Dinuclear metallocenes with a modulated biphenylene bridge for olefin polymerization

Article abstract of DOI:10.1002/ejic.200600833

Dinuclear group 4 metallocene catalysts linked by a biphenylene or 1,2-diphenylethylene bridge, namely [4,4′-(C₅Me ₄)₂-(C₆H₄)₂][CpZrCl ₂]₂ (2a), [p-(C₅Me

Full text of DOI:10.1002/ejic.200600833

FULL PAPER
DOI: 10.1002/ejic.200600833
Dinuclear Metallocenes with a Modulated Biphenylene Bridge for Olefin
Polymerization
Seong Kyun Kim,[a] Hwa Kyu Kim,[a] Min Hyung Lee,[a][‡] Seung Woong Yoon,[a]
Yonggyu Han,[a] Sungjin Park,[a] Junseong Lee,[a] and Youngkyu Do*[a]
Keywords: Homogeneous catalysis / Metallocenes / Olefins / Polymerization / Titanium / Zirconium
Dinuclear group 4 metallocene catalysts linked by a biphen-
ylene or 1,2-diphenylethylene bridge, namely [4,4Ј-(C5Me4)2-
(C6H4)2][CpZrCl2]2 (2a), [p-(C5Me4)C6H4CH2]2[CpZrCl2]2
(2b), [p-(3,4-Me2C5H2)C6H4CH2]2[CpZrCl2]2 (2c), [(C5Me4)2-
(C6H4)2][TiCl3]2 (3a), [p-(C5Me4)C6H4CH2]2[TiCl3]2 (3b), and
the corresponding mononuclear analogues [(PhC5Me4)-
CpZrCl2] (4a), [(p-TolC5Me4)CpZrCl2] (4b), [(1-p-Tol-3,4-
Me2C5H2)CpZrCl2] (4c), [(PhC5Me4)TiCl3] (5a), [(p-
TolC5Me4)TiCl3] (5b), and [(1-p-Tol-3,4-Me2C5H2)TiCl3] (5c)
were performed. The dinuclear zirconocenes show a high ac-
[p-(3,4-Me2C5H2)C6H4CH2]2[TiCl3]2 (3c), have been pre- tivity in ethylene polymerization comparable with those of
pared and the crystal structures of 2b and 3b determined by
X-ray diffraction methods. The crystal structures reveal that
these complexes consist of two equivalent metal units in-
verted with respect to the center of the bridge. All the com-
plexes were tested for the polymerization of ethylene and
styrene in the presence of methylaluminoxane (MAO), and
direct comparisons of their catalytic properties with those of
the corresponding mononuclear catalysts and give an in-
creased molecular weight of polyethylene. The dinuclear
half-sandwich titanocenes exhibit similar or slightly lower
activity and molecular weight in styrene polymerization com-
pared with their mononuclear analogues.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
effective in olefin polymerization[8–11] but they have still re-
mained much less defined in terms of structural aspects,
class of catalysts, and kinds of polymerization they can per-
form in comparison with the well-known mononuclear sys-
tems.
Introduction
Single-site catalytic systems for olefin polymerization
based on group 4 metal complexes have become well estab-
lished during the last two decades and have provided vari-
ous opportunities to tailor the polymer properties, espe-
cially molecular weight, molecular weight distribution, and
stereochemistry, as well as high catalytic activity.[1–6] The
fruits of these endeavors are the various kinds of catalyst
systems that are now being used in practical applications.
Syndiotactic polystyrene (sPS) from half-sandwich metallo-
cene catalysts and linear low-density polyethylene (LLDPE)
from constrained-geometry catalysts are typical products
available commercially from single-site catalyst systems.
Most of these catalyst systems, however, involve mononu-
clear complexes, as dinuclear systems that consist of two
active centers linked within the same molecule have become
a focus of attention only since the first report by Mülhaupt
et al.[7] on a phenylene-bridged dinuclear zirconocene sys-
tem for propylene polymerization. Initial efforts made by
several groups have shown that these catalyst systems are
Recently, it has been found that dinuclear systems are
able to show interesting catalytic behaviors that are dif-
ferent from those of mononuclear systems. Systematic poly-
merization studies by Noh et al. using polysiloxane- and
polymethylene-bridged dinuclear complexes have demon-
strated that the catalytic activity[12,13] and co-monomer in-
corporation ratio[14–16] are strongly correlated with both the
nature and the length of the bridging group employed.
Marks et al. have revealed that dinuclear constrained-geom-
etry catalysts connected by ethylene and/or methylene brid-
ges exhibit unique polymerization behaviors such as high α-
olefin incorporation,[17,18] high activity in styrene polymeri-
zation,[19] and branched or significantly increased molecular
weights in ethylene polymerization[18,20–22] mainly due to
the cooperative interactions between two active centers. Alt
et al. have also reported asymmetric dinuclear zirconocenes
that are capable of producing polyethylene with a bimodal
[a] Department of Chemistry, School of Molecular Science BK-21,
Center for Molecular Design and Synthesis, Korea Advanced molecular weight distribution.[23,24]
Institute of Science and Technology,
Although it has been suggested from the foregoing stud-
Daejeon, 305-701, Republic of Korea
Fax: +82-42-869-2810
E-mail: ykdo@kaist.ac.kr
ies that the catalytic properties of dinuclear complexes can
be strongly affected by the nature of the bridging group
and possible cooperative metal–metal interactions, very few
studies on the variation of the bridging group have been
[‡] Current address: Department of Chemistry, Texas A&M Uni-
versity,
College Station, TX 77843, USA
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Y. Do et al.
FULL PAPER
performed. Flexible alkylene groups still constitute the ma- by the direct transmetalation of dilithium salts of the li-
jority of bridges,[7–26] therefore it is of great value to exam- gands with two equivalents of [CpZrCl3] in thf. Complexes
ine the electronic and/or steric effects of the bridging group 2b and 2c have much better solubility then 1a in hydro-
that play an important role in governing the catalytic prop- carbon solvents, which could be an important advantage
erties of dinuclear complexes and thereby rationalize the when the immobilization of the catalysts is considered for
cooperative reactivity of dinuclear catalysts. In this regard, industrial applications. Reaction of the dilithium salt of the
our group recently reported the well-defined dinuclear ligands with two equivalents of ClTi(OiPr)3 in thf, followed
group 4 metal complexes [4,4Ј-(C5Me4)2(C6H4)2][CpZrCl2]2 by in situ chlorination with an excess of Me3SiCl or Me2-
(2a) and [4,4Ј-(C5Me4)2(C6H4)2][TiCl3]2 (3a), which are SiCl2 in CH2Cl2, also afforded the final titanium trichloride
linked by a rigid biphenylene bridge, and the direct com- complexes 3b and 3c (Scheme 1). Complex 3c is less soluble
parison of their catalytic properties with those of the corre- in CHCl3 and CH2Cl2 than 3a and 3b, which suggests that
sponding mononuclear analogues in ethylene and styrene the sterically less congested nature of 3c allows the reten-
polymerization.[27] We observed an increase of both molec- tion of planarity between the phenyl and cyclopentadienido
ular weight of polymer and catalytic activity, irrespective of rings in the ligand backbone. Two singlets for the methyl
1
the co-catalyst employed, especially in ethylene polymeriza- proton resonance in the H NMR spectra of 2a, 2b and 3a,
tion.
3b, and one singlet methyl resonance for 2c and 3c indicate
In the present report, which includes a further investiga- that the two metal units in these dinuclear complexes are in
tion of the polymerization behavior of the biphenylene- an identical chemical environment in solution.
bridged system, we aim to endow the existing biphenylene
group with flexibility that could provide additional metal–
X-ray Crystallographic Structures of 2b and 3b
metal interactions and at the same time to keep each metal
center highly active by minimizing the steric hindrance be-
tween the two active centers. To this end, we have developed
novel dinuclear group 4 catalysts containing bis(cyclopenta-
dienido) ligands bound to a rigid but flexible 1,2-diphenyl-
ethylene bridge. A complete set of comparative polymeriza-
tion studies in olefin polymerization with the corresponding
mononuclear catalysts is also reported.
The molecular structures of 2b and 3b are depicted in
Figure 1 and selected interatomic distances and angles are
listed in Table 1. The zirconium complex 2b crystallizes in
the space group C2/c with only one half of the molecule
in the asymmetric unit. Interestingly, the diphenylethylene
bridge adopts a gauche conformation in which the molecule
has a C2-symmetric axis perpendicular to the C(16)–C(16Ј)
bond. Thus, two [CpЈCpZrCl2] (CpЈ = C5Me4Ph) fragments
are perfectly inverted along the rotation axis, which indi-
cates that complex 2b consists of two equivalent units in the
solid state. The detailed structural analysis indicates that
the bonding geometry around the zirconium center, such as
Results and Discussion
Complexes Synthesis and Characterization
Two new ligands (1b and 1c) were synthesized by a pro- the Cl(1)–Zr–Cl(2) and Cg(1)–Zr–Cg(2) bond angles and
cedure analogous to that for ligand 1a reported in our pre- Zr–Cl and Zr–Cg bond lengths shown in Table 1, are in a
vious communication.[27] These ligands are poorly soluble similar range to those of mononuclear, unbridged zir-
in common organic solvents but are more soluble than 1a, conocene complexes.[28–30] The dihedral angle of 41.28(18)°
thus reflecting their flexible nature. The zirconium com- between the C5Me4 ring [Cp(1)] and the adjacent phenylene
plexes 2b and 2c were prepared in a straightforward manner ring [Ph(1)] is closer to that of the phenyl-substituted mo-
Scheme 1.
538
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Dinuclear Metallocenes for Olefin Polymerization
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Figure 1. Molecular structures of 2b (top) and 3b (bottom).
nonuclear zirconocene 4a (47.2°)[31] than that observed in [62.6(3)°] than those of the corresponding dinuclear zir-
the biphenylene-bridged 2a [63.6(2)°],[27] which suggests conocene 2b [41.28(18)°] and [(C6H4C5Me4)TiCl2]2(µ-O)
that flexible nature of the bridging group makes the steric (50.4°).[32]
environment of each metallocene unit of 2b similar to that
of the mononuclear 4a.
Ethylene Polymerization
Table 1. Selected bond lengths [Å] and angles [°] for 2b and 3b.
Ethylene polymerizations with the dinuclear zirconocene
Compound
2a (M = Zr)[a] 2b (M = Zr)
3b (M = Ti)
complexes 2a–c were carried out in toluene solution under
1 bar of ethylene. To compare their catalytic properties with
those of the corresponding mononuclear catalysts, polyme-
rizations with 4a–c were also performed under identical
conditions (Table 2). All the catalysts show high activities
that are in a range similar to that of the corresponding mo-
nonuclear complexes 4a–c at all reaction temperatures. The
polyethylenes produced by the dinuclear zirconocenes also
show a narrow molecular weight distribution (Mw/Mn) sim-
ilar to that of polyethylenes obtained with the mononuclear
complexes, which suggests that the two zirconium centers in
the dinuclear complexes behave as independent single active
Cl(1)–M–Cl(2)
Cg(1)–M–Cg(2)[b]
CpЈ(1)–Ph(1)[c]
M–Cl(1)
M–Cl(2)
M–Cl(3)
96.5(0)
129.8
63.6(2)
2.429(1)
2.440(1)
–
97.07(3)
130.98
41.28(18)
2.4337(11)
2.467(10)
–
103.57(11)
–
62.6(3)
2.242(4)
2.245(4)
2.240(4)
2.026(4)
–
M–Cg(1)
M–Cg(2)
2.224(1)
2.199(2)
2.2231(15)
2.213(2)
[a] Data taken from ref.[27] [b] Cg(1) and Cg(2) are the centroids of
the C5Me4 (C1–C5) and Cp (C21–C25) rings, respectively. [c]
CpЈ(1) is the plane of C5Me4 (C1–C5) and Ph(1) the plane of C6H4
(C10–C15).
The titanium complex 3b crystallizes in the space group sites, as expected from the crystal structures and NMR
C2/c and contains half of each of two independent mole- spectra. In particular, biphenylene-bridged 2a shows higher
cules in the asymmetric unit. Similarly to 2a and 3a, two activity than mononuclear 4a at high temperature, while di-
CpЈTiCl3 (CpЈ = C5Me4Ph) fragments are also perfectly in- phenylethylene-bridged 2b and 2c show lower activity than
verted with respect to the C(16)–C(16Ј) bond axis, thus in- mononuclear 4b and 4c at the low- and high-temperature
dicating that complex 3b consists of two equivalent units in limits. Thus, an enhanced thermal stability of the active spe-
the solid state. According to the solid-state structure, 3b cies is seen only for biphenylene-bridged 2a among the three
adopts an anti conformation of the diphenylethylene bridge. dinuclear systems. Moreover, the activity of 2a is higher
The bond angles and distances around titanium are also than that of 2b at all temperatures, while the corresponding
similar to those for mononuclear complexes but, interest- mononuclear analogues 4a and 4b exhibit a similar activity.
ingly, the dihedral angle between the C5Me4 ring [Cp(1)] In addition, in the case of the flexible diphenylethylene-
and the adjacent phenylene ring [Ph(1)] is much larger bridged systems, a higher activity was observed for di-
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539

Y. Do et al.
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Table 2. Ethylene polymerization results with catalysts 2a–c and 4a–c.[a]
Entry
Cat. [µmol]
Tp [°C]
Yield [g]
A (ϫ10–3)[b]
Mw (ϫ10–3)
Mw/Mn
Tm [°C]
1
2
3
4
5
6
7
8
2a (1.0)
2a (1.0)
2a (1.0)
2a (1.0)
4a (1.0)
4a (2.0)
4a (2.0)
4a (2.0)
2b (1.0)
2b (1.0)
2b (1.0)
2b (1.0)
4b (2.0)
4b (2.0)
4b (2.0)
4b (2.0)
2c (1.0)
2c (1.0)
2c (1.0)
2c (1.0)
4c (2.0)
4c (2.0)
4c (2.0)
4c (2.0)
Cp2ZrCl2 (2.0)
30
50
70
90
30
50
70
90
30
50
70
90
30
50
70
90
30
50
70
90
30
50
70
90
50
0.628
0.631
1.035
0.548
0.615
0.782
0.633
0.426
0.383
0.556
0.935
0.238
0.545
0.582
0.850
0.451
0.496
0.798
0.897
0.546
0.690
0.714
1.026
0.560
0.571
9.42
9.47
15.53
8.22
9.23
11.73
9.50
6.39
5.75
8.34
14.03
3.57
8.18
8.73
12.75
6.77
7.44
11.97
13.46
8.19
10.35
10.71
15.39
8.40
732
392
135
54
534
317
121
67
821
525
230
88
413
298
222
73
654
334
114
47
552
267
147
59
1.97
2.23
1.96
2.02
2.10
2.28
2.14
2.54
1.93
2.31
2.2
2.72
2.02
2.87
3.85
3.22
2.21
2.57
2.90
2.99
2.39
2.92
3.65
3.97
2.92
131.9
135.1
134.0
133.3
135.7
134.9
134.5
132.9
131.2
133.7
134.1
133.8
136.8
135.8
133.8
134.2
135.7
135.4
133.2
131.6
136.0
135.8
134.3
131.8
134.7
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
8.57
235
[a] Conditions: P(ethylene): 1 bar; solvent: 50 mL of toluene; tp: 2.0 min; MAO: s-MAO; [Al]/[Zr]: 1000. [b] Activity: kg of PE per mol
of Zr per hour per bar.
methyl-substituted 2c than for tetramethyl-substituted 2b, activity. Due to the flexible nature of the bridge, the two
which implies that the steric effect of the ligand strongly metal centers in 2b can exert mutual steric hindrance by
influences the activity. These results may indicate that the being located in proximal positions despite the partial relief
lower steric hindrance and the possible electronic stabiliza- of such an interaction due to the presence of an additional
tion caused by the rigid and conjugative nature of the bi- phenylene linkage. This increased steric hindrance towards
phenylene bridge in 2a lead to the higher activity.
the growing polymer chains presumably leads to a reduced
Thus, it can be suggested that the biphenylene group acts rate of chain-transfer reactions.[33] This assumption also ap-
as a much more effective bridge in terms of catalytic ac- pears to be valid for the higher molecular weight produced
tivity. Noh et al. have pointed out that the more electron by 2b and 2c in comparison to mononuclear 4b and 4c,
releasing and the longer the bridge, the higher the activity respectively.
of the dinuclear zirconium complexes compared with that
of the mononuclear catalyst in ethylene polymerization.[13]
Styrene Polymerization
In our case, the rigidity, coupled with the appropriate length
of the bridging unit, provides favorable electronic stabiliza-
From the polymerization results in Table 3, it can be seen
tion and steric effects and thus likely plays an important that dinuclear half-sandwich titanocenes behave as highly
role in governing catalytic activity when compared with the active, single-site catalysts for styrene polymerization, and
flexible diphenylethylene-bridged systems.
the syndiotactic index (SI) and melting temperature (Tm) of
The characteristic most noteworthy of mention is the the polystyrenes suggest that the syndiospecific stereocon-
molecular weight of the polyethylene: the polyethylenes trol is also well maintained. For a given Cp ligand, a bi-
produced by 2a–c have a higher molecular weight than phenylene bridge appears to form a more efficient dinuclear
those of 4a–c, especially at temperatures below 50 °C, while catalytic system than a diphenylethylene bridge, as judged
at high temperature (Ͼ70 °C), the values are similar to from the polymerization behavior of 3a and 3b at all tem-
those of the mononuclear analogues. Between two diphenyl- peratures (note the higher activity of biphenylene-bridged
ethylene-bridged systems, the more electron-releasing 2b 3a than diphenylethylene-bridged 3b and the retention of
gives higher molecular weights than 2c at all temperatures, the high activity of 3a even at 90 °C). For a given bridging
as expected. However, in contrast to the trend in activity, ligand, the sterically less congested dimethyl-substituted Cp
the molecular weight given by 2b is greater than the biphen- ligand fragment affords a catalytically more active system
ylene-bridged 2a under identical conditions. Note that the than the tetramethyl-substituted Cp ligand fragment, as ex-
ratio of molecular weights between 2b and 4b is about 2.0 emplified by 3b and 3c. A similar effect of the Cp ligand
while that between 2a and 4a is about 1.5 (Figure 2). This on the catalytic system has been observed with 5c and 5b
result can be mainly explained by steric reasons, as for the and other reported mononuclear catalyst systems.[34–36]
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Dinuclear Metallocenes for Olefin Polymerization
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Figure 2. Molecular weight difference between the polymers obtained with 2a and 4a (left) and 2b and 4b (right).
The activities of the dinuclear complexes are slightly ence on each other which slows down the rate of chain
lower than those of the corresponding mononuclear sys- propagation.[39]
tems. The extent of the activity decrease is more significant
The polystyrenes produced by dinuclear 3a–c have a
in 3b and 3c, which have a flexible diphenylethylene bridge, lower molecular weight than those of the corresponding
than in 3a, which has a rigid biphenylene bridge, thereby mononuclear 5a–c at all reaction temperatures. This can be
indicating the effect of the steric influence on the catalytic explained in terms of the steric effect of the ligand, which
activity in styrene polymerization.[37] Rausch et al. have also means that β-H elimination becomes preferred to propaga-
reported that ethylene-bridged dinuclear indenyltitanium tion as the steric hindrance between the polymer chain and
trichloride shows much lower activity than the correspond- ligand in half-sandwich metallocenes increases.[39] However,
ing mononuclear compound in spite of similar syndioselec- in contrast to the activity trend, the molecular weights of
tivity of these two complexes.[38] This result may imply that the polymers formed by the dinuclear systems are in the
the bridge flexibility in 3b and 3c makes the two polymer order 3a Ͼ 3b Ͼ 3c, which is similar to the order of the
chains growing at the two active centers exert a steric influ- mononuclear systems (5a ≈ 5b Ͼ 5c). The low molecular
Eur. J. Inorg. Chem. 2007, 537–545
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Y. Do et al.
SI [%][c]
FULL PAPER
Table 3. Styrene polymerization results with catalysts 3a–3c and 5a–5c.[a]
Entry
Cat. [µmol]
Tp [°C]
Yield [g]
Activity[b]
Mw (ϫ10–3)
Mw/Mn
Tm [°C]
1
2
3
4
5
6
7
8
3a (5.0)
3a (5.0)
3a (5.0)
5a (10.0)
5a (10.0)
5a (10.0)
3b (5.0)
3b (5.0)
3b (5.0)
5b (10.0)
5b (10.0)
5b (10.0)
3c (5.0)
50
70
90
50
70
90
50
70
90
50
70
90
50
70
90
50
70
90
50
1.334
1.694
1.636
1.153
1.996
1.872
1.055
1.694
1.400
1.192
2.671
2.565
1.640
2.804
2.119
2.672
3.256
3.083
0.963
400.2
508.2
490.8
345.9
598.8
561.6
316.5
508.2
420.0
357.6
801.3
769.5
492.0
851.2
635.7
801.6
976.8
924.9
288.9
297
214
98.7
460
246
151
267
182
93.8
420
269
139
279
119
57.9
347
147
58.5
310
1.99
1.81
1.91
1.82
1.95
1.88
1.77
1.77
1.92
1.86
2.03
1.92
1.94
2.05
1.92
2.01
2.02
1.91
1.90
267
267
272
268
268
268
268
269
271
269
272
272
268
270
268
271
270
266
266
93
96
95
93
99
95
98
93
95
92
96
97
95
97
96
96
98
96
96
9
10
11
12
13
14
15
16
17
18
19
3c (5.0)
3c (5.0)
5c (10.0)
5c (10.0)
5c (10.0)
Cp*TiCl3
[a] Conditions: solvent: 50 mL of toluene; [Al]/[Ti]: 1000; styrene: 5.0 mL; tp: 20 min; MAO: s-MAO. [b] Activity: kg of PS per mol of
Ti per hour. [c] Syndiotacticity determined from the amount of polymer insoluble in 2-butanone.
lar sieves (5 Å). All other chemicals were used without any further
purification. 3,4-Dimethylcyclopent-2-enone,[40] 4,4Ј-(C6H4)2-
(C5Me4H)2 (1a),[27] (p-BrC6H4CH2)2,[41] [4,4Ј-(C5Me4)2(C6H4)2]-
weight obtained with both the most active complexes (3c
and 5c) appears to be mainly ascribed to the lower electron-
donating effect of the dimethyl-substituted ligand. The mo-
lecular weight trend 3a Ͼ 3b can be considered to be a
manifestation of the reduced steric effects in 3a compared
to 3b.
[CpZrCl2]2
[(PhC5Me4)CpZrCl2] (4a),[31] [(p-tolylC5Me4)CpZrCl2] (4b),[31] 1-
tolyl-3,4-Me2C5H3,[7] (4c),[7]
[(1-tolyl-3,4-Me2C5H2)CpZrCl2]
(2a),[27]
[4,4Ј-(C5Me4)2(C6H4)2][TiCl3]2
(3a),[27]
[(PhC5Me4)TiCl3] (5a),[42] and [(p-tolylC5Me4)TiCl3] (5b)[43] were
prepared according to literature procedures. Methylaluminoxane
(MAO) was used as a solid (s-MAO). This was obtained by com-
plete evaporation of the solvent and residual AlMe3 from a toluene
solution of PMAO (Witco, EUROCEN 30T) and a toluene solu-
tion of PMAO (Witco, EUROCEN 10T). Polymerization-grade
ethylene monomer from Honam Petrochemical Corporation was
used after purification by passing through LabclearTM and Oxicle-
arTM filters. Styrene monomer purchased from Aldrich was used
Conclusions
The biphenylene- and diphenylethylene-bridged dinu-
clear zirconocenes [4,4Ј-(C5Me4)2(C6H4)2][CpZrCl2]2 (2a),
[p-(C5Me4)C6H4CH2]2[CpZrCl2]2
(2b),
and
[p-(3,4-
Me2C5H2)C6H4CH2]2[CpZrCl2]2 (2c) consistently provide
high molecular weight polymers and have a high catalyst
activity in ethylene polymerization, although there are some
differences, including both structural and polymerization
properties, between rigid and flexible bridged dinuclear
complexes in terms of activity and molecular weight trends.
In contrast, the corresponding dinuclear half-sandwich tit-
anocenes [(C5Me4)2(C6H4)2][TiCl3]2 (3a), [p-(C5Me4)-
C6H4CH2]2[TiCl3]2 (3b), and [p-(3,4-Me2C5H2)C6H4CH2]2-
[TiCl3]2 (3c) do not show any enhanced polymerization
properties in styrene polymerization compared to their mo-
nonuclear analogues. Indeed, they show a significant de-
crease in the molecular weight of the polymer produced and
a slight decrease of catalytic activity. These results appear
to be due to the cooperative participation of the electronic
effect of the two cationic metal centers through the biphen-
ylene or diphenylethylene bridge and/or the steric effects
between them.
1
after purification by passing through an alumina column. H and
13C NMR spectra were recorded with a Bruker Spectropin 400
spectrometer at ambient temperature. All chemical shifts are re-
ported in δ units with reference to the residual peaks of CDCl3 for
proton (δ = 7.24 ppm) and carbon (δ = 77.0 ppm). Elemental analy-
ses were carried out with an EA 1110-FISONS (CE Instruments)
at KAIST.
Synthesis of [p-(C5Me4H)C6H4CH2]2 (1b): A solution of (p-
BrC6H4CH2)2 (3.40 g, 10 mmol) in 50 mL of diethyl ether was
treated with 2.2 equiv. of nBuLi (8.8 mL) at 0 °C and the reaction
mixture was stirred at this temperature for 1 h. The slow formation
of a white precipitate was observed and the reaction mixture was
then warmed to room temperature and stirred for a further 2 h.
The colorless solution was then decanted off and 30 mL of thf was
added to the resulting dilithium salt. Subsequently, two equivalents
of 2,3,4,5-tetramethylcyclopent-2-enone (2.76 g) in 20 mL of thf
was added slowly through a cannula at –78 °C. The reaction mix-
ture was slowly warmed to room temperature and stirred overnight.
The resulting light orange solution was treated with 30 mL of a
saturated aqueous solution of NH4Cl. The organic portion was
separated and the aqueous layer was further extracted with diethyl
ether (50 mL). The combined organic portions were dried with an-
hydrous MgSO4, filtered, and the solvents evaporated to dryness to
afford a colorless oily product. The crude product was redissolved
in CH2Cl2 (30 mL) and a catalytic amount of solid p-TsOH (0.1 g)
Experimental Section
General: Tetrahydrofuran, toluene, n-hexane, and n-pentane were
distilled from Na-K alloy, Et2O from Na-benzophenone ketyl, and
CH2Cl2 from CaH2. All solvents were stored over activated molecu-
542
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Dinuclear Metallocenes for Olefin Polymerization
FULL PAPER
was added to the solution at room temperature. A yellow solid was
immediately formed, and the stirring was continued for a further
hour. The volume of the resulting reaction mixture was reduced to
10%, and 30 mL of n-hexane was poured into the flask in order to
precipitate the product and dissolve the unreacted materials. The
large amount of yellow solid obtained was filtered through a glass
frit and washed successively with ethanol (30 mL), diethyl ether
(30 mL), and n-pentane (30 mL). Drying in vacuo afforded 2.83 g
dissolved in 10 mL of thf was added to the reaction mixture
through a cannula at –78 °C. The resulting reaction mixture was
then warmed to room temperature and stirred for 24 h. The golden-
yellow solution formed was evaporated to dryness and extracted
with 30 mL of CH2Cl2. The mixture was subsequently treated with
an excess amount of Me3SiCl (3 to 4 equiv.) at 0 °C. After warming
to room temperature, the reaction mixture was further stirred over-
night. During the course of the reaction, the slow formation of a
red precipitate was observed. The resulting red mixture was evapo-
rated, and the shiny red product was washed twice with 20 mL of
1
of 1b in 67% yield. H NMR (400.13 MHz, CDCl3): δ = 7.18 (m,
8 H), 3.17 (q, 2 H), 2.93 (m, 4 H), 2.02 (s, 6 H), 1.91 (s, 6 H), 1.85
(s, 6 H), 0.95 (d, 6 H) ppm. 13C{1H} NMR (100.62 MHz, CDCl3): a mixture of n-hexane and CH2Cl2 (4:1, v/v). Drying in vacuo af-
δ = 142.7, 140.4, 139.0, 136.7, 135.0, 134.8, 128.4, 128.1, 50.1, 37.6,
forded 0.445 g of scarlet microcrystals of 3b in 61% yield.
Recrystallization of a concentrated CH2Cl2 solution of 3b layered
with n-hexane at room temperature afforded red single crystals suit-
able for an X-ray diffraction study. 1H NMR (400.13 MHz,
CDCl3): δ = 7.24 (m, 8 H), 2.99 (s, 4 H), 2.46 (s, 12 H), 2.41 (s, 12
H) ppm. 13C{1H} NMR (100.62 MHz, CDCl3): δ = 142.9, 142.0,
138.7, 136.1, 130.8, 130.3, 128.4, 37.3, 15.5, 14.6 ppm.
C32H36Cl6Ti2 (729.08): calcd. C 52.72, H 4.98; found C 52.65, H
5.44.
14.9, 12.7, 11.9, 11.1 ppm. EIMS: m/z 422 (85) [M+], 408 (9) [M+
–
CH2], 225 (15) [M+ – C6H4C5Me4H], 211 (100) [M+/2]. C32H38
(422.64): calcd. C 90.94, H 9.06; found C 90.33, H 9.44.
Synthesis of [p-(3,4-Me2C5H3)C6H4CH2]2 (1c): An identical pro-
cedure to that for the synthesis of 1b was employed with 3,4-di-
methylcyclopent-2-enone (2.18 g) instead of 2,3,4,5-tetramethylcy-
clopent-2-enone. This afforded 2.31 g of an ivory solid (1c) in 63%
1
yield. H NMR (400.13 MHz, CDCl3): δ = 7.35 (d, 4 H), 7.09 (d,
4 H), 6.60 (s, 2 H), 3.24 (s, 4 H), 2.86 (s, 4 H), 1.96 (s, 6 H), 1.87
(s, 6 H) ppm. 13C{1H} NMR (100.62 MHz, CDCl3): δ = 142.4,
139.7, 135.5, 135.4, 134.2, 131.0, 128.6, 124.5, 45.3, 37.6, 13.4,
12.6 ppm. EIMS: m/z 366 (76) [M+], 183 (100) [M+/2], 167 (61)
Synthesis of [{[p-(3,4-Me2C5H2)C6H4CH2][TiCl3]}2] (3c): A similar
procedure to that used for the synthesis of 3b was employed with
the ligand 1c (0.366 g, 1.00 mmol), but with an excess of Me2SiCl2
instead of Me3SiCl, to afford 3c as a dark-red solid (0.451 g, 67%).
[M+/2 – CH3]. C28H30 (366.54): calcd. C 91.75, H 8.25; found C 1H NMR (400.13 MHz, CDCl3): δ = 7.57 (d, 4 H), 7.17 (s, 4 H),
91.23, H 8.52.
7.10 (d, 4 H), 2.93 (s, 4 H), 2.47 (s, 12 H) ppm. 13C{1H} NMR
(100.62 MHz, CDCl3): δ = 143.3, 140.6, 139.3, 130.8, 129.2, 126.1,
119.1, 37.4, 16.0 ppm. C28H28Cl6Ti2 (672.97): calcd. C 49.97, H
4.19; found C 49.60, H 5.02.
Synthesis of [{[p-(C5Me4)C6H4CH2][CpZrCl2]}2] (2b): A slurry of
1b (0.422 g, 1.00 mmol) in 20 mL of thf was treated with two equiv-
alents of nBuLi (0.8 mL) at –78 °C. The reaction mixture was
warmed to room temperature and stirred for 4 h. Two equivalents
of [CpZrCl3] (2.0 mmol, 0.525 g) dissolved in 10 mL of thf was
added to the resulting yellow suspension through a cannula at
–78 °C. The reaction mixture was then warmed to room tempera-
ture and stirred for 24 h. The golden-yellow solution formed was
then evaporated to dryness and extracted with 30 mL of toluene.
The mixture was filtered through a Celite pad, and the light-yellow
filtrate was evaporated to dryness. The crude product was washed
twice with 10 mL of a mixture of n-hexane and diethyl ether (2:1,
v/v). Drying in vacuo afforded spectroscopically pure 2b as a light-
yellow solid (0.639 g, 73%). Recrystallization of a concentrated
CH2Cl2 solution of 2b layered with n-hexane at room temperature
afforded light golden colored, single crystals suitable for an X-ray
diffraction study. 1H NMR (400.13 MHz, CDCl3): δ = 7.19 (d, 4
H), 7.05 (d, 4 H), 6.13 (s, 10 H), 2.99 (s, 4 H), 2.21 (s, 12 H), 2.04
(s, 12 H) ppm. 13C{1H} NMR (100.62 MHz, CDCl3): δ = 140.5,
131.6, 129.7, 128.5, 126.5, 126.1, 124.2, 116.7, 37.3, 14.0, 12.3 ppm.
C42H46Cl4Zr2 (875.07): calcd. C 57.65, H 5.30; found C 56.64, H
5.72.
Synthesis of [(1-p-tolyl-3,4-Me2C5H2)TiCl3] (5c): A similar pro-
cedure to that used for the synthesis of 3b was employed with 1-
tolyl-3,4-Me2C5H3 (0.366 g, 1.00 mmol), but with an excess of Me2-
SiCl2 instead of Me3SiCl, to afford 6c as dark red microcrystals
1
(0.432 g, 64% yield). H NMR (400.13 MHz, CDCl3): δ = 7.61 (d,
2 H), 7.22 (d, 2 H), 7.18 (s, 2 H), 2.47 (s, 6 H), 2.37 (s, 3 H) ppm.
13C{1H} NMR (100.62 MHz, CDCl3): δ = 140.8, 140.4, 139.2,
130.2, 129.6, 126.0, 119.0, 21.4, 15.9 ppm. C14H15Cl3Ti (337.49):
calcd. C 49.82, H 4.48; found C 49.42, H 4.61.
Ethylene Polymerization: Freshly distilled toluene (48 mL) was
placed in a degassed 250-mL glass reactor charged with a pre-
weighed amount of s-MAO (Al/Zr = 1000) and the temperature
was adjusted using an external bath. The flask was then filled with
ethylene monomer at 1 bar with vigorous stirring after degassing
with the monomer several times. Polymerization was started by ad-
dition of a toluene solution of catalyst (2.0 mL, 2.0 µmol of Zr).
After 2 min, all the reactions were quenched by addition of an
acidified ethanol solution (10% HCl in EtOH) and the resulting
polyethylene was precipitated by the addition of 200 mL of ethanol.
After stirring for 1 to 2 h, the polyethylenes were filtered off,
washed with ethanol several times, and dried under vacuum to a
constant weight at 80 °C.
Synthesis of [{[p-(3,4-Me2C5H2)C6H4CH2][CpZrCl2]}2] (2c): An
identical procedure to that used for the synthesis of 2b was em-
ployed with the ligand 1c (0.366 g, 1.00 mmol) to afford 2c as a
1
light-yellow solid (0.573 g, 70%). H NMR (400.13 MHz, CDCl3):
Styrene Polymerization: Freshly distilled toluene (48 mL) and sty-
rene (5.0 mL) were successively added to a degassed, 250-mL glass
reactor charged with a pre-weighed amount of s-MAO (Al/Ti =
1000) with vigorous stirring. The temperature was adjusted using
an external bath. Polymerization was started by addition of a tolu-
ene solution of catalyst (2.0 mL, 10.0 µmol of Ti). After 20 min, all
the reactions were quenched by addition of an acidified ethanol
solution (10% HCl in EtOH) and the resulting polystyrene was
further precipitated by addition of 200 mL of ethanol. After stir-
ring for 1 to 2 h, polystyrenes were filtered off, washed with ethanol
several times, and dried under vacuum to a constant weight at
δ = 7.36 (d, 4 H), 7.12 (d, 4 H), 6.49 (s, 4 H), 6.11 (s, 10 H), 2.86
(s, 4 H), 2.15 (s, 12 H) ppm. 13C{1H} NMR (100.62 MHz, CDCl3):
δ = 140.8, 131.4, 129.4, 128.7, 125.1, 122.6, 116.5, 114.0, 37.3,
13.8 ppm. C38H38Cl4Zr2 (818.97): calcd. C 55.73, H 4.68; found C
55.74, H 4.87.
Synthesis of [p-(C5Me4)C6H4CH2]2[TiCl3]2 (3b): A slurry of 1b
(0.422 g, 1.00 mmol) in 20 mL of thf was treated with two equiva-
lents of nBuLi (0.8 mL) at –78 °C. The reaction mixture was
warmed to room temperature and stirred for 4 h to give a yellow
suspension. Two equivalents of [ClTi(OiPr)3] (2.0 mmol, 0.521 g)
Eur. J. Inorg. Chem. 2007, 537–545
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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543

Y. Do et al.
FULL PAPER
[2]
[3]
S. Park, Y. Han, S. K. Kim, J. Lee, H. K. Kim, Y. Do, J. Or-
ganomet. Chem. 2004, 689, 4263–4276.
V. C. Gibson, S. K. Spitzmesser, Chem. Rev. 2003, 103, 283–
316.
W. Kaminsky, Adv. Catal. 2001, 46, 89–159.
T. J. Marks, J. C. Stevens (Eds.), Top. Catal. 1999, 7, 1–208.
G. J. P. Britovsek, V. C. Gibson, D. F. Wass, Angew. Chem. Int.
Ed. 1999, 38, 428–447.
S. Jüngling, R. Mülhaupt, H. Plenio, J. Organomet. Chem.
1993, 460, 191–195.
80 °C. The crude polymer was extracted with refluxing 2-butanone
for 12 h, and the insoluble fraction was filtered and dried under
vacuum overnight at 80 °C in order to determine the syndiotactic
polystyrene portion.
[4]
[5]
[6]
Polymer Analysis: The molecular weight (Mw) and molecular
weight distribution (Mw/Mn) of polypropylenes were determined by
GPC (Polymer Laboratories PL-GPC 220) in 1,2,4-trichloroben-
zene using standard polystyrenes as a reference. The melting tem-
peratures (Tm) of polypropylenes were measured by DSC (TA In-
strument, 2910 MDSC).
[7]
[8]
K. Soga, T. H. Ban, T. Uozumi, J. Mol. Catal. A 1998, 128,
273–278.
X-ray Structure Determination: X-ray diffraction measurements
were performed with a Bruker AXS diffractometer with a CCD
area detector, using graphite-monochromated Mo-Kα radiation (λ
= 0.71073 Å) at 293 K. A hemisphere of data was collected using
ω scans. The frame data sets were processed using the SAINT and
XPREP processing package. An empirical absorption correction
was applied to each data set with the program SADABS. All the
intensity data were corrected for Lorentz and polarization effects.
The structure was solved by direct methods and refined by full-
matrix least-squares methods using the SHELXTL program pack-
age with anisotropic thermal parameters for all non-hydrogen
atoms. Hydrogen atoms were placed at their geometrically calcu-
lated positions and refined as riding on the corresponding carbon
atoms with isotropic thermal parameters. For 2b, final refinement
based on the reflections with I Ͼ 2σ(I) converged at R1 = 0.0348,
wR2 = 0.0851, GOF = 0.963, and for 3b, R1 = 0.0506, wR2 =
0.1156 and GOF = 0.845 (Table 4).[44]
[9]
W. Spaleck, F. Kuber, B. Bachmann, C. Firtze, A. Winter, J.
Mol. Catal. A 1998, 128, 279–287.
T. Ushioda, M. L. H. Green, J. Haggitt, X. Yan, J. Organomet.
Chem. 1996, 518, 155–166.
M. L. H. Green, N. H. Popham, J. Chem. Soc., Dalton Trans.
1999, 1049–1059.
S. K. Noh, J. Kim, J. Jung, C. S. Ra, D. H. Lee, H. B. Lee, S. W.
Lee, W. S. Huh, J. Organomet. Chem. 1999, 580, 90–97.
S. K. Noh, S. Kim, J. Kim, D. H. Lee, K. B. Yoon, H. B. Lee,
S. W. Lee, W. S. Huh, J. Polym. Sci. Part A: Polym. Chem. 1997,
35, 3717–3728.
S. K. Noh, M. Lee, D. H. Kum, W. S. Lyoo, D. H. Lee, J. Po-
lym. Sci. Part A: Polym. Chem. 2004, 42, 1712–1723.
S. K. Noh, Y. Yang, W. S. Lyoo, J. Appl. Polym. Sci. 2003, 90,
2469–2474.
S. K. Noh, J. Lee, D. H. Lee, J. Organomet. Chem. 2003, 667,
53–60.
H. Li, L. Li, T. J. Marks, L. Liable-Sands, A. L. Rheingold, J.
Am. Chem. Soc. 2003, 125, 10788–10789.
L. Li, M. V. Metz, H. Li, M.-C. Chen, T. J. Marks, L. Liable-
Sands, A. L. Rheingold, J. Am. Chem. Soc. 2002, 124, 12725–
12741.
N. Guo, L. Li, T. J. Marks, J. Am. Chem. Soc. 2004, 126, 6542–
6543.
H. Li, L. Li, T. J. Marks, Angew. Chem. Int. Ed. 2004, 43, 4937–
4940.
J. Wang, H. Li, N. Guo, L. Li, C. L. Stern, T. J. Marks, Organo-
metallics 2004, 23, 5112–5114.
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
Table 4. X-ray crystallographic data.
Compound
2b
3b
Formula
Formula weight
C42H46Cl4Zr2
875.07
C32H36Cl6Ti2
729.08
[19]
[20]
[21]
[22]
Crystal system; space group
monoclinic; C2/c
21.509(5)
16.944(4)
12.933(3)
90, 124.370(4), 90 90, 94.59(9), 90
3890.5(16)
4
1.494
monoclinic; C2/c
36.11(6)
6.625(11)
a [Å]
b [Å]
c [Å]
α, β, γ [°]
V [Å3]
Z
15.33(2)
H. Li, C. L. Stern, T. J. Marks, Macromolecules 2005, 38, 9015–
9027.
3656(10)
8
1.325
1496
[23]
[24]
[25]
H. G. Alt, R. Ernst, Inorg. Chim. Acta 2003, 350, 1–11.
H. G. Alt, R. Ernst, J. Mol. Catal. A 2003, 195, 11–27.
J. C. Sierra, D. Hüerländer, M. Hill, G. Kehr, G. Erker, R.
Fröhlich, Chem. Eur. J. 2003, 9, 3618–3622.
J. Kuwabara, D. Takeuchi, K. Osakada, Organometallics 2005,
24, 2705–2712.
M. H. Lee, S. K. Kim, Y. Do, Organometallics 2005, 24, 3618–
3620.
J. L. M. Petoff, M. D. Bruce, R. M. Waymouth, A. Masood,
T. K. Lal, R. W. Quan, S. J. Behrend, Organometallics 1997, 16,
5909–5916.
Dcalcd. [gcm–3
F(000)
]
1784
T [K]
µ (Mo-Kα) [mm–1
θ range [°]
293
0.839
1.66–28.37
293
0.895
1.13–27.97
]
[26]
[27]
[28]
No. of unique/observed
[I Ͼ 2σ(I)] reflections
No. of parameters refined
R1, wR2[a]
4499/12111
221
0.0348, 0.0851
1.045
4059/10577
193
0.0506, 0.1156
0.845
GOF
Min./max. electron density [eÅ–3
]
–0.692/0.302
–0.360/0.313
[29]
K. Kimura, K. Takaishi, T. Matsukawa, T. Yoshimura, H. Ya-
mazaki, Chem. Lett. 1998, 571–572.
2
2 2
[a] R1 = ∑||Fo| – |Fc||/∑|Fo|; wR2 = [∑[w(Fo – Fc ) ]/∑[w(Fo2)2]]1/2
.
[30]
[31]
M. H. Lee, Y. Do, J. Organomet. Chem. 2005, 690, 1240–1248.
X. Deng, B. Wang, S. Xu, X. Zhou, L. Yang, Y. Li, Y. Hu, Y.
Li, F. Zou, J. Mol. Catal. A 2002, 184, 57–64.
M. Björgvinsson, S. Halldorsson, I. Arnason, J. Magull, D.
Fenske, J. Organomet. Chem. 1997, 544, 207–215.
As usual, a higher degree of steric bulk gives a higher molecu-
lar weight of polyethylene: H. G. Alt, A. Köppl, Chem. Rev.
2000, 100, 1205–1222.
Acknowledgments
[32]
[33]
Financial support from Center for Molecular Design and Synthesis
(CMDS), Korea Advanced Institute of Science and Technology
and the BK-21 project is gratefully acknowledged. We also thank
Honam Petrochemical Corporation for high quality ethylene
monomer and financial support. S. K. K thanks Dr. J.-W. Hwang
for help in obtaining the X-ray crystal structures.
[34]
[35]
[36]
W. Kaminsky, V. Scholz, R. Werner, Macromol. Symp. 2000,
159, 9–18.
K. Nomura, T. Komatsu, Y. Imanishi, Macromolecules 2000,
33, 8122–8124.
D. J. Byun, A. F. Fudo, A. Tanaka, M. Fujiki, K. Nomura,
Macromolecules 2004, 37, 5520–5530.
[1] Special issue on “Frontiers in Metal-Catalyzed Polymeriza-
tion” (Ed.: J. A. Gladysz), Chem. Rev. 2000, 100, 1167–1604.
544
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Eur. J. Inorg. Chem. 2007, 537–545

Dinuclear Metallocenes for Olefin Polymerization
FULL PAPER
[37] K. Yokota, T. Inoue, S. Naganuma, H. Shozaki, N. Tomotsu,
M. Kuramoto, N. Ishihara, Syndiospecific Polymerization of
Styrene, in Metal-Organic Catalysts for Synthesis and Polymeri-
zation (Ed.: W. Kaminsky), Springer, Berlin, 1999, p. 435–446.
[38] J. C. Flores, T. E. Ready, J. C. W. Chien, M. D. Rausch, J. Or-
ganomet. Chem. 1998, 562, 11–15.
[42] M. Bjoergvinsson, S. Halldorsson, I. Arnason, J. Magull, D.
Fenske, J. Organomet. Chem. 1997, 544, 207–215.
[43] Y. Kim, Y. Han, J.-W. Hwang, M. W. Kim, Y. Do, Organome-
tallics 2002, 21, 1127–1135.
[44] CCDC-617759 (for 2b) and -617760 (for 3b) contain the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallo-
graphic Data Center via www.ccdc.cam.ac.uk/data_request/cif.
Received: September 7, 2006
[39] J. Schellenberg, N. Tomotsu, Prog. Polym. Sci. 2002, 27, 1925–
1982 and references therein.
[40] J. M. Conia, M. L. Leriverend, Bull. Soc. Chim. Fr. 1970, 2981–
2991.
Published Online: December 12, 2006
[41] Y. Suh, J.-S. Lee, S.-H. Kim, R. D. Rieke, J. Organomet. Chem.
2003, 684, 20–36.
Eur. J. Inorg. Chem. 2007, 537–545
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