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Mechanistic insights into dioxygen activation by a manganese corrole complex: a broken-symmetry DFT study.

ABSTRACT: The Mn-oxygen species have been implicated as key intermediates in various Mn-mediated oxidation reactions. However, artificial oxidants were often used for the synthesis of the Mn-oxygen intermediates. Remarkably, the Mn(v)-oxo and Mn(iv)-peroxo species have been observed in the activation of O₂ by Mn(iii) corroles in the presence of base (OH^-) and hydrogen donors. In this work, density functional theory methods were used to get insight into the mechanism of dioxygen activation and formation of Mn(v)-oxo. The results demonstrated that the dioxygen cannot bind to Mn without the axial OH^- ligand. Upon the addition of the axial OH^- ligand, the dioxygen can bind to Mn in an end-on fashion to give the Mn(iv)-superoxo species. The hydrogen atom transfer from the hydrogen donor (substrate) to the Mn(iv)-superoxo species is the rate-limiting step, having a high reaction barrier and a large endothermicity. Subsequently, the O-C bond formation is concerted with an electron transfer from the substrate radical to the Mn and a proton transfer from the hydroperoxo moiety to the nearby N atom of the corrole ring, generating an alkylperoxo Mn(iii) complex. The alkylperoxo O-O bond cleavage affords a Mn(v)-oxo complex and a hydroxylated substrate. This novel mechanism for the Mn(v)-oxo formation via an alkylperoxo Mn(iii) intermediate gives insight into the O-O bond activation by manganese complexes.

SUBMITTER: Yu J

PROVIDER: S-EPMC9036905 | biostudies-literature | 2021 Jul

REPOSITORIES: biostudies-literature

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Mechanistic insights into dioxygen activation by a manganese corrole complex: a broken-symmetry DFT study.

Yu Jiangfeng J Lai Wenzhen W

RSC advances 20210716 40

The Mn-oxygen species have been implicated as key intermediates in various Mn-mediated oxidation reactions. However, artificial oxidants were often used for the synthesis of the Mn-oxygen intermediates. Remarkably, the Mn(v)-oxo and Mn(iv)-peroxo species have been observed in the activation of O<sub>2</sub> by Mn(iii) corroles in the presence of base (OH<sup>-</sup>) and hydrogen donors. In this work, density functional theory methods were used to get insight into the mechanism of dioxygen activ ...[more]

PMID: 35481047

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Project description:The recently discovered methylerythritol phosphate (MEP) pathway provides new targets for the development of antibacterial and antimalarial drugs. In the final step of the MEP pathway, the [4Fe-4S] IspH protein catalyzes the 2e(-)/2H(+) reductive dehydroxylation of (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) to afford the isoprenoid precursors isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). Recent experiments have attempted to elucidate the IspH catalytic mechanism to drive inhibitor development. Two competing mechanisms have recently emerged, differentiated by their proposed HMBPP binding modes upon 1e(-) reduction of the [4Fe-4S] cluster: (1) a Birch reduction mechanism, in which HMBPP remains bound to the [4Fe-4S] cluster through its terminal C4-OH group (ROH-bound) until the -OH is cleaved as water; and (2) an organometallic mechanism, in which the C4-OH group rotates away from the [4Fe-4S] cluster, allowing the HMBPP olefin group to form a metallacycle complex with the apical iron (η(2)-bound). We perform broken-symmetry density functional theory computations to assess the energies and reduction potentials associated with the ROH- and η(2)-bound states implicated by these competing mechanisms. Reduction potentials obtained for ROH-bound states are more negative (-1.4 to -1.0 V) than what is typically expected of [4Fe-4S] ferredoxin proteins. Instead, we find that η(2)-bound states are lower in energy than ROH-bound states when the [4Fe-4S] cluster is 1e(-) reduced. Furthermore, η(2)-bound states can already be generated in the oxidized state, yielding reduction potentials of ca. -700 mV when electron addition occurs after rotation of the HMBPP C4-OH group. We demonstrate that such η(2)-bound states are kinetically accessible both when the IspH [4Fe-4S] cluster is oxidized and 1e(-) reduced. The energetically preferred pathway gives 1e(-) reduction of the cluster after substrate conformational change, generating the 1e(-) reduced intermediate proposed in the organometallic mechanism.

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Mechanistic insights into dioxygen activation by a manganese corrole complex: a broken-symmetry DFT study.

Publications

Mechanistic insights into dioxygen activation by a manganese corrole complex: a broken-symmetry DFT study.

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