Preparation of titanocene and zirconocene dichlorides bearing bulky 1,4-dimethyl-2,3-diphenylcyclopentadienyl ligand and their behavior in polymerization of ethylene

Article abstract of DOI:10.1016/j.jorganchem.2008.10.019

New metallocene dichlorides [η⁵-(1,4-Me₂-2,3-Ph₂-C₅H )₂TiCl₂] (2), [η⁵-(1,4-Me₂-2,3-Ph₂-C₅H )₂ZrCl₂] (3) and [η⁵

Full text of DOI:10.1016/j.jorganchem.2008.10.019

Journal of Organometallic Chemistry 694 (2009) 173–178
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Journal of Organometallic Chemistry
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Preparation of titanocene and zirconocene dichlorides bearing bulky
1,4-dimethyl-2,3-diphenylcyclopentadienyl ligand and their behavior
in polymerization of ethylene
a
a,
b
c
d
*
ˇ
ˇ
Michal Horácek , Jirí Pinkas , Jan Merna , Róbert Gyepes , Philippe Meunier
a
´
J. Heyrovsky Institute of Physical Chemistry of ASCR, v.v.i., Dolejškova 2155/3, 182 23 Prague 8, Czech Republic
b Institute of Chemical Technology, Prague, Department of Polymers, Technická 5, 166 28 Prague 6, Czech Republic
c Charles University, Department of Inorganic Chemistry, Hlavova 2030, 128 40 Prague 2, Czech Republic
d Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB, UMR CNRS 5260), Université de Bourgogne, 9, Avenue Alain Savary, 21078 Dijon, France
a r t i c l e i n f o
a b s t r a c t
5-(1,4-Me2-2,3-Ph2-C5H)2TiCl2] (2), [
5-(C5H5)ZrCl2] (4) were prepared from lithium salt of 1,4-dimethyl-2,3-
5-(C5H5)ZrCl3(DME)], respectively. Com-
g
5-(1,4-Me2-2,3-Ph2-C5H)2ZrCl2] (3)
Article history:
Received 1 April 2008
Received in revised form 7 October 2008
Accepted 10 October 2008
Available online 18 October 2008
New metallocene dichlorides [
and [
diphenylcyclopentadiene (1) and [TiCl3(THF)3], [ZrCl4] and [
pounds 2–4 were characterized by NMR spectroscopy, EI-MS and IR spectroscopy, and the solid state
structure of 3 was determined by single crystal X-ray crystallography. The catalytic systems 3/MAO
and 4/MAO were almost inactive in polymerization of ethylene at 30–50 °C, however, they exhibited high
activity at temperature 80 °C. The catalyst formed from 2 and excess of MAO was practically inactive at
all temperatures.
g
g g
5-(1,4-Me2-2,3-Ph2-C5H)
g
Keywords:
Substituted cyclopentadienes
Titanocene
Ó 2008 Elsevier B.V. All rights reserved.
Zirconocene
Ethylene polymerization
Crystal structure
1. Introduction
ethylene-styrene copolymerization with substantially increased
ratio of styrene units in the resulting resin compared to other cat-
Highly substituted cyclopentadienes as ligands for group 4
metallocene complexes are still one of the important subjects of
organometallic chemistry. Apart from complexes bearing persub-
stituted bulky cyclopentadienes [1], which were extensively
studied in past decades, examples of complexes with relatively
bulky phenyl substituted cyclopentadienyl rings still remain rather
rare.
alytic systems [6].
Coming from our permanent interest in group 4 metallocene
dichlorides bearing phenyl substituted cyclopentadienyl ligand
[7] we have investigated the cyclopentadienyl ligand having two
methyl groups in 1,4- positions in addition to two vicinal phenyl
groups (i.e. 1,4-Me2-2,3-Ph2-C5H). Although the parent 1,4-di-
methyl-2,3-diphenylcyclopentadiene is known for more than 40
years, its utilization as a ligand in organometallic chemistry has
been so far limited to only one example [8,9].
Here, we report the preparation and characterization of
titanium and zirconium complexes containing 1,4-dimethyl-2,3-
diphenylcyclopentadienyl ligand and the catalytic behavior of
catalysts prepared thereof in polymerization of ethylene.
Complexes containing the substituted cyclopentadienyl ligand
of general formula (1,2-Ph2-4-R-C5H2) became exploited after the
first zirconocene dichlorides with R = H in their ligands were devel-
oped [2]. Molecular orbitals of
[g
5-(1,2-Ph2-4-R-C5H2)2ZrCl2]
(where R = H, Me, Ph) were calculated by DFT method and the
theoretical and experimental UV spectra were compared [3].
Monocyclopentadienyl titanium trichlorides with the ligand 1,2-
Ph2-4-R-C5H2 (where R = Me, Bu, Ph) after activation with MAO
(MAO – methylaluminoxane) afforded syndiotactic polystyrene
with high productivity and selectivity [4,5]. Very recently, the con-
2. Experimental
2.1. Materials and equipments
strained geometry complex
[g
5-(1,2-Ph2-C5H3)(SiMe2N-tBu)-
TiMe2] developed by Arriola et al. showed a high activity in
All reactions with moisture- and air-sensitive compounds
were carried out under argon (99.999%) or nitrogen (Siad
99.999%) atmosphere using standard Schlenk techniques. Solvents
were dried, and freshly distilled prior to use. ZrCl4 and n-butyllith-
ium (1.6 M) were obtained from Aldrich and used as received.
* Corresponding author. Tel.: +420 2 8658 3735; fax: +420 2 8658 2307.
E-mail address: pinkas@jh-inst.cas.cz (J. Pinkas).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.10.019

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M. Horácek et al. / Journal of Organometallic Chemistry 694 (2009) 173–178
174
[TiCl3(THF)3] [10] (THF – tetrahydrofuran) and [
(DME)] [11] (DME – dimethoxyethane) were prepared according
to literature procedures.
Ethylene (Siad 99.5%) for polymerization experiments was puri-
fied by passing through columns with copper catalyst and molecu-
lar sieves to remove traces of oxygen and moisture. Metallocene
precatalysts were used as toluene solutions, which were stored
in Schlenk vessels at 5 °C. MAO (Crompton, 10% in toluene) was
used as received.
1,4-Dimethyl-2,3-diphenylcyclopentadiene was prepared fol-
lowing a published procedure and characterized by spectroscopic
data which were missing in [8]. 1H NMR (500 MHz) and 13C{1H}
NMR (125 MHz) were measured on a Bruker DRX500 spectrometer
in C6D6 or CDCl3 solution at 300 K. Chemical shifts are given rela-
tive to the solvent signal (dH 7.15 ppm, dC 128.00 ppm for C6D6
and dH 7.26 ppm, dC 77.16 ppm for CDCl3). Mass spectra were mea-
sured on a KRATOS concept IS instrument (Centre de Spectroscopie
Moléculaire de l’Université de Bourgogne) at 70 eV. Infrared spec-
tra were recorded on a Nicolet Avatar FT IR spectrometer in the
range 400–4000 cmꢀ1. Melting points of organic compounds and
complexes were measured on Koffler block and were uncorrected.
Elemental analyses (EA) were carried out on an Elementar vario EL
III facility (Elementar) and average values from at least two mea-
surements were taken. The polyethylene melting temperature
was determined by DSC (TA Instruments, Q100) from the second
heating run using heating and cooling rate 10 °C minꢀ1. Molar
masses of polyethylenes were determined by viscometry in deca-
line at 135 °C using Mark-Houwink parameters K = 6.2 ꢁ 10ꢀ4
and a = 0.70 [12].
g
5-(C5H5)ZrCl3-
was dissolved in 60 ml of toluene, and filtered through cellite
pad. The volume of a dark brown toluene extract was concentrated
to ca. 15 ml and stored at ꢀ18 °C for several days. Dark brown
microcrystals were isolated, washed with cold toluene (5 ml), hex-
ane (3 ꢁ 10 ml) and dried in vacuum. Yield 1.12 g (56%).
M.p. 235 °C. 1H NMR (C6D6): 2.06 (s, 6H, Me); 2.10 (s, 1.5H,
PhMe)*; 5.77 (s, 1H, CH, C5Me2Ph2H); 6.93–6.98 (m, 2H, CHpara
,
Ph); 6.99–7.02 (m, 1.5H, PhMe)*; 7.03–7.07 (m, 4H, CHortho, Ph);
7.10–7.15 (m, 1H, PhMe)*; 7.42–7.47 (m, 4H, CHmeta, Ph). 1H NMR
(CDCl3): 2.38 (s, 6H, Me); 2.43 (s, 1.5H, PhMe)*; 6.41 (s, 1H, CH,
C5Me2Ph2H); 7.22–7.36 (m, 10H + 2.5H*, CH, C5Ph and PhMe*). 13C
{1H} (CDCl3): 17.15 (C5Me2Ph2); 21.61 (PhMe)*; 116.98 (CH,
C5Me2Ph2H); 125.44, 128.37, 129.18 (CH, PhMe)*; 127.30, 127.40,
132.08 (CH, C5Ph); 125.25, 134.12, 139.27 (Cq; C5Me2Ph2H and
Ph) 138.02 (Cq; PhMe)*. Signals denoted by asterisk belong to half
equivalent of solvating toluene. EI-MS (200 °C): m/z (relative abun-
dance) 610 (12), 609 (8), 608 (M+Å; 17), 573 ([MꢀCl]+; 47), 400 (10),
399 (8), 365 (78), 364 (33), 363 ([MꢀC5Me2Ph2H]+; 100), 328
([MꢀC5Me2Ph2HꢀCl]+; 22), 327 (21), 326 (14), 325 (27), 246 (62),
245 ([C5Me2Ph2H]+; 88), 230 ([C5MePh2H]+; 27), 229 (35), 228
(25), 215 ([C5Ph2H]+; 49), 167 (14), 165 (12), 152 (11), 129 (7),
128 (5), 115 (9), 91 (22). IR (KBr, cmꢀ1): 3087 (m), 3055 (s), 3026
(s), 2957 (m), 2917 (s), 1601 (m), 1575 (w), 1505 (w), 1494 (m),
1486 (m), 1463 (s), 1439 (s), 1422 (m), 1381 (m), 1366 (m), 1324
(vw), 1283 (vw), 1237 (vw), 1183 (w), 1156 (vw), 1079 (w), 1019
(m), 1002 (vw), 981 (vw), 919 (vw), 868 (w), 767 (s), 753 (vs),
731 (s), 698 (vs), 644 (w), 624 (m), 613 (w), 572 (vw), 506 (w),
465 (w). EA for C38H34Cl2Ti ꢂ 1/2 C7H8 (655.55) calcd. C 76.04, H
5.84%; found C 75.49, H 5.95%.
2.4. Preparation of bis(g
5-1,4-dimethyl-2,3-diphenylcyclopenta-
dienyl)zirconocene dichloride (3)
2.2. Characterization of 1,4-dimethyl-2,3-diphenylcyclopenta-1,3-
diene (1) [8]
A 1.6 M n-butyllithium in hexane (13.4 ml, 21.4 mmol) was
added dropwise to a stirred solution of 1 (5.27 g, 21.4 mmol) in tol-
uene (60 ml). The reaction mixture with the precipitated lithium
salt of 1 was stirred for 5 h, and ZrCl4 (2.50 g, 10.7 mmol) was
added in one portion. The resulting suspension was stirred for
1 h at ambient temperature and then refluxed for 2 days. The vol-
atiles were evaporated and the residue was heated to 170 °C in
vacuum for 4 h to remove traces of unreacted 1. The resulting yel-
low-brown solid was extracted in Soxhlet extractor with boiling
hexane within 2 days. The yellow solid which precipitated during
extraction from the hexane solution was isolated, washed with
hexane (3 ꢁ 15 ml), ethanol (3 ꢁ 15 ml), and dried in vacuum.
Yield 2.06 g (30%).
1H NMR (C6D6): 1.94 (s, 6H, Me); 2.74 (s, 2H, CH2), 6.97–7.01 (m,
2H, CHpara, Ph), 7.05–7.12 (m, 8H, CH, Ph). 13C{1H}(C6D6): 14.43
(Me); 49.90 (CH2); 126.37, 128.02, 129.92 (CH, Ph); 136.19,
137.24, 142.19 (Cq; C5Me2Ph2 and Ph). EI-MS (70 °C): m/z (relative
abundance) 247 (25), 246 (M+Å; 100), 231 ([MꢀMe]+; 16), 216
([Mꢀ2Me]+; 14), 215 (22), 202 (9), 165 (5), 155 (6), 153 (6), 152
(6), 128 (4), 115 (6), 91 (3), 77 (2). IR (KBr, cmꢀ1): 3100 (vw),
3076 (w), 3050 (m), 3028 (w), 2980 (w), 2969 (w), 2939 (w),
2902 (s), 2849 (m), 2731 (vw), 1955 (vw), 1888 (vw), 1816 (vw),
1767 (vw), 1602 (s), 1570 (w), 1494 (s), 1484 (m), 1440 (vs),
1373 (s), 1308 (w), 1240 (w), 1228 (vw), 1179 (vw), 1154 (w),
1128 (vw), 1076 (m), 1031 (vw), 1014 (vw), 1004 (w), 983 (m),
923 (w), 834 (vw), 772 (s), 756 (vs), 707 (vs), 683 (w), 646 (w),
620 (vw), 567 (m), 501 (vw), 433 (vw).
M.p. 264 °C. 1H NMR (C6D6): 2.10 (s, 6H, Me); 5.69 (s, 1H, CH,
C5Me2Ph2H); 6.91–6.98 (m, 2H, CHpara, Ph); 7.01–7.09 (m, 4H,
CHortho, Ph); 7.40–7.45 (m, 4H, CHmeta, Ph). 13C{1H}(C6D6): 16.05
(Me); 114.02 (CH, C5Me2Ph2H); 127.35, 127.88, 132.06 (CH, Ph);
122.01, 134.31, 134.43 (Cq; C5Me2Ph2H and Ph). EI-MS (210 °C):
m/z (relative abundance) 654 (9), 653 (6), 652 (M+Å; 11), 651 (7),
650 (10), 411 (50), 410 (25), 409 (97), 408 (51), 407
([MꢀC5Me2Ph2H]+; 100), 406 (61), 405 (99), 393 (16), 392 (8),
391 (23), 390 (15), 389 (31), 373 (28), 371 (19), 370 (12), 369
(30), 368 (12), 367 (24), 365 (12), 246 (39), 245 ([C5Me2Ph2H]+;
18), 244 (14), 230 ([C5MePh2H]+; 14), 229 (28), 228 (20), 216
(13), 215 ([C5Ph2H]+; 27), 167 (11), 165 (13), 152 (12), 115 (16),
91 (19), 77 (10). IR (KBr, cmꢀ1): 3089 (m), 3051 (m), 2988 (w),
2955 (m), 2923 (m), 1601 (m), 1576 (w), 1506 (m), 1485 (w),
1462 (m), 1441 (s), 1381 (w), 1322 (vw), 1311 (vw), 1283 (vw),
1238 (vw), 1184 (w), 1157 (vw), 1079 (w), 1032 (w), 1017 (w),
1003 (vw), 983 (vw), 920 (vw), 863 (vw), 844 (m), 767 (s), 753
(vs), 699 (vs), 645 (w), 626 (m), 614 (w), 571 (w), 506 (vw), 416
(vw). EA for C38H34Cl2Zr (652.82) calcd. C 69.92, H 5.25%; found
C 69.64, H 5.36%.
2.3. Preparation of bis(g
5-1,4-dimethyl-2,3-diphenylcyclopenta-
dienyl)titanocene dichloride (2)
A 1.6 M n-butyllithium in hexane (4.5 ml, 7.19 mmol) was
added dropwise to a solution of 1 (1.77 g, 7.19 mmol) in diethyl
ether (80 ml) cooled to 0 °C. The reaction mixture was allowed to
warm to room temperature and then stirred overnight. The result-
ing pale beige precipitate was filtered, washed three times with
20 ml of diethyl ether and dried in vacuum. A beige powder of lith-
ium salt of 1 (1.65 g, 6.54 mmol) was dissolved in THF to give a the
deep red solution. This was cooled to ꢀ78 °C, and [TiCl3(THF)3]
(1.21 g, 3.27 mmol) was gradually added under stirring. The reac-
tion mixture was allowed to warm to room temperature, and then
refluxed for 12 h. The resulting dark green mixture was cooled to
room temperature, and carbon tetrachloride (2.0 ml) was added.
This caused an immediate color change to deep brown. After reflux
for 2 h, all volatiles were evaporated to vacuum, the solid residue

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M. Horácek et al. / Journal of Organometallic Chemistry 694 (2009) 173–178
175
2.5. Preparation of (
diphenylcyclopentadienyl)zirconocene dichloride (4)
g
5-cyclopentadienyl)(
g
5-1,4-dimethyl-2,3-
atoms were refined with anisotropic thermal motion parameters.
The hydrogen atoms were included in calculated positions. Rele-
vant crystallographic data are collected in Table 1.
A mixture of solid lithium salt of 1 (prepared as for 2) (0.36 g,
1.42 mmol) and [(
g
5-C5H5)ZrCl3(DME)] (0.50 g, 1.42 mmol) was
2.7. Ethylene polymerization
cooled to ꢀ78 °C and 20 ml of toluene was added. The reaction
mixture was stirred for 10 min at this temperature, then allowed
to warm to room temperature, and refluxed for 2 days. The result-
ing greenish suspension was filtered through a cellite pad. The
resulting yellow filtrate was concentrated to ca. 8 ml and stored
in a freezer (ꢀ18 °C) for several days. Yellowish microcrystals were
collected, washed with cold toluene (5 ml), hexane (3 ꢁ 5 ml), and
dried in vacuum. Yield 0.26 g (39%).
Polymerizations were carried out in 100 ml magnetically stirred
jacket glass reactor. Toluene, ethylene and MAO solution were
dosed in this order and the mixture was stirred for 15 min to equil-
ibrate reaction temperature. The polymerization was started by
injection of the precatalyst solution. The ethylene pressure was
kept constant (1.1 atm) during the whole polymerization. The
polymerization was quenched by 2 ml of EtOH/HCl mixture and
polymer precipitated in a large excess of 3% HCl solution in EtOH.
The polymer was filtered and dried in vacuum to constant weight.
M.p. 164–165 °C. 1H NMR (C6D6): 2.01 (s, 6H, Me); 5.42 (s, 1H,
CH, C5Me2Ph2H); 5.98 (s, 5H, CH, C5H5); 6.94–6.99 (m, 2H, CHpara
,
Ph); 7.02–7.07 (m, 4H, CHortho, Ph); 7.30–7.34 (m, 4H, CHmeta, Ph).
13C{1H}(C6D6): 15.97 (Me); 115.22 (CH, C5Me2Ph2H); 116.51 (CH,
C5H5); 127.40, 128.04, 131.54 (CH, Ph); 124.24, 131.49, 134.04
(Cq; C5Me2Ph2H and Ph). EI-MS (210 °C): m/z (relative abundance)
474 (20), 473 (12), 472 (M+Å; 28), 471 (14), 470 (27), 435 ([MꢀCl]+;
5), 411 (33), 410 (18), 409 (71), 408 (36), 407 ([MꢀC5H5]+; 99), 406
(43), 405 (100), 391 (12), 389 (16), 371 (13), 369 (22), 367 (19), 365
(11), 246 (15), 245 ([C5Me2Ph2H]+; 8), 244 (9), 229 (21), 228 (17),
227 ([MꢀC5Me2Ph2H]+; 16), 225 (16), 215 (22), 202 (11), 165
(11), 152 (11), 128 (11), 115 (14), 91 (15), 77 (11). IR (KBr,
cmꢀ1): 3112 (m), 3089 (m), 3060 (m), 2989 (w), 2956 (w), 2929
(w), 1601 (w), 1576 (vw), 1505 (w), 1485 (w), 1464 (w), 1441
(s), 1380 (w), 1314 (vw), 1239 (vw), 1185 (vw), 1157 (vw), 1127
(vw), 1077 (w), 1016 (m), 1003 (vw), 986 (vw), 919 (vw), 819
(vs), 766 (s), 754 (s), 701 (vs), 669 (w), 654 (w), 628 (w), 615
(w), 572 (w), 508 (w), 418 (w). EA for C24H22Cl2Zr (472.57) calcd.
C 61.00, H 4.69%; found C 60.62, H 4.52%.
3. Results and discussion
3.1. Preparation of 1,4-dimethyl-2,3-diphenylcyclopentadiene (1)
Compound 1 was prepared according to a reported synthetic
procedure (Scheme 1) [8]. Although direct preparation of trans-
2,5-dimethyl-3,4-diphenylcyclopent-2-en-1-one (as the key inter-
mediate) by condensation of 3-pentanone with 2 equivalents of
benzaldehyde catalyzed by ZrOCl2 ꢂ 8H2O was reported, the pub-
lished conditions were compatible rather with a microscale prepa-
ration [15]. Recently it has been observed that replacement of
ZrOCl2 ꢂ 8H2O catalyst by [TiCl4(THF)2] leads to higher yields and
the reaction scale can be enlarged to a multigram quantity [16].
Nevertheless, the use of inert conditions still makes the reaction
quite difficult. Thus, we preferred base-catalyzed condensation of
3-pentanone with benzil [17–19], followed by repeated reduction
and acid-catalyzed dehydration providing 1 as a yellow crystalline
solid (Scheme 1). In dependence on the conditions of the last dehy-
dration step we obtained the desired product as cyclopentadiene
with C2v symmetry or as a mixture of isomers. The cyclopentadiene
1 has very similar EI-MS pattern to previously prepared substitu-
tion isomer 2,3-dimethyl-1,4-diphenylcyclopentadiene (I) [7]. Both
compounds have the molecular ion m/z 246 as a base peak,
whereas the abundance of other ions is rather low. On the other
hand 1H NMR of C6D6 solutions of the compounds are quite differ-
ent showing remarkable redistribution of electron density as a con-
sequence of different position of methyl and phenyl groups in 1
and I. As the most remarkable was a significant downfield shift
2.6. X-ray crystallography
The yellow-green crystal of 3 was grown from its dichlorometh-
ane solution during hexane diffusion. Diffraction data were col-
lected on a Nonius KappaCCD diffractometer. The structure was
solved by direct methods (SIR-97) [13] and refined by weighted
full-matrix least-squares on F2
(SHELXL-97) [14]. All non hydrogen
Table 1
Crystallographic data, data collection and structure refinement data for compound 3.a
Chemical formula
C38H34Cl2Zr
of methylene protons in
1 compared to I (2.74 ppm in 1,
Molecular weight
Crystal system
Space group
Temperature (K)
a (Å)
652.77
3.47 ppm in I; for comparison: 1,2,3,4-tetramethylcyclopentadiene
in CDCl3 2.60 ppm [20], 1,2,3,4-tetraphenylcyclopentadiene in
C6D6 3.72 ppm [21]). The similar downfield shift was observed
for all aromatic protons in 1 with respect to I. A lower stability
Monoclinic
P21/c (No. 14)
150(2)
21.7600(4)
14.9530(3)
19.2860(4)
90.000
b (Å)
c (Å)
a
(°)
b (°)
91.8930(13)
90.000
c
(°)
Z
8
Crystal size (mm3)
0.50 ꢁ 0.05 ꢁ 0.05
Dcalc (g ꢁ cmꢀ3
)
1.383
l
(Mo K
a
) (mmꢀ1
)
0.546
F(000)
2688
h range (°)
hkl range
Reflections collected/unique
Parameters
1.72–26.73
ꢀ27/27, ꢀ15/18, ꢀ24/24
46774/13245
747
R, wR [I > 2
R, wR (all data)
r
(I)]
0.0403, 0.0727
0.0761, 0.0842
1.011
0.362, ꢀ0.576
S
D
qmax,min (e Åꢀ3
)
P
P
P
2
2
a
R(F) =
R
||Fo|ꢀ |Fc||/
R
|Fo|, wRðF2Þ¼½ ðwðF2o ꢀ Fc2Þ Þ=ð wðFo2Þ Þꢃ1=2, S ¼ ½ ðwðF2o
Scheme 1. Synthesis of 1,4-dimethyl-2,3-diphenylcyclopentadiene (1) as published
in Ref. [8].
2
1=2
ꢀF2c Þ Þ=ðNdiffrs ꢀ NparamsÞꢃ
.

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M. Horácek et al. / Journal of Organometallic Chemistry 694 (2009) 173–178
176
of 1 compared to I is to be noticed, since prolonged storage at room
temperature led to the compound decomposition. We suggest that
this behavior results from a lower extent of conjugation of cyclo-
pentadiene and phenyl rings in 1.
For synthesis of complex 4 bearing different cyclopentadienyl
ligands two synthetic pathways were attempted. Initially, a con-
secutive addition of the lithium salt of 1 and cyclopentadienyllithi-
um to ZrCl4 was performed. The NMR characterization of crude
product revealed a mixture of 4, 3 and [g
5-(C5H5)2ZrCl2] in ratio
3.2. Preparation of group 4 metallocene dichlorides
78:8:14. Although 3 was removed from the mixture by fractional
crystallization, 4 could not be obtained in pure form due to its sim-
Synthetic procedure for preparation of metallocene dichlorides
2–4 is depicted in Scheme 2. Deprotonation of ligand precursor 1
with n-butyllithium in diethyl ether affords lithium salt in almost
quantitative yield. The reaction of two equivalents of the lithium
salt with [TiCl3(THF)3] in THF gives a titanocene chloride, whose
oxidation with an excess of CCl4 yields titanocene dichloride 2 in
moderate yield. The complex 2 crystallizes from toluene solution
as hemisolvate with toluene as was detected by NMR spectroscopy
and elementary analysis. The zirconocene dichloride 3 was pre-
pared in modest yield by the reaction of ZrCl4 with two equivalents
of the lithium salt of ligand 1 in boiling toluene.
ilar solubility to that of [g
5-(C5H5)2ZrCl2] (the final product still
contained about 10% of [
g
5-(C5H5)2ZrCl2]). Therefore the reaction
5-(C5H5)ZrCl3(DME)] was used as an
of lithium salt of 1 with [
g
alternative reaction pathway. The later reaction led to zirconocene
dichloride 4 as a sole product in moderate yield.
The 1H and 13C NMR spectra of 2–4 showed the C2v time aver-
aged symmetry indicating free rotation of both cyclopentadienyl
and phenyl rings at room temperature. All complexes displayed
characteristic signals for methyl groups directly bonded to ring
moiety with chemical shifts 2.06 ppm for 2, 2.10 ppm for 3 and
2.01 ppm for 4. The singlet signals belonging to the CH group of
cyclopentadienyl ring appeared at 5.77 ppm for 2, 5.69 ppm for 3
and 5.42 ppm for 4.
EI-MS spectra of all complexes showed only low abundant
molecular ions (m/z = 608 for 2, m/z = 652 for 3 and m/z = 472 for
4), while the most abundant fragment ion was [Cp0MCl2]+. All spec-
tra showed a surprisingly abundant fragment m/z = 246 which
could be assigned to a protonated form of ligand [Cp0H]+, which
is for 3 and 4 even more abundant then [Cp0]+ (m/z = 245).
3.3. Crystal structure analysis
The complex 3 crystallizes with two independent molecules
(denoted 3a and 3b) in the unit cell (space group P21/c). Molecular
structures of molecules 3a and 3b are shown in Fig. 1, selected
bond lengths and angles for both independent molecules are given
in Table 2. The zirconium atoms have distorted tetrahedral envi-
ronment with the Zr–Cl distances 2.4247(6) Å and 2.4262(7) Å
for 3a and 2.4103(8) Å and 2.4326(8) Å for 3b which is close to
other octasubstituted zirconocene dichlorides (average Zr–Cl
distance in [ZrCl2{g -
5-(C5Me4H)}2] is 2.434(3) Å [22], in [ZrCl2{g5
(C5H-1,4-Ph2-2,3-Me2)}2] is 2.432(1) Å [7]). The dihedral angles
between least-square planes of cyclopentadienyl rings are similar
for both independent molecules (56.01(16)° in 3a and 57.94(16)°
in 3b). The values are comparable to the value found in
[ZrCl2{
than in corresponding nonmethylated analogue [ZrCl2{
g
5-(C5H2-1,2-Ph2-4-Me)}2] (56.8°) and substantially smaller
Scheme 2. Preparation of complexes 2–4.
g
5-(C5H3-1,
Fig. 1. Molecular structures of 3a and 3b (thermal ellipsoids are given with 30% probability). Hydrogen atoms are omitted for clarity.

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M. Horácek et al. / Journal of Organometallic Chemistry 694 (2009) 173–178
177
Table 2
Table 4
Selected bond lengths (Å) and angles (°) for molecules 3a and 3b.a
The effect of catalyst/cocatalyst ratio on polymerization activity of zirconocene
3/MAO system.
3a
Zr1–Cl1
2.4247(6)
2.2498(12)
2.467(2)–2.624(2)
1.404(4)–1.437(4)
1.479(4)–1.487(4)
96.81(3)
Zr1–Cl2
2.4262(7)
2.2507(11)
Al/Zr
[Zr] ꢁ 104
2.4
1.8
1.6
M
mPE (g)
Activity (kgPE/molMet/h)
Zr1–Cg(1)b
Zr1–Cring
Zr1–Cg(2)b
200
500
900
0.103
1.089
3.526
4
61
221
C–CCp
C–CPh
1.365(5)–1.400(4)
1.503(4)–1.511(4)
130.21(4)
ring
ring
Cring–CPh
Cl1–Zr1–Cl2
uc
Cring–CMe
Cg(1)–Zr1–Cg(2)b
sd
Polymerization conditions: temperature 80 °C, polymerization time 2 h, toluene
50 ml, ethylene pressure 1.1 atm.
56.01(16)
56.35(4)
3b
Zr2–Cl3
Zr2–Cg(3)b
Zr2–Cring
2.4326(8)
2.2432(13)
2.468(3)-2.637(2)
1.399(4)-1.433(4)
1.478(4)–1.485(4)
94.60(3)
Zr2–Cl4
2.4103(8)
2.2495(12)
Zr2–Cg(4)b
that the abstraction of a methyl group to form the cationic active
species was endotermic (8.5 kcal/mol) [23]. Moreover, the DFT cal-
culation showed that barrier for insertion of ethylene into Zr–Me
bond is relatively high (12–24 kcal/mol for [Cp2ZrMe]+) [24,25].
Therefore, an elevated temperature is crucial for the polymeriza-
tion promoted by catalysts derived from bulky 3 or 4.
C–CCp
C–CPh
1.363(6)–1.400(4)
1.504(4)–1.508(4)
129.19(5)
ring
ring
Cring–CPh
Cl3–Zr2–Cl4
uc
Cring–CMe
Cg(3)–Zr2–Cg(4)b
sd
57.94(16)
44.19(5)
aExtreme values in the two independent molecules 3a, 3b of the unit cell, the
cyclopentadienyl ring atoms are denoted C101–C105 and C120–C124 for 3a, and
C201–C205 and C220–C224 for 3b as shown in Fig. 1.
About half value of activity of complexes 3 and 4 in comparison
with the standard [ZrCl2{g
5-(C5H5)}2] at 80 °C can be attributed to
b
Cg(1), Cg(2), Cg(3) and Cg(4) are centroids of the C(101–105), C(120–124),
a lower concentration of cationic active species during polymeriza-
tion, because the electron-attracting phenyl substituents on cyclo-
pentadienyl rings are known to destabilize the cationic center [26].
A low stability of cationic species is in line with the observed de-
crease in activity with lowering of the Al/Zr ratio at 80 °C (Table
4). However, it should be noted that is a general trend for most
metallocene catalysts [27,28].
C(201–205) and C(220–224) cyclopentadienyl rings.
c
Dihedral angle between the least-squares planes of the cyclopentadienyl rings.
Torsion angles C(105)–Cg(1)–Cg(2)–C(124) and C(205)–Cg(3)–Cg(4)–C(224).
d
2-Ph2)}2] (61.6°, 62.3°) [2]. Similarly the Cg–Zr–Cg angle value in-
creases in the opposite order [ZrCl2{
and 126.9°) [ZrCl2{
g
5-(C5H3-1,2-Ph2)}2] (126.6°
g
5-(C5H2-1,2-Ph2-4-Me)}2] (129.5°) and
3
Molar masses of polyethylenes prepared using 3,
4 and
(130.21(4)° and 129.19(15)°). The both data reflect an increased
crowding of open side of molecules with increasing number of
methyl groups at the cyclopentadienyl rings. The cyclopentadienyl
rings in 3a and 3b are staggered. There mutual rotation, however,
differs as indicated by torsion angles C(105)–Cg(1)–Cg(2)–C(124)
56.35° for 3a and C(205)–Cg(3)–Cg(4)–C(224) 44.19° for 3b. All
phenyl groups are rotated away from coplanar conformation with
cyclopentadienyl moiety, the dihedral angles between least-square
planes of Cp0 and Ph rings ranging 38.09(16)–55.16(14)°. This
diminishes the conjugation of both aromatic systems.
[ZrCl2{g
5-(C5H5)}2] under given experimental conditions (Table
3) are in the range 10000–18000 g molꢀ1. These relatively low val-
ues are due to a low ethylene pressure, high reaction temperature
(necessary for a reasonable propagation rate) and rather high
catalyst concentration, all factors enabling b-H elimination and
chain-transfer to aluminium as observed previously in [ZrCl2{g5
-
(C5H5)}2]/MAO catalyzed ethylene polymerization under similar
conditions [29,30], the molar mass of polyethylene obtained with
bulky complex 3, for which the lower extent of b-H elimination
could be expected, is surprisingly similar to molar mass of the
polymer produced by the standard [ZrCl2{g
5-(C5H5)}2] catalysts.
3.4. Polymerization of ethylene
In contrast, the highest molar mass polyethylene was obtained
by less sterically hindered complex 4. This shows the complexity
of polymerization process in which the simultaneous propagation
and chain-transfer reactions take place and their proportion deter-
mines final chain length. The melting transition temperatures of
prepared polyethylene matrices (129.0–131.7 °C) are in range typ-
ical for linear polyethylene, about 10 °C lower than in the case of
Complexes 2–4 (and [ZrCl2{g
5-(C5H5)}2] for comparison) were
activated by excess MAO and evaluated in polymerization of ethyl-
ene (Table 3). The complexes 3 and 4 showed only negligible activ-
ity at 30–50 °C, whereas at 80 °C they both possessed high activity
at almost the same level (370–390 kgPE/molMet/h). The dramatic in-
crease of activity by raising temperature from 50 °C to 80 °C could
be attributed to a steric crowding of the active center by the bulky
phenyl and methyl groups. The crowding of the active site then
influenced either formation of cationic centre by cocatalyst or
insertion of ethylene into Zr–C bond. The influence of steric crowd-
[ZrCl2{g
5-(C5H3-1,2-Ph2)}2]/MAO catalyst [2]. This difference arise
from different conditions for polymerization used in [2] (low tem-
perature, high ethylene pressure, lower catalyst concentration)
where chain-transfer reactions were significantly suppressed and
polyethylenes with very high molar masses were prepared.
Contrary to catalysts derived from zirconocene dichlorides 3
and 4, the catalyst formed from mixing 2 with MAO is practically
inactive at any temperature. The same behavior was found in
ing on activation of bulky [Zr{Me2Si(g g
5-C5Ph4)( 5-C5H3t-Bu)}] by
MAO was recently elucidated by DFT calculation, which showed
Table 3
[TiCl2{g
5-(C5H-1,4-Ph2-2,3-Me2)}2]/MAO system [7]. We sug-
Comparison of 2–4/MAO activity in ethylene polymerization.
gested the behavior as a consequence of the reduction of a titanium
cationic center to catalytically inactive Ti(III) center induced by
MAO and/or trimethylaluminum (inherent part of MAO solutions).
An easier reduction of titanocene dichlorides compared to zircono-
cene dichlorides is well known and was evaluated by cyclic volta-
metry [31,32].
Catalyst
T
t
[M] ꢁ 104
M
mPE
(g)
Activity
Mv
Tm
(°C)
(°C) (h)
(kgPE/molMet/h) (kg molꢀ1
)
2/MAO
2/MAO
3/MAO
3/MAO
3/MAO
4/MAO
4/MAO
50
80
30
2
2
3
2.0
2.0
1.0
0.012
0.028
0.0002
0.017
1.939 388
0.032
1.845 369
0.721 144
3.748 750
1
1
0
0
50 12 2.0
80
50
80
1
2
1
1
1
1.0
2.0
1.0
1.0
1.0
10.6
18.0
11.4
130.7
131.7
129.0
2
4. Conclusions
Cp2ZrCl2/MAO 30
Cp2ZrCl2/MAO 80
Combination of phenyl and methyl groups in the cyclopen-
tadienyl ligand framework has a specific impact on catalysts
performance. The catalysts formed from combination of MAO with
Polymerization conditions: Al/M = 900 (M = Ti, Zr), toluene 50 ml, ethylene pressure
1.1 atm.

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M. Horácek et al. / Journal of Organometallic Chemistry 694 (2009) 173–178
178
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titanium to reduction increased by the presence of electron-
attracting phenyl groups is probably responsible for negligible
activity of the catalyst derived from 2 at all studied temperatures.
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This investigation was supported by the Academy of Sciences of
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port. J.P. acknowledges the support of the French Government
(Grant No. 20006842).
Appendix A. Supplementary material
CCDC 679430 contains the supplementary crystallographic data
for 3. These data can be obtained free of charge from The Cam-
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ta_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.jorganchem.
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