Issue 38, 2021

Characterization and chemical reactivity of room-temperature-stable MnIII–alkylperoxo complexes

Abstract

While alkylperoxomanganese(III) (MnIII–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 MnIII–OOR complexes are likely to be highly dependent on their local coordination environment, we have generated two new MnIII–OOR complexes using a new amide-containing N5 ligand. Using the 2-(bis((6-methylpyridin-2-yl)methyl)amino)-N-(quinolin-8-yl)acetamide (H6Medpaq) ligand, we generated the [MnIII(OOtBu)(6Medpaq)]OTf and [MnIII(OOCm)(6Medpaq)]OTf complexes through reaction of their MnII or MnIII precursors with tBuOOH and CmOOH, respectively. Both of the new MnIII–OOR complexes are stable at room-temperature (t1/2 = 5 and 8 days, respectively, at 298 K in CH3CN) and capable of reacting directly with phosphine substrates. The stability of these MnIII–OOR adducts render them amenable for detailed characterization, including by X-ray crystallography for [MnIII(OOCm)(6Medpaq)]OTf. Thermal decomposition studies support a decay pathway of the MnIII–OOR complexes by O–O bond homolysis. In contrast, direct reaction of [MnIII(OOCm)(6Medpaq)]+ with PPh3 provided evidence of heterolytic cleavage of the O–O bond. These studies reveal that both the stability and chemical reactivity of MnIII–OOR complexes can be tuned by the local coordination sphere.

Graphical abstract: Characterization and chemical reactivity of room-temperature-stable MnIII–alkylperoxo complexes

Supplementary files

Article information

Article type
Edge Article
Submitted
08 apr 2021
Accepted
20 avq 2021
First published
20 avq 2021
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2021,12, 12564-12575

Characterization and chemical reactivity of room-temperature-stable MnIII–alkylperoxo complexes

A. A. Opalade, J. D. Parham, V. W. Day and T. A. Jackson, Chem. Sci., 2021, 12, 12564 DOI: 10.1039/D1SC01976G

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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