One-electron oxidation of an oxoiron(IV) complex to form an [O═FeV═NR]+ center.
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 one-electron oxidation of the S = 1 complex [Fe(IV)(O)(TMC)(NCCH(3))](2+) (1, where TMC is tetramethylcyclam) by treatment with tert -butyl hydroperoxide and strong base in acetonitrile to generate a metastable 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 (57)Fe and (17)O A tensors associated with the high-valent Fe═O unit and for the (14)N 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 d(xz) and d(yz) orbitals, which cannot correspond to an Fe(IV)═O unit but is fully consistent with an Fe(V) center, like that found for [Fe(V)(O)(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 [Fe(V)(O)(TMC)(NC(O)CH(3))](+).
Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.
Katherine M
KM
Van Heuvelen
Adam T
AT
Fiedler
Xiaopeng
X
Shan
Raymond F
RF
De Hont
Katlyn K
KK
Meier
Emile L
EL
Bominaar
Eckard
E
Münck
Lawrence
L
Que
D016880:Anisotropy; D004583:Electrons; D007503:Iron Isotopes / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry*; D013058:Mass Spectrometry; D015394:Molecular Structure; D009587:Nitrogen Isotopes / Q000737:chemistry; D010084:Oxidation-Reduction; D010103:Oxygen Isotopes / Q000737:chemistry*
D007503:Iron Isotopes; D046911:Macromolecular Substances; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes