Bio‐inspired Oxidation of 1‐Aminocarboxylic Acids by a Nonheme Iron(II) Complex: Mimicking the Activity of 1‐Aminocyclopropane‐1‐carboxylic Acid Oxidase

Abstract

Three new ternary iron(II) complexes, [(TpPh2)FeII(ACC)] (1), [(TpPh2)FeII(ACH)] (2), and [(TpPh2)FeII(ADP)] (3) [TpPh2 = hydrotris(3,5‐diphenylpyrazol‐1‐yl)borate, ACC‐H = 1‐aminocyclopropane‐1‐carboxylic acid, ACH‐H = 1‐aminocyclohexane‐1‐carboxylic acid, and ADP‐H = 2‐amino‐2,2‐diphenylacetic acid] were isolated and characterized. X‐ray crystal structures of 1 and 2 reveal that in both the complexes the TpPh2 ligand binds to the central iron atom in a facial mode, and the respective 1‐aminocarboxylate monoanion displays bidentate binding mode through one carboxylate oxygen and one amine nitrogen donor. Complex 1 represents a structural model of the enzyme‐substrate adduct of the enzyme, 1‐aminocyclopropane‐1‐carboxylic acid oxidase (ACCO). The iron(II) complexes react with O2 at ambient temperature to convert the metal coordinated coligands to the corresponding carbonyl compound but in low yields. The yields of the decarboxylated products, however, increase upon increasing the reaction temperature. Isotope labelling experiments and interception studies indicate that the reductive activation of O2 at the central iron atom concomitant with two‐electron oxidative decarboxylation of the coligand following a pathway very similar to that proposed for the iron(II)‐α‐hydroxy acid complexes of the TpPh2 ligand.