Ligand Influence on Structural Properties and Reactivity of Bis(μ‐oxo)dimanganese(III,IV) Species and Comparison of Reactivity with Terminal MnIV‐oxo Complexes

Abstract

AbstractThe ligand influence on structure and reactivity of a pair of bis(μ‐oxo)dimanganese(III,IV) complexes was investigated. The pentadentate N4py and DMMN4py ligands were employed to assemble the [MnIIIMnIV(μ‐O)2(N4py)2]3+ (1) and [MnIIIMnIV(μ‐O)2(DMMN4py)2]3+ (2) species by H2O2 oxidation of the corresponding MnII complexes. The electronic absorption and EPR properties of 1 and 2 are nearly identical. Analysis of the EXAFS region of the Mn K‐edge XAS spectra of 1 and 2 reveals comparable Mn‐ligand and Mn−Mn distances. Molecular structures of 1 and 2 from DFT calculations showed only minor variations in Mn‐ligand bond lengths between these complexes. Despite these structural similarities, a ligand influence was observed on the MnIIIMnIV to MnIIIMnIII reduction potential. Nonetheless, the oxidation of 2,4‐di‐tert‐butylphenol by 1 and 2 proceeded at essentially identical rates. In contrast, reactivity comparison between 2 and the corresponding monomeric MnIV‐oxo species, [MnIV(O)(DMMN4py)]2+, showed that the latter complex is a vastly superior oxidant for O−H bond oxidation, showing a rate enhancement of 105 at parity of substrate and temperature.