CHIRAL CYCLOPENTANE-1,3-DIYL-BRIDGED ANSA-TITANOCENE DICHLORIDES

Displacement of cis-1,3-cyclopentanediol bis(tosylate) (12) or bis(mesylate) (11) with cyclopentadienylmagnesium bromide or indenyllithium afforded cyclopentane-bridged bis-(cyclopentadiene) and bis(indene) species 13 and 19, respectively. Bis(cyclopentadiene) 13 was converted via dimethylpentafulvene 16 to the isopropyl- and tert-butyl-substituted bis-(cyclopentadienes) 17 and 18. Each of the ligands 13, 17, 18, and 19 was converted into the corresponding cyclopentane-1,3-diyl-bridged ansa-titanocene dichloride complexes 5 (unsubstituted cyclopentadienyl), 7 (3-isopropyl-substituted cyclopentadienyl), 8 (3-tert-butyl-substituted cyclopentadienyl), and 6 (indenyl), respectively. Three diastereomers were observed in complexes 7 and 8 in a ratio of dl-C1-symmetrical to C(s)-symmetrical (R over methano bridge) to C(s)-symmetrical (R over ethano bridge) of 8:3:1 and 5:5:1, respectively. The major two isomeric components of 7 and 8 were isolated by fractional crystallization. The bis(indenyl) complex 6 was obtained from the initial reaction mixture as a pure C1-symmetrical diastereomer. Complexes 5 and 6 were characterized by X-ray crystallography. No evidence for hindered interchange between conformations was observed for any of the complexes.