ON/OFF receptor-like enantioseparation of planar chiral 1,2-ferrocenes on an amylose-based chiral stationary phase: The role played by 2-propanol.

A set of nine planar chiral 1,2-ferrocenes was analyzed by high-performance liquid chromatography (HPLC) on the amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase. The enantioseparations were carried out using neat methanol, ethanol, 1-propanol, and 2- propanol as well as mixtures of n-hexane-2-propanol as mobile phases. The differences in retention times between the second eluted (Rp)-enantiomers and the first eluted (Sp)-enantiomers were significantly influenced by elution modes and the steric hindrance of substituents at the aromatic rings of the ferrocene backbone. It has been demonstrated an ON/OFF switching of receptor-like chiral discrimination through the employment of different alcohols as mobile phases. In particular, the presence of pure 2-propanol triggers exceptional conditions of enantioselectivity that for some ferrocenes result in values of the enantioseparation factor higher than 80.