An efficient and new protocol for the Heck reaction using palladium nanoparticle-engineered dibenzo-18-crown-6-ether/MCM-41 nanocomposite in water

Article abstract of DOI:10.1002/aoc.4271

Palladium nanoparticle-incorporated mesoporous organosilica (MCM-41-Crown.Pd) was synthesized via the grafting of dibenzo-18-crown-6-ether moieties on the MCM-41 surface, followed by reaction of the nanocomposite with palladium acetate and then its reduction in ethanol. The cavity of the immobilized dibenzo-18-crown-6 as host material can stabilize the palladium nanoparticles effectively and prevent their aggregation and separation from the surface. The structure of the nanocomposite was characterized using various techniques. The catalytic properties of the nanocomposite in the Heck coupling reaction, one of the most useful transformations in organic synthesis, between aryl halides and olefins in water were also explored. The main advantages of the method are low cost, high yields, easy work-up and short reaction time. The nanocatalyst can be easily separated from a reaction mixture and was successfully examined for seven runs, with a slight loss of catalytic activity.

Full text of DOI:10.1002/aoc.4271

Received: 7 November 2017
DOI: 10.1002/aoc.4271
Revised: 15 December 2017
Accepted: 19 December 2017
F U L L P A P E R
An efficient and new protocol for the Heck reaction using
palladium nanoparticle‐engineered dibenzo‐18‐crown‐6‐
ether/MCM‐41 nanocomposite in water
Maedeh Azaroon1
| Ali Reza Kiasat1,2
1 Chemistry Department, College of
Science, Shahid Chamran University of
Ahvaz, Ahvaz, Iran
2 Petroleum Geology and Geochemistry
Research Centre (PGGRC), Shahid
Chamran University of Ahvaz, Ahvaz,
Iran
Palladium nanoparticle‐incorporated mesoporous organosilica (MCM‐41‐
Crown.Pd) was synthesized via the grafting of dibenzo‐18‐crown‐6‐ether moie-
ties on the MCM‐41 surface, followed by reaction of the nanocomposite with
palladium acetate and then its reduction in ethanol. The cavity of the
immobilized dibenzo‐18‐crown‐6 as host material can stabilize the palladium
nanoparticles effectively and prevent their aggregation and separation from
the surface. The structure of the nanocomposite was characterized using
various techniques. The catalytic properties of the nanocomposite in the Heck
coupling reaction, one of the most useful transformations in organic synthesis,
between aryl halides and olefins in water were also explored. The main advan-
tages of the method are low cost, high yields, easy work‐up and short reaction
time. The nanocatalyst can be easily separated from a reaction mixture and was
successfully examined for seven runs, with a slight loss of catalytic activity.
Correspondence
Maedeh Azaroon, Chemistry Department,
College of Science, Shahid Chamran
University of Ahvaz, Ahvaz, Iran.
Email: m‐azaroon@phdstu.scu.ac.ir
KEYWORDS
Heck coupling reaction, heterogeneous nanocatalyst, MCM‐41‐Crown.Pd, Pd nanoparticle‐
incorporated mesoporous organosilica
1 | INTRODUCTION
owing to the enhanced dispersion of active sites and faster
diffusion of large organic molecules.[4–9] Furthermore,
The economic improvement of feasible materials and
processes to eliminate harmful substances and toxic waste
materials is of paramount importance to organic synthesis
and environmental aspects.[1] Recently, in regards to this
challenge, research has been focused on the synthesis
and functionalization of mesoporous materials such as
organic polymers, silica, zeolite, alumina, hydroxyapatite
and clays as supports for homogeneous catalysts. Among
these, MCM‐41, because of its various advantages such
as tunable pore size, controlled size, morphology and
dual‐functional surface (external and internal), has
attracted a great deal of attention.[2,3]
such functionalized silica is notable for its low toxicity,
environmental friendliness and high chemical stability.
These advantages can be developed by using water as a
non‐toxic and non‐flammable solvent.[10–13]
The Pd‐catalysed cross‐coupling reactions, especially
Heck arylation of olefins with aryl halides, are simple,
efficient and versatile routes to the formation of carbon–
carbon bonds commonly used in modern organic synthe-
sis.[14–17] For excellent performance of Pd‐catalysed
processes, use of high‐activity Pd catalysts and green reac-
tion conditions are two important strategies for the design
of new heterogeneous Pd catalytic systems.[18–22]
Organometallic catalysts immobilized on mesoporous
silica supports including MCM‐41, SBA‐15 and PMO
exhibit significant improvement in the catalytic activity
Pd nanoparticles in catalyst systems have some disad-
vantages, such as agglomeration due to their high surface
energy and difficulty in separation from a reaction
Appl Organometal Chem. 2018;e4271.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4271

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AZAROON AND KIASAT
mixture due to the homogeneous character. Recently,
using immobilized metal nanoparticles as heterogeneous
catalysts has considerably expanded the scope and led to
interesting applications.[23–29]
tetramethylsilane as the internal standard. X‐ray diffraction
(XRD) patterns of the catalyst were obtained using a Philips
X‐ray diffractometer (model PW 1840) with a wavelength
of1.54056 Å, the diffraction angles (2θ) being set between
1° and 80°. Scanning electron microscopy (SEM) was con-
ducted using a MIRA3 FEG‐SEM (TESCAN, 1–30 kV). An
Analytik Jena (Germany) flame atomic absorption spectros-
copy (AAS) instrument was used for determination of Pd.
Energy‐dispersive X‐ray spectroscopy (EDS) analysis was
conducted with a VEGA\\TESCAN‐XMUT instrument.
Transmission electron microscopy (TEM) images were
obtained using a Zeiss EM10C (80 kV) instrument. Thermo-
gravimetric analysis (TGA) was carried out with a BAHR
SPA 503 under a nitrogen atmosphere at a heating rate of
10 °C min−1. Mass spectra were obtained with an Agilent
Technology ((HP) 5973 Network Mass Selective Detector)
instrument at 70 eV.
Many studies have been focused on Pd loaded on
modified MCM‐41, such as Schiff base anchored on
MCM‐41,[30–32] thioether‐functionalized MCM‐41,[33]
thiol‐functionalized MCM‐41[34] and diphosphino‐func-
tionalized MCM‐41.[22,35] However, to our knowledge,
there has been no general study of the Heck reaction
catalysed by a crown ether‐functionalized MCM‐41‐
anchored Pd (0) catalyst. Crown ethers are a class of mac-
rocyclic ligands with high affinity and selectivity for alkali
and alkaline earth metal ions.[36] Because of their hydro-
phobic exteriors and hydrophilic cores, they are typically
appropriate moieties to make junctions with larger
organic molecules.[37]
By considering all of the points mentioned above and
in the course of our investigations into the development
of novel inorganic–organic hybrid heterogeneous
nanocatalysts in organic transformations, the aim of the
work presented here was to highlight the synergistic
effects of the combined properties of MCM‐41, crown
ether cavity and stabilizing of Pd nanoparticles. The cata-
lytic properties of Pd nanoparticle‐incorporated mesopo-
rous organosilica, MCM‐41‐Crown.Pd, in Heck cross‐
coupling reactions were also investigated.
2.2 | Preparation of MCM‐41‐Crown.Pd
2.2.1 | Preparation of aminopropyl‐grafted
mesoporous MCM‐41
Aminopropyl‐grafted mesoporous MCM‐41 was synthe-
sized via surfactant‐templated sol–gel methodology and
then post‐modification process. First, a mixture of CTAB
(1 mmol, 0.4 g) and NaOH (2.54 mmol, 0.102 g) in water
was heated at 80 °C for 30 min. When the pH reached
12.3, TEOS (8 mmol, 1.7 g) was slowly added and the reac-
tion mixture stirred at 80 °C for 2 h. After quenching by
cooling the solution to room temperature, MCM‐41 silica
was precipitated.[6]
2 | EXPERIMENTAL
2.1 | General Remarks
For the grafting of aminopropyl moieties to the
surface of MCM‐41, 3‐aminopropyltrimethoxysilane
(10 mmol) was added to a suspension of MCM‐41 (1 g)
in anhydrous toluene (100 ml). The mixture was heated
under reflux conditions for 24 h under argon protection.
The light yellow solution was allowed to cool and was
then collected by filtration, washed thoroughly with tolu-
ene and dried under vacuum to afford pure 3‐
aminopropyl‐modified MCM‐41. The surfactant (CTAB)
was removed by acid extraction with concentrated HCl
(1 ml) in methanol (100 ml) at 60 °C for 6 h.
Cetyltrimethylammonium bromide (CTAB; 98%),
tetraethyl orthosilicate (TEOS; 98%), palladium(II) acetate
(Pd(OAc)2; 98%), absolute ethanol (99.8%), 3‐
aminopropyltrimethoxysilane (97%, Aldrich), aryl halides
and other chemical materials were purchased from Fluka
and Merck and used without further purification. The
purity determination of the products and reaction moni-
toring were accomplished using TLC on silica gel
polygram SILG/UV 254 plates. Products were character-
ized by comparison of their physical and spectral data
with those reported in the literature.
The surface area and pore size distribution of the support
were measured at 77 K using the nitrogen adsorption–
desorption method (ASAP 2000, Micromeritics). All samples
were degassed at 120 °C during 2 h before such measure-
ments. Fourier transform infrared (FT‐IR) spectra were
recorded with a BOMEM MB‐Series 1998 FT‐IR spectrome-
2.2.2 | Synthesis of 4′,4″‐diformyldibenzo‐
18‐crown‐6‐ether (DFBCE)
Diethylene glycol ditosylate (DEDT) wasfirstly synthesized
and used as the precursor for the synthesis of benzo crown
ether according to Pederson's method with suitable adapta-
tion.[7,8] Briefly, for the preparation of DEDT,[9] diethylene
glycol (140 mmol, 14.86 g) was dissolved in tetrahydrofuran
(THF; 80 ml). Meanwhile, an aqueous solution of sodium
1
ter. Products were characterized using H NMR and 13C
NMR spectra with known samples (S1–S6, supporting infor-
mation). NMR spectra were recorded in CDCl3 with a
Bruker Advance DPX 400 MHz spectrometer using

AZAROON AND KIASAT
3 of 11
hydroxide (400 mmol, 16 g) in water (80 ml) was prepared.
The two solutions were mixed and cooled using an ice bath
with magnetic stirring. To this mixture was added dropwise
tosyl chloride (260 mmol, 48.6 g) in THF (80 ml) over 2 h
with continuous stirring and cooling of the mixture below
5 °C. The solution was stirred at 0–5 °C for an additional
2 h. After this, the mixture was poured into ice–water
(250 ml). The DEDT product was filtered, washed with dis-
tilledwater,driedandrecrystallizedtwicefrommethanolto
afford a pure product.
Then for the synthesis of DFBCE, a mixture of 3,4‐
dihydroxybenzaldehyde (60 mmol, 8.28 g) and sodium
SCHEME 1 Synthetic route for preparation of MCM‐41‐Crown.Pd.
FIGURE 1 FT‐IR spectra of (a) MCM‐
41 with CTAB, (b) MCM‐41‐NH2 and (c)
MCM‐41‐Crown

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AZAROON AND KIASAT
hydroxide pellets (60 mmol, 2.44 g) in 1‐butanol (40 ml)
was refluxed under argon for 30 min to ensure complete
dissolution of sodium hydroxide. A solution of DEDT
(30 mmol, 12.36 g) in 1‐butanol (20 ml) was added slowly
over 1 h, and the mixture was refluxed for 1 h. The
temperature was lowered to 90 °C and sodium hydroxide
pellets (2.44 g) were added. Refluxing was continued for
30 min and DEDT (30 mmol, 12.36 g) in 1‐butanol
(20 ml) was added slowly over 1 h. Refluxing was contin-
ued for 16 h. Concentrated hydrochloric acid (1 ml) was
slowly added, and then a third of the solvent was rapidly
removed by distillation. The distillation was continued
but the volume in the flask was kept constant by the
steady addition of water until the vapour temperature
reached 100 °C. The mixture was filtered, washed with
200 ml of water and sucked dry. The DFBCE product
was dispersed in 200 ml of acetone, stirred for 30 min,
filtered, washed with 50 ml of acetone and dried in an
oven at 100 °C.
2.2.3 | Preparation of MCM‐41‐anchored
dibenzo‐18‐crown‐6‐ether
DFBCE (1.5 mmol, 0.624 g) was dissolved in CHCl3
(50 ml) and refluxed to complete dissolution of the
crown ether. Aminopropyl‐grafted mesoporous MCM‐41
(1 g) was added to the mixture and refluxed for 24 h.
The precipitate, MCM‐41‐Crown, was filtered, washed
with dry CHCl3 (3 × 20 ml) and dried in an oven at
50 °C for 4 h.
FIGURE 2 SEM images of (a) MCM‐41, (b) MCM‐41‐Crown and
(c) MCM‐41‐Crown.Pd.
FIGURE 3 TEM images of MCM‐41‐Crown.Pd.

AZAROON AND KIASAT
5 of 11
FIGURE 4 EDS spectrum of MCM‐41‐Crown.Pd.
2.2.4 | Incorporation of Pd nanoparticles
into MCM‐41‐Crown
2.3 | General Procedure for Heck
Coupling Reaction Catalysed by MCM‐41‐
Crown.Pd Nanocomposite in Water
Palladium acetate (0.12 g, 0.52 mmol) was added to
MCM‐41‐Crown (2 g) in absolute ethanol (20 ml), and
stirred for 24 h at room temperature under argon protec-
tion. Then, the mixture was filtered and washed with etha-
nol (3 × 10 ml) and diethyl ether (3 × 10 ml). After drying in
a vacuum oven at 80 °C overnight, the MCM‐41‐Crown.Pd
(1.3 mol% Pd) catalyst was obtained as a dark solid.
Inatypicalexperiment, toamixtureofarylhalide(1mmol),
styrene(1mmol)andK2CO3 (2.5mmol)in5mlofdeionized
water,MCM‐41‐Crown.Pd(0.07g,1.3mol%)wasaddedand
heated in an oil bath (90 °C) for the required time. The reac-
tionwasmonitoredusingTLC.Aftercompletionofthereac-
tion, the mixture was cooled to room temperature and
filtered, and the remaining solid was washed with CH2Cl2
(3 × 5 ml). After extraction, the organic layer was dried over
Na2SO4 and evaporated under reduced pressure; the crude
product was purified by silica gel chromatography (n‐hex-
ane–AcOEt as eluent).
FIGURE 5 (a) High‐angle and (b) low‐angle XRD patterns of
MCM‐41‐Crown.Pd nanocomposite
FIGURE 6 TGA thermogram of MCM‐41‐Crown nanocomposite

6 of 11
AZAROON AND KIASAT
FIGURE 7 Nitrogen adsorption–desorption isotherms (left) and pore size distributions (right) of (a) MCM‐41‐Crown and (b) MCM‐41‐
Crown.Pd.

AZAROON AND KIASAT
7 of 11
The UV diffuse reflectance spectrum (S7, supporting
information) showed complete conversion of Pd(II) to
Pd(0) by the absence of a peak at 420 nm of the Pd(II) spe-
cies.[40–42] To confirm the crystallinity of the Pd nanopar-
ticles, the sample was characterized using XRD analysis
(Figure 5a). The result reveals the presence of Pd nano-
particles on the silica surface with characteristic peaks at
2θ of 40.0°, 46.9°, 67.9° and 80.1° corresponding to
[111], [200], [220] and [311], respectively, and the stron-
gest peak of the XRD pattern corresponding to the struc-
ture of silica phase. This observation confirms the
presence of metallic Pd particles on the mesoporous
MCM‐41 surface.[15] The low‐angle XRD pattern of the
MCM‐41‐Crown.Pd nanocomposite (Figure 5b) shows
one peak at 2θ = 2.6°, corresponding to the [100] plane,
which is characteristic of a hexagonal pore system. The
size of the Pd nanoparticles is estimated as 12 nm using
the Scherrer equation.
TGA was used to determine the percentage of organic
functional groups chemisorbed onto MCM‐41. The TGA
curve of MCM‐41‐Crown shows the mass loss of the
organic materials as they decompose upon heating
(Figure 6). According to this curve, there are two weight
loss steps. The first weight loss is of 11.87% below
200 °C which might be due to the loss of physically
adsorbed water as well as dehydration of the surface OH
groups and organic solvents. The second weight loss step
of about 23.78% in the range 200–800 °C is due to thermal
decomposition of organic parts, and probably the conden-
sation of the silanol groups of the silica shell. Thus, TGA
also confirms the successful grafting of crown ether onto
the surface of mesoporous MCM‐41. The total weight loss
over the full temperature range is estimated to be 35.65%
due to the loss of the adsorbed water and organic units.
3 | RESULTS AND DISCUSSION
MCM‐41‐Crown.Pd was conveniently synthesized via the
grafting of dibenzo‐18‐crown‐6‐ether moieties on the
MCM‐41 surface by surfactant‐templated sol–gel method-
ology and post‐modification process, followed by reaction
of the resulting MCM‐41‐Crown with palladium acetate
and then reduction in ethanol.[38,39] The systematic steps
of MCM‐41‐Crown.Pd preparation are shown in
Scheme 1.
To characterize the nanocomposite, and to confirm
the immobilization of the active components on the pore
surface of MCM‐41, FT‐IR spectroscopy was utilized
(Figure 1). In all spectra, the typical Si―O―Si bands at
around 1212, 1080, 795 and 462 cm−1 associated with
the formation of a condensed silica network are present,
but a weak peak associated with Si―OH groups at
964 cm−1 is also present, and peaks appearing at 2916
and 2851 cm−1 are characteristic of C―H stretching
vibrations. A broad band at 3100 to 3600 cm−1 and a
weak band at around 1520 cm−1 observed in the spec-
trum of MCM‐41‐NH2 are attributed to NH2 stretching
vibrations, indicating the presence of amino‐functional-
ized groups in MCM‐41‐NH2. In addition, the FT‐IR
spectrum of MCM‐41‐Crown exhibits a new peak at
1682 cm−1 which is assigned imine band and confirms
that DFBCE was covalently grafted onto the surface of
MCM‐41‐NH2.
SEM was used to determine the particle size and
particle morphology. Figure 2 shows SEM images of
MCM‐41, MCM‐41‐Crown and MCM‐41‐Crown.Pd
composite, indicating spherically shaped morphology
without intergrowth aggregation and monodisperse and
regular uniform nanoparticles. The particles exhibit a size
distribution from 300 to 500 nm with an average size of
around 350 nm.
TABLE 1 Comparison of textural parameters of MCM‐Crown
and MCM‐41‐Crown.Pd
TEM studies of the MCM‐41‐Crown and MCM‐41‐
Crown.Pd organic–inorganic composites (Figure 3)
revealed that the Pd nanoparticles had been incorporated
successfully in the mesoporous organosilica. Some dark
spots appearing on the surface of MCM‐41‐Crown.Pd
can be attributed to the presence of Pd nanoparticles on
the support matrix, shown with arrows in Figure 3. The
nanocomposite morphology is close to spherical and the
particle size of Pd(0) is around 11 nm which is near to
the value calculated from XRD data.
The EDS analysis (Figure 4) of the nanocomposite
shows the elements, including C, O, N and Si, that are
present in the structure of the nanocomposite. In
addition, the presence of palladium is indicated on
MCM‐41‐Crown.Pd. The incorporation of Pd(0) in the
nanocomposite was also confirmed and determined
(2 wt%) using AAS.
BET surface
area (m2 g−1
Pore volume
Sample
)
(cm3 g−1
)
MCM‐Crown
225
162
3.66
MCM‐41‐Crown.Pd
1.38
TABLE 2 Optimization of MCM‐41‐Crown.Pd nanocomposite in
proposed reaction
Entry Catalyst (mg) Base (mmol) Time (min) Yield (%)
1
2
3
4
5
—
40
50
70
70
2.5
2.5
2.5
2
360
45
25
30
25
—
70
80
80
98
2.5

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AZAROON AND KIASAT
Figure
7
shows the low‐temperature nitrogen
The hysteresis loops are very narrow, which clearly indi-
cates the narrow channels of the MCM‐41 mesoporous
support.[43] But as shown in Figure 7(b), MCM‐41‐
Crown.Pd exhibits a type‐III isotherm. Regarding the syn-
thetic strategy of nanocomposite synthesis, in the
aminopropyl grafting step, pores of MCM‐41 were occu-
pied by the surfactant. Because of this, a large amount
adsorption–desorption isotherms and pore size distribu-
tions of MCM‐41‐Crown and MCM‐41‐Crown.Pd nano-
composites. MCM‐41‐Crown (Figure 7a) exhibited a
type‐IV isotherm with sharp capillary condensation steps
at relative pressure (P/P0) range and an H1‐type narrow
hysteresis loop, which is typical of mesoporous solids.
TABLE 3 Heck cross‐coupling reactions catalysed by MCM‐41‐Crown.Pd nanocomposite
Entry
R
X
Y
Time (min)
Yield (%)a
1
H
I
Ph
25
92
2
H
I
CO2H
Ph
30
16
27
60
90
40
50
53
70
90
94
92
85
89
75
75
87
85
3
4‐NO2
4‐NO2
H
I
4
I
CO2H
Ph
5
Br
Br
Br
Br
Br
Br
6
H
CO2H
Ph
7
4‐OMe
4‐OMe
4‐Me
4‐Me
8
CO2H
Ph
9
10
CO2H
aReaction conditions: 1 mmol of aryl halide, 1 mmol of terminal alkene, 5 ml of H2O, 0.07 g of MCM‐41‐Crown.Pd and 2.5 mmol of K2CO3.
SCHEME 2 Plausible reaction mechanism for Heck reaction catalysed by MCM‐41‐Crown.Pd.

AZAROON AND KIASAT
9 of 11
of grafting units were dispersed onto the MCM‐41 surface
and some of them were trapped in the interior of MCM‐
41, and so consequently surface area and pore volume of
MCM‐41‐Crown were reduced.
selected as a model system in aqueous medium under
thermal conditions (90 °C). According to TLC, only one
spot of alkene product was produced after 25 min. Opti-
mization of a number of reactants and the catalyst showed
that 2.5 mmol of K2CO3 and 0.07 g of the catalyst com-
pleted the reaction in the minimum time (Table 2). It is
worth mentioning that the reaction in the absence of
nanocomposite after prolonged reaction time did not
afford any product.
The generality and synthetic scope of this coupling
protocol were demonstrated by synthesizing a series of
stilbenes in 25–90 min and in yields of 75–94%. As clearly
evident from Table 3, the MCM‐41‐Crown.Pd nanocom-
posite can catalyse the Heck cross‐coupling reactions of
various aryl halides containing electron‐withdrawing
and electron‐donating groups with styrene and acrylic
acid.
Some important data of Brunauer–Emmett–Teller
(BET) surface area and pore volume of MCM‐41‐Crown
and MCM‐41‐Crown.Pd are presented in Table 1. As a
result of the Pd nanoparticles depositing inside the
cavities of the crown ether and onto the surface of MCM‐
41, thereis adecreasein surfacearea andpore volume.[44,45]
To evaluate the catalytic activity of MCM‐41‐Crown.
Pd as a reusable and heterogeneous porous inorganic–
organic hybrid nanocatalyst and with an aim of develop-
ing a simple practical method for carbon–carbon bond
formation through Heck coupling reactions, initially the
reaction of iodobenzene (1 mmol) and styrene (1 mmol)
in the presence of K2CO3 and the nanocomposite was
The cavity size of the crown ether is 2.6–3.2 Å in diam-
eter. Hydrophilic Pd(0) atoms have a radius of 1.37 Å,
which makes them suitable for enclosure in the crown
cavity. Further, the crown has an open structure, and thus
can allow Pd(0) orbitals to engage in the Heck coupling
reaction. A plausible reaction mechanism for the Heck
coupling reaction is shown in Scheme 2, giving us a gen-
eral picture of the steps needed for catalytic olefination.
The first step is oxidation addition of Pd(0) catalyst to
afford σ‐arylpalladium(II) complexes. Coordination of
the terminal alkene and subsequent C―C bond formation
by syn addition provide σ‐alkylpalladium(II) intermedi-
ates which readily undergo β‐hydride elimination to
release the alkene Heck product. For the continuance of
the cycle, a base (K2CO3) is needed for the conversion of
FIGURE 8 Recyclability of nanocatalyst
TABLE 4 Comparison of results of present system with those of some recently reported procedures
Entry
Catalyst and conditions
Yield
Ref.
[49]
1
MCM‐41‐Pd, Bu3N, NMP, 100 °C, 72 h
95
[50]
[18]
[19]
[20]
[21]
[39]
[22]
[38]
2
MCM‐41‐S‐Pd(0), Bu3N, NMP, 100 °C, 6 h
NHC‐Pd/MCM‐41a, DMA/H2O, 130 °C, 2 h
MCM–NH2·Pd(0), Et3N, DMF, 70 °C, 2 h
Pd(0)‐MCM‐41, DMF, NaOAC, 100 °C, 24 h
Pd‐MCM‐41, NMP, Na2CO3, 150 °C, 1 h
MCM‐41‐2P‐Pd(0)b, Bu3N, NMP, 100 °C, 5 h
MCM‐41‐SH‐Pd(0), Bu3N, NMP, 100 °C, 6 h
PdNP‐SβCDc, K2CO3, H2O, 90 °C, 2 h
98
96
95
90
84
94
92
98
98
3
4
5
6
7
8
9
10
MCM‐41‐Crown.Pd, K2CO3, H2O, 90 °C, 0.4 h
This work
aMCM‐41‐supported N‐heterocyclic carbene–Pd complex.
bDiphosphino‐functionalized MCM‐41‐anchored palladium (0) complex.
cPd nanoparticles on silica β‐CD substrate.

10 of 11
AZAROON AND KIASAT
hydridopalladium(II) complex [HPdXL] to the active
Pd(0) catalyst. This mechanism is proposed based on
reported literature.[46–48]
ACKNOWLEDGEMENT
This work was supported by the Research Council at the
Shahid Chamran University of Ahvaz.
Reusability is one of the most important benefits of
heterogeneous catalytic systems from economic and envi-
ronmental points of view. The recyclability of the nano-
composite was investigated for the reaction between
iodobenzene and styrene by carrying out seven consecu-
tive cycles using the same reaction conditions. After each
run, the catalyst was easily recovered by vacuum filtration
using Whatman filter paper, then washed with Et2O
(5 ml) and n‐hexane (5 ml). The solid catalyst was dried
under vacuum after each cycle and then reused for the
next reaction (Figure 8).
In view of the leaching problems observed with palla-
dium supported on MCM‐41‐Crown, quantitative analysis
using AAS was employed to determine the amount of
metal in the reaction. The heterogeneity of the MCM‐41‐
Crown.Pd catalyst was examined by carrying out a hot
filtration test using styrene and iodobenzene as model
substrates. No palladium could be detected in the liquid
phase using AAS and, more significantly, after hot filtra-
tion, the reaction of the residual mixture was completely
stopped.
ORCID
Maedeh Azaroon http://orcid.org/0000-0002-6867-3418
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How to cite this article: Azaroon M, Kiasat AR.
An efficient and new protocol for the Heck reaction
using palladium nanoparticle‐engineered dibenzo‐
18‐crown‐6‐ether/MCM‐41 nanocomposite in
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