Synthesis of titanocenes

Details Synthesis of titanocenes Synthesis of titanocenes

1998-07-22

2001-04-17

Nazario-Gonzalez, Porfirio (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heavy metal containing

C556S053000, C526S126000, C526S160000, C526S943000, C502S103000, C502S117000

Reexamination Certificate

active

06218557

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the synthesis of titanocenes including constrained geometry titanocene catalysts utilizing a unique titanium trichloride reagent.
BACKGROUND OF THE INVENTION
The evolution of metallocene-based catalysts for the polymerization of ethylene and higher &agr;-olefins is reviewed in H. H. Brintzinger, et al.,
Angew. Chem. Int. Ed. Engl.
34: 1143-1170 (1995) and in P. C. Mohring, et al.,
J. Organometal. Chem.
479: 1-29 (1994). The applications of chiral metallocenes in organic synthesis are reviewed in R. L. Halterman,
Chem. Rev.
92: 965-994 (1992). These reviews highlight the applications of state-of-the art metallocenes. Most often, these applications center on the use of titanium containing and other Group IV metallocenes.
The early preparations of Group IV metallocenes involved reactions of the metal tetrahalides, typically the tetrachlorides, with deprotonated ligands, such as sodium cyclopentadienide, to give the metallocenes in good yields. The metallocenes of current interest possess more complicated ligand structures, and their preparations are not as straightforward. For the preparation of these metallocenes, the use of titanium tetrachloride often results in low yields of the desired metallocenes. Titanium trichloride (TiCl
3
) is often specified for use in place of titanium tetrachloride (TiCl
4
); subsequent oxidation gives the desired metallocenes in greatly improved yields.
For some recent examples which specify the use of titanium trichloride, see L. A. Paquette, et al.,
Organometallics
14: 4865-4878 (1995); F. Zaegel, et al.,
Organometallics
14: 4576-4584 (1995); and M. E. Huttenloch, et al.,
Organometallics
11: 3600-3607 (1992). Halterman, supra, cites references which show the use of titanium trichloride in several metallocene preparations. The titanium trichloride so used is produced from commercial titanium tetrachloride. Titanium trichloride produced by hydrogen reduction of the tetrachloride is most often used in lab-scale preparations. For commercial-scale preparations, this is impractical due to cost and the presence of acidic impurities. These impurities require purification of the titanium trichloride, typically by preparation and isolation of an ether complex, usually the tetrahydrofuran complex.
Commercially-available titanium trichloride is produced by the reduction of the tetrachloride with alkyl aluminum compounds. The titanium trichloride so produced contains aluminum chloride, which is not removed. Typical analyses specify 76-79 weight percent of titanium trichloride with the remaining weight percent comprised mostly of aluminum chloride. The use of aluminum-reduced titanium trichloride in metallocene preparations often gives products which contain varying amounts of aluminum-containing impurities. Separation of these impurities from the product titanocenes is not straightforward in most cases, especially on a commercial scale. The presence of these impurities can have significant adverse effects during subsequent uses of the titanocenes, particularly in olefin polymerizations.
Accordingly, a need exists for a titanium trichloride reagent useful to produce titanocenes free of aluminum containing impurities.
DEFINITIONS
For the purposes of this invention, the following terms have the meaning stated:
Titanocene Compound—A compound comprised of titanium bonded to one or more cyclopentadienyl rings.
Titanocene Ligand—A chemical precursor which contains cyclopentadienyl or substituted cyclopentadienyl moieties (including indenyl, fluorenyl, etc.) used to prepare a titanocene compound.
Constrained Geometry Catalyst (CGC)—A catalyst in which the metal center is contained in a ring structure and covalently bonded to a cyclic group via a delocalized &pgr;-system and covalently bonded via a sigma-bond to another atom such as carbon, nitrogen, oxygen, etc. A small ring size induces constraint about the metal atom center. For titanium-containing CGC's, the incorporated titanium atom can be in a formal +4, +3, or +2 oxidation state. See EP application 90309496.9, WO 95/00526 and U.S. Pat. No. 5,470,996.
CpSA Ligand—(t-butylamino)(tetramethylcyclopentadienyl)dimethylsilane.
(CpSA)
2−
—doubly-deprotonated CpSA ligand.
(CpSA)
2−
TiCl
2
—[(t-butylamido) (tetramethylcyclopentadienyl)dimethylsilane]titanium dichloride.
Substantially Stoichiometric Amount—An amount not less than 90% nor more that 110% of stoichiometric.
SUMMARY OF THE INVENTION
This invention includes a general method for producing titanium trichloride containing mixtures suitable for the preparation of titanium-containing metallocenes including constrained geometry Ti(IV), Ti(III) and Ti(II) complexes free of aluminum containing impurities.
The titanium trichloride containing mixtures are produced by the preferably stoichiometric (1:1) reaction of an organometallic compound, such as n-butyl lithium or n-butyl magnesium chloride, with titanium tetrachloride in a non-interfering solvent medium. These mixtures are used directly without isolation of the titanium trichloride in reactions with appropriate ligands to produce the desired titanocenes, including constrained geometry titanium complexes, in good yields. The resulting titanocene products are specifically free of aluminum-containing impurities.
DETAILED DESCRIPTION OF THE INVENTION
The invention is a method for producing a titanium-containing metallocene compound which comprises separately providing a first reaction mixture containing titanium trichloride and a second reaction mixture containing a magnesium or alkali metal or alkaline earth metal salt of a metallocene compound ligand. The first and second mixtures are combined for reaction to produce an intermediate from which an aluminum-free titanocene useful as an olefin polymerization catalyst may be synthesized.
The first reaction mixture is produced by reacting TiCl
4
with an alkali metal compound having the formula R
X
—M or a Grignard reagent having the formula RMgX. In each formula, R is a straight or branched chain aliphatic hydrocarbon group, preferably an alkyl group, having 2 to 10 carbon atoms. R may also be an alkaline earth metal such as calcium, barium or strontium. X is the value of M. In the formula R
X
—M, M is an alkali metal such as sodium, potassium or lithium. In the formula RMgX, X is a halogen, preferably chlorine. n-butyl lithium or n-butyl magnesium chloride are preferred. The reactants are combined in substantially stoichiometric amounts in a non-interfering, preferably hydrocarbon, medium.
Useful hydrocarbon media include aliphatic or aromatic hydrocarbons, such as hexane, heptane, cyclohexane, benzene, toluene and xylene. Toluene is preferred for the specific examples shown here. Useful ether and polyether solvents include tetrahydrofuran, diethyl ether, ethylene glycol dimethyl ether, and dioxane. Mixtures of any hydrocarbon and ether solvents are useful for the reaction.
The reaction is preferably accomplished under dry, oxygen-free conditions. The temperature at which the reaction is conveniently conducted is −20° C. or 120° C., with the optimum temperature range being 30-40° C.
The second reaction mixture is separately provided by deprotonating the desired metallocene ligand with the appropriate base by known methods. See, generally, Paquette, et al., supra; Zaegel, et al., supra; and Halterman, supra.
The first reaction mixture, which includes the medium or solvent, titanium trichloride and a metal halide such a LiCl or MCl
2
, is added directly without isolation of the titanium trichloride to the second deprotonated ligand reaction mixture to produce a first titanocene.


REFERENCES:
patent: 5350723 (1994-09-01), Neithamer et al.
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patent: 5866704 (1999-02-01), Nickias et al.
Feld et al., The Organic Chemistry of Titanium, Washington D.C. (Butterworths) p. 154, 1965.*
Cotton et al., Advanced Inorganic Chemistry A Comprehensive Text,

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