An interesting class of metallocene compounds according to the present invention is that of formula (I) wherein both Y and Z are a moiety of formula (II), R1 is a C1-C20-alkyl group, preferably a methyl group, R2 is hydrogen, R3 is different from hydrogen, B and D are carbon atoms, A is an element of the group 16 of the Periodic Table of the Elements (new IUPAC version), preferably sulphur, m is 0