Chiroptical properties of binuclear rhodium complexes of lanostane alcohols

The circular dichroism (CD) of the in situ-formed Rh2(OCOCF3)4 complexes of sterically hindered, secondary lanostane alcohols was investigated. The main object of the present studies are derivatives of 3beta-, 7alpha-, 7beta-, and 11beta-hydroxylanostanes with or without an additional functional group, e.g., double bond, oxo-, hydroxy-, or acetoxy groups. Up to five Cotton effects (CEs) can be found in the CD spectra of Rh-complexes of these alcohols in the spectral range between 650-300 nm. Correlation of the CEs signs with the absolute stereochemistry at the carbon atom bearing the hydroxy group was investigated. The Rh-complex with the 3beta-acetoxylanostan-11beta-ol ligand was isolated in the crystalline form. Its polymeric structure, determined by the X-ray method, shows the di-Rh-units linked by the axially ligating oxygen atoms of the hydroxy and acetoxy groups. In the latter case, the coordination takes place through the carbonyl oxygen.