A new Pd(II)-supported catalyst on magnetic SBA-15 for C-C bond formation via the Heck and Hiyama cross-coupling reactions

Article abstract of DOI:10.1002/aoc.6078

Magnetic mesoporous silica composite (MNP@SiO₂-SBA) was obtained via embedding magnetite nanoparticles between SBA-15 channels. It was silylated with N-(3-(trimethoxysilyl)propyl)picolinamide (TMS-PCA) and then complexed with Pd(II). The obtained supported Pd(II) catalyst (MNP@SiO₂-SBA-PCA) was characterized by conventional methods. The prepared magnetic catalyst showed high activity in the Heck and Hiyama reactions under optimal reaction conditions, including solvent, amount of catalyst, base, and temperature. Aryl bromides and iodides showed better results than aryl chlorides, and the catalyst exhibited noticeable stability and reused several times.

Full text of DOI:10.1002/aoc.6078

Received: 30 May 2020
DOI: 10.1002/aoc.6078
Revised: 2 October 2020
Accepted: 5 October 2020
F U L L P A P E R
A new Pd(II)-supported catalyst on magnetic SBA-15 for
C C bond formation via the Heck and Hiyama
cross-coupling reactions
Leila Rahimi1
Behzad Koohi-Zargar3
| Yagoub Mansoori1,2
| Ayat Nuri1
|
| Dolores Esquivel4
1Department of Applied Chemistry,
Faculty of Science, University of
Mohaghegh Ardabili, Ardabil, Iran
2Nanoscience and Nanotechnology
Research Group, Faculty of Science,
University of Mohaghegh Ardabili,
Ardabil, Iran
Magnetic mesoporous silica composite (MNP@SiO2-SBA) was obtained via
embedding magnetite nanoparticles between SBA-15 channels. It was silylated
with N-(3-(trimethoxysilyl)propyl)picolinamide (TMS-PCA) and then
complexed with Pd(II). The obtained supported Pd(II) catalyst (MNP@SiO2-
SBA-PCA) was characterized by conventional methods. The prepared magnetic
catalyst showed high activity in the Heck and Hiyama reactions under optimal
reaction conditions, including solvent, amount of catalyst, base, and tempera-
ture. Aryl bromides and iodides showed better results than aryl chlorides, and
the catalyst exhibited noticeable stability and reused several times.
3Farabi Chemical and Medical
Laboratory, Ardabil, Iran
4Departamento de Química Orgánica,
Instituto Universitario de, Nanoquímica
IUNAN, Facultad de Ciencias,
Universidad de Córdoba, Campus de
Rabanales, Edificio Marie Curie, Córdoba,
Spain
K E Y W O R D S
Heck reaction, heterogenized catalyst, Hiyama reaction, magnetic mesoporous silica
Correspondence
Yagoub Mansoori, Department of Applied
Chemistry, Faculty of Science, University
of Mohaghegh Ardabili, Ardabil, Iran.
Email: ya_mansoori@uma.ac.ir;
ya_mansoori@yahoo.com
Funding information
Graduate Council of the University of
Mohaghegh Ardabili
1 | INTRODUCTION
years, the preparation of a broad spectrum of supported
Pd(II) complexes with different ligands as catalysts for
Heck, Hiyama, Suzuki, Sonogashira, and Stille cross-
coupling reactions are those reactions that they are
widely used for C C bond formation in the modern
organic synthesis.[1] Among various metals for catalyzing
these reactions, palladium is more preferred and widely
used due to enhanced activity and selectivity.[2] Among
the Pd-involved organic preparations, the Heck reaction
is one of the most noted transformations. Nowadays,
Heck-type chemistry is a known method to assemble
molecules via the formation of C C bonds in both
conventional and modern organic syntheses.[3] In recent
coupling reactions have been reported. Improving the
reaction yields and decreasing reactions time, processes
costs, and byproducts are some of the results of these
investigations.[4] On the other hand, the Hiyama cross-
coupling reaction enjoys from easily prepared, accessible,
low cost, and stable starting materials (halogenated
hydrocarbons and organosilicon compounds).[5]
In recent years, anchoring catalysts on MNPs have
been extensively studied.[6,7] Magnetite nanoparticles are
nontoxic, highly dispersible, and biocompatible, and
they have a high surface-to-volume ratio. Furthermore,
Appl Organomet Chem. 2020;e6078.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6078

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RAHIMI ET AL.
MNP-supported catalysts enjoy the benefit of easy and
rapid separation from different reaction mixtures mag-
netically.[8,9] It is highly recommended to coat MNPs
before any treatment because they agglomerate intrinsi-
cally due to strong magnetic dipole–dipole interactions
and high specific surface area.[10,11] The most popular
way to overcome this problem is using MNPs in the form
of a composite with other metal oxides. Combinations of
MNPs with different forms of mesoporous silica such as
MCMs and SBAs have been widely investigated in recent
years.[12,13] There are plenty of reports on the incorpora-
tion of magnetic mesoporous for preparing magnetically
retrievable supported catalyst in the literature.[14,15] For
example, Tai et al. reported the preparation of sulfonic
acid-functionalized magnetic mesoporous silica, which
has been used in the esterification of propionic acid. The
activity of the prepared nanocomposite is high, and the
catalyst can be recovered quickly and reuse several
times.[16] In another work, Snoussi et al. prepared a
core/double-shell nanocomposite sonochemically, that is,
MNP@NH2-mesoporous silica@polypyrrole/Pd. The
obtained magnetic mesoporous composite showed high
reactivity in the NO2 group reduction and degradation of
methyl orange.[17] Recently, we reported the synthesis of
a new NHC-Pd(II) complex supported on magnetic meso-
porous silica. The supported catalyst showed enhanced
activity in C C bond formation reactions.[18,19]
MNPs provides high density of catalytic sites for
enhanced activity along with the advantage of simple
magnetic decantation of the catalyst at the end of reac-
tion. The magnetic nanocomposite was silylated by
TMSP-PCA and then treated with a Pd(II) solution in
EtOH to give a new Pd(II)-supported magnetic catalyst
(MNP@SiO2-SBA-PCA). Therefore, the supported cata-
lyst obtains via simple silylation and subsequent com-
plexation reactions. The obtained recoverable magnetic
catalyst can efficiently catalyze Heck and Hiyama
reactions than most reported catalysts reported in the
literature.
2 | EXPERIMENTAL
2.1 | Materials
MNPs[20] and MNP@SiO2-SBA nanocomposite[19,21] were
prepared according to the literature reported methods.
Laboratory grade solvents used in this work were dried
according to the procedures reported in literature.[22] The
remaining chemicals were obtained from Merck and used
as received.
2.2 | Instruments
In the present study, the magnetic mesoporous
nanocomposite was obtained via embedding the MNPs
between mesoporous silica channels. The combination of
SBA-15 porous structure with the magnetic property of
A PerkinElmer RXI spectrophotometer was used for
recording the FT-IR spectra. Sample concentrations in
the KBr pellets were 2 w/w%. NMR spectra were
SCHEME 1 Synthesis of supported MNP@SiO2-SBA-PCA-Pd(II)

RAHIMI ET AL.
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obtained on Bruker Avance 400 MHz and Bruker Avance
300 MHz spectrophotometers using tetramethylsilane
(TMS) and locked on CDCl3. TGA curves were recorded
on a Linseis STA PT 1000 for the powdered samples
(scanning rate 10ꢀC/min). XRD measurements were done
on a diffractometer (Philips, X-Pro) at room temperature.
The instrument was equipped with a X-ray radiation
source using Cu Kα (λ = 0.15406 nm). The diffractograms
were obtained in 2θ range of 10–80ꢀ with scanning
rate 1ꢀ/min. The SEM and TEM images were recorded
on LEO 1430VP and Zeiss EM10C (acceleration
voltage = 80 kV) instruments, respectively. A vibrating
sample magnetometer with a maximum magnetic field of
10 kOe (VSM, Maghnatis Daghigh Kavir Co.) was used
for magnetization measurements at room temperature.
product as a highly viscous yellow oil. The FT-IR
spectrum of the product was in accordance with the
literature.
2.4 | Synthesis of MNP@SiO2-SBA-PCA
TMSP-PCA obtained in Section 2.3 were added
dropwise to the dispersion of magnetic nanoparticles of
MNP@SiO2-SBA (1.000 g) in 40 ml of toluene and
2.3 | Synthesis of N-(3-(trimethoxysilyl)
propyl)picolinamide (TMSP-PCA)
TMSP-PCA was prepared according to the method
described by Singh et al.[23] In a round-bottomed flask,
pyridine-2-carboxylic acid (1.000 g, 8.00 mmol) and a cat-
alytic amount of N,N-dimethylformamide (three drops)
were dissolved in the excess amount of freshly distilled
thionyl chloride (5 ml) at 0ꢀC under an argon atmosphere
and then refluxed for 3 h. Thionyl chloride was distilled
off, and the residue was washed with dry petroleum ether
(10 ml) and then dried in a vacuum to give pyridine-
2-carbonyl chloride. The obtained product was suspended
in sodium dried THF (30 ml), and triethylamine (3.37 ml,
24 mmol) was added at 0ꢀC under argon. After stirring
for 15 min, 3-aminopropyltrimethoxysilane (1.58 ml,
8.00 mmol) was added slowly, refluxed for 24 h, cooled to
room temperature, and then filtered. The solvent was
rotary evaporated to leave the corresponding silane
FIGURE 2 Portion FTIR spectra: (a) MNP@SiO2-SBA-PCA
and (b) MNP@SiO2-SBA-PCA-Pd(II)
FIGURE 1 FT-IR spectra
(KBr) of (a) MNP@SiO2-SBA,
(b) MNP@SiO2-SBA-PCA, and
(c) TMSP-PCA™

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FIGURE 3 High resolution XPS spectrum of MNP@SiO2-SBA-PCA-Pd(II): (a) survey spectrum, (b) C 1 s region, (c) Ns 1 s region, and
(d) Pd 3d5/2 and Pd 3d3/2 core levels
FIGURE 4 TGA thermograms
(N2 atmosphere, scan rate of 10ꢀC/min) of
(a) MNP@SiO2-SBA and (b) MNP@SiO2-
SBA-PCA-Pd(II)

RAHIMI ET AL.
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refluxed for 24 h. The particles were collected magneti-
cally, washed thoroughly with ethanol and acetone, and
then dried.
of dry dimethylsulfoxide (DMSO) for 8 min. Aryl halide
(0.2 mmol), triethoxyphenylsilane (0.2 mmol), and Et3N
(0.4 mmol) were then added, and the mixture was
stirred at 120ꢀC. The reaction was followed by TLC, and
upon completion, the catalyst was removed, and the
2.5 | Synthesis of MNP@SiO2-SBA-PCA-
Pd(II)
PCA functionalized magnetic mesoporous silica (1.000 g)
was dispersed in a PdCl2 (0.080 g, 0.45 mmol) solution in
EtOH (8 ml) in an ultrasonic bath for 15 min. The
suspension was stirred at room temperature for 12 h. The
catalyst was decanted magnetically, washed thoroughly
with EtOH, and then dried in a vacuum.
2.6 | General procedure for the Heck
reaction
Typically, the supported catalyst (0.2 mol%) was dis-
persed in 1 ml N-methylpyrrolidone (NMP) through
8 min ultrasonication. Olefin (1.00 mmol), aryl halide
(1.00 mmol), and NaOAc (1.50 mmol) were then
added, and the reaction mixture was stirred at 120ꢀC;
the catalyst was magnetically decanted after comple-
tion of the reaction (followed by TLC), and the mix-
ture was analyzed by GC. The samples for NMR
analysis were chromatographed on glass plates covered
by silica gel. Please see the supporting information for
the NMR spectra.
2.7 | General procedure for the Hiyama
reaction
FIGURE 6 SEM images of (a) MNPs and (b) the supported
complex
In a 25 ml round-bottom flask, the magnetic catalyst
(1.56 mol%) was dispersed in an ultrasonic bath in 1 ml
FIGURE 5 Low angle powder XRD patterns of (a) magnetic
SBA-15 and (b) the supported complex
FIGURE 7 TEM image of magnetic SBA-15

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RAHIMI ET AL.
residue was chromatographed on glass plates covered by
silica gel.
MNPs between regular SBA channels.[19,24] TMSP-
PCA
obtained
from
the
reaction
between
3-aminopropyltrimethoxysilane (APTMS) and picolinoyl
chloride[23] was used for the silylation of MNP@SiO2-SBA.
The functionalized magnetic composite was subsequently
treated with an ethanolic solution of PdCl2 in order to
prepare MNP@SiO2-SBA-PCA-Pd(II) (Scheme 1).
3 | RESULTS AND DISCUSSION
3.1 | Catalyst preparation
The FT-IR spectra of the MNP@SiO2, MNP@SiO2-
SBA-PCA, and SP-PCA™ are presented in Figure 1a–c.
Figure 1a shows the characteristic peak of magnetite at
570 cm−1. The strong absorption band observed at
1086 cm−1 (νas Si O Si) reveals the formation of
MNP@SiO2 nanocomposite.[25] Figure 1b confirms the
presence of characteristic peaks related to magnetite and
silylating compound in the silylated magnetic meso-
porous nanoparticles. The vibrations related to C N
bending, C O stretching, and NH stretching appeared at
1558, 1646, and 3387 cm−1, respectively. The stretching
vibrations related to aliphatic and aromatic C Hs are
also observed at 2928 and 3058 cm−1, respectively.
Figure 2a,b shows the FT-IR spectra of the MNP@SiO2-
SBA-PCA and the supported Pd(II) complex, respectively.
As it can be seen, the C O stretching band is shifted to
Magnetite nanocomposite of mesoporous SBA
(MNP@SiO2-SBA) was prepared via embedding
lower frequencies by 18 cm−1 and appeared at 1628 cm−1
.
This can be attributed to weakening of C O bonds upon
coordination to Pd(II) ions.
FIGURE 8 Wide angle powder XRD patterns of (a) MNPs and
(b) MNP@SiO2-SBA-PCA-Pd(II)
FIGURE 9 Magnetization curves for the MNP, MNP@SiO2, and MNP@SiO2-SBA-PCA-Pd(II)

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Surface qualitative elemental analysis at random
points by EDX confirmed the presence of palladium
atoms. Please see Figure S1.
XPS analysis was utilized to confirm the incorpora-
tion of the metal and evaluate the oxidation state of Pd
in the catalyst. Figure 3a–d show the high-resolution
survey, C1s, N1s, and Pd3d spectra of MNP@SiO2-SBA-
PCA-Pd(II). The high resolution C1s spectrum is fitted
with three components at 284.7, 286.1, and 288.0 eV,
which are assigned to C H/C C/Car, C N, and
TABLE 1 Physical properties of
the prepared materials
MNP@SiO2-SBA
Sample
D
pore (nm)
pore volume (cm3 g−1
)
SBET (m2 g−1
482.9
)
7.63
6.74
0.77
0.33
MNP@SiO2-SBA-PCA-Pd(II)
151.7
TABLE 2 Optimization of conditions for the Heck reactiona
Entry
1
Solvent
Ethyl acetate
Methanol
CHCl3
CH3CN
EtOAc
EtOH
DMF
Pd (mol%)b
0.12
0.12
0.12
0.12
0.12
0.12
0.12
0.12
0.12
0.12
0.20
0.27
0.20
0.20
0.20
0.20
0.20
0.20
0.20
0.20
—
Base
ArX:Sty.
1:1e
1:1e
1:1e
1:1e
1:1e
1:1
1:1e
1:1e
1:1e
1:1e
1:1
Temperature
Conversion (%)c
TON/TOF (h−1 d
)
f
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Et3N
—
—
—
f
2
—
—
—
f
3
—
—
—
f
4
—
—
—
f
5
—
—
—
f
6
—
—
—
7
120
120
120
120
120
120
120
120
120
120
120
120
80
20.5
20.9
18.1
85.3
90.2
92.9
68.4
85.0
17.0
82.5
96.0
94.0
—
315/126
321/129
278/111
1312/524
462/185
340/136
351/140
435/174
87/35
423/136
492/197
482/241
—
8
DMAc
DMSO
NMP
9
10
11
12
13
14
15
16
17
18
19
20
21
NMP
NMP
1:1
NMP
1:1
NMP
CsF
1:1
NMP
Pyridine
NaOAcg
NaOAc
NaOAch
NaOAc
NaOAc
NaOAc
1:1
NMP
1:1
NMP
NMP
1:1
1:1
NMP
1:1
NMP
1:1
100
120
—
—
NMP
1:1
—
—
Optimal reaction conditions are in bold.
aReaction conditions: 1-bromonaphthalene (1.00 mmol), styrene (1.00 mmol), solvent (1.0 ml), base (1.50 mmol), and reaction time 2.5 h.
bThe palladium loading is 0.39 mmol g−1 (4.15 wt%) based on atomic absorption spectroscopy measurement.
cDetermined by GC analysis.
dTurn over number (TON): the number of moles of desired product/the number of moles of metal active sites. Turn over frequency (TOF): the number of
moles of reactant converted/(the number of moles of metal active sites × time in hours).
e1-Bromonaphthalene (3.00 mmol), styrene (3.00 mmol), solvent (2.0 ml), base (4.50 mmol), and reaction time 2.5 h.
fReflux temperature.
g1.00 mmol.
h2.00 mmol.

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RAHIMI ET AL.
C O/C N species, respectively (Figure 3b).[26–28] The
N1s spectrum of MNP@SiO2-SBA-PCA-Pd(II) is fitted
with two components assigned to N C (399.5 eV) and
N H/N C (400.7 eV), respectively (Figure 3c). This
spectrum confirms the successful surface silylation of
MNP@SiO2-SBA by TMSP-PCA. The high-resolution
Pd3d spectrum exhibits two well-resolved peaks cen-
tered at 338.1 and 343.5 eV, which are assigned to
Pd3d5/2 and Pd3d3/2, respectively (Figure 3d). These
observed binding energy peaks are characteristic of pal-
ladium in a +2-oxidation state.[29–31] Therefore, it may
be conclude that the PCA-functionalized magnetic SBA
prevents aggregation of Pd species and formation of
Pd(0) particles.
aggregated probably due to adsorption of water molecules
by surface silanol groups.[35]
The image obtained by TEM also confirmed the
ordered structure of magnetic SBA-15 (Figure 7). Highly
ordered arrays of 1D mesoporous channels in which
Thermal stability of the supported catalyst and
estimation of the loaded complex were studied by ther-
mogravimetric analysis (TGA), Figure 4. MNP@SiO2-
SBA shows a mass loss of about 2.02% from ambient
temperature to 590ꢀC, which can be attributed to the
removal of surface bound physically adsorbed H2O
molecules and chemical dehydration of silanol groups,
Figure 4a.[32] Under the same condition, a very distinct
mass loss of about 26.84% is observed for the supported
complex, mainly related to the thermal breakdown of the
complex from ambient temperature to 400ꢀC along with
the removal of H2O molecules until 590ꢀC, Figure 4b.
Therefore, the loaded amount of the complex can be
estimated by subtracting these two values (4m = 24.82%
or 248.2 mg g−1 of magnetic SBA-15).
The loaded amount of palladium was 0.39 mmol g−1
(4.15 wt%) based on atomic absorption spectroscopy
measurement.
The low-angle XRD patterns of the magnetic SBA-15
and supported catalyst are shown in Figure 5a,b. The
characteristic peak corresponding to (100) diffraction of
ordered mesoporous 2D hexagonal (p6mm) structure is
seen at 2θ = 1.06ꢀ.[33] In the diffraction pattern of
MNP@SiO2-SBA-PCA, this peak is also displayed with
low intensity, Figure 5b. It means that the ordered meso-
porous structure is maintained. The formation of the
Pd(II) complex inside the channels may be responsible
for attenuation of the peak intensity. The low intensity
peaks relating to (110) and (200) diffractions at
2θ = 1.58ꢀ and 1.82ꢀ of pure SBA-15 are absent in the
Figure 5a,b, because the ordering of hexagonal channels
is reduced due to the presence of magnetite between the
channels.[24,34]
The SEM images of the MNPs and supported catalyst
are shown in Figure 6a,b, respectively. The obtained
MNPs have a uniform spherical morphology with diame-
ters below 50 nm. The particles of the supported catalyst
have a uniform size distribution and possess diameters
greater than 100 nm (Figure 6b). These particles are
FIGURE 10 Optimization of the Heck reaction conditions:
(a) solvent, (b) catalyst loading, and (c) base. Reaction conditions:
1-bromonaphthalene (1.0 mmol), styrene (1.0 mmol), and
solvent (1 ml)

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MNPs with 20 to 50 nm diameter are located between the
channels of MNP@SiO2@SBA are seen in this image.
Figure 8a,b shows the XRD patterns of MNP and
MNP@SiO2-SBA-PCA-Pd(II). Both samples exhibit
well-resolved six characteristic diffraction peaks that can
be indexed as (220), (311), (400), (422), (511), and (440)
planes associated with cubic magnetite nanoparticles
(JCPDS-ICDD Copyright 1938, file No. 01-1111) with the
Fd-3m space group.[36] However, due to reposing of
MNPs between the highly congested channels of meso-
porous silica, intensities of these characteristic diffraction
peaks were attenuated in the pattern of supported cata-
lyst, Figure 8b.
Figure 9 shows the hysteresis loops of MNP,
MNP@SiO2, and MNP@SiO2-SBA-PCA-Pd(II) at room
temperature. Superparamagnetic behavior of the samples
is shown by small remanence, hysteresis, coercivity
values, and narrow width of the loop, as seen in the
inset of Figure 9.[37] Dropping the maximal saturation
magnetization of supported catalyst may be due to the
entangling of MNPs between SBA channels.
The results for surface analyses by Brunauer–
Emmett–Teller (BET) are summarized in Table 1. The
BET surface area and average values of pore diameter
and pore volume of MNP@SiO2-SBA are 482.9 m2 g−1
,
7.63 nm, and 0.77 cm3 g−1
corresponding parameters in the supported catalyst are
dropped to 151.7 m2 g−1, 6.74 nm, and 0.33 cm3 g−1
,
respectively. The
,
respectively. Therefore, it can be concluded that the sup-
port of PCA-Pd(II) complex inside the pores of SBA-15
is performed successfully without blocking the intra-
channels space by MNPs. Therefore, molecules can
readily slip the channels for subsequent transformations.
For more discussion and isotherms (Figure S2a,b), please
see the supporting information.
3.2 | Heck and Hiyama reactions
Styrene and 1-bromonaphthalene were chosen as the
model compounds for optimizing the Heck coupling
reaction conditions. Reaction parameters such as the
TABLE 4 Optimization of conditions for the Hiyama reactiona
Entry
1
Solvent
DMF
Pd (mol%)
1.95
Base
Et3N
Temperature (ꢀC)
Conversion (%)b
90.0
TON/TOF (h−1
46.1/11.5
38.2/9.56
41.1/10.3
28.5/7.11
20.8/5.20
—
)
120
120
120
120
120
120
120
120
100
Reflux
Reflux
120
120
120
80
2
DMF
1.95
Et3N c
NaOH
TBAB
Cs2CO3
NaOAc
K2CO3
Et3N
74.6
3
DMF
1.95
80.1
4
DMF
1.95
55.5
5
DMF
1.95
40.5
6
DMF
1.95
Trace
Trace
95.0
7
DMF
1.95
—
8
DMAc
DMF/H2O(1:1)
EtOAc
Toluene
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
1.95
48.7/12.2
—
9
1.95
Et3N
Trace
Trace
Trace
97.0
10
11
12
13
14
15
16
17
1.95
Et3N
—
1.95
Et3N
—
1.95
Et3N
49.8/12.4
33.3/8.32
61.5/15.4
—
2.92
Et3N
97.3
1.56
1.56
Et3N
Et3N
96.0
Trace
Trace
96.4
1.56
Et3N
100
140
—
1.56
Et3N
61.8/15.4
Optimal reaction conditions are in bold.
aReaction conditions: iodobenzene (0.2 mmol), triethoxyphenylsilane (0.2 mmol), solvent (1.0 ml), base (0.4 mmol), and reaction time 4 h.
bIsolated yields.
cEt3N (0.2 mmol).

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solvent, catalyst loading, reaction temperature, and base
were studied. The results are shown in Table 2 and
Figure 10a–c. Solvent screening (Entries 1 to 10) shows
that the NMP solvent is the best choice by giving the
highest yield (Entry 10, 85.3% yield) along with using
0.20 mol% catalyst (Entry 11, 90.2% yield). The effect of
the base and its quantity were also evaluated (Entries 11
and 13 to 18). The highest conversion is achieved with
the NaOAc base (Entry 17, 96.0% yield). The amounts of
base higher or lower than 1.5 folds of the reactants
diminish the reaction conversion (Entries 16 and 18). It
should be added that the reaction does not proceed at the
temperatures lower than 120ꢀC and also in the absence
of the catalyst (Entries 19 to 21).
Various aryl halides were subjected to the optimized
reaction conditions with different olefins, Table 3.
As seen, aryl iodides and bromides showed excellent
conversions and TOFs (Entries 1 to 11), excluding
2-bromopyridine and 4-bromoaniline (Entries 12 and 13).
Aryl chlorides showed low reactivities under the applied
reaction conditions (Entries 14 and 17).
In an additional investigation, we decided to examine
our catalytic system in the Hiyama cross-coupling
reaction. Different parameters including base, solvent,
catalyst dosage, and temperature were studied in the cou-
pling reaction of iodobenzene with triethoxyphenylsilane
as a benchmark. The reaction yields were calculated
based on separated product, and the results are tabulated
in Table 4 and Figure 11a–c. As shown in Table 4, Et3N
as the base, DMSO as the solvent, and 1.56 mol% of the
catalyst are the best conditions for Hiyama reaction at
120ꢀC (Entry 14).
Different aryl halides were subjected to the optimized
reaction conditions with triethoxyphenylsilane, Table 5.
As seen, aryl iodides and bromides showed acceptable
results in the most cases (Entries 1 to 6), excluding
p-acetyl-bromobenzene and 2-bromopyridine (Entries
7 and 8). Aryl chlorides also did not show any activity
under the applied reaction conditions (Entries 9 and 11).
The observed moderate yield for 1-Br-naphthalene
(Entry 3) may be attributed to the developing steric
hindrance around the supported Pd reaction center upon
coordination.
The comparison of the prepared magnetic catalyst
with a few literature reported catalysts in the Heck
(Table 6) and Hiyama (Table 7) coupling reactions
reveals that our prepared magnetic catalyst has enhanced
reactivity in the Heck reaction. As for the Hiyama
reaction, the catalyst showed almost similar activity with
the catalysts reported in the literature. The prepared
magnetic catalyst also enjoys magnetic separation as
other important advantage.
3.3 | Recyclability of the catalyst
Supported catalysts are usually prepared via complicated
and expensive routes. Therefore, it is necessary to pay
sufficient attention to retrieving of a used catalyst. The
stability and reusability of the magnetic catalyst were
FIGURE 11 Optimization of the Hiyama reaction conditions:
(a) solvent, (b) catalyst loading, and (c) base. Reaction conditions:
iodobenzene (0.2 mmol), triethoxyphenylsilane (0.2 mmol),
solvent (1 ml)

14 of 18
RAHIMI ET AL.
TABLE 5 Hiyama reaction of arylhalides with triethoxyphenylsilane catalyzed by the supported Pd(II) complexa
mp (ꢀC)
Entry
1
Aryl halide
Product
Found
Reported [Ref.]
Time (h)
TON/TOF (h−1
)
Conversion (%)
68–70
68–70[46]
4
61.5/15.4
96.0
2
3
44–48
44–48[37]
4
5
59.0/14.7
35.3/7.1
92.0
55.1
45
45[37]
4
86–90
86–90[37]
3
61.5/20.5
96.0
5
6
67–69
87–89
68–70[46]
4
6
60.3/15.1
41.7/6.9
94.0
65.0
88–90[47]
7
—
117–123[48]
10
—
Trace
(Continues)

RAHIMI ET AL.
15 of 18
TABLE 5 (Continued)
mp (ꢀC)
Entry
8
Aryl halide
Product
Found
Reported [Ref.]
Time (h)
TON/TOF (h−1
)
Conversion (%)
—
−5[49]
24
—
Trace
9
—
—
52–54[50]
24
24
—
—
Trace
10
38–39[51]
Trace
Trace
11
—
68–70[46]
24
—
aReaction conditions: aryl halide (0.2 mmol), triethoxyphenylsilane (0.2 mmol), catalyst (8.0 mg, 1.56 mol% Pd), Et3N (0.4 mmol), DMSO (1.0 ml), and reaction
temperature 120ꢀC.
TABLE 6 Comparison of the prepared catalyst with other catalysts for Heck cross-coupling reactions from iodobenzene with styrene
Time
(h)
Conversion
(%)
TOF
Entry
Catalyst
Conditions
(h−1
86.5
90.8
)
Ref.
1
2
Agarose-Pd(0)
PdNP-SβCD
Solvent free, Et3N, 120ꢀC
H2O, K2CO3, 100ꢀC
2.0
2.0
90
99
Firouzabadi et al.[52]
Khalafi-Nezhad
et al.[53]
3
4
5
6
7
Palladacycle
DMA, Et3N, 140ꢀC
H2O, Et3N, 100ꢀC
18.0
24.0
6.0
100
23
92
93
80
27.7
0.2
Gruber et al.[54]
Cassez et al.[55]
Mondal et al.[56]
Han et al.[57]
Pd/C particles
Pd-MPTA-1
H2O, Cs2CO3, 100ꢀC
PEG-400, CH3COONa, 80ꢀC
Et3N, DMA, 80ꢀC
217.0
62.0
53.3
Pd (OAc)2 (ligand free)
1.5
1-Carbopalladated
complexes
3.0
Rosol et al.[58]
8
9
Supported NHC complex
NMP, K2CO3, 120ꢀC
NMP, K2CO3, 120ꢀC
2.0
1.0
96
192.0
483.0
Nuri et al.[19]
This work
MNP@SiO2-SBA-PCA-Pd(II)
94.1

16 of 18
RAHIMI ET AL.
TABLE 7 Comparison of the prepared catalyst with other catalysts for Hiyama cross-coupling reactions from iodobenzene with
triethoxyphenylsilane
Conversion
(%)
TOF
Entry Catalyst
Conditions
Time
10 h
(h−1
)
Ref.
59
1
2
3
4
5
Palladium chloride
Toluene, TBAF.3H2O, 100ꢀC
THF, TBAF, 60ꢀC, N2
90
94
80
99
1.8
Fe3O4@SiO2-Pd catalyst
PS-tsu-Pd(II) complex
NCN-Pincer-Pd Complex
10 h
18.8
16.0
1.6
Zhang et al.[60]
Keesara et al.[61]
Marset et al.[62]
Nuri et al.[19]
Ethylene glycol, LiOH.H2O, 100ꢀC 10 h
K2CO3, Glycerol, 100ꢀC
DMF, CsF, 120ꢀC
24 h
The supported NHC Pd(II)
complex
90 min 99
99.9
6
MNP@SiO2-SBA-PCA-Pd(II)
DMSO, Et3N, 120ꢀC
4.0 h 96
15.4
This work
FIGURE 12 Recycling of MNP@SiO2-
SBA-PCA-Pd(II) for the Heck cross-coupling
reaction of 1-bromonaphthalene and styrene
and Hiyama cross-coupling reaction of
iodobenzene triethoxyphenylsilane
tested in the Heck and Hiyama coupling reactions,
Figure 12. After each reaction, the catalyst was collected
magnetically, washed with diethyl ether, and then dried.
As seen, the conversion reaches to 96.0% in the first run
and then slightly dropped to 92.1% during five
consecutive runs of the Heck reaction. Almost
similar results were obtained for the Hiyama reaction,
and the conversion changes from 92.0% to 89.0% during
five consecutive runs. Therefore, it can be concluded
that the prepared supported catalyst is active and
recyclable.
medium for Pd(II) ions and prevents the formation of
aggregated Pd(0) particles. It was also shown that the
prepared supported complex can efficiently catalyze
the Heck and Hiyama cross-coupling reactions and
excellent conversions are obtained. It was also shown
that the catalyst can be retrieved magnetically and reused
several times.
ACKNOWLEDGMENTS
The financial support provided by Graduate Council of
the University of Mohaghegh Ardabili is gratefully
acknowledged.
4 | CONCLUSION
AUTHOR CONTRIBUTIONS
Leila Rahimi: Conceptualization; data curation.
Yagoub Mansoori: Conceptualization; data curation;
formal analysis; funding acquisition; investigation; meth-
odology; project administration; resources; software;
supervision; validation; visualization. Ayat Nuri: Con-
ceptualization; data curation; investigation; methodology;
project administration; supervision. Behzad Koohi-
Zargar: Formal analysis; methodology. Dolores
Esquivel: Data curation; formal analysis.
In summary, the present work reports the synthesis,
characterization, and application of a retrievable mag-
netic catalyst. The catalyst was obtained by supporting a
Pd(II) complex, PCA-Pd(II), onto magnetic mesoporous
silica. It was fully characterized by conventional tech-
niques. XPS analysis reveals that the palladium presents
in a +2-oxidation state in the prepared catalyst. It seems
that the matrix of magnetic SBA acts as a dispersing

RAHIMI ET AL.
17 of 18
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ORCID
Leila Rahimi https://orcid.org/0000-0002-3890-7789
Yagoub Mansoori https://orcid.org/0000-0002-0562-
3704
Ayat Nuri https://orcid.org/0000-0002-8153-1246
Behzad Koohi-Zargar https://orcid.org/0000-0001-5333-
7879
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How to cite this article: Rahimi L, Mansoori Y,
Nuri A, Koohi-Zargar B, Esquivel D. A new Pd(II)-
supported catalyst on magnetic SBA-15 for C C
bond formation via the Heck and Hiyama cross-
coupling reactions. Appl Organomet Chem. 2020;
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.