Abstract: Polymers of C2-C10 alkenes are prepared in the presence of catalyst systems comprising as active constituents A) a metallocene complex of the general formula I  where the substituents and indices have the following meanings: M is titanium, zirconium, hafnium, vanadium, niobium or tantalum, R1 to R4 are hydrogen, C1-C10-alkyl, 5- to 7-membered cycloalkyl which in turn can bear a C1-C10-alkyl as substituent, C6-C15-aryl or arylalkyl, where two adjacent radicals may also together be cyclic groups having from 4 to 15 carbon atoms, Si(R6)3,  where R6 is C1-C10-alkyl, C6-C15-aryl or C3-C10-cycloalkyl, R7 and R8 are hydrogen, C1-C10-alkyl, C6-C15-aryl or C3-C10-cycloalkyl, R9 and R10 are C1-C10-alkyl, C6-C15-aryl or C3-C10-cycloalkyl, Y is nitrogen, phosphorus, arsenic, antimony, or bismuth, Z is oxygen, sulfur, selenium or tellurium, n is an integer in the range from 0 to 10, B) a compound forming metallocenium ions.

Abstract: Metallocene complexes of the formula I ##STR1## where M is titanium, zirconium, hafnium, vanadium, niobium or tantalum,n is an integer from 0 to 10,R.sup.5 is ##STR2## R.sup.11 to R.sup.14 are as designated in the disclosure, n.sup.1 is an integer from 0 to 10,X.sup.1 to X.sup.4 are each fluorine, chlorine, bromine, iodine, hydrogen, C.sub.1 -C.sub.10 -alkyl, C.sub.6 -C.sub.15 -aryl, alkylaryl having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, --OR.sup.15 --, --NR.sup.15 R.sup.16 or ##STR3## R.sup.15 to R.sup.21 are as designated in the disclosure, and o, p, q, r are each an integer from 0 to 4, the sum o+p+q+r+1 corresponding to the valency of M,which were used as active catalyst components in the preparation of polymers of C.sub.2 -C.sub.10 -alkenes, are recovered by a process wherein the polymerization is stopped by adding an acid and the metallocene complexes of the formula I are recovered by extraction from the reaction mixture.

Abstract: Metallocene complexes of the formula I ##STR1## where M is titanium, zirconium, hafnium, vanadium, niobium or tantalum,R.sup.1 and R.sup.4 are as defined in the specificationY is nitrogen, phosphorus, arsenic, antimony or bismuth,Z is oxygen, sulfur, selenium or tellurium,n is an integer from 0 to 10,R.sup.5 is ##STR2## R.sup.11 to R.sup.14 and m are as defined in the specification, and X.sup.1 to X.sup.4 are each fluorine, chlorine, bromine, iodine, hydrogen, C.sub.1 -C.sub.10 -alkyl, C.sub.6 -C.sub.15 -aryl, alkylaryl having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, --OR.sup.15 --, --NR.sup.15 R.sup.16 or ##STR3## and R.sup.15 to R.sup.21 are as defined in the specification. The complexes are used as catalyst components for polymerizing olefins.