Synthesis and styrene polymerization behavior of new titanium complexes Cp*TiCl(OCHRCH2NAr)

Article abstract of DOI:10.1016/j.molcata.2005.01.007

A series of titanium complexes Cp*TiCl(OCHRCH₂NAr) (Cp* = C₅Me₅, R = H, Ar = phenyl (2a); R = H, Ar = 2,6-dimethylphenyl (2b); R = Me, Ar = phenyl (2c); R = Me, Ar = 2,6-dimethylphenyl (2d)) was prepared by the reaction of corresponding 2-phenylamino-ethanol derivatives with Cp*TiCl₃ in the presence of excessive triethylamine. All the titanium complexes display higher catalytic activity towards the syndiospecific polymerization of styrene in the presence of modified methylaluminoxane (MMAO) as a cocatalyst, yielding higher molecular weight polystyrenes with higher syndiotacticities and melting temperatures (T_m) than their mother complex Cp*TiCl₃. When 2-(2,6-diisopropyl-phenylamino)-ethanol was reacted with Cp*TiCl ₃, an unexpected monodentate complex Cp*TiCl ₂(OCH₂CH₂NHC₆H₃ ⁱPr₂-2,6) 3 was obtained. The complex 3 displays relative low catalytic activity towards styrene polymerization, but produces higher molecular weight polystyrene with higher syndiotacticities.

Full text of DOI:10.1016/j.molcata.2005.01.007

Journal of Molecular Catalysis A: Chemical 232 (2005) 1–7
Synthesis and styrene polymerization behavior of
new titanium complexes Cp*TiCl(OCHRCH2NAr)
Jie Chen, Yue-Sheng Li∗, Ji-Qian Wu,
Ning-Hai Hu
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, China
Received 9 May 2004; received in revised form 6 January 2005; accepted 6 January 2005
Abstract
A series of titanium complexes Cp*TiCl(OCHRCH2NAr) (Cp* = C5Me5, R = H, Ar = phenyl (2a); R = H, Ar = 2,6-dimethylphenyl (2b);
R = Me, Ar = phenyl (2c); R = Me, Ar = 2,6-dimethylphenyl (2d)) was prepared by the reaction of corresponding 2-phenylamino-ethanol
derivatives with Cp*TiCl3 in the presence of excessive triethylamine. All the titanium complexes display higher catalytic activity towards
the syndiospecific polymerization of styrene in the presence of modified methylaluminoxane (MMAO) as a cocatalyst, yielding higher
molecular weight polystyrenes with higher syndiotacticities and melting temperatures (Tm) than their mother complex Cp*TiCl3. When 2-(2,6-
diisopropyl-phenylamino)-ethanol was reacted with Cp*TiCl3, an unexpected monodentate complex Cp*TiCl2(OCH2CH2NHC6H3 Pr2-2,6)
i
3 was obtained. The complex 3 displays relative low catalytic activity towards styrene polymerization, but produces higher molecular weight
polystyrene with higher syndiotacticities.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Titanium complex; Catalyst; Styrene; Modified methylaluminoxane; Syndiospecific polymerization; Polystyrene
tuted complexes, e.g. CpTiCl2(OR) or Cp*Ti(OR)3, in place
of chlorinated counterparts [13–15], some research groups
have found that the former have much higher activity than
the latter [16–23].
1. Introduction
Olefin polymerization by homogeneous catalysis has be-
come one of the most attractive subjects in the field of
both organometallic chemistry and catalysis. The use of tita-
nium complex/methylaluminoxane catalyst system in the first
preparation of syndiotactic polystyrene (sPS) by Ishihara and
his colleagues has impelled an active search for new types of
sPS catalysts [1–4]. A wide variety of catalytic systems based
on titanium complexes have been reported in [5–12]. Most of
the extensive work on sPS catalysts has been focused on the
modification of the ␩5 ligand system. In addition, the ␴-donor
X (X = halogen, alkoxy or hydrocarbyl) ligand has been also
found to affect both catalytic activities and polymer prop-
erties. For instance, by application of alkoxy ligand substi-
In 1998, Doherty et al. reported that the mixed-
ligand titanium complexes CpTi(NC5H4(CR2O))Cl2
(NC5H4(CR2O) = bidentate pyridylalkoxide ligand) and
CpTi(ONO)Cl2(ONO = tridentate N-alkoxy-␤-ketoiminate
ligand) are more active towards ethylene polymerization than
their mother complex CpTiCl3 [24]. Qian and coworkers
reported that two kinds of titanium complexes with mono-Cp
and Schiff base ligands display improved catalytic activities
for olefin polymerization in comparison with CpTiCl3 [25].
Xu et al. showed that the complexes CpTi(dbm)xCl3−x
(dbm = 1,3-diphenylpropane-1,3-dione
ligand)
[26],
CpTi[O,N]Cl2 containing 8-hydroxy-quioline ligand [27],
and CpTi[O,O]Cl bearing bisphenoxy ligands [28] can act as
active catalysts for ethylene polymerization in the presence
∗
Corresponding author. Tel.: +86 431 5262124; fax: +86 431 5685653.
E-mail address: ysli@ciac.jl.cn (Y.-S. Li).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.01.007

2
J. Chen et al. / Journal of Molecular Catalysis A: Chemical 232 (2005) 1–7
MAO. We deduce that some mixed-ligand titanium com-
plexes Cp*(L)TiClx (Cp* = pentamethylcyclopentadienyl,
L = multidentate ligands, x = 0–3) could display higher
activities for styrene polymerization than their mother
complex Cp*TiCl3.
Herein we report the synthesis, characterization and
styrene polymerization behavior of a series of new tita-
nium complexes Cp*TiCl(OCHRCH2NAr) in the presence
of MMAO as a cocatalyst, and compare their performance
with that of their mother complex Cp*TiCl3.
2.2. Synthesis of complexes
To solution of 2-phenylamino-ethanol (0.686 g,
a
5.0 mmol) and triethylamine (1.4 mL) in 40 mL of CH2Cl2
was added dropwise a reddish solution of Cp*TiCl3 (1.45 g,
5.0 mmol) in 40 mL of CH2Cl2 under stirring and at −78 ◦C.
The reaction mixture was warmed to room temperature and
stirred for 12 h. The residue, obtained by removing the sol-
vent under reduced pressure, was redissolved in toluene, and
the resulting mixture was filtered through a Celite bed. The
removal of solvent from the orange filtrate afforded the tita-
niumcomplex(Cp*TiCl(OCH2CH2NC6H5))2ain88%yield
(1.55 g). The other complexes were prepared by a similar pro-
cedure in similar yields.
2. Experimental
2a (Cp*TiCl(OCH2CH2NC6H5)): 1H NMR (CDCl3):
δ 7.32–7.13 (m, 5H, C6H5), 3.92–3.88 (t, 2H, OCH2),
3.38–3.35 (t, 2H, NCH2), 2.05 (s, 15H, C5(CH3)5). 13C NMR
(CDCl3): δ 147.2, 131.7, 129.2, 128.2 (Ph), 113.4 (C5Me5),
74.71 (OCH2), 46.65 (NCH2), 12.32 (C5(CH3)5). EIMS:
m/z (relative intensity): 352 ([M+], 44), 322 ([M+ CH2O],
100), 217 ([M+ Cp*], 50), 216 ([M+ ArNCH2CH2O], 40).
Anal. Calc. for C18H24ClNOTi: C, 61.12; H, 6.84; N, 3.96%.
Found: C, 61.26; H, 6.78; N, 4.01%.
2.1. General procedures and materials
All work involving air and moisture sensitive compounds
was carried out using standard Schlenk techniques. Elec-
tron impact mass spectra were obtained with a VG Auto
Spectrometer. Elemental analyses were performed with an
EA-1106 spectrometer. The NMR data of ligands and com-
plexes were obtained on a Bruker 300 MHz spectrometer
at ambient temperature, with CDCl3 as solvent and TMS
as internal standard. The NMR data of the polystyrenes
were obtained on a Varian Unity 400 MHz spectrome-
ter at 100 ◦C with 1,1,2,2-tetrachloroethane-d2 as the sol-
vent and TMS as internal standard. The pulse interval
was 7.93 s, the acquisition time was 0.33 s, the pulse an-
gle was 90◦, and the number of transients accumulated
was ca. 5000. The molecular weights and the polydis-
persity indices of the polymer samples were determined
at 150 ◦C by a PL-GPC 220 type high temperature chro-
matograph equipped with three PLgel 10 ␮m Mixed-B LS
type columns. 1,2,4-Trichlorobenzene (TCB) was employed
as the solvent at a flow rate of 1.0 mL/min. The calibra-
tion was made by polystyrene standard EasiCal PS-1 (PL
Ltd.).
Toluene was dried over sodium with dibenzophenone
as indicator. Dichloromethane and triethylamine were re-
fluxed over calcium hydride for two weeks before use.
CDCl3 was obtained from Aldrich and dried over CaH2,
vacuum-transferred, degassed by repeated freeze-pump-thaw
cycles, and stored over activated molecular sieves (4A).
The aniline, 2,6-dimethylaniline, 2,6-diisopropylaniline and
1,1,2,2-tetrachloroethane-d2 were obtained from Acros and
purified by distillation before use. Modified methylalumi-
noxane (MMAO, 7 wt.% Aluminum in heptane solution)
was purchased from Akzo Nobel Chemical Inc. Styrene was
distilled from CaH2 and stored in a refrigerator. Pentamethyl-
cyclopentadienyl titanium trichloride were obtained from
Strem and used without purification. 2-phenylamino-ethanol,
2-(2,6-dimethyl-phenylamino)-ethanol, 2-(2,6-diisopropyl-
phenylamino)-ethanol, 1-phenylamino-propan-2-ol, and 1-
(2,6-dimethyl-phenylamino)-propan-2-ol were synthesized
in good yields according to the published literature proce-
dures [29].
2b (Cp*TiCl(OCH2CH2NC6H3(CH3)2) (85%): 1H NMR
(CDCl3): δ 7.28–6.99 (m, 3H, C6H3), 4.20–4.17 (t, 2H,
OCH2), 3.43–3.40 (t, 2H, NCH2), 2.05 (s, 6H, PhCH3), 2.08
(s, 15H, C5(CH3)5). 13C NMR (CDCl3): δ 142.5, 132.7,
130.6, 129.6 (Ph), 128.2 (C5(CH3)5), 58.26 (OCH2), 46.20
(NCH2), 18.95 (PhCH3), 12.75 (C5(CH3)5). Anal. Calc. for
C20H28ClNOTi: C, 62.92; H, 7.39; N, 3.67. Found: C, 63.09;
H, 7.35; N, 3.71%.
2c (Cp*TiCl(OCH(CH3)CH2NC6H5) (82%): 1H NMR
(CDCl3): δ 7.30–7.09 (m, 5H, C6H5), 4.19–4.15 (m, 1H,
OCH), 3.28–3.23 (d, 2H, NCH2), 2.12 (s, 15H, C5(CH3)5),
1.16 (d, 3H, CHCH3). 13C NMR (CDCl3): δ 146.5, 132.7,
126.9, 125.1 (Ph), 117.8 (C5Me5), 76.58 (OCH), 49.66
(NCH2), 22.5 (CHCH3), 12.58 (C5(CH3)5). Anal. Calc. for
C19H26ClNOTi: C, 62.07; H, 7.08; N, 3.81. Found: C, 62.19;
H, 7.13; N, 3.89%.
1
2d (Cp*TiCl(OCH(CH3)CH2NC6H3(CH3)2) (79%): H
NMR (CDCl3): δ 7.18–7.12 (m, 3H, C6H5), 4.61–4.59 (m,
1H, OCH), 3.44–3.40 (d, 2H, NCH2), 2.55 (s, 6H, PhCH3),
2.06 (s, 15H, C5(CH3)5). 1.16 (d, 3H, CHCH3). 13C NMR
(CDCl3): δ 147.7, 132.5, 129.1, 127.1 (Ph), 113.9 (C5Me5),
75.4 (OCH), 55.5 (NCH2), 22.9 (PhCH3), 22.5 (CHCH3),
13.2 (C5(CH3)5). Anal. Calc. for C21H30ClNOTi: C, 63.73;
H, 7.63; N, 3.54. Found: C, 63.58; H, 7.58; N, 3.58%.
3 (Cp*TiCl2(OCH2CH2NHC6H3(iPr)2) (82%): 1H NMR
(CDCl3): δ 7.12–7.05 (m, 3H, Ph-H), 4.80 (t, 2H, OCH2),
4.16 (s, 1H, NH), 3.32 (m, 2H, CHMe2), 3.16–3.09 (t,
2H, NCH2), 2.26 (s, 15H, C5(CH3)5), 1.23 (d, 12H,
CH(CH3)2). 13C NMR (CDCl3): δ 143.5, 132.0, 129.4,
125.7 (Ph), 123.9 (C5Me5), 59.2 (OCH2), 54.2 (NCH2), 28.3
(CHMe2), 25.1 (CH(CH3)2), 13.11 (C5(CH3)5). Anal. Calc.
for C24H37Cl2NOTi: C, 60.77; H, 7.86; N, 2.95. Found: C,
60.58; H, 7.83; N, 2.99%.

J. Chen et al. / Journal of Molecular Catalysis A: Chemical 232 (2005) 1–7
3
and 13C NMR spectra of the complexes 2a–d are shifted to
the downfield, which is a consequence of the high Lewis acid-
ity of titanium. In the 1H NMR spectra, the resonance signals
of group OCH2 shifted downfield by 0.8–1.1 ppm versus the
free ligand, while only a small downfield shift by 0.3–0.5 ppm
was observed for the CH2N resonance. This suggests that a
strong bond formed between the titanium atom and oxygen
atom of the ligand, and a weak bond formed between the tita-
nium and the nitrogen atom of the ligand. The NMR signals
were sharp, and variable-temperature studies showed no evi-
dence of inter- or intramolecular ligand exchange at ambient
temperature. In the absence of X-ray structure determina-
tion of the complexes 2a–d, it is difficult to clarify whether
2a–daremonomeric, dimericorpolymericspecies. However,
we tentatively suggest that 2a–d should exist most likely as
monomeric species in solution, because the NMR spectra of
the complexes 2a–d are sharp, they have some volatile na-
ture, and the EI mass spectra exhibit molecular peaks for the
corresponding complexes.
2.3. Polymerization procedure
Polymerization was carried out in toluene in a 150 mL
glass reactor equipped with a mechanical stirrer. Toluene,
styrene, and the solution of titanium complex were intro-
duced into the nitrogen-purged reactor and stirred vigorously
(600 rpm) at the desired temperature. The reaction was started
by the addition of an MMAO solution. After 10 min, re-
action was terminated by the addition of 100 mL of acidic
ethanol (ethanol/HClconc. = 20/1). The resulting precipitated
polymer was washed three times with 500 mL portions of
methanol and dried in vacuo at 70 ◦C for 24 h. The poly-
mer was extracted with refluxing 2-butanone for 12 h in or-
der to determine the syndiotacticity of the polymer obtained
by measuring of 13C NMR spectra at 100 ◦C in 1,1,2,2-
tetrachloroethane-d2.
3. Results and discussion
Attempts to prepare Cp*TiCl[OCH2CH2N(2,6-iPr2Ph)]
2e via the approach aforementioned were unsuccessful, giv-
ing acyclic complex 3 in which the nitrogen atom is not found
coordinated with titanium atom, as shown in Scheme 2. The
reason why the complex 2e cannot be formed is that there is a
steric hindrance betweenbulkyisopropyl andpentamethylcy-
clopentadienyl groups. Crystal structure determination con-
firms the deduction aforementioned. The molecular structure
of 3 is shown in Fig. 1. The data collection and refinement
data of the analysis are summarized in Table 1.
3.1. Synthesis and characterization of titanium
complexes
A general synthetic route for new titanium complexes
Cp*TiCl(OCHRCH2NAr) used in this study is shown in
Scheme 1. Complexes 2a–d were obtained in good yields
(2a, 88%; 2b, 85%; 2c, 82%; 2d, 79%) by the reaction of cor-
responding 2-phenylamino-ethanol derivative with Cp*TiCl3
in the presence of excessive triethylamine. Attempted use of
dilithiated species instead of neutral 2-phenylamino-ethanol
derivatives in toluene or diethyl ether was not successful and
a mixture of several unidentified compounds was obtained,
suggesting that mild reaction condition of HCl elimination is
essential and required for the synthesis of titanium complexes
Cp*TiCl(OCHRCH2NAr).
Owing to the failure in obtaining single crystals for 2a–d,
their structural characters were established by NMR spec-
troscopy, EI mass spectroscopy, and elemental analyses. The
1H and 13C NMR of 2a–d show the presence of only one
pure compound. The stoichiometry of the reaction was as-
certained from the ratio of 1H NMR. In comparison with the
free 2-phenylamino-ethanol derivatives, all signals in the 1H
3.2. Catalysis
Polymerizations of styrene with 2a–d, 3/MMAO catalytic
systems were performed in toluene under various conditions.
In order to assess the significance of the observed activity
values, we also carried out the polymerization experiments
by using Cp*TiCl3/MMAO catalytic system under the same
polymerization conditions. The polymerization data, sum-
marized in Table 2, reveal that the 2a–d/MMAO catalytic
systems are more efficient in producing highly syndiotactic
polystyrene in terms of activity, conversion, and stereospeci-
ficity at all the polymerization temperatures.
Scheme 1.

4
J. Chen et al. / Journal of Molecular Catalysis A: Chemical 232 (2005) 1–7
Scheme 2.
Catalyst activities and polymer yields as well as molecular
shown in Fig. 2, the activity of the complex 2a rapidly in-
creases at first with an increase in the Al/Ti molar ratio, and
then decreases gradually. The optimal Al/Ti molar ratio is ca.
1100/1. Contrarily, the molecular weight of polymer grad-
ually decreases in line with an increase in the Al/Ti molar
ratio.
weights depend significantly on the reaction conditions. The
variation of the ratio of MMAO/2a, which is expressed here
as Al/Ti molar ratio, showed considerable effects on polymer
yield, polymer molecular weights and catalyst activities. As
Considerable effects of the molar ratio of monomer to
catalyst on the catalyst activities and the molecular weight
of polymer were also observed. An increase in the styrene/Ti
molar ratio, which also means an increase in the monomer
concentration (the reaction volume was kept constant), first
Table 1
Crystal data and structure refinement of the titanium complex 3
Empirical formula
Formula mass
C24H37Cl2NOTi
474.35
Crystal size (mm)
Crystal system
Space group
0.55 × 0.52 × 0.10
Monoclinic
P2(1)/n
˚
a (A)
8.5183 (2)
15.8836 (5)
19.4969 (7)
90
92.3170 (10)
90
2635.80 (14)
4
1.195
˚
b (A)
˚
c (A)
␣ (◦)
␤ (◦)
␥ (◦)
3
˚
Volume (A )
Z
ρcalc (Mg cm−3
)
Absorption coefficient (mm−1
F (0 0 0)
)
0.541
1008
θ range for data collected (◦)
Limiting indices
2.45–27.48
0 ≤ h ≤ 11, 0 ≤ k ≤ 20,
−25 ≤ l ≤ 25
12710/5860
0.0277
Reflections collected/unique
R(int)
Completeness to θ
Maximum and minimum
transmission
27.48–97.1%
0.9474 and 0.7558
Fig. 1. ORTEPplotofthemolecularstructureofthetitaniumcomplex 3. Dis-
Refinement method
Full-matrix least-squares
on F2
5860/0/287
placement ellipsoids are drawn at the 30% probability level. Hydrogen atoms
◦
˚
are omitted for clarity. Selected bond lengths (A) and angles ( ): Ti(1) O(1),
1.7493(17); Ti(1) Cl(1), 2.2588(9); Ti(1) Cl(2), 2.2553(9); Ti(1) C(1),
2.330(2); Ti(1) C(4), 2.383(2); Ti(1) C(5), 2.385(2); O(1) C(11),
1.417(3); C(1) C(2), 1.409(3); C(1) C(5), 1.426(3); C(2) C(3), 1.403(3);
C(3) C(4), 1.396(4); C(4) C(5), 1.396(4); O(1) Ti(1) Cl(1), 101.82(8);
O(1) Ti(1) Cl(2), 101.87(8); Cl(2) Ti(1) Cl(1), 102.60(5).
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ (I)]
R indices (all data)
0.870
R1 = 0.0455, wR2 = 0.1195
R1 = 0.0859, wR2 = 0.1279
0.512 and −0.304 eA−3
Largest different peak and hole

J. Chen et al. / Journal of Molecular Catalysis A: Chemical 232 (2005) 1–7
5
Table 2
Polymerization results of styrene with titanium complexes/MMAOa
Tp (◦C)
PS (g)
Activityb
Conversion (%)
sPSc (%)
SId (%)
Mw (kg/mol)
e
¯
¯ ¯
Mw/Mn
Catalyst
Cp*TiCl3
30
50
70
0.88
2.62
3.00
0.60
1.80
2.06
19.3
57.6
65.9
96.9
96.5
95.2
97.7
96.0
95.4
231
197
182
1.71
1.73
2.08
2a
2b
2c
2d
30
50
70
0.89
2.68
3.27
0.61
1.84
2.25
19.6
58.9
72.0
99.2
99.0
98.5
98.9
98.5
98.6
247
222
196
2.53
2.16
2.09
30
50
70
0.93
2.72
3.35
0.64
1.87
2.30
20.5
59.9
73.7
98.9
98.8
98.2
99.1
98.7
99.0
253
226
200
2.45
2.10
1.98
30
50
70
0.99
2.79
3.45
0.68
1.92
2.37
21.8
61.3
75.9
99.1
99.2
98.3
99.2
99.1
98.5
268
231
202
2.37
2.03
2.01
30
50
70
1.17
2.82
3.54
0.81
1.94
2.43
25.8
62.1
77.9
98.9
98.7
98.1
99.3
98.9
98.7
270
235
204
2.29
1.99
1.93
3
30
50
70
0.44
1.30
2.89
0.30
0.89
1.98
9.7
28.6
63.6
98.5
98.4
97.9
98.7
98.2
98.3
315
293
272
2.35
2.19
2.02
a
Polymerization condition: 20 ␮mol catalyst, Al/Ti = 1000 (molar ratio), styrene/Ti = 2200 (molar ratio), Vtotal = 100 mL, polymerization for 10 min.
Activity = 104 kg sPS/molTi molSt h.
b
c
d
e
sPS% = (g of polymer soluble in 2-butone)/(g of total polymer) × 100%.
SI = syndiotacticity (2-butanone insoluble portion whose tacticity established by 13C NMR in 1,1,2,2-tetra-chloroethane-d2).
Determined by GPC.
caused a dramatic increase in the catalytic activity of the
70 ◦C. In contrast, the molecular weights of the polymer
obtained decrease monotonously with reaction temperature.
The stereospecificities of the polymers obtained exhibit the
similar reaction temperature dependency. As many homo-
geneous half-sandwich metallocene catalysts based on tri-
dentate ligands [15,30], 2a–d/MMAO systems also show a
slightly low syndiotacticity values with an increase in reac-
tion temperature.
The data, listed in Table 2, indicate clearly that the struc-
tures of the titanium complexes considerably affect their per-
formance. It is well known that steric effect could control the
deactivation of the catalysts for olefin polymerization, the
chain transfer such as ␤-hydride elimination, and chain ter-
mination [31–34]. As a result, the catalytic activities, poly-
mer yields and molecular weights increase gradually from
2a through 2b and 2c to 2d under the same conditions, in ac-
cord with steric hindrance between bidentate ligand and Cp*
group. The 2a–d/MMAO systems afford polystyrenes with
high stereospecificities of greater than 98.6% over the entire
range studied.
complex 2a and then a rapid decrease. The optimum molar
ratio of monomer to catalyst is ca. 2000, as shown in Fig. 3.
Contrarily, the molecular weights of polymers increase in the
range of the conditions studied.
It is very interesting to note that reaction temperature
also affects considerably the activities of catalysts and the
molecular weights of polymers (see Table 2). With increase
of reaction temperature, the catalyst activity of the complex
2a rapidly increases at first, and then decreases slowly, as
shown in Fig. 4. The optimum reaction temperature is ca.
Interestingly, all the titanium complexes 2a–d display
higher catalytic activities towards styrene polymerization,
and produce higher molecular weight polystyrenes with
higher syndiotacticities than their mother complex Cp*TiCl3
(see Table 2). When Cp*TiCl3 was replaced by the titanium
complexes bearing bidentate ligand at 70 ◦C, the syndiotac-
¯
ticity, and Mw of the polymers increase by 3.2–3.8%, and
7.6–12%, respectively. This fact indicates that the chelating
2-phenylamino-ethanol derivative ligands with the unique
steric effect and transannular structure seem to play an
¯
Fig. 2. Plot of activity and Mw vs. Al/Ti molar ratio. A 20 ␮mol 2a,
styrene/Ti = 2200 (molar ratio), Vtotal = 100 mL, polymerization reaction at
70 ◦C for 10 min.

6
J. Chen et al. / Journal of Molecular Catalysis A: Chemical 232 (2005) 1–7
Fig. 3. Plot of activity and Mw vs. styrene/Ti molar ratio. A 20 ␮mol 2a, Al/Ti = 1000 (molar ratio), Vtotal = 100 mL, polymerization reaction at 70 ◦C for 10 min.
¯
important role in stabilizing the active species generated from
the reaction between the precursors and MMAO. It is known
that the type CpTiIIIR+ for the Cp-based system proposed by
Zambelli et al. was accepted as the active species in styrene
syndiospecific polymerization [35], although it is still de-
bated in the literature. We tentatively deduce that the lone pair
of electrons on the nitrogen atom of 2-phenylamino-ethanol
ligand can interact with the Ti+(III) species, and then nitro-
gen atom burdens positive charge which wouldbe delocalized
by the p–␲ conjugation between the nitrogen atom and the
aromatic ring. As a result, the active species would become
much more stable. The molecular weight distributions for
sPS produced by 2a–d/MMAO show reaction temperature
dependence quite different from those by Cp*TiCl3/MMAO
due to different structures.
The complex 3/MMAO system displays only relatively
low catalytic activity towards styrene polymerization at 30
and 50 ◦C, but its catalytic activity at 70 ◦C is comparable
with that of the Cp*TiCl3/MMAO system. Furthermore, the
complex 3/MMAO system yields higher molecular weight
polystyrene with higher syndiotacticities than its mother
complex Cp*TiCl3/MMAO system under all the conditions
used.
4. Conclusions
In this article,
a series of new titanium com-
plexes Cp*TiCl(OCHRCH2NAr) (Cp* = C5Me5, R = H, Me;
Ar = phenyl, 2,6-dimethylphenyl) was synthesized and char-
acterized. High catalytic activities can be reached using these
complexes activated with MMAO for syndiospecific poly-
merization of styrene. All the titanium complexes display
higher catalytic activity towards the syndiospecific polymer-
ization of styrene in the presence of MMAO as a cocat-
alyst, yielding higher molecular weight polystyrenes with
higher syndiotacticities than their mother complex Cp*TiCl3.
Catalytic activities of up to 2.57 × 104 kg sPS/molTi molSt h,
weight–average molecular weights of up to 315 kg/mol,
and syndiotacticities of up to 99.1% were observed. Cat-
alytic activities and polymer yields as well as polymer
properties are considerably affected by the steric hin-
drance of bidentate ligands. Catalytic activities, polymer
yields, and polymer properties such as syndiotacticity
could be controlled in a wide range by changing struc-
ture of the catalysts and reaction parameters. A titanium
i
complex Cp*TiCl2(OCHMeCH2NC6H3 Pr2-2,6) also pro-
duces higher molecular weight polystyrenes with higher
syndiotacticities, though it shows lower catalytic activity than
their mother complex Cp*TiCl3.
¯
Fig. 4. Plot of activity and Mw vs. reaction temperature. 20 ␮mol 2a,
Al/Ti = 1000 (molar ratio), styrene/Ti = 2200 (molar ratio), Vtotal = 100 mL,
polymerization reaction for 10 min.

J. Chen et al. / Journal of Molecular Catalysis A: Chemical 232 (2005) 1–7
7
5. Supplementary material
[13] Y.L. Qian, H. Zhang, X.M. Qian, J.L. Huang, C. Shen, J. Mol. Catal.
A: Chem. 192 (2003) 25.
[14] X.M. Qian, J.L. Huang, Y.L. Qian, C. Wang, Appl. Organometal.
Chem. 17 (2003) 17.
[15] Y.L. Qian, H. Zhang, J.X. Zhou, W. Zhao, X.Q. Sun, J.L. Huang, J.
Mol. Catal. A: Chem. 208 (2004) 45.
[16] G. Xu, D. Cheng, Macromolecules 33 (2000) 2825.
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[18] A. Ku¨nzel, E. Parisini, H.W. Roesky, G.M. Sheldrick, J. Organomet.
Chem. 177 (1997) 536.
Crystallographic data for the structure reported in this pa-
per have been deposited at the Cambridge Crystallographic
Data Center as supplementary publication number CCDC-
237699. Copies of the data can be obtained on application to:
The Director, CCDC, 12 Union Road, Cambridge, CB21EZ,
UK (fax: +44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk).
[19] H. Ma, Y. Zhang, B. Chen, J. Huang, Y. Qian, J. Polym. Sci. A:
Polym. Chem. 39 (2001) 1817.
[20] H. Ma, B. Chen, J. Huang, Y. Qian, J. Mol. Catal. A: Chem. 170
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Acknowledgement
[21] K. Nomura, T. Komatsu, Y. Imanishi, Macromolecules 33 (2000)
8122.
[22] K. Nomura, K. Fujii, Macromolecules 36 (2003) 2633.
[23] Z.G. Shen, W.L. Zhou, F.M. Zhu, S.G. Lin, Acta Polym. Sinica
(2004) 45.
The authors are grateful for the financial support by the
National Natural Science Foundation of China and SINOPEC
(No. 20334030).
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