Copolymerization behavior of unbridged indenyl metallocenes: Substituent effects on the degree of comonomer incorporation

Article abstract of DOI:10.1021/ma011517d

The copolymerization of ethylene and 1-hexene with a variety of unbridged indenylmetallocenes was investigated and compared to unbridged bis(indenyl)zirconium dichloride and bis(cyclopentadienyl)zirconium dichloride as well as ansa-bridged rac-ethylenebis(indenyl)zirconium dichloride (EBIZrCl₂). The unbridged bis(2-phenylindenyl)zirconium dichloride showed higher selectivity for the incorporation of 1-hexene than the bridged rac-ethylenebis(indenyl)zirconium dichloride and much higher 1-hexene incorporation than the unbridged bis(indenyl)zirconium dichloride and bis(cyclopentadienyl)-zirconium dichloride. Both ligands appear to be important since the 1-hexene incorporation of the mixed ligand compound (cyclopentadienyl)(2-phenylindenyl)zirconium dichloride is much lower than that of bis-(2-phenylindenyl)zirconium dichloride. For unbridged bis(indenyl)metallocenes, the nature of the substituent in the 2-position plays an important role in comonomer selectivity: bis(2-methylindenyl)zirconium dichloride and bis(2-phenylethynylindenyl)zirconium dichloride exhibit much higher 1-hexene incorporation than bis(indenyl)zirconium dichloride but lower than bis(2-phenylindenyl)zirconium dichloride.

Full text of DOI:10.1021/ma011517d

Macromolecules 2002, 35, 637-643
637
Copolymerization Behavior of Unbridged Indenyl Metallocenes:
Substituent Effects on the Degree of Comonomer Incorporation
Sa r a h E. Reybu ck , Ar n d t Meyer , a n d Rober t M. Wa ym ou th *
Department of Chemistry, Stanford University, Stanford, California 94305
Received August 23, 2001; Revised Manuscript Received November 7, 2001
ABSTRACT: The copolymerization of ethylene and 1-hexene with a variety of unbridged indenylmetal-
locenes was investigated and compared to unbridged bis(indenyl)zirconium dichloride and bis(cyclopen-
tadienyl)zirconium dichloride as well as ansa-bridged rac-ethylenebis(indenyl)zirconium dichloride
(EBIZrCl2). The unbridged bis(2-phenylindenyl)zirconium dichloride showed higher selectivity for the
incorporation of 1-hexene than the bridged rac-ethylenebis(indenyl)zirconium dichloride and much higher
1-hexene incoporation than the unbridged bis(indenyl)zirconium dichloride and bis(cyclopentadienyl)-
zirconium dichloride. Both ligands appear to be important since the 1-hexene incorporation of the mixed
ligand compound (cyclopentadienyl)(2-phenylindenyl)zirconium dichloride is much lower than that of bis-
(2-phenylindenyl)zirconium dichloride. For unbridged bis(indenyl)metallocenes, the nature of the sub-
stituent in the 2-position plays an important role in comonomer selectivity: bis(2-methylindenyl)zirconium
dichloride and bis(2-phenylethynylindenyl)zirconium dichloride exhibit much higher 1-hexene incorpora-
tion than bis(indenyl)zirconium dichloride but lower than bis(2-phenylindenyl)zirconium dichloride.
In tr od u ction
incorporation in ethylene/1-hexene copolymerizations
when activated by methylaluminoxane (MAO). In a
previous contribution, we observed that 1/MAO shows
high reactivity toward propylene in ethylene/propylene
copolymerization.30 In this paper we report a syste-
matic study on the influence of cyclopentadienyl sub-
stitutents on the ethylene/1-hexene copolymerization
behavior of a family of unbridged zirconocenes activated
by MAO including: 1 as well as (cyclopentadienyl)(2-
phenylindenyl)zirconium dichloride, (Cp)(2-PhInd)ZrCl2,
2, bis(2-phenylethynylindenyl)zirconium dichloride, (2-
PhEthInd)2ZrCl2, 3, and bis(2-methylindenyl)zirconium
dichloride, (2-MeInd)2ZrCl2, 7. The copolymerization
reactivity ratios, comonomer content, and comonomer
distributions produced by these zirconocenes are dis-
cussed and compared to those observed with rac-
ethylenebis(indenyl)zirconium dichloride, EBIZrCl2, 4,
bis(indenyl)zirconium dichloride, Ind2ZrCl2, 5, and bis-
(cyclopentadienyl)zirconium dichloride, Cp2ZrCl2, 6.
Ethylene copolymers of higher R-olefins such as
1-butene, 1-hexene, and 1-octene are industrially im-
portant materials. In 1996, worldwide production of
ethylene/R-olefin copolymers exceeded 24 million metric
tons1 or approximately 30% of the market share of
polymer products from ethylene. Control over the in-
corporation and distribution of R-olefins in ethylene/R-
olefin copolymers is industrially important for the
control of polymer properties such as melting point,
glass transition temperature, tensile strength, flex-
ibility, and processability.2-11 In general, the short-chain
branching introduced into polyolefins by R-olefin comono-
mers results in lower melting points, lower crystallinity,
and lower density, making these polymer films more
flexible and processable.
For both the production and study of ethylene/R-olefin
copolymers, metallocenes offer several advantages over
traditional Ziegler-Natta catalysts. In contrast to Zie-
gler-Natta catalysts, metallocene systems give narrow
molecular weight distributions, high comonomer incor-
poration, and narrow compositional distributions.12 In
addition, the relationship between copolymerization
behavior and catalyst structure is more readily inves-
tigated with metallocene catalysts and can provide
insight into the mechanism of olefin polymerization.
Studies of metallocene-catalyzed copolymerization of
ethylene with R-olefins ranging from C3-C18 have been
reported by several groups.13-29 Incorporation of R-olefin
comonomers has been studied as a function of ligand
substitution pattern, interannular bridge, and metal.
One common observation from these studies is that
ansa-metallocenes with one- or two-membered bridges
between the ligands incorporate R-olefin comonomers
better than unbridged metallocenes.21,22,29 Other studies
have shown that benzannelation of bridged indenyl
ligands increases reactivity toward R-olefins.23
Resu lts
Seven metallocenes were studied for their ethylene/
1-hexene copolymerization behavior (Figure 1). Ethyl-
ene/1-hexene copolymerizations with metallocenes 4-7
have been reported in the literature22,25,28,31 but were
reproduced under our conditions for comparison. Copo-
lymerizations were carried out over a variety of comono-
mer feed ratios to obtain copolymers with a wide range
of ethylene incorporation; the results are reported in
Table 1. The experiments were carried out at low
conversions to optimize the determination of the copo-
lymerization parameters. These conditions are likely to
lead to large uncertainties in the productivities ob-
tained.
Metallocene 1 showed the highest molecular weights
with distributions that were monomodal but broader
than expected for a single-site metallocene catalyst (Mw/
Mn ) 2.8-4.9). Metallocene 2 also produced high mo-
lecular weight copolymer; however, this polymer had a
very broad molecular weight distribution (Mw/Mn ) 7.0)
due to low molecular weight tailing. This may be an
In this paper, we show that certain classes of un-
bridged indenyl metallocenes, in particular the un-
bridged bis(2-phenylindenyl)zirconium dichloride, (2-
PhInd)2ZrCl2 (1), exhibit very high selectivity for hexene
10.1021/ma011517d CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/27/2001

638 Reybuck et al.
Macromolecules, Vol. 35, No. 3, 2002
F igu r e 1. Metallocenes investigated for ethylene/hexene copolymerization.
Ta ble 1. Eth ylen e/Hexen e Cop olym er iza tion w ith Meta llocen e/MAO System
[Zr]
(µmol)
prodb
(E)copolymer
(mol %)
% hexene
conversion
Mw (×103)
Mn (×103)
a
metallocene
run
Xe/Xh
yield (g)
(×103)
(g/mol)
(g/mol)
Mw/Mn
1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
1.60
0.80
0.80
0.49
0.49
3.00
3.00
3.00
1.50
1.50
1.50
2.25
1.50
1.50
1.50
4.50
1.50
4.50
1.00
0.75
1.00
2.00
1.00
1.25
1.00
4.50
4.50
1.60
0.80
0.80
0.80
0.078
0.119
0.163
0.214
0.266
0.030
0.035
0.042
0.068
0.111
0.057
0.058
0.080
0.112
0.163
0.067
0.112
0.171
0.214
0.275
0.022
0.026
0.030
0.034
0.040
0.045
0.080
0.057
0.080
0.119
0.165
0.504
0.460
0.936
0.700
1.211
0.418
0.359
0.862
3.863
0.732
0.347
0.641
0.846
0.563
0.692
2.493
1.298
1.828
1.662
0.349
0.393
0.654
0.260
0.842
0.680
0.315
1.046
0.922
0.265
1.988
1.091
11.8
19.2
39.0
53.8
93.2
6.97
5.98
14.4
85.8
24.4
6.94
14.2
16.9
18.7
34.6
27.7
51.9
40.6
62.3
17.4
9.83
10.9
19.5
25.3
51.0
3.50
7.75
28.8
16.6
186
39.0
51.4
55.9
61.8
66.8
68.6
74.0
78.1
82.4
87.4
47.0
48.8
56.9
65.1
78.0
52.7
66.7
76.6
77.4
80.8
76.0
78.8
82.9
84.0
89.2
73.8
79.4
47.4
57.2
69.0
77.3
1.1
0.8
1.5
1.0
1.5
0.5
0.3
0.7
2.5
0.3
0.7
1.2
1.4
0.7
0.6
4.4
1.6
1.6
1.4
0.2
0.4
0.5
0.2
0.5
0.3
0.3
0.8
1.8
0.4
2.3
0.9
142
628
500
1169
1192
50.3
172
102
369
322
2.8
3.7
4.9
3.2
3.7
2
3
4
5
856
349
7.0
882
306
2.9
2.3
57.5
25.2
492
32.2
983
194
14.9
279
2.5
2.2
3.5
6
7
68.2
a
b
Monomer feed ratio: Xe ) mole fraction of ethylene, Xh ) mole fraction of hexene. Productivity ) kg of polymer/(mol of Zr h).
indication that the catalyst is decomposing during
(2[EEE] + [EEH])
polymerization. Metallocenes 3 and 7 gave high molec-
ular weight polymers and molecular weight distribu-
tions of 2.9 and 3.5, respectively, while complexes 4-6
produced copolymers with lower molecular weights and
narrower molecular weight distributions (Mw/Mn ) 2.2-
2.5).
Comonomer feed compositions were determined using
an empirical equation reported by Spitz and co-work-
ers.32 Copolymer compositions and n-ad distributions
calculated from 13C NMR using the method of Cheng33
are reported in Table 2. Comparison of copolymers of
the same ethylene content prepared at different feed
ratios by different metallocenes shows similar sequence
distributions for each of the polymers. Reactivity ratios
for each run were calculated from these experimental
triad distributions according to the following two equa-
tions.34
re )
Xe
(2[EHE] + [HHE])
Xh
Xe
(2[HHH] + [HHE])
Xh
(2[EHE] + [HHE])
rh )
The reactivity ratios were also calculated over all
triads for all feed ratios simultaneously by optimizing
the variation of the reaction probabilities Pij (the prob-
ability that a monomer j will add to a polymer chain
ending in monomer i) until the best fit between experi-
mental triads and those calculated from the first-order
Markov model was obtained. Reactivity ratios are cal-
culated by this method with the following two equa-

Macromolecules, Vol. 35, No. 3, 2002
Unbridged Indenyl Metallocenes 639
Ta ble 2. 13C NMR Ch a r a cter iza tion of E/H Cop olym er s P r ep a r ed w ith Meta llocen e/MAO
f
(E)copolymer
(mol %)
triadsa
EHE
metallocene
run
(mol/mol)
HHH
HHE + EHH
HEH
HEE + EEH
EEE
re
6.5
8.7
6.8
7.2
7.4
rh
1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
0.078
0.119
0.163
0.214
0.265
0.030
0.036
0.042
0.068
0.111
0.057
0.058
0.080
0.112
0.163
0.067
0.112
0.171
0.214
0.275
0.022
0.026
0.030
0.034
0.040
0.045
0.080
0.057
0.080
0.119
0.165
39.0
51.4
55.9
61.8
66.8
68.6
74.0
78.1
82.4
87.4
47.0
48.4
56.9
65.1
78.0
52.7
66.7
76.6
77.4
80.8
76.0
78.8
82.9
84.0
89.2
73.8
79.4
47.4
57.2
69.0
77.3
0.196
0.125
0.079
0.069
0.041
0.028
0.021
0.000
0.000
0.000
0.152
0.141
0.063
0.049
0.000
0.094
0.018
0.004
0.007
0.000
0.013
0.017
0.056
0.000
0.000
0.000
0.000
0.154
0.090
0.048
0.026
0.253
0.186
0.160
0.127
0.105
0.072
0.055
0.052
0.026
0.012
0.198
0.201
0.159
0.104
0.048
0.140
0.087
0.093
0.041
0.022
0.044
0.033
0.016
0.024
0.000
0.030
0.026
0.194
0.152
0.094
0.049
0.161
0.175
0.202
0.186
0.186
0.213
0.185
0.167
0.151
0.114
0.180
0.174
0.209
0.196
0.172
0.239
0.228
0.192
0.177
0.170
0.183
0.162
0.098
0.136
0.108
0.232
0.180
0.179
0.186
0.168
0.152
0.162
0.131
0.120
0.108
0.070
0.081
0.069
0.049
0.037
0.018
0.118
0.147
0.115
0.087
0.051
0.169
0.098
0.078
0.050
0.019
0.053
0.039
0.015
0.023
0.000
0.112
0.039
0.137
0.112
0.072
0.048
0.156
0.200
0.244
0.268
0.279
0.267
0.268
0.257
0.238
0.152
0.228
0.217
0.253
0.280
0.307
0.234
0.272
0.288
0.256
0.229
0.255
0.237
0.213
0.197
0.184
0.295
0.226
0.208
0.240
0.270
0.247
0.069
0.177
0.191
0.248
0.331
0.325
0.393
0.467
0.539
0.698
0.125
0.112
0.192
0.278
0.439
0.115
0.279
0.331
0.456
0.551
0.442
0.509
0.459
0.608
0.639
0.331
0.514
0.124
0.212
0.345
0.477
0.088
0.097
0.092
0.114
0.105
0.008
0.008
0.006
0.005
0.006
0.051
0.051
0.039
0.045
0.020
0.035
0.025
0.036
0.029
0.017
0.004
0.005
0.016
0.003
0.000
0.003
0.005
0.051
0.050
0.053
0.047
2
3
4
5
62.3
69.7
74.1
59.1
58.3
15.2
13.9
13.9
15.0
18.5
11.3
13.6
11.7
13.8
13.4
123.7
135.2
180.5
139.0
167.5
42.8
40.8
14.6
15.9
18.8
20.7
6
7
a
Triads do not sum to 1.00 for all runs. This reflects the experimental error in the calculation of triads from 13C NMR.
Ta ble 3. Rea ctivity Ra tios for Eth ylen e/Hexen e Cop olym er iza tion s
% E in polymerc
re
rh
rerh
rh/re (×105)
a
b
d,e
d,e
d,f
metallocene
Nexp
Xe/Xh
1
2
3
4
5
6
7
5
5
5
5
5
2
4
0.08-0.27
0.03-0.11
0.06-0.16
0.07-0.28
0.02-0.04
0.05-0.08
0.06-0.16
39-67
69-87
47-78
53-81
76-89
74-79
47-77
8 ( 1
70 ( 10
17 ( 2
0.09 ( 0.01
0.006 ( 0.001
0.04 ( 0.01
0.027 ( 0.008
0.004 ( 0.006
0.003 ( 0.002
0.048 ( 0.003
0.7 ( 0.1
0.4 ( 0.1
0.7 ( 0.2
0.4 ( 0.1
0.5 ( 0.9
0.16 ( 0.09
0.9 ( 0.2
1100
9
240
190
3
14 ( 2
149 ( 23
47 ( 7
19 ( 3.5
6
250
a
b
Number of experiments used for determination of the average reactivity ratios. Range of the ratios of mole fractions of ethylene and
1-hexene in the monomer feed. c Range of mol % E in the copolymers as determined by 13C NMR. Calculated by optimization of reaction
d
probabilities from the triads over all N runs simultaneously (see ref 37). e Standard deviation calculated as [(1/(N - 1))∑(re,h(exp) - re,h(opt))2]1/2
where re,h(exp) is the reactivity ratio calculated for the triads of an individual run and re,h(opt) is the optimized reactivity ratio. f Standard
deviation calculated as (rerh)[(σre)2 + (σrh)2]1/2
.
tions.34
nyl)zirconium dichloride (4) exhibited much higher
1-hexene incorporation than the unbridged bis(indenyl)-
zirconium dichloride (5), as manifested in the lower re
and higher rh values (Table 3). In contrast, substituting
the two indene ligands of the unbridged metallocene 5
with phenyl groups in the 2-position gives the metal-
locene 1, which shows comparable or slightly better
1-hexene incorporation compared to that of 4 (compare
run 4 vs 19 in Table 1 and re rh values in Table 3). The
1-hexene incorporation of the mixed-ligand metallocene
2 is also quite poor and comparable to that of Cp2ZrCl2
(6) (compare run 8 vs 26, Table 1; rerh values in Table
3).
Xh
Xe
1
Peh
re )
rh )
- 1
- 1
(
)
Xe
1
Phe
(
)
Xh
The optimized reactivity ratios are reported in Table
3.35 All seven metallocenes showed a significantly higher
reactivity toward ethylene as compared to 1-hexene. The
product of reactivity ratios, rerh, was between 0.16 and
0.9 in each case. As previously observed, the unbridged
metallocenes bis(indenyl)zirconium dichloride (5) and
bis(cyclopentadienyl)zirconium dichloride (6) exhibit
very poor 1-hexene incorporation as manifested in high
re ) 47-149 and low rh ) 0.003-0.004. The ethylene/
1-hexene copolymerization reactivity ratios determined
for the bridged zirconocene EBIZrCl2, 4, under our
conditions are consistent with literature values.21 As
previously observed, the bridged rac-ethylenebis(inde-
For the unbridged indenyl series (1, 3, 5, 7) introduc-
tion of a substituent on the 2-position has a significant
effect on the ability to incorporate 1-hexene: metal-
locenes 3 and 7 incorporate 1-hexene much better than
the unsubstituted 5 (compare runs 15, 22, and 31 of
Table 1 or rerh values in Table 3) but not as well as the
2-phenyl-substituted metallocene 1 (run 2 vs 14 and 30,
Table 1, or rerh values in Table 3).

640 Reybuck et al.
Macromolecules, Vol. 35, No. 3, 2002
Ta ble 4. Selected Bon d in g P a r a m eter s for Meta llocen es 1, 4, a n d 5
zirconocene
Zr-C (min-max) (Å)
Zr-Cl (av) (Å)
Cen-Zr-Cen (deg)
Cl-Zr-Cl (deg)
ref
1
anti rotamer
syn rotamer
4
5
2.465-2.622
2.476-2.624
2.438-2.624
2.478-2.616
2.433
2.427
2.388
2.440
131.3
131.0
125.3
128.3
95.44
94.39
99.09
94.71
44
51
52
Discu ssion
5 implies that factors other than coordination gap
aperture and ligand geometry are important for deter-
mining the reactivity of 1 toward R-olefins.
The incorporation of R-olefin comonomers is an im-
portant means of influencing the architecture and
properties of ethylene/R-olefin copolymers. The use of
metallocenes in these copolymerizations makes it pos-
sible to control both the degree of incorporation and to
some extent the distribution of comonomers in the
chain.36-43 To design metallocenes rationally for these
copolymerizations, it is useful to determine which
structural features of metallocenes influence comonomer
selectivity.
To further investigate the influence of the 2-phenyl
substituent on comonomer reactivity, ethylene/1-hexene
copolymerizations were carried out with the mixed
ligand zirconocene 2. The reactivity of 2 toward 1-hex-
ene is more similar to the unsubstituted compound 6
than to 1, which seems to indicate that the high
reactivity of 1 toward 1-hexene arises from the additive
effect of having both indenes substituted with a 2-phenyl
group.
We have found that the unbridged metallocene, (2-
PhInd)2ZrCl2, incorporates surprisingly high amounts
of 1-hexene comonomer in ethylene/1-hexene copoly-
merizations. Previous studies comparing metallocenes
such as Ind2ZrCl2 and Cp2ZrCl2 with rac-EBI have led
to the suggestion that bridged metallocenes incorporate
R-olefin comonomers more readily than unbridged met-
allocenes.21,22 One explanation proposed for this phe-
nomenon is that the larger coordination gap aperture
of the bridged compounds allows the incoming R-olefin
better accessibility to the zirconium center.1,21,22 Our
results with metallocenes 4, 5, and 6 are consistent with
the literature observations that the bridged metallocene
4 incorporates 1-hexene more readily than the un-
bridged metallocenes 5 and 6; however, systematic
studies with the series of metallocenes 1-7 suggest that
the presence or absence of a bridging group may not be
as important as the nature of the substituents for
controlling the comonomer incorporation.
The results of this study reveal that, among the
metallocenes 1-7, the unbridged (2-PhInd)2ZrCl2 (1)
exhibits the highest tendency to incorporate 1-hexene.
One crude measure of this selectivity is the ratio rh/re
(Table 3), which reveals that the reactivity toward
1-hexene follows the general trend 1 > 3, 4, 7 . 2, 5, 6.
Thus, these results suggest that unbridged metallocenes
can exhibit comonomer selectivity equal to or greater
than that of analogous bridged metallocenes. As pointed
out previously, introduction of a bridge has a significant
influence on the ability to incorporate comonomer
(compare 4 vs 5); however, it is clear from this study
that introduction of a 2-substituent can have an equal
or even greater influence (compare 1 vs 5).
Previous studies have invoked a structural argument
to explain the better comonomer incorporation for the
bridged metallocenes 4 relative to the unbridged 5.21,22
To assess the role of coordination geometry on the
copolymerization behavior, selected structural param-
eters from the literature for 1, 4, and 5 are presented
in Table 4. Two torsional isomers, syn and anti confor-
mations, were found in the X-ray crystal structure of
1;44 parameters for both isomers are reported in Table
4. Analysis of the reported structural features for
metallocenes 1, 4, and 5 reveals that bond lengths and
angles for 1 are closer to those of 5 than to those of 4.
Steric arguments alone would predict, therefore, that
the reactivity of 1 would be closer to 5 than 4. The
observation that 1 has much higher rh and lower re than
For the unbridged indenyl metallocenes, the presence
and nature of the 2-substituent on the indene have a
significant effect on the ability to incorporate comono-
mer. In this study, we have shown that the 2-substituted
indenyl complexes 1, 3, and 7 all incorporate 1-hexene
more readily than the unsubstituted complex 5. Similar
observations were reported for a variety of 2-alkyl-
substituted unbridged indenylmetallocenes45 as well as
for 7 and bis(2-benzylindenyl)zirconium dichloride,28
both of which showed unusually high comonomer in-
corporation. Consistent with the data from Yoon,28 we
find that 7 gives much better 1-hexene incorporation
than 5, but under our conditions, we calculate copolym-
erization parameters for 7 (re ) 19, rh ) 0.048 compared
to re ) 4.53, rh ) 0.1528)46 that are roughly comparable
to that of 4 and 3.
The higher comonomer incorporation of the 2-phenyl-
substituted 1 relative to the 2-methyl-substituted 7 (run
2 vs 30 and 3 vs 31 and Table 3) prompted us to
speculate that the high comonomer incorporation may
require a conjugated substituent in the 2-position.
Consequently, we synthesized 3 and studied its copo-
lymerization behavior.47 Zirconocene 3 retains the ex-
tended conjugation of 1 but spaces the phenyl group
farther from the coordination site of the catalyst.
Ethylene/1-hexene copolymerization with 3 showed
1-hexene reactivity lower than that of 1, comparable to
that of 7, but much higher than that of 5. While steric
arguments might predict that spacing the phenyl group
farther from the coordination site would increase reac-
tivity toward 1-hexene, the observed reactivity ratios
suggest that having the phenyl group closer to the
coordination site increases the selectivity for 1-hexene.
Moreover, the similar copolymerization behavior of 3
and 7 suggests that any substituent larger than hydro-
gen is sufficient to improve the 1-hexene incorporation
relative to 5.
Although we do not fully understand the high comono-
mer incorporation by the unbridged metallocenes 1, 3,
and 7, one possible explanation is that the substituent
in the 2-position affects the conformational dynamics
for the activated unbridged metallocene. For unbridged
metallocenes, conformational dynamics may be influ-
enced by factors including identity of the counterion,48
steric effects of the coordinated polymer chain, and
substituents on the ligands. For the unbridged metal-
locene with no indenyl substituents, Ind2ZrCl2, many

Macromolecules, Vol. 35, No. 3, 2002
Unbridged Indenyl Metallocenes 641
F igu r e 2. Possible rotamers of unbridged indenylmetallocenes.
conformations for the indenyl ligands of the active cation
are imaginable, including those in which the indenyl
ligands project out directly over the metal coordination
site (Figure 2). Placing a large phenyl group in the
2-position of both indene ligands, such as in metallocene
1, may sterically restrict conformations in which the
indenyl groups block the metal coordination sites, thus
making these sites more open for coordination of the
larger comonomer. For metallocene 2, the presence of a
2-phenyl substituent on only one ligand again makes
accessible conformations with blocked coordination sites.
While conformational effects may in part explain the
high comonomer reactivity by metallocene 1, we suspect
that having arenes near the metal coordination site also
plays a role in comonomer coordination. This factor
might explain the higher comonomer incorporation of
1 vs 3 and 7 as well as the higher comonomer incorpo-
rations observed for benzannelated bridged zirconocenes
in ethylene/1-hexene copolymerization.23
reactivity differences may be at least partially explained
by the phenyl groups decreasing the accessibility of
conformations in which the metal coordination sites are
blocked by the indene ligands. Further copolymerization
studies with these metallocenes are underway.
Exp er im en ta l Section
Ma ter ia ls. Standard Schlenk techniques and a Vacuum
Atmospheres drybox were used in handling air- and moisture-
sensitive compounds. The catalyst precursors bis(cyclopenta-
dienyl)zirconium dichloride, 6, and bis(indenyl)zirconium dichlo-
ride, 5, were supplied by Witco. Bis(indenyl)zirconium dichloride
was sublimed prior to use. rac-Ethylenebis(indenyl)zirconium
dichloride, 4, was supplied by Witco and recrystallized prior
to use. Bis(2-phenylindenyl)zirconium dichloride,44 1, and
(cyclopentadienyl)(2-phenylindenyl)zirconium dichloride,49 2,
were prepared according to literature procedures. Bis(2-
methylindenyl)zirconium dichloride, 7, was prepared analo-
gous to 1 and characterized by comparison to a literature
procedure.50 Polymerization grade ethylene (supplied by Mathe-
son) and toluene were purified by passage through columns
containing Q5 and alumina. Modified methylaluminoxane
(MMAO type 4) was supplied as a toluene solution by Akzo
Nobel and dried under vacuum to remove solvent and residual
trimethylaluminum prior to use. 1-Hexene (97%) was dried
over CaH2, distilled, and degassed prior to use.
Con clu sion s
(2-PhInd)2ZrCl2 shows higher reactivity toward 1-hex-
ene in ethylene/1-hexene copolymerization than the
unbridged metallocenes Ind2ZrCl2 and Cp2ZrCl2 as well
as the bridged rac-EBIZrCl2. Substitution in the 2-posi-
tion of unbridged bis(indenyl)zirconium dichloride com-
plexes, in general, leads to higher comonomer incorpo-
ration as seen by high 1-hexene incorporation with (2-
PhInd)2ZrCl2, (2-MeInd)2ZrCl2, and (2-PhEthInd)2ZrCl2.
The effect of the 2-phenyl substituent appears to be
additive as demonstrated by the lower 1-hexene reactiv-
ity of (Cp)(2-PhInd)ZrCl2. Spacing the phenyl groups
farther from the indene ligand, as in (2-PhEthInd)2ZrCl2,
results in slightly decreased 1-hexene reactivity. These
2-P h en yleth yn ylin d en e. Phenylacetylene (1.86 g, 18.21
mmol) dissolved in diethyl ether (50 mL) was added to a
solution of phenyllithium (1.8 M in cyclohexane-diethyl ether
70:30, 10.12 mL, 18.21 mmol) in diethyl ether (50 mL) at -78
°C. After warming to 22 °C and stirring for 1 h, 2-indanone
(1.92 g, 18.21 mmol) was dissolved in diethyl ether (50 mL)
and added dropwise at -78 °C. The reaction was warmed to
22 °C and stirred overnight. The reaction mixture was
quenched with ice and washed with aqueous NH4Cl. The
aqueous layer was extracted with diethyl ether and dried. The

642 Reybuck et al.
Macromolecules, Vol. 35, No. 3, 2002
Refer en ces a n d Notes
residue was dissolved in toluene (50 mL) and refluxed with
p-toluenesulfonic acid monohydrate (0.35 g, 1.82 mmol) for 4
h. After cooling to 22 °C the reaction was washed twice with
aqueous KHCO3, and the aqueous layer was extracted with
diethyl ether. The combined organics were dried over magne-
sium sulfate, filtered, and concentrated on a solvent evapora-
tor. Recrystallization from methanol gave the pure product.
Yield: 2.75 g (70%). 1H NMR (CDCl3, 400 MHz): δ (ppm) 3.64
(s, 2H), 7.17 (s, 1H), 7.22-7.31 (m, 2H), 7.32-7.37 (m, 3H),
7.41 (d, 1H, J ) 7.4 Hz), 7.45 (d, 1H, J ) 7.3 Hz), 7.51-7.53
(m, 2H). 13C NMR (CDCl3, 100 MHz): δ (ppm) 42.7, 86.7, 94.1,
121.4, 123.3, 123.6, 125.7, 126.8, 127.3, 128.2, 128.3, 131.5,
137.3. 143.0, 144.1.
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1
crystals. Yield: 0.88 g (32%). H NMR (CDCl3, 400 MHz): δ
(ppm) 6.74 (s, 2H), 7.22-7.24 (m, 2H), 7.38-7.41 (m, 3H),
7.48-7.5 (m, 2H), 7.58-7.61 (m, 2H). 13C NMR (CDCl3, 100
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Macromolecules, Vol. 35, No. 3, 2002
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MA011517D