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

Abstract

Metal-halides that perform proton coupled electrontransfer (PCET) oxidation are an important new class of high-valent oxidant. In investigating metal-dihalides, we reacted [Fe III (Cl)(T-(OMe)PP)] (1, T(OMe)PP = meso-tetra(4-methoxyphenyl)porphyrinyl) with (dichloroiodo)benzene. An Fe III -meso-chloro-isoporphyrin complex [Fe III (Cl) 2 (T(OMe)PP-Cl)] (2) was obtained. 2 was characterized by electronic absorption, 1 H NMR, EPR, and X-ray absorption spectroscopies and mass spectrometry with support from computational analyses. 2 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 meso-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.

Rapid Iron(III)−Fluoride‐Mediated Hydrogen Atom Transfer

“…For an ideal HAT or CPET, a slope of 0.5 would be expected and for a non‐concerted PCET mechanism a slope close to one is expected [31b, 32] . Although the measured slope here is slightly less than the expected 0.5, there have been several reports of similar deviations for a HAT mechanism, and the value is comparable for those obtained for other high‐valent metal–halides [5a,c, 11, 31b, 33] …”

Rapid Iron(III)−Fluoride‐Mediated Hydrogen Atom Transfer

“…[ 31b , 32 ] Although the measured slope here is slightly less than the expected 0.5, there have been several reports of similar deviations for a HAT mechanism, and the value is comparable for those obtained for other high‐valent metal–halides. [ 5a , 5c , 11 , 31b , 33 ]…”

Comparing Metal–Halide and −Oxygen Adducts in Oxidative C/O–H Activation: AuIII–Cl versus AuIII–OH

“…The oxidative functionalization of inert saturated hydrocarbons remains a challenge. , High-valent metal oxidants are ideal candidates for C–H bond activation via a hydrogen atom transfer (HAT) mechanism. High-valent metal–halides have attracted attention as acting as potent oxidants. − We showed that a Ni III –Cl entity performs HAT and postulated that the thermodynamic driving force for HAT was the bond dissociation free energy (BDFE) of the free HCl product . Subsequently, a Ni III –F complex showed 4300-fold enhanced rate constants in the oxidation of xanthene and CHD compared to those of Ni III –Cl, the enhanced reactivity attributed to a stronger H–F bond .…”