CARBOXYLATION OF ALKANES WITH CARBON-MONOXIDE VIA PALLADIUM-CATALYZED C-H BOND ACTIVATION

Palladium(II)-catalyzed carboxylation of alkanes including propane, ethane, and methane with carbon monoxide has been achieved in the presence of potassium peroxodisulfate and trifluoroacetic acid. Regioselectivity by this method is secondary > primary > tertiary due to steric and electronic factors. Stereochemistry is determined thermodynamically. An equimolar amount of copper additive improves the catalyst activity dramatically and thus gives higher yield than Pd and Cu alone except for the reaction of methane. In contrast, acetic acid synthesis from methane is best promoted by the copper catalyst. The reaction with Pd and Pd-Cu catalysts has been proved to be electrophilic C-H activation, whereas radical process is at work in the carboxylation with Cu catalyst. In the former systems, clear isotope effect has been observed. Spectroscopic investigation of the Pd-Cu mixed catalyst suggests that copper forms a 1:1 complex with palladium and enhances the electrophilicity of Pd.