Oxo-Free Hydrocarbon Oxidation by an Iron(III)-Isoporphyrin Complex

Abstract

Metal-halides that perform proton coupled electron-transfer (PCET) oxidation are an important new class of high-valent oxidant. In investigating metal-dihalides, we reacted [Fe^III(Cl)(T(OMe)PP)] (<b>1</b>, T(OMe)PP = <i>meso</i>-tetra(4-methoxyphenyl)porphyrinyl) with (dichloroiodo)benzene. An Fe^III-<i>meso</i>-chloro-isoporphyrin complex [Fe^III(Cl)₂(T(OMe)PP-Cl)] (<b>2</b>) was obtained. <b>2</b> was characterized by electronic absorption, ¹H NMR, EPR, and X-ray absorption spectroscopies and mass spectrometry with support from computational analyses. <b>2</b> was reacted with a series of hydrocarbon substrates. The measured kinetic data exhibited a nonlinear behavior, whereby the oxidation followed a hydrogen-atom-transfer (HAT) PCET mechanism. The <i>meso</i>-chlorine atom was identified as the HAT agent. In one case, a halogenated product was identified by mass spectrometry. Our findings demonstrate that oxo-free hydrocarbon oxidation with heme systems is possible and show the potential for iron-dihalides in oxidative hydrocarbon halogenation.