (ppm): 167.2, 144.4,
3
1
40.4, 131.0, 129.4, 128.0, 117.3, 64.2, 30.8, 21.4, 19.4,
1
4.0; Anal. Calcd for C H O : C, 77.03; H, 8.31. Found:
1
4
18
2
1
C, 77.03; H, 8.25.
(
E)-1-Nitro-4-styrylbenzene (4e) [70]:
H
NMR
(
250 MHz, CDCl ) δ (ppm): 8.14–8.10 (m, 2H), 7.55–7.52
3
(
m, 2H), 7.48–7.44 (m, 2H), 7.42–7.39 (m, 2H), 7.36–7.32
O
O
(
m, 1H), 7.15 (d, J=16.3 Hz, 1H), 7.05 (d, J=16.2 Hz,
1
3
1
H); C NMR (62.9 MHz, CDCl ) δ (ppm):147.0, 144.0,
3
H CO
3CH3
(CH )
3
2
1
36.5, 133.5, 129.2, 129.0, 127.5, 127.0, 126.8, 124.3;
Anal. Calcd for C H NO : C, 74.65; H, 4.92; N, 6.22.
14
11
2
Found: C, 74.61; H, 4.92; N, 6.18.
(
(
(
(
(
1
E)-3-(4-Methoxyphenyl)acrylic acid butyl ester
1
4i) [73]: H NMR (250 MHz, CDCl ) δ (ppm): 6.63
3
d, J=15.75 Hz, 1H), 7.48 (d, J=9.0 Hz, 2H), 6.90
d, J=9.0 Hz, 2H), 6.30 (d, J=16.0 Hz, 1H), 4.19
t, J=6.75 Hz, 2H), 3.83 (s, 3H), 1.71–1.63 (m ,2H),
CH3
1
3
.48–1.39 (m, 2H), 0.96 (t, J=7.5 Hz, 3H); C NMR
1
(62.9 MHz, CDCl ) δ (ppm): 167.4, 161.4, 144.1, 129.9,
3
(
(
(
(
E)-1-Methyl-2-styryl-benzene (4f) [69]:
H
NMR
1
27.6, 115.8, 114.4, 64.3, 55.3, 30.8, 19.4, 14.0; Anal.
250 MHz, CDCl ) δ (ppm): 7.56–7.44 (m, 3H), 7.30–7.09
3
1
3
Calcd for C H O : C, 71.77; H, 7.74. Found: C, 71.85;
1
4
18
3
m, 7H), 6.90 (d, J=16.2 Hz, 1H), 2.38 (s, 3H); C NMR
H, 7.67.
62.9 MHz, CDCl ) δ (ppm): 137.6, 136.3, 135.7, 130.4,
3
1
2
30.1, 128.7, 127.6, 127.5, 126.7, 126.5, 126.1, 124.9,
0.0; Anal. Calcd for C H : C, 92.74; H, 7.26; N, 6.22.
1
5
14
Found: C, 92.65; H, 7.35.
1
3

Palladium Stabilized by Amino-Vinyl Silica Functionalized Magnetic Carbon Nanotube:…
References
O
O
NC
3CH3
CH )
1. Chen A, Ostrom C (2015) Chem Rev 115:11999–12044
(
2
2
3
4
5
.
.
.
.
Chatterjee A, Ward TR (2016) Catal Lett 146:820–840
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Liu Q, Dong X, Li J, Xiao J, Dong Y, Liu H (2015) ACS Catal
1
5
:6111–6137
(
E)-Butyl 3-(4-cyanophenyl)acrylate (4j) [74]: H NMR
6
.
Miyaura N, Suzuki A (1979) J Chem Soc Chem Commun
9:866–867
Milstein D, Stille JK (1978) J Am Chem Soc 100:3636–3638
(
250 MHz, CDCl ) δ (ppm): 7.66–7.57 (m, 5H), 6.50 (d,
3
1
J=Hz, 16.0, 1H), 4.20 (t, J=6.5 Hz, 2H), 1.72–1.61 (m,
7
.
1
3
2
H), 1.48–1.36 (m, 2H), 0.93 (t, J=7.25 Hz, 3H);
C
8. Cordovilla C, Bartolomé C, Martínez-Ilarduya JM, Espinet P
(
2015) ACS Catal 5:3040–3053
NMR (62.9 MHz, CDCl ) δ (ppm): 166.5, 142.0, 138.7,
3
9
. Heck RF, Nolley JP (1972) J Org Chem 37:2320–2322
1
33.0, 128.5, 121.8, 118.3, 113.5, 64.7, 30.8, 19.1, 14.0;
1
0. Sonogashira K, Tohda Y, Hagihara N (1975) Tetrahedron Lett
16:4467–4470
Anal. Calcd for C H NO : C, 73.34; H, 6.59; N, 6.11.
14
15
2
Found: C, 73.34; H, 6.62; N, 6.17.
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5CH
3
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CH
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1
(
E)-1-Phenyl-1-octene (4k) [75]: H NMR (250 MHz,
CDCl ) δ (ppm):7.35–7.20 (m, 5H), 6.40 (d, J=16.1 Hz,
3
1
H), 6.24–6.15 (m, 1H), 2.25–2.18 (m, 2H), 1.31–1.22
2
2
2
2
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(
m, 8H), 0.87 (t, J=6.0 Hz, 3H). C NMR (62.9 MHz,
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3
4
07:47–52
3
2.9, 31.6, 29.5, 29.1, 22.5, 14.0; Anal. Calcd for C H :
14 20
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In summary, a new separable magnetic nano-Pd catalyst
was synthesized and characterized which showed high effi-
ciency towards Suzuki–Miyaura and Heck–Mizoroki cou-
pling reactions of aryl electrophiles under low Pd loading
and phosphine-free condition. The desired products were
obtained in good to high yields. The heterogeneous nature
of the catalyst was identified by hot filtration test (insignifi-
cant Pd leaching) and application of Hg(0) as a poisoning
agent. The presence of amino-vinyl groups on the function-
alized silica excludes the need for using reducing agents for
the last step in the catalyst synthesis (reduction of Pd(II) to
Pd(0)) and the catalyst was removed easily by an external
magnet. The MCNTs@(A-V)-silica-Pd catalyst exhibited
good recyclability after being reused for consecutive six
runs without significant loss in activity.
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