Osmium-catalyzed asymmetric dihydroxylation of olefins in ionic liquidsThe effect of the chiral ligand structure on recyclability

Abstract

Abstract Effective osmium-catalyzed asymmetric dihydroxylation was observed with 1,4-bis(9-O-diquininyl)phthalazine, (DQ)2PHAL, as the chiral ligand in the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6]. It was shown that the ligand undergoes dihydroxylation during the reaction, affording a more polar ligand which remains in the ionic liquid phase, when the latter is extracted with diethyl ether, thus facilitating catalyst recycling. In contrast, when 1,4-bis(9-O-dihydroquininyl)phthalazine, (DHQ)2PHAL, which cannot undergo dihydroxylation, was used as the chiral ligand, the catalyst was extracted into the organic layer.