Siloxy-substituted tetramethylcyclopentadienyl and indenyl trichlorotitanium complexes for syndiospecific polymerization of styrene

Article abstract of DOI:10.1016/S0022-328X(98)00388-X

(η⁵-trimethylsiloxytetramethylcyclopentadienyl)- and (η⁵-2- trimethylsiloxyindenyl)trichloro titanium have been synthesized and characterized. Their catalytic behavior for the polymerization of styrene was studied in the presence of methylaluminoxane (MAO) as a cocatalyst. They show only low activity for styrene polymerization.

Full text of DOI:10.1016/S0022-328X(98)00388-X

Journal of Organometallic Chemistry 558 (1998) 231–233
Preliminary communication
Siloxy-substituted tetramethylcyclopentadienyl and indenyl
trichlorotitanium complexes for syndiospecific polymerization of
styrene
Gonglu Tian, Shansheng Xu, Yongqiang Zhang, Baiquan Wang, Xiuzhong Zhou *
Department of chemistry, Nankai Uni6ersity, Tianjin, 300071, China
Received 24 September 1997; received in revised form 16 December 1997
Abstract
(p5-trimethylsiloxytetramethylcyclopentadienyl)- and (p5-2- trimethylsiloxyindenyl)trichloro titanium have been synthesized and
characterized. Their catalytic behavior for the polymerization of styrene was studied in the presence of methylaluminoxane
(MAO) as a cocatalyst. They show only low activity for styrene polymerization. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Titanium; Polymerization; Syndiotactic polystyrene; Catalysts
1. Introduction
2. Results and discussion
Ishihara and coworkers discovered that syndiotactic
polystyrene (s-PS) could be produced with high stere-
oregularity and yield under conventional conditions
using CpTiCl3 activated with methylaluminoxane
(MAO) [1,2]. Since the initial discovery, several studies
on the effect of ligand substitution on polymerization
behavior have been reported [3–7]. In addition to the
well-known alkyl and aryl derivatives, mono-cyclopen-
tadienyltrichloride and trialkoxide derivatives of tita-
nium that contain functional ring substituents, such as
diphenylphosphinyl, N,N-dimethylamino and methyl-
thio, have also been prepared and investigated as cata-
lysts for styrene polymerization [3,6,8].
2,3,4,5-tetramethylcyclopent-2-enone was treated
with two equivalents of lithium diisopropylamide
(LDA), then reacted with two equivalents of
trimethylchlorosilane to afford 2-trimethylsiloxy-5-
trimethylsilyl-1,3,4,5-tetramethylcyclopentadiene (1) in
76% yield. 2-trimethylsiloxy substituted trimethylsilyl
indene (2) was prepared similarly from 2-indanone in
moderate yield.
We now report on the synthesis of trimethylsiloxy
substituted (tetramethylcyclopentadienyl)- and (in-
denyl)trichlorotitanium, and their catalytic activities to-
ward the polymerization of styrene with MAO as a
cocatalyst.
The reaction between 1 and TiCl4 was carried out at
both −78 and 0°C in toluene. Both attempts gave a
* Corresponding author. Fax +86 22 23508473.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00388-X

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G. Tian et al. / Journal of Organometallic Chemistry 558 (1998) 231–233
dark solid, which was insoluble in most solvents (e.g.
CHCl3, THF and acetone). When 1 was added in one
portion to TiCl4 in toluene at elevated temperature, the
corresponding titanium complex (3) was isolated in
33% yield.
siloxy group only caused decrease in activity for 3 and
4 compared with their unsubstituted analogues. Oxy-
gen–aluminum coordination may be responsible for the
low activity. It should be kept in mind that these
complexes act as ‘pre-catalyst’ and become active spe-
cies after treated with cocatalyst. The cocatalyst MAO,
as a Lewis-acid, may coordinate with oxygen atom of
siloxy group. The coordination suppresses the reso-
nance effect and enhances the inductive effect of the
siloxy group. As a result 3 and 4 show only low
activity. A similar result was observed previously when
some metallocene catalysts with functionally substituted
ligands were used for olefin polymerization [3,5,14].
(2-trimethylsiloxyindenyl)trichlorotitanium (4) was
prepared in a similar manner to the procedure for 3
except using CH2Cl2 as solvent. An attempt to synthe-
size 4 by the reaction of 2-trimethylsiloxyindene, after
treated with n-butyl lithium, with TiC4 · THF failed to
produce 4.
3. Experimental section
Reactions were carried out under an argon atmo-
sphere using standard schlenk techniques. Methylene
chloride was distilled under argon from P2O5. Diiso-
propylamine was distilled from CaH2. THF, hexane
and toluene were distilled under argon from sodium-
diphenyl Ketone. TiCl4 and Me3SiCl were distilled
prior to use. 1H NMR spectra were recorded on a
Bruker AC-200. Electron impact mass spectra were
obtained on a VG-7070EHF. 2,3,4,5-tetramethylcy-
clopent-2-enone [15], 2-indanone [16], IndTiCl3 [4],
(C5Me4H)TiCl3 [17] were prepared by literature
procedures.
The preparation of 3 and 4 is remarkable for it
represents a simple route to monocyclopentadienyltita-
nium trichloride with an oxygen atom directly bonded
to the C5 ring, although the yield is not very satisfac-
tory. In general, the reaction of an appropriate substi-
tuted trimethylsilylcyclopentadiene and titanium
tetrachloride is an efficient route to CpTiCl3 and substi-
tuted derivatives [9,10], and the yield is usually excel-
lent. The low yield of these two synthese may be
attributed to the interaction of TiCl4 with the sily enol
ether to yield Me3SiCl and a trichlorotitanium enol
ether [11].
3.1. Synthesis of 2-trimethylsiloxy-5-trimethylsilyl-
1,3,4,5-tetramethylcyclopentadiene (1)
To a solution of 48.8 ml of diisopropylamine (0.345
mol) in 120 ml of THF was added 208 ml of n-BuLi
(0.342 mol, 1.64 N in hexane). This solution was stirred
for 0.5 h at 0°C. To this solution was added 22.8 g of
2,3,4,5-tetramethylcyclopent-2-enone (0.164 mol) in 30
ml of THF at 0°C. The reaction mixture was then
refluxed for 20 h. Then diisopropylamine and solvent
were removed under vacuum, leaving an orange semi-
solid. THF (200 ml) was added, the resulting suspen-
sion was cooled to 0°C, and 62 ml of Me3SiCl (0.490
mol) was quickly added. The resulting suspension was
allowed to warm to room temperature and stirred for 3
h, then refluxed for 3 h. The resulting suspension was
filtered and washed with two portions of ether. The
solvent of filtrate was removed to produce a sticky red
oil. Distillation at 72–78°C/0.3 mmHg gave 35.0 g of 1
3 and 4 are stable in the solid state when stored at
−20°C in an argon atmosphere, but they decompose
gradually on standing at room temperature.
When 4-MAO was used to polymerize styrene, it
exhibited low activities (0.11×107 gPS/(molTi mol
styrene h)) and low stereoselectivity (ca.70%). The cata-
lyst 3-MAO had almost no activity for styrene polymer-
ization. It did not produce a sufficient amount of
polymer for characterization. In comparison, their un-
substituted analogues, IndTiCl3 and C5Me4HTiCl3, ex-
hibited high activities (3.2×107 and 0.37×107
gPS/(molTi mol styrene h) respectively) and high
stereoselectivity (\91%).
Zambelli and coworkers considered that the syndio-
tactic-specific polymerization of styrene might be an
‘electrophilic’ polyinsertion reaction at the metal center,
suggesting that titanium compounds with metal centers
rich in electron density would be more effective cata-
lysts [12,13]. Although trimethylsiloxy substituent has
electron-releasing properties, the addition of trimethyl-
1
(76%) as a yellow oil, which was reasonably pure by H
1
NMR and was used without further purification. H
NMR (CDCl3): l 1.76 (s, 3H, CH3), 1.71 (s, 6H, CH3),
1.10 (s, 3H, CH3), 0.18 (s, OSiMe3), −0.12 (s, 9H,
SiMe3).

G. Tian et al. / Journal of Organometallic Chemistry 558 (1998) 231–233
233
3.2. Synthesis of 1-trimethylsilyl-2-trimethyl-
siloxyindene (2)
as the solvent. Styrene was distilled from calcium hy-
dride and stored at −20°C under argon in darkness.
Toluene (50 ml), styrene (5.00 ml, 4.54 g, 43.6 mmol)
and MAO (6.6 ml, 10 wt.% in toluene from Aldrich),
and the catalysts (25 mmol, 1 ml of a 2.5 mM solution)
were injected into the flask. The polymerizations were
performed at 50°C for 30 min periods. After this time
the polymerizations were terminated by the addition of
100 ml of 10% HCl in methanol. The precipitated
polymer was washed three times each with 50 ml of
methanol, and dried in vacuum to a constant weight.
The polymer was extracted with refluxing 2-butanone
for 12 h in order to determine the S-PS portion of the
obtained polymer.
2 was prepared in a manner analogous to the proce-
dure for 1. 2-indanone (10.0 g, 0.075 mol) was treated
with LDA (0.165 mol), then reacted with Me3SiCl
(0.236 mol) to afford 2 (7.2 g, 37%) as a yellow oil. b.p.
1
76–82°C/1 mmHg. H NMR (CDCl3): l 7.4–7.0 (m,
4H, arom), 5.75 (s, 1H, sp2, 2-position), 3.23 (s, 1H, sp3,
1-position), 0.30 (s, 9H, OSiMe3), −0.05 (s, 9H,
SiMe3).
3.3. Synthesis of (1-trimethylsiloxy-2,3,4,5-tetramethyl-
cyclopentadienyl)trichlorotitanium (3)
A solution of 1 (12.9 g, 45.6 mmol) in 20 ml of
toluene was added in one portion to a solution of TiCl4
(5.0 ml, 45.6 mmol) in 100 ml of toluene at 40°C. The
reaction mixture was allowed to cool to room tempera-
ture and stirred overnight. The resulting suspension was
passed through a Celite plug. After removal of the
solvent under vacuum, the dark red residue was ex-
tracted with 50 ml of hexane/CH2Cl2=1:1. The ex-
tracts was filtered, concentrated under reduced pressure
and cooled to −20°C, affording red needle crystals of
Acknowledgements
We are grateful to the National Science Foundation,
China Petro-Chemical Corporation and State Commis-
sion of Science and Technology of the P.R. China for
financial support of this work.
References
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3 (5.4 g, 33%). H NMR (CDCl3): l 2.34 (s, 6H, CH3),
2.28 (s, 6H, CH3), 0.30 (s, 9H, SiMe3). MS (m/e, %
intensity), 209 (100, M-3Cl-Ti+), 73 (53, SiMe3+).
Anal. Found: C, 39.41; H, 5.21. C12H2Cl3OSiTi. Calc.:
C, 39.64; H, 5.82%.
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A solution of 2 (3.5 g, 12.6 mmol) in 5 ml of CH2Cl2
was added in one portion to a solution of TiCl4 (1.4 ml,
12.6 mmol) in 20 ml of CH2Cl2 at 40°C. The reaction
mixture was stirred overnight at room temperature. The
solvent was removed under vacuum. The residue was
extracted in 40 ml of hexane/CH2Cl2=1:1, passed
through a Celite plug, concentrated and stored at −
20°C, affording dark red needle crystals of 4 (1.25 g,
28%). 1H NMR (CDCl3) l 7.64 (m, 2H, arom), 7.42 (m,
2H, arom), 6.50 (s, 2H, 1- and 3-positions), 0.42 (s, 9H,
OSiMe3). MS (m/e, % intensity) 229 (100, M-3Cl-Ti+),
73 (20, SiMe3). Anal. Found: C, 40.17; H, 4.28.
C12H2Cl3OSiTi. Calc.: C, 40.31; H, 4.23%.
3.5. Polymerization studies
Styrene polymerizations were carried out in 250 ml
schlenk flask with magnetic stirring and using toluene
.