Diphenyl substituted cyclopentadienyl titanium trichloride derivatives: Synthesis, crystal structure and properties as catalysts for styrene polymerization

Article abstract of DOI:10.1016/j.poly.2006.03.006

New titanium complexes, 1,2-diphenyl-4-R-cyclopentadienyl titanium trichloride (R = Me (4), n-Bu (5), Ph (6)) have been synthesized. The crystal structure of complex 4 has been determined by X-ray diffraction analysis. All the titanium complexes were char

Full text of DOI:10.1016/j.poly.2006.03.006

Polyhedron 25 (2006) 2565–2570
www.elsevier.com/locate/poly
Diphenyl substituted cyclopentadienyl titanium trichloride
derivatives: Synthesis, crystal structure and properties as catalysts
for styrene polymerization
a
a
b
a
a,
b
Qiao-Lin Wu , Qing Su , Guang-Hua Li , Wei Gao , Ying Mu *, Shou-Hua Feng
a
Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, School of Chemistry, Jilin University,
2699 Qianjin Street, Changchun 130012, People’s Republic of China
b
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, School of Chemistry, Jilin University,
2699 Qianjin Street, Changchun 130012, People’s Republic of China
Received 11 October 2005; accepted 4 March 2006
Available online 22 March 2006
Abstract
New titanium complexes, 1,2-diphenyl-4-R-cyclopentadienyl titanium trichloride (R = Me (4), n-Bu (5), Ph (6)) have been synthe-
sized. The crystal structure of complex 4 has been determined by X-ray diffraction analysis. All the titanium complexes were character-
ized by 1H and 13C NMR spectroscopy. In the presence of methylaluminoxane (MAO), these complexes show high catalytic activity and
syndiospecificity for the polymerization of styrene. The catalytic activity of the three complexes increases in the order of 6 < 5 < 4.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Titanocene; Titanium complex; Metallocene catalyst; Syndiotactic polystyrene; Styrene polymerization
1. Introduction
pentadienyl ligand can result in a remarkable change in
the catalytic properties of this type of catalysts, such as
the catalytic activity, stereospecificity and polymer proper-
ties [9–18]. However, to our knowledge, few groups have
studied the synthesis of monocyclopentadienyl titanium
complexes with aromatic substituents on the cyclopentadie-
nyl ring. In this paper, we wish to report the synthesis and
characterization of three new 1,2-diphenyl-4-R-cyclopenta-
dienyl titanium trichloride complexes (R = Me (4), n-Bu
(5), Ph (6)), as well as their properties as catalysts for
styrene polymerization.
In recent years, group IV metallocene complexes have
been extensively studied as homogeneous catalysts for ole-
fin polymerization in the fields of organometallic chemis-
try, catalysis and polymer science [1–5]. Stereospecific
olefin polymerization catalyzed by metallocene catalysts
can produce polymers with new microstructures and has
thus attracted extensive attention in both academic and
industrial communities [6]. Syndiotactic polystyrene (sPS)
was first synthesized by Ishihara and coworkers with
monocyclopentadienyl titanium catalysts activated with
methylaluminoxane (MAO) [7]. Subsequently, a large num-
ber of monocyclopentadienyl titanium complexes were syn-
thesized and studied to obtain better catalysts [8]. It has
been known that even a minor modification of the cyclo-
2. Experimental
2.1. General procedures
All manipulations involving air and moisture sensitive
compounds were carried out under a nitrogen (ultrahigh
purity) atmosphere using standard Schlenk techniques.
Tetrahydrofuran, diethyl ether and toluene were refluxed
*
Corresponding author. Tel.: +86 431 5168472; fax: +86 431 5193421.
E-mail address: ymu@jlu.edu.cn (Y. Mu).
0277-5387/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.03.006

2566
Q.-L. Wu et al. / Polyhedron 25 (2006) 2565–2570
under nitrogen over Nanbenzophenone and distilled before
use. Methylene chloride, n-hexane and petroleum ether
were refluxed under nitrogen over calcium hydride and dis-
tilled before use. Methylaluminoxane (MAO, 10 wt.% solu-
tion in toluene, M = 800 g molꢀ1, Al = 5.3 wt.%) was
purchased from Wtico, n-butyl lithium, methyl lithium,
phenyl lithium trimethylchlorosilane and titanium tetra-
v/v) as a yellowish oil. ESI-MS, m/z: 274.4 [M]+, 232.3
1
[MꢀC3H6]+, 178.2 [MꢀCH3–C3H3]+. H NMR (CDCl3,
300 MHz): d 0.96 (s, 3H, CH3), 1.41 (q, 2H, CH2), 1.52
(q, 2H, CH2), 2.47 (t, 2H, CH2), 3.46 (s, 2H, C5H3), 6.34
(s, 1H, C5H3), 7.10–7.41 (m, 10H, C6H5). 13C NMR
(CDCl3, 75 MHz): d 14.2, 22.8, 30.7, 31.9 (n-Bu), 47.5,
131.2, 137.6, 141.4, 149.4 (C5H3), 126.2, 127.1, 127.9,
128.4, 128.6, 128.6, 137.6, 137.8 (C6H5).
1
chloride were purchased from Aldrich. H and 13C NMR
spectra were recorded on a Varian Mercury-300 NMR
spectrometer with CDCl3 as solvent and TMS as an inter-
nal standard. IR spectra were recorded on a Nicolet Impact
410 FTIR spectrometer using KBr pellets. Elemental anal-
yses were performed on a Perkin–Elmer 240c element ana-
lyzer. The crystal structure was determined with a CCD
diffraction apparatus. Viscosity-average molecular weights
of the polystyrenes were determined in o-dichlorobenzene
at 135 ꢁC using a Schott Gerate Mod. AVS/T2 Ubbelohde
viscosimeter. Melting transition temperatures (Tm) of the
polystyrenes were determined by DSC (Du Pont 910 differ-
2.3. Synthesis of 1,2-diphenyl-4-methyl-
cyclopentadienyltitanium trichloride (4)
To a solution of 1,2-diphenyl-4-methyl-cyclopentadiene
(1.16 g, 5.0 mmol) in diethyl ether (40 mL) was slowly
added a solution of n-BuLi (5.1 mmol) in n-hexane
(20 mL) at ꢀ78 ꢁC with stirring. After 1 h, the reaction
mixture was allowed to warm to room temperature and
stirred overnight. The solvent was removed under vacuum
and the residue was washed with dry n-hexane (3 · 20 mL).
The obtained white powder was dissolved in THF (30 mL),
and Me3SiCl (5.1 mmol) was slowly added at ꢀ78 ꢁC. The
reaction mixture was allowed to warm to room tempera-
ture and stirred for 2 h. The solvent and excess Me3SiCl
were removed under reduced pressure. The residue was
extracted with toluene (20 mL) and slowly added to a solu-
tion of TiCl4 (4.75 mmol) in 30 mL of toluene at ꢀ78 ꢁC.
The reaction mixture was allowed to warm to room tem-
perature and stirred for 24 h. The precipitate was filtered
off and the solvent was removed to leave a red solid.
Recrystallization from methylene chloride/n-hexane (1:3
in v/v) gave pure 4 (1.30 g, 68.2%). Anal. Calc. for
C18H16Cl3Ti (385.54): C, 56.08; H, 3.92. Found: C, 56.00;
H, 3.98%. IR (KBr, cmꢀ1): 3100w, 2957w, 2925m, 2850w,
1491m, 1453w, 1424m, 1163w, 1079w, 1050w, 1022w,
889m, 769vs, 706vs, 676m, 663m. 1H NMR (CDCl3,
300 MHz): d 2.59 (s, 3H, CH3), 7.12 (s, 2H, C5H2), 7.56–
7.35 (m, 10H, C6H5). 13C NMR (CDCl3, 75 MHz): d 18.4
(CH3), 129.4, 132.8, 140.5 (C5H2), 124.3, 128.4, 129.4,
138.4 (C6H5).
ential scanning calorimeter) at
10 ꢁC minꢀ1
a heating rate of
.
2.2. Synthesis of ligands
1,2-Diphenyl-4-methylcyclopentadiene (1) and 1,2,4-tri-
phenylcyclopentadiene (3) were synthesized according to
the literature procedures [19,20]. Compound 1 was
obtained as a white crystalline material after purification
by column chromatography through silica (methylene chlo-
ride/petroleum ether, 1:4 in v/v). Yield: 68%. ESI-MS, m/z:
232.4 [M]+, 178.1 [MꢀCH3–C3H3]+. 13C NMR (CDCl3,
75 MHz): d 16.4 (CH3), 49.1, 132.3, 137.6, 141.6, 144.3
(C5H3), 126.2, 127.1, 127.9, 128.4, 128.6, 137.6, 137.8
(C6H5).
Compound 3 was purified by column chromatography
through silica (methylene chloride/petroleum ether, 1:5 in
v/v) as a white solid. Yield: 61%. ESI-MS, m/z: 294.3
[M]+, 178.2 [MꢀC6H5–C3H3]+. 13C NMR (CDCl3,
75 MHz): d 45.2, 132.1, 137.1, 142.3, 145.3 (C5H3), 125.2,
126.8, 127.2, 127.4, 128.0, 128.5, 128.7, 128.8, 129.0,
136.0, 137.4, 139.6 (C6H5).
1,2-Diphenyl-4-n-butylcyclopentadiene (2) was synthe-
sized by a similar procedure as follows: To a solution of
butyl lithium (27.7 mmol) in THF (20 mL) was slowly
added a solution of 3,4-diphenyl-2-cyclopentenone (7.03 g,
30 mmol) in THF (40 mL) under nitrogen with stirring at
0 ꢁC. The resulting solution was allowed to warm to room
temperature slowly and stirred overnight. The reaction mix-
ture was quenched with ice-water (60 mL), treated with con-
centrated hydrochloric acid (9 mL) and the organic layer
was separated. The aqueous layer was extracted with diethyl
ether (3 · 20 mL). The combined organic layers were
washed with 80 mL of saturated aqueous solution of
sodium chloride, dried over anhydrous MgSO4, filtered
and evaporated under reduced pressure. The pure product
(5.15 g, 62.5%) was obtained by column chromatography
through silica (methylene chloride/petroleum ether, 1:4 in
2.4. Synthesis of 1,2-diphenyl-4-n-butyl-
cyclopentadienyltitanium trichloride (5)
Complex 5 was synthesized in almost the same manner
as complex 4 except that 1,2-diphenyl-4-butyl-cyclopent-
adiene (1.37 g, 5.0 mmol) was used as the starting material
and its deprotonation reaction was carried out in n-hexane.
Pure 5 (1.32 g, 61.5%) was obtained as red crystals by
recrystallization from methylene chloride/n-hexane (1:4 in
v/v). Anal. Calc. for C21H21Cl3Ti (427.62): C, 58.98; H,
4.95. Found: C, 59.05; H, 4.89. IR (KBr, cmꢀ1): 3086w,
2960m, 2932m, 2875w, 1494m, 1452w, 1427m, 1156w,
1079w, 1030w, 923w, 885m, 853m, 796s, 772vs, 757vs,
1
729m, 698s, 670m, 606m. H NMR (CDCl3, 300 MHz): d
3
3
0.98 (t, JHH = 7.5 Hz, 3H, CH3), 1.47 (m, JHH = 7.4 Hz,
3
2H, CH2), 1.73 (m, JHH = 7.3 Hz, 2H, CH2), 2.93 (t,
3JHH = 7.5 Hz, 2H, CH2), 7.13 (s, 2H, C5H2), 7.36–7.57

Q.-L. Wu et al. / Polyhedron 25 (2006) 2565–2570
2567
(m, 10H, C6H5). 13C NMR (CDCl3, 75 MHz): d 13.8, 22.5,
32.2, 32.5 (C4H9), 129.4, 132.9, 145.9 (C5H2), 123.4, 128.4,
129.5, 138.3 (C6H5).
Table 1
Crystal data and structure refinement for complex 1,2-Ph2-4-Me-CpTiCl3
Formula
Fw
C18H15Cl3Ti
385.55
Temperature (K)
Crystal system
Space group
293(2)
orthorhombic
P212121
6.6086(10)
12.2932(3)
21.8492(5)
90
2.5. Synthesis of 1,2,4-triphenyl-cyclopentadienyltitanium
trichloride (6)
˚
a (A)
˚
b (A)
Complex 6 was synthesized in the same manner as
complex 4 with 1,2,4-triphenylcyclopentadiene (1.47 g,
5.0 mmol) as the starting material. Pure 6 (1.36 g, 60.6%)
was obtained as red crystals by recrystallization from meth-
ylene chloride/n-hexane (1:3 in v/v). Anal. Calc. for
C23H17Cl3Ti (447.61): C, 61.72; H, 3.83. Found: C, 61.55;
H, 3.78%. IR (KBr, cmꢀ1): 3079w, 2959w, 2931m, 2867w,
1487m, 1452w, 1425m, 1157w, 1072w, 1018w, 924w,
882w, 875m, 854m, 792s, 773vs, 759vs, 726m, 699s, 669m,
661m, 609m. 1H NMR (300 MHz, CDCl3): d 7.08
(C5H2), 7.24–7.55 (C6H5). 13C NMR (CDCl3, 75 MHz): d
123.2, 132.4 (C5H2), 123.8, 128.5, 129.6, 138.3 (C6H5).
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
3
˚
V (A )
1775.05(7)
4
1.443
784
0.926
0.37 · 0.31 · 0.26
1.86 6 h 6 23.25
ꢀ7 6 h 6 7
ꢀ13 6 k 6 6
ꢀ24 6 l 6 24
empirical
0.5093 and 0.4542
8620
Z
Dc (g cmꢀ3
F(000)
)
Absorption coefficient (mmꢀ1
Crystal size (mm3)
)
Collect range (ꢁ)
Collection region
Absorption correction
Maximum and minimum transmission
Number of reflections
2.6. X-ray structural determination of complex 4
Number of independent reflections
Rint
2547
0.0286
Single crystals of complex 4 suitable for X-ray diffrac-
tion were grown from a saturated solution in methylene
chloride/n-hexane (1:4, v/v) at room temperature. A red
crystal of dimensions 0.37 · 0.31 · 0.26 mm sealed in a
glass capillary was used. Data collection was performed
using a standard Siemens SMART CCD diffractometer
with graphite monochromated Mo Ka radiation. The
data were integrated using the siemens SAINT program
with intensities corrections for lorentz factor, polarization
and air absorption [21]. The structure was solved by the
direct method and was refined by full-matrix least squares
techniques [22]. All non-hydrogen atoms were refined with
anisotropic thermal parameters, while all hydrogen atoms
were placed by geometrical considerations and refined
isotropically. Crystallographic data, details of the data
collection and refinement parameters are summarized in
Table 1.
Number of data/restraints/parameters
Final R indices [I > 2r(I)]
2547/0/200
R1 = 0.0240
wR2 = 0.0636
R1 = 0.0260
wR2 = 0.0645
1.072
R indices (all data)
Goodness-of-fit
Largest difference in peak and hole (e/A
ꢀ3
˚
)
0.210 and ꢀ0.157
3. Results and discussion
3.1. Synthesis of ligands
1,2-Diphenyl-4-methyl-1,3-cyclopentadiene (1) and
1,2,4-diphenyl-1,3-cyclopentadiene (3) were synthesized
according to the literature procedures [19,20] and character-
ized by 1H and 13C NMR as well as mass spectroscopy. The
1H NMR data are identical to that reported. The 13C NMR
and mass spectroscopy data are in agreement with the struc-
tures of compounds 1 and 3. 1,2-Diphenyl-4-butyl-1,3-
cyclopentadiene (2) was synthesized in similar way via the
1,2-addition reaction of 3,4-diphenyl-2-cyclopentenone
with butyllithium, followed by dehydration of the 1-
hydroxy-1-butyl-3,4-diphenyl-2-cyclopentene with concen-
trated HCl. Compound 2 was also characterized by 1H
and 13C NMR as well as mass spectroscopy. These spectros-
copy data are consistent with the structure of compound 2.
2.7. Polymerization of styrene
Styrene polymerization experiments were carried out in
a 250 mL Schlenk flask with magnetic stirring. Fifty milli-
liters of toluene, 5 mL of freshly distilled styrene and an
appropriate amount of MAO were added to the flask that
was placed in an oil bath at the desired temperature and the
mixture was stirred for 10 min. The titanium catalyst
(2.5 lmol in toluene) was injected into the flask and the
polymerization was performed at 25, 50 or 75 ꢁC for 30
or 60 min periods. The polymerization was terminated by
addition of 10% HCl in methanol. The precipitated poly-
mer was washed three times with methanol and dried at
100 ꢁC in vacuo to a constant weight. The polymer was
extracted with refluxing 2-butanone for 24 h in a Soxhlet
extractor to remove atactic polymer and dried again at
100 ꢁC for 24 h.
3.2. Synthesis of titanium complexes
Complexes 4, 5 and 6 were synthesized in similar way to
the published procedure [23,24]. Treatment of compounds
1, 2 and 3 with n-butyl lithium, followed by reaction
with trimethylchlorosilane, produced the trimethylsilyl
substituted derivatives of 1, 2 and 3, respectively. The

2568
Q.-L. Wu et al. / Polyhedron 25 (2006) 2565–2570
deprotonation reaction of compounds 1 and 3 was carried
out in diethyl ether, while the same reaction of compound 2
was conducted in n-hexane since 2 has pretty good solubil-
ity in n-hexane and the produced lithium salt readily pre-
cipitated from n-hexane, which resulted in the easy
separation of the lithium salt. Reactions of the trimethylsi-
lyl substituted derivatives with TiCl4 in toluene (Scheme 1)
gave the corresponding complexes 4, 5 and 6, respectively.
These titanium complexes are quite soluble in benzene,
toluene and methylene chloride, whilst being slightly solu-
ble in n-pentane and n-hexane. Therefore, they can be
recrystallized from a mixture of methylene chloride and
n-hexane. These complexes were found to be relatively
stable to air and moisture in the solid state, and could be
exposed to air for several hours without obvious decompo-
sition, but they decomposed readily in solution when
exposed to air.
3.3. The crystal structure of complex 4
Fig. 1. Structure of complex 4.
The crystal structure of the complex 4 is shown in Fig. 1,
and selected bond distances and angles are summarized in
Table 2. The coordination geometry about the Ti atom can
be described as a distorted tetrahedron, formed by the substi-
tuted Cp ring and three Cl atoms, which is similar to that of
known titanium complexes (g5-C9H7)TiCl3 and (g5-
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) for complex 4
Complex 4
˚
C9Me7)TiCl3 [8j,25]. The distances of Ti–C1 (2.388(2) A)
Ti(1)–Cl(1)
Ti(1)–Cl(3)
Ti(1)–Cl(2)
Ti(1)–C(3)
Ti(1)–C(4)
Ti(1)–C(5)
Ti(1)–C(2)
Cl(1)–Ti(1)–Cl(2)
Cl(1)–Ti(1)–Cl(3)
Cl(3)–Ti(1)–Cl(2)
2.2437(9)
2.2466(8)
2.2138(9)
2.338(3)
2.334(3)
2.327(3)
2.405(3)
Ti(1)–C(1)
Ti(1)–centroid
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
2.388(2)
2.028(3)
1.430(3)
1.419(3)
1.417(3)
1.396(4)
˚
and Ti–C2 (2.405(3) A) are longer than those of known Ti–
Cp-ring carbon distances [8j,8k], which could be obviously
attributed to the steric effect of the two phenyl groups on
the Cp-ring. The C–C distances in the substituted Cp ring
˚
range from 1.396(4) to 1.430(3) A, and the C1–C2 bond
˚
103.27(4)
103.66(3)
101.19(4)
Cl(1)–Ti(1)–centroid
Cl(2)–Ti(1)–centroid
Cl(3)–Ti(1)–centroid
115.8(2)
116.0(3)
115.0(3)
length (1.430(3) A) is the longest among these values, which
could also be explained by the steric and conjugate effects of
the two phenyl groups on the Cp-ring. The average Ti–Cl
˚
˚
distance of 2.2347(9) A is close to that of 2.2308(1) A in
(g5-C9H7)TiCl3 [8j]. The Cl–Ti–Cl angles in complex 4 are
in the range of 101.19(4)ꢁ–103.66(3)ꢁ. The two phenyl groups
on the Cp-ring construct a partially crowded environment
around the metal center, which might have a greater or lesser
effect on the polymerization of styrene (see Table 2).
tactic polystyrene. The results of styrene polymerization
catalyzed by these complexes under different conditions
are summarized in Table 3. For comparison, polymeriza-
tion experiments catalyzed by CpTiCl3/MAO were also
carried out under identical conditions. As can be seen from
Table 3, the 4–6/MAO systems show better catalytic per-
formance than the CpTiCl3/MAO system for styrene poly-
merization in terms of catalytic activity, syndiotacticity,
melting temperature and molecular weight of the produced
polystyrene. It has been known that the phenyl substituent
3.4. Styrene polymerization
Upon activation with MAO, complexes 4, 5 and 6 can
all catalyze the polymerization of styrene to form syndio-
1. n-BuLi
2. TMSCl
3. TiCl4
Ph
Ph
1. RLi
2. H+
Ph
Ph
R
O
R
Ti
Ph
Ph
Cl
Cl
Cl
1 R= Me
2 R= n-Bu
3 R= Ph
4 R= Me
5 R= n-Bu
6 R= Ph
Scheme 1. Synthetic procedure of complexes 4–6.

Q.-L. Wu et al. / Polyhedron 25 (2006) 2565–2570
2569
Table 3
Styrene polymerization catalyzed by complexes 4, 5 and 6, activated by MAOa
Ab (·10ꢀ7
)
SYc (%)
Tm (ꢁC)
Mg (·10ꢀ5
)
d
e
No.
Catalyst
Time (min.)
Tp (ꢁC)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
a
4
30
30
30
60
30
30
30
60
30
30
30
60
30
30
30
60
25
50
75
50
25
50
75
50
25
50
75
50
25
50
75
50
0.71
1.32
1.05
1.10
0.67
1.20
1.12
1.03
0.56
1.05
0.75
0.92
0.61
1.14
0.95
1.05
92.1
96.8
94.0
94.6
93.2
96.1
95.0
95.5
94.5
96.1
95.0
96.0
83.1
87.5
84.3
86.7
273.8
269.5
270.6
272.3
273.4
270.3
271.5
272.4
272.1
269.5
267.7
270.8
263.2
261.6
259.0
260.9
1.69
1.63
1.55
1.58
1.65
1.54
1.38
1.44
1.45
1.24
1.26
1.31
1.26
1.21
1.05
1.17
5
6
CpTiCl3
Polymerization conditions: [Ti] = 50 lM; [Al]/[Ti] = 3000; reaction time = 0.5 or 1 h; [styrene] = 0.87 M.
A (activity) = (g bulk polymer)/(mol Ti)(mol monomer)(h).
b
c
Percentage s-PS = [(g of 2-butanone insoluble polymer)/(g of butanone polymer)] · 100.
d
e
Tm, melting temperature of s-PS, determined with DSC at a heating rate of 10 ꢁC minꢀ1
Mg, measured in o-dichlorobenzene at 135 ꢁC.
.
on the cyclopentadienyl group of similar titanium catalysts
can improve the catalytic property due to the increased res-
onance stabilization [8l,26].
Acknowledgement
This work was supported by the National Natural
Science Foundation of China (No. 20374023).
For all complexes 4, 5 and 6, the catalytic activity
increases with the increase in polymerization temperature,
and reaches the highest value at about 50 ꢁC. Further
increase in the polymerization temperature results in a
decrease in the catalytic activity. All catalytic systems
exhibit higher catalytic activities for 30 min polymeriza-
tion experiments than 60 min ones, which indicates that
the active catalysts deactivate during the polymerization.
The results in Table 3 also demonstrate the substituent
effect of the R group on the cyclopentadienyl ligand of
complexes 4, 5 and 6 on their catalytic properties. The
catalytic activity of these complexes is in the order of
6 < 5 < 4, which implies that both the electronic and ste-
ric factors of the R group play roles in determining the
catalytic activity of these complexes. In addition, in com-
parison with the CpTiCl3 catalyst system, the syndiotac-
ticity of polystyrenes produced with the 4, 5 or 6
catalyst system is higher, which might be attributed to
the relatively crowded environment around the metal
center of 4, 5 and 6.
Appendix A. Supplementary data
Crystallographic data (excluding structure factors) for
the structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Center as Sup-
plementary Publication No. CCDC-260775. Copies of the
data can be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, fax:
+44 1223 336 033, e-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.poly.2006.03.006.
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4. Conclusions
We have synthesized and characterized 1,2-diphenyl-4-
R-cyclopentadienyl titanium trichloride (R = Me (4), n-
Bu (5), Ph (6)). The molecular structure of complex 4
has been confirmed by X-ray crystallography. When acti-
vated with MAO, these titanium complexes are efficient
catalysts for the syndioselective polymerization of
styrene.
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