Synthesis of chiral square planar cobalt(III) complexes and catalytic asymmetric epoxidations with these complexes

Abstract

The chiral square planar cobalt(III) complexes, Na[Co(η⁴-(R)-HMBA-DMP)](2), {H₄(R)-HMBA-DMP =(–)2,4-bis[(R)-2-hydroxy-2-methylbutyramido]-2,4-dimethylpentan-3-one} and complexes with two or four chiral centres, Co{[OC(R)R′C(O)N]₂L}[(3; R = Et, R′= Ph, L = CMe₂COCMe₂); (4; R = Et, R′= Me, L =o-phenylene); (5; R = Et, R′= Me, L = CH(Me)CH₂CHMe); (6; R = Et, R′= Ph, L = CH(Me)CH₂CHMe)] have been prepared and characterized by ¹H NMR spectroscopy, solution magnetic properties, and X-ray crystallography. Asymmetric epoxidations of styrenes with these chiral cobalt(III) complexes and iodosylbenzene have been investigated. Various substituted styrenes were epoxidized with chemical yields of (25–86%) and enantiomeric excesses between 0 and 17%.