Palladium-anchored multidentate SBA-15/di-urea nanoreactor: A highly active catalyst for Suzuki coupling reaction

Article abstract of DOI:10.1002/aoc.4397

Modification of mesoporous silica was carried out by reaction of SBA-15 with di-urea-based ligand. Next, with the help of this ligand, palladium ions were anchored within the multidentate SBA-15/di-urea pore channels with high dispersion. The SBA-15/di-urea/Pd catalyst was characterized using various techniques. Theoretical calculations indicated that each palladium ion was strongly interacted with one nitrogen and two oxygen atoms from the multidentate di-urea ligand located in SBA-15 channels and these interactions remained during the catalytic cycle. These results are in good agreement with those of hot filtration test: the palladium ions have very high stability against leaching from the SBA-15/di-urea support. The catalytic performance of SBA-15/di-urea/Pd nanostructure was examined for the Suzuki coupling reaction of phenylboronic acid and electronically diverse aryl halides under mild conditions with a minimal amount of Pd (0.26?mol%). Compared to previous reports, this protocol afforded some advantages such as short reaction times, high yields of products, catalyst stability without leaching, easy catalyst recovery and preservation of catalytic activity for at least six successive runs.

Full text of DOI:10.1002/aoc.4397

Received: 19 February 2018
DOI: 10.1002/aoc.4397
Revised: 23 March 2018
Accepted: 25 March 2018
F U L L P A P E R
Palladium‐anchored multidentate SBA‐15/di‐urea
nanoreactor: A highly active catalyst for Suzuki coupling
reaction
1
1
2,3
2
Sahar Rohani | Ghodsi Mohammadi Ziarani
| Alireza Badiei
| Abolfazl Ziarati |
2
2
Maryam Jafari | Alireza Shayesteh
1
Department of Chemistry, Faculty of
Modification of mesoporous silica was carried out by reaction of SBA‐15 with
di‐urea‐based ligand. Next, with the help of this ligand, palladium ions were
anchored within the multidentate SBA‐15/di‐urea pore channels with high dis-
persion. The SBA‐15/di‐urea/Pd catalyst was characterized using various tech-
niques. Theoretical calculations indicated that each palladium ion was strongly
interacted with one nitrogen and two oxygen atoms from the multidentate di‐
urea ligand located in SBA‐15 channels and these interactions remained during
the catalytic cycle. These results are in good agreement with those of hot filtra-
tion test: the palladium ions have very high stability against leaching from the
SBA‐15/di‐urea support. The catalytic performance of SBA‐15/di‐urea/Pd
nanostructure was examined for the Suzuki coupling reaction of phenylboronic
acid and electronically diverse aryl halides under mild conditions with a min-
imal amount of Pd (0.26 mol%). Compared to previous reports, this protocol
afforded some advantages such as short reaction times, high yields of products,
catalyst stability without leaching, easy catalyst recovery and preservation of
catalytic activity for at least six successive runs.
Science, University of Alzahra, Tehran,
Iran
2
School of Chemistry, College of Science,
University of Tehran, Tehran, Iran
3
Nanobiomedicine Center of Excellence,
Nanoscience and Nanotechnology
Research Center, University of Tehran,
Tehran, Iran
Correspondence
Ghodsi Mohammadi Ziarani, Department
of Chemistry, Faculty of Science,
University of Alzahra, Tehran, Iran.
Email: gmohammadi@alzahra.ac.ir
KEYWORDS
functionalization of SBA‐15, palladium nanoparticles, SBA‐15/di‐urea/Pd, Suzuki coupling reaction
1
| INTRODUCTION
mesoporous silicas, particularly SBA‐15, have been
[
15–17]
widely studied.
Large surface areas, highly ordered
Nanoreactors are a means of creating specific nanoscale
chemical environments divided from the surrounding
mesoporous structures with regular channels, high
hydrothermal and mechanical stability, uniform pore
sizes, thick walls, wide accessibility and inert environ-
[6]
bulk space.
Because of the nanoscale confinement
effect of such nanoreactors, the physical and chemical
properties of catalysts can also be modulated. Higher
selectivity and reactivity have been observed when
ment for immobilization of transition metal nanoparti-
[7]
[18–22]
cles
make these structures excellent carriers for
[
23]
many metal species.
[
8]
reactions occur in nanoreactors.
nanoreactors have been developed,
carbon nanotubes,
Various types of
Investigation the application of metal nanoparticles in
[
24]
including
catalysis,
marked interest in research of nanocatalysis.
them, palladium nanoparticles (Pd NPs) have attracted
especially in organic synthesis, has received
[
9]
[10]
[12]
[25]
dendrimers,
metal–organic
Among
[
11]
[13]
frameworks,
montmorillonites,
zeolites
and
[14]
[26–28]
mesoporous silicas.
Among the various nanoreactors,
much attention.
Pd NPs supported on the two‐
Appl Organometal Chem. 2018;e4397.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
1 of 11
https://doi.org/10.1002/aoc.4397

2
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ROHANI ET AL.
dimensional hexagonal structure of SBA‐15 can be evenly
holding ability (each Pd ion is connected to one nitrogen
and two oxygen atoms per ligand based on theoretical cal-
culations), which is expected to be favourable for Suzuki–
Miyaura catalytic coupling reactions (Scheme 1).
dispersed, thus efficiently preventing Pd NP aggrega-
[29,30]
tion.
The inner mesochannels of SBA‐15 are rich in
siloxy groups; hence, these hydrophilic moieties could
hinder the mass transportation of hydrophobic mole-
[31]
cules, causing a reaction to slow down.
Hybrid porous
2
2
| EXPERIMENTAL
materials such as SBA‐15 combined with ligands bearing
organic groups would make the materials hydrophobic
and hydrothermally stable and thus endow them with
improved catalytic activities in applications for organic
.1 | Synthesis of SBA‐15 Mesoporous Silica
The SBA‐15 mesoporous silica sample was prepared
[32]
[47]
synthesis.
Therefore, to extend the applicability as well
according to our previously published procedure.
as stability of Pd‐decorated SBA‐15 materials in air and in
aqueous media, it is necessary to improve the surface
using organic functional groups by suitable organic
2
.2 | Synthesis of SBA‐15/Di‐urea
[5]
ligands as linkers between SBA‐15 silica and Pd.
For the synthesis of SBA‐15/di‐urea, 3‐(triethoxysilyl)
propylisocyanate (2 mmol) and o‐phenylenediamine
(1 mmol) were added to dry toluene (30 ml) and the solu-
tion was refluxed for 6 h under an inert atmosphere
(progress of the reaction was monitored using Fourier
transform infrared (FT‐IR) spectroscopy). After comple-
tion of the reaction, SBA‐15 (0.4 g) was added to the solu-
tion together with stirring for 24 h under reflux. The solid
product was then centrifuged, washed with ethanol and
tetrahydrofuran, and dried overnight in an oven at
80 °C. The final product was denoted as SBA‐15/di‐urea.
Pd‐catalysed cross‐coupling reactions are an impor-
tant class of carbon–carbon bond forming reactions that
remain the most broadly explored area in the field of syn-
[33]
thetic organic chemistry.
Among C─C coupling reac-
tions, Pd‐catalysed Suzuki–Miyaura coupling has
become an exceedingly powerful synthetic method for
[34,35]
preparing biaryl compounds.
Biaryls have broad
applications in the synthesis of natural products,
[36–38]
advanced materials and pharmaceuticals.
Recently
various types of Pd‐anchored ligand‐based SBA‐15 have
[
39–
been reported for the synthesis of biaryl compounds.
43]
Cao and co‐workers described the synthesis of a Pd‐
2
.3 | Immobilization of Pd(II) Ions on
diimine@SBA‐15 catalyst for Suzuki–Miyaura coupling
Surface of SBA‐15/Di‐urea
through immobilizing Pd ions into the pore channels of
[
2]
diimine‐functionalized SBA‐15 mesoporous silica.
Generally, 1.0 g of as‐synthesized SBA‐15/di‐urea and
Sarkar et al. prepared a thiol‐modified SBA‐15‐supported
0.056 g of Pd(OAc) in 40 ml of ethanol were refluxed
2
Pd catalyst for Suzuki coupling reaction under mild reac-
for 12 h. The brown solid obtained was separated using fil-
tration, washed with ethanol and dried in a vacuum oven
at 70 °C for 60 min. The Pd content in the SBA‐15/di‐urea/
Pd catalyst was 3.6 wt%, as determined using inductively
coupled plasma atomic emission spectrometry (ICP‐AES).
[44]
tion conditions.
Ghorbani‐Vaghei et al. described the
synthesis of a novel SBA‐15/AO/Pd(II) nanocatalyst by
anchoring of amidoxime group on SBA‐15 silica and
[45]
followed by deposition of PdCl2.
Veisi et al. were able
to prepare SBA‐15/CCPy/Pd(II) as a heterogeneous cata-
lyst for C─C coupling reactions through functionalization
2.4 | Suzuki–Miyaura Coupling Reaction
[46]
of SBA‐15 with 3‐aminopropyltriethoxysilane.
All of
the prepared Pd@functionalized SBA‐15 catalysts men-
tioned above showed higher activity and Pd holding abil-
ity than Pd@SBA‐15 in Suzuki coupling reactions.
However, to improve upon these advantages, herein we
report a multidentate SBA‐15/di‐urea with high Pd
In a general method, a 25 ml two‐neck round‐bottom
flask was charged with aryl halide (1 mmol),
phenylboronic acid (1.3 mmol), potassium carbonate
(3 mmol), tetrabutylammonium bromide (TBAB) as a
phase transfer agent (0.5 mmol), SBA‐15/di‐urea/Pd
SCHEME 1 Suzuki coupling using
SBA‐15/di‐urea/Pd

ROHANI ET AL.
3 of 11
(
0.005 g, 0.26 mol% Pd) and a mixture of ethanol and
nanocatalyst was prepared by the reaction of Pd(OAc)2
with SBA‐15/di‐urea.
water (2:1, 6 ml). The solution was then stirred for the
desired time at 70 °C. An aliquot was taken at arbitrary
time intervals, filtered and analysed using GC–MS. After
completion of the reaction, the mixture was allowed to
cool to room temperature. The catalyst was easily
removed via filtration and then washed with ethyl acetate
and ethanol. The organic layer was separated and dried
over anhydrous magnesium sulfate and evaporated under
reduced pressure to afford biaryl compounds. The spec-
tral data for selected compounds are available in the
supporting information (Figures S3 and S4).
FT‐IR spectroscopy was used to investigate the prepa-
ration of SBA‐15/di‐urea/Pd. The FT‐IR spectra of the
free di‐urea ligand, SBA‐15, SBA‐15/di‐urea and SBA‐
15/di‐urea/Pd are depicted in Figure 1. As can be seen,
the characteristic absorption bands for free di‐urea ligand
−
1
are present at 3342 and 1741 cm due to the N─H and
C═O stretching vibrations, respectively. The absence of
−
1
a broad band at 2300 cm from isocyanate group and
the absence of two sharp peaks of ─NH groups from o‐
2
−
1
phenylenediamine at 3400 cm also point to the fact that
isocyanate groups successfully reacted with o‐
phenylenediamine. The spectrum of parent SBA‐15
shows the bands of symmetric and asymmetric stretching
3
3
| RESULTS AND DISCUSSION
.1 | Catalyst Characterization
−
1
vibrations of Si─O─Si bonds at 800 and 1085 cm ,
−
1
respectively, and a band at 1634 cm due to O─H bend-
[
48]
ing vibration.
Furthermore in the spectrum of SBA‐15
−
1
The preparation of the SBA‐15/di‐urea/Pd catalyst
followed the steps described in Scheme 2. First, o‐
phenylenediamine was reacted with 2 mol of 3‐
isocyanatopropyltriethoxysilane via formation of C─N
bond between amine and isocyanate parts to give 1,1′‐
there is a weak peak at 961 cm corresponding to the
symmetric stretching vibration of Si─OH which is absent
in the spectrum of SBA‐15/di‐urea. Compared with the
spectrum of SBA‐15/di‐urea, it can be observed that the
SBA‐15/di‐urea/Pd spectrum shows similar bands. More-
−
1
(
1,2‐phenylene)bis(3‐(triethoxysilyl)propyl)urea. Subse-
over, the stretching frequency at 576 cm in the spec-
[49]
quently this di‐urea‐based ligand was reacted with
ordered SBA‐15 mesoporous silica to afford the di‐urea‐
functionalized SBA‐15. Finally, the SBA‐15/di‐urea/Pd
trum of SBA‐15/di‐urea/Pd is assigned to νPd─N.
These results provide evidence that the SBA‐15/di‐urea
sample was successfully functionalized with Pd species.
SCHEME 2 Schematic of SBA‐15/di‐
urea/Pd fabrication

4
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ROHANI ET AL.
X‐ray spectroscopy (EDS), the spectrum also showing
the presence of N, C, O and Si (Figure 2b). The maps of
Si, O, C, N and Pd (Figure 2d–h) are well defined with
sharp contrast.
Low‐angle XRD patterns of SBA‐15 and the SBA‐15/
di‐urea/Pd catalyst are displayed in Figure 3. SBA‐15
shows a strong diffraction reflection (100) and two small
[
48]
diffraction reflections (110) and (200).
All reflections
indicate that the mesoporous SBA‐15 has a well‐defined
hexagonal symmetry and has long‐range ordering of its
structure. The presence of the di‐urea ligand results in a
minor decrease in the overall intensity of the (100),
(
110) and (200) reflections owing to the loading of organic
moieties in the mesostructured SBA‐15 material. Com-
parison of the diffraction patterns of SBA‐15 and SBA‐
15/di‐urea/Pd demonstrates that the ordered mesoporous
FIGURE 1 FT‐IR spectra of free di‐urea ligand, SBA‐15, SBA‐15/
di‐urea and SBA‐15/di‐urea/Pd
structure of the sample remains intact even after incorpo-
ration of the Pd complex in the SBA‐15 silica.
The results for N adsorption–desorption isotherms
2
A typical scanning electronic microscopy (SEM)
image of SBA‐15/di‐urea/Pd (Figure 2a) demonstrates
rod‐shaped morphology aggregated into bundles. A trans-
mission electron microscopy (TEM) image of SBA‐15/di‐
urea/Pd shows that the material is organized in ordered
arrays of two‐dimensional hexagonal mesoporous SBA‐
concerning the Brunauer–Emmett–Teller (BET) surface
area (SBET), the total pore volume (Vtotal) and the pore
diameter (DBJH) of SBA‐15, SBA‐15/di‐urea and SBA‐15/
di‐urea/Pd are presented in Table 1.
The materials demonstrated a type IV nature with an
H hysteresis loop, characteristic of mesoporous solids
1
1
5 and the attachment of organic components inside the
with uniform cylindrical pores according to the IUPAC
classification. From the data of Table 1, the incorporation
of the di‐urea ligand into mesoporous SBA‐15 silica pores
and the inclusion of Pd into this structure shifted the pore
size to a smaller value and led to decreased in pore vol-
ume and surface area. SBET decreased during the two
functionalization processes as compared to the parent
pore channels of SBA‐15 silica has no distinct influence
on the morphology of composition (Figure 2c). Moreover,
the dark spots in the TEM image are the Pd NPs with
diameters of about 3 nm that are clearly obvious.
The presence of Pd in the SBA‐15/di‐urea/Pd
nanocatalyst was clearly confirmed via energy‐dispersive
FIGURE 2 (a) SEM image, (b) EDS spectrum, (c) TEM image and (d–h) EDS mapping images of SBA‐15/di‐urea/Pd. The arrows in (c)
indicate Pd NPs

ROHANI ET AL.
5 of 11
FIGURE 4
N
2
adsorption–desorption isotherms and BJH pore
size distribution curves of SBA‐15 and SBA/di‐urea
groups. Since free silanols groups on the surface of SBA‐
1
5 can be dehydrated at high temperatures, the slight
weight loss (2.2%) detected at temperatures above
70 °C can be ascribed to this phenomenon.
5
FIGURE 3 Low‐angle XRD patterns of SBA‐15 and SBA‐15/di‐
urea/Pd
3
.2 | Computational Details
SBA‐15. These results confirm that the surface modifica-
tion indeed occurred within the primary mesopores of
SBA‐15 silica which can be ascribed to the di‐urea and
di‐urea/Pd functionalization. Additionally, Barrett–
Joyner–Halenda (BJH) analysis indicated that the pri-
mary pore size of SBA‐15 decreased during the
functionalization process for the same reason (Figure 4).
The amount of grafted organic compounds on the
mesoporous SBA‐15/di‐urea/Pd surface was also esti-
mated using thermogravimetric analysis (TGA), from
room temperature up to 1000 °C. The related curves are
shown in Figure 5. The initial weight of SBA‐15/di‐
urea/Pd exceeding 100% is related to the buoyancy
Quantum chemical calculations were carried out with
density functional theory using the ORCA 3.0.3 pro-
gram.
[
51]
Geometries were optimized using the BP86
[50]
effect.
The obtained results revealed that the first
weight loss (4.1%) below 200 °C can be attributed to
trapped solvents and physically adsorbed compounds
trapped in the SBA‐15 channels pores. After that, the
obvious mass change (23.1%) from 200 up to 570 °C can
be assigned to covalently functionalized organic motifs
(
di‐urea ligand) in the material. The amount was esti-
−
1
mated to be 0.82 mmol g for degradation of organic
FIGURE 5 TGA profile of SBA‐15/di‐urea/Pd
TABLE 1 Textural properties of SBA‐15, SBA‐15/di‐urea and SBA‐15/di‐urea/Pd
2
−1
3
−1
Entry
Sample
S
BET (m g
)
DBJH (nm)
Vtotal (cm g )
1
2
3
SBA‐15
824
518
501
8.1
6.5
6.2
1.45
0.81
0.79
SBA‐15/di‐urea
SBA‐15/di‐urea/Pd

6
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ROHANI ET AL.
[
52,53]
[54]
functional
and the def2‐TZVP basis sets,
and the
Phenylboronic acid provides another phenyl group,
which is transferred to the Pd complex with
ΔE = −181.0 kJ mol .
solvent effects were included in all calculations using
the conductor‐like screening model (COSMO).
PBE0 hybrid functional
[
55]
−1
The
[56]
was used for single‐point
energy calculations. The optimized geometries of the
ligand and the Pd complex (two different structures) are
displayed in Figure 6, and the bond lengths, Mayer bond
orders and Mulliken atomic charges are listed in Table
S1. In the more symmetric structure, Pd is connected to
two nitrogen atoms (bond orders ~ 0.69) and two oxygen
atoms (bond orders ~ 0.40). However, this structure is less
stable than the asymmetric structure, and the energy dif-
ference including zero‐point energy is about 40 kJ mol .
In the optimized structure of the asymmetric Pd complex
catalyst, Pd is connected to one nitrogen atom and two
oxygen atoms through Mayer bond orders of 0.83, 0.53
and 0.49, respectively. Consequently, the C─O bond
orders in carbonyl groups have been reduced from 1.87
and 1.73 in the free ligand to 1.44 and 1.28 in the SBA‐
The final step is reductive elimination in which the Pd
complex eliminates the product and regenerates the cata-
lyst. For this step ΔE was calculated to be −68.0 kJ mol .
−
1
−
1
1
5/di‐urea/Pd (L–Pd) complex. The asymmetric structure
of the L–Pd complex was used in subsequent calculations
for the Suzuki reaction.
The optimized structures of all intermediates are
displayed in Table S2 of the supporting information,
and the bond lengths, bond orders and Mulliken atomic
charges are listed. As evident from Table S2, Pd─O and
Pd─N bond orders are relatively high in all intermediate
structures of the Suzuki reaction. This indicates that Pd is
strongly attached to the ligand, and the L–Pd structure
remains relatively intact in the reaction cycle.
The Suzuki coupling reaction catalysed by the L–Pd
complex was studied step by step. In the first step, the cat-
alyst is coupled with phenyl iodide to yield an
organopalladium complex. For the formation of this
−
1
intermediate, ΔE was calculated to be −5.2 kJ mol .
3.3 | Catalytic Activity
After characterization of the synthesized catalyst, it was
investigated in the Suzuki coupling reaction. Various
chemical parameters including solvent, kind of base,
reaction temperature, amount of catalyst and type of aryl
halide substrate were studied to determine the best
possible combination. To optimize the reaction condi-
tions, the Suzuki coupling between 4‐iodobenzene and
phenylboronic acid was chosen as a model reaction. To
examine the influence of solvent, dimethylformamide,
ethanol, water and toluene were studied. As shown in
In the next step, iodide is replaced with a hydroxyl
ion, and ΔE for this step was found to be −152.4 kJ mol .
−
1
FIGURE 6 Optimized structure of (a) asymmetric and (b) and symmetric Pd complex catalyst

ROHANI ET AL.
7 of 11
[
2]
during the Suzuki coupling reaction. According to this,
K CO was selected as the best base for the reaction.
2
3
It seems that the temperature has an influence on the
catalytic efficiency of SBA‐15/di‐urea/Pd. Based on this,
increasing the temperature up to 70 °C was vital to obtain
a high yield of products while no significant increase in
reaction yield was observed at higher temperatures (Figure
S2). It is noteworthy that when the reaction was carried out
below 40 °C, only a poor yield of products was obtained.
Also, the influence of amount of catalyst on the
Suzuki coupling reaction of 4‐iodobenzene and
phenylboronic acid was studied. It was found that
0.26 mol% of Pd was optimum in the reaction. Neverthe-
FIGURE 7 Effect of base on progress of Suzuki reaction in
presence of SBA‐15/di‐urea/Pd catalyst in EtOH–H O (2:1)
2
less, aside from the overall amount of Pd in the coupling
reaction, weight percentage of Pd inside SBA‐15/di‐urea/
Pd was also investigated. According to Figure 8, the best
result was obtained with 3.6 wt% of Pd, because higher
catalyst loading (4.8 wt%) led to higher Pd leaching
(determined usingICP‐AES).
Figure S1, the single solvents afforded low yields for the
reaction whereas the organic–aqueous co‐solvent EtOH–
H O gave high yields of products. Next the effect of vari-
2
ous volume ratios of EtOH–H O as a solvent in the
Upon optimization of the reaction conditions, the cat-
alytic activity of SBA‐15/di‐urea/Pd for Suzuki coupling
reactions of various aryl halides and phenylboronic acid
was investigated, and the results are presented in
Table 2. It is evident that aryl iodides versus aryl bro-
mides exhibited more activity towards products (Table 2,
entries 2 and 5) but, with the reaction of aryl chlorides,
a low yield of products was obtained because of the
strength of the C─Cl bond. In most cases of Suzuki reac-
tion, oxidative addition is the rate‐determining step of the
catalytic cycle. During this step, coupling reactions
involving halogenated substrates typically decrease in
the order R─I > R─Br > R─Cl. This may be explained
according to the R─X bond dissociation enthalpies. For
example, the X─Ph bond dissociation enthalpies range
2
Suzuki reaction was studied. It was found that the
optional volume ratio should be set at 2:1. The merit of
the co‐solvent can be attributed to the good solubility of
the inorganic base and the organic reactants.
Unlike other cross‐coupling reactions such as the Stille
or Sonogashira reactions, the Suzuki–Miyaura reaction
requires aqueous base to activate the boronate ester com-
ponent. So various types of inorganic and organic bases,
such as NaOH, NaHCO , K CO , K PO , KOH and NEt ,
3
2
3
3
4
3
were investigated in the Suzuki coupling reaction in
EtOH–H O (2:1). Comparing all the results shown in
2
Figure 7, it was found that an organic base like NEt was
3
less reactive than inorganic bases such as K CO and
2
3
KOH. The results indicate that stronger alkalinity could
increase the product yield but the high alkalinity of KOH
solution might damage the structure of the SBA‐15 silica
−
1
from 65.0 ± 1 kcal mol (X = I) to 80.4 ± 1.5 kcal mol
−
1
−1
[57]
(X = Br) and 95.5 ± 1.5 kcal mol (X = Cl).
FIGURE 8 Influence of weight
percentage of Pd in SBA‐15/di‐urea/Pd

8
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ROHANI ET AL.
TABLE 2 Suzuki coupling reactions of various aryl halides and
phenylboronic acid over SBA‐15/di‐urea/Pd catalyst
Based on the results discussed above and also the
computational details (Section 3.2), a proposed mecha-
nism for the Suzuki coupling reaction over SBA‐15/di‐
urea/Pd can be described through a catalytic cycle which
involves three fundamental steps: oxidative addition,
transmetalation and reductive elimination (Scheme 3).
The oxidative addition of aryl halides to Pd(0) complex
is the initial step to give intermediate 1, a Pd(II) species.
With the participation of base, an organoborane com-
pound reacts with intermediate 1 in transmetalation to
give intermediate 2. This is followed by reductive elimina-
tion to produce the corresponding biphenyl product and
regeneration of the original Pd(0) species.
a
Time
(h)
Yield
(%)
TOF
b
c
−1 d
Entry
R
X
TON
(h
)
1
2
3
4
5
6
7
8
9
H
I
20 min
>99
>99
88
385
385
338.5
377
365
371
369
331
358
315
308
300
354
308
277
270
1283
770
4‐OCH
3
3
I
30 min
2‐NH
2
I
1
338.5
377
183
249
185
66
H
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
1
98
4‐OCH
2
95
4‐COCH
4‐CHO
3‐CHO
3
1.5
2
97
96
5
86
4‐NO
2
3
93
119
64
3
3
.4 | Catalyst Leaching and Recyclability
.4.1 | Hot filtration test
e
10
11
12
13
14
15
16
4‐OH
4‐NH
5
82
2
5.5
7
80
78
56
2‐NO
4‐Br
H
2
43
To test if Pd was leached out from the catalyst during the
reaction, a hot filtration test for the model Suzuki reac-
tion under the optimal conditions was carried out. In this
method, hot reaction mixture was filtered after 10 min
and the coupling reaction was permitted to continue
under the same conditions with the supernatant solution.
No increase in the product was observed (determined
using GC–MS measurements) and no Pd could be
detected in the hot filtered solution using ICP‐AES. This
result showed that the Pd NPs were firmly grafted on
the SBA‐15/di‐urea nanoreactor because of the excellent
affinity between Pd NPs and di‐urea ligand.
f
4
92
89
8
80
72
70
38
4‐NH
4‐CH
2
12
12
24
2
‐Cl
22
a
Reaction conditions: ArX (1 mmol), PhB(OH)
2
(1.3 mmol), K
2
CO
3
(3 mmol),
2
TBAB (0.5 mmol), EtOH–H O (2:1, 6 ml) in the presence of catalyst (0.005 g,
0.26 mol% Pd) at 70 °C.
b
GC‐MS yield.
c
Turnover number, calculated as: moles of product/moles of active sites.
d
e
Turnover frequency, calculated as TON/time.
Isolated yield.
f
2 2 3
Isolated yield using ArX (2 mmol), PhB(OH) (2.5 mmol), K CO (5 mmol).
3
.4.2 | Reusability of catalyst
Therefore monosubstituted aryl halides iodobenzene,
bromobenzene and chlorobenzene with phenylboronic
acid gave yields of biphenyl of >99, 98 and 80%, respec-
tively (Table 2, entries 1, 4 and 14). In the case of
iodobenzene and bromobenzene, the corresponding prod-
ucts were obtained with high turnover frequencies
The recyclability of catalysts is one of the most important
advantages of heterogeneous catalytic systems from an
economic point of view. The process of recycling of the
SBA‐15/di‐urea/Pd catalyst was performed for the Suzuki
coupling reaction of 4‐iodobenzene and phenylboronic
acid under optimized reaction conditions. After the com-
pletion of each cycle, the solid catalyst was filtered off
from the reaction, washed with ethyl acetate and hot eth-
anol followed by drying under vacuum overnight and
reused in a subsequent run. The results in Figure 9 dem-
onstrate that the supported catalyst was highly reusable
under the examined reaction conditions, preserving
almost unaltered its initial catalytic performance after
six uses. The ICP analysis results for fresh and reused
Pd catalyst were 3.6 and 3.4 wt%, respectively.
−
1
(TOFs) of 1283 and 377 h . When aryl halides contain-
ing both electron‐withdrawing and electron‐donating
groups were coupled with phenylboronic acid, the corre-
sponding biphenyl products were obtained in excellent
yields. Moreover, para‐substituted aryl halides afforded
high yields of the desired biaryls whereas sterically hin-
dered ortho‐substituted halides provided moderate yields
of products. For example, the Suzuki coupling reaction
of 4‐ and 3‐bromobenzaldehyde with phenylboronic acid
gave 96 and 86% yields after 2 and 5 h (Table 2, entries
7
and 8). Additionally, meta‐substituted aryl halides led
to lower yield than the para‐substituted derivatives such
as in the case of 4‐ and 2‐nitrobenzaldehyde, where the
corresponding products were obtained in yields of 93
and 78%, respectively (Table 2, entries 9 and 12).
3
.5 | Comparison
Several reports on the use of Pd‐based SBA‐15‐catalysed
Suzuki coupling reactions have appeared in the

ROHANI ET AL.
9 of 11
SCHEME 3 Proposed mechanism of
Suzuki coupling reaction
the previously reported catalysts in terms of shorter reac-
tion times, higher stability and also better isolated yields.
4
| CONCLUSIONS
In summary, the present work reports a highly stable and
recyclable mutidentate SBA‐15/di‐urea/Pd nanoreactor as
heterogeneous catalyst for Suzuki–Miyaura cross‐cou-
pling reactions of aryl halides with phenylboronic acid
in mixed EtOH–H O solvent under mild conditions. The-
2
FIGURE 9 Recycling study of SBA‐15/di‐urea/Pd
oretical calculations indicated that each Pd ion was
interacted with one nitrogen and two oxygen atoms from
the multidentate di‐urea ligand located in SBA‐15 chan-
nels. Moreover these calculations suggested that the
interactions of Pd with nitrogen and oxygen atoms
remained during catalytic cycle. It is noteworthy that
the high stability and activity of the presented
[1–5]
literature.
Table 3 presents a comparison of the cata-
lytic activity of SBA‐15/di‐urea/Pd in the coupling of
bromobenzene and phenylboronic acid with that of other
supported Pd catalysts. As is evident, the SBA‐15/di‐urea/
Pd catalyst showed a higher performance than some of
TABLE 3 Comparison of catalytic activity of various catalysts in the coupling of bromobenzene and phenylboronic acid
Entry
Catalyst
Temp. (°C)
Time (h)
Yield (%)
Ref.
1
D‐2PA‐Pd(II)@SBA‐15
120
5
85
[
[
[
[
[
1]
2]
3]
4]
5]
2
3
4
5
6
Pd‐Diimine@SBA‐15
Pd@SBA‐15/ILDABCO
80
12
12
4
87
80
95
0
Pd /SBA‐15
110
120
70
80.2
83
SBA‐15–EDTA–Pd
SBA‐15/di‐urea/Pd
8
1
98
This work

10 of 11
ROHANI ET AL.
nanoreactor system could be directly assigned to the
nature of the applied mutidentate di‐urea ligand, which
is not only an inherently air‐ and moisture‐stable ligand,
but also acts to stabilize active Pd species to protect Pd
NPs against agglomeration and Pd black formation. Addi-
tionally, the SBA‐15/di‐urea/Pd catalyst could be easily
separated by filtration and reused at least six times with-
out significant decrease of catalytic activity.
[18] G. Mohammadi Ziarani, P. Gholamzadeh, A. Badiei, V. Fathi
Vavsari, Res. Chem. Intermed. 2018, 44, 277.
[19] V. Fathi Vavsari, G. Mohammadi Ziarani, A. Badiei, RSC Adv.
2015, 5, 91686.
[20] V. Fathi Vavsari, G. Mohammadi Ziarani, S. Balalaie, A. Badiei,
F. Golmohammadi, S. Ramezanpour, F. Rominger, Chem.
Select 2017, 2, 3496.
[21] G. Mohammadi Ziarani, N. Lashgari, A. Badiei, J. Mol. Catal. A
2015, 397, 166.
[
[
[
[
[
[
22] A. Badiei, H. Goldooz, G. Mohammadi Ziarani, A. Abbasi,
ACKNOWLEDGEMENTS
J. Colloid Interface Sci. 2011, 357, 63.
We gratefully acknowledge financial support from the
Research Council of the University of Alzahra and the
University of Tehran.
23] C. Singh, K. Jawade, P. Sharma, A. P. Singh, P. Kumar, Catal.
Commun. 2015, 69, 11.
24] D. Astruc, F. Lu, J. R. Aranzaes, Angew. Chem. Int. Ed. 2005,
44, 7852.
25] L. A. Bivona, F. Giacalone, L. Vaccaro, C. Aprile, M.
ORCID
Gruttadauria, ChemCatChem 2015, 7, 2526.
Ghodsi Mohammadi Ziarani
177-7889
http://orcid.org/0000-0001-
26] N. Miyaura, T. Yanagi, A. Suzuki, Synth. Commun. 1981, 11,
5
5
13.
27] K. C. Nicolaou, P. G. Bulger, D. Sarlah, Angew. Chem. Int. Ed.
005, 44, 4442.
Alireza Badiei http://orcid.org/0000-0002-6985-7497
2
REFERENCES
[28] R. Narayanan, Molecules 2010, 15, 2124.
[
[
[
1] A. Pathak, A. P. Singh, J. Porous Mater. 2017, 24, 327.
[29] C. Yang, H. Wustefeld, M. Kalwei, F. Schiith, Stud. Surf. Sci.
Catal. 2004, 154, 2574.
2] J. Yu, A. Shen, Y. Cao, G. Lu, Catalysts 2016, 6, 181.
[30] M. Opanasenko, P. Štěpnička, J. Čejka, RSC Adv. 2014, 4,
5137.
3] S. Rostamnia, E. Doustkhah, B. Zeynizadeh, Micropor.
Mesopor. Mater. 2016, 222, 87.
6
[
31] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F.
[
4] P. Ncube, T. Hlabathe, R. Meijboom, J. Cluster Sci. 2015, 26,
Chmelka, G. D. Stucky, Science 1998, 279, 548.
1
873.
[
32] S. Rostamnia, H. Xin, Appl. Organometal. Chem. 2013, 27, 348.
33] A. Feiz, M. M. Amini, A. Bazgir, Mol. Catal. 2017, 438, 159.
[
[
5] P. Sharma, A. Singh, Catal. Sci. Technol. 2014, 4, 2978.
[
6] S. H. Petrosko, R. Johnson, H. White, C. A. Mirkin, J. Am.
Chem. Soc. 2016, 138, 7443.
[34] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457.
[
[
[
7] J. Zhi, D. Song, Z. Li, X. Lei, A. Hu, Chem. Commun. 2011, 47,
[35] W. Zhang, L. Peng, C. Deng, Y. Zhang, H. Qian, Mol. Catal.
2018, 445, 170.
1
0707.
8] V. Fathi Vavsari, G. Mohammadi Ziarani, A. Badiei, S. Balalaie,
J. Iran. Chem. Soc. 2016, 13, 1037.
[36] M. C. Kozlowski, B. J. Morgan, E. C. Linton, Chem. Soc. Rev.
2009, 38, 3193.
9] C. Deraedt, L. Salmon, D. Astruc, Adv. Synth. Catal. 2014, 356,
[37] K. C. Nicolaou, C. N. Boddy, S. Bräse, N. Winssinger, Angew.
Chem. Int. Ed. 1999, 38, 2096.
2
525.
[
[
10] P. Serp, E. Castillejos, ChemCatChem 2010, 2, 41.
[
[
[
38] W. Fu, Z. Zhang, P. Zhuang, J. Shen, M. Ye, J. Colloid Interface
Sci. 2017, 497, 83.
11] D. A. Gomez‐Gualdron, S. T. Dix, R. B. Getman, R. Q. Snurr,
Phys. Chem. Chem. Phys. 2015, 17, 27596.
39] B. A. Khakiani, K. Pourshamsian, H. Veisi, Appl. Organometal.
Chem. 2015, 5, 259.
[
12] T. Mitsudome, K. Nose, K. Mori, T. Mizugaki, K. Ebitani, K.
Jitsukawa, K. Kaneda, Angew. Chem. 2007, 119, 3352.
40] H. Veisi, M. Pirhayati, A. Kakanejadifard, Tetrahedron Lett.
2017, 58, 4269.
[
[
13] S. Lee, C. Jo, R. Ryoo, J. Mater. Chem. A 2017, 5, 11086.
14] G. Mohammadi Ziarani, N. Lashgari, A. Badiei, Curr. Org.
Chem. 2017, 21, 674.
[41] H. Veisi, M. Ghadermazi, A. Naderi, Appl. Organometal. Chem.
2016, 30, 341.
[
[
[
15] V. Fathi Vavsari, G. Mohammadi Ziarani, S. Balalaie, A. Latifi,
[42] H. Veisi, S. A. Mirshokraie, H. Ahmadian, Int. J. Biol.
Macromol. 2018, 108, 419.
M. Karimi, A. Badiei, Tetrahedron 2016, 72, 5420.
16] Z. Bahrami, A. Badiei, F. Atyabi, Chem. Eng. Res. Des. 2014, 92,
[43] S. Lebaschi, M. Hekmati, H. Veisi, J. Colloid Interface Sci. 2017,
485, 223.
1
296.
17] M. Karimi, A. Badiei, G. Mohammadi Ziarani, RSC Adv. 2015,
, 36530.
[44] S. M. Sarkar, M. L. Rahman, M. M. Yusoff, RSC Adv. 2015, 5,
5
1295.

ROHANI ET AL.
11 of 11
[
[
[
[
[
45] R. Ghorbani‐Vaghei, S. Hemmati, H. Veisi, J. Mol. Catal. A
[56] J. P. Perdew, M. Ernzerhof, K. Burke, J. Chem. Phys. 1996, 105,
2
014, 393, 240.
9982.
46] H. Veisi, M. Hamelian, S. Hemmati, J. Mol. Catal. A 2014, 395,
5.
[57] G. E. Davico, V. M. Bierbaum, C. H. Depuy, G. B. Ellison, R. R.
2
Squires, J. Am. Chem. Soc. 1995, 117, 2590.
47] Z. Bahrami, A. Badiei, F. Atyabi, H. R. Darabi, B. Mehravi,
Mater. Sci. Eng. C 2015, 49, 66.
SUPPORTING INFORMATION
48] H. Vojoudi, A. Badiei, S. Bahar, G. Mohammadi Ziarani, F.
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
Faridbod, M. R. Ganjali, Powder Technol. 2017, 319, 271.
49] K. Mukhopadhyay, B. R. Sarkar, R. V. Chaudhari, J. Am. Chem.
Soc. 2002, 124, 9692.
[
[
[
[
[
50] A. E. Newkirk, Anal. Chem. 1960, 32, 1558.
51] F. Neese, Wiley Interdiscip. Rev. Comput. Mol. Sci. 2012, 2, 73.
52] A. D. Becke, Phys. Rev. A 1988, 38, 3098.
How to cite this article: Rohani S, Mohammadi
Ziarani G, Badiei A, Ziarati A, Jafari M, Shayesteh
A. Palladium‐anchored multidentate SBA‐15/di‐
urea nanoreactor: A highly active catalyst for
Suzuki coupling reaction. Appl Organometal Chem.
53] J. P. Perdew, Phys. Rev. B 1986, 33, 8822.
54] F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 2005, 7,
3
297.
2018;e4397. https://doi.org/10.1002/aoc.4397
[
55] A. Klamt, J. Phys. Chem. 1995, 99, 2224.