Ethylene polymerization behavior of new titanium complexes having two phenoxy-pyridine chelate ligands

Article abstract of DOI:10.1246/cl.2001.1060

Two new titanium complexes having two phenoxy-pyridine chelate ligands were synthesized and investigated for their potential as ethylene polymerization catalysts. On activation with Ph₃C⁺B^-(C₆F₅) ₄/ i-Bu₃Al, one of the complexes, bis[2-(2′-pyridyl)phenolato] titanium complex, exhibited high activity (227-564 kg-PE/mol-cat·h) and produced high molecular weight polyethylene (M_r; 140000-3230000) at 25-75°C.

Full text of DOI:10.1246/cl.2001.1060

1060
Chemistry Letters 2001
Ethylene Polymerization Behavior of New Titanium Complexes
Having Two Phenoxy–Pyridine Chelate Ligands
Yoshihisa Inoue, Takashi Nakano, Hidetsugu Tanaka, Norio Kashiwa, and Terunori Fujita*
R&D Center, Mitsui Chemicals, Inc., Nagaura, Sodegaura, Chiba 299-0265
(Received July 27, 2001; CL-0107140)
Two new titanium complexes having two phenoxy–pyri-
dine chelate ligands were synthesized and investigated for their
potential as ethylene polymerization catalysts. On activation
with Ph3C+B–(C6F5)4 / i-Bu3Al, one of the complexes, bis[2-(2'-
pyridyl)phenolato] titanium complex, exhibited high activity
(227–564 kg-PE/mol-cat·h) and produced high molecular
weight polyethylene (Mv; 140000–3230000) at 25–75 °C.
The design and application of group 4 metallocene cata-
lysts have revolutionized not only polyolefin chemistry but also
the polyolefin industry to create a variety of high performance
polyolefins such as linear low-density polyethylene, isotactic
and syndiotactic polypropylene, syndiotactic polystyrene, etc.1
However, since the discovery of the group 4 metallocene cata-
lysts, the metallocene catalysts have been thoroughly investi-
gated by both academic and industrial research groups.
Therefore, in recent years, there has been increasing interest in
the development of new olefin polymerization catalysts using
transition metal complexes with no Cp ligand. In consequence,
quite a few new olefin polymerization catalysts based on both
early and late transition metal complexes have been developed.2
In our own efforts, we have recently reported that transi-
tion metal complexes featuring non-symmetric bidentate lig-
and(s) (e.g., phenoxy–imine, pyrrolide–imine, indolide–imine,
and imine–pyridine ligands) possess high catalytic performance
for olefin polymerization including living olefin polymeriza-
tion.3 In this communication, we describe the synthesis and
ethylene polymerization behavior of two titanium complexes
bearing two phenoxy–pyridine chelate ligands. In addition, the
ethylene polymerization behavior was compared with that of
analogous titanium complexes having two phenoxy–imine
chelate ligands (titanium FI Catalysts). The titanium complexes
used in this study are bis[2-(2'-pyridyl)phenolato]titanium(IV)-
diamide, complex 1, and bis[4,6-di-tert-butyl-2-(2'-pyridyl)phe-
nolato]titanium(IV)diamide, complex 2. Phenoxy–pyridine
chelate ligands, HL1 and HL2, were prapared by the coupling
reaction of the Grignard reagent derived from the desired bro-
moanisole with 2-bromopyridine using Ni(dppe)Cl2 (dppe =
Ph2PCH2CH2PPh2) as a catalyst, followed by the demethylation
of the resulting coupling product by pyridinium chloride (HL1;
68%, HL2; 54%, based on bromoanisole).4 The phenoxy–pyri-
dine ligands reacted smoothly with Ti(NMe2)4 in toluene to
yield the target complexes (1; 71%, 2; 61%)(Scheme 1).5
complex 1 exhibited higher activities (25 °C; 227 kg-PE/mol-
cat·h, 50 °C; 331 kg-PE / mol-cat·h, 75 °C; 421 kg-PE / mol-
cat·h) with somewhat lower, but still high, molecular weight
values (Mv, 25 °C; 3231000, 50 °C; 656000, 75 °C; 200000),9
relative to complex 1/ MAO catalyst system. Increasing the
polymerization temperature (entries 2, 4, and 5) gave a corre-
sponding increase in activity. Complex 1 (5 µmol) using
Ph3C+B–(C6F5)4 (6 µmol)/ i-Bu3Al (0.25 mmol) afforded a
reproducible activity of 564 kg-PE / mol-cat·h at 75 °C under
The new complexes are active procatalysts for the poly-
merization of ethylene (Table 1)6 and not simply a source of
titanium amide.7 Complex 1, when activated with MAO, dis-
played moderate activities (25 °C; 37 kg-PE/mol-cat·h, 75 °C;
110 kg-PE / mol-cat·h) and produced high molecular weight
polyethylenes8 (Mv, 25 °C; 4167000: 75 °C; 580000).9 On the
other hand, upon activation with Ph3C+B–(C6F5)4 / i-Bu3Al,
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
1061
ethylene at atmospheric pressure,10 the activity being very high
for titanium complexes having no Cp ligand. With the rationale
that the introduction of bulky alkyl group ortho to the phenoxy
group would provide better steric protection of the titanium
center and result in greater separation between the cationic tita-
nium center and anionic cocatalyst,3b complex 2 with tert-butyl
group ortho to the phenoxy group in the ligand was evaluated in
the hope of acquiring much higher catalytic activity. As a
result, unexpectedly, complex 2 was found to show lower activ-
ities using MAO or Ph3C+B–(C6F5)4 /i-Bu3Al as the cocatalyst
compared with complex 1,9 unlike the analogous titanium com-
plexes having two phenoxy–imine chelate ligands whose activi-
ty is enhanced by placing bulky alkyl group ortho to the phe-
noxy group.3b,3g,11,12 One possible explanation for the differ-
ence in polymerization behavior between the complexes having
phenoxy–pyridine and those with phenoxy–imine ligands is that
the structures of the active species are different between the
two.13 DFT calculations suggest that complexes 1 and 2 pos-
sess cis-located active sites trans to the anionic phenoxy-oxy-
gens (Figure 1 (A)) whereas, as already reported, titanium com-
plexes having phenoxy–imine ligands have cis-located active
sites trans to the neutral imine-nitrogens (Figure 1 (B)).3b It is
apparent that, in Figure 1 (A), a substituent ortho to the phe-
noxy group is not effective for steric protection of the titanium
center and for ion separation between the cationic titanium cen-
ter and anionic cocatalyst, explaining the difference in polymer-
ization behavior between the titanium complexes having phe-
noxy–pyridine and those with phenoxy–imine ligands. In addi-
tion, the lower activities exhibited by the titanium complexes
with phenoxy–pyridine ligands relative to those with
phenoxy–imine ligands can be explained when the titanium
complexes with phenoxy–pyridine ligands possess active sites
trans to the anionic phenoxy-oxygens because the neutral
imine-nitrogens trans to the active sites are thought to be
responsible for high activities displayed by the titanium com-
plexes bearing phenoxy–imine ligands.
References and Notes
1
a) H. H. Brintzinger, D. Fischer, R. Muelhaupt, B. Rieger, and R. M.
Waymouth, Angew. Chem., Int. Ed. Engl., 34, 1143 (1995). b) W.
Kaminsky and H. Sinn, “Transition Metals and Organometallics for
Catalysts Olefin Polymerization,” Springer, New York (1998).
2
a) G. J. P. Biritovsek, V. C. Gibson, and D. F. Wass, Angew. Chem. Int.
Ed., 38, 428 (1999). b) S. D. Ittel, L. K. Johnson, and M. Brookhart,
Chem. Rev., 100, 1169 (2000). c) T. R. Younkin, E. F. Connor, J. I.
Henderson, S. K. Friedrich, R. H. Grubbs, and D. A. Bansleben,
Science, 287, 460 (2000). d) D. W. Stephan, F. Guerin, R. E. V. H.
Spence, L. Koch, X. Gao, S. J. Brown, J. W. Swabey, Q. Wang, W, Xu,
P. Zoricak, and D. G. Harrison, Organometallics, 18, 2046 (1999). e)
Y. Matsuo, K. Mashima, and K. Tani, Chem. Lett., 2000, 1114. f) K.
Nomura, A. Sagara, and Y. Imanishi, Chem. Lett., 2001, 36. g) F. A.
Hicks and M. Brookhart, Organometallics, 20, 3217 (2001).
3
a) T. Fujita, Y. Tohi, M. Mitani, S. Matsui, J. Saito, M. Nitabaru, K.
Sugi, H. Makio, and T. Tsutsui, (Mitsui Chemicals, Inc.), European
Patent 0874005 (1998); Chem. Abstr., 129, 331166 (1998). b) S.
Matsui, M. Mitani, J. Saito, Y. Tohi, H. Makio, N. Matsukawa, Y.
Takagi, K. Tsuru, M. Nitabaru, T. Nakano, H. Tanaka, N. Kashiwa, and
T. Fujita, J. Am. Chem. Soc., 123, 6847 (2001) and references therein.
c) S. Matsui, Y. Inoue, and T. Fujita, J. Synth. Org. Chem. Jpn., 59, 232
(2001). d) T. Matsugi, S. Matsui, S. Kojoh, Y. Takagi, Y. Inoue, T.
Fujita, and N. Kashiwa, Chem. Lett., 2001, 566. e) S. Kojoh, T.
Matsugi, J. Saito, M. Mitani, T. Fujita, and N. Kashiwa, Chem. Lett.,
2001, 822. f) Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, T. Nakano,
H. Tanaka, N. Kashiwa, and T. Fujita , Organometallics, in press. g) J.
Saito, M. Mitani, S. Matsui, Y. Tohi, H. Makio, T. Nakano, H. Tanaka,
N. Kashiwa, and T. Fujita, Macromol. Chem. Phys., in press. h) S. Ishii,
J. Saito, M. Mitani, J. Mohri, N. Matsukawa, Y. Tohi, S. Matsui, N.
Kashiwa, and T. Fujita, J. Mol. Catal. A, in press. i) J. Saito, M. Mitani,
J. Mohri, Y. Yoshida, S. Matsui, S. Ishii, S. Kojoh, N. Kashiwa, and T.
Fujita, Angew. Chem. Int. Ed., 40, 2918 (2001).
4
5
B. M. Holligan, J. C. Jeffery, M. K. Norgett, E. Schatz, and M. D.
Ward, J. Chem. Soc., Dalton Trans., 1992, 3345.
Spectral data of the complexes: Complex 1 (C26H28N4O2Ti); H NMR
1
(270 MHz, CDCl3, TMS): δ 3.11 (s, 12H), 6.66 (m, 2H), 6.76 (m, 2H),
6.99 (dd, 2H), 7.24 (dd, 2H), 7.40 (dd, 2H), 7.54 (m, 4H), 8.23 (m, 2H).
Anal. Calcd for C26H28N4O2Ti: C, 65.55; H, 5.92; N, 11.76%. Found; C,
66.13; H, 5.72; N, 10.72%. Complex 2 (C42H60N4O2Ti); 1H NMR (270
MHz, CDCl3, TMS): δ 1.32 (s, 18H), 1.63 (s, 18H), 2.93 (s, 12H), 6.62
(m, 2H), 7.24 (d, 2H), 7.40 (d, 2H), 7.51 (m, 4H), 8.43 (d, 2H). Anal.
Calcd for C42H60N4O2Ti: C, 71.98; H, 8.63; N, 7.99%. Found; C, 71.28;
H, 8.84; N, 7.79%. FD-MS; m/z; 700 (M+). The structures of the com-
plexes were supported by 1H NMR and FD-MS spectra, though reason-
able elemental analysis data were not obtained because of impurities.
General polymerization procedure: Flow of ethylene gas (100 L/h) was
charged into 250 mL of toluene at 25 °C. To this solution, MAO
(Albemarle MAO, 1.2 M toluene solution) and a toluene solution of a
complex was added at the desired polymerization temperature. After
the prescribed time, 25 mL of isobutyl alcohol was added to terminate
the polymerization.
6
7
8
9
Ti(NMe2)4 /MAO; 4 kg-PE/mol-cat·h (25 °C), 82 kg-PE/mol-cat·h (75
°C): Ti(NMe2)4 /Ph3C+B–(C6F5)4 /i-Bu3Al; 78 kg-PE/mol-cat·h (25 °C),
252 kg-PE/mol-cat·h (75 °C).
Mv values were calculated from the following equation, [η] = 6.2 ×
10–4Mv0.7; R. Chiang, J. Polymer Sci., 36, 91 (1959). Intrinsic viscosity
[η] was measured in decaline at 135 °C using an Ubbelohde viscometer.
The polyethylenes formed with complexes 1 and 2 possess relatively
broad molecular weight distributions (PDIs 4.45 – 8.67). These will be
discussed in more detail in connection with the structures of active
species in a future publication.
10 For all runs in Table 1, the polymer yield increased constantly with
polymerization time, indicating that complexes 1 and 2 retain their cat-
alytic activities for at least 30 min.
11 J. Strauch, T. H. Warren, G. Erker, R. Frohlich, and P. Saarenketo,
Inorg. Chem. Acta., 300–302, 810 (2000).
12 On activation with MAO at 25 °C, bis[N-(3-tert-butylsalicylidene)-
phenylaminato]titanium(IV) dichloride displays about 100 times higher
ethylene polymerization activity (3400 kg-PE/mol-cat·h) than the corre-
sponding titanium complex having no t-Bu group ortho to the phenoxy
group (38 kg-PE/mol-cat·h).
13 The titanium complexes potentially possess more than one active
species since the complexes have two non-symmetric bidentate phe-
noxy–pyridine ligands.
In conclusion, two new titanium complexes having phe-
noxy–pyridine chelate ligands have been introduced. The
results described herein show the importance of the active
species’s structure of complexes, which potentially possess
more than one active species, for catalytic performance. These
results would contribute to further discovery and development
of high performance olefin polymerization catalysts.