Olefin polymerization catalysts based on convex, polcyclic...

Details Olefin polymerization catalysts based on convex, polcyclic... Olefin polymerization catalysts based on convex, polcyclic...

2003-02-25

2004-03-30

Rabago, Roberto (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S134000, C526S943000, C526S170000, C502S103000, C502S117000, C502S152000, C556S053000

Reexamination Certificate

active

06713576

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to catalysts useful for olefin polymerization. In particular, the invention relates to catalysts based on organometallic complexes that incorporate a convex, polycyclic ligand.
BACKGROUND OF THE INVENTION
While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, single-site (metallocene and non-metallocene) catalysts represent the industry's future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they often produce polymers with improved physical properties.
Many single-site catalysts incorporate cyclopentadienyl, indenyl, or fluorenyl ligands (hereinafter “Cp-like ligands”). In these catalysts, the Cp-like ligand is planar or substantially planar (i.e., the calculated curvature index of the ligand is 0 or close to 0) and donates pi electrons to a transition metal center (sometimes referred to as &eegr;-5 coordination). Because it contributes pi electrons to the metal, the ligand stabilizes the cationic active site during polymerization. At the same time, however, the bulky ligand inhibits pi-complexation of olefin to the metal and interferes with polymer chain propagation. Ideally, the ligand would stabilize the active site electronically with minimal steric inhibition of olefin complexation and chain growth.
Outside the area of olefin polymerization catalysis, there is considerable theoretical and practical interest in fullerenes, especially buckminsterfullerene, other “buckyballs,” “buckybowls,” and other hydrocarbons that have pi electron density distributed over a curved surface (see, e.g., Rabideau and Sygula et al.,
Acc. Chem. Res.
29 (1996) 235;
Tetrahedron
57 (2001) 3637;
J. Am. Chem. Soc.
122 (2000) 6323; and Scott et al.,
Org. Lett.
2 (2000) 1427). These molecules are polycyclic and—in contrast to the Cp-like compounds discussed above—they are nonplanar. Corannulenes and other “buckybowls” have been synthesized and studied.
Nakamura, Sawamura, and coworkers reported the preparation of pentahaptofullerene metal complexes (see, e.g.,
J. Am. Chem. Soc.
118 (1996) 12850 and
Chem. Letters
(2000) 270). Conjugate addition using a large excess (25-60 equivalents) of an organocuprate reagent, followed by inverse quenching, gives a pentaalkylated cyclopentadienyl precursor. The precursor can be deprotonated and combined with a transition metal source to generate a fullerene-cyclopentadienyl complex. The complexes have been suggested to have potential utility for ethylene polymerizations (see Patent Abstracts of Japan, Publ. No. 10-167994). In spite of the interesting work performed in this area to date, “buckyballs” remain expensive and challenging to synthesize.
Recently, Chin et al. (
Organometallics
21 (2002) 2027) described the synthesis of a zirconium complex that incorporates an anionic, bowl-shaped corannulene-like ligand. As the authors note, the “bowl-shaped ligand has two sides due to the curvature of the molecule: an endo (concave) and an exo (convex) side.” By X-ray diffraction, it was found that the zirconium coordinates to the convex side of the ligand:
The corranulene ligand used by Chin is reminiscent of a fluorenyl group, which is a common element of single-site olefin polymerization catalysts. Unlike a fluorenyl ligand, however, the corranulenyl ligand is curved because of the three annealed cyclohexane rings around the central cyclopentadienyl moiety. Chin reports structural details, but does not suggest using the complex with an activator to polymerize olefins.
The polyolefins industry continues to need new polymerization catalysts. In particular, the industry needs catalysts having activities that are as good or better than the activities of single-site catalysts based on Cp-like ligands. A valuable catalyst would incorporate ligands that can stabilize a cationically active site (as a Cp-like ligand does) without sacrificing reactivity toward olefin monomers. Ideally, the catalysts could be made economically using well-established synthetic routes.
SUMMARY OF THE INVENTION
The invention is a catalyst system useful for polymerizing olefins. The catalyst system comprises an activator and an organometallic complex. The complex incorporates a Group 3-10 transition metal and an anionic, polycyclic, convex ligand that is pi-bonded to the metal.
Molecular modeling studies reveal that organometallic complexes incorporating such convex ligands, when combined with an activator such as MAO, should actively polymerize olefins. The convex ligand uniquely stabilizes the active site by donating pi electrons while simultaneously minimizing steric interference with olefin complexation and chain growth. Interestingly, the calculations predict that complexes from ligands with a high curvature index (>25) should have favorable reactivities with olefin monomers compared with similar complexes that incorporate Cp-like ligands. The invention enables the production of next-generation olefin polymerization catalysts.
DETAILED DESCRIPTION OF THE INVENTION
Catalyst systems of the invention include an organometallic complex and an activator. The complex contains a Group 3-10 transition metal. “Transition metal” as used herein includes, in addition to the main transition group elements, elements of the lanthanide and actinide series. More preferred complexes include a Group 4 or a Group 8 to 10 transition metal.
The organometallic complex includes an anionic, polycyclic, convex ligand. The ligand is “anionic,” and is thus able to donate electrons to and satisfy the valence of a positively charged transition metal. Preferred ligands incorporate a cyclopentadienyl moiety and are monoanionic.
By “polycyclic,” we mean that the ligand has multiple carbocyclic rings. In preferred convex ligands, a central five-membered ring, six-membered ring, or carbon-carbon double bond is surrounded by at least three, and preferably at least five, rings. The rings may be exclusively aromatic, exclusively non-aromatic, or a combination of these.
The ligands are also convex. By “convex,” we mean that the ligands are—like a chemist's watch glass—non-planar. They have both concave and convex pi-surfaces and a high degree of strain energy (see Scott et al.,
Org. Lett.
2 (2000) 1427) compared with planar anions. The ligands are also “convex” because the transition metal bonds to the convex (exo) surface of the ligand, as is illustrated by complex 4 in Chin et al.,
Organometallics
21 (2002) 2027.
Spherical anions, such as those derived from buckminsterfullerene and other “buckyballs” (as described by Sawamura and Nakamura in
J. Am. Chem. Soc.
118 (1996) 12850 and
Chem. Letters
(2000) 270), are excluded from our definition of “convex” ligands. (Note that spherical anions lack a concave pi-surface.) While spherical anions can be made, their preparation and purification remains considerably more challenging compared with methods for making and isolating convex ligands, and the possible benefits arising from using spherical ligands for olefin polymerization catalysis remain unclear.
The framework of the convex ligand can be substituted with other atoms that do not interfere with the ability of the anionic ligand to form complexes with transition metals. For example, the framework of the convex ligand can be substituted with alkyl, aryl, halide, alkoxy, thioether, alkylsilyl, or other groups. As an example, alkylated corannulenes are conveniently prepared by the recently reported two-step method of Sygula et al. (
J. Org. Chem.
67 (2002) 6487).
Suitable convex ligands include, for example, perannulated cyclopentadienyls—including annulated indenyls and annulated flurorenyls—as well as boracorannulenyls and the like. The convex ligand has a curvature index at the cyclopentadienyl fragment greater than zero. Preferably, the convex ligand has a curvature index greater than 15, and most preferably greater than 25. “Curvature index” is the average angle (in degrees) between the plane of the cyclopentadienyl ring fragment and the bonds to the five atoms that are covalently attached to the cyclopentad

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