Titanium-catalyzed hydrosilylation of olefins: A comparison study on Cp2TiCl2/Sm and Cp2TiCl2/LiAlH4 catalyst system

Article abstract of DOI:10.1080/10426507.2018.1487440

Hydrosilylation of olefins catalyzed by Cp₂TiCl₂/Sm (Cp = cyclopentadienyl) under solvent free conditions have been investigated. By using Cp₂TiCl₂/Sm as catalyst system, β-adducts and hydrogenation products were detected. Hydrosilylation of olefins catalyzed by Cp₂TiCl₂/LiAlH₄ under room temperature has also been studied. The influence of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) on Cp₂TiCl₂/Sm and Cp₂TiCl₂/LiAlH₄, respectively, indicated that hydrosilylation of olefins catalyzed with Cp₂TiCl₂/Sm went through a free radical reaction pathway while a coordination mechanism was applied for Cp₂TiCl₂/LiAlH₄ catalyst system.

Full text of DOI:10.1080/10426507.2018.1487440

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Titanium-catalyzed hydrosilylation of olefins: A
comparison study on Cp2TiCl2/Sm and Cp2TiCl2/
LiAlH4 catalyst system
Xiaoling Yang, Ying Bai, Jiayun Li, Yu Liu, Jiajian Peng, Tianbo Li, Rui Lang &
Botao Qiao
To cite this article: Xiaoling Yang, Ying Bai, Jiayun Li, Yu Liu, Jiajian Peng, Tianbo Li, Rui
Lang & Botao Qiao (2018): Titanium-catalyzed hydrosilylation of olefins: A comparison study on
Cp2TiCl2/Sm and Cp2TiCl2/LiAlH4 catalyst system, Phosphorus, Sulfur, and Silicon and the Related
Elements, DOI: 10.1080/10426507.2018.1487440
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Titanium-catalyzed hydrosilylation of olefins: A comparison
study on Cp2TiCl2/Sm and Cp2TiCl2/LiAlH4 catalyst system
Xiaoling Yanga, Ying Baia*, Jiayun Lia, Yu Liua, Jiajian Penga*, Tianbo
Lib, Rui Langb and Botao Qiaob
aKey Laboratory of Organosilicon Chemistry and Material Technology of Ministry of
Education, Hangzhou Normal University, Hangzhou 311121, China
bDalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116011,
China
∗ E-mail: ybai@hznu.edu.cn (Y. Bai), jjpeng@hznu.edu.cn (J.J. Peng)
Abstract Hydrosilylation of olefins catalyzed by Cp2TiCl2/Sm (Cp
cyclopentadienyl) under solvent free conditions have been investigated. By using
Cp2TiCl2/Sm as catalyst system, β-adducts and hydrogenation products were detected.
Hydrosilylation of olefins catalyzed by Cp2TiCl2/LiAlH4 under room temperature has
also been studied. The influence of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) on
Cp2TiCl2/Sm and Cp2TiCl2/LiAlH4, respectively, indicated that hydrosilylation of
olefins catalyzed with Cp2TiCl2/Sm went through a free radical reaction pathway
while a coordination mechanism was applied for Cp2TiCl2/LiAlH4 catalyst system.
Keywords Hydrosilylation; Titanocene; Samarium; LiAlH4; Mechanism; TEMPO
=

1. INTRODUCTION
Hydrosilylation of olefins is a superior method for preparing alkylsilanes and
other organsilicon polymers, which is particularly useful for the construction of C-Si
bond [1]. Hydrosilylation of olefins was effectively promoted by transition metal
complexes. Among of the metal complexes used, noble metal complexes, e.g.
Karstedt’s catalyst (Pt complex with 1,3-divinyltetramethyldisiloxane) and Speier’s
catalyst (H2PtCl6 in i-PrOH solution) often exhibit high catalytic activity. However,
low selectivity of the product as well as limitation for the substrates was observed.
Additionally, the high cost of these noble metal complexes also limits their
application in the industry process. Hence, the development of low-cost metal catalyst
systems including an iron complex [2] and a cobalt complex [3] for hydrosilylation is
highly desired but remains an ongoing challenge. Although these iron or cobalt
catalysts exhibit excellent catalytic activity and/or regioselectivity, these complexes
exhibit one or more limitations with regard to preparation and operational
convenience. The group 4 transition metal complexes, used as hydrosilylation
catalysts, have been reported. Meyer et al [4] reported that a one-pot synthesis of
functional polysilanes could be achieved through the dehydrogenative coupling of
hydrosilanes and hydrosilylation reaction by using Cp2Ti(OPh)2 as catalyst. Gendre et
al [5] reported that 1,4-hydrosilylation of dienes to allysilanes could be catalyzed by
cheap and stable Cp2TiF2 complex, and Cp2TiH(SiH2Ph) generated from
Cp2TiF2/PhSiH3 and regenerated from titanocene “Cp2Ti” oxidative addition with
PhSiH3 as the active catalytic center was assumed, thus low-valent titanium complex

plays an important role in the catalytic cycle. Silytitanocene complexes [6] and
metallocene-type Ti(III) complexes [7] were synthesized and used as catalysts for the
hydrosilylation of olefins. As is well-known, low-valent organotitanium complexes
play a key role in the development of both synthetic organometallic and catalytic
chemistry, and among the applications of low-valent titanium in organic synthesis, the
reductive coupling of carbonyl compounds to produce alkenes (the McMurry reaction)
is particularly prominent [8, 9]. As a simple low-valent titanium complex system,
Cp2TiCl2/M (M=Zn [10], Al [11], Mg [12] and Sm [13-15]) has been applied as
reduction system for several organic syntheses.
The catalytic hydroalumination of olefins made it possible to synthesize
organoaluminum compounds following to find new promising approaches to the
synthesis of alcohols, terminal acetylenes and other functional organic compounds
[16-18]. Otsuji et al reported that titanium-aluminium complex Cp2Ti(AlH3)2
generated from titanocene dichloride and excess LiAlH4 promoted the catalytic
hydroalumination of olefins with LiAlH4 to give lithium alkylhydroaluminates [19].
The study on the synthesis of organoaluminum compounds indicated that Ti and Zr
complexes were usually considered as catalysts [20]. On the other hand, the
hydrosilylation of olefins with monosilane in the presence of LiAlH4 had been
reported [21].
Here we describe the hydrosilylation of olefins can be processed with catalytic
amount of Cp2TiCl2/M (M = Zn, Al, Mg, Fe, Co, In, Mn, Ni and Sm) or
Cp2TiCl2/LiAlH4 (Scheme 1). The comparison of these two kinds of catalyst system

was studied.
[Insert Schemed 1]
2. RESULTS AND DISCUSSION
2.1 Cp2TiCl2/metal system for the catalytic hydrosilylation of 1-octene
In first experiments, the hydrosilylation of 1-octene with diphenylsilane
catalyzed with Cp2TiCl2/metal as a model reaction was studied. Initially the catalytic
properties of Cp2TiCl2, in the presence of a different metal powder for the
hydrosilylation of 1-octene, were compared (Table 1). The results showed that
Cp2TiCl2/Sm exhibit the highest catalytic activity among Cp2TiCl2/metals tested
though all the Cp2TiCl2/metal tested exhibit some catalytic activity. Both β-adduct 1
and hydrogenation product 3 were obtained by using Cp2TiCl2/metal as catalyst, while
neither α-adduct 2 nor dehydrosilylation product 4 was detected.
[Insert Table 1]
2.2 Influence of mole ratio of Cp2TiCl2/Sm on the catalytic hydrosilylation
Next, the influence of the mole ratio of Cp2TiCl2/Sm on the catalytic
hydrosilylation has been investigated, and the results were summarized in Table 2.
The results listed in Table 2 indicated that both the amount of catalyst and the mole
ratio of Cp2TiCl2 /Sm have influence on the catalytic activity. The hydrosilylation

reaction couldn’t be conducted when only Cp2TiCl2 was used as catalyst (Entry 1,
Table 2). Low conversion was obtained when the reaction was conducted in the
presence of samarium (Entry 2, Table 2). When the amount of Cp2TiCl2 was 3 mol %
based on 1-octene, catalytic activity was increased along with the increasing amount
of samarium used from 1.5 mol % to 6 mol % (Entries 3-5, Table 2), however,
further increasing the amount of samarium used resulted in the decreasing of the
conversion (Entry 6, Table 2). When the amount of Cp2TiCl2 was 6 mol % based on
1-octene, conversion of 1-octene was decreased from 85.5 % to 65.9 % (Entry 4 vs
Entry 7, Table 2).
[Insert Table 2]
2.3 Influence of reaction temperature on Cp2TiCl2/Sm catalyzed hydrosilylation
The influence of reaction temperature on hydrosilylation had been investigated,
and the results were summarized in Table 3. It indicated that conversion of 1-octene
increased along with the reaction temperature raising from room temperature to
120 ℃. The reaction couldn’t conducted at room temperature (Entry 1, Table 3). 27.7%
conversion of 1-octene was obtained at 50 ℃, and the conversion was increasing
along with higher the reaction temperature. However, the best selectivity was
obtained when the reaction was conducted at 100 ℃ (Entry 6, Table 3).
[Insert Table 3]

2.4 Scope of the substrates examination
By using Cp2TiCl2 /Sm as a catalyst, the scope of the substrates for the
hydrosilylation was studied (Table 4). When Ph2SiH2 was used as hydrosilane, both
straight chain fatty and aromatic olefins could conducted hydrosilylation reaction
(Entries 1-3, Table 4), however, the addition of Ph2SiH2 with cyclohexene couldn’t be
conducted under the same conditions (Entry 4, Table 4). The steric hindrance of
internal olefin should result in the lower reactive activity of cyclohexene. When
(EtO)3SiH and Ph2MeSiH was used as hydrosilane, respectively, excellent conversion
of 1-octene was obtained (Entries 5-6, Table 4). No reaction occurs with Et3SiH as
hydrosilane (Entry 7, Table 4). It indicated that some silane -dependence was
observed for Cp2TiCl2 /Sm catalyzed hydrosilylation of olefins.
[Insert Table 4]
2.5 Cp2TiCl2/LiAlH4 catalyzed hydrosilylation of olefins
The hydrosilylation of olefins catalyzed with Cp2TiCl2/LiAlH4 was studied
(Table 5). 43.5% conversion of 1-octene was obtained by using LiAlH4 (10 mol % )
as catalyst at room temperature (Entry 1, Table 5). Improving the catalytic activity
can be obtained by using Cp2TiCl2/LiAlH4 as catalyst (Entries 2-7, Table 5). Among
the olefins tested, both straight chain and aromatic olefins showed higher reactive for
the hydrosilylation with diphenylsilane.

[Insert Table 5]
2.6 Mechanistic proposal
Related to the titanium-catalyzed hydrosilylation of olefins, two different
mechanisms were proposed (Scheme 2) [1(a)]. The influence of charging sequence on
the reaction had been investigated.
[Insert Scheme 2]
When the Cp2TiCl2/Sm was mixed with 1-octene and stirred at 100 ºC for 6 h,
and then hydrosilane was added and stirred for another 6 h, no product was detected,
while 71.5% conversion was obtained when the Cp2TiCl2/Sm was initially mixed with
diphenylsilane and stirred at 100 ºC for 6 h, then 1-octene was added and continued to
stirred for another 6 h. Therefore, it indicated that the formation of [Cp2Ti]-SiR3
through path (B) rather than the formation of olefin complex or alkyl complex
through path (A) as the intermediate was proposed. Furthermore, the influence of
TEMPO on the hydrosilylation by using Cp2TiCl2/Sm and Cp2TiCl2/LiAlH4 as
catalyst, respectively, had been investigated (Table 6). 76.8% conversion of 1-octene
was obtained when 0.5 mol % TEMPO was added to the reaction mixtures (Entry 1,
Table 6), and the reaction was completely suppressed when 3 mol % TEMPO was
added (Entry 3, Table 6). In contrast, TEMPO can produce some positive effect on the
hydrosilylation when Cp2TiCl2/LiAlH4 was used as catalyst (Entries 4-6, Table 6).

Thus a free radical mechanism was proposed for Cp2TiCl2/Sm catalyzed
hydrosilylation (Scheme 3), while coordination catalytic pathway was proposed for
Cp2TiCl2/LiAlH4 catalyzed hydrosilylation (Scheme 4). The hydrogenation products
may arise from direct transfer of H from an Si-H or Ti-H moity.
[Insert Scheme 3]
[Insert Scheme 4]
[Insert Table 6]
3. CONCLUSION
The hydrosilylation of olefins can be catalyzed by Cp2TiCl2/metal (metal = Mg,
Al, Zn, Sm, Fe, Mn, In, Co, Ni, etc.). And Cp2TiCl2/Sm exhibited excellent catalytic
activity as well as selectivity. The hydrosilylation of olefins can also be carried out by
using Cp2TiCl2/LiAlH4 as catalyst. The difference of Cp2TiCl2/Sm and
Cp2TiCl2/LiAlH4 catalyst system had been examined. Though some silane
-dependence was observed for both Cp2TiCl2 /Sm and Cp2TiCl2/LiAlH4 catalyzed
hydrosilylation of olefins, the reaction could be conducted under milder conditions by
using Cp2TiCl2/LiAlH4 as catalyst. The negative effect of TEMPO
(2,2,6,6-tetramethylpiperidine-1-oxyl) on the Cp2TiCl2/Sm catalyst system and some
postive effect on the Cp2TiCl2/LiAlH4 catalyst system, respectively, had been
observed. The free radical pathway of hydrosilylation of olefins catalyzed with
Cp2TiCl2/Sm was proposed, while the hydrosilylation of olefins through a
coordination pathway by using Cp2TiCl2/LiAlH4 as catalyst system.

4. EXPERIMENTAL
4.1 General information
Cp2TiCl2, zinc, aluminum, magnesium, iron, manganese, indium, cobalt,
samarium,
nickel
powder,
1-octene,
diphenylsilane,
TEMPO
(2,2,6,6-tetramethylpiperidine-1-oxyl), and other reagents were commercially
available and were used without further purification.
Gas Chromatography: Trace DSQ GC Column = DB-5 30 m×2.5 mm×0.25 μm,
split = 50:1, flow = 1 mL min-1 constant flow, inlet temperature = 260 ºC, column
temperature = 50 ºC (hold 1 min) then 15 ºC min-1 up to 260 ºC (hold 10 min). The
1
Supplemental Materials contains sample H and 13C NMR spectra of the known
products (Figures S 1 – S 10)
4.2 General procedure for the catalytic hydrosilylation of olefins with Cp2TiCl2/metal
Cp2TiCl2 and metal powder were placed into a 10 mL round-bottomed flask
equipped with a magnetic stir bar and flushed with nitrogen, and then olefin (4.0
mmol) and hydrosilane (4.4 mmol) were charged into the flask, and the resulting
mixture was stirred at desired temperature for desired time. At the end of the reaction,
the products were determined by GC/MS, and the conversion of alkene as well as the
selectivity of products was determined by GC.
4.3 General procedure for the catalytic hydrosilylation of olefins with

Cp2TiCl2/LiAlH4
Cp2TiCl2 and LiAlH4 were placed into a 10 mL round-bottomed flask equipped
with a magnetic stir bar and flushed with nitrogen, and then 1.0 mL diethyl ether was
added, the mixture was stirred for 30 min, then olefin (4.0 mmol) and hydrosilane (4.4
mmol) were charged into the flask, and the resulting mixture was stirred at room
temperature for 1 h. The products were determined by GC/MS, and the conversion of
alkene as well as the selectivity of products was determined by GC.
ACKNOWLEDGMENTS
This work was supported by Natural Science Foundation of Zhejiang Province
(LY18B020012) and Zhejiang Provincial Technologies R&D Program of China
(grant no. 2017C31105).
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SiHPh2
SiHPh2
SiHPh2
+
+
R
R
1
2
Cp2TiCl2/M or LiAlH4
+ Ph2SiH2
R
M= Sm, Mg, Al and Zn, etc.
R = C4H9, C6H13, C6H5
R
+
R
4
3
Scheme 1 Hydrosilylation of olefins catalyzed with Cp2TiCl2/M or LiAlH4
(B)
(A)
[M]-SiR3
[M]-H
R3Si
R3Si
[M]=[Cp2Ti]
[M]
[M]
SiR3
SiR3
H
H
SiR3
[M]
[M]
R3SiH
SiR3
R3SiH
Scheme 2 Proposed mechanism of titanium-catalyzed hydrosilylation of olefin
.
Cp2Ti(III)Cl
Cp2Ti(IV)Cl2
Sm
Sm(II)
Ph2SiH2
.
+ Ph2SiH
Cp2TiHCl
.
.
SiHPh2
+
Ph2SiH
R
R
Ph2SiH2
.
SiHPh2
+
Ph2SiH
R
Scheme 3 Proposal mechanism for Cp2TiCl2/Sm catalyzed hydrosilylation

Cp2TiCl2
Al-H
Cp2TiCl2
LiAlH4
[low-valent Ti]
R3SiH
[Ti-Al complex]
R'
R3Si
R'
[Cp2Ti]-SiR3
R'
[Al]-H
path 2
R3Si
or
path 1
SiR3
[Cp2Ti]
R'
R'
R3Si
H
R3SiH
[Al]
R'
R3SiH
SiR3
[Cp2Ti]
R'
Scheme 4 Proposal mechanism for Cp2TiCl2/LiAlH4 catalyzed hydrosilylation

Table 1 Hydrosilylation of 1-octene catalyzed with Cp2TiCl2/metal
Selectivity (%)
Conv.
(%)
Entry
Metal
1
2
/
/
/
/
/
/
/
/
/
3
4
/
/
/
/
/
/
/
/
/
1
2
3
4
5
6
7
8
9
Mg
Al
80.1
5.4
88.1
100
11.9
/
Zn
Sm
Fe
57.4
89.0
65.0
78.9
70.5
32.9
76.5
67.1
87.6
83.5
88.5
86.0
77.2
89.0
32.9
12.4
16.5
11.5
14.0
22.8
11.0
Mn
In
Co
Ni
Reaction conditions: 1-octene 4.0 mmol，Ph2SiH2 4.4 mmol， Cp2TiCl2 3 mol %，
Metal 6 mol %, 100 ℃，12h，

Table 2 Influence of mole ratio of Cp2TiCl2/Sm on the catalytic hydrosilylation
Conv.
(%)
/
Selectivity(%)
Cp2TiCl2(
Sm
Entry
mol%)
(mol%)
1
2
/
/
/
/
/
/
/
3
4
/
/
/
/
/
/
/
1
2
3
4
5
6
7
3
/
/
3
/
/
8.2
100
88.4
87.5
87.6
86.1
75.1
/
3
3
3
3
6
1.5
3
77.7
85.5
89.0
88.6
65.9
11.6
12.5
12.4
13.9
24.9
6
9
3
Reaction conditions: 1-octene 4.0 mmol，Ph2SiH2 4.4 mmol，100 ℃，12h

Table 3 Influence of reaction temperature on Cp2TiCl2/Sm catalyzed
hydrosilylation
Conv.
(%)
Selectivity (%)
Temp.
（℃）
rt
Entry
1
2
/
/
/
/
/
/
/
/
3
4
/
/
/
/
/
/
/
/
1
2
3
4
5
6
7
8
/
/
/
50
27.7
32.7
75.9
78.5
89.0
91.0
93.5
67.9
70.0
77.7
87.2
87.6
85.2
84.3
32.1
30.0
22.3
12.8
12.4
14.8
15.7
70
80
90
100
110
120
Reaction conditions: 1-octene 4.0 mmol，Ph2SiH2 4.4 mmol，Cp2TiCl2 3 mol %，Sm
6 mol %, 12h

Table 4 Substrates screened examination
Conv.
(%)
96.5
100
69.0
/
Selectivity (%)
Entry
Olefin
Silane
1
2
/
/
/
/
/
/
/
3
4
/
/
/
/
/
/
/
1a
2a
3
1-hexene
styrene
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
(EtO)3SiH
Ph2MeSiH
Et3SiH
89.8
73.5
82.5
/
10.2
26.5
17.5
/
1-dodecene
cyclohexene
1-octene
4
5
76.9
76.8
/
41.1
84.1
/
58.9
15.9
/
6
1-octene
7
1-octene
a Reaction temperature: 90 ℃
Reaction conditions: olefin 4.0 mmol，silane 4.4 mmol，Cp2TiCl2 3 mol %，Sm 6
mol %, 100 ℃, 12h

Table 5 Cp2TiCl2/LiAlH4 catalyzed hydrosilylation of olefins
Cp2TiCl2 LiAlH4
Conv.
(%)
43.5
44.0
84.4
92.3
99.2
100
45.7
100
/
Selectivity (%)
Silane
Entry
Olefin
(mol%)
(mol%)
10
4
1
2
/
/
/
/
/
/
/
/
/
/
/
/
3
4
/
/
/
/
/
/
/
1
2
/
1-octene
1-octene
1-octene
1-octene
1-octene
1-hexene
1-dodecene
styrene
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2MeSiH
(EtO)3SiH
Et3SiH
87.4
87.5
85.1
79.0
85.3
90.6
76.4
47.0
/
12.6
12.5
14.9
13.3
13.9
9.4
2
3
4
5
5
5
5
5
5
5
5
3
6
4
8
5
10
10
10
10
10
10
10
10
6
7
23.6
8
12.3 40.7
9
cyclohexene
1-octene
1-octene
1-octene
/
/
/
/
/
10
11
12
76.8
37.3
/
84.1
65.5
/
15.9
34.5
/
Reaction conditions: olefin 4.0 mmol，hydrosilane 4.4 mmol，Et2O 1.0 mL, rt, 1 h

Table 6 Influence of TEMPO on the catalytic hydrosilylation
Conv.
(%)
Selectivity (%)
TEMPO
(mol %)
0.5
Entry
Conditions
1
2
/
3
4
/
1
2
Cp2TiCl2 3
mol %，Sm 6
mol %,
76.8
73.8
84.9
85.0
15.1
15.0
2
/
/
3
100℃,12h
3
/
/
/
/
/
4
5
Cp2TiCl2 5
mol %，LiAlH4
10 mol %,
3
5
90.4
91.5
82.8
85.7
/
/
17.2
14.3
/
/
6a
10
97.1
88.1
/
11.9
/
r.t.,1h
Reaction conditions: 1-octene 4.0 mmol，Ph2SiH2 4.4 mmol，
a12h.

SiHPh2
SiHPh2
SiHPh2
+
+
R
R
1
2
Cp2TiCl2/M or LiAlH4
+ Ph2SiH2
R
M= Sm, Mg, Al and Zn, etc.
R = C4H9, C6H13, C6H5
R
+
R
4
3
Hydrosilylation of olefins catalyzed with Cp2TiCl2/M or LiAlH4