Highly active titanium-based olefin polymerization catalysts supported by bidentate phenoxyamide ligands

Article abstract of DOI:10.1021/ic060146k

Phenoxyamide complexes of Ti-containing 2,6-X₂C ₆H₃ (X = Cl, Br) substituents, when activated by methyl aluminoxane, afford catalysts with very high activities for the polymerization of ethylene and with good incorporation

Full text of DOI:10.1021/ic060146k

Inorg. Chem. 2006, 45, 3476−3477
Highly Active Titanium-Based Olefin Polymerization Catalysts Supported
by Bidentate Phenoxyamide Ligands
Daniel C. H. Oakes, Vernon C. Gibson,* Andrew J. P. White, and David J. Williams
Imperial College, Exhibition Road, London SW7 2AZ, U.K.
Received January 25, 2006
Scheme 1
Phenoxyamide complexes of Ti-containing 2,6-X2C6H3 (X
) Cl,
Br) substituents, when activated by methyl aluminoxane, afford
catalysts with very high activities for the polymerization of ethylene
and with good incorporation of 1-hexene.
Bidentate phenoxyimine ligands have made a dramatic
impact on group 4 metal olefin polymerization catalysis.1-6
Such ligands are attractive because of their ease of synthesis
and elaboration by straightforward Schiff base condensation
procedures. An additionally attractive yet, to date, little
exploited feature of the reaction chemistry of phenoxyimines
is their ready reduction to phenoxyamines, which may serve
as convenient precursors to phenoxyamide ligands. The wide
range of ligand substitution patterns already elaborated for
their phenoxyimine precursors highlights the potential for
forming a similarly extensive library of dianionic ligands
based on the phenoxide and amide donor combination.
Recently, we described highly active ethylene polymeri-
zation catalysts supported by tridentate phenoxyamide ligands7
but, at the same time, found surprisingly low activities for a
simple bidentate derivative containing the bulky 2,6-Pri2C6H3
imino substituent. Here we show that incorporation of halo
substituents within the amido aryl units leads to catalysts
with dramatically improved ethylene polymerization activities
and excellent 1-hexene incorporation.
according to Scheme 1. Treatment of 1-4 with TiCl2(NMe2)2
gave the phenoxyamide complexes 5-8 with concomitant
formation of dimethylamine. The hydrocarbon derivative 5
retains one molecule of dimethylamine within the metal’s
coordination sphere, whereas complexes 6-8 retain two
molecules, reflecting the enhanced electrophilicity of the
metal center in the halo-substituted products. Crystals of 8
suitable for an X-ray structure determination (see the
Supporting Information for details) were grown from a
saturated pentane solution. The geometry at Ti is slightly
distorted octahedral (Figure 1) with cis angles in the range
of 83.18(14)-94.7(2)°; the trans angles are between 171.3(2)
and 176.42(16)°. The six-membered chelate ring adopts a
shallow boat conformation with O(1) and C(7) lying +0.12
and +0.28 Å, respectively, out of the plane of the other four
atoms, which are coplanar to better than 0.01 Å. The C6F5
ring is oriented orthogonally (ca. 89°) to this latter plane, a
conformation perhaps stabilized by a pair of weak N-H‚‚‚F
interactions. The amide character of the C(7)-N(7) linkage
is clearly evident from its bond length of 1.491(6) Å, and
the Ti-N distance to this formally anionic N [1.965(4) Å]
is very much shorter than those to the neutral dimethylamine
ligands [2.232(5) and 2.243(6) Å]. The geometry at N(7) is
distorted trigonal planar with the N lying ca. 0.07 Å out of
The aminophenol proligands 1-4 were readily synthesized
in good yields via the reduction of the corresponding
iminophenols and isolated as colorless crystalline solids
* To whom correspondence should be addressed. E-mail:
v.gibson@ic.ac.uk.
(1) Suzuki, Y.; Terao, H.; Fujita, T. Bull. Chem. Soc. Jpn. 2003, 76, 1493.
(2) Matsui, S.; Fujita, T. Catal. Today 2001, 66, 63.
(3) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.; Matsukawa,
N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.; Tanaka, H.;
Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2001, 123, 6847.
(4) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru, K.;
Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.-i.;
Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124,
3327.
(5) Saito, J.; Onda, M.; Matsui, S.; Mitani, M.; Furuyama, R.; Tanaka,
H.; Fujita, T. Macromol. Rapid Commun. 2002, 23, 1118.
(6) For a general review, see: Gibson, V. C.; Spitzmesser, S. K. Chem.
ReV. 2003, 103, 283.
(7) Oakes, D. C. H.; Kimberley, B. S.; Gibson, V. C.; Jones, D. J.; White
A. J. P.; Williams, D. J. Chem. Commun. 2004, 2174.
3476 Inorganic Chemistry, Vol. 45, No. 9, 2006
10.1021/ic060146k CCC: $33.50
© 2006 American Chemical Society
Published on Web 04/05/2006

COMMUNICATION
conditions. Upon lowering of the catalyst loading for 7
(entries 8-10), the activity level was optimized in the region
12-13 000 g mmol-1 bar-1 h-1 (entries 10 and 11). High-
molecular-weight (>2 × 106), linear polyethylene was
obtained in each case. Examination of the effect of the
ethylene pressure on the polymer yield for 7 (entries 10-
13) revealed a first-order dependence. Contrasting the
impressive activities found for the 2,6-dichloro and dibromo
derivatives, the pentafluorophenyl catalyst 8/MAO gave poor
activities in tests under the same conditions (entries 15 and
16).
Complexes 5-8 were tested for 1-hexene comonomer
incorporation. For the low-activity catalysts 5/MAO (entry
3) and 8/MAO (entry 17), 1-hexene incorporation was
insignificant (by NMR). By contrast, catalyst 6/MAO (entry
6) afforded 4.5 mol % 1-hexene incorporation, which
increased to 6.8 mol % for 7/MAO (entry 14). Both
copolymers afforded relatively narrow molecular weight
distribution products. Interestingly, the activity for the
copolymerization using 7 was raised substantially relative
to that for ethylene homopolymerization (compare entries 8
and 14).
Figure 1. Molecular structure of 8. The geometries of the N-H‚‚‚F
interactions are [N‚‚‚F], [H‚‚‚F] (Å), and [N-H‚‚‚F] (deg): (a) 3.148(9),
2.29, and 161; (b) 3.081(6), 2.35, and 139.
Table 1. Ethylene Polymerization and Copolymerization Results for
Complexes 5-8a
procatalyst
(µmol)
pressure
(bar)
yield
(g)
activity
entry
(g mmol-1 bar-1 h-1
)
1
2
5 (5.0)
5 (5.0)
5 (5.0)
6 (0.2)
6 (0.5)
6 (0.5)
7 (1.0)
7 (1.0)
7 (0.5)
7 (0.2)
7 (0.2)
7 (0.2)
7 (0.2)
7 (1.0)
8 (10.0)
8 (10.0)
8 (10.0)
1
4
4
1
4
4
1
4
4
4
3
2
1
4
1
4
4
0.17
0.72
0.68
0.16
1.37
0.95
3.10
7.65
7.60
4.85
3.85
1.79
1.02
14.21
0.25
0.80
0.40
70c
72c
3b
4
68c
1600c
1370c
950d
The enhanced activities of the 2,6-dichloro- and 2,6-
dibromophenyl catalysts relative to their hydrocarbon ana-
logue may be attributed to the increased electrophilicity of
the metal center in the halo-substituted systems.8,9 However,
the poor activity found for the pentafluorophenyl catalyst
suggests a deactivating effect for this highly electron-
withdrawing substituent, which contrasts its beneficial effect
in phenoxyimine catalyst systems, where it not only has been
found to support to good activities but also has been shown
to suppress chain termination processes.4,10-12 It is possible
that, for monochelate phenoxyamide catalysts, the smaller
pentafluorophenyl-containing ligand offers inadequate steric
protection of the active site, leading to catalyst deactivation.
5
6b
7
6200c
3825c
7600c
12130c
12830
8950c
10200c
7110e
50c
8
9
10
11
12
13
14b
15
16
17b
40c
20c
a General conditions: Fisher Porter reactor, heptane solvent (200 mL),
MAO cocatalyst (4.0 mmol), 25 °C, 30 min of reaction. b 1-Hexene (20
mL). c Mw > 2 × 106. d Mw ) 708 000, Mn ) 253 300, PDI ) 2.8. e Mw
)
475 200, Mn ) 159 100, PDI ) 2.9.
Acknowledgment. Innovene Ltd. is thanked for financial
support of this work.
the plane of its substituents; the angles subtended at this
center are 108.4(4), 124.5(3), and 126.6(4)°, with the smallest
being for the C-N-C angle. There are no intermolecular
interactions of note.
A comparison of the ethylene polymerization and 1-hexene
copolymerization capabilities of 5-8 (Table 1) reveals that
the chloro- and bromo-substituted ligands afford catalysts
with much higher activities than their hydrocarbon or
pentafluorophenyl relatives. Thus, whereas 5/methyl alumin-
oxane (MAO) gave activities of ca. 70 gPE mmol-1 h-1 bar-1
(entries 1 and 2; PE ) polyethylene), the 2,6-dibromophenyl
derivative 6 afforded activities as high as 1600 gPE mmol-1
h-1 bar-1 (entries 4 and 5).
Supporting Information Available: Experimental and spec-
troscopic details for the ligands and precatalysts, crystal data for
8, and polymerization procedure. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC060146K
(8) Ishii, S.; Saito, J.; Mitani, M.; Mohri, J.; Matsukawa, N.; Tohi, Y.;
Matsui, S.; Kashiwa, N.; Fujita, T. J. Mol. Catal. A 2002, 179, 11.
(9) Ishii, S.; Furuyama, R.; Matsukawa, N.; Saito, J.; Mitani, M.; Tanaka,
H.; Fujita, T. Macromol. Rapid Commun. 2003, 24, 452.
(10) Tian, J.; Hustad, P. D.; Coates, G. W. J. Am. Chem. Soc. 2001, 123,
5134.
(11) Saito, J.; Mitani, M.; Matsui, S.; Mohri, J.; Kojoh, Y. Y. S.; Kashiwa,
N.; Fujita, T. Angew. Chem., Int. Ed. 2001, 40, 2918.
(12) Mitani, M.; Furuyama, R.; Mohri, J.; Saito, J.; Ishii, S.; Terao, H.;
Nakano, T.; Tanaka, H.; Fujita, T. J. Am. Chem. Soc. 2003, 125, 4293.
For the chloro derivative 7, the activity is further raised
to 6200 g mmol-1 bar-1 h-1 (entry 7) under the same
Inorganic Chemistry, Vol. 45, No. 9, 2006 3477