Unbridged metallocene dichloride complexes with mono-substituted indenyl ligands and their application for the polymerization of propene

Article abstract of DOI:10.1016/S0022-328X(00)00776-2

The synthesis of unbridged metallocene dichloride complexes of the type Ind′₂ZrCl₂ (Ind′ = 2-alkyl- or arylalkyl-substituted indenyl) is described. The complexes are characterized by ¹H- and ¹³C-NMR spectroscopy and mass spectrometry. After activation with methylalumoxane these complexes can be used for propene polymerization; they produce block copolymers consisting of alternating isotactic and atactic blocks. The polymerization results and the polymer properties are presented. The influence of the catalyst structure on the polymerization behaviour is discussed.

Full text of DOI:10.1016/S0022-328X(00)00776-2

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Journal of Organometallic Chemistry 621 (2001) 304–309
Unbridged metallocene dichloride complexes with
mono-substituted indenyl ligands and their application for the
polymerization of propene
Roland Schmidt, Helmut G. Alt *
Laboratorium fu¨r Anorganische Chemie, Uni6ersita¨t Bayreuth, Postfach 10 12 51, D-95440 Bayreuth, Germany
Received 16 May 2000; accepted 25 June 2000
Dedicated to Professor Henri Brunner on the occasion of his 65th birthday
Abstract
The synthesis of unbridged metallocene dichloride complexes of the type Ind%2ZrCl2 (Ind%=2-alkyl- or arylalkyl-substituted
indenyl) is described. The complexes are characterized by 1H- and 13C-NMR spectroscopy and mass spectrometry. After
activation with methylalumoxane these complexes can be used for propene polymerization; they produce block copolymers
consisting of alternating isotactic and atactic blocks. The polymerization results and the polymer properties are presented. The
influence of the catalyst structure on the polymerization behaviour is discussed. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Catalysis; Polymer properties; Propene polymerization; Unbridged metallocene complexes
great potential for the polymerization of olefins. The
properties of the resulting polymers depend very much
on the structure of the metallocene complex (see Refs.
[4–24] and references cited therein).
1. Introduction
After activation with methylalumoxane (MAO) [1–3]
the metallocene complexes with Group 4 metals have
Unbridged, symmetrically substituted bis(indenyl)
complexes are able to produce block copolymers con-
sisting of atactic and isotactic blocks (‘oscillating cata-
lysts’) [9–22]. Depending on the substituent in position
2 of the indenyl ligand, two different symmetries (rac or
meso) can be formed (Fig. 1).
The meso form produces atactic polypropene, and
the rac form isotactic polypropene. The ratio of these
blocks and their block lengths can be controlled by the
temperature to a certain extent. Differently substituted
indenyl ligands can also have a considerable influence
on these parameters. Up to now, no systematic investi-
gations have been performed with alkyl and aryl sub-
stituents in position 2 of unbridged indenyl ligands to
study the effect on catalytic propene polymerization.
Here, we describe the synthesis and polymerization
behaviour of unbridged metallocene complexes with
mono-substituted indenyl ligands for the polymeriza-
tion of propene.
Fig. 1. Possible symmetries (rac and meso) of the model complex
bis(2-phenylindenyl)zirconium dichloride.
* Corresponding author. Tel.: +49-921-552555; fax: +49-921-
552157.
E-mail address: helmut.alt@uni-bayreuth.de (H.G. Alt).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00776-2

R. Schmidt, H.G. Alt / Journal of Organometallic Chemistry 621 (2001) 304–309
305
found a decrease with rising polymerization tempera-
ture, except for catalysts 4 [9] and 5, which showed
their top productivities at 30°C. This behaviour could
be rather due to the partial decomposition of the cata-
lysts at elevated temperatures and not to different
kinetics.
All other catalysts show their highest productivities
at a polymerization temperature of 0°C. Complexes
with an alkyl group as substituent in position 2 of the
indenyl ligand (1–3) are more active than complexes
with an alkylaryl substituent in the same position (4, 5,
7) except catalyst 6. This complex with two methylene
spacer groups shows the highest productivity
(273.900 g h−1 of polypropene per gram of Zr) (Fig. 2).
A direct comparison of the alkyl chain length shows
a decrease in productivity with growing alkyl chains
independent of the polymerization temperature. This
trend cannot be found for catalysts with alkylaryl
groups.
Scheme 1. Preparation of indene derivatives with a substituent in
position 2.
2. Results and discussion
2.1. Synthesis of indene deri6ati6es with an arylalkyl or
alkyl substituent in position 2
The preparation of various indene derivatives with an
arylalkyl or alkyl substituent in position 2 was accom-
plished according to Scheme 1.
2.3.2. Molar masses and polydispersities of the
polypropenes obtained
The molar mass averages Mn and Mw show the
expected trend. The higher the polymerization tempera-
(
(
2.2. Synthesis of complexes 1–7
(
(
The preparation of unbridged bis(indenyl) complexes
can be achieved in the manner shown in Scheme 2.
ture the lower Mn and Mw. The reason could be an
accelerated b-H-elimination reaction at higher tempera-
tures. Only those polypropenes that show a significant
difference in their molar mass averages were produced
at 0°C.
2.3. Polymerization results
The metallocene complexes 1–7 were activated with
an excess of MAO (Al:Zr=3000:1). The polymeriza-
tion of propene was conducted as a bulk polymeriza-
tion in 500 ml of liquid propene at 0, 30 and 60°C. The
tacticities of the polypropenes obtained were deter-
mined by 13C-NMR spectroscopy at 90°C in 1,2,4-
trichlorobenzene. The data obtained are shown in
Table 1.
At higher polymerization temperatures the observed
molar masses reach a similar level. The length of the
alkyl chain has no decisive influence on these polymer
data. Among the catalysts with alkylaryl groups on the
indenyl ligand no uniform trend is observed.
Metallocene catalysts produce polymers with polydis-
persities about the factor two (‘single-site catalysts’)
[25]. At a polymerization temperature of 0°C all
polypropenes obtained behave similarly. With increas-
ing temperature the polydispersity increases. Here, a
dependence on the length of the alkyl chain can be
observed: the longer the alkyl chain the higher the
polydispersity.
2.3.1. Influence of the polymerization temperature on
producti6ity
With increasing reaction temperature the productiv-
ity is expected to increase. In most cases investigated we
Scheme 2. Synthesis of the bis(indenyl) complexes 1–7.

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R. Schmidt, H.G. Alt / Journal of Organometallic Chemistry 621 (2001) 304–309
Table 1
Polymerization and polymer dataa

R. Schmidt, H.G. Alt / Journal of Organometallic Chemistry 621 (2001) 304–309
307
2.3.3. Influence of polymerization temperature and
catalyst structure on tacticity
Polymerizations were conducted in a 1 l Bu¨chi steel
reactor equipped with a mechanical stirrer. Propene
was polymerized in bulk at different temperatures: 0,
30, and 60°C. MAO was used as a 30% solution in
toluene from Witco, Germany. The polymerizations
were stopped by venting excess propene. The polymer
obtained was washed with HCl–methanol and dried in
vacuo.
Polymer data were recorded on a Millipore Waters
GPC 150C instrument. For the separation, four succes-
sively connected polystyrene columns were used. The
pore diameters of the single columns were 500, 1000,
Complexes 1–7 activated with MAO produce a block
copolymer consisting of alternating atactic and isotactic
blocks [9,26]. The isotacticity [27–29] of the polyprope-
nes obtained is reduced with increasing polymerization
temperature. At higher temperatures the speed of the
ligand oscillation is higher, and thus the atactic ratio of
the polymer increases.
An alkyl chain at the indenyl ligand of the metal-
locene catalyst causes polypropenes with a lower isotac-
ticity than complexes 4 and 5 with no or one methylene
spacer group. Both polypropenes of catalysts 4 and 5
show a high degree of isotacticity at polymerization
temperatures of 0°C and 30°C (4: 26.0%, 19.6%; 5:
37.4%, 29.6%). Complexes 6 and 7 are comparable to
the alkyl-substituted ones in relation to the tacticities.
It should be noted that a butyl-substituted indenyl
complex produces a polypropene with only small
changes in the isotacticity at different temperatures.
The oscillation speed seems to be almost independent of
the polymerization temperature. The steric hindrance
must be low, and so is the influence on the polymer
produced.
,
10 000 and 100 000 A. For the refractometric detection
an RI Waters 401 refractometer was used. Degassed
chloroform (flow rate 1 ml min−1) was used as eluent.
Polymer samples were dissolved in boiling chloroform
and hot filtered. The GPC was calibrated with
polystyrene standards.
3.1. General synthesis procedure for 2-arylalkyl- or
alkyl-substituted indene deri6ati6es
To a suspension of 2.24 g (92.5 mmol) magnesium
shavings in 100 ml of diethyl ether 10 mmol of the
corresponding alkylaryl bromide (or alkyl bromide)
were added. After 10 min, 82.5 mmol of the alkylaryl
bromide, dissolved in 50 ml of diethyl ether, were added
dropwise followed by a stirring period of about 2 h.
8.0 g (61.5 mmol) of 2-indanone [30], dissolved in
100 ml diethyl ether, were added slowly. The stirring
was continued overnight and subsequently the mixture
was hydrolysed with a diluted HCl solution at 0°C. The
organic layer was washed twice with an NaHCO3 solu-
tion and dried over Na2SO4. The solvent was removed.
The yield of the corresponding alcoholic compounds
was between 75 and 90%.
The alcoholic product was dissolved in 150 ml of
toluene and 8.3 mmol of p-toluene sulfonic acid were
added. The mixture was refluxed until all water formed
was separated via a Dean–Stark apparatus. After cool-
ing to room temperature the mixture was washed with
an NaHCO3 solution. The organic layer was dried over
Na2SO4 and the solvent was removed in vacuo. The
residue was dissolved in n-pentane and filtered over
silica. After evaporation of the solvent, the desired
indene derivatives were obtained in an overall yield of
45–75%.
3. Experimental
All experiments were performed under inert gas at-
mosphere using standard Schlenk technique. The inert
gas used was purified and dried argon (BTS catalyst,
molecular sieves). All solvents were purchased in tech-
nical grade and purified by distillation over Na–K
alloy. All other chemicals were commercially available
or were synthesized according to literature procedures.
NMR spectra were recorded in CDCl3 at 25°C on a
Bruker ARX 250 instrument. The chemical shifts in the
1H-NMR spectra were referenced to the residual proton
signal of the solvent (l=7.24 ppm for CHCl3); the
carbon resonances in the 13C-NMR spectra were also
referenced to the solvent signal (l=77.0 ppm for
CDCl3).
Mass spectra were recorded on a Varian MAT CH7
instrument (direct inlet system, electron impact ioniza-
tion 70 eV).
3.2. General procedure for the synthesis of unbridged
metallocene dichloride complexes
20 mmol of the substituted indene were dissolved in
diethyl ether and cooled to −78°C. 13 ml (20.8 mmol)
of n-butyllithium (1.6 M in n-hexane) were added
slowly. At room temperature the mixture was stirred
until gas evolution had stopped. Subsequently, 10 mmol
Fig. 2. Catalyst productivities at 0°C depending on the various
substituents at the indenyl ligand (in position 2).

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R. Schmidt, H.G. Alt / Journal of Organometallic Chemistry 621 (2001) 304–309
Table 2
NMR and mass spectroscopic data of complexes 1–7
.

R. Schmidt, H.G. Alt / Journal of Organometallic Chemistry 621 (2001) 304–309
309
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