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The activation of O 2 at thiolate–ligated iron( ii ) sites is essential to the function of numerous metalloenzymes and synthetic catalysts. Iron–thiolate bonds in the active sites of nonheme iron enzymes arise from either coordination of an endogenous cysteinate residue or binding of a deprotonated thiol-containing substrate. Examples of the latter include sulfoxide synthases, such as EgtB and OvoA, that utilize O 2 to catalyze tandem S–C bond formation and S -oxygenation steps in thiohistidine biosyntheses. We recently reported the preparation of two mononuclear nonheme iron–thiolate complexes (1 and 2) that serve as structural active-site models of substrate-bound EgtB and OvoA ( Dalton Trans. 2020, 49 , 17745–17757). These models feature monodentate thiolate ligands and tripodal N 4 ligands with mixed pyridyl/imidazolyl donors. Here, we describe the reactivity of 1 and 2 with O 2 at low temperatures to give metastable intermediates (3 and 4, respectively). Characterization with multiple spectroscopic techniques (UV-vis absorption, NMR, variable-field and -temperature Mössbauer, and resonance Raman) revealed that these intermediates are thiolate-ligated iron( iii ) dimers with a bridging oxo ligand derived from the four-electron reduction of O 2 . Structural models of 3 and 4 consistent with the experimental data were generated via density functional theory (DFT) calculations. The combined experimental and computational results illuminate the geometric and electronic origins of the unique spectral features of diiron( iii )-μ-oxo complexes with thiolate ligands, and the spectroscopic signatures of 3 and 4 are compared to those of closely-related diiron( iii )-μ-peroxo species. Collectively, these results will assist in the identification of intermediates that appear on the O 2 reaction landscapes of iron–thiolate species in both biological and synthetic environments.
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Synthetic Motifs for Understanding Lewis Acid Interactions with Persulfides and Thioselenides
Abstract Persulfides (RSS–) and thioselenides (RSSe–) play important roles in biological S and Se transfer reactions, and their interactions with Lewis acidic moieties exert control over reactivity. Here, we report the synthesis and reactivity of mononuclear Zn2+persulfide and thioselenide complexes from a unified synthetic strategy of using isolable dichalcogenide precursors. Highlighting the benefits of replacing S with Se, we use77Se NMR spectroscopy to reveal the effects of Lewis acid coordination (K+, Na+, Zn2+) on the electronic environment of the terminal Se of the thioselenide (R–Sβ–Seα–). Coordination of RSSe–to Zn2+polarizes the Se─S bond, rendering the internal sulfur atom (R–Sβ–Seα–) susceptible to nucleophilic attack and resulting in selenide (Se2–) release. We also prepared a mononuclear Zn2+persulfide complex and probed differences in persulfide nucleophilicity when compared to the parent thiolate. Alkylation of the Zn2+persulfide is considerably faster than the Zn2+thiolate, supporting the proposed nucleophilicity enhancement of persulfides due to the α‐effect, and providing new insights into persulfide reactivity when coordinated to metals. Taken together, these investigations highlight the utility of small molecule synthetic models in advancing insights into the biological chemistry of metal dichaclogenides.
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- Award ID(s):
- 2004150
- PAR ID:
- 10659891
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 65
- Issue:
- 3
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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