Selective Oxidation of Hydrocarbons by Molecular Iron Catalysts Based on Molecular Recognition through - Interaction in Aqueous Medium

Oxidation enzymes possess finely organized structures to recognize specific substrates, leading to the efficient catalysis of selective oxidation reactions to generate the desired products. Inspired by such enzymes, molecular catalysts with substrate-recognition sites have been developed for decades. Here, we report the highly selective oxidation of aromatic substrates in aqueous media by catalysis with an Fe-II complex featuring a hydrophobic second coordination sphere (SCS) constructed by four anthracenyl groups. The Fe-II catalyst showed a much higher turnover frequency for the benzene-to-phenol oxidation (1.0 x 10(4) h(-1)) than for the cyclohexane-to-cyclohexanol oxidation (12 h(-1)). The SCS of the Fe-II complex works as a trapping site of aromatic substrates through pi-pi interaction and assists the release of the hydrophilic oxidized products to the aqueous media. A "recognition-and-release" approach also allowed the selective formation of anthracen-9-ol and 1-naphthol by direct oxidation of anthracene and naphthalene, respectively.