Metallocenes containing ligands of 2-substituted idenyl derivatives, process for their preparation, and their use as catalysts

A compound of the formula I for preparing essentially isotactic olefin polymers ##STR11## in which M.sup.1 is a metal from group IVb, Vb or VIb of the Periodic Table

• R.sup.1 and R.sup.2 are identical or different and are a hydrogen atom, a C.sub.1 -C.sub.10 -alkyl group, a C.sub.1 -C.sub.10 -alkoxy group, a C.sub.6 -C.sub.10 -aryl group, a C.sub.6 -C.sub.10 -aryloxy group, a C.sub.2 -C.sub.10 -alkenyl group, a C.sub.7 -C.sub.40 -arylalkyl group, a C.sub.7 -C.sub.40 -alkylaryl group, a C.sub.8 -C.sub.40 -arylalkenyl group or a halogen atom,
• R.sup.3 and R.sup.4 are identical or different and are a hydrogen atom, a halogen atom, a halogen atom, a C.sub.1 -C.sub.10 -alkyl group, which is optionally halogenated, a C.sub.6 -C.sub.10 -aryl group, an --NR.sub.2.sup.15, --SR.sup.15, --OSiR.sub.3.sup.15, --SiR.sub.3.sup.15 or --PR.sub.2.sup.15 radical in which R.sup.15 is a halogen atom, a C.sub.1 -C.sub.10 -alkyl group or a C.sub.6 -C.sub.10 -aryl group,
• R.sup.5 and R.sup.6 are identical or different and are as defined for R.sup.3 and R.sup.4, with the proviso that R.sup.5 and R.sup.6 are not hydrogen,
• R.sup.7 is ##STR12## where R.sup.11, R.sup.12 and R.sup.13 are identical or different and are a hydrogen atom, a halogen atom, a C.sub.1 -C.sub.10 -alkyl group, a C.sub.1 -C.sub.10 -fluoroalkyl group, a C.sub.6 -C.sub.10 -aryl group, a C.sub.6 -C.sub.10 -fluoroaryl group, a C.sub.1 -C.sub.10 -alkoxy group, a C.sub.2 -C.sub.10 -alkenyl group, a C.sub.7 -C.sub.40 -arylalkyl group, a C.sub.8 -C.sub.40 -arylalkenyl group or a C.sub.7 -C.sub.40 -alkylaryl group, or R.sup.11 and R.sup.12 or R.sup.11 and R.sup.13, in each case with the atoms connecting them, form a ring,
• M.sup.2 is silicon, germanium or tin,
• R.sup.8 and R.sup.9 are identical or different and are as defined for R.sup.11
• m and n are identical or different and are zero, 1 or 2, m plus n being zero, 1 or 2, and
• the radicals R.sup.10 are identical or different and are as defined for R.sup.11, R.sup.12 and R.sup.13.