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 π-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 °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. 1H 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.