Single-site catalysts containing homoaromatic ligands

Details Single-site catalysts containing homoaromatic ligands Single-site catalysts containing homoaromatic ligands

1999-10-15

2001-05-08

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, C526S161000, C526S172000, C526S943000, C502S104000, C502S117000, C502S152000, C502S154000, C502S155000, C556S052000, C556S053000

Reexamination Certificate

active

06228959

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to catalysts useful for olefin polymerization. In particular, the invention relates to “single-site” catalysts that incorporate at least one homoaromatic ligand.
BACKGROUND OF THE INVENTION
Interest in single-site (metallocene and non-metallocene) catalysts continues to grow rapidly in the polyolefin industry. These catalysts are 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 commonly include one or more cyclopentadienyl groups, but many other ligands have been used. Putting substituents on the cyclopentadienyl ring, for example, changes the geometry and electronic character of the active site. Thus, a catalyst structure can be fine-tuned to give polymers with desirable properties. Other known single-site catalysts replace cyclopentadienyl groups with one or more heteroatomic ring ligands such as boraaryl (see, e.g., U.S. Pat. No. 5,554,775), pyrrolyl, indolyl, (U.S. Pat. No. 5,539,124), or azaborolinyl groups (U.S. Pat. No. 5,902,866).
Single-site catalysts typically feature at least one polymerization-stable, anionic ligand that is purely aromatic, as in a cyclopentadienyl system. All five carbons in the planar cyclopentadienyl ring participate in bonding to the metal in &eegr;-5 fashion. The cyclopentadienyl anion functions as a 6&pgr;-electron donor. Similar bonding apparently occurs with heteroatomic ligands such as boratabenzenyl or azaborolinyl.
In contrast, olefin polymerization catalysts that contain “homoaromatic” anions are not known. “Homoaromatic” refers to systems in which a stabilized, conjugated ring system is formed by bypassing a saturated atom. (See F. Carey and R. Sundberg,
Advanced Organic Chemistry,
3
rd
Ed., Part A, 518-520 (1990).) The observation of
1
H NMR aromatic ring currents helped to identify the homotropilium cation (see R. Childs,
Acc. Chem. Res.
(1984) 17, 347). Unexpectedly rapid deprotonation of bicyclo[3.2.1]octa-2,6-diene demonstrated generation of a bishomoaromatic cyclopentadienide anion (see J. Brown and J. Occolowitz,
Chem. Commun.
(1965) 376):
This is a “bishomoaromatic” system because two saturated carbons (at the bridgeheads) are bypassed to give the conjugated, stabilized anion. S. Winstein and coworkers confirmed the presence of the bishomoaromatic anion by
1
H NMR (see
J. Am. Chem. Soc.
89 (1967) 3656). L. Paquette summarizes a wealth of information about homoaromaticity in a thorough review article (
Angew. Chem. Int. Ed. Engl.
17 (1978) 106).
In spite of the availability of synthetic routes to homoaromatic anions, their use as ligands for metallocene or single-site catalysts for olefin polymerization has not been suggested. On the other hand, the ease with which a host of interesting homoaromatic ligands can be prepared suggests that 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, multi-step syntheses from expensive, hard-to-handle starting materials and reagents.
SUMMARY OF THE INVENTION
The invention is a single-site olefin polymerization catalyst. The catalyst comprises an activator and an organometallic complex. The organometallic complex comprises a Group 3 to 10 transition or lanthanide metal, M, and at least one homoaromatic anion that is &pgr;-bonded to M.
Evidence from molecular modeling studies suggests that single-site catalysts based on homoaromatic anionic ligands (e.g., bicyclo[3.2.1]octa-2,6-dienyl) will rival the performance of catalysts based on cyclopentadienyl and substituted cyclopentadienyl ligands.
The invention includes a simple synthetic route to the single-site olefin polymerization catalysts. The ease and inherent flexibility of the synthesis puts polyolefin makers in charge of a new family of single-site catalysts.
DETAILED DESCRIPTION OF THE INVENTION
Catalysts of the invention comprise an activator and an organometallic complex. The catalysts are “single site” in nature, i.e., they are distinct chemical species rather than mixtures of different species. They typically give polyolefins with characteristically narrow molecular weight distributions (Mw/Mn<3) and good, uniform comonomer incorporation.
The organometallic complex includes a Group 3 to 10 transition or lanthanide metal, M. More preferred complexes include a Group 4 to 6 transition metal; most preferably, the complex contains a Group 4 metal such as titanium or zirconium.
The organometallic complex also comprises at least one homoaromatic anion that is &pgr;-bonded to the metal. By “homoaromatic,” we mean a stabilized, conjugated ring system formed by bypassing a saturated atom. In other words, at least one atom in the ring is not part of the &pgr;-electron system that bonds to M in the organometallic complex. Preferably, the homoaromatic anion is a monoanionic, 6&pgr;-electron system. The homoaromatic anion can be mono, bis, or trishomoaromatic (i.e., it can contain one, two, or three saturated atoms that do not participate in the aromaticity). Bishomoaromatic anions are preferred. The homoaromatic anions are usually generated from the corresponding neutral compounds by deprotonation with a potent base as is described in more detail below.
Preferred homoaromatic anions are bicyclic [3.2.1] and [3.2.2] ring systems that may be hydrocarbons or may include heteroatoms. The homoaromatic anion may be bridged to another ligand, which may or may not be another homoaromatic anion. Exemplary homoaromatic anions are illustrated below:
The organometallic complex optionally includes one or more additional polymerization-stable, anionic ligands. Examples include substituted and unsubstituted cyclopentadienyl, fluorenyl, and indenyl, or the like, such as those described in U.S. Pat. Nos. 4,791,180 and 4,752,597, the teachings of which are incorporated herein by reference. A preferred group of polymerization-stable ligands are heteroatomic ligands such as boraaryl, pyrrolyl, indolyl, quinolinyl, pyridinyl, and azaborolinyl as described in U.S. Pat. Nos. 5,554,775, 5,539,124, 5,637,660, and 5,902,866, the teachings of which are incorporated herein by reference. The organometallic complex also usually includes one or more labile ligands such as halides, alkyls, alkaryls, aryls, dialkylaminos, or the like. Particularly preferred are halides, alkyls, and alkaryls (e.g., chloride, methyl, benzyl).
The homoaromatic anions and/or polymerization-stable ligands can be bridged. For instance, a —CH
2
—, —CH
2
CH
2
—, or (CH
3
)
2
Si bridge can be used to link two homoaromatic anions or a homoaromatic anion and a polymerization-stable ligand. Groups that can be used to bridge the ligands include, for example, methylene, ethylene, 1,2-phenylene, and dialkyl silyls. Normally, only a single bridge is included. Bridging changes the geometry around the transition or lanthanide metal and can improve catalyst activity and other properties such as comonomer incorporation.
Exemplary organometallic complexes:
(bicyclo[3.2.1]octa-2,6-dienyl)zirconium trichloride,
(bicyclo[3.2.1]octa-2,6-dienyl)titanium trimethyl,
(cyclopentadienyl)(bicyclo[3.2.1]octa-2,6-dienyl)zirconium dichloride,
bis(bicyclo[3.2.1]octa-2,6-dienyl)zirconium dichloride,
(4-azabicyclo[3.2.1]octa-2,6-dienyl)zirconium trichloride,
(1,5-diazabicyclo[3.2.2]nona-2,6-dienyl)titanium tribenzyl,
(benzo[f]bicyclo[3.2.1]octa-2,6-dienyl)hafnium trichloride,
(8-oxabicyclo[3.2.1]octa-2,6-dienyl)(cyclopentadienyl)hafnium dichloride,
(8,8-dimethylbicyclo[3.2.1]octa-2,6-dienyl)zirconium trichoride,
(8-methyl-8-azabicyclo&ls

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