Biphenylene-bridged dinuclear group 4 metal complexes: Enhanced polymerization properties in olefin polymerization

Article abstract of DOI:10.1021/om049316w

The well-defined, novel dinuclear group 4 metal complexes [4,4′-(C₆H₄)₂(C₅Me ₄)₂][CpZrX₂]₂ (X = Cl (2a), Me (2b)), [4,4′-(C₆H₄)2(C₅Me

Full text of DOI:10.1021/om049316w

3618
Organometallics 2005, 24, 3618-3620
Biphenylene-Bridged Dinuclear Group 4 Metal
Complexes: Enhanced Polymerization Properties in
Olefin Polymerization
Min Hyung Lee, Seong Kyun Kim, and Youngkyu Do*
Department of Chemistry, School of Molecular Science BK-21 and Center for Molecular Design
and Synthesis, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
Received September 2, 2004
Scheme 1
Summary: The well-defined, novel dinuclear group 4
metal complexes [4,4′-(C6H4)2(C5Me4)2][CpZrX2]2 (X ) Cl
(2a), Me (2b)), [4,4′-(C6H4)2(C5Me4)2][TiCl3]2 (3), and
[4,4′-(C6H4)2(C5Me4)2][Ti(O-2,6-iPr2Ph)Cl2]2 (4) exhibit
an increase of molecular weight as well as comparable
or even higher catalytic activity in ethylene (2 and 4)
and styrene (3 and 4) polymerization than their mono-
nuclear counterparts.
Dinuclear group 4 catalysts which consist of two
linked active centers in a molecule have been recently
investigated due to their potential catalytic properties
in olefin polymerization, ascribed to cooperative effects
between two active centers.1 Although several studies
on dinuclear catalysts connected by flexible bridging
groups suggest that the polymerization properties such
as catalyst activity and molecular weight of the polymer
are strongly correlated with the nature of the bridging
group employed,2 systematic polymerization studies
utilizing well-defined dinuclear catalyst systems have
still been less explored in comparison with those of well-
known mononuclear systems.3 Herein, we report the
synthesis and characterization of novel dinuclear group
4 complexes linked by a biphenylene-bridged bis(cyclo-
pentadienyl) ligand, 4,4′-(C6H4)2(C5Me4H)2 (1), where
the biphenylene group was chosen due to the nature of
steric rigidity, a proper length, and electronic conjuga-
tion. Also, the direct comparison of their polymerization
behavior in olefin polymerization with those of the
corresponding mononuclear catalysts was described.
Transmetalation of the dilithium salt of the ligand 1,
prepared from the modified literature procedure,4 with
2 equiv of CpZrCl3 in refluxing THF afforded the
dinuclear zirconocene complex [4,4′-(C6H4)2(C5Me4)2]-
[CpZrCl2]2 (2a). The dinuclear half-titanocene complex
[4,4′-(C6H4)2(C5Me4)2][TiCl3]2 (3) was synthesized from
the reaction of the dilithium salt of 1 with 2 equiv of
ClTi(OiPr)3 in refluxing THF, followed by in situ chlo-
rination with an excess amount of Me3SiCl in CH2Cl2.5
The complex 3 was further converted cleanly to the
corresponding aryloxide complex [4,4′-(C6H4)2(C5Me4)2]-
[Ti(O-2,6-iPr2Ph)Cl2]2 (4) by treating it with 2 equiv of
LiO-2,6-iPr2Ph in THF (Scheme 1).
The solid-state structures of 2a and 4 have been
determined by X-ray diffraction methods,6 and the
structure of 2a7 is depicted in Figure 1. The zirconium
complex 2a crystallizes in the space group P21/n with
only half of the molecule in the asymmetric unit. Thus,
two [C5Me4Ph]CpZrCl2 fragments are perfectly inverted
with respect to the phenylene-phenylene single bond,
indicating that 2a consists of two equivalent units in
the solid state. It can be also seen that the large
biphenylene bridge is oriented away from the chlorine
atoms. The detailed structural analysis indicates that
the structural parameters around the zirconium center,
such as the bond angles and bond distances listed in
the caption to Figure 1, are in a range similar to those
* To whom correspondence should be addressed. E-mail:
ykdo@kaist.ac.kr.
(1) (a) Guo, N.; Li, L.; Marks, T. J. J. Am. Chem. Soc. 2004, 126,
6542. (b) Li, H.; Li, L.; Marks, T. J.; Liable-Sands, L.; Rheingold, A. L.
J. Am. Chem. Soc. 2003, 125, 10788. (c) Noh, S. K.; Lee, J.; Lee, D. H.
J. Organomet. Chem. 2003, 667, 53. (d) Li, L.; Metz, M. V.; Li, H.;
Chen, M.-C.; Marks, T. J.; Liable-Sands, L.; Rheingold, A. L. J. Am.
Chem. Soc. 2002, 124, 12725.
(2) (a) Noh, S. K.; Kim, J.; Jung, J.; Ra, C. S.; Lee, D. H.; Lee, H. B.;
Lee, S. W.; Huh, W. S. J. Organomet. Chem. 1999, 580, 90. (b) Spaleck,
W.; Ku¨ber, F.; Bachmann, B.; Fritze, C.; Winter, A. J. Mol. Catal. A:
Chem. 1998, 128, 279. (c) Noh, S. K.; Kim, S.; Kim, J.; Lee, D. H.; Yoon,
K. B.; Lee, H. B.; Lee, S. W.; Huh, W. S. J. Polym. Sci.: Part A: Polym.
Chem. 1997, 35, 3717.
(3) For recent reviews of group 4 catalysts for olefin polymerization,
see: (a) Gladysz, J. A., Ed. Frontiers in Metal-Catalyzed Polymeriza-
tion. Chem. Rev. 2000, 100. (b) Britovsek, G. J. P.; Gibson, V. C.; Wass,
D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (c) McKnight, A. L.;
Waymouth, R. M. Chem. Rev. 1998, 98, 2587. (d) Bochmann, M. J.
Chem. Soc., Dalton Trans. 1996, 255. (e) Brintzinger, H. H.; Fischer,
D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1143.
(5) Fokken, S.; Spaniol, T. P.; Okuda, J. Organometallics 1997, 16,
4240.
(6) See the Supporting Information for details.
(7) Crystal data for 2: C40H42Cl4Zr2, Mr ) 847.02, monoclinic, a )
9.312(2) Å, b ) 15.201(3) Å, c ) 13.422(2) Å, â ) 101.35(0)°, V ) 1862.8-
(5) Å3, T ) 293 K, space group P21/n, Z ) 4, µ(Mo KR) ) 0.874 mm-1
,
11 945 reflections measured, 4449 unique (Rint ) 0.0203), which were
used in all calculations. The final refinement based on 3581 reflections
(I > 2σ(I)) converged at R1 ) 0.0348 and wR2 ) 0.0995.
(4) Bunel, E. E.; Campos, P.; Ruz, J.; Valle, L. Organometallics 1988,
7, 474.
10.1021/om049316w CCC: $30.25 © 2005 American Chemical Society
Publication on Web 06/10/2005

Communications
Organometallics, Vol. 24, No. 15, 2005 3619
Table 1. Ethylene Polymerization Data with
Catalysts 2, 5, and 6aa
cat.
(amt,
yield
A
Mw
Mw/ Tm
) Mn (°C)
entry µmol) cocat. Al/Zr (g) (×10-3
)
(×10-3
b
1
2
3
4
5
6
7
2a (1.0) MAO 1000 0.607
5a (2.0) MAO 1000 0.551
6a (2.0) MAO 1000 0.633
9.10
8.26
9.49
398
299
270
294
219
779
543
2.21 134.4
2.14 137.0
2.09 136.8
2.11 135.9
2.18 134.6
2.13 135.1
2.60 135.4
2a (1.0) MAO 2000 0.789 11.83
5a (2.0) MAO 2000 0.588
8.82
6.67
5.67
2b (1.0) borate
5b (2.0) borate
0.445
0.378
a Conditions: P(ethylene), 1 bar; Tp, 50 °C; solvent, 50 mL of
toluene; tp, 2.0 min; MAO, solid MAO; borate, [Ph3C][B(C6F5)4];
[B]/[Zr] ) 1. b Activity is given in units of (kg of PE)/((mol of Zr) h
bar).
Figure 1. Molecular structure of [4,4′-(C6H4)2(C5Me4)2]-
[CpZrCl2]2 (2a). Selected bond distances (Å) and angles
(deg): Zr-Cl(1) ) 2.429(1), Zr-Cl(2) ) 2.440(1), Zr-Cg(1)
) 2.224(1), Zr-Cg(2) ) 2.199(2); Cl(1)-Zr-Cl(2) ) 96.5(0),
Cg(1)-Zr-Cg(2) ) 129.8, Cp′(1)-Ph(1) ) 63.6(2). Cg(1) and
Cg(2) are the centroids of the C5Me4 and Cp rings,
respectively, Cp′(1) is the plane of C5Me4, and Ph(1) is the
plane of C6H4.
half of 2a (entries 1-3). Also, the polyethylene produced
by 2a exhibits a narrow molecular weight distribution
(Mw/Mn) of 2.21, suggesting that the two zirconium
centers in 2a are identical and each of them behaves
as a single-site catalyst, as expected from the crystal
structure of 2a. Importantly, the polyethylene from 2a
has a molecular weight that is much higher than those
of the polyethylenes from 5a and 6a. Considering that
the polyethylenes by the mononuclear catalysts 5a and
6a exhibit nearly similar values in molecular weight,
the molecular weight increase caused by 2a is remark-
able.
Chart 1
Since the ion-pair structure of catalytically active
species in the MAO-activated system could be much
affected by the ligand environment and the amount of
MAO employed,11 which in turn may influence both the
catalytic activity and the rate of termination reactions
such as chain transfer to Al or â-H transfer reactions,
further ethylene polymerizations in the presence of an
increased amount of Al components and the absence of
any of them were carried out to gain a brief insight into
the polymerization behavior of the biphenylene-bridged
dinuclear zirconocenes. The use of an increased amount
of MAO (entries 4 and 5) or borate as a discrete activator
(entries 6 and 7) did not change the catalytic trend that
the dinuclear zirconocenes provide higher activity and
molecular weight under otherwise identical conditions
in comparison to their mononuclear analogues, implying
that such a catalytic trend is intrinsic to the present
dinuclear systems. The decreased molecular weight in
both di- and mononuclear catalyst systems at the
increased amount of MAO also indicates the involve-
ment of chain transfer to Al under MAO activation,
probably to a similar extent.12 In addition, on activation
with 1 equiv of [Ph3C][B(C6F5)4], the dimethyl complexes
2b and 5b6 afforded polyethylenes with much increased
molecular weight, reflecting prevailing chain transfer
to Al under the above MAO-activated catalyst systems.
Furthermore, the production of the higher molecular
weight polymer by 2b than by 5b under borate activa-
tion suggests that ethylene polymerizations with the
for mononuclear nonbridged zirconocene complexes.8,9
Interestingly, the dihedral angle of 63.6(2)° between the
C5Me4 ring and the adjacent phenylene ring is some-
what larger than that observed in the corresponding
mononuclear zirconocene (C5Me4Ph)CpZrCl2 (5a; 47.2°),8
while the biphenylene group is nearly planar, showing
no apparent distortion between two phenylene planes
despite the possible presence of nonbonded repulsion
interactions between the ortho hydrogen atoms. The
structural analysis of the titanium complex 46 also
reveals that the overall features in 4 very much re-
semble those in 2a, except for the fact that the Cp ring
is replaced by the aryloxide group and the bonding
geometry of each [C5Me4Ph]Ti(OAr)Cl2 unit is nearly
identical with that of similar mononuclear complexes.10
To investigate the catalytic properties of the dinuclear
complexes in olefin polymerization, the ethylene poly-
merization behavior of the zirconocene complex 2a was
first examined along with those of the mononuclear
catalysts 5a8 and (C5Me4biPh)CpZrCl2 (6a)6 (Chart 1).
In the presence of an excess amount of methylalumi-
noxane (MAO; Al/Zr ) 1000 in Table 1), 2a shows high
activity, comparable to that of the sterically encumbered
6a and slightly higher than that of 5a, which is an exact
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A.; Brintzinger, H. H.; Ystenes, M.; Rytter, E.; Talsi, E. P. J.
Organomet. Chem. 2003, 683, 92. (c) Bryliakov, K. P.; Semikolenova,
N. V.; Yudaev, D. V.; Ystenes, M.; Rytter, E.; Zakharov, V. A.; Talsi,
E. P. Macromol. Chem. Phys. 2003, 204, 1110. (d) Babushkin, D. E.;
Brintzinger, H. H. J. Am. Chem. Soc. 2002, 124, 12869.
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Y.; Zou, F. J. Mol. Catal. A: Chem. 2002, 184, 57.
(9) (a) Kimura, K.; Takaishi, K.; Matsukawa, T.; Yoshimura, T.;
Yamazaki, H. Chem. Lett. 1998, 571. (b) Petoff, J. L. M.; Bruce, M. D.;
Waymouth, R. M.; Masood, A.; Lal, T. K.; Quan, R. W.; Behrend, S. J.
Organometallics 1997, 16, 5909.
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Phys. 1998, 199, 955.

3620 Organometallics, Vol. 24, No. 15, 2005
Communications
Table 2. Styrene and Ethylene Polymerization
Data with Catalysts 3, 4, 7, and 8a
According to the ethylene polymerization data with
the dinuclear and mononuclear titanocene aryloxides 4
and 8 (entries 5 and 6 of Table 2), respectively, it is the
dinuclear 4 that produces polyethylene with higher
molecular weight at a slightly increased level of activity.
Thus, the pattern of the increase in activity and mo-
lecular weight of the polymers that is consistently
observed for 2-4 might be the characteristic polymer-
ization property of the present dinuclear catalytic
systems derived from the biphenylene-bridged bis-
(cyclopentadienyl) ligand 1.
In conclusion, we have synthesized and characterized
the well-defined dinuclear group 4 metallocene catalysts
linked by a biphenylene bridge and examined their
catalytic properties with the direct comparison with
those for the corresponding mononuclear catalysts in
the polymerization of ethylene and styrene. The di-
nuclear catalysts consistently exhibit an increase of
molecular weight of polyethylene and polystyrene as
well as high catalyst activity. The detailed polymeriza-
tion behavior, including the origin of these interesting
results and the synthesis of relevant dinuclear catalysts,
is under investigation.
cat.
(amt,
yield
A
Mw
Mw/ Tm
SI
entry µmol) monomer (g) (×10-3
)
(×10-3
)
Mn (°C) (%)d
1
2
3
4
5
6
3 (5.0) styreneb 0.590 0.177
4 (5.0) styreneb 0.552 0.166
7 (10.0) styreneb 0.361 0.108
8 (10.0) styreneb 0.525 0.157
4 (2.5) ethylenec 0.840 2.02
8 (5.0) ethylenec 0.744 1.79
51.8 1.79 272.2 95
57.0 1.86 272.3 95
37.2 1.70 272.5 90
56.5 1.76 272.2 93
401
283
6.50 130.4
4.91 128.5
a Conditions: solvent, 50 mL of toluene; [Al]/[Ti], 1000; Tp, 50
°C. b Conditions and definitions: [styrene], 5.0 mL; tp, 20 min;
MAO, modified MAO in toluene; activity given in units of (kg of
PS)/((mol of Ti) h). c Conditions and definitions: P(ethylene), 1 bar;
tp, 5 min; MAO, solid MAO; activity given in units of (kg of PE)/
((mol of Ti) h bar). d Syndiotacticity determined by 2-butanone-
insoluble portion.
foregoing dinuclear zirconocenes are likely to proceed
with reduced rates of â-H transfer reactions.
In the case of the dinuclear half-titanocenes 3 and 4,
their styrene polymerization behavior was compared
with that of the corresponding mononuclear catalysts
(C5Me4Ph)TiCl3 (7)13 and (C5Me4Ph)Ti(O-2,6-iPr2Ph)Cl2
(8),6,14 respectively. From the polymerization results in
Table 2, it can be easily noted that 3 and 4 behave as
highly active single-site catalysts for styrene polymer-
ization. Moreover, 3 provides higher activity and mo-
lecular weight than its mononuclear counterpart 7 while
4 and 8 show similar styrene polymerization behavior.
Further investigation of syndiotactic index (SI) and
melting temperature (Tm) of the polystyrenes suggests
that the syndiospecific stereocontrol is also well main-
tained in 3 and 4.
Acknowledgment. Financial support from the Ko-
rea Science and Engineering Foundation (Grant No.
R02-2002-000-00057-0), the CMDS, and the BK 21
project are gratefully acknowledged. We thank Honam
Petrochemical Corp. for GPC analyses. M.H.L. thanks
Dr. J.-W. Hwang for help in obtaining the X-ray crystal
structures.
Supporting Information Available: Text, tables, and
figures describing the full synthesis, characterization, and
polymerization procedure and detailed crystallographic data
and ORTEP drawings for 2a and 4; crystallographic data for
2a and 4 are also available as a CIF file. This material is
available free of charge via the Internet at http://pubs.acs.org.
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OM049316W