cis Donor Influence on O–OBond Lability in Iron(III) Hydroperoxo Complexes: Oxidation Catalysis and Ligand Transformation

The FeIII/FeII redox potentials for [Fe(tpen)]2+/3+, [Fe(tpena)]+/2+, and [Fe(tpenO)]+/2+ (N-R-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine, where R = CH2C6H4N, CH2COO–, CH2CH2O–, respectively) span 470 mV with the oxidation potentials following the order [FeII(tpenO)]+ (MeOH) < [FeII(tpena)]+ (MeCN) < [FeII(tpen)]2+ (MeCN). In their +3 oxidation states the complexes react with 1 equiv of H2O2 to give the purple [FeIII(OOH)(HL)]n+ (n = 2 for L = tpena, tpenO; n = 3 for L = tpen). A pyridine arm is decoordinated in these complexes, furnishing a second coordination sphere base which is protonated at ambient pH. The lifetimes of these transient species depend on how readily the substrate (sometimes the solvent) is oxidized and reflect the trend in both the O–O bond lability and oxidizing potency of the putative iron-based oxidant derived from the iron(III) peroxides. In methanol solution, [FeIII(tpenO)]2+ and [FeIII(tpena)]2+ exist in their Fe(III) states and hence the formation of [FeIII(OOH)(Htpena)]2+ ...