Web Release Date: February 3,
Catalytically Active 
-Oxodiiron(IV) Oxidants from Iron(III) and
Dioxygen
and
Contribution from the Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, Molecular Materials Science Department, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto Sumiyoshi, Osaka 5588585, Japan
Received July 2, 2004
Abstract:
The reaction between an FeIII complex and O2 to afford a stable catalytically active diiron(IV)--oxo compound is described. Phosphonium salts of orange five-coordinated FeIII-TAML complexes with
an axial aqua ligand ([PPh4]1-H2O, tetraamidato macrocyclic FeIII 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 O2 in CH2Cl2 or other weakly coordinating solvents to produce black -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, Mössbauer, and 1H NMR spectroscopies. Mössbauer
data show that the diamagnetic Fe-O-Fe unit contains antiferromagnetically coupled S = 1 FeIV sites;
diamagnetic 1H NMR spectra are observed. The oxidation of PPh3 to OPPh3 by 2 was confirmed by UV/Vis and GC-MS. Labeling experiments with 18O2 and H218O established that the bridging oxygen atom of
2 derives from O2. Complexes 2 catalyze the selective oxidation of benzylic alcohols into the corresponding
aldehydes and bleach rapidly organic dyes, such as Orange II in MeCN-H2O 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 O2 is an abundant, clean, and inexpensive oxidizing
agent.
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