Aerobic C-H Acetoxylation of 8-Methylquinoline in PdII-Pyridinecarboxylic Acid Systems: Some Structure-Reactivity Relationships

Catalytic oxidative C-H acetoxylation of 8-methylquinoline as a model substrate with O-2 as oxidant was performed using palladium(II) carboxylate catalysts derived from four different pyridinecarboxylic acids able to form palladium(II) chelates of different size. A comparison of the rates of the substrate C-H activation and the O-2 activation steps shows that the C-H activation step is rate-limiting, whereas the O-2 activation occurs at a much faster rate already at 20 degrees C. The chelate ring size and the chelate ring strain of the catalytically active species are proposed to be the key factors affecting the rate of the C-H activation.