Probing the role of weak outer sphere interactions (H-bonds) in VO(3,5-tBu2-salophen) – Epoxide adducts by EPR, ENDOR and HYSCORE

The role of H-bonds in controlling the binding mode of epoxides, namely propylene oxide (3) and cis-2,3-epoxybutane (4), to the vanadyl salen-type complexes, N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino-vanadium (IV) oxide, [VO(1)], and VO(3,5-tBu2-salophen), [VO(2)], have been examined using cw-EPR, cw-ENDOR and HYSCORE spectroscopy. One of the methine protons from the cyclohexyl backbone in [VO(1)] has previously been shown to form a weak H-bond with the epoxide oxygen atom. The absence of this methine proton in the salophen derivative [VO(2)] removes this H-bonding ability of the complex and in turn weakens the epoxide interaction.