H2O2-Dependent Fe-Catalyzed Oxidations: Control of the Active Species

Abstract

Manipulation of the coordination sphere of an FeII ion can be used to tune the balance between different catalytic pathways for oxidation (OH. versus iron‐based oxidant; see scheme). This reinvestigation of Fenton chemistry uses the iron complex shown as a mechanistic probe.

Molecular iron complexes as catalysts for selective C–H bond oxygenation reactions

“…57 This structural motif was further employed by Ménage and co-workers who synthesised iron complexes incorporating a tetradentate N-(trimethoxybenzyl)ethane substituted BPMEN ligand (17). 58,59 It became clear that beside the structure of the tetradentate Ndonor ligand the nature of the additional monodentate ligands filling the coordination sphere of the metal cation strongly influences the balance between metal-and radical-based reaction pathways. Thus, with [Fe II (17)(CH3CN)2](ClO4)2 as catalyst cyclohexane is oxidised yielding 25.5% cyclohexanol and cyclohexanone with an A/K ratio of 9.2 (Table 1).…”

Non-heme iron polyazadentate complexes as catalysts for oxidations by H2O2: particular efficiency in aromatic hydroxylations and beneficial effects of a reducing agent

“…More recently, non-heme iron complexes that were developed as mimics of non-heme iron-containing monooxygenases, have also been found to act as good catalysts for the epoxidation or cis-dihydroxylation of alkenes by H 2 O 2 (for recent articles, see for instance [7][8][9][10][11][12]). Cytochromes P450 and some non-heme iron-containing monooxygenases also catalyze the selective and efficient hydroxylation of aromatic compounds [13].…”

Secondary Coordination Sphere Influence on the Reactivity of Nonheme Iron(II) Complexes: An Experimental and DFT Approach

“…4 We turned toward oxygen-atom transfer (OAT) agents in an attempt to generate an Fe IV (O) species directly. Addition of PhIO or the more soluble analog isopropyl 2-iodoxybenzoate (IBX-ester) 4d,5 (1 equiv) to 3 in CH 3 CN resulted in the rapid formation of a green species with an almost identical UV–vis signature (λ max = 763 nm, ε = 2190 M –1 cm –1 ) and LDI-MS spectrum ( m / z 589.892) as that seen for the product obtained from t BuOOH.…”

“…4,8 However, the mechanism of hydroxylation and identity of the active oxidant in these systems remain poorly understood. In the case of 3 , rapid intramolecular phenyl hydroxylation is observed, but there is a complete lack of reactivity between [Fe IV (O)(N4Py)] 2+ and C 6 H 6 .…”