1365836-53-8Relevant articles and documents
High-valent nonheme iron intermediate. Structure and properties of [Fe2(μ-O)2(5-Me-TPA)2](ClO4)3
Dong,Fujii,Hendrich,Leising,Pan,Randall,Wilkinson,Zang,Que Jr.,Fox,Kauffmann,Muenck
, p. 2778 - 2792 (1995)
In our efforts to model oxidizing species of diiron enzymes, we observed a transient high-valent species in the reaction of a (μ-oxo)diiron(III) TpA complex with H2O2 in CH3CN at -40°C. This intermediate exhibits an S= 3/2 EPR spectrum and a Moessbauer isomer shift of 0.11 mm/s, i.e., the complex has properties very similar to those of synthetic oxoiron(IV) porphyrin radical cation species. Because the initial EPR quantitations gave spin concentrations of 0.3 spin for samples that contained 30% of the iron associated with the S = 3/2 species, we formulated the intermediate as [Fe-(TPA)O]3+; however, this mononuclear formulation has turned out to be incorrect. The use of 5-alkyl-TPA ligands in place of TPA has allowed the isolation of the high-valent species as a solid; the spectroscopic properties of the isolated solid identify it as [Fe2(O)2(5-R-TPA)2](ClO4)3, a bis(μ-oxo)diiron(III,IV) complex. We detail the spectroscopic studies in this paper. Among the models considered, the only one that could possibly explain the observed site equivalence, isomer shift. and other properties consists of a valence-delocalized low-spin (S = 1/2) FeIII-low-spin (S = 1) FeIV pair coupled by Heisenberg as well as double exchange. Whatever its electronic structure, 3b is the only well-characterized high-valent nonheme iron species that is derived from the reaction of H2O2 and a (μ-oxo)diiron(III) complex. As such, it is relevant to the transient species observed in the oxidation chemistry of MMO and RNR R2 and provides a synthetic example of how a high-valent state can be attained in a nonheme environment.
