Oxomanganese (IV) complexes are proposed to be reactive intermediates in biological systems such as the oxygen evolving complex of photosystem II. Additionally, oxomanganese (IV) complexes have been observed to be involved in the catalytic cycles of synthetic oxidation complexes. A neutral pentadentate ligand, N4py, has been used to support an oxomanganese (IV) intermediate that activates strong C-H bonds via a hydrogen atom transfer (HAT) mechanism. Derivatives of the N4py ligand with only subtle perturbations to the ligand framework were synthesized and used to support new oxomanganese (IV) species in order to probe the effects of ligand modifications on electronic structure and chemical reactivity. While EPR and XAS properties of these complexes are similar, these ligand modifications cause a shift in near-infrared ligand-field absorption band, with more electron-donating ligands showing a higher energy electronic absorption band. The ligand modifications also affect the rates of both HAT and oxygen-atom transfer reactions of the oxomanganese (IV) centers. A dramatic change in HAT reactivity is seen to be correlated with the shift in the near-infrared absorption band. The basis for this relationship will be discussed within the framework of density functional theory calculations

Exploring the structure-reactivity relationship of a series of N5-ligated oxomanganese (IV) complexes

253rd National Meeting (2017)

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