Exploring the influence of H-bonding and ligand constraints on thiolate ligated non-heme iron mediated dioxygen activation.

Converting triplet dioxygen into a powerful oxidant is fundamentally important to life. The study reported herein quantitatively examines the formation of a well-characterized, reactive, O-derived thiolate ligated Fe-superoxo using low-temperature stopped-flow kinetics. Comparison of the kinetic barriers to the formation of this species two routes, involving either the addition of (a) O to [Fe(S N(Pr,Pr))] (1) or (b) superoxide to [Fe(S N(Pr,Pr))] (3) is shown to provide insight into the mechanism of O activation.

Kinetic Studies on the Oxoiron(IV) Complex with Tetradentate Aminopyridine Ligand PDP*: Restoration of Catalytic Activity by Reduction with HO.

Oxoiron(IV) is a common catalytic byproduct observed in the oxidation of alkenes by the combination of HO and nonheme iron catalysts including complex , FePDP* (where PDP* = bis(3,5-dimethyl-4-methoxypyridyl-2-methyl)-(,)-2,2'-bipyrrolidine). The oxoiron(IV) species have been proposed to arise by O-O homolysis of the peroxyiron(III) or acylperoxyiron(III) intermediates formed during the presumed Fe-Fe catalytic cycle and have generally been regarded as off-pathway. We generated complex (λ = 730 nm, ε = 350 M cm) directly from and an oxygen atom donor IBX (isopropyl 2-iodoxybenzoate) in acetonitrile in the temperature range from -35 to +25 °C under stopped-flow conditions.

How Metal Ion Lewis Acidity and Steric Properties Influence the Barrier to Dioxygen Binding, Peroxo O-O Bond Cleavage, and Reactivity.

Herein we quantitatively investigate how metal ion Lewis acidity and steric properties influence the kinetics and thermodynamics of dioxygen binding versus release from structurally analogous Mn-O complexes, as well as the barrier to Mn peroxo O-O bond cleavage, and the reactivity of Mn oxo intermediates. Previously we demonstrated that the steric and electronic properties of Mn-OOR complexes containing N-heterocyclic (N) ligand scaffolds can have a dramatic influence on alkylperoxo O-O bond lengths and the barrier to alkylperoxo O-O bond cleavage. Herein, we examine the dioxygen reactivity of a new Mn complex containing a more electron-rich, less sterically demanding N ligand scaffold, and compare it with previously reported Mn complexes.