Fluorous Hydrocarbon Oxidation

Numerous examples of easily separable fluorous catalysts and reagents have been reported in the past two decades, with interesting applications in major classes of organic transformations, including hydrocarbon oxidation processes. The initial motivation for the development of fluorous chemistry was for catalyst recycling via liquid-liquid biphase protocols, which are based on the mutual immiscibility of organic solvents and nonpolar, perfluorinated saturated inert fluids, known as perfluorocarbons, at room temperature. Because of the chemical inertness of perfluorocarbons and their ability to solubilize significant volumes of molecular oxygen, fluorous biphasic catalysis was readily recognized as a very attractive procedure for alkane and alkene oxidative functionalization. Recyclable catalytic systems for the epoxidation or allylic oxidation of olefins and for the aerobic oxidation of cycloalkanes and alkylated aromatic hydrocarbons, mostly based on transition metal complexes of robust fluorous nitrogen ligands designed to be selectively soluble in perfluorocarbons, have been developed starting from the late 1990s. Since then, fluorous chemistry has continued to evolve to include separation and recycling strategies that do not necessarily demand the use of perfluorocarbons at the reaction stage. The viability of fluorous protocols as alternatives to the classical liquid-liquid biphase scheme has been demonstrated for selective hydrocarbon oxidation reactions run under environmentally benign conditions. The development of this field of research is outlined here.