Aromatic substituted group 4 metallocene catalysts for the polymerization of α-olefins

Article abstract of DOI:10.1021/om960519x

Six new group 4 metallocene complexes were synthesized as precursors for the polymerization of α-olefins. The phenyl-substituted precursors 2b-4b when activated by methylaluminoxane (MAO) were highly active for the polymerization of ethylene but exhibited

Full text of DOI:10.1021/om960519x

Organometallics 1996, 15, 4951-4953
4951
Ar om a tic Su bstitu ted Gr ou p 4 Meta llocen e Ca ta lysts for
th e P olym er iza tion of r-Olefin s
Patrick Foster, J ames C. W. Chien,* and Marvin D. Rausch*
Department of Chemistry and Department of Polymer Science & Engineering, University of
Massachusetts, Amherst, Massachusetts 01003
Received J une 28, 1996X
Six new group 4 metallocene complexes were synthesized as precursors for the polymer-
ization of R-olefins. The phenyl-substituted precursors 2b-4b when activated by methy-
laluminoxane (MAO) were highly active for the polymerization of ethylene but exhibited no
activity for the polymerization of propylene. Bis(2-methylbenz[e]indenyl)zirconium dichloride
(5b) was activated with both MAO and triphenylcarbenium tetrakis(pentafluorophenyl)-
borate (trityl)/triisobutylaluminum producing polypropylene with varying molecular weight
depending on polymerization temperature. The titanium precursor 6b had lower activity
for ethylene as compared to the zirconium analog 5b and virtually no activity for propylene
when activated with either MAO or trityl.
Sch em e 1
In tr od u ction
In 1980, Kaminsky et al.1 reported that group 4
metallocenes when activated by methylaluminoxane
were efficient catalysts for the polymerization of R-ole-
fins. Subsequently, it was found that bridging the two
hapto ligands in the metallocene precursor produced
catalysts which polymerized propylene in a stereospe-
cific manner when activated with MAO.2 A variety of
bridges have been used in studies of these systems;
however the most commonly used bridges are the
methylene,3 ethylene,2,4 and dimethylsilylene5 units.
Recently, Waymouth et al.6 found that unbridged bis-
(η5-2-phenylindenyl)zirconium dichloride (1) activated
with MAO produced elastomeric polypropylene. Elas-
tomeric polypropylene was first reported by Natta in
1957,7 and subsequently Chien et al.3b,8 found that
elastomeric polypropylene could be produced using a
bridged titanocene catalyst. The explanation by Rausch
et al. for the production of elastomeric polypropylene is
the existence of two separate catalytic sites. The
aspecific site produces blocks of atactic polypropylene,
while the isospecific site produces isotactic blocks. In
the case of 1, the formation of elastomeric polypropylene
is thought to be due to the fact that two isomers of 1
are possible which can interconvert by rotation of the
indenyl rings. The meso-like form produces atactic
blocks of polypropylene while the rac-like form produces
isotactic blocks.
In the present study, a series of unbridged bis-
(indenyl)zirconium and -titanium dichlorides containing
phenyl and benzo substituents have been synthesized
and evaluated as catalyst precursors for the polymeri-
zation of ethylene and propylene.
X Abstract published in Advance ACS Abstracts, October 15, 1996.
(1) (a) Sinn, H.; Kaminsky, W. Adv. Organomet. Chem. 1980, 18,
99. (b) Sinn, H.; Kaminsky, W.; Vollmer, H. J .; Woldt, R. Angew. Chem.,
Int. Ed. Engl. 1980, 19, 390. (c) Kaminsky, W.; Miri, M.; Sinn, H.;
Woldt, R. Makromol. Chem. Rapid Commun. 1983, 4, 225.
(2) (a) Wild, F. R. W. P.; Zsolnai, L.; Huttner, G.; Brintzinger, H. H.
J . Organomet. Chem. 1982, 232, 233. (b) Ewen, J . A. J . Am. Chem.
Soc. 1984, 106, 6355. (c) Wild, F. R. W. P.; Wasiucionek, M.; Huttner,
G.; Brintzinger, H. H. J . Organomet. Chem. 1985, 288, 63. (d)
Kaminsky, W.; Ku¨lper, K.; Brintzinger, H. H.; Wild, F. R. W. P. Angew.
Chem., Int. Ed. Engl. 1985, 24, 507.
(3) (a) Ewen, J . A.; J ones, R. L.; Razavi, A.; Ferrara, J . D. J . Am.
Chem. Soc. 1988, 110, 6255. (b) Mallin, D. T.; Rausch, M. D.; Lin, Y.
G.; Chien, J . C. W. J . Am. Chem. Soc. 1990, 112, 2030. (c) Razavi, A.;
Ferrara, J . J . Organomet. Chem. 1992, 435, 299.
(4) Lee, I.-K.; Gauthier, W. J .; Ball, J . M.; Iyengar, B.; Collins, S.
Organometallics 1992, 11, 2115. (b) Rieger, B.; Steimann, M.; Fawzi,
R. Chem. Ber. 1992, 125, 2373. (c) Rieger, B.; J any, G.; Fawzi, R.;
Steimann, M. Organometallics 1994, 13, 647.
(5) Herrmann, W. A.; Rohrmann, J .; Herdtweck, E.; Spaleck, W.;
Winter, A. Angew. Chem., Int. Ed. Engl. 1989, 28, 1511. (b) Spaleck,
W.; Antberg, M.; Rohrmann, J .; Winter, A.; Bachmann, B.; Kiprof, P.;
Behm, J .; Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1992, 31,
1347. (c) Spaleck, W.; Kuber, F.; Wimter, A.; Rohrmann, J .; Bachmann,
B.; Antberg, M.; Dolle, V.; Paulus, E. F. Organometallics 1994, 13, 954.
(d) Stehling, U.; Diebold, J .; Kirsten, R.; Roll, W.; Brintzinger, H. H.;
J ungling, S.; Mulhaupt, R.; Langhauser, F. Organometallics 1994, 13,
964. (e) Resconi, L.; J ones, R. L.; Rheingold, A. L.; Yap, G. P. A.
Organometallics 1996, 15, 998.
(6) (a) Coates, G. W.; Waymouth, R. M. Science 1995, 267, 217. (b)
Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
(7) (a) Natta, G.; Mazzanti, G.; Crespi, G.; Moraglio, G. Chim. Ind.
Milan 1957, 39, 275. (b) Natta, G. J . Polym. Sci. 1959, 34, 531.
(8) Chien, J . C. W.; Llinas, H.; Rausch, M. D.; Lin, Y. G.; Winter,
H. H. J . Am. Chem. Soc. 1991, 113, 8569.
Resu lts a n d Discu ssion
Syn th esis of Ca ta lyst P r ecu r sor s. The precursors
2b-4b were prepared by the same general procedure
(Scheme 1). The appropriately substituted indene was
deprotonated with 1 equiv of butyllithium in diethyl
1
ether solution, and /2 equiv of zirconium tetrachloride
was added in the same solvent. Recrystallization of the
complexes from either toluene or CH2Cl2 gave 2b-4b
in 50-55% yield.
The complexes 5b and 6b were prepared by deproto-
nation of 2-methylbenz[e]indene (5a ) in diethyl ether
1
and toluene, respectively, followed by addition of
/
2
(9) Miller, W. G.; Pittman, C. U., J r. J . Org. Chem. 1974, 39, 1955.
S0276-7333(96)00519-5 CCC: $12.00 © 1996 American Chemical Society

4952 Organometallics, Vol. 15, No. 23, 1996
Foster et al.
Ta ble 2. P olym er iza tion of Eth ylen e a n d
P r op ylen e w ith P r ecu r sor s 5b, 6b, a n d 7 Activa ted
by MAO or Tr ip h en ylca r ben iu m
Sch em e 2
Tetr a k is(p en ta flu or op h en yl)bor a te (Tr ityl)/
Tr iisobu tyla lu m in u m (TIBA)a
Tp yield
10-7Ab 10-5Mw
c
compd monomer cocatalyst (°C)
(g)
25 2.32
trityl/TIBA 25 3.02
MAO 25 1.25
trityl/TIBA 25 4.58
trityl/TIBA 6.76
trityl/TIBA 25 0.16
trityl/TIBA trace
trityl/TIBA 25 4.18
trityl/TIBA trace
5b
5b
5b
5b
5b
6b
6b
7
C2H4
C2H4
C3H6
C3H6
C3H6
C2H4
C3H6
C2H4
C3H6
MAO
1.0
1.3
0.3
1.1
1.2
0.07
3.0
0.4
5.0
2.1
Sch em e 3
0
0
1.8
7
0
a
For MAO polymerizations: [Zr] or [Ti] ) 50 µM; Al/Zr or Ti )
4000:1; 15 psi of C2H4 or C3H6. For trityl polymerizations: [Zr]
or [Ti] ) 50 µM; Al/Zr or Ti ) 20:1; [Zr] or [Ti]/trityl ) 1:1; 15 psi
b
of C2H4 or C3H6; time of polymerization ) 15 min. Activity ) g
of polymer/(mol of catalyst‚[monomer]‚h). c Molecular weights
Ta ble 1. P olym er iza tion of Eth ylen e w ith
P r ecu r sor s 2b-4b Activa ted w ith MAOa
determined by GPC.
compd
time (min)
10-7Ab
yield (g)
Tm (°C)
Precursors 5b and 6b were activated using either
MAO or triphenylcarbenium tetrakis(pentafluorophe-
nyl)borate (trityl)/triisobutylaluminum. The catalysts
5b/MAO and 5b/trityl were both used to polymerize
ethylene and propylene (Table 2). Both systems showed
high activity for the polymerization of ethylene; how-
ever, in propylene polymerizations, 5b/trityl exhibited
higher activity than did the 5b/MAO system (Table 2).
The polypropylene (PP) produced by 5b/trityl and 5b/
MAO was atactic as shown by 13C NMR at both Tp
investigated. However, the molecular weight (Mw)
varied greatly at different Tp. At Tp ) 25 °C, the
catalyst 5b/trityl had an activity of 1.1 × 107 g of PP/
(mol Zr‚[C3H6]‚h) and the Mw of the PP was 0.4 × 105.
When Tp was lowered to 0 °C, the activity of the catalyst
5b/trityl was comparable to 5b/trityl at 25 °C; however,
the Mw of the PP increased to 5.0 × 105. The large
increase in Mw could be attributed to the fact that at
lower temperature rotation of the hapto ligands is
decreased allowing monomer coordination and insertion
to proceed with less steric interaction. In addition, since
â-hydride elimination requires a significant activation
energy, lowering the Tp should decrease the rate of
â-hydride elimination and increase the molecular weight
of the polymer.
The titanium-based catalyst system 6b/trityl exhib-
ited lower activity for the polymerization of ethylene and
virtually no activity for propylene (Table 2). This
phenomenum can be attributed to the smaller size of
the titanium metal center as compared to the zirconium
analog which would decrease the angle between the two
bulky hapto ligands and make monomer coordination
more difficult. Therefore, precursor 7 was synthesized
in order to decrease the steric bulk around the metal
center. For the polymerization of ethylene, the activity
of 7/trityl was 30 times that exhibited by 6b/trityl under
similar polymerization conditions (Table 2). However,
only trace amounts of polypropylene were produced by
7/trityl at various polymerization conditions.
2b
30
1
1
0.4
5.1
5.0
8.8
1.38
0.62
0.60
1.05
130.1
133.0
132.2
134.7
3b (isomer 1)
3b (isomer 2)
4b
1
a
Polymerization conditions: [Zr] ) 50 µM; Al/Zr ) 4000:1; Tp
b
) 50 °C; 15 psi of C2H4. Activity ) g of PE/(mol of Zr‚[C2H4]‚h).
equiv of MCl4 (M ) Zr, Ti) in the same solvent.
Crystallization of the products from toluene gave 5b and
6b in 60% and 47% yield, respectively (Scheme 2).
The mixed-ring complex 7 was synthesized from
2-methylbenz[e]indenyltitanium trichloride (8), which
we have previously reported,10 and CpTl in toluene
solution. Crystallization of the product from toluene
gave 7 in 42% yield (Scheme 3).
P olym er iza tion Resu lts. Precursors 2b-4b were
activated with MAO and used to polymerize both
ethylene and propylene. No visible polypropylene was
produced by precursors 2b-4b, and variation of polym-
erization conditions (i.e., temperature, concentration of
catalyst, etc.) failed to produce any satisfactory result.
However, precursors 2b-4b are highly active catalysts
for the polymerization of ethylene when activated by
MAO (Table 1). Catalyst 2b/MAO exhibited an activity
of 4.0 × 106 g of PE/(mol Zr‚[C2H4]‚h) at a polymeriza-
tion temperature (Tp) of 50 °C. When one of the phenyl
rings in 2b was replaced by a methyl group, two isomers
of the desired complex (3b) were obtained. However,
both isomers exhibited comparable polymerization be-
havior. The catalyst 3b/MAO exhibited higher activity
as compared to 2b/MAO. In addition, the melting point
(Tm) of the polyethylene (PE) increased when 3b/MAO
was used as the catalyst. In order to further reduce
steric factors at the C-3 position on the indenyl ring,
the precursor 4b was synthesized. The catalyst 4b/
MAO exhibited higher activity and Tm of the PE
produced as compared to both 2b/MAO and 3b/MAO.
Therefore, a comparison of these catalyst systems shows
that phenyl substitution on both the C-1 and C-3
positions leads to catalysts with lower activity and lower
Tm of PE, while removal of the steric bulk from the C-3
position increased both activity and Tm of PE.
Exp er im en ta l Section
Gen er a l P r oced u r es. Reactions were carried out under
an argon atmosphere using standard Schlenk techniques.
Methylaluminoxane (MAO) was purchased from Akzo, and all
other reagents were purchased from Aldrich and used without
(10) Foster, P.; Chien, J . C. W.; Rausch, M. D. Organometallics 1996,
15, 2404.

Group 4 Metallocene Catalysts
Organometallics, Vol. 15, No. 23, 1996 4953
further purification. Toluene, diethyl ether, tetrahydrofuran
(THF), hexane, and pentane were distilled from Na/K alloy
under argon. Methylene chloride and styrene were distilled
from CaH2. 2a ,9 3a ,9 4a ,10 5a ,5d 8,10 and CpTl11 were synthe-
sized by literature procedures. 1H NMR spectra were recorded
on a Varian XL-200 or a Bruker NR-80 spectrometer. 13C
NMR spectra were recorded on a Bruker MSL-300 spectrom-
eter. Elemental analyses were performed by the Microana-
lytical Laboratory, University of Massachusetts, Amherst, MA.
The procedure used to polymerize ethylene and propylene has
been reported in detail.12
Bis(η5-1,3-d ip h en ylin d en yl)zir con iu m Dich lor id e (2b).
To a solution of 1,3-diphenylindene (2a ) (3.33 g, 12.4 mmol)
in diethyl ether (75 mL) at 0 °C was added 1.6 M butyllithium
(7.8 mL, 12.4 mmol). The reaction mixture was warmed to
room temperature and stirred overnight. The solvent was
removed, and the solid residue was washed with pentane (2
× 20 mL) and dried in vacuo. The lithium salt was redissolved
in diethyl ether (50 mL), the solution was cooled to 0 °C, and
a suspension of ZrCl4 (1.44 g, 6.18 mmol) in diethyl ether (10
mL) was added. The mixture was warmed to room tempera-
ture and stirred overnight. The suspension was filtered and
the solid residue extracted with toluene. Concentration of the
solvent and cooling to -20 °C gave 2b (2.24 g, 52%) as orange
crystals. 1H NMR (C7D8): δ 7.85-7.37 (m, 8H, Ind-arom H),
7.09-6.79 (m, 20H, Ph), 6.69 (s, 2H, Ind-C5). Anal. Calcd for
from CH2Cl2. Isomer 1: 1H NMR (CD2Cl2) δ 7.74-7.23 (m,
18H, arom H), 6.10 (s, 2H, C5-H), 2.02 (s, 6H, CH3). Isomer 2:
1H NMR (CD2Cl2) δ 7.85-7.12 (m, 18H, arom H), 6.45 (s, 2H,
C5-H), 2.18 (s, 6H, CH3).
Bis(η5-1-ph en ylin den yl)zir con iu m Dich lor ide (4b). Fol-
lowing the procedure described for 2b, 3-phenylindene (4a )
(2.50 g, 13.0 mmol), 1.6 M butyllithium (8.13 mL, 13.0 mmol),
and ZrCl4 (1.51 g, 6.50 mmol) gave 4b (1.66 g, 47%) as yellow
crystals. 1H NMR (CD2Cl2): δ 7.83-7.16 (m, 18H, arom H),
6.59 (d, 2H, C5-H), 6.03 (d, 2H, C5-H). Anal. Calcd for C30H22
Cl2Zr: C, 66.16; H, 4.07. Found: C, 65.69; H, 3.88.
-
Bis(η5-2-m eth ylben z[e]in d en yl)zir con iu m Dich lor id e
(5b). Following the procedure described for 2b, 2-methylbenz-
[e]indene (5a ) (5.25 g, 29.1 mmol), 1.6 M butyllithium (18.2
mL, 29.1 mmol), and ZrCl4 (3.38 g, 14.5 mmol) gave 5b (5.40
g, 60%) as a yellow solid. 1H NMR (CD2Cl2): δ 8.08-7.11 (m,
12H, arom H), 6.67 (m, 2H, C5-H), 6.02 (m, 2H, C5-H), 1.92
(m, 6H, CH3). Anal. Calcd for C28H22Cl2Zr: C, 64.60; H, 4.23.
Found: C, 64.82; H, 4.49.
Bis(η5-2-m eth ylben z[e]in den yl)titan iu m Dich lor ide (6b).
To a solution of 5a (3.79 g, 21.0 mmol) in toluene (75 mL) at
0 °C was added 1.6 M butyllithium (13.1 mL, 21.0 mmol). The
solution was warmed to room temperature and stirred over-
night. The reaction mixture was recooled to 0 °C, TiCl4 (1.99
g, 10.5 mmol) was added via a syringe, and the solution was
stirred overnight at room temperature. The suspension was
1
C
42H30Cl2Zr: C, 72.39; H, 4.34. Found: C, 71.98; H, 4.77.
Bis(η5-1-m et h yl-3-p h en ylin d en yl)zir con iu m Dich lo-
filtered, and the solution was concentrated to /4 its original
volume. Cooling to -20 °C gave 6b (2.36 g, 47%) as a red solid.
1H NMR (CD2Cl2): δ 7.77-7.47 (m, 12H, arom H), 6.67 (m,
2H, C5-H), 6.02 (m, 2H, C5-H), 1.91 (m, 6H, CH3). Anal. Calcd
for C28H22Cl2Ti: C, 70.46; H, 4.65. Found: C, 70.02; H, 4.71.
(η5-Be n z[e]in d e n yl)(η5-cyclop e n t a d ie n yl)t it a n iu m
Dich lor id e (7). Benz[e]indenyltitanium trichloride (8) (300
mg, 0.94 mmol) was dissolved in toluene (40 mL), CpTl (253
mg, 0.94 mmol) was added, and the reaction mixture was
stirred overnight. The resulting suspension was filtered to
give a red solution and a gray solid. Concentration of the
solution and cooling to -20 °C gave 7 (138 mg, 42%) as red
crystals. 1H NMR (CDCl3): δ 8.25-7.58 (m, 6H, arom H),
7.06-7.02 (m, 2H, C5-H), 6.80 (m, 1H, C5-H), 6.16 (s, 5H, Cp).
Anal. Calcd for C18H14Cl2Ti: C, 61.93; H, 4.04. Found: C,
61.28; H, 3.97.
r id e (3b). 1-Methyl-3-phenylindene (3a ) (3.38 g, 16.4 mmol)
was dissolved in diethyl ether (50 mL) and cooled to 0 °C. After
addition of 1.6 M butyllithium (10.2 mL, 16.4 mmol), the
solution was warmed to room temperature and stirred for 8
h. The reaction mixture was recooled to 0 °C, ZrCl4 (1.91 g,
8.20 mmol) was added, and the solution was stirred overnight
at room temperature. The suspension was filtered, and the
solid residue was extracted with toluene. Concentration of the
solvent and cooling to -20 °C gave a mixture of isomers of 3b
(2.52 g, 55%) as an orange-yellow powder. Anal. Calcd for
C
32H26Cl2Zr: C, 67.11; H, 4.58. Found: C, 66.83; H, 4.50. The
mixture of isomers was separated by fractional crystallization
(11) Hunt, C. C.; Doyle, J . R. Inorg. Nucl. Chem. Lett. 1966, 2, 283.
(12) Kucht, A.; Kucht, H.; Song, W.; Rausch, M. D.; Chien, J . C. W.
Appl. Organomet. Chem. 1994, 8, 437.
OM960519X