Aerobic C–H Acetoxylation of 8‑Methylquinoline
in Pd<sup>II</sup>–Pyridinecarboxylic Acid Systems: Some Structure–Reactivity
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Abstract
Catalytic
oxidative C–H acetoxylation of 8-methylquinoline
as a model substrate with O<sub>2</sub> 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<sub>2</sub> activation steps shows that the C–H activation step
is rate-limiting, whereas the O<sub>2</sub> 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