Preparation of efficient and environment-friendly silica-supported EDTA platinum catalyst and its applications in hydrosilylation of olefins and methyldichlorosilane

Article abstract of DOI:10.1016/j.molcata.2016.04.019

A novel catalyst by preparing silica supported ethylenediaminetetraacetic acid (EDTA) platinum complex was developed. The preparation conditions, such as heating temperature and solvent types, were optimized. The catalyst was phosphine-free and sulfur-free which was characterized by infrared spectroscopy (IR), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet spectroscopy (UV) and atomic absorption spectroscopy (AAS). Its catalytic activity was evaluated by catalyzing solventless hydrosilylation reactions. In the hydrosilylation reaction between 1-hexene and methyldicholosilane, the new catalyst showed a higher catalytic activity than that provided by Spiere's catalyst. Moreover, the new catalyst could be reused for 12 times without obvious loss of catalytic activity. To confirm its practical feasibility, catalyzing the hydrosilylation reaction between 1-octene and methyldichlorosilane was performed. Our results indicated that the new catalyst can efficiently catalyze the hydrosilylation reaction.

Full text of DOI:10.1016/j.molcata.2016.04.019

Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Preparation of efficient and environment-friendly silica-supported
EDTA platinum catalyst and its applications in hydrosilylation of
olefins and methyldichlorosilane
∗
Futing Li, Youxin Li
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, Tianjin 300072, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel catalyst by preparing silica supported ethylenediaminetetraacetic acid (EDTA) platinum com-
plex was developed. The preparation conditions, such as heating temperature and solvent types, were
optimized. The catalyst was phosphine-free and sulfur-free which was characterized by infrared spec-
troscopy (IR), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM), high
resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultravi-
olet spectroscopy (UV) and atomic absorption spectroscopy (AAS). Its catalytic activity was evaluated by
catalyzing solventless hydrosilylation reactions. In the hydrosilylation reaction between 1-hexene and
methyldicholosilane, the new catalyst showed a higher catalytic activity than that provided by Spiere’s
catalyst. Moreover, the new catalyst could be reused for 12 times without obvious loss of catalytic activ-
ity. To confirm its practical feasibility, catalyzing the hydrosilylation reaction between 1-octene and
methyldichlorosilane was performed. Our results indicated that the new catalyst can efficiently catalyze
the hydrosilylation reaction.
Received 31 January 2016
Received in revised form 2 April 2016
Accepted 18 April 2016
Available online 23 April 2016
Keywords:
Environment-friendly immobilized
platinum
Hydrosilylation
Heterogeneous catalyst
Ethylenediaminetetraacetic acid
©
2016 Elsevier B.V. All rights reserved.
1
. Introduction
there are some drawbacks for these homogenous platinum cata-
lysts, such as deactivation caused by formation of black platinum
colloid, high cost, environmental pollution, difficult recycling, and
risk of reacting violently [7].
Hydrosilylation of olefins is the key catalytic reaction for the pro-
duction of industrially important organosilicon compounds such
as organofunctional silanes and silicones [1,2]. Homogenous plat-
inum catalysts, such as Speier’s catalyst [3], Karstedt’s catalyst [4]
and various modified Karstedt’s catalysts [5,6], are usually used to
catalyze those hydrosilylation reactions which are between olefins
and alkoxysilanes, or between olefins and chlorosilanes. However,
Consequently, immobilized platinum catalysts were developed
over the past few decades. Many substances have been used as sup-
ported materials, such as cross-linked polymers (e.g. polyamides
[8], polystyrene [9,10]), silica [11,12], glass [13], aluminum oxide
[14], and carbon [15,16]. The supported materials are usually able
to be anchored with a variety of functional groups and ther-
mally and chemically stable during the reaction process. Yves
Fort et al. [14] prepared alumina-supported phosphinate plat-
inum catalyst, which showed excellent catalytic performance in
hydrosilylation of 1-octene and dimethylphenylsilane. Hu et al.
[17] immobilized platinum on MCM-41-supported material by
mercapto group and proved the catalyst was simply, convenient,
highly efficient through catalyzing the hydrosilylation reaction of
olefins and triethoxysilane. Ye et al. [18] immobilized platinum on
MCM-41-supported material by the mercapto and vinyl bi-groups.
Compared with single vinyl group (MCM-41-vinyl-Pt) or mercapto
group (MCM-41-SH-Pt), the bi-groups immobilized platinum has
superior activity in hydrosilylation reaction.
Abbreviations: MCM-41-vinyl-Pt, MCM-41 supported vinyl platinum; MCM-
4
1-SH-Pt, MCM-41 supported mercapto platinum; IR, Infrared Spectroscopy; EDS,
Energy Dispersive X-ray Spectrometer; TEM, Transmission Electron Microscopy;
HRTEM, High Resolution Transmission Electron Microscopy; XPS, X-ray Photo-
electron Spectroscopy; UV, Ultraviolet Spectroscopy; AAS, Atomic Absorption
Spectroscopy; NMR, Nuclear Magnetic Resonance; GC, Gas Chromatography; EDTA,
Ethylenediaminetetraacetic Acid; EDTAD, Ethylenediaminetetraacetic Dianhydride;
APTES, ␥-aminopropyltriethoxysilane; APSG, Aminopropyl Silica Gel; SiO2-EDTA,
Silica-supported EDTA; SiO2-EDTA-Pt, Immobilized Platinum on SiO2-EDTA; TMS,
Tetramethylsilane; TOF, Turnover Frequency.
∗ Corresponding author at: Room A606, Building 24, School of Pharmaceutical
Science and Technology, Tianjin University, 92 Weijin Road, Nankai District, Tianjin
3
00072, China.
E-mail addresses: lyx@tju.edu.cn, liyouxin2008@163.com (Y. Li).
http://dx.doi.org/10.1016/j.molcata.2016.04.019
381-1169/© 2016 Elsevier B.V. All rights reserved.
1

F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
255
Compared with polymers, functionalized inorganic supports
without swelling phenomenon have attracted widespread atten-
tion for their rigid structures which could effectively prevent being
deformed during the reaction. Among these inorganic supports,
functionalized silica is known as a good supported material because
of its large surface area, high mechanical strength, thermal and
chemical stability. Many silica supported catalysts, silica-supported
sulfide platinum [19], Karstedt (Pt)-type catalyst [12], phosphi-
nate platinum [20,21], polyamidoamine dendrimers platinum, and
nitrogenous platinum complex [22] were developed to catalyze
hydrosilylation reactions. But they are still far away from practical
applications for large-scale manufacture of organosilicon com-
pounds. The stability and cost of those immobilized catalysts are
the main reasons hampering their practical applications. The cata-
lysts anchored by phosphine ligands or sulfur ligands were unstable
at high temperatures [23,24]. The deciduous ligands may not only
contaminate the product leading to lower repeatability and reli-
ability of reaction results, but also have a negative impact on the
environment and catalyst activity resulting from catalyst poison-
ing [25]. Therefore, it is highly required to develop a recyclable
phosphine-free and sulfur-free silica supported catalyst. Ethylene-
diaminetetraacetic acid (EDTA), a hexadentate ligand containing
both carboxylate and amine groups, is becoming attractive reagent
in organic synthesis for its non-volatile, cheap, and non-toxic
nature. Moreover, its properties can be tuned by modifying with
functional groups. The commercially available and powerful com-
plexing agent [26] was proved to be efficient in the complexation of
a verity of metals [27,28]. To the best of our knowledge, however,
silica modified by EDTA never was used as metal immobilization
support until now.
Jiangtian Scientific Co., Ltd. (Tianjin, China). Nitric acid (HNO ) and
3
hydrofluoric acid (HF) were from Sigma Aldrich Co., LLC (Missouri,
USA). Platinum standard liquid was from Beijing Gangyan Nano
Detection and Technology Co., Ltd. (Beijing, China). Distilled water
was from Yongyuan Distilled Water Manufacturing Centre (Tian-
jin, China). CDCl and DMSO were purchased from Beijing Coupling
3
Technology Co. Ltd. (Beijing, China).
2.2. Instruments
All separation experiments were performed in GC 2020 with a
flame ionization detector (Wuhan Trust Century Technology Co.,
Ltd., Hubei, China) and a 30m × 0.25mm × 0.25 ␮m capillary col-
umn (Lanzhou ATEO Analytical Technology Co., Ltd., Gansu, China).
Data were collected and analyzed using ZB2020 Data System from
Surwit Technology (Hangzhou) Co., Ltd. (Zhejiang, China). Bruker
Advance 600 MHz spectrometer (Bruker, Germany) was used for
analyzing of products using tetramethylsilane (TMS) as an inter-
nal standard and CDCl3 or DMSO as solvent. 1H NMR spectra
were recorded using an IconNMR Data System (Bruker, Germany).
Fourier transform infrared spectra were recorded on a Bruker TEN-
SOR 27 spectrophotometer (Bruker, Germany). Energy dispersive
X-ray spectrum was recorded on an ISRF-550i spectrophotometer
(IXRF, Texas, USA). Ultraviolet–visible (UV–vis) absorption spectra
were recorded on a Cary-300 Ultraviolet–visible Spectropho-
tometer (Agilent Technology, California, USA). The immobilization
amounts of Pt were determined by a Thermo SOLAAR M6 Atomic
Absorption Spectrophotometer (Thermo Fisher Scientific Inc., USA).
All deionized water for Pt determination in atomic absorption
spectrophotometer was prepared by a Milli-Q Deionizer (Mil-
lipore, Massachusetts, USA). Microwave dissolver for digesting
immobilized Pt catalysts was from Milestone S.r.L. (Sorisole, Italy).
Transmission Electron Microscopy (TEM) and High Resolution
Transmission Electron Microscopy (HRTEM) were recorded on
JEM-2100F (JEOL Ltd., Tokyo, Japan). The X-ray photoelectron spec-
troscopy (XPS) experiments were carried out in a Kratos Analytical
Axis Ultra DLD instrument (Shimadzu, Tokyo, Japan).
In this work, we reported a new catalyst immobilizing plat-
inum on silica modified by EDTA. Ethylenediaminetetraacetic acid
(
EDTA) is a hexadentate ligand containing both carboxylate and
amine groups and is easy to be modified by functional groups
26–28]. The conditions of immobilizing platinum on silica were
[
systematically investigated. The complex was then characterized
by infrared spectroscopy (IR), energy dispersive X-ray spectrome-
ter (EDS), transmission electron microscopy (TEM), high resolution
transmission electron microscopy (HRTEM), X-ray photoelectron
spectroscopy (XPS), ultraviolet spectroscopy (UV) and atomic
absorption spectroscopy (AAS). Its catalytic ability was evaluated
by catalyzing hydrosilylation reaction of methyldichlorosilane and
2.3. Preparation of the immobilized platinum catalyst
2.3.1. Preparation of ethylenediaminetetraacetic dianhydride
(EDTAD)
1
-hexene or 1-octene. Under the optimization hydrosilylation con-
EDTAD was synthesized according to the method described [29].
A 20 g EDTA was suspended in 34 ml anhydrous pyridine and fol-
lowed by adding 26 ml acetic anhydride. The mixture solution was
ditions, the reaction product was identified by nuclear magnetic
resonance (NMR) and quantified by gas chromatography (GC).
◦
stirred at 65 C of external heating temperature for 24 h. Collection
of raw product (EDTAD) was performed by filtration, following a
washing step with diethyl ether. To purify the raw EDTAD, the solid
product was re-dispersed in 55 ml acetic anhydride and stirred
intermittently for 30 min. After filtration, solid EDTAD was then
washed by acetic anhydride and diethyl ether. The product was
2
. Experimental
2.1. Reagents and chemicals
◦
Unless otherwise stated, all reagents were analytical reagent
dried at 65 C in vacuum. The synthetic route was shown in Fig. 1
1
grade or better. Silica was purchased from Yantai Xinnuo Chem-
ical Industry Co., Ltd. (Shandong, China). Methyldichlorosilane
was purchased from Zhejiang Kaihua Synthetic Co., Ltd. (Zhe-
jiang, China). 1-Hexene was from Shanghai Aladdin Biological
Technology Co., Ltd. (Shanghai, China). 1-Octene was from J & K
Scientific Ltd. (Beijing, China). 1-Hexyl-methyldichlorosilane was
from CNW Technologies Co., Ltd. (Nordrhein Westfalen, Germany).
Step 1 and the prepared EDTAD was characterized using H NMR
spectroscopy, 13C NMR spectroscopy and IR spectroscopy.
2.3.2. Preparation of silica-supported EDTA (SiO -EDTA)
2
◦
Silica gel was pretreated by 6 M HCl at 60 C of external heating
temperature for 6 h. And it was washed by distilled water until pH
◦
neutral, followed by drying at 60 C for 12 h and further drying at
◦
1
-Octyl-methyldichlorosilane was from Alfa Aesar Co., Ltd. (Mas-
130 C for 3 h to remove residual water. To modify the silica gel,
sachusetts, USA). ␥-Aminopropyltriethoxysilane was from Qufu
Chenguang Chemical Co., Ltd. (Shandong, China). H PtCl ·6H O
5 g silica gel, 50 ml toluene and 7 ml ␥-aminopropyltriethoxysilane
(APTES) were added into 100 ml 3-neck boiling flask. The sus-
pended solution was mechanically stirred at 300 rpm and the
2
6
2
was from Shanghai Jiuyue Chemcial Engineering Co., Ltd. (Shang-
hai, China). Ethylenediaminetetraacetic acid, anhydrous pyridine,
acetic anhydride, diethyl ether, HCl, toluene, acetone, ethanol, n-
decane, i-propanol, n-butanol and n-hexanol were from Tianjin
◦
reaction was performed at 80 C of external heating temperature for
24 h. The modified silica gel, Aminopropyl silica gel (APSG), was fil-
◦
tered and washed by toluene and acetone. It was then dried at 70 C

2
56
F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
Fig. 1. The synthesis route of SiO2-EDTA.
for 12 h. To prepare silica-supported EDTA, 2 g APSG, 4 g EDTAD and
2.4. Hydrosilylation reactions
5
1
7
0 ml mixture of ethanol and acetic acid (v/v, 1/1) were added into
00 ml 3-neck boiling flask and mechanically stirred at 300 rpm at
The catalytic activity of SiO -EDTA-Pt was evaluated by
2
◦
0 C of external heating temperature for 24 h. After filtration, the
catalyzing a model hydrosilylation reaction of 1-hexene and
methyldichlorosilane. The reaction was carried out in a 50 ml flat-
bottomed centrifuge tube with a magnetic stirrer and a homemade
product was washed by acetone and water respectively, and then
dried at 70 C [30]. The synthetic route was shown in Fig. 1 Steps 2
◦
and 3.
reflux condenser. A 10 mmol 1-hexene and SiO -EDTA-Pt contain-
2
−
4
ing 10.0 × 10 mmol Pt were added into the centrifuge tube and
◦
stirred at 60 C of external heating temperature for 0.5 h before
2.3.3. Preparation of the immobilized platinum on SiO -EDTA
2
adding 18 mmol methyldichlorosilane. The mixture was magnet-
(
SiO -EDTA-Pt)
◦
2
ically stirred at 60 C of external heating temperature for 3 h and
An i-propanl-H PtCl solution (0.0386 mol/L) was prepared by
2
6
then cooled to room temperature. The product was characterized
dissolving 1.0 g H PtCl ·6H O in 50 i-propanol. The reactants, 1.01 g
by GC and 1H NMR.
2
6
2
SiO -EDTA, 80 ml ethanol and 10 ml i-propanl-H PtCl solution,
2
2
6
In order to evaluate the recyclable character of SiO -EDTA-Pt,
2
were added in a 250 ml 3-neck boiling flask. Under nitrogen protec-
tion, the suspended solution was mechanically stirred at 300 rpm
and the reaction was carried out at 100 C of external heating tem-
perature for 9 h. After filtration, the solid product was washed by
ethanol and acetone successively and dried in an oven at 70 C for
the immobilized catalyst was repeatedly used 12 times. After each
hydrosilylation reaction, the immobilized Pt was kept in the cen-
trifuge tube by centrifuging the mixture and pouring out all of
liquid. Fresh 1-hexene and methyldichlorosilane were added to
perform the new reaction under the same conditions.
◦
◦
1
2 h to obtain SiO -EDTA-Pt power.
2

F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
257
The feasibility of SiO -EDTA-Pt to catalyze hydrosilylation reac-
2
tions was further confirmed in the reaction between 1-octene and
methyldichlorosilane. The reaction was also carried out in a 50 ml
flat-bottomed centrifuge tube with a magnetic stirrer and a home-
made reflux condenser. A 10 mmol 1-octene and SiO -EDTA-Pt
2
−
4
containing 10.0 × 10 mmol Pt were added into the centrifuge
◦
tube and stirred at 60 C of external heating temperature for 0.5 h
before adding 18 mmol methyldichlorosilane. The mixture was
◦
magnetically stirred at 60 C of external heating temperature for
4
h and then cooled to room temperature. The product was charac-
1
terized by GC and H NMR.
2.5. Charactering methods
All middle products and products, EDTAD, SiO , SiO -EDTA, and
2
2
SiO -EDTA-Pt were characterized by IR. The samples were dried in
2
IR oven for 3 h and were then dispersed on KBr power at the ratio
of 1:100 to prepare KBr tablets for IR measurement.
SiO -EDTA-Pt was characterized by EDS, SEM and XPS. The
2
valance state of platinum in i-propanol-H PtCl6 was character-
2
ized by scanning the sample by UV spectrometry from 200 nm
to 400 nm. The different valance state of platinum causes the
maximum wavelength change. The amount of immobilized plat-
inum was determined by AAS with a working standard curve. A
0
.1 g SiO -EDTA-Pt was added in 2 ml HF and 3 ml HNO3 solu-
2
tion. The digestion was accelerated by a microwave dissolver.
◦
◦
The microwave digestion procedures: 130 C for 15 min, 160 C for
◦
◦
5
min, 170 C for 10 min, and then 180 C for 20 min. After diges-
◦
tion, the residual acids were removed at 145 C for 1 h. The activity
of the immobilization platinum was evaluated by a model reaction,
i.e. the hydrosilylation between 1-hexene and methyldichlorosi-
lane and further applied to the hydrosilylation of 1-octene and
methyldichlorosilane. The structures of the products were iden-
1
13
tified by NMR. H NMR or C NMR spectroscopies of EDTAD and
hydrosilylation products were performed on 600 MHz NMR at 20 C
◦
using tetramethylsilane (TMS) as an internal standard and DMSO or
CDCl3 as solvent. Qualitative and quantitative analysis of the reac-
tion products were performed in GC, using n-decane as the internal
standard. The programming of GC was as following: the injection
volume was 0.8 ␮l, the split ratio was 30:1, the inlet temperature
◦
◦
was 260 C, the detection temperature was 260 C, the column tem-
◦
◦
perature was first 60 C for 3 min, and then increased to 250 C at
the speed of 10 C·min , finally, 250 C was maintained for 5 min.
◦
−1
◦
3
3
3
. Results and discussion
.1. Characterization of products
.1.1. Characterization of EDTAD
The two groups of splitting peaks in IR spectrum of EDTAD
(Fig. 2(A)) were the preliminary evidence of the anhydride struc-
ture. The peaks in the high frequency region split at 1810,
− −1
1
1
761 cm with a gap of about 50 cm between adjacent peaks.
−
1
The low frequency groups split at 1127, 1072, and 1008 cm with
−
1
the same interval. Additionally, the bands at 1247 and 1423 cm
were related to C–O and C–N stretching respectively. 1H NMR
(
4
600 MHz, DMSO, Fig. 2(B)): ␦ 3.71 (s, 8H, O CCH N), 2.67 (s,
2
1
3
H, N (CH ) N), C NMR (600 MHz, DMSO, Fig. 2(C)): ␦ 51.17 (N
2 2
(
CH ) N), 52.24(O CCH N), 165.76 (C O) which consisted with the
2 2 2
characteristic peaks in the ideal product [31].
Fig. 2. (A) IR spectrum of EDTAD, (B) 1H NMR spectrum of EDTAD and (C) 13C NMR
spectrum of EDTAD.
3
.1.2. Characterization of SiO -EDTA-Pt
2
The prepared SiO -EDTA-Pt was firstly characterized by IR, EDS,
2
SEM, XPS, UV, and AAS. The IR spectra of the silica, SiO -EDTA and
2
SiO -EDTA-Pt were shown in Fig. 3(A). In the three spectra, there
2
−1
−1
are two broad bands at 1110 cm and 803 cm arising from Si–O

2
58
F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
Fig. 3. (A) IR spectra of bare silica, SiO2-EDTA and SiO2-EDTA-Pt, (B) EDS image of SiO2-EDTA-Pt, (C) The TEM of SiO2-EDTA-Pt, (D) The HRTEM of SiO2-EDTA-Pt, (E) The
XPS entire spectrum scanning images of SiO2-EDTA-Pt, (F) The XPS of SiO2-EDTA-Pt in the region of Pt 4f5/2 and 4f7/2, and (G) UV/Vis absorption spectrum of SiO2-EDTA-Pt
◦
prepared in 100 C.
stretching, and a band at 475 cm−1 arising from O–Si–O bending
of Pt induced some changes of carbonyl groups, which might be
resulted from interaction or charge transfer.
−
1
[
32]. In the SiO2 spectrum, two bands at 1639 and 3453 cm cor-
respond to unassociated hydroxyl groups on the silica surface [33]
The energy dispersive X-ray spectrum was recorded by using an
IXRF-550i instrument and the EDS analysis showed the elements
present in the material. As shown in Fig. 3(B), the EDS analysis of
and O–H vibrations respectively [34]. For the SiO -EDTA, two bands
2
−1
at 1678 and 1743 cm were from carbonyl groups of amides and
carboxylic groups, respectively [35]. However, the immobilization

F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
259
fresh SiO -EDTA-Pt catalyst indicated the presence of Si, C, O, N, Pt,
Cl elements.
evaporated during the reaction process. This caused an insufficient
reaction. Based on the results, 60 C was chosen as the heating
2
◦
The TEM and HRTEM of SiO -EDTA-Pt have been performed to
temperature in the following experiments.
2
observe the morphology and distribution of Pt and the results were
shown in Fig. 3(C) and (D). From the TEM image, nanoparticles on
To achieve a sufficient reaction, a series of reaction time were
investigated whilst keeping the other conditions constant. Namely,
the reaction was performed in 0.5 h, 1 h, 2 h, 3 h, and 4 h, respec-
tively. As shown in Fig. 4(D), the yield was lower than 20% in the
first 1 h reaction. It indicated that there was an induction period of
1 h for this reaction. There was then a yield jump to 65% from 1 h
to 2 h reaction. It indicated that the reaction was activated. The
yield increased slowly after 2 h reaction and reached the maxi-
mum (87.97%) after 4 h reaction. During this period, the amount of
reactants decreased and the amount of products increased. Thus,
the surface of SiO -EDTA can be observed. According to the lattice
2
fringes analysis, the lattice fringes at (111) surface of nanoparticle
was 0.227 nm, which was very consistent to the lattice fringes of
platinum crystal.
X-ray photoelectron spectroscopy (XPS) was further performed
to probe the electronic state of Pt in SiO -EDTA-Pt. The XPS survey
2
spectra (Fig. 3(E)) also indicated the presence of elements Pt, Si, C,
N and O as expected. The XPS spectrum of Pt 4f region was shown
in Fig. 3(F). Compared with bulk Pt (71.2 eV) [17], the positive shift
approximately +1.5 eV indicated charge transfer from Pt to coor-
dination atoms of the ligand [36] which was consistent to the IR
results.
the reaction time of hydrosilylation was fixed at 4 h in the follow-
◦
ing experiments when SiO -EDTA-Pt prepared at 90 C of external
2
heating temperature was used.
The effect of additive sequence of reactants on the hydrosily-
lation reaction was also investigated and the results were shown
in Fig. 4(E). It was found that the additive sequence was also
an essential factor for this hydrosilylation. The yield of 1-hexyl-
methyldichlorosilane was up to 88.0% when methyldichlorosilane
was added to 1-hexene, whereas the yield reduced to 62.1%
when 1-hexene was added to methyldichlorosilane and the
yield was 72.6% when all reactants were added simultaneously.
The results demonstrated that the activation of double bond
maybe benefit to promotion on the activity of the active cen-
ter Pt and the activation of catalyst which was might critical for
improving catalytic properties. Thus, the order of methyldichlorosi-
lane to 1-hexene was adapted in the following experi-
ments.
According to the UV spectrum (Fig. 3(G)), maximum absorbance
appeared at 247 nm and 262 nm in the residual i-propanol- H PtCl6
2
solution when the external heating temperature of immobilization
◦
was 100 C, which was consistent with reported data of reduced
Pt particle and Pt (IV) [37,38]. It indicated that Pt may have been
immobilized on the support material at different forms. Some
researchers reported the reduced form Pt had the catalytic activity
[
39]. In order to evaluate the amount of Pt anchored on SiO -EDTA,
2
the complex was analyzed by atomic absorption spectroscopy. The
data indicated that the amount of platinum immobilized onto SiO2-
EDTA was 0.197 mmol/g or 3.84 wt%, which was higher than 1 wt%
immobilized onto TiO [40] and functionalized polyethylene glycol
2
[
38]. However, the immobilized platinum amount in the conditions
was lower than 0.292 mmol/g [33] and 0.22 mmol/g [17].
The catalyst dosage was a key factor to estimate catalyst activ-
ity. Thus, the effect of the amount of the SiO -EDTA-Pt containing
2
−
3
−3
−3
3
.1.3. Catalytic activity evaluation of SiO -EDTA-Pt
0.25 × 10 , 1.0 × 10 or 4.0 × 10 mmol Pt on the hydrosilylation
2
To evaluate the catalytic activity of immobilized Pt, hydrosilyla-
reaction was investigated. Results indicated the maximum yield
tion of 1-hexene with methyldichlorosilane was chosen as a model
reaction catalyzed by SiO -EDTA-Pt. SiO -EDTA-Pt was prepared
of 1-hexyl-methyldichlorosilane was up to 88% when SiO -EDTA-
2
−
3
Pt containing 1.0 × 10 mmol Pt was used. When SiO -EDTA-Pt
2
2
2
◦
−3
at 90 C of external heating temperature. The other experimental
conditions, including external heating temperature, time, addi-
tive sequence of reactants, the catalyst dosage, and the ratio of
reactants, were systematically investigated. The results showed
that the hydrosilylation of 1-hexene with methyldichlorosilane
containing 0.25 × 10 mmol Pt was used, the yield of 1-hexyl-
methyldichlorosilane at 4 h was only 38.2%. A large number of the
residual reactants proved the whole of reaction rate was appar-
ently restricted by the limited amount of Pt catalyst, which may
be the main reason of the low yield. Another reason may be
the increase of by-product whose retention time was twice as
could be catalyzed by SiO -EDTA-Pt (Fig. 4(A)). In all GC analysis,
2
there was only one product with the same retention time as the
much as 1-hexyl-methyldichlorosilane in GC. When SiO -EDTA-Pt
2
−
3
1
-hexyl-methyldichlorosilane standard substance. The hydrosily-
containing 4.0 × 10 mmol Pt was used, the final yield of 1-hexyl-
methyldichlorosilane was only 71.7%. As increasing the amount
of the catalyst, the accelerated reaction rate and intensely heat-
emission might lead to a rapid temperature rise in reactions, and
therefore might lead to more by-products. This could be proved
by the three peaks around 1-hexene and a peak whose reten-
tion time was twice as much as 1-hexyl-methyldichlorosilane.
1
lation product of the model reaction was characterized by HNMR.
As shown in Fig. 4(B), the spectrum displayed six peaks, which
were 0.77 (s, 3H, CH3 SiCl2 ), 1.12 (t, 2H, CH3 SiCl2 CH2 ),
1
1
.30
.38
(m,
(m,
2H,
4H,
2H,
CH3 SiCl2 CH2 CH2 CH2 (CH2)2 ),
CH3 SiCl2 CH2 CH2 CH2 ),
0.89 (t, 3H,
1.50
CH3-
(m,
CH3 SiCl2 CH2 CH2 ),
SiCl2 CH2 CH2 CH2 (CH2)2 CH3 ), respectively. Moreover, the
spectral data matched with that of 1-hexyl-methyldichlorosilane
standard.
Thus, the amount of the SiO -EDTA-Pt should be controlled and
2
−
3
fixed at 1.0 × 10 mmol to catalyze 10.0 mmol 1-hexene in this
paper.
The hydrosilylation reaction of 1-octene with triethoxysilane
was clearly faster at higher temperature and obtained higher
turnover number within shorter time [41], which indicated that
the reaction temperature had an important effect on the hydrosi-
lylation. Therefore, the effect of external heating temperature from
In the platinum-catalyzed hydrosilylation of trichlorosilane
HSiCl3 with allyl chloride, most experiments were carried out
in an excess of HSiCl3 which was reported to be the optimum
ratio of these two reactants [42]. Therefore, the effect of ratio
of methyldichlorosilane and 1-hexene including 0.60:1, 1.02:1,
1.40:1, 1.80:1, 2.00:1, and 2.20:1 was also investigated. The results
were shown in Fig. 4(F). The data indicated the apparent 1-
hexane was residual when the reactant ratio was 0.60:1. The
limited amount methyldichlorosilane contributed to a low yield,
66.4%. When ratio of methyldichlorosilane and 1-hexene increased
from 1.02:1 to 1.80:1, the yield of product arose from 88.0% to
94.1%. With the continuous increase of reactant ratio, the yields
of 1-hexyl-methyldichlorosilane were dramatically dropped from
◦
◦
4
0 C to 80 C on the yield of 1-hexyl-methyldichlorosilane was
investigated. As shown in Fig. 4(C), maximum yield (about 90%) was
◦
◦
◦
obtained at 60 C. When reaction temperature was lower than 60 C,
◦
fewer yields was achieved in 4 h, i.e., 30% at 40 C and 45% at 50 C.
It indicated that a high temperature may lead to a more efficient
reaction. When reaction temperature was higher than 60 C, the
◦
◦
yield decreased to about 60% at 70/80 C. The possible reason was
that the reactants, especially methyldichlorosilane, dramatically

2
60
F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
Fig. 4. (A) Typical GC chromatogram of reaction catalyzed by SiO2-EDTA-Pt, (B) The 1H NMR spectrum of 1-hexyl-methyldichlorosilane, (C) Effect of external heating
temperature on the yield of 1-hexyl-methyldichlorosilane, (D) Effect of reaction time on the yield of 1-hexyl-methyldichlorosilane, (E) Effect of additive sequence of reactants
on the yield of 1-hexylmethyldichlorosilane, (F) Effect of reactant ratio on the yield of 1-hexyl-methyldichlorosilane.
Conditions: (A) Chromatographic column: SE-54 (30 m × 0.25 mm × 0.25 ␮m), internal standard: n-decane, injection volume: 0.8 ␮l, temperature programming: split ratio
◦
◦
◦
◦
was 30:1, inlet temperature was set at 260 C, detection temperature was 260 C, column temperature was first 60 C 3 min, and then was up to 250 C at the speed of
◦
−1
◦
−4
1
0
C min , finally, 250 C was maintained 5 min. (C) 1-Hexene: 10.0 mmol; methyldichlorosilane: 10.2 mmol; the amount of the catalyst: 10.0 × 10 mmol Pt; reaction
◦ ◦
temperature: 40, 50, 60, 70, and 80 C; reaction time: 4 h; additive sequence: Methyldichlorosilane is added to 1-hexene. (D) Reaction temperature: 60 C; reaction time: 0.5,
1
1
, 2, 3, and 4 h. The other conditions were the same as (C). (E) Reaction time: 4 h 1: all materials are added simultaneously. 2: methyldichlorosilane is added to 1-hexene. 3:
-hexene is added to methyldichlorosilane. The other conditions were the same as (D). (F) Additive sequence: Methyldichlorosilane is added to 1-hexene. Reactants ratio of
methyldichlorosilane and 1-hexene was 0.60:1, 1.02:1, 1.40:1, 1.80:1, 2.00:1or 2.20:1. The other conditions were the same as (E).
8
5.5% to 55.6% and a large number of by-products were observed.
3.2.1. Effect of the temperature on SiO -EDTA-Pt
2
◦
Thus, the ratio of methyldichlorosilane and 1-hexene was fixed at
SiO -EDTA-Pt was prepared at 30, 50, 70, 90, or 100 C of exter-
2
1
.80:1.
nal heating temperature in accordance with the experimental steps
of Section 2.3.3 respectively. Their catalytic activities were shown
in Table 1. The results indicated that the catalytic activity and
immobilized amount of platinum were strongly dependent on the
temperature and the catalytic activity was not completely corre-
lated to the immobilized amount of platinum. With increase of
heating temperature prepared SiO2-EDTA-Pt, induction periods of
the catalytic reaction were gradually shortened and reaction rates
at the beginning of the model reaction were gradually acceler-
3.2. Effect of immobilization conditions on SiO -EDTA-Pt
2
Alumina-supported platinum catalyst properties could be
affected by conditions of immobilized catalyst [14]. As a result, after
verifying the good catalytic effect of SiO -EDTA-Pt, the effects of
immobilization conditions including temperature, platinum den-
sity and solvent were investigated.
2
◦
ated. When the heating temperature was lower than 90 C, such
◦
◦
◦
as 30 C, 50 C, 70 C, although the immobilized amount of plat-

F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
261
Table 1
Effect of the external heating temperature on Pt immobilization.
Catalyst
Yield (%)a
0.5 h
TOFb (s−1
)
◦
External heating temperature ( C)
Platinum content (mmol/g)
1.0 h
2.0 h
3.0 h
4.0 h
3
5
7
9
0
0
0
0
0.243
0.251
0.269
0.210
0.197
7.5
10.3
15.5
66.7
87.7
9.3
30.2
71.7
83.9
88.7
60.7
80.4
79.5
88.1
96.8
75.7
81.8
84.9
90.9
99.1
81.3
82.5
86.3
94.1
–
0.42
0.57
0.86
3.71
4.87
1
00
a
−4
Conditions: 1-hexene: 10.0 mmol; methyldichlorosilane: 18.0 mmol; the amount of the catalyst: 10.0 × 10 mmol Pt; external heating temperature of hydrosilylation:
C; additive sequence: Methyldichlorosilane is added to 1-hexene.
Turnover frequency calculated after 0.5 h of reaction.
◦
6
0
b
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Table 2
3
5
7
9
1
0
0
0
0
Effect of the immobilization catalyst loading amount.
Yield (%)a
TOFb (s−1
Platinum content (mmol/g)
)
00
0.5 h
1.0 h
2.0 h
3.0 h
0.073
18.8
32.6
87.7
30.0
35.6
88.7
34.3
65.6
96.8
66.8
78.4
99.1
1.04
1.81
4.87
0.138
0.197
a
Conditions: 1-hexene: 10.0 mmol; methyldichlorosilane: 18.0 mmol; the
−
4
amount of the catalyst: 10.0 × 10 mmol Pt; external heating temperature of
◦
hydrosilylation: 60 C; reaction time: 3 h; additive sequence: Methyldichlorosilane
is added to 1-hexene.
b
Turnover frequency calculated after 0.5 h of reaction.
Table 3
Effect of the solvent on Pt immobilization and activity.
240
260
280
300
320
340
360
380
400
Catalyst
Yield (%)a
TOFb (s−1
)
Wavelengh (nm)
Solvent of preparationPlatinum content(mmol/g)0.5 h1 h 2 h 3 h
Fig. 5. UV/Vis absorption spectra of SiO2-EDTA-Pt prepared at different external
heating temperatures.
ethanol
0.197
0.153
0.166
0.162
87.7 88.7 96.8 99.1 4.87
i-propanol
n-butanol
n-hexanol
8.8 77.2 78.0 86.4 0.49
62.6 74.6 75.0 95.1 3.48
86.5 91.8 96.7 97.3 4.81
inum was increasing from 0.243 mmol/g to 0.269 mmol/g, the
reaction was not finished until 4 h and the yield was only 81.3%,
a
Conditions: 1-hexene: 10.0 mmol; methyldichlorosilane: 18.0 mmol; the
−
4
amount of the catalyst: 10.0 × 10 mmol Pt; external heating temperature of
8
2.5 and 86.3%, respectively. When the temperature increased
◦
◦
◦
hydrosilylation: 60 C; reaction time: 3 h; additive sequence: Methyldichlorosilane
from 90 C to 100 C, the immobilized amount of platinum was
decreasing from 0.210 mmol/g to 0.197 mmol/g, but the catalytic
activity of SiO -EDTA-Pt apparently increased. Using SiO -EDTA-
is added to 1-hexene.
b
Turnover frequency calculated after 0.5 h of reaction.
2
2
◦
Pt prepared at 100 C of external heating temperature, the yield of
3
.2.3. Effect of the solvent on Pt immobilization and activity
The significant temperature effect encouraged us to investi-
gate whether coordination solvent with higher reflux temperatures
could cause a better catalytic activity. In accordance with the
1
3
-hexyl-methyldichlorosilane could reach the maximum 99.1% at
h. According to the above results, it could be hypothesized that the
high temperature allowed the efficient reduction of Pt (IV) in active
and stable low oxidation state platinum species and this assump-
tion is consistent with the UV/Vis spectra. As shown in the Ref. [38]
and Ref. [39], the absorbance of Pt (IV) and Pt particle is 262 nm,
experimental steps of Section 2.3.3, we prepared SiO -EDTA-Pt
2
◦
at 100 C of external heating temperature in ethanol, i-propanol,
n-butanol and n-hexanol respectively. As shown in Table 3, the
platinum content and the hydrosilylation activity were depen-
2
47 nm respectively. As Fig. 5 shown, it could be observed that more
and more Pt (IV) was reduced to Pt particle with the increase of the
dent on the solvent. Platinum content of SiO -EDTA-Pt prepared in
2
immobilized temperature. Thus, the external heating temperature
ethanol, i-propanol, n-butanol and n-hexanol was decreased grad-
◦
immobilized Pt onto SiO -EDTA was chosen at 100 C.
2
ually. However, activity sequence was SiO -EDTA-Pt prepared in
2
ethanol, n-hexanol, n-butanol and i-propanol when the reactions
were added equal amount Pt. Finally, ethanol was chosen as solvent
for further use.
3
.2.2. Effect of the platinum loading amount on platinum
catalytic activity
Because the catalytic activity was not completely correlated to
the platinum amount, it may be meaningful to investigate the effect
of catalyst density on the activity of SiO -EDTA-Pt. As result, we
3
.3. Comparison of SiO -EDTA-Pt and other Pt catalysts
2
2
prepared different immobilized Pt catalysts in accordance with
the experimental steps of Section 2.3.3 respectively. The three
In order to further evaluate the SiO -EDTA-Pt, we also prepared
2
immobilized platinum catalysts with bare SiO2 and SiO -NH . The
2
2
kinds of SiO -EDTA-Pt catalysts containing equal total Pt amount
2
results showed that when a non-functionalized SiO2 was sub-
mitted to a similar metal solution, the isolated solid contained
merely 0.029% of Pt. Furthermore, the model hydrosilylation reac-
tion was carried out using the homogeneous Spiere’s catalyst at
but different platinum density of 0.073 mmol/g, 0.138 mmol/g
and 0.197 mmol/g were used for hydrosilylation reaction between
methyldichlorosilane and 1-hexene. The data were shown in
Table 2. Results indicated that the reaction rate decreased with
decrease of the platinum density. The highest yield still was
obtained when Pt immobilization amount was 0.197 mmol/g.
the above optimum reaction conditions, and using SiO -NH -Pt
2
2
at the following conditions. (Conditions: 1-hexene: 10.0 mmol;
methyldichlorosilane: 18.0 mmol; the amount of the catalyst:

2
62
F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Number times of run
Fig. 6. The reusability of SiO2-EDTA-Pt.
Conditions: GC chromatographic conditions were the same as Fig. 4A.
−
4
◦
1
0.0 × 10 mmol Pt; external heating temperature: 60 C; additive
sequence: Methyldichlorosilane and 1-hexene were added simul-
taneously)
The yield of 1-hexyl-methyldichlorosilane reached the maxi-
mum (89.6%) at 2 h using an equal content of i-propanol-H PtCl .
2
6
The turnover frequency (TOF), defined as the molar ratio of pro-
duced product to the amount of Pt immobilized on SiO -EDTA
2
after 30 min of reaction, could reach 4.90. With SiO -NH -Pt, we
2
2
found that the TOF is only 1.09 with 43.18% yield of the 1-hexyl-
methyldichlorosilane at 3 h. The yield can reach 86.91% when
the reaction was performed for 4 h, whilst the yield of 1-hexyl-
methyldichlorosilane was up to 99.1% and the TOF was 4.87 when
using SiO -EDTA-Pt. By comparison, the SiO -EDTA-Pt not only can
2
2
ensure high catalytic activity, but also high selectivity.
Fig. 7. (A) GC chromatogram of reaction system of 1-octene and methyldichlorosi-
lane catalyzed by SiO2-EDTA-Pt, (B) H NMR of 1-octyl-methyldichlorosilane.
1
Conditions: (A) GC chromatographic conditions were the same as Fig. 4A except
sample.
3
.4. Reusability of SiO -EDTA-Pt
2
To test the reusability of SiO -EDTA-Pt, hydrosilylation reaction
2
4
. Conclusions
between 1-hexene with methyldichlorosilane was performed 12
runs. After each run, the mixture solution of the reaction was cen-
trifuged. The solid catalyst remained in the tube and liquid solution
was removed. Fresh reactants were added in the tube and per-
A new catalyst, silica supported platinum, has been success-
fully developed in this work. According to the optimization results,
◦
1
00 C of external heating temperature is the best immobilized
formed the reaction again. As shown in Fig. 6, SiO -EDTA-Pt could
2
temperature and ethanol is the best solvent for preparing SiO2-
EDTA-Pt. In the model solvent-less hydrosilylation of 1-hexene
and methyldichlorosilane, our results indicates that the new cat-
alyst has the advantages of high catalytic activity, environmentally
be recycled up to twelve consecutive runs and kept above 80% final
yield of product. The little drop of activity may be because of the loss
of SiO -EDTA-Pt in each pouring out liquid after reaction comple-
2
tion. By contrast, SiO -NH -Pt can effectively catalyze the reaction
2
2
friendly, easy handling, and recyclable. Application of SiO -EDTA-Pt
2
for 4 times.
in catalyzing the hydrosilylation of 1-octene and methyldichlorosi-
lane indicates that the new catalyst may be potentially used in other
hydrosilylation reactions. From an industrial point of view, the new
catalyst is in accordance with the principle of green chemistry. This
will bring it a good future both in laboratory and in industry.
3
.5. Application of SiO -EDTA-Pt
2
1
-Octene was hydrosilylated with methyldichlorosilane cat-
alyzed by SiO -EDTA-Pt to investigate the catalytic scope of
2
SiO -EDTA-Pt in other hydrosilylation reactions. The highest yield
Acknowledgements
2
of 1-octyl-methyldichlorosilane (98.5%) could be obtained when
◦
SiO -EDTA-Pt was prepared at 100 C of external heating tempera-
The authors would like to appreciate the financial supports from
the National Natural Science Foundation of China (No. 21375093),
the Specialized Research Fund for the Doctoral Program of Higher
Education (No. 20130032120081), Youth Fund of the Science and
Technology Committee of Tianjin Municipal Government (No.
15JCQNJC43200) and the Independent innovation foundation of
Tianjin University (No. 1102213).
2
1
ture. The product of the reaction was characterized by H NMR. The
data was consistent with that of commercially available 1-octyl-
methyldichlorosilane. In particular, 1-Octyl-methyldichlorosilane,
H NMR (CDCl ) ␦: 1.50 (m, 2H), 1.35(m, 10H), 1.11 (m, 2H), 0.88
t, 3H), 0.77 (s, 3H). The spectrum was shown in Fig. 7. The result
indicated the SiO -EDTA-Pt might have wide application prospect.
1
3
(
2

F. Li, Y. Li / Journal of Molecular Catalysis A: Chemical 420 (2016) 254–263
[20] A.L. Prignano, W.C. Trogler, J. Amer. Chem. Soc. 109 (1987) 3586–3595.
263
References
[
[
[
[
21] Z.M. Michalska, J. Mol. Catal. 3 (1977) 125–134.
22] S. Dierick, E. Vercruysse, G. Berthon-Gelloz, Chem.-Eur. J 21 (2015) 1–7.
23] J. Masllorens, M. Moreno-Manas, Synthesis 2002 (2002) 1903–1911.
24] K.I. Shimizu, S. Koizumi, T. Hatamachi, H. Yoshida, S. Komai, T. Kodama, Y.
Kitayama, J. Catal. 228 (2004) 141–151.
25] D. Troegel, J. Stohrer, Coord. Chem. Rev. 255 (2011) 1440–1459.
26] L.V.A. Gurgel, O.K. Junior, Bioresour. Technol. 99 (2008) 3077–3083.
27] M. Sillanpaa, M. Orama, J. Ramo, Sci. Total Environ. 267 (2001) 23–31.
28] E. Repo, J.K. Warchoł, A. Bhatnagar, J. Colloid Interface Sci. 358 (2011)
[
[
[
[
[
1] P.B. Glaser, T.D. Tilley, J. Am. Chem. Soc. 125 (2003) 13640–13641.
2] A.K. Roy, Adv. Organomet. Chem. 55 (2007) 1–59.
3] J. Speier, J. Webster, G. Barnes, J. Am. Chem. Soc. 79 (1957) 974–979.
4] B.D. Karstedt, US: 3775452 (1973).
5] B. Olivier, G. Berthon-Gelloz, S. Sterin, G. Mignani, Chem. Commun. 30 (2005)
[
[
[
[
3
856–3858.
[
[
[
6] J.Y. Li, C.B. Niu, J.J. Peng, Appl. Organomet. Chem. 28 (2014) 454–460.
7] K. Kiyotomi, E. Kohki, Bull. Chem. Soc. Jpn. 79 (2006) 981–1016.
8] Z.M. Michalska, K. Strzelec, J. Sobczak, J. Mol. Catal. A: Chem. 156 (2000)
261–267.
[
[
[
[
29] M. Tu, K.E. Geckeler, Polym. Int. 48 (1999) 909–914.
9
1–102.
30] Y. Shiraishi, G. Nishimura, Ind. Eng. Chem. Res. 41 (2002) 5065–5070.
31] M. Mayor, R. Scheffold, HeIv. Chim. Acta. 80 (1997) 1183–1189.
32] E.R. Lippincott, A.V. Valkenburg, C.E. Weir, E.N. Bunting, J. Res. Natl. Bur.
Stand. 61 (1958) 61–70.
[
9] B.R. Stranix, H.Q. Liu, G.D. Darling, J. Org. Chem. 62 (1997) 6183–6186.
[
[
10] R. Drake, D.C. Sherrington, S.J. Thomson, React. Funct. Polym. 60 (2004) 65–75.
11] Z.M. Michalska, K. Rozga-Wijas, J. Chojnowski, W. Fortuniak, J. Mol. Catal. A:
Chem. 208 (2004) 187–194.
12] Q.J. Miao, Z.P. Fang, G.P. Cai, Catal. Commun. 4 (2003) 637–639.
13] H.T. Yang, Z.P. Fang, X.Y. Fu, L.F. Tong, Catal. Commun. 9 (2008) 1092–1095.
14] Y. Fort, A. Silvestri, H. Graindorge, J. Mol. Catal. A: Chem. 112 (1996) 31l–316.
15] M. Chauhan, B.J. Hauck, L.P. Keller, P. Boudjouk, J. Organomet. Chem. 645
[
[
[
[
[
[
[
[
[
[
33] J. Li, C.H. Yang, L. Zhang, J. Organomet. Chem. 696 (2011) 1845–1849.
[
[
[
[
34] M. Shahabi nejada, G. Ghasemi, J. Mol. Catal. A: Chem. 406 (2015) 118–126.
35] S. Nagib, K. Inoue, T. Yamaguchi, Hydrometallurgy 51 (1999) 73–85.
36] C. Liu, G. Li, D. Kauffman, J. Colloid Interface Sci. 423 (2014) 123–128.
37] M. Luty-Blocho, M. Wojnicki, K. Pacławski, Chem. Eng. J. 226 (2013) 46–51.
38] Y. Bai, S.F. Zhang, Y. Deng, J. Colloid Interface Sci. 394 (2013) 428–433.
39] M. Pagliaro, R. Ciriminna, Eur. J. Org. Chem. 2013 (2013) 6227–6235.
40] F. Alonso, R. Buitrago, Y. Moglie, J. Organomet. Chem. 696 (2011) 368–372.
41] H.S. Hilal, M.A. Suleiman, J. Mol. Catal. A: Chem. Chem. 144 (1999) 47–59.
42] B. Marciniec, H. Maciejewski, W. Duczmal, R. Fiedorow, D. Kitynski, Appl.
Organomet. Chem. 17 (2003) 127–134.
(
2002) l–13.
[
16] B. Marciniec, H. Maciejewski, W. Duczmal, R. Fiedorow, D. Kitynski, Appl.
Organomet. Chem. 17 (2003) 127–134.
[
[
17] R.H. Hu, L.F. Zha, M.Z. Cai, Catal. Commun. 11 (2010) 563–566.
18] Z.G. Ye, H.X. Shi, H.M. Shen, Phosphorus, Sulfur Silicon Relat. Elem. 190 (2015)
1
621–1631.
[19] D.A. de Vekki, M.A. Il’ina, Russ. J. Gen. Chem. 84 (2014) 1580–1586.