title: Catalytically active mu-Oxodiiron(IV) oxidants from Iron(III) and dioxygen.
abstract: The reaction between an Fe(III) complex and O(2) to afford a stable catalytically active diiron(IV)-mu-oxo compound is described. Phosphonium salts of orange five-coordinated Fe(III)-TAML complexes with an axial aqua ligand ([PPh(4)]1-H(2)O, tetraamidato macrocyclic Fe(III) species derived from 3,3,6,6,9,9-hexamethyl-3,4,8,9-tetrahydro-1H-1,4,8,11-benzotetraazacyclotridecine-2,5,7,10(6H,11H)-tetraone) react rapidly with O(2) in CH(2)Cl(2) or other weakly coordinating solvents to produce black mu-oxo-bridged diiron(IV) complexes, 2, in high yields. Complexes 2 have been characterized by X-ray crystallography (2 cases), microanalytical data, mass spectrometry, UV/Vis, Mossbauer, and (1)H NMR spectroscopies. Mossbauer data show that the diamagnetic Fe-O-Fe unit contains antiferromagnetically coupled S = 1 Fe(IV) sites; diamagnetic (1)H NMR spectra are observed. The oxidation of PPh(3) to OPPh(3) by 2 was confirmed by UV/Vis and GC-MS. Labeling experiments with (18)O(2) and H(2)(18)O established that the bridging oxygen atom of 2 derives from O(2). Complexes 2 catalyze the selective oxidation of benzylic alcohols into the corresponding aldehydes and bleach rapidly organic dyes, such as Orange II in MeCN-H(2)O mixtures; reactivity evidence suggests that free radical autoxidation is not involved. This work highlights a promising development for the advancement of green oxidation technology, as O(2) is an abundant, clean, and inexpensive oxidizing agent.
authors.affiliation: Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Anindya
authors.initials: A
authors.lastname: Ghosh
authors.forename: Filipe
authors.initials: F
authors.lastname: Tiago de Oliveira
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Yano
authors.forename: Takanori
authors.initials: T
authors.lastname: Nishioka
authors.forename: Evan S
authors.initials: ES
authors.lastname: Beach
authors.forename: Isamu
authors.initials: I
authors.lastname: Kinoshita
authors.forename: Eckard
authors.initials: E
authors.lastname: Münck
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Ryabov
authors.forename: Colin P
authors.initials: CP
authors.lastname: Horwitz
authors.forename: Terrence J
authors.initials: TJ
authors.lastname: Collins