Significant Solvent Effect on Reactivity of Oxoiron(IV) Porphyrin π-Cation Radical Complex: Activation in n-Alkane Solvent

The solvent effect on the reactivity of high-valent metal oxo complexes has not been studied well, because of their solubility and stability. We synthesize oxoiron(IV) porphyrin p-cation radical complexes (1-CompI and 2-CompI) having the n-hexyl side chains. 1-CompI and 2-CompI are soluble in various solvents, even in hexane, at -80 degrees C, allowing for the study of their reactivity in various organic solvents. We show that pentane, hexane, heptane, and tert-butyl methyl ether significantly increase the reactivity of 1-CompI and 2-CompI, but dichloromethane, the most frequently used solvent in previous studies, is the worst for increasing the reactivity among the solvents. H-1 NMR and EPR spectroscopies show no significant change in hexane, but the Eyring plots for the epoxidation reactions indicate that the entropies of activation in n-alkane solvents are larger than those in dichloromethane. The observed solvent effect can be rationalized with reorganization energy of the solvent in the reaction.