MXPA97002083A - Metalocenos without bridges of an indensil substitute - Google Patents

Abstract

The present invention relates to a bridged metallocene of the formula (In) (Cp) MeQ2, characterized in that In is a substituted indenyl radical having a substituent in at least one of positions 1,2 and 3, the substituents are selected of a hydrocarbyl radical having 1 to 10 carbon atoms, or a trialkylsilyl radical wherein the alkyl has from 1 to 4 carbon atoms, Cp is an unsubstituted cyclopentadienyl radical, Me is a transition metal, which is titanium, zirconium , or hafnium, and each Q is the same or different, and is a hydrocarbyl radical having 1 to 12 carbon atoms, an alkoxy radical having 1 to 12 carbon atoms, an aryloxy radical having 6 to 12 carbon atoms , hydrogen or a halu

Description

METALOCENOS WITHOUT BRIDGES OF A SUBSTITUTE SUBSTITUTED TECHNICAL FIELD This invention relates to metallocenes. In another aspect this invention relates to catalyst systems useful for the polymerization of olefins. In another aspect, this invention relates to methods for polymerizing olefins using specific types of metallocenes, which may be referred to as non-bridged metallocenes of a substituted indenyl and cyclopentadienyl. BACKGROUND OF THE INVENTION Since the discovery of ferrocene in 1951, a number of metallocenes have been prepared by the combination of compounds prepared from cyclopentadiene-type compounds and various transition metals. The term "cyclopentadiene-type compounds" as used herein refers to compounds that contain the cyclopentadiene structure. Examples include unsubstituted cyclopentadiene, unsubstituted indene, unsubstituted fluorene, and substituted varieties of such compounds. Also included is tetrahydroindene. It has been found that many of the cyclopentadiene-type metallocenes are useful in catalyst systems for the polymerization of olefins. It has been noted in the art that variations in the chemical structure of such cyclopentadienyl type metallocenes can have significant effects on the desirability of metallocenes as polymerization catalysts. For example, it has been found that the size and location of the REF: 24279 substitutions on the cyclopentadienyl type ligands affect the activity of the catalyst, the stereoselectivity of the catalyst, the stability of the catalyst or various properties of the resulting polymer; however, the effects of various substituents are still largely an empirical matter, that is, experiments must be conducted to determine exactly what effect a particular variation in the chemical structure of the metallocene will have on its behavior as a polymerization catalyst. While there are references in the prior art containing general formulas encompassing a vast number of unbridged metallocenes, it is considered unlikely that all metallocenes within the broad descriptions of the publications have been effectively prepared and evaluated to determine their effects on polymerization . For example, while the Patents of E.U.A. Nos. 5, 049,535; 5.225, 092; and 5, 126, 303 and WO 94/11406 contain arguments with respect to a broad range of both metallocenes, bridges and bridges, the only effective examples of bridged metallocenes are those in which two identical cyclopentadienyl ligands are present. , that is, symmetrical metallocenes without bridges. Similarly, while US 5, 331, 054 names two unbalanced asymmetric metallocenes, ie, (cyclopentadienyl) (indenyl) and (cyclopentadienyl) (fluorenyl) zirconium dichlorides, these compounds do not contain substituted indenyl groups, and again, Current examples used symmetric metallocenes without bridges. While published European Application 685,485 describes unbalanced asymmetric metallocenes containing substituted indenyl groups, the metallocenes also contain a pentamethylcyclopentadienyl group. Similarly, while U.S. 5,223,467 proposes asymmetric unbridged metallocenes that could include substituted indenyl groups, also specifies that the other cyclopentadienyl ring is also substituted, and does not contain any effective example having an indenyl ligand. It has been found that many of the bridged metallocenes are not sufficiently active in the polymerization of olefins to be of significant commercial interest. The European application 685,485 mentioned above reveals that indenyl dichloride pentamethylcyclopentadienyl Zr is much more active than indenyl cyclopentadienyl, which in turn is much more active than its counterpartseither the bis indenyl or the bis ciciopentadienil. Before the present work of the applicants, there seems to be no work to suggest what effect the substituents on the indenyl would have on an asymmetric (indenyl) (unsubstituted cyclopentadienyl) unsymmetrical metallocene without bridges. An object of the present invention is to provide certain novel metallocenes containing substituted indenyl. Still another object of the present invention is to provide polymerization catalyst systems employing specific indenyl-type metallocenes. Still another object of the present invention is to provide processes for the polymerization of olefins, which use specific indenyl-type metallocene catalyst systems. Still another object of the present invention is to provide catalyst systems that provide extraordinarily high activity or molecular weight in the polymerization of olefins. BRIEF DESCRIPTION OF THE INVENTION According to the present invention, novel substituted metallocenes are provided without bridges of the formula (ln) (Cp) MeQ2, wherein In is a substituted indenyl radical having a substituent in at least one of the positions 1 , 2, and 3, the substituents are selected from hydrocarbyl radicals having from 1 to 10 carbon atoms, more preferably from 1 to 6 carbon atoms, and trialkylsilyl radicals wherein the alkyl groups have from 1 to 4 carbon atoms; Cp is an unsubstituted cyclopentadienyl radical; Me is a transition metal, selected from the group consisting of titanium, zirconium, and hafnium; and each Q is the same or different, and is selected from the group consisting of hydrocarbyl radicals having from 1 to 12 carbon atoms, alkoxy radicals having from 1 to 12 carbon atoms, aryloxy radicals having from 6 to 12 atoms of carbon, hydrogen, and halides. In accordance with another aspect of the present invention, there is provided a catalyst system comprising the specific types of indenyl-free bridged metallocenes described above, in combination with a suitable cocatalyst. According to still another aspect of the present invention, there is provided a process for the polymerization of olefins, which comprises contacting the olefins, under suitable reaction conditions, with a catalyst system comprising a metallocene containing indenyl described above, in combination with a suitable cocatalyst. DETAILED DESCRIPTION OF THE INVENTION The novel metallocenes provided in accordance with the present invention are bridged, that is, the indenyl ligand and the cyclopentadienyl ligand that are attached to the metal are not attached to each other. In this description, the locations of the substituents are numbered according to the Organic Chemistry Nomenclature of the IUPAC, 1979, rule A 21.1. Such numbering is illustrated in the figure found in lines 22-26 of page 2 of WO 94/11406 mentioned above. More preferably, the indenyl has from 1 to 3 hydrocarbyl substituents, or a trialkylsilyl substituent, optionally with 1 or 2 hydrocarbyl substituents, and each substituent is located at a position different from positions 1, 2, or 3 of the indenyl. It has been found that the metallocenes dichloride of (1-phenyl indenyl) (cyclopentadienyl) zirconium, dichloride of (1,2,3-trimethyl indenyl) (cyclopentadienyl) zirconium, dichloride of (2-methyl indenyl) (cyclopentadienyl) zirconium, dichloride of (1-trimethylmethylsilyl indenyl) (cyclopentadienyl) zirconium, and (1,2-dimethyl indenyl) (cyclopentadienyl) zirconium dichloride have particularly desirable characteristics. The metallocenes of the invention can be prepared using techniques similar to those that have been used in the past to make asymmetric metallocenes. An example involves reacting an alkali metal salt of the indenyl compound in a suitable solvent, under suitable reaction conditions, with a suitable transition metal compound, for example CpMeC, where Me is Zr, Hf, or Ti. An especially preferred method involves carrying out the reaction of the salt containing the indenyl and the transition metal compound in the presence of a liquid diluent that is non-halogenated and non-coordinating towards the transition metal compound. Examples of such a suitable liquid include hydrocarbons such as toluene, pentane, or hexane, as well as non-cyclic ether compounds such as diethyl ether. It has been found that the use of such non-halogenated and non-coordinating solvents usually allows one to obtain large quantities of substantially pure metallocenes in a more stable form, and often allows the reaction to be conducted under higher temperature conditions, which when dichloromethane is used as the diluent. The formation of the alkali metal salt of the indenyl compound can be carried out using generally any technique known in the art. For example, it can be prepared by reacting an alkali metal alkyl with the substituted indene. The molar ratio of the alkali metal alkyl to the indene may vary; in general, however, the ratio would be in the range of about 0.5 / 1 to about 1.5 / 1, still more preferably about 1/1.Typically, the alkali metal of the alkali metal alkyl would be selected from sodium, potassium, and lithium, and the alkyl group would have from 1 to 8 carbon atoms, more preferably from 1 to 4 carbon atoms. In the preferred embodiment, if the indenyl salt is formed using tetrahydrofuran (THF) as the liquid solvent, the salt is isolated, and substantially all of the THF is removed before the salt is contacted with the transition metal halide. . The molar ratio of the indenyl salt to the transition metal compound can vary over a wide range, depending on the desired results. Typically, however, the indenyl salt is used in a molar ratio of the indenyl compound to the transition metal compound, ie, CpMeC, of about 1 to 1. The resulting metallocene can be recovered and purified using known conventional techniques in the art, such as filtration, extraction, crystallization, and recrystallization. It is generally desirable to recover the metallocene in a form that is free of any substantial amount of side product impurities. Accordingly, recrystallization and fractional crystallization are desirable to obtain relatively pure metallocenes. Dichloromethane has been found to be particularly useful for such recrystallizations. Since the stability of the various metallocenes varies, it is generally desirable to use the metallocenes shortly after their preparation, or at least to store the metallocene under conditions that favor its stability. For example, metallocenes can generally be stored in the dark at low temperature, that is, below 0o C, in the absence of oxygen and water. The resulting indenyl-containing metallocenes of the invention can be used in combination with a cocatalyst suitable for the polymerization of olefinic monomers. In such processes, the metallocene or cocatalyst can be employed on a solid insoluble particulate support. Examples of suitable cocatalysts generally include any of those cocatalysts that have been used in the past in conjunction with metallocene olefin polymerization catalysts containing transition metals. Some typical examples include metal organometallic compounds of Groups IA, HA, and IIIB of the Periodic table. Examples of such compounds have included compounds of organometallic halides, organometallic hydrides and even metal hydrides. Some specific examples include triethyl aluminum, triisobutyl aluminum, diethyl aluminum chloride, diethyl aluminum hydride, and the like. The most preferred cocatalyst is currently an aluminoxane. Such compounds include those compounds that have repeated levels of the formula: - AW- wherein R is an alkyl group which generally has from 1 to 5 carbon atoms. Aluminoxanes, sometimes also referred to as poly (hydrocarbyl aluminum oxides), are well known in the art, and are generally prepared by reacting a hydrocarbyl aluminum organ compound with water. Such preparation techniques are described in U.S. 3,242,099 and 4,808,561. Presently preferred cocatalysts are prepared either from trimethylaluminum or triethylaluminum, sometimes referred to as poly (methyl aluminum oxide) and poly (ethyl aluminum oxide), respectively. It is also within the scope of the invention to use an aluminoxane in combination with a trialkylaluminum, such as that described in the U.S. Patent. No. 4,794,096. Metallocenes containing indenyl, in combination with the aluminoxane cocatalyst can be used to polymerize olefins, especially alpha olefins having from 2 to 12 carbon atoms. Frequently, such polymerizations would be carried out in a homogeneous system, in which the catalyst and the cocatalyst were soluble; Nevertheless, it is within the scope of the present invention to carry out the polymerizations in the presence of insoluble supported or particulate forms of the catalyst and / or the cocatalyst. The catalyst is thus considered suitable for solution, suspension or gas phase polymerization. It is within the scope of the invention to use a mixture of two or more of the metallocenes of the invention containing indenyl, or a mixture of a metallocene of the invention containing indenyl with one or more other cyclopentadienyl type metallocenes. Indenyl-containing metallocenes, when used with aluminoxane, are particularly useful for the polymerization of ethylene in the presence or absence of other olefins. Examples of other defines that may be present include the mono-unsaturated aliphatic alpha-olefins having from 3 to 10 carbon atoms. Examples of such olefins include propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1 -octene, 1-decene, 4,4-dimethyl-1-pentene, 4,4-diethyl-1-hexene, 3,4-dimethyl-1-hexene, and similar compounds, and mixtures thereof. The polymerizations can be carried out under a wide range of conditions, depending on the particular metallocene employed, and the desired results. Examples of the typical conditions under which the metallocenes may be used in the polymerization of olefins include conditions such as those described in U.S. Pat. Nos. 3,242,099; 4,892,851; and 4,530,914. It is considered that generally any of the polymerization processes used in the prior art can be used with any of the transition metal-based catalyst systems with the indenyl-containing metallocenes of the present invention. The amount of cocatalyst can vary within a wide range. It is currently preferred for the molar ratio of the aluminum in the aluminoxane to the transition metal in the metallocene to be in the range of about 0.1: 1 to about 100,000: 1, and more preferably from about 5: 1 to about 15,000. :1. In many cases, the polymerizations would be carried out in the presence of liquid diluents that do not have an adverse effect on the catalyst system. Examples of such liquid diluents include propane, butane, isobutane, pentane, hexane, heptane, octane, cyclohexane, methylcyclohexane, toluene, xylene, and the like. The polymerization temperature can vary within a wide range, the temperatures would typically be in the range of about -60 ° C to about 300 ° C, more preferably in the range of about 20 ° C to about 160 ° C Typically, the pressure would be in the range from about 1033 to about 516.5 kg / cm2 (1 to 500 atmospheres) or higher. The polymers produced with this invention have a wide range of uses, which will be apparent to those skilled in the art from the physical properties of the respective polymer. Various techniques can be used to prepare the substituted indenes necessary to produce the metallocenes of the present invention. The indenos substituted with monoalkyl can be produced by alkylation of the indenyl lithium. It has been found that less of the disubstitution products are obtained if the alkylation is conducted using diethyl ether as a reaction medium, rather than THF. 1-phenyl indenyl can be produced by reacting 1-indanone with phenylmagnesium bromide, and then dehydrating the resulting 1-phenyl-1-indanol. This is preferably conducted in the presence of p-toluensuiphonic acid in toluene. An analogous procedure can be used to produce 2-substituted indenes with alkyl and aryl. For example, a Grignard reaction of 2-indanone can be conducted, using the respective alkyl or aryl halide. Indenos substituted with multiple alkyls or aryls can be produced through the reaction of the respective substituted 1-indanone with the appropriate Grignard reagent, followed by dehydration of the produced indanol. For example, 2,3-dimethyl-1-indanone or 3-methyl indanone can be reacted with methyl magnesium iodide, to provide the substituted indanol with the respective methyl, which is dehydrated to 1,2,3-trimethylindene or 1 , 3-dimethyl indene, respectively. In the latter case, a mixture of p-tosyl chloride and pyridine is preferably used to effect dehydration of the hydroxy group. The reduction of 2, 3-dimethyl-1-indanone with lithium aluminum hydride and subsequent removal of water with p-toluenesulfonic acid yields 1,2-dimethylindene. The 3-phenyl-1-methyl indene compound can be prepared by reacting 3,3-diphenylpropionic acid with aluminum trichloride in dichloromethane, to obtain 3-phenyl-1-indanone, which in turn is reacted with methyl iodide magnesium, to produce indanol, which is then dehydrated with p-toluenesulfonic acid. A similar technique can be used to prepare 1-phenyl-3-phenyl indene, replacing the phenyl magnesium bromide with the methyl Grignard reagent. Indenos substituted with trimethylsilyl can be obtained by reacting the lithium salt of a substituted or unsubstituted indene with trimethylchlorosilane. Preferably, this is done in diethyl ether. Such a technique has been used to produce 1-trimethylsilyl-3-methyl indene, 1 -trimethylsilyl-3-phenyl indene, 1,3-di-trimethylsilyl indene, 1-trimethylsilyl-2-methyl indene, 1-trimethylsilyl-2-phenyl indene, and 1-trimethylsilyl-1-methyl-2-methyl-3-methyl indene. A further understanding of the present invention, its various aspects, objects and advantages will be provided by the following examples. In the following examples, preparations of the metallocenes were routinely carried out, using the Schlenk technique, with strict exclusion of air and moisture, by means of inert purified and dry gas. The solvents that were used were dried on a sodium / potassium alloy, or on phosphorus pentoxide in the case of dichloromethane, and distilled in circulating equipment under an inert atmosphere. The toluene was further distilled over phosphorus pentoxide, and the dichloromethane was distilled over calcium hydride. Deuterated solvents for NMR spectroscopy were stored on a molecular sieve. The melting points of the organic compounds were determined in open tubes, and those of the organometallic compounds, were determined in closed tubes under nitrogen. The organic compounds were characterized using a gas chromatograph, with a flame ionization detector and a fused silica column, with helium as the carrier gas. The mass spectra were made using a mass spectrometer with an electronic impact ionization energy of 70 eV. Samples were introduced with the help of a direct entry system, or injected in the form of solutions.

The thermal properties of the produced polymers were evaluated using a Differential Scanning Calorimetry Device, a DSC 7 model obtained from Perkin Elmer. The polymer samples were dried under vacuum before measurements. The technique involved melting samples of 5 to 10 grams in standard aluminum crucibles, first heating at 20 degrees K minute from -40 ° C to 200 ° C, holding at 200 ° C for 3 minutes, and then cooling to 20 degrees K / minute at -40 ° C. A second heating phase was then conducted as the first heating phase. Melting points and fusion enthalpies were measured during the second heating phase. The temperature was linearly corrected using indium as standard (melting point 156.63 ° C (429.78 ° K) and melting enthalpy 28.45J / g). The molecular weight of the polymers was determined using a Ubbelohde capillary viscometer, in cis / trans-decalin at 135 +/- 0.1 ° C. The samples were dried under vacuum before measurement, and then weighed in small flasks that could be sealed. The polymer was then dissolved in a precisely measured amount of the decalin, within three to four hours at 140 ° to 150 ° C. Any insoluble material was separated by filtration using glass fiber. Calibration curves were evaluated for three different concentrations of polymers, for the determination of the viscosity average molecular weight, ie, M ?. EXAMPLE I Bridged metallocenes were prepared by dissolving about 2.4 mmoles of the selected indenyl compound in diethyl ether, and then mixing it with about 1.5 ml of a 1.6 M solution in hexane of n-butyl lithium. After stirring for about three hours at room temperature, an equimolar amount of a metallocene of cyclopentadienyl trichloride was added, and the mixture was stirred for about four more hours at room temperature. The liquid was evaporated using vacuum. The residue was extracted with toluene, and the suspension was filtered over sodium sulfate. The resulting filtrate was concentrated by evaporation, and brought to the point of crystallization by cooling to -78 ° C. EXAMPLE II Various metallocenes without bridges, prepared as described in Example I were then evaluated to determine their effectiveness in the polymerization of ethylene. The technique involved combining about 1 to 5 mg of the metallocene with 1 to 5 ml of a 30 percent by weight solution of commercial metaluminoxane in toluene. The resulting solution was further diluted with additional toluene, to result in a solution containing about 1 to 5 mg of the metallocene in about 20 ml of the solution. The resulting mixture was used as the catalyst system within about 30 minutes of its preparation. The polymerizations were conducted in a 1 liter autoclave. First, 500 ml of pentane was mixed with 1 ml of the commercial methylaluminoxane, and stirred for 15 minutes at 30 ° C. Then the solution of the catalyst system was added. The autoclave was regulated thermostatically at 60 ° C, and ethylene was supplied at a pressure of 10.19 kg / cm 2 (10 bars). After a reaction time of one hour, the pressure was released, and the polymer was dried under vacuum. Some comparable control runs were performed, using unbridged metallocenes of the prior art, such as bis cyclopentadienyl, bis indenyl, and 1-methyl indenyl pentamethylcyclopentadienyl metallocenes. A new metallocene ((1-phenyl indenyl) indenyl zirconium dichloride) was also evaluated. The activities observed with the various metallocenes without bridges, and some of the properties of the resulting polymers are compared in the following tables. Note that in a few cases noted in the tables, the polymerization was conducted at 30 ° C rather than at 60 ° C.

I r-1 00 The data show that the metallocenes of the invention were more active either bis (cyclopentadienyl) zirconium dichloride or (1-methylindenyl) (pentamethylcyclopentadienyl) zirconium dichloride, and a number was even more active than bis (indenyl) zirconium dichloride. The catalysts with the highest activities were (1-phenyl indenyl) (cyclopentadienyl) zirconium dichloride and (1,2,3-trimethyl indenyl) (cyclopentadienyl) zirconium dichloride. Runs using (1-methyl indenyl) (trimethylsilylcyclopentadienyl) zirconium dichloride and (1-methyl indenyl) (pentamethylcyclopentadienyl) zirconium dichloride suggest that the introduction of a substituent on the cyclopentadienyl ligand has an adverse effect on the activity. A similar result is noted when one compares the activity of (1-phenyl indenyl) (indenyl) zirconium dichloride with that of (1-phenyl indenyl) (cyclopentadienyl) zirconium dichloride. The polymers with the greatest molecular weight were produced using the metallocenes of the invention having a trimethylsilyl substituent at the 1-position of the indenyl, or a methyl substituent at the 2-position of the indenyl. EXAMPLE III Another set of polymerizations was conducted using various indenyl metallocenes without bridges containing titanium. The conditions were as described in Example II. The polymerization temperature was generally 30 ° C. The results are shown in the following table.

TABLE 2 Activity Corri Complex da [g PE M? Do not . (npnol Mh)] [103 g / mol] 16 (l-Ph-Inl CpTiCl, 2100 920 17 (2 -PhIn) CpTiCl, 1100 680 18 (l, 2, 3 -Mß3In) CpTiCl2 390 * 830 * 680 1500 19 (l-Me-. SiIn) CpTiCl, 1700 1120 20 (In) (MeCp) TiCl2 1700 21 (l-Mßln) (Cp) TiCl2 900 * 195 * 2200 1625 *) Polymerization temperature 60 C.

A comparison of the data found in Table 2 with those found in Table 1 demonstrates that the titanium metallocenes of the invention are not as active as the zirconium metallocenes of the invention, however, they generally produce a polymer with a higher molecular weight. In contrast, applicants have observed that the hafnium metallocenes of the invention were found to produce products with lower molecular weight than the comparable zirconium metallocenes of the invention.

EXAMPLE IV A series of zirconium-based metallocenes of the invention were also evaluated to determine their effectiveness in the polymerization of propylene. The polymerizations were also conducted in the one liter autoclave, using solutions of the catalyst system prepared as described in Example II. In the polymerizations, about 500 ml of propylene were condensed in the autoclave, and were stirred with about 5 ml of the commercial solution at 30 percent by weight in toluene of methylaluminoxane. The catalyst solution was added by means of a barometric burette. The autoclave was thermostatically set at 0 ° C, and the reaction mixture was stirred for one hour. Then the pressure was released, and the polymer was dried under vacuum. The results are summarized in the following table. ro r? The table shows that the metallocenes of the invention can be used to polymerize propylene. The activity and molecular weight of the polymer produced varies depending on the type and position of the substituents. The relatively high melting temperatures, and the low tacticity may be due to block-like polymer structures. The polymer produced with (2-methylindenyl) (cyclopentadienyl) zirconium dichloride possesses an unusually broad Mw / Mn for a metallocene, and a fusion enthalpy of 0.5 J / g. This implies a low crystalline percentage, despite an isotactic content of 9.7%. In contrast, the polymer produced with (2-phenylindenii) (cyclopentadienyl) zirconium dichloride shows lower isotacticity, narrower molecular weight distribution, and larger enthalpy of fusion. The metallocene of Run 25 produces a polymer that has almost twice the molecular weight of the polymer produced with the metallocene used in Run 22.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (13)

1. CLAIMS 1. A bridged metallocene of formula (ln) (Cp) MeQ2, characterized in that In is a substituted indenyl radical having a substituent in at least one of positions 1, 2, and 3, the substituents are selected from a hydrocarbyl radical having from 1 to 10 carbon atoms, or a trialkylsilyl radical wherein the alkyl has from 1 to 4 carbon atoms; Cp is an unsubstituted cyclopentadienyl radical; Me is a transition metal, which is titanium, zirconium, or -hafnium; and each Q is the same or different, and is a hydrocarbyl radical having from 1 to 12 carbon atoms, an alkoxy radical having from 1 to 12 carbon atoms, an aryloxy radical having from 6 to 12 carbon atoms, hydrogen, or a halide.
2. 2. A metallocene according to claim 1, characterized in that each Q is a halide.
3. 3. A metallocene according to claim 1, characterized in that each Q is chloride.
4. 4. A metallocene according to any of the preceding claims, characterized in that Me is zirconium.
5. 5. A metallocene according to claim 4, characterized in that it is (1-phenyl indenyl) (cyclopentadienyl) zirconium dichloride, (1, 2,3-trimethyl indenyl) (cyclopentadienyl) zirconium dichloride, (2-methylindenyl) dichloride ) (cyclopentadienyl) zirconium, (1-trimethylmethylsilyl indenyl) (cyclopentadienyl) zirconium dichloride, or (1,2-dimethyl indenyl) (cyclopentadienyl) zirconium dichloride.
6. 6. A catalyst system useful for the polymerization of olefins, characterized in that it comprises a metallocene according to any of the preceding claims, and a suitable cocatalyst.
7. 7. A catalyst system according to claim 6, characterized in that the cocatalyst is an organoaluminum compound.
8. A catalyst system according to claim 7, characterized in that an organoaluminoxane cocatalyst having repeating units of the formula R I - £ -AM »is used. wherein each R is an alkyl radical having from 1 to 5 carbon atoms.
9. 9. A catalyst system according to claim 8, characterized in that methylaluminoxane is used as cocatalyst.
10. A process for preparing a polymer, characterized in that it comprises contacting at least one olefin under suitable reaction conditions with a catalyst system according to any of claims 6-9.
11. 11. A process according to claim 10, characterized in that ethylene or propylene is polymerized.
12. 12. A process according to claim 10 or 11, characterized in that the polymerization is conducted under polymerization conditions that form particles.
13. 13. A process according to any of claims 10-12, characterized in that the polymerization is conducted in a loop reactor or continuous loop.