High comonomer selectivity in ethylene/hexene copolymerization by unbridged indenyl metallocenes

Article abstract of DOI:10.1021/ma021075l

Catalysts derived from unbridged 2-arylindene metallocenes of Hf and Zr are active for ethylene/hexene copolymerization and show a much higher selectivity toward hexene than unsubstituted bis(indenyl) metallocenes. The ligand substitution pattern and the

Full text of DOI:10.1021/ma021075l

Macromolecules 2003, 36, 3815-3820
3815
Articles
High Comonomer Selectivity in Ethylene/Hexene Copolymerization by
Unbridged Indenyl Metallocenes
Mich a ela Da n k ova a n d Rober t M. Wa ym ou th *
Chemistry Department, Stanford University, Stanford, California 94305
Received J uly 8, 2002; Revised Manuscript Received March 4, 2003
ABSTRACT: Catalysts derived from unbridged 2-arylindene metallocenes of Hf and Zr are active for
ethylene/hexene copolymerization and show a much higher selectivity toward hexene than unsubstituted
bis(indenyl) metallocenes. The ligand substitution pattern and the nature of the metal ion have a strong
influence on the ability of unbridged 2-arylindenyl metallocenes to incorporate 1-hexene comonomer in
ethylene/hexene copolymerizations. Our data support the hypothesis that arene substituents near the
active site promote the R-olefin coordination and insertion, thereby providing comonomer-rich polyeth-
ylenes. Hafnium-based metallocenes incorporate R-olefins better than their zirconium congeners. The
sterically encumbered bis(3′,5′-di-tert-butyl-2-phenylindenyl)hafnium dichloride incorporates R-olefins with
an ability comparable to the cyclopentadienylamido metallocene {η1:η5-[(tert-butylamido)dimethylsilyl]-
(2,3,4,5-tetramethyl-1-cyclopentadienyl)}titanium dichloride (Me2Si(Me4Cp)tBuNTiCl2).
In tr od u ction
surprisingly effective at incorporating R-olefins and far
superior to unsubstituted bis(indenyl) metallocenes.22,27-29
In this paper, we report the synthesis and copolymer-
ization behavior of a series of 2-arylindene metallocenes
with diverse ligand substitution patterns to study the
influence of the type and the position of the substituents
on the catalysts’ reactivity toward ethylene and 1-
hexene. Reactivity ratios are used as a measure of the
catalysts’ ability to incorporate comonomer2,30 and are
defined as the ratio of the rate constants of the homo-
propagation to the cross-propagation rates (re ) kee/keh,
rh ) khh/khe). The copolymerization behavior of closely
isostructural zirconium and hafnium analogues was
investigated to probe the role of the transition metal
on monomer selectivity.
Polyethylene is one of the world’s largest volume
thermoplastics.1,2 The density of polyethylene, one of the
critical parameters influencing its properties, is con-
trolled by the level and distribution of branching. The
catalytic copolymerization of ethylene with R-olefins is
a typical way of introducing short-chain branching. New
generations of catalysts are leading to new families of
polyethylenes due to the ability of these catalyst systems
to introduce controlled amounts of R-olefins into poly-
ethylene with uniform and homogeneous sequence and
composition distributions. Differences in comonomer
content and distribution can cause significant changes
in the polymer properties, such as differences in melting
and glass transition temperatures, melt viscosity, and
mechanical and optical properties, all of which define
the type and useful range of application of these
materials.3-11 One of the basic parameters governing
the synthesis of well-defined ethylene copolymers is the
kinetic selectivity of the catalyst for ethylene and the
R-olefin. Despite the importance of this parameter, our
understanding of the relationship between the catalyst
structure and its ability to incorporate both monomers
is incomplete. While important advances are being made
both experimentally12-24 and computationally,25,26 it is
still impossible to predict a priori the kinetic selectivity
between ethylene and an R-olefin for a given catalyst
structure or given catalyst/cocatalyst combination. Most
of our understanding is based on empirical correlations
and are largely based on steric concepts, which have
nevertheless proven a useful and powerful guide for
catalyst design.
Resu lts
Five metallocene catalysts were investigated for
their ethylene/1-hexene copolymerization character-
istics: (1-methyl-2-phenylindenyl)(2-phenylindenyl)-
zirconium dichloride (1), bis(4,7-dimethyl-2-phenyl-
indenyl)zirconium dichloride (2), bis(4,7-dimethyl-2-
phenylindenyl)hafnium dichloride (3), bis(3′,5′-di-tert-
butyl-2-phenylindenyl)zirconium dichloride (4), bis-
(3′,5′-di-tert-butyl-2-phenylindenyl)hafnium dichloride
(5), and the known15,31,32 (cyclopentadienyldimethylsilyl-
tert-butylamido)titanium dichloride (6) (Figure 1). All
compounds were prepared according to modified litera-
ture procedures.31,33-35 The 3′,5′-di-tert-butyl-2-phenyl-
indene ligand was synthesized by a slight modification
of the procedure reported by Witte et al.34 Metalation
conditions with hafnium were similar to the conditions
published and used to prepare zirconocene catalysts.28,33,36
As part of our investigations on the polymerization
behavior of unbridged metallocene catalysts, we ob-
served that bis(2-arylindenyl) metallocene catalysts are
Ethylene/1-hexene copolymerizations were carried out
in a 300 mL stainless steel reactor in neat 1-hexene with
10.1021/ma021075l CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/09/2003

3816 Dankova and Waymouth
Macromolecules, Vol. 36, No. 11, 2003
Ta ble 1. Eth ylen e/1-Hexen e Cop olym er iza tion s a t 20 °C in Nea t 1-Hexen e
[M]
(µmol)
E pressure
(psig)
% E in
Mn
polymer
yield (g)
b
metallocene
polymera
(g/mol)b
Mw/Mn
productivityc
1
2
3
4
5
6
2.4
2.0
6.0
0.4
4.0
60
45
120
150
191
211
51
55
51
53
52
52
66 300
45 600
15 100
140 000
22 000
7 700
5.6
3.1
3.4
4.2
2.7
2.8
1.26
0.75
0.35
0.43
0.30
0.41
15 934
11 333
1 170
21 350
1 505
211
10.0
a
Determined by 13C NMR. b Determine by high-temperature gel permeation chromatography using polyethylene standards. c Calculated
as kg of polymer/(mol of Zr h).
Ta ble 2. Rea ctivity Ra tion s for Eth ylen e/1-h exen e Cop olym er iza tion s
a
b
d,e
d,e
f
metallocene
Nexp
Xe/Xh
% E (polymer)c
re
rh
rerh
rh/re (×105)
1
2
3
4
5
6
7
5
5
5
6
3
0.04-0.19
0.05-0.16
0.09-0.28
0.09-0.31
0.26-0.47
0.30-0.32
24-75
44-76
31-59
29-66
45-62
42-56
13 ( 3
19 ( 3
4.5 ( 0.9
7 ( 3
3.2 ( 0.5
4 ( 1
0.091 ( 0.008
0.064 ( 0.006
0.16 ( 0.01
0.18 ( 0.04
0.25 ( 0.03
0.4 ( 0.1
1.2 ( 0.3
1.2 ( 0.2
0.7 ( 0.1
1.2 ( 0.5
0.8 ( 0.2
1.5 ( 0.6
700
337
3555
2571
7812
10000
a
b
Number of experiments used to determine the average reactivity ratios. Range of the ratios of mole fractions of ethylene and 1-hexene
in the monomer feed. c Range of the 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. e Standard deviation calculated as [(1/(N - 1))∑(re,h(exp) - re,h(opt))2]1/2 f Standard
.
deviation calculated as [(σrerh)2 + (σrhre)2]1/2
Ta ble 3. Selected Str u ctu r a l P a r a m eter s for Com p a r ison betw een Zir con ocen e a n d Ha fn ocen e Ca ta lystsa
.
catalyst
Cen-M (av), Å
Cen-M-Cenb (av), deg
M-Cl (av), Å
Cl-M-Clc (av), deg
reference
Cp2ZrCl2
Cp2HfCl2
Ind2ZrCl2
(2PhInd)2ZrCl2 syn (meso)
(2PhInd)2HfCl2 syn (meso)
(2PhInd)2ZrCl2 anti (rac)
(2PhInd)2HfCl2 anti (rac)
2
3
2.198
2.182
2.230
2.237
2.222
2.242
2.225
2.248
2.227
129.38
129.14
128.27
131.19
131.41
131.54
131.89
132.15
132.53
2.448
2.424
2.440
2.427
2.405
2.424
2.403
2.431
2.402
96.97
96.18
94.74
94.39
94.02
95.44
95.07
96.12
96.12
52, 53
53
52
41
54
41
54
35
35
a
Literature data obtained as .cif file from Cambridge Structural Database. All bond lengths and angles calculated using crystallographic
tool Platon (shareware available online). Cp centroid-metal-Cp centroid angle. c Chloride-metal-chloride angle.
b
similar monomer feeds (e.g., Xe/Xh ) 0.092; 0.148-0.163,
see Table 4) than 3′,5′-di-tert-butylphenyl-substituted
catalysts. The zirconocenes are more productive than
the hafnocenes and yield higher molecular weights at
20 °C.17,39 The low productivity of 6 is due to the low
polymerization temperatures of 20 °C employedsthis
catalyst is typically utilized at higher temperatures
(160 °C)1,3 but was run under similar conditions for
comparison.
The reactivity ratios reported in Table 2 provide an
indication of the kinetic selectivities of these catalysts.
All of the metallocenes incorporate hexene reasonably
well with re’s ranging from 3.2 to 19 and rh’s from 0.064
to 0.25. These values were determined using the first-
order Markov model and are optimized over the full
F igu r e 1. Structures of catalyst precursors studied.
range of feed ratios using Microsoft Excel Solver opti-
an overpressure of ethylene. Conversion of 1-hexene was
kept below 5% to ensure a constant comonomer feed
throughout the polymerization; polymer yields were
mization.27 The ratio rh/re provides a crude measure of
the selectivity of the various catalysts to incorporate
hexene (Table 2). These ratios show that both the ligand
kept below 3 g to avoid mass transfer limitations.37
substitution pattern and the nature of the metal ion
Copolymerizations were carried out over a variety of
influence the selectivity toward 1-hexene. The 3′,5′-di-
comonomer feed ratios to obtain copolymers with a wide
range of ethylene incorporation.38
tert-butylphenyl-substituted catalyst 4 incorporates hex-
ene more readily than the 4,7-dimethyl-substituted
complex 2 or the 1-methyl-substituted complex 1. For
comparable ligand environments, the hafnocene cata-
lysts 3 and 5 show a significantly higher selectivity for
hexene than the zirconocenes 2 and 4, and the un-
bridged metallocene 5 is comparable to 6 in its ability
to incorporate hexene.
The productivities of copolymerizations are reported
in Tables 1 and 4. All metallocene catalysts are active
ethylene/1-hexene copolymerization catalysts with simi-
lar productivities, suggesting that at no point do the
substituents interfere with the ability to coordinate
and insert monomer. The 4,7-dimethyl- and 1-methyl-
substituted metallocenes show higher productivities at

Macromolecules, Vol. 36, No. 11, 2003
Ethylene/Hexene Copolymerization 3817
Ta ble 4. Eth ylen e/1-Hexen e Cop olym er iza tion s w ith th e Meta llocen e/MAO System
Ea
(psig)
T b
(°C)
[M]c
polymer
yield (g)
% E in
productivity f
d
entry
metallocene
(×10-6
)
Xe/Xh
polymere
(×103)
1
2
3
4
5
6
(1-Me,2-PhInd)(2PhInd)ZrCl2 (1)
15
31
45
60
80
100
130
30
45
60
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
0
9
9
9
6
9
6
5
5
5
5
5
1
20
20
15
15
15
2.5
1
0.37
0.79
1.25
1.26
1.93
2.02
1.36
0.43
0.75
1.01
1.90
0.49
0.39
0.40
0.35
0.76
0.75
0.23
0.18
0.43
0.73
1.56
1.41
0.30
0.85
0.27
0.61
0.51
0.51
0.41
0.70
0.035
0.054
0.072
0.092
0.119
0.148
0.195
0.053
0.072
0.092
0.112
0.163
0.093
0.135
0.179
0.228
0.281
0.093
0.148
0.228
0.262
0.315
0.262
0.301
0.341
0.353
0.410
0.469
0.301
0.341
0.323
23.8
35.3
42.6
50.9
61.0
64.0
74.8
43.8
55.0
60.0
67.7
75.7
30.7
40.4
51.3
54.7
59.0
29.0
39.5
53.3
66.2
71
44.5
52.2
57.3
52.2
57.2
61.9
42.1
51.9
56.3
3.1
6.6
10.5
15.9
16.2
25.5
13.6
6.5
11.3
15.3
28.8
36.8
1.0
7g,h
8
9
bis(4,7- Me2-PhInd)ZrCl2 (2)
bis(4,7- Me2-PhInd)HfCl2 (3)
bis(2-(3′,5′-ditBuPhInd))ZrCl2 (4)
bis(2-(3′,5′-ditBuPhInd))HfCl2 (5)
10
11
12
13
14
15
16
17
18
19
20g
21h
22h
23
24
25
26
27
28
29
30
31h
75
110
61
91
1.0
1.2
2.5
2.5
120
150
180
61
7.0
100
150
170
200
170
191
211
170
191
211
191
211
200
13.6
21.4
15.3
23.7
2.8
1.5
1.7
0.5
1.2
1.0
1.6
1.2
4.2
1
5
5
25
10
25
25
25
25
25
25
12.5
0
0
20
20
20
6
a
b
Pressure of ethylene during the polymerization. Temperature during polymerization. c Catalyst’s concentration in the polymerization
media. Monomer feed ratio (mole fraction of E/mole fraction of H). e Determined by 13C NMR. f Productivity ) kg of polymer/(mol of
catalyst h). Polymerizations run for 30 min. MMAO of a different batch was used.
d
g
h
reveals that steric effects are insufficient to predict
copolymerization behavior.
Discu ssion
Among the zirconocene catalysts studied, all show
productivities between 3000 to 37 000 kg of polymer/
(mol of Zr h). While metallocenes 1, 2, and 4 are less
productive than catalysts derived from bis(2-phenylin-
denyl)zirconocene dichloride (12 000-93 000 kg of poly-
mer/(mol of Zr h)),27,43 it is clear that their bulky alkyl
substituents do not inhibit R-olefin insertion. The ligand
environment can be used to tune the catalysts’ activities
as evidenced by the fact that 4,7-dimethyl substituents
increase the productivities while 3′,5′-di-tert-butyl sub-
stituents cause a drop in activity.16,44
In an effort to develop understanding of copolymeri-
zation characteristics of homogeneous metallocene cata-
lysts and of the factors influencing the polymer micro-
structure in metallocene-catalyzed copolymerization, it
is critical to address the relationship between metal-
locene structure with its ability to incorporate mono-
mers. Such fundamental structure-function relation-
ship studies are focused toward better understanding
of the combination of the parameters contributing to the
polymerization and copolymerization behavior of these
homogeneous systems.16,18,20,21,38,40,41 We aimed our cur-
rent efforts at understanding the monomer kinetic
selectivities of a series of unbridged arylindenyl-based
metallocene systems as we see these catalysts being
excellent candidates for production of new generation
of polyethylene copolymers with novel properties.27,28
Early encouraging results from our group suggested
that not only are arylindenyl metallocenes active cata-
lysts for copolymerization of ethylene with higher R-ole-
fins, they also show a unexpected tendency to incorpo-
rate high amounts of comonomer when compared to
known cyclopentadienyl or indenyl systems.27,28,33 Most
of the correlations from the literature reports imply that
high comonomer incorporation relies on an open coor-
dination geometry where bulkier comonomer can easily
coordinate and subsequently insert. As such, bridged
metallocenes when compared to unbridged analogues
typically show a significantly lower re, which corre-
sponds to higher comonomer incorporation under iden-
tical conditions.1 However, recent evidence12,27,28,35,42
The hafnocene analogues 3 and 5 are significantly less
productive and yield lower molecular weights at 20 °C
than the zirconocenes.17,23,39,45 The lower productivities43
might be rationalized by the higher hafnium-carbon
(Hf-C) bond strengths. Despite the hafnocene’s low
productivity, they exhibit a higher selectivity for incor-
poration of R-olefins (Table 2). The lower molecular
weights of the hafnium congeners may be related to this
behavior if chain transfer to hexene is more facile for
hafnium; further studies would be required to test this
hypothesis. The reactivity ratio rh more than doubles
going from 2 to 3 (0.064 vs 0.16); for 3 re drops to a
quarter of the value obtained with 2 (4.5 vs 19). Less
drastic changes are noticed when comparing metal-
locenes 4 and 5: the already low re of 4 drops by ∼50%
(7 (4) vs 3.2 (5)) (Table 2). Kaminsky and Koivumaki17,39
have also observed that hafnocenes show higher comono-
mer incorporation relative to zirconocenes. Given the
fact that hafnium and zirconium catalysts of known

3818 Dankova and Waymouth
Macromolecules, Vol. 36, No. 11, 2003
structure are practically identical structurally (see Table
3), it is difficult to invoke steric arguments to interpret
these differences. The higher selectivity of the hafnocenes
toward 1-hexene insertion may be due to either some
subtle electronic influence of the metal or the metal’s
interaction with the cocatalyst counterion.40,44
independent data on the copolymerization behavior of
well-defined conformationally locked metallocenes as
well as a better understanding on the influence of
counterions on copolymerization behavior. Studies along
these lines are ongoing in our laboratories.
Con clu sion
The open coordination gap of constrained geometry
catalyst 6 has been proposed as the origin of these
catalysts’ ability to incorporate a high amount of
comonomer.19,31 For this reason, the selection of ansa-
metallocenes with large coordination gap apertures has
proven a useful guiding principle for incorporating high
amounts of R-olefin comonomer.22,29 However, as our
results distinctly show, appropriately substituted un-
bridged metallocenes can exhibit comonomer selectivi-
ties competitive with some of the best ansa-metallocenes
(Table 2). The origin of these high comonomer selectivi-
ties remains obscure, but it appears that highly conju-
gated metallocenes, such as those containing fluorenyl
ligands,46,47 or those substituted with aryl substituents
near the coordination gap are particularly adept at
comonomer incorporation.27 The conjugation with the
ligand framework may not necessarily be responsible
for the observed “arene effect” as in most cases the
phenyl substituents are tilted away from the plane of
the indenyl portion of the ligand, evidenced by the X-ray
structure of catalysts 1,33 2, and 3.35
Unbridged 2-arylindene metallocenes can exhibit very
high incorporations of 1-hexene into ethylene/hexene
copolymers. Hafnocenes incorporate 1-hexene better
than zirconocenes, and metallocenes derived from the
bis(3′,5′-di-tert-butyl-2-phenylindenyl)HfCl2 metallocene
incorporate 1-hexene as well as the CpA ansa-metal-
locenes 6, which are utilized commercially. While the
precise origin of these high R-olefin selectivities is
unknown, it is clear that simple structural arguments
are insufficient to predict high comonomer selectivity
in ethylene/R-olefin copolymerization reactions.
Exp er im en ta l Section
Gen er a l Con sid er a tion . All organometallic reactions were
conducted using standard Schlenk and drybox techniques.
Elemental analyses were performed by E&R Microanalytical
Laboratory. Diethyl ether and tetrahydrofuran (THF) were
distilled from sodium/benzophenone ketyl. 1-Hexene, methyl-
ene chloride, and pentane were distilled from calcium hydride
prior to use. Toluene was passed through two purification
columns packed with activated alumina and supported copper
catalyst and collected under argon. Chloroform-d was vacuum-
transferred from calcium hydride. Benzene-d6 was vacuum-
transferred from sodium benzophenone. Magnesium powder,
R,R′-dichloro-o-xylene, and 3,5-di-tert-butylbenzoic acid were
purchased from Aldrich. Zirconium tetrachloride (ZrCl4) was
purchased from Fluka, and hafnium tetrachloride was pur-
chased from Cerac Inc. Modified methylaluminoxane type 4
(MMAO-4)) was purchased from AkzoNobel as a solution in
toluene. It was dried under vacuum and used in its powder
form in polymerizations. NMR spectra were recorded on a
Varian Gemini 400 MHz and a Varian UI 300 MHz. 3-Methyl-
2-phenylindene, (1-methyl-2-phenylindenyl)(2-phenylindenyl)-
zirconium dichloride (1),50 and {η1:η5-[(tert-butylamido)dimeth-
ylsilyl](2,3,4,5-tetramethyl-1-cyclopentadienyl)}titanium di-
chloride (6) were prepared according to literature procedures.
P r ep a r a tion of 3,5-Di-ter t-bu tylm eth ylben zoa te. 3,5-
Di-tert-butylbenzoic acid (10.7 mmol) was dissolved in 25 mL
of methanol. The reaction flask was cooled in an ice bath under
nitrogen and thionyl chloride (16.05 mmol) was added. The
reaction was stirred at room temperature under a nitrogen
atmosphere overnight. All solvent was removed by vacuum to
For the unbridged 2-arylindenyl metallocenes, both
the nature and the position of substituents influence the
ability to incorporate hexene. Introduction of methyl
substituents at one of the 1-indenyl positions or at both
4,7-positions results in a modest drop in the hexene
selectivity relative to bis(2-phenylindenyl)ZrCl2 (7) (re
) 8, rh ) 0.09,), but 1 and 2 are still comparable or
slightly better than the prototypical ansa-metallocene
ethylenebis(indenyl)ZrCl2 (re ) 14, rh ) 0.03).27 Intro-
duction of sterically demanding tert-butyl substituents
at the 3′,5′-positions of the 2-aryl results in an ap-
proximately 2-fold increase in the selectivity toward
1-hexene 4 (rh/re (×105) ) 2571) relative to bis(2-
phenylindenyl)ZrCl2 (rh/re (×105) ) 1100).27 Because of
this effect and the greater incorporating abilities of the
hafnium congeners, the unbridged hafnocene 5 exhibits
outstanding selectivity for incorporating 1-hexene, com-
parable to that of 6.
As we have previously discussed, the conformational
dynamics of unbridged metallocenes27 and the possible
role of counterions48 add additional levels of complexity
to the interpretation of the very high comonomer
selectivities of metallocenes 1-5. One very important
and fairly unexplored factor is the anion interaction
with the cationic metal center.49 From a purely struc-
tural standpoint, it would appear that the slightly larger
Cen-M-Cen angles of the unbridged 2-arylindene
ligands would if anything suggest that these metal-
locenes should be less able to incorporate R-olefins than
the unsubstituted bis(cyclopentadienyl) and bis(indenyl)
metallocenes (Table 3). A sterically crowded metal
center that is shielded by virtue of its substituents from
close contact with the bulky and ill-defined MAO
counterion might allow for an easier approach of the
R-olefin. In addition, it is possible that for unbridged
metallocenes the role of substituents is to influence the
conformational dynamics to yield higher populations of
conformational states that are better able to incorporate
R-olefins. At this time, it is impossible to assess the
relative importance of these factors in the absence of
1
yield a white solid, pure by H NMR. Yield: 98%.
Syn th esis of 3′,5′-Di-ter t-bu tyl-2-ph en ylin den e. A slightly
modified literature procedure was followed.34 Magnesium
powder (50 mesh, 1.167 g, 48.00 mmol) was dried in a 500 mL
three-necked, round-bottomed flask equipped with a pressure-
equalizing addition funnel by heating to 120 °C under vacuum
(10-20 mTorr) overnight. After the mixture was cooled to room
temperature, the apparatus was repressurized with argon.
THF (10 mL) and 0.25 mL (3.00 mmol) of 1,2-dibromoethane
were added, and the mixture was heated with a heat gun. The
heating was stopped 1 min after gas evolution occurred. All
volatiles were removed in vacuo. After the apparatus was
purged with argon, 10 mL of THF was added, and 2.3 g (12.00
mmol) of R,R′-dichloro-o-xylene (purified by Kugelrohr distil-
lation prior to use) was dissolved in 125 mL of THF in the
addition funnel while the apparatus was purged with argon.
The solution in the addition funnel was added dropwise over
a period of 3-4 h, and the reaction mixture was stirred
vigorously for 15 h at room temperature. The magnesium was
filtered off using a Schlenk frit under argon to yield a pale
green solution. The receiving flask was equipped with a
pressure-equalizing addition funnel, and the apparatus was
purged with a vigorous argon flow for 15 min. The 3,5-di-tert-

Macromolecules, Vol. 36, No. 11, 2003
Ethylene/Hexene Copolymerization 3819
butylmethylbenzoate (1.99 g, 8 mmol) was dissolved in 65 mL
of THF in the addition funnel and added to the di-Grignard
solution at -78 °C over approximately 60 min, with the
temperature consistently maintained below -70 °C during the
addition. The reaction mixture was warmed to room temper-
ature over 3-4 h, cooled again to 0 °C, and quenched by slow
addition of 15-20 mL of distilled water. After the reaction
mixture was warmed to room temperature, the THF was
removed, and the remaining suspension was acidified to pH 1
and extracted with diethyl ether. The combined organic layers
were dried over magnesium sulfate, and all solvent was
removed by a rotavap. 0.300 g (1.57 mmol) of p-toluenesulfonic
acid hydrate and 100 mL of toluene were added, and the
mixture was refluxed for 2 h. The toluene was washed with
water, and subsequently, the water layer was extracted with
diethyl ether. All organic layers were combined and dried with
magnesium sulfate, and solvents were removed by a rotavap.
The crude productsdark brown/orange oilswas transferred
to silica gel and purified by flash chromatography with pentane
to give an off-white solid in 47% yield. The 1H and 13C NMR
were identical to that previously reported.51
was then quenched by injection of MeOH (20 mL), and the
reactor was slowly vented and opened. The polymer was
precipitated in acidified MeOH (5% HCl), filtered, washed with
MeOH, and dried in a vacuum oven at 40 °C to a constant
weight.
P olym er Ch a r a cter iza tion . Polymer molecular weights
and molecular weight distributions were determined by high-
temperature gel permeation chromatography using polyeth-
ylene for GPC calibration. A Varian UI 300 spectrometer was
used to perform 13C NMR measurements. Copolymer samples
were prepared by dissolving 100-200 mg of each copolymer
in 3 mL of o-dichlorobenzene/10 vol % benzene-d6 with addition
of paramagnetic “relaxation agent” chromium acetylacetonate,
Cr(acac)3, into a 10 mm tube. The spectra were measured at
100 °C using acquisition times ) 1 s, additional delays ) 5 s,
and gated proton decoupling.
Ack n ow led gm en t. We acknowledge BP for finan-
cial support and for high-temperature GPC analysis.
M.D. is the recipient of the Roche Bioscience Fellowship,
for which she is grateful.
Syn th esis of Bis(3′,5′-d i-ter t-bu tyl-2-p h en ylin d en yl)-
zir con iu m (Ha fn iu m ) Dich lor id e. The ligand (2.3 mmol)
was dissolved in 80-100 mL of diethyl ether. The solution was
cooled to -78 °C, and 0.95 mL (2.38 mmol) of n-butyllithium
(2.5 M in hexanes) was added via a syringe dropwise. The
cooling bath was removed, and the mixture was stirred at
ambient temperature for 2 h. Zirconium (hafnium) tetrachlo-
ride (1.16 mmol) was weighed into another Schlenk flask and
suspended in 80 mL of pentane. Both the ligand solution and
the metal slurry were cooled to -78 °C, and the ligand solution
was added via a cannula to the metal salt suspension. The
solution was allowed to stirr overnight at room temperature
to form a dark yellow suspension. All volatiles were then
removed in vacuo, and 50 mL of methylene chloride was added.
The suspension was filtered over Celite through a Schlenk frit
under argon to obtain a light yellow clear solution. The Celite
was washed with methylene chloride until the filtered liquid
remained colorless. All solvent was removed in vacuo, and the
remaining solid was washed twice with diethyl ether to afford
bis(3′,5′-di-tert-butyl-2-phenylindenyl)zirconium dichloride as
a yellow solid in 10% yield. Elemental analysis: % C 71.84
calcd, 71.79 found; % H 7.08 calcd, 7.10 found. The 1H NMR
and 13C NMR spectra were as previously reported.51 Bis(3′,5′-
di-tert-butyl-2-phenylindenyl)hafnium dichloride: Yield: yel-
low solid, 30%. Elemental analysis: % C 59.35 calcd, 59.08
found. % H 4.40 calcd, 4.54 found. 1H NMR (300 MHz,
CDCl3): δ (ppm) 7.58 ppm (2H, d), 7.55 ppm (1H, t), 6.98 (2H,
dd), 6.70 ppm (2H, dd), 6.67 (2H, s), 1.48 ppm (18H, s). 13C
NMR (75 MHz, CDCl3): δ (ppm) 31.78, 35.34, 103.46, 121.65,
122.98, 124.59, 125.38, 127.10, 128.61, 131.64, 151.83.
Syn th esis of Bis(4,7-d im eth yl-2-p h en yln d en yl)zir co-
n iu m (Ha fn iu m ) Dich lor id e. Full synthesis, characteriza-
tion, and X-ray structure details will be reported in an
upcoming publication.35
Eth ylen e/1-Hexen e Cop olym er iza tion . The reactor was
flushed 3-4 times with ethylene. In a nitrogen drybox, 130
mg of MAO was suspended and stirred in 35 mL of 1-hexene.
An injector was charged with the 1-hexene/MAO mixture, and
the solution was injected into the reactor under ethylene
pressure. The reaction mixture was cooled to the reaction
temperature and overpressurized with ethylene to a certain
total pressure. This monomer mixture (1-hexene, MAO, eth-
ylene) was equilibrated at the reaction temperature under
constant ethylene pressure for at least 20 min. Catalyst stock
solution in toluene was prepared in a drybox. The appropriate
volume of catalyst solution (less than 1 mL) was diluted with
1-hexene to a total volume of 5 mL, added into a 10 mL
injector, and injected into the reactor under ethylene pressure.
Please note that, immediately prior to catalyst injection, the
ethylene line was disconnected and the reactor was vented by
5 psi to provide the pressure differential and allow catalyst
solution to flow into the reactor. The ethylene hose was
reconnected directly after the catalysts injection. The reaction
was run for 20 min at constant pressure and temperature; it
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MA021075L