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

Török, Patrik; Lakk-Bogáth, Dóra; Kaizer, József

doi:10.3390/molecules28041855

Cited by 4 publications

(5 citation statements)

References 31 publications

(39 reference statements)

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“…In the first case we have obtained direct kinetic and computational evidence for the formation of low-spin oxoiron(IV) via the dissociation process [ 40 ], whereas in the second case the peroxo-diiron(III) intermediate was the key intermediate [ 45 ]. As a continuation of these studies, five heterobidentate-ligand-containing model compounds, including the previously reported and fully characterized [Fe II (L 1−2 ) 3 ] 2+ [ 39 ], [Fe II (L 3 ) 3 ] 2+ [ 46 ] and [Fe II (L 4 ) 3 ] 2+ [ 47 ] (L 1 = 2-(2′-pyridyl)-1 H -benzimidazole, L 2 = 2-(2′-pyridyl)- N -methyl-benzimidazole, L 3 = 2-(4-thiazolyl)-1 H -benzimidazole and L 4 = 2-(4′-methyl-2′-pyridyl)-1 H -benzimidazole) and the novel [Fe II (L 5 ) 3 ] 2+ (L 5 = 2-(1 H -1,2,4-triazol-3-yl)pyridine), were selected to investigate the mechanism and the effect of the redox potential and the spin-state of the catalyst on the reactivity towards H 2 O 2 ( Scheme 2 ).…”

Section: Introductionmentioning

confidence: 93%

Effect of Redox Potential on Diiron-Mediated Disproportionation of Hydrogen Peroxide

2023

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Heme and nonheme dimanganese catalases are widely distributed in living organisms to participate in antioxidant defenses that protect biological systems from oxidative stress. The key step in these processes is the disproportionation of H2O2 to O2 and water, which can be interpreted via two different mechanisms, namely via the formation of high-valent oxoiron(IV) and peroxodimanganese(III) or diiron(III) intermediates. In order to better understand the mechanism of this important process, we have chosen such synthetic model compounds that can be used to map the nature of the catalytically active species and the factors influencing their activities. Our previously reported μ-1,2-peroxo-diiron(III)-containing biomimics are good candidates, as both proposed reactive intermediates (FeIVO and FeIII2(μ-O2)) can be derived from them. Based on this, we have investigated and compared five heterobidentate-ligand-containing model systems including the previously reported and fully characterized [FeII(L1−4)3]2+ (L1 = 2-(2′-pyridyl)-1H-benzimidazole, L2 = 2-(2′-pyridyl)-N-methyl-benzimidazole, L3 = 2-(4-thiazolyl)-1H-benzimidazole and L4 = 2-(4′-methyl-2′-pyridyl)-1H-benzimidazole) and the novel [FeII(L5)3]2+ (L5 = 2-(1H-1,2,4-triazol-3-yl)-pyridine) precursor complexes with their spectroscopically characterized μ-1,2-peroxo-diiron(III) intermediates. Based on the reaction kinetic measurements and previous computational studies, it can be said that the disproportionation reaction of H2O2 can be interpreted through the formation of an electrophilic oxoiron(IV) intermediate that can be derived from the homolysis of the O–O bond of the forming μ-1,2-peroxo-diiron(III) complexes. We also found that the disproportionation rate of the H2O2 shows a linear correlation with the FeIII/FeII redox potential (in the range of 804 mV-1039 mV vs. SCE) of the catalysts controlled by the modification of the ligand environment. Furthermore, it is important to note that the two most active catalysts with L3 and L5 ligands have a high-spin electronic configuration.

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Section: Introductionmentioning

confidence: 93%

Effect of Redox Potential on Diiron-Mediated Disproportionation of Hydrogen Peroxide

2023

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“…The structure and reactivity of the iodosylarene adduct of heme and non-heme Mn(III), Mn(IV) and Fe(III) complexes have been thoroughly investigated. Recent studies have shown that the metal-iodosylbenzene adduct itself can play an important role in transition metal-catalyzed oxidation reactions [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. For some multiple oxidation mechanisms, some of showed better reactivity than the corresponding metal-oxo intermediates.…”

Section: Introductionmentioning

confidence: 99%

“…Its reaction with H2O2 and PhIO results in the formation of µ-1,2-peroxo-diiron(III) and iron(III)-iodosylbenzene complexes, respectively [28][29][30]. The spectral properties, reactivity and kinetics of Fe III (OIPh) bearing PBI ligands towards cycloketones in nucleophilic Baeyer-Villiger reactions [15], and towards benzaldehydes and triphenylmethane in electrophilic C-H oxygenation reactions, were investigated in detail [27]. Significant progress has been made in the last three decades in the understanding and application of nonheme iron complexes in oxidation catalysis.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of Sulfoxidation and Epoxidation Mediated by Iron(III)-Iodosylbenzene Adduct: Electron-Transfer vs. Oxygen-Transfer Mechanism

2023

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The mechanisms of sulfoxidation and epoxidation mediated by previously synthesized and characterized iron(III)-iodosylbenzene adduct, FeIII(OIPh) were investigated using para-substituted thioanisole and styrene derivatives as model substrates. Based on detailed kinetic reaction experiments, including the linear free-energy relationships between the relative reaction rates (logkrel) and the σp (4R-PhSMe) with ρ = −0.65 (catalytic) and ρ = −1.13 (stoichiometric), we obtained strong evidence that the stoichiometric and catalytic oxidation of thioanisoles mediated by FeIII(OIPh) species involves direct oxygen transfer. The small negative slope −2.18 from log kobs versus Eox for 4R-PhSMe gives further clear evidence for the direct oxygen atom transfer mechanism. On the contrary, with the linear free-energy relationships between the relative reaction rates (logkrel) and total substituent effect (TE, 4R-PhCHCH2) parameters with slope = 0.33 (catalytic) and 2.02 (stoichiometric), the stoichiometric and catalytic epoxidation of styrenes takes place through a nonconcerted electron transfer (ET) mechanism, including the formation of the radicaloid benzylic radical intermediate in the rate-determining step. On the basis of mechanistic studies, we came to the conclusion that the title iron(III)-iodosylbenzene complex is able to oxygenate sulfides and alkenes before it is transformed into the oxo-iron form by cleavage of the O−I bond.

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“…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].…”

Section: Introductionmentioning

confidence: 99%

“…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 ].…”

Section: Introductionmentioning

confidence: 99%

Influence of Equatorial Co-Ligands on the Reactivity of LFeIIIOIPh

Lakk-Bogáth,

Pintarics,

Török

et al. 2023

Molecules

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Previous biomimetic studies clearly proved that equatorial ligands significantly influence the redox potential and thus the stability/reactivity of biologically important oxoiron intermediates; however, no such studies were performed on FeIIIOIPh species. In this study, the influence of substituted pyridine co-ligands on the reactivity of iron(III)-iodosylbenzene adduct has been investigated in sulfoxidation and epoxidation reactions. Selective oxidation of thioanisole, cis-cyclooctene, and cis- and trans-stilbene in the presence of a catalytic amount of [FeII(PBI)3](OTf)2 with PhI(OAc)2 provide products in good to excellent yields through an FeIIIOIPh intermediate depending on the co-ligand (4R-Py) used. Several mechanistic studies were performed to gain more insight into the mechanism of oxygen atom transfer (OAT) reactions to support the reactive intermediate and investigate the effect of the equatorial co-ligands. Based on competitive experiments, including a linear free-energy relationship between the relative reaction rates (logkrel) and the σp (4R-Py) parameters, strong evidence has been observed for the electrophilic character of the reactive species. The presence of the [(PBI)2(4R-Py)FeIIIOIPh]3+ intermediates and the effect of the co-ligands was also supported by UV-visible measurements, including the color change from red to green and the hypsochromic shifts in the presence of co-ligands. This is another indication that the title iron(III)-iodosylbenzene adduct is able to oxygenate sulfides and alkenes before it is transformed into the oxoiron form by cleavage of the O−I bond.

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

Cited by 4 publications

References 31 publications

Effect of Redox Potential on Diiron-Mediated Disproportionation of Hydrogen Peroxide

Effect of Redox Potential on Diiron-Mediated Disproportionation of Hydrogen Peroxide

Mechanisms of Sulfoxidation and Epoxidation Mediated by Iron(III)-Iodosylbenzene Adduct: Electron-Transfer vs. Oxygen-Transfer Mechanism

Influence of Equatorial Co-Ligands on the Reactivity of LFeIIIOIPh

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