The effect of the metal in propene polimerisation using unbridged bicyclic catalysts: from zirconium to titanium

Fluxional catalysts based on unbridged metallocenes of Zr are increasingly becoming of interest in the synthesis of elastomeric polypropylene. In particular, bicyclic systems in which the ring fused to the cyclopentadienyl moiety is saturated, due to the introduction of a conformational flexibility parameter that can be finely tuned, can be of help in elucidating the structure/activity relationship for this kind of catalysts. Furthermore, very little is known about the behaviour of the corresponding titanium complexes. We report here our recent results about the study of the reactivity of new titanium complexes compared to the corresponding zirconium derivatives. Among the microstructural data, the most striking result is that, although the isotactic pentad content is lower with the titanium based catalysts, the average length of the isotactic blocks is slightly higher.