Sterically expanded CGC catalysts: Substituent effects on ethylene and α-olefin polymerization

Article abstract of DOI:10.1039/c3dt50163a

Several analogues of the sterically expanded constrained geometry catalyst Me₂Si(η¹-C₂₉H₃₆) (η¹-N-tBu)ZrCl₂·OEt₂ (2) were synthesized to assess the effect on branching and molecular weight for ethylene homopolymerization. Catalysts based on tetramethyltetrahydrobenzofluorene (TetH), ethylTetH, t-butylTetH, and octamethyloctahydrodibenzofluorenyl (OctH) bearing a diphenylsilyl bridge were prepared and characterized: Me ₂Si(η⁵-C₂₁H₂₂) (η¹-N-tBu)ZrCl₂ (3); Me₂Si(η ⁵-C₂₃H₂₆)(η¹-N-tBu)ZrCl ₂ (4); and Me₂Si(η⁵-C₂₅H ₃₀)(η¹-N-tBu)ZrCl₂ (5); Me ₂Si(η⁵-C₂₁H₂₂) (η¹-N-tBu)ZrMe₂ (6); and Ph₂Si(η ⁵-C₂₉H₃₆)(η¹-N-tBu)ZrCl ₂ (7). Complexes 4, 5, 6, and 7 were characterized by X-ray crystallography and displayed η⁵ hapticity to the carbon ring in each case, in contrast to 2. In comparison to 2, complexes 3, 4, 5, and 7 (in combination with methylaluminoxane = MAO) showed diminished branching, higher molecular weight, and higher polydispersity indices for obtained ethylene homopolymers. While 4/MAO produced the greatest molecular weight polymers, no branching was observed. Reactivity ratios were determined for the copolymerization of ethylene and 1-decene with 2/MAO. A value of r _ethylene = 14.9 and an exceedingly high value of r_1-decene = 0.49 were found - in line with previous reports of this catalyst's unusual affinity for α-olefins.

Full text of DOI:10.1039/c3dt50163a

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Sterically expanded CGC catalysts: substituent effects
on ethylene and α-olefin polymerization†
Cite this: Dalton Trans., 2013, 42, 9139
Jianfang Chai, Khalil A. Abboud and Stephen A. Miller*
Several analogues of the sterically expanded constrained geometry catalyst Me2Si(η1-C29H36)(η1-N-tBu)-
ZrCl2·OEt2 (2) were synthesized to assess the effect on branching and molecular weight for ethylene
homopolymerization. Catalysts based on tetramethyltetrahydrobenzofluorene (TetH), ethylTetH, t-butyl-
TetH, and octamethyloctahydrodibenzofluorenyl (OctH) bearing a diphenylsilyl bridge were prepared
and characterized: Me2Si(η5-C21H22)(η1-N-tBu)ZrCl2 (3); Me2Si(η5-C23H26)(η1-N-tBu)ZrCl2 (4); and Me2Si-
(η5-C25H30)(η1-N-tBu)ZrCl2 (5); Me2Si(η5-C21H22)(η1-N-tBu)ZrMe2 (6); and Ph2Si(η5-C29H36)(η1-N-tBu)ZrCl2
(7). Complexes 4, 5, 6, and 7 were characterized by X-ray crystallography and displayed η5 hapticity to the
carbon ring in each case, in contrast to 2. In comparison to 2, complexes 3, 4, 5, and 7 (in combination
with methylaluminoxane = MAO) showed diminished branching, higher molecular weight, and higher
polydispersity indices for obtained ethylene homopolymers. While 4/MAO produced the greatest mole-
cular weight polymers, no branching was observed. Reactivity ratios were determined for the copoly-
merization of ethylene and 1-decene with 2/MAO. A value of rethylene = 14.9 and an exceedingly high
value of r1-decene = 0.49 were found—in line with previous reports of this catalyst’s unusual affinity for
α-olefins.
Received 16th January 2013,
Accepted 1st March 2013
DOI: 10.1039/c3dt50163a
www.rsc.org/dalton
environmental interest. Additionally, ethylene can be obtained
from biorenewable ethanol relatively easily and inexpensively.4
Introduction
Low density polyethylene (LDPE) and linear low density poly-
Recently, we reported that highly branched polyethylene
ethylene (LLDPE) are important classes of materials and have can be obtained from ethylene alone catalyzed by a sterically
been widely used for manufacturing various commercial expanded zirconium complex Me2Si(η1-C29H36)(η1-N-tBu)-
goods, including: containers, dispensing bottles, wash bottles, ZrCl2·OEt2 (2, Fig. 1) combined with methylaluminoxane
piping and tubing, wire and cable insulation, and plastic (MAO).2a Compound 2 is a CGC type catalyst, but exhibits an
bags.1 LDPE and LLDPE are often desirable compared to unusual η1-ligation to the carbon-based five-membered ring.
HDPE because of their unique processing properties related to The 2/MAO system is capable of producing over fifty long
their low melting temperatures, smaller crystallite size, and branches per 1000 carbon atoms along with two to eight ethyl
lower melt viscosities.1,2 However, the high temperature and branches per 1000 carbon atoms and minimal branches of
high pressure free radical process used to produce LDPE com- other lengths.
mercially is energy intensive.
Interestingly, 2/MAO is found to be more active toward
More recently, LLDPE has been achieved by the copolymeri- α-olefins than it is toward ethylene, greatly exceeding the
zation of α-olefins with ethylene catalyzed by early transition activity of the Dow-Exxon CGC for α-olefin homopolymeriza-
metal complexes, exemplified by the Dow-Exxon titanium Con- tions and certain copolymerizations.5 This proclivity toward
strained Geometry Catalyst (CGC, 1, Fig. 1).3 However, the puri- α-olefins explains the high degree of branching. Some long
fied olefinic comonomers (typically 1-hexene or 1-octene) are
much more expensive than ethylene. Therefore, a method for
obtaining branched polyethylene under relatively mild con-
ditions from a pure ethylene feed is of great commercial and
The George and Josephine Butler Laboratory for Polymer Research, Department of
Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA.
E-mail: miller@chem.ufl.edu; Fax: +1-352-392-9741; Tel: +1-352-392-7773
†CCDC 919740 (4), 919741 (5), 919742 (6), and 919743 (7). For crystallographic
Fig. 1 The Dow-Exxon constrained geometry catalyst (CGC) (1) and a sterically
expanded zirconium analogue (2).
data in CIF or other electronic format see DOI: 10.1039/c3dt50163a
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chain α-olefin macromonomers are produced in situ via
β-hydride transfer to monomer and then are incorporated into
the main chain because of the high activity of 2/MAO toward
α-olefins. The unusual affinity of this catalytic system for
α-olefins relative to ethylene is not only related to the obvious
steric features of the large octamethyloctahydrodibenzofluore-
nyl (OctH) ligand, but also the electron richness of the ligand.6
The pKa of OctH is 3.9 units greater than that of fluorene. The
four tertiary alkyl groups are responsible for the unusual steric
and electronic properties. One interpretation is that the elec-
tron richness of the Oct ligand allows the ring slip to η1 hapti-
city and this slippage allows more steric accommodation at the
metal site. Unfortunately 2/MAO generally results in low mole-
cular weight polyethylene. Hence, we pursued catalyst re-
engineering that might sacrifice some branching in exchange
for less likely termination events and higher polyethylene mole-
cular weight. This pursuit focused on the substituents of the
Oct ligand, which should modify both the steric and electronic
properties of the catalyst. The substituent effects of t-butyl
groups on the fluorenyl ligand in propylene polymerization
have been investigated.7 The introduction of t-butyl groups on
the fluorenyl ligand improve the catalyst activity regardless of
location in the 2, 7 or 3, 6 positions. In the case of 2, all 2, 3, 6
and 7 positions are occupied by tertiary alkyl groups. Thus,
some branch density might be traded for increased polymer
molecular weight if substituents are not employed at the 2, 3,
6, or 7 positions. Herein, we report several ligand modification
strategies, synthesis and characterization of zirconium com-
pounds, as well as the catalytic behavior toward ethylene
polymerization of the new catalytic systems.
Scheme 1 Synthetic route and conditions to modified fluorenyl ligands. Reac-
tion conditions: (a) acetic anhydride, AlCl3, MeNO2, 0 °C; (b) Pd, acetic acid,
40 psi H2; (c) 2,5-dimethyl-2,5-dichlorohexane, AlCl3, MeNO2; (d) 2,5-dimethyl-
2,5-dichlorohexane, AlCl3, MeNO2; (e) acetic anhydride, AlCl3, 1 : 1 MeNO2
:
ClCH2CH2Cl, 0 °C; (f) AlMe3, toluene, reflux 16 h.
Scheme 2 Synthetic routes to complexes 3, 4, 5, 6, and 7. Reaction conditions:
(a) (1) n-BuLi, (2) excess Me2SiCl2 or Ph2SiCl2; (b) Me3CNHLi; (c) (1) 2 n-BuLi, (2)
ZrCl4; (d) 2 MeLi.
Results and discussion
Modification of the fluorene ligand
Three modified fluorenes were prepared: 1,1,4,4-tetramethyl-
1,2,3,4-tetrahydrobenzo[b]fluorene (TetH); 1,1,4,4-tetramethyl-
7-ethyl-1,2,3,4-tetrahydrobenzo[b]fluorene (ethylTetH), and
1,1,4,4-tetramethyl-7-t-butyl-1,2,3,4-tetrahydrobenzo[b]fluorene
(t-butylTetH). The preparation of TetH mostly followed the
literature method, making sure to employ an excess of fluorene
during alkylation.8 The ethylTetH ligand was prepared from
2-ethylfluorene9 and 2,5-dimethyl-2,5-dichlorohexane. The
t-butylTetH ligand was prepared by acylation of TetH with
acetic anhydride followed by treatment with AlMe3 to install
the t-butyl group (Scheme 1).
readily obtained by addition of 2 equivalents of MeLi to 3 in
diethyl ether. The expanded bridge complex Ph2Si(η5-C29H36)-
(η1-N-tBu)ZrCl2 (7) was prepared with a procedure similar to
that of 2 except Ph2SiCl2 was used instead of Me2SiCl2.5 Two
1
signals were observed in the H NMR and 13C NMR spectra of
complexes 3, 4, 5, and 6 for the two silicon bridge methyl
groups because they lack an internal mirror plane of sym-
metry. In addition, no coordinated diethyl ether was observed
in the NMR spectra of 3–7, which all exhibit η5-fluorenyl
coordination (vide infra), in stark contrast to the η1-fluorenyl
coordination of 2.
Complex synthesis and characterization
The zirconium complexes Me2Si(η5-C21H22)(η1-N-tBu)ZrCl2 (3),
X-ray crystallography of 4, 5, 6, and 7
Me2Si(η5-C23H26)(η1-N-tBu)ZrCl2 (4), and Me2Si(η5-C25H30)-
(η1-N-tBu)ZrCl2 (5) were prepared from the corresponding Compounds 4, 5, 6, and 7 have been characterized by X-ray
ligand and characterized. The syntheses of the compounds are crystallography (Fig. 2, Table 1). Single crystals suitable for
similar and require no isolation or purification of any inter- X-ray crystallography were obtained by cooling saturated heptane
mediates (Scheme 2). The compounds were prepared as yellow solutions in a glove box freezer. These species were treated
powders in approximately 20% isolated yield from the corres- with petroleum ether—not diethyl ether—during workup and
ponding ligands. Me2Si(η5-C21H22)(η1-N-tBu)ZrMe2 (6) is thus, they indicate no coordinated ether in the solid state
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Table 1 Selected bond lengths (Å) and angles (°) for 4, 5, 6, and 7
4
5
6
7
M–C(1)
M–Cring
M–Cring
M–Cring
M–Cring
M–N
2.370(2)
2.496(2)
2.519(2)
2.633(2)
2.635(2)
2.3862(18) 2.3997(13) 2.372(6)
2.4803(18) 2.5059(13) 2.447(6)
2.5181(18) 2.5425(13) 2.532(7)
2.5977(18) 2.6647(13) 2.601(7)
2.6193(17) 2.6687(13) 2.627(7)
2.0376(19) 2.0346(15) 2.0609(11) 2.052(4)
2.4029(7)
2.3975(7)
M–X(1)
M–X(2)
2.3935(6)
2.3969(5)
154.82
2.2549(14) 2.3845(10)
2.2681(14) 2.3926(17)
Centroida-C(1)–Si 156.01
155.8
154.25
Si–N–M
X–M–X
103.82(9)
105.03(2)
104.53(7)
104.26(2)
103.94(5)
105.35(5)
102.7(3)
104.65(5)
a Centroid is defined as the centroid of the five-membered ligand ring.
from 2.37 Å to 2.67 Å—demonstrating η5 coordination in these
compounds instead of the η1 coordination observed in 2 and
its Hf analogue.10 Similarly, Oct-bearing titanium dimethyl
compounds show two different hapticities, depending on
whether coordinated THF is present (η1) or absent (η3).11 In
compounds 4–7, the metal center is of pseudotetrahedral geo-
metry. The Ccentroid–C(1)–Si angles are less than 180°, which is
in the normal range of those for η5 CGC complexes (152°–164°)
and much smaller than those for η1 complexes (198°–205°).10
Hapticity analysis of 4, 5, 6, and 7 by X-ray crystallography
There are three hapticities observed with fluorenyl ligands: η1,
η3 and η5—with η5 being the most common.10,12 Sometimes
the assignment of hapticity can be arbitrary,13 but the dis-
tances (2.37–2.67 Å) between the Zr metal and C atoms
support the conclusion that 4–7 are η5. In some η1 and η3 com-
plexes, the ‘non-bonded’ Zr–C distances are above 2.73 Å.10,14
For example, the bonded Zr–C distance is 2.30 Å in (η1) 2, but
there are non-bonded Zr–C distances of 2.73, 3.27, 3.73 and
4.00 Å.
An alternative method for assessing hapticity is via analysis
of the carbon–carbon bond lengths of the five-membered ring.
The parameter δ has been defined as the average difference
between the two short and two long bonds of the fluorenyl
ligand: δ = (a + e − b − d)/2 (Fig. 3). A large value of δ is
expected for the free ligand and has been measured as δ =
0.114 Å for octamethyloctahydrodibenzofluorene.10 The value
of δ approaches zero as the bonds become more uniform in
length and the hapticity increases; for example, a value of δ =
0.000 has been measured for Me2C(η5-C5H4)(η5-C13H8)ZrCl2.10
Fig. 2 X-ray structures of 4–7 with 50% probability ellipsoids. Deposited at the
CCDC 919740–919743.
(unlike 2), which was also consistent with the NMR spectra
obtained.
The Zr–C(1) distance in these compounds ranges from
Fig. 3 The bond length difference parameter for the fluorenyl ligand is
2.37 Å to 2.40 Å and the Zr–Cring distances altogether range defined as δ = (a + e − b − d)/2.
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The results are summarized in Table 4. The activity of 3/MAO
is much lower (3–4 times) compared to 2/MAO under similar
conditions, although the difference is small with low tempera-
ture and low ethylene pressure. This result is consistent with
our expectations and in good agreement with Shiono’s obser-
vation that reducing the number of tertiary alkyl groups on the
fluorenyl ligand decreases the catalyst activity.7 As expected,
addition of an alkyl group to the tetrahydrotetramethylbenzo-
fluorenyl ligand (ethyl for 4 or tert-butyl for 5) improves the
activity. Catalyst systems 4/MAO and 5/MAO showed more than
double the activity of 3/MAO.
Table 2 Carbon–carbon bond lengths (Å) of the fluorenyl five-membered ring
along with the bond length difference parameter δ = (a + e − b − d)/2 for 2,10
4, 5, 6, and 7
Parameter
2
4
5
6
7
a
b
c
d
e
δ
1.468(9)
1.431(8)
1.434(8)
1.437(9)
1.441(9)
0.021
1.460(3)
1.435(3)
1.444(3)
1.432(3)
1.463(3)
0.028
1.458(2)
1.427(3)
1.447(2)
1.429(2)
1.448(2)
0.025
1.454(18)
1.435(18)
1.449(18)
1.443(19)
1.451(18)
0.014
1.444(6)
1.435(5)
1.456(6)
1.444(5)
1.465(6)
0.015
The GPC analysis indicates that the polyethylenes obtained
from 3/MAO have number average molecular weights (Mn,
1030–4440) comparable to those afforded by 2/MAO
(780–2860). However, the weight average molecular weights
(Mw, 196 200–382 100) were vastly larger than those provided
by 2/MAO (1340–6780) because the polydispersity indices
(PDI = Mw/Mn) were extremely high (86–191) in comparison
(2.13–3.57).2a These high PDI values suggest slow initiation
and/or partial catalyst decomposition.
Table 2 lists the carbon–carbon bond lengths and the calcu-
lated parameter δ for 210 and 4–7. The value of δ in 2 and 4–7
varies from 0.014 to 0.028 Å, which is in good agreement with
δ measured for other η5 fluorenyl complexes (0.030 Å or less).10
Hapticity analysis by solution NMR
It has been established that the C(1) 13C NMR chemical shift
1
and the benzo-H H NMR chemical shifts can reveal fluorenyl
hapticities.10 Thus, the solution 1H and 13C NMR of com-
pounds 3–7 were measured in C6D6 (Table 3). For comparison,
the THF adducts of compounds 3, 4, 5, and 7 were prepared,
in quantitative yield, by dissolving the corresponding com-
pound in THF and removing solvent under vacuum at room
temperature. The THF adducts show one THF molecule coordi-
nated to the Zr center with broad NMR resonances for the
ethereal protons. The chemical shifts of C(1) for the THF
adducts have a significant downfield shift (>94 ppm) com-
pared to their THF-free analogues (<76 ppm). In addition, the
two benzo hydrogens for the THF adducts (<7.96, <8.08 ppm)
are mostly upfield of those for the THF-free analogues (>7.92,
>8.06 ppm). These chemical shifts comport with those of
adducts Me2Si(η5-C29H36)(η1-N-tBu)ZrCl2·THF and Me2Si-
(η5-C29H36)(η1-N-tBu)ZrCl2·NCMe (Table 3), which exhibit η1
coordination in solution.10
The 13C NMR spectra for the polymers from 3/MAO show
that the polymers are considerably branched with ethyl (NE)
and long (NL that are ≥hexyl) branches, but no C1, C3, C4, or
C5 branches were observed. However, the branch content (NE =
1.0–3.5 branches per 1000 carbons; NL = 8.2–14.3; NTOTAL
=
10.1–17.2) is lower than observed with 2/MAO (NE = 3.0–8.2; NL
= 13.4–53.2; NTOTAL = 20.2–59.4) under similar conditions.2a
The significant decrease of the long branch content is prob-
ably related to the decreased steric bulk and decreased elec-
tron density of the Tet ligand compared to the Oct ligand.6
The polymers produced using ethyl-substituted 4/MAO were
found to have relatively high molecular weights—with Mn
values (12 100–18 100) several times higher than those
obtained with 2/MAO (780–2860) and 3/MAO (1030–4440). PDI
values for 4/MAO were still high (30–40) but much lower than
those found for 3/MAO (86–191). Unexpectedly, the 1H and 13
C
NMR analyses of the polymers show there are no branches or
olefinic groups in any polyethylenes produced by 4/MAO. A
high propensity for chain transfer to aluminium can explain
the lack of olefinic termini, but the reason for a total absence
of branches is not yet clear. The high Tm values (up to 139 °C)
corroborate the production of linear polyethylene by 4/MAO.
The polymers produced by 5/MAO contain ethyl and long
(NE = 2.5–4.2; NL = 4.7–13.0; NTOTAL = 7.2–17.0) branches
similar in concentration to those made by 3/MAO. However,
with its three tertiary alkyl groups, the molecular weight
Polymerization of ethylene with 3, 4, 5, and 7 activated by
MAO
Ethylene polymerizations were performed with 3, 4, 5, and 7
activated with solid MAO in toluene under various conditions.
Table 3 The 1H and 13C NMR chemical shifts (ppm) of selected nuclei
Compound
C(1) Benzo-H Benzo-H Ref.
2
3
71.9 8.01
70.2 7.99
96.3 7.95
75.5 7.99
95.9 7.95
75.8 8.03
96.3 7.96
72.0 7.92
74.2 8.09
94.6 7.49
96.5 7.94
8.24
8.07
7.98
8.06
7.96
8.11
8.08
8.07
8.29
8.06
8.02
5
This work results are intermediate between 2/MAO (with four tertiary
3·THF
4
4·THF
5
5·THF
6
7
This work
This work
This work
alkyl groups) and 3/MAO (with two tertiary alkyl groups). The
Mn values (1500–2200) are comparable, but the Mw values
This work (7900–76 700) and, therefore, the PDI results (4.4–35) are
This work
This work
This work
intermediate.
Replacement of the silicon bridge methyl groups of 2 with
This work phenyl groups to afford 7 has a significant effect on the cata-
7·THF
Me2Si(η5-C29H36)(η1-N-tBu)
ZrCl2·THF
10
lyst behavior. Compared to 2/MAO, the activity of 7/MAO is 2–3
times lower. In addition, the long branch content of the
polymer obtained (NL = 3.4–7.6) is drastically lower than that
Me2Si(η5-C29H36)(η1-N-tBu)- 93.0 8.03
8.03
10
ZrCl2·NCMe
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Table 4 Ethylene polymerization results with 3.33 μmol Zr catalyst activated by 1000 equivalents of MAO in 25 mL toluene
Temperature
(°C)
Ethylene
pressure (psi)
Time
(minutes)
Yield
(g)
Activity
Tm
(°C)
Entry
Zr
(kg mol−1 h−1
)
NE
NL
NT
Mw
Mn
PDI
1
2
3
4
5
6
7
8
3
3
3
3
3
3
3
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
7
7
7
7
7
7
7
25
60
60
80
80
100
100
25
60
60
60
80
80
100
25
60
60
60
80
80
60
80
80
100
80
100
80
60
80
100
80
100
80
80
60
80
100
80
100
80
100
80
80
20
15
15
10
10
6
5
6
5
4
3
3
3
3
18
13
7
7
7
7
5
5
20
10
15
10
10
10
10
0.31
0.59
0.94
1.07
1.51
0.84
0.83
1.14
0.94
1.08
0.98
0.99
1.03
0.81
0.53
1.81
1.3
1.55
1.41
1.99
1.45
1.81
0.34
1.05
0.9
279
709
1129
1928
2721
2523
2991
3423
3387
4865
5886
5946
6186
4865
531
2509
3346
3990
3629
5122
5225
6523
306
1.8
1.8
3.5
1.9
1.0
0
0
0
0
10.0
14.3
13.7
8.2
10.5
0
0
0
0
11.8
16.1
17.2
10.1
11.5
0
0
0
0
134
137
127
135
131
196 200
338 700
382 100
219 700
247 500
1030
191
89
86
146
152
3810
4440
1510
1630
9
139
139
134
577 700
483 600
472 100
18 100
12 100
15 700
32
40
30
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
0
0
0
0
0
0
0
0
0
2.5
3.7
4.2
2.8
4.0
3.3
4.7
11.8
12.6
8.2
13.0
11.6
7.2
15.5
16.8
11.0
17.0
14.9
124
125
125
125
123
123
124
123
124
125
125
125
123
123
124
76 700
56 800
7900
33 800
33 600
2200
1800
1800
1500
1900
35
31
4.4
22
17
80
100
100
25
60
60
60
80
80
100
1892
1081
2162
3369
3622
3874
5.5
6.2
5.1
5.8
4.0
6.3
5.6
3.4
7.6
5.1
11.8
11.8
8.5
13.4
9.1
9290
9050
46 800
6360
2900
2510
4000
2350
2960
3.2
60
100
80
100
100
3.6
11.7
2.7
1.2
1.87
2.01
2.15
7390
2.5
of 2/MAO (NL = 13.4–53.2), although the ethyl branch content rethylene = 14.9 and r1-decene = 0.49 by plotting F(f − 1)/f versus
seems to be fairly independent of catalyst identity and F2/f, where F = [ethylene]/[1-decene] in the feed and f = [ethy-
polymerization conditions. The decreased long branch content lene]/[1-decene] in the copolymer. Table 5 shows the results of
might be related to the steric influence of the phenyl groups, the five copolymerizations performed to create the Fineman–
which seemingly enforce η5 hapticity. In fact, 7 stands alone as Ross plot. Note that the value for r1-decene = 0.49 is about an
the only Oct-bearing CGC that forgoes diethyl ether coordi- order of magnitude larger than that for typical metallocenes;
nation in the solid state and solution (although it does bind for example, ethylene bis(indenyl)ZrCl2/MAO gives rethylene = 45
THF in solution; see Table 3). Hence the ligand flexibility and and r1-octene = 0.05.16 Our obtained value of r1-decene = 0.49 is
ring-slip capacity that seemingly accommodate macromono- also notably larger than that reported for 1-octene with the
mer incorporation for 2/MAO2a is diminished for 7/MAO. Dow-Exxon CGC 1/MAO (rethylene = 7.90 and r1-octene = 0.10)17
Unfortunately, the lower branch content is not traded for a sig- and even that reported for propylene with 1/MAO (rethylene
=
nificant increase in the polymer molecular weights compared 4.33 and rpropylene = 0.38).18 Adding to the impressive behavior
to 2/MAO.
Reactivity ratios for ethylene/1-decene polymerization with
2/MAO
The proposed mechanism for forming long branches relies
upon in situ production of macromonomers via β-hydrogen
elimination and their subsequent incorporation into another
chain.2a This process for 2/MAO apparently produces the most
highly branched polyethylene (from ethylene alone) of any
early transition metal catalyst. This unprecedented affinity
toward α-olefin macromonomers should be apparent in ethyl-
ene/α-olefin copolymerizations by identifying a large α-olefin
reactivity ratio.
Fig. 4 Fineman–Ross plot for copolymerization of ethylene and 1-decene with
Fig. 4 shows the Fineman–Ross analysis15 for the copoly-
2/MAO (F = [ethylene]/[1-decene] in the feed and f = [ethylene]/[1-decene] in
merization of ethylene and 1-decene, which reveals that the copolymer).15
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Table 5 Copolymerization of ethylene and 1-decene with 2/MAO for determination of reactivity ratios by the Fineman–Ross method: rethylene = 14.9 and r1-decene
0.49a
=
Entry
Ethylene pressure (bar)
[Ethylene] M
[1-Decene] M
Productivity (kg mol−1 h−1 M−1
)
1-Decene incorporation (%)
1
2
3
4
5
2.41
3.45
5.52
6.55
7.58
0.26
0.38
0.60
0.71
0.83
0.37
0.37
0.37
0.37
0.37
730
1201
439
1067
840
12.6
8.7
4.8
4.2
3.4
a Polymerization conditions: 3.33 μmol 2 activated with 1000 equivalents of MAO in 25 mL toluene at 40 °C. 1-Decene incorporation was
measured by 13C NMR.
of 2/MAO is the fact that r1-decene = 0.49 is obtained at Tp
40 °C, whereas the reactivity ratios just cited for 1/MAO were transients collected at 120 °C using
=
NMR spectrometer observing at 75.4 MHz with at least 1500
pulse width of
a
obtained fully 100 °C higher at Tp = 140 °C.
16 501.7 Hz, a pulse angle of 70°, and a recycle delay of 5.5 s to
allow complete relaxation of the nuclei. Chemical shifts were
referenced to the main chain “δ+δ+” polyethylene peak at
30.0 ppm. Peak assignments and branch density formulas
have been reported before.2a The polymer molecular weight
measurements were performed by Sumitomo Chemical on a
Waters 150 C gel permeation chromatograph with o-dichloro-
benzene as the solvent and an elution temperature of 140 °C;
polystyrene standards were employed.
Experimental
Materials
Toluene was dried over elemental sodium and distilled under
nitrogen into a Straus flask. Ethylene (99.5+%, polymerization
grade) was obtained from Matheson and used following
passage through a Matheson 6410 drying system equipped
with an OXYSORB column. Zirconium precatalysts were pre-
pared as a 3.33 mM toluene stock solution in a volumetric
flask in a nitrogen-filled glove-box. MAO (Albemarle, 30 wt% in
toluene) was dried at 70 °C under high vacuum for 3 days and
stored as a solid in the glove-box.
Ligand and complex synthesis
Preparation of 3 (TetZrCl2). The preparation of 3 essentially
follows the published procedure for 2.5 However, intermedi-
ates were not isolated and instead, used directly for the next
step. A 250 mL round bottom flask was charged with 10.00 g
(36.2 mmol) 1,1,4,4-tetramethyl-1,2,3,4-tetrahydrobenzo[b]-
fluorene (TetH),8 and a 180° needle valve was attached. The
system was evacuated and dry diethyl ether (120 mL) was
vacuum transferred in. Next, n-butyllithium (15.9 mL,
39.9 mmol, 2.50 M in hexanes) was syringed in over five
minutes and the red slurry was stirred for 20 hours. Mean-
while, a 7 cm swivel frit was assembled with two 500 mL
round bottom flasks and evacuated. Hexanes (100 mL) were
then vacuum transferred into the frit followed by an excess of
Me2SiCl2 (75 mL, 615 mmol). The red TetLi slurry was cannu-
lated directly into the 7 cm frit over 15 minutes, resulting in a
pale yellow slurry. After 17.5 hours, the solvents and excess
Me2SiCl2 were removed under vacuum to yield an off-white
solid. To this solid, Me3CNHLi (2.87 g, 36.3 mmol) was added
in the glove-box. Diethyl ether (200 mL) was vacuum trans-
ferred in at −78 °C. The round bottom was allowed to warm
slowly to room temperature for 15 h. The slurry was cooled to
−78 °C and 2 equivalents of n-butyllithium (31.88 mL,
79.71 mmol, 2.50 M in hexanes) were added. The orange slurry
was stirred for 20 hours and then the diethyl ether was
removed under vacuum. ZrCl4 (8.44 g, 36.23 mmol) was added
in the glove box and diethyl ether (200 mL) vacuum transferred
in on the line at −78 °C. After slowly warming to room temp-
Polymerizations
All polymerizations should be carried out in a fume hood
behind a blast shield. Ethylene polymerizations were per-
formed in an 85 mL glass Lab-Crest (Andrews Glass Co.)
cylindrical polymerization vessel equipped with a 2.5 in. octa-
gonal stir bar. In the glove-box, the reactor was charged with
MAO (0.193 g, 3.33 mmol) and 25 mL of toluene. Then 1.0 mL
(3.33 μmol Zr) of a 3.33 mM stock solution of zirconium pre-
catalyst was drawn into a 2.5 mL Hamilton gastight syringe,
which was capped with a septum. The reactor was removed
from the box, placed in an oil bath at the desired temperature,
pressurized with ethylene, and allowed to equilibrate for at
least 10 min while stirring. After equilibration, the solution
of zirconium precatalyst was injected. The reaction was
stopped by rapidly venting the reactor and pouring the
polymerization solution into approximately 200 mL of 10%
aqueous HCl in MeOH. This solution was stirred overnight to
quench the MAO completely, and the polymer was collected by
filtration, thrice rinsed with fresh methanol, and dried in
vacuum.
Polymer analyses
Polymer samples for 1H and 13C NMR characterization were erature and stirring the light brown slurry for 15 hours, the
prepared by dissolving 60 mg of polymer in 0.7 mL of 1,1,2,2- LiCl was filtered off and the cake extracted until colorless. The
tetrachloroethane-d2. Spectra were obtained on a Mercury 300 solvent was removed under vacuum and the residue was
9144 | Dalton Trans., 2013, 42, 9139–9147
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washed with heptane to yield 4.20 g (20%) of a bright yellow 72.1, 95.9, 118.0, 118.5, 120.1, 120.3, 122.8, 135.2, 136.0, 137.8,
solid. 1H NMR (C6D6) δ (ppm): 0.75 (s, SiMe, 3H), 0.84 (s, SiMe, 140.2, 142.0, 142.7, 143.1.
3H), 1.25 (s, CMe3, 9H), 1.31 (s, Tet-Me, 3H), 1.36 (s, Tet-Me,
Preparation of 1,1,4,4-tetramethyl-7-acetyl-1,2,3,4-tetra-hydro-
°C, AlCl3 (3.60 g,
3H), 1.39 (s, Tet-Me, 3H), 1.45 (s, Tet-Me, 3H), 1.64 (m, Tet-CH2, benzo[b]fluorene (acetylTetH). At
0
4H), 7.16, 7.21, 7.73, 7.84, 7.99, 8.07 (Ar, 6H). 13C NMR (C6D6) 30.0 mmol) in 10 mL MeNO2 was syringed into a mixture of
δ (ppm): 6.0, 6.0, 32.4, 32.7, 32.9, 33.1, 33.4, 35.0, 35.1, 35.2, TetH (5.0 g, 18.1 mmol) and acetic anhydride (2.40 g,
35.5, 56.4, 70.2, 121.9, 123.1, 124.6, 126.0, 126.1, 128.6, 130.2, 23.5 mmol) in 50 mL MeNO2/50 mL 1,2-dichloroethane. The
134.3, 136.0, 139.3, 146.1, 149.5.
mixture was stirred for 30 minutes and poured into a beaker
Preparation of 3·THF (TetZrCl2·THF). 3·THF was prepared with 100 g of ice to decompose the excess AlCl3. The mixture
by dissolving 3 in THF and removing the solvent under was extracted with hexane (3 × 100). The solvent was evapo-
vacuum at room temperature. 1H NMR (C6D6) δ (ppm): 0.46 rated and a pale yellow solid (5.31 g, 93% yield) was obtained.
(s, SiMe, 3H), 0.71 (s, SiMe, 3H), 1.09 (br, THF-CH2, 4H), 1.06 It was used without further purification. 1H NMR (CDCl3) δ
(s, Tet-Me, 3H), 1.27 (s, Tet-Me, 3H), 1.34 (s, Tet-Me, 3H), (ppm): 1.35 (s, Tet-Me, 6H), 1.38 (s, Tet-Me, 6H), 1.74 (s,
1.47 (s, Tet-Me, 3H), 1.68 (s, CMe3, 9H), 1.72 (s, Tet-CH2, 4H), Tet-CH2, 4H), 2.65 (s, MeC(O), 3H), 3.90 (s, 9-H, 2H), 7.55, 7.80,
2.97 (br, THF-CH2, 4H), 7.14, 7.33, 7.71, 7.83, 7.95, 7.98 7.83, 8.00, 8.11 (Ar, 5H). 13C NMR (CDCl3) δ (ppm): 26.8, 32.2,
(Ar, 6H). 13C NMR (C6D6) δ (ppm): 0.3, 2.7, 25.7, 31.8, 32.4, 32.4, 34.7, 34.9, 35.29, 35.32, 36.7, 118.8, 119.4, 123.4, 125.0,
32.6, 33.1, 33.8, 33.9, 34.8, 35.3, 35.8, 59.9, 69.0, 96.3, 117.9, 127.8, 135.4, 138.3, 141.9, 143.7, 144.3, 145.7, 146.9, 198.1.
118.5, 119.8, 121.9, 122.1, 126.2, 136.3, 136.5, 137.0, 140.4,
143.3, 143.4.
Preparation of 1,1,4,4-tetramethyl-7-t-butyl-1,2,3,4-tetra-
hydrobenzo[b]fluorene (t-butylTetH). Under N2, AlMe3 (1.4 g,
Preparation of 1,1,4,4-tetramethyl-7-ethyl-1,2,3,4-tetra-hydro- 19.4 mmol) was syringed into a 40 mL toluene solution of acetyl-
benzo[b]fluorene (ethylTetH). At 0 °C, AlCl3 (9.3 g, 70.0 mmol) TetH (3.0 g, 9.4 mmol). The mixture was refluxed 14 h and
in 10 mL MeNO2 was syringed into a mixture of 2-ethylfluor- quenched with dilute aqueous HCl. The organic layer was iso-
ene9 (9.0 g, 46.4 mmol) and 2,5-dichloro-2,5-dimethylhexane lated and dried with MgSO4. Removal the solvent gave the
1
(8.5 g, 46.4 mmol) in MeNO2 (100 mL). The mixture was product as a pale yellow solid. H NMR (CDCl3) δ (ppm): 1.35
stirred for 30 minutes and poured into a beaker with 100 g ice (s, Tet-Me, 6H), 1.38 (s, Tet-Me, 6H), 1.38 (s, CMe3, 9H), 1.74
to decompose the excess AlCl3. The mixture was extracted with (s, Tet-CH2, 4H), 3.83 (s, 9-H, 2H), 7.38, 7.48, 7.53, 7.66, 7.69
hexane (3 × 100 mL). The solvent was evaporated and 13.6 g (Ar, 5H). 13C NMR (CDCl3) δ (ppm): 31.8, 32.3, 32.4, 34.67,
(96%) of a pale yellow solid was obtained, which was used 34.71, 34.9, 35.46, 35.47, 36.8, 117.4, 119.1, 122.0, 123.0, 123.8,
1
without further purification. H NMR (CDCl3) δ (ppm): 1.37 (t, 139.4, 139.5, 140.8, 143.3, 143.52, 143.52, 149.5.
J = 7.6, CH2Me, 3H), 1.39 (s, Tet-Me, 6H), 1.43 (s, Tet-Me, 6H),
Preparation of 5 (t-butylTetZrCl2). The procedure followed
1.78 (s, Tet-CH2, 4H), 2.76 (q, J = 7.6 Hz, CH2Me, 2H), 3.85 (s, that employed for 3—using t-butylTetH instead—and the iso-
1
9-H, 2H), 7.22, 7.38, 7.52, 7.71, 7.74 (Ar, 5H). 13C NMR (CDCl3) lated yield was 21%. H NMR (C6D6) δ (ppm): 0.878 (s, SiMe,
δ (ppm): 16.0, 29.2, 32.3, 32.4, 34.62, 32.64, 35.45, 35.46, 36.5, 3H), 0.882 (s, SiMe, 3H), 1.26 (s, NCMe3, 9H), 1.33 (s, CCMe3,
117.3, 119.4, 122.9, 124.5, 126.4, 139.6, 139.7, 140.6, 142.5, 9H), 1.32 (s, Tet-Me, 3H), 1.37 (s, Tet-Me, 3H), 1.40 (s, Tet-Me,
143.2, 143.4, 143.8.
3H), 1.46 (s, Tet-Me, 3H), 1.65 (m, Tet-CH2, 4H), 7.40, 7.81,
Preparation of 4 (ethylTetZrCl2). The procedure followed 7.98, 8.03, 8.11 (Ar, 5H). 13C NMR (C6D6) δ (ppm): 6.2, 6.3,
that employed for 3—using ethylTetH instead—and the iso- 31.1, 32.4, 32.7, 23.9, 33.1, 33.4, 35.06, 35.07, 35.3, 35.4, 35.5,
lated yield was 22%. 1H NMR (C6D6) δ (ppm): 0.84 (s, SiMe, 56.3, 75.8, 121.4, 121.8, 123.2, 124.2, 124.8, 125.5, 128.6, 134.5,
3H), 0.86 (s, SiMe, 3H), 1.16 (t, J = 7.6 Hz, CH2Me, 3H), 1.25 (s, 136.5, 146.1, 149.1, 153.4.
CMe3, 9H), 1.31 (s, Tet-Me, 3H), 1.36 (s, Tet-Me, 3H), 1.38 (s,
Preparation of 5·THF (t-butylTetZrCl2·THF). Preparation of
Tet-Me, 3H), 1.45 (s, Tet-Me, 3H), 1.64 (m, Tet-CH2, 4H), 2.56 5·THF was accomplished by dissolving 5 in THF and removing
(q, J = 7.6 Hz, CH2Me, 2H), 7.08, 7.74, 7.75, 7.99, 8.06 (Ar, 5H). the solvent under vacuum at room temperature. 1H NMR
13C NMR (C6D6) δ (ppm): 6.2, 6.3 15.4, 30.0, 32.4, 32.7, 32.9, (C6D6) δ (ppm): 0.63 (s, SiMe, 3H), 0.66 (s, SiMe, 3H), 1.02 (br,
33.1, 33.4, 35.06, 35.07, 35.3, 35.4, 56.3, 75.5, 121.8, 123.2, THF-CH2, 4H), 1.30 (s, Tet-Me, 3H), 1.38 (s, Tet-Me, 3H), 1.50
123.9, 124.4, 124.5, 124.9, 128.6, 134.4, 136.9, 146.1, 146.9, (s, Tet-Me, 3H), 1.55 (s, Tet-Me, 3H), 1.49 (s, CCMe3, 9H), 1.70
149.1.
(s, NCMe3, 9H), 1.72 (m, Tet-CH2, 4H), 2.88 (br, THF-CH2, 4H),
Preparation of 4·THF (ethylTetZrCl2·THF). Preparation of 7.34, 7.83, 7.95, 7.96, 8.08 (Ar, 5H). 13C NMR (C6D6) δ (ppm):
4·THF was accomplished by dissolving 4 in THF and removing 1.4, 1.8, 25.5, 31.8, 32.3, 32.5, 32.9, 33.0, 33.9, 34.7, 35.2, 35.4,
the solvent under vacuum at room temperature. 1H NMR 35.7, 35.9, 59.7, 71.7, 96.3, 117.87, 117.91, 119.1, 120.0, 120.4,
(C6D6) δ (ppm): 0.61 (s, SiMe, 3H), 0.68 (s, SiMe, 3H), 0.88 (br, 135.1, 135.3, 138.8, 140.1, 140.5, 143.3, 149.4.
THF-CH2, 4H), 1.31 (s, Tet-Me, 3H), 1.38 (s, Tet-Me, 3H), 1.47
Preparation of 6 (TetZrMe2). In the glove box 3 (0.50 g,
(s, Tet-Me, 3H), 1.56 (s, Tet-Me, 3H), 1.34 (t, J = 7.6 Hz, CH2Me, 0.88 mmol) was charged into a 100 mL pear-shaped round
3H), 1.65 (s, CMe3, 9H), 1.72 (m, Tet-CH2, 4H), 2.67 (q, J = 7.6 bottom flask, which was then attached to a 3 cm swivel frit.
Hz, CH2Me, 2H), 2.75 (br, THF-CH2, 4H), 7.06, 7.75, 7.85, 7.95. The frit was evacuated on the vacuum line and diethyl ether
7.96 (Ar, 5H). 13C NMR (C6D6) δ (ppm): 1.2, 1.9, 16.3, 25.4, (50 mL) was then vacuum transferred in. Next, MeLi (1.20 mL,
30.0, 32.1, 32.5, 33.0, 33.1, 33.9, 34.7, 35.2, 35.8, 35.9, 59.8, 1.92 mmol, 1.6 M in diethyl ether) was slowly syringed into the
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yellow solution while vigorously stirring at −78 °C. After slowly
For 5, a total of 337 parameters were refined in the final
warm to room temperature and stirring for 1 h, solvent was cycle of refinement using 6794 reflections with I > 2σ(I) to yield
removed by vacuum. 20 mL of heptane were vacuumed trans- R1 and wR2 of 2.24% and 5.35%, respectively. Refinement was
ferred in and the solution was filtered. The residue was done using F2.
washed with heptane until the solids were colorless. Concen-
For 6, data were collected at 173 K on a Siemens SMART
tration of the filtrate to 5 mL and collection of the yellow solid PLATFORM equipped with A CCD area detector and a graphite
on the frit gave 0.34 g (73%). Crystals suitable for X-ray crystal- monochromator utilizing MoKα radiation (λ = 0.71073 Å). Cell
lography were obtained by slowly cooling a saturated heptane parameters were refined using up to 8192 reflections. A full
1
solution. H NMR (C6D6) δ (ppm): −0.63 (s, Zr-Me, 3H), −0.54 sphere of data (1850 frames) was collected using the ω-scan
(s, Zr-Me, 3H), 0.77 (s, SiMe, 3H), 0.85 (s, SiMe, 3H), 1.31 (s, method (0.3° frame width). The first 50 frames were re-
CMe3, 9H), 1.32 (s, Tet-Me, 3H), 1.35 (s, Tet-Me, 3H), 1.37 (s, measured at the end of data collection to monitor instrument
Tet-Me, 3H), 1.41 (s, Tet-Me, 3H), 1.65 (s, Tet-CH2, 4H), 7.17, and crystal stability (maximum correction on I was <1%).
7.43, 7.81, 7.82, 7.92, 8.07 (Ar, 6H). 13C NMR (C6D6) δ (ppm): Absorption corrections by integration were applied based on
6.64, 6.69, 11.3, 32.7, 32.9, 33.0, 33.4, 34.5, 34.9, 35.3, 35.5, measured indexed crystal faces. The structure was solved by
40.0, 40.5, 55.1, 72.0, 120.8, 122.6, 123.28, 123.34, 123.9, 124.7, the Direct Methods in SHELXTL6,19 and refined using full-
125.6, 127.4, 134.5, 136.3, 143.0, 147.2.
matrix least squares. The non-H atoms were treated anisotropi-
Preparation of 7 (SiPh2OctZrCl2). The procedure followed cally, whereas the hydrogen atoms were calculated in ideal posi-
that employed for 3—using OctH and Ph2SiCl2 instead—and tions and were riding on their respective carbon atoms.
the isolated yield was 20%. 1H NMR (C6D6) δ (ppm): 1.06 (s, A total of 300 parameters were refined in the final cycle of
Oct-Me, 6H), 1.24 (s, Oct-Me, 6H), 1.27 (s, Oct-Me, 6H), 1.41 (s, refinement using 5704 reflections with I > 2σ(I) to yield R1 and
Oct-Me, 6H), 1.51 (s, CMe3, 9H), 1.56–1.76 (br, Oct-CH2, 8H), wR2 of 2.31% and 5.95%, respectively. Refinement was done
7.31, 7.33, 7.50, 8.09, 8.29 (Ar, 14H). 13C NMR (C6D6) δ (ppm): using F2.
31.9, 32.3, 32.7, 32.9, 34.1, 35.0, 35.2, 35.3, 35.4, 56.1, 74.2,
121.3, 124.7, 125.6, 128.5, 130.4, 134.1, 136.8, 137.6, 146.4, diffractometer using MoKα radiation (λ = 0.71073 Å) and an
149.0. APEXII CCD area detector. Raw data frames were read by
For 7, X-ray data were collected at 100 K on a Bruker DUO
Preparation of 7·THF (SiPh2OctZrCl2·THF). Preparation of program SAINT and integrated using 3D profiling algorithms.
7·THF was accomplished by dissolving 7 in THF and removing The resulting data were reduced to produce hkl reflections and
the solvent under vacuum at room temperature. 1H NMR their intensities and estimated standard deviations. The data
(C6D6) δ (ppm): 1.02 (br, THF-CH2, 4H), 1.06 (s, Oct-Me, 6H), were corrected for Lorentz and polarization effects and
1.26 (s, Oct-Me, 6H), 1.33 (s, Oct-Me, 6H), 1.44, (s, Oct-Me, 6H), numerical absorption corrections were applied based on
1.65 (m, Oct-CH2, 8H), 1.84 (s, CMe3, 9H), 2.71 (br, THF, 4H), indexed and measured faces. The structure was solved and
7.18, 7.18, 7.49, 7.93, 8.06 (Ar, 14H). 13C NMR (C6D6) δ (ppm): refined in SHELXTL6.1,19 using full-matrix least-squares refine-
25.6, 32.0, 32.2, 32.5, 33.1, 34.6, 34.7, 35.2, 35.76, 35.84, 59.4, ment. The non-H atoms were refined with anisotropic thermal
71.1, 94.6, 117.7, 119.8, 128.1, 130.0, 135.84, 135.88, 137.4, parameters and all of the H atoms were calculated in idealized
138.4, 140.3, 143.5.
positions and refined riding on their parent atoms. One end of
the ligand is disordered whereby atoms C15, C16 of the ring
and consequently the ring’s methyl groups (C22–C25) are dis-
X-ray crystallography
The four structures have been deposited at the Cambridge ordered. They were refined in two parts and their site occu-
Crystallographic Data Centre (CCDC) as 919740 (4), 919741 (5), pation factors dependently refined. The latter refined to 50%
919742 (6), and 919743 (7).
but was fixed at this value for the final refinement model. All
For 4 and 5, data were collected at 100 K on a Bruker DUO of the disordered atoms were refined with isotropic displace-
system equipped with an APEX II area detector and a graphite ment parameters. In the final cycle of refinement, 9379 reflec-
monochromator utilizing MoKα radiation (λ = 0.71073 Å). Cell tions (of which 6953 are observed with I > 2σ(I)) were used to
parameters were refined using up to 9999 reflections. A hemi- refine 442 parameters and the resulting R1, wR2 and S (good-
sphere of data was collected using the ω-scan method (0.5° ness of fit) were 3.40%, 8.41% and 1.037, respectively. The
frame width). Absorption corrections by integration were refinement was carried out by minimizing the wR2 function
applied based on measured indexed crystal faces. The struc- using F2 rather than F values. R1 is calculated to provide a
ture was solved by the Direct Methods in SHELXTL6,19 and reference to the conventional R value but its function is not
refined using full-matrix least squares. The non-H atoms were minimized.
treated anisotropically, whereas the hydrogen atoms were cal-
culated in ideal positions and were riding on their respective
carbon atoms.
Conclusions
For 4, A total of 317 parameters were refined in the final
cycle of refinement using 4953 reflections with I > 2σ(I) to yield In summary, a series of fluorenyl/amido complexes 3–7 was
R1 and wR2 of 3.31% and 7.34%, respectively. Refinement was prepared by modification of the sterically expanded catalyst 2.
done using F2.
X-ray structure analysis reveals that complexes 4–7 adopt η5
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coordination to the fluorenyl ligand instead of the η1 hapticity
observed for 2. The ethylene homopolymerization behavior of
3, 4, 5, and 7 was explored by activation with MAO. Branched
polyethylene (ethyl and long branches) was obtained except in
the case of ethyl-substituted 4/MAO, for which linear polyethy-
lene was obtained. The branches are found to be ethyl and
long branches (≥hexyl) and no other branches are observed.
The density of ethyl branches decreases slightly in the order of
2 > 7 > 5 > 3 while the density of long branches decreases more
steeply in the order of 2 ≫ 3 ≈ 5 > 7. All these modifications
on the ligand have resulted in a decrease of the catalyst activity
compared to 2/MAO. Molecular weights were generally larger,
but this was accomplished with a drastic increase in the poly-
dispersity index. Reactivity ratios were determined for the
copolymerization of ethylene/1-decene with 2/MAO. This
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Acknowledgements
This research is supported by the U.S. National Science Foun-
dation (CHE-1058079) and Sumitomo Chemical. K.A.A. thanks
the University of Florida and the National Science Foundation
(CHE-0821346) for funding the purchase of X-ray equipment.
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