New Zirconium Complexes For 1-Olefins Photocatalysis And Ziegler-Natta Homogeneous Catalysis

Metallocene complexes of Group IV transition metals are well established highly active co-catalysts for the homo- and co-polymerisation of 1-olefins [1]. Tetrahydroindenyl derivatives can be more effective co-catalysts than the corresponding unsaturated derivatives, since they exhibit greater solution stability, combined with different steric and electronic properties. Recently R. Waymouth [2] has developed a new catalytic system based on substituted indenyl systems designed to produce elastomeric polypropylene (characterised by isotactic and atactic stereoblocks). This result can be obtained if the interconversion between chiral and achiral torsional isomers of the catalyst occurs on the time scale of the polymerisation reaction. Still a lot has to be done to understand which structural features are necessary to achieve the desired stereochemical control, since relatively slight changes in the catalyst structure are enough to disrupt the delicate balance necessary to yield this type of polymer. Up to now few systematic investigations have been carried out to establish which features are strictly necessary. In our studies about the structure/activity relationship in olefin polymerisation, we have recently developed a new synthetic method [3] that has proved successful for a "tuned" synthesis of a variety of bicyclic cyclopentadienyl ligands and their corresponding organometallic compounds, in good yields, with only minor purification steps, and reproducible in large-scale quantities.