Reusable magnetic Pd:XCoy nanoalloys confined in mesoporous carbons for green Suzuki-Miyaura reactions

Article abstract of DOI:10.1039/c8ra02214c

We report herein Pd_xCo_y nanoalloys confined in mesoporous carbons (Pd_x-Co_y@MC) prepared by an eco-friendly one-pot approach consisting in the co-assembly of readily available and non-toxic carbon precursors (phloroglucinol, glyoxal) with a porogen template (pluronic F-127) and metallic salts (H₂PdCl₄ and Co(NO₃)₂·6H₂O) followed by thermal annealing. Three Pd_xCo_y@MC materials with different alloy compositions were prepared (C1: x/y = 90/10; C2: x/y = 75/25; C3 and C4: x/y = 50/50). The nanoalloys were uniformly distributed in the carbon framework and the particle sizes depended on the alloy composition. These composites were then used for Suzuki-Miyaura reactions using either H₂O or a 1:1 H₂O/EtOH mixture as solvent. The Pd₅₀Co₅₀@MC catalyst C3 proved to be the most efficient catalyst (in terms of efficiency and magnetic recovery) affording the coupling products in good to excellent yields. After reaction, C3 was recovered quantitatively by simple magnetic separation and reused up to six times without loss of efficiency. The amount of palladium lost in the reaction mixture after magnetic separation was very low (ca. 0.1 % wt of the amount initially used).

Full text of DOI:10.1039/c8ra02214c

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Reusable magnetic PdxCoy nanoalloys confined in
mesoporous carbons for green Suzuki–Miyaura
Cite this: RSC Adv., 2018, 8, 17176
reactions†
ab
Mohamed Enneiymy,ab Claude Le Drian,ab Camelia Matei Ghimbeu
´
ab
*
and Jean-Michel Becht
We report herein PdxCoy nanoalloys confined in mesoporous carbons (Pdx–Coy@MC) prepared by an eco-
friendly one-pot approach consisting in the co-assembly of readily available and non-toxic carbon
precursors (phloroglucinol, glyoxal) with a porogen template (pluronic F-127) and metallic salts (H2PdCl4
and Co(NO3)2$6H2O) followed by thermal annealing. Three PdxCoy@MC materials with different alloy
compositions were prepared (C1: x/y ¼ 90/10; C2: x/y ¼ 75/25; C3 and C4: x/y ¼ 50/50). The nanoalloys
were uniformly distributed in the carbon framework and the particle sizes depended on the alloy
composition. These composites were then used for Suzuki–Miyaura reactions using either H2O or a 1 : 1
H2O/EtOH mixture as solvent. The Pd50Co50@MC catalyst C3 proved to be the most efficient catalyst (in
terms of efficiency and magnetic recovery) affording the coupling products in good to excellent yields.
After reaction, C3 was recovered quantitatively by simple magnetic separation and reused up to six times
without loss of efficiency. The amount of palladium lost in the reaction mixture after magnetic
separation was very low (ca. 0.1 % wt of the amount initially used).
Received 13th March 2018
Accepted 26th April 2018
DOI: 10.1039/c8ra02214c
rsc.li/rsc-advances
27 kV/kg (for comparison ca. 25 kV/kg for platinum and ca. 35
kV/kg for gold). For these reasons it is of crucial importance to
A Introduction
preserve the palladium natural resources. In addition, residual
amounts of palladium are oen present in the coupling
products. Therefore tedious and costly purication steps are
oen necessary to get the almost palladium-free product
which is oen required.5 For this purpose, during the last
decade, numerous groups have developed heterogeneous
reusable palladium catalysts.6 In most cases the precious
metal is encapsulated in a polymeric shell,7 adsorbed on
various inorganic supports or graed to an organic or inor-
ganic support bearing ligands.6 For example we have reported
several polymer-supported reusable palladium catalysts for
versatile carbon–carbon bond forming reactions.8 More
recently magnetic palladium catalysts have emerged as
a promising class of reusable catalysts since they can be
recovered from any reaction mixture by simple application of
an external magnetic eld and reused.9 Most of them are ob-
tained by graing the palladium catalyst on a magnetic iron
oxide (magnetite or maghemite) core surrounded by a polymer
The syntheses at an industrial scale of numerous compounds
possessing important therapeutical (valsartan),1 fungicidal
(boscalid)2 or physical (semiconductor materials for OLEDs)3
properties require oen as a crucial step the creation of
a carbon–carbon bond at the core of the molecule. The
formation of new carbon–carbon bonds, and in particular
aryl–aryl bonds, is traditionally performed using a Suzuki–
Miyaura cross-coupling.4 This reaction is to date the most
powerful and the most widely used for this purpose. It is
generally performed in high yields and mild conditions by
reacting an aryl bromide (sometimes an aryl chloride) with an
areneboronic acid in the presence of a base and of a homoge-
neous palladium catalyst (ca. 10–50 mequiv.) containing in
most cases a ligand.4a The major drawback of this cross-
coupling lies in the use of palladium and of expensive
ligands. It is noteworthy that no economically workable
palladium ores exist: this precious metal is generally extracted
as a byproduct from nickel, copper, chromium or other plati-
noids ores. Since palladium is a scarce natural resource with
growing uses, its price has considerably increased: it was
multiplied by 7 during the last 20 years to reach in late 2017 ca.
or a silica shell bearing ligands.10 Other reusable magnetic
11
palladium catalysts are obtained by using a NiFe2O4
or
cobalt core recovered by a carbon shell.12 However some
drawbacks are still present: one of them is the multi-step
preparation of these catalysts which can be tedious and/or
requiring toxic and sensitive compounds; a second is the use
of traditional organic solvents (DMF, toluene.) for reactions
such as Suzuki–Miyaura. Consequently, in order to full the
a
´
Universite de Haute-Alsace, CNRS, IS2M UMR 7361, F-68100 Mulhouse, France
b
´
Universite de Strasbourg, France. E-mail: jean-michel.becht@uha.fr
† Electronic supplementary information (ESI) available: Experimental procedures
and 1H and 13C-NMR Spectra of Compounds 1a–i. See DOI: 10.1039/c8ra02214c
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criteria of Green Chemistry, the development of efficient eco-
friendly and ligand-free reusable catalysts prepared in one
pot from easily accessible starting materials and at least as
efficient as their homogeneous analogues suscites huge
interest. For example the group of Grison has recently reported
Suzuki–Miyaura couplings in the presence of a heterogeneous
palladium-containing carbon “ecocatalyst” obtained from
plants able to bioconcentrate the precious metal.13 We have
also recently reported a green one-pot synthesis of a meso-
porous carbon (MC) containing palladium nanoparticles
(Pd@MC) starting from a biosourced tannin precursor. This
catalyst was successfully used for ligand-free Suzuki–Miyaura
reactions in an environment-friendly and non-toxic solvent
Fig. 1 Schematic representation of the one-pot synthesis of meso-
porous carbons containing confined particles.
B Results and discussion
Preparation and characterization of catalysts C1–C4
(propane-1,2-diol) but at high temperature (140 C).14
ꢀ
In the last years bimetallic catalysts have emerged as PdxCoy alloys conned in mesoporous carbons were obtained by
a promising class of heterogeneous catalysts since the pres- a one-pot so-template approach consisting in the co-assembly
ence of two metals could bring new properties. It is important of phloroglucinol-glyoxal phenolic resin with an amphiphilic
to note that the use of such catalysts for carbon–carbon bond triblock co-polymer template (pluronic F-127) and Pd and Co
forming reactions has only been very sparsely studied. For salts. A thermal annealing step allowed the decomposition of
example, the group of Li has reported a reusable carbon- the phenolic resin and template with formation of a porous
supported Fe–Pd core–shell catalyst for Suzuki–Miyaura carbon network containing PdCo nanoparticles (Fig. 1). The
reactions in DMF.15 Later Kutubi et al. have reported poly(N- XRD patterns showed the presence of several peaks (Fig. 2)
vinyl-2-pyrrolidone)-stabilized Pd–Ru solid solutions and which could be indexed to a face-centered-cubic (fcc) crystalline
their use for Suzuki–Miyaura reactions in a 1 : 1 DMA/H2O structure of Pd. The position of the peaks was shied towards
mixture.16,17 In 2014 the group of Zhang has described higher 2q angles compared to the reported values for single
a delicate preparation of Pd–Rh nanocrystals of tunable phase Pd, demonstrating the formation of PdCo alloys. The
compositions and morphologies (via
a
hydrothermal textural characteristics of the obtained materials were previ-
approach) for Suzuki–Miyaura reactions.18 Inspired by our ously evaluated by nitrogen adsorption. The materials are
previous work on Pd@MC, we have developed a magnetic micro/mesoporous and exhibit a specic surface area of 800–
mesoporous carbon containing Pd–Fe alloys for Suzuki– 850 m2 gꢁ1 and a mesopore average size of ca. 3.5 nm, almost
Miyaura reactions in a green solvent (propane-1,2-diol)19 and, independently of the alloy composition or annealing tempera-
more recently, easy “one-pot synthesis” pathways to obtain ture as shown in more detail elsewhere.24
metallic alloys (NiCo, PdNi, PdRh, PdAu, PdCo) conned in
The morphology of the materials was then studied by
mesoporous carbons.20 From a practical point of view, the transmission electron microscopy (TEM) the images of the
advantages of our MC preparation lie in the use of PdxCoy@MC materials (C1–C3) and their particle size distri-
environment-friendly carbon precursors, in the simulta- bution histograms are presented in Fig. 3. The catalysts exhibit
neous preparation of carbon and metallic alloys without homogenously distributed Pd–Co nanoparticles in the carbon
using external chemical reduction agents and in its network. A narrow particle size distribution is observed for
simplicity. It is noteworthy that the connement of metal Pd50Co50 C3 with an average particle size of ca. 7 nm. The
nanoparticles in mesoporous carbons with high surface area particle size increased with the percentage of Pd in the alloy
and controlled pore size suscites huge attention since it and reached 13 nm for Pd75Co25 (C2) while for a higher Pd
allows to obtain small and well dispersed metal nano- content, a more important increase of both particle size (25
particles, avoids particle coalescence by Ostwald maturation nm) and width of distribution was observed for Pd90Co10 (C1).
during the preparation and by chemical processes during Performing the thermal annealing at higher temperatures (800
use. Therefore this connement has numerous applica- ꢀC) on Pd50Co50 (C4) increased the particle size from 7 nm for
tions.21,22 In addition, metal nanoparticles possessing C3 to ꢂ11 nm for C4.
magnetic properties are very interesting since they allow the
recovery of the catalyst from almost any reaction medium by
applying an external magnetic eld. The PdCo alloys sup-
ported on carbons have already attracted attention as effi-
Optimization of the conditions for the Suzuki–Miyaura
reaction
cient electrocatalyst for formic acid oxidation, as catalyst in The reaction conditions were optimized (Table 1) using 4-bro-
oxygen reduction reactions in fuel cells, hydrogen absorbent moacetophenone and benzeneboronic acid as model
and as biosensor material.23 Herein we would like to report substrates, K2CO3 as base and catalyst C3 (Pd50Co50). No reac-
the use of mesoporous carbons containing conned PdxCoy tion was observed by performing the cross-coupling in toluene,
nanoalloys as magnetic catalysts for Suzuki–Miyaura 1,4-dioxane or acetonitrile (entries 1–3). We then turned our
couplings under environment-friendly conditions.
attention to the use of green solvents. Gratifyingly the coupling
product was obtained in respectively 92% and 98% yields by
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Table 1 Optimization of the reaction conditions
Entrya
Catalyst
Solvent
Pd (mequiv.)
Yieldsb
1
2
3
4
5
6
7
8
C3
C3
C3
C3
C3
C3
C3
C3
C2
C1
C4
Toluene
1,4-Dioxane
Acetonitrile
EtOH/H2O 95 : 5
EtOH/H2O 50 : 50
H2O
H2O
H2O
H2O
H2O
10
10
10
10
10
10
5
No reaction
No reaction
No reaction
92
98
99 (97)c
75
Fig. 2 XRD patterns of two different batches of catalyst C3 before and
after one use for Suzuki–Miyaura coupling.
1
<10
98
98
9
10
11
10
10
10
performing the reaction in 95 : 5 or 50 : 50 EtOH/H2O mixtures
(entries 4 and 5) and even in 99% using water (entry 6).
Reducing the amount of supported palladium from 10 to 5 and
H2O
99
a
Reactions performed using 4-bromoacetophenone (0.5 mmol,
1
equiv.), benzeneboronic acid (0.55 mmol, 1.1 equiv.), K2CO3
then 1 mequiv. resulted in a decrease of the yields from 99% to (0.6 mmol, 1.2 equiv.) and catalyst C1–C4 (10 mequiv.) in a solvent (3
mL). Calculated yields by 1H-NMR of the crude reaction mixture.
Isolated yield aer purication of the crude product on silica gel.
b
75% and <10% (entries 7–8). Noteworthily aer only 2 h, 6 h and
8 h of reaction the desired biaryl was respectively obtained in
c
8%, 81% and 90% yields (in the conditions of entry 6). Finally,
the cross-coupling between 4-chloroacetophenone and benze-
neboronic acid was unsuccessful and the aryl chloride was
recovered in the conditions of entry 6.
interpretation is sustained by our recent results on magnetic
PdNi alloys conned in mesoporous carbon where we have
shown that the magnetization value is closely related to the Ni
Catalyst C3 was then replaced by C2 (Pd75Co25) or C1
content of the alloys.20c Finally the Suzuki–Miyaura coupling
(Pd90Co10) in order to evaluate the inuence of PdCo alloy
was performed in the presence of catalyst C4 (Pd50Co50 but
composition and particle size on the catalytic efficiency. The
desired biaryl was obtained in almost quantitative yields (Table
1, entries 9 and 10). As expected it turned out that during the
magnetic separation the catalysts C1 and C2 were more difficult
to recover than C3, this being probably related to the lower
amount of magnetic Co present in C2 and C1 alloys. This
ꢀ
ꢀ
obtained by calcination at 800 C instead of 600 C for C1–C3)
affording almost quantitatively 1a (entry 11) which was
somehow expected. We decided to pursue our study using
catalyst C3 which possesses both good catalyst efficiency and
good magnetic properties and is easier to prepare than C4.
Under the best reaction conditions we determined the
possibility to reuse C3. For this purpose, at the end of the
Fig. 4 Magnetic separation of catalyst C3: (a) reaction mixture after
Fig. 3 TEM images of catalysts C1–C3 (a–c) along with their particle reaction, (b) reaction mixture 10 s after placement of the magnet; (c)
size distribution (d).
reaction mixture 2 min after placement of the magnet.
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Table 2 Reuse of catalyst C3
Table 3 Syntheses of biaryls
Entrya
R1
R2
Method (A or B)b
Yieldsc
Runa
1
99
2
97
3
97
4
98
5
96
6
97
1
2
3
4
5
6
7
8
9
4-Ac
4-Ac
4-Ac
4-Ac
H
A
A
A
A
A
A
B
B
B
B
97 (1a)
99 (1b)
98 (1c)
86 (1d)
99 (1e)
<40%
98 (1f)
67 (1g)
62 (1h)
99 (1i)
Yieldb
4-Me
3-Me
4-OMe
4-Cl
H
H
H
H
H
a
Reactions performed using 4-bromoacetophenone (0.5 mmol,
1
equiv.), benzeneboronic acid (0.55 mmol, 1.1 equiv.), K2CO3
4-Ac
(0.6 mmol, 1.2 equiv.) and catalyst C3 (25 mg, 10 mequiv.) in H2O (3
mL). b Calculated yields by H-NMR of the crude reaction mixture.
1
4-C(O)–Et
4-C(O)–Et
4-C(O)–Ph
4-CHO
4-CN
reaction C3 was almost quantitatively recovered by application
of an external neodymium magnet (Fig. 4), washed with water,
EtOH and dried. In addition, we found that C3 can be used
successfully at least six times with no loss of efficiency (Table 2).
The XRD analyses performed on the pristine C3 catalyst and
aer one catalytic utilisation (Fig. 2) showed almost perfect
superposition of XRD peaks with no changes of either their
position or their FWHM (full width at half maximum). This
suggests that the alloy crystalline phase was conserved as well as
the crystallite size which was found to be the same, ca. 6.0 nm,
before and aer use (Fig. 2). These results are in accordance
with the good reusability of catalyst C3. We also measured the
amount of palladium lost in the reaction product aer magnetic
recovery of C3. It turned out that only ca. 0.12% of the initial
amount of supported palladium was present in the reaction
medium (for further details on the determination of the
residual amount of palladium see ESI†). This corresponds to ca.
12 mequiv. Besides, we checked if soluble palladium entities
play a signicant role in this Suzuki–Miyaura reaction. For this
purpose a cross-coupling was performed between 4-bromoace-
tophenone and benzeneboronic acid in conditions of Table 1,
entry 6. Aer 2 h 30 of reaction in reuxing water the catalyst
was removed magnetically (yield at that point: 11%) and the rest
of the reaction mixture was reuxed for another 12 h which
brought the yield to 19%. This result showed that, in accor-
dance with literature results,25 soluble palladium entities seem
to play only a minor role in this reaction. We have also shown
that the preparation of catalyst C3 is reproducible since various
batches of this catalyst (all prepared according to the general
procedure given in the Experimental part) present the same
crystallite size (6.0 ꢃ 0.5 nm) and catalytic activity. Finally
catalyst C3 is air- and moisture-stable since it could be stored
for months without particular precautions and showed no
decrease of efficiency.
10
a
Reactions performed using an aryl bromide (0.5 mmol, 1 equiv.), an
areneboronic acid (0.55 mmol, 1.1 equiv.), K2CO3 (0.6 mmol, 1.2
b
equiv.) and catalyst C3 (10 mequiv.). Method A: reaction performed
in reuxing H2O (3 mL) for 15 h; method B: reaction performed in
a reuxing 1 : 1 H2O/EtOH mixture (3 mL) for 15 h. c Isolated yields.
cross-coupling between 4-bromoacetophenone and 4-chlor-
obenzeneboronic acid afforded also successfully the corre-
sponding biaryl in almost quantitative yield (entry 5). However
the cross-couplings between 4-bromoacetophenone and 2-
methyl- or 4-nitrobenzeneboronic acid or 3-thiopheneboronic
acid were unsuccessful and in each case the aryl bromide was
recovered unchanged. We also replaced 4-bromoacetophenone
by other aryl bromides. To our surprise, under the conditions
described in Table 3 entries 1–6, the yields were reproducible but
extremely dependent on the nature of the aryl bromide: the cross-
coupling between 4-bromopropiophenone and benzeneboronic
acid (entry 6) afforded the corresponding biaryl in <40% yield
whereas no reaction products were obtained by performing the
cross-couplings with 4-bromobenzophenone, 4-bromobenzalde-
hyde, 4-bromobenzonitrile, 4-bromonitrobenzene, or 4-bromo-
toluene. It is noteworthy that these couplings have been
performed several times with different batches of C3 and in each
case the aryl bromide was recovered quantitatively. Gratifyingly
we found that performing the reaction between 4-bromopropio-
phenone and benzeneboronic acid in a 50 : 50 H2O/EtOH
mixture (method B) instead of pure H2O (method A) afforded
the desired product in 98% yield (entry 7). These conditions were
also successfully used for the cross-couplings between benzene-
boronic acid and 4-bromobenzophenone, 4-bromobenzaldehyde,
4-bromobenzonitrile (entries 8–10). But, regretfully, no reactions
were observed using either benzeneboronic acid and 4-bromo-
nitrobenzene, 4-bromotoluene, 2- or 3-bromoacetophenone. On
the bases of our results it was impossible for us to explain the
outcome of the reaction.
The scope of use of this catalyst for the Suzuki–Miyaura
reaction was then determined under the previously optimized
conditions (Table 3, entries 1–6). Reacting 4-bromoacetophenone
with various areneboronic acids bearing electrodonating groups
gave the expected biaryls in 99–86% yields (entries 1–4). The
Finally we compared the efficiency of catalyst C3 with other
catalysts described in the literature (Table 4). It is noteworthy
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Table 4 TON and TOF of Suzuki–Miyaura reactions catalyzed by some representative magnetic Pd catalysts
Entry
Catalyst
Solvent, T ꢀC
Pd mequiv.
TON
TOF (hꢁ1
)
1
C3
H2O, 100 ꢀ
EtOH, 80 ꢀ
EtOH, 80 ꢀ
EtOH, 80 ꢀ
C
C
C
C
10
40
16
0.05
11
5
73
0.25–1
0.2
5
100
24
58
19 600
91
200
14
4000
4950
186
40 600
7
12
12
980
46
2 26
3 27
4 12a
5 12b
6 28
6 29
7 30
8 31
9 32
10 33
Pd–Co/graphene
Pd@(CoFe2O4)
Pd@(Co/C-PPh2)
Pd@(Co/C-polymer-PPh2)
Pd@(Co/C–pyrene-PPh2)
Ironoxide-Pd
THF/H2O 1 : 2, 65 ꢀ
THF/H2O 2 : 5, 60 ꢀ
DMF, 50 ꢀC
C
C
14
1.1
667
206
93
Mag-IL-Pd
H2O, 60 ꢀ
C
Pd@(Fe2O3/SiO2-dendrimer)
Pd@(Fe3O4/SiO2-iminophosphine)
SPIONs-bis(NHC)-Pd
EtOH/H20 1 : 1, 80 ꢀ
Toluene, 65 ꢀ
DMF/H2O 1 : 2, 90 ꢀ
C
C
C
0.02
5800
that most catalysts shown in this table are prepared via multi- mL). Ethyl acetate (40 mL) was then added and the combined
step syntheses requiring toxic and sensitive starting materials organic phases were washed with H2O (20 mL), dried with
whereas C3 is prepared in one-pot from “green” reagents. In MgSO4, ltered and concentrated under vacuum. When neces-
addition our reaction was run using only water as solvent, albeit sary the residue was puried by ash-chromatography on silica
only in certain cases.
gel using AcOEt/cyclohexane as eluant. Aer drying under
vacuum (0.1 mbar) pure biaryls were obtained as shown by their
1H-NMR spectra (CDCl3, 300 MHz) which were in accordance
with the literature (see ESI†).
Characterization of catalyst C1–C4. X-ray powder diffraction
(XRD) data were collected with a Philips X'Pert MPD diffrac-
tometer equipped with Cu Ka1,2 doublet and a at-plate Bragg–
Brentano theta–theta geometry. The pristine catalyst materials
as well as the recovered C3 catalyst were analysed. In the latter
case, the catalyst was successively washed with water (3 ꢄ 30
mL) and diethyl ether (2 ꢄ 20 mL) and nally dried. The crys-
tallite size was calculated with Scherrer formula34 using the
(111) diffraction peak.
C Experimental
Materials and methods
All reagents and solvents were obtained from commercial
sources (Acros Organics, Sigma-Aldrich and Alfa Aesar) and
were used without further purications. Pluronic F-127 (Sigma-
Aldrich) is a triblock copolymer of average formula (PEO)106(-
PPO)70(PEO)106. The silica gel was purchased from Merck and
had a 0.063–0.2 mm granulometry (70–230 mesh ASTM). The
external magnet used for magnetic separation was a S-25-07-N
(Supermagnete, Uster, Switzerland).
The metallic particle morphology and distribution in the
carbon framework were evaluated by transmission electron
microscopy (TEM) with a Jeol ARM-200F instrument working at
200 kV. The particle size distribution was further determined
based on TEM images and ImageJ soware. About 250 particles
were counted using several TEM images in order to ensure
a good representation of the material.
Synthetic procedures
Preparation of catalyst C1–C4.24 PdxCoy@MC catalysts were
prepared via a one-pot evaporation induced self-assembly (EISA)
approach as described previously.24 Briey, the carbon precur-
sors, i.e., phloroglucinol and glyoxal, the porogen agent (plur-
onic F-127) and the metallic salts H2PdCl4 and Co(NO3)2$6H2O
were dissolved in ethanol. The solution was placed in Petri
dishes, evaporated and the obtained polymer lm containing
the metal salts was dried at 80 ꢀC and pyrolysed at 600 ꢀC under
D Conclusions
Ar. Different amounts of Pd and Co metallic salts were used in Mesoporous carbons containing PdxCoy alloys were prepared by
order to obtain different PdxCoy compositions, i.e., Pd90Co10 a fast, efficient and eco-friendly route and used for Suzuki–
(C1), Pd75Co25 (C2), Pd50Co50 (C3). A supplementary sample Miyaura coupling reactions. They possessed small particles of
having the composition of C3 (Pd50Co50) was in addition narrowly distributed size trapped in the carbon network. The
ꢀ
prepared but the thermal annealing was done at 800 C, thus particle size was inuenced by the alloy composition but only
yielding C4. The total amount of metals in the catalyst was kept marginally by the annealing temperature. Several catalysts were
at ca. 5wt% of the carbon.
evaluated and all demonstrated a good catalytic activity.
Suzuki–Miyaura reactions. Catalyst C3 (ca. 25 mg, 10 mequiv. Therefore, Co-rich C3 (Pd50Co50) was chosen and successfully
of supported Pd) was added to a solution of aryl bromide used as a reusable magnetic catalyst for Suzuki–Miyaura
(0.5 mmol, 1 equiv), areneboronic acid (0.55 mmol, 1.1 equiv.), couplings in green solvents (H2O or 1 : 1 H2O/EtOH mixture). In
K2CO3 (0.6 mmol, 1.2 equiv) in H2O (3 mL) or in a 1 : 1 H2O/ addition, we have shown that the catalytic activity was very
EtOH mixture (3 mL). The reaction mixture was reuxed for dependent on the nature of the coupling partners. Studies are
15 h. Aer cooling to 20 ꢀC, C3 was magnetically recovered and currently underway in our group to better understand this
then washed successively with EtOH (2 ꢄ 5 mL) and H2O (2 ꢄ 5 dependence and to extend the use of catalyst C3 to other
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important palladium-catalyzed reactions (Mizoroki–Heck,
Sonogashira, Buchwald reactions and “green” carbonylations).
Finally other mesoporous carbons containing various Pd-metal
9 (a) V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara
and J.-M. Basset, Chem. Rev., 2011, 111, 3036–3075; (b)
Q. M. Kainz and O. Reiser, Acc. Chem. Res., 2014, 47, 667–677.
´
alloys have already been prepared and their applications in ne 10 (a) D. Rosario-Amorin, M. Gaboyard, R. Clerac, L. Vellutini,
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11 (a) B. Baruwati, D. Guin and S. V. Manorama, Org. Lett., 2007,
9, 5377–5380; (b) Z. Gao, Y. Feng, F. Cui, Z. Hua, J. Zhou,
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There are no conicts to declare.
Acknowledgements
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A. Schatz, T. R. Long, R. N. Grass, W. J. Stark, P. R. Hanson
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Financial support of this work by the French National Research
Agency (ANR) via Genesis project (ANR-13-BS08-0004-02) is
acknowledged. We are also grateful to J. Demichel, S. Garnier, B.
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Dr J.-M. Le Meins for the XRD analyses and to the Fondation
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pour l'Ecole Nationale Superieure de Chimie de Mulhouse for
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