Synthesis of a dinuclear ansa-zirconocene catalyst having a biphenyl bridge and application to ethene polymerization

Article abstract of DOI:10.1016/S1381-1169(97)00180-5

A novel dinuclear ansa-zirconocene catalyst (μ-C₁₂H₈{[SiPh(Ind)₂]ZrCl₂}₂) (I) was prepared by a Wurtz coupling reaction between two equivalent of bisindenylphenylchlorosilane and one equivalent of 4,4'-dibromobiphenyl in THF at reflux temperature for 12 h, followed by a successive reaction with ZrCl₄ · 2THF in THF at -78°C. Polymerization of ethene was conducted in a 300 cm³ glass reactor equipped with a stirrer at 40, 60, 80 and 100°C using MAO or Ph₃C[B(C₆F⁵)₄] as cocatalyst and toluene as the solvent. The catalyst (I) gave linear polyethene with a broader molecular mass distribution (MMD) in a much higher yield as compared to the corresponding mononuclear catalyst derived from [Ph₂Si(Ind)₂]ZrC1₂ (II). The apparent activity increased monotonously from 40°C up to 100°C. The replacement of MAO with Ph₃C[B(C₆F₅)₄] gave polyethene with a higher molecular weight.

Full text of DOI:10.1016/S1381-1169(97)00180-5

Ž
.
Journal of Molecular Catalysis A: Chemical 128 1998 273–278
Synthesis of a dinuclear ansa-zirconocene catalyst having a
biphenyl bridge and application to ethene polymerization
)
Kazuo Soga , Hoang The Ban, Toshiya Uozumi
School of Materials Science, Japan AdÕanced Institute of Science and Technology, 1-1 Asahidai, Tatsunokuchi, Nomi-gun, Ishikawa Pref.
923-12, Japan
Abstract
Ž
Äw
Ž
. x
4 . Ž .
A novel dinuclear ansa-zirconocene catalyst m-C12H8 SiPh Ind ZrCl2 2 I was prepared by a Wurtz coupling
2
reaction between two equivalent of bisindenylphenylchlorosilane and one equivalent of 4,4X-dibromobiphenyl in THF at
reflux temperature for 12 h, followed by a successive reaction with ZrCl4P2THF in THF at y788C. Polymerization of
ethene was conducted in a 300 cm3 glass reactor equipped with a stirrer at 40, 60, 80 and 1008C using MAO or
w Ž
. x
Ž .
Ph3C B C6F5 4 as cocatalyst and toluene as the solvent. The catalyst I gave linear polyethene with a broader molecular
Ž
.
mass distribution MMD in a much higher yield as compared to the corresponding mononuclear catalyst derived from
w
Ž
. x
Ž .
. x
Ph2Si Ind ZrCl2 II . The apparent activity increased monotonously from 408C up to 1008C. The replacement of MAO
w 2 Ž
with Ph3C B C6F5 4 gave polyethene with a higher molecular weight. q 1998 Elsevier Science B.V.
Keywords: Dinuclear ansa-zirconocene catalyst; Biphenyl bridge; Ethene polymerization
1. Introduction
disadvantages on the processability due to the
high shear viscosity and low melt extensional
w
x
The practical application of metallocene cata-
lysts still requires to improve their thermal sta-
bility for adaptation to the various existing olefin
viscosity of the product 6,7 . To overcome
those problems, combined metallocene catalysts
w x
like Cp2TiCl2rCp2 ZrCl2 8 and Cp2 ZrCl2r
w
x
w x
polymerization processes 1–4 . It was reported
that some ansa-metallocenes with phenyl
Cp2 HfCl2 9 have been developed. On the
other hand, several kinds of dinuclear metal-
w x
substitutions on
a
w
silicon bridge like
locene catalysts with diphenyl 10 , phenyl-
w
Ž
.
x
Ž
.
x
w x
Ph2Si Ind ZrCl2, Ph2CCp Flu ZrCl2, etc.
ene 11 or siloxane bridge have also been syn-
thesized and applied to olefin polymerizations
2
display high activities to give linear polyethenes
w
x
with high molecular weights even at elevated
12,13 .
In the present study, we have prepared a
w x
temperatures 5 . However, the molecular mass
distributions of resulting polyethenes are very
dinuclear ansa-zirconocene catalyst having a
biphenyl bridge from bisindenylphenylchlorosi-
lane and 4,4X-dibromobiphenyl using a modified
Ž
.
narrow MwrMn s2–3 , which caused some
w
x
Wurtz coupling reaction 14 and tested it to
ethene polymerization. This paper reports the
synthetic method of the dinuclear zirconocene
)
Corresponding author. Fax: q81-761-511625; e-mail:
uozumi@jaist.ac.jp
1381-1169r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.
Ž
.
PII S1381-1169 97 00180-5

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K. Soga et al.rJournal of Molecular Catalysis A: Chemical 128 1998 273–278
catalyst together with preliminary results of
ethene polymerization with it.
2.2. Synthesis of bisindenylphenylchlorosilane
A modified method to prepare bisin-
w
x
denyldichlorosilane 15 was employed for the
Ž
.
2. Experimental
synthesis of PhSi Ind Cl. A 500 ml three-neck
2
flask was equipped with a reflux condenser, a
2.1. Materials
dropping funnel and a magnetic stirring bar.
Ž
.
Indenylmagnesiumbromide 22 g, 100 mmol
Ethene of research grade purity donated by
Mitsui Petrochemical Japan was further purified
by passing through NaOH and P2O5 columns.
was added to the flask followed by the addition
of 250 ml of diethylether. Then, trichlo-
Ž
.
rophenylsilane 10.6 g, 8 ml, 50 mmol in 100
ml of diethylether was added dropwise at room
temperature and the reaction mixture was heated
to reflux temperature with stirring for 10 h.
After removing the solvent in vacuo, 300 ml of
hexane was added followed by stirring at room
temperature for 2 h. The solid fraction was
removed by filtration through a Celite plug.
Recrystallization of the filtrate from hexane gave
Ž
Solvents toluene, hexane, tetrahydrofuran
Ž
.
.
THF , dichloromethane and diethylether were
commercially obtained from Kanto Chemicals
Japan and purified according to the usual proce-
Ž
.
dures. Methylalumoxane MAO , triethylalu-
Ž
.
w
Ž
. x
minum TEA and Ph3C B C6F5 4 were do-
nated by Tosoh Akzo Japan and used without
further purification. Trichlorophenylsilane com-
mercially obtained from Kanto Chemicals Japan
was further purified by reduced distillation un-
der nitrogen atmosphere. 4,4X-dibromobiphenyl
and n-butyllithium were commercially obtained
from Kanto Chemicals Japan and used without
further purification.
Ž
.
Ž
.
3.8 g 10.2 mmol, 20.4% of PhSi Ind Cl as
2
1
white solid powders, which was shown by H-
Ž
.
NMR Fig. 1 to be the mixture of two diastereo-
1
Ž
.
mers. H-NMR CDCl3, 300 MHz, 258C ds
7.59–7.38 m, 10H, Ph , 7.32–7.01 m, 16H,
H-4, H-5, H-6, H-7 , 6.98–6.90 dd, 4H, H-3 ,
Ž
.
Ž
.
Ž
.
Fig. 1. 1H-NMR CDCl3 spectrum of a mixture of two diastereomers PhSi Ind 2Cl : solvent impurity .
Ž)
Ž
.
Ž
.
.

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)
K. Soga et al.rJournal of Molecular Catalysis A: Chemical 128 1998 273–278
275
Ž
.
Ž
6.57–6.54 dd, 2H, H-2 , 6.31–.28 dd, 2H,
Recrystallization of the filtrate from toluene
.
Ž
.
Ž
.
Ž
.
H-2 , 4.03 s, 2H, H-1 , 3.98 s, 2H, H-1 .
Further recrystallization from hexane gave a
gave 2.2 g 2.7 mmol, 38.6% of the catalyst
1
precursor as a pale yellow powder. H-NMR
Ž
. Ž
pure racemic isomer as white microcrystals, mp
CDCl3, 300 MHz, 258C ds7.60–7.38 m,
1
Ž
.
Ž
. Ž
18H, Ph , 7.35–7.12 m, 16H, H-4, H-5, H-6,
130.38C Fig. 2 . H-NMR CDCl3, 300 MHz,
.
Ž
.
. Ž . Ž
H-7 , 6.96–6.92 m, 4H, H-3 , 6.66–6.62 dd,
2H, H-2 , 6.42–6.40 dd, 2H, H-2 , 4.07 s, 2H,
H-1 , 4.03 s, 2H, H-1 .
258C ds7.50–7.42 m, 5H, Ph , 7.30–7.24
m, 4H, H-4, H-5, H-6, H-7 , 7.18–7.12 m,
4H, H-4, H-5, H-6, H-7 , 6.95–6.92 dd, 2H,
H-3 , 6.31–6.30 dd, 2H, H-2 , 3.98 s, 2H,
Ž
.
Ž
. Ž . Ž
.
Ž
.
Ž
.
.
Ž
.
Ž
Ž .
The catalyst I was prepared by an addi-
.
H-1 . The meso isomer was enriched in the
tional reaction of dilithiosalt of the precursor
with a solution of ZrCl4.2THF in THF at
y788C. The reaction mixture was slowly
warmed up to room temperature and stirred over
night. Lithium chloride was removed by adding
toluene followed by filtration through a Celite
plug. The filtrate was recrystallized from toluene
mother liquor as a sticky yellow oil after re-
moval of the recrystallization solvent.
( )
2.3. Synthesis of the catalyst I
A modified method to prepare diphenyldi-p-
Ž
.
Ž
.
w
x
Ž
.
biphenylylsilane C6H5 2Si C6H4C6H5 2 14
to give 1.6 g 1.4 mmol, 51.8% of the catalyst
as orange powders. Despite much effort on fur-
ther purification, the catalyst crystals could not
be obtained at the present stage. We are trying
to obtain the catalyst crystals by using pure
was used to synthesize the catalyst precursor.
To a 500 ml three-neck flask equipped with a
reflux condenser, a dropping funnel and a mag-
netic stirring bar, were introduced 1.1 g 3.5
mmol of 4,4 -dibromobiphenyl, 50 ml of THF
Ž
X
.
Ž
.
isomers of PhSi Ind Cl.
2
and 0.5 g of sodium ribbon. Then, two equiva-
Ž
lent of bisindenylphenylchlorosilane the mix-
2.4. Polymerization and analytical procedures
.
ture of two diastereomers, 2.6 g, 7 mmol in 50
ml of THF was added dropwise at room temper-
ature. The reaction mixture was heated up to
reflux temperature and kept standing with vigor-
ous stirring for 12 h. After the THF was re-
moved by distillation, 300 ml of toluene was
added. The resulting suspension was stirred at
room temperature for 2 h, and the solid fraction
was removed by filtration through a Celite plug.
All operations were carried out under nitro-
gen atmosphere. In a 300 cm3 glass reactor
equipped with a magnetic stirrer was introduced
Ž
w x
100 ml of toluene solution of MAO Al s0.6
.
mmolrl . The reactor was thermostated at an
appropriate polymerization temperature and sat-
urated with ethene. An activated metallocene
y
6
Ž
w x
w
x
Ž
.
solution Zr s1.0=10
molrl, Al MAO
Fig. 2. 1H-NMR CDCl3 spectrum of a pure racemic isomer of PhSi Ind 2Cl.
Ž
.
Ž
.

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276
K. Soga et al.rJournal of Molecular Catalysis A: Chemical 128 1998 273–278
.
w x
s0.4 mmolrl was then injected to start the
polymerization reaction. Ethene was continu-
ously fed to the reactor to keep the pressure at 1
bar during the polymerization. The polymeriza-
tion reaction was terminated by adding acidic
methanol. The precipitated polymers were ade-
quately washed with methanol and dried in
vacuo at 608C for 6 h. The weight average
developed in our laboratory 16 . The synthetic
Ž .
route of the catalyst I is illustrated in Scheme
1. The present catalyst having
a
w
Ž
.x
C6H5 Si C6H4 2C6H5 backbone looks highly
rigid, suggesting that its thermal stability is
much better than the corresponding zirconocene
w
x
catalyst with a siloxane bridge 17,18 . In this
study, we have conducted ethene polymeriza-
Ž
.
Ž .
molecular weight Mw and molecular mass
tion as the first application of the catalyst I .
Ž
.
Ž
distribution MMD of polymers were measured
at 1458C by GPC gel-permeation chromatogra-
phy, Senshu Scientific SSC7100 using o-di-
chlorobenzene as the solvent. The melting points
Therefore, the two diastereomers were used
without separation. Polymerization of ethene
was conducted in a 300 cm3 glass reactor at
various temperatures using MAO or
.
Ž
.
Ž
w
Ž
. x
of polymers Tm were measured by DSC dif-
Ph3C B C6F5 4 as cocatalyst, the results of
which are summarized in Table 1. For refer-
ence, the corresponding mononuclear ansa-
zirconocene catalyst derived from
.
ferential scanning calorimetry, Seiko DSC220C
at a heating rate of 108Crmin.
w
Ž
.
x
Ž .
Ph2Si Ind ZrCl2 II was also prepared ac-
2
w
x
3. Results and discussion
cording to the literature 19 and tested to ethene
polymerization. It is apparent from Table 1 that
Ž .
the catalyst I displays a much higher activity
The main objective of our present study is to
prepare a metallocene catalyst with a high sta-
bility at elevated polymerization temperatures.
The current catalyst structure stems from the
Ž
.
as compared to the catalyst II . When MAO is
used as cocatalyst, the polymerization activity
increased monotonously from 408C up to 1008C.
Such a high activity and high thermal stability
of the present catalyst might result from the
Ž
.
model of poly silylene phenylene-supported
metallocene catalysts which have been recently
Ž . Ž 4 .
Scheme 1. A synthetic route of the catalyst I m-C12 H8 SiPh Ind ZrCl2 .
2
Äw
Ž
. x
2

Table 1
Ž .
Ž .
Results of ethene polymerization with the catalysts I and II
a
y3
Crystallinityb
%
Ž .
Ž
.
w
x Ž
.
Ž
w
x
.
Ž
.
Ž
.
Ž
.
Run No.
Catalyst Cocatalyst
Tp 8C
Et molrl
Activity kgrmol Zr Et h
Mw =10
Mw rMn
Tm 8C
D H mJrmg
1
2
3
4
5
6
7
8
9
I
I
I
MAO
40
40
60
60
60
60
80
80
0.109
0.109
0.085
0.169
0.255
0.085
0.065
0.065
0.028
0.028
0.109
0.085
11400
19900
3200
47.2
87.7
35.5
100.1
100.0
42.3
30.1
36.8
15.7
19.3
74.0
70.1
8.3
10.8
13.7
9.3
8.1
7.3
6.0
4.2
6.0
5.6
134.8
136.8
134.6
138.9
136.4
138.3
136.0
136.5
136.5
137.6
138.8
135.6
211.3
204.9
221.8
204.2
209.2
211.7
211.9
226.2
233.2
234.5
208.0
213.4
79.0
76.0
82.2
75.6
77.5
82.1
82.2
83.8
86.4
86.9
77.0
79.0
w Ž
. x
Ph3C B C6 F5
MAO
4
Ic
Id
I
MAO
MAO
44800
44700
21500
69000
60000
70700
18200
3500
w Ž
. x
Ph3C B C6 F5
4
I
I
I
I
II
II
MAO
w Ž
. x
Ph3C B C6 F5
4
MAO
100
100
40
w Ž
. x
10
11
12
Ph3C B C6 F5
4
MAO
MAO
3.6
3.4
60
8000
y6
w
x
Ž
.
Ž
.
w Ž
. x
Polymerization conditions: monomer pressures1 bar, Zr s1.0=10 molrl, Al MAO rZrs1000, Al TEA rZrs100 when Ph3C B C6 F5 was used as cocatalyst, toluenes100
4
ml, polymn. times10 min.
a
w
x
Calculated from literature 20 .
b
w
x
Calculated from literature 21 .
c Monomer pressures2 bar.
d Monomer pressures3 bar.

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K. Soga et al.rJournal of Molecular Catalysis A: Chemical 128 1998 273–278
cooperating interaction between the two adja-
cent zirconocenes which are electronically cou-
pled through a biphenyl bridge. However, the
precise reasons are not clear at the moment. It is
also uncertain why the replacement of MAO
1008C. We are now preparing similar catalysts
using the pure meso and racemic isomers of
Ž
.
PhSi Ind Cl. The detailed characterization of
2
those catalysts together with the results of
propene polymerization over them will be re-
ported elsewhere.
w
Ž
. x
with Ph3C B C6F5 4 caused a marked decrease
in the activity at 1008C. Whereas, the weight
Ž
.
average molecular weight Mw of polyethene
decreased substantially with an increase in the
polymerization temperature. The use of
References
w
Ž
.4 x
Ph 3C B C 6 F5
as cocatalyst yielded
w x
1
H.H. Brintzinger, D. Fischer, R. Mulhaupt, B. Rieger, R.M.
polyethene with a slightly higher Mw. The cata-
Ž
.
Waymouth, Angew. Chem. Int. Ed. Engl. 34 1995 1143.
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Germany, 6–7 March 1996, p. 259.
Ž .
w x
2
lyst I , especially combined with MAO, yielded
polyethene with a broader molecular mass dis-
w x
3
Ž
.
tribution MMD , which may reflect the differ-
ence in catalytic performance between the two
diastereomers.
Then, the effect of ethene pressure on the
activity and Mw was briefly investigated, the
w x
4
w x
5
w x
6
Ž
results of which are shown in Table 1 runs No.
4 and 5 . Both the activity and the Mw of
.
w x
7
W. Hellmuth, Proc. 2nd Int. Congress on Metallocene Poly-
mers, Metallocene ’96, Germany, 6–7 March 1996, p. 239.
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polyethene increased markedly with raising the
ethene pressure from 1 to 2 bar. However, a
further increase in the ethene pressure did not
change the activity of the catalyst or the Mw of
polyethene. Since the activity of the present
dinuclear zirconocene catalyst is extremely high,
a lot of polyethene was produced under such
conditions. The use of a bigger reactor equipped
with a mechanical stirrer might be necessary to
evaluate those values more precisely.
w x
8
Ž
.
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.
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w
w
w
w
w
w
w
w
w
w
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.
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temperatures. It was found that the dinuclear
catalyst shows an extremely high activity for
ethene polymerization to give linear polyethene
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Ž
.
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.
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Ž
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