Probing the Reactivity of Redox‐Active 2‐Aminophenolates on Iron Complexes of a Carbanionic N3C Donor Ligand

Abstract

AbstractThree iron(II)‐2‐aminophenolate complexes [(L1)FeII(4‐tBu‐HAP)] (2), [(L1)FeII(HAP)] (3), and [(L1)FeII(4‐NO2‐HAP)] (4) [L1 = tris(2‐pyridylthio)methanido anion, 4‐tBu‐HAP = 2‐amino‐4‐tert‐butylphenolate, HAP = 2‐aminophenolate, and 4‐NO2‐HAP = 2‐amino‐4‐nitrophenolate] were isolated and characterized to study their reactivity towards dioxygen. The complexes were synthesized from the iron(II)‐acetonitrile complex [(L1)FeII(CH3CN)2]+ (1) using substituted 2‐aminophenolates. Single crystal structure of 4 reveals that the mononuclear central iron atom is coordinated by a tetradentate N3C ligand and a monoanionic bidentate 4‐NO2‐HAP giving rise to a distorted octahedral coordination arrangement. The six‐coordinate iron(II) complexes, 2 and 4, react with dioxygen to form the corresponding iron(III)‐2‐iminobenzosemiquinonato radical complexes, [(L1)FeIII(4‐tBu‐ISQ)]+ (2Ox) and [(L1)FeIII(4‐NO2‐ISQ)] (4Ox). Complex 3, on the other hand, undergoes an oxidative C–S bond forming reaction between HAP and pyridine‐2‐thiolate (PyS) to afford [(L1)FeIII(ISQ′)]+ (3Ox) [ISQ′ = 5‐(2‐thiopyridyl)‐2‐iminobenzosemiquinonato radical]. In each case, the reaction proceeds via a low‐spin iron(III)‐2‐amidophenolate intermediate species. All the complexes exhibit strong iron–carbon bonding interaction. The bond parameters of the oxidized complexes, obtained from the single crystal structures, clearly establish the presence of ligand‐centered radical.