The inventive metallocenes are transition metal-containing trihalo complexes represented by the formula ZAMX3 wherein Z is a cyclopentadienyl-type group as described above, A is as described above, M is a Group IVB or VB transition metal, preferably titanium, zirconium, hafnium or vanadium, more preferably zirconium or titanium, most preferably zirconium, and X is a halide, preferably X is chlorin