A variety of manganese-dependent enzymes eschew the formation of high-valent intermediates and instead rely upon mid-valent manganese(III) centers to promote redox reactions with substrates. Examples include manganese superoxide dismutase and manganese lipoxygenase, which respectively defend organisms from the problematic superoxide radical and promote peroxidation of poly unsaturated fatty acids. In these enzymes, MnIII-hydroxo and MnIII-peroxo intermediates feature prominently in proposed catalytic mechanisms. In order to understand the fundamental properties and chemical reactivity of such mid-valent manganese adducts, our lab has generated models of these intermediates that are amenable to detailed structure-function studies. Using an amide-containing pentadentate ligand, we have generated a family of MnIII-hydroxo complexes with systematically perturbed geometric and electronic structures. Combined kinetic and computational investigations of these complexes have allowed us to identify structure-function relationships for concerted proton-electron transfer reactions. Using a newly developed amide-containing pentadentate ligand, we have recently obtained a set of MnIII-alkylperoxo complexes that are stable at room temperature, permitting the determination the X-ray crystal structure for one of these complexes. Despite their stability, these MnIII-alkylperoxo complexes show unprecedented reactivity in substrate oxidation reactions. This reactivity demonstrates that perturbations in the ligand sphere can be employed to modulate the reactivity of MnIII-alkylperoxo adducts.

Mimicking intermediates in Mn-dependent enzymes: Properties and reactivity of MnIII-hydroxo and MnIII-alkylperoxo complexes

ACS Spring Meeting 2021

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