Asymmetric Epoxidation of Alkenes Catalyzed by a Cobalt Complex

Asymmetric epoxidation of alkenes catalyzed by nonhemechiral Mn-Oand Fe-O catalysts has been well established, but chiral Co-Ocatalysts for the purpose remain virtually undeveloped due to theoxo wall. Herein is first reported a chiral cobalt complex to realizethe enantioselective epoxidation of cyclic and acyclic trisubstitutedalkenes by using PhIO as the oxidant in acetone, wherein the tetra-oxygen-basedchiral N,N & PRIME;-dioxide withsterically hindered amide subunits plays a crucial role in supportingthe formation of the Co-O intermediate and enantioselectiveelectrophilic oxygen transfer. Mechanistic studies, including HRMSmeasurements, UV-vis absorption spectroscopy, magnetic susceptibility,as well as DFT calculations, were carried out, confirming the formationof Co-O species as a quartet Co(III)-oxyl tautomer. The mechanismand the origin of enantioselectivity were also elucidated based oncontrol experiments, nonlinear effects, kinetic studies, and DFT calculations.

Automated summary

A chiral cobalt complex was reported as a catalyst for the enantioselective epoxidation of cyclic and acyclic trisubstituted alkenes. The chiral complex played a crucial role in the formation of Co-O intermediate and enantioselective electrophilic oxygen transfer. Mechanistic studies and DFT calculations confirmed the formation of Co-O species as a quartet Co(III)-oxyl tautomer. The origin of enantioselectivity was elucidated through control experiments, nonlinear effects, kinetic studies, and DFT calculations.