Chiral non-racemic C60 derivatives: A proposed sector rule for fullerene absolute configuration

A number of higher fullerenes as well as carbon nanotubes have been predicted to be chiral. Our lab has recently reported the resolution and CD spectra of several enantiomeric C60 derivatives. It appears that chromatographic resolutions using Whelk-O columns are rather general. Using optically active enones and dienes, non-racemic C60 adducts can also be formed. Recently we have discovered that fullerene CD spectra appear to arise from a UV band diagnostic for reaction at the CC bond between two six membered rings, the most common site for mono-addition. A Cotton effect is observed in the CD associated with this chromophore and allows proposal of a sector rule for fullerene chirality. Preparation of chiral (non-racemic) fullerene adducts of known absolute configuration allows assignment of the sign to each of the sectors. These CD bands are due to asymmetric perturbation of an intrinsically symmetric chromophore and provide a new tool for a priori determination of absolute configuration.