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One-electron oxidation of an oxoiron(IV) complex to form an [0=Fev=NR]+ center.

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Title:	One-electron oxidation of an oxoiron(IV) complex to form an [0=Fe^v=NR]⁺ center.
Authors:	Van Heuvelen, Katherine M.^1,2, Fiedler, Adam T.^1,2,3, Shan, Xiaopeng^1,2, De Hont, Raymond F.⁴, Meier, Katlyn K.⁴, Bominaar, Emile L.⁴ eb7g@andrew.cmu.edu, Münck, Eckard⁴ emunck@cmu.edu, Que Jr., Lawrence^1,2 larryque@umn.edu
Source:	Proceedings of the National Academy of Sciences of the United States of America. 7/24/2012, Vol. 109 Issue 30, p11933-11938. 6p.
Subjects:	Electrons, Oxidation, Iron catalysts, Dioxygenases, Metal complexes, Bioinorganic chemistry
Abstract:	Oxoiron(V) species are postulated to be involved in the mechanisms of the arene cis-dihydroxylating Rieske dioxygenases and of bioinspired nonheme iron catalysts for alkane hydroxylation, olefin cis-dihydroxylation, and water oxidation. In an effort to obtain a synthetic oxoiron(V) complex, we report herein the oneelectron oxidation of the S = 1 complex [FeIv(0)(TMC)(NCCH3)]2+ (1, where TMC is tetramethylcyclam) by treatment with tert -butyl hydroperoxide and strong base in acetonitrile to generate a metastable s = 1/2 complex 2 at -44°C, which has been characterized by UV-visible, resonance Raman, Mössbauer, and EPR methods. The defining spectroscopic characteristic of 2 is the unusual x / y anisotropy observed for the 57Fe and 170 A tensors associated with the high-valent Fe=0 unit and for the 14N A tensor of a ligand derived from acetonitrile. As shown by detailed density functional theory (DFT) calculations, the unusual x / y anisotropy observed can only arise from an iron center with substantially different spin populations in the dxz and dyz orbitals, which cannot correspond to an FeIV=0 unit but is fully consistent with an s = 1/2 Fev center, like that found for [Fev(0)(TAML)]- (where TAML is tetraamido macrocyclic ligand), the only well-characterized oxoiron(V) complex reported. Mass spectral analysis shows that the generation of 2 entails the addition of an oxygen atom to 1 and the loss of one positive charge. Taken together, the spectroscopic data and DFT calculations support the formulation of 2 as an iron(V) complex having axial oxo and acetylimido ligands, namely [Fev(0)(TMC)(NC(0)CH3)]+. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

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Abstract:	Oxoiron(V) species are postulated to be involved in the mechanisms of the arene cis-dihydroxylating Rieske dioxygenases and of bioinspired nonheme iron catalysts for alkane hydroxylation, olefin cis-dihydroxylation, and water oxidation. In an effort to obtain a synthetic oxoiron(V) complex, we report herein the oneelectron oxidation of the S = 1 complex [FeIv(0)(TMC)(NCCH3)]2+ (1, where TMC is tetramethylcyclam) by treatment with tert -butyl hydroperoxide and strong base in acetonitrile to generate a metastable s = 1/2 complex 2 at -44°C, which has been characterized by UV-visible, resonance Raman, Mössbauer, and EPR methods. The defining spectroscopic characteristic of 2 is the unusual x / y anisotropy observed for the 57Fe and 170 A tensors associated with the high-valent Fe=0 unit and for the 14N A tensor of a ligand derived from acetonitrile. As shown by detailed density functional theory (DFT) calculations, the unusual x / y anisotropy observed can only arise from an iron center with substantially different spin populations in the dxz and dyz orbitals, which cannot correspond to an FeIV=0 unit but is fully consistent with an s = 1/2 Fev center, like that found for [Fev(0)(TAML)]- (where TAML is tetraamido macrocyclic ligand), the only well-characterized oxoiron(V) complex reported. Mass spectral analysis shows that the generation of 2 entails the addition of an oxygen atom to 1 and the loss of one positive charge. Taken together, the spectroscopic data and DFT calculations support the formulation of 2 as an iron(V) complex having axial oxo and acetylimido ligands, namely [Fev(0)(TMC)(NC(0)CH3)]+. [ABSTRACT FROM AUTHOR]
ISSN:	00278424
DOI:	10.1073/pnas.1206457109