Novel octahydro- and tetrahydro-fluorenyl containing C1 symmetric zirconocenes for the stereoregular polymerization of propylene

Article abstract of DOI:10.1016/S0022-328X(01)01004-X

The synthesis and polymerization behavior of two new asymmetric metallocenes containing partially or fully hydrogenated fluorenyl moieties is reported. The zirconocenes, dimethylsilylene-[η⁵-1-(2-methyl-4-phenyl)indenyl]-(η ⁵-9-tetra

Full text of DOI:10.1016/S0022-328X(01)01004-X

Journal of Organometallic Chemistry 631 (2001) 29–35
www.elsevier.com/locate/jorganchem
Novel octahydro- and tetrahydro-fluorenyl containing C1
symmetric zirconocenes for the stereoregular polymerization of
propylene
Emma J. Thomas, Marvin D. Rausch *, James C.W. Chien
Department of Chemistry, Lederle Grad Research Center, Uni6ersity of Massachusetts, Amherst, MA 01003-4510, USA
Received 26 December 2000; received in revised form 11 May 2001; accepted 14 May 2001
Abstract
The synthesis and polymerization behavior of two new asymmetric metallocenes containing partially or fully hydrogenated
fluorenyl moieties is reported. The zirconocenes, dimethylsilylene-[h5-1-(2-methyl-4-phenyl)indenyl]-(h5-9-tetrahydrofluorenyl)
zirconium dichloride (9) and dimethylsilylene-[h5-1-(2-methyl-4-phenyl)indenyl]-(h5-9-octahydrofluorenyl) zirconium dichloride
(10) were both found to be very stable complexes that were highly active catalyst precursors for the polymerization of ethylene
and propylene. In the case of propylene, activities approaching 108 g polymer ([mol Zr] [monomer] h)−1 were obtained. Highly
stereoregular polypropylene was produced at room temperature. The complexes 9 and 10 were significantly more stable and more
active than the previously prepared fluorenyl analog. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Zirconocenes; Asymmetric metallocenes; Polymerization; Isotactic polypropylene; Octahydrofluorenyl; Tetrahydrofluorenyl
1. Introduction
We were interested to investigate the effects of plac-
ing substituents on the indenyl moiety of 1 on polymer-
ization behavior and particularly PP microstructure. A
series of substituted zirconocenes were prepared, which
were all shown to be highly efficient catalyst precursors
for both ethylene and propylene polymerization [9].
Depending on the substitution pattern on the indenyl
ring and the polymerization conditions, polymers vary-
ing from aspecific to highly isotactic were obtained. We
found that by placing substituents at both the 2- and
4-positions of the indenyl moiety, highly isotactic PP
The production of highly isotactic polypropylene
(PP) using Ziegler–Natta type homogeneous metal-
locenes is an area of great interest industrially and
academically. The discovery that chiral C2 symmetric
metallocenes could produce stereoregular polypropyle-
nes [1] efficiently led to many studies in order to fully
optimize the polymerization behavior of this class of
metallocene [2,3]. In recent years, research has in-
creased in the area of C1 symmetric systems, which
have been shown to polymerize propylene to PP with
varying microstructures from aspecific [4] to
stereoblock [5] to syndiotactic [6] to hemiisotactic [7] to
isotactic [8], depending on the nature of the hapto
ligands.
Rieger et al. [8b] published a study on the use of an
asymmetric ethylene bridged indenyl-fluorenyl zir-
conocene: ethylene-1-[-9-fluorenyl]-2-[-1-indenyl] zirco-
nium dichloride (1) that produced moderately isotactic
PP (Chart 1).
* Corresponding author. Tel.: +1-413-545-4490.
E-mail address: rausch@chem.unmass.edu (M.D. Rausch).
Chart 1.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01004-X

30
E.J. Thomas et al. / Journal of Organometallic Chemistry 631 (2001) 29–35
have been found to be lower by a factor of ten com-
pared to the ethylene bridged complexes. We believe
that this trend is a direct consequence of the nature of
the Si–fluorenyl bond and the resulting Zr–fluorenyl
bond. There are several reports of the instability of
some fluorenyl containing metallocenes due to ‘ring
slippage’ [12].
In 1997, Marks et al. published the results of a
comparative study of the polymerization behavior of
dimethylsilyl - [9 - octahydrofluorenyl] - (−) - [menthyl-
cyclopentadienyl] zirconium dichloride and the
fluorenyl containing analog [13]. The former was shown
to have similar or higher activities for propylene poly-
merization than the latter, and the polymers obtained
were more isotactic [13]. Similar results are observed
when indenyl is replaced by tetrahydroindenyl [14]. A
second example of the use of octahydrofluorenyl in
place of fluorenyl was reported by Na¨sman et al. in
1997 [15]. In that study, it was found that the use of the
fully hydrogenated octahydrofluorenyl ligand led to
higher Mw polyethylene (PE) than with the fluorenyl
analog [15]. We were therefore interested in investigat-
ing the effect of changing the fluorenyl moiety to a
partially or fully hydrogenated fluorenyl derivative, te-
trahydrofluorenyl (THFlu) or octahydrofluorenyl
(OHFlu), respectively, in asymmetric systems.
Scheme 1.
Scheme 2.
was produced. Ethylene-1-[-9-fluorenyl]-2-[-1-(2,4,7-
trimethyl)indenyl] zirconium dichloride (2) (Chart 1)
polymerized propylene with a productivity of 1.3×108
g polymer [(mol Zr) h]−1 and the resulting polymer was
91% isotactic with a molecular weight of 27 000 [9,10].
In an effort to increase the molecular weight of the
polymer, the silicon bridged analog of 2 was prepared
[10].
Surprisingly
however,
dimethylsilylene-[9-
2. Results and discussion
fluorenyl]-[1-(2,4,7-trimethyl)indenyl] zirconium dichlo-
ride (3) (Chart 1) was found to be a highly unstable
complex that showed lower activity and lower stereose-
lectivity towards propylene polymerization. The insta-
bility of 3 was attributed to a weak Zr-fluorenyl bond,
and also to the presence of the 7-methyl group, which
we believed interfered sterically with the methyl groups
on the dimethylsilylene bridge [10]. We recently pre-
pared several new asymmetric metallocenes including
ethylene-1-(9-fluorenyl)-2-[1-(2-methyl-4-phenyl)in-
denyl]zirconium dichloride (4) and dimethylsilylene-(9-
fluorenyl) - [1 - (2 - methyl - 4 - phenyl)indenyl]zirconium
dichloride (5) (Chart 1) [11]. Both 4 and 5, polymerized
propylene in the presence of methylaluminoxane
(MAO) to highly isotactic PP ([mmmm]]90%) with
high Mw. However, it was found that the dimethylsi-
lylene bridged analog was again lower in activity than
the ethylene bridged complex.
To date, the focus of our investigations has been the
effect of placing substituents on the indenyl moiety and
also varying the bridging ligand. We were interested to
extend this study to include changing the nature of the
fluorenyl moiety. In particular, we were interested in
trying to improve the polymerization behavior of the
dimethylsilylene bridged metallocenes that we had pre-
pared. The activities obtained with these complexes
2.1. Synthesis of the organic ligands
The synthesis of tetrahydrofluorene was reported by
Colonge et al. in the 1950s [16]. Octahydrofluorene was
prepared according to the method described by Marks
et al. and further reacted as published to prepare the
9-(chlorodimethylsilyl)-octahydrofluorenyl (6) deriva-
tive [13]. Two new asymmetric dimethylsilylene bridged
ligands were prepared containing the tetrahy-
drofluorenyl (7) (Scheme 1) and octahydrofluorenyl
(Scheme 2) (8) moieties, respectively. Both compounds
were isolated as oily solids in ca. 50% yields. It was
difficult to purify the two compounds, as they would
not crystallize fully in common solvent systems such as
ethanol or toluene/hexane. The best results were ob-
tained in 100% ethanol at −20 °C although the prod-
ucts became oily once isolated at room temperature.
1
The new ligands were characterized by H-NMR and
mass spectrometry.
Attempts to prepare the ethylene bridged analogs of
7 and 8 were unsuccessful due to a preference for
acid–base chemistry over nucleophilic substitution, as a
result of the more acidic nature of the protons in the
hydrogenated fluorenyl compounds relative to fluorene

E.J. Thomas et al. / Journal of Organometallic Chemistry 631 (2001) 29–35
31
Scheme 3.
itself. Under various reaction conditions, either starting
materials were recovered or spiro derivatives of the
fluorenyl ligands were produced.
for the ethylene bridged systems such as 2/MAO and
4/MAO [9,11].
The polypropylenes produced at room temperature
are highly isotactic for both 9 and 10/MAO with
[mmmm]=84 and 87%, respectively. However, at
higher Tp, the stereoregularity of the PP decreases and
is only moderately isotactic with [mmmm]=ca. 50%
for both systems. This is different to the results ob-
tained for the fluorenyl analog 5, which produced
highly isotactic PP under all polymerization conditions
[11]. The full pentad analysis for the polymers obtained
is shown in Table 3.
The pentad distribution patterns for the polymer
samples obtained at Tp=20 °C with 9 and 10 are very
similar for the polymer samples obtained with 5 at both
Tp. This suggests that changing the nature of the
fluorenyl moiety to a hydrogenated analog has no effect
on stereoregularity at Tp=20 °C and leads to a much
more active precursor. At Tp=70 °C for the new pre-
cursors 9 and 10, the stereoerrors become more signifi-
cant and [mmmm] is much lower indicating that under
2.2. Synthesis of the zirconocenes
The bridged ligands 7 and 8 were converted to their
corresponding zirconocenes 9 (Scheme 3) and 10
(Scheme 4) by reaction of the appropriate dianion with
one equivalent of ZrCl4 in diethyl ether. The complexes
could be isolated from either methylene chloride or
toluene in good yields as highly stable solids. The
tetrahydrofluorenyl complex 9 was isolated as a mixture
of two isomers (9a and 9b ca. 1:9) but as both isomers
should lead to isospecific propylene polymerization, this
was not thought to be a problem. The new zirconocenes
9 and 10 and were highly stable in solution and did not
decompose upon exposure to air for short periods of
time. Qualitatively, they appear much more stable than
the
dimethylsilylene-2,4,7-trimethylindenyl-fluorenyl
zirconocene 3 [10]. The complexes were characterized
1
by H-NMR and mass spectrometry.
2.3. Polymerization results
Polymerization studies were carried out in order to
compare the behavior of the new zirconocenes 9 and 10
with the previously prepared fluorenyl analog 5 [11].
Table 1 summarizes the results obtained for the poly-
merization of ethylene. As can be seen, the two new
catalyst precursors are highly efficient and the activities
are comparable with the results for 5/MAO as well as
the other zirconocenes prepared in this series [9]. Com-
plexes 9 and 10 were not preactivated due to their high
stability in solution.
Table 2 summarizes the propylene polymerization
results obtained in our laboratories at 30 psi propylene
pressure, and at two different temperatures, 20 and
70 °C. It can be seen that the two new catalyst precur-
sors are both highly efficient for the polymerization of
propylene with activities of high 107, approaching 108 g
polymer [(mol Zr) [C3] h]−1 for 9/MAO at 70 °C.
These activities are higher by a factor of at least 10
than those reported for 5/MAO under the same condi-
tions and are equal if not greater than those reported
Scheme 4.
Table 1
Polymerization of ethylene with asymmetric zirconocenes 9 and 10/
MAO: comparison with 5/MAO a
b
Catalyst precursor
Yield (g)
A
9
10
5 c
0.59
0.65
0.54
8.6×107
9.5×107
7.9×107
a Polymerization conditions: [Zr]=5 mM; Al/Zr=4000:1; time of
polymerization=6 min; Tp=50 °C; monomer pressure=15 psi.
b A (activity)=g polymer [(mol Zr)[C2] h]−1
.
c Preactivated for 10 min with 1 ml of MAO.

32
E.J. Thomas et al. / Journal of Organometallic Chemistry 631 (2001) 29–35
Table 2
Propylene polymerization results for catalyst precursors 9 and 10/MAO at 30 psi: comparison with 5/MAO a
Catalyst precursor
Temperature (°C)
Yield (g)
A b
Tm (°C)
[mmmm] c
9
9
10
10
5 d
5 d
20
70
20
70
20
70
17.90
15.94
6.49
11.30
0.7
1.40×107
9.00×107
0.52×107
6.40×107
0.06×107
0.43×107
118
No m.p.
138
81
137
84
49
87
56
91
89
0.8
135
a Conditions: Toluene solution, polymerization pressure=30 psi; time of polymerization=1 h; [Zr]=25 mM; Al:Zr=4000:1.
b Activity expressed as g polymer [(mol Zr) [C3] h]−1
c [mmmm] pentad analysis by 13C-NMR.
.
d Preactivated for 10 min with 1 ml of MAO.
Table 3
Pentad distributions for polypropylenes produced in Table 2 for 9 and 10/MAO: comparison with 5/MAO a
b
Catalyst
Temperature
mmmm
mmmr
rmmr
mmrr
mmrm+rmrr
mrmr
rrrr
mrrr
mrrm
9
9
10
10
5
20
70
20
70
20
70
83.7
49.1
87.0
56.1
90.5
88.9
6.99
19.4
5.6
16.8
5.60
3.91
0
0
0
0
0
0
6.89
20.8
5.61
19.3
3.94
6.14
0
4.48
0
1.69
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1.20
0
0.95
0
0
2.40
5.02
1.81
5.21
0
5
1.0
a Pentad distributions expressed as %.
b Tp (°C).
Table 4
Propylene polymerization results for asymmetric catalyst precursors 9 and 10/MAO in liquid propylene: comparison with 5/MAO a
Catalyst precursor
Productivity b
Isotacticity (mm, mol%)
Tm (°C)
Mw 10−5g mol−1 c
9
10
5
0.62×108
1.06×108
0.10×108
85
91
91
125
140
138
0.2
0.3
0.5
a Conditions; liquid pool, pressure=30 bar, temperature=70 °C, time of polymerization=1 h.
b Productivity expressed as g polymer [(mol Zr) h]−1
c Molecular weights determined by GPC.
.
these conditions, the use of a hydrogenated fluorenyl
moiety negatively effects the stereoregularity of the
propylene polymeriation. We believe this may be due to
the hydrogenated rings of the fluorenyl moieties that
can ‘ring flip’ and are therefore less stereorigid than
fluorenyl itself. At higher Tp, ring flip can occur more
rapidly, therefore reducing the steric directing effect on
both the polymer configuration and the incoming
monomer leading to more random chain propagation.
Polymerizations were also carried out in liquid pool
propylene. The results are shown in Table 4. Under
these conditions, it can be seen that the isotacticity of
the polypropylene remains high at Tp=70 °C with
[mm]=85 and 91% for 9 and 10, respectively (Table 4).
This may be explained by the fact that the tendency of
the hydrogenated rings to flip at higher temperature
may be overcome by the higher propylene
concentration.
The molecular weights of the polymers obtained un-
der liquid pool conditions with 9 and 10 are lower than
for 5. This may be due to the more indenyl like
character of the hapto ligand. It is known that
bisfluorenyl metallocenes produce very high molecular
weight polymers. A further explanation may be that the
less stereorigid geometry of the partially and fully hy-
drogenated analogs allows for easier b-hydride elimina-
tion and therefore lower molecular weight polymer.
We have discussed the mechanisms of polymerization
for the asymmetric catalyst precursors [10]. A related
discussion for a different series of asymmetric metal-
locenes was also published by Rieger et al. [17]. In the
case of 5 a chain stationary mechanism similar to that
proposed by Razavi et al. was proposed due to the
steric bulk of the phenyl group prohibiting chain migra-
tion [11]. Due to the less stereorigid geometry of 9 and
10, however, any restriction placed on the polymer

E.J. Thomas et al. / Journal of Organometallic Chemistry 631 (2001) 29–35
33
chain by the steric nature of the phenyl group and the
4.1. [1-(2-Methyl-4-phenyl)indenyl]-
fluorenyl moiety in 5 may be relieved, allowing for a
chain migratory insertion mechanism instead of the
chain stationary mechanism proposed for 5 [18]. The
only other report of octahydrofluorenyl containing
metallocenes as propylene polymerization catalysts was
by Marks et al. and in this case, polymerizations were
carried out at 25 °C and below [13].
The high stability of the complexes compared to
Si–fluorenyl analogs can be explained by the fact that
the ligand actually behaves more like a substituted
indenyl (Ind) in the case of tetrahydrofluorenyl, and
more like a cyclopentadienyl (Cp) ligand in the case of
octahydrofluorenyl. Zirconium complexes of Cp and
Ind are generally more stable and less susceptible to
fluctuating hapticity [12]. Our findings support the the-
ory that the instability of complexes such as 5 was a
consequence of the nature of the weak Si–fluorenyl
bond and the resulting Zr–fluorenyl bond.
[-9-tetrahydrofluorenyl] dimethylsilane (7)
To a solution of 2.00 g (9.70 mmol) of 2-methyl-7-
phenylindene in 40 ml of dry diethyl ether at 0 °C was
added dropwise a 1.6 M solution of butyllithium in
hexane (6.06 ml, 9.70 mmol). The solution was stirred
at room temperature (r.t.) for 5 h. The solvent was
removed under vacuum and the residue was washed
with 2×20 ml of dry pentane. The anion was dried
under vacuum, dissolved in 40 ml of dry diethyl ether
and 5 ml of dry THF, and then added dropwise via
cannula to 2.36 ml (19.4 mmol) of dichlorodimethylsi-
lane in 20 ml of dry diethyl ether at 20 °C. The
addition was carried out over a 1 h period and the
suspension was then stirred for 1 h at r.t. The solvents
and excess dichlorodimethylsilane were then removed
under vacuum and the resulting oil was suspended in 30
ml of dry diethyl ether at 0 °C. To this was added
dropwise by cannula one equivalent of 5,6,7,8-tetrahy-
drofluorenyllithium, prepared from 1.65 g (9.70 mmol)
of 5,6,7,8-tetrahydrofluorene and 6.06 ml (9.70 mmol)
of butyllithium in 30 ml of dry ether and 10 ml of dry
tetrahydrofuran. The suspension was allowed to stir
overnight at r.t. and hydrolyzed with aqueous NH4Cl.
The organic phase was separated and the aqueous layer
was extracted with ether. The combined organic phases
were dried (MgSO4), filtered and the solvent was re-
moved. The oily residue was crystallized from 100%
ethanol to give 2.10 g of 7 (50%). The compound was
3. Conclusion
In summary, we have shown that by replacing the
fluorenyl moiety of mixed ring indenyl-fluorenyl
dimethylsilylene bridged metallocenes with a partially
or fully hydrogenated fluorenyl derivative, highly stable
complexes can be prepared. The new zirconocenes were
found to be highly efficient catalyst precursors for the
polymerization of propylene and ethylene. In the case
of propylene, the activities were at least tenfold higher
than those obtained with fluorenyl analogs. In addition,
polymerization of propylene at room temperature or
under liquid pool conditions leads to highly isotactic
PP.
1
an oily solid that did not display a true m.p. H-NMR
(CDCl3): l 7.57–7.11 (m, 12 H, arom), 6.78 (bs, 1 H
Ind-C5-sp2), 3.77 (bs, 1 H, Ind-C5-sp3), 3.63 (bs, 1 H,
THFlu-C5-sp3), 2.54–2.42 (m, 4 H, CH2), 2.20–2.17 (d,
3 H, CH3), 1.95–1.55 (m, 4 H, CH2), −0.26 (s, 3 H,
Si–CH3), −0.27 (s, 3 H, Si–CH3). HRMS (EI) m/z for
C31H32Si: Anal. Calc.: 432.2273; Found: 432.2253.
4. Experimental
Reactions were carried out under an argon atmo-
sphere using standard Schlenk techniques. MAO was
purchased as a solution in toluene from Akzo Nobel
and used as received. All other reagents were purchased
from Aldrich and used without further purification.
Diethyl ether, THF, and pentane were distilled from
Na/K alloy under argon. Dichloromethane was distilled
from CaH2 under argon. Tetrahydrofluorene [16], oc-
tahydrofluorene [13], 2-methyl-7-phenylindene [3a] and
chlorodimethylsilyloctahydrofluorene (6) [13] were syn-
4.2. [1-(2-Methyl-4-phenyl)indenyl]-
[-9-octahydrofluorenyl] dimethylsilane (8)
To a solution of 1.55 g (7.51 mmol) of 2-methyl-7-
phenylindene in 30 ml of dry diethyl ether at 0 °C was
added dropwise a 1.6 M solution of butyllithium in
hexane (4.68 ml, 7.51 mmol). The solution was stirred
at r.t. for 5 h. The solvent was removed under vacuum
and the residue was washed with 2×20 ml of dry
pentane. The anion was dried under vacuum, dissolved
in 30 ml of dry diethyl ether and 5 ml of dry THF and
then added dropwise to 2.00 g (7.51 mmol) of 9-
(chlorodimethylsilyl)-octahdrofluorene (6) in 20 ml of
dry diethyl ether at −78 °C. The mixture was allowed
to warm to r.t. and stirred overnight to give a yellow
suspension which was hydrolyzed with aqueous NH4Cl.
1
thesized according to literature procedures. H-NMR
spectra were recorded on an AC-200 spectrometer.
13C-NMR spectra were recorded on an AMX500 spec-
trometer. Elemental analyses were performed by the
Microanalytical Laboratory, University of Massachu-
setts, Amherst, MA. Mass spectra were recorded at the
University of Massachusetts, Amherst, MA.

34
E.J. Thomas et al. / Journal of Organometallic Chemistry 631 (2001) 29–35
The organic phase was separated and the aqueous layer
was extracted with ether. The combined organic phases
were dried (MgSO4), filtered and the solvent was re-
moved. The oily residue was crystallized from 100%
ethanol to give 1.85 g of 8 (56%). The compound was
stirred for 5 min. One milliliter of the appropriate
catalyst solution in toluene was added and the mixture
was stirred until the desired reaction time was reached.
The mixture was quenched with 2% HCl in methanol,
filtered (or extracted in hexane in the case of a-PP), and
dried in a vacuum oven at an appropriate temperature
for the polymer sample.
1
an oily solid that did not display a true m.p. H-NMR
(CDCl3): l 7.52–7.15 (m, 8 H, arom), 6.79 (s, 1 H
Ind-C5-sp2), 3.74 (s, 1 H, Ind-C5-sp3), 3.18 (bs, 1 H,
OHFlu-C5-sp3), 2.44–1.59 (m, 16 H, CH2), 2.22 (s, 3 H,
CH3), −0.21 (s, 3 H, Si–CH3), −0.25 (s, 3 H, S–CH3)
HRMS (EI) m/z for C31H36Si: Anal. Calc.: 436.2586;
Found: 436.2608.
4.6. Polymer analyses
M.p.s were determined by DSC with a Perkin–Elmer
DSC-4 system. 13C-NMR spectra were determined at
90 °C in C6H3Cl3 with C6D6 on an AMX 500 spec-
trometer. Molecular weights were determined by gel
permeation chromatography using a Waters 150C in-
strument (solution in 1,2,4-trichlorobenzene at 135 °C
and PS standards for calibration.
4.3. Dimethylsilylene-[p5-1-(2-methyl-4-phenyl)indenyl]-
(p5-9-tetrahydrofluorenyl) zirconium dichloride (9)
To a solution of 7(0.50 g, 1.16 mmol), in 20 ml of dry
diethyl ether at 0 °C was added dropwise two equiva-
lents of 1.6 M butyllithium in hexane (1.45 ml, 2.32
mmol). The resulting suspension was stirred for 6 h at
r.t. The solvent was removed under vacuum and the
residue was washed with 2×10 ml portions of dry
pentane. The yellow solid was suspended in 20 ml of
dry diethyl ether and cooled to 0 °C. ZrCl4 (0.27 g,
1.16 mmol) was added as a solid. The orange suspen-
sion was stirred overnight at r.t. and the solvent was
removed by filtration. The residue was extracted in dry
methylene chloride, concentrated and stored at −
20 °C to give 9 (290 mg, 42.2%), an orange solid, as a
mixture of isomers (ca. 9:1). 1H-NMR (CDCl3): l
7.65–6.90 (m, 12 H, arom), 6.89 (s, 1 H, Ind-C5-sp2),
3.04–2.55 (m, 4 H, CH2), 2.34 minor, 2.23 major (s, 3
H, CH3), 1.90–1.35 (m, 4 H, CH2), 1.46 minor, 1.31–
1.29 major, 1.19 minor (s, 6 H, Si–CH3). HRMS (EI)
m/z for C31H30Cl2SiZr: Anal. Calc.: 590.0541; Found:
590.0535.
Acknowledgements
We would like to thank Dr. G. Dabkowski for
microanalyses and Dr. L.C. Dickinson for help with
13C-NMR and Dr. I. Kalteshov for mass spectral data.
We would also like to thank SOLVAY Polyolefins
Europe-Belgium for their financial support of this re-
search program.
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4.4. Dimethylsilylene-[p5-1-(2-methyl-4-phenyl)indenyl]-
(p5-9-octahydrofluorenyl) zirconium dichloride (10)
Following the procedure described for 9, 8 (0.50 g,
1.14 mmol), 1.6 M butyllithium in hexane (1.43 ml, 2.28
mmol and ZrCl4 (0.27 g, 1.14 mmol) gave 10 (310 mg,
1
45.6%) as a yellow solid. H-NMR (CDCl3): l 7.74–
7.02 (m, 8 H, arom and 1 H, Ind-C5-sp2), 2.76–1.20 (m,
16 H, CH2), 2.30 (s, 3 H, CH3), 1.17 (s, 3 H, Si–CH3),
1.05 (s,
3 H, Si–CH3). HRMS (EI) m/z for
C31H34Cl2SiZr: Anal. Calc.: 594.0854; Found: 594.0829.
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A 250-ml crown capped glass pressure reactor con-
taining 50 ml of toluene was equilibrated with the
appropriate monomer at the desired temperature and
pressure. The desired amount of MAO was added as a
solution in toluene via syringe, and the solution was
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[18] We would like to thank a reviewer for the following insightful
comments regarding an alternative possible explanation for the
differences in stereoregularity observed between the fluorenyl
complexes (e.g. 5) and the hydrogenated fluorenyl complexes (9
and 10). It was suggested that instead of ring-flip causing a
decrease in polymer stereoregularity, increased steric crowding
due to the hydrogenated rings leads to poorer coordination of
propylene and that a chain end epimerization mechanism is
occurring instead of the proposed enantiomorphic site control
with varying degrees of chain stationary insertions.
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