Aerobic Oxidation of Alcohols with Bifunctional Transition‐Metal Catalysts Bearing C–N Chelate Ligands

Abstract

The aerobic oxidation of alcohols with a family of bifunctional Ir, Rh, and Ru complexes bearing C-N chelating ligands derived from primary benzylic amines was investigated. The isolable amido-Ir complexes [Cp*Ir{kappa(2)(N,C)-(NHCR(2)-2-C(6)H(4))}] (R=C(6)H(5), CH(3); Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) effected the oxidation of secondary alcohols smoothly under atmospheric pressure of air at 30 degrees C in THF to give the corresponding ketones in good yields. The hydrido(amine)-Ir complexes [Cp*IrH{kappa(2)(N,C)-(NH(2)CR(2)-2-C(6)H(4))}] and the combined catalyst system involving the chloro(amine)-Ir complex [Cp*IrCl{kappa(2)(N,C)-(NH(2)CR(2)-2-C(6)H(4))}] and KOC(CH(3))(3) were also found to be effective catalysts, whereas the tertiary amine complex [Cp*IrCl{kappa(2)(N,C)-(N(CH(3))(2)CH(2)-2-C(6)H(4))}], which does not have a metal/NH moiety, did not show catalytic activity. The employment of primary alcohols in the aerobic reaction with the Cp*IrCl complex and KOC(CH(3))(3) resulted in the formation of esters through oxidative dimerization.