Direct enantiomeric resolution of diphosphine and diphosphine oxide ligands by high-performance liquid chromatography

Abstract

High-performance liquid chromatography was employed for the determination of the optical purity of diphosphine and diphosphine oxide ligands of transition metals used in stereoselective reactions. The separation of the enantiomers was accomplished, without any derivatization, on chiral columns containing, as chiral selectors, urea derivatives [Supelcosil LC-( R)-Phenyl Urea and ( R)-Naphthyl Urea] and cellulose carbamate derivative (Chiralcel OG). The use of these three columns is complementary. The mobile phases were optimised to obtain enantiomeric resolution. The α and R s values ranged from 1.12 to 1.83 and from 0.62 to 4.97 on Supelcosil LC-( R)-Phenyl and ( R)-Naphthyl Urea based columns, whereas α and R s values were between 1.11 and 1.38 and 0.24 and 2.00 on a cellulose carbamate based column. Poor α and R s values were obtained with columns containing tetrahydronaphthyl [( R, R)-Whelk-01] and cellulose derivatives (Chiralcel OJ) as chiral selectors. The method is capable of determining a minimum limit of 2.5 ng of each enantiomer of compound 1.