Core-satellite heterostruture of Fe3O4-Pd nanocomposite: Selective and magnetically recyclable catalyst for decarboxylative coupling reaction in aqueous media

Article abstract of DOI:10.1246/cl.2008.116

Fe₃O₄-Pd nanocomposite having core-satellite heterostructure, prepared through the reaction of Pluronic polymer (P123, PEO₁₉-PPO₆₉-PEO₁₉)-coated Fe₃O ₄ nanoparticle and Na_2<

Full text of DOI:10.1246/cl.2008.116

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Chemistry Letters Vol.37, No.1 (2008)
Core–Satellite Heterostruture of Fe O –Pd Nanocomposite: Selective and Magnetically
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Recyclable Catalyst for Decarboxylative Coupling Reaction in Aqueous Media
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Kyung Min Yeo, Sang Ick Lee, Young Tak Lee, Young Keun Chung, and In Su Lee
Department of Chemistry & Advanced Material Sciences, College of Environment and Applied Chemistry,
Kyung Hee University, Gyeonggi-do 449-701, Korea
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Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-742, Korea
(Received September 18, 2007; CL-071029; E-mail: ykchung@plaza.snu.ac.kr, insulee97@khu.ac.kr)
Fe3O4–Pd nanocomposite having core–satellite heterostruc-
ture, prepared through the reaction of Pluronic polymer
P123, PEO19–PPO69–PEO19)-coated Fe3O4 nanoparticle and
(
Na2PdCl4, showed high catalytic activity, selectivity, and reusa-
bility for decarboxylative coupling reactions in aqueous media.
Scheme 1. Synthetic approach for Pd–Fe3O4 nanocomposite.
The utilization of nanoparticles for catalysis of organic reac-
1
tions is of great recent interest. As the size of particle decreases,
larger fraction of active metal atoms is exposed at the surface
and, consequently, nanoparticles of transition metals often ex-
hibit as high activity as molecular catalysts. Especially, nanopar-
ticles of noble metals such as Pd and Pt have been extensively
employed for various reactions, such as olefin hydrogenation
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2
1–3
and cross-coupling reactions between sp –sp carbons.
On
the other hand, the small size of nanoparticles makes their sepa-
ration from reaction solution and recycling difficult, which ob-
structs their utilization for environment friendly process. In
order to circumvent such a recycling problem, the immobiliza-
tion of nanoparticles on superparamagnetic support matrix,
which can be reversibly flocculated and dispersed with applying
4
,5
Figure 1. TEM images of PCMNP (a) and Pd–MNP (b), (c). (d)
HRTEM image focusing a Pd nanoparticle on Fe3O4 surface. (e)
Pictures showing magnetic attraction of Pd–MNP.
external magnetic field, has been examined very recently.
For instance, Ying and co-workers reported nanocomposites
containing Pd nanocluster on silica-coated Fe3O4 particle and
4
c
3
their catalysis for hydrogenation reaction. Although the immo-
bilization can provide nanoparticle catalysts with the recyclabil-
ity, they still require an organic solvent as a reaction medium.
Recently, the organic reaction in aqueous solution has attracted
tremendous attention for many catalytic reactions owing to in-
tion between sp and sp carbon. The Pd–Fe3O4 nanocomposite
showed excellent and selective catalytic performance and was
conveniently separated and recycled by simply applying external
magnetic field.
The superparamagnetic Fe3O4 nanoparticles of 20 nm in
particle diameter stabilized by oleic acid were prepared through
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creasing demand for environment friendly processes.
8
In this respect, we have been making an effort to develop
magnetically recyclable nanoparticle catalyst system which ena-
bles the organic reactions in aqueous media. Recently, some of
us helped develop fabrication of uniform Pd nanoparticles from
aqueous solution by using triblock Pluronic copolymer both as a
the previously reported procedure. The surface coating of Plur-
onic copolymer (P123, PEO19–PPO69–PEO19) was conducted by
mixing Fe3O4 nanoparticles and P123 in CHCl3 solution, evap-
ꢀ
orating solvent, and annealing at 150 C in vacuo for 1 h. The ad-
dition of water and filtering off floating matters generated trans-
parent dark brown suspension of well-dispersed Fe3O4 nanopar-
ticles (Pluronic copolymer-Coated Magnetic NanoParticle,
PCMNP, Figure 1a). Isolation of PCMNP from excess Pluronic
polymer was done by repeating ultracentrifugation and disper-
sion in water. For the introduction of Pd nanoparticles, an aque-
ous solution containing Na2PdCl4 was reacted with a suspension
of PCMNP and vigorously shaken at room temperature. Within
2 h, a dark brown precipitate appeared, indicating the formation
of Pd nanoparticles on the surface of PCMNP. The precipitate
was concentrated, isolated by magnetic decantation and washed
with water three times. The resulting solid are well dispersed in
water by shaking, vortexing, or sonication, resulting in clear
dark-brown-colored dispersion, and they can be easily attracted
within several minutes by placing a small magnet on a side of
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reductant and as a surface capping agent. Based on this, it oc-
curred to us that the surface coating with Pluronic polymer
would provide the magnetic nanoparticles with water-dispersity
and allow the growth of Pd nanoparticles only at the magnetic
nanoparticle surface. It was also envisioned that nanoparticle
surface stabilized by Pluronic copolymer would act as nanoreac-
tors to induce the solubilization of organic reactants and allow
the reactants to interact more intimately with the Pd nanoparti-
cles, ultimately, catalyzing the reaction in aqueous media. The
present communication reports preparation of Fe3O4–Pd nano-
composite having core–satellite heterostructure (Scheme 1)
and their successful utilization for catalyzing decarboxylative re-
actions in aqueous media. To the best of our knowledge, this is
the first report for the use of Pd nanoparticles for coupling reac-
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.1 (2008)
117
Table 1. Catalytic decarboxylic coupling reaction of allyl alky-
noate
tivity of the second reused catalyst was only slightly reduced,
and ICP measurement showed 85% of Pd species was remain-
ing.
1
2
Ph
O
In conclusion, we prepared Pd–Fe3O4 nanocomposite hav-
Ph
Ph
Catalyst
O
ing core–satellite heterostructure by generating of Pd nano-
particles at the Pluronic polymer-coated surface of Fe3O4 nano-
particle. We demonstrated the high activity and selectivity of the
Pd–Fe3O4 nanocomposite for catalyzing decarboxylative cou-
pling reaction in aqueous media, avoiding hazardous organic
solvent and its recovery and reusability upon application of
magnetic separation.
+
2
H O
85 °C
Ph
1
2
3
ꢀ
T/ C t/h
Yield/%a
25(3)(70)b
95(3)
88(3)
Entry
Catalyst
1
2
3
4
5
5 mol % Pd/Fe3O4
5 mol % Pd/Fe3O4
Recovered from Entry 2 85
85
85
2
12
12
c
5 mol % Pd/C
5 mol % Pd(PPh3)4
85
85
12 20(4(2):1(3))
92(4(2):1(3))c
We thank Prof. Taeghwan Hyeon and Mr. Sung Cheol Kim
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(
SNU) for TEM characterization. This research was supported
by the Kyung Hee University Research Fund in 2006
No. KHU-20061282).
a
b
Isolated yield. Yield in parenthesis is of the recovered reac-
tant. The ratio was determined by H NMR.
c
1
(
vessel (Figure 1e). Most of solids were aggregated and precipi-
tated within 2 h after standing at room temperature and could be
easily re-dispersed by shaking, vortexing, or sonication.
Transmission electron microscopy (TEM) reveals the gener-
ation of Pd nanoparticles having 2:1 Æ 0:4 nm in average size
around Fe3O4 nanoparticle and core–satellites heterostructure
References and Notes
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3
4
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II
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5
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9
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(
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5
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ꢀ
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3
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2
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1
2 Supporting Information is also available electronically on the
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index.html.
Published on the web (Advance View) December 19, 2007; doi:10.1246/cl.2008.116