Alkylaminophosphazenes as Efficient and Tuneable Phase-Transfer Agents for Polyoxometalate-Catalysed Biphasic Oxidation with Hydrogen Peroxide

摘要

Alkylaminophosphazenes (RPN) are efficient and tuneable phase-transfer agents for environmentally benign biphasic oxidation with hydrogen peroxide catalysed by polyoxometalates (POMs). Substituent groups on the phosphazene ring can be varied to modify the phase-transfer efficiency of RPN for use in water-organic two-phase systems. Active phosphazene-polyoxometalate aggregates that self-assemble in situ from RPN and Keggin POMs, such as PMo12O403- and PW12O403-, were found to be efficient and recyclable catalysts for the oxidation of benzothiophenes and the epoxidation of alkenes with hydrogen peroxide. Lipophilic phosphazene cations present in these aggregates render the POM soluble in organic media. Catalyst activity in the biphasic oxidation with H2O2 varies with the RPN substituent alkylamino groups with respect to the solvent system used. The activity decreases in the series of POMs: PMo12O403- > PW12O403- SiW12O404- irrespective of the solvent system used.