Propylene polymerization with unbridged metallocenes: Ligand effects on the selectivity for elastomeric polypropylene

Article abstract of DOI:10.1021/om9706119

Bis(2-arylindenyl)zirconium dichlorides activated by methylaluminoxane produce elastomeric polypropylene with a stereoblock microstructure. In an effort to experimentally explore the importance of the 2-arylindene ligand in producing these materials, a series of catalysts was investigated that differed significantly from the parent ligand architecture. In particular, we sought to examine the influence of ligand aryl stacking on the polymerization behavior of these metallocenes. We discovered that the bis(2-arylindenyl) framework is important for the production of elastomeric polypropylene by this type of unbridged complex. Small changes in the fundamental catalyst structure upset the delicate balance between ligand rotation and monomer insertion resulting in the production of amorphous polymers.

Full text of DOI:10.1021/om9706119

Organometallics 1997, 16, 5909-5916
5909
P r op ylen e P olym er iza tion w ith Un br id ged Meta llocen es:
Liga n d Effects on th e Selectivity for Ela stom er ic
P olyp r op ylen e
J ennifer L. Maciejewski Petoff,† Michael D. Bruce,† Robert M. Waymouth,*,†
Athar Masood,† Tapan K. Lal,† Roger W. Quan,‡ and Steven J . Behrend‡
Department of Chemistry, Stanford University,† Stanford, California 94305, and
Amoco Chemical Company Research Center, Naperville, Illinois 60566
Received J uly 17, 1997X
Bis(2-arylindenyl)zirconium dichlorides activated by methylaluminoxane produce elasto-
meric polypropylene with a stereoblock microstructure. In an effort to experimentally explore
the importance of the 2-arylindene ligand in producing these materials, a series of catalysts
was investigated that differed significantly from the parent ligand architecture. In particular,
we sought to examine the influence of ligand aryl stacking on the polymerization behavior
of these metallocenes. We discovered that the bis(2-arylindenyl) framework is important
for the production of elastomeric polypropylene by this type of unbridged complex. Small
changes in the fundamental catalyst structure upset the delicate balance between ligand
rotation and monomer insertion resulting in the production of amorphous polymers.
In tr od u ction
Natta was the first to discover an elastomeric polypro-
pylene and interpret its properties in terms of an
atactic-isotactic stereoblock microstructure.22-24 Col-
lette and co-workers observed that elastomeric polypro-
pylene could also be produced by supported tetralkyl
group IVB catalysts.25,26 The first metallocene system
for the production of elastomeric polypropylene was
introduced by Chien and co-workers in 1990.19-21 Chien’s
catalyst precursor was a chiral, stereorigid ansa-ti-
tanocene where polymer chain growth was purported
to alternate between aspecific and isospecific metal-
locene coordination sites, although other interpretations
have recently been forwarded.11,12
Homogeneous metallocene polymerization catalysts
provide new opportunities to tailor the structure and
properties of poly(R-olefins) through manipulations of
the catalyst ligand structure.1,2 A wide variety of homo-
and copolymer architectures are possible using metal-
locene catalysts.1 For polypropylene, isotactic,3-7 syn-
diotactic,4,6,8,9 heterotactic,4,6 and stereoblock micro-
structures10-21 can be prepared using metallocene cata-
lysts.
† Stanford University.
‡ Amoco Chemical Co. Research Center.
We have reported that bis(2-arylindenyl)zirconium
dichlorides, when activated by methylaluminoxane
(MAO), produce elastomeric polypropylene. These cata-
lysts were designed to interconvert between chiral, C2
symmetric (rac) and achiral, Cs symmetric (meso) ge-
ometries to give isotactic and atactic blocks in the same
polymer chain (Scheme 1).10,13 We have observed
significant substituent effects for derivatives of bis(2-
phenylindenyl)zirconium dichloride where electron do-
nating (CH3) and electron-withdrawing (CF3) groups
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) Brintzinger, H. H.; Fischer, D.; Muelhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-70.
(2) Ziegler Catalysts: Recent Scientific Innovations and Technolog-
ical Improvements; Fink, G.; Muelhaupt, R.; Brintzinger, H. H., Ed.;
Springer-Verlag: 1995.
(3) Ewen, J . A. J . Am. Chem. Soc. 1984, 106, 6355-6364.
(4) Ewen, J . A. Macromol. Symp. 1995, 89, 181-196.
(5) Kaminsky, W.; Ku¨lper, K.; Brintzinger, H. H.; Wild, F. R. W. P.
Angew. Chem., Int. Ed. Engl. 1985, 24, 507-508.
(6) Ewen, J . A.; Elder, M. J .; J ones, R. L.; Haspeslagh, L.; Atwood,
J . L.; Bott, S. G.; Robingson, K. Makromol. Chem., Macromol. Symp.
1991, 48/ 49, 253-295.
(7) 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 ; W. Kaminsky and H. Sinn, Ed.;
Springer-Verlag: Berlin, 1988; pp 281-289.
(8) Ewen, J . A.; J ones, R. L.; Razavi, A. J . Am. Chem. Soc. 1988,
110, 6255-5256.
(16) Knickmeier, M.; Erker, G.; Fox, T. J . Am. Chem. Soc. 1996,
118, 9623-9630.
(17) Erker, G.; Nolte, R.; Tsay, Y.-H.; Kruger, C. Angew. Chem. Int.
Ed. Engl. 1989, 28, 628-629.
(9) Ewen, J . A.; Elder, M. J .; J ones, R. L.; Curtis, S.; Cheng, H. N.
In Catalytic Olefin Polymerization (Stud. Surf. Sci. Catal.); T. Keii and
K. Soga, Ed.; Elsevier: Tokyo, 1990; Vol. 56; pp 439-483.
(10) Coates, G. W.; Waymouth, R. M. Science 1995, 267(5195), 217-
19.
(18) Erker, G.; Nolte, R.; Tsay, Y. H.; Krueger, C. Angew. Chem.
1989, 101, 642-4.
(19) Mallin, D. T.; Rausch, M. D.; Lin, Y.-G.; Dong, S.; Chien, J . C.
W. J . Am. Chem. Soc. 1990, 112, 2030-2031.
(20) Chien, J . C. W.; Llinas, G. H.; Rausch, M. D.; Lin, G.-Y.; Winter,
H. H. J . Am. Chem. Soc. 1991, 113, 8569-8570.
(21) Llinas, G. H.; Dong, S.-H.; Mallin, D. T.; Rausch, M. D.; Lin,
Y.-G.; Winter, H. H.; Chien, J . C. W. Macromolecules 1992, 25, 1242-
1253.
(11) Gauthier, W. J .; Collins, S. Macromolecules 1995, 28, 3779-
86.
(12) Gauthier, W. J .; Corrigan, J . F.; Taylor, N. J .; Collins, S.
Macromolecules 1995, 28, 3771-8.
(13) Hauptman, E.; Waymouth, R. M.; Ziller, J . W. J . Am. Chem.
Soc. 1995, 117, 11586-7.
(22) Natta, G.; Mazzanti, G.; Crespi, G.; Moraglio, G. Chim. Ind.
(Milan) 1957, 39, 275-283.
(14) Kaminsky, W.; Buschermohle, M. In Recent Advances in
Mechanistic and Synthetic Aspects of Polymerization (NATO ASI
Series. Series C: Mathematical and Physical Sciences); M. Fontanille
and A. Guyot, Ed.; D. Reidel Publishing Company: Dordrecht, 1987;
Vol. 215; pp 503-514.
(15) Erker, G.; Aulbach, M.; Kruger, C.; Werner, S. J . Organomet.
Chem. 1993, 450, 1-7.
(23) Natta, G. J . Polym. Sci. 1959, 34, 531-549.
(24) Natta, G.; Crespi, G. (Montecatini) U. S. Patent 3,175,999, 1965.
(25) Collette, J . W.; Tullock, C. W.; MacDonald, R. N.; Buck, W. H.;
Su, A. C. L.; Harrell, J . R.; Mulhaupt, R.; Anderson, B. C. Macromol-
ecules 1989, 22, 3851.
(26) Collette, J . W.; Ovenall, D. W.; Buck, W. H.; Ferguson, R. C.
Macromolecules 1989, 22, 3858-3866.
S0276-7333(97)00611-0 CCC: $14.00 © 1997 American Chemical Society

5910 Organometallics, Vol. 16, No. 26, 1997
Maciejewski Petoff et eal.
Ch a r t 1
Sch em e 1
Resu lts
Bis(2-cyclohexylindenyl)zirconium dichloride (2), bis(2-
cyclohexyl-4,5,6,7-tetrahydroindenyl)zirconium dichlo-
ride (3), and bis(2-phenyl-4,5,6,7-tetrahydroindenyl)(2-
cyclohexylindenyl)zirconium dibromide (4) were syn-
thesized to investigate the role of the aromaticity of the
ligands on the polymerization behavior.35 Bis(1-aryl-
3,4-dimethylcyclopentadienyl)zirconium dichlorides 5-7
were chosen as models of a “truncated” indene ligand
system where the methyl groups attached to the Cp
ligand represent an altered version of the fused benzo
ring present in 1. (See Chart 1).
1-Aryl-3,4-dimethyl-1,3-cyclopentadienes and 2-phen-
yl-4,5,6,7-tetrahydroindene were prepared by reacting
the appropriate arylmagnesium bromide with 3,4-di-
methylcyclopent-2-en-1-one36 and 3,3a,4,5,6,7-hexahy-
dro-2(2H)-indenone,37 respectively. 2-Cyclohexylindene
was produced by a nickel-catalyzed coupling38 of 2-bro-
moindene39 and cyclohexylmagnesium chloride.
The parent metallocene, 1, was prepared by a previ-
ously reported procedure.13 The fully saturated metal-
locene, 3, was prepared by catalytic hydrogenation of 1
with PtO2 at 80 psig H2 for 4 h.40 Catalysts 2 and 5-7
were obtained using standard metalation procedures.13
4 was prepared by a new method developed in our
laboratories.41 In this procedure, the indene ligand is
reacted with tetrakis(dimethylamino)zirconium to give
the indenylzirconium triamide with elimination of di-
methylamine.42 The triamide is then treated with
bromotrimethylsilane and the resulting (2-phenyl-4,5,6,7-
tetrahydroindenyl)zirconium tribromide treated with (2-
cyclohexylindenyl)lithium to give 4 upon recrystalliza-
tion from toluene.
have been introduced at the 3 and 5 positions of the
phenyl ring.13 These minor changes have a significant
influence on the tacticity of the resulting polymers with
the isotactic pentad content, percent mmmm (m4),
ranging from 24 to 73%.
The design of the bis(2-arylindene) metallocene cata-
lysts was based on a 1,3,4-substitution pattern on the
cyclopentadienyl ligand such that rotation of the cyclo-
pentadienyl ligands would lead to chiral and achiral
torsional isomers.15,27-33 A further consideration was
that the substituents on the cyclopentadienyl ligand be
sufficiently demanding such that each torsional isomer
would have a lifetime sufficient to insert a sequence of
propylene units prior to interconverting to the other
isomer.10 (Thus, for example, bis(indenyl)zirconium
dichloride can interconvert between a chiral and achiral
torsional isomer, but this metallocene produces atactic
polypropylene34). In an effort to further study the role
of the nature of the ligand on the polymerization
behavior of this class of catalysts, we have prepared a
series of unbridged metallocenes that retain the sym-
metry of the 2-arylindenyl complexes, but where we
have varied the substituents at the 1, 3, and 4 positions
of the cyclopentadienyl ligand. These studies reveal
that the 2-arylindenes are rather specialized in being
able to produce elastomeric polypropylenes.
The molecular structure of the mixed-ring compound
4 was confirmed by X-ray crystallography. The metal-
locene crystallizes as two independent molecules in the
asymmetric unit which differ only in the orientation of
the cyclohexyl substituent (Figure 1). The other bond-
ing parameters for the mixed-ring 4 are normal and
comparable to the parent bis(2-phenylindenyl)zirconium
dichloride (1).
(27) Luke, W. D.; Streitweiser, A. J . J . Am. Chem. Soc. 1981, 103,
3241-3243.
(28) Erker, G.; Nolte, R.; Krueger, C.; Schlund, R.; Benn, R.;
Grondey, H.; Mynott, R. J . Organomet. Chem. 1989, 364, 119-32.
(29) Erker, G.; Temme, B. J ACS 1992, 114, 4004-4006.
(30) Kruger, C.; Lutz, F.; Nolte, M.; Erker, G.; Aulbach, M. J .
Organomet. Chem. 1993, 452, 79-86.
(31) Erker, G.; Aulbach, M.; Knickmeier, M.; Wingbermuhle, D.;
Kruger, C.; Nolte, M.; Werner, S. J . Am. Chem. Soc. 1993, 115, 4590-
4601.
(32) Okuda, J . J . Organomet. Chem. 1988, 356, C43-C46.
(33) Kruger, C.; Nolte, M.; Erker, G.; Thiele, S. Z. Naturforsch 1992,
47b, 995-999.
(34) Resconi, L.; Abis, L.; Franciscono, G. Macromolecules 1992, 25,
6814-6817.
(35) Pietsch, M. A.; Rappe, A. K. J . Am. Chem. Soc. 1996, 118,
10908-10909.
(36) Conia, J .-M.; Leriverend, M.-L. Bull. Soc. Chim. Fr. 1970, 1981.
(37) Welch, S. C.; Assercq, J .-M.; Loh, J .-P.; Glase, S. A. J . Org.
Chem. 1987, 52, 1440.
(38) Tamao, K.; Sumitani, K.; Kumada, M. J . Am. Chem. Soc 1972,
94, 4405-4407.
(39) McEwen, I.; Ronnqvist, M.; Ahlberg, P. J . Am. Chem. Soc. 1993,
115, 3989-3996.
(40) Waymouth, R. M.; Bangerter, F.; Pino, P. Inorg. Chem. 1988,
27, 758-759.
(41) Tagge, C.; Waymouth, R. M., Unpublished results.
(42) Chandra, G.; Lappert, M. F. J . Chem. Soc. (A) 1968, 1940-
1945.

Propylene Polymerization with Unbridged Metallocenes
Organometallics, Vol. 16, No. 26, 1997 5911
Ta ble 1. Su m m a r y of P olym er iza tion Resu lts Usin g Un br id ged Meta llocen esa
d
entry
catalyst
propylene press (psig)
prodvityb
% mmmmc
% m
Mw (×10-3
)
Mw/Mn
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
1
50e
75f
bulkg
50
75
bulk
50
75
bulk
50
75
bulk
50
75
bulk
50
75
bulk
50
1380
1480
2525
374
602
2340
940
2020
2390
531
31
35
32
11
11
15
3
3
5
6
7
13
10
10
10
10
10
10
10
11
11
69
71
70
57
55
62
46
45
52
49
51
58
59
58
59
59
58
60
59
59
61
310
399
542
117
131
219
20
27
40
52
78
186
146
215
392
201
290
323
94
3.2
3.8
3.5
3.8
3.9
3.3
1.9
1.9
1.9
2.6
2.9
3.1
2.0
2.2
3.2
3.1
2.9
3.1
2.1
2.2
2.7
2
3
4
5
6
7
957
3394
3657
4511
8797
2325
3235
7120
867
75
bulk
1027
2833
140
217
a
b
Conditions: T ) 20 °C; [Zr] ) 5.0 × 10-5 M; [Al]/[Zr] ) 1000. Kilograms of polypropylene per mole of Zr per hour. c Determined by
13C NMR spectroscopy. Determined by gel permeation chromatography versus polypropylene standards. e [C3H6] ) 3.24 M. f [C3H6] )
4.49 M. 100 of mL liquid propylene and 25 mL of toluene.
d
g
F igu r e 2. ORTEP diagram of complex 6.
Cl differs marginally for these two complexes. This
angle is 95.44°, 94.39°, and 97.03° for rac-1, meso-1, and
6, respectively. The dihedral angle between the planes
containing the phenyl and substituted cyclopentadienyl
rings is less than 10° for 1 and derivatives. However,
F igu r e 1. ORTEP diagram of complex 4. The two inde-
pendent molecules in the asymmetric unit are separated
for clarity.
in 6, this angle has increased to 22.5°. Compound 6
crystallizes in a C2-symmetric conformation where the
4: Cp-Zr-Cp ) 130.3 (A), 131.0° (B); Br-Zr-Br )
methyl groups of the cyclopentadienyl ring are stag-
95 (A), 94.5° (B); Zr1-Br1 ) 2.60 Å; Zr1-Br2 ) 2.59 Å;
gered over the chloride ligands; a configuration that is
Zr2-Br3 ) 2.59 Å; Zr2-Br4 ) 2.61 Å. 1: Cp-Zr-Cp
reminiscent of the δ conformation recognized by Brint-
) 131°; Cl-Zr-Cl ) 94.39° (rac-1), 97.03° (meso-1); Zr-
zinger and co-workers as being easily accessible to
Cl ) 2.43 Å.10 The Zr-Br bonds from 4 are somewhat
various ansa-titanocenes and zirconocenes.43
longer than the Zr-Cl bonds in 1.
Propylene (PP) polymerizations were carried out in
Bis(1-aryl-3,4-dimethylcyclopentadienyl)zirconium
the presence of the metallocene dichlorides and MAO
dichlorides are stable to air and moisture: 5 and 6 have
(Al:Zr ) 1000:1) in toluene solution under a variety of
been stored for months in air with no decomposition. 7
propylene pressures or in liquid propylene (Table 1).
does discolor in air over several months but is still pure
While the productivities for 1 differ somewhat from
by 1H NMR. 5-7 may be purified using “wet” solvents.
values previously reported (880 vs 1380 kg of PP/mol
The solid-state structure of 6 was also determined by
of Zr at 50 psig),13 the degrees of isotacticity are in the
X-ray crystallography (Figure 2). Relevant structural
same range.
parameters for 6 are nearly identical to those reported
for 1 and related compounds:10,13 6: Cp-Zr-Cp )
130.7°, Zr-Cl ) 2.44 Å, and Zr-Cp ) 2.22 Å. Cl-Zr-
(43) Burger, P.; Diebold, J .; Gutmann, S.; Hund, H.-U.; Brintzinger,
H. H. Organometallics 1992, 11, 1319-1327.

5912 Organometallics, Vol. 16, No. 26, 1997
Maciejewski Petoff et eal.
Dimethylcyclopentadienyl derivatives were up to 3
times more productive than bis(2-phenylindenyl) 1.
Substitution of the phenyl ring tempered productivity
gains somewhat, with 7 producing the least polymer.
Solution polymerizations using 2-4 were more sluggish
than those utilizing 1, but the productivities in bulk
polymerizations were comparable. The weight-average
molecular weights (Mw) of polypropylenes produced from
the various catalysts are significantly different. Fully
hydrogenated 3 gave the lowest molecular weights and
narrowest molecular weight distributions (Mw/Mn) of all
catalysts investigated. Mw also increased with propyl-
ene pressure for catalysts 1-7.
interactions46,47 might help stabilize the rac and meso
geometries of the 2-arylindenyl metallocenes and con-
tribute to the barrier for interconversion.
To investigate the role of the 2-arylindene ligands on
the polymerization behavior of these metallocenes, we
made systematic modifications of the ligand structure
by replacing the aromatic substituents (phenyl and
indenyl) with their saturated analogs. For 2, the phenyl
ring was replaced with a saturated cyclohexyl moiety.
For complex 3 both the phenyl and benzo groups of the
indenyl ligand were converted to their saturated ana-
logs. The mixed-ring complex 4 was prepared to test
whether π-stacking interactions35 might bias the tor-
sional isomers to favor the anti conformation. The
truncated ligands 5-7 were prepared to study the role
of the indenyl ligand. All metallocenes prepared were
dichlorides except for the mixed-ring complex 4. In this
instance, the intermediate 2-phenyl-4,5,6,7-tetrahy-
droindenylzirconium tribromide is easier to prepare and
purify than the corresponding trichloride. Polymers
prepared from the metallocene dibromide 4 and metal-
locene dichlorides were directly compared in this work.
Investigations of the parent metallocene 1 and 1-Br2
indicate that the choice of halide does not significantly
affect polymerization behavior or the microstructure of
the resulting polypropylene.41
The solid-state structure of 4 was investigated by
X-ray crystallography. Two independent molecules
were observed in the asymmetric unit each with slightly
different conformations of the cyclohexyl ring.48 The
cyclohexyl ring adopts a chair conformation in both
structures with the indenyl framework occupying an
equatorial position. Steric factors appear to dictate the
solid-state structure of 4 in that the catalyst adopts
“meso-like” geometries in the crystal structure, placing
the bulky cyclohexyl and tetrahydroindene substituents
furthest apart. These steric factors appear to dominate
whatever π-stacking interaction might exist between the
indenyl and phenyl substituent. The solid-state struc-
ture of the 3,4-dimethylcyclopentadienyl derivative (6)
was also investigated. This compound crystallizes in a
C2-symmetric conformation where the phenyl groups of
the ligand are oriented trans to the Zr-Cl bonds.
The polymerization behavior of all these metallocenes
reveals some important differences. Productivities in
liquid propylene (20 °C) are in the range of 2300-8800
kg of PP/mol of Zr and appear to be highest for the 3,4-
dimethyl substituted complexes 5 and 6. Molecular
weights of the polymers are in the range of 20 000-
500 000 and are lowest for complexes 3 and 4 containing
the tetrahydroindenyl ligands.
Ligand effects on the stereospecificity of propylene
polymerization with this class of unbridged catalysts are
dramatic. For these studies, the isotacticity of the
polypropylenes is reported in terms of the mole fractions
of isotactic pentads ([mmmm]), as determined by 13C
NMR.44 Substitution of the phenyl group of the phen-
ylindenyl complex by a cyclohexyl substituent results
in a dramatic decrease in the isotacticity of the polymer
produced: polypropylene produced in liquid propylene
from the bis(2-cyclohexylindenyl)zirconium dichloride
(2) has an isotactic pentad content [mmmm] ) 15%,
whereas [mmmm] ) 32% for the polymer produced
under similar conditions with 1. Under like conditions,
the fully hydrogenated derivative 3 yields atactic polypro-
pylene ([mmmm] ) 5%). Similarly, polypropylenes
obtained from the mixed ring complex and (2-aryl-3,4-
dimethyl)cyclopentadienyl derivatives 4-7 were amor-
phous with isotactic contents in the range of 10-11%.
IR spectra were nearly identical for polypropylene
samples prepared using catalysts 2-7. The structure
of polypropylene can also be represented by the IR index
(A998/A974), which is a measure of the helical content of
the polypropylene.45 Values of the IR index of polypro-
pylenes obtained from catalysts 2-7 ranged from 0.14
to 0.22, indicative of atactic polypropylene. For com-
parison, the IR index of polypropylene produced by 1
([mmmm] ) 26%) is A998/A974 ) 0.59.13 Highly isotactic
polypropylene has an IR index approaching 1. Dif-
ferential scanning calorimetry (DSC) profiles of polymer
samples prepared using 2-7 provided no evidence of
crystallinity. In contrast, polypropylene prepared from
1 (Table 1, Entry 3) exhibits a broad melting transition,
Tm ) 30-152 °C and ∆H ) 28.0 J /g.
Discu ssion
In this study, we sought to investigate the polymer-
ization behavior of structural analogs of bis(2-arylin-
denyl)zirconium dihalides to gain insight into the
breadth of unbridged catalyst types that can produce
elastomeric polypropylene. For these studies, metal-
locenes with symmetries comparable to the 2-arylindene
metallocenes were prepared to study electronic and
steric effects of the ligands and to explore the relevance
of aryl stacking46 on the polymerization behavior of
these unbridged metallocene complexes. Calculations
by Pietsch and Rappe35 have indicated that π-stacking
The increase in molecular weight with increasing
monomer concentration evidenced for all catalysts in-
vestigated is not unprecedented49 and implies that â-H
elimination is an important chain-transfer process. The
literature suggests that substitution of the indenyl
ligand framework of ansa-metallocenes in the 2 position
hinders chain transfer to monomer.49
The most striking difference in the polymerization
behavior of these complexes is the stereospecificity.
(44) For random polypropylene [mmmm] ) 6%, for highly isotactic
polypropylene, [mmmm] ) 100%
(45) Luongo, J . P. J . Appl. Polym. Sci. 1960, 3, 302-309.
(46) Aryl stacking is defined as an electrostatic interaction between
the partially positive σ framework of an aromatic system and the
negatively charged π cloud of a nearby neighbor.
(47) Hunter, C. A.; Sanders, J . K. M. J . Am. Chem. Soc. 1990, 112,
5525-5534.
(48) Close inspection reveals that the two structures are related via
pseudo-translational symmetry.
(49) Stehling, U.; Diebold, J .; Kirsten, R.; Roll, W.; Hans-Herbert,
B.; J ungling, S.; Muelhaupt, R. Organometallics 1994, 13, 964-970.

Propylene Polymerization with Unbridged Metallocenes
Organometallics, Vol. 16, No. 26, 1997 5913
Under comparable conditions, only the 2-phenylindenyl
complex 1 produced a semicrystalline elastomeric
polypropylene. Whereas complex 1 in liquid propylene
yielded a polymer with an an isotactic content [mmmm]
) 32%, complexes 2-7 all produce amorphous polymers
with isotactic contents ranging from [mmmm] ) 5 to
15%.44 Complex 2 yielded polymers with the highest
isotactic content ([mmmm] ) 15%), but this material
was amorphous by DSC. Rappe had suggested on the
basis of steric grounds (UFF force field)35 that this
complex should give isotactic polypropylene as he
calculated that the rac isomer was more stable than the
meso for this derivative.
In summary, our results indicate that catalysts
derived from a 2-arylindenyl metallocene framework are
unusual in being able to produce elastomeric stereoblock
polypropylenes. The symmetry of this ligand allows it
to interconvert between chiral and achiral torsional
isomers, but this appears to be a necessary but not
sufficient condition for producing elastomeric polypro-
pylenes. While we have found no experimental evidence
for π-stacking as an important influence on the behavior
of these unbridged 2-arylindene metallocenes, we cannot
rule out that π-stacking occurs in these complexes. The
results of this study imply that relatively slight changes
in structure are enough to disrupt the carefully balanced
interplay of rates that are necessary to yield stereoblock
polymers.
The 2-cyclohexyltetrahydroindenyl complex 3 afforded
atactic polypropylene. On the basis of steric grounds,
one might argue that this ligand is even more sterically
demanding than the 2-phenylindene ligand (see Figure
1) and should thus yield isotactic polypropylene. How-
ever, in this compound, we have removed all possible
π-stacking interactions thus eliminating an electronic
preference for a rac or meso conformation. To further
test this aryl-stacking hypothesis,35 the mixed-ring
compound 4 was prepared. For this compound, the
2-phenyl substituent of one ring was envisioned to be
appropriately positioned to undergo a favorable stacking
interaction with the geminal indenyl ligand to favor the
chiral or isospecific form. However, only the meso form
is observed in the solid-state (Figure 1) and the catalyst
derived from this metallocene yielded amorphous polypro-
pylene. That 4 gives lower tacticity polymers than
2-cyclohexyl derivative 2 suggests that ligand contribu-
tions in these metallocenes are additive rather than
synergistic, a result seemingly at odds with the aryl-
stacking hypothesis. Catalysts derived from 5-7 also
produce amorphous polypropylenes, indicating that the
indenyl ligand also plays an important role.
Exp er im en ta l Section
Standard inert atmosphere techniques were used in han-
dling air- and moisture-sensitive compounds.50 Diethyl ether
and tetrahydrofuran (THF) were distilled from Na/benzophe-
none ketyl and methylene chloride was distilled from calcium
hydride prior to use in reactions. Toluene was dried over Q5
and alumina. 3,4-Dimethylcyclopent-2-en-1-one,36 3,3a,4,5,6,7-
hexahydro-2(2H)-indenone,37 2-bromoindene,39 ZrCl4(THF)2,51
1,52 and zirconium tetrakis(dimethylamide)53 were prepared
by reported methods. n-Butyllithium (nBuLi), phenylmagne-
sium bromide, p-tolylmagnesium bromide, cyclohexylmagne-
sium chloride, [1,2-bis(diphenylphosphino)ethane]nickel dichlo-
ride, and 2-naphthyl bromide were purchased from Aldrich.
Bromotrimethylsilane and ZrCl4 was obtained from Fluka and
Adam’s catalyst (PtO) was purchased from Strem. NMR
spectra were recorded on Varian Gemini 200 and 400 MHz
spectrometers.
3,4-Dim et h yl-1-p h en yl-1,3-cyclop en t a d ien e. Diethyl
ether (30 mL) was added to a dry 100 mL Schlenk flask under
argon. Phenyl magnesium bromide (3 M in ether, 6.1 mL) was
added followed by dropwise addition of 3,4-dimethyl-2-cyclo-
penten-1-one at 0 °C to yield a slurry which was stirred at
room temperature for 1 h. The reaction was quenched with
50 mL of ether and 50 mL of saturated NH4Cl(aq). The
aqueous layer was extracted with ether, and the combined
organics were stirred with p-toluenesulfonic acid monohydrate
(1 g) for 30 min. The mixture was washed twice with 50 mL
of water, and then the organic solution was dried over MgSO4,
filtered, and concentrated via rotovap. The resulting solid was
washed with cold methanol followed by cold hexanes. A second
crop of product was obtained by recrystallizing the methanol
solution at -20 °C. The purified product was stored at -20
°C to prevent decomposition.54 Yield: 0.93 g (30%). 1H NMR
(CDCl3, 400 MHz): δ 1.88 (s, 3H), 1.96 (s 3H), 3.26 (s, 2H),
6.65 (s, 1H), 7.13 (t, 1H, J ) 7 Hz), 7.27 (t, 2H, J ) 7 Hz), 7.44
(d, 2H, J ) 7 Hz) ppm. 13C NMR (CDCl3, 100 MHz): δ 12.6,
13.4, 45.2, 124.5, 126.0, 128.5, 131.7, 135.5, 136.4 ppm. C, H
analysis for C13H14. Anal. Found (Calcd): C, 91.51 (91.71);
H, 8.49 (8.29).
The fact that compounds 2-7 all yield amorphous
polypropylenes under conditions where the 2-phenylin-
dene complex 1 yields a semicrystalline elastomeric
polypropylene suggests that both the 2-aryl substituent
and the indenyl ligand are important for producing
elastomeric polypropylenes. We have previously pro-
posed a mechanism (Scheme 1) that involves intercon-
version of the chiral and achiral torsional isomers to
produce stereoblock microstructures. In order for a
stereoblock microstructure to be produced by this mech-
anism, several factors have to be closely balanced: the
two forms of the catalyst must be close in energy to be
nearly equally populated and the rate of interconversion
must be slower than insertion of the olefin but faster
than the time it takes to construct a single polymer
chain.10,13 All of the complexes 1-7 have the appropri-
ate symmetries to interconvert between chiral and
achiral forms. Solution NMR spectroscopy of complexes
1-7 at room temperature reveal time-averaged C2
symmetry, indicating that rotation of the ligands for the
dichlorides is facile for 1-7. Catalysts derived from
metallocenes 1-7 all produce polypropylene with roughly
comparable productivities. The fact that only 1 yields
an elastomeric polymer indicates that the competition
among the various rates is extraordinarily subtle. For
the derivatives examined here, only the 2-arylindenyl
metallocenes maintain the appropriate balance between
rates of catalyst isomerization and monomer insertion
to give rise to thermoplastic elastomers.
3,4-Dim eth yl-1-p-tolyl-1,3-cyclop en ta d ien e. A modified
literature procedure was employed.55 The preparation of 3,4-
dimethyl-1-p-tolyl-1,3-cyclopentadiene follows the same pro-
cedure as that used to make 3,4-dimethyl-1-phenyl-1,3-
(50) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds; J ohn Wiley & Sons: New York, 1986.
(51) In Inorganic Syntheses ; J . P. J . Fackler, Ed.; J ohn Wiley &
Sons: New York, 1982; Vol. XXI; pp 136.
(52) Coates, G. W. Ph.D. Thesis, Stanford University, May 1994.
(53) Diamond, G. M.; Rodewald, S.; J ordan, R. F. Organometallics
1995, 14, 5-7.
(54) The ligand quickly decomposes at elevated temperature to give
a sticky red solid. At room temperature, decomposition occurs over
several hours.
(55) J ungling, S.; Muelhaupt, R. J . Organomet. Chem. 1993, 460,
191-195.

5914 Organometallics, Vol. 16, No. 26, 1997
Maciejewski Petoff et eal.
cyclopentadiene substituting p-tolylmagnesium bromide for
phenylmagnesium bromide. Yield: 69%. 1H NMR (CDCl3, 200
MHz): δ 1.88 (s, 3H), 1.96 (s, 3H), 2.31 (s, 3H), 3.24 (s, 2H),
6.59 (s, 1H), 7.08 (d, 2H, J ) 8 Hz), 7.32 (d, 2H, 8 Hz) ppm.
13C NMR (CDCl3, 50 MHz): δ 12.5, 13.3, 21.0, 45.3, 124.4,
129.1, 130.8, 133.7, 135.2, 135.4, 135.6, 142.5 ppm. C, H
analysis for C14H16. Anal. Found (Calcd): C, 91.04 (91.24);
H, 8.54 (8.75).
200 MHz): δ 1.22-1.41 (br m, 4 H), 1.69-1.97 (br m, 4 H),
2.40 (br m, 1 H), 3.31 (s, 2 H), 6.48 (s, 1 H), 7.08 (dt, 1 H,
J )1.7, 7 Hz), 7.24 (dd, 2 H, J ) 8, 8 Hz), 7.37 (d, 2 H, 1 H)
ppm. 13C NMR (CDCl3, 50 MHz): δ 26.3, 26.4, 33.1, 39.2, 39.9,
120.0, 123.4, 123.5, 126.2, 142.8, 145.6, 156.2 ppm. C, H
analysis for C15H18. Anal. Found (Calcd): C, 90.62 (90.85);
H, 8.95 (9.15).
Bis(2-cycloh exylin d en yl)zir con iu m Dich lor id e (2).
ZrCl4 (575 mg, 2.47 mmol) and (2-cyclohexylindenyl)lithium57
(1.01 g, 4.94 mmol) were placed in a 100 mL round-bottom
flask and a swivel frit was attached. Toluene (50 mL) was
added to the combined solids at -78 °C. The reaction was
allowed to warm to room temperature and stir for 24 h.
Toluene was removed from the yellow, heterogeneous mixture,
and methylene chloride was introduced. The solution was
filtered through Celite, which was then rinsed with CH2Cl2.
The solution was concentrated in vacuo and washed with
pentane. Analytically pure material was obtained upon
solvent evaporation under reduced pressure. Yield: 793 mg
(58%). 1H NMR (C6D6, 400 MHz): δ 0.89-1.01 (br m, 3 H),
1.23-1.33 (br m, 2 H), 1.52-1.62 (m, 4 H), 1.72 (br d, 2 H),
2.75 (m, 1 H), 5.61 (s, 2 H), 6.93 (m, 2 H), 7.48 (m, 2 H) ppm.
13C NMR (C6D6, 100 MHz): δ 26.5, 33.7, 39.2, 103.4, 124.7,
126.0, 126.2, 127.6, 151.2 ppm. C, H analysis for C30H34Cl2Zr.
Anal. Found (Calcd): C, 64.51 (64.72); H, 6.37 (6.16).
Bis(2-cycloh exyl-4,5,6,7-t et r a h yd r oin d en yl)zir con i-
u m Dich lor id e (3). 1 (1.07 g, 1.97 mmol) and Adam’s catalyst
(60 mg) were loaded into a Fischer Porter bottle. CH2Cl2 (100
mL) was introduced, and then the reactor was pressurized to
80 psig H2 for 4 h. During this time, the solution color changed
from orange to gray. The reactor was vented and the product
solution filtered. The solvent was removed in vacuo to give a
white powder which was recrystallized from toluene at -20
°C to give analytically pure material. Yield: 847 mg (76%).
1H NMR (C6D6, 400 MHz): δ 1.04-1.22 (m, 3 H), 1.30-1.40
(m, 4H), 1.58 (br d, 1 H), 1.66-1.73 (m, 4 H), 2.11 (d, 2 H),
2.37-2.44 (m, 2 H), 2.6-2.66 (m, 1 H), 2.83-2.9 (m, 2 H), 5.86
(s, 2 H). 13C NMR (C6D6, 100 MHz): δ 22.8, 25.0, 26.4, 26.6,
3,4-Dim et h yl-1-(2-n a p h t h yl)-1,3-cyclop en t a d ien e.
A
three-neck round-bottom flask equipped with a reflux con-
denser and dropping funnel was charged with Mg turnings
(0.515 g, 20 mmol) under argon. A few crystals of I2 were
added followed by 5 mL of diethyl ether. After 1 h, when the
solution color faded, 2-bromonaphthalene (4.14 g, 20 mmol)
in 25 mL of ether was added dropwise. The reaction was
heated to reflux and stirred for 2 h. The solution was cooled
in an ice bath and then transferred to a clean Schlenk flask.
3,4-Dimethylcyclopent-2-en-1-one was added dropwise at 0 °C,
and the resulting solution was stirred at room temperature
for 2 h. The reaction was then quenched with 75 mL of ether
and 75 mL of saturated NH4Cl(aq). The aqueous layer was
extracted with ether, and the combined organics were stirred
with 2 g of p-toluenesulfonic acid monohydrate for 30 min. The
solution was washed three times with water, and then the
organic layer was dried over MgSO4, filtered, and concentrated
via rotovap to a yellow/orange paste. The crude product was
washed with methanol at -78 °C to give analytically pure
material. The product was stored at -20 °C. Yield: 2.4 g
(60.4%). 1H NMR (CDCl3, 200 MHz): δ 1.92 (s, 3 H), 2.01 (s,
3 H), 3.40 (s, 2 H), 6.79 (s, 1 H), 7.39-7.42 (m, 2 H,), 7.62-
7.77 (m, 5 H) ppm. 13C NMR (CDCl3, 50 MHz): δ 12.9, 13.4,
45.3, 122.3, 123.6, 125.1, 126.1, 127.6, 127.7, 127.9, 132.2,
132.5, 133.8, 133.9, 135.6, 136.2, 142.5 ppm. C, H analysis
for C17H16
(7.32).
. Anal. Found (Calcd): C, 92.59 (92.68); H, 7.56
2-P h en yl-4,5,6,7-tetr a h yd r oin d en e. A modified litera-
ture procedure was used.56 A 100 mL Schlenk flask was
charged with 3,3a,4,5,6,7-hexahydro-2(2H)-indenone (1.69 g,
12.4 mmol) and 25 mL of diethyl ether. Phenylmagnesium
bromide (3 M in diethyl ether, 6.2 mmol) was added dropwise
under argon at 0 °C. The reaction was allowed to warm to
room temperature to give a milky solution that was stirred
for 24 h. The reaction was carefully quenched with 20 mL of
distilled water, and the organic layer was washed with 10%
HCl(aq) (25 mL). The combined aqueous layers were extracted
into 50 mL of diethyl ether. The combined organics were dried
over MgSO4, filtered, and concentrated via rotovap. The
resulting orange solid was recrystallized from diethyl ether
at -30 °C to give an analytically pure white powder upon
drying in vacuo. Yield: 567 mg (23%). 1H NMR (CDCl3, 400
MHz): δ 1.72 (br s, 4 H), 2.33 (br d, 4 H), 3.24 (s, 2 H), 6.66 (s,
1 H), 7.13 (t, 1 H, J ) 7 Hz), 7.29 (t, 2 H, J ) 8 Hz), 7.46 (d,
2 H, J ) 8 Hz) ppm. 13C NMR (CDCl3, 100 MHz): δ 11.8,
23.0, 23.2, 24.4, 25.5, 43.1, 124.6, 126.0, 128.4, 129.5, 136.6,
139.2, 143.1 ppm.
2-Cycloh exylin d en e. 2-Bromoindene (2.2 g, 11 mmol) and
[1,2-bis(diphenylphosphino)ethane]nickel dichloride (0.1 g, 0.02
mmol) were combined in a two-neck 100 mL round-bottom
flask equipped with a reflux condenser, N2 inlet, and magnetic
stir bar. Anhydrous diethyl ether (40 mL) was introduced, and
the mixture was cooled to 5 °C. Cyclohexylmagnesium chloride
(2 M in ether, 5 mL), was added dropwise via syringe, causing
an exothermic reaction that produces a heavy precipitate. The
reaction was stirred at room temperature for 12 h and then
was quenched with dilute HCl(aq). The ether layer was
washed with water and then dried over Na2SO4. The solvent
was removed in vacuo to give a yellow oil which was purified
by fractional distillation (140 °C (0.2 mmHg)) to give analyti-
cally pure material. Yield: 1.01 g (46.5%). 1H NMR (CDCl3,
34.0, 38.8, 112.0, 129.0, 137.5 ppm. C, H analysis for C30H42
-
Cl2Zr. Anal. Found (Calcd): C, 63.89 (63.80); H, 7.35 (7.49).
Bis(2-p h en yl-4,5,6,7-tetr a h yd r oin d en yl)(2-cycloh exyl-
in d en yl)zir con iu m Dibr om id e (4). A Schlenk flask was
charged with 2-phenyl-4,5,6,7-tetrahydroindene (236 mg, 1.2
mmol), zirconium tetrakis(dimethylamide) (321 mg, 1.2 mmol),
and toluene (10 mL). The resulting solution was stirred for 1
h at room temperature. The solvent and liberated dimethyl-
amine were then removed in vacuo to give (2-phenyl-4,5,6,7-
tetrahydroindenyl)zirconium tris(dimethylamide) which was
used without further purification. 1H NMR (C6D6, 400 MHz):
δ 1.65 (m, 4 H), 2.54 (m, 4 H), 2.82 (s, 18 H), 6.12 (s, 2 H), 7.05
(t, 1 H), 7.19 (dd, 2 H), 7.44 (d, 2 H) ppm.
The crude yellow oil was redissolved in toluene (10 mL) and
was cooled to 0 °C. Bromotrimethylsilane (1.1 mL, 8.25 mmol)
was slowly added to give a bright yellow solution laden with
precipitate. The solution was allowed to warm to room
temperature. After 30 min, the solution was filtered and the
remaining yellow solids were extracted with toluene. The
combined organics were concentrated in vacuo to to give crude
(2-phenyl-4,5,6,7-tetrahydroindenyl)zirconium tribromide which
was used without further purification. 1H NMR (C6D6, 400
MHz): δ 1.27 (m, 2 H), 1.75 (m, 2 H), 2.22 (m, 2 H), 2.74 (m,
2 H), 6.34 (s, 2 H), 7.52 (d, 2 H) ppm. (The remaining aromatic
resonances are partially obscured by C6D6).
Cyclohexylindene (243 mg, 1.2 mmol) was dissolved in
diethyl ether (15 mL). nBuLi (2.5 M in hexanes, 0.5 mL) was
added dropwise via syringe at 0 °C to give a slightly yellow
solution laden with precipitate. The reaction was allowed to
warm to room temperature and stir for 30 min. The solvent
was then removed in vacuo, and the crude product was washed
(56) Halterman, R. L.; Ramsey, T. M. J . Organomet. Chem. 1994,
465, 175-179.
(57) See experimental preparation of 4 for details regarding lithium
salt generation.

Propylene Polymerization with Unbridged Metallocenes
Organometallics, Vol. 16, No. 26, 1997 5915
with hexanes to give a bright white solid which was then
diluted with toluene (10 mL). The (2-phenyl-4,5,6,7-tetrahy-
droindenyl)zirconium tribromide was dissolved in toluene and
was added to the lithium salt at -78 °C. The solution was
allowed to warm to room temperature to give a bright yellow/
orange slurry. After 6 h, the toluene solution was filtered, and
the solid residues were extracted with hot toluene. The
combined organics were concentrated in vacuo and then
washed with pentane. The product was redissolved in toluene
and filtered through Celite. Bis(2-phenyl-4,5,6,7-tetrahydroin-
denyl)(2-cyclohexylindenyl)zirconium dibromide recrystallized
with 0.75 equiv of toluene at -30 °C as analytically pure
material. 1H NMR (C6D6, 400 MHz): δ 0.85-1.1 (br m, 3 H),
1.2-1.31 (br m, 4 H), 1.53 (m, 3 H), 1.69 (m, 2 H), 1.87 (m, 2
H), 2.15-2.25 (br m, 2 H), 2.5-2.56 (br m, 2 H), 2.66 (m, 1 H),
6.09 (s, 2 H), 6.22 (s, 2 H), 6.82 (m, 2 H), 7.1-7.2 (m, partially
obscured by C6D6), 7.51 (d, 2 H) ppm. 13C NMR (C6D6, 100
MHz): δ 21.6, 22.5, 24.8, 26.6, 26.7, 33.6, 40.1, 104.4, 113.5,
125.0, 125.7, 125.9, 126.5, 127.8, 128.7, 129.2, 129.5, 131.3,
134.0 ppm. C, H analysis for C30H38Br2Zr.0.75(C7H8). Anal.
Found (Calcd): C, 59.21 (59.41); H, 5.28 (5.37).
was then stripped in vacuo to give a pale yellow solid.
Meanwhile, ZrCl4(THF)2 (0.856 g, 2.27 mmol) was weighed into
a clean, dry Schlenk flask in the N2 drybox. The solids were
individually dissolved in THF (10 mL). The solution contain-
ing the lithium salt was cooled to -78 °C, and then the
ZrCl4(THF)2 solution was added via cannula. The reaction was
allowed to warm to room temperature and stir for 1 h. During
this time, the solution color went from bright red to dull
orange. The solvent was removed in vacuo to give a sticky
yellow/orange solid. The product was dissolved in CH3CN,
filtered, and layered with hexanes. Shaking the immiscible
solutions caused a bright yellow solid to precipitate at the
interface which was collected via vacuum filtration. The
product was dissolved in CHCl3 to give a bright yellow solution
which was filtered through Celite. The solvent was removed
in vacuo to give the analytically pure metallocene. Yield: 65
mg (4.8%). 1H NMR: (CDCl3, 400 MHz): δ 1.8 (s, 12 H), 6.27
(s, 4 H), 7.50-7.82 (m, 6 H), 7.86-7.93 (m, 8 H) ppm. 13C NMR
(CDCl3, 100 MHz): δ 13.3, 116.3, 122.6, 123.6, 123.7, 126.2,
126.9, 127.8, 128.0, 128.6, 129.0, 131.1, 132.5, 133.6 ppm. C,
H analysis for C34H30Cl2Zr. Anal. Found (Calcd): C, 68.11
(67.98); H, 4.80 (5.03).
Bis(3,4-d im et h yl-1-p h en ylcyclop en t a d ien yl)zir con i-
u m Dich lor id e (5). 3,4-Dimethyl-1-phenyl-1,3-cyclopenta-
diene (1 g, 5.87 mmol) was dissolved in 20 mL of diethyl ether.
nBuLi (1.6 M in hexanes, 3.7 mL) was added dropwise at 0 °C
to give a creamy precipitate. The reaction was allowed to
proceed for 30 min at room temperature, and then the lithium
salt was collected via filtration. The solid was washed three
times with 10 mL of hexanes and then dried in vacuo. The
lithium salt (0.81 g, 4.6 mmol) was combined with ZrCl4(THF)2
(0.867 g, 2.3 mmol) in the N2 drybox. THF (20 mL) was slowly
added at -78 °C to give a yellow solution upon warming to
room temperature. The reaction was allowed to stir for 1 h,
and then the solvent was removed in vacuo to give a sticky
yellow solid. The product was reprecipitated from CH3CN to
give an air- and moisture-stable yellow powder. The product
was dissolved in CHCl3 and filtered through Celite. The
solvent was stripped in vacuo to give analytically pure 5.
Yield: 369 mg (32%). 1H NMR (CDCl3, 400 MHz): δ 1.75 (s,
12 H), 6.25 (s, 4 H), 7.28 (t, 2 H, J ) 7 Hz), 7.46 (m, 8 H) ppm.
13C NMR (CDCl3, 100 MHz): δ 13.0, 116.1, 122.1, 125.1, 127.3,
128.2, 129.1, 133.1 ppm. C, H analysis for C26H26Cl2Zr. Anal.
Found (Calcd): C, 62.12 (62.38); H, 5.30 (5.23).
P olym er iza tion s. Toluene, gaseous propylene, and liquid
propylene were passed over towers containing Q5 and alumina
prior to use. Methylaluminoxane (MMAO Type 4) was ob-
tained from Akzo Nobel as a toluene solution and was dried
in vacuo to give a white solid before use. Polymerizations were
carried out in
a 300 mL Parr reactor equipped with a
mechanical stirrer. Temperature was maintained at 20 °C via
an ethylene glycol/water cooling loop. Catalyst solutions were
prepared in the N2 drybox by dissolving 294 mg of MAO in 23
mL of toluene. A 2 mL aliquot of a 5 × 10-5 M metallocene
solution was then added to give the activated catalyst with
Al:Zr ) 1000:1. Propylene concentrations were calculated for
runs using gaseous propylene by utilizing a method reported
by Busico (P, concentration 50 psig, 3.24 M; 75 psig, 4.49 M).58
(1) Solu tion P olym er iza tion s. Toluene (75 mL) was
introduced to the reactor under 50 psig argon which was then
vented. The solvent was allowed to saturate with the desired
amount of propylene and then the catalyst solution was
injected under propylene pressure. After sufficient time had
passed, 30 min for 5 (due to its high activity) and 60 min for
all other catalysts, the reaction was quenched with 15 mL of
methanol injected under argon pressure.
(2) Bu lk P olym er iza tion s. The catalyst solution was
introduced to the reactor under argon pressure which was then
vented. Liquid propylene (100 mL) was then added to start
the reaction. Polymerizations were allowed to proceed for 20
min and then were quenched with 15 mL of methanol injected
under argon pressure.
The polymers were collected and precipitated into acidified
methanol (5% HCl). After being stirred overnight, the poly-
mers were dried in a vacuum oven at 40 °C.
P olym er Ch a r a cter iza tion . Number- and weight-average
molecular weights (Mn, Mw) were obtained using a Waters
150C high-temperature chromatograph. Samples were run in
1,2,4-trichlorobenzene at 139 °C using two Polymer Labora-
tories PL GEL Mixed-B columns at a flow rate of 1 mL/min.
m4 was determined via 13C NMR spectra recorded at 75.425
MHz on a Varian UI 300 spectrometer at 100 °C using 10 mm
sample tubes. Samples were prepared in 1,1,2,2-tetrachloro-
ethane containing about 0.5 mL of 1,1,2,2-tetrachloroethane-
d2. IR spectra were obtained from polypropylene films on a
Perkin Elmer 1600 Series FTIR. DSC traces were acquired
by heating samples from -25 to 200 °C at 20 °C/min on a
Perkin Elmer DSC 7.
Bis(3,4-d im et h yl-1-p -t olylcyclop en t a d ien yl)zir con i-
u m Dich lor id e (6). 3,4-Dimethyl-1-p-tolyl-1,3-cyclopentadi-
ene (2 g, 10.8 mmol) was dissolved in 25 mL of diethyl ether
in a 100 mL Schlenk flask. nBuLi (1.6 M in hexanes, 6.7 mL)
was added dropwise at 0 °C to give a creamy precipitate. The
mixture was allowed to stir at room temperature for 30 min.
The solvent was removed in vacuo, and then ZrCl4(THF)2 (2.04
g, 5.4 mmol) was added in the N2 drybox. THF (25 mL) was
added slowly at -78 °C under argon flow to give a bright
yellow solution. The solution was stirred overnight at room
temperature. The solvent was stripped in vacuo, and the
resulting sticky yellow solid was washed with cold, dry
hexanes. The remaining material was reprecipitated from
acetone at -20 °C. The solid was dissolved in CHCl3, filtered
through Celite, and layered with hexanes. Air- and moisture-
stable crystals that formed were analytically pure. Yield: 2.8
1
g (49%). H NMR (CDCl3, 400 MHz): δ 1.76 (s, 12 H), 2.39 (s,
6H), 6.19 (s, 4H), 7.23 (d, 4H, J ) 8 Hz), 7.35 (d, 4H, J ) 8
Hz) ppm. 13C NMR (CDCl3, 100 MHz): δ 13.1, 21.2, 115.8,
122.6, 125.1, 127.9, 129.8, 130.5, 137.2 ppm. C, H analysis
for C28H30Cl2Zr. Anal. Found (Calcd): C, 63.77 (63.61); H,
5.67 (5.72).
Bis(3,4-d im eth yl-1-(2-n a p h th yl)cyclop en ta d ien yl)zir -
con iu m Dich lor id e (7). 3,4-Dimethyl-1-(2-naphthyl)-1,3-
cyclopentadiene (1 g, 4.54 mmol) was dissolved in 25 mL of
diethyl ether in a 50 mL Schlenk flask. nBuLi (1.6 M in
hexanes, 2.8 mL) was added dropwise at 0 °C to give a solution
laden with a yellow precipitate. The reaction was allowed to
warm to room temperature and stir for 30 min. The solvent
X-r a y Diffr a ction Stu d ies. (1) Bis(2-p h en yl-4,5,6,7-
tetr a h yd r oin d en yl)(2-cycloh exylin d en yl)zir con iu m Di-
br om id e (4). An orange block crystal of C67H84Br4Zr2 (FW )
(58) Busico, V.; Brita, D.; Caporaso, L.; Cipullo, R.; Vacatello, M.
Macromolecules 1997, 30, 3971-3977.

5916 Organometallics, Vol. 16, No. 26, 1997
Ta ble 2. Su m m a r y of Cr ysta l Str u ctu r e P a r a m eter s
Maciejewski Petoff et eal.
compound
4
6
formula
FW
C67H84Br4Zr2
1391.46
C28H30Cl2Zr
528.67
temp (K)
119
156
space group
P21/n (No. 14); monoclinic
P41212 (No. 92); tetragonal
cell constantsa,b
a (Å)
17.6826(2)
12.7602(1)
b (Å)
14.0689(2)
12.7602(1)
c (Å)
23.6703(1)
5738.85(9)
15.1049(2)
2459.42(4)
volume (Å3)
Z
4
4
6.77
1088
1.428
abs coeff, µcalc (cm-1
)
31.98
2824
1.61
F000
dobsc (dcalc) (g cm-3
crystal size (mm3)
radiation
)
0.29 × 0.21 × 0.12
Mo KR (λ ) 0.710 73 Å)
highly oriented graphite
Siemens SMART
+h,(k,(l
2.4° < 2θ < 52.0°
ω
0.3
10-s frame exposure
27 318
10 568 (Rint ) 0.045)
4606
0.16 × 0.19 × 0.20
Mo KR (λ ) 0.710 73 Å)
monochromator
diffractometer
reflections measured
2θ range
scan type
highly oriented graphite
Siemens SMART
-14ehe13; -15eke14; -18ele17
4.5° < 2θ < 50.50°
ω
0.3
scan width (deg)
scan speed
10-s frame exposure
11 537
2286 (Rint ) 0.035)
1934
no. of reflctns colltd
no. of unique reflctns
reflctns with (Fo > 3σ(Fo2))
2
no. of variables
335
141
parameter-to-variable ratio
13.75
0.038 (0.048)
+0.80; -0.6
13.7
0.022 (0.028)
+0.24; -0.27
R (Rw)d
final diff Fmax (e-/Å3)e
a
Unit cell parameters and their ESDs were derived by a least-squares fitting of 8192 reflections with I > 10 σ(I) and 2θ between 4.0
and 45.5°. The ESDs of all parameters are given in parentheses. c The density of the crystal was not measured. The unweighted and
b
d
weighted agreement factors in the least-squares refinements were as follows: R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) (∑w(|Fo| - |Fc|)2/∑wFo
)
,
2
1/2
where w ) 4Fo2/s2(Fo2); s2(Fo2) ) (S2(C + R2B) + (pFo2)2)/Lp2. S, scan rate; C, total integrated peak count; R, ratio of scan time to background
counting time; B, total background count; Lp, Lorentz-polarization factor; p, p-factor (0.00). e Maximum negative and positive difference
peaks.
1391.46)59 with approximate dimensions of 0.29 × 0.21 × 0.12
mm3 was mounted on a glass fiber in Paratone oil at -80 °C.
All measurements were made on a Siemens SMART60 diffrac-
tometer with graphite-monochromated Mo KR radiation. The
structure was solved by direct methods61 and expanded using
Fourier techniques.62 Two independent molecules were found
in the Fourier map. Only Zr and Br atoms were refined
anisotropically. A number of carbons were nonpositive definite
so all carbon atoms were refined isotropically. Hydrogen
atoms were included at idealized positions 0.95 Å from their
parent atoms except for the disordered toluene molecule which
was found as a solvent of recrystallization. The disordered
toluene was refined as 50/50 disordered. Crystal data and
details of data collection and structure analysis are sum-
marized in Table 2.
Paratone oil at -118 °C. All measurements were made on a
Siemens SMART60 diffractometer with graphite-monochro-
mated Mo KR radiation.
The structure was solved by direct methods61 and expanded
using Fourier techniques.62 All non-hydrogen atoms were
refined anisotropically. From the Fourier map, the hydrogen
atoms were located on the cyclopentadienyl ring and its two
methyl substituents, while on the benzene ring and its
corresponding methyl substituent, the hydrogen atoms were
positioned at an idealized geometry, 0.95 Å from their parent
atoms before the last cycle of refinement. All calculations were
performed using the teXsan crystallographic software pack-
age.63 Crystal data and details of data collection and structure
analysis are summarized in Table 2.
(2) Bis(3,4-d im eth yl-1-p-tolylcyclop en ta d ien yl)zir co-
n iu m Dich lor id e (6). A deep yellow single crystal of
Ack n ow led gm en t. Financial support from Amoco
and the NSF Waterman Award to R.M.W. (Grant NSF
CHE-9615699) is gratefully acknowledged. We thank
Eric Enemark and Eric Moore for helpful discussions
and aid in data analysis.
C
28H30Cl2Zr (FW ) 530.12) with approximate dimensions of
0.16 × 0.19 × 0.2 mm3 was mounted on a glass fiber in
(59) Formula and Formula Weight values count both molecules in
the asymmetric unit and the disordered toluene molecule that is
present.
(60) SMART: Area-Detector Software Package; Siemens Industrial
Automation, Inc.: Madison, WI, (1995).
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic determination of 4 and 6 (52 pages). Ordering
information is given on any current masthead page.
(61) SHELXS-86: Sheldrich, G. (1986).
(62) DIRDIF92: Beurskens, P. T., Admiraal, G., Beurskens, G.,
Bosman, W. P., Garcia-Granda, S., Gould, R. O., Smits, J . M. M. and
Smykalla, C. (1992). The DIRDIF program system, Technical Report
of the Crystallography Laboratory, University of Nijmegen, The
Netherlands, 1992.
OM9706119
(63) teXsan: Crystal Structure Analysis Package, Molecular Struc-
ture Corporation (1985 & 1992).