Reactivity of High-Valent Iron–Oxo Species in Enzymes and Synthetic Reagents: A Tale of Many States

Abstract

The Account discusses the phenomenon of two-state reactivity (TSR) or multistate reactivity (MSR) in high-valent metal-oxo reagents, projecting its wide-ranging applicability starting from the bare species, through the reagents made by Que, Nam, and collaborators, to the Mn(V)-oxo substituted polyoxometalate, all the way to Compound I species of heme enzymes. The Account shows how the behaviors of all these variegated species derive from a simple set of electronic structure principles. Experimental trends that demonstrate TSR and MSR are discussed. Diagnostic mechanistic probes are proposed for the TSR/MSR scenario, based on kinetic isotope effect, stereochemical studies, and magnetic- and electric-field effects.

How a Quantum Chemical Topology Analysis Enables Prediction of Electron Density Transfers in Chemical Reactions. The Degenerated Cope Rearrangement of Semibullvalene

“…64,65 In particular, It is well known that density functional based calculations overestimate the values of vibrational frequencies, especially for stretching modes, however no additional scaling factors have been applied to the calculated frequencies. In particular, for TiO 2 and ZrO 2 molecules the calculated harmonic B3LYP/6-311++G(2df,2pd)/SDD frequencies for symmetric stretching 1 v and asymmetric stretching 3 v bands were overestimated in the range of 56-33 cm -1 and 67-42 cm -1 , respectively 68 (see Table 1).…”

A synthetic precedent for the [Fe IV 2 (μ-O) 2 ] diamond core proposed for methane monooxygenase intermediate Q

“…MMO-Q oxidizes methane and is thus a superior oxidant than any of these synthetic low-spin iron(IV) complexes. Its greater reactivity may arise from the fact that it has high-spin iron(IV) centers, which DFT calculations find to be more reactive than their low-spin counterparts in hydrogen-atom abstraction (40)(41)(42). However, our observations suggest in addition that its [Fe IV 2 ( -O) 2 ] core may be further activated in the course of the reaction with methane by isomerization to a more reactive ring-opened form with a terminal Fe V AO unit, such as Fe III OOOFe V AO, as originally proposed in 1997 by Siegbahn and Crabtree (7).…”

The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

“…The reactivity of non-haem oxoiron(IV) complexes in C-H hydroxylation and oxo-transfer reactions has been considered in depth by theoretical [61][62][63] and experimental methods 44,64,65 . So far, all theoretical studies have led to the common conclusion that the ferryl species are better oxidants on the quintet-state than the corresponding triplet-state.…”