Complexes based on four-membered cyclic anionic...

Details Complexes based on four-membered cyclic anionic... Complexes based on four-membered cyclic anionic...

2001-12-20

2003-07-01

Wilson, D. R. (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S160000, C526S172000, C526S170000, C526S134000, C526S348000, C502S103000, C502S117000, C502S208000, C502S216000

Reexamination Certificate

active

06586545

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 anionic heterocyclobutenyl 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 a-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 heterocyclobutenyl ligands are not known. The neutral ligand precursors can be prepared by known literature procedures.
In spite of the availability of synthetic routes to heterocyclobutenyl anions, their use as ligands for metallocene or single-site catalysts for olefin polymerization has not been suggested. Organometallic complexes from these ligands would provide a new class of potentially valuable catalysts to polyolefin producers.
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 metal, M, and at least one anionic heterocyclobutenyl ligand that is bonded to M.
Evidence from molecular modeling studies indicates that single-site catalysts based on anionic heterocyclobutenyl ligands will exhibit improved stability versus catalysts based on cyclopentadienyl and substituted cyclopentadienyl ligands. This improved stability should impart increased catalyst efficiency, especially at higher process temperatures.
Also provided is a two-step method of producing the catalyst. Step one involves deprotonating a heterocyclobutene and reacting the resulting anion with a Group 3 to 10 transition metal source to produce an organometallic complex comprising the metal, M, and at least one heterocyclobutenyl ligand that is bonded to M. In step two, the product is combined with an activator. 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 probably “single site” in nature, i.e., they are distinct chemical species rather than mixtures of different species. They should 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 metal, M. As used herein, “transition metal” includes metals of the lanthanide and actinide series. More preferred complexes include a Group 4 to 6 transition metal; most preferably, the complex contains a Group 4 metal, i.e., titanium, zirconium or hafnium.
The organometallic complex also comprises at least one heterocyclobutenyl anion that is bonded, most likely &pgr;-bonded, to the metal. By “heterocyclobutenyl anion,” we mean an anion formed from a four-membered cyclobutene ring where one of the saturated carbons in the cyclobutene is replaced with a heteroatom.
The heterocyclobutenyl anions are usually generated from the corresponding neutral compounds by deprotonation with a potent base as is described in more detail below. The synthesis of phosphacyclobutenes (dihydrophosphetes) from the corresponding titanacyclobutene is known (see K. Doxsee et al.,
J. Am. Chem. Soc
. 111 (1989) 9129), and azacyclobutenes (azetines) should be available from the same method. Alternatively, azetines should be available from a method analogous to that described in the literature for 1-acyl-2-azetines (see M. Jung et al.,
J. Org. Chem
. 56 (1991) 6729), where an azetidonol is mesylated, and then the mesylate is treated with base to eliminate methanesulfonic acid and afford the azetine. The synthesis of thiacyclobutenes (thietes) by facile Hofmann elimination of the 3-aminothietane derivatives has been described (see D. Ditmer et al.,
J. Org. Chem
. 37 (1972) 1111). The chemistry of oxetenes has been reviewed (see R. Linderman,
Compr. Heterocycl. Chem. II
(1996), 1B 721-753, Editor A. Padwa, Elsevier Publishers Oxford, UK).
The heterocyclobutenyl anion may be bridged to another ligand, which may or may not be another heterocyclobutenyl anion. Preferred heterocyclobutenyl anions have the general structure:
where A is N, P, O or S. R is C
1
-C
30
hydrocarbyl or trialkylsilyl. When A is N or P, n is 1; when A is O or S, n is 0; each R
1
is independently selected from the group consisting of R, H, Cl, and Br. When A is N, the anion is said to be an azetinyl anion. When A is P, the anion is said to be a phosphetyl anion. When A is S, the anion is said to be a thietyl anion and when A is O, the anion is an oxetenyl anion.
Exemplary anions are:
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, indenoindolyl, quinolinoxy, pyridinoxy, and azaborolinyl as described in U.S. Pat. Nos. 5,554,775, 5,539,124, 5,637,660, 5,902,866 and 6,232,260, 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 heterocyclobutenyl 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 heterocyclobutenyl anions or a heterocyclobutenyl 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 metal and can improve catalyst activity and other properties such as comonomer incorporation.
The organometallic complex preferably has the general structure:
where M is a transition metal and A is N, P, O or S. R is C
1
-C
30
hydrocarbyl or trialkylsilyl. When A is N or P, n is 1; when A is O or S, n is 0; each R
1
is independently selected from the group consisting of R, H, Cl, and Br. Each L is independently halide, alkoxy, siloxy, alkylamino or C
1
-C
30
hydrocarbyl. L′ is substituted or unsubstituted cyclopentadienyl, indeny

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