New substituted metallocenes of the Group 4 transition metals as homogeneous Ziegler-Natta Catalysts

Organometallic complexes of transition metals containing bulky or chiral ligands are very interesting in synthetic methodology as catalytic or stoichiometric mediators of stereoselective or enantioselective reactions. The application of ??-cyclopentadienyl ligands as a support for introducing chirality is particularly attractive because of the large range of possible synthetic modifications and of the its vast range of applications. The most intensively studied reaction that utilises cyclopentadienyl complexes is the application of Group 4 metallocenes as Ziegler-Natta catalysts for the polymerisation of alkenes, a reaction known since 1957. Here we report the synthesis and characterisation of new metallocene complexes bearing sterically hindered cyclopentadienyl rings: the target is of inducing stereoregularity in olefin polymerisation (homogeneous Ziegler-Natta catalysis) by modification of the stereochemistry of the ligand environment of the transition atom. These metal complexes have been synthetised, characterised and tested to check their activity and efficiency in polymer synthesis.