MnIV-Oxo complex of a bis(benzimidazolyl)-containing N5 ligand reveals different reactivity trends for MnIV-oxo than FeIV-oxo species

Abstract

Using the pentadentate ligand (N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine, 2pyN2B), presenting two pyridyl and two (N-methyl)benzimidazolyl donor moieties in addition to a central tertiary amine, new Mn^II and Mn^IV-oxo complexes were generated and characterized. The [Mn^IV(O)(2pyN2B)]²⁺ complex showed spectroscopic signatures (i.e., electronic absorption band maxima and intensities, EPR signals, and Mn K-edge X-ray absorption edge and near-edge data) similar to those observed for other Mn^IV-oxo complexes with neutral, pentadentate N₅ supporting ligands. The near-IR electronic absorption band maximum of [Mn^IV(O)(2pyN2B)]²⁺, as well as DFT-computed metric parameters, are consistent with the equatorial (N-methyl)benzimidazolyl ligands being stronger donors to the Mn^IV center than the pyridyl and quinolinyl ligands found in analogous Mn^IV-oxo complexes. The hydrogen- and oxygen-atom transfer reactivities of [Mn^IV(O)(2pyN2B)]²⁺ were assessed through reactions with hydrocarbons and thioanisole, respectively. When compared with related Mn^IV-oxo adducts, [Mn^IV(O)(2pyN2B)]²⁺ showed muted reactivity in hydrogen-atom transfer reactions with hydrocarbons. This result stands in contrast to observations for the analogous Fe^IV-oxo complexes, where [Fe^IV(O)(2pyN2B)]²⁺ was found to be one of the more reactive members of its class.