Synthesis of enantiomerically pure ethylene-bridged ansa-zirconocene and -hafnocene complexes bearing fluorenyl, indenyl, octahydrofluorenyl, and tetrahydroindenyl ligands

We report on an efficient synthetic route for the preparation of enantiomerically pure ethylene-bridged ansa-zirconocene and -hafnocene complexes, bearing different cyclopentadienyl fragments. Ring opening of (R)-epoxystyrene (1) with fluorenyllithium proceeds enantiospecifically and leads to optically pure 2-(9-fluorenyl)-1-(S)-phenylethanol (2a) and 2-(9-fluorenyl)-2-(S)-phenylethanol (2b) in nearly quantitative yield. Treatment of 5, the trifluoromethanesulfonate derivative of 2b, with fluorenyl- and indenyllithium results in the formation of 1-(9-fluorenyl)-1-(S)-phenyl-2-(1-indenyl)ethane (6a) and 1,2-bis(9-fluorenyl)-1-(S)-phenylethane (6b), respectively. Reaction of the dilithio salts of 6a with ZrCl₄ and of 6b with MOU (M = Zr, Hf) affords the formation of the enantiomerically pure complexes [1-(η⁵-9-nuorenyl)-1-(fl)-phenyl-2-(η ⁵-1-(R,S)-indenyl)ethane]ZrCl₂ (7a = R,R; 7b=R,S) and of [1,2-bis(η⁵-9-fluorenyl)-1-(A)-phenylethane]MCl₂ (7c, M = Zr; 7d, M = Hf) in up to 63% yield. Hydrogenation of 7a-d with H₂/PtO₂ gives the complexes 8a-d, bearing octahydrofluorenyl and tetrahydroindenyl ligands. Hydrolysis of 8a,b in basic, aqueous media leads to the formation of C₂-symmetric μ-oxo dimers (12a,b). The solid-state structures of enantiomerically pure 7b and 8c and of 12b are reported.