Alkylperoxomanganese(III) (MnIII-OOR) intermediates are proposed in the catalytic cycles of several manganese-dependent enzymes. These enzymes include manganese lipoxygenase (MnLOX), and manganese superoxide dismutase (MnSOD) enzymes. These enzymes catalyze the hydroperoxidation of fatty acids, and the decomposition of superoxide radical anions, respectively. The characterization of MnIII-OOR complexes has been difficult due to their inherent thermal instability. Fundamental understanding of the structure and electronic properties that determine the stability of these important intermediates is limited to a series of metastable complexes with thiolate containing ligands, reported by Kovacs and co-workers. However, these complexes were unreactive in the direct oxidation of organic substrates, which contrasts with studies of analogous MnIII-hydroperoxo complexes supported by neutral N4 ligands, which are known to react directly with aldehydes, sulfides, and hydrocarbons possessing weak C-H bonds. However, the reactivities of both MnIII-OOR and MnIII-OOH complexes are likely to be highly dependent on the local coordination environment. To understand how the ligand field affects the properties of MnIII-OOR species, we investigated MnIII-OOR complexes of ligands lacking thiolate ligation using the dpaq ligand (Figure 1, left). Our goal is to expand structure-reactivity correlations for MnIII-OOR adducts and understand the factors that mediate particular decomposition pathways of the MnIII-OOR adducts. This study will contribute knowledge that will help understand the roles of MnIII-OOR intermediates in manganese-dependent enzymes. Using the H6Medpaq ligand, we have developed MnIII-OOR adducts (Figure 1, right) that are both room-temperature stable and reactive towards a range of substrates. The stability of our MnIII-OOR adducts make them amenable for detailed characterization, including by X-ray crystallography and reactivity studies. Decomposition studies to determine the decay mechanism of the MnIII-OOR were also performed, and the results of these studies confirmed decay by homolytic cleavage of the O-O bond.

Structural and spectroscopic characterization of a room-temperature stable Mn(III)-alkylperoxo adduct supported by an amide-containing ligand

ACS Spring Meeting 2021

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