Theoretical study of the mechanism of oxoiron(IV) formation from H 2O2 and a nonheme iron(II) complex : O-O cleavage involving proton-coupled electron transfer

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Detail(s)

Original languageEnglish
Pages (from-to)6637-6648
Journal / PublicationInorganic Chemistry
Volume50
Issue number14
Publication statusPublished - 18 Jul 2011
Externally publishedYes

Abstract

It has recently been shown that the nonheme oxoiron(IV) species supported by the 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane ligand (TMC) can be generated in near-quantitative yield by reacting [FeII(TMC)(OTf) 2] with a stoichiometric amount of H2O2 in CH3CN in the presence of 2,6-lutidine (Li, F.; England, J.; Que, L., Jr.J. Am. Chem. Soc. 2010, 132, 2134 -2135). This finding has major implications for O-O bond cleavage events in both Fenton chemistry and nonheme iron enzymes. To understand the mechanism of this process, especially the intimate details of the O-O bond cleavage step, a series of density functional theory (DFT) calculations and analyses have been carried out. Two distinct reaction paths (A and B) were identified. Path A consists of two principal steps: (1) coordination of H2O2 to Fe(II) and (2) a combination of partial homolytic O-O bond cleavage and proton-coupled electron transfer (PCET). The latter combination renders the rate-limiting O-O cleavage effectively a heterolytic process. Path B proceeds via a simultaneous homolytic O-O bond cleavage of H2O2 and Fe-O bond formation. This is followed by H abstraction from the resultant Fe(III)-OH species by an •OH radical. Calculations suggest that path B is plausible in the absence of base. However, once 2,6-lutidine is added to the reacting system, the reaction barrier is lowered and more importantly the mechanistic path switches to path A, where 2,6-lutidine plays an essential role as an acid-base catalyst in a manner similar to how the distal histidine or glutamate residue assists in compound I formation in heme peroxidases. The reaction was found to proceed predominantly on the quintet spin state surface, and a transition to the triplet state, the experimentally known ground state for the TMC-oxoiron(IV) species, occurs in the last stage of the oxoiron(IV) formation process. © 2011 American Chemical Society.

Citation Format(s)

Theoretical study of the mechanism of oxoiron(IV) formation from H 2O2 and a nonheme iron(II) complex : O-O cleavage involving proton-coupled electron transfer. / Hirao, Hajime; Li, Feifei; Que, Lawrence; Morokuma, Keiji.

In: Inorganic Chemistry, Vol. 50, No. 14, 18.07.2011, p. 6637-6648.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review