Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille and Heck Cross Coupling Reactions

Article abstract of DOI:10.1007/s10562-016-1904-5

Abstract: Herein for the first time, a Schiff base alumoxane-supported palladium (SBA-Pd°) were successfully synthesized and reported as a new mesoporous nanocatalyst for C–C cross coupling reactions. The SBA-Pd° nanocatalyst could be dispersed in poly(ethylene glycol) and showed excellent catalytic activity for Suzuki–Miyaura, Stille and Heck coupling reactions. In addition, the nanocatalyst could be recovered and reused several times without significant loss of its catalytic activity. Pd leaching from SBA-Pd° is very negligible for this coupling reaction. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1904-5

Catal Lett
DOI 10.1007/s10562-016-1904-5
Palladium-Alumoxane Framework as a Novel and Reusable
Nanocatalyst for Suzuki–Miyaura, Stille and Heck Cross
Coupling Reactions
Arash Ghorbani-Choghamarani1 · Ali Ashraf Derakhshan1 · Maryam Hajjami1 ·
Laleh Rajabi2
Received: 24 July 2016 / Accepted: 30 October 2016
© Springer Science+Business Media New York 2016
Abstract Herein for the irst time, a Schif base alumox-
ane-supported palladium (SBA-Pd°) were successfully syn-
thesized and reported as a new mesoporous nanocatalyst
for C–C cross coupling reactions. The SBA-Pd° nanocata-
lyst could be dispersed in poly(ethylene glycol) and showed
excellent catalytic activity for Suzuki–Miyaura, Stille and
Heck coupling reactions. In addition, the nanocatalyst
could be recovered and reused several times without sig-
niicant loss of its catalytic activity. Pd leaching from SBA-
Pd° is very negligible for this coupling reaction.
Keywords Alumoxane · Mesoporous · Nanocatalyst ·
C–C coupling reaction
1 Introduction
Palladium (Pd) is the most convenient and widely used
metal as an efective catalyst for C(sp2)–C(sp2) coupling
reactions. In the meantime, the Pd-catalyzed Suzuki–
Miyaura coupling reaction is an excellent method for the
synthesis of biaryl compounds, which have found impor-
tant role in the synthesis of agrochemicals, pharmaceuti-
cals, and natural products [1–7]. Traditionally, copious Pd
complexes have been utilized as homogeneous catalysts in
the presence of various ligands for coupling reaction [8–
11]. Despite of higher activity of homogeneous catalysts,
utilizing them has been accompanied by some challenges
such as: diicult separation from reaction mixture, weak
reusability and contamination of products [12]. Providing
heterogeneous catalyst through immobilization of Pd spe-
cies on solid supports facilitates minimizing contamina-
tion, separation and reusability of expensive catalysts. In
this regard, various solid supports have been used for het-
erogenization of catalysts such as polymers, zeolites, silica,
carbon nanotubes and metal–organic frameworks (MOFs)
[13–20].
Graphical Abstract
Palladium-alumoxane framework as a novel and reusable nanocatalyst for
Suzuki–Miyaura, Sꢀlle and Heck cross coupling reacꢀons
Arash Ghorbani-Choghamarani, Maryam Hajjami, Ali Ashraf Derakhshan and Laleh Rajabi
For the first time, palladium supported on Schiff-base alumoxane framework was used
as an effective and recyclable nanocatalyst in Suzuki-Miyaura, Stille and Heck coupling
reactions.
Pd leaching from the supports causes to the lower reac-
tivity for some heterogeneous catalyst than homogeneous
ones. Therefore, the nature of supports is an important fac-
tor in Pd heterogeneous catalysis and there is a need to uti-
lize novel supports to obtain more efective catalysts [21].
Carboxylate–alumoxane is a versatile compound which has
been introduced as a novel support for heterogonous cata-
lysts. Carboxylate alumoxanes with general formula [Al(O)x
(OH)y(O2CR)z]n, 2x+y+z=3 are prepared through the
* Arash Ghorbani-Choghamarani
a.ghorbani@mail.ilam.ac.ir; arashghch58@yahoo.com
1
Chemistry Department, Faculty of Science, Ilam University,
Ilam, Iran
2
Polymer Research Laboratory, Department of Chemical
Engineering, Razi University, Kermanshah, Iran
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A. Ghorbani-Choghamarani et al.
reaction of boehmite (γ-AlOOH) and carboxylic acids. The
surface of the alumoxanes is covered with covalently bound
carboxylate groups. The physical and chemical properties
of the alumoxane can be afected by the type of carboxylic
acid, and range from water soluble powders to hard solids
that are resistant to acids, bases and organic solvents [22–
24]. As a precursor for alumoxane synthesis, Boehmite is
a metastable phase of aluminium oxide with oxide-hydrox-
ide bonds which commonly used as supporting matrix [25,
26]. The advantages of alumoxane as a catalyst support are
included the low price of boehmite and the availability of
an almost ininite range of carboxylic acids [27]. Zircono-
cene complex supported by para-hydroxybenzoate-alu-
moxane (PHBA) were reported as novel catalyst for olein
polymerization [28]. In another study, Pd was immobilized
on the boehmite through tannic acid and used as a highly
active catalyst for hydrogenation of oleins [26].
In recent decades, the Suzuki–Miyaura, Stille and Heck
reactions have been introduced as efective C–C coupling
methodologies [29–32]. Nevertheless, there is no signii-
cant works about application of alumoxanes in the cataly-
sis ield especially for coupling reactions. Currently there is
no report about using the alumoxane supports for Suzuki–
Miyaura, Stille and Heck coupling reactions. In this work
for the irst time we report the successful synthesis of pal-
ladium–alumoxane through covalent bonding of Pd-Schif
base carboxylic acid on boehmite nanoparticles and using
them as a new nanocatalyst for the coupling reaction
(Fig. 1).
2.2 Instrumentation
The X-ray powder difraction (XRD) of the nano materi-
als were carried out on a Philips PW 3040 X-ray difrac-
tometer with Cu Kα source (λ=1.5406 Å) in a range of
Bragg’s angle (10°–100°) at 25°C. Scanning electron
microscope (SEM) images were taken using FE-SEM
MIRA3 TESCAN microscope (acceleration voltage 30 kV)
that equipped with an energy dispersive X-ray detector
(EDS) for the chemical composition analysis. Transmis-
sion electron microscopy (TEM) images were taken by a
JEOL-2100 microscope. Fourier-transform infrared (FTIR)
spectra were recorded with KBr pellets at room tem-
perature (Bruker alpha, German). The NMR spectra were
recorded on a Bruker AVANCE DPX-400 (400 MHz for
1H). Chemical shifts are given in ppm (δ) relative to inter-
nal TMS and coupling constants Jare reported in Hz. TG-
DTA analysis was carried out using a STA PT-1000 instru-
ment in N2 atmosphere at a heating rate of 10°C min−1.
Nitrogen sorption measurement was measured on a Belsorp
mini II apparatus at 77 K. Prior to the measurements, all
the samples were degassed at 373 K in a vacuum line for
5 h. The content of Pd was estimated using an inductively
coupled plasma atomic emission spectrometer (ICP-OES
simultaneous, Varian VISTA-PRO Model). The ultra-
sonication of solutions has been done by ultrasonic bath
(240 W–35 kHz, SONREX, DT52 H model made by the
Bandelin, Germany).
2.3 Catalyst Preparation
2.3.1 Preparation of Boehmite Nano Particles (Bo)
2 Experimental
Boehmite nanoparticles (Bo) were synthesized via previ-
ously reported procedure [25]. In brief, NaOH solution
(6.5 g in 50 mL distilled water) was slowly added to a solu-
tion of hexahydrated Aluminium nitrate (20 g in 30 mL dis-
tilled water) by vigorous stirring. Then obtained precipitate
was subjected to mixing in the ultrasonic bath for 3 h at the
2.1 Reagents and Materials
Palladium(II) acetate, Al(NO3)3·9H2O and other chemi-
cals were all analytic reagents and purchased from Merck,
Sigma-Aldrich, Fluka and Fisher chemical Companies.
Fig. 1 Stepwise synthesis of palladium–alumoxane (SBA-Pd°) from boehmite schematically
1 3

Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille…
room temperature, iltered and washed with distilled water.
The precipitate was kept in the oven at 220°C for 4 h.
adding water. Finally the solvent was evaporated to give
the corresponding biaryl product.
The 1H NMR spectra were used for characterization of
biaryl products. Some selected 1H NMR data for entries 4
and 8 (Table 3) are in good agreement with those previ-
ously reported.
2.3.2 Preparation of Schif-Base (SB)
Schif base (SB) was synthesized according to litera-
ture [33]. Briely, salicylaldehyde (12.2 g, 0.1 mol) was
slowly added to a stirred solution of para-aminobenzoic
acid (13.7 g, 0.1 mol in 100 mL ethanol) and the mixture
was stirred for 30 min at room temperature. The precipi-
tated yellow Schif-base was iltered and recrystallized with
methanol to obtain SB.
2.4.1 4-Methoxy-1,1′-Biphenyl
1H NMR (400 MHz, CDCl3):δH (ppm) = 7.61–7.57 (m,
4H), 7.48–7.44 (t, 2H, J = 7.6 Hz), 7.35–7.31 (tt, 1H,
2.3.3 Preparation of Schif-Base Alumoxane (SBA)
The amount of 2 g Boehmite (Bo) powder added to a
stirred solution of Schif-base SB (0.266 g, 0.001 mol in
50 mL Dimethylformamide) and the resulting mixture was
reluxed for 17 h. Then the yellow precipitation of resulting
Schif-Base alumoxane (SBA) was iltered of and washed
thoroughly by ethanol and methanol, and dried at 70°C.
2.3.4 Preparation of Pd°-Schif-Base Alumoxane
(SBA-Pd°)
At 100 mL round-bottom lask, 0.5 g of SBA powder
and 0.023 g (0.0001 mol) palladium(II) acetate were dis-
persed into 40 mL methanol and closed its lid. The mix-
ture was stirred for 24 h at ambient temperature. Then the
orange precipitate was iltered of and washed several time
with methanol to obtain SBA-Pd2+ complex. In continu-
ous, 0.3 g dry SBA-Pd2+ complex was dispersed in 30 mL
methanol at a 100 mL round-bottom lask and then 1 mL of
hydrazine hydrate was added slowly over 5 min under con-
stant stirring. The reduction of Pd2+ to Pd° started immedi-
ately, and the color changed from orange to black (Fig. 1).
The resulting black SBA-Pd° was collected and washed
with distilled water for several times and then dried in oven
at 70°C.
2.4 General Procedure for Suzuki–Miyaura Reaction
A test tube equipped with a magnetic stirrer bar was
charged with aryl halides (1 mmol), sodium tetraphenylbo-
rate (171 mg, 0.5 mmol), Na2CO3 (318 mg, 3 mmol), SBA-
Pd° catalyst (10 mg) and 2 mL solvent (PEG). The reaction
mixture was heated for the required time at 80°C until reac-
tion completed (the progress of reaction was monitored by
TLC). Then the mixture was cooled to room temperature.
The catalyst was separated by iltration, washed by acetone
and dried in oven.
The organic layer was extracted with Et2O (3 mL, four
times) from PEG iltrate in a separating funnel by aid of
Fig. 2 FT-IR spectra of a Bo, b SB, c SBA, d SBA-Pd2+ and e SBA-
Pd°
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A. Ghorbani-Choghamarani et al.
J = 1.2, 7.6 Hz), 7.05–7.02 (dt, 2H, J = 8.8, 2.4 Hz), 3.90
(s, 3H).
the mixture was cooled to room temperature. The cata-
lyst was separated by iltration, washed by acetone and
dried in oven. The organic layer was extracted with Et2O
(3 mL, four times) from PEG iltrate in a separating fun-
nel by aid of adding water. Finally the solvent was evapo-
rated to give the corresponding biaryl product.
2.4.2 4-Chloro-1,1′-Biphenyl
1H NMR (400 MHz, CDCl3):δH (ppm)=7.61–7.59 (m,
2H), 7.58–7.55 (m, 2H), 7.52–7.44 (m, 4H), 7.43–7.39 (tt,
1H, J=6, 1.6 Hz).
The 1H NMR spectra were used for characterization of
biaryl products. Some selected 1H NMR data for entries 1
and 6 (Table 5) are in good agreement with those previ-
ously reported.
2.5 General Procedure for Stille Reaction
A test tube equipped with a magnetic stirrer bar was
charged with aryl halides (1 mmol), triphenyltin chlo-
ride (192.7 mg, 0.5 mmol), Na2CO3 (318 mg, 3 mmol),
SBA-Pd° catalyst (10 mg) and 2 mL solvent (PEG). The
reaction mixture was heated for the required time at
80 °C. Progress of reaction was monitored by TLC. Then
2.5.1 1,1′-Biphenyl
1H NMR (400 MHz, CDCl3):δH (ppm) = 7.63–7.65
(m, 4H), 7.41–7.51 (m, 4H), 7.37–7.41 (tt, 2H, J = 7.6,
1.2 Hz).
Fig. 3 N2 adsorption–desorption isotherms and the corresponding pore size distributions for boehmite nanoparticles (a, b), SBA-Pd° (c, d)
1 3

Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille…
Table 1 Surface properties
Sample
Speciic surface area
Speciic pore volume (cm3 g−1
)
Pore diameter (nm)
of SBA-Pd° and boehmite
(m2 g−1
)
precursor
SBET
SBJH
Vtot (BET)
V (BJH)
Dav
D (BJH)
Boehmite
SBA-Pd◦
2.28
2.48
0.0125
0.345
0.0125
0.310
22
1.21
1.21
315.26
269.24
4.37
2.5.2 4-Nitro-1,1′-Biphenyl
in a separating funnel by aid of adding water. Finally the
solvent was evaporated to give the corresponding product.
1
1H NMR (400 MHz, CDCl3):δH (ppm)=8.32–8.35 (dt,
2H, J=8.8, 2.4 Hz), 7.76–7.79 (dt, 2H, J=8.8, 2.4 Hz),
7.65–7.68 (m, 2H), 7.51–7.56 (m, 2H), 7.46–7.50 (tt, 1 H,
J=7.6, 2.4 Hz).
The H NMR spectra were used for characterization of
1
products. Some selected H NMR data for entries 4 and
5 (Table 7) are in good agreement with those previously
reported.
2.6 General Procedure for Heck Reaction
2.6.1 (E)-Butyl 3-(4-Methoxyphenyl)Acrylate
A test tube including aryl halide (1 mmol), butyl acrylate
(153.8 mmol, 1.2 mmol), Na2CO3 (318 mg, 3 mmol),
SBA-Pd° (10 mg) and PEG (2 mL) was stirred in 100°C
and the completion of the reaction was monitored by TLC.
After completion, the mixture was cooled to room temper-
ature and the catalyst was separated by iltration, washed
by acetone and dried in oven. The organic layer was
extracted with Et2O (3 mL, four times) from PEG iltrate
1H NMR (400 MHz, CDCl3):δH (ppm)=0.97 (t, J=7.2 Hz,
3H), 1.43 (sex, J=6.8 Hz, 2H), 1.67 (quint, J=6.8 Hz, 2H),
3.89 (s, 3H), 4.24 (t, J=6.4 Hz, 2H), 6.33 (d, J=16 Hz,
1H), 6.92 (d, J=8.8 Hz, 2H), 7.49 (d, J=8.8 Hz, 2H), 7.64
(d, J=15.6 Hz, 1H).
2.6.2 Butyl Cinnamate
1H NMR (400 MHz, CDCl3):δH (ppm)=1.05 (t, J=7.8 Hz,
3H), 1.46 (six, J=2 Hz, 2H), 1.74 (quint, J=3.2 Hz, 2H),
4.25 (t, J=6.4 Hz, 2H), 6.49 (d, J=16 Hz, 1H), 7.40 (m,
3H), 7.43 (m, 2H), 7.73 (d, J=16 Hz, 1H).
3 Results and Discussion
3.1 Catalyst Characterization
3.1.1 FT-IR Analysis
Fourier transform infrared spectroscopy (FT-IR) is an
adequate technique for the determination of the molecu-
lar structure of organic–inorganic materials. Therefore,
FT-IR spectra were recorded for Bo, SB, SBA, SBA-Pd2+
and SBA-Pd° (Fig. 2). In the spectrum of Bo (Fig. 2a),
two strong peaks at 3092 and 3316 cm−1 are related to the
stretching vibration of Al–OH. Also the tow frequencies
1071 and 1166 cm−1 are allocated to the symmetrical bend-
ing vibrations of hydrogen bands between Al–OH groups at
the surface of boehmite. The three bands of 741, 615 and
482 cm−1 also refer to the Al–O–Al vibration modes [25].
The frequency peaks of 1385 and 1637 cm−1 are related to
the stretching vibration of the nitrate impurity and absorbed
water in the crystal structure consecutively.
In the spectrum of SB (Fig. 2b), the strong peak at
1703 cm−1 was related to stretching vibrations of C=O
Fig. 4 XRD spectra of a Bo, b SBA and c SBA-Pd°
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A. Ghorbani-Choghamarani et al.
Fig. 5 SEM images of a Bo, b
SBA and c SBA-Pd°
groups and the broad peak at range of 2480–3000 cm−1 was
referred to stretching vibrations of acidic OH. These peaks
of carboxylic groups were eliminated when reacted with
boehmite through carboxylate formation (Fig. 2b).
In the spectrum of SBA (Fig. 2c), the emersion of
several peaks in 1200–1800 cm−1 region is assigned of
carboxylate–alumoxane formation through the covalent
bonding between boehmite (Bo) and Schif base (SB).
Two peaks emerged in 1492 and 1560 cm−1 are referred
to symmetrical and asymmetrical stretching vibrations
of bidentate carboxylate bonding respectively. Also the
peak of 1626 cm−1 is related to vibrations of uniden-
tate carboxylate bonding [22, 34]. Schif bases displays
the imine (C=N) vibrations in the band of 1663 cm−1
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Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille…
Fig. 6 Negative SEM images
of a SBA, b SBA-Pd° in various
magniications
which vanished in Fig. 2b because of overlapping. Also
stretching vibrations of the phenolic C–O is observed at
1282 cm−1. Finally the peaks of 1600 and 1417 cm−1 are
refer to the vibrations of sp2 C=C in the aromatic rings
for SBA [35]. In the spectra of SBA-Pd2+ and SBA-Pd°
(Fig. 2d, e), it can be seen to decrease in intensity of
ligand peaks that is related to chelation of Pd2+ at the
surface of SBA. It seems that chelation caused to the
high rigidity and decreasing in bond vibrations. Also a
shift to lower wave number has been observed for C=N
(1663 cm−1) upon chelation. This shows that it may be
considered as a center of chelation to Pd [35].
3.1.2 Speciic Surface Area
The nitrogen adsorption–desorption isotherms and pore
size distribution of boehmite (Bo) precursor and SBA-Pd°
are illustrated in Fig. 3. It can be seen from Fig. 3a, c, these
nano materials indicate a typical type IV isotherm (deined
by IUPAC), which are identiied as mesoporous materials.
Pore size distributions (Fig. 3b, d) are indicated the micro
and meso porosity in both of them which there is decreas-
ing in pore size for SBA-Pd° versus Bo precursor.
All data obtained by Brunauer–Emmett–Teller (BET)
and Barrett–Joyner–Halenda (BJH) method are presented
in Table 1. The Bo precursor with average pore diam-
eter 22 nm contained a speciic surface area (SBET) of
2.28 m2 g−1 and a speciic pore volume of 0.0125 cm3 g−1.
Despite being nanoparticles, Bo has shown the very low
speciic surface area which can be result of the sever
agglomeration between their particles. In contrast, SBA-
Pd° with average pore diameter 4.37 nm has shown the
The presence of boehmite index peaks in the other
spectra may be considered as existence of free Al–
OH groups that cannot be reacted with Schif base SB
because of some spherical hindrances.
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A. Ghorbani-Choghamarani et al.
Fig. 7 SEM-EDS data of a Bo, b SBA, c SBA-Pd° and d schematic of Pd° nano particles immobilized on SBA nano lakes
speciic surface area (SBET) of 315.26 m2 g−1 and a spe-
ciic pore volume of 0.345 cm3 g−1. These could be sign
of decrease in agglomeration through alumoxane forma-
tion as a framework for Pd nanoparticles. In fact attachment
of schif base at the surface of Bo nanoparticles caused
to disintegrate agglomerates and formation of nano lake
frameworks with the high surface area. The Dav for SBA-
Pd° indicated meso porosity while DBJH values showed the
micro porosity for them.
(080), (231), (002), (171), (251) and (271), respectively
which can be identiied obviously as orthorhombic boe-
hmite γ-AlOOH (JCPDS card 21-1307). The broad and
less intense difraction peaks of Bo reveals that Bo had
lower crystallinity.
XRD pattern of SBA (Fig. 4b) exhibited the same dif-
fraction lines of Bo with sharper and more intense peaks.
It may be considered as inadequate functionalization of
boehmite with Schif-base molecules due to some spherical
hindrances. On the other hand, augmentation in sharpness
and intensity of SBA peaks indicates its higher crystallinity
versus Bo.
3.1.3 X-Ray Difraction
X-ray difraction (XRD) is a useful and versatile tech-
nique for the phase analysis and determination of the
crystal structure of materials. Hence, X-ray difrac-
tion patterns were recorded for Bo, SBA and SBA-Pd°
(Fig. 4). XRD pattern of Bo (Fig. 4a) shows broad peaks
at 2ϴ = 14°, 28.1°, 38.5°, 45.7°, 49.2°, 51.2°, 55.2°, 61°,
64.3°, 67°, 68.3°, 72° and 81°corresponding to difrac-
tion lines (020), (120), (031), (131), (051), (220), (151),
Also difraction pattern of SBA-Pd° (Fig. 4c) exhibited
the same difraction lines of SBA with the same peaks
sharpness. With further observation, it can be seen some
small diferences in SBA-Pd° versus SBA. These difer-
ences in XRD patterns are referred to the small Pd° nan-
oparticles with good dispersion were formed in the SBA-
Pd°, which is conirmed by following SEM images. The
difraction lines related to Pd° species clearly cannot be
1 3

Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille…
Fig. 8 TEM images of Bo (a)
and SBA-Pd° catalyst (b)
observed in the SBA-Pd° pattern because of weak intensity
of the Pd° peaks and overlapping with SBA lines.
Pd species in the SBA-Pd° spectrum exhibited peaks at
2ϴ=40.2°, 46.42°, 68.04°, 82.05° and 87.3° correspond-
ing to difraction lines (111), (200), (220), (311) and (222),
respectively. However the presence of Pd° can be detected
only in the lines of (111) and (200).
Comparison between the SEM images of Bo (Fig. 5a)
and SBA (Fig. 5b) reveals that the morphological features
are changed signiicantly by SBA formation from Bo.
It can be seen that SBA sample was composed of nano
lakes with irregular shapes, about 20–30 nm thickness
and 50–100 nm across. It seems that rearrangement of
boehmite (Bo) crystallites with Schif-base (SB) inter-
actions caused to formation of 2-D morphology of nano
lakes. Figure 5c shows the SEM images of SBA-Pd°
nanocatalyst which approves well dispersion of the Pd°
nanoparticles at the surface of SBA-Pd° nano lakes.
The Fig. 6 obviously shows the negative SEM images
of SBA and SBA-Pd° in various magniications. The
presence of spherical Pd° nanoparticles (approximate
particle size about 5 nm) are approved by comparing
between Fig. 6a, b. As shown in Fig. 6b, the spherical
3.1.4 SEM and TEM Investigation
The morphological and structural characterizations of Bo,
SBA and SBA-Pd° were studied by SEM (Fig. 5). It can be
observed that Bo sample (Fig. 5a) was mainly composed of
nanoparticles. These Bo nanoparticles were agglomerated
due to presence of OH groups at their surfaces and ten-
dency to hydrogen bonding among them.
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A. Ghorbani-Choghamarani et al.
Fig. 9 TG-DTA diagrams of
SBA-Pd° nano catalyst (a) and
schematic for mechanism of
weight loss in the irst stage (b)
Pd° nanoparticles are formed in the surface of SBA nano
lakes.
3.1.5 Thermal Analysis (TG-DTA)
SEM-EDS analysis for Bo investigates the presence
of the expected elements in the structure of Boehmite,
namely C, O, Al (Fig. 7a). Furthermore, SEM-EDS data
for SBA also reveals the presence of N element which
refers to the Schif-base molecules (Fig. 7b). SEM-EDS
analysis for SBA-Pd° also indicates the presence of Pd°
nanoparticle on the surface of SBA supports with the
weight present about 5.38 w% (Fig. 7c). The immobiliza-
tion of spherical Pd° nanoparticles on the surface of SBA
support has been shown schematically in Fig. 7d.
Figure 8 shows the TEM images of boehmite nanopar-
ticles (a) and SBA-Pd° (b). It can be seen that boehmite
nanoparticles with average particle size 10–30 nm have
shown an orthorhombic structure. Also Fig. 8b conirmed
the distribution of Pd° nanoparticles at the surface of
SBA-Pd° which is quite consistent with the SEM images.
It can be seen the spherical Pd nanoparticles at the sur-
face of nano lakes formed a mesoporous structure.
The thermal behavior of the SBA-Pd° nanocatalyst was
studied by thermo gravimetric-diferential thermal analy-
sis (TG-DTA). The TG curve in Fig. 9a presents a minor
weight loss (mass change: 0.78%, 0.097 mg) at 190°C ini-
tially, which was followed by a weight increase immedi-
ately. The DTA curve shows an endothermic peak at 190°C
that can be related to dehydroxylation process of free OH
groups in SBA-Pd°. Generally dehydroxylation process
starts about 200°C for boehmite (γ-AlOOH) structure [25].
As can be seen from Fig. 9b, the weight loss in the irst
stage may be related to the dehydroxylation process and
increasing in the weight can be due to the recapturing of
OH by Pd.
The TG curve in Fig. 9a also presents a major weight
loss (mass change: 11%, 1.364 mg) started at 406 °C.
The DTA curve also shows an exothermic peak at 450 °C
that can be referred to the combustion process of schif-
base groups in SBA-Pd°. According to the second weight
loss, the amount of these organic groups was calculated
0.451 mmol g−1. Therefore it can be concluded that
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Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille…
SBA-Pd° nano catalyst is thermally stable up to 406 °C.
The calculation based on the second stage weight loss
show that the percentage of Pd° in SBA-Pd° nano catalyst
is 4.85 w%.
that Pd leaching from SBA-Pd° is very negligible for
coupling reaction.
3.2 SBA-Pd° Catalytic Studies
The catalytic performance of SBA-Pd° was evaluated in
the carbon–carbon coupling reaction of aryl halides with
sodium tetraphenylborate, triphenyltin chloride and butyl
acrylate. In our primary experiments, Suzuki–Miyaura cou-
pling reaction between 4-bromonitrobenzene and sodium
tetraphenylborate in the presence of catalytic amounts of
SBA-Pd° was chosen as a model reaction to optimize the
efects of base, solvent, temperature and amount of nano-
catalyst. The results of optimization conditions are pre-
sented in Table 2. At the beginning, Na2CO3 was used as
base and PEG as solvent in the presence of 4–11 mg of
SBA-Pd° at 80°C.
3.1.6 Palladium Content
Amount of loaded Pd on SBA-Pd° catalyst was evalu-
ated by inductively coupled plasma-optical emission
spectrometry (ICP-OES) to be 15.7 × 10−5 mol g−1 (1.67
w% Pd). We performed the hot iltration test to conirm
the heterogeneous nature of the nano catalyst. The solid
nano catalyst was removed by hot iltration after 47% of
the reaction was completed and the liquid phase of the
reaction mixture (4-bromonitrobenzene, NaPh4B, PEG
and Na2CO3) was kept in reaction conditions (80 °C) for
another 60 min. The negligible increase in the amount
of product was observed (only 1%). This result indicates
The best results were achieved using 10 mg
(0.157×10−5 mol g−1) of the nanocatalyst (Table 2, entry
8). By increasing the amount of the nanocatalyst, no
Table 2 Optimization of
Suzuki–Miyaura coupling
reaction over the SBA-Pd° nano
catalyst
Entry
Solvent
Base
Catalyst (mg)
Temp (°C)
Time (h)
Yield (%)a
1
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
H2O
DMF
DMSO
PEG
PEG
PEG
PEG
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
NaHCO3
NaOAc
KH2PO4
NaOH
–
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
25
45
60
95
2
3
3
3
3
2
2
2
2
2
2
2
2
2
2
2
2
4
4
2
1
–
2
4
–
3
5
17
42
64
75
81
95
96
78
38
31
–
4
6
5
7
6
8
7
9
8
10
11
10
10
10
10
10
10
10
10
10
10
10
10
9
10
11
12
13
14
15
16
17
18
19
20
21
K2CO3
–
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
83
8
–
–
–
30
95
Reaction conditions: 4-bromonitrobenzene (202 mg, 1 mmol), NaPh4B (171 mg, 0.5 mmol), PEG (2 mL),
and 3 mmol base
aIsolated yield
1 3

A. Ghorbani-Choghamarani et al.
remarkable improvement in yield was observed (Table 2,
entry 9). Afterward studies focused on the efect of other
bases on the coupling reaction (Table 2, entry 10–14).
The results showed that Na2O3 was still the more efec-
tive base among the bases to perform a high yield of the
product. The optimization was continued in various sol-
vents such as DMSO, H2O and DMF instead of PEG to
study solvent efects (Table 2, entries 15–17). Changing
the solvent did not provide any improvement in the reac-
tion yield and showed that protic solvents (PEG, H2O) were
more efective than aprotic solvents (DMF, DMSO). It may
be related to the efective interactions between Al–OH
groups in SBA-Pd° and protic solvent. Also PEG as a phase
transfer catalyst, can enhance the solubility of NaBPh4 and
Na2CO3, as well as promote basicity of Na2CO3. Efect of
various temperatures were examined in ranging from 25 to
95°C (Table 2, entries 8, 18–21) and it was revealed that
the coupling reaction proceeds eiciently at 80°C (Table 2,
entry 8). Afterward, we successfully utilized the optimized
conditions (SBA-Pd° as catalyst, Na2CO3 as base in PEG
Table 3 Suzuki–Miyaura
coupling reaction with aryl
halides and NaPh4B catalyzed
by SBA-Pd°
Entry Aryl halide
Time (min) Yield (%)a
TON TOF (h−1
611 1834
)
M.p. (°C)
Found
Reported
1
20
60
70
96
92
90
67–69
68–70 [36]
I
2
43–45
44–46 [36]
586
573
586
491
H
I
3C
3
109–110
111–113 [37]
COOH
I
4
5
6
7
8
75
93
93
95
93
94
86–88
67–69
110–112
83–84
75–76
88–90 [36]
68–70 [36]
112–114 [36]
85–86 [38]
77–79 [36]
592
474
I
MeO
20
592 1777
B r
120
140
60
605
592
599
302
254
599
N
Br
O2
Br
NC
Cl
Br
Br
9
60
92
89
63
43–45
44–46 [36]
586
567
586
243
50
H
3C
10
11
140
8 h
161–163
163–164 [38]
Br
HO
Colorless oil Colorless oil [39] 401
Br
12
13
4 h
78
67–69
83–84
68–70 [36]
85–86 [38]
497
111
124
11
Cl
10 h
35b
NC
Cl
Reaction conditions: aryl halides (1 mmol), NaPh4B (171 mg, 0.5 mmol), PEG (2 mL), Na2CO3 (318 mg,
3 mmol), SBA-Pd° catalyst (10 mg, 0.157 mol%) and 80°C.
aIsolated yield
bContaining 20 mg nano catalyst and 95°C reaction temperature
1 3

Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille…
solvent) for the Suzuki–Miyaura coupling reaction of dif-
ferent aryl halides to obtain the corresponding biaryls
(Table 3).
As expected for aryl iodides, coupling reaction gave
excellent yields in the shorter times (Table 3, entries 1–4).
Aryl bromides as well as aryl iodides indicates high reac-
tivity in high yields but relatively shows higher reaction
times versus aryl iodides (Table 3, entries 5–11). The reac-
tions of aryl chlorides were carried out in more diicult
conditions which relatively gave lower yields versus other
aryl halides (Table 3, entries 12–13). The mechanism of
the Suzuki–Miyaura coupling reaction by SBA-Pd° catalyst
has been shown schematically in the Fig. 10.
In order to demonstrate the broad application of SBA-
Pd° as a catalyst, the Stille reaction were studied. For opti-
mizing the reaction and obtain the best catalytic system, the
reaction of iodobenzene (1 mmol) with triphenyltin chlo-
ride (0.5 mmol) was chosen as a model reaction, and was
evaluated efect of parameters such as base, solvent, tem-
perature and amount of SBA-Pd° (Table 4).
Fig. 10 Scheme of the Suzuki–Miyaura coupling mechanism by
SBA-Pd°
Table 4 Optimization of Stille
coupling reaction over the
SBA-Pd° nano catalyst
Entry
Solvent
Base
Catalyst (mg)
Temp (°C)
Time (min)
Yield (%)a
1
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
H2O
DMF
DMSO
PEG
PEG
PEG
PEG
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
NaHCO3
NaOAc
KH2PO4
K2CO3
–
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
25
40
60
120
120
30
30
30
30
10
10
10
10
10
10
10
10
10
10
10
300
75
35
3
–
2
4
Trace
21
38
56
72
83
96
97
75
45
36
–
3
5
4
6
5
7
6
8
7
9
8
10
11
10
10
10
10
10
10
10
10
10
10
10
9
10
11
12
13
14
15
16
17
18
19
20
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
80
26
15
68
73
84
97
Reaction conditions: Iodobenzene (204 mg, 1 mmol), triphenyltin chloride (193 mg, 0.5 mmol), PEG
(2 mL), and 3 mmol base
aIsolated yield
1 3

A. Ghorbani-Choghamarani et al.
Table 5 The Stille coupling reaction with aryl halides and Ph3SnCl catalyzed by SBA-Pd°
Entry Aryl halide
Time (min) Yield (%)a
TON TOF (h−1
)
M.p. (°C)
Found
Reported
1
10
80
70
96
95
91
67–69
68–70 [36]
611
605
579
3668
453
I
2
43–45
44–46 [36]
H
I
3C
3
109–110
111–113 [37]
496
COOH
I
4
5
6
7
8
70
15
35
40
55
85
95
94
96
90
86–88
67–69
110–112
83–84
75–76
88–90 [36]
68–70 [36]
112–114 [36]
85–86 [38]
77–79 [36]
541
605
598
611
573
464
2420
1026
917
I
MeO
Br
N
Br
O2
Br
NC
625
Cl
Br
Br
9
50
60
91
93
68
43–45
44–46 [36]
579
592
695
592
72
H
3C
10
11
161–163
163–164 [38]
Br
HO
360
Colorless oil Colorless oil [39] 433
Br
12
210
71
67–69
68–70 [36]
452
129
Cl
Reaction conditions: aryl halides (1 mmol), triphenyltin chloride (193 mg, 0.5 mmol), PEG (2 mL), Na2CO3 (318 mg, 3 mmol), SBA-Pd° cata-
lyst (10 mg, 0.157 mol%) and 80°C.
aIsolated yield
As expected, no product is obtained in the absence
of SBA-Pd° (Table 4, entry 1). Initially, the efect of
various solvents in model reaction revealed that PEG
gives the best yields in compared with other solvents
(Table 4, entries 14–16). Like the Suzuki reaction,
the optimum amount of catalyst were achieved 10 mg
(0.157 × 10−5 mol g−1) of the SBA-Pd° (Table 4, entry 8).
By increasing the amount of the nanocatalyst, no remark-
able improvement in yield was observed (Table 4, entry
9). Also the results revealed that Na2O3 was still the more
efective base among the bases (Table 4, entries 10–13) to
perform a high yield of the product. Finally the efect of
various temperatures were examined in ranging from 25
to 120 °C (Table 4, entries 8, 17–20) and it was observed
that the reaction proceeds eiciently at 80 °C (Table 4,
entry 8). Also it is found that unlike the Suzuki reaction,
SBA-Pd° has been able to carry out the Stille reaction
at the room temperature and the lower times’ reaction.
Therefore, the best results are obtained in PEG solvent at
80 °C in the presence of 10 mg (0.157 mol%) of SBA-Pd°
1 3

Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille…
As expected in compared to aryl chlorides, aryl iodides
and aryl bromides react in shorter times. The mechanism
of the Stille coupling reaction by SBA-Pd° catalyst has
been shown schematically in the Fig. 11.
In addition to the Suzuki and Stille reactions, the SBA-
Pd° also shows applicable performance in the Heck reac-
tion. So we examined the SBA-Pd° catalyzed Heck reac-
tion through the coupling of butyl acrylate with various
aryl halides. Therefore, the reaction of butyl acrylate and
iodobenzene was selected as a model to optimize condi-
tions. Table 6 illustrates the catalytic activity of SBA-Pd°
for Heck reaction in various conditions of base, solvent,
temperature and amount of catalyst. The optimum result
is observed in PEG solvent at 100 °C in the presence
of 10 mg (0.157 mol%) of SBA-Pd° and using Na2CO3
(Table 6, entry 7).
Fig. 11 Scheme of the Stille coupling mechanism by SBA-Pd°
After optimization of conditions, various aryl halides
were investigated in Heck reaction in order to obtain the
corresponding biaryls (Table 7). A variety of aryl halides
(including Cl, Br and I) with electron-donor and electron-
withdrawing substituents were catalyzed by SBA-Pd° to
obtain the corresponding biphenyls in good performance.
The mechanism of the Heck coupling reaction by SBA-
Pd° catalyst has been shown schematically in the Fig. 12.
and using Na2CO3 (Table 4, entry 8). After obtaining the
optimum conditions, various aryl halides were utilized in
Stille reaction in order to obtain the corresponding biar-
yls (Table 5). A variety of aryl halides (including Cl, Br
and I) with electron-donor and electron-withdrawing sub-
stituents were catalyzed by SBA-Pd° to obtain the cor-
responding biphenyls in excellent yields and lower times.
Table 6 Optimization of Heck
coupling reaction over the
SBA-Pd° nano catalyst
Entry
Solvent
Base
Catalyst (mg)
Temp (°C)
Time (min)
Yield (%)a
1
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
H2O
DMF
DMSO
PEG
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
NaHCO3
NaOAc
KH2PO4
Na2CO3
Na2CO3
Na2CO3
Na2CO3
–
100
100
100
100
100
100
100
100
100
100
100
100
100
100
80
180
50
40
30
20
20
20
20
35
35
35
35
35
35
120
–
2
5
26
34
44
63
85
91
92
45
35
19
Trace
53
42
70
3
6
4
7
5
8
6
9
7
10
11
10
10
10
10
10
10
10
8
9
10
11
12
13
14
15
Reaction conditions: Iodobenzene (204 mg, 1 mmol), butyl acrylate (153.8 mg, 1.2 mmol), PEG (2 mL),
and 3 mmol base
aIsolated yield
1 3

A. Ghorbani-Choghamarani et al.
Table 7 The Heck coupling
reaction with aryl halides and
butyl acrylate catalyzed by
SBA-Pd°
Entry
1
Aryl halide
Time (min)
20
Yield (%)a
91
TON
579
TOF (h−1
1738
)
I
2
3
45
95
95
605
528
806
333
H
I
3C
83b
COOH
I
4
65
390
80
96b
85
611
541
573
566
535
573
458
564
83
I
MeO
5
Br
6
90
429
309
26
N
O2
Br
7
110
1220
135
1560
89
Br
NC
8
84b
90b
72b
H
Br
Br
3C
9
254
2.7
HO
10
Br
11
1440
89b
566
3.7
NC
Cl
Reaction conditions: aryl halides (1 mmol), butyl acrylate (153.8 mg, 1.2 mmol), PEG (2 mL), Na2CO3
(318 mg, 3 mmol), SBA-Pd° catalyst (10 mg, 0.157 mol%) and 100°C.
aIsolated yield
bReaction was carried out at 120°C
3.3 Reusability of Catalyst
The amount of Pd leaching was evaluated by ICP-OES
analysis of recycled nano catalyst. The result indicated neg-
In order to commercial applications, the recovery and
reusability of the catalyst are very important factors.
Therefore, after the reaction completion, SBA-Pd° recov-
ered by centrifugation, thoroughly washed with methanol
and water and after drying in oven, it can be reused for
next coupling reactions including the Suzuki–Miyaura,
Stille and Heck. It was found that SBA-Pd° has been
recovered and reused without remarkable loss of its reac-
tivity at least for six runs (Fig. 13). The average isolated
yield for six runs is 93, 94.3 and 88.6% in the Suzuki,
Stille and Heck reaction respectively.
ligible changes of Pd contents (15.7×10−5 mol g−1), only
1% leaching was observed.
3.4 Catalyst Comparison
The activity of this nanocatalyst is presented by compari-
son our results on the Suzuki coupling of bromobenzene
with the previously reported heterogeneous catalysts in
the literature (Table 8). This comparison reveals that SBA-
Pd is comparable or may be better in some terms of reac-
tion (Pd mol%, temperature, time and yield) than the other
reported catalysts. Furthermore, this nano catalyst in terms
1 3

Palladium-Alumoxane Framework as a Novel and Reusable Nanocatalyst for Suzuki–Miyaura, Stille…
of price, stability and toxicity is can be better than the
other catalysts. Unlike the Alumoxane frameworks, some
expensive materials such as MCM-41, SBA-15, polymers
or MWCNT which have been used as catalyst support,
requires high temperature, a lot of time or tedious condi-
tions to prepare.
4 Conclusion
In summary, SBA-Pd° as a new mesoporous nanocatalyst
was synthesized and characterized. Analysis data conirmed
the synthesized schif-base alumoxane with nano lakes
morphology formed the stable framework for Pd nanopar-
ticles which can be thermally stable up to 406°C. Also the
Pd° percentage in nano catalyst were indicated (1.67 w%;
15.7×10−5 mol g−1). The SBA-Pd° showed excellent cata-
lytic activity and high reusability for the Suzuki–Miyaura,
Fig. 12 Scheme of the Heck coupling mechanism by SBA-Pd°
Fig. 13 Reusability of SBA-
Pd° in the coupling reaction
of iodobenzene (1 mmol) with
a NaBPh4 (0.5 mmol) and b
Ph3SnCl (0.5 mmol) and c butyl
acrylate (1.2 mmol) under reac-
tion conditions
Table 8 Comparison of SBA-Pd° nano catalyst for the C–C coupling of bromobenzene with previously reported procedure
Entry
Substrate
Reagent
Catalyst type
Pd mol%
Time (min)
Temp (°C)
Yield (%)
References
1
2
Ph–Br
Ph–Br
Ph–Br
Ph–Br
Ph–Br
Ph–Br
Ph–Br
Ph–Br
Ph–Br
Ph–Br
Ph–B(OH)2
Ph–B(OH)2
Ph–B(OH)2
Ph–B(OH)2
Ph–B(OH)2
Ph–B(OH)2
Ph–B(OH)2
Ph–B(OH)2
Ph4BNa
Fe3O4@SiO2-NH2-Pd
SiO2-imidazole-Pd
Pd(II)-sepiolite
1
480
180
1440
180
240
35
100
95
95
95
65
98
60
97
86
80
90
93
[40]
1.62
0.001
0.1
[41]
3
130
60
[42]
4
Pd–Schif base@MWCNT
Pd doped KF/Al2O3
Pd@SBA-15/SH
[43]
5
10
100
80
[44]
6
0.05
0.75
0.002
1
[45]
7
SiO2/TEG/Pd
720
240
18
110
120
120
85
[46]
8
Hydroxyapatite@ Pd
Polystyrene@ Pd2+
Schif base alumoxane-Pd
[47]
9
[20]
10
Ph4BNa
0.157
20
This work
1 3

A. Ghorbani-Choghamarani et al.
20. Bai L, Wang JX (2008) Adv Synth Catal 350:315
21. Ghorbani-Vaghei R, Hemmati S, Veisi H (2014) J Mol Catal A
Chem 393:240–247
22. Derakhshan AA, Rajabi L, Karimnezhad H (2012) Powder Tech-
nol 225:156
23. Surivet F, Lam TM, Pascualt JP, Mai C (1992) Macromolecules
25:5742
24. Whitesides GM, Mathias JP, Seto CT (1991) Science 254:1312
25. Rajabi L, Derakhshan AA (2010) Sci Adv Mater 2:163
26. Liu J, Liao X, Shi B (2014) Res Chem Intermed 40:249
27. Rajabi L, Derakhshan AA (2012) Powder Technol 226:117
28. Obrey SJ, Barron AR (2002) Macromolecules 35:1499
29. Tobisu M, Xu T, Shimasaki T, Chatani N (2011) J Am Chem
Soc 133:19505
Stille and Heck reactions. This nanocatalyst is efective
for reaction of various aryl halides (including chlorides,
bromides and iodides) with NaBPh4, Ph3SnCl and butyl
acrylate. In addition, this nanocatalyst could be recovered
and reused at least for six times without signiicant loss of
catalytic activity. Pd leaching from SBA-Pd° is very negli-
gible for this coupling reaction.
Acknowledgements Authors thank Ilam University and Iran
National Science Foundation (INSF) for inancial support of this
research project.
30. Li JH, Liang Y, Xie YY (2005) Tetrahedron 61:7289
31. Kantam ML, Srinivas P, Yadav J, Likhar PR, Bhargava S (2009)
J Org Chem 74:4882
References
32. Ghorbani-Choghamarani A, Tahmasbi B, Moradi P (2016) Appl
Organometal Chem 30:422
33. Leng Y, Liu J, Zhang C, Jiang P (2014) Catal Sci Technol 4:997
34. Landry CC, Pappe N, Mason MR, Apblett AW, Tyler AN,
Maclnnes AN, Barron AR (1995) J Mater Chem 5(2):331
35. Abdel-Latif SA, Hassib HB, YM Issa (2007) Spectrochim Acta
A 67:950
36. Peng YY, Liu J, Lei X, Yin Z (2010) Green Chem 12:1072
37. Ghorbani-Choghamarani A, Norouzi M (2016) Appl Organo-
metal Chem 30:140
38. Bai L, Wang JX (2007) Adv Synth Catal 350:315
39. Binns EH, Squire KH (1962) Trans Faraday Soc 58:762
40. Choi KH, Shokouhimehr M, Sung YE (2013) Bull Korean Chem
Soc 34(5):1477
41. Mubofu EB, Clark JH, Macquarrie DJ (2001) Green Chem 3:23
42. Shimizu KI, Kan-no T, Kodama T, Hagiwara H, Kitayama Y
(2002) Tetrahedron Lett 43:5653
43. Navidi M, Rezaei N, Movassagh B (2013) J Organomet Chem
743:63
44. Kabalka GW, Pagni RM, Hair CM (1999) Org Lett 1:1423
45. Rostamnia S, Lamei K, Pourhassan F (2015) RSC Adv 5:1033
46. Kim N, Kwon MS, Park CM, Park J (2004) Tetrahedron Lett
45:7057
47. Mori K, Yamaguchi K, Hara T, Mizugaki T, Ebitani K, Kaneda
K (2002) J Am Chem Soc 124:11572
1. Suzuki A (2003) Modern arene chemistry, Ch. 3. Astruc D (ed)
Wiley-VCH, Weinheim
2. Miyaura N, Suzuki A (1995) Chem Rev 95:2457
3. Suzuki A (1999) J Organomet Chem 576:147
4. Baudoin O, Cesario M, Guenard D, Gueritte F (2002) J Org
Chem 67:1199
5. Hassan J, Se’vignon M, Gozzi C, Schulz E, Lemaire M (2002)
Chem Rev 102:1359
6. Walker JA, Murry JA, Soheili A, Ceglia S, Springield SA,
Bazaral C, Dormer PG, Hughes DL (2005) Tetrahedron 61:6330
7. Kertesz M, Choi CH, Yang S (2005) Chem Rev 105:3448
8. Baleizao C, Corma A, Garcia H, Leyva A (2004) J Org Chem
69:439
9. Wolfe JP, Singer RA, Yang BH, Buchwald SL (2000) J Am
Chem Soc 122:4020
10. Wolfe JP, Buchwald SL (1999) Angew Chem Int Ed 38:2413
11. Grasa GA, Hillier AC, Nolan SP (2001) Org Lett 3:1077
12. Martin R, Buchwald SL (2008) Acc Chem Res 41:1461–1473
13. Karimi B, Fadavi Akhavan P (2011) Chem Commun 47:7686
14. Rostamnia S, Xin H (2013) Appl Organomet Chem 27:348
15. Zhang R, Ding W, Tu B, Zhao D (2007) Chem Mater 19:4379
16. Mandal S, Roy D, Chaudhari RV, Sastry M (2004) Chem Mater
16:3714
17. Wu CD, Hu A, Zhang L, Lin WB (2005) J Am Chem Soc
127:8940
18. Pan X, Fan Z, Chen W, Ding Y, Luo H, Bao X (2007) Nat Mater
6:507
19. Castillejos E, Debouttiere PJ, Roiban L, Solhy A, Martinez V,
Kihn Y, Ersen O, Philippot K, Chaudret B, Serp P (2009) Angew
Chem Int Ed 48:2529
1 3