Octahedral Iron(V)-nitrido species with neutral ligand platform

Iron complex [FeIII(N3)(MePy2tacn)](PF6)2 (1), containing a neutral triazacyclononane-based pentadentate ligand, and a terminally bound azide ligand has been prepared and spectroscopically and structurally characterized. Structural details, magnetic susceptibility data and Mössbauer spectra demonstrate that 1 has a low-spin state (S = 1/2) ferric center. X-Ray diffraction analysis of 1 reveals remarkably short Fe – N (1.859 Å) and long FeN – N2 (1.246 Å) distances, respectively, and the FT-IR spectra showed an unusually low N – N stretching frequency (2019 cm-1), suggesting that the FeN – N2 bond is particularly weak. Photolysis of 1 at 470 nm or 530 nm in frozen solutions caused N2 elimination and generation of a nitride species that on the basis of Mössbauer, magnetic susceptibility, EPR, and X – ray absorption (XANES) data in conjunction with DFT computational analyses is formulated as [FeV(N)(MePy2tacn)]2+ (2). The results showed that 2 is a low-spin S =1/2 iron(V) species and exhibits a short Fe-N distance (1.64 Å), as deduced from EXAFS analysis. Compound 2 is only stable at cryogenic (liquid N2) temperatures, and frozen solutions as well as solid samples decompose rapidly upon warming, producing N2. The high-valent compound could also be generated in the gas phase and its reactivity against olefins, sulphides and substrates with weak C-H bonds has been studied. It proved to be a powerful two-electron oxidant that can add the nitride ligand to olefin and sulphide sites, and oxidizes cyclohexadiene substrates to benzene, in a formal H2 transfer process. In summary compound 2 constitutes the first case of an octahedral FeV(N) species prepared within a neutral ligand framework, and adds to the few examples of FeV species that could be spectroscopically and chemically characterized. The results were published today in Journal of the American Chemical Society (J. Am. Chem. Soc. 2017, ASAP):
G. Sabenya, L. Lazaro, I. Gamba, V. Martin-Diaconescu, E. Andris, T. Weyhermüller, F. Neese, J. Roithova, E. Bill, J. Lloret-Fillol, and M. Costas
“Generation, spectroscopic and chemical characterization of an octahedral iron (V) – nitrido species with a neutral ligand platform”
J. Am. Chem. Soc. 2017, ASAP [abstract]
DOI: 10.1021/jacs.7b00429