Aerobic C–H Acetoxylation of 8‑Methylquinoline in Pd^II–Pyridinecarboxylic Acid Systems: Some Structure–Reactivity Relationships

Catalytic oxidative C–H acetoxylation of 8-methylquinoline as a model substrate with O2 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 O2 activation steps shows that the C–H activation step is rate-limiting, whereas the O2 activation occurs at a much faster rate already at 20 °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.