Study On Non-redox Metal Ions Promoted Oxidative Dehydrogenation Of Saturated C-C Bond And Aerobic Oxidation Of Alcohols By Pd?OAc?₂ Catalyst

Recently,non-redox metal ions promoted stoichiometric and catalytic oxidations by transation metal ions have attracted much attention.In our previous work,we found that the non-redox metal ions can promote Pd(?)-catalyzed benzene hydroxylation,Wacker-type oxidations,olefin isomerization and oxidative coupling of indole with olefin.The promotion effects were attributed to the formation of heterometallic Pd(?)/Lewis acid complexes which improved C-H bond activation capability of Pd(?)cation.Herein we demonstrate two examples about non-redox metal ions promoted Pd(?)catalytic reaction system.The presence of non-redox metal ions can remarkably improve the catalytic efficiency of simple Pd(OAc)2 catalyst in aerobic dehydrogenation of the saturated C-C bond to obtain indoles from heterocyclic compounds,and phenols from cycloketone.Through UV—vis and NMR characterizations of the catalyst,it was proposed that in-situ generated heteronuclear Pd(?)/Zn(?)dimer is the key active species for dehydrogenation.Except the oxidative dehydrogenation of saturated C-C bond,we also found another palladium-catalyzed reaction system for the oxidation of benzyl alcohol and its derivatives.Adding non-redox metal ions(such as Sc(?)ions)significantly increased the rate of reaction.The reaction is almost non-reactive under anaerobic conditions,indicating that the alcohol is not dehydrogenated to form an aldehyde,but an oxidation reaction occurs.The kinetic study shows that there is a triggering period in the reaction process.We speculate that this time produces nano-paladium which may be the key species of the reaction.Based on the experimental facts,a new design concept of non-redox metal ions promoted oxidation of alcohol by Pd(OAc)2 catalyst was proposed,which provided a new idea for the design of alcohol oxidation catalyst.The reaction mechanism is still under further study.