First example of water-soluble transition-metal catalysts for Oppenauer-type oxidation of secondary alcohols

The first water-soluble transition-metal catalysts for Oppenauer-type oxidation of secondary alcohols have been developed. The catalytic system composed of [Ir(COD)Cl]2, 2,2′-biquinoline-4,4′-dicarboxylic acid dipotassium salt (BQC) and sodium carbonate is highly efficient for the selective oxidation of benzylic and aliphatic secondary alcohols to the corresponding ketones with catalyst/substrate ratios ranging from 0.4 to 2.5%. The substitution of [Ir(COD)Cl]2 by its rhodium analog [Rh(COD)Cl]2 generates a less active catalytic system. [Ir(COD)Cl]2/BQC was also found to be more active than its water-insoluble analog system [Ir(COD)Cl]2/2,2′-biquinoline (BC).