##STR00001## A metallocene compound of general formula (I): LGZMXp, wherein L is a divalent group, Z is a moiety of formula (II), wherein R.sup.3 and R.sup.4 are selected from hydrogen and hydrocarbon groups; A and B are selected from S, O or CR.sup.5, wherein R.sup.5 is selected from hydrogen and hydrocarbon groups, either A or B being different from CR.sup.5; G is a moiety of formula (III), wherein R.sup.6, R.sup.7, R.sup.8 and R.sup.9 are selected from hydrogen and hydrocarbon groups, M is an atom of a transition metal, X is selected from a halogen atom, a R.sup.10, OR.sup.10, OSO.sub.2CF.sub.3, OCOR.sub.10, SR.sup.10, NR.sup.10.sub.2 or PR.sup.10.sub.2 group, wherein the substituents R.sup.10 is hydrogen and a hydrocarbon group; p is an integer from 0 to 3.