TEMPO and a co-reductant mediated aerobic epoxidation of olefins using a new magnetically recoverable iron(III) bis(phenol)diamine complex: experimental and computational studies

A magnetically recoverable catalyst of an iron(III) bis(phenol) diamine complex immobilized onto amine functionalized silica-coated magnetic nanoparticles has been synthesized. The catalyst was characterized using FESEM, TEM and XRD which confirmed the nano structure of the catalyst. The physicochemical techniques of ICP, FT-IR, XPS, EDS and TGA proved the loading of the ligand and metal complex on silica-coated magnetic nanoparticles. Using the prepared heterogeneous catalyst, aerobic epoxidation reactions of different alkenes have been investigated in the presence of SO32− as a reducing agent. Moreover, using TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to discover the mechanism of the aerobic epoxidation of olefins, a new TEMPO-assisted route has been explored. Both of the reaction pathways led to a moderate to high percentage yield of epoxides in water at room temperature. For further understanding mechanistic aspects, density functional theory (DFT) computational studies have been performed. The DFT calculations confirm the suggested mechanism for the title reaction and show the electron density in the vicinity of Fe(II) in the presence of TEMPO as a co-catalyst was more than that in the presence of SO32−.