Single-site catalysts containing chelating N-oxide ligands

Details Single-site catalysts containing chelating N-oxide ligands Single-site catalysts containing chelating N-oxide ligands

2000-03-30

2002-12-24

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...

C526S170000, C526S171000, C526S134000, C526S943000, C556S051000, C556S052000, C502S103000, C502S117000

Reexamination Certificate

active

06498221

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 chelating N-oxide 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). Amine oxides are widely used in the polymer industry as stabilizers (see, for example, U.S. Pat. No. 5,268,114), and many are commercially available. Seldom, however, have amine oxides been used in a process for polymerizing olefins or as a component of an olefin polymerization catalyst. An exception is U.S. Pat. No. 4,015,060, which teaches to use sterically hindered heterocyclic amine oxides (such as pyridine N-oxide or 2,6-lutidine N-oxide) in combination with a Ziegler-Natta catalyst (titanium trichloride, a trialkyl aluminum, and a dialkyl aluminum halide) to polymerize propylene. The amine oxide reduces the amount of low-molecular-weight, alkane-soluble impurities in the desired product, crystalline polypropylene.
In contrast, single-site olefin polymerization catalysts that contain N-oxide ligands are not known. Also unknown are catalysts that incorporate a chelating N-oxide ligand, i.e., one that can form a chelate using the N-oxide oxygen atom and a second atom that can donate an electron pair to the transition metal.
The commercial availability of many N-oxides and the ease with which a host of other interesting N-oxide ligands can be prepared (e.g., by simply oxidizing the corresponding tertiary amine with hydrogen peroxide or a peracid) suggests that single-site 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 chelating N-oxide ligand that is bonded to M.
Evidence from molecular modeling studies suggests that single-site catalysts based on chelating N-oxide ligands (e.g., 2-hydroxypyridine N-oxide) 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 chelating N-oxide ligand that is bonded to the metal. By “chelating,” we mean that the ligand can bind to a transition metal using the oxygen atom of the amine oxide and one other atom that can donate an electron pair to the metal. The other atom is preferably separated from the amine oxide oxygen by 2 to 5 atoms. The other electron-donating atom can be neutral (as in a hydroxyl, alkoxy, or amino group) or anionic (as in a deprotonated hydroxyl, deprotonated amine, or carbanion). In preferred chelating N-oxide ligands, the electron-donating atom is anionic. In other words, the ligand is preferably deprotonated before incorporating it into the transition metal complex. The electron-donating atom can be oxygen, nitrogen, sulfur, phosphorus, or carbon.
A preferred class of chelating N-oxide ligands are heterocyclic aromatic amine oxides that have an electron-donating atom ortho to the amine oxide nitrogen. Deprotonation of these ligands generates a resonance-stabilized anion. Ligands in this group include, for example, N-substituted imidazole N-oxides, pyridine N-oxides, and lutidine N-oxides that have an electron-donating group in the ortho position. Examples include 2-hydroxy-1-methylimidazole N-oxide, 2-hydroxypyridine N-oxide, 2-hydroxyquinoline N-oxide, 2-hydroxy-4,6-dimethyllutidine N-oxide, 2-(N′-methylamino)pyridine N-oxide, 2-(2-phenethyl-2-oxo)pyridine N-oxide, and the like. Also suitable are heterocyclic amine oxides having an electron-donating atom within 3 atoms of the amine oxide nitrogen. An example is 8-hydroxyquinoline N-oxide.
Other aliphatic and cycloaliphatic amine oxides having electron donor groups are also suitable because of their ability to stabilize the transition metal in an active single-site complex. Examples are N-hydroxyethyl-N,N-dibutylamine N-oxide, N-hydroxyethyl-N,N-diphenylamine N-oxide, N-methyl(2-hydroxymethyl)piperidine N-oxide, N-methoxyethyl-N,N-dimethylamine N-oxide, and the like.
The amine oxides are conveniently prepared by oxidizing the corresponding tertiary amines with hydrogen peroxide or a peroxyacid in aqueous or organic media according to well-known methods. See, for example, U.S. Pat. Nos. 5,955,633, 5,710,333, 5,082,940, 4,748,275, 4,504,666, and 4,247,480, the teachings of which are incorporated herein by reference.
Suitable chelating N-oxides also include those prepared by oxidizing a nitrogen of the corresponding imines (R—N═CR′R″) or azo compounds (R—N═N—R′) that have an electron donor group within 5 atoms of the N-oxide oxygen. In the formulas, R and R′ are alkyl, aryl, or aralkyl (preferably both aryl) groups, and R″ is hydrogen or an alkyl, aryl, or aralkyl group. Examples from these groups are azobis(2-hydroxybenzene) N-oxide (I) and benzophenone N-(2-hydroxyphenyl)imine N-oxide (II):
More precisely, compound (I) is an “azoxybenzene” (see J. March,
Advanced Organic Chemistry,
2
nd
ed., (1977) p. 1111) and compound (II) is a “nitrone.” Nitrones are conveniently prepared by condensing aldehydes (e.g., benzaldehyde) and hydroxylamines (e.g., N-phenylhydroxylamine) as shown in
Organic Syntheses, Coll. Vol. V,
p. 1124. Nitrones can also be made by imine oxidation using a peroxyacid (
J. Chem. Soc., Perkin Trans. I
(1977) 254), by hydrogen peroxide oxidation of secondary amines in the presence of aqueous sodium tungstate (
Org. Synth., Coll. Vol. IX,
p. 632 and
J. Chem. Soc., Chem. Commun.
(1984) 874), and by imine oxidation with N-methylhydroxylamine-O-sulfonic acid (
Synthesis
(1977) 318).
The organometallic complex optionally includes one or more additional polymerization-stable, anionic ligands. Examples include substituted and unsubst

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