Nanostructured Pyrophosphate Na2PdP2O7-Catalyzed Suzuki-Miyaura Cross-Coupling Under Microwave Irradiation

Article abstract of DOI:10.1002/aoc.4232

Nanostructured palladium pyrophosphate (Na₂PdP₂O₇) catalyst was synthesized and well characterized by using different techniques (TGA, XRD, SEM, TEM..). This nanocatalyst exhibited excellent catalytic activity in the synth

Full text of DOI:10.1002/aoc.4232

Received: 12 October 2017
DOI: 10.1002/aoc.4232
Revised: 21 November 2017
Accepted: 25 November 2017
F U L L P A P E R
Nanostructured Pyrophosphate Na PdP O ‐Catalyzed
2
2 7
Suzuki‐Miyaura Cross‐Coupling Under Microwave
Irradiation
1
,2
1
1
2
1
Karim Dânoun | Younes Essamlali | Othmane Amadine | Rida Tabit | Aziz Fihri |
3,4
1,2
Christophe Len | Mohamed Zahouily
1
MASCIR Foundation, Rabat Design, Rue
Nanostructured palladium pyrophosphate (Na PdP O ) catalyst was synthesized
Mohamed El Jazouli, Madinat El Irfane,
2
2 7
1
2
0100 Rabat, Morocco
and well characterized by using different techniques (TGA, XRD, SEM, TEM....).
This nanocatalyst exhibited excellent catalytic activity in the synthesis of biaryl
compounds via Suzuki‐Miyaura cross‐coupling to produce their corresponding
products in good to excellent yields under mild conditions. The catalyst is
recyclable and was recycled for four runs for the reaction of 4‐bromoacetophenone
with phenylboronic acid without appreciable loss of its catalytic activity.
Laboratoire de Matériaux, Catalyse et
Valorisation des Ressources Naturelles,
URAC 24, FST, Université Hassan II‐
Casablanca, B.P. 146, 20650, Morocco
3
Transformations Intégrées de la Matière
Renouvelable, UTC/ESCOM, Centre de
Recherche Royallieu, B.P. 20529, 60205
Compiègne, France
KEYWORDS
4
PSL Research University, Chimie
green chemistry, heterogeneous catalysis,microwave irradiation, palladium pyrophosphate, Suzuki‐
ParisTech, CNRS, Institut de Recherche de
Chimie Paris, 11 rue Pierre et Marie Curie,
F‐75231 Paris Cedex 05, France
Miyaura reaction
Correspondence
Prof. Mohamed Zahouily, MASCIR
Foundation, Rabat Design, Rue Mohamed
El Jazouli, Madinat El Irfane 10100‐Rabat,
Morocco; Laboratoire de Matériaux,
Catalyse et Valorisation des Ressources
Naturelles, URAC 24, FST, Université
Hassan II‐Mohammedia B.P. 146, 20650,
Morocco.
Email: m.zahouily@mascir.com
1
| INTRODUCTION
Recently, much attention has been directed toward the
Suzuki reaction due to a variety of factors, such as its mild
The Suzuki‐Miyaura coupling reaction of arylboronic
acids with aryl halides is one of the most useful and fun-
damental transformations in modern synthetic organic
chemistry for the construction of carbon‐carbon bonds.
This palladium‐catalyzed carbon‐carbon bond‐forming
process is particularly useful for the preparation of biaryl
compounds that have a diverse spectrum of applications,
reaction conditions, the availability and chemical stability
of a large number of boronic acids, and high product
yields; at the same time, due to its the highly tolerant with
many functional groups specifically when selective cou-
pling of molecules at specific positions without affecting
[
8–12]
other functional groups is required.
These reactions
are usually catalyzed with palladium in presence of auxil-
iary ligands using homogeneous catalytic systems as they
[
1–7]
ranging from pharmaceuticals to materials science.
Appl Organometal Chem. 2018;e4232.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4232

2
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DÂNOUN ET AL.
provide high reactivity, high turnover numbers and work
under milder reaction conditions and particularly the
possibility of coupling the widely available and relatively
2 | EXPERIMENTAL
2.1 | Materials
[13–22]
low‐cost of aryl chlorides.
However, these traditional
All commercial reagents were purchased from Aldrich
Chemical Company and were used without further purifi-
cation. X‐ray diffraction (XRD) patterns of the catalyst
were obtained at room temperature on a Bruker AXS
D‐8 diffractometer using Cu‐Kα radiation in Bragg‐
Brentano geometry (θ‐2θ). Fourier transform infrared
catalytic systems continue to pose significant difficulties
like palladium residue contamination of the products after
purification, and it is impossible to regain the costly cata-
[23,24]
lyst for reuse.
The synthesis of heterogeneous cata-
lysts and the design of protocols that minimize the
consumption of expensive transition‐metals, toxic ligands
and the use of green solvents has increased rapidly, and
numerous heterogeneous catalytic systems have been
reported to be successful for Suzuki‐Miyaura coupling in
(
FT‐IR) was performed on an ABB Bomem FTLA 2000
spectrometer equipped with a Golden Gate single reflec-
tion ATR accessory. Thermogravimetric analysis‐Deriva-
tive Thermogravimetry (TGA‐DTG) were conducted
under air in a TA Instrument Q500 apparatus with a
10 °C/min ramp between 25 and 1000 °C. Scanning elec-
tron microscopy (SEM) pictures were recorded on a FEI
Quanta 200 microscope after carbon metallization. Trans-
mission Electron Microscopy (TEM) micrographs were
obtained on a FEI microscope at 120 kV. The local chem-
ical composition of the prepared catalysts was analyzed
using an energy dispersive X‐ray spectrometer (EDS)
embedded on TEM microscope. The N2 adsorption‐
desoption isotherms were collected using a Micromeritics
[25]
water.
Through covalent and non‐covalent bonding,
palladium was immobilized on various solids and supports
[
26]
[27]
such as organic polymers,
carbon,
layered clays,
activated
[28]
[29]
[30]
magnetic nanoparticles,
and silica.
Nano‐structures are commonly much more active than
their massive counterparts. The design of nanoscale
objects in order to broaden their spectrum of emerging
applications has become a topic of tremendously expanded
study owing to their outstanding properties. On the other
hand, metal pyrophosphates (MP O ) offer a considerable
2
7
number of structures which can give original physical
[31]
3Flex Surface characterization analyzer. Prior to N sorp-
2
properties. These materials possess high capacity to sta-
bilize various oxidations states due to the high negative
tion, the sample was degassed under vacuum at 120 °C
overnight. The specific surface areas were determined
from the nitrogen adsorption‐desorption isotherms (at
‐196 °C), using the BET (Brunauer‐Emmett‐Teller)
method. Pore size distributions were calculated from the
3
‐
charge of the anionic phosphate anion (PO4 ) which pro-
motes formation of a framework with a high degree of
[32–34]
mechanical, chemical and thermal stability.
Metal
Pyrophosphates have attracted considerable scrutiny
owing to their interesting properties needed in a wide
N adsorption isotherms with the ‘classic theory model’
2
[
35]
of Barret, Joyney and Halenda (BJH). NMR spectra were
recorded on a Bruker Avance III 600 MHz NMR spec-
trometer at 298 K, with working frequencies of 600.13
and 150.902 MHz for proton and carbon, respectively,
range of application such as ceramics
optical mate-
[36]
rials
columns.
and packing materials for chromatographic
[37]
Different catalytic systems based on metal
pyrophosphates have been used in the activation of light
alkanes. Among these materials, the Ni P O , Ag P O ,
CDCl as the solvent and TMS as the internal standard.
3
2
2
7
4 2 7
The local chemical structure around phosphorus atoms
Zn P O and rare earth phosphates that were found to cat-
2
2 7
31
was examined by solid‐state P‐nuclear magnetic reso-
nance under magic angle spinning conditions (MAS‐
NMR) spectroscopy on a Bruker. The microwave (MW)
used in this study is StartSynth (Milestone Srl.) with a
microwave power delivery system ranging from 0 to
alyze the oxidative dehydrogenation of n‐butane to maleic
[38,39]
anhydride and the iso‐butane to iso‐butene.
How-
ever, only few studies have been reported in the literature
concerning the use of palladium phosphate as a catalyst
and to the best of our knowledge, the use of a palladium
pyrophosphate as a heterogeneous catalyst for the
Suzuki‐Miyaura cross coupling in water has not been
1
5
200 W. Open vessel experiments were carried out in a
0‐mL round bottom flask fitted with a reflux condenser.
[40]
reported in literature.
In the present work, as part of
our ongoing interest in the synthesis of highly added value
2
.2 | Preparation of the catalyst
organic compounds via highly efficient and eco‐friendly
[41–43]
protocols,
we report our investigations on the devel-
The synthesis of nanostructured pyrophosphate
opment of an environmentally friendly route for the
practical and economical synthesis of biaryls through
Suzuki‐Miyaura cross‐coupling reaction under microwave
Na PdP O was carried out by the conventional solid‐state
2
2 7
reaction technique using NaH PO .2H O and PdCl as
2
4
2
2
starting materials in a molar ratio 2:1 respectively. Reac-
tants were ground together in an agate mortar and heated
progressively in an alumina crucible from 150 to 650 °C,
irradiation
using
nanostructured
pyrophosphate
(
Na PdP O ) as a highly efficient heterogeneous catalyst.
2
2 7

DÂNOUN ET AL.
3 of 10
thus leading to yellow powder that was obtained after
quenching (Figure 1).
and tetra‐n‐butylammonium bromide (TBAB) (64 mg,
0.2 mmol) were combined in a 50 ml round‐bottom flask
under nitrogen atmosphere. Then, water (4 ml) and aryl
chloride (1.76 mmol) were added and the resulting
mixture was exposed to microwave at 100 °C for
2
.3 | Typical procedure for Suzuki
coupling of aryl bromides using Na PdP O
2 7
2
90 minutes. After the completion of the reaction, the
as catalyst
catalyst was filtered. The obtained filtrate was extracted
with dichloromethane and dried with anhydrous sodium
sulfate. After removing the solvent, the crude material
was chromatographed on silica gel to yield the final biaryl
product.
Na PdP O (5 mg, 0.9 mmol%), K CO3 (486.4 mg,
2
2
7
2
3
.52 mmol), and phenylboronic acid (322 mg, 2.64 mmol)
were placed in a round bottom flask under nitrogen atmo-
sphere. Water (2 ml) and aryl bromide (1.76 mmol) were
added and the resulting mixture was then heated under
microwave irradiation at 150 °C for 15 min. After the
completion of the reaction, the catalyst was removed by
simple filtration and the reaction mixture was repeatedly
extracted with dichloromethane. The organic layers were
combined, dried over Na SO , filtered and evaporated
3
| RESULTS AND DISCUSSION
.1 | Catalyst characterization
3
2
4
FT‐IR spectrum of the Na PdP O catalyst showed the
2
2 7
under reduced pressure. The resulting residue was puri-
fied by column chromatography over a silica gel column
presence of P O7 units (Figure 2). This finding con-
2
firmed by the symmetrical vibration bands of P‐O‐P at
(100‐200 mesh) affording the biphenyl product.
‐1
7
60 cm as well as the anti‐symmetric vibration bands
‐
1
at 910 cm . The related vibrations of the PO groups
4
were shared between two distinct regions: a region of
2
.4 | Typical procedure for Suzuki
coupling of aryl chloride using Na PdP O
2 7
‐1
symmetrical vibrations at 987 and 1033 cm and
2
‐1
another observed at 1180 cm . Furthermore, the bands
as catalyst
around 400‐700 cm‐ were assigned to the deformation
1
Na PdP O (50 mg, 0.9 mmol %), Na CO (373.12 mg,
2
2
7
2
3
and rocking modes of PO groups.
4
3
.52 mmol), phenylboronic acid (322 mg, 2.64 mmol)
TGA analysis of the mixture of the starting reagents
revealed the formation of the desired palladium pyrophos-
phate material (Figure 3). According to the TGA curve,
the first weight loss below 86 °C can be attributed to the
evaporation of surface bonded water according to equa-
tion 1. The second weight loss occurred between 150
and 215 °C can be attributed to a complete loss of crystal
water in NaH PO ·2H O. The third weight loss took place
2
4
2
between 250 and 320 °C and can be attributed to the melt-
ing process and the dehydration of NaH PO as shown in
2
4
equation 2. It was reported that the NaH PO decomposes
2
4
FIGURE
Na PdP
1
Schematic illustration of the preparation of
2
2
O
7
2 2 7
FIGURE 2 FT‐IR spectrum of Na PdP O

4
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DÂNOUN ET AL.
according to the Scherer equation, the average crystallite
size of the synthesized nanostructured Na PdP O is
2
2 7
about 7.9 nm.
In order to confirm the various interpretations and the
structural analysis that was previously proposed while
particularly focusing on the nature of the phosphate
31
groups present in our material, P NMR experiments
were conducted (Figure 5). For rotation frequencies
greater than or equal to 6 kHz, there is a clear separation
between the isotropic signal and the rotation bands on
31
the magic angle spinning spectra of the P, which
makes it possible to confirm that the isotropic part of
the spectrum contains a single contribution (Figure 5a).
Indeed, the presence of a single isotropic signal at
20.11 ppm proves the existence of only one type of
phosphorus site in the sodium palladium phosphate
structure (Figure 5b).
SEM was used for studying the morphology of the
surface of the Na PdP O catalyst (Figure 6). The micro-
FIGURE
3
TGA and DTG curves of the mixture of
O and PdCl
2
2 7
NaH PO .2H
2
4
2
2
graphs clearly revealed that the surface is homogeneous
in size and the shapes and the agglomerates were
arranged randomly. In addition, the surface of these
agglomerates is fairly smooth with low visible porosity.
This can be explained by a heterogeneous growth of the
crystallites caused the adopted synthesis method, conse-
quently affecting the morphology and porosity.
and dehydrates to acid pyrophosphate when the tempera-
ture is higher than its melting points.
[44]
The continuous
weight loss observed between 330 and 800 °C can be
attributed to the reaction of melted alkali metal phos-
phates with palladium chloride according to equation 3.
XRD pattern of the as‐prepared material (Figure 4)
exhibits clear diffraction peaks of Na PdP O according
TEM was used to analyze the microstructure of our
material. The TEM data acquired showed that the
Na PdP O particles were clustered and formed heteroge-
2
2
7
2
2 7
to JCPDS File No. 10‐6543. The diffraction peaks are
intense and narrow suggesting that the as‐prepared
Na PdP O particles are very small in size and have an
excellent crystallinity. No characteristic peaks of impurity
were observed in the pattern indicating the formation of
pure sodium palladium phosphate material. Furthermore,
neous aggregates of nanoparticles that were small in size
and irregularly formed (Figure 7a). From the data
obtained by TEM, the particle size histogram was drawn
(from 2.3 to 24 nm), and the mean size of the particles
was determined to be around 7 nm (Figure 7b).
2
2 7
Elemental analysis by EDS was conducted to prove the
presence of different components of our nanocatalyst
(
Figure 8). This analysis revealed the presence of sodium,
palladium, phosphorus and oxygen with relative atomic
ratio. The result in atomic % is as follow: Na: 17.26; Pd:
7.60; P: 17.54; O: 57.60. In addition, no trace of any
impurity was detected.
The surface area of Na PdP O nanocatalyst was
2
2 7
determined by BET method from the adsorption‐desorp-
tion isotherm of N2 at 77 K. According to IUPAC
classification, the Na PdP O exhibits a nitrogen adsorp-
2
2 7
tion‐desorption isotherm type (IV) with a distinct hystere-
[
45]
sis loop (Figure 9a).
The average surface area was
2
‐1
around 1.16 m g . The pore size distribution of the
calcined Na PdP O nanocatalyst, determined according
2
2 7
to the BJH method was given in figure 9b, which shows
the presence of three populations centered at 2.88, 5.79
and 10.10 nm, respectively (Figure 9b) which indicates
the existence of textural mesopores.
2 2 7
FIGURE 4 XRD pattern of Na PdP O

DÂNOUN ET AL.
5 of 10
3
1
FIGURE 5 Solid‐state P‐MAS NMR spectra of Na
2
PdP
2
O
7
for frequencies of 6 and 12 kHz (Asterisks indicate the rotation bands) (a).
Zoom on the isotropic signal (b)
2 2 7
FIGURE 6 SEM micrographs of Na PdP O
2 2 7 2 2 7
FIGURE 7 TEM micrograph of the Na PdP O nanocatalyst (a) and particle size distribution of the Na PdP O (b)

6
of 10
DÂNOUN ET AL.
2 2 7
FIGURE 8 EDS spectrum of Na PdP O
FIGURE 10 The effect of the base on Suzuki‐Miyaura reaction
3.2 | Catalytic activity studies
To explore the potential activity of this heterogeneous
catalyst, the parameters like selection of base, reaction
time and volume solvent should be optimized before the
activity of a catalyst is tested. We initially investigated
the Suzuki‐Miyaura cross coupling reaction between
4‐bromoacetophenone (1a) and phenylboronic acid (2a)
under MW irradiation using water as green solvent. To
establish the workability of our approach and to optimize
the reaction conditions, we initially conducted the reac-
tion without a base, yet no activity was observed despite
a prolonged reaction time. After screening different bases,
K CO , Na CO , NaOH and KF showed similar activities.
FIGURE 11 The effect of reaction time on Suzuki‐Miyaura
reaction
2
3
2
3
The relatively weak and less expensive K CO was chosen
2
3
for the continuation of the methodology study (Figure 10).
Next, we investigated the effects of reaction time on
the catalytic activity of the Na PdP O nanocatalyst
anymore. Shorter reaction times are desired in catalysis
systems to reduce labor and operational.
On the other hand, with its high dielectric constant,
water is potentially a very practical solvent for the micro-
wave‐assisted Suzuki‐Miyaura cross coupling reaction of
aryl halides with aryl boronic acids. To investigate the
effect of water on the Suzuki cross‐coupling reaction cata-
2
2 7
(Figure 11). When the reaction time was 5 minutes, the
yield was modest (69%). The increase in reaction time
induced an increase in yield. The optimal time to couple
aryl bromides with arylboronic acids is 15 minutes since,
over this period of time, the yield does not evolve
lyzed by Na PdP O , different volumes of water were used
2 2 7
2 2 7
FIGURE 9 Nitrogen adsorption‐desorption isotherm of Na PdP O (a) and BJH pore size distribution (b)

DÂNOUN ET AL.
7 of 10
for this reaction (Figure 12). The reaction conducted with
9‐12). Similar results were reported in literature in the
coupling of 4‐ formylphenylboronic acid with 1‐bromo‐
1
1
2 ml of water gave only 76 % of the desired product in
5 min. Fortunately, the product yield was found to
[
49]
4‐nitrobenzene and 4‐bromobenzaldehyde.
These
increase significantly by reducing the volume of water
from 12 to 2 ml. Indeed, the reaction conducted with
results confirmed that microwave heating in water drasti-
cally reduced the reaction time compared to thermal
heating (0.25‐1 hour vs 5‐15 hours). After achieving excel-
lent results with aryl bromides, we further applied this
catalytic system to the activated chloroarenes. Therefore,
2
9
ml of water produced the corresponding product in
5% yield. The decrease of the yield could be attributed
to the dispersion of the reagents when a large volume of
water is used, or it can also be attributed to the
protodeboronation of the boronic acids in water as no side
cross‐coupling
of
1‐nitro‐4‐chlorobenzene
and
phenylboronic acid in water under microwave heating
was chosen as a model reaction to study the efficiency of
our palladium based catalyst. Initially, the same optimal
conditions determined for the aryl bromides were used.
Without surprise, the reaction did not proceed sufficiently
since chlorides have high bond dissociation energy.
Therefore, we optimized several reaction parameters
including the base, the amount of catalyst and the reac-
tion time. Finally, the use of an additive such as tetra‐n‐
butylammonium bromide (TBAB), the substitution of
K CO3 with Na CO3 and a higher catalyst loading
[46–48]
product was detected.
The tendency to
protodeboronate quite often manifests itself during
cross‐coupling reactions carried out in polar protic sol-
vents and influences the stoichiometry of the reaction.
In view of green chemistry and sustainable development,
the reduction in the volume of solvent (2 ml) giving a bet-
ter yield was selected for the rest of the study.
With these results, we then determined the scope and
limitations of this reaction. The scope of the Suzuki‐
Miyaura cross coupling of various aryl bromides with aryl
boronic acids in water under MW irradiation using the
adopted best conditions was realized (Table 1). Our cata-
lytic system was active for a range of aryl bromides having
2
2
(50 mg, 0.9 mmol %) were necessary to achieve a good
yield (Table 2, Entry 1). When TBAB was added, the cou-
pling yield improved dramatically. These results indicated
that the ammonium salt facilitated solvation of the sub-
strates in water and enhanced the rate of coupling by acti-
vating boronic acid toward the formation of a boronate
either an electron‐withdrawing (NO and CHO) or an
2
electron‐donating group (OMe, Me) with phenylboronic
acid in fairly good yields (86‐96%) within 15 minutes
‐
+.[50,51]
(Table 1, entries 1‐4). Surprisingly, starting from the four
complex [ArB(OH) ] [R N]
Two determined fac-
3
4
aryl bromides, cross coupling reaction using 4‐
methoxyphenylboronic acid afforded the corresponding
products in good yields (81‐89%) but lower than those
obtained in presence of phenylboronic acid (Table 1,
entries 5‐8). In accordance with the literature, the cross‐
coupling reaction of 4‐formylphenylboronic acid (an elec-
tron deficient boronic acid) with the determined aryl bro-
mides gave the desired coupling products in only
moderate yields (50‐67%) after 60 minutes, most likely
due to the increased of steric hindrance (Table 1, entries
tors: (i) better solubility of organic substrates in water
and consequently by higher concentration of reactive spe-
cies and (ii) formation of a complex between the boronic
acid and the ammonium salt permitted to reduce the
extent of hydrodeboronation in our experiments. Unfortu-
nately, the use of 4‐chlorobenzaldehyde and the unstable
4‐formylphenylboronic acid (Table 2, entry 2) yielded very
low amounts of product under identical conditions.
3.3 | Recyclability
The lifetime of the catalyst and its level of reusability are
very important factors from both an economic and envi-
ronmental perspectives. In this context, the recoverability
and reusability of the catalyst was studied. To achieve this
goal, the model reaction of 4‐bromoacetophenone with
phenylboronic acid was carried out in the presence of
Na PdP O as the catalyst under MW heating in water
2
2 7
as the sole solvent. After completion of the first reaction,
the catalyst was recovered, washed sequentially and dried
at 100 °C. Utilizing the used catalyst, the above test reac-
tion was performed again under the same conditions with
a result of a slight loss of performance after the fourth
cycle (Figure 13). This result can be explained by the pres-
ence of a small amount of remaining reagents adsorbed
on the catalyst even after it was dried there by blocking
FIGURE 12 The influence of water volume on Suzuki‐Miyaura
reaction

8
of 10
DÂNOUN ET AL.
2 2 7
TABLE 1 Suzuki–Miyaura reaction of aryl bromides with arylboronic acids catalyzed by Na PdP O under MW
a
Entry
Aryl bromide
Arylboronic acid
Product
Yield (%) /time
1
95/15 min
96/15 min
86/15 min
90/15 min
83/15 min
2
3
4
5
6
7
89/15 min
81/15 min
8
9
84/15 min
50/60 min
67/60 min
1
1
1
0
1
2
58/60 min
64/60 min
2 3 2 2 7 2
Reaction conditions: Aryl bromides (1.76 mmol), Aryl boronic acid (2.64 mmol), K CO (3.52 mmol), NA PdP O (5 mg, 0.009 mol%), 2 mL of H O, 100 °C.
a
Isolation yields were determined after column chromatography.
TABLE 2 Suzuki–Miyaura reaction of aryl chlorides with
phenylboronic acid catalyzed by Na PdP O under MW
2 2 7
Entry
R
Yield (%)
1
NO
2
71
20
2
HCO
molecular traffic and accessibility of reagents to the active
sites of catalyst. Additionally, the activity loss can also be
attributed to the material loss during the recovery of the
used catalyst from the previous run media. As mentioned
2
2 7
FIGURE 13 Reuse performance of Na PdP O catalyst in the
synthesis of 4‐acetylbiphenyl

DÂNOUN ET AL.
9 of 10
2 2 7
FIGURE 14 SEM‐EDS analysis of Na PdP O catalyst after the reactivity tests
above we used very low catalyst loading and it was not
possible to recover all the catalyst after work‐up.
catalyst gave good yields in the coupling of activated
1‐nitro‐4‐chlorobenzene with phenylboronic acid in the
presence of TBAB as a phase transfer agent within
90 minutes. Furthermore, the catalyst showed great
potential to be reused several times, with only a slight
decrease in its catalytic activity after fourth cycles. The
high product yields, operational simplicity, mild reaction
conditions, short reaction times, recyclability and its envi-
ronmental compatibility are the notable advantages of the
present procedure.
In order to investigate morphology changes of the
catalyst during the reaction, SEM‐EDS studies were
performed (Figure 14). SEM images of Na PdP O after
2
2 7
the reactivity tests clearly indicate that more compact
grains are formed with no visible porosity. The chemical
compositions of the catalyst determined from the EDS
data were similar to those obtained before reaction tests.
The formation of a carbon deposit on the catalysts under
the reaction conditions was evidenced by the EDS
observations.
ACKNOWLEDGEMENTS
To investigate the heterogeneity of the Na PdP O
2 7
2
catalyst, we have performed the hot filtration test. The
solid Na PdP O catalyst was filtered off after 50% of the
The financial assistance of the MAScIR Foundation,
towards this research is hereby acknowledged. We also
acknowledge the financial assistance of the CNRST.
2
2 7
completion of the reaction and the reaction was kept in
reaction conditions. After 15 min, no product was
detected. This observation gave the indication that no Pd
is being leached out from the solid catalyst during the
cross‐coupling reactions.
ORCID
Mohamed Zahouily http://orcid.org/0000-0002-1711-5344
REFERENCES
4
| CONCLUSION
[
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3
In summary, the preparation of an efficient and recyclable
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reaction under microwave irradiation in water were
reported. The findings of the study demonstrated this
solid catalyst exhibited higher catalytic activity in the
coupling of aryl bromides and a wide variety of
arylboronic acids without employing any phase transfer
reagent at 100 °C within short reaction times. Also, this
[
[3] N. Miyaura, in Metal‐Catalyzed Cross‐Coupling Reactions, (Eds:
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