Fabrication of PEI grafted Fe3O4/SiO2/P(GMA-co-EGDMA) nanoparticle anchored palladium nanocatalyst and its application in Sonogashira cross-coupling reactions

Article abstract of DOI:10.1039/c4nj02117g

Novel magnetic Fe₃O₄/SiO₂/P(GMA-co-EGDMA) composite nanoparticles grafted with hyperbranched/linear polyethylenimine ligands were fabricated. Subsequently, nano palladium was effectively anchored on this carrier through complexation between Pd²⁺ ions and multifunctional organic ligands, then a novel supported Pd nanoparticle catalyst with good dispersion and high loading of Pd nanoparticles was successfully prepared after the following reduction process. Afterwards, the as-prepared supported Pd nanoparticle catalyst was characterized by SEM, TEM, XRD, FTIR, TG and ICP-AES. Ultimately, the catalytic performance of the supported Pd nanoparticle catalyst was investigated by catalysing the Sonogashira cross-coupling reaction between aryl halides and arylacetylene. Research shows that the novel supported Pd nanoparticle catalyst exhibits very superior catalytic activity in catalysing the Sonogashira cross-coupling reaction between aryl halides and arylacetylene, even in the absence of the cocatalyst (CuI), and the side reaction producing the by-product (1,3-diyne) can be inhibited effectively. In addition, this supported Pd nanoparticle catalyst exhibits stable recovery and high catalytic activity, for it can be effectively reused 8 times without obvious loss of catalytic activity. Furthermore, the yields of the target products of the Sonogashira cross-coupling reaction between iodobenzene and phenylacetylene, 3-aminophenylacetylene and 4-(ethynyl)phthalic anhydride can reach approximately 79%, 78% and 95% after this novel supported Pd nanoparticle catalyst has been used eight times, respectively.

Full text of DOI:10.1039/c4nj02117g

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1Fabrication of PEI Grafted Fe3O4/SiO2/P(GMA-co-EGDMA)
Nanoparticles Anchored Palladium Nano-Catalyst and Its Application in
Sonogashira Cross-Coupling Reaction
Wei Li,ab Xiangkun Jia,ab Baoliang Zhang,ab Lei Tian,ab Xiangjie Li,ab Hepeng Zhang,ab Qiuyu
Zhang*ab
aDepartment of Applied Chemistry, College of Science, Northwestern Polytechnical University,
Xi’an 710072, China.
bKey Laboratory of Space Physics and Chemistry, Ministry of Education, Northwestern
Polytechnical University, P. O. Box 624, Xi’an 710072, China.
Abstract: A novel magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles
grafted with hyperbranched/linear polyethylenimine ligand was fabricated. Subsequently,
Nano palladium was effectively anchored on this carrier through the complexation between
Pd2+ ions and multifunctional organic ligands, then a novel supported Pd nanoparticles
catalyst with good dispersion and high loading of Pd nanoparticles was successfully prepared
after the follow reduction process. Afterwards, the asꢀprepared supported Pd nanoparticles
catalyst was characterized by SEM, TEM, XRD, FITR, TG, ICPꢀAES, respectively.
Ultimately, the catalytic performance of the supported Pd nanoparticles catalyst was
investigated by catalysing the Sonogashira CrossꢀCoupling Reaction between aryl halides
and arylacetylene. Research shows that the novel supported Pd nanoparticles catalyst
exhibits very superior catalytic activity in catalysing Sonogashira crossꢀcoupling reaction
between aryl halides and arylacetylene even at the absence of the cocatalyst (CuI), and the
side reaction to produce byꢀproduct (1,3ꢀdiyne) can be inhibited effectively. In addition, this
supported Pd nanoparticles catalyst exhibites stable recovery and high catalytic activity for it
can be effectively reused 8 times without obvious loss of catalytic activity. Especially, the
yields of the target products of the Sonogashira crossꢀcoupling reaction between
iodobenzene and phenylacetylene, 3ꢀaminophenylacetylene and 4ꢀ(ethynyl)phthalic
anhydride can reach up to about 79%, 78% and 95% after this novel supported Pd
nanoparticles catalyst being used eight times, respectively.
1
Phone: +86ꢀ029ꢀ88431675, Fax: +86ꢀ029ꢀ88431675, Eꢀmail: qyzhang@nwpu.edu.cn (Qiuyu Zhang).

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Keywords: Fe3O4 nanocrystallines; GMA; PEI; palladium; Sonogashira crossꢀcoupling reaction
1. Introduction
Generally, the crossꢀcoupling reaction between aryl halides and alkene halides or terminal alkyne
catalyzed by palladium complexes is named Sonogashira crossꢀcoupling reaction, and it is the
effective reaction to synthesis aryne, eneyne and acetyenic ketone[1ꢀ5]. The general equation of the
reaction has been shown as below:
R1
X
H
RCat/CuI, base R1
R
R= aryl, hetaryl, vinyl, acyl
R1= alkyl, aryl
X= I, Br, Cl, OTf
The crossꢀcoupling reaction between aryl halides and alkenes or terminal alkynes catalyzed by
palladium complexes had undergone such a period that Cassar firstly discovered it, then Heck and
Sonogashira et al. modified it subsequently. Therefore, these kind of reactions were named
CassarꢀHeckꢀSonogashira reaction in some previous literatures. In some subsequent literatures,
whether the cocatalyst CuI was added or not, the reaction was named Sonogashira reaction. However,
the byꢀproduct 1,3ꢀdiyne would be inevitably generated if CuI was existent in the reaction system,
and it can not only reduce the effective availability of alkynes, but also can complicate the separation
and purification of the organic product. Therefore, the investigation of the Sonogashira
crossꢀcoupling reactions without the cocatalyst CuI naturally shows a great significance. R. Wang et
al.[3] chosen 2, 2’ꢀdipyridylamine as a supporting ligand in the palladiumꢀcatalyzed Sonogashira
crossꢀcoupling reaction, then they found that this palladium complexe can effectively catalyze the
reactions between aryl iodides and terminal alkynes with different steric hindrance in the absence of
copper in neat water at room temperature. H. Wu et al.[6] synthesized
a
diꢀ(1ꢀbutylꢀ2ꢀdiphenylphosphinoꢀ3ꢀmethylimidazolium)ꢀdichloropalladium(II) hexafluorophosphat,
and it can fulfill the high catalytic efficiency for the Sonogashira reactions between aryl iodides and
aryl bromides with several terminal acetylenes under aerobic and CuIꢀfree conditions. In addition, M.
Nasrollahzadeh et al.[7] prepared a Pd nanoparticles catalyst by green method, and high activity for
amineꢀ and copperꢀfree Sonogashira coupling reaction between aryl iodides and terminal alkynes
under mild and aerobic conditions can be achieved.
To our knowledge, noble metal palladium is a favourable catalyst for catalyzing a series of
coupling reactions to form CꢀC bond and CꢀN bond [8ꢀ12]. In particular, homogeneous palladium

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catalyst has shown superior catalytic activity for catalyzing Sonogashira crossꢀcoupling reaction. S. J.
Sabounchei et al.[13] chosen palladacycle phosphineꢀylide complexes as catalyst precursors and used
it in additiveꢀ and amineꢀfree Sonogashira crossꢀcoupling reactions. Various aryl halides were
successfully coupled with phenylacetylene in dimethyl formamide (DMF) under air, and the
corresponding crossꢀcoupled products in excellent yields were obtained. M. H. Huang et al.[14] had
synthesized the palladium tripod nanocrystals, and the large Pd tripods can serve as an active and
recyclable catalyst for Sonogashira coupling reactions of a variety of aromatic halides containing
electrondonating and ꢀwithdrawing substituents in water. In addition, M.ꢀJ. Jin et al.[15] reported that
the βꢀdiketiminatophosphane palladium catalyst can effectively catalyze copperꢀfree Sonogashira
coupling reaction of aryl chlorides with alkynes, and the high performance under relatively mild
reaction conditions can be achieved. The superior performance of the homogeneous palladium
catalyst is beyond doubt, however, some problems such as high price and limited noble metal reserve
limit its largeꢀscale applications. To immobilize palladium catalyst on suitable materials indeed is an
effective method to separate palladium catalyst from reaction system. For instance, L. A. Aronica et
al.[16] supported palladium nanoparticles on two Smopex® commercial metal scavengers (1% w/w),
and it exhibited effective performance in the synthesis of alkynl ketones even working with a low
amount of palladium (0.2—0.5 mol%). F. Panahi et al.[17] immobilized Pd nanoparticles on a
silicaꢀstarch substrate, and it can prevent the aggregation of nanoparticles and improve the stability
of palladium catalyst. The invesigation of heterogeneous supported palladium catalyst had indeed got
a great development in the past decades.
For supported palladium catalyst, it generally demands that the palladium catalyst should show
ultrasmall nanoscale as far as possible, which can significantly increase the effective contact area of
palladium catalyst with reactants. Simultaneously, the high stability is also demanded, which can
effectively reduce the loss of palladium catalyst during the reaction process. Furthermore, some
researches and our previous studies have shown that the ligands on the supports also show an
important role in improving the catalytic activity of the supported catalyst [18ꢀ22]. In recent years,
the fabrication and application of the branched organic segments grafted materials have became a
very hot research topic, and these materials have been widely applied in drug delivery system,
adsorption, catalysis, photonics, imprinting and so on for the unique spatial conformation and a large
number of functional groups of the branched organic segments [23ꢀ32]. Especially, when the

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materials grafted by branched organic segments are used to anchor noble metal catalyst, it can well
fulfill the high density loads and strong stability of the noble metal catalyst for the unique steric
hindrance and multifunctional oaganic ligands on the carrier surface [33,34]. PEI, which
simultaneously has unique branched/linear conformation and multifunctional groups, is a superior
ligand to chelate noble metal catalyst, but its corresponding application in anchoring noble metal
catalyst has been rarely reported to date. For this reason, to investigate the effect of PEI in catalytic
efficiency of supported palladium, we carried out the relevant research work. Primarily, to improve
the dispersibility and surface properties, a layer of silica was coated on the surface of the magnetic
Fe3O4 nanocrystallines by the traditional Stöber hydrolysis.[35] Then a layer of polymer was coated
on the outer surface of the magnetic Fe3O4/SiO2 nanoparticles through the grafted copolymerization
after being modified by γꢀmethacryloxypropyltrimethoxylsilane, and
a
novel magnetic
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticle was successfully prepared. To the best of
our knowledge, plenty of epoxy groups exist in the surface of magnetic
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles for the introduction of the monomer
GMA in the polymer coating, by which the branched/linear PEI can be successfully grafted on the
surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles through the ring
opening reaction between amono groups and epoxy groups. For the existence of a lot of imidogen
groups and tertiary amine groups in the branched/linear PEI segments, Pd2+ ions were successfully
immobilized on the carrier surface through the complexation between Pd2+ ions and multifunctional
organic ligands, then a novel Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEIꢀPd(0) catalyst was successfully
prepared after the following reduction process. Finally, the catalytic performance and stability of this
supported catalyst was investigated by catalysing a series of Sonogashira crossꢀcoupling reactions.
2. Experimental
2.1. Reagents and Materials. Ferric chloride hexahydrate (FeCl3·6H2O), ferrous sulfate
heptahydrate (FeSO4·7H2O), sodium hydroxide (NaOH), NH3·H2O (28 wt%, A. R.), tetraethyl
orthosilicate (TEOS), anhydrous alcohol, γꢀmethacryloxypropyltrimethoxylsilane (Aꢀ174), glycidyl
methacrylate (GMA), ethyleneglycol dimethacrylate (EGDMA), hexadecyltrimethylammonium
bromide (CTAB), 2, 2´ꢀazobis (2ꢀmethylpropionamide) dihydrochloride (Vꢀ50), polyethylenimine
(PEI), palladium acetate (Pd(OAc)2), sodium borohydride (NaBH4), phenylacetylene,

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3ꢀaminophenylacetylene, 4ꢀ(ethynyl) phthalic anhydride and all aryl halides were purchased from J
﹠K Chemical and were used without further treatment.
2.2. Synthesis of Magnetic Fe3O4 Nanocrystallines. The magnetic Fe3O4 nanocrystallines were
prepared by coprecipitation method. Primarily, 6.8 g of FeCl3·6H2O and 4.2 g of FeSO4·7H2O were
dissolved into 50 mL of deionized water. Then, the temperature was adjusted to 55℃, and 60 mL of
NaOH solution containing 4.8 g of NaOH was quickly injected into this system to adjust its pH to 13.
Subsequently, the temperature was rised to 65—70℃ and kept for 2 h, then the temperature was
further rised to 80℃ to ripen for 2 h. After the reaction finished, the product was collected by
supplying an external magnetic field and washed several times with ethanol and distilled water,
respectively. At last, the product was redispersed into the distilled water to form the dispersion with
the concentration of 0.02 g/mL.
2.3. Preparation of Magnetic Fe3O4/SiO2 Composite Nanoparticles. Silica film was coated on the
outer surface of the magnetic Fe3O4 nanocrystallines by the Stöber hydrolysis method, then the
magnetic Fe3O4@SiO2 composite nanoparticles were successfully obtained. Briefly, 0.9 g of Fe3O4
was added into the mixture of 70 mL of distilled water and 140 mL of absolute ethanol, and the
mixed system was kept for 5 min under the ultrasonic. Then, 7 mL of NH3·H2O (28 wt%, A. R.) was
added to the aforementioned mixed system, and the system was vigorously stirred for 30 min.
Subsequently, 3.0 g of TEOS was dropwise added into this suspension, and the system was stirred
constantly for 6 h under the speed of 250 rpm. After the reaction finished, the product was collected
by supplying an external magnetic field and washed several times with ethanol and distilled water,
respectively. At last, the product was redispersed into the distilled water to form the dispersion with
the concentration of 0.02 g/mL.
2.4. Grafting of A-174 on Magnetic Fe3O4/SiO2 Composite Nanoparticle. The magnetic
Fe3O4/SiO2 composite nanoparticles with doubleꢀbond on the outer surface were successfully
obtained by grafting Aꢀ174 on their outer surface. Briefly, 1.5 g of Fe3O4@SiO2 was added into the
threeꢀnecked roundꢀbottomed flask of 100 mL containing 80 mL of absolute ethanol. Subsequently,
0.5 mL of NH3·H2O (28 wt%, A. R.) was added into the aforementioned system, and the mixed
system was vigorously stirred for 10 min. Then 4 mL of Aꢀ174 was quickly added into the mixed

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dispersion, and it was constantly stirred for 12 h under the speed of 200 rpm at 60℃. After the
reaction finished, the product was collected by supplying an external magnetic field and washed
several times with ethanol and deionized water, respectively. At last, the final product was dispersed
into distilled water to form the dispersion with the concentration of 0.02 g/mL.
2.5. Preparation of Magnetic Fe3O4/SiO2/P(GMA-co-EGDMA) Composite Nanoparticles. Here,
a layer of polymer was coated on the surface of the magnetic Fe3O4/SiO2 composite nanoparticles by
the graft copolymerization between monomer and crossꢀlinking agent, then the magnetic
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles with doubleꢀshell structure were
successfully prepared. Briefly, 0.5 g of Aꢀ174 modified Fe3O4/SiO2 was added into the threeꢀnecked
roundꢀbottomed flask of 1000 mL containing 55 mL of absolute ethanol, then 4 g of GMA and 0.7 g
of EGDMA were added into this dispersion. After being stirred vigorously for 5 min, 500 mL of
distilled water containing 0.2 g of CTAB was added into aforementioned system, then the
temperature was adjusted to 75℃, and 100 mL of distilled water containing 0.2 g of Vꢀ50 was added
into this system, and it was vigorously stirred for 12 h. After the reaction finished, the product was
collected by supplying an external magnetic field and washed several times with ethanol and distilled
water, respectively. At last, the final product was redispersed into distilled water to form the
dispersion with the concentration of 0.02 g/mL.
2.6. Preparation of Magnetic Fe3O4/SiO2/P(GMA-co-EGDMA)-PEI Composite Nanoparticles.
The branched/linear PEI was grafted on the surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)
composite nanoparticles by the ring opening reaction between amino groups and epoxy groups, then
the branched/linear PEI grafted magnetic composite nanoparticles were successfully obtained.
Briefly, 0.5 g of Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) was dispersed into 30 mL of absolute ethanol,
then 30 mL of absolute ethanol containing 0.7 g of PEI was added into this system, and the mixed
system was vigorously stirred for 12 h at 50℃. After the reaction finished, the product was collected
by supplying an external magnetic field and washed several times with ethanol and distilled water,
respectively. At last, the sample was redispersed into the distilled water to form the dispersion with
the concentration of 0.02 g/mL.
2.7. Preparation of Fe3O4/SiO2/P(GMA-co-EGDMA)-PEI-Pd(0) Supported Nanocatalyst. The

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Pd
NPs
were
successfully
anchored
on
the
surface
of
the
magnetic
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEI composite nanoparticles through the complexation between
Pd2+ ions and imidogen groups or tertiary amine groups in the branched/linear PEI segments. Briefly,
0.3 g of Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) was dispersed into 50 mL of absolute ethanol, and 100 mg
of Pd(OAc)2 was added into this dispersion, then this mixed system was vigorously stirred for 24 h at
room temperature. After the reaction finished, the sample was washed several times with distilled
water to remove the unimmobilized Pd2+ ions. Subsequently, 200 mg of NaBH4 was added into
aforementioned system, and it was vigorously stirred for 10 h at room temperature. After the reaction
finished, the product was collected by supplying an external magnetic field and washed several times
with ethanol and distilled water, respectively. At last, the wet sample was kept for 12 h in a vacuum
freeze drying device to produce the dried sample.
2.8. Characterization. The fourier transformꢀinfrared (FTꢀIR) spectra of all samples were recorded
on
a
PerkinꢀElmer 580BIR spectrophotometer using the KBr pellet technique. The
thermogravimetric analysis (TG) was performed on a Q5000IR (TA Instruments, US) apparatus. The
Xꢀray power diffraction (XRD) analysis was performed on a Bruker AXS D8ꢀadvance Xꢀray
diffractometer with Cu Kα radiation. The magnetic moment was recorded at 300 K on a
JPMSꢀ9HꢀEVERCOOL (QD) vibratingꢀsample magnetometer (VSM). The transmission electron
microscopy (TEM), energy dispersive Xꢀray (EDS) spectra and transmission electron diffraction
patterns were performed on a JEOL JEL2010 electron microscope at 200 kV. The high performance
liquid chromatography (HPLC) analysis was performed on a HITACHI Lꢀ2400. The inductively
coupled plasma spectrum instrument (ICPꢀAES) was performed on an ICAP6300.
2.9. The Tests of Sonogashira Cross-Coupling Reactions. Aryl halides (1.0 mmol), aryl acetylenes
(2.0 mmol), K2CO3 (2.0 mmol) and Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEIꢀPd(0) (0.1 mol% Pd)
were added into a roundꢀbottomed flask of 10 mL, then 5 mL of DMF was added into this system,
and the reaction system was vigorously stirred for 5 h at 120℃. After the reaction finished, the
catalyst was regenerated by supplying an external field (1000 Gauss) and being washed several times
with ethanol and distilled water, respectively, and the organic phase was extracted 6~8 times with
right amount of ether. Subsequently, the collected organic phase was concentrated by reduced
pressure distillation and detected by the HPLC.

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The yields of the Sonogashira crossꢀcoupling reactions were calculated by the following formulas:
ꢀ
/ꢃ
/ꢃ
ꢁꢂ
ꢁꢂ
ee = ꢀ
× 100%
(1)
ꢂꢄ
ꢂꢄ
Wsa is the mass of the produced diaryl substituted acetylenes, and Wah is the mass of the aryl
halides in the coupling reaction before the reaction. Msa and Mah is the corresponding relative
molecular mass of the diaryl substituted acetylenes and aryl halides, respectively.
Wꢅꢆ = Cꢅꢆ × Vꢅꢆ
(2)
Csa is the mass concentration of the produced diaryl substituted acetylenes, and Vsa is the volume
of the reaction system after the reaction.
ꢇꢇꢇ
ꢀ
ꢋ
∙ꢌ
ꢋ
ꢍ
ꢈꢉ
ꢈꢉ
ꢈꢉ
ꢈ
ꢈꢉ
=
=
=
ꢍ
ꢈꢉꢊ
(3)
ꢇꢇꢇ
ꢀ
ꢋ
∙ꢌ
ꢋ
ꢈꢉꢊ
ꢈꢉꢊ
ꢈ
ꢈꢉꢊ
Csar is the known mass concentration of the reference standard solution, and Vs is the volume of
the testing solution. Asa and Asar is the peak areas of the diaryl substituted acetylenes in the reaction
solution and in the standard solution, respectively.
The following formula can be obtained by jointing three equations of above:
ꢋ
ꢌ ꢃ
ꢈꢉ ꢈꢉꢊ ꢈꢉ
ꢉꢎ
ee = ꢍ
(4)
ꢍ
ꢃ ꢀ
ꢈꢉꢊ ꢈꢉ
ꢉꢎ
TEOS
KH570
ammonia
Fe3O4
Fe3O4/SiO2
O
Si
O
Fe3O4/SiO2/P(GMA-co-EGDMA)
CH2CH2NCH2CH2NH
CH2CH2NH
n
NaBH4
Pd(OAc)2
Pd2+
HO
Fe3O4/SiO2/P(GMA-co-EGDMA)-PEI
Fe3O4/SiO2/P(GMA-co-EGDMA)-PEI-Pd(0)
Scheme1 Preparation process of the Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst.

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3. Results and discussion
3.1. The Structure and Morphology of Materials.
The fabrication of the Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEIꢀPd(0) catalyst was shown as scheme
1. To investigate the composition of each material, the Fe3O4, Fe3O4@SiO2, Aꢀ174 modified
Fe3O4@SiO2, Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) and Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEI was
characterized by FTIR, respectively. As shown as Fig.1, all curves show the characteristic absorption
peak corresponding to stretching vibration of the FeꢀO bond at 572 cmꢀ1, and it indicates the presence
of Fe3O4. Simultaneously, Fig.1a shows a characteristic absorption peak corresponding to the
stretching vibration of νOꢀH, and it indicates the existence of the hydroxy groups on the surface of the
magnetic Fe3O4 nanocrystallines. Compared with Fig.1a, Fig.1b shows a strong absorption peak and
a moderate absorption peak at 1081 cmꢀ1 and 793 cmꢀ1, respectively. It can be respectively attributed
to the antisymmetrical and symmetrical stretching vibration of SiꢀOꢀSi bond in oxygenꢀsilicon
tetrahedron, and it well indicates the presence of silica. After being modified by Aꢀ174, Fig.1c
appears a characteristic absorption peak at 1728 cmꢀ1 which is attributed to the stretching vibration of
νC=O. Obviously, the absorption peak is very weak because the content is very low relative to the
materials, but it can still indicate that the surface of Fe3O4@SiO2 had been successfully modified by
Aꢀ174. At the same time, the nanoparticles transformed into strong hydrophobicity from previous
strong hydrophilcity after this modification, so that wallꢀclimbing phenomenon can be clearly
observed when the Aꢀ174 modified magnetic Fe3O4@SiO2 composite nanoparticles were dispersed
in water (as Fig.2b) by comparing with the previous magnetic Fe3O4@SiO2 composite nanoparticles
(as Fig.1f), but it can be well dispersed in ethanol (as Fig.1h). All of which demonstrates the
aforementioned conclusion well. In addition, Fig.1d shows that all the absorption peaks at 2921 cmꢀ1,
2852 cmꢀ1 and 1728 cmꢀ1 had been significantly enhanced after the coating of P(GMAꢀcoꢀEGDMA),
and it powerfully illustrates that the polymer shell had been successfully coated on the outer surface
of the Aꢀ174 modified magnetic Fe3O4/SiO2 composite nanoparticles. Subsequently, the
branched/linear PEI was grafted on the surface of the Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) through the
ring opening reaction between amino groups and epoxy groups. As shown as Fig.1e, all the
characteristic absorption peaks at 3437 cmꢀ1, 2921 cmꢀ1 and 2852 cmꢀ1 had been enhanced to some
extent based on the sbsorption peak at 1081 cmꢀ1. Primarily, the enhancement of the peak at 3437

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cmꢀ1 was caused by the stretching vibration of νNꢀH, and the enhancement of the peaks at 2921 cmꢀ1
and 2852 cmꢀ1 was caused by the stretching vibration of νCꢀH of methyl and methylene in PEI. All of
which indicates that the PEI had been successfully grafted on the surface of the magnetic
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles.
a
b
c
d
f
g
h
e
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumbers(cm )
Fig.1 FTIR spectra of the Fe3O4 nanocrystallines (a), Fe3O4/SiO2 NPs (b), Aꢀ174 modified Fe3O4/SiO2 NPs (c)
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) NPs (d), PEI grafted Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) NPs (e). And the digital
photographs of the Fe3O4@SiO2 NPs dispersed in water (f), Aꢀ174 modified Fe3O4@SiO2 NPs dispersed in water
(g) and in ethanol (h).
To demonstrate the successful grafting of the branched/linear PEI on the surface of the magnetic
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)
composite
nanoparticles,
all
the
Fe3O4@SiO2,
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) and Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEI were characterized by
TG under the protection of nitrogen. As shown as Fig.2, the magnetic Fe3O4/SiO2 composite
nanoparticles showed a slight weight loss of about 3.8 wt% in the range of 300—600℃ (as Fig.2a),
and it should be attributed to the decomposition of the residual organic oligomer in silica shell at
high temperature. After being coated with P(GMAꢀcoꢀEGDMA), an obvious weight loss of about
21.4 wt% can be observed in the range of 260—600℃(as Fig.2b), which demonstrates the existence
of the polymer in the sample, and it also indicates that the content of the polymer is above 17.6 wt%.
Fig.2c shows the thermal gravimetric curve of Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEI, and a weight
loss of about 24.1 wt% can be observed in the range of 260—650℃, which is 2.7 wt% more than
that of Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA). All of which indicates that the branched/linear PEI had
been successfully grafted on the surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)

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composite nanoparticles, and the content is above 2.7 wt%. Because the polymer shell and organic
segments would generate carbon residues when the samples were calcined at high temperature in
nitrogen atmosphere, thus the actual content is more than the weight loss displayed as Fig.2b and
Fig.2c.
105
100
a
95
90
85
b
80
75
70
C
65
60
55
50
0
100
200
300
400
500
600
700
800
900
Temperature (℃)
Fig.2 TG analysis of the Fe3O4/SiO2 nanocrystallines (a), Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) NPs (b) and PEI
grafted Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) NPs (c).
To investigate the morphologies, all of the Fe3O4, Fe3O4/SiO2, Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)
and Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) was characterized by TEM. As shown as Fig.3a and
Fig.3b, the diameter of the magnetic Fe3O4 nanocrystallines prepared via the coprecipitation method
is about 15 nm, then it would increase to about 19 nm after the silica coating process, and the
obvious coreꢀshell structure can be observed. In addition, the introduction of the silica coating to the
magnetic materials can improve the dispersibility and the surface properties, which had been proved
by Paszczynski[35]. Subsequently, a layer of P(GMAꢀcoꢀEGDMA) film was coated on the outer
surface of the magnetic Fe3O4/SiO2 nanoparticles by the graft copolymerization after the
modification of Aꢀ174, and the doubleꢀshell magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite
nanoparticles were successfully prepared. Fig.3c shows the clear doubleꢀshell structure, and the
diameter of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles is about 30 nm.
It indicates that the P(GMAꢀcoꢀEGDMA) film was indeed coated on the outer surface of the
magnetic Fe3O4/SiO2 nanoparticles. Subsequently, the branched/linear PEI was grafted chemically on

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the outer surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles through
the ring opening reaction between amino groups and epoxy groups on the polymer surface. Then Pd
NPs with ultrasmall nanostructure were successfully anchored on the surface of the magnetic
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEI composite nanoparticles by the complexation between Pd2+
ions and imidogen groups or tertiary amine groups and the following reduction reaction, and the
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst with superior magnetic responsibility was
successfully fabricated. As shown as Fig.3d, the size of the Pd NPs was about 4—8 nm, and it is
immobilized on the surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEI composite
nanoparticles in the form of uniform dispersion, and no palladium aggregation can be observed. It
indicates that the unique surface structure of this novel support is very conducive to the uniform
immobilization of the Pd NPs on its outer surface. Furthermore, the insert in Fig.3d gives the
electronic diffraction pattern of the Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst, the diffraction
rings show typical faceꢀcenteredꢀcubic structure characteristic of Pd NPs, which indicates that the Pd
NPs on the surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEI composite nanoparticles
exhibit good crystallinity. In summary, this Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst not only
can fulfill the high density loads in the form of ultrasmall nanoscale but also can meet the good
crystallinity.
In
addition,
Fig.4a
gives
the
EDS
spectrum
of
the
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst, which shows that all the Fe, O, Si and Pd exist in
this supported catalyst. It also indicates the existence of Fe3O4, SiO2 and palladium. Furthermore, the
loading capacity of the palladium is about 5.26 wt%, which was obtained by ICPꢀAES.

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Fig.3. TEM images of the Fe3O4 nanocrystallines (a), Fe3O4/SiO2 NPs (b), Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) NPs
(c), Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst (d), and the insert is the corresponding selected area electron
diffraction of the novel supported catalyst. The scale bars of all figures are 100 nm.
40
60
20
b
c
d
e
a
40
20
0
-20
-40
-2000 -1500 -1000
-500
0
500
1000
1500
2000
Applied magnetic field (Oe)
0
-20
-40
-60
-30000 -20000 -10000
0
10000
20000
30000
Applied magnetic field (Oe)
Fig.4 EDS spectrum of the Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst (a), and magnetization curves of Fe3O4
nanocrystallines (b), Fe3O4/SiO2 NPs (c), Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) NPs (d) and
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst (e). The insert at the lower right corner is the corresponding
magnetic seperation digital photos, and the insert at the top left is the low field magnification.
To magnetic materials, the magnetic responsivity is very important to their usability. Therefore, the

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magnetic performance of the Fe3O4, Fe3O4/nSiO2, Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) and
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) was characterized by the vibratingꢀsample magnetometer
(VSM), respectively. As shown as Fig.4bꢀe, all magnetization curves of aforementioned magnetic
materials exhibit a typical feature of superparamagnetism as no hysteresis is observed in low fields
of the insert, which indicates that any remanence can not be observed after removing the external
magnetic field. In addition, the magnetic saturation of aforementioned magnetic materials is about
56.17, 39.74, 32.19 and 28.26 emu/g, respectively, which indicates that the magnetic saturation of the
materials would be reduced to some extent with the increase of shell thickness. This is an apparent
tricky, because the Fe3O4 nanoparticles are always of the same size but their mass (and volumen)
changes due to the addition of SiO2, and the rest of elements, therefore the magnetization per mass
reduces its value but maintaining the superparamagnetic behavior because the size of nanoparticles
remains unchanged. Furthermore, it indicates that the magnetic responsivity can completely fulfill
the simple magnetic separation and the regeneration of the noble metal catalyst, and the digital
photos in the insert of Fig.4 can well demonstrate this point.
d
c
b
a
20
30
40
50
60
70
80
2θ
(deg.)
Fig.5 XRD pattern of the Fe3O4 nanocrystallines (a), Fe3O4/SiO2 NPs (b), Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) NPs (c)
and Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst (d).
To further investigate the crystal structure, Fe3O4, Fe3O4/nSiO2, Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)
and Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) was characterized by XRD, respectively. As shown as
Fig.5, six characteristic diffraction peaks (2θ = 30.2°, 35.6°, 43.3°, 53.8°, 57.3° and 63.0°)

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corresponding to (220), (311), (400), (422), (511) and (440) reflections of inverse spinel Fe3O4 can
be observed clearly in all four curves (as Fig.5a to Fig.5d), which indicates that the crystallization of
the prepared superparamagnetic Fe3O4 nanocrystallines is very complete and mostly exist in the form
of faceꢀcentered cubic structure. Fig.5b to Fig.5d show that a broad peak around 2θ = 24°
corresponding to the characteristic diffraction peak of amorphous silica can be observed after the
silica coating and polymer coating, which indicates that both the silica and polymer coating exist in
the form of amorphous state.[36] In addition, new characteristic diffraction peaks (2θ = 40° and 46°)
corresponding to (111) and (200) reflections of palladium can be observed clearly after the
immobilization of the Pd NPs (as Fig.5d), which indicates that the Pd NPs were successfully
anchored on the surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPEI composite
nanoparticles in the form of faceꢀcenteredꢀcubic structure.
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
Reaction time
Fig.6 The reaction kinetic curve of the Sonogashira coupling reaction between iodobenzene and 4ꢀ(ethynyl)phthalic
anhydride at 120℃.
To further investigate the catalytic activity of the novel Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0)
catalyst, the Sonogashira crossꢀcoupling reaction between iodobenzene and 4ꢀ(ethynyl)phthalic
anhydride was carried out, and the ctalytic yields in differnet reaction time were obtained. As shown
as Fig.6, the yield is zero before 1 h, then it would gradually increase among 1 h—5 h, and it would
keep balanced in 5 h. It is not hard to see that the slope of the catalytic kinetic curve has an
increasing trend in the period of 1 h—5 h, which is mainly because that the precursor molecules in

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the reaction system have not been activated when the reaction time is very short, thus the reaction
would hardly happen.Subsequently, a small amount of precursor molecules in the reaction system
would be activated with the prolonging of time, then more and more activated precursor molecules
would be generated and involve in the reaction to generate the target product. Ultimately, the reaction
yield of about 95 % would basically remain stable when the reaction time exceed 5 h, which is
because that almost all activated molecules have participated in the reaction. Therefore, the
maximum value of turnover frequency (TOF) should be in the range of 4 h—5 h to this reaction.
Table1 The summarized catalytic results of the Sonogashira coupling reaction between aryl halides and
arylacetylene at 120℃. 1, 2 and 3 in this table represents phenylacetylene, 3ꢀaminophenylacetylene and
4ꢀ(ethynyl)phthalic anhydride, respectively.
R2
R1
R1
R2
Cat, base
X
Entry
1
Aryl halidea b
arylacetylenec Yield (%)
1
1
1
1
1
1
2
2
2
2
2
2
3
85
79
72
82
80
46
84
71
57
79
75
20
100
I
2
3
Br
Cl
4
OH3C
O2N
Cl
5
Cl
6
H3C
Cl
7
I
8
Br
Cl
9
10
11
12
13
OH3C
O2N
Cl
Cl
Cl
H3C
I

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14
15
16
17
18
3
3
3
3
3
95
81
96
94
53
Br
Cl
OH3C
O2N
Cl
Cl
H3C
Cl
a X represents I, Br or Cl.
b R1 represents Hꢀ, CH3Oꢀ, O2Nꢀ or CH3ꢀ.
c 1, 2 and 3 represents phenylacetylene, 3ꢀaminophenylacetylene and 4ꢀ(ethynyl)phthalic anhydride, respectively.
Afterwards, a series of Sonogashira crossꢀcoupling reactions of aryl halides with phenylacetylene,
3ꢀaminophenylacetylene and 4ꢀ(ethynyl)phthalic anhydride were carried out under the catalysis of
the asꢀprepared Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst, and the corresponding catalytic
yields were summarized in Table 1. As shown as Table1, the yield of phenylacetylene with
iodobenzene, bromobenzene, chlorobenzene, 4ꢀchloroacetophenone, 4ꢀnitrochlorobenzene and
4ꢀchlorotoluene is respectively about 85 %, 79 %, 72 %, 82 %, 80 % and 46 %, and it is respectively
about 84 %, 71 %, 57 %, 79 %, 75 % and 20 % to 3ꢀaminophenylacetylene, and it is about 100 %,
95 %, 81 %, 96 %, 94 % and 53 % to 4ꢀ(ethynyl)phthalic anhydride, respectively. Aforementioned
data indicates that the activity order from strong to weak is iodobenzene＞bromobenzene＞
chlorobenzene to the Sonogashira crossꢀcoupling reaction between aryl halide and arylacetylene, and
it is 4ꢀchloroacetophenone ＞ 4ꢀnitrochlorobenzene ＞ chlorobenzene ＞ 4ꢀchlorotoluene to the
Sonogashira crossꢀcoupling reaction between aryl chloride and arylacetylene, and it is
4ꢀ(ethynyl)phthalic anhydride ＞ phenylacetylene ＞ 3ꢀaminophenylacetylene to the Sonogashira
crossꢀcoupling reaction between aryl halides and arylacetylene.

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Scheme2 The reaction mechanism of the Sonogashira reaction catalyzed by Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0)
catalyst.
To explain the aforementioned results, the reaction mechanism of the Sonogashira crossꢀcoupling
reaction was necessary to be discussed firstly, and the corresponding catalytic mechanism had also
been shown in Scheme 2. The advantage of this novel Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0)
catalyst is that the existence of the zerovalent palladium catalyst can effectively avoid the additon of
cocatalyst CuI, so that the byꢀproduct 1,3ꢀdiyne can be effectively prevented to some extent. Briefly,
it mainly includes three steps: the first step is the oxidative addition reaction between halogenated
compounds (R1ꢀX) and (Ln)2Pd(0); the second step is the substitution reaction between terminal
alkynes and (Ln)2PdXR1; and the final step is the reductive elimination reaction to form CꢀC bond.
Among them, the first step is the rateꢀdetermining step. In addition, it is not hard to see from the
reaction mechanism that it would be very beneficial to the Sonogashira crossꢀcoupling reaction of the
aryl chloride when its substituent group is electron withdrawing group. The stronger the
electronegativity of the substituent group is, the faster the reaction rate is, and the higher the
corresponding yield is. Similarly, it is not hard to see that it would be also very beneficial to the
Sonogashira crossꢀcoupling reaction of the arylacetylene when its electronꢀwithdrawing substituent
exist in the benzene ring, thus the reaction activity would be enhanced with the increase of the
electronegativity. Then, aforementioned conclusion would get a good explaination.

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100
80
60
40
20
0
phenylacetylene
3-aminophenylacetylene
4-(ethynyl)phthalic anhydride
1
2
3
4
5
6
7
8
Cycle times
Fig.7 Investigation of the reusability of the Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst for catalyzing
Sonogashira coupling reaction between iodobenzene and phenylacetylene (blue), 3ꢀaminophenylacetylene (orange)
and 4ꢀ(ethynyl)phthalic anhydride (dark yellow), respectively.
The catalytic activity of the novel Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst is one of the
most important parameters for evaluating its performance superiority. Furthermore, the stability of
this novel supported catalyst is also an important performance for its application. For this, three
Sonogashira crossꢀcoupling reactions between iodobenzene and three arylacetylenes were carried out
under the repeated catalysis of the Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst, and the
corresponding catalytic yields were shown in as Fig.7. Research shows that this novel
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst would still show good catalytic activity even after
being reused several times, and the reaction activity of phenylacetylene, 3ꢀaminophenylacetylene and
4ꢀ(ethynyl)phthalic anhydride can still reach up to about 79 %, 78 % and 95 % after being catalyzed
8 times, respectively. In addition, the recyclable catalyst was characterized again through TEM, and
Fig.8a shows that the Pd NPs are still retained on the surface of the magnetic
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles in the form of ultrasmall nanoscale after
being reused several times. In addition, the FTIR spectrum in Fig.8b also demonstrates that the
changes of the reused catalyst is very tiny. Besides, the ICP result shows that the loading density of
palladium can still remain around 5.018 wt%, and the loss of palladium is only about 4.58 wt%. All
of which shows that this novel Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst indeed has robust

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stability, and it is very conducive to its application.
a
b
4000
3500
3000
2500
2000
1500
1000
500
-1
)
Wavenumbers(cm
Fig.8 TEM image (a) and FTIR spectrum (b) of the Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst after being
reused eight times. The scale bars is 100 nm.
4. Conclusion
This paper mainly focused on the fabrication and application of
a
novel
Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst by choosing the branched/linear polyethylenimine
grafted magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles as the support. Firstly,
the silica film was coated on the surface of magnetic Fe3O4 nanocrystallines via the traditional Stöber
hydrolysis method, and the magnetic Fe3O4/SiO2 composite nanoparticles with coreꢀshell structure
were successfully prepared. Subsequently, the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite
nanoparticles were successfully prepared by the surface grafted copolymerization. Ultimately, Pd2+
ions were successfully immobilized on the surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)
composite nanoparticles by the complexation between Pd2+ ions and imidogen groups or tertiary
amine groups after the successful grafting of the branched/linear polyethylenimine by chemical
method, then a novel Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst was successfully fabricated
after the following reduction reaction. Research shows that the Pd nanoparticles were anchored on
the surface of the magnetic Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA) composite nanoparticles in the form of
ultrasmall nanoscale for the unique surface structure of this novel support, and it can simultaniously
increase the loading capacity and the specific surface area of Pd nanoparticlesa. In addition, this
novel Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0) catalyst can effectively catalyze the Sonogashira
crossꢀcoupling reaction between aryl halides and arylacetylene. More importantly, because the

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palladium exists in the form of zero valence state, it can well avoid the generation of 1,3ꢀdiyne for
the absence of the cocatalyst CuI. Gratifyingly, this novel Fe3O4/SiO2/P(GMAꢀcoꢀEGDMA)ꢀPd(0)
catalyst can be reused at least eight times without significant loss of its catalytic activity, which is
very conducive to its application.
Acknowledgements
We gratefully acknowledge support from the National Natural Science Foundation of China (No.
51173146), National Basic Research Program of China (2010CB635111) and Basic Research
Foundation of Northwestern Polytechnical University (JC20120248).
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DOI: 10.1039/C4NJ02117G
Graphical Abstract
A novel Fe3O4/SiO2/P(GMA-co-EGDMA)-Pd(0) catalyst and its high-effective activities for
Sonogashira cross-coupling reactions.