Reactivity of an Aminopyridine [LMn^II]²⁺ Complex with H₂O₂. Detection of Intermediates at Low Temperature

Abstract

In the present work we report the reactivity of [LMnII]2+ toward addition of hydrogen peroxide (H2O2) in acetonitrile solution, where L is a pentadentate polypyridine ligand. Formation of peroxo complexes is evidenced by low-temperature UV-visible spectroscopy, ESI-mass spectrometry, and EPR spectroscopy using parallel as well as perpendicular mode detection. The influence of the medium (basicity, water content) on the formation of various species is investigated. In basic nonanhydrous medium the fate of the reaction mixture solution is the formation of the di-mu-oxo mixed-valent Mn(III)Mn(IV) dinuclear complex. In acidic medium the building of the oxo bridges is avoided and the reaction mixture evolves toward oxidation of the ligand L. This reaction route offers new opportunities for the study of oxidation reactivity of Mn (hydro)peroxo complexes.

Redox‐State Dependent Ligand Exchange in Manganese‐Based Oxidation Catalysis

“…A key challenge presented by these systems with regard to mechanistic studies lay in the extensive disproportionation of H 2 O 2 that competed with oxidation of substrates. The instability of this ligand class was first raised as an issue by Groni et al [163] in the identification of products arising from oxidation at the benzylic positions of these ligands. Que [164] and, more recently, Britovsek [165] and co-workers have also noted these pathways for iron complexes.…”

Molecular Iron-Based Oxidants and Their Stoichiometric Reactions

“…Alternatively if the amine group is linked to a methylpyridine or a methylbenzyl group, a cleavage reaction can occur with the formation of an amide complex, or it can perhaps further oxidized to a picolinate complex. Formation of stable picolinate complexes of transition metal ions derived from more elaborate ligands have been reported on several occasions [152,153,163,164]. There is no reason to assume that iron complexes will be immune to this particular ligand degradation.…”

Diaquabis(pyridine-2-carboxylato-κ2N,O)zinc dimethylformamide hemisolvate

“…For background to polydentate ligands, see: Udvardy et al (2013); Groni et al (2008); Golenya et al (2011);Ma et al (2009). For related structures, see : Chen & Hu (2011);Li et al (2008); Lumme et al (1969); Takenaka et al (1970); Uggla et al (1969).…”

“…The combination of pyridyl and carboxyl groups in a single bridge-type ligand results in highly interconnected networks and gives limitless possibilities for increased network stability (Udvardy et al, 2013;Groni et al, 2008;Golenya et al 2011). The COO -group and the nitrogen atom in Hpic have strong coordination abilities and multiple coordination modes (Ma et al, 2009).…”

“…Complex molecules are combined into ladder-like tapes via alternation of two similar R 2 2 (8) (Bernstein et al, 1995) graph-set motifs ( (Groni et al, 2008), where the dimethylformamide solvent in the title compound is substituted by the acetonitrile.…”