Group IV Saturated Fused Bicyclic Complexes For Ziegler-Natta Catalysis: New Direct Synthesis

Metallocene complexes of Group IV metals having ansa-bridged ligands1 are well established highly active co-catalysts for the polymerisation of 1-olefins. Their corresponding tetrahydroindenyl derivatives are recognized to be more effective co-catalysts than the parent unsaturated derivatives, mainly because they are more resistant to hydrolysis and stable in solution. Moreover, the hydrogenation induces changes in the steric and electronic properties of these metallocenes modifying their catalytic activity. The normal route to tetrahydroindenyl ligands is via the catalytic hydrogenation of the corresponding unsaturated indenyl complexes2. Due to the disadvantages and limitations of this kind of synthetic procedure, the synthesis of tetrahydroindenyl-type ligands prior to their attachment to the transition metal have been explored by several3 research groups. However, often the overall yields were low or the method used was of limited applicability. We report here a versatile and flexible new route to tetrahydroindenyl systems and to related ligands containing also larger saturated ring systems attached to the cyclopentadienyl ring starting from readily available cycloalkanones.