Center for Functional Nanomaterials Seminar

Under ambient conditions the catalytic oxidation of alkenes by most iron porphyrins using a variety of oxygen sources, but generally not dioxygen, yields the epoxide with only minor quantities of other possible products. The turnover numbers for these catalysts are modest, ranging from a few hundred to a few thousand depending on the degree of halogenation of the porphyrin, the substrate catalysts ratio, axial ligands, and other conditions. Halogenation of the macrocycle increases the reactivity metalloporphyrin catalyst and/or makes it more robust to oxidative degradation.
The oxidation of cyclohexene by 5,10,15,10-tetrakis-(2,3,4,5,6-pentafluorophenyl)porphyrinato iron (III), (FeTPPF20), prepared as the chloride, is typical of the latter: the epoxide accounts for ca. 99% of the product with turnover numbers of ca. 350.1-4 But we report that 10 nm diameter organic nanoparticles (ONP) of Fe(III)TPPF20, formed by host/guest solvent methods, catalytically oxidize cyclohexene to yield only 2-cyclohexene-1-one and 2-cyclohexene-1-ol with ca. 10-fold greater turnover number compared to the epoxide production by the non-aggregated metalloporphyrin in methanol/acetonitrile solution. Moreover, these ONP facilitate a greener reaction because the reaction solvent is 89% water and O2 is efficiently used as oxidant in place of H2O2 or other synthetic oxygen sources. The allylic products suggest a different oxidative mechanism compared to that of the solvated metalloporphyrins. These results further illustrate the unique properties of some ONP relative to the component molecules or those attached to supports, and serve as a functional probe of the role of supramolecular organization and dynamics.