NaCl-Promoted Cobalt-Catalyzed Dioxygen-Mediated Methane Oxidation to Methylene Bis(trifluoroacetate) with a Dramatic Salt Effect

Although O2 is an ideal oxidant in the transformation of methane, very limited studies realize this process in homogeneous solvent systems with high efficiency under mild conditions. Herein, we present a NaCl-promoted cobalt-catalyzed O2-mediated methane oxidation with turnovers over 700 at 120 °C with a dramatic salt effect. The unexpected methylene bis(trifluoroacetate) can be produced with a selectivity up to 90%. This product is used in the reaction with TsNH2 and 1,2-diimine to efficiently form triazinane and imidazole salt, respectively. The Co-NaCl catalytic system is also applied in the oxidation of other hydrocarbons such as adamantane, 9,10-dihydrophenanthrene, 9,10-dihydroanthracene, and 9,10-dihydroacridine. Mechanistic studies indicate that NaCl can promote the decomposition of trifluoroacetic anhydride (TFAA) in the presence of Co(II), and a highly reactive fluorine radical might be formed to react with methane, generating a methyl radical, which will further react with O2 and then with trifluoroacetic anhydride to form methylene bis(trifluoroacetate).