Photochemical Generation of a Highly Reactive Iron−Oxo Intermediate. A True Iron(V)−Oxo Species?

Abstract

Laser flash photolysis of 5,10,15-tris(pentafluorophenyl)corrole-iron(IV) chlorate or nitrate, prepared from the corresponding chloride, gave a highly reactive iron-oxo transient identified as an iron(V)-oxo species on the basis of its UV-visible spectrum and high reactivity as well as by analogy to photochemical ligand cleavage reactions of related manganese species. The transient was shown to be an oxo transfer agent in a preparative reaction with cis-cyclooctene. Representative rate constants for oxidation reactions by the new transient at ambient temperature were k = 5900 M-1 s-1 for cyclooctene and k = 570 M-1 s-1 for ethylbenzene. The new transient is more than 6 orders of magnitude more reactive with typical organic reductants than expected for an iron(IV)-oxo corrole radical cation and 100 times more reactive than an analogous positively charged iron(IV)-oxo porphyrin radical cation. Slow electron transfer isomerization of ligand iron(V)-oxo species to iron(IV)-oxo ligand radical cations might be important in reactions of porphyrin-iron catalysts in the laboratory and in nature.