oa New synthetic pathway for preparation of cyclic-substituted bridged bicycopentadiene derivatives

Since their discovery in the 1950's, cyclopentadiene-based metallocene complexes have attracted considerable attention in biochemistry as well as in catalytic processes in the chemical and pharmaceutical industries and more recently in the field of medicine as a potential treatment for cancer. Amongst them, complexes containing saturated cycles as substituents on the cyclopentadienyl ring itself (Figure 1) are particularly interesting as precursors to a-olefins polymerization catalysts. Their interest might lie in the greater stability or increased activity or differentiated selectivity of the resulting catalyst and in the better control of the catalyst residues. The unsaturated ligands and most specifically the ?5-indenyl types might be directly available, while the classical way to obtain the saturated ones is via the catalytic hydrogenation of the parent molecules. However, catalytic hydrogenation reactions usually require severe conditions that are not always compatible with the stability of the target molecules. We are interested in developing versatile, flexible and efficient routes to ligands containing saturated ring systems attached to the cyclopentadienyl ring. This type of ligands, characterized by new structures, allows the synthesis of differentiated metallocene complexes, having outstanding performance in catalytic processes for the polymerization of a-olefins. We report here the synthetic protocols for saturated ligands precluding the hydrogenation step, starting from cycloalkanones. Elegant synthetic routes have been studied. However, the overall yields were often low or the method used was of limited applicability.