Process for the preparation of cyclopentadienyl compounds and compounds obtained therefrom

A bridged cyclopentadienyl compound having the general formula (I):

• wherein the double bonds in the cyclopentadienyl rings can be in any of the allowed positions, wherein R1, R2, R3, and R4 can be identical or different from each other, but wherein the two R1 groups are the same as each other, the two R2 groups are the same as each other, the two R3 groups are the same as each other, and the two R4 groups are the same as each other, the R1, R2, R3, and R4 groups being selected from the group consisting of hydrogen atoms, C1-C20-alkyl, C2-C20-alkenyl, C3-C20-cycloalkyl, C6-C20-aryl, C7-C20 alkylaryl, or C7-C20-arylalkyl radicals, each of which can contain atoms of Si or Ge, and furthermore two adjacent R1, R2, R3, and R4 substituents 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;
• R7, R8, R9, and R10, which can be identical or different, are hydrogen atoms or C1-C20-alkyl, C2-C20-alkenyl, C3-C20-cycloalkyl, C6-C20-aryl, C7-C20 alkylaryl, or C7-C20-arylalkyl radicals, each of which can contain heteroatoms, or two R7, R8, R9, and R10 substituents can form a ring having 3 to 8 carbon atoms;
• wherein each group of carbon atoms represented by a five-member ring in formula (I) and their attached substituents are called “bridged ligands”;
• wherein when the R5 and R6 substituents are methyl groups, one of following conditions applies:
• at least one of the R1, R2, R3, and R4 substituents is different from hydrogen, or
• if the R1 and R4 substituents are hydrogen atoms, the R3 substituents are other than isopropyl or tert-butyl groups, or
• the two bridged ligands are other than unsubstituted indenyls, or
• the two bridged ligands are other than 2-methyl-inden-1-yl, 3-isopropyl-inden-1-yl, 3-tert-butyl-inden-1-yl, 4-tert-butyl-fluoren-9-yl, and fluoren-9-yl groups.