On the feasibility of N2 fixation via a single-site Fe I/FeIV cycle: Spectroscopic studies of Fe I(N2)FeI, FeIV≡N, and related species

Michael P. Hendrich, William Gunderson, Rachel K. Behan, Michael T. Green, Mark P. Mehn, Theodore A. Betley, Connie C. Lu, Jonas C. Peters

Research output: Contribution to journalArticlepeer-review

147 Scopus citations

Abstract

The electronic properties of an unusually redox-rich iron system, [PhBPR3]Fe-Nx (where [PhBPR 3] is [PhB(CH2PR2)3]-), are explored by Mössbauer, EPR, magnetization, and density-functional methods to gain a detailed picture regarding their oxidation states and electronic structures. The complexes of primary interest in this article are the two terminal iron(IV) nitride species, [PhBPiPr3] Fe≡N (3a) and [PhBPCH2Cy3]Fe≡N (3b), and the formally diiron(I) bridged-Fe(μ-N2)Fe species, {[PhBP iPr3]Fe}2(μ-N2) (4). Complex 4 is chemically related to 3a via a spontaneous nitride coupling reaction. The diamagnetic iron(IV) nitrides 3a and 3b exhibit unique electronic environments that are reflected in their unusual Mössbauer parameters, including quadrupole-splitting values of 6.01(1) mm/s and isomer shift values of -0.34(1) mm/s. The data for 4 suggest that this complex can be described by a weak ferromagnetic interaction (J/D < 1) between two iron(I) centers. For comparison, four other relevant complexes also are characterized: a diamagnetic iron(IV) trihydride [PhBPiPr3]Fe(H)3(PMe 3) (5), an S = 3/2 iron(I) phosphine adduct [PhBPiPr 3]FePMe3 (6), and the S = 2 iron(II) precursors to 3a, [PhBPiPr3]Fe-Cl and [PhBPiPr 3]Fe-2,3:5,6-dibenzo-7-aza bicyclo[2.2.1]hepta-2,5-diene (dbabh). The electronic properties of these respective complexes also have been explored by density-functional methods to help corroborate our spectral assignments and to probe their electronic structures further.

Original languageEnglish (US)
Pages (from-to)17107-17112
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume103
Issue number46
DOIs
StatePublished - Nov 14 2006

Keywords

  • Dinitrogen activation
  • High-valent iron
  • High-valent iron nitride
  • Nitrogenase
  • Spectroscopy

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