Synthesis, Structure, and Catalase-Like Activity of Dimanganese(III) Complexes of 1,5-Bis[(2-hydroxy-5-X-benzyl)(2-pyridylmethyl)amino]pentan-3-ol (X = H, Br, OCH₃)

New diMnIII complexes of general formula [Mn2L(μ-OR)(μ-OAc)]BPh4 (H3L = 1,5-bis[(2-hydroxy-5-X-benzyl)(2-pyridylmethyl)amino]pentan-3-ol, 1: X = H, R = Me, 2: X = OMe, R = Me, 3: X = Br, R = Me, 4: X = Br, R = Et) have been prepared and structurally characterized. The synthesized complexes possess a triply bridged (μ-alkoxo)2(μ-acetato)Mn23+ core, a short intermetallic distance of 2.95/6 Å modulated by the aliphatic spacers between the central alcoholato and N-amino donor sites, and the remaining coordination sites of the two MnIII centers occupied by the six donor atoms of the polydentate ligand. In dimethylformamide, complexes 1−3 are able to disproportionate more than 1500 equiv of H2O2 without significant decomposition, with first-order dependence on catalyst and saturation kinetic on [H2O2]. Spectroscopic monitoring of the reaction mixtures revealed that the catalyst converts into [Mn2III(μ-O)(μ-OAc)L], which is the major active form during cycling. Overall, kinetics and spectroscopic studies of H2O2 dismutation by these complexes converge at a catalytic cycle between MnIII2 and MnII2 oxidation levels. Comparison to other alkoxo-bridged complexes suggests that the binding mode of peroxide to the metal center of the MnIII2 form of the catalyst is a key factor for tuning the Mn oxidation states involved in the H2O2 dismutation mechanism.