Catalytic and Stoichiometric Baeyer–Villiger Oxidation Mediated by Nonheme Peroxo-Diiron(III), Acylperoxo, and Iodosylbenzene Iron(III) Intermediates

Abstract

In this paper we describe a detailed mechanistic studies on the [FeII(PBO)2(CF3SO3)2] (1), [FeII(PBT)2(CF3SO3)2] (2), and [FeII(PBI)3](CF3SO3)2 (3)-catalyzed (PBO = 2-(2′-pyridyl)benzoxazole, PBT = 2-(2′-pyridyl)benzthiazole, PBI = 2-(2′-pyridyl)benzimidazole) Baeyer–Villiger oxidation of cycloketones by dioxygen with cooxidation of aldehydes and peroxycarboxylic acids, including the kinetics on the reactivity of (μ-1,2-peroxo)diiron(III), acylperoxo- and iodosylbenzene-iron(III) species as key intermediates.

Stoichiometric Alkane and Aldehyde Hydroxylation Reactions Mediated by In Situ Generated Iron(III)-Iodosylbenzene Adduct

“…As previously reported, [Fe II (PBI) 3 ](CF 3 SO 3 ) 2 ( 1 ) reacts with 1 equivalent of PhIO at 293 K in CH 3 CN to generate a transient green intermediate 2 (λ max = 760 nm; ε = 1400 M −1 cm −1 ; with S = ½ low-spin state) ( Figure 1 a) [ 19 ]. Its decay results in the formation of a new species, different from the starting complex 1 .…”

“…The [Fe II (PBI) 3 ](CF 3 SO 3 ) 2 ( 1 ) (PBI = 2-(2-pyridyl)benzimidazole) complex has been shown to be suitable for the generation of various oxidants depending on the co-oxidant used. Its reaction with H 2 O 2 and PhIO results in the formation of different reactive intermediates, namely, μ -1,2-peroxo-diiron(III) and iron(III)-iodosylbenzene, respectively ( Scheme 1 ) [ 18 , 19 ]. These species can be used as structural models for nonheme mono and diiron enzymes [ 20 , 21 , 22 , 23 , 24 ].…”

“…They are also available for oxidative N -demethylation of DMA via electrophilic C–H activation [ 27 ]. Spectral properties, reactivity and kinetics of Fe III OIPh ( 2 ) bearing PBI ligands towards cycloketones in nucleophilic Baeyer-Villiger reactions were investigated in detail [ 19 ]. The question arises whether Fe III OIPh has ambiphilic properties, and whether it can participate in electrophilic reactions.…”

Influence of Equatorial Co-Ligands on the Reactivity of LFeIIIOIPh

“…Previous studies show that the nature of the equatorial ligands plays a decisive role in the redox potential values of iron-oxo complexes [18]. There are only a few examples in the literature where the role of precursor intermediates, such as Fe III OIPh, can be clearly demonstrated in C-H activation and oxygen atom transfer reactions [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Well-characterized penta-and hepta-coordinated Fe III OIPh intermediates were reported using tetradentate 13-TMC (13-TMC = 1,4,7,10tetramethyl-1,4,7,10-tetraazacyclotridecane) and hexadentate tpena (tpena = N,N,N'tris(2-pyridylmethyl)ethylenediamine-N′-acetate) ligands [32][33][34].…”

“…Based on experimental studies of (13-TMC)Fe III OIPh-mediated styrene epoxidation, a DOT mechanism was proposed, which is consistent with the theoretical calculation resulting in simultaneous cleavage of the I−O bond and O−C bond formation during the epoxide formation [ 18 , 36 ]. Related to this area, we investigated the reactivity of the in situ formed (PBI)Fe III OPh (PBI = 2-(2-pyridyl)benzimidazole) intermediate in oxygen atom transfer reactions towards thioanisole and styrene derivatives [ 45 , 46 , 47 ]. Based on mechanistic studies, we obtained clear evidence that the stoichiometric and catalytic thioanisole sulfoxidation reactions mediated by the Fe III OIPh intermediate proceeds via a DOT mechanism, in contrast to styrene oxygenation, where the epoxidation can be depicted by a nonconcerted ET mechanism [ 47 ].…”