Olefin polymerization catalysts containing 1,3-diboretanyl...

Details Olefin polymerization catalysts containing 1,3-diboretanyl... Olefin polymerization catalysts containing 1,3-diboretanyl...

2001-12-20

2003-07-22

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...

C526S131000, C526S133000, C526S160000, C526S161000, C526S170000, C526S172000, C502S103000

Reexamination Certificate

active

06596826

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to catalysts useful for olefin polymerization. In particular, the invention relates to organometallic catalysts that incorporate at least one anionic 1,3-diboretanyl 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) or azaborolinyl groups (U.S. Pat. No. 5,902,866).
Single-site catalysts typically feature at least one polymerization-stable, anionic ligand that is 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 some heteroatomic ligands such as boratabenzenyl or azaborolinyl. Catalysts that incorporate bicyclic “homoaromatic” anions (also 6&pgr;-electron donors) have also been described (see U.S. Pat. No. 6,228,959).
The anionic ligands described to date are normally “conjugated” ring systems. Electron density in the anions is thought to be “delocalized,” or shared among three or more atoms in the ring. Some atoms may be bypassed, as in the bishomoaromatic ligands. Most of the known 6&pgr;-electron-donor ligands have five-membered rings (as in cyclopentadienyl or azaborolinyl), six-membered rings (as in borabenzenyl), or even seven-membered rings (e.g., the bishomoaromatic systems of the '959 patent). Delocalization of the electron density is presumed to impart stability to the anionic ligand. In practice, the ligands are often easily generated by deprotonating suitable precursors (e.g., cyclopentadiene). The relatively high acidity of cyclopentadiene is a reflection of a high degree of stabilization of its conjugate anion.
Anion stability, however, is only one factor in making stable organometallic complexes. Consider cyclobutadiene, which is “anti-aromatic,” unstable, and cannot be isolated at ordinary temperatures. In spite of its instability, cyclobutadiene can be “trapped” as a stable organometallic complex (see J. March,
Advanced Organic Chemistry
, 2d ed. (1977) pp. 55-59).
Thus, when evaluating the potential of organometallic complexes as catalysts for olefin polymerization, it is important to consider more than just the stabilities of the anionic ligands. It is also necessary to consider the degree to which the ligand helps to stabilize an incipient cationically active site. Moreover, the reactivity of the active site toward olefins and the rate of monomer insertion are also important. A ligand precursor with relatively low acidity might be valuable anyway if other factors (such as those noted above) are favorable. As is shown below, molecular modeling studies can help to identify valuable ligands and complexes.
Little is known about the prospect of using anionic ligands having four-membered rings to make organometallic complexes for olefin polymerizations. However, convenient synthetic routes to some interesting anionic, 1,3-diboretanyl ligands exist. 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 catalyst system for polymerizing olefins. The catalyst system comprises an activator and an organometallic complex. The complex comprises a Group 3 to 10 transition or lanthanide metal, M, and at least one 1,3-diboretanyl anion that is bonded to M.
Evidence from molecular modeling studies suggests that catalysts incorporating anionic 1,3-diboretanyl ligands will rival the performance of catalysts based on cyclopentadienyl and substituted cyclopentadienyl ligands, i.e., traditional metallocenes.
The invention includes some straightforward synthetic routes to olefin polymerization catalysts that incorporate the 1,3-diboretanyl ligands. The ease and flexibility of these techniques put polyolefin makers in charge of a new family of catalysts.
DETAILED DESCRIPTION OF THE INVENTION
Catalyst systems of the invention comprise an activator and an organometallic complex. The catalysts are likely to be “single site” in nature, i.e., they are distinct chemical species rather than mixtures of different species. Single-site catalysts normally 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 anionic 1,3-diboretanyl ligand that is bonded to the metal. By “1,3-diboretanyl,” we mean a monoanionic ligand that has two boron atoms at opposite “corners” of a four-membered ring. The ligand further includes a carbanionic center, which resides between the two borons, and carbon or a heteroatom (oxygen, sulfur, phosphorus, or nitrogen) at the fourth corner. Thus, the anionic 1,3-diboretanyl ligand is either a 2-pi electron donor (with carbon at the fourth corner) or a 4-pi electron donor (with a heteroatom at the fourth corner).
Preferably, the anionic 1,3-diboretanyl ligand has the structure:
in which A is O, S, NR, PR, or CR
2
; and each of R and R′ is independently hydrogen, C
1
-C
30
hydrocarbyl, dialkylamino, halide, or organosilyl. A few exemplary anionic 1,3-diboretanyl ligands:
The anionic 1,3-diboretanyl ligands are conveniently generated by any suitable method. In one approach, they are made by deprotonating, using conventional means, suitable neutral precursors (“1,3-diboretanes”) in which the 1,3-diboretane carbon is attached to at least one hydrogen atom. Normally, this hydrogen is the most acidic hydrogen in the precursor. As the calculations below demonstrate, the acidity of 1,3-diboretanes can exceed that of even cyclopentadiene, so deprotonation is facile. In another approach, described later, a synthetic equivalent of the 1,3-diboretanyl ligand is used to make the complex.
The 1,3-diboretanes preferably have the structure:
in which A is O, S, NR, PR, or CR
2
; and each of R and R′ is independently hydrogen, C
1
-C
30
hydrocarbyl, dialkylamino, halide, or organosilyl.
The 1,3-diboretanes are made by any suitable method. One useful approach was developed by Siebert and coworkers (see
Chem. Ber
. 122 (1989) 1881 and
Angew. Chem., I.E. Engl
. 25 (1986) 1112). First, bis(trimethylsilyl)acetylene and tetrachlorodiborane react to give 1,1-bis(dichloroboryl)-2,2-bis(trimethylsilyl)ethylene (I). Reaction of (I) with 4 moles of diisopropylamine (with elimination of two moles of amine hydrochloride salt) replaces two chlorine atoms with diisopropylamino groups. Elimination of KCl by addition of two equivalents of potassium metal gives an unsaturated “diborete,” which is easily hydrogenated using palladium on carbon at room temperature to produce 1,2-bis(diisopropylamino)-2,4-bis(trimethylsilyl)-1,3-diboretane (II):
In another interesting approach developed by Siebert et al. (
Angew. Chem., I.E. Engl
. 24

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