Extended architectures constructed of thiourea-modified SBA-15 nanoreactor: A versatile new support for the fabrication of palladium pre-catalyst

Article abstract of DOI:10.1002/aoc.5452

We designed and synthesized a novel catalyst consisting of ordered mesoporous silica (SBA-15) functionalized with bis(thiourea) (BTU) linker. The regular and unique pore channels of BTU-SBA-15 ensure proper control of the size and homogeneous distribution of palladium nanoparticles. The physiochemical properties of the hybrid Pd?BTU-SBA-15 pre-catalyst were investigated using various techniques. The proposed catalyst is found to be very active, reusable, stable and scalable, and has excellent reactivity and selectivity for Suzuki and Heck coupling reactions under very mild and sustainable reaction conditions.

Full text of DOI:10.1002/aoc.5452

Received: 9 September 2019
DOI: 10.1002/aoc.5452
Revised: 14 November 2019
Accepted: 28 November 2019
F U L L P A P E R
Extended architectures constructed of thiourea-modified
SBA-15 nanoreactor: A versatile new support for the
fabrication of palladium pre-catalyst
Hassan Alamgholiloo1,2 | Sadegh Rostamnia1
| Nader Noroozi Pesyan2
1Organic and Nano Group (ONG),
We designed and synthesized a novel catalyst consisting of ordered meso-
porous silica (SBA-15) functionalized with bis(thiourea) (BTU) linker. The
regular and unique pore channels of BTU-SBA-15 ensure proper control of
the size and homogeneous distribution of palladium nanoparticles. The
physiochemical properties of the hybrid Pd@BTU-SBA-15 pre-catalyst were
investigated using various techniques. The proposed catalyst is found to be
very active, reusable, stable and scalable, and has excellent reactivity and selec-
tivity for Suzuki and Heck coupling reactions under very mild and sustainable
reaction conditions.
Department of Chemistry, Faculty of
Science, University of Maragheh, PO Box
55181-83111, Maragheh, Iran
2Department of Organic Chemistry,
Faculty of Chemistry, Urmia University,
57159 Urmia, Iran
Correspondence
Sadegh Rostamnia, Organic and Nano
Group (ONG), Department of Chemistry,
Faculty of Science, University of
Maragheh, PO Box 55181-83111,
Maragheh, Iran.
K E Y W O R D S
Email: rostamnia@maragheh.ac.ir,
srostamnia@gmail.com
C–C coupling reaction, heterogeneous catalysisordered mesoporous silicaPd@BTU-SBA-15
Nader Noroozi Pesyan, Department of
Organic Chemistry, Faculty of Chemistry,
Urmia University, 57159 Urmia, Iran.
Email: nnp403@gmail.com
1 | INTRODUCTION
have been applied as efficient catalysts for many
reactions such as cross-coupling, domino reactions,
Within the field of mesoscale nanoarchitecturing,[1]
ordered mesoporous silica (OMS) including the family
of MCM and SBA has attracted increased interest in
recent years because of its unique properties including
narrow pore distribution, high loading and adjustable
pore diameter.[2,3] Because of these properties, numerous
applications of these nanoreactors in different fields have
been explored including sensing,[4,5] chromatography,[6]
drug delivery,[7,8] energy storage[9,10] and catalysis.[11–14]
Recently, an enormous research effort has been made
into the modification of OMS with noble metal
nanoparticles. Incorporation of noble metals such as
gold, palladium and platinum into OMS has been
explored via methods such as impregnation,[15]
dehydrogenation/hydrogenation, oxidation and reduc-
tion, and others. Among carbon–carbon coupling reac-
tions, the Suzuki and Heck reactions due to mild
reaction conditions, insensitivity to moisture, tolerance
of active functional groups and low toxicity are the
most explored examples.[20–23] Numerous investigations
have indicated that supports with functional groups
such as amines,[24] imines,[25] thiols,[2] phosphine[26]
and sulfonic acids[27] could be anchored on the surface
of silica materials and then interacted with Pd NPs for
use in coupling reactions. Very recently, our research
group has explored several silica materials and PMO-
type hybrid support for encapsulation of transition
metal nanoparticles and organic functional groups for
catalytic aims.[14,28,29]
deposition–precipitation,[16]
vacuum
calcination,[17]
hybrid grafting,[18] colloid immobilization,[19] etc.
Palladium nanoparticles (Pd NPs) have been
immobilized on a wide range of solid materials and
In the work reported here, uniform Pd NPs were
synthesized on SBA-15 mesoporous silica and modified
with bis(thiourea) (BTU) ligand. Good affinity between
Appl Organometal Chem. 2020;e5452.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5452

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ALAMGHOLILOO ET AL.
the BTU ligand and the template walls is vitally
important for anchoring and stabilizing the Pd NPs.
Finally, we found that BTU-SBA-15 is not only a superb
scavenger for Pd NPs, but also for both Suzuki and
Heck reactions, there is negligible leaching of Pd into
solution.
slowly to 353ꢀC for 2 hours. A change in the color and
evolution of hydrogen sulfide (H2S) gas from the mixture
showed completion of the synthesis process. Finally, the
reaction was allowed to cool to ambient conditions and
the final product in 78.5% yield was obtained (Scheme 1
and supporting information).
2 | EXPERIMENTAL
2.1 | Characterization
2.3 | Synthesis of BTU-SBA-15
The mesoporous material was synthesized based on our
previous reports of the synthesis of SBA-15 with slight
modifications.[31,32] An amount of 1.0 g of calcined
SBA-15 was dispersed in 25 ml of toluene under an
inert atmosphere. A mixture of the BTU ligand pre-
pared as described above (5.0 mmol, 2.42 ml) was
added dropwise to the reaction. Then, the temperature
was raised to 383 K and allowed to stir for 12 hours
under an inert atmosphere. To remove residual
unreacted ligand, the synthesized BTU-SBA-15 was
purified with absolute EtOH and CH2Cl2 several times,
and finally it was filtered and dried at 353 K during
12 hours. The loading of BTU ligand in the nanoreactor
structure was approximately 54% as measured using ele-
mental analysis with energy-dispersive X-ray spectros-
copy (EDS).
The mesoporous material was characterized using pow-
der X-ray diffraction (XRD) measurements (Philips-PW
1800 diffractometer). Scanning electron microscopy
(SEM) images were recorded with a Hitachi S-4800 field
emission scanning electron microscope. Transmission
electron microscopy (TEM) and elemental mapping
images were obtained using a JEM-2100F with an accel-
erating voltage of 200 kV. The electronic state of metal
present in samples was determined using X-ray photo-
electron spectroscopy (XPS). Fourier transform infrared
(FT-IR) spectra were obtained using a Shimadzu IR-640
spectrometer. Nitrogen adsorption–desorption isotherms
were measured at 77 K with a Quantachrome Autosorb,
from which the specific surface area (SBET) and the aver-
age pore diameter (DP) were calculated using the
multiple-point Brunauer–Emmett–Teller method. 1H
NMR and 13C NMR spectra were recorded with a Bruker
Avance 300 spectrometer. The Pd loading was deter-
mined using inductively coupled plasma atomic emission
spectroscopy (ICP-AES) with a PerkinElmer 2100DV.
2.4 | Preparation of Pd@BTU-SBA-15
PdCl2 (20 mg) and poly(vinyl alcohol) (PVA; PVA
monomer-to-PdCl2 molar ratio = 9:1) were mixed in
50 ml of deionized water and then was stirred for 1 hour
at 273 K. Then, 20 ml of 0.1 M NaBH4 was added
dropwise to the mixture to fabricate a colloidal Pd solu-
tion. Finally, 0.50 g of BTU-SBA-15 prepared as described
above was added to the solution. The mixture reaction
was stirred for 6 hours under ambient conditions. The
Pd@BTU-SBA-15 was filtered and washed several times
with EtOH and CH2Cl2 and dried at 373 K overnight.
The amount of palladium in Pd@BTU-SBA-15 was
3.04 wt% as measured using atomic absorption spectrom-
etry (AAS).
2.2 | Fabrication of BTU ligand
The
synthesis
of
the
BTU
ligand
(N,N0-
bis(3triethoxysilylpropyl)) was performed following our
previously reported methodology with modifications.[30]
Typically, carbon disulfide (CS2; 10 mmol, 600 μl) and
3-aminopropyltriethoxysilane (APTES; 20 mmol, 4.68 ml)
were added to a two-necked 20 ml glass balloon under
inert atmosphere. Then, the temperature was raised
SCHEME 1 Procedure for preparation
of BTU linker

BIS(THIOUREA)-MODIFIED SBA-15 FOR HECK AND SUZUKI REACTIONS
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2.5 | Catalysis with Pd@BTU-SBA-15
(Suzuki and Heck coupling reactions)
thiourea ligand and pore structure of the nanoreactor
play an important role in the good control of the Pd
metal size and homogeneous dispersion, thus enhancing
the catalytic activity for both Suzuki and Heck reactions.
To verify this speculation, FT-IR analysis was utilized
to explore the chemical structure of SBA-15, BTU-SBA-15
and Pd@BTU-SBA-15. As illustrated in Figure 2a, a
broad and small band at 3241 cm−1 corresponded to
N&bond;H stretching. The spectra also contain strong
absorption bands at 2920 and 2852 cm−1 which can be
ascribed to the symmetric and asymmetric stretching
mode of aliphatic C&bond;H bonds, respectively.[14,33–35]
A new peak appears at 936 cm−1 corresponding to
C&bond;N bond, suggesting the successful preparation of
BTU-SBA-15. The porous structure of the resulting mate-
rials was confirmed using nitrogen adsorption–
desorption isotherm measurements. As shown in
Figure 2b, the isotherm is a type IV curve with a hystere-
sis loop in the relative pressure range 0.45–0.9, which
demonstrates a mesoporous structure. As presented in
Figure 2b, immobilization Pd@thiourea into the pore
cage of SBA-15 is evidenced with a simultaneous
decrease of the mesoporous surface area from 670 cm2 g−1
for SBA-15 to 286 cm2 g−1 for Pd@BTU-SBA-15. As calcu-
lated using the Barrett–Joyner–Halenda method, the pore
diameters for native SBA-15 and Pd@BTU-SBA-15 were
6.8 and 4.3 nm, respectively. The small-angle XRD pat-
tern for nanoreactor SBA-15 shows one sharp peak at
2θ = 0.94ꢀ, the peak positions matching well with the
simulated diffraction pattern.[36,37] After BTU ligand
immobilization, this peak was maintained and slightly
shifted to 2θ = 0.98ꢀ, which originates from the periodic-
ity of the nanoreactor structure. A comparison of the
XRD pattern of Pd@BTU-SBA-15 with that of SBA-15
revealed a shift to higher 2θ angles, although other main
diffraction peaks showed some slight decreases of peak
The Suzuki reaction was carried out under ambient con-
ditions in a 20 ml Schlenk tube containing 1 mmol of aryl
halide, 1.1 mmol of arylboronic acid, 2 mmol of K2CO3
and Pd@BTU-SBA-15 (0.30 mol%) in 5 ml od deionized
water. The resultant mixture was stirred at room temper-
ature for 2 hours, diluted with absolute EtOH and cen-
1
trifuged. H NMR and 13C NMR spectroscopy was used
to identify the main product. For the Heck reaction,
1 mmol of aryl halide and 1.2 mmol of alkene were added
to a mixture of 2 mmol of K2CO3 and Pd@BTU-SBA-15
catalyst (0.25 mol%) in 5 ml of dimethylformamide
(DMF)–H2O (1: 1 v/v). The resultant mixture was reflux
at 120ꢀC for 12 hours. Finally, desired product was
extracted followed by analysis according to the method
described above. To determine the catalyst durability for
both Suzuki and Heck reactions, the Pd pre-catalyst was
centrifuged after each cycle of the reactions. The Pd cata-
lyst was washed thoroughly with absolute EtOH and
CH2Cl2, followed by drying at 373 K under vacuum
condition.
3 | RESULTS AND DISCUSSION
In the present study, we designed BTU-functionalized
SBA-15 for immobilization of ultrafine Pd NPs. In fact,
we demonstrate a facile preparation method for the syn-
thesis of three-dimensional OMS with Pd NPs loaded on
both external and internal channels of the mesopores. By
embedding the organic ligands within the pore walls, the
hydrophobic–hydrophilic properties of the nanoreactor
are well controlled. A schematic illustration of the syn-
thesis of Pd@BTU-SBA-15 is shown in Figure 1. Also, the
FIGURE 1 General pathway for
preparation of Pd@TU-SBA-15

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ALAMGHOLILOO ET AL.
FIGURE 2 (a) FT-IR spectra of
SBA-15 and Pd@BTU-SBA-15.
(b) Nitrogen adsorption–desorption
profiles of SBA-15, BTU-SBA-15 and
Pd@BTU-SBA-15. (c) Small-angle XRD
patterns of SBA-15, BTU-SBA-15 and
Pd@BTU-SBA-15. (d) TGA of Pd@BTU-
SBA-15
intensities with the immobilization of Pd NPs, due to the
partial filling by the grafting guest molecules. To estimate
the ratio of the organic moiety to silica in the Pd@BTU-
SBA-15 structure, thermogravimetric analysis (TGA) was
conducted (Figure 2d). Based on the TGA, the pure SBA-
15 nanoreactor had a 5.11% weight loss at temperatures
up to 800ꢀC, which was attributed to the loss from the
surface decomposition of silanol groups and a small
amount of adsorbed water. In the case of BTU@SBA-15
and Pd@BTU-SBA-15, the weight losses were 17.36 and
22.53 wt%, respectively, due to the decomposition of
small-molecule functionalized organic matter.
SBA-15 morphology barely shows the Pd NPs inside
and outside of the SBA-15 pores. The TEM images can
provide more detailed information that enables one to
observe the presence of porosity and Pd NPs on BTU-
SBA-15 (Figure 4c,f). As shown in Figure 4d, the Pd
NPs in Pd@BTU-SBA-15d was found to be ultra-small,
having an average size ranging from 1.8 to 4 nm. When
only SBA-15 was utilized instead of the BTU-
functionalized SBA-15 for the deposition of Pd NPs,
particle sizes of greater than 5.5 nm in the nanoreator
were found.[43,44] Also, SEM–EDS analysis was per-
formed for the mesoporous materials. Based on this
The electronic states of metallic Pd particles in
Pd@BTU-SBA-15 were identified through XPS analysis
(Figure 3). The XPS spectrum of the Pd (3d) core levels
shows to two intense photopeaks with maximum binding
energy values of 337.2 and 342.5 eV ascribed to the Pd
3d5/2 and 3d3/2 doublet, respectively. These binding
energy values are consistent with the presence of palla-
dium species in the metallic state and are in agreement
with the theoretical value.[38–42] Therefore, these analyses
demonstrate that immobilized Pd NPs were thoroughly
reduced in the nanoreactor structure.
The morphology of the obtained mesostructure was
investigated through SEM and TEM, and the elemental
composition studied using EDS as shown in Figure 4.
SEM images exhibit the rod-like morphology of BTU-
SBA-15 and even Pd growth in surface mesopores
(Figure 4a,d). But after the deposition of Pd NPs, the
FIGURE 3 XPS pattern of Pd@BTU-SBA-15

BIS(THIOUREA)-MODIFIED SBA-15 FOR HECK AND SUZUKI REACTIONS
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FIGURE 4 (a) SEM and (c) TEM images of BTU-SBA-15. (d) SEM and (f) TEM images of Pd@TU-SBA-15. (b, e) magnified SEM
images of BTU-SBA-15 and Pd@BTU-SBA-15. (j, h) EDS analysis of BTU-SBA-15 and Pd@BTU-SBA-15
analysis, palladium, sulfur and nitrogen atoms are pre-
sent in the structure of Pd@BTU-SBA-15 which exhibits
purity and successful deposition of Pd to SBA-15. The
amount of Pd in the mesoporous material structure was
determined using AAS. According to this, the amount
of Pd was 3.04 wt%.
FIGURE 5 (a) Reaction progress in
various solvents under similar conditions.
(b) Base effect under optimized conditions for
Suzuki reaction catalyzed by Pd@BTU-SBA-15
at room temperature. (c) Effect of temperature
on progress of Suzuki coupling reaction.
(d) Kinetic study and effect of amount of
catalyst on progress of Suzuki coupling reaction

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ALAMGHOLILOO ET AL.
TABLE 1 Substrate scope for Suzuki couplinga
Entry
1
Ar
Hal
I
R
Conversion (%)
Yield (%)b
98(87)
97
Ph
H
>99(89)c
2
Ph
I
p-Me
H
98
3
p-Me-Ph
o-Me-Ph
p-MeO-Ph
p-MeO-Ph
o-MeO-Ph
o-MeO-Ph
p-MeCO-Ph
p-MeCO-Ph
m-NO2-Ph
Ph
I
>99
98
98
4
I
H
96
5
I
H
98
97
6
I
m-Me
H
97
96
7
I
98
97
8
I
m-Me
H
93
95
9
I
99
98
10
11
12
13
14
15
16
17
18
19
20
21
I
m-Me
H
98
98
I
97
96
Br
Br
Br
Br
Br
Br
Cl
Cl
F
H
97(87)
95
96(86)
88
o-MeO-Ph
m-CHO-Ph
m-NO2-Ph
p-MeCO-Ph
p-MeCO-Ph
m-CHO-Ph
p-MeCO-Ph
Ph
m-Me
H
90
87
p-Me
H
89
85
97
97
m-Me
H
96
95
66(51)
78
59(50)
69
m-Me
m-Me
H
Trace
Traced
Trace
Trace
Ph
I
aReaction conditions: 1 (1.0 mmol), 2 (1.1 mmol), catalyst (0.3 mol% Pd), K2CO3 (2.0 mmol), deionized water (5 ml), 25ꢀC.
bIsolated yield.
cPd(II)@BTU-SBA-15 was applied.
dBTU-SBA-15 and SBA-15 were applied.
3.1 | Catalytic activity
because it afforded the highest conversion (Figure 5b).
When we studied the reaction progress with various
solvents including EtOH, MeOH, DMF, CH3CN, hex-
ane, toluene and water, we found that MeOH and
water affording 99% conversion are more efficient than
the other solvents (Figure 5a). Our interest was in
using water to replace organic solvents in such reac-
tions because water solvent endows the reaction with
green character, and is readily available, of low cost
and safe.[45] In EtOH, MeOH, DMF and CH3CN, the
catalyst system afforded the corresponding coupling
product in moderate yields; however, hexane was
found to be a poor solvent for the same process.
Despite increasing the reaction conversion by increas-
ing the temperature, based on the importance of room
3.1.1 | Suzuki coupling reaction
The Suzuki reaction is considered one of the most
popular methods for forming C&bond;C sp2 bonds
in modern synthesis. We initiated our study by
examining the reaction of phenylboronic acid and
p-bromoacetophenone as a model reaction for optimi-
zation of the reaction conditions (base, solvent, tem-
perature and reaction time). Obviously, reaction in the
absence of any Pd catalyst and base did not afford the
desired product. Among a variety of bases that showed
satisfactory results such as K2CO3, KOH, K3PO4,
NH4OH and Et3N, we chose to proceed with K2CO3

BIS(THIOUREA)-MODIFIED SBA-15 FOR HECK AND SUZUKI REACTIONS
7 of 11
temperature in chemical processes and for energy
issues, we continued our studies under ambient condi-
tions (Figure 5c). Finally, we noted that the reaction
progress was initially slow and then the rate of reac-
tion increased until completion at 2 hours (Figure 5d).
We also screened the amount of supported Pd catalyst,
and 0.30 mol% loading of Pd in Pd@BTU-SBA-15 was
found to be optimal (Figure 5d, inset).
the optimized conditions, the reaction of 1b and 2 for
2 hours gave biaryl product 3b in a yield of 89% and
corresponding benzophenone derivative 3a was not
observed (Scheme 2). The present result indicates the
chemoselectivity Pd@BTU-SBA-15.
3.1.2 | Heck coupling reaction
To gain further insights into the generality and limita-
tions of the catalytic system in the Suzuki coupling reac-
tion, we extended our studies to various types of aryl
halides and phenylboronic acid derivatives (Table 1). A
variety of aryl halides and phenylboronic acids were read-
ily coupled to afford the desired product in excellent con-
version without homocoupling.
After finding that the Pd catalyst was compatible with
aryl halides and phenylboronic acid, investigation was
undertaken of the chemoselectivity with the reaction of
phenylboronic acid and m-bromobenzaldehyde. Under
Due to the promising results for Suzuki coupling, we
became interested in testing the Pd catalytic system in
the Heck coupling reaction. We found that Pd@BTU-
SBA-15 was very active for the Heck reaction of a
variety of aliphatic and aromatic alkenes with aryl
halides. First, the coupling of iodobenzene with methyl
acrylate was chosen as a model reaction. In a prelimi-
nary experiment, it was found that K2CO3 afforded the
best conversion in comparison with other bases such
as KOH, K3PO4, NH4OH and Et3N (Figure 6a). Due to
the low cost and high conversion, K2CO3 was chosen
as a base for this coupling reaction. In the next step,
the influence of the solvent on the catalytic activity
was investigated. The catalytic performance in
DMF–H2O (1:1 v/v) was higher than that in water,
DMF and other polar/nonpolar solvents. In addition,
toluene was found to be a poor solvent for the same
process (Figure 6b). Increasing the temperature to
reflux condition (120ꢀC) improved the conversion of
the reaction slightly to 97% (Figure 6c). By increasing
the amount of the catalyst from 10 to 25 mg, conver-
sion and selectivity of the reaction were also increased
(Figure 6d). From the results shown in Figure 6d,
SCHEME 2 Chemoselectivity of Pd@BTU-SBA-15 in Suzuki
coupling
FIGURE 6 (a) Base effect under
optimized conditions for Heck coupling
reaction catalyzed by Pd@BTU-SBA-15
at 120ꢀC. (b) Reaction progress in
various solvents under similar
conditions. (c) Effect of temperature on
progress of Heck reaction. (d) Effect of
amount of catalyst on progress of Heck
coupling reaction

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ALAMGHOLILOO ET AL.
when the amount of Pd catalyst was reduced to
0.10 mol%, the yield and selectivity decreased to 58%
and 61%.
ligands for stabilizing and keeping the Pd NPs in an
active state in the SBA-15 structure.
Considering the promising results obtained, as
described above, we were interested in demonstrating the
usefulness of the developed catalytic system for other
substrates. As presented in Table 2, aryl iodides com-
pared to aryl bromides and aryl chlorides gave a high
conversion in a short reaction time. We found that using
Pd@BTU-SBA-15 the Heck reaction between aryl halides
and alkenes proceeded with a low amount of catalyst
loading under sustainable and environmentally benign
conditions.
Among various Pd-based catalysts, the proposed pre-
catalyst afforded excellent yield and selectivity for both
coupling reactions, superior to that of most of the
reported catalysts (Table 3). However, yield is lower than
that for Pd(II)-doped UiO-67,[50] Pd/ED-MIL-101[54] and
homogeneous catalysts. The results demonstrate the
strong effects of the BTU ligand in comparison with other
3.2 | Heterogeneity studies
In order to reach a deeper understanding of whether or
not the proposed catalyst is heterogeneous in nature, we
performed a series of control experiments such as those
involving ICP-AES analysis and hot filtration. ICP-AES
analysis of both coupling reactions indicated that negligi-
ble Pd leaching occurred (detection limit of 0.7–10 ppm).
The hot filtration test of the reaction suspension with
removal of the insoluble Pd@BTU-SBA-15 also led to the
inhibition of both Suzuki and Heck reactions (Figure 7).
ICP-AES analysis and the hot filtration test confirmed
that the proposed catalyst is truly heterogeneous in
nature.
Taking into account the above observations and the
mechanism for Suzuki and Heck coupling reactions
TABLE 2 Substrate scope for Heck couplinga
Entry
Ar
Hal
I
R
Conversion (%)b
Selectivity (%)c
1
p-Me-Ph
p-Me-Ph
p-OMe-Ph
p-OMe-Ph
m-NO2-Ph
m-NO2-Ph
Ph
Ph
97(90)d
98(96)
98
2
I
CO2Me
Ph
96
3
I
94
97
4
I
CN
97
98
5
I
CN
94
94
6
I
CO2Et
CO2Me
CO2Et
CO2Bt
CO2Me
CO2Et
CO2Me
CO2Et
Ph
92
94
7
Br
Br
Br
Br
Br
Cl
Cl
I
91(82)
90
98(96)
98
8
Ph
9
Ph
88
97
10
11
12
13
14
p-COMe-Ph
p-COMe-Ph
m-CHO-Ph
p-MeCO-Ph
p-Me-Ph
92
98
91
97
64(43)
95(94)
95
69
Tracee
Trace
aReaction conditions: 1 (1.0 mmol), 4 (1.2 mmol), catalyst (0.25 mol% Pd), K2CO3 (2.0 mmol), DMF–H2O(1:1 v/v, 5 ml), 120ꢀC.
bConversion determined by TLC.
cSelectivity to trans-alkene.
dPd(II)@BTU-SBA-15 was applied.
eBTU-SBA-15 and SBA-15 were applied.

BIS(THIOUREA)-MODIFIED SBA-15 FOR HECK AND SUZUKI REACTIONS
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TABLE 3 Comparison of catalytic activity of various catalysts for Suzuki and Heck coupling
Reaction
Catalyst
Reaction conditions
K2CO3, H2O, 80ꢀC
Yield (%)
Ref.
[32]
Suzuki reaction
Pd@SBA-15(SH)2
Pd@BTU-PMO
98
95
97
96
98
80
98
97
97
98
95
98
90
96
[14]
[46]
[47]
[48]
[2]
K2CO3, H2O, 25ꢀC
Pd-PPh2-SBA-15
K2CO3, isopropanol, 80ꢀC
K2CO3, H2O, 70ꢀC
Pd(0)/MCoS-1
Pd@CuBDC/Py-SI
m-MCFSH-Pd
K2CO3, DMF/H2O, 80ꢀC
EtOH, Na3PO4, 60ꢀC
K2CO3, H2O, 25ꢀC
Pd@BTU-SBA-15
Fe3O4@SiO2/Schiff base/PdII
Pd(II)-doped UiO-67
PdII@Cu (BDC)/2-Py-SI
(PdCl2/bpy)10 multilayers
Pd/ED-MIL-101
This study
[49]
Heck reaction
K2CO3, DMF, 110ꢀC
K2CO3, DMF, TBAB, 100ꢀC
K2CO3, DMF,120ꢀC
Na2CO3, DMF, 140ꢀC
Et3N, DMF, 120ꢀC
[50]
[51]
[52]
[53]
[46]
Pd-PPh2-SBA-15
Et3N, NMP, 80ꢀC
Pd@BTU-SBA-15
K2CO3, DMF/H2O, 120ꢀC
This study
previously reported,[55,56] a plausible catalyst cycle is pro-
posed in Scheme 3. For the Suzuki reaction, the oxidative
addition of aryl halides to zero-valent Pd immobilized in
BTU-SBA-15 is the initial step to give divalent Pd species
and intermediate II. With the participation of base
(K2CO3), an organoborane reacts with intermediate II in
transmetalation to afford intermediate III. Finally, reduc-
tive elimination gives the desired product and regener-
ates the active zero-valent Pd in the nanoreactor. In the
Heck reaction, a different catalytic cycle involves cou-
pling between aryl halides and olefins. In the first step,
the olefin is coordinated to intermediate II and then a
syn insertion occurs. Intermediate V formed in the previ-
ous step, undergoes β-hydride elimination to form the
trans-alkene product. Finally, a base (K2CO3) removes
H&bond;X to regenerate the zero-valent Pd species in the
BTU/SBA-15 structure.
FIGURE 7 Activity profile for Suzuki reaction. Reaction
conditions: 4-bromoacetophenone (1 mmol), phenylboronic acid
(1.1 mmol) containing 3 mol% Pd@BTU-SBA-15 in 5 ml of water,
at room temperature
Finally, in order to determine the activities and sta-
bilities of Pd@SBA-15 for repeat runs, reusability
experiments were also performed in both Suzuki and
Heck reactions under optimal conditions. The results
shown in Figure 8a indicate that proposed catalyst
could be recycled for both reactions in up to seven
successive runs. However, a small decrease of yield
was observed after each reaction cycle which could be
ascribed to the fact that a small fraction of the catalyst
is lost in each recovery. This indicated that the Pd
immobilized in BTU-SBA-15 was robust and recyclable.
According to AAS analysis, negligible Pd was detected
in the reaction solution up to the seventh run, and
SEM imaging revealed the formidable stability of the
catalyst under the investigated reaction conditions even
after the seventh run (Figure 8b).
SCHEME 3 Possible mechanism of Suzuki and Heck
reactions using Pd@BTU-SBA-15

10 of 11
ALAMGHOLILOO ET AL.
FIGURE 8 (a) Durability of catalyst
in seven consecutive runs. (b) SEM image
after seventh recycling of Pd@BTU-SBA-
15
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Sadegh Rostamnia https://orcid.org/0000-0001-6310-
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SUPPORTING INFORMATION
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in the Supporting Information section at the end of this
article.
How to cite this article: Alamgholiloo H,
Rostamnia S, Noroozi Pesyan N. Extended
architectures constructed of thiourea-modified
SBA-15 nanoreactor: A versatile new support for
the fabrication of palladium pre-catalyst. Appl
Organometal Chem. 2020;e5452. https://doi.org/10.
1002/aoc.5452
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