A novel fumed silica-supported nitrogenous platinum complex as a highly efficient catalyst for the hydrosilylation of olefins with triethoxysilane

Article abstract of DOI:10.1016/j.jorganchem.2011.02.021

A novel fumed silica-supported nitrogenous platinum complex was conveniently prepared from cheap γ-aminopropyltriethoxysilane via immobilization on fumed silica in toluene, followed by a reaction with hexachloroplatinic acid. The title complex was characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that the complex is an efficient and stable catalyst for the hydrosilylation of olefins with triethoxysilane. The title platinum complex could be separated by simple filtration and reused several times without any appreciable loss in the catalytic activity. Crown Copyright

Full text of DOI:10.1016/j.jorganchem.2011.02.021

Journal of Organometallic Chemistry 696 (2011) 1845e1849
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A novel fumed silica-supported nitrogenous platinum complex as a highly
efficient catalyst for the hydrosilylation of olefins with triethoxysilane
*
Ji Li, Chunhui Yang , Lei Zhang, Tianlong Ma
School of Chemical Engineering & Technology, Harbin Institute of Technology, Heilongjiang Province, Harbin 150001, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel fumed silica-supported nitrogenous platinum complex was conveniently prepared from cheap g-
Received 12 December 2010
Received in revised form
12 February 2011
aminopropyltriethoxysilane via immobilization on fumed silica in toluene, followed by a reaction with
hexachloroplatinic acid. The title complex was characterized by fourier transform infrared spectroscopy
(FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was found
that the complex is an efficient and stable catalyst for the hydrosilylation of olefins with triethoxysilane.
The title platinum complex could be separated by simple filtration and reused several times without any
appreciable loss in the catalytic activity.
Accepted 18 February 2011
Keywords:
Supported catalyst
Nitrogenous platinum complex
Hydrosilylation
Crown Copyright Ó 2011 Published by Elsevier B.V. All rights reserved.
Heterogeneous catalysis
1. Introduction
Particularly, fumed silica is an excellent support because it has high
mechanical strength, large surface area, chemical and heat stability.
Hydrosilylation of alkenes is one of the most important methods
for the syntheses of organosilicon compounds, and is particularly
widely used for the production of silicon monomers containing
functional groups and for cross-linking silicon polymers [1,2]. Many
metal complexes are known to be efficient catalysts for the
hydrosilylation reactions, but the discovery by Speier et al. [3] that
hexachloroplatinic acid is a very active catalyst even under ambient
conditions has led to Pt complexes becoming the catalyst of choice
for these reactions. Generally, Speier’s and Karstedt’s [4] catalysts
(‘second generation’ catalyst) are all homogeneous catalysts, but
problems of separating the catalyst from the reaction mixture exist.
A new generation of heterogeneous transition metal complexes has
been developed quickly in recent years [5,6]. It can combine the
advantages of the high activity and selectivity of homogeneous
catalysts, with easy catalyst recovery, and characteristics for
a heterogeneous catalyst. Thus these ‘third generation’ catalysts
have received much attention [7e9]. Transition metal complexes
can be immobilized on inorganic substrates [10,11] (such as carbon
Polysiloxane grafted on fumed silica-supported phosphine plat-
inum, sulfur platinum and arsine platinum complexes have been
proved to be efficient catalysts for the reaction [14e16]. However, it
is known that phosphorus and sulfur are unstable at high
temperatures and have negative environmental impacts [17].
Therefore, the development of phosphorus-free and sulfur-free
heterogeneous platinum catalysts having high activity, stability and
environmentally is a topic of urgent issue.
Recently, Hu et al. described the synthesis of MCM-41-sup-
ported mercapto platinum complex and their catalytic behavior in
the hydrosilylation of olefins with triethoxysilane [15]. Yang et al.
reported the preparation of glass fiber-supported platinum
complex for catalytic hydrosilylation of olefins [18]. However, to the
best of our knowledge, no hydrosilylation of olefins with trie-
thoxysilane catalyzed by a fumed silica-supported nitrogenous
platinum complex has been reported until now. In this paper, we
wish to report the synthesis of nitrogenous platinum complex and
its catalytic properties in the hydrosilylation of some olefins with
triethoxysilane.
black, silica, g-Al2O3, and carbon nanotubes) or organic polymers
[12,13] (such as polyamides, polystyrene, and polyphenylsilanes)
and are commonly anchored through a variety of functional link-
ages. Inorganic substrates possess a rigid structure which can not
be deformed by the swelling of solvents during catalytic reactions.
2. Experimental
Fumed silica was obtained from Jilin Chemical Industry CO. Ltd.,
and washed by alcohol prior to use. Triethoxysilane, olefins, and
g-
aminopropyltriethoxysilane were purchased from Jingzhou Jian-
ghan Fine Chemical Co. Ltd. and distilled before use. H2PtCl6$6H2O
* Corresponding author. Tel.: þ86 451 86413707; fax: þ86 451 86418270.
E-mail address: yangchh@hit.edu.cn (C. Yang).
0022-328X/$ e see front matter Crown Copyright Ó 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.02.021

1846
J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 1845e1849
Scheme 1. Preparation of fumed silica-supported nitrogenous platinum complex.
was purchased from Shanxi Kaida Chemcial Engineering Co. Ltd.
Other reagents were used as received without further purification.
2.3. Hydrosilylation of olefins with triethoxysilane
Reactions were carried out in three-necked flask with
a
a magnetic stirrer and a reflux condenser with an attached drying
system on the upper condenser. Olefin and platinum catalyst were
stirred at the reaction temperature for 30 min before triethox-
ysilane which was added at a constant speed. The reaction mixture
was heated at the reaction temperature within the stipulated time
and then catalyst was separated from the raw product by decan-
tation. After the removal of the raw product, a new portion of
substrates was added and the reaction was repeated under the
same conditions. Gas chromatography was employed to follow the
course of the reaction by the appearance of product. All hydro-
silylation products were characterized by 1H NMR and 13C NMR.
2.1. Preparation of silica-supported g-aminopropyltriethoxysilane
(‘SiO2’eNH2)
Fume silica (6.00 g) was placed in toluene (150 ml) containing g-
aminopropyltriethoxysilane (8.00 g) under nitrogen atmosphere.
The mixture was stirred at ambient temperature for 0.5 h and then
heated at reflux temperature for 30 h. The solid was filtered and
washed five times with acetone (5 ꢀ 30 ml) and dried in vacuum at
0
150 ꢁC for 6 h to obtain 6.23 g of functional fume silica (‘SiO2 eNH2).
The nitrogen content was found to be 1.124 mmol gꢂ1 by XPS
analysis.
2.4. Characterizations
2.2. Preparation of silica-supported nitrogenous platinum complex
(‘SiO2’eNH2ePt)
The SEM micrographs of the samples were acquired using
a Quanta-100 field emission scanning electron microscope (FEI,
America). 1H NMR and 13C NMR spectroscopies were performed on
AVANCEⅢ 300 MHz NMR instrument (BRUKER, Switzerland) at
20 ꢁC and the samples were dissolved in CDCl3. FTIR spectra were
obtained using a AVatav360 instrument (Nicolet, America). X-ray
photoelectron spectroscopy (XPS) spectra were obtained using
a KRATOS XSAM 800 electron energy spectrometer (Electrophysics,
America).
A ‘SiO2’eNH2 (1.20 g) was added to a solution of H2PtCl6$6H2O
(0.16 g) in absolute ethyl alcohol (40 ml). The mixture was stirred
under nitrogen for 10 h at 70 ꢁC. The solid product was filtered by
suction, washed with acetone and alcohol successively and dried in
a vacuum at 80 ꢁC for 6 h, producing 1.18 g of fumed silica-sup-
ported nitrogenous platinum complex (‘SiO2’eNH2ePt). The
nitrogen and platinum content was 0.920 and 0.292 mmol gꢂ1
respectively.
,
3. Results and discussion
3.1. Structure of fumed silica-supported nitrogenous platinum
catalyst
A novel fumed silica-supported nitrogenous platinum complex
was conveniently prepared by a treatment of
g-aminopropyl-
triethoxysilane with fumed silica in toluene and then reacted with
hydrochloroplatinic acid in absolute ethyl alcohol (Scheme 1).
Table 1
XPS data for ‘SiO2’eNH2ePt, ‘SiO2’eNH2, H2PtCl6$6H2O and Pt foil (in eV.)a
Sample
Pt4f7/2
72.9
N1s
Si2p
O1s
Cl2p
‘Si’eNH2ePt
‘Si’eNH2
400.3
399.4
103.4
103.5
532.6
532.6
199.8
H2PtCl6$6H2O
Pt foil
73.5
71.2
199.9
a
The binding energies are referenced to C1s (285.0 eV), and the energy differ-
Fig. 1. FTIR spectra of fumed silica (a), ‘SiO2’eNH2 (b), ‘SiO2’eNH2ePt(c).
ences were determined with an accuracy of ꢃ0.2 eV.

J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 1845e1849
1847
Fig. 2. SEM micrograph of fumed silica (a), ‘SiO2’eNH2 (b), ‘SiO2’eNH2ePt (c).
The FTIR spectra of the (a) fumed silica, (b) fumed silica-sup-
ported nitrogenous groups (‘SiO2’eNH2), (c) fumed silica-supported
nitrogenous platinum complex catalyst (‘SiO2’eNH2ePt) are shown
in Fig. 1. In the fumed silica spectrum (Fig. 1a), a big broad intense
band at 1103 cmꢂ1 corresponds to the vibration of SieO groups
(observed in all the samples), and another two bands at 1622 and
3417 cmꢂ1 correspond tounassociated (isolated) hydroxylgroupson
the silica surface and OeH vibrations respectively. After functional
is formed. Considering the fact that the mole ratio of N:Pt in
‘SiO2’eNH2ePt is3.15, wesupposed thatthereistheinteraction ofone
or two NH2 groups combining with one Pt metal in ‘SiO2’eNH2ePt.
The SEM micrograph of the fumed silica (a), ‘SiO2’eNH2 (b),
‘SiO2’eNH2ePt (c) are shown in Fig. 2. A non-uniform structure
(some are globular structures, others are block structures) is
observed after treated by g-aminopropyltriethoxysilane (Fig. 2b),
whereas globular structures are shown in the fumed silica (Fig. 2a).
And the block structures are shown in ‘SiO2’eNH2ePt, while
particle size increased (Fig. 2c), meaning the immobilization of Pt
complexes on the functional silica.
process of fumed silica with g-aminopropyltriethoxysilane (Fig.1b),
the bands at 2928 and 2850 cmꢂ1 corresponding to asymmetric and
symmetric vibrations, respectively, of the eCH2e groups of the
pendant propyl chain are observed. The three bands at 3299, 3349
and 1565 cmꢂ1 corresponds to asymmetric, symmetric and scissor
bending vibrations of eNH2 respectively. The significant decrease in
the unassociated (isolated) hydroxyl groups and OeH vibrations at
1622 and 3417 cmꢂ1 provides evidence of the grafting of
3.2. Hydrosilylation of olefins with triethoxysilane
The hydrosilylation reaction of some olefins with triethox-
ysilane was examined to evaluate the catalytic activity of the novel
fumed silica-supported nitrogenous platinum complex catalyst.
The reaction formula is shown in Scheme 2.
First, the catalytic activity of this silica-supported nitrogenous
platinum complex at different temperatures was investigated using
the hydrosilylation of allyl glycidyl ether with triethoxysilane as the
model reaction. The results are presented in Fig. 3. The experi-
mental results show that the reaction temperature is a critical
condition for the yield of 3-glycidoxypropyltriethoxysilane. There is
a lower or no yield when the reaction temperature was below 70 ꢁC,
g-aminopropyltriethoxysilane. Compared with the spectra of
fumed silica, those peaks indicate the presence of -amino-
g
propyltriethoxysilane ring on the surface of silica. Further, the
significant decrease in the asymmetric, symmetric and scissor
bending vibrations of eNH2 reveals that most of the amino groups
on the surface of the functional silica have coordinated with plat-
inum ion (Fig. 1c), signifying the immobilization of Pt complexes on
the fumed silica.
The X-ray photoelectron spectroscopy was used to characterize
this polymeric platinum catalyst. The XPS data for ‘SiO2’eNH2ePt,
‘SiO2’eNH2, H2PtCl6$6H2O and Pt foil are listed in Table 1. It clearly
shows thatthe bindingenergies ofSi 2pand O1sof ‘SiO2’eNH2ePt are
similar to those of ‘SiO2’eNH2, and the binding energy of Cl 2p of
‘SiO2’eNH2ePt is similar to that of H2PtCl6$6H2O. However, the
difference of N 1s binding energies between ‘SiO2’eNH2ePt and
‘SiO2’eNH2 is 0.9 eV. The binding energy of Pt 4f7/2 in ‘Si’eNH2ePt is
0.6 eV less than that in H2PtCl6.6H2O, but 1.7 eV bigger than that in Pt
foil. These results show that a coordination bond between N and Pt
Fig. 3. Effect of reaction temperature on the yield of 3-glycidoxypropyltriethoxysilane.
Conditions: allyl glycidyl ether: 0.1 mol; triethoxysilane: 0.08 mol; the amount of the
catalyst: 0.292 mmol Pt; reaction time: 2 h; feeding fashion: Triethoxysilane is added
dropwise to allyl glycidyl ether.
Scheme 2. The hydrosilylation reaction of olefins with triethoxysilane.

1848
J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 1845e1849
Fig. 4. Effect of feeding fashion on the yield of 3-glycidoxypropyltriethoxysilane. 1:
Allyl glycidyl ether is added dropwise to triethoxysilane. 2: Triethoxysilane is added
dropwise to allyl glycidyl ether. Conditions: allyl glycidyl ether: 0.1 mol; triethox-
ysilane: 0.08 mol; the amount of the catalyst: 0.292 mmol Pt; reaction time: 2 h;
reaction temperature: 110 ꢁC.
Fig. 5. Effect of reaction time on the yield of 3-glycidoxypropyltriethoxysilane.
Conditions: allyl glycidyl ether: 0.1 mol; triethoxysilane: 0.08 mol; the amount of the
catalyst: 0.292 mmol Pt; reaction temperature: 110 ꢁC; feeding fashion: Triethox-
ysilane is added dropwise to allyl glycidyl ether.
however, the yield increases with the increasing of temperature.
When the hydrosilylation reaction is carried out at 110 ꢁC, 3-gly-
cidoxypropyltriethoxysilane is obtained in 74.7% as a maximum
yield.
result from the strong coordination of nitrogenous ligand on
platinum.
Hydrosilylation reactions of some olefins with triethoxysilane
were investigated using ‘SiO2’eNH2ePt as catalyst and the typical
results are listed in Table 3. It can be seen that the hydrosilylation
reactions of 1-octene, 1-decene, 1-dodecene and allyl glycidyl ether
with triethoxysilane proceeded smoothly, while the corresponding
hydrosilylation products are obtained in 93.8e96.5% yields in the
presence of catalytic amount of ‘SiO2’eNH2ePt catalyst. It also was
found that the ‘SiO2’eNH2ePt catalyst is especially effective in
regioselectivity of the corresponding hydrosilylation reactions.
Hydrosilylation of the corresponding olefins with HSi(OEt)3 affor-
The effect of feeding fashion of material on the hydrosilylation
reaction was also investigated at 110 ꢁC and the results are shown in
Fig. 4. It is found that the feeding is also an essential condition for
this hydrosilylation. 3-Glycidoxypropyltriethoxysilane could be
obtained in 74.7%, whereas the yield when triethoxysilane is added
dropwise to allyl glycidyl ether reduces to 12.7%. The results also
demonstrate that the activation of double bond leads to great
promotion on both the activity and stability of the active center Pt
and the activation of catalyst are critical for improving catalytic
properties.
ded the
b-adduct as a major product. However, Speier’s catalyst was
The effect of reaction time on the yield is presented in Fig. 5. The
results manifest that there is not an obvious induction period in the
reaction, and the reaction rate is the fastest at the beginning, then
decreases after 2 h. The yield increases as the reaction proceeds in
the case of the heterogeneous complex catalysts, and reaches
a maximum after 9 h.
The hydrosilylation of allyl glycidyl ether with triethoxysilane
was examined to evaluate the reusable property of ‘SiO2’eNH2ePt,
the results are showed inTable 2. It is found that the novel supported
nitrogenous platinum complex could be recovered by simple filtra-
tion and reused several times without noticeable loss of activity. The
high stability and good reusable property of ‘SiO2’eNH2ePt should
Table 2
Result of the reuse test.a
Reuse cycles
Yield (%)
1
2
3
4
5
93.8
92.4
92.2
91.9
87.4
a
Conditions: allyl glycidyl ether: 0.1 mol; trie-
thoxysilane: 0.08 mol; reaction temperature: 110 ꢁC;
the amount of the catalyst: 0.292 mmol Pt; reaction
time: 9 h; feeding fashion: triethoxysilane is added
dropwise to allyl glycidyl ether.
Table 3
Catalytic activity of ‘SiO2’eNH2ePt for the hydrosilylation reaction of olefins with triethoxysilane.a
Olefin
Productb
Time (h)
Regioselectivity (%)
Yield (%)c
CH3(CH2)5CH]CH2
CH3(CH2)7CH]CH2
CH3(CH2)9CH]CH2
CH3(CH2)11CH]CH2
CH3(CH2)7Si(OEt)3
CH3(CH2)9Si(OEt)3
CH3(CH2)11Si(OEt)3
CH3(CH2)13Si(OEt)3
2.5
2.5
2.5
2.5
9.0
98.3
98.5
98.5
98.2
97.6
96.5
94.3
94.1
91.6
93.8
a
Conditions: olefins: 0.3 mol; triethoxysilane: 0.24 mol; reaction temperature: 110 ꢁC; the amount of the catalyst: 1.0 mmol Pt; reaction time: 9 h; feeding fashion:
triethoxysilane is added dropwise to olefins.
b
The structure of product was further identified by 1H NMR.
No increase in yield with increasing the reaction time.
c

J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 1845e1849
1849
not so effective when HSi(OEt)3 was used. It was reported that the
yield of decyltriethoxysilane was only 40% in the case of using
Speier’s catalyst [19]. And the yields were 93% and 91% respectively
in the presence of some other heterogeneous catalysts [7,14]. All of
these results show that the nitrogenous ligand of ‘SiO2’eNH2 plays
an important role in hydrosilylation reaction catalyzed by
‘SiO2’eNH2ePt. And the structures of ‘SiO2’eNH2ePt also were
important for catalytic activity and regioselectivity. Furthermore,
hydrosilylation reaction of 1-tetradecene with triethoxysilane
could also proceed smoothly to give the better yield of 91.6%. The
results confirm that the corresponding yields of linear olefins
decrease slightly with increasing alkyl-ligand length.
handling, separation from the product and reuse some times
without obvious loss in the catalytic activity especially.
Acknowledgment
This work was supported by the National Technology Support
Project. (Project No. 2006BAE01B09).
References
[1] P.B. Glaser, T.D. Tilley, J. Am. Chem. Soc. 125 (2003) 13640.
[2] A.K. Roy, Adv. Organomet. Chem. 55 (2008) 1.
[3] J.L. Speier, J.A. Webster, C.H. Barnes, J. Am. Chem. Soc. 79 (1957) 974.
[4] B.D. Karstedt, US Patent, 3 775 452 (1973).
4. Conclusions
[5] H. Zhao, L.F. Zha, M.Z. Cai, Reac. Kinet. Mech. Cat. 100 (2010) 187.
[6] B. Marciniec, K. Szubert, R. Fiedorow, J. Mol. Catal. A: Chem. 310 (2009) 9.
[7] G. Liu, M.Z. Cai, J. Mol. Catal. A: Chem. 258 (2006) 257.
[8] R. Drakea, D.C. Sherringtonb, S.J. Thomson, React. Funct. Polym. 60 (2004) 65.
[9] Z.M. Michalska, q Rogalski, K. Rózga-Wijas, J. Mol. Catal. A: Chem. 208 (2004)
187.
[10] T. Onoe, S. Iwamoto, M. Inoue, Catal. Commun. 8 (2007) 701.
[11] G. Hamasaka, S. Kawamorita, A. Ochida, Organometallics 27 (2008) 6495.
[12] A. Corma, H. García, A. Leyva, J. Catal. 240 (2006) 87.
[13] H.H. Shih, D. Williams, N.H. Mack, Macromolecules 42 (2009) 14.
[14] W.R. Cullen, N.F. Han, J. Organomet. Chem. 333 (1987) 269.
[15] R.H. Hu, L.F. Zha, M.H. Cai, Catal. Commun. 11 (2010) 563.
[16] G. Liu, B. Huang, M. Cai, React. Funct. Polym. 67 (2007) 294.
[17] K.I. Shimizu, S. Koizumi, T. Hatamachi, J. Catal. 228 (2004) 141.
[18] H.T. Yang, Z.P. Fang, X.Y. Fu, Catal. Commun. 9 (2008) 1092.
[19] M. Capka, J. Hetflejs, Collect. Czech. Chem. Commun. 39 (1974) 154.
In summary, a novel fumed silica-supported nitrogenous plat-
inum complex has been prepared and structurally characterized.
The FTIR and SEM micrograph results indicated the coating of
g-aminopropyltriethoxysilane on the silica surface and the immo-
bilization of Pt complexes on the fumed silica. The XPS analysis
showed that there is an interaction of NH2 groups combining with
Pt metal in ‘SiO2’eNH2ePt, verifying a coordination bond between
N and Pt is formed. The reaction results demonstrate that this
platinum complex has high activity for hydrosilylation of some
olefins with triethoxysilane in atmosphere conditions, and has
advantages of third generation catalysts such as high activity, easy