Propylene polymerization with chiral and achiral unbridged 2-arylindene metallocenes

Article abstract of DOI:10.1021/om9702082

Unbridged 2-arylindenyl metallocene complexes, such as bis(2-phenylindenyl)zirconium dichloride, in the presence of methyaluminoxane (MAO) are catalyst precursors for the synthesis of elastomeric polypropylenes. The effects of 1-methyl substitution on the polymerization behavior of these unbridged 2-arylindene complexes have been studied. The reaction of the lithium salt of 1-methyl-2-phenylindene with ZrCl₄ leads to the formation of two diastereomers of bis(1-methyl-2-phenylindenyl)zirconium dichloride: rac- and meso-(1-Me-2-PhInd)₂ZrCl₂. The two isomers have been separated by fractional crystallization and identified by X-ray crystallography. X-ray crystallographic analysis reveals that the dihedral angles between the planes of the phenyl and the indenyl rings have significantly increased upon 1-methyl substitution (28-34° compared to 10-12° for unsubstituted (2-PhInd)₂ZrCl₂), which suggests strong steric repulsion between the 1-methyl and 2-phenyl groups. In ethylene polymerization, the productivity of the catalyst derived from the meso-isomer is similar to that of the catalyst derived from (2-PhInd)₂ZrCl₂; higher productivity is observed for the catalyst derived from the rac-isomer. In polymerization of propylene, both substituted catalysts have a significantly lower productivity than the catalyst derived from unsubstituted (2-PhInd)₂ZrCl₂ and generate amorphous polypropylene with a low molecular weight and isotacticity.

Full text of DOI:10.1021/om9702082

Organometallics 1997, 16, 3635-3639
3635
P r op ylen e P olym er iza tion w ith Ch ir a l a n d Ach ir a l
Un br id ged 2-Ar ylin d en e Meta llocen es
Raisa Kravchenko, Athar Masood, and Robert M. Waymouth*
Department of Chemistry, Stanford University, Stanford, California 94305
Received March 13, 1997X
Unbridged 2-arylindenyl metallocene complexes, such as bis(2-phenylindenyl)zirconium
dichloride, in the presence of methyaluminoxane (MAO) are catalyst precursors for the
synthesis of elastomeric polypropylenes. The effects of 1-methyl substitution on the
polymerization behavior of these unbridged 2-arylindene complexes have been studied. The
reaction of the lithium salt of 1-methyl-2-phenylindene with ZrCl4 leads to the formation of
two diastereomers of bis(1-methyl-2-phenylindenyl)zirconium dichloride: r a c- and m eso-
(1-Me-2-PhInd)2ZrCl2. The two isomers have been separated by fractional crystallization
and identified by X-ray crystallography. X-ray crystallographic analysis reveals that the
dihedral angles between the planes of the phenyl and the indenyl rings have significantly
increased upon 1-methyl substitution (28-34° compared to 10-12° for unsubstituted (2-
PhInd)2ZrCl2), which suggests strong steric repulsion between the 1-methyl and 2-phenyl
groups. In ethylene polymerization, the productivity of the catalyst derived from the meso-
isomer is similar to that of the catalyst derived from (2-PhInd)2ZrCl2; higher productivity is
observed for the catalyst derived from the rac-isomer. In polymerization of propylene, both
substituted catalysts have a significantly lower productivity than the catalyst derived from
unsubstituted (2-PhInd)2ZrCl2 and generate amorphous polypropylene with a low molecular
weight and isotacticity.
Sch em e 1
The physical properties of polyolefins are strongly
influenced by the microstructure of the polymer. Ster-
eoregular isotactic polypropylene is a high-melting
thermoplastic material, while stereorandom atactic
polypropylene is amorphous. Polypropylene consisting
of isotactic and atactic blocks is a thermoplastic elas-
tomer. Natta was the first to produce rubbery polypro-
pylene and to interpret its properties in terms of a
stereoblock microstrucure.1,2 Subsequent studies,3-5
particularly those by Collette and co-workers led to
improved heterogeneous catalysts for the production of
elastomeric polypropylene.6,7 The first homogeneous
bridged titanocene-based system that generated elas-
tomeric polypropylene was described by Chien and co-
workers.8-10 Chien proposed a mechanism where the
monomer insertion occured sequentially at aspecific and
isospecific coordination sites of the Cs-symmetric met-
allocene. Collins has investigated a closely related
system and proposed a different mechanism to account
for the stereoblock structure.11,12 We have recently
reported a strategy for the production of stereoblock
polypropylene with a nonbridged metallocene, bis(2-
phenylindenyl)zirconium dichloride, (2-PhInd)2ZrCl2
(1).13-15 This catalyst was designed to switch its
coordination geometry from aspecific to isospecific dur-
ing the course of polymerization in order to generate
atactic and isotactic blocks (Scheme 1). An advantage
of this system is the ability to influence the structure
and properties of the polymers by manipulation of the
catalyst structure or polymerization conditions.13-15 For
example, we have shown that catalyst modification
through ligand substitution in 3,5-positions on the
phenyl ring has a dramatic effect on its productivity and
stereospecificity.14 Thus, by changes in catalyst or
X Abstract published in Advance ACS Abstracts, J uly 15, 1997.
(1) Natta, G.; Mazzanti, G.; Crespi, G.; Moraglio, G. G. Chim. Ind.
1957, 39, 275-283.
(2) Natta, G. J . Polym. Sci. 1959, 34, 531-549.
(3) J ob, R. C. (Shell Oil Co.) U.S. Patent 5,118,649, 1992.
(4) Pellon, B. J .; Allen, G. C. (Rexene) Eur. Pat. Appl. 0 475 307 A1,
1992.
(5) Smith, C. A. (Himont) Eur. Pat. Appl. 423 786 A2, 1991.
(6) Collette, J . W.; Tullock, C. W.; MacDonald, R. N.; Buck, W. H.;
Su, A. C. L.; Harrel, J . R.; Mulhaupt, R.; Anderson, B. C. Macromol-
ecules 1989, 22, 3851-3858.
(11) Gauthier, W. J .; Corrigan, J . F.; Taylor, N. J .; Collins, S.
Macromolecules 1995, 28, 3771-3778.
(12) Gauthier, W. J .; Collins, S. Macromolecules 1995, 28, 3779-
3786.
(7) Collette, J . W.; Ovenall, D. W.; Buck, W. H.; Ferguson, R. C.
Macromolecules 1989, 22, 3858-3866.
(8) Mallin, D. T.; Rausch, M. D.; Lin, Y. G.; Dong, S.; Chien, J . C.
W. J . Am. Chem. Soc. 1990, 112, 2030-2031.
(13) Coates, G. W.; Waymouth, R. M. Science 1995, 267 (5195), 217-
(9) Chien, J . C. W.; Llinas, G. H.; Rausch, M. D.; Lin, G. Y.; Winter,
H. H.; Atwood, J . L.; Bott, S. G. J . Am. Chem. Soc. 1991, 113, 8569-
8570.
19.
(14) Hauptman, E.; Waymouth, R. M.; Ziller, J . W. J . Am. Chem.
Soc. 1995, 117, 11586-7.
(15) Waymouth, R. M.; Coates, G. W.; Hauptman, E. M. (Stanford
University) U.S. Patent 5,594,080, 1997.
(10) Babu, G. N.; Newmark, R. A.; Cheng, H. N.; Llinas, G. H.;
Chien, J . C. W. Macromolecules 1992, 25, 7400-7402.
S0276-7333(97)00208-2 CCC: $14.00 © 1997 American Chemical Society

3636 Organometallics, Vol. 16, No. 16, 1997
Kravchenko et al.
reaction mixture was stirred at 40 °C for 24 h. The turbid
lemon yellow solution was cooled to room temperature and
filtered through a frit packed with Celite. The Celite layer
was washed with toluene (3 × 30 mL). The filtrates were
evaporated to dryness. The resulting yellow solid (3.536 g,
65% yield) contained 3-r a c and 3-m eso in a 60:40 ratio.
Repeated crystallization from CH2Cl2 afforded orange cubes
of 3-m eso (554 mg, 10%). Repeated crystallization from THF/
pentane (4:1) gave 3-r a c as yellow rods (610 mg, 11%).
Spectroscopic data for 3-r a c: 1H NMR (20 °C, CDCl3, 300
MHz): δ 7.56 (t, J )7.2 Hz, 4H), 7.45 (m, 8H), 7.26 (t, J )7.6
Hz, 2H), 7.05 (t, J )7.6 Hz, 2H), 6.85 (d, J )8.6 Hz, 2H), 6.06
(s, 2H), 2.52 (s, 6H); 13C{1H} NMR (CDCl3, 20 °C, 75 MHz) δ
134.03 (C), 130.68 (C), 129.05 (CH), 128.70 (CH), 128.35 (C),
128.22 (CH), 126.64 (CH), 126.17 (CH), 125.17 (C), 124.74
(CH), 123.67 (CH), 120.91 (C), 98.64 (CH), 12.75 (CH3).18 Anal.
Found (Calcd): C, 67.26 (67.11); H, 4.86 (4.58). Spectroscopic
data for 3-m eso: 1H NMR (20 °C, CDCl3, 300 MHz) δ 7.49 (d,
J ) 8.5 Hz, 2H), 7.34 (m, 11H), 7.19 (m, 5H), 6.07 (s, 2H),
2.57 (s, 6H); 13C{1H} NMR (CDCl3, 20 °C, 75 MHz) δ 133.61
(C), 133.51 (C), 129.31 (C), 128.12 (CH), 128.24 (CH), 127.85
(CH), 125.90 (CH), 125.43 (CH), 124.39 (CH), 123.88 (C),
123.84 (CH), 119.24 (C), 97.87 (CH), 12.64 (CH3).18 Anal.
Found (Calcd): C, 66.81 (67.11); H, 4.66 (4.58).
polymerization conditions, we have prepared materials
ranging in properties from amorphous to elastomeric to
tough plastics.15
As part of our continuing studies of ligand effects on
the polymerization behavior of bis(2-arylindenyl) met-
allocenes, we now report the synthesis and study of
zirconocenes with 1-methyl-substituted 2-phenylindenyl
ligands, 1-Me-2-PhInd (2). In contrast to the previously
studied 3,5-substitution on the phenyl ring, unsymmet-
ric substitution in the 1-position on the indenyl reduces
the overall symmetry of the ligand. As a result, two
diastereomers: rac- and meso-(1-Me-2-PhInd)2ZrCl2
(3-r a c and 3-m eso) are expected. The ligand rotation
in 3-r a c and 3-m eso can generate additional rotamers
with a type of symmetry not accessible in the case of
the previously studied bis(2-arylindenyl) complexes.
Furthermore, these complexes provide insight on the
effect of the 1-methyl substituent on the structure and
polymerization behavior of 2-arylindene metallocene
catalysts.
Exp er im en ta l Section
X-r a y Str u ctu r e Deter m in a tion of 3-m eso. A single
crystal of meso-(1-Me-2-PhInd)2ZrCl2 was mounted in paratone
oil on a glass fiber and placed in a cold stream of nitrogen on
an Enraf-Nonius CAD4 diffractometer with graphite-mono-
chromated Mo KR radiation. Cell constants and an orientation
matrix for data collection, obtained from a least-squares
refinement using the setting angles of 25 centered reflections
(22 in the range 35 < 2θ < 37° and 3 in the range 20 < 2θ <
21°) corresponded to a face-centered orthorhombic cell. The
data were collected at -75 °C using the ω scan technique to a
maximum 2θ value of 50°.
Gen er a l Con sid er a tion s. All organometallic reactions
were conducted using standard Schlenk and drybox tech-
niques. Elemental analyses were conducted by Desert Ana-
lytics. Unless otherwise specified, all reagents were purchased
from commercial suppliers and used without further purifica-
tion. Bis(2-phenylindenyl)zirconium dichloride (1) was pre-
pared according to the literature procedure.16 Pentane and
methylene chloride used in organometallic synthesis were
distilled from calcium hydride under nitrogen. Tetrahydro-
furan was distilled from sodium/benzophenone under nitrogen.
Toluene was passed through two purification columns packed
with activated alumina and supported copper catalyst.17
Chloroform-d3 and methylene chloride-d2 were distilled from
calcium hydride.
A total of 2624 reflections were collected of which 2529 were
unique. Over the course of data collection, the intensity
standards decreased by an average of 0.2%. No decay correc-
tion was applied.
The structure was solved by direct methods and expanded
using Fourier techniques. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were located by
difference Fourier maps but included initially at idealized
positions 0.95 Å from their parent atoms before the last cycle
of refinement. The final cycle of full-matrix least-squares
refinement was based on 2325 observed reflections and 330
variable parameters and converged with R (Rw) ) 2.6 (2.8).
X-r a y Str u ctu r e Deter m in a tion of 3-r a c. The crystal
mounting procedure and conversion of the raw intensity data
were the same as those described above. The complex was
found to crystallize in a primitive monoclinic cell. Over the
course of the data collection, the intensity standards decreased
by an average of 2.2%. No decay correction was applied.
The structure was solved by the methods described above.
The final cycle of full-matrix least-squares refinement was
based on 3681 observed reflections and 316 variable param-
eters and converged with R (Rw) ) 4.5 (6.5).
Tables of the anisotropic thermal coefficients, bond lengths,
bond angles, torsion angles, and H-atom coordinates for both
complexes are available as Supporting Information.
Eth ylen e a n d P r op ylen e P olym er iza tion s. Polymeri-
zation grade ethylene and propylene from Matheson and liquid
propylene from Amoco were used. Both monomers were
further purified by passage through two columns packed with
activated alumina and supported copper catalyst. Methyla-
luminoxane (MAO), type 3A, from Akzo, was dried in vacuo
prior to use.
1-Meth yl-2-p h en ylin d en e (2). Butyllithium (2.5 M in
hexanes, 3.0 mL, 7.6 mmol) was added dropwise to a suspen-
sion of 2-phenylindene (1.382 g, 7.2 mmol) in THF (50 mL) at
-78 °C to yield a dark orange solution. The solution was
allowed to warm to room temperature and stirred for 30 min.
Methyl iodide (1.3 mL, 22 mmol) was added to this solution
dropwise, and the light brown reaction mixture was heated to
40 °C and stirred for 24 h. After that the solvents were
removed in vacuo, and the resulting light brown solid was
recrystallized from EtOH (25 mL) at room temperature af-
fording white needles (1.075 g, 75% yield). 1H NMR (CDCl3,
20 °C, 300 MHz): δ 7.52-7.19 (overlapping signals from
aromatic protons, 9H), 3.74 (q, J ) 1.0 Hz, 2H), 2.31 (t, J )
1.1 Hz, 3H). 13C{1H} NMR (CDCl3, 20 °C, 75 MHz): δ 147.49
(C), 142.42 (C), 140.31 (C), 137.56 (C), 134.70 (C), 128.37 (CH),
128.24 (CH), 126.63 (CH), 126.40 (CH), 124.74 (CH), 123.32
(CH), 119.11 (CH), 40.96 (CH2), 11.94 (CH3).18
r a c- a n d m eso-Bis(1-m eth yl-2-p h en ylin d en yl)zir con i-
u m Dich lor id e (3-r a c a n d 3-m eso, Resp ectively). Butyl-
lithium (2.5 M in hexanes, 6.7 mL, 17 mmol) was added
dropwise to a colorless solution of 1-methyl-2-phenylindene
(3.447 g, 17 mmol) in THF (50 mL) at -78 °C to give a dark
yellow solution. The solution was slowly warmed to room
temperature, stirred for 30 min, and then evaporated to
dryness. Toluene (50 mL) was added to the resulting yellow
solid. The resulting suspension was combined with ZrCl4
(1.974 g, 8.4 mmol) suspended in toluene (70 mL). The
(16) Coates, G. W. Ph.D. Thesis, Stanford University, Stanford, CA,
1994.
(17) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518-1520.
(18) Primary, secondary, and tertiary carbon atoms were assigned
based on APT experiments.
P olym er iza tion s in Tolu en e Solu tion . A 300 mL stain-
less steel Parr reactor equipped with a mechanical stirrer was
charged with dry methylaluminoxane and toluene (80 mL). A
50 mL pressure tube was charged with the zirconocene solution
in toluene (20 mL). The reactor was purged with the corre-

Achiral Unbridged 2-Arylindene Metallocenes
Organometallics, Vol. 16, No. 16, 1997 3637
sponding monomer 3-4 times by pressurizing and venting.
The monomer was then equilibrated with the toluene in the
reactor for 30 min at the polymerization temperature and
pressure with constant stirring. The pressure tube with the
metallocene solution was pressurized to 200 psig with argon,
and the solution was injected into the reactor. After 1 h, the
reaction was quenched by injecting methanol (20 mL). In the
case of polypropylene, the polymer was precipitated by pouring
its toluene solution into acidified MeOH (5% HCl), filtered,
washed with MeOH, and dried in a vacuum oven at 40 °C to
constant weight. In the case of polyethylene, the polymer was
collected by filtration and dried in a vacuum oven at 40 °C to
constant weight.
P olym er iza tion s in Liqu id P r op ylen e. A 300 mL stain-
less steel Parr reactor equipped with a mechanical stirrer was
evacuated, purged 4-5 times with gaseous propylene by
pressurizing and venting, and charged with liquid propylene
(100 mL). The monomer was equilibrated at the reaction
temperature, and the reaction was initiated by injecting the
zirconocene/MAO solution in toluene (20 mL) under Ar pres-
sure (250 psig × 30 mL). After 60 min, the reaction was
quenched by injecting MeOH (20 mL). The polymer was
precipitated in acidified MeOH (5% HCl), filtered, washed with
methanol, and dried in a vacuum oven at 40 °C to constant
weight.
F igu r e 1. Molecular structure of complex 3-r a c, showing
atom-labeling scheme.
Sch em e 2
P olym er An a lyses. Molecular weights were determined
by high-temperature gel permeation chromatography using
polypropylene and polyethylene as GPC calibration standards.
13C NMR measurements were performed on Varian XL 400
and Varian UI 300 instruments at 100 °C in 1,1,2,2-terachlo-
roethane-d2 using the acquisition time of 1 s with no additional
delays between pulses and continuous proton decoupling. All
spectra were referenced using the solvent peak. It was
assumed that spin-lattice relaxation times and NOEs of all
methyl groups were the same.19-23 The areas of the nine peaks
in the methyl region determined from spectral integrations
were used to characterize the sample microstructure.
of bis(1-methyl-2-phenylindenyl)zirconium dichloride in
60:40 ratio and 65% crude yield (Scheme 2). The two
complexes were isolated by fractional crystallization.
Orange rhombic crystals of 3-m eso were isolated from
a methylene chloride solution stored at -18 °C over-
night in 11% yield. Yellow rod-like crystals of complex
3-r a c crystallized out of a THF/pentane solution at room
temperature in 10% yield. Only one narrow signal
corresponding to the methyl protons (2.57 ppm for
3-m eso, 2.52 ppm for 3-r a c) and one narrow signal
corresponding to the proton of the CH group of the five-
membered ring (6.07 ppm for 3-m eso, 6.06 ppm for
Resu lts
Literature procedures for the synthesis of 1-methyl-
2-phenylindene starting from commercially available
reagents gave this compound in less than 55% yield.24-26
We developed a higher yield synthesis of 2 from 2-phe-
nylindene. A 75% yield was achieved when the lithium
salt of 2-phenylindenyl was reacted with a 3-fold molar
excess of methyl iodide at 40 °C in THF for 24 h. This
procedure gave the isomer with a tetrasubstituted
1
3-r a c) were observed in the H NMR spectra of the two
complexes, consistent with the rapid ligand rotation at
room temperature.28
The two diastereomers were identified by X-ray
crystallography. The ORTEP drawings and atom-
labeling schemes of 3-r a c and 3-m eso are shown in
Figures 1 and 2. In contrast to (2-PhInd)2ZrCl2, 1,13
only one rotamer in which the two methyl groups are
on the more open side of the complex was found in the
crystal cell for both substituted complexes: the anti-
rotamer for 3-r a c and the syn-rotamer for 3-m eso.
Typical Zr-Cl and Zr-centroid bond lengths and angles
were observed for both complexes.13,14 However, a
marked increase was found in the magnitude of the
dihedral angle between the planes of the indenyl and
the phenyl rings: 26-33° in 3-r a c and 3-m eso com-
pared to 10-13° for complex 1 (Table 1), suggesting a
strong steric interaction between the 1-methyl and
2-phenyl substituents. The increase of the dihedral
angle was accompanied by a slight lengthening of the
1
double bond (1-methyl-2-phenylindene), which in its H
NMR spectrum showed a characteristic methyl triplet
at 2.31 ppm and a methylene quartet at 3.74 ppm, in
agreement with the literature.25,27 The structure of 2
was confirmed by its successful use in zirconocene
synthesis and subsequent X-ray analysis.
The reaction of 2 equiv of the lithium salt of 2 with
ZrCl4 in toluene gave 3-r a c and 3-m eso diastereomers
(19) Vizzini, J . C.; Chien, J . C. W.; Babu, G. N.; Newmark, R. A. J .
Polym. Sci., Part A: Polym. Chem. 1994, 32, 2049-2056.
(20) Segre, A. L.; Andruzzi, F.; Lupinacci, D.; Magagnini, P. L.
Macromolecules 1983, 16, 1207-1212.
(21) Inoue, Y.; Nishioka, A.; Chujo, R. Makromol. Chem. 1973, 168,
163-172.
(22) Randall, J . C. J . Polym. Sci., Polym. Phys. Ed. 1976, 14, 1693-
1700.
(23) Schilling, F. C. Macromolecules 1978, 11, 1290-1291.
(24) Christol, H.; Martin, C.; Mousseron, M. Bull. Soc. Chim. Fr.
1960, 1696-1699.
(28) Note that in the conformations of 2-r a c and 2-m eso which are
depicted in Scheme 2, the two CH3 groups and the two Cp protons can
be interconverted through symmetry operations, and thus, if the
complexes are completely frozen in these conformations, the groups
under consideration will be equivalent by NMR. However, closely
related 2-arylindene metallocene dihalides are known to undergo rapid
ligand rotation at room temperature.
(25) Heindel, N. D.; McNeill Lemke, S.; Mosher, W. A. J . Org. Chem.
1966, 31, 2080-2682.
(26) Buddrus, J . Chem. Ber. 1968, 101, 4152-4162.
(27) Miller, L. L.; Boyer, R. F. J . Am. Chem. Soc. 1971, 93, 646-
650.

3638 Organometallics, Vol. 16, No. 16, 1997
Kravchenko et al.
duced polypropylene with a much broader molecular
weight distribution (MWD) than 1/MAO, which was
especially noticeable in the case of polymerization in
bulk propylene.
The isotactic pentad content determined by 13C NMR
spectroscopy29-34 was much lower for polypropylene
prepared with 3-r a c/MAO and 3-m eso/MAO than that
for samples generated with 1/MAO. No difference in
%mmmm was observed for the samples prepared using
catalyst 3-m eso/MAO in toluene solution at 75 psig of
propylene (%mmmm ) 12) or in bulk propylene
(%mmmm ) 11). Catalyst 3-r a c/MAO gave polypro-
pylene with %mmmm ) 20 in toluene solution at 75 psig
of propylene, but in liquid propylene, %mmmm de-
creased to 14.35 In contrast to polymerization catalyzed
by 1/MAO, polypropylene samples prepared with 3-r a c/
MAO and 3-m eso/MAO were not elastomeric, which
could be a consequence of their lower molecular weight
and/or lower isotacticity.
F igu r e 2. Molecular structure of complex 3-m eso, showing
atom-labeling scheme.
Discu ssion
The crystal structures of 3-r a c and 3-m eso reveal
that the 1-methyl substituents influence the dihedral
angle of the 2-phenyl substituent relative to the plane
of the cyclopentadienyl ligand. The dihedral angle
between the planes of the indenyl and the phenyl ring
has increased by as much as 15-23°, as compared to
unsubstituted (2-PhInd)2ZrCl2, 1 (Table 1).
Ta ble 1. Selected Dih ed r a l An gles a n d Bon d
Len gth s for Com p lexes 3-r a c a n d 3-m eso
dihedral angle (deg)
bond distance (Å)
plane 1/
plane 2a
plane 3/
plane 4
b
complex
C(2)-C(10) C(17)-C(25)
3-r a c
31.4(8)
26.4(8)
11.54
27.9(9)
33.3(7)
13.53
1.496(7)
1.482(8)
1.476(5)
1.468(7)
1.480(7)
1.482(7)
1.472(6)
1.485(5)
3-m eso
1-anti13
1-syn13
Electronically, both 3-r a c/MAO and 3-m eso/MAO
appear to be suitable for R-olefin polymerization: both
of them are quite active in polymerization of ethylene
(Table 2). However, in polymerization of propylene,
1-methyl substitution results in a significant decrease
of productivity as compared to unsubstituted catalyst
1/MAO (Table 3). Most likely, the decrease in propylene
polymerization productivity is due to the increased
steric hindrance of the catalyst active sites introduced
by the methyl substituents. A similar decrease in
propylene polymerization productivity was reported for
3-methyl-substituted ethylene-bridged rac-Et(3-MeInd)2-
ZrCl2 and silicon-bridged rac-Me2Si(3-MeInd)2ZrCl2 when
compared to their unsubstituted analogs.36-38 It ap-
pears that in the case of a more open ethylene-bridged
structure of rac-Et(3-MeInd)2ZrCl2 (metal-centroid angle,
θ ) 126.4°),37 the steric effect of the methyl substituents
is less dramatic (productivity is lowered by a factor of
10.44
12.72
a
b
Plane 1 ) C(1)-C(9), plane 2 ) C(10)-C(15). Plane 3 )
C(16)-C(24), plane 4 ) C(25)-C(30).
Ta ble 2. Eth ylen e P olym er iza tion Usin g
Com p lexes 1,3-r a c a n d 3-m esoa
catalyst
productivityb
Mw ×10-3 c
MWDc
3-m eso/MAO
1/MAO
3-r a c/MAO
3050
3570
7280
1966
2040
1034
4.0
3.2
3.4
Reaction conditions: PE ) 25 psig, [Zr] ) 5 × 10-6 M, trxn
)
a
b
1 h, T ) 20 ( 1 °C, [Zr]:[MAO] ) 1:2750.
kg‚PE/mol‚Zr‚h.
c Determined by high-temperature GPC.
carbon-carbon bond connecting the 2-phenyl and the
indenyl ring. The complete summary of structural
parameters can be found in the Supporting Information.
Ethylene polymerization results are summarized in
Table 2. Both substituted catalysts were characterized
by fairly high ethylene polymerization productivities.
Productivity and polyethylene molecular weight for
3-m eso/MAO were similar to those achieved with
catalyst 1/MAO. Catalyst 3-r a c/MAO had a higher
productivity but made polyethylene of a lower molecular
weight than the other two catalysts.
(29) Bovey, F. A. Chain structure and conformation of macromol-
ecules; Academic press: New York, 1982.
(30) Zambelli, A.; Locatelli, P.; Bajo, G.; Bovey, F. A. Macromolecules
1975, 8, 687-689.
(31) Randall, J . C. Polymer Sequence Determination by the Carbon
13 NMR Method; Academic Press: New York, 1977.
(32) Randall, J . C. In Polymer Charactarization by ESR and NMR;
Woodward, A. E., Bovey, F. A., Eds.; American Chemical Society:
Washington, DC, 1980; p 142.
For the polymerization of propylene (Table 3), both
3-r a c/MAO and 3-m eso/MAO had a much lower pro-
ductivity and produced polypropylene of a much lower
molecular weight than unsubstituted catalyst 1/MAO.
As observed for ethylene polymerization, 3-r a c/MAO
was more productive but generated polypropylene with
a lower molecular weight than 3-m eso/MAO. For
propylene polymerization catalyzed by 3-r a c/MAO, the
productivity and polymer molecular weights increased
with propylene concentration. Polymerization catalyzed
by 3-m eso/MAO showed no dependence on monomer
concentration. Both 3-r a c/MAO and 3-m eso/MAO pro-
(33) Zhu, S.-N.; Yang, X.-Z.; Chujo, R. Polym. J . 1983, 15, 859-
868.
(34) Koenig, J . L. Spectroscopy of Polymers; American Chemical
Society: Washington, DC, 1991.
(35) Propylene polymerizations under each set of conditions were
conducted at least twice, and in all cases mmmm contents were found
to be reproducible.
(36) Ewen, J . A.; Haspeslagh, L.; Elder, M. J .; Atwood, J . L.; Zhang,
H.; Cheng, H. N. In Transition Metals and Organometallics as
Catalysts for Olefin Polymerization; Kaminsky, W., Sinn, H., Eds.;
Springer-Verlag: Berlin, 1988; p 281.
(37) Ewen, J . A.; Elder, M. J .; J ones, R. L.; Haspeslagh, L.; Atwood,
J . L.; Bott, S. G.; Robinson, K. Makromol. Chem., Macromol. Symp.
1991, 48/ 49, 253-295.
(38) Spaleck, W.; Antberg, M.; Dolle, V.; Klein, R.; Rohrmann, J .;
Winter, A. New J . Chem. 1990, 14, 499-503.

Achiral Unbridged 2-Arylindene Metallocenes
Organometallics, Vol. 16, No. 16, 1997 3639
Ta ble 3. P r op ylen e P olym er iza tion Usin g Com p lexes 3-r a c a n d 3-m esoa
catalyst
propylene
productivityb
%mc
%mmmmc
Mw ×10-3 d
MWDd
3-m eso/MAO
3-m eso/MAO
3-r a c/MAO
3-r a c/MAO
1/MAO14
75 psig
bulk
75 psig
bulk
140
140
220
360
1700
55
54
60
55
70
12
11
20
14
33
68.1
69.1
41.3
55.9
369
5.8
8.6
4.2
15.3
3.9
75 psig
a
b
Reaction conditions: T ) 20 ( 1 °C, [Zr]:[MAO] ) 1000, trxn ) 1 h, [Zr] ) 5 × 10-5 M. kg‚PP/mol‚Zr‚h. c Determined from13C NMR
d
spectroscopy. Determined by high-temperature GPC.
which are twisted out of the plane of the indenyl ring
by 1-methyl substituents, with each other as well as
with the growing polymer chain. Due to their very low
yield, no detailed fractionation study was conducted on
polypropylene samples made with 3-r a c/MAO and
3-m eso/MAO.
The fact that in propylene polymerization 3-r a c/MAO
is more productive but produces a polymer of lower
molecular weight than 3-m eso/MAO deserves attention.
It had been previously observed that in the case of some
bridged bis(indenyl) complexes, the rac-isomer was more
active and made polypropylene of higher molecular
weight than the meso-isomer.40 It is interesting that
the behavior of our unbridged complexes partially
correlates with this finding (3-r a c/MAO is more produc-
tive than 3-m eso /MAO), but the order of the polymer
molecular weights is not the same.
F igu r e 3. The possible rotamers of complexes (a) 3-r a c
and (b) 3-m eso.
2) than in the case of unbridged complex 3-r a c (θ )
132.1°, productivity is lowered by a factor of 8).
The stereospecificity of bis(1-methyl-2-phenylinde-
nyl)zirconocene catalysts 3-r a c/MAO and 3-m eso/MAO
is lower than that of the unsubstituted bis(2-phenylin-
denyl)zirconocene 1/MAO. At a propylene pressure of
75 psig, 3-r a c/MAO produces polypropylene with an
isotactic index ([mmmm] ) 20%) which is higher than
that of the polypropylene produced with 3-m eso/MAO
under similar conditions ([mmmm] ) 12%). These
results might be rationalized by the greater number of
isospecific coordination sites available among the vari-
ous rotameric forms of the chiral 3-r a c relative to the
achiral 3-m eso (Figure 3; here olefin coordination sites
are represented as isospecific (I) or aspecific (A)).
However, in liquid propylene, there does not seem to
be a significant difference in the stereospecificity of the
two catalysts ([mmmm] ) 14% for 3-r a c/MAO and 11%
for 3-m eso/MAO). The decrease in stereospecificity for
3-r a c/MAO from [mmmm] ) 20% at 75 psig of propy-
lene to [mmmm] ) 14% in liquid propylene is unusual
and merits further investigation.35 Typically, the iso-
specificity of 2-arylindene catalysts increases with
increasing monomer concentration.13,14
Con clu sion s
Propylene polymerization with unbridged bis(1-meth-
yl-2-phenylindenyl)zirconocene catalysts yields amor-
phous polypropylenes under conditions where the bis(2-
phenylindenyl)zirconocene catalysts yield elastomeric
polypropylenes. 1-Methyl substitution of the 2-phenyl-
indene ligand lowered propylene polymerization pro-
ductivity, polymer molecular weights, and catalyst
stereospecificity. In addition, broad molecular weight
distributions of the polymers prepared with the substi-
tuted catalysts suggested the possibility of slower ligand
rotation than in the case of unsubstituted catalyst
1/MAO. These results underscore the subtle balance
that is necessary for these dynamic unbridged metal-
locenes to produce stereoblock, elastomeric polypropy-
lenes.
Broad (Mw/Mn ) 4-15) and, in some cases, even
bimodal molecular weight distributions were observed
for polypropylenes generated with catalysts 3-r a c/MAO
and 3-m eso/MAO. This may indicate that the rate of
interconversion of their rotamers is lower than that in
the case of catalyst 1/MAO,39 leading to the situation
in which the growth of an individual polypropylene
chain may be completed before the rotamers intercon-
vert to form heterogeneous blend-like materials with
molecular weight distributions being a superposition of
molecular weights corresponding to individual rotamers.
The slower rate of ligand rotation could be rationalized
by the increased steric interaction of the phenyl groups,
Ackn owledgm en t. We gratefully acknowledge Amo-
co for financial support. We thank Dr. Christopher
Tagge for helpful discussions and Amoco for carrying
out high-temperature GPC analyses.
Su p p or tin g In for m a tion Ava ila ble: Text giving a com-
plete description of the X-ray structure determination of
complexes 3-r a c and 3-m eso and tables of crystallographic
parameters, atomic coordinates, anisotropic thermal coef-
ficients, bond lengths and angles, and torsion angles (20
pages). Ordering information is given on any current mast-
head page.
OM9702082
(39) We assume that ligand rotation in the actual active species
3-r a c/MAO and 3-m eso/MAO is slower than that of the corresponding
dichlorides (see ref 28) due to the interactions with the growing polymer
chain and MAO anion.
(40) Kaminsky, W.; Freidanck, F. Polym. Prepr. 1996, 37, 266-267.