Stereoselective synthesis of an ansa-zirconocene in a spirane scaffold

Methodology is described for the preparation of a rigid C2-bridged zirconocene catalyst system where the C2-bridge is embedded in a spirane scaffold. The ligand was prepared from 3,4-dihydro-2H-fluoren-1(9H)-one. Initially, the oxo group was converted into a spirocyclobutanone function. Further conversion to a fulvene was followed by regio- and stereoselective saturation to provide the ligand cis-2-(cyclopentadienyl)-1′,2′,3′,4′-tetrahydro-9H-spiro[cyclobutane-1,1′-fluorene]. The ligand was dilithiated and reacted with zirconium tetrachloride to provide the corresponding (η5-cyclopentadienyl)-spiro[cyclobutane-1,1′-(η5-fluorenyl)]zirconium dichloride complex. The structure of the zirconocene dichloride has been established by crystal X-ray analysis.