title: An FeIV=O complex of a tetradentate tripodal nonheme ligand.
abstract: The reaction of [Fe(II)(tris(2-pyridylmethyl)amine, TPA)(NCCH(3))(2)](2+) with 1 equiv. peracetic acid in CH(3)CN at -40 degrees C results in the nearly quantitative formation of a pale green intermediate with lambda(max) at 724 nm ( epsilon approximately 300 M(-1).cm(-1)) formulated as [Fe(IV)(O)(TPA)](2+) by a combination of spectroscopic techniques. Its electrospray mass spectrum shows a prominent feature at mz 461, corresponding to the [Fe(IV)(O)(TPA)(ClO(4))](+) ion. The Mössbauer spectra recorded in zero field reveal a doublet with DeltaE(Q) = 0.92(2) mms and delta = 0.01(2) mms; analysis of spectra obtained in strong magnetic fields yields parameters characteristic of S = 1 Fe(IV)O complexes. The presence of an Fe(IV)O unit is also indicated in its Fe K-edge x-ray absorption spectrum by an intense 1-s --> 3-d transition and the requirement for an ON scatterer at 1.67 A to fit the extended x-ray absorption fine structure region. The [Fe(IV)(O)(TPA)](2+) intermediate is stable at -40 degrees C for several days but decays quantitatively on warming to [Fe(2)(mu-O)(mu-OAc)(TPA)(2)](3+). Addition of thioanisole or cyclooctene at -40 degrees C results in the formation of thioanisole oxide (100% yield) or cyclooctene oxide (30% yield), respectively; thus [Fe(IV)(O)(TPA)](2+) is an effective oxygen-atom transfer agent. It is proposed that the Fe(IV)O species derives from OO bond heterolysis of an unobserved Fe(II)(TPA)-acyl peroxide complex. The characterization of [Fe(IV)(O)(TPA)](2+) as having a reactive terminal Fe(IV)O unit in a nonheme ligand environment lends credence to the proposed participation of analogous species in the oxygen activation mechanisms of many mononuclear nonheme iron enzymes.
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA.
authors.forename: Mi Hee
authors.initials: MH
authors.lastname: Lim
authors.forename: Jan-Uwe
authors.initials: JU
authors.lastname: Rohde
authors.forename: Audria
authors.initials: A
authors.lastname: Stubna
authors.forename: Michael R
authors.initials: MR
authors.lastname: Bukowski
authors.forename: Miquel
authors.initials: M
authors.lastname: Costas
authors.forename: Raymond Y N
authors.initials: RY
authors.lastname: Ho
authors.forename: Eckard
authors.initials: E
authors.lastname: Munck
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Nam
authors.forename: Lawrence
authors.initials: L
authors.lastname: Que
mesh_terms: D004355:Drug Stability; D005290:Ferric Compounds / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D015204:Spectroscopy, Mossbauer
chemical_list: D005290:Ferric Compounds; D008024:Ligands; D009942:Organometallic Compounds; C473935:oxotris(2-pyridylmethyl)amineiron(IV); D010100:Oxygen