Precatalyst separation paradigms: Alkane functionalization in water utilizing in situ formed [Fe₂O(η¹-H₂O)(η¹- OAc)(TPA)₂]³⁺, embedded in surface-derivatized silica, as an MMO model, and fluorous biphasic catalysis for alkane, alkene, and alcohol oxidation chemistry

Two new paradigms for separating the homogeneous catalyst from the substrate and products of oxidation were reviewed. The first example demonstrated the functionalization in water of hydrophobic substrates, i.e., hydrocarbons, with methane monooxygenase biomimetic complexes embedded in a derivatized surface silica system using tert-butyl hydroperoxide/O₂ as the oxidants. For example, cyclohexane was oxidized to a mixture of cyclohexanone, cyclohexanol, and cyclohexyl-tert-butyl peroxide, in a ratio of ∼ 3:1:2. The balance between polyethylene oxide and polypropylene oxide, tethered on the silica surface, was crucial for maximizing the catalytic activity. The mechanism for the silica-based catalytic assembly occurred via the Haber-Weiss process. The second precatalyst separation paradigm, the use of the fluorous solvents, which was predicted on solubilizing the precatalyst in a fluorocarbon solution, allowed the functionalization of alkanes and alkenes, while selective oxidation of alcohols to aldehydes was also possible; both precatalyst and product were in separate solvent phases.