Manganese-containing enzymes are known to react with dioxygen molecule, superoxide, peroxide, etc. and these enzymes play important roles in vivo. Commonly involvement of peroxide intermediates has been reported in the reaction mechanisms proposed for each of these enzymes. mMny researches have been explored to elucidate these intermediates and reaction mechanism. The model complexes of their intermediate of manganese superoxide dismutase (MnSOD), [MnIII(L1)(L1pzH)(O2)] and [MnIII(L5)(thf)(O2)], L1 = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate anion, and hydrotris(3,5-diphenyl-1-pyrazolyl)borate anion), have been synthesized using N3 type ligands, which was introduced by the substituents in the 3 and 5 positions with iPr group (L1) and Ph group (L5) and these structures and some properties were reported. In this study, we synthesized new manganese(III) peroxido complexes ligated by highly hindered hydrotris(pyrazolyl)borates, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate anion (L3) and hydrotris(3-adamantyl-5-isopropyl-1-pyrazolyl)borate anion (L10). In addition, the synthesis and analysis of the manganese(II) complexes were also carried out. Manganese(III) peroxido complexes, [MnIII(L3)(O2)] and [MnIII(L10)(O2)], were synthesized by the reaction of these manganese(II) complexes with hydrogen peroxide or potassium superoxide. X-ray structural analysis revealed that both complexes were pentacoordinate manganese(III) peroxido complexes, which were the first structural characterization for their coordination number. However, the correct distances and bond angles around oxygen atoms could not be obtained due to disordered problem, so that the optimized structure was determined by DFT calculation for [MnIII(L3)(O2)], collaborated with Solomon group. From [MnIII(L3)(O2)], some decomposition products as trinuclear and multinuclear complexes were obtained. On the other hand, from [MnIII(L10)(O2)], the hydroxylated complex as [MnIII(OL10)(OH)] were obtained. This decomposition behavior depends on the humidity in the air, so that it seems that some water molecule involved in the decomposition reaction.

Structures and characterization of manganese(III) peroxido complexes ligated by highly hindered N3 type ligands

ACS Spring Meeting 2021

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