PREPARATION AND PROPERTIES OF CHIRAL TITANOCENE AND ZIRCONOCENE DICHLORIDE COMPLEXES OF A CHIRAL LIGAND

The ligand (S,S)-2,3-butylene-1,1'-bis(indene) was prepared from diindenylmagnesium and the dimesylate of (R,R)-2,3-butanediol after conventional synthetic methods had failed. Reaction of the dilithium salt of (S,S)-2,3-butylene-1,1'-bis(indene) with TiCl4.2THF in THF under high-dilution conditions gave [Ti((S,S)-2,3-butylene-1,1'-bis(indenyl))Cl2], which, upon PtO2/H2 reduction, gave [Ti((S,S)-chiracene)Cl2] as a mixture of kinetically formed isomers. These consisted of the R,R, R,S, and S,S diastereomers. Upon irradiation, a photostationary state consisting of 85% of the RR isomer and 15% of the R,S isomer was obtained. The desired pure (R,R)-[Ti((S,S)-chiracene)Cl2] complex was isolated, and its crystal structure was determined by X-ray diffraction. It was found that this complex was configurationally stable under normal conditions, confirming our initial expectations. The circular dichroism spectra of the R,R and R,S isomers have been recorded and discussed, and a connection between the photostationary state and thermodynamic equilibrium of the isomers is suggested. The corresponding zirconium complexes were obtained in low yield. There is a strong kinetic preference for the (R,S)-[Zr((S,S)-chiracene)Cl2] isomer. This isomer was isolated, and its structure was determined by X-ray diffraction. The photostationary state is different from that of the titanium analogue. It consists of a mixture of R,R and S,S diastereomers.