Process for preparing and using meso/racemic-(bis(indenyl)ethane)zirconium dichloride compounds

Abstract: A process for the preparation of a meso/racemic-[bis(indenyl)ethane] zirconium dichloride compound comprising (a) reacting zirconium tetrachloride with the solid reaction product of the bis(indenyl)ethane ligand with an alkyllithium in a solvent as reaction medium and (b) recovering a solid mixture of lithium chloride and meso/racemic composition of [bis(indenyl)ethane]zirconium dichloride, characterized in that the solvent used as reaction medium in reaction (a) is an ether, pentane or a mixture thereof.

Description: The present invention relates to supported meso/racemic-[bis(indenyl)ethane]zirconium dichloride compounds having a meso/racemic ratio of at least 75/25, their preparation and their use as catalysts in the polymerization or copolymerization of olefins. The existing synthetic procedures for the preparation of meso/racemic-[bis(indenyl)ethane]zirconium dichlorides involve time consuming preparative and purifying steps, the catalyst prices being in the range of 8000-10000 U.S. dollars/kg. According to these procedures, the racemic isomer is formed as the main component since the aim of these procedures was to provide more and more (higher than 95 %) of this racemic isomer for the ITP production purpose and it can be isolated after the purification with 99 % of purity, See for example EP-A-576970. Thus there is a need in the art for an improved, modified and simple process to lower the final catalyst production and to facilitate the accessibility of the meso isomer or highly meso enriched mixture of the two isomers. Additionally, an easy route for the separation of the two isomers is required to replace the conventional method of separation, i.e. the fractionation crystallization, which is not acceptable for the large scale catalyst production. To this end, according to the present invention, said process is a process for the preparation of a supported meso/racemic [bis(indenyl) ethane] zirconium dichloride compound having a meso/racemic ratio of at least 75/25 comprising: a. reacting zirconium tetrachloride with the solid reaction product of the bis(indenyl)ethane ligand with an alkyllithium in diethyl ether, pentane or mixture thereof, b. recovering a solid mixture of lithium chloride and a meso/racemic composition of [bis(indenyl) ethane] zirconium dichloride; c. separating the meso/racemic composition of bis (indenyl) ethane zirconium dichloride from the lithium chloride with an extractant solvent; d. treating the meso/racemic composition of [bis (indenyl) ethane] zirconium dichloride obtained in step (c) with an extractant solvent; e. supporting the meso/racemic composition of [bis (indenyl) ethane] dichloride obtained in step (d) This invention relates also to a process for the polymerization or copolymerization of olefins comprising contacting at least one olefinic monomer in the presence as catalyst of a supported meso/racemic-[bis-(indenyl)ethane]zirconium dichloride compound having a meso/racemic ratio of at least 75/25 such as prepared. Further details and features of the invention will be evident from the description given below by way of a non-limiting example of several particular embodiments of the invention. As has already been indicated above the supported meso/racemic-[bis(indenyl)ethane]ZrCl 2 metallocenes of the invention are obtained by reacting zirconium tetrachloride with the solid reaction product of the bis(indenyl)ethane ligand with an alkyllithium in an ether, preferably diethyl ether, pentane or a mixture thereof, as reaction medium and by recovering a solid mixture of lithium salt and of the meso/racemic compound, the reaction between ZrCl 4 and the above mentioned solid reaction product being conducted under stirring at a temperature from 15 to 30°C, room temperature (about 25°C) being preferred for obvious reasons. As one of ordinary skill in the art knows, lowering the temperature will require a longer reaction time, while increasing the temperature may result in a complete evaporation of the reaction solvent. The duration of reaction is generally between 1 and 3 hours, preferably of the order of about 2 hours. The reaction pressure is usually atmospheric. As known in the art, dry and oxygen-free conditions are required for this type of reaction and for the storage of the metallocenes. The ligand may be prepared by using various methods well known in the art, depending on the selection of the specific substituents. The reaction of the ligand with an alkyllithium is also well known in the art ;it is generally carried out by dropwise addition of an alkyllithium solution in a solution of the ligand. Methyllithium and n-butyllithium are most often used, as are stoechiometric ratios of the reactants. The solid reaction product may be recovered by complete evaporation of the solvent. During the evaporation conditions, said product may have to be reduced to a fine powder, e.g. by grinding in a mortar. After completion of the reaction step between ZnCl 4 and the solid reaction product of the ligand with alkyllithium, the reaction solvent is decanted and a solid mixture of lithium chloride and the isomeric metallocene is collected. Then the metallocene is separated from the lithium salt with an extractant solvent. Suitable solvents are methylene chloride and dichloromethane. Thus the process of the invention provides a quantitative yield of the meso/racemic-(bisindenyl)ZrCl 2 mixture with an isomeric ratio of meso/rac = 50/50 within a short time. Furthermore, the presence of high percentage of the meso isomer in the original crude mixture now allows its separation by a simple solvent extraction. In this way, meso/rac ratios close to 75/25 can be obtained without difficulty. The isomeric metallocene catalyst is used in a supported form. Suitable supports are silicae having a surface area comprised between 200 and 600 m 2 /g and a pore volume comprised between 0.5 and 4.5 ml/g. According to The present invention, there is also provided a process for the polymerization or copolymerization of olefins comprising contacting one or more olefinic monomers such as ethylene or propylene in the presence as catalyst of an isomeric metallocene such as obtained hereinabove. The invention will be now described by two examples according to the invention. In the drawings : Figure 1 represents the 1 H-NMR spectrum of a meso/racemic metallocene of 50/50 prepared by the process of the invention. Figure 2 represents the 1 H-NMR spectrum of a meso/racemic metallocene of 75/25 prepared by the process of the invention. Figure 3 represents the 1 H-NMR spectrum of a meso/racemic metallocene of 50/50 prepared by the process of the invention. Example 1 a. Reaction of the ligand with alkyllithium (synthesis of the dianion) In a 500 ml round bottom flask equipped with addition funnel and magnetic stirring bar 5 g of the 1,2-bisindenylethane ligand is suspended in 100 ml of diethyl ether. Immediately after, under constant stirring, a solution of two equimol methyllithium in ether is added in a 10 min period. After an hour the gas evolution is ceased and the reaction is practically completed. The mixture is stirred for one more hour at ambient temperature and then the stirring is stopped, the supernatant ether is decanted and the dianion is isolated as a white solid. b. Reaction of ZrCl 4 with the lithiated ligand (synthesis of the metallocene) To the white dianion obtained above, 4.8 g of ZrCl 4 suspended in 200 ml of diethyl ether is added under stirring. The color of the reaction mixture changes from white to yellow-orange instantly. After two hours the ether is decanted and a yellow-orange solid consisting of the isomeric metallocene and LiCl is collected. The metallocene is separated from LiCl with the aid of methylene chloride. According to the 1 H-NMR spectrum (Figure 1) of the crude product, a meso/racemic composition of 50/50 is formed quantitatively and it is of spectroscopic purity. Due to the higher solubility of the meso isomer in dichloromethane a simple solvent extraction provides a sample with a meso/racemic composition of 75/25 (Figure 2). Example 2 To the white dianion described above in a) of the Example, 4.8 g of ZrCl 4 suspended in pentane is added. The reaction mixture is stirred for two more hours at room temperature. At the end of this period, the yellow-orange solid is filtered and extracted with methylene chloride to separate the LiCl by-product. The isomer composition and the yield is substantially the same as the ether procedure but the crude product contains some impurities (see Figure 3). The simplicity and rapidity of the process of the invention and the high meso content of the end product show that all the set objectives are attained. 100 % pure meso isomer can be obtained when products in large scale are synthesized. It is possible to produce by this process supported catalyst with a (bisindenyl)-ZrCl 2 metallocene with 50/50 and 75/25 isomeric ratios without any problems. Since a large part of racemic isomer is converted to the meso isomer during supporting reaction the final supported catalyst can have up to 85/15 meso/rac composition. Nevertheless, the presence of such quantities of racemic isomer may be beneficial to the mechanical and optical properties of the polyethylene or polypropylene film obtained since it would give rise to a high molecular weight tailing in the distribution. The process of the present invention can be also extended to other bis(indenyl)ethane)ZrCl 2 complexes with different substituents, in particular those with 2,2'-substituted and 2,2',4,4'-substituted indenyl ligands.

Claims: A process for the preparation of a supported meso/racemic [bis(indenyl) ethane] zirconium dichloride compound having a meso/racemic ratio of at least 75/25 comprising: a. reacting zirconium tetrachloride with the solid reaction product of the bis(indenyl)ethane ligand with an alkyllithium in diethyl ether, pentane or mixture thereof, b. recovering a solid mixture of lithium chloride and a meso/racemic composition of [bis(indenyl) ethane] zirconium dichloride; c. separating the meso/racemic composition of bis (indenyl) ethane zirconium dichloride from the lithium chloride with an extractant solvent; d. treating the meso/racemic composition of [bis (indenyl) ethane] zirconium dichloride obtained in step (c) with an extractant solvent; e. supporting the meso/racemic composition of [bis (indenyl) ethane] zirconium dichloride obtained in step (d) A process according to claim 1 wherein the reaction (a) is carried out under stirring at a temperature from 15 to 30°C. A process according to claims 1 or 2 wherein the duration of said reaction (a) is between 1 and 3 hours. A process according to claim 3 wherein said duration is of 2 hours. A process according to any one of claims 1 to 4 wherein the reaction product of the ligand with an alkyllithium is added as powder. A process according to any one of claims 1 to 5 wherein the extractant solvent is methylene chloride or dichloromethane. A process according to any one of claims 1 to 6 wherein the bis (indenyl) ethane ligand is selected from the 2,2'-substituted and 2,2', 4,4'-substituted indenyl ligands. A process according to any one of claims 1 to 7 wherein the support is silica having a surface area comprised between 200 and 600m2/g and a pore volume comprised between 0.5 and 4.5 mUg. A supported [bis (indenyl) ethane] zirconium dichloride compound obtained by the process according to claims 1 to 8 characterised in that the compound has a meso/racemic ratio of at least 75/25. A process for the polymerization or copolymerization of olefins comprising contacting at least one olefinic monomer in the presence of a compound such as prepared according to any one of claims 1 to 8, as catalyst. A process according to claim 10 wherein the olefinic monomer is ethylene or propylene. A process according to any one of claims 1 to 11, wherin the support is a silica having a surface area comprised between 200 and 600m2/g and a pore volume comprised between 0.5 and 4.5 ml/g.

Inventors: RAZAVI ABBAS, RAZAVI, ABBAS
Applicants: ATOFINA RES, ATOFINA RESEARCH
Application year: 1996
Main classification: C08F10
IPC codes: C08F4, C08F10, C07F17