Aerobic oxidation of alcohols with bifunctional transition-metal catalysts bearing C-N chelate ligands

The aerobic oxidation of alcohols with a family of bifunctional It, Rh, and Ru complexes bearing C-N chelating ligands derived from primary benzylic amines was investigated. The isolable amido-Ir complexes [Cp*Ir{k(2)-(N,C)-(NHCR2-2-C6H4)}] (R = C6H5, CH3; 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{k(2)-(N,C)-(NH2CR2-2-C6H4)}] and the combined catalyst system involving the chloro(amine)-Ir complex [Cp*IrCl{k(2)-(N,C)-(NH2CR2-2-C6H4)}] and KOC(CH3)(3) were also found to be effective catalysts, whereas the tertiary amine complex [Cp*IrCl{k(2)-(N,C)-(N(CH3)(2)CH2-2-C6H4)}] 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(CH3)(3) resulted in the formation of esters through oxidative dimerization.