Date : 2014. 6. 5, 4:30 PM Place : Int"l conf. room, Bldg.25-1 -Abstract- Redox Non-Innocent ligands have attracted much attention lately, as they appear to play a major role in small molecule activation catalysis: During catalysis ligands participate in redox event by accepting or donating electrons, which affords non-classical electronic structures wherein standard electron counting rules produce misleading clues about the redox state of the metal center. Whereas the existence of this non-classical metal-ligand bonding has now been widely acknowledged, there is only a few examples where the micromechanistic role of these unusual bonding has been precisely identified. I will discuss two examples where redox non-innocence plays a major role in promoting a difficult chemical transformation: (i) Water oxidation by a dinuclear Ru-complex, where the reactive species contains a (IV)Ru-O· moiety, the redox non-innocent resonant form of the classical (V)Ru=O fragment. (ii) Dioxygen activation in gas phase by [Ni(H)(OH)]⁺ complex, where a redox non-innocent ligand helps to protect the reactive state against decomposition.