title: Enantioselective binding of structural epoxide isomers by a chiral vanadyl salen complex: a pulsed EPR, cw-ENDOR and DFT investigation.
abstract: The mode of chiral interaction between a series of asymmetric epoxides (propylene oxide, butylene oxide, epifluorohydrin and epichlorohydrin) and a chiral vanadyl salen complex, N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino-vanadium (iv) oxide, [VO()], was investigated by a range of electron magnetic resonance techniques (EPR, ENDOR, HYSCORE) and DFT. Enantiomer discrimination of the weakly bound epoxides by the vanadyl complex was evident by cw-ENDOR. The origin of this discrimination was attributed to a number of factors including H-bonds, steric properties and electrostatic contributions, which collectively control the outcome of the chiral interaction. DFT revealed the role of a key H-bond, formed between the epoxide oxygen atom (O(epoxide)) and the methine proton (H(exo)) attached to the asymmetric carbon atom of the chiral vanadyl salen complex, thereby providing a direct pathway for stereochemical communication between complex and substrate. These findings reveal the potential importance of weak outer sphere interactions in stereoselectivities of enantioselective homogeneous catalysis.
authors.affiliation: Cardiff University, Cardiff, UKCF10 3AT. MurphyDM@cf.ac.uk Fallis@cf.ac.uk
authors.forename: Damien M
authors.initials: DM
authors.lastname: Murphy
authors.forename: Ian A
authors.initials: IA
authors.lastname: Fallis
authors.forename: Emma
authors.initials: E
authors.lastname: Carter
authors.forename: David J
authors.initials: DJ
authors.lastname: Willock
authors.forename: James
authors.initials: J
authors.lastname: Landon
authors.forename: Sabine
authors.initials: S
authors.lastname: Van Doorslaer
authors.forename: Evi
authors.initials: E
authors.lastname: Vinck