Characterization and chemical reactivity of room-temperature-stable Mn-III-alkylperoxo complexes

While alkylperoxomanganese(iii) (Mn-III-OOR) intermediates are proposed in the catalytic cycles of several manganese-dependent enzymes, their characterization has proven to be a challenge due to their inherent thermal instability. Fundamental understanding of the structural and electronic properties...

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Published inChemical science (Cambridge) Vol. 12; no. 38; pp. 12564 - 12575
Main Authors Opalade, Adedamola A., Parham, Joshua D., Day, Victor W., Jackson, Timothy A.
Format Journal Article
LanguageEnglish
Published CAMBRIDGE Royal Soc Chemistry 06.10.2021
Subjects
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
OXIDATION
THIOLATE
HIGH-SPIN IRON(III)-ALKYLPEROXO
SPECTROSCOPIC CHARACTERIZATION
STRUCTURAL-CHARACTERIZATION
MANGANESE(III)
CUMYLOXYL RADICALS
HIGH-FREQUENCY EPR
BOND
ELECTRONIC-STRUCTURE
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Summary:While alkylperoxomanganese(iii) (Mn-III-OOR) intermediates are proposed in the catalytic cycles of several manganese-dependent enzymes, their characterization has proven to be a challenge due to their inherent thermal instability. Fundamental understanding of the structural and electronic properties of these important intermediates is limited to a series of complexes with thiolate-containing N4S- ligands. These well-characterized complexes are metastable yet unreactive in the direct oxidation of organic substrates. Because the stability and reactivity of Mn-III-OOR complexes are likely to be highly dependent on their local coordination environment, we have generated two new Mn-III-OOR complexes using a new amide-containing N-5(-) ligand. Using the 2-(bis((6-methylpyridin-2-yl)methyl)amino)-N-(quinolin-8-yl)acetamide (H(6Me)dpaq) ligand, we generated the [Mn-III((OOBu)-Bu-t)((6Me)dpaq)]OTf and [Mn-III(OOCm)((6Me)dpaq)]OTf complexes through reaction of their Mn-II or Mn-III precursors with (BuOOH)-Bu-t and CmOOH, respectively. Both of the new Mn-III-OOR complexes are stable at room-temperature (t(1/2) = 5 and 8 days, respectively, at 298 K in CH3CN) and capable of reacting directly with phosphine substrates. The stability of these Mn-III-OOR adducts render them amenable for detailed characterization, including by X-ray crystallography for [Mn-III(OOCm)((6Me)dpaq)]OTf. Thermal decomposition studies support a decay pathway of the Mn-III-OOR complexes by O-O bond homolysis. In contrast, direct reaction of [Mn-III(OOCm)((6Me)dpaq)](+) with PPh3 provided evidence of heterolytic cleavage of the O-O bond. These studies reveal that both the stability and chemical reactivity of Mn-III-OOR complexes can be tuned by the local coordination sphere.
ISSN:2041-6520
2041-6539
DOI:10.1039/d1sc01976g