Assemblies of copper ferrite and palladium nanoparticles on silica microparticles as a magnetically recoverable catalyst for Sonogashira reaction under mild conditions

Article abstract of DOI:10.1002/cplu.201500015

Abstract Copper ferrite and palladium nanoparticles assembled on silica microparticles are prepared successfully and characterized by scanning electron microscopy, transmission electron microscopy, electron-dispersive X-ray analysis, X-ray diffraction, th

Full text of DOI:10.1002/cplu.201500015

DOI: 10.1002/cplu.201500015
Full Papers
Assemblies of Copper Ferrite and Palladium Nanoparticles
on Silica Microparticles as a Magnetically Recoverable
Catalyst for Sonogashira Reaction under Mild Conditions
Mohammad Gholinejad* and Jahantab Ahmadi[a]
Dedicated to Dr. Diego A. Alonso
Copper ferrite and palladium nanoparticles assembled on silica
microparticles are prepared successfully and characterized by
scanning electron microscopy, transmission electron microsco-
py, electron-dispersive X-ray analysis, X-ray diffraction, ther-
mogravimetric analysis, atomic absorption spectroscopy, and
infrared studies. The catalyst is applied effectively for the Sono-
gashira coupling reaction of aryl iodides and bromides under
heterogeneous and phosphine-free reaction conditions. The re-
actions proceed at 508C with a low loading of palladium cata-
lyst. The magnetically recoverable catalyst is recycled success-
fully for five consecutive runs with very small drops in catalytic
activity.
Introduction
Heterogeneous catalysts have been widely involved in differ-
ent organic reactions, because the reuse of catalysts is highly
desirable for economic and ecological reasons and to meet
today’s green chemistry objectives.[1] Thus, the choice of cata-
lyst support plays an important role in the overall per-
formance, catalytic activity, and reusability of heterogeneous
catalysts.[1] However, despite the important achievements in
this field, heterogeneous catalysts are difficult to separate from
the reaction mixture by usual methods such as filtration and
centrifugation.
aryl-alkynes and conjugated enynes through the coupling of
vinyl or aryl halides or triflates with terminal alkynes in the
presence of a copper(I) cocatalyst. The aryl-alkynes and conju-
gated enynes obtained by the Sonogashira reaction have wide
applications in the chemistry of natural products and pharma-
ceuticals.[6]
The Sonogashira reaction usually requires a palladium cata-
lyst in the presence of a copper cocatalyst.[6,7] Despite the dif-
ferent reported copper-free Sonogashira reactions, the addition
of copper can increase the efficiency of the reaction under
oxygen-free conditions to prevent the formation of alkyne ho-
mocoupling products.[6] A literature search revealed that some
effort has been made to perform this reaction using copper[8]
or other transition metal catalysts[9] in the absence of palladi-
um. For example, we recently reported magnetite (Fe3O4)
nanoparticles as a catalyst for Sonogashira coupling of aryl io-
dides in ethylene glycol.[4d] However, the reactions were per-
formed at high temperatures and only aryl iodides were react-
ed efficiently. In addition, the Sonogashira reaction of aryl hal-
ides with alkynes catalyzed by copper ferrite (CuFe2O4) nano-
particles has been reported.[8m] However, with this catalyst, the
reactions did not proceed efficiently and 70% isolated yield
was the best reaction yield obtained for the reaction of iodo-
benzene with phenyl acetylene at 1108C. Furthermore, copper-
catalyzed Sonogashira reactions have been performed at high
temperatures using aryl iodides and active aryl bromides with
the view that the presence of the palladium impurity is re-
sponsible for the reaction.[6,10] For example, a new study by
Buchwald and Bolm revealed the fundamental role of metal
contaminants in iron-catalyzed CÀC bond-forming reactions.[11]
In recent years there has been growing interest in using bi-
metallic nanoparticles for heterogeneous catalysis.[12,13] The
presence of two metal nanoparticles in the catalyst can en-
hance its activity and selectivity and reduce environmentally
In this regard, magnetic nanoparticles are increasingly en-
gaged as excellent supports for catalytic systems in the design
of new efficient and green processes.[2] In addition, because of
their large ratio of surface area to volume, superparamagnetic
behavior, and low toxicity, magnetic nanoparticles have attract-
ed much attention in manifold technological fields such as bio-
medicine, biotechnology, and materials science.[3] However, de-
spite the wide applications of magnetic nanoparticles as sup-
ports, less attention has been devoted to the catalytic per-
formance of magnetic nanoparticles in organic reactions.[4]
Among different magnetic compounds, CuFe2O4 nanoparticles
are one of the most essential magnetic materials, and has re-
cently been applied as a heterogeneous catalyst in different or-
ganic transformations.[5]
The palladium-catalyzed Sonogashira coupling reaction is
one of the most potent approaches for the construction of
[a] Dr. M. Gholinejad, J. Ahmadi
Department of Chemistry
Institute for Advanced Studies in Basic Sciences (IASBS)
P. O. Box 45195-1159, Gava zang, Zanjan 45137-6731 (Iran)
Fax: (+98) 2433153232
E-mail: gholinejad@iasbs.ac.ir
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201500015.
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harmful side effects. Recently, the synthesis of composite parti-
cles with a gold surface, silica core, and magnetic inner layer
for DNA interaction was reported.[14] In addition, silica spheres
modified with (3-aminopropyl)trimethoxysilane were used as
a template for the assembly of Fe3O4 nanoparticles and the
subsequent assembly of nanoparticles of Au, CdSe/ZnS, or Pd
on the magnetite-nanoparticle-bearing silica spheres.[15] The
catalyst carrying palladium was tested in the Sonogashira cou-
pling reaction in the presence CuI and PPh3 additives. Recently,
the combination of CuFe2O4 nanoparticles and palladium has
been shown to exhibit high activity in the selective hydrogena-
tion of arylacetylenes.[16] Moreover, very recently, we intro-
duced copper-ferrite-supported palladium nanoparticles as an
efficient catalyst for the cyanation of aryl halides.[17] The syner-
gistic effect between palladium and copper nanoparticles
played an important role in the catalytic activity of the catalyst.
In this study, we have prepared CuFe2O4 nanoparticles support-
ed on 500 nm spherical silica followed by the assembly of pal-
ladium nanoparticles (Scheme 1). The new magnetically recov-
Figure 1. SEM images of silica particles prepared using the Stçber method.
Figure 2. Thermogravimetric diagram of 3-aminopropyltriethoxysilane-func-
tionalized silica particles.
The prepared silica particles were functionalized using 3-
aminopropyltriethoxysilane in dry toluene. Thermal gravimetric
analysis of 3-aminopropyltriethoxysilane-functionalized silica
showed two weight-loss steps (Figure 2). The first weight loss
is related to the removal of H2O, and the second loss to the
grafted organic group with a loading of 1.6 mmolgÀ1.
CuFe2O4 nanoparticles were synthesized through the con-
ventional coprecipitation method using FeCl3·6H2O and CuCl2
2H2O in an argon atmosphere.[5i] A transmission electron mi-
croscopy (TEM) image of the prepared CuFe2O4 NPs confirmed
the formation of nanoparticles of average size 30–40 nm
(Figure 3).
Scheme 1. Preparation steps of the catalyst. PVP=polyvinylpyrrolidone.
The stabilization of CuFe2O4 on 3-aminopropyltriethoxysi-
lane-modified silica particles was achieved by reflux of func-
erable catalyst is successfully applied in Sonogashira coupling
reactions of aryl iodides and bromides with alkynes at 508C
under phosphine-free reaction conditions.
Results and Discussion
Uniform and monodisperse spherical silica particles were pre-
pared through the Stçber process using tetraethyl orthosili-
cate. Scanning electron microscopy (SEM) images of prepared
silica particles showed the formation of monodisperse and uni-
form silica particles of 500 nm in size (Figure 1).
Figure 3. TEM image of prepared CuFe2O4 NPs.
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Figure 6. TEM images of prepared Pd@SiO2·AP·CuFe2O4 catalyst.
Figure 4. SEM images of prepared Pd@SiO2·AP·CuFe2O4 catalyst.
tionalized silica particles and CuFe2O4 in toluene for 24 h. Final-
ly, the catalyst was obtained by mixing the prepared palladium
nanoparticles and silica-supported CuFe2O4 NPs. The presence
of palladium in the final catalyst was confirmed by atomic ab-
sorption spectroscopy (AAS), which showed 0.3 mmolgÀ1 palla-
dium. SEM images of the prepared catalyst showed the preser-
vation of the size and monodispersity of the silica nanoparti-
cles and the presence of CuFe2O4 and palladium nanoparticles
in the catalyst (Figure 4). In addition, the electron-dispersive X-
Figure 7. XRD pattern of the catalyst.
formed to optimize the reaction conditions such as the base,
solvent, reaction temperature, and amount of catalyst used
(Table 1).
The results showed that the use of dimethyl acetamide
(DMA) as a solvent and 1,4-diazabicyclo[2.2.2]octane (DABCO)
as a base at 508C provides the most suitable reaction condi-
tions (Table 1, entry 22). Notably, the use of DMA and DABCO
at 708C afforded 87% yield (Table 1, entry 9); however, we pre-
ferred to select 508C as a milder reaction temperature. Having
optimized the conditions, reactions of a variety of aryl halides
with alkenes were studied in the presence of the catalyst.
Under the optimized conditions, reactions of aryl iodides were
Figure 5. EDX spectrum of prepared Pd@SiO2·AP·CuFe2O4 catalyst.
ray (EDX) spectrum of the catalyst exhibited the presence of
Pd, Cu, Fe, and Si species in the structure of catalyst (Figure 5).
Furthermore, the TEM image of the catalyst indicated the pres-
ence of CuFe2O4 and palladium nanoparticles on the surface of
the silica particles (Figure 6).
X-ray diffraction (XRD) analy-
Table 1. Screening of different reaction conditions for the reaction of iodobenzene with phenylacetylene.
sis of the prepared catalyst
showed the presence of
CuFe2O4
nanoparticles
by
screening Bragg’s reflections re-
lated in 2q=18.38, 30.38, 35.68,
57.18, and 62.988[17] and Bragg’s
reflections related to palladium
in 2q=40.18, 46.78, and 68.18[19]
and also related to silica parti-
cles 2q=228[20] (Figure 7).
The catalytic activity of the
prepared Pd-CuFe2O4@SiO2 NPs
was investigated in the Sonoga-
shira coupling reaction. Initial
experiments with iodobenzene
and phenylacetylene were per-
Entry Pd [mol%] Base
Solvent T [8C] Yield [%][a] Entry Pd [mol%] Base
Solvent T [8C] Yield [%][a]
1
2
3
4
5
6
7
8
0.3
0.3
0.3
0.3
0.6
0.3
0.3
0.3
0.3
0.3
0.3
0.3
K2CO3 DMF
K2CO3 DMF
K2CO3 DMF
K2CO3 H2O
K2CO3 H2O
K2CO3 H2O
K2CO3 DMA
Cs2CO3 DMSO 50
DABCO DMA 70
DABCO DMSO 50
DABCO DMSO RT
60
50
60
60
25
50
50
10
7
8
9
7
13
14
15
16
17
18
19
20
21
22
23
24
0.3
0.3
0.6
0.6
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
DABCO dioxane 50
DABCO DMF 50
DABCO DMSO 25
DABCO H2O
tBuOK DMA
tBuOK DMSO 50
DABCO DMSO 70
DABCO DMSO 60
DABCO DMSO 50
20
27
9
25
50
12
3
10
5
7
78
76
35
83
6
7
9
87
52
19
67
10
11
12
DABCO DMA
DABCO DMSO RT
DABCO DMA RT
50
DABCO H2O
50
25
[a] Yield determined by CG analysis.
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performed efficiently and the
desired alkyne products were
obtained in good to excellent
yields. In addition, the reactions
of aryl bromides proceeded well
and the desired aryl alkynes
were obtained in 69–94% yields
of isolated product. The results
in Table 2 show that mostly the
presence of electron-withdraw-
ing groups at the para-position
of the aryl halides affords high
yields compared with electron-
donating groups at the para-
position. Reactions of 2-iodo-
thiophene and 5-bromopyrimi-
dine as heterocyclic aryl halides
under optimized reaction condi-
tions proceeded efficiently and
afforded coupling products in
82–98% yields. We decided to
examine the catalytic activity of
Pd-CuFe2O4@SiO2 for Sonoga-
shira coupling reactions of aryl
chlorides. However, the results
indicated that under optimized
reaction conditions, the reac-
tions of chlorobenzene and 4-
chlorobenzonitrile with phenyla-
cetylene were sluggish, and the
coupling products were ob-
tained in 4–13% yields based
on GC analysis. Notably, with
a similar catalyst prepared from
Fe3O4 NPs, the Sonogashira cou-
pling reaction was performed in
the presence of CuI and PPh3 as
additives, and a high reaction
temperature was required.[15]
Table 2. Sonogashira reactions of structurally different aryl iodides and bromides with alkynes in the presence
of the catalyst.[a]
Entry
1
A1X
R2
t [h]
Product
Yield [%][b]
80
C6H5
24
2
3
4
4-CH3C6H4
C6H5
24
24
48
73
82
69
C6H5
5
6
7
C6H5
7
48
7
95
71
97
C6H5
4-CH3C6H4
8
C6H5
48
24
24
94
68
97
9
C6H5
10
4-CH3C6H4
11
12
C6H5
24
24
95
98
4-CH3C6H4
13
14
4-CH3C6H4
C6H5
48
30
95
93
The stability and recovery of
heterogeneous catalysts be-
comes an important factor
owing to strict economic and
ecological demands for sustain-
ability. Therefore, we studied
the possibility of recovery of
the catalyst from the reaction
mixture. For this purpose, the
reaction of iodobenzene with
phenylacetylene under opti-
mized reaction conditions was
selected. After 24 h, the catalyst
was isolated from the reaction
mixture by an external rod, and
after washing with diethyl ether
and drying, it was charged for
another batch of the reaction.
15
16
17
18
19
20
21
C6H5
24
17
48
8
98
85
74
95
97
84
94
4-CH3C6H4
4-CH3C6H4
C6H5
C6H5
24
24
48
4-CH3C6H4
C6H5
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run. The results showed that
the catalyst is thermally stable
up to 2008C and organic func-
tional groups were presented in
the structure of the catalyst
(Figure 9). In addition, the SEM
images of the catalyst after the
third run showed the preserva-
tion of catalyst structure and
the presence of nanoparticles
on silica cores (Figure 10). EDX
analysis of the recycled catalyst
after the third run confirmed
the presence of Fe, Cu, and Pd
species in the structure of the
reused catalyst (Figure 11).
Table 2. (Continued)
Entry
A1X
R2
t [h]
Product
Yield [%][b]
82
22
4-CH3C6H4
48
23
24
25
CH2OH
CH2OH
CH2OH
24
24
24
88
98
95
26
CH2OH
8
98
[a] Reaction conditions: Ar1X (1 mmol), alkyne (1.5 mmol), DABCO (2 mmol), DMA (2 mL), catalyst (10 mg, con-
taining 0.3 mol% Pd) at 508C. [b] Yield of isolated product.
Figure 10. SEM images of recycled catalyst after third run.
Figure 8. Recycling of catalyst for the reaction of iodobenzene with phenyla-
cetylene.
Using this process, the catalyst was recycled for five consecu-
tive runs with restoration of its catalytic activity (Figure 8). AAS
analysis of the solution obtained after isolation of the catalyst
in the first run showed 6% leaching of Pd.
To get information about stability of the catalyst, we per-
formed TGA analysis of the recycled catalyst after the third
Figure 11. EDX spectrum of recycled catalyst after third run.
Conclusion
In conclusion, in this study we successfully prepared copper
ferrite and palladium nanoparticles assembled on silica micro
cores. The catalyst was characterized by SEM, TEM, EDX, XRD,
TGA, AAS, and FTIR analysis. The catalytic activity of the cata-
lyst was assessed in Sonogashira coupling reactions of aryl io-
dides and bromides under low Pd loading and mild, phos-
phine-free reaction conditions. The magnetically separable cat-
alyst was recycled successfully for five consecutive runs with
small drops in catalytic activity.
Figure 9. Thermogravimetric diagram of catalyst after third run.
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Experimental Section
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separately in toluene (15 mL) for 30 min, and then mixed together
and heated at reflux for 24 h under an argon atmosphere. Then,
the mixture was subjected to magnetic separation, and isolated
SiO2·AP·CuFe2O4 was washed sequentially with EtOH (3ꢁ10 mL)
and dried under vacuum for 24 h.
Assembly of Pd NPs on prepared SiO2·AP·CuFe2O4: Polyvinylpyr-
rolidone was added an acidic aqueous solution (5 mL) of PdCl2
(0.14 mmol, 25 mg) under stirring. A solution of NaBH4 (2 mmol in
5 mL H2O) was added dropwise to the resulting mixture, and the
obtained mixture was added to the sonicated SiO2·AP·CuFe2O4 in
20 mL H2O. The mixture was stirred for 24 h at 608C under an
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tion time at 508C under an argon atmosphere. The progress of the
reactions was monitored by gas chromatography. After completion
of the reaction, 2 mL H2O was added to the reaction mixture and
the crude product was extracted with ethyl acetate (3ꢁ5 mL). The
crude product was further purified by column chromatography
using n-hexane and ethyl acetate as eluents.
Acknowledgements
We are grateful to the Institute for Advanced Studies in Basic Sci-
ences (IASBS), the Research Council and Iran National Science
Foundation (INSF-Grant number 93020713) for support of this
study. We are also thankful to Dr. Habib. Kazemi and Ali Kiani for
SEM images.
Keywords: copper ferrite · heterogeneous catalysis · magnetic
properties · palladium · Sonogashira coupling
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Received: January 15, 2015
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M. Gholinejad,* J. Ahmadi
&& – &&
Assemblies of Copper Ferrite and
Palladium Nanoparticles on Silica
Microparticles as a Magnetically
Recoverable Catalyst for Sonogashira
Reaction under Mild Conditions
Heterogeneous catalysts: Copper fer-
rite and palladium nanoparticles on
silica have been used to catalyze the So-
nogashira reaction under mild reaction
conditions (see scheme). The catalyst
was recoverable and reusable, with only
small drops in catalytic activity.
DABCO=1,4-diazabicyclo[2.2.2]octane,
DMA=dimethyl acetamide.
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