Synthesis and characterisation of low valent Mn-complexes as models for Mn-catalases

Abstract

In this work we report the synthesis of two novel manganese complexes, [L1₃Mn^II₆](ClO₄)₆ (1·(ClO₄)₆) and [L2Mn^II₂(μ-OAc)(μ-Cl)](ClO₄)₂ (2·(ClO₄)₂), where L1²⁻ is the 2,2′-(1,3-phenylenebis(methylene))bis((2-(bis(pyridin-2-ylmethyl)amino)ethyl)azanediyl)diacetic acid anion and L2 is N1,N1′-(1,3-phenylenebis(methylene))bis(N2,N2′-bis(pyridin-2-ylmethyl)ethane-1,2-diamine). The ligands Na₂L1 and L2 are built on the same backbone, L2 only contains nitrogen donors, while two carboxylate arms have been introduced in Na₂L1. The two complexes have been characterized by single-crystal X-ray diffraction, magnetic susceptibility, EPR spectroscopy, and electrochemistry. X-Ray crystallography revealed that 1 is a manganese(II) hexamer and 2 is a manganese(II) dimer featuring an unprecedented mono-μ-acetato, mono-μ-chlorido bridging motif. The ability of the complexes to catalyse H₂O₂ disproportionation, thereby acting as models for manganese catalases, has been investigated and compared to the activity of two other related manganese complexes. The introduction of carboxylate donors in the ligands, leading to increased denticity, resulted in a drop in H₂O₂ disproportionation activity.