A Mononuclear Non-heme Iron(III)–Peroxo Complex with an Unprecedented High O–O Stretch and Electrophilic Reactivity

Zhu, Wenjuan; Jang, Semin; Xiong, Jin; Ezhov, Roman; Li, Xiaoxi; Kim, Taeyeon; Seo, Mi Sook; Lee, Yong Min; Pushkar, Yulia; Sarangi, Ritimukta; Guo, Yisong; Nam, Wonwoo

doi:10.1021/jacs.1c03358

Cited by 12 publications

(19 citation statements)

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“…The evident correlation, along with the influence of substrate deuteration on the ratio of productive coupling, is best rationalized through a mechanism involving direct electrophilic attack of C4−H by BesC-P, as shown in Figure 7. A peroxobased HAT mechanism is further supported by (i) the overall sluggish decay of the intermediate; (ii) a 2 H KIE within the semiclassical limit 32,33 (diiron Fe(IV)-oxo intermediates often exhibit significantly larger 2 H KIEs due to significant tunneling contributions 34 ); and (iii) the narrow window of substrate BDEs that can be efficiently metabolized. These characteristics disfavor a mechanism involving the formation of an undetected high-valent species on several grounds.…”

Section: ■ Discussionmentioning

confidence: 85%

BesC Initiates C–C Cleavage through a Substrate-Triggered and Reactive Diferric-Peroxo Intermediate

et al. 2021

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BesC catalyzes the iron- and O2-dependent cleavage of 4-chloro-l-lysine to form 4-chloro-l-allylglycine, formaldehyde, and ammonia. This process is a critical step for a biosynthetic pathway that generates a terminal alkyne amino acid which can be leveraged as a useful bio-orthogonal handle for protein labeling. As a member of an emerging family of diiron enzymes that are typified by their heme oxygenase-like fold and a very similar set of coordinating ligands, recently termed HDOs, BesC performs an unusual type of carbon–carbon cleavage reaction that is a significant departure from reactions catalyzed by canonical dinuclear-iron enzymes. Here, we show that BesC activates O2 in a substrate-gated manner to generate a diferric-peroxo intermediate. Examination of the reactivity of the peroxo intermediate with a series of lysine derivatives demonstrates that BesC initiates this unique reaction trajectory via cleavage of the C4–H bond; this process represents the rate-limiting step in a single turnover reaction. The observed reactivity of BesC represents the first example of a dinuclear-iron enzyme that utilizes a diferric-peroxo intermediate to capably cleave a C–H bond as part of its native function, thus circumventing the formation of a high-valent intermediate more commonly associated with substrate monooxygenations.

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Section: ■ Discussionmentioning

confidence: 85%

BesC Initiates C–C Cleavage through a Substrate-Triggered and Reactive Diferric-Peroxo Intermediate

et al. 2021

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“…Notably, this result is in contrast to the metal peroxo chemistry where nucleophilicity of the metal peroxo moiety is involved in the aldehyde deformylating reaction . Only one example of the rate-determining electrophilic attack of an iron(III) peroxo species to benzaldehydes was reported very recently by Nam and co-workers . It should be noticed that the K eq values of the reaction of 1 with para -X–Ph–CHO also have a good correlation with the electron-donating abilities of benzaldehyde analogues (Figure S8).…”

Section: Resultsmentioning

confidence: 86%

“…9 Only one example of the rate-determining electrophilic attack of an iron(III) peroxo species to benzaldehydes was reported very recently by Nam and co-workers. 15 It should be noticed that the K eq values of the reaction of 1 with para-X−Ph−CHO also have a good correlation with the electron-donating abilities of benzaldehyde analogues (Figure S8). The more electron-donating substituent on the phenyl ring of benzaldehyde analogues resulted in the larger equilibrium constant, which implies that 1 interacts with the electronegative oxygen atom of aldehyde in the pre-equilibrium state.…”

Section: ■ Results and Discussionmentioning

confidence: 89%

Oxidation of Aldehydes into Carboxylic Acids by a Mononuclear Manganese(III) Iodosylbenzene Complex through Electrophilic C–H Bond Activation

2023

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The oxidation of aldehyde is one of the fundamental reactions in the biological system. Various synthetic procedures and catalysts have been developed to convert aldehydes into corresponding carboxylic acids efficiently under ambient conditions. In this work, we report the oxidation of aldehydes by a mononuclear manganese(III) iodosylbenzene complex, [MnIII(TBDAP)(OIPh)(OH)]2+ (1), with kinetic and mechanistic studies in detail. The reaction of 1 with aldehydes resulted in the formation of corresponding carboxylic acids via a pre-equilibrium state. Hammett plot and reaction rates of 1 with 1°-, 2°-, and 3°-aldehydes revealed the electrophilicity of 1 in the aldehyde oxidation. A kinetic isotope effect experiment and reactivity of 1 toward cyclohexanecarboxaldehyde (CCA) analogues indicate that the reaction of 1 with aldehyde occurs through the rate-determining C–H bond activation at the formyl group. The reaction rate of 1 with CCA is correlated to the bond dissociation energy of the formyl group plotting a linear correlation with other aliphatic C–H bonds. Density functional theory calculations found that 1 electrostatically interacts with CCA at the pre-equilibrium state in which the C–H bond activation of the formyl group is performed as the most feasible pathway. Surprisingly, the rate-determining step is characterized as hydride transfer from CCA to 1, affording an (oxo)methylium intermediate. At the fundamental level, it is revealed that the hydride transfer is composed of H atom abstraction followed by a fast electron transfer. Catalytic reactions of aldehydes by 1 are also presented with a broad substrate scope. This novel mechanistic study gives better insights into the metal oxygen chemistry and would be prominently valuable for development of transition metal catalysts.

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“…TM–O 2 complexes often feature amphoteric reactivity, including the electrophilic reactivity as exhibited in the hydrogen atom abstraction reactions − and the nucleophilic reactivity as found in the aldehyde deformylations. ,,− In the past two decades, using aldehydes such as 2-phenylpropionaldehyde (2-PPA), trimethylacetaldehyde (TMA), cyclohexanecarboxaldehyde (CCA), and other electrophiles as probes, the nucleophilic reactivity of a wide range of TM–O 2 complexes has been investigated, where TM = V, , Mn, ,,,, Fe, , Co, , Ni, , and Cu . Notably, using O 2 as an oxidant, catalytic deformylation of 2-PPA has also been reported. ,, As de Visser and co-workers in 2021 have presented an excellent and comprehensive review on this topic, we herein highlight the works relevant to the present study.…”

Section: Introductionmentioning

confidence: 99%

DFT Mechanistic Insights into Aldehyde Deformylations with Biomimetic Metal–Dioxygen Complexes: Distinct Mechanisms and Reaction Rules

Zhao

Zhang

Liu

et al. 2022

JACS Au

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Aldehyde deformylations occurring in organisms are catalyzed by metalloenzymes through metal–dioxygen active cores, attracting great interest to study small-molecule metal–dioxygen complexes for understanding relevant biological processes and developing biomimetic catalysts for aerobic transformations. As the known deformylation mechanisms, including nucleophilic attack, aldehyde α-H-atom abstraction, and aldehyde hydrogen atom abstraction, undergo outer-sphere pathways, we herein report a distinct inner-sphere mechanism based on density functional theory (DFT) mechanistic studies of aldehyde deformylations with a copper (II)–superoxo complex. The inner-sphere mechanism proceeds via a sequence mainly including aldehyde end-on coordination, homolytic aldehyde C–C bond cleavage, and dioxygen O–O bond cleavage, among which the C–C bond cleavage is the rate-determining step with a barrier substantially lower than those of outer-sphere pathways. The aldehyde C–C bond cleavage, enabled through the activation of the dioxygen ligand radical in a second-order nucleophilic substitution (SN2)-like fashion, leads to an alkyl radical and facilitates the subsequent dioxygen O–O bond cleavage. Furthermore, we deduced the rules for the reactions of metal–dioxygen complexes with aldehydes and nitriles via the inner-sphere mechanism. Expectedly, our proposed inner-sphere mechanisms and the reaction rules offer another perspective to understand relevant biological processes involving metal–dioxygen cores and to discover metal–dioxygen catalysts for aerobic transformations.

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A Mononuclear Non-heme Iron(III)–Peroxo Complex with an Unprecedented High O–O Stretch and Electrophilic Reactivity

Cited by 12 publications

References 49 publications

BesC Initiates C–C Cleavage through a Substrate-Triggered and Reactive Diferric-Peroxo Intermediate

BesC Initiates C–C Cleavage through a Substrate-Triggered and Reactive Diferric-Peroxo Intermediate

Oxidation of Aldehydes into Carboxylic Acids by a Mononuclear Manganese(III) Iodosylbenzene Complex through Electrophilic C–H Bond Activation

DFT Mechanistic Insights into Aldehyde Deformylations with Biomimetic Metal–Dioxygen Complexes: Distinct Mechanisms and Reaction Rules

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