Synthesis of a novel cyclodextrin-derived chiral stationary phase with multiple urea linkages and enantioseparation toward chiral osmabenzene complex

A novel chiral stationary phase was synthesized by immobilizing heptakis(6-azido-6-deoxy-2,3-di-O-p-chlorophenylcarbamoylated)-β-cyclodextrin onto silica gel surface via Staudinger reaction, and applied in enantiomeric separation of a pair of osmabenzene complexes, {Os[CHC(PPh3)CHC(PPh3)CH](C9H6NO)2}Cl (1), which is the first report for enantioseparation of the chiral-only-at-metal osmabenzene complex till now. The effects of separation conditions including salt additives, organic modifiers, pH values, and column temperature on the retention and resolution of the complex have been investigated in detail. Meanwhile, possible chiral recognition mechanism was presented. Chiral complex 1 was well resolved via semi-preparative chiral HPLC technique under optimization conditions and two pure enantiomers were further characterized by analytical HPLC, NMR spectra and solution circular dichroism (CD) spectra, respectively. Furthermore, absolute configuration of the enantiomer was confirmed by theoretical investigation of CD spectra.