Inorganic Chemistry, Vol.54, No.4, 1720-1727, 2015
Oxygenative Aromatic Ring Cleavage of 2-Aminophenol with Dioxygen Catalyzed by a Nonheme Iron Complex: Catalytic Functional Model of 2-Aminophenol Dioxygenases
2-Aminophenol dioxygenases catalyze the oxidative ring cleavage of 2-aminophenol to 2-picolinic acid using O-2 as the oxidant. Inspired by the reaction catalyzed by these nonheme iron enzymes, a biomimetic iron(III)-2-amidophenolate complex, [(tBu-L-Me)Fe-III(4,6-di-tBu-AP)](ClO4) (1a ) of a facial tridentate ligand (tBu-L-Me = 1-[bis(6-methyl-pyridin-2-yl)-methyl]-3-tert-butyl-urea and 4,6-di-tBu-H(2)AP = 2-amino-4,6-di-tert-butylphenol) bearing a urea group have been isolated. The complex reacts with O-2 to cleave the C-C bond of 4,6-di-tBu-AP regioselectively and catalytically to afford 4,6-di-tert-butyl-2-picolinic acid. An iron(II)-chloro complex [(tBu-L-Me)(FeCl2)-Cl-II(MeOH)] (1 ) of the same ligand also cleaves the aromatic ring of 4,6-di-tBu-AP catalytically in the reaction with O-2. To assess the effect of urea group on the ring cleavage reaction of 2-aminophenol, two iron complexes, [(BA-L-Me)(2)Fe(2)(II)Cl4] (2 ) and [(BA-L-Me)Fe-III(4,6-di-tBu-AP)](ClO4) (2a ), of a tridentate ligand devoid of urea group (BA-L-Me = benzyl-[bis(6-methyl-pyridin-2-yl)-methyl]-amine) have been isolated and characterized. Although the iron complexes (1 and 1a ) of the ligand with urea group display catalytic reaction, the iron complexes (2 and 2a ) of the ligand without urea group do not exhibit catalytic aromatic ring fission reactivity. The results support the role of urea group in directing the catalytic reactivity exhibited by 1 and 1a .