Styrene polymerization with half-sandwich titanium complexes bearing pendent alkenyl groups: From atactic to syndiotactic

Article abstract of DOI:10.1016/j.molcata.2006.05.011

A new series of substituted half-sandwich titanium complexes bearing bridged alkenyl groups [η⁵-C₅H₄-(bridge)-(alkenyl)] TiCl₃ have been synthesized and characterized. All the titanium complexes display considerable catalytic activity towards the polymerization of styrene in the presence of methylaluminoxane (MAO). Bridging unit between the cyclopentadienyl moiety and the allyl groups plays a crucial role in reactivity and stereoselectivity of styrene polymerization. By modification of the bridging unit, the syndioselectivity of the polymer can be tailor-made, providing a new guideline to design catalyst for polymers having desired properties.

Full text of DOI:10.1016/j.molcata.2006.05.011

Journal of Molecular Catalysis A: Chemical 258 (2006) 139–145
Styrene polymerization with half-sandwich titanium complexes bearing
pendent alkenyl groups: From atactic to syndiotactic
Chen Wang, Rucheng Liu, Jiling Huang∗, Wei Xiao
Laboratory of Organometallic Chemistry, Mailbox 310, East China University of Science and Technology, Shanghai 200237, PR China
Received 7 March 2006; received in revised form 2 May 2006; accepted 2 May 2006
Available online 23 June 2006
Abstract
A new series of substituted half-sandwich titanium complexes bearing bridged alkenyl groups [η5-C5H4-(bridge)-(alkenyl)]TiCl3 have been
synthesized and characterized. All the titanium complexes display considerable catalytic activity towards the polymerization of styrene in the
presence of methylaluminoxane (MAO). Bridging unit between the cyclopentadienyl moiety and the allyl groups plays a crucial role in reactivity
and stereoselectivity of styrene polymerization. By modification of the bridging unit, the syndioselectivity of the polymer can be tailor-made,
providing a new guideline to design catalyst for polymers having desired properties.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Alkenyl; Atactic; Syndiotactic; Polystyrene
1. Introduction
Recently, the use of ligands substituted by weaker donors has
focused attention on olefin polymerization [11,12]. Hessen [13]
reported that titanium complexes with an arene-pendant Cp lig-
and could selectively trimerize ethylene with high activity. The
arene-pendant moiety is likely to exhibit hemilabile behavior
by η6-coordination. Chien [14] demonstrated that the aromatic
substituent also plays a very important role in styrene polymer-
ization. We previously reported that introduction of an alkenyl
group into the Cp ring can remarkably influence the catalyst’s
activity [15].
As a part of study of the influence of double bond on the
styrene polymerization, herein, we report a new series of tita-
nium complexes bearing bridged alkenyl groups, and investigate
the relationship between the structure and their catalytic behav-
ior. By modification of the bridging unit, the syndioselectivity
of the polymer can be tailor-made, providing a new guideline to
design catalyst for polymers having desired properties.
Design and synthesis for efficient transition metal catalyst
towards precisely controlled polymer properties have attracted
considerable attention in the field of organometallic chem-
istry [1,2]. Since Ishihara and coworkers succeeded in the
synthesis of syndiotactic polystyrene (s-PS) in 1985 [3,4]
based on titanium compounds and methylaluminoxane (MAO),
the cyclopentadienyl ring of the titanium complexes Cp’TiX3
(Cp’ = substituted or unsubstituted cyclopentadienyl (Cp) or
indenyl ligand; X = halogen, alkoxy, phenoxy) has experienced
a wide structure variation in the search for catalysts with higher
activity and stereoselectivity [5–9].
It is found that the introduction of electron-donating groups
to the Cp ring usually leads to catalysts with higher activity
due to the long-term stability of the active species and a lower
probability of chain termination [7]. In contrast, introduction of
a heteroatom containing substituent leads to a dramatic reduc-
tion of polymerization activity. It is believed that the pendant
heteroatom intramolecularly coordinates to the active center
reducing its electrophilicity, and sterically hinders the coordi-
nation and insertion of the styrene molecule [10,11].
2. Results and discussion
2.1. Synthesis of catalyst precursors
Thetitaniumcomplexesusedinthisstudycanallbedescribed
by the general formula [η5-C5H4-(bridge)-(alkenyl)]TiCl3
(alkenyl allyl or butenyl). The routes employed for the synthe-
∗
Corresponding author. Tel.: +86 21 5428 2375; fax: +86 21 5428 2375.
E-mail address: qianling@online.sh.cn (J. Huang).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.05.011

140
C. Wang et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 139–145
Scheme 1.
As shown in Table 1, all the catalysts exhibited considerable
activities in styrene polymerization. The activities of the cata-
lysts and the syndiotacticity of the polymers located in a wide
range of distribution.
2.2.1. Effect of the bridge between the cyclopentadienyl
and allyl groups
To probe the structure–performance relationship in the poly-
merization, the effect of the bridging unit was investigated. We
Scheme 2.
sis of the [η5-C5H4-(bridge)-(alkenyl)]TiCl3 compounds were
summarized in Schemes 1–3.
Cyclopentadienyl ligands with [-(bridge)-(alkenyl)] sub-
stituents were readily accessible from the reaction of 6,6-
dialkylfulvenes [16,17] with the appropriate alkenyl magnesium
bromide [18] or methyllithium. The resulting addition products
reacted with trimethylsilyl chloride to afford the correspond-
ing [C5H4-(bridge)-(alkenyl)]SiMe3 as yellow oils, which were
used for subsequent reactions.
The various (cyclopentadienyl) titanium trichlorides were
readily prepared via Me3SiCl elimination upon reaction of the
appropriate (trimethylsilyl) cyclopentadienyl intermediates with
TiCl4. All titanium compounds were characterized by 1H NMR,
elemental analysis, MS and IR.
Table 1
Polymerization of styrene catalyzed by [η5-C5H4-(bridge)-(alkenyl)]TiCl3/
MAO systemsa
Run
Catalyst
Al/Ti
(mol/mol)
Activityb
(×105)
s-PSc (%)
1
2
3
1 (R1 = R2 = Me)
2000
4000
8000
37.0
52.4
63.8
88.3
79.5
81.3
4
5
6
2 (R1 = Me, R2 = Et)
3 (R1 = R2 = Et)
4
2000
4000
8000
4.0
4.8
16.0
45.2
55.9
66.6
7
8
9
2000
4000
8000
2.6
4.6
3.2
13.9
9.5
5.8
2.2. Polymerization results
10
11
12
2000
4000
8000
23.1
30.2
31.9
89.8
94.0
81.5
The procedure of polymerization reported by Kaminsky [19]
was used in our experiment. Constant amounts of MAO were
used to ensure the same scavenger effect in each polymerization
[19]. All polymerizations were carried out for 30 min and the
results are summarized in Table 1.
13
14
15
5 (R1 = R2 = cyclo-C5H10
6 (R1 = R2 = H)
7 (CpSiMe3)
)
2000
4000
8000
17.9
27.7
13.1
96.4
99.9
85.6
16
17
18
2000
4000
8000
108.3
173.1
310.4
86.4
92.8
89.0
19
20
21
2000
4000
8000
35.2
89.8
122.3
91.3
84.3
75.5
22
23
24
8 (R1 = Me, R2 = Ph)
2000
4000
8000
5.14
2.34
0.73
8.5
2.9
6.2
a
Polymerization conditions: 50 ◦C for 0.5 h; styrene = 4 ml; MAO = 6.6 ml
[MAO] = 1.53M; Vtotal = 12 ml.
b
g PS/(mol Ti·mol S·h).
c
(g of 2-butanone insoluble polymer)/(g of bulk polymer).
Scheme 3.

C. Wang et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 139–145
141
found that, with the increase of steric bulkiness of the sub-
stituents on the tertiary carbon between the Cp and allyl moiety,
the activities of the catalysts reduced dramatically and the pro-
portion of atactic polystyrene increased significantly.
The catalyst with unsubstituted CH2 bridge (complex 6
(R1 R2 H)) between Cp ligand and the allyl moiety exhibited
extraordinary high activity, which was about 5 times higher than
that of 1 at Al/Ti ratio 8000. We early reported that the activ-
ity of complex 6/MAO system was even higher than that of
CpTiCl3/MAO system [15], which implied that the double bond
of complex 6 did not coordinate to the active center and could
not affect the coordination and insertion of monomer.
When CH2 bridge between Cp ligand and the allyl moiety
was substituted by alkyl groups (Me, Et, etc.), the activities of
the catalysts reduced significantly. Intramolecular coordination
might rationalize the phenomena.
The evidence is the variation of the chemical shifts of the
terminal protons attached to the double bond. According to 1H
NMR, if the double bond is near the titanium atom, the highly
electrophilic titanium center will attract the electrons of double
bond towards itself and away from the spinning nucleus. This
deshielding effect lead to the NMR signal occurring at a lower
magnetic field. Table 2 summarised the chemical shifts of the
terminal protons attached to the double bond.
It shows that, with the increase of steric bulkness of the sub-
stituents, the chemical shifts slightly move to downfield in the
order 1 < 2 < 3. This implies that the tendency of coordination
of the double bond to the titanium center is strengthened. As a
result, the catalytic activity of the complex and syndiotactivity
of the polymer should reduce in the order: 1 > 2 > 3. As shown
in Table 2, the experiment result is consistent perfectly with this
presumption. The influence of the substituents on the tertiary
carbon is so remarkable that the activity of complex 3 is nearly
twenty times lower than that of complex 1, and the polymer
produced by 3/MAO system is nearly atactic polystyrene.
Unexpectedly, the chemical shift of complex 5 bearing
C(cyclo-C5H10) bridge (Table 2) is even smaller in value than
that of complex 1. This implies that the interaction between the
double bond and the titanium center in complex 5 is weaker than
that of complex 1, because the rigid 6-member ring skelecton
of cyclohexane limit the double bond coordinate to the titanium
center. As a result, the polystyrene catalyzed by 5/MAO exhib-
ited the highest syndiotacticity (99.9%, Table 1, run 14).
In our early research, we reported another evidence that the
increasing steric bulkiness of the substituents on the tertiary
carbon between the Cp ligand and arene moiety forced the
arene group move to titanium center. In the preparaion of o-
MeO-containing benzyl-substituted cyclopentadienyl titanium
complexes, when the C1 bridge is substituted by ethyl or big-
ger group, the reaction always gives titanoxacycle complexes
[20]. Hessen also indicated that disubstituted C1 bridge between
the cyclopentadienyl and arene moieties in [η5-C5H3R-(bridge)-
Ar]TiCl3 was much more prone to arene coordination, which
was the prerequisite for ethylene trimerization [13].
On the basis of experiment result, we propose that, with
the increase of steric bulkiness of the substituents on the ter-
tiary carbon between the Cp and allyl moiety, the tendency of
intramolecular coordination of the double bond to the titanium
center is increased.
The intramolecular coordination, according to the mecha-
nism supposed by Mahanthappa and Waymouth [21], Jo et al.
[22], Nifant’ev et al. [23], Cavallo and co-workers [24,25], limits
the optimization of the chirality of titanium center and disorder
the styrene monomer inserting at a syn position, leading to a
result that the atactic proportion is increased in the polymeriza-
tion.
There might be an intramolecular competition of coordi-
nation between the phenyl moiety and the alkenyl moiety in
catalyst 8/MAO. The 8/MAO system displayed significantly
lower polymerization activity and afforded predominantly atac-
tic polystyrene, presumably due to stronger arene coordination
to the titanium center [26].
To investigate the intramolecular coordination further, we
prolong the chain length between the double bond and the
Cp moiety. Complex 4 was synthesized and compared with its
C(Me, Me) bridge analogue (complex 1). The activity of com-
plex 4 is relatively slower than that of complex 1. Although the
prolonged double bond is less prone to coordination, the effect
of steric hindrance is also increased remarkably.
2.2.2. Effect of substituents on the cyclopentadienyl group
Theeffectoftheattachmentofsubstituentsonthecyclopenta-
dienyl moiety was probed by the catalytic behavior of the precat-
alyst CH2 CHCH2C(CH3)2Cp(SiMe3)TiCl3. As expected, the
activity of 7/MAO can reach 1.22 × 107 g PS/(mol Ti·mol S·h)
which is remarkably higher than that of 1/MAO under the same
condition. Obviously, the electron-donating trimethylsilyl group
of 7 increases the electron density on the titanium center, and
better stabilizes the electrophilic titanium center. As a result, the
concentration of active species increases, which leads to higher
activity. Furthermore, chaintransfervia␤-Heliminationislikely
to be suppressed, because of the stronger electron-donating abil-
ity of the substituent Cp ligand as compared to unsubstituent Cp
ligand [24,25].
Table 2
The chemical shifts of the terminal protons attached to the double bond
Complex
Chemical shift of
Ha, Hb (δ, ppm)
Activitya (×105) s-PSa (%)
1 (R1 = Me, R2 = Me)
2 (R1 = Me, R2 = Et)
3 (R1 = Et, R2 = Et)
5 [R1 = R2 = (cyclo-
C5H10)]
5.06–4.94
5.08–5.00
5.10–5.07
4.97–4.89
63.8
16.0
3.2
81.3
66.6
5.8
13.1
85.6
2.2.3. The influence of temperature
Generally, the activities of complexes, which contain
intramolecular coordination groups, increase with the tempera-
a
Under the same condition. See also Table 1.

142
C. Wang et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 139–145
Fig. 3. First and second heatings of a DSC thermogram of an s-PS sample
produced with 2/MAO.
Fig. 1. Dependence of the activity on polymerization temperatures. Polymer-
ization conditions: catalyst = 5 ␮mol; Al/Ti = 2000; TP = 0.5 h; styrene = 4 ml;
MAO = 6.6 ml; [MAO] = 1.53 M; Vtotal = 12 ml.
2.2.4. Polymer analyses
Thermal property of s-PS produced by 1/MAO and 2/MAO
were measured using differential scanning calorimetry (DSC).
A melting point of 267 ◦C was observed for s-PS produced by
complex 1 (Table 1, run 1). However, s-PS produced by 2/MAO
(Table 1, run 4) shows a more complex behavior. A melting point
of 266 ◦C was observed during the first heating, but two melting
points (256 and 265 ◦C) were observed during the second heat-
ing (Fig. 3). Kaminsky and co-workers have reported that the
s-PS produced by BzCpTiCl3/MAO have three melting points
during the second heating [19]. We presume this may be owing
to different crystalline polymorphic structure of s-PS produced
by [η5-C5H4-(bridge)-(alkenyl)]TiCl3/MAO catalytic systems.
ture, because the intramolecular coordination is less tight at high
temperatures. The dependence of activity and syndiotacticity on
thetemperaturesissummarizedin Figs. 1and2. Withintherange
of 25–75 ◦C, the activities of the most of catalysts increase with
the temperature, which is consistent with the [η5-C5H4-(bridge)-
Ar]TiCl3 /MAO system reported by Zambelli and co-workers
[26]. It was noteworthy pointing out that complex 7 exhibited
the highest activity at 75 ◦C. We presume that, the tendency of
the intramolecular coordination of the double bond to the tita-
nium center is weakened at higher temperatures.
At 100 ◦C, the activity of some of the catalysts (5, 7) some-
what decreased. This decrease is attributed to decomposition of
the catalyst or to deactivation of the active centers. Basically,
all the complexes exhibited remarkable thermal stability at high
temperatures.
2.2.5. Combination effects of ligand and polymerization
condition
Three major parameters in the styrene polymerization: activ-
ity, selectivity, and stability can be remarkably influenced by
the substituents on the key positions (backbone, cyclopentadi-
enyl, and alkene). Combined with the polymerization condition,
the styrene polymerization can be adjusted within syndiotactic
and atactic polymerization. The syndiotactic proportion range
from 0–99.9% (Fig. 2). Catalyst 8 afforded atactic polystyrene,
whereas catalyst 5 afforded syndiotactic polystyrene (99.9%).
Other catalysts exhibited the behavior of transition states. These
adjustable results provided a possibility that the polymer can
be tailor-made, providing a new guideline to design catalyst for
polymers having desired properties.
3. Experimental part
3.1. Materials and general procedures
All manipulations were carried out under a dry argon
atmosphere using standard Schlenk techniques. Solvents were
purified by distillation over sodium benzophenone (diethyl
ether, tetrahydrofuran(THF), toluene and n-hexane) and P2O5
(dichloromethane). MAO was produced by Witco GmbH.
Styrene was purified by washing several times with dilute NaOH
solution, dried over anhydrous CaCl2, vacuum distillation from
Fig. 2. Dependence of the syndiotacticity on polymerization temperatures. a(g
of 2-butanone insoluble polymer)/(g of bulk polymer); polymerization condi-
tions: catalyst = 5 ␮mol; Al/Ti = 2000; TP = 0.5 h; styrene = 4 ml; MAO = 6.6 ml;
[MAO] = 1.53 M; Vtotal = 12 ml.

C. Wang et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 139–145
143
CaH2 and stored at −20 ◦C in darkness. Complex 6 was synthe-
sized according to the literature [15].
1050 s, 1000 m, 700 s. Anal. calc. for C11H15Cl3Ti: C, 43.82;H,
5.01; found C, 43.85; H, 5.29.
Mass spectra were measured on an HP5989A spectrometer.
IR spectra were recorded on a Nicolet FTIR 5SXC spectrom-
eter. H NMRwas measured on a Brucker AVANCE-500 Hz
3.3.2. Synthesis of complex 2
1
3.3.2.1. Synthesis of CH2 CHCH2C(CH3) (C2H5) CpSiMe3.
To the solution of CH2 CHCH2MgCl (58 mmol) in 100 ml of
diethyl ether, was added dropwise 7 g (58 mmol) of 6-methyl-
6-ethylfulene in 10 ml of diethyl ether. The mixture was stirred
overnight, and 6.5 g (60 mmol) of Me3SiCl in 20 ml of THF was
slowly added. The reaction mixture was stirred for 4 h. Subse-
quently, the mixture was poured into ice water and extracted
with petroleum. The organic phase was dried over magnesium
sulphate. The volatiles were removed in vacuo, and the residue
was distilled at 51–52 ◦C/10 Pa to give a yellow oil. Yield: 8.7 g,
62.0%. 1H NMR (δ, ppm, CDCl3): 6.59 (d, J = 4.8 Hz, 1H,
Cp–H), 6.47 (d, J = 4.8 Hz, 1H, Cp–H), 6.08 (s, 1H, Cp–H),
5.76–5.68 (m, 1H, CH ), 5.04–4.98 (m, 2H, CH2 ), 3.25 (s,
1H, Cp–H), 2.35–2.21 (m, 2H, CH2), 1.63–1.48 (m, 2H, CH2),
1.13 (s, 3H, CH3), 0.79–0.74 (m, 3H, CH3), 0.18–0 (m, 9H,
SiMe3).
spectrometer using tetramethylsilane (TMS) as an internal
standard.
Elemental analyses were performed on an EA-1106
spectrometer. DSC was performed on a TA DSC 2910. The
samples (10 mg) were heated to 330 ◦C, cooled at 5 ◦C/min
to 30 ◦C, and heated again to 330 ◦C at a heating rate of
20 ◦C/min.
3.2. Polymerization procedure
Polymerization was conducted in small ampoules heated
under vacuum and flushed with argon several times. Styrene,
toluene, and MAO were sequentially injected, and the catalyst
precursor in toluene was then added. The bottle was immediately
placed in an oil bath at the desired polymerization temperature.
After 30 min, the polymerization was quenched with 10% HCl
in ethanol, filtered, and dried under vacuum at 80 ◦C for 24 h
to a constant weight. The syndiotactivity of s-PS was calculated
according to the equation: s-PS(%) = [(g of 2-butanone insoluble
polymer)/(g of bulk polymer)] × 100.
3.3.2.2. Synthesis of CH2 CHCH2C (CH3) (C2H5) Cp TiCl3
(2). To the solution of 1.1 ml (10 mmol) of TiCl4 in 10 ml of
CH2Cl2 was added dropwise 2 g (8.5 mmol) of CH2 CHCH2C
(CH3) (C2H5) CpSiMe3 in 30 ml CH2Cl2. The colour changed to
dark-red. The mixture was stirred overnight and the solvent was
removed in vacuo to give a dark-red oil which solidified after 1
day. Recrystallization in hexane afforded bright brown crystals.
3.3. Synthesis of complexes
1
3.3.1. Synthesis of complex 1
Yield: 1.113 g, 41.5%. H NMR (δ, ppm, CDCl3): 7.04–7.02
3.3.1.1. Synthesis of CH2 CHCH2C(CH3)2CpSiMe3. To the
solution of CH2 CHCH2MgCl (94 mmol) in 100 ml of diethyl
ether,was added dropwise 10.1 g (94 mmol) of dimethylfu-
lene. The mixture was stirred overnight, and 10.2 g (94 mmol)
Me3SiCl in 50 ml of THF was slowly added. The reaction mix-
ture was stirred for 4 h. Subsequently, the mixture was poured
into ice water and extracted with petroleum. The organic phase
was dried over magnesium sulphate. The volatiles were removed
in vacuo, and the residue was distilled at 48 ◦C/9 Pa to give a yel-
low oil. Yield 10 g, 48.4%. 1H NMR (δ, ppm, CDCl3): 6.61 (d,
J = 4.8 Hz, 1H, Cp–H), 6.45 (d, J = 4.8 Hz, 1H, Cp–H), 6.06 (s,
1H, Cp–H), 5.76–5.64 (m, 1H, CH ), 5.01–4.96 (m, 2H, CH2 ),
3.24 (s, 1H, Cp–H), 2.26–2.21 (m, 2H, CH2), 1.16 (s, 6H, CH3),
0.16–0.05 (m, 9H, SiMe3).
(m, 2H, Cp–H), 6.91–6.88 (m, 2H, Cp–H), 5.67–5.59 (m, 1H,
CH ), 5.08–5.00 (m, 2H, CH2 ), 2.46 (d, J = 7.3 Hz, 2H, CH2),
1.76–1.71 (m, 2H, CH2), 1.40 (s, 3H, CH3), 0.77 (m, 3H, CH3).
EIMS (m/e): 273 (M+–CH2 CHCH2, 11), 237
(M+–CH2 CHCH2-HCl, 100), 238 (M+–CH2 CHCH2-
Cl, 23). IR (KBr, cm−1): 2890 s, 1640 m, 1380 m, 1050 s,
1000 m, 890 s, 700 s. Anal. calc. for C12H17Cl3Ti: C, 45.68; H,
5.43; found C, 45.98; H, 5.65.
3.3.3. Synthesis of complex 3
3.3.3.1. Synthesis of CH2 CHCH2C (C2H5)2CpSiMe3. To the
suspension of CH2 CHCH2MgCl (60 mmol) in 100 ml of
diethyl ether was added dropwise 7 g (60 mmol) of diethylfu-
lene. The mixture was stirred overnight, and 6.5 g (60 mmol) of
Me3SiCl in 20 ml of THF was slowly added. The reaction mix-
ture was stirred for 4 h. Subsequently, the mixture was poured
into ice water and extracted with petroleum. The organic phase
was dried over magnesium sulphate. The volatiles were removed
in vacuo, and the residue was distilled at 51–52 ◦C/10 Pa to give
3.3.1.2. Synthesis of CH2 CHCH2C(CH3)2CpTiCl3 (1). To
the solution of 1 ml (9 mmol) of TiCl4 was added dropwise 2 g
(9 mmol) CH2 CHCH2C(CH3)2CpSiMe3 in 30 ml of CH2Cl2.
The colour changed to dark red. The mixture was stirred
overnight and the solvent was removed in vacuo to give a
dark-red oil which solidified after 1 day. Recrystallization in
hexane afforded bright yellow crystals. Yield: 1.59 g, 58.4%.
1H NMR (δ, ppm, CDCl3): 7.02 (t, J = 2.7 Hz, 2H, Cp–H),
6.89 (t, J = 2.7 Hz, 2H, Cp–H), 5.63–5.54 (m, 1H, CH ),
5.06–4.94 (m, 2H, CH2 ), 2.30 (d, J = 7.2 Hz, 2H, CH2), 1.43
(s, 6H, CH3). EIMS (m/e): 259 (M+–CH2 CHCH2, 18), 223
(M+–CH2 CHCH2–HCl, 100), 224 (M+–CH2 CHCH2–Cl,
19). IR (KBr, cm−1): 3100 m, 3080 m, 2990 s, 1640 m, 1480 m,
1
a yellow oil. Yield 9.1 g, 61.1%. H NMR (δ, ppm, CDCl3):
6.56 (d, J = 4.8 Hz, 1H, Cp–H), 6.47–6.4 6 (m, 1H, Cp–H), 6.08
(d, J = 1.2 Hz, 1H, Cp–H), 5.72–5.64 (m, 1H, CH ), 5.06–4.97
(m, 2H, CH2 ), 3.23 (s, 1H, Cp–H), 2.31–2.28 (m, 2H, CH2),
1.56–1.50 (m, 4H, CH2), 0.74–0.69 (m, 6H, CH3), 0.17–0 (m,
9H, SiMe3).
3.3.3.2. Synthesis of CH2 CHCH2C (C2H5)2 CpTiCl3 (3). To
the solution of 1 ml (9 mmol) of TiCl4 in10 ml of CH2Cl2

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C. Wang et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 139–145
69–85 ◦C/20 Pato giveayellowoil. Yield 7.2 g, 40.5%. 1HNMR
(δ, ppm, CDCl3): 6.58–6.55 (m, 1H, Cp–H), 6.46–6.4 4 (m, 1H,
Cp–H), 6.11 (s, 1H, Cp–H), 5.67–5.59 (m, 1H, CH ), 4.97–4.92
(m, 2H, CH2 ), 3.26 (s, 1H, Cp–H), 2.21 (d, J = 7.2 Hz, 2H,
CH2), 1.52–1.35 (m, 10H, CH2), 0.17–0 (m, 9H, SiMe3).
was added dropwise 2 g (8.1 mmol) of CH2 CHCH2C (C2H5)2
CpSiMe3 in 30 ml CH2Cl2. The colour changed to dark-red. The
mixture was stirred overnight and the solvent was removed in
vacuo to give a dark-red oil which solidified after 1 day. Recrys-
tallization in hexane afforded bright yellow crystals. Yield:
1.0 g, 38%. 1H NMR (δ, ppm, CDCl3): 7.06 (t, J = 2.7 Hz, 2H,
Cp–H), 6.91 (t, J = 2.7 Hz, 2H, Cp–H), 5.81–5.73 (m, 1H, CH ),
5.10–5.07 (m, 2H, CH2 ), 2.53 (d, J = 7.3 Hz, 2H, CH2), 1.81
(q, J = 7.5, 4H, CH2), 0.86 (t, J = 7.5, 6H, CH3). EIMS (m/e):
287 (M+–CH2 CHCH2, 8), 251 (M+–CH2 CHCH2–HCl, 100),
252 (M+–CH2 CHCH2–Cl, 18). IR (KBr, cm−1): 2890 s,
1640 m, 1380 m, 1050 s, 1000 m, 920 s, 700 s. Anal. calc. for
C13H19Cl3Ti: C, 47.38; H, 5.81; found C, 47.44; H, 6.10.
3.3.5.2. Synthesis of CH2 CHCH2C (cyclo-C5H10) CpTiCl3
(5). To the solution of 0.72 ml (4.2 mmol) of TiCl4 in 10 ml of
CH2Cl2 was added dropwise 1 g (3.8 mmol) of CH2 CHCH2C
(cyclo-C5H10) CpSiMe3 in 10 ml of CH2Cl2. The colour
changed to dark red. The mixture was stirred overnight and
the solvent was removed in vacuo to give a dark-red oil which
solidified after 1 day. Recrystallization in hexane afforded
bright yellow crystals. Yield: 29 mg, 40.8%. 1H NMR (δ, ppm,
CDCl3): 7.01 (t, J = 2.7 Hz, 2H, Cp–H), 6.88 (t, J = 2.7 Hz,
2H, Cp–H), 5.42–5.34 (m, 1H, CH ), 4.97 (m, 1H, CH2 ),
4.89 (m, 1H, CH2 ), 2.44 (d, J = 7.4 Hz, 2H, CH2), 1.99–1.22
(m, 10H, CH2). EIMS (m/e): 299 (M+–CH2 CHCH2, 7), 263
(M+–CH2 CHCH2–HCl, 100). IR (KBr, cm−1): 2890 s, 1640 w,
1420 m, 920 w, 800 m, 700 m. Anal. calc. for C14H19Cl3Ti: C,
49.23; H,5.61; found C, 49.04; H, 5.74.
3.3.4. Synthesis of complex 4
3.3.4.1. Synthesis of CH2 CHCH2 CH2C(CH3)2CpSiMe3. To
the solution of CH3Li in diethyl ether (82 ml, 59 mmol)
was added dropwise 7.8 g (53.4 mmol) of (CH2 CHCH2CH2)
(CH3)C C5H4 fulvene.. The mixture was stirred overnight, and
5.8 g(53.4 mmol)ofMe3SiClin20 mlofTHFwasslowlyadded.
The reaction mixture was stirred for 4 h. Subsequently, the mix-
ture was poured into ice water and extracted with petroleum.
The organic phase was dried over magnesium sulphate. The
volatiles were removed in vacuo, and the residue was distilled at
58 ◦C/7.5 Pa to give a yellow oil. Yield 6.5 g, 48.4%. 1H NMR
(δ, ppm, CDCl3): 6.58–6.55 (m, 1H, Cp–H), 6.44–6.43(m, 1H,
Cp–H), 6.05 (s, 1H, Cp–H), 5.83–5.74 (m, 1H, CH ), 4.97–4.85
(m, 2H, CH2 ), 3.23 (s, 1H, Cp–H), 1.93–1.87 (m, 2H, CH2),
1.60–1.51 (m, 2H, CH2), 1.16 (s, 6H, CH3), 0.18–0.00 (m, 9H,
SiMe3).
3.3.6. Synthesis of complex 7
3.3.6.1. Synthesis of CH2 CHCH2C(CH3)2Cp(SiMe3)2. To
the solution of CH2 CHCH2C(CH3)2CpSiMe3(36 mmol) in
50 ml diethyl ether and 20 ml THF was added dropwise 19.5 ml
(36 mmol) of BuLi. The mixture was stirred overnight, and
4.34 g (40 mmol) of Me3SiCl in 20 ml of THF was slowly added.
The reaction mixture was stirred for 4 h. Subsequently, the mix-
ture was poured into ice water and extracted with petroleum.
The organic phase was dried over magnesium sulphate. The
volatiles were removed in vacuo, and the residue was distilled at
57–71 ◦C/2 Pa to give a red oil. Yield 8.1 g, 77.1%. 1H NMR (δ,
ppm, CDCl3): 6.66 (m, 1H, Cp–H), 6.41 (m, 1H, Cp–H), 6.06 (t,
J = 1.7 Hz, 1H, Cp–H), 5.74–5.65 (m, 1H, CH ), 4.99–4.93 (m,
2H, CH2 ), 2.25 (d, J = 7.3 Hz, 2H, CH2), 1.14 (s, 6H, CH3), 0
(m, 18H, SiMe3).
3.3.4.2. Synthesis of CH2 CHCH2 CH2C(CH3)2CpTiCl3 (4).
To the solution of 1 ml (9 mmol) of TiCl4 was added drop-
wise 1 g (4.3 mmol) CH2 CHCH2C(CH3)2CpSiMe3 in 25 ml
of toluene. The colour changed to dark-red. The mixture was
stirred overnight and the solvent was removed in vacuo to
give a dark-red oil which solidified after 1 day. Recrystal-
lization in hexane afforded bright red crystals. Yield: 339 mg,
1
3.3.6.2. Synthesis of CH2 CHCH2C(CH3)2Cp(SiMe3)TiCl3
25%. H NMR (δ, ppm, CDCl3): 7.01 (m, 2H, Cp–H), 6.88
(7). To
a solution of 0.4 ml (3.6 mmol) of TiCl4 in
(m, 2H, Cp–H), 5.76–5.66 (m, 1H, CH ), 4.98–4.88 (m, 2H,
CH2 ), 1.89–1.81 (m, 2H, CH2), 1.67–1.61 (m, 2H, CH2), 1.43
(s, 6H, CH3). EIMS (m/e): 259 (M+–CH2 CHCH2, 28), 223
(M+–CH2 CHCH2–HCl, 100), 224 (M+–CH2 CHCH2–Cl,
24). IR (KBr, cm−1): 3100 m, 3080 m, 2890 s, 1640 m, 1370 m,
1050 s, 1000 m, 920 s, 690 s. Anal. calc. for C12H17Cl3Ti: C,
45.68; H,5.43; found C, 46.05; H, 5.67.
15 ml of CH2Cl2 was added dropwise 1 g (3.4 mmol) of
CH2 CHCH2C(CH3)2Cp(SiMe3)2 in 25 ml CH2Cl2. The
colour changed to dark red. The mixture was stirred overnight
and the volatiles were removed in vacuo to yield the dark-
red oil, which was 95% pure, as seen by NMR spectroscopy.
Yield: 457 mg, 36%. 1H NMR (δ, ppm, CDCl3): 7.11 (s,
1H, Cp–H), 7.00 (m, 1H, Cp–H), 6.95 (m, 1H, Cp–H),
5.56–5.47 (m, 1H, CH ), 4.98–4.80(m, 2H, CH2 ), 2.28–2.15
(m, 2H, CH2), 1.39 (s, 3H, CH3), 1.32 (s, 3H, CH3), 0.28 (s,
9H, SiMe3). EIMS (m/e): 331 (M+–CH2 CHCH2, 22), 295
(M+–CH2 CHCH2–HCl, 100), 296 (M+–CH2 CHCH2–Cl,
22). IR (KBr, cm−1): 3100 m, 3080 m, 2890 s, 1640 m, 1370 m,
1050 s, 920 s, 690 s.
3.3.5. Synthesis of complex 5
3.3.5.1. Synthesis of CH2 CHCH2C (cyclo-C5H10) CpSiMe3.
To the solution of CH2 CHCH2MgCl (68.4 mmol) in 100 ml of
diethyl ether was added dropwise 10 g (68.4 mmol) of (cyclo-
C5H10) C C5H4 fulvene.. The mixture was stirred overnight,
and 7.4 g (60 mmol) Me3SiCl in 40 ml of THF was slowly added.
The reaction mixture was stirred for 4 h. Subsequently, the mix-
ture was poured into ice water and extracted with petroleum.
The organic phase was dried over magnesium sulphate. The
volatiles were removed in vacuo, and the residue was distilled at
3.3.7. Synthesis of complex 8
3.3.7.1. Synthesis of CH2 CHCH2C(CH3) (C6H5) CpSiMe3.
To the solution of CH2 CHCH2MgCl (26.8 mmol) in 30 ml

C. Wang et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 139–145
145
of diethyl ether was added dropwise 4.5 g (26.8 mmol) of
Acknowledgement
(CH3)(C6H5)C C5H4. The mixture was stirred overnight, and
3.0 g(26.7 mmol)ofMe3SiClin25 mlofTHFwasslowlyadded.
The reaction mixture was stirred for 4 h. Subsequently, the mix-
ture was poured into ice water and extracted with petroleum.
The organic phase was dried over magnesium sulphate. The
volatiles were removed in vacuo, and the residue was distilled
at 97–100 ◦C/25 Pa to give a yellow oil. Yield 3.0 g, 39.7%. 1H
NMR (δ, ppm, CDCl3): 7.40–7.15 (m, 5H, Ph-H), 6.42–6.21 (m,
3H, Cp–H), 5.62–5.53 (m, 1H, CH ), 5.05–4.95 (m, 2H, CH2 ),
3.27 (m, 1H, Cp–H), 2.80–2.73 (m, 2H, CH2), 1.53–1.50 (m, 3H,
CH3), 0.12–0 (m, 9H, SiMe3).
We gratefully acknowledge financial support from the
National Natural Science Foundation of China (NNSFC) (no.
20372022) and National Basic Research Program of China
(2005CB623801).
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4. Conclusion
A new series of substituted half-sandwich titanium
complexes bearing bridged alkenyl groups [η5-C5H4-(bridge)-
(alkenyl)]TiCl3 have been synthesized and characterized. All
the titanium complexes display considerable catalytic activity
towards the polymerization of styrene in the presence of
methylaluminoxane (MAO). The highest activity of 1.22 × 107
g PS/(mol Ti·mol S·h) was obtained in 7/MAO catalytic system.
Bridging unit between the cyclopentadienyl moiety and the allyl
groups plays a crucial role in reactivity and stereoselectivity
of styrene polymerization. By modification of the bridging
unit, the syndioselectivity of the polymer can be tailor-made,
providing a new guideline to design catalyst for polymers
having desired properties.