A magnetically recyclable superparamagnetic silica supported Pt nanocatalyst through a multi-carboxyl linker: Synthesis, characterization, and applications in alkene hydrosilylation

Article abstract of DOI:10.1039/c9ra00375d

To simplify separation procedures, improve the reusability and decrease the loss of Pt, two Pt catalysts anchored on superparamagnetic silica (Fe₃O₄@SiO₂-EDTA@Pt and Fe₃O₄@SiO₂-DTPA@Pt) were prepared for the first time. The stable magnetic properties made them easily recyclable using a magnet rather than filtration, decantation or centrifugation. After 12 catalytic runs for both 30-50 nm Pt catalysts, the yield of 1-heptylmethyldichlorosilane was still up to 90%. The average loss of Pt in each reaction was only 0.87% for Fe₃O₄@SiO₂-EDTA@Pt and 0.66% for Fe₃O₄@SiO₂-DTPA@Pt owing to the strong interaction between Pt and carboxyl. The unprecedented activity and selectivity of the two Pt nanoparticle catalysts were observed in the hydrosilylation of alkenes. The turnover number in the reaction between 1-hexene and methyldichlorosilane using 5 × 10^-8 mol of the Pt approached 662733 for Fe₃O₄@SiO₂-EDTA@Pt and 579947 for Fe₃O₄@SiO₂-DTPA@Pt over 12 h. The corresponding hydrosilylation products in excellent yields were obtained when we employed a broad range of alkenes as substrates, including 5 isomerous hexenes and 14 important industry raw materials. Fe₃O₄@SiO₂-DTPA@Pt showed a better activity. They have potential for catalyzing more reactions and replacing the current homogeneous Pt catalysts in industry.

Full text of DOI:10.1039/c9ra00375d

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PAPER
A magnetically recyclable superparamagnetic silica
supported Pt nanocatalyst through a multi-
carboxyl linker: synthesis, characterization, and
applications in alkene hydrosilylation†
Cite this: RSC Adv., 2019, 9, 12696
Laiming Li, Youxin Li, * Jincong Yan, Hang Cao, Dongyun Shao and James J. Bao
To simplify separation procedures, improve the reusability and decrease the loss of Pt, two Pt catalysts
3 4 2 3 4 2
anchored on superparamagnetic silica (Fe O @SiO -EDTA@Pt and Fe O @SiO -DTPA@Pt) were
prepared for the first time. The stable magnetic properties made them easily recyclable using a magnet
rather than filtration, decantation or centrifugation. After 12 catalytic runs for both 30–50 nm Pt
catalysts, the yield of 1-heptylmethyldichlorosilane was still up to 90%. The average loss of Pt in each
3 4 2 3 4 2
reaction was only 0.87% for Fe O @SiO -EDTA@Pt and 0.66% for Fe O @SiO -DTPA@Pt owing to the
strong interaction between Pt and carboxyl. The unprecedented activity and selectivity of the two Pt
nanoparticle catalysts were observed in the hydrosilylation of alkenes. The turnover number in the
ꢁ8
reaction between 1-hexene and methyldichlorosilane using 5 ꢀ 10 mol of the Pt approached 662 733
for Fe @SiO -EDTA@Pt and 579 947 for Fe @SiO -DTPA@Pt over 12 h. The corresponding
hydrosilylation products in excellent yields were obtained when we employed a broad range of alkenes
as substrates, including 5 isomerous hexenes and 14 important industry raw materials. Fe @SiO
3
O
4
2
O
3 4
2
Received 16th January 2019
Accepted 26th March 2019
O
3 4
2
-
DOI: 10.1039/c9ra00375d
DTPA@Pt showed a better activity. They have potential for catalyzing more reactions and replacing the
current homogeneous Pt catalysts in industry.
rsc.li/rsc-advances
Among these transition metal catalysts, such as copper (Cu),
platinum (Pt), palladium (Pd), rhodium (Rh), nickel (Ni) or
1
. Introduction
15–20
Magnetic materials such as magnetite (Fe
3
O
4
) and maghemite ruthenium (Ru),
Pt is one of the most widely used owing to
2 3
(g-Fe O
) are widely utilized in various elds, such as high- its unparalleled catalytic activity and mild reaction conditions
density data storage, chemical sensors, catalysts, drug in various elds, such as hydrosilylation, aldehyde oxidation,
delivery, biological assays, and electro photographic devel- sulfuric acid decomposition. Although homogeneous Pt cata-
1–5
opers. Compared with traditional techniques such as ltra- lysts such as Speier's catalyst and the Karstedt's catalyst suffer
tion, decantation or centrifugation, magnetic materials could from a number of drawbacks, like side reactions and low
be easily separated from solution and re-dispersed through an selectivity and reusability, there isn't efficient substitution in
6
external magnetic eld, which overcomes time- and solvent- industry. The immobilization of platinum catalyst is a wise
6
consuming procedures. Magnetite Fe
3
O
4
, especially nano- choice. Numerous researches were being reported on how to
21–26
3 4
Fe O
possessing super paramagnetic behavior at a nano- immobilize Pt on magnetic materials.
particle size with high surface area, is attractive for practical
Magnetic silica is used as an ideal inorganic support because
7
–10
applications.
An ongoing application of magnetic materials of its merits, like magnetic property, easy modication, high
is to immobilize metal catalysts because efficient separation, biocompatibility, solvent compatibility, adsorption capacity,
recovery and recycling of the catalyst may enhance their lifetime acid–base properties, and chemical and thermal stability when
2
7–29
and minimize their consumption to result in signicant compared to other structures.
economical and environmental benets.
A number of multi-carboxyl
based affinity ligands, such as ethylenediaminetetraacetic acid
EDTA) and diethylenetriaminepentaacetic acid (DTPA), are
well-known chelators for their strong metal-complexing prop-
11–14
(
Tianjin Key Laboratory for Modern Drug Delivery and High-Efficiency, Collaborative
Innovation Center of Chemical Science and Engineering, School of Pharmaceutical
Science and Technology, Tianjin University, Room 412-8, Building No. 24, 92 Weijin
30
erty. Magnetic silica particles modied by EDTA or DTPA were
widely used in industries including cleaning, the nuclear
Road, Nankai District, Tianjin 300037, China. E-mail: lyx@tju.edu.cn; Fax: +86-22- industry, pharmaceuticals, and the manufacturing of textile
3
1–35
2
†
1
789-2820; Tel: +86-22-2789-2820
leather, rubber, and paper, etc.
The immobilized Pt catalysts
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra00375d
on silica gel through EDTA and DTPA were developed by our
12696 | RSC Adv., 2019, 9, 12696–12709
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36,37
group.
EDTA and DTPA showed a strong interaction with precipitate was collected from the reaction mixture by a power-
platinum, but the kinds of heterogeneous catalysts still need to ful magnet and washed three times with distilled water before it
reuse through centrifugation and 31% Pt was loss aer 13 was re-dispersed into a 100 mL distilled water to form a nano-
ꢁ
1
recycles.
Here, we rst time try to immobilize Pt catalysts through
carboxyl ligands like EDTA or DTPA graed onto the surface of two sol–gel approach. First, the surface of Fe
magnetite silica (Fe @SiO -EDTA@Pt and Fe @SiO was covered by silica layer (SiO encapsulated Fe
DTPA@Pt) to simplify separation procedure, improve the reus- Fe @SiO ). Briey, sodium silicate was dissolved in deion-
particle suspension of ca. 50 mg mL
The magnetite Fe @SiO nanoparticles were prepared by
nanoparticles
particles,
.
3
O
4
2
3 4
O
3
O
4
2
3
O
4
2
-
2
3 4
O
3
O
4
2
ability and decrease the loss of Pt. In addition, the two catalysts ized water in a glass beaker equipped with a mechanical stirrer
are applied rst time in 4 isomerization–hydrosilylation and and the pH was adjusted to 12–13 by sodium hydroxide. Fe O4
3
hydrosilylation of 14 compounds, which are important industry nanoparticles were added to the sodium silicate solution. The
raw materials. These make the current two catalysts more mixture was treated ultrasonically for 30 min. Then, the
ꢂ
valuable industry.
temperature of the mixture was increased to 85 C and nitrogen
gas was used to prevent the intrusion of oxygen. 2 M hydro-
chloric acid was added dropwise to adjust pH value to 6.0. Then,
the precipitates were washed several times with deionized water
by magnetic decantation. The Fe O @SiO was coated again to
2. Experimental section
2
.1. Materials and reagents
All chemicals were used as received without further purica-
tion. Iron chloride hexahydrate (FeCl $6H O, >99%) and ferrous
chloride tetrahydrate (FeCl $4H O, >99%) were from Yuanli
3
4
2
ensure that the desired amount of silica on all magnetite
For this, Fe O @SiO was re-dispersed in 100 mL
3 4 2
methanol–water (1 : 1, v/v) mixture and followed by the addition
44,45
Fe O .
3
4
3
2
2
2
of 1 mL ammonium hydroxide (25% aqueous solution). Then,
Chemical. g-Aminopropyltrimethoxysilane (APTMS) was from
Qufu Chenguang Chemical. Tetraethylorthosilicate (TEOS) was
1
mL of TEOS was dissolved in 10 mL methanol and added
dropwise to the mixture by gently stirring for 1 h. The obtained
nanoparticles (Fe @SiO ) were collected by magnet and
washed several times with distilled water and ethanol. Finally,
the nanoparticles were dried at room temperature under
vacuum and brown yellow solid was observed.
.2.2. Preparation of amino-magnetic silica (Fe O @SiO -
AP). It was prepared according to previous reported method.
Ten grams as-made magnetic silica nanoparticles were ultra-
sonically dispersed in 100 mL distilled toluene for 30 min.
Then, it was transferred into a 250 mL three-necked ask
from
Tianjin
Kemiou
Chemical
Reagent.
Ethyl-
3
O
4
2
enediaminetetraacetic acid (EDTA), diethylenetriaminepenta-
acetic acid (DTPA), sodium silicate, ammonia solution (25%),
anhydrous pyridine, acetic anhydride, diethyl ether, hydro-
chloric acid (HCl), toluene, acetone, ethanol, methanol, n-
decane, i-propanol, n-butanol and n-hexanol were from Jiang-
tian Chemical Technology. Methyldichlorosilane was from
Kaihua Synthetic. 1-Hexene, trans-2-hexene, cis-2-hexene, trans-
2
3 4 2
46
3
-hexene and cis-3-hexene were form Tokyo Chemical Industry
Co., Ltd. N,N-Dimethylacrylamide, 1,2-epoxy-4-
vinylcyclohexane, methyl methacrylate, butyl acrylate, ethane-
,2-diyl bis(2-methylacrylate), crotonic acid ethyl ester and
equipped
with
a
mechanical
stirrer.
3-Amino-
propyltrimethoxysilane (20 mL) was added into this mixture.
The temperature was kept at 110 C with continuous stirring for
4 h. The resulting nanoparticles were separated by magnet,
washed with methanol for several times and then dried at 60 C
1
ꢂ
trans-2-hexenyl acetate were from Bid Pharmatech Ltd. 1,2-
Epoxy-7-octene, allyl glycidyl ether, 5-hexen-2-one, allylchloride
and trans-2-hexen-1-yl phenylacetate were from Nanjin Sheng-
bicheng Chemical Technology Co., Ltd. Cyclohexene and nor-
bornylene were from Shanghai Macklin Biochemical Co., Ltd.
H PtCl $6H O was from Tianjin Fengchuan Chemical Reagent
2
ꢂ
under vacuum for 12 h. The product was referred to as Fe
3
-
O
4
@SiO
.2.3. Preparation of multi-carboxyl magnetic silica (Fe
@SiO -EDTA and Fe @SiO
2
-AP.
2
3
-
2
6
2
O
4
2
3
O
4
2
-DTPA). The preparation of
Technologies. 1-Hexyl-methyldichlorosilane was from CNW
Technologies. Deionized water was from Tianjin Yongyuan
Distilled Water Manufacturing Center.
EDTA or DTPA dianhydride was done according to a previous
reported method with minor modication. EDTA or DTPA was
suspended in pyridine followed by the addition of acetic anhy-
dride. The mixture was stirred at 65 C for 24 h. The product was
47
ꢂ
2.2. Materials synthesis

ltered, washed with acetic anhydride and diethyl ether, and
@SiO -AP was sus-
nanoparticles were prepared pended in 100 mL mixture solution of ethanol and acetic acid
2.2.1. Preparation of Fe O and Fe O @SiO . The magne- dried in an oven for 6 h. Next, 5 g of Fe
3
O
4
2
3
4
3
4
2
tite Fe
3
O
4
and Fe
3
O
4
@SiO
2
according to previous reported method with a minor modi- (1 : 1, v/v). Aer the addition of 25 g of EDTA dianhydride or 30 g
3
8–43
ꢂ
cation.
chemical co-precipitation of ferric and ferrous ions in ammo- allow the amino groups on the silica gel to react with the
The magnetite Fe O
3 4
nanoparticles were prepared by DTPA dianhydride, the mixture was kept at 80 C for 24 h to
48,49
nium hydroxide solution. Briey, under nitrogen protection, carboxyl groups.
Finally the yellowish-brown product was
0
.04 mol FeCl $6H O and 0.02 mol FeCl $4H O were dissolved separated by magnet and washed with 4 M ammonia water
3
2
2
2
ꢂ
50
in distilled water with vigorous stirring at 80 C for 20 min. Aer solution to remove unreacted EDTA or DTPA. Then products
5 mL ammonium hydroxide (25% aqueous solution) was were washed again with ethanol/acetic acid (1 : 1, v/v), water
1
51
added to the solution, the color of the bulk solution turned from and methanol sequentially. The multi-carboxyl modied
orange to black immediately. Aer 30 min of reaction, the black
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magnetic silica gels (Fe
were dried in an oven at 90 C for 8 h.
3
O
4
@SiO
2
-EDTA or Fe
3
O
4
@SiO
2
-DTPA) a Rigaku D/MAX-2500 diffractometer with Cu-Ka radiation (l ¼
ꢂ
0.1540 nm). Particle sizes of the catalysts were studied using
2.2.4. Preparation of catalysts. The above multi-carboxyl a JEOL JEM-2100F apparatus with an accelerating voltage of 200
modied magnetic silica gels (Fe O @SiO -EDTA or Fe O @- kV. TEM of Fe O @SiO -EDTA@Pt, Fe O @SiO -DTPA@Pt were
3
4
2
3
4
3
4
2
3
4
2
SiO
2
-DTPA) (1.51 g) were added to 50 mL H
2
PtCl
6
$6H
2
O (0.20 g) prepared by placing a drop containing the nanoparticles in
ꢂ
ethanol solution. The mixture was carried out in a reux at 80 C a coated carbon grid. The morphology of the catalysts was
under nitrogen atmosphere and stirred for 9 h. The solid investigated using a Hitachi S2800 SEM. The EDS analysis,
product was ltered by a magnet and washed with ethanol which was simultaneously performed during the SEM exami-
ꢂ
successively and dried at 70 C for 3 h. The light yellow platinum nations, was conducted to conrm the element distribution on
complex was obtained, which were denoted as Fe O @SiO - the surface of adsorbents. FT-IR spectra were taken in KBr
3
4
2
EDTA@Pt and Fe O @SiO -DTPA@Pt. The process was sche- pressed pellets on a TENSOR 27 Spectrometer. EA was used to
3
4
2
matically illustrated in Fig. 1.
measure the nitrogen content in the materials on an Elementar
Vario Micro cube. The thermal stabilities were measured by TGA
employing a NETZSCH STA 409 TG-DTA under a dynamic
nitrogen atmosphere at a heating rate of 10 C min . The
magnetization and hysteresis loops were measured at room
temperature by a LDJ9600 VSM. The BET measurement was
carried out on a Quantachrome NOVA 1000 system at liquid-N2
temperature.
ꢂ
ꢁ1
2
.3. Characterization of the catalysts
The crystal lattice structure of the magnetic intermediates
Fe , Fe @SiO , Fe @SiO -AP), and products (Fe @-
SiO -EDTA@Pt, Fe O @SiO -DTPA@Pt) were identied by XRD,
(
3
O
4
3
O
4
2
3
O
4
2
3 4
O
2
3
4
2
ꢂ
ꢂ
ꢁ1
in the 2q range of 10–90 at a scan speed of 4 min , using
3 4 2 3 4 2
Fig. 1 Preparation of Fe O @SiO -EDTA@Pt and Fe O @SiO -DTPA@Pt catalysts.
12698 | RSC Adv., 2019, 9, 12696–12709
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.4. Catalytic alkene hydrosilylation
RSC Advances
2
in turn, serve as a new matrix to immobilize metallic Pt. The
chemical structures of the resulting product were depicted in
Fig. 1. The multi-carboxyl functionalized magnetic silica mate-
rials were found to be a yellow powder with an excellent shelf
life. These magnetite nanoparticles functionalized with EDTA
In a general procedure, hydrosilylation was carried out in
a 50 mL round-bottomed tube equipped with a homemade
reux condenser to the upper of which a heating system was
attached. An appropriate amount of alkene and platinum
magnetic complex were stirred at a specic reaction tempera-
ture for 30 min before 15 mmol methyldichlorosilane was
added. The structure and yield of hydrosilylation products were
determined based on calibration curves of standards. The
catalyst was collected by simple magnetic separation and reused
in subsequent runs without any treatment. All hydrosilylation
products were characterized by comparing their spectra and
physical parameters with authentic samples. The reaction
product was quantied by gas chromatography (GC) and the
structures of products were identied by nuclear magnetic
resonance (NMR). GC equipped with a ame ionization detector
or DTPA will be referred to as Fe
@SiO -DTPA@Pt.
3 4 2 3
O @SiO -EDTA@Pt and Fe -
O
4
2
3
.2. Characterization
The data from AAS analysis indicated the amounts of Pt in
Fe @SiO -EDTA@Pt and Fe @SiO -DTPA@Pt were 173.80
3
O
4
2
3
O
4
2
ꢁ1
and 192.77 mmol g , respectively. As a comparison, Pt was also
immobilized on Fe O @SiO -AP and Fe O @SiO , which had
3
4
2
ꢁ
3
4
2
1
only 33.40 and 0.10 mmol g of Pt, respectively. It means the
interaction between Pt and carboxyl is stronger than amino
group, which is benet to the immobilization and stability of Pt.
Morphology of the two novel catalysts was characterized by
SEM, EDS and TEM (Fig. 2). Results showed that the dried
(FID) (Wuhan Trustworthy Technology, China) and a long
capillary column (30 m ꢀ 0.25 mm ꢀ 0.25 mm) coated by 5%
phenyl and 95% methyl polysiloxane. Injector and detector
ꢂ
3 4 2 3 4 2
power of Fe O @SiO -EDTA@Pt and Fe O @SiO -DTPA@Pt
temperature was 260 C, carrier gas was nitrogen, injection
nanoparticles had an irregular surface with sharp edge and
slight agglomeration, which could be dispersed well in solution.
The presence of Si, O and Fe signals in the EDS pattern
volume at 0.8 mL, temperature programme: the column was kept
ꢂ
ꢂ
ꢂ
ꢁ1
at 60 C for 3 min, then heated to 260 C at a rate of 10 C min
.
1
H NMR spectra were recorded on a Bruker AC-P400 (400 MHz)
conrmed that Fe
higher intensity of Si peak compared with that of Fe peak
showed that the Fe nanoparticles were coated by SiO . The
collected process by a magnet avoids the SiO nanoparticles
without Fe . The EDS analysis results also conrmed the
3 4
O was successfully mixed with silica. The
spectrometer in CDCl as solvent.
3
3
O
4
2
2
3. Results and discussion
3 4
O
3.1. Synthesis
elemental composition of the nanoparticles and the existence of
Pt in the prepared nanoparticle catalysts. Through second
In the synthetic procedures described earlier, magnetite Fe O
3
4
nanoparticles were prepared by the co-precipitation method robust sol–gel approach, the high magnication TEM images
from ferrous and ferric ion solutions at a mol ratio of 1 : 2. The revealed that the Fe @SiO -EDTA@Pt and Fe @SiO
magnetic nanoparticles have extensive hydroxyl groups on its DTPA@Pt particles obtained were uniform with a diameter of
3
O
4
2
3
O
4
2
-
52
surface when contacted with aqueous phase. Silicic acid as about 30–50 nm. Each magnetic particle was composed of dark
silica precursors encapsulated the Fe nanoparticles by two magnetic Fe nanoparticles of about 10–15 nm diameter.
sol–gel approaches. First silicate acid layer was formed gradu- Even further, it clearly showed that those dark magnetic parti-
3
O
4
3 4
O
ally from sodium silicate solution by dropwise addition of cles were coated with a light-gray SiO
hydrochloric acid. The second silicate acid layer was formed by around 15 nm.
2
layer with a thickness of
dropwise addition of TEOS solution. However, the TEOS is non-
polar in nature and it is necessary to use organic reagent like Fe
The XRD patterns of Fe O , Fe O @SiO , Fe O @SiO -AP,
3
4
3
4
2
3
4
2
3
O
4
@SiO
2
-EDTA@Pt and Fe
3
O
4
2
@SiO -DTPA@Pt nano-
methanol as a mutual solvent to make TEOS and water miscible. particles were shown in Fig. 3. It showed typical X-ray diffraction
5
4
Subsequently, the silanol groups (Si–OH) on the surface are patterns of Fe
transformed into siloxane bonds (Si–O–Si) via the condensation appeared in Fe
3
O
4
.
The characteristic diffraction peaks
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
3
O
4
at 30.1 , 35.5 , 43.3 , 54.3 , 57.3 and 62.6
reaction and the silica coating is formed. Notably, the intro- could be assigned to the planes of Fe (JCPDS No. 19629),
53
3 4
O
duction of a dense silica coating on the magnetic nanoparticles respectively. These characteristic diffraction peaks were
is necessary for this study. It protects the magnetic Fe O from observed in Fe O @SiO , Fe O @SiO -AP, Fe O @SiO -
3
4
3
4
2
3
4
2
3
4
2
oxidation and provides the surface charges needed to prevent EDTA@Pt and Fe O @SiO -DTPA@Pt nanoparticles which
3
4
2
aggregation in the subsequent condensation reactions and indicated that Fe
practical applications. The silanol groups change the surface the whole preparation processes did not result in the phase
properties making it easier and more effective to perform change of Fe . The obvious characteristic peak of Pt wasn't
surface modication with organic silane molecules. observed in Fe @SiO -EDTA@Pt and Fe @SiO -DTPA@Pt,
Before being modied by EDTA or DTPA group, the magnetic which may indicate that the amount of Pt was low or the Pt
3 4
O was existent in all synthesized samples and
3 4
O
3
O
4
2
3
O
4
2
55
silica nanoparticles were functionalized with APTMS, which particles were highly dispersed on the surface of support.
acted as an auto-catalyst. Those amino groups on the magnetic In order to conrm properties of the surface of composite
silica surface enable the magnetic silica materials to be func- nanoparticles, the molecular structure of the different
tionalized with EDTA and DTPA by graing the corresponding composites was characterized using FT-IR spectra (Fig. 4.). The
ꢁ
1
3 4
anhydrides on those amino groups. The EDTA or DTPA groups, typical absorption peak for Fe O at 635 and 576 cm was
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attributed to the stretching vibration of Fe–O bond. The typical
peaks of Fe O were observed in all of spectra, which further
3
4
conrmed Fe O nanoparticles existed in all of intermediates
3
4
and products. Whereas the gradual decrease of peak signals
indicated the Fe nanoparticles were at core of Fe @SiO
-AP, Fe @SiO -EDTA, Fe @SiO -EDTA@Pt,
-DTPA and Fe @SiO -DTPA@Pt. For Fe @-
3
O
4
3
O
4
2
,
Fe
Fe
SiO
3
O
O
4
4
@SiO
@SiO
2
3
O
4
2
3
O
4
2
3
2
3
O
4
2
3 4
O
ꢁ1
2
, a new board absorption peak at 1092 cm resulted from
Si–O–Si antisymmetric stretching vibration of silica layer, which
5
6,57
veried the successful coating of silica layers onto Fe O .
3
4
ꢁ1
The peak around 1627 cm was attributed to the absorbed
water on the silica shell or the silanol group of the silica. The
58
ꢁ1
characteristic absorption band at 3422 cm
stretching vibrations of hydroxyl groups. These peaks from
Fe @SiO were also observed in Fe @SiO -AP, Fe @-
SiO -EDTA, Fe @SiO -DTPA, Fe @SiO -EDTA@Pt and
Fe @SiO -DTPA@Pt. Aer the functionalization of Fe @-
SiO2 with APTMS, the new absorption peaks at 2925 and
was from the
3
O
4
2
3
O
4
2
3 4
O
2
3
O
4
2
3
O
4
2
3
O
4
2
3 4
O
ꢁ
1
2
858 cm represented the symmetric vibrations of aliphatic
C–H stretching of the methylene group for silane coupling
agent, which indicated that amino group was successfully
graed onto the surface of Fe
3 4 2
O @SiO . Aer graing multi-
carboxyl groups, the strong characteristic absorption band
ꢁ
1
appeared at 1733 and 1404 cm could be assigned to C]O and
C–O stretching vibration of the –COO– group, which indicated
the formation of carboxylic groups (EDTA and DTPA) on the
59
surface of the Fe O @SiO -AP. As a result of the presence of
3
4
2
large quantities of metallic Pt on the surface of the nano-
particles, the decrease in vibration of C]O and C–O suggests
that the carboxyl group on the surface of the functional
magnetic silica have coordinated with platinum, signifying the
immobilization of platinum complex on the Fe
and Fe @SiO -DTPA surface.
3 4 2
O @SiO -EDTA
3
O
4
2
XPS was used to further characterize the above catalysts
Fig. 5.). XPS results showed distinct Fe, O, N, C, Si and Pt peaks
(
from the two novel nanoparticles (Fig. 5a). The detail XPS data
for Fe
DTPA@Pt and H
that the binding energies of Si 2p and O 1s in Fe
EDTA@Pt and Fe @SiO
Fe @SiO -AP. The banding energy of Cl 2p in Fe
EDTA@Pt and Fe O @SiO -DTPA@Pt was similar to that of
3
O
4
@SiO
2
-AP, Fe
3
O
4
@SiO
2
-EDTA@Pt, Fe
3
O
4
@SiO
2
-
2
PtCl $6H
6
2
O were listed in Table 1. It revealed
3
O
4
@SiO
2
-
3
O
4
2
-DTPA@Pt were similar to those of
2
@SiO -
3
O
4
2
3
O
4
3
4
2
H PtCl $6H O. It was noteworthy that the banding energy of Pt
2
6
2
4
3
f7/2 in Fe O @SiO -EDTA@Pt and Fe O @SiO -DTPA@Pt was
3 4 2 3 4 2
–5 eV more than that in H PtCl $6H O. It could be summa-
2 6 2
rized that electron donation from carboxyl group to Pt to form
the coordination bond between carboxyl and Pt in Fe @SiO
EDTA@Pt and Fe @SiO -DTPA@Pt, which was also consis-
3
O
4
2
-
3
O
4
2
tent with the FT-IR results. The Pt 4f XPS spectra contain two
peaks corresponding to Pt 4f7/2 and 4f5/2 states from the spin-
orbital splitting and each peak was de-convoluted with Pt(0),
6
0–62
Pt(II) and Pt(IV).
In Fe O @SiO -EDTA@Pt, the percentage of
3 4 2
4
+
2+
0
Pt , Pt and Pt peaks were 28.9, 46.5 and 24.6%, respectively.
Fig. 2 SEM micrographs of (a) Fe
3
O
4
@SiO
@SiO
-DTPA@Pt, TEM micrographs of (e) Fe
@SiO -DTPA@Pt.
2
-EDTA@Pt and (b) Fe
-EDTA@Pt and (d) Fe
@SiO
3
-
-
2+
0
In Fe
3
O
4
@SiO
2
-DTPA@Pt, the ratio of Pt (50.3%) and Pt
@SiO -EDTA@Pt,
whereas the Pt decreased to 23.3%. Results indicated the Pt
O
O
4
@SiO
@SiO
2
-DTPA@Pt, EDS of (c) Fe
3
O
4
2
3
(
26.4%) were higher than that of Fe
3
O
4
2
4
2
3
O
4
2
-EDTA@Pt
4
+
2+
3
and (f) Fe O
4
2
0
and Pt were predominant species that may be corresponding to
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3 4 3 4 2 3 4 2 3 4 2 3 4 2
Fig. 3 XRD patterns of Fe O , Fe O @SiO , Fe O @SiO -AP, Fe O @SiO -EDTA@Pt and Fe O @SiO -DTPA@Pt nanoparticles.
good catalytic activity and might be produced on the catalyst and pore-size distribution of Fe
3
O
4
@SiO
-DTPA@Pt catalysts. Both of two samples showed type
III isotherms with type H3 hysteresis loops which is related to
2 3
-EDTA@Pt and Fe -
surface through passivation process during the sample
preparation.
4 2
O @SiO
63
BET analysis showed another important characteristic of the the slit-like pores because of aggregation of particles. When we
Pt catalysts. Fig. 6a shows the nitrogen adsorption isotherms dispersed these nanoparticles in aqueous solution and
3 4 3 4 2 3 4 2 3 4 2 3 4 2 3 4 2 3 4 2
Fig. 4 FT-IR spectra of Fe O , Fe O @SiO , Fe O @SiO -AP, Fe O @SiO -EDTA, Fe O @SiO -EDTA@Pt, Fe O @SiO -DTPA, and Fe O @SiO -
DTPA@Pt nanoparticles.
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Fig. 5 (a) XPS spectra of Fe
O
3 4
@SiO
2
-EDTA@Pt and Fe @SiO
3
O
4
2 3 4 2
-DTPA@Pt. (b) High-resolution XPS spectra of Pt 4f for Fe O @SiO -EDTA@Pt.
(
c) High-resolution XPS spectra of Pt 4f for Fe
3
O
4
@SiO -DTPA@Pt.
2
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Table
DTPA@Pt, Fe
1
XPS data for Fe
3
O
4
@SiO
2
-EDTA@Pt and Fe
O
3 4
2
@SiO -
Although the saturation magnetization values of Fe
3 4 2
O @SiO -
a
O
3 4
2
@SiO -AP and H PtCl
2
6 2
$6H O (eV)
EDTA@Pt and Fe O @SiO -DTPA@Pt were lower than that of
3
4
2
Fe O , Fe O @SiO and Fe O @SiO -AP, they could be readily
separated from their dispersion in 1 min with an external
3
4
3
4
2
3
4
2
Samples
Pt 4f7/2 Si 2p
N 1s
O 1s
Cl 2p
Fe
Fe
Fe
3
3
3
O
O
O
4
4
4
@SiO
@SiO
@SiO
2
2
2
-EDTA@Pt 78.40
-DTPA@Pt 76.80
107.21 405.59 536.88 201.29 magnetic eld owing to their high magnetite content and thus
106.40 403.23 536.86 200.40 good magnetic response (Fig. 7, inset). These results indicated
-AP
—
108.78 407.24 537.60
—
199.50
3 4
that the magnetization of Fe O decreases considerably aer
H
2
PtCl
6
$6H
2
O
73.10
—
—
—
coated with SiO
nonmagnetic SiO
2
due to the weight contribution from the
2
. Nevertheless, both of the catalysts exhibited
a
The banding energies are referred to C 1s (284.6 eV).
enough magnetic response to meet the need of magnetic
separation.
observed using microscope, these nanoparticles were mono-
disperse. It means the aggregation is temporary in BET anal-
ysis. The BET data including surface area, average pore size and
total pore volume derived from the isotherms were calculated.
3
.3. Catalyst performances for hydrosilylation
3.3.1 Activity and reusability in catalyzing hydrosilylation
The BET specic surface area, the pore size and the total pore of 1-hexene. Hydrosilylation of alkene with silane is a typical
2
ꢁ1
volume of Fe
3
O
4
@SiO
2
-EDTA@Pt were 75.68 m g , 17.50 nm reaction catalyzed by platinum, which exist two reaction path-
3
ꢁ1
67,68
and 0.685 cm g , respectively. They were corresponding to ways a-addition and b-addition.
6.65 m g , 29.86 nm and 0.366 cm g for Fe O @SiO - of alkenes with methyldichlorosilane were catalyzed by the two
3 4 2
Hydrosilylation of a series
2
ꢁ1
3
ꢁ1
3
DTPA@Pt.
3 4 2 3 4 2
novel Pt catalysts, Fe O @SiO -EDTA@Pt and Fe O @SiO -
To test the thermal stability and the graing amount of DTPA@Pt, to evaluate their activity and regioselectivity.
carboxyl groups on the magnetic silica nanoparticles, TGA
analysis was performed for Fe @SiO -EDTA@Pt and Fe
@SiO
TGA curve of the prepared nanoparticles, the weight loss below dichlorosilane, including reaction temperatures (30, 40, 50, 60,
Hydrosilylation conditions are important for yield and
regioselectivity. To exhibit well the activities of two catalysts, we
3
O
4
2
3
-
O
4
2
-DTPA@Pt nanoparticles (Fig. 6b.). As shown in the optimized hydrosilylation conditions of 1-hexene and methyl-
ꢂ
ꢂ
2
00 C was attributed to the removal the water, and the organic 70, and 80 C), times (0.5, 1, 2, 3, 4, and 5 h), the molar ratio of
ꢂ
parts were decomposed completely at about 700 C. The TGA methyldichlorosilane and 1-hexene (0.5 : 1.0, 1.0 : 1.0, 1.2 : 1.0,
curve of bare Fe O @SiO nanoparticles showed that the weight 1.5 : 1.0, 1.8 : 1.0, and 2.0 : 1.0) and the additive sequence of 1-
loss over a temperature range from 50 to 800 C was about 4%, hexene and methyldichlorosilane (1-hexene added to methyl-
3
4
2
ꢂ
which was attributed to the escape of physically adsorbed water dichlorosilane aer methyldichlorosilane mixing with the
64
or/and structural water on the surface. Moreover, the weight catalyst for 30 min, simultaneous addition of 1-hexene and
ꢂ
increases slightly in the temperature range of 700–800 C, which methyldichlorosilane, methyldichlorosilane added to 1-hexene
65
might be caused by the slight oxidation of Fe
3
O
4
.
For Fe
3
-
aer mixing with the catalyst for 30 min). The detail results were
O
4
@SiO
2
-EDTA@Pt and Fe
3
O
4
@SiO
2
-DTPA@Pt nanoparticles, summarized in support information (Fig. 1S†). Results indi-
ꢂ
the weight loss at temperatures below 200 C was about 3%, cated both Fe O @SiO -EDTA@Pt and Fe O @SiO -DTPA@Pt
3
4
2
ꢁ
3
4
2
3
which was related to the release of moisture and structural (containing 2.01 ꢀ 10 mmol Pt in each catalyst) could effi-
water on the surface of the silica layer. However, apart from the ciently catalyze the hydrosilylation. The yields were up to 99.4%
water loss, organic components inside the particles began to and 98.77% when 19.2 mmol methyldichlorosilane was added
degrade rapidly at a temperature higher than 200 C, and to 11.8 mmol 1-hexene aer mixing with the catalyst for 30 min
almost completely decomposed at 550 C for Fe
ꢂ
ꢂ
ꢂ
3
O
4
@SiO
2
-
and maintained the reaction 3 h at 50–60 C. As a comparison,
ꢂ
EDTA@Pt and 700 C for Fe
3
O
4
@SiO
2
-DTPA@Pt, respectively. the yield only was 35.46% when Fe O @SiO @Pt was used as
3
4
2
ꢂ
Therefore, the weight loss from 200 to 800 C in the TGA curves catalyst.
of Fe O @SiO -EDTA@Pt (about 28 wt%) and Fe O @SiO -
In research of platinum catalyst, the turnover number (TON)
DTPA@Pt (about 30 wt%) could be used to estimate the weight of Pt oen is used as criteria. Thus, we calculated the TON
proportions of EDTA or DTPA-modied on Fe @SiO . This approached 3628 and 3550 when Fe O @SiO -EDTA@Pt and
phenomenon suggested that the weight proportion of multi- Fe O @SiO -DTPA@Pt with 2.60 mmol Pt catalyzed 11.2 mmol
3
4
2
3
4
2
3
O
4
2
3
4
2
3
4
2
carboxyl groups on Fe
higher than that on Fe
consistent with one more carboxyl group in DTPA than EDTA.
3
O
4
@SiO
@SiO -EDTA@Pt (28 wt%). It was silylation, amount of Pt catalyst was gradually decreased to 2.10,
1.82, 1.47, 0.87, even 0.34 mmol. Results indicated the hydro-
2
-DTPA@Pt (30 wt%) was of 1-hexene in 4 h. To further increase the TON for hydro-
3
O
4
2
The key for magnetic materials is the sufficient magnetic silylation between 1-hexene and methyldichlorosilane with low
property. Therefore the magnetic properties of these nano- amount of Pt could be catalyzed and the TON quickly increased
particles were analyzed by VSM (Fig. 7.). The saturation to 4721, 5435, 6744, 10 905 and 16 006 for Fe O @SiO -
3
4
2
magnetization was found to be 74.7, 48.4, 44.4, 25.4 and 23.0 EDTA@Pt, 4750, 5464, 6794 and 10 789 for Fe O @SiO -
3
4
2
ꢁ
1
emu g for Fe
EDTA@Pt and Fe
showed superparamagnetic properties due to the presence of using only 0.3 mg Fe O @SiO -EDTA@Pt (0.0052 mmol Pt) or
3
O
4
, Fe
3
O
4
@SiO
2
, Fe
3
O
4
@SiO
2
-AP, Fe
3
O
4
@SiO
2
-
DTPA@Pt. Furthermore, we catalyzed the hydrosilylation of
3
O
4
@SiO
2
-DTPA@Pt, respectively. All of them methyldichlorosilane (180 mmol) and 1-hexene (110 mmol)
3
4
2
6
6
nanometer-sized magnetic Fe
3
O
4
particles in the core.
3 4 2
0.3 mg Fe O @SiO -DTPA@Pt (0.057 mmol Pt) in 12 h.
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Fig. 6 (a) Nitrogen adsorption–desorption isotherms and (inset) the corresponding pore-size distribution curves of Fe
O
3 4
@SiO , Fe
2
3 4 2
O @SiO -
AP, Fe @SiO
3
O
4
2
-EDTA@Pt and Fe
3
O
4
@SiO
2
-DTPA@Pt catalysts, (b) TGA curves of Fe
O
3 4
@SiO , Fe O
2 3 4
@SiO
2
-AP, SiO
2
3 4
@Fe O -EDTA@Pt and
SiO @Fe O -DTPA@Pt.
2
3 4
Remarkably, the region-selectivity was still around 99% and
Usually, the stability of a catalyst is an important charac-
TON increased to 662 733 for Fe O @SiO -EDTA@Pt, 579 947 teristic before it can be used in an industrial application.
3
4
2
for Fe O @SiO -DTPA@Pt, respectively.
Therefore, the reusability of Fe O @SiO -EDTA@Pt and
3 4 2
3
4
2
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Fig. 7 VSM magnetization curves of Fe
3
O , Fe O
4 3 4
@SiO , Fe O
2 3 4
@SiO
2
3
-AP, Fe O
4
@SiO
2
-EDTA@Pt and Fe
3
O
4
@SiO
2
-DTPA@Pt. Inset: magnetic
separation of Fe
3
O
4
@SiO
2
-EDTA@Pt and Fe
O
3 4
@SiO -DTPA@Pt from the aqueous suspensions.
2
Fe
itively catalyzing the hydrosilylation of 1-hexene with methyl- the recycled Pt catalyst in both Fe
dichlorosilane. A series of 12 consecutive hydrosilylation Fe @SiO -DTPA@Pt. This also indicated both of catalysts,
reactions were carried out under optimal reaction conditions. especially Fe @SiO -DTPA@Pt, were very stable, which
3
O
4
@SiO
2
-DTPA@Pt catalysts were evaluated through repet- According to the data, there wasn't the apparent state change of
3
O
4
@SiO -EDTA@Pt and
2
3
O
4
2
3
O
4
2
Aer each catalytic reaction, the two platinum catalysts were maybe result from strong coordination interaction between
held in the original system using a magnet and catalyzed next carboxyl group and the metallic Pt. The residual four carboxyl
hydrosilylation without any other process. The results were groups of DTPA in Fe O @SiO -DTPA maybe produce a stronger
3
4
2
showed in Fig. 8. Data showed a satisfactory yield of 1-heptyl- interaction with Pt than the residual three carboxyl groups of
methyldichlorosilane (about 90% aer 12 catalytic runs for both EDTA in Fe @SiO -EDTA (Table 2).
of Pt catalysts) which was apparent better than the Pt catalysts 3.3.2 Catalyzing hydrosilylation of internal and terminal
immobilized on non-magnetic SiO supports (only 80% aer 12 hexene. The unprecedented activity and selectivity of the two Pt
Aer 12 runs, the magnetism both of Pt catalysts nanoparticle catalysts prompted us to further exploit its
3
O
4
2
2
36,37
or 13 runs).
were similar and the platinum amount was 155.78 mmol g for potential applications in the isomerization–hydrosilylation
ꢁ
1
ꢁ1
Fe O @SiO -EDTA@Pt and 177.62 mmol g for Fe O @SiO - tandem process. Five hexene, including 1-hexene, trans-2-hex-
3
4
2
3
4
2
DTPA@Pt. There were only 10.4% Pt loss in Fe O @SiO - ene, cis-2-hexene, trans-3-hexene and cis-3-hexene were used as
3
4
2
EDTA@Pt and 7.9% Pt loss in Fe
average loss of Pt was 0.87% for Fe
.66% for Fe @SiO -DTPA@Pt in each reaction which was SiO
2
3
O
4
@SiO
2
-DTPA@Pt. The alkene. The hydrosilylation between methyldichlorosilane and
-EDTA@Pt and hexene were catalyzed by Fe @SiO -EDTA@Pt or Fe @-
-DTPA@Pt under the aforementioned optimal conditions.
3
O
4
@SiO
2
3
O
4
2
3 4
O
0
3
O
4
2
apparent better than homogeneous Pt catalyst (about 10 ppm) Products were monitored by GC and NMR (see Fig. S2 in ESI†).
and Pt catalysts immobilized on non-magnetic support. The Data were summarized in Table 3. It was interesting that the
data were listed in Table S1.† In order to identify the active main product was 1-hexylmethyldichlorosilane in hydro-
species of Pt catalysts, the state of Pt catalysts in high-resolution silylation of all of hexene, which was typical isomerization–
XPS aer recycle experiments was tested. The data were listed in hydrosilylation and the b-adduct as a major product. The
2
+
0
69,70
Fig. S3 and Table S2.† The total amount of Pt and Pt was similar phenomena were observed in previous studies.
1.1% (before recycle) and 76.1% (aer recycle) for Fe @SiO bought the standard substance of 1-hexylmethyldichlorosilane
EDTA@Pt. The total amount of Pt and Pt was 73.6% (before which was compared with the synthesized 1-hexylmethyldi-
recycle) and 79.6% (aer recycle) for Fe @SiO -DTPA@Pt. chlorosilane, in GC chromatograms, all 1-
We
7
3
O
4
2
-
2
+
0
3
O
4
2
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Fig. 8 Catalyst recycle experiments for the hydrosilylation of 1-hexene with methyldichlorosilane.
hexylmethyldichlorosilane peek shown at around 8.45 min. For
The yield of 1-hexylmethyldichlorosilane changed in hydro-
silylation of different hexane and methyldichlorosilane. When
Fe O @SiO -EDTA@Pt was used as catalyst, the highest yield
3 4 2
1
NMR: H NMR (600 MHz, CDCl
CH –CH –SiCl –CH ), 1.38 (m, 2H, CH
SiCl –CH ), 1.20 (s, 4H, CH –(CH –(CH
m, 2H, CH –(CH –CH –SiCl –CH ), 0.88 (t, 3H, CH
SiCl –CH ), 0.77 (s, 3H, CH –(CH –SiCl –CH ).
3
) d: 1.50 (m, 2H, CH
–(CH –CH
–SiCl
3
–(CH
–(CH
2
2
)
)
3
–
–
2
2
2
3
3
2
)
2
2
2
2
3
3
2
)
2
2
)
3
2
–CH
3
), 1.12 (97%) was from 1-hexene. The yield of 1-hexylmethyldi-
(
3
2
)
4
2
2
3
3
–(CH
2
)
5
–
chlorosilane decreased to 95% for cis-2-hexene and 83% for cis-
3-hexene. When cis-2-hexene and cis-3-hexene were changed to
2
3
3
2
)
5
2
3
Table 2 Fe
with methyldichlorosilane
3
O
4
@SiO
2
-EDTA@Pt and Fe
O
3 4
2
@SiO -DTPA@Pt-catalyzed tandem isomerization–hydrosilylation of trans- and cis-internal alkenes
a
b
Yield (%)
b/a
Entry
Alkene
a
b
Product
a
b
1
2
97
87
99
88
>20 : 1
>20 : 1
>20 : 1
>20 : 1
3
4
5
a
95
78
83
98
84
87
>20 : 1
>20 : 1
>20 : 1
>20 : 1
>20 : 1
>20 : 1
Conditions: alkenes, 10 mmol; methyldichlorosilane, 15 mmol; 8 h; a, Fe
yield were determined by GC using n-decane as an internal standard.
3
O
4
2
@SiO -EDTA@Pt as catalyst; b Fe
3
O
4
@SiO
2
-DTPA@Pt as catalyst.
b
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a
3 4 2 3 4 2
Table 3 Hydrosilylation of alkenes with methyldichlorosilane catalyzed by Fe O @SiO -EDTA@Pt and Fe O @SiO -DTPA@Pt
b
c
3
ꢁ1
Conv. (%)
TOF (10 h )
Entry
1
Alkene
Structure
Time/h
4
a
2
b
a
b
Cyclohexene
13
<0.1
<0.1
2
3
N,N-Dimethylacrylamide
4
4
96
99
98
98
8.9
9.5
8.2
9.3
1,2-Epoxy-4-vinylcyclohexane
4
Norbornylene
4
97
99
7.1
6.8
5
6
Methyl methacrylate
Butyl acrylate
5
5
58
57
67
87
4.9
4.1
5.1
3.8
7
Ethane-1,2-diyl bis(2-methylacrylate)
5
72
81
5.1
5.8
8
9
Crotonic acid ethyl ester
5
5
69
68
87
97
6.6
5.6
6.1
4.9
trans-2-Hexenyl acetate
1
0
trans-2-Hexen-1-yl phenylacetate
6
61
68
7.0
8.2
1
1
1
2
1,2-Epoxy-7-octene
Allyl glycidyl ether
6
6
98
84
99
98
8.7
5.1
9.1
4.4
1
1
3
4
5-Hexen-2-one
Allylchloride
6
4
86
58
97
64
8.2
7.6
6.1
6.2
a
ꢂ
ꢁ3
Conditions: 15 mmol methyldichlorosilane, 10 mmol alkene; temperature: 60 C; a, Fe
3
O
4
@SiO
2
-EDTA@Pt as catalyst (1.74 ꢀ 10 mmol Pt); b,
ꢁ3
b
c
Fe
3
O
4
@SiO
2
-DTPA@Pt as catalyst (1.93 ꢀ 10 mmol Pt). The conversion was based on the amount of alkene consumed. Initial TOFs were
calculated by GC aer 30 min of reaction time.
trans-2-hexene and trans-3-hexene, the yield further decreased octene, allyl glycidyl ether, 5-hexen-2-one and allylchloride),
corresponding to 87% and 78%. The similar phenomenon was three trans- internal alkenes (crotonic acid ethyl ester, trans-2-
observed when Fe O @SiO -DTPA@Pt was used as catalyst. It hexenyl acetate, and trans-2-hexen-1-yl phenylacetate) and two
3 4 2
indicated the hydrosilylation was harder for internal hexane ring type alkenes (cyclohexene and norbornylene). These
than 1-hexene and trans-hexene than cis-hexane. The results compounds are important industry raw materials. For example,
also veried both of Pt catalysts could be used for the remote allyl glycidyl ether is an important substrate because the
functionalization of alkenes, which has been shown to be alkoxysilanes derived from this alkene have broad applications
7
1,72
a remarkable step in organic synthesis.
in coatings and as coupling agents for epoxy composites used as
73
3
.3.3 Catalyzing hydrosilylation of other alkenes. The electronic chip encapsulation. Catalytic results were summa-
catalytic activities of the two Pt nanoparticles were further rized in Table 3. The multi-products were observed in GC
evaluated through employing another 14 alkenes with different chromatograms, different substrates peak at different times due
substituent, including nine terminal alkenes (N,N-dimethyla- to the diversity of their boiling point, for example, cyclohexene
crylamide, 1,2-epoxy-4-vinylcyclohexane, methyl methacrylate, peek at around 6.86 min, 1,2-epoxy-4-vinylcyclohexane peek at
butyl acrylate, ethane-1,2-diyl bis(2-methylacrylate), 1,2-epoxy-7- around 9.55 min, and allyl glycidyl ether peek at around
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.18 min. Because of multi-products were observed, n-decane
used as internal standard to get alkene conversion, which used
to evaluate the versatility of the prepared catalysts. Various
linear alkenes containing either electron-donating or electron-
withdrawing groups such as amine (entry 2), ester (entries 5–
Paper
8
References
1 R. M. Cornell and U. Schwertmann, The Iron Oxides:
Structure, Properties, Reactions, Occurrence and Uses, VCH
Publications, Weinheim, New York, 1996.
1
0), epoxide (entries 3, 11, and 12), ketone (entry 13), alkyl
chloride (entry 14) and ring type norbornylene (entry 4) except
cyclohexene (entry 1) were well catalyzed by Fe @SiO
EDTA@Pt and Fe @SiO -DTPA@Pt. In catalyzing N,N-dime-
2 S. Xuan, Y. X. Wang, J. C. Yu and K. C. Leung, Langmuir, 2009,
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3
O
4
2
-
3
O
4
2
thylacrylamide, 1,2-epoxy-4-vinylcyclohexane, norbornylene,
and 1,2-epoxy-7-octene, both Fe O @SiO -EDTA@Pt and Fe -
4 N. Kohler, C. Sun, A. Fichtenholtz, J. Gunn, C. Fang and
M. Zhang, Small, 2006, 2, 785–792.
3
4
2
3
O @SiO -DTPA@Pt showed similar high activity (>96%). The
5 H. Lee, M. K. Yu, S. Park, S. Moon, J. J. Min, Y. Y. Jeong,
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12739–12745.
4
2
catalytic activity of Fe @SiO
3
O
4
2
-DTPA@Pt was signicantly
higher than Fe @SiO -EDTA@Pt in hydrosilylation of cro-
3
O
4
2
tonic acid ethyl ester, trans-2-hexen-1-yl phenylacetate, trans-2-
hexenyl acetate, methyl methacrylate, butyl acrylate, ethane-1,2-
diyl bis(2-methylacrylate), allyl glycidyl ether, 5-hexen-2-one and
allylchloride. Even Fe O @SiO -DTPA@Pt could catalyze the
6 H. Liu, Z. Jia, S. Ji, Y. Zheng, M. Li and H. Yang, Catal. Today,
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3
4
2
hydrosilylation of cyclohexene (13%), whereas a very low yield
8 N. Nuryono, N. M. Rosiati, B. Rusdiarso, S. C. W. Sakti and
S. Tanaka, SpringerPlus, 2014, 3, 515–526.
(
2%) in Fe O @SiO -EDTA@Pt as catalyst. These results indi-
3
4
2
cated Fe
3
O
4
@SiO
2
-EDTA@Pt was more efficient.
9 S. Hokkanen, E. Repo, S. Lou and M. Sillanpaa, Chem. Eng. J.,
2
015, 260, 886–894.
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6.
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1
1
4
. Conclusions
8
Two novel magnetic Fe
DTPA@Pt catalysts were successfully prepared. The saturation
magnetization was 25.4 and 23.0 emu g for Fe
EDTA@Pt and Fe @SiO -DTPA@Pt, respectively. The Pt
amount of the 30–50 nm nanoparticles was corresponding to
3 4 2 3 4 2
O @SiO -EDTA@Pt and Fe O @SiO -
2
ꢁ1
12 Y. Fang, Y. Chen, X. Li, X. Zhou, J. Li, W. Tang, J. Huang,
3 4 2
O @SiO -
J. Jin and J. Ma, J. Mol. Catal. A: Chem., 2014, 392, 16–21.
3
O
4
2
13 B. Panella, A. Vargas and A. Baiker, J. Catal., 2009, 261, 88–
ꢁ
1
93.
173.80 and 192.77 mmol g , which the predominant valence
2
+
0
14 R. L. Oliveira, P. K. Kiyohara and L. M. Rossi, Green Chem.,
010, 12, 144–149.
5 M. Amir, U. Kurtan and A. Baykal, Chin. J. Catal., 2015, 36,
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was Pt and Pt . In catalyzing hydrosilylation of 1-hexene and
methyldichlorosilane, the yield of 1-heptylmethyldichlorosilane
was about 99% for both of catalysts and the TON were up to
2
1
1
1
1
1
6
62 733 for Fe
SiO -DTPA@Pt, respectively. The two catalysts, especially Fe
@SiO -DTPA@Pt, showed good activity in hydrosilylation of 5
3 4 2 3 4
O @SiO -EDTA@Pt and 579 947 for Fe O @-
6 J. Sun, Z. Dong, X. Sun, P. Li, F. Zhang, W. Hu, H. Yang,
H. Wang and R. Li, J. Mol. Catal. A: Chem., 2013, 367, 46–51.
7 J. J. Mart ´ı neza, E. X. Aguileraa, J. Cubillosa, H. Rojasa,
A. G ´o mez-Cort ´e sb and G. D ´ı az, Mol. Catal., 2019, 465, 54–60.
8 S. A. Theofanidis, V. V. Galvita, H. Poelman, R. Batchu,
L. C. Buelens, C. Detavernier and G. B. Marin, J. Mol.
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2
3
-
O
4
2
isomerous hexanes and 14 other alkene with different substit-
uent. Fe O @SiO -DTPA@Pt even could catalyze the hydro-
silylation of cyclohexene. Aer 12 catalytic runs for both of Pt
catalysts, yield of 1-heptylmethyldichlorosilane was still up to
3
4
2
9
0% and the magnetism was similar. The average loss of Pt in
each reaction was 0.87% for Fe @SiO -EDTA@Pt and 0.66%
for Fe @SiO -DTPA@Pt. The unprecedented activity and
1
2
2
2
2
2
2
9 Z. Mohamed, V. D. Dasireddy, S. Singh and H. B. Friedrich,
Int. J. Hydrogen Energy, 2018, 43, 22291–22302.
0 B. Cheng, W. Liu and Z. Lu, J. Am. Chem. Soc., 2018, 140,
3
O
4
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selectivity of the two Pt nanoparticle catalysts are prospective
and potential in catalyzing more reactions and replacing the
current homogeneous Pt catalyst industry.
5
014–5017.
1 B. Panella, A. Vargas and A. Baiker, J. Catal., 2009, 261, 88–
3.
9
2 M. Walczak, K. Stefanowska, A. Franczyk, J. Walkowiak,
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3 T. Yang, Y. Huo, Y. Liu, Z. Rui and H. Ji, Appl. Catal., B, 2017,
Conflicts of interest
There are no conicts to declare.
2
00, 543–551.
4 H. A. Khan, P. Natarajan and K. Jung, Appl. Catal., B, 2018,
31, 151–160.
2
Acknowledgements
5 H. Zai, Y. Zhao, S. Chen, L. Ge and C. Chen, Nano Res., 2018,
61, 2544–2552.
The authors would like to appreciate the nancial supports
from the National Natural Science foundation of China (No.
21605112).
12708 | RSC Adv., 2019, 9, 12696–12709
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