Dual-side ansa-zirconocene dichlorides for high molecular weight isotactic polypropene elastomers

Article abstract of DOI:10.1021/om000224q

The four new asymmetric ansa-zirconocene dichlorides rac-[1-(9-η⁵-fluorenyl)-2-(2-phenyl- 1-η⁵-indenyl)ethane]zirconium dichloride (4c), rac-[(9-η⁵-fluorenyl)(5,6-cyclopenta-2-methyl-1-η⁵-indenyl) dimethylsilane]zirconium dichloride (4d), rac-[(9-η⁵-fluorenyl)(2-methyl-1-η⁵indenyl) dimethylsilane]zirconium dichloride (4e), and rac-[(9-η⁵-fluorenyl)(2-phenyl-1-η⁵-indenyl) dimethylsilane]zirconium dichloride (4f) have been prepared, and their polymerization behavior was compared to the recently published rac-[1-(9-η⁵-fluorenyl)-2-(5,6-cyclopenta-2-methyl-1-η⁵- indenyl)ethane]zirconium dichloride (4a) and rac-[1-(9-η⁵-fluorenyl)-2-(2-methyl-1-η⁵-indenyl) ethane]zirconium dichloride (4b). The Si-bridged ligands are easily accessible by the reaction of fluorenyllithium with dimethyldichlorosilane and the subsequent addition of indenyllithium. A similar route using 1-(9-fluorenyl)-2-bromoethane was applied for the synthesis of the ethylene-bridged ligands. The Zr(IV) complexes of all ligands are highly active catalysts for the propene polymerization reaction after activation with MAO. The influence of the bridge and the particular substitution pattern of the indenyl fragments has been studied with respect to monomer concentration and polymerization temperature. The exchange of the ethylene bridge by a dimethylsilane unit results in a strong increase of the molecular weights but also in a decreased polymerization activity deriving from a fast decomposition of the active catalyst species. Interestingly, significantly higher polymer molecular weights could be found for the complexes that contain the 5,6-cyclopentyl substituent on the indenyl moiety. All catalysts showed the effect of a declining stereo-selectivity with increasing monomer concentration, leading to the formation of homopolypropene elastomers. The mechanism of stereoerror formation of these C₁-symmetric species was investigated by deuterium labeling studies on the propene monomers and by comparison with C₂-symmetric complexes.

Full text of DOI:10.1021/om000224q

Organometallics 2000, 19, 3767-3775
3767
Du a l-Sid e a n sa -Zir con ocen e Dich lor id es for High
Molecu la r Weigh t Isota ctic P olyp r op en e Ela stom er s
J u¨rgen Kukral, Petri Lehmus, Tanja Feifel, Carsten Troll, and Bernhard Rieger*
Department for Materials and Catalysis, University of Ulm, D-89069 Ulm, Germany
Received March 13, 2000
The four new asymmetric ansa-zirconocene dichlorides rac-[1-(9-η5-fluorenyl)-2-(2-phenyl-
1-η5-indenyl)ethane]zirconium dichloride (4c), rac-[(9-η5-fluorenyl)(5,6-cyclopenta-2-methyl-
1-η5-indenyl)dimethylsilane]zirconium dichloride (4d ), rac-[(9-η5-fluorenyl)(2-methyl-1-η5-
indenyl)dimethylsilane]zirconium dichloride (4e), and rac-[(9-η5-fluorenyl)(2-phenyl-1-η5-
indenyl)dimethylsilane]zirconium dichloride (4f) have been prepared, and their polymerization
behavior was compared to the recently published rac-[1-(9-η5-fluorenyl)-2-(5,6-cyclopenta-
2-methyl-1-η5-indenyl)ethane]zirconium dichloride (4a ) and rac-[1-(9-η5-fluorenyl)-2-(2-
methyl-1-η5-indenyl)ethane]zirconium dichloride (4b). The Si-bridged ligands are easily
accessible by the reaction of fluorenyllithium with dimethyldichlorosilane and the subsequent
addition of indenyllithium. A similar route using 1-(9-fluorenyl)-2-bromoethane was applied
for the synthesis of the ethylene-bridged ligands. The Zr(IV) complexes of all ligands are
highly active catalysts for the propene polymerization reaction after activation with MAO.
The influence of the bridge and the particular substitution pattern of the indenyl fragments
has been studied with respect to monomer concentration and polymerization temperature.
The exchange of the ethylene bridge by a dimethylsilane unit results in a strong increase of
the molecular weights but also in a decreased polymerization activity deriving from a fast
decomposition of the active catalyst species. Interestingly, significantly higher polymer
molecular weights could be found for the complexes that contain the 5,6-cyclopentyl
substituent on the indenyl moiety. All catalysts showed the effect of a declining stereo-
selectivity with increasing monomer concentration, leading to the formation of homopolypro-
pene elastomers. The mechanism of stereoerror formation of these C1-symmetric species
was investigated by deuterium labeling studies on the propene monomers and by comparison
with C2-symmetric complexes.
In tr od u ction
metric homogeneous titanocene catalyst [MeHC(Me4-
Cp)(Ind)]TiCl2 resulted in a variety of research activities
on suitable catalysts for the production of elastic
polypropene. Collins et al.4,5 reported the modification
of Chien’s basic catalyst structure toward a dimethyl-
silane bridge and hafnium as the transition metal. The
elastic properties were ascribed to arise from blocklike
structures of isotactic and atactic sequences, in analogy
with Chien’s work.3 Recently, we reported on the use of
the highly active zirconocene dichloride 4a/MAO (Scheme
1) for the production of the first high molecular weight,
isotactic polypropene with controllable amounts of
isolated stereoerrors for achieving and adjusting elastic
properties.6 It was found that the 2-methyl group and
the 5,6-substitution are necessary requirements to
obtain a high enough molecular weight and a sufficient
amount of stereoerrors for the formation of elastic,
isotactic polypropenes. Contrary, the 4,5-front substitu-
tion resulted only in partly isotactic polymers of rela-
tively low molecular weight.6-8
Since the first introduction of homogeneous ansa-
metallocene catalysts for the stereoregular polymeriza-
tion of propene,1 attempts to find new insights into the
stereochemical control of propene polymerization reac-
tions have rapidly increased.2 The observation by Chien
et al.3 that elastic polypropene of narrow molecular
weight distribution could be obtained with the asym-
(1) Wild, F. R. W. P.; Zsolnai, L.; Hu¨ttner, G.; Brintzinger, H. H. J .
Organomet. Chem. 1982, 232, 233. (b) Wild, F. R. W. P.; Wasciucionek,
M.; Hu¨ttner, G.; Brintzinger, H. H. J . Organomet. Chem. 1985, 288,
63. (c) Kaminsky, W.; Ku¨lper, K.; Brintzinger, H. H.; Wild, F. R. W. P.
Angew. Chem. 1985, 507, 97. (d) Ewen, J . A.; J ones, R. L.; Razavi, A.;
Ferrara, J . D. J . Am. Chem. Soc. 1988, 110, 6255. (e) Ewen, J . A.; Elder,
M. J .; J ones, R. L.; Haspelagh, L.; Attwood, J . L.; Bott, S. G.; Robinson,
K. Makromol. Chem., Macromol. Symp. 1991, 48/49, 253.
(2) (a) Spaleck, W.; Antberg, M.; Rohrmann, J .; Winter, A.; Bach-
mann, B.; Kiprof, P.; Behm, J .; Herrmann, W. A. Angew. Chem., Int.
Ed. Engl. 1992, 31, 1347. (b) Razavi, A.; Atwood, J . L. J . Am. Chem.
Soc. 1993, 115, 7529. (c) Spaleck, W.; Ku¨ber, F.; Winter, A.; Rohrmann,
J .; Bachmann, B.; Antberg, M.; Dolle, V.; Paulus, E. F. Organometallics
1994, 13, 954. (d) Giardello, M. A.; Eisen, M. S.; Stern, C. L.; Marks,
T. J . J . Am. Chem. Soc. 1995, 117, 12114. (c) Coates, G. W.; Waymouth,
R. M. Science 1995, 267, 217.
(3) (a) Mallin, D. T.; Rausch, M. D.; Lin, Y.; Dong, S.; Chien, J . C.
W. J . Am. Chem. Soc. 1990, 112, 2030. (b) Chien, J . C. W.; Llinas, G.
H.; Rausch, M. D.; Lin, Y.; Winter, H. H. J . Am. Chem. Soc. 1991,
113, 8569. (c) Llinas, G. H.; Dong, S.-H.; Mallin, D. T.; Rausch, M. D.;
Lin, Y.-G.; Winter, H. H.; Chien, J . C. W. Macromolecules 1992, 25,
1242. (d) Llinas, G. H.; Day, R. O.; Rausch, M. D.; Chien, J . C. W.
Organometallics 1993, 12, 1283.
(4) (a) Gauthier, W. J .; Corrigan, J . F.; Nicholas, N. J .; Collins, S.
Macromolecules 1995, 28, 3771. (b) Gauthier, W. J .; Collins, S.
Macromolecules 1995, 28, 3778.
(5) Bravakis, A. M.; Bailey, L. E.; Pigeon, M.; Collins, S. Macromol-
ecules 1998, 31, 1000.
(6) Dietrich, U.; Hackmann, M.; Rieger, B.; Klinga, M.; Leskela¨, M.
J . Am. Chem. Soc. 1999, 121, 4348.
10.1021/om000224q CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/16/2000

3768 Organometallics, Vol. 19, No. 19, 2000
Kukral et al.
Sch em e 1
In our present work we prepared and investigated the
asymmetric complexes 4c-f in comparison with the
recently published zirconocenes 4a 6 and 4b8 to gain
more information on the influence of the 5,6-substitution
on the polymerization behavior. By exchanging the
ethylene bridge with a dimethylsilane unit, we intended
to increase the molecular weight and the catalyst
activity to make the polymers even more interesting for
industrial application. Furthermore, we continued our
investigations on the mechanism of stereoerror forma-
tion of the C1-symmetric metallocenes by applying
deuterium-labeled monomers and compared the results
with the mechanism of some representative C2-sym-
metric complexes.
indenyl and fluorenyl fragments was developed in our
group.10 By nucleophilic ring-opening of substituted
epoxides with fluorenyllithium, a wide variety of sub-
stituents can easily be introduced, and even more, a
stereogenic center is introduced into the ethylene bridge.
The resulting chiral ligands are obtained after func-
tionalization of the alcohols with trifluoromethane sul-
fonic acid anhydride and further reaction with a second
indenyl moiety. Another route8,11 similar to the proce-
dure leading to the Si-bridged ligands was used for the
synthesis of the C2H4-bridged ligands 3a -c (Scheme 2,
path A, Sp ) C2H4). The 1-(9-fluorenyl)-2-bromoethane
(1a ) can be prepared by the addition of 1,2-dibromo-
ethane to fluorenyllithium. This stable intermediate was
employed in subsequent reactions with indenyllithium
compounds 2a -c without purification, leading to the
ethylene bridged ligands 3a -c in up to 65% yield.
The ligands 3a -c were converted into their corre-
sponding zirconocenes by deprotonation with n-BuLi in
diethyl ether at -78 °C, stirring for 2 h at ambient
temperature, and subsequent addition of ZrCl4 to a
toluene solution of the dianion. The reaction was stirred
at room temperature overnight. The Zr(IV) complexes
were isolated in up to 90% yield after separation from
LiCl.12 A similar approach was used for the Si analogues
3d -f. The precipitated orange complexes were sepa-
rated from the toluene solution and rapidly extracted
with cold toluene. The toluene was immediately re-
moved, and the orange powder was washed several
times with dry Et2O and pentane. The Si-bridged
zirconocenes are only slightly soluble in organic sol-
vents. They are quite unstable in solution and show an
Resu lts a n d Discu ssion
Liga n d a n d Com p lex Syn th esis. The Si-bridged
ligands are easily accessible by the addition of Me2Cl2-
Si to an ether solution of the fluorenyl anion. The
resulting (9-fluorenyl)dimethylchorosilane (Scheme 2,
path A, Sp ) Me2Si) can be used without further
purification after removing the solvent and excessive
Me2Cl2Si. The separately prepared indenyllithium is
subsequently added to an ether solution of (9-fluorenyl)-
dimethylchorosilane (1b) at room temperature.9 Stirring
overnight and recrystallization from hexane gave yields
up to 80%.
The synthesis of ethylene-bridged asymmetric zir-
conocenes can be realized in two different ways. In 1994
a new route to asymmetric zirconocenes containing
(7) Nippon Chemicals, EP 0707016A1.
(8) Thomas, E. J .; Chien, J . C. W.; Rausch, M. D. Organometallics
1999, 18, 1439.
(9) (a) Ewen, J . A.; Elder, M. J . Ziegler Catalysts; Springer-Verlag:
Berlin, 1995. (b) Chen, Y.-X.; Rausch, M. D.; Chien, J . C. W. J .
Organomet. Chem. 1995, 497, 1. (c) Patsidis, K.; Alt, G. H.; Milius,
W.; Palackal, S. J . J . Organomet. Chem. 1996, 509, 63.
(10) Fawzi, R.; Steinmann, M.; J any, G.; Rieger, B. Organometallics
1994, 13, 647.
(11) Alt, H. G. U.S. Patent 5191132, 1993.
(12) The ethylene-bridged complexes were obtained with the fol-
lowing yields. 4a : 92%; 4b: 85%, 4c: 56%.

Dual-Side ansa-Zirconocene Dichlorides
Organometallics, Vol. 19, No. 19, 2000 3769
Sch em e 2
extreme sensitivity to moisture.13 However, they can be
stored under dry argon. Resconi et al.14 reported on a
similar behavior for Me2Si(9-Flu)2ZrCl2. The high in-
stability of this molecule was attributed to the decreas-
ing ligand hapticity resulting from repulsive interac-
tions of the phenyl hydrogens in the rear fluorenyl
positions R-standing to the Me2Si unit. The same
destabilizing effect is assumed to be responsible for the
low stability of our Si-bridged zirconocene catalysts15
and leads to significantly reduced catalytic activities in
propene polymerization experiments (see below).
to obtain polypropenes with tailored isotacticities (Table
1).
Surprisingly, large differences were observed in the
polymerization behavior of the examined catalysts. The
highest polymer yields could be obtained with the
ethylene-bridged metallocenes 4a /MAO and 4b/MAO (at
Tp ) 30 °C up to 2.5 × 103 and at Tp ) 50 °C up to 4.6
× 103 kg of PP (mol of Zr [C3] h)-1). Exchange of the
ethylene bridge by a dimethylsilane unit (4d -f/MAO)
resulted in a rapid decline of the propene consumption
curve during the course of the polymerization reaction.
The activated species decompose quickly, especially at
elevated temperatures, so that already after the first
15 min only about 20% of the starting activity is left
(Figure 1, 4d /MAO). In contrast, the propene consump-
tion of the ethylene-bridged complexes increases within
the first 15-30 min of the polymerization experiment
(Figure 1, 4a /MAO), indicating a slow activation reac-
tion with MAO, resulting presumably from the sterically
demanding substituents around the zirconium center.
P r op en e P olym er iza tion s. Monomer concentration
and temperature dependency of the different catalysts
were investigated in propene polymerizations in order
(13) Thomas, E. J .; Chien, J . C. W.; Rausch, M. D. Macromolecules
2000, 33, 1546.
(14) Resconi, L.; J ones, R. L.; Rheingold, A. L.; Yap, G. P. A.
Organometallics 1996, 15, 998.
(15) Intensive trials to grow crystals suitable for X-ray structure
analysis remained unsuccessful due to the low stability of the Me2Si-
bridged complexes in solution.

3770 Organometallics, Vol. 19, No. 19, 2000
Ta ble 1. P olym er iza tion Resu lts of P r op en e w ith Asym m etr ic Com p lexes 4a -f/MAO
Kukral et al.
b
d
g
h
run
cat.
amounta
Tp
[C3]c
tp
yielde
activityf
niso
Mw
Mw/Mn
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
4a
4a
4a
4a
4d
4d
4d
4d
4b
4b
4b
4e
4e
4e
4e
4c
4c
4f
6
3.8
2.7
3.8
10
10
10
10
5
30
30
30
50
30
30
30
50
30
30
30
30
30
30
50
30
30
30
30
30
50
1.2
3.0
5.1
3.0
1.2
3.0
5.1
3.0
1.2
3.0
5.1
1.2
3.0
5.1
3.0
3.0
5.1
1.2
3.0
5.1
3.0
73
39
30
21
120
61
30
25
72
39
25
106
69
33
65
27
29
193
118
125
101
17.3
18.0
17.6
18.3
12.5
15.2
17.4
13.2
15.6
16.7
16.6
16.1
15.7
16.4
12.6
18.4
20.3
8.5
2000
2400
2600
4600
n.d.i
n.d.
n.d.
n.d.
2100
1700
1600
n.d.
n.d.
n.d.
n.d.
1400
800
n.d.
n.d.
n.d.
n.d.
8.9
7.4
7.1
10.3
12.2
10.5
9.4
14.7
6.1
5.7
4.7
9.3
8.5
55
1.8
1.8
1.9
1.9
1.8
1.9
1.9
1.9
1.8
1.9
1.9
1.8
2.0
2.0
1.9
2.3
2.5
1.9
1.8
1.8
1.9
89
125
46
103
132
158
85
62
81
83
73
81
92
64
62
86
32
74
99
5
5
20
10
10
10
10
10
50
30
30
30
8.0
10.8
100.0
35.8
15.9
13.6
12.3
16.3
4f
4f
4f
8.9
16.2
5.2
31
a
b
d
g
µmol (Al/Zr ) 2000). °C. c mol L-1
.
min. e g. f kg of PP (mol of Zr [C3] h)-1
.
Average isotactic block length niso)4+2[mmmm]/
[mmmr]. kg mol-1
. n.d. ) not determined, because of rapid deactivation of the catalyst active species.
h
i
The [mmmm]-pentad concentration of the polymers
produced with the different C1-symmetric metallocene
catalysts varies over a broad range (10%-98%, cf. Table
2). The most conspicuous effect of the Si-bridged ansa-
metallocenes 4d /MAO and 4e/MAO is the distinct
ascent of the isotacticity compared with their ethylene-
bridged counterparts 4a /MAO and 4b/MAO. With 5,6-
cyclopentyl substitution of the indenyl fragment (4a ,d )
an increase of the isotacticity is observed. This effect
can be explained by a favored back-skip of the growing
polymer chain before a new monomer inserts on the
aspecific side of the complexes, induced by the additional
steric hindrance of the 5,6-cycloaliphatic substituent
(Scheme 3).6
The series of propene polymerizations applying the
2-phenyl-substituted complexes 4c/MAO has produced
polymers with the highest isotacticities (e.g., 4c: mmmm
) 98%, Table 2, entry 16). Exchange of the C2H4 bridge
by a Me2Si unit (4f) results in a strong decrease of the
isotacticity of the polypropene products (e.g., Table 2,
entry 20), while for both complexes the same influence
of the monomer concentration on the stereoselectivity
is observed (Table 2, 4c: entries 16, 17; 4f: entries 19,
20), suggesting that a mechanism like the one depicted
in Scheme 3 might still be active. Generally, 2-phenyl
substitution leads to a strong decrease in polymerization
activity, while the molecular weight is not essentially
altered.
Mech a n ism s of Ster eoer r or F or m a tion . C2-Sym -
m etr ic Ca ta lysts. Brintzinger et al.17 and Busico et
al.18 have demonstrated by using deuterated propene
monomers that formation of the [mrrm]-stereoerror
pentad at low monomer concentrations is, to a large
extent, a consequence of an isomerization (“chain end
epimerization”) of the Zr-alkyl bond19 in C2-symmetric
F igu r e 1. Propene consumption curves obtained with 4a /
MAO and 4d /MAO under the following polymerization
conditions. 4a /MAO: Tp ) 50 °C, [C3] ) 3.0 mol L-1, nZr
3.8 µmol; 4d /MAO: Tp ) 50 °C, [C3] ) 3.0 mol L-1, nZr
10 µmol
)
)
This behavior is significantly different compared with
C2-symmetric ansa-metallocenes that show higher ac-
tivities for the Si-bridged species due to the enlarged
bite angle of the Cp ligands in such complexes.16
The highest molecular weights were obtained for
polymers produced with the Si-bridged, 5,6-cyclopentyl-
substituted complex 4d /MAO (Table 1, entries 6, 7).
Interestingly, the 5,6-cyclopentyl group seems to have
generally a beneficial influence on the molecular weight,
despite its remote position within the complex relative
to the active Zr(IV) center (Table 1, entry 3). We have
no genuine explanation for this surprising effect. How-
ever, experiments with deuterated propene monomers
(see below) show that the 5,6-alkyl substituents sup-
press effectively a chain end epimerization process
(found to be responsible for the formation of stereoerrors
in C2-symmetric catalysts)17,18 and hinder at the same
time a subsequent chain termination reaction, leading
to higher molecular weight products.
(17) (a) Leclerc, M. K.; Brintzinger, H. H. J . Am. Chem. Soc. 1996,
118, 9024. (b) Leclerc, M. K.; Brintzinger, H. H. J . Am. Chem. Soc.
1995, 117, 1651.
(18) (a) Busico, V.; Caporaso, L.; Cipullo, R.; Landriani, L.; Angelini,
G.; Margonelli, A.; Segre, A. L. J . Am. Chem. Soc. 1996, 118, 2105. (b)
Busico, V.; Brita, D.; Caporaso, L.; Cipullo, R.; Vacatello, M. Macro-
molecules 1997, 30, 3971. (c) Busico, V.; Cipullo, R.; Caporaso, L.;
Angelini, G.; Segre, A. L. J . Mol. Catal. A 1998, 128, 53.
(16) Cf.: Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;
Waymouth, R. Angew. Chem. 1995, 107, 1255, and references therein.

Dual-Side ansa-Zirconocene Dichlorides
Organometallics, Vol. 19, No. 19, 2000 3771
Ta ble 2. P olyp r op en e P en ta d Distr ibu tion a (in %)
run
cat.
[mmmm]
[mmmr]
[rmmr]
[mmrr]
[mmrm]+[rrmr]
[rrrr]
[rrrm]
[mrrm]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
4a
4a
4a
4a
4d
4d
4d
4d
4b
4b
4b
4e
4e
4e
4e
4c
4c
4f
42.5
30.3
27.8
49.1
61.6
50.6
44.0
67.4
17.6
13.4
9.7
44.1
39.3
35.3
56.2
98.0
86.0
70.5
62.2
57.9
71.7
17.5
17.7
17.7
15.7
15.0
15.6
16.3
12.6
16.5
15.6
13.7
16.7
17.5
17.6
16.4
2.0
2.1
2.7
2.7
1.5
19.9
21.3
22.0
17.7
16.3
16.8
17.8
13.0
21.6
22.5
18.5
18.5
20.6
21.2
18.0
3.4
5.9
6.6
3.1
1.6
4.6
5.3
2.4
2.8
6.6
7.4
1.8
10.2
10.9
10.5
8.7
7.1
8.2
9.1
5.5
11.4
7.0
11.4
8.3
1.4
1.8
3.1
4.1
0.9
20.8
10.3
10.7
4.0
3.8
4.2
2.1
1.7
3.0
2.5
3.9
0.5
10.4
11.8
14.8
3.5
4.8
6.1
1.6
3.8
5.4
5.5
1.8
2.3
2.4
8.9
14.0
15.7
3.1
3.7
5.4
8.0
7.9
5.8
5.4
6.3
12.6
12.0
12.8
11.9
2.3
5.1
5.9
6.2
4.7
11.8
12.9
13.9
11.7
4f
4f
4f
1.1
1.4
2.5
3.2
0.9
1.2
1.7
2.1
a
[mrmr] e 1% (ref 24).
Sch em e 3
catalysts (e.g., EBTHI).20 Such deuterium labeling
studies enable differentiation between intrinsic errors
that are formed by a wrong enantiofacial discrimination
of the prochiral monomer and isomerization-induced
errors, which result from an intramolecular rearrange-
ment of the Zr-bound chain.17,18 In the methyl region of
the 13C NMR spectrum of polypropene produced with
1-d-propene, the [mrrm]-pentad due to intrinsic errors
can be identified at 19.6 ppm, while a deuterium-
containing methyl groupsresulting from an isomeriza-
tion of the Zr-alkyl bondsappears upfield as a triplet
(J (13C, 2H) ) 19 Hz) centered at 19.3 ppm (Figure 2 A).
Table 321 summarizes data on the stereoselectivity of
EBI/MAO22 depending on the monomer concentration
at constant polymerization temperature (50 °C). These
results are in good agreement with literature values.23
The amount of [mrrm]-error pentads increases from
(21) To obtain sufficient polymer yields with the deuterated mono-
mer, which obviously contained traces of catalyst-poisoning impurities,
the applied catalyst and cocatalyst concentrations were high. As a
consequence, the start of the polymerizations was retarded and chain
termination occurred mainly by chain transfer to aluminum. Polymer-
izations with undeuterated propene at different MAO concentrations
up to 0.5 mol L-1 showed that the amount of stereoerrors was not
influenced by the MAO concentration.
(22) EBI ) rac-ethylenebis(1-η5-indenyl)zirconium dichloride.
(23) Resconi et al. (Macromolecules 1995, 28, 6667) reported under
comparable polymerization conditions [mmmm]-pentad values of 86%
at 4.4 and 2.8 mol/L, 82% at 0.85 mol/L, 80% at 0.5 mol/L, and 55-
68% at e0.4 mol/L (diffusion controlled). Busico et al. (J . Am. Chem.
Soc. 1994, 116, 9329) reported correspondingly [m]-diads ranging from
82% at 0.4 mol/L to a maximum value of 92% in bulk.
(19) For isomerization via an allyl mechanism, see: (a) Resconi, L.;
Camurati, I.; Sudmeijer, O. Topics Catal. 1999, 7, 145. (b) Resconi, L.
J . Mol. Catal. A 1999, 146, 167.
(20) EBTHI ) rac-ethylenbis(4,5,6,7-tetrahydro-1-η5-indenyl)zirco-
nium dichloride.

3772 Organometallics, Vol. 19, No. 19, 2000
Kukral et al.
F igu r e 2. 13C NMR spectra of the methyl region of deuterated polypropenes obtained at 50 °C with EBI/MAO and 0.4
mol L-1 1-d-propene (A), with 4b/MAO and 0.4 mol L-1 1-d-propene (B), with 4a /MAO and 0.4 mol L-1 1-d-propene (C),
and 3.0 mol L-1 1-d-propene (D). Asterisks denote signals arising from n-propyl end groups and 3,1-misinsertions for A,
and from isobutyl end groups for B, C, and D.
Ta ble 3. P olyp r op en e P en ta d Distr ibu tion (in %) for C2-Sym m etr ic Ca ta lysts EBI/MAO a n d EBTHI/MAO
(Tp ) 50 °C)
cat.a
mon.b
[mon.]c
Al/Zr
[mmmm]
[mmrr]
[mrrm]
d-[mrrm]
EBI
EBI
EBI
EBI
EBI
EBI
EBI
EBTHI
C3
C3
C3
C3
d-C3
d-C3
d-C3
d-C3
0.4
0.85
1.9
3.3
0.4
0.85
1.3
0.4
3000
3000
3000
3000
1500
1500
1500
200
74
80
84
85
69
79
82
50
8.6
5.6
5.7
4.7
9.5
6.4
5.5
16.4
4.0
2.9
2.3
1.9
1.9
2.0
2.0
3.3
2.6
1.3
<0.2
6.7
a
b
[Zr] ) (1-2) × 10-5 mol L-1 for C3 polymerizations, [Zr] ) 3.3 × 10-4 mol L-1 for d-C3 polymerizations (ref 19). Monomers: C3
)
propene, d-C3 ) 1-d-propene. c mol L-1
.
1.9% to 4.0% with a decline of the monomer concentra-
tion from 3.3 to 0.4 mol L-1. Results obtained with the
deuterated monomer under the same conditions dem-
onstrate that the amount of intrinsic errors [mrrm] is
nearly constant (1.9% to 2.0%, respectively) and is
essentially independent of the monomer concentration,
as expected. Isomerization-induced errors d-[mrrm]24
start to play a significant role at propene concentrations
below 1 mol L-1. Hydrogenation of the indenyl ligand
increases the amount of intrinsic [mrrm]-error pentads
from 1.9% to 3.3% at 50 °C. The amount of isomeriza-
tion-induced errors is nearly 3-fold for the hydrogenated
catalyst at a monomer concentration of 0.4 mol L-1. The
experimentally verified higher probability of the EBTHI
catalyst to produce stereoerrors by chain end isomer-
ization indicates that it must have a lower kins/kiso ratio
than EBI. This is in agreement with results obtained
by Busico et al.18b by fitting data from propene poly-
merizations to a model accounting for chain growth and
chain epimerization. We found further that at this
temperature the amount of intrinsic errors is higher for
the hydrogenated catalyst, which may (beyond lower
enantioselectivity) be a consequence of an increased
probability for error formation by a reaction path
involving â-H abstraction.25 An increased probability of
the hydrogenated catalyst to undergo reactions via â-H
elimination and Zr-H bond formation is reflected in its
higher sensitivity toward chain termination by hydrogen
and after insertion of a comonomer.26
For C2-symmetric catalysts the origin of stereoerrors
is thus based on two mechanisms: (1) their structure-
dependent ability for the enantioselective discrimination
of the prochiral propene monomer and (2) the monomer
insertion rate, which is slow enough to allow kinetic
competition of error-inducing side reactions, from which
the step of Zr-H bond formation might play a decisive
role.
(25) Busico et al. (ref 18) observed that the amount of nondeuterated
stereoirregular [mrrm]-units decreases when using 2-deuterated pro-
pene instead of 1-deuterated propene, which indicates that the [mrrm]-
pentad also represents errors formed by a mechanism involving â-H/D
abstraction, being slower for the 2-deuterated monomer because of an
isotope effect.
(24) For the mechanism of d-[mrrm] formation see refs 17-19.
(26) (a) Malmberg, A.; Kokko, E.; Lehmus, P.; Lo¨fgren, B.; Seppa¨la¨,
J . V. Macromolecules 1998, 31, 8448. (b) Kokko, E.; Malmberg, A.;
Lehmus, P.; Lo¨fgren, B.; Seppa¨la¨, J . V. J . Polym. Sci., Part A 2000,
38, 376.

Dual-Side ansa-Zirconocene Dichlorides
Organometallics, Vol. 19, No. 19, 2000 3773
Ta ble 4. P en ta d Distr ibu tion (in %) for
C1-Sym m etr ic Ca ta lysts 4a /MAO, 4b/MAO, a n d
4d /MAO
does not bear the 5,6-cycloalkyl substitution, the d-
[mrrm]-pentad is observable, however only in reduced
quantities. The observation that the 5,6-cycloalkyl sub-
stituent suppresses the isomerization reaction might be
a preliminary explanation of the higher molecular
weights of polypropenes prepared with 4a /MAO and 4d /
MAO.30 This hypothesis is supported by Brintzinger et
al., who recently reported that the epimerization process
seems to be linked to chain termination via hydride
abstraction.17 Further work on the influence of 5,6-
substituents on the polymerization behavior of indenyl-
containing asymmetric complexes is underway.
b
cat.a Tp [d-C3]c Al/Zr [mmmm] [mmrr] [mrrm] d-[mrrm]
1
1
1
2
2
4
4
50
50
50
50
50
30
30
0.4
1.9
3.0
0.4
1.9
0.6
3.0
1000
750
500
375
375
500
500
66
56
49
51
32
48
46
12.6
14.1
15.1
14.3
17.2
16.8
16.9
5.3
6.7
7.5
6.6
8.7
7.6
7.8
n.o.
n.o.
n.o.
0.8
n.o.
n.o.
n.o.
a
b
[Zr] ) (3-10) × 10-4 mol L-1
.
°C. c mol L-1
.
C1-Sym m etr ic Ca ta lysts. For catalysts such as
those applied in the present study the mechanism of
stereoerror formation is different compared with C2-
symmetric species, which is already indicated by their
tendency to produce less stereoregular polypropenes
with increasing monomer concentration. We have previ-
ously presented a possible explanation for the observed
polymerization behavior of asymmetric dual-side cata-
lysts such as 4a /MAO.6 Isotactic sequences are formed
by a reaction path that involves repeated migratory
insertion of the chain to the monomer coordinated
between the sterically demanding fluorenyl-indenyl
moieties (Scheme 3, A f B) and a consecutive back-
skip of the chain to the sterically less encumbered side
(B f C). Increasing the monomer concentration leads
to a higher probability for monomer coordination at the
less hindered side before a back-skip of the growing
polymer chain can occur.27 Migratory insertion of the
chain to the free side results in a nonselective insertion
of the monomer (D f C). The next insertion from A f
B is again stereoselective,28 leadingsafter a back-skip
of the polymer chainsto an isolated [mrrm]-error pen-
tad. For these catalysts the ratio of the rate of back-
skip of the chain to the rate of monomer coordination
at the free side can be understood to determine to a
large extent the amount of isolated stereoerrors formed
during the polymerization reaction. The amount of
stereoerrors increases with the monomer concentration
(cf. Table 2, 4), because the rate of monomer coordina-
tion at the free side (B f D) depends on monomer
concentration, while the rate of back-skip of the chain
(B f C) is an intramolecular reaction. To elucidate the
role of kinetically feasible isomerization reactions pos-
sibly contributing to stereoerror formation for these
asymmetric dual-side catalysts, we performed a series
of experiments using 1-d-propene and analyzed the
deuterium distribution in the resulting polymers (Table
4). The most important result is the fact that for the
5,6-cyclopentyl-containing complexes 4a /MAO and 4d /
MAO the methyl d-[mrrm]-pentad is entirely missing.
This indicates that isomerization reactions such as those
observed for C2-symmetric species do not play any
significant role in stereoerror formation for the com-
plexes of this type.29 Interestingly, for 4b/MAO, which
Con clu sion
The asymmetric, dual-side catalysts presented in the
present study open the access to a broad range of
isotactic polypropene microstructures. A controlled tai-
loring of the properties of the polymer products from
highly elastic to crystalline thermoplastic is enabled by
varying the catalyst structure and the polymerization
conditions. Introduction of a Si-bridge into the ligand
frame results in a further increase of the molecular
weight, unfortunately combined with a strong decline
of the polymerization activity due to decomposition of
the active species. Interestingly, the 5,6-substitution on
the indenyl moiety of the ethylene-bridged species was
found to play an important role in obtaining a good
balance between optimized activity, increased molecular
weight, and a sufficient amount of stereoerrors for the
design of thermoplastic elastomers. In C2-symmetric
complexes the stereoerrors are formed at low monomer
concentrations to a large extent by kinetically competi-
tive side reactions, like Brintzinger’s and Busico’s chain
end epimerization processes. For the C1-symmetric
catalysts of the present study, the stereoerror formation
originates predominantly from the kinetic competition
between chain back-skip and monomer coordination at
the aspecific side of the catalyst structure.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were performed under
dry argon atmosphere using standard Schlenk techniques.
Hydrocarbon and ether solvents were dried by distillation from
LiAlH4, and methylene chloride was distilled from CaH2.
Indane, fluorene, benzene, 1,2-dibromoethane, 2-phenylindene,
ZrCl4, HfCl4, AlCl3, cis/ trans-1-bromo-1-propene (98%), and
methanol-d1 (99.5%) were used as received from Merck and
Aldrich. 2-Methylindene was prepared according to literature
procedures.31 The syntheses of the ethylene-bridged ligands
3a ,b have been previously described in the literature.6,8 The
corresponding complexes 4a ,b and the zirconocenes EBI and
EBTHI were prepared according to literature recipes.6 Me-
thylaluminoxane and triisobutylaluminum were purchased
from Witco, and toluene for the polymerization reactions was
purchased from Merck.
1
All compounds were analyzed by H NMR on a Bruker AC
200 or AMX 500 at ambient temperatures and referenced to
TMS. Mass spectra were aquired with Finnigan (SSQ 7000)
(27) For theoretical calculations on the occurrence of back-skip of
the growing chain in the case of asymmetric metallocenes, see: Guerra,
G.; Cavallo, L.; Moscardi, G.; Vacatello, M.; Corradini, P. Macromol-
ecules 1996, 29, 4834.
(28) Monomer misinsertion from A f B after D f C will result in
[mrmr]-error pentads, the concentration of which is however close to
zero in polypropenes obtained with asymmetric catalysts of the type
studied here.
(30) The hypothesis that epimerization reaction leads to a higher
chance for chain termination finds further support by end-group
analysis. 1H NMR spectra indicate that the deuterated polypropenes
obtained with 4b/MAO contain vinylidenic protons that are shifted
downfield by ca. 0.02 ppm. This shift is caused (ref 17) by a neighboring
methyl group that contains deuterium, resulting from isomerization.
For 4a /MAO such vinylidenic protons were not observed, as expected.
(29) Brintzinger et al. reported
a similar observation for C2-
symmetric metallocenes bearing bulky ligand frameworks (ref 17a).

3774 Organometallics, Vol. 19, No. 19, 2000
Kukral et al.
and Varian (MAT-711) instruments. Elemental analyses were
determined in the microanalytical laboratory of the University
of Ulm.
excess of 1,2-dibromoethane yielded 1a as a beige solid. A
solution of 1a in 80 mL of Et2O was added at room temperature
to the separately prepared lithium salt of 2-phenylindene 2c
(5.5 g, 28.9 mmol). The reaction mixture was stirred overnight
and refluxed for 2 h. The crude product was treated with a
saturated aqueous solution of NH4Cl and washed several times
with water. The organic phase was separated and dried over
Na2SO4. Evaporation of the solvent and recrystallization from
n-hexane yielded 3c as a white solid (7.7 g, 20.2 mmol, 69%).
3c: 1H NMR (200 MHz, CDCl3) δ 2.2-2.65 (m, 4H, CH2
bridge), 3.7 (s, 2H, CH2 indene), 4.2 (t, 1H, CH 9-H-fluorene),
6.8-7.9 (m, 18H, indene olefinic, aromatic protons indene
system, aromatic fluorene); MS (FD) m/z 384 (M+, 100%). Anal.
Calcd C, 93.71; H, 6.29. Found: C, 93.53; H, 6.37.
1-d -P r op en e. A mixture of cis/ trans-1-bromo-1-propene (72
g, 0.6 mol) was added to freshly cut lithium (12.5 g, 1.8 mol)
in 300 mL of ether at 0 °C. After stirring overnight, the
mixture was filtered and the filtrate evaporated to dryness.
The resulting white solid lithium compounds were suspended
in 200 mL of toluene. At 0 °C methanol-d1 (24 g, 0.73 mol)
was added, and the evolving gas was condensed through a cold
trap at -50 °C into a steel vessel at -196 °C. The gas was
further purified by passing it through molecular sieves and
bubbling it through triisobutylaluminum, resulting in a yield
1
of 20.5 g of 1-d-propene (80%). The H NMR spectrum (CDCl3
P r ep a r a tion of 1-(9-F lu or en yl)-1-(5,6-cyclop en ta -2-m e-
th ylin d en yl)d im eth ylsila n e (3d ). A portion of 5 g (30.1
mmol) of fluorene was diluted in 100 mL of Et2O and cooled
to -78 °C. Addition of a 1.6 M solution of n-BuLi in hexane
(18.8 mL, 30.1 mmol) and stirring for an additional 2 h resulted
in the formation of fluorenyllithium. Subsequent cooling to -78
°C and further treatment with an excess of dimethyldichlo-
rosilane (14.6 mL, 120 mmol) afforded the substituted fluore-
nyl compound 1b. The remaining mixture was allowed to
attain room temperature and stirred for an additional 2 h.
Removal of the solvent and excess of dimethyldichlorosilane
in vacuo gave 1b as a beige powder. This solution was added
after dilution with 100 mL of Et2O at ambient temperature to
the separately prepared lithium salt of the 5,6-cyclopenta-2-
methylindene 2a (5.1 g, 30.1 mmol). The reaction mixture was
stirred overnight and refluxed for 2 h. The crude product was
treated with a saturated aqueous solution of NH4Cl and
washed several times with water. The organic phase was
separated and dried over Na2SO4. Evaporation of the solvent
and recrystallization from n-hexane yielded 3d as a white solid
(8.9 g, 22.7 mmol, 75%).
3d : 1H NMR (200 MHz, CDCl3) δ -0.46, -0.51 (2 s, 6H, CH3
bridge), 2.01 (m, 2H, CH2 five-membered aliphatic ring), 2.11
(s, 3H, CH3) 2.83 (pseudo-q, 4H, CH2 five-membered aliphatic
ring), 3.58 (s, 1H, CH indene), 4.18 (s, 1H, CH 9-H-fluorene),
6.5 (s, 1H, indene olefinic), 7.08-7.87 (m, 10H, aromatic
protons indene system, aromatic fluorene); MS (FD) m/z 392
(M+, 100%). Anal. Calcd C, 85.66; H, 7.19. Found: C, 85.69;
H, 7.14.
P r ep a r a tion of 1-(9-F lu or en yl)-1-(2-m eth ylin d en yl)-
d im eth ylsila n e (3e). Following the procedure described for
3d , fluorene (4.5 g, 27.2 mmol), dimethyldichlorosilane (13.5
mL, 114 mmol), and 2-methylindene 2b (3.5 g, 27.2 mmol) gave
3e as a white solid (7.1 g, 20.1 mmol, 74%).
3e: 1H NMR (200 MHz, CDCl3) δ -0.49, 0.53 (2 s, 6H, CH3
bridge), 2.11 (s, 3H, CH3), 3.65 (s, 1H, CH indene), 4.15 (s,
1H, CH 9-H-fluorene), 6.54 (s, 1H, indene olefinic), 6.92-7.89
(m, 10H, aromatic protons indene system, aromatic fluorene);
MS (FD) m/z 352 (M+, 100%). Anal. Calcd C, 85.17; H, 6.86.
Found: C, 85.45; H, 6.82.
P r ep a r a tion of 1-(9-F lu or en yl)-1-(2-p h en ylin d en yl)-
d im eth ylsila n e (3f). Following the procedure described for
3d , fluorene (4.3 g, 26.0 mmol), dimethyldichlorosilane (12.5
mL, 104 mmol), and 2-phenylindene 2c (5.0 g, 26.0 mmol) gave
3f as a white solid (8.4 g, 20.2 mmol, 78%).
3f: 1H NMR (200 MHz, CDCl3) δ -0.89, -0.61 (2 s, 6H, CH3
bridge), 3.97 (s, 1H, CH indene), 4.30 (s, 1H, CH 9-H-fluorene),
6.95-7.86 (m, 18H, indene olefinic, aromatic protons indene
system, aromatic fluorene); MS (FD) m/z 414 (M+, 100%). Anal.
Calcd C, 86.91; H, 6.32. Found: C, 86.62; H, 6.32.
P r ep a r a tion of r a c-[1-(9-η5-F lu or en yl)-2-(2-p h en yl-1-η5-
in d en yl)eth a n e]zir con iu m Dich lor id e (4c). A 1.5 g portion
(4.9 mmol) of 1-(9-fluorenyl)-2-(2-phenylindenyl)ethane, 3c,
was diluted in 60 mL of Et2O and cooled to -78 °C. After
treatment of the ligand precursor with 4.9 mL of n-BuLi at
-78 °C the reaction mixture was warmed to room temperature
and stirred for 2 h. Subsequently, the solvent was removed in
(δ ) 7.24 ppm), 500 MHz) showed that the product contained
41% of cis-1-d-propene HDCdCHCH3 (dq, δ ) 4.91 ppm, 3J )
4
10 Hz, J ) 1.5 Hz, 1H) and 59% of trans-1-d-propene (dq, δ
3
4
) 5.00 ppm, J ) 17 Hz, J ) 1.8 Hz, 1H).
P olym er iza tion Rea ction s w ith 1-d -P r op en e. Polymer-
izations with deuterated propene were performed in a 50 mL
steel autoclave. The solvent toluene, cocatalyst MAO, and the
catalyst were fed under argon and allowed to reach the desired
polymerization temperature. After a 10 min contact time
monomer was added and temperature ((1 °C) and pressure
((100 mbar) were kept constant. The polymerization was
stopped by pouring the reaction mixture into acidified metha-
nol. The polymer product was washed with a methanol/HCl
solution and with methanol. The product was filtered and dried
in vacuo at 60 °C overnight. The yields of deuterated polypro-
pene were between 0.2 and 0.8 g.
P r op en e P olym er iza tion Rea ction s. The polymerization
reactions were performed in a 1 L Bu¨chi steel reactor at
constant pressure and temperature. The autoclave was charged
with 300 mL of toluene and with the desired amount of MAO.
Subsequently, the polymerization temperature was adjusted,
the reactor was charged with propene up to the desired partial
pressure, and the preactivated catalyst solution (Al:Zr ) 100:
1) was injected into the autoclave via a pressure buret. The
monomer consumption was measured by the use of a calibrated
gas flow meter (Bronkhorst F-111C-HA-33P), and the pressure
was kept constant during the entire polymerization period
(Bronkhorst pressure controller P-602C-EA-33P). Pressure,
temperature, and consumption of propene were monitored and
recorded online. The polymerization reactions were stopped
and treated as described above.
P olym er An a lysis. 13C NMR spectra were recorded on a
Varian GEMINI 2000 spectrometer (C2D2Cl4, 100 °C, 75 MHz,
10 mm probe) or on a Bruker AMX 500 spectrometer (C2D2-
Cl4, 80 °C, 125 MHz, 5 mm probe) in the inverse gated
decoupling mode with a 3 s pulse delay and a 45° pulse to
attain conditions close to the maximum signal-to-noise ratio.
The number of transients accumulated was between 5 and 15
K. The spectra were analyzed by known methods.32 Molecular
weights and molecular weight distributions were determined
by gel permeation chromatography (GPC, Waters 150 C ALC,
140 °C in 1,2,4-trichlorobenzene) relative to polystyrene and
polypropene standards.
P r ep a r a tion of 1-(9-F lu or en yl)-2-(2-p h en ylin d en yl)-
eth a n e (3c). A portion of 4.8 g (28.9 mmol) of fluorene was
diluted in 100 mL of Et2O and cooled to -78 °C. Addition of a
1.6 M solution of n-BuLi in hexane (18.1 mL, 28.9 mmol) and
stirring for an additional 2 h afforded the formation of
fluorenyllithium. Subsequent cooling to -78 °C and further
treatment with an excess of 1,2-dibromoethane (14.9 mL, 173
mmol) formed the substituted fluorenyl compound 1a . The
remaining mixture was allowed to attain room temperature
and stirred for an additional 2 h. Removal of the solvent and
(31) Chang, Y. H.; Ford, W. T. J . Org. Chem. 1981, 46, 3758
(32) Busico, V.; Cipullo, R.; Corradini, P.; Landriani, L.; Vacatello,
M.; Segre, A. L. Macromolecules 1995, 28, 1887

Dual-Side ansa-Zirconocene Dichlorides
Organometallics, Vol. 19, No. 19, 2000 3775
vacuo and the resulting lithium salt was diluted with 60 mL
of toluene. Cooling to -78 °C and addition of solid ZrCl4 (0.91
g, 3.9 mmol) afforded the formation of an orange suspension,
which was warmed to room temperature and stirred overnight.
The mixture was filtered, and the remaining solid fraction was
extracted with toluene until the organic phase remained
colorless. Removal of the solvent gave an orange powder, from
which pure 4c (1.2 g, 2.3 mmol, 56%) could be obtained by
recrystallization from toluene solution.
distribution of isotopes according to expected contents. Anal.
Calcd C, 60.84; H, 4.74. Found: C, 60.58; H, 4.91.
P r ep a r a t ion of r a c-[Dim et h ylsila n ed iyl-(9-η5-flu or -
en yl)(2-m eth yl-1-η5-in d en yl)]zir con iu m Dich lor id e (4e).
Following the procedure described for 4d , 1-(9-fluorenyl)-1-
(2-methylindenyl)dimethylsilane, 3e (1.43 g, 4.06 mmol), 1.6
M n-BuLi in n-hexane (5.07 mL, 8.12 mmol), and ZrCl4 (0.94
g, 4.06 mmol) gave 4e as a orange solid (0.59 g, 1.15 mmol,
28%).
4e: 1H NMR (200 MHz, CDCl3) δ 1.35, 1.48 (2 s, 6H, CH3
bridge), 2.21 (s, 3H, CH3), 6.60 (s, 1H, indene), 6.90-8.04 (m,
10H, aromatic); MS (EI) m/z 512, peak distribution of isotopes
according to expected contents. Anal. Calcd C, 58.57; H, 4.33.
Found: C, 58.28; H, 4.48.
4c: 1H NMR (200 MHz, CDCl3) δ 3.9-4.65 (m, 4H, CH2
bridge), 6.65 (s, 1H, indene), 6.8-7.9 (m, 17H, aromatic); MS
(EI) m/z 544, peak distribution of isotopes according to
expected contents. Anal. Calcd C, 66.16; H, 4.07. Found: C,
65.88; H, 4.23.
P r ep a r a t ion of r a c-[Dim et h ylsila n ed iyl-(9-η5-flu or -
en yl)(5,6-cyclopen ta-2-m eth yl-1-η5-in den yl)]zir con iu m Di-
ch lor id e (4d ). 1-(9-Fluorenyl)-1-(5,6-cyclopenta-2-methylin-
denyl)dimethylsilane, 3d (1.4 g, 3.56 mmol), was diluted in
60 mL of Et2O and cooled to -78 °C. After treatment of the
ligand precursor with 4.45 mL of n-BuLi at -78 °C the reaction
mixture was warmed to ambient temperature and stirred for
2 h. Subsequently, the solvent was removed in vacuo, and the
resulting lithium salt was diluted with 60 mL of toluene.
Cooling to -78 °C and addition of solid ZrCl4 (0.83 g, 3.56
mmol) afforded the formation of an orange suspension, which
was warmed to room temperature and stirred overnight. The
mixture was filtered, and the remaining solid fraction was
extracted with toluene until the organic phase remained
colorless. Removal of the solvent gave an orange powder. The
zirconocene 4d (0.65 g, 1.18 mmol, 33%) could be purified by
washing with Et2O and pentane.
P r ep a r a t ion of r a c-[Dim et h ylsila n ed iyl-(9-η5-flu or -
en yl)(2-p h en yl-1-η5-in d en yl)]zir con iu m Dich lor id e (4f).
Following the procedure described for 4d , 1-(9-fluorenyl)-1-
(2-phenylindenyl)dimethylsilane, 3f (1.53 g, 3.68 mmol), 1.6
M n-BuLi in n-hexane (4.6 mL, 7.36 mmol), and ZrCl4 (0.86 g,
3.68 mmol) gave 4f as a orange solid (0.59 g, 1.03 mmol, 28%).
4f: 1H NMR (200 MHz, CDCl3) δ 0.9, 1.53 (2 s, 6H, CH3
bridge), 6.97-7.98 (m, 18H, indene, aromatic); MS (EI) m/z
574, peak distribution of isotopes according to expected
contents. Anal. Calcd C, 62.69; H, 4.21. Found: C, 62.31; H,
4.43.
Ack n ow led gm en t. Generous financial assistance is
gratefully acknowledged from Deutscher Akademischer
Austauschdienst (DAAD) and Procter & Gamble. We
also wish to thank Prof. Seppa¨la¨ (Helsinki University
of Technology) for the comprehensive support in polymer
characterization.
1
4d : H NMR (200 MHz, CDCl3) δ 1.33, 1.46 (2 s, 6H, CH3
bridge), 1.74-1.99 (m, 2H, CH2 cyclopentane ring), 2.17 (s, 3H,
CH3), 2.45-2.99 (m, 4H, CH2 cyclopentane ring), 6.49 (s, 1H,
indene), 6.85-7.98 (m, 10H, aromatic); MS (EI) m/z 552, peak
OM000224Q