Mononuclear manganese carboxylate complexes: Synthesis and structural studies

Several manganese carboxylates complexes having Pz^iPr2H (3,5-diisopropylpyrazole), Tp^Ph,Me (hydrotris(3-phenyl,5-methyl-pyrazol-1-yl)borate), Tp^ipr2 (hydrotris(3,5-diisopropyl-pyrazol-1-yl)borate) as supporting ligands have been synthesised and structurally characterized. Single-crystal X-ray diffraction studies suggest that the manganese center in complexes (Pz^iPr2H)₄Mn(NO₂–OBz)₂ (5) and (Pz^iPr2H)₄Mn(F–OBz)₂ (6) have same coordination environment and geometry whereas the complex [Tp^Ph,MeMn(OAc)Pz^Ph,MeH] (7) has a five coordinate manganese center. In all these complexes, the carboxylate groups are coordinated as monodentate and the uncoordinated oxygen atom of the carboxylate groups form intramolecular hydrogen bonds with the NH group of the corresponding coordinated pyrazole (Pz^iPr2H/Pz^Ph,MeH). The complexes 5–8 and 10 were tested for their superoxide dismutase activity and it was found that only complex 7 has SOD activity as its structure is very similar to the active site structure of the native Mn–SOD enzyme. The SOD activity studies on these carboxylate complexes suggest that any model compound with analogous active site structure and intramolecular hydrogen bonding may be a suitable mimic for the Mn–SOD enzyme.