Iron Complexes as Bio-inspired Catalysts for Efficient and Selective Oxidation of Organic Compounds

In this chapter, we describe a strategy for efficient and selective catalytic oxidation of organic substrates such as methane and aromatics in aqueous media. In this strategy, pentadentate ligands containing one N-heterocyclic carbene (NHC) moiety were employed as ancillary ligands of triplet FeIV–oxo complexes. The FeIV–oxo species show strong oxidation activity owing to the strong trans-influence of the NHC moiety. Upon introducing bulky aromatic substituents to the NHC ligand, the hydrophobic second coordination sphere (SCS) was successfully formed to surround the FeIV–oxo moiety and achieve highly selective oxidation of organic substrates by trapping the organic substrates in the close vicinity of the FeIV–oxo moiety based on attractive hydrophobic interaction. The hydrophobic SCS can capture hydrophobic gaseous alkane molecules by CH/π interaction (“catch”) and can also release hydrophilic alcoholic products into the aqueous media (“release”). The hydrophobic SCS also traps aromatic substrates over non-aromatic hydrocarbon substrates through π–π interactions (“recognition”) and promotes the release of the hydrophilic oxidized products into the aqueous media (“release”). The “catch and release” and “recognition and release” approaches exemplified in these studies will provide a new venue for oxidation catalysis toward efficient and selective conversion of hydrocarbons, as naturally abundant feedstocks, into value-added chemicals.