WO2002038625A1

WO2002038625A1 - Late transition metal diimide catalysts for olefin oligomerization and polymerization

Info

Publication number: WO2002038625A1
Application number: PCT/US2001/042616
Authority: WO
Inventors: Linda N. Winslow
Original assignee: Equistar Chemicals, Lp
Priority date: 2000-11-10
Filing date: 2001-10-10
Publication date: 2002-05-16
Also published as: AU2002211887A1

Abstract

Catalyst systems useful for oligomerizing or polymerizing olefins are disclosed. The catalyst systems comprise an activator and an organometallic complex. The complex includes a late transition metal (Group 8 to 10) and an aromatic 1,2-diimine ligand chelated to the metal. The diimine ligands are easily made using Schiff base chemistry from readily available aromatic 1,2-diamines and an aldehyde or ketone.

Description

LATE TRANSITION METAL DIIMIDE CATALYSTS FOR OLEFIN OLIGOMERIZATION AND POLYMERIZATION

FIELD OF THE INVENTION The invention relates to transition metal catalysts useful for polymerizing or oligomerizing olefins. In particular, the invention pertains to "late" transition metal catalysts that incorporate a 1 ,2-diimine ligand that is chelated to the metal.

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 α-olefin comonomers, lower polymer density, controlled content and distribution of long-chain branching, and modified melt rheology and relaxation characteristics. While traditional metallocenes commonly include one or more cyclopentadienyl groups, 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 based on "late" transition metals (i.e., those in Groups 8-10, such as Fe, Ni, Pd, and Co) and diimines or other ligands have recently sparked considerable research activity because of the unusual ability of these catalysts to incorporate functionalized comonomers or to give branched polyethylenes without including a comonomer. See, for example, U.S. Pat. Nos. 5,714,556 and 5,866,663 and PCT international applications WO 96/23010, WO 98/47933, and WO 99/32226. These catalysts are often less active than would otherwise be desirable.

The diimine ligands described above are often called "Brookhart" ligands or "Brookhart-DuPont" ligands because much of the early work in this area was performed by Professor Maurice Brookhart (University of North Carolina at Chapel Hill) and scientists at E.I. du Pont de Nemours and Company (Wilmington, DE). The vast majority of Brookhart ligands used to date are α-diimines, i.e., they derive from α-diketones (as indicated by the "DAB" acronym used in the references to identify the 1 ,4-diaza-1 ,3-butadiene structural subunit). Because α-diketones are relatively uncommon, the need to start with one to make the α-diimines is a disadvantage of this approach.

Diimines derived from alkylene diamines (e.g., ethylene diamine or 1 ,3-propanediamine) and simple aldehydes or ketones are also taught by Brookhart (see, e.g., U.S. Pat. No. 5,866,663, formula (XXX), column 3, where n=2 or 3). In a preferred example, the diimine is the aldimine made by reacting ethylene diamine with two equivalents of commercially available 9- anthraldehyde (see column 41 , lines 50-55). Diimines derived from aromatic diamines are not described. Chelating bis(amido) ligands have been described. See, for example,

Cloke et al., J. Organometal. Chem. 506 (1996) 343, which discloses a ligand having secondary amine groups that chelate with a Group 4 transition metal. Similarly, Johnson et al. have described nickel-olefin pi-complexes in which two primary, secondary, or tertiary amine groups chelate the nickel atom (see, e.g., U.S. Pat. No. 5,714,556 at columns 45-47). Tridentate complexes in which two secondary amine groups and a pyridinyl group bind to the transition metal are also known from McConville et al. (see, e.g., Organometallics 15 (1996) 5085, 5586). In each of the examples in described in this paragraph, an amine group bonds to the transition metal. None of the references discloses a metal-imine complex. Improved single-site catalysts for olefin oligomerization and polymerization are still needed. Preferably, the catalysts would be easy to synthesize and would have high activities. Ideally, the catalysts would include diimine ligands, but ones that could be prepared from readily available starting materials rather than α-diketones. Preferred catalysts would incorporate late transition metals and allow polyolefin makers to incorporate polar comonomers.

SUMMARY OF THE INVENTION The invention is a catalyst system for oligomerizing or polymerizing olefins. The catalyst system includes an activator and an organometallic complex that incorporates a Group 8 to 10 transition metal. A key feature of the complex is an aromatic 1 ,2-diimine ligand that is chelated to the metal. Catalyst systems of the invention are useful for making olefin oligomers and polymers. The 1 ,2-diimines used as ligands are easily made from readily available aromatic diamines and ketones or aldehydes using well-known Schiff base chemistry. The invention includes oligomerization or polymerization processes that use the catalyst systems.

DETAILED DESCRIPTION OF THE INVENTION

Catalyst systems of the invention comprise an activator and an organometallic complex. The catalyst systems 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 8 to 10 transition metal, M. Preferred complexes include a Group 10 transition metal, i.e., nickel, palladium, or platinum.

A key component of the complex is an aromatic 1 ,2-diimine ligand that is chelated to the transition metal. The aromatic 1 ,2-diimine is normally produced by condensing an aromatic 1 ,2-diamine with two equivalents of an aliphatic or aromatic ketone or aldehyde. This reaction is known as a "Schiff base reaction," and the resulting 1 ,2-diimine is commonly described as a "Schiff base."

Suitable aromatic 1 ,2-diamines contain at least one benzene ring and two primary amino groups that are attached to adjacent carbons on the benzene ring. Examples include o-phenylenediamines, diaminotoluenes, diaminoxylenes, diaminonaphthalenes, diaminoanthracenes, diamino- phenanthrenes, and the like. The aromatic 1 ,2-diamines can have additional substituents, provided that the substituents do not interfere with the Schiff base reaction. For example, the 1 ,2-diamine can include a halogen, hydroxy, alkoxy, hydrocarbyl, sulfonic acid, or nitro group, or the like, or combinations of these. Thus, suitable 1 ,2-diamines include 3,4-diamino-5-chlorotoluene, 3,4-diamino-6-methylphenol, 3,4-diaminoanisole, 4-t-b uty 1-1 ,2- diaminobenzene, or the like. A wide variety of aromatic 1 ,2-diamines are commercially available; others are readily synthesized. For example, aromatic diamines are easily made by reducing or hydrogenating the corresponding dinitro compounds.

As defined herein, suitable aromatic 1 ,2-diamines also include aromatic diamino compounds in which the amino groups are not attached to carbons on the same aromatic ring but are oriented in close proximity and are separated by not more than 4, preferably not more than 3, carbons. An example is 1 ,8-diaminonaphthalene:

While there are numerous synthetic approaches to aromatic 1 ,2- diimines, the most common and preferred approach is to use the well-known Schiff base reaction. Usually, an aromatic 1 ,2-diamine is reacted with at least two equivalents of an aliphatic or aromatic ketone or aldehyde, and the water of reaction is removed. Preferably, the ketone or aldehyde is a Cι-C₃₀ linear, branched, or cyclic aliphatic ketone or aldehyde. The reaction is either catalyzed or uncatalyzed, and catalysts are often needed with ketone reactants. The reaction of o-phenylene-diamine with two equivalents of acetophenone in the presence of buffered acetic acid and toluene illustrates the approach:

In one suitable method, the ketone or aldehyde is heated with the aromatic 1 ,2-diamine in the absence of a catalyst, and water is removed by distillation, preferably using an azeotroping solvent such as toluene. This method is described, for example, in U.S. Pat. Nos. 5,264,615, 2,975,213, 2,218,587, and 2,000,039.

A variety of catalytic methods are also known. Common catalysts include sulfonic acids (as taught in U.S. Pat. Nos. 2,965,605 and 5,442,068) activated carbon (see U.S. Pat. No. 3,414,616), gaseous hydrochloric acid (U.S. Pat. No. 4,394,521), calcium hydrogen phosphate or Fuller's earth (U.S. Pat. No. 4,281 ,195), acetic acid buffered with an acetate salt (U.S. Pat. No. 3,135,796), and dehydrating agents such as molecular sieves (Bull. Chem. Soc. Japan 46 (1973) 675) or phosphorus pentoxide (U.S. Pat. No. 3,998,836). Other suitable methods will be apparent to those skilled in the art. It will also be appreciated that under some conditions, aromatic diamines react with ketones in the presence of sulfonic acids to give a benzimidazole (see U.S. Pat. No. 4,427,802, example 5); these conditions should be avoided. Most of the above reactions involve combining the aromatic 1 ,2- diamine with the aldehyde or ketone, along with any catalyst or dehydrating agent, and heating the mixture to effect the reaction. The mixture is commonly heated in the presence of toluene or another solvent that functions as an azeotroping agent. A Dean-Stark or other suitable distillation apparatus is advantageously used to continuously separate the water of reaction from the diimine product. The resulting diimine is then preferably isolated and purifed by any suitable means, including recrystallization, vacuum distillation, column chromatography, or the like. In one preferred isolation method, an organic solution of the crude imine is combined with a drying agent (e.g., anhydrous sodium sulfate, magnesium sulfate, calcium chloride, molecular sieves, or the like), the mixture is filtered or decanted to remove the spent drying agent, and the dried solution is stripped to give a crude imine product that can be used "as is" in the next step to make the organometallic complex.

The organometallic complex is produced by reacting a suitable transition metal precursor with the aromatic 1 ,2-diimine, which functions as a neutral ligand. Often, the organometallic complex is simply an adduct of the precursor and the 1 ,2-diimine. For example, when nickel(ll) bromide is combined with an aromatic 1 ,2-diimine, the resulting organometallic complex is an adduct that contains nickel, two bromine atoms, and the 1 ,2-diimine ligand. Other organometallic complexes result from substitution of one or more labile ligands in the precursor with the 1 ,2-diimine. For example, reaction of nickel(ll) bromide dimethoxyethane complex with an aromatic 1 ,2- diimine replaces the neutral solvent ligand:

Often, preparation of the organometallic complex involves little more than combining the aromatic 1 ,2-diimine with the transition metal precursor in a suitable organic solvent under an inert atmosphere and stirring at room temperature until the reaction is complete. Evaporation of the solvent gives the desired complex, which can be used directly to polymerize or oligomerize olefins. A skilled person will routinely adjust the reaction conditions (solvent choice, temperature and time of reaction, reagent proportions) to optimize the selectivity and yield of the desired complex.

The catalyst systems include an activator. Suitable activators ionize the organometallic complex to produce an active olefin oligomerization or polymerization catalyst. Suitable activators are well known in the art. They include alumoxanes (methyl alumoxane (MAO), PMAO, ethyl alumoxane, diisobutyl alumoxane), aluminum alkyls (e.g., triethylaluminum, triisobutylaluminum), alkyl aluminum halides (e.g., diethylaluminum chloride), and the like. Suitable activators include acid salts that contain non- nucleophilic anions. These compounds generally consist of bulky ligands attached to boron or aluminum. Examples include lithium tetrakis(pentafluorophenyl)borate, lithium tetrakis(pentafluorophenyl)- aluminate, anilinium tetrakis(pentafluoro-phenyl)borate, and the like. Suitable activators also include organoboranes, which include boron and one or more alkyl, aryl, or aralkyl groups. Suitable activators include substituted and unsubstituted trialkyl and triarylboranes such as tris(pentafluorophenyl)- borane, triphenylborane, tri-n-octylborane, and the like. These and other suitable boron-containing activators are described in U.S. Pat. Nos. 5,153,157, 5,198,401 , and 5,241 ,025.

The amount of activator needed relative to the amount of organometallic complex depends on many factors, including the nature of the complex and activator, the desired reaction rate, the kind of oligomer or polyolefin product, the reaction conditions, and other factors. Generally, however, when the activator is an alumoxane, an aluminum alkyl, or a dialkylaluminum halide, the amount used will be within the range of about 0.01 to about 5000 moles, preferably from about 0.1 to about 500 moles, of aluminum per mole of M. When the activator is an organoborane or an ionic borate or aluminate, the amount used will be within the range of about 0.01 to about 5000 moles, preferably from about 0.1 to about 500 moles, of activator per mole of M. If desired, a catalyst support such as silica or alumina can be used.

However, the use of a support is generally not necessary for practicing the process of the invention. When a support is used, it can be pretreated by any of a number of known techniques, including thermal or chemical treatment, as is described, for example, in Appl. Ser. No. 09/318,008, filed May 25, 1999. These support treatment methods are normally used to improve catalyst activity, prolong catalyst lifetime, or control important polymer properties such as molecular weight distribution or morphology.

The catalysts are particularly valuable for oligomerizing or polymerizing olefins. Preferred olefins are ethylene and C₃-C₂₀ α-olefins such as propylene, 1-butene, 1-hexene, 1-octene, and the like. Mixtures of olefins can be used. Ethylene and mixtures of ethylene with C₃-C₁0 α-olefins are especially preferred.

Many types of olefin polymerization processes can be used. Preferably, the process is practiced in the liquid phase, which can include slurry, solution, suspension, or bulk processes, or a combination of these. High-pressure fluid phase or gas phase techniques can also be used. The process of the invention is particularly valuable for solution and slurry processes. Suitable methods for polymerizing olefins using the catalysts of the invention are described, for example, in U.S. Pat. Nos. 5,902,866, 5,637,659, and 5,539,124.

The olefin oligomerizations or polymerizations can be performed over a wide temperature range, such as about -30°C to about 280°C. A more preferred range is from about 30°C to about 180°C; most preferred is the range from about 30°C to about 100°C. Olefin partial pressures normally range from about 15 psia to about 50,000 psia. More preferred is the range from about 15 psia to about 1000 psia. Catalyst concentrations used for the olefin oligomerizations and polymerizations depend on many factors. Preferably, however, the concentration ranges from about 0.01 micromoles per liter to about 100 micromoles per liter. Reaction times depend on the type of process, the catalyst concentration, and other factors. Generally, reactions are complete within several seconds to several hours.

The following examples merely illustrate the invention. Those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims.

EXAMPLE 1 Preparation of an Aromatic 1 ,2-Diimine Ligand Toluene-3,4-diamine (12.2 g, 0.10 mol) is combined with acetophenone (25.2 g, 0.21 mol), sodium acetate (0.1 g), glacial acetic acid (0.2 g), and toluene (150 mL). The mixture is heated to reflux (115°C) for 24 h, and a Dean-Stark trap is used to collect the water of reaction. After the water removal is complete, the organic phase is washed with water (3 x 50 mL) and saturated aqueous sodium chloride (1 x 50 mL). The mixture is then is dried over anhydrous magnesium sulfate, filtered, and stripped to obtain the crude aromatic 1 ,2-diimine product (I), which is used in the next step without further purification.

EXAMPLE 2 Preparation of a Nickel Diimine Complex A portion of the crude diimine product obtained in Example 1 (6.5 g, 0.020 mol) is dissolved in diethyl ether (25 mL) and is stirred at room temperature under nitrogen. Nickel(ll) bromide ethylene glycol dimethyl ether complex (6.2 g, 0.020 mol) is carefully added in small portions to the stirred mixture. The mixture is stirred for 6 h at room temperature, and solvents are removed in vacuo. The residue is an organometallic complex believed to have structure (II) below:

l)

EXAMPLE 3 Ethylene Polymerization Methyl alumoxane (5 mL of 10 wt.% MAO in toluene) is added to the product of Example 2 (200 mg). The mixture is injected into a 1.7 L stainless- steel autoclave containing dry, deoxygenated isobutane (850 mL) and triisobutylaluminum (0.2 mmol). The autoclave is heated to 80°C and is pressurized with ethylene (150 psi). After 1 h, the autoclave is cooled, and isobutane is flashed off. Polyethylene is the expected product.

EXAMPLE 4 Ligand and Complex Preparation A methanol solution containing 3,4-diaminotoluene (0.61 g, 5.0 mmol) and acetone (0.73 mL, 10 mmol) is stirred at room temperature for 72 h. The solution turns from colorless to orange. The solvent is removed using a rotary evaporator to give the crude diimine as a red oil. In a drybox, the red oil is dissolved in dry dichloromethane (30 mL), and nickel(ll) dibromide dimethoxyethane complex (1.54 g, 5.0 mmol) is added. The mixture is stirred under inert atmosphere for 19 h. Removal of solvent by vacuum gives a purple-brown-red solid (2.0 g), presumably the desired nickel diimine dibromide complex.

EXAMPLE 5 Ethylene Oligomerizations A sample of the solid organometallic complex prepared in Example 4 (0.025 g) is added to a 1-L stainless-steel pressure vessel containing isobutane (500 mL) and methylaluminoxane (MMAOVheptane solution (1.0 mL of 6.7% MMAO) at 40°C. Ethylene is fed on demand to maintain a pressure of 300 psig in the reactor. After 30 min., ethylene uptake is 13 g, and catalyst activity is 7460 g ethylene converted/g Ni ^• h. A similar experiment is performed at 40°C and 400 psig ethylene.

After 30 min., ethylene uptake is 16 g; activity: 8820 g/g Ni ^• h.

An experiment performed at 80°C and 520 psig ethylene results in an ethylene uptake of 3 g; activity: 1540 g/g Ni ^• h.

In each case, the reactor is vented to recover butenes as the principal product.

EXAMPLE 6 Ligand and Complex Preparation Acetone (1.4 mL, 20 mmol) is added to a stirring solution of 3,4- diaminotoluene (0.61 g, 5.0 mmol) in methanol (30 mL), also containing 4λ molecular sieves (about 2 g). After 72 h at room temperature, the orange solution is filtered through Celite. The solvent is stripped to give a red oil. Preparative thin-layer chromatography yields a red solid, the desired aromatic 1 ,2-diimine. In a drybox, a portion of the purified 1 ,2-diimine (0.042 g, 0.21 mmol) is dissolved in dichloromethane (10 mL), and nickel(ll) dibromide dimethoxyethane complex (0.064 g, 0.21 mmol) is added. After stirring overnight, the mixture is filtered to produce a dark red solid. The solid is washed with dichloromethane (3 mL), then with pentane (10 mL), and is then dried under vacuum to give the desired nickel complex (0.070 g).

EXAMPLE 7

Ethylene Oligomerizations The nickel complex of Example 6 (1.0 mL of a 0.0020 M solution in dichloromethane) is added to a 1-L stainless-steel pressure vessel containing isobutane (500 mL) and methylaluminoxane (MMAO)/heptane solution (1 .0 mL of 6.7% MMAO) at 40°C. Ethylene is fed on demand to maintain a pressure of 300 psig in the reactor. After 30 min., ethylene uptake is 12 g, and catalyst activity is 204,000 g ethylene converted/g Ni ^• h.

A similar experiment is performed at 60°C and 400 psig ethylene. After 30 min., ethylene uptake is 6 g; activity: 102,000 g/g Ni ^• h. An experiment performed at 80°C and 520 psig ethylene results in an ethylene uptake of 2 g; activity: 34,000 g/g Ni ^• h.

EXAMPLE 8

Ligand and Complex Preparation Benzaldehyde (0.66 mL, 6.5 mmol) is added to a stirring solution of 3,4-diaminotoluene (0.40 g, 3.3 mmol) in methanol (30 mL), also containing 4A molecular sieves (about 2 g). The solution turns yellow immediately. After stirring 20 h at room temperature, the mixture is filtered through Celite. The solvent is stripped, and purification by preparative thin-layer chromatography gives a yellow solid, the desired aromatic 1 ,2-diimine.

In a drybox, a portion of the purified 1 ,2-diimine (0.036 g, 0.12 mmol) is dissolved in dichloromethane (10 mL), and nickel(ll) dibromide dimethoxyethane complex (0.037 g, 0.12 mmol) is added. After stirring overnight at room temperature, the mixture is filtered to produce a blue-purple solution and a beige solid. The filtrate is stripped to give a purple solid (0.031 g), which is the desired nickel complex.

EXAMPLE 9 Ethylene Oligomerizations

The nickel complex of Example 8 is used to oligomerize ethylene using the general procedure of Example 7. In one experiment, performed at 40°C and 300 psig ethylene, the ethylene uptake after 30 min. is 16 g, and the catalyst activity is 273,000 g ethylene converted/g Ni ^• h. A similar experiment is performed at 60°C and 400 psig ethylene.

After 30 min., ethylene uptake is 6 g; activity: 102,000 g/g Ni ^• h.

An experiment performed at 80°C and 520 psig ethylene results in an ethylene uptake of 2 g; activity: 34,000 g/g Ni ^• h.

The preceding examples are meant only as illustrations; the following claims define the scope of the invention.

Claims

I claim:

1. A catalyst system which comprises an activator and an organometallic complex, wherein the organometallic complex comprises a Group 8 to 10 transition metal and an aromatic 1 ,2-diimine ligand chelated to the metal.

2. The catalyst system of claim 1 wherein the activator is an aluminum alkyl, an alkyl aluminum halide, an alumoxane, or an ionic borate or aluminate.

3. The catalyst system of claim 1 wherein the organometallic complex includes a Group 10 transition metal.

4. The catalyst system of claim 1 wherein the aromatic 1 ,2-diimine ligand is produced by condensing an aromatic 1 ,2-diamine with two equivalents of an aliphatic or aromatic ketone or aldehyde.

5. The catalyst system of claim 4 wherein the aromatic 1 ,2-diamine is selected from the group consisting of o-phenylene diamines, diaminotoluenes, diaminoxylenes, diaminonaphthalenes, diamino- anthracenes, and diaminophenanthrenes.

6. The catalyst system of claim 4 wherein the ketone or aldehyde is a C₁-C₃₀ linear, branched, or cyclic aliphatic ketone or aldehyde.

7. The catalyst system of claim 1 wherein the organometallic complex further comprises one or more ligands selected from the group consisting of hydride, halide, C1-C₃₀ alkoxy, siloxy, hydrocarbyl, and dialkylamido.

8. A process which comprises oligomerizing or polymerizing an olefin in the presence of the catalyst system of claim 1.