Non-redox metal ions promoted dehydrogenation of saturated C–C bond by a ruthenium catalyst with dioxygen activation

Abstract

Dioxygen activation as the solely terminal oxidant in organic synthesis and catalytic oxidation is particularly attractive from the point of economic and environmental view. In our previous study, we have displayed that the introducing of non-redox metal ions can sharply improve the olefin epoxidation catalyzed by ruthenium complex with PhI(OAc)2 as the organic oxidation. Inspired by the successful strategy and dioxygen activation, in this study, we demonstrate an alternative protocol that adding non-redox metal ions to cis-Ru(bpy)2Cl2 catalyst can remarkably improve the oxidation from Ru(II) to Ru(IV)=O with dioxygen as the oxidant and promote oxidative dehydrogenation of saturated C–C bond whereas Ru(bpy)2Cl2 alone is very sluggish. Through UV–Vis, NMR, cyclic voltammogram and EPR characterization, it has been testified that oxidation from Ru(II) to Ru(IV)=O can be realized under the condition of 1atm of dioxygen and 323K within 25min while extreme tough condition of 20atm of dioxygen, 343K and 8h is necessary for Ru(bpy)2Cl2 alone. Combined the reaction data with characterization results, an adduct of Ru(IV)=O/Sc(III) is proposed as the key active species to improve the catalytic efficiency. The activity improvement in oxidative dehydrogenation illustrated a novel strategy of that adding non-redox metal ions to sluggish catalysts can remarkably improve its efficiency for dehydrogenation of saturated C–C bond, especially through dioxygen as ultimate oxidant.