Olefin polymerization catalysts containing triquinane ligands

Details Olefin polymerization catalysts containing triquinane ligands Olefin polymerization catalysts containing triquinane ligands

2002-04-08

2004-02-17

Wu, David W. (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S160000, C526S131000, C526S134000, C526S943000, C526S348000, C502S117000, C502S103000

Reexamination Certificate

active

06693157

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to catalysts useful for olefin polymerization. In particular, the invention relates to transition metal polymerization catalysts that incorporate a chelating, dianionic triquinane 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 produce polymers with improved physical properties. The improved properties include narrow molecular weight distribution, reduced low molecular weight extractables, enhanced incorporation of &agr;-olefin comonomers, lower polymer density, controlled content and distribution of long-chain branching, and modified melt rheology and relaxation characteristics.
Traditional metallocenes incorporate one or more cyclopentadienyl (Cp) or Cp-like anionic ligands such as indenyl, fluorenyl, or the like, that donate pi-electrons to the transition metal. Non-metallocene single-site catalysts, including ones that capitalize on the chelate effect, have evolved more recently. Examples are 8-quinolinoxy or 2-pyridinoxy ligands (see U.S. Pat. No. 5,637,660) and the bidentate bisimines of Brookhart (see
Chem. Rev
. 100 (2000) 1169).
Recently, we described chelating bicyclic dianionic ligands useful for olefin polymerization catalysts (see copending application Ser. No. 09/907,180, filed Jul. 17, 2001). In these complexes, one ligand chelates to the metal through two separate allylic anions, each of which is a 4-pi electron donor. Molecular modeling calculations indicate that the steric and electronic environments of these ligands are comparable to those of conventional metallocene ligands. Their “open architecture” suggests that comonomer incorporation will be facile. Triquinane or other tricyclic dianionic ligands are not disclosed.
We also described earlier the use of Diels-Alder and photo-chemical [2+2] cycloaddition reactions in tandem to make “caged diimide” complexes (see copending application Ser. No. 09/691,285, filed Oct. 18, 2000). Conversion of a caged diketone to the corresponding diimine, followed by preparation of a transition metal complex incorporating the neutral diimine ligand affords complexes useful for olefin polymerization.
The tandem strategy was used by G. Mehta et al. (
J. Am. Chem. Soc
. 108 (1986) 3443) in a remarkable route to triquinane natural products such as (±)-hirsutene and (±)-capnellene. The key to assembling these skeletons efficiently was recognizing that the cis,syn,cis-triquinane skeleton is available in three steps in near-quanitative yield (>80% overall) from inexpensive starting materials (p-benzoquinone and cyclopentadienes), and essentially no chemical reagents other than a reaction solvent (in addition to heat, and light):
In the example shown above, simple thermolysis of pentacyclic diketones 3 and 4 gave only the cis,syn,cis-triquinane bis(enone)s 5 and 6. After these pivotal, elegant steps, Mehta further elaborated the bis(enone)s to make the desired natural product, capnellene.
The polyolefins industry continues to need new polymerization catalysts. Unfortunately, the organometallic complexes are becoming increasingly complicated and more expensive to manufacture. The industry would benefit from ways to achieve a high level of molecular complexity in relatively few synthetic steps. The accessibility of a host of interesting triquinane skeletons invites polyolefin makers to explore their applicability outside the realm of natural products synthesis. Catalysts with advantages such as higher activity and better control over polyolefin properties are within reach. Ideally, these catalysts would avoid the all-too-common, low-yield, multi-step syntheses from expensive, hard-to-handle starting materials and reagents.
SUMMARY OF THE INVENTION
The invention is a catalyst system useful for polymerizing olefins and a method for making it. The catalyst system comprises an activator and an organometallic complex. The complex incorporates a Group 3 to 10 transition metal and a chelating, dianionic triquinane ligand that is pi-bonded to the metal. The required cis,syn,cis-tricyclic framework is generated in high yield in three steps from inexpensive starting materials, and with heat and light as the only “reagents.” Further elaboration to a triquinane diene, a dianionic ligand, and an organometallic complex incorporating the ligand, are facile. By modifying substituents on the triquinane ligand, polyolefin makers can control catalyst activity, comonomer incorporation, and polymer properties.
DETAILED DESCRIPTION OF THE INVENTION
Catalyst systems of the invention include an organometallic complex that 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 at least one chelating, dianionic triquinane ligand. The ligand “chelates” with the transition metal by bonding to it with two separate allylic bonds, each of which is a 4-pi electron donor. The ligand is “dianionic,” i.e., it has a net charge of −2; each of two electron pairs generated by deprotonation is conjugated with a carbon—carbon double bond.
By “triquinane,” we mean a carbocyclic framework characterized by three rings in which a central five-membered ring is cis,syn,cis-fused to two additional five- or six-membered rings. Preferably, all of the rings are five-membered. Thus, in an unsubstituted dianionic triquinane, all four bridgehead methine hydrogen atoms occupy the same face of the central five-membered ring. For example:
The triquinane framework can be substituted with other atoms that do not interfere with formation of the allylic dianion or incorporation of the dianion into a transition metal complex. For example, the triquinane can be substituted with alkyl, aryl, halide, alkoxy, thioether, alkylsilyl, or other groups. Preferably, the framework is hydrocarbyl.
Preferred triquinane ligands have the general structure:
in which each R is independently hydrogen, halide, or C
1
-C
30
hydrocarbyl. Preferably, each R is a hydrogen.
The triquinane ligand is made by any suitable method. A preferred method utilizes tandem Diels-Alder and photochemical [2+2] cycloaddition reactions to generate a pentacyclic diketone, which is then converted to a triquinane diene. Double deprotonation generates the desired dianionic ligand.
In one aspect, the invention is a method for making an organometallic complex useful for olefin polymerization. In this method, a pentacyclic diketone such as 7 is first converted to a triquinane diene (e.g., 8) by methods that are detailed further below. Double deprotonation of the diene using a strong base gives a triquinane dianion such as 9. Reaction with a transition metal source gives an organometallic complex (e.g., 10) that incorporates the chelating, dianionic triquinane ligand. Preferably, the pentacyclic diketone is produced by reacting a cyclopentadiene and a p-benzoquinone, optionally in the presence of an organic solvent, to produce a Diels-Alder adduct. The adduct is then preferably irradiated with light of a suitable energy, optionally in the presence of a solvent and sensitizer, to effect a [2+2] cycloaddition reaction to give the pentacyclic diketone.
For example:
As noted above, the pentacyclic diketone can be converted to a triquinane diene such as 8 by several methods. In one approach, the pentacyclic diketone is first heated to cause a [2+2] cycloreversion reaction to give a cis,syn,cis-triquinane bis(enone), e.g. 11. See Mehta et al.,
J. Am. Chem. Soc
. 108 (1986) 3443. For example:
Any suitable method is used to convert the bis(enone) to the triquinane diene. In a two-step approach, the bis(enone) reacts with an arylhydrazine to produce

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