title: Intermediates in the oxygenation of a nonheme diiron(II) complex, including the first evidence for a bound superoxo species.
abstract: The reaction of [Fe(2)(mu-OH)(2)(6-Me(3)-TPA)(2)](2+) (1) [6-Me(3)-TPA, Tris(6-methyl-2-pyridylmethyl)amine] with O(2) in CH(2)Cl(2) at -80 degrees C gives rise to two new intermediates, 2 and 3, before the formation of previously characterized [Fe(2)(O)(O(2))(6-Me(3)-TPA)(2)](2+) (4) that allow the oxygenation reaction to be monitored one electron-transfer step at a time. Raman evidence assigns 2 and 3 as a diiron-superoxo species and a diiron-peroxo species, respectively. Intermediate 2 exhibits its nu(O-O) at 1,310 cm(-1) with a -71-cm(-1) (18)O isotope shift. A doublet peak pattern for the (16)O(18)O isotopomer of 2 in mixed-isotope Raman experiments strongly suggests that the superoxide ligand of 2 is bound end-on. This first example of a nonheme iron-superoxo intermediate exhibits the highest frequency nu(O-O) yet observed for a biomimetic metal-dioxygen adduct. The bound superoxide of 2, unlike the bound peroxide of 4, is readily reduced by 2,4-di-tert-butylphenol via a proton-coupled electron-transfer mechanism, emphasizing that metal-superoxo species may serve as oxidants in oxygen activation mechanisms of metalloenzymes. The discovery of intermediates 2 and 3 allows us to dissect the initial steps of dioxygen binding at a diiron center leading to its activation for substrate oxidation.
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, MN 55455, USA.
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Shan
authors.forename: Lawrence
authors.initials: L
authors.lastname: Que
mesh_terms: D003510:Cyclohexanes / Q000737:chemistry / Q000378:metabolism; D004579:Electron Transport; D005296:Ferrous Compounds / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D018716:Molecular Mimicry; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism*; D010545:Peroxides / Q000737:chemistry / Q000378:metabolism; D013059:Spectrum Analysis, Raman; D013481:Superoxides / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D014732:Vibration
chemical_list: D003510:Cyclohexanes; C430763:Fe(II)(2)(mu-OH)2(6-Me3-TPA)2; D005296:Ferrous Compounds; D010545:Peroxides; D013481:Superoxides; C067220:di-tert-butylperoxy-3,3,5-trimethylcyclohexane peroxide; D010100:Oxygen