Metallocene compounds, process for their preparation, and their use in catalysts for the polymerization of olefins

A metallocene compound of the formula (I):

• 7
• wherein R1, R2, R3 and R4, which can be identical or different, are hydrogen atoms or C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-aryl-alkyl groups which can contain silicon or germanium atoms, R3 being different from R2 and from a hydrogen atom, and wherein
• R1 and R2 on the same cyclopentadienyl ring can form a ring having 5 to 8 carbon atoms;
• R5 is a hydrogen atom or a —CHR7R8 group;
• R6 is a C6-C20-aryl radical or a —CHR9R10 group;
• R5 and R6 can form a ring having 3 to 8 carbon atoms which can contain hetero atoms;
• R7, R8, R9 and R10, which can be identical or different, are hydrogen atoms or C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals which can contain hetero atoms such as nitrogen, phosphor, oxygen or sulphur, and two R7, R8, R9 and R10 substituents can form a ring having 3 to 8 carbon atoms which can contain hetero atoms;
• M is an atom of a transition metal selected from those belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups in the Periodic Table of the Elements (new IUPAC version);
• the X substituents, which can be identical or different, are hydrogen atoms, halogen atoms or R, OR, SR, NR2 or PR2 groups, wherein the R substituents are C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals which can contain silicon or germanium atoms;
• with the proviso that, when the R1, R2 and R4 substituents are hydrogen atoms and the R5 and the R6 substituents are methyl groups, then the R3 substituents are other than an isopropropyl or tertbutyl group.