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Title: Characterization of an Fe≡N–NH 2 intermediate relevant to catalytic N 2 reduction to NH 3

The ability of certain transition metals to mediate the reduction of N 2 to NH 3 has attracted broad interest in the biological and inorganic chemistry communities. Early transition metals such as Mo and W readily bind N 2 and mediate its protonation at one or more N atoms to furnish M(N xH y) species that can be characterized and, in turn, extrude NH 3. By contrast, the direct protonation of Fe–N 2 species to Fe(N xH y) products that can be characterized has been elusive. In this paper, we show that addition of acid at low temperature to [(TPB)Fe(N 2)][Na(12-crown-4)] results in a new S = 1/2 Fe species. EPR, ENDOR, Mössbauer, and EXAFS analysis, coupled with a DFT study, unequivocally assign this new species as [(TPB)Fe≡N–NH 2] +, a doubly protonated hydrazido(2–) complex featuring an Fe-to-N triple bond. This unstable species offers strong evidence that the first steps in Fe-mediated nitrogen reduction by [(TPB)Fe(N 2)][Na(12-crown-4)] can proceed along a distal or “Chatt-type” pathway. Finally, a brief discussion of whether subsequent catalytic steps may involve early or late stage cleavage of the N–N bond, as would be found in limiting distal or alternating mechanisms, respectively, is also provided.
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [3] ;  [4] ;  [2] ;  [1]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  2. Northwestern Univ., Evanston, IL (United States)
  3. Northwestern Univ., Evanston, IL (United States); Illinois College, Jacksonville, IL (United States)
  4. California Inst. of Technology (CalTech), Pasadena, CA (United States); Univ. of Nebraska, Lincoln, NE (United States)
Publication Date:
Grant/Contract Number:
MCB-1118613; DGE-0824162; GM 070757; GM 111097; P41GM103393; P31RR001209
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 137; Journal Issue: 24; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
California Inst. of Technology, Pasadena, CA (United States); Northwestern Univ., Evanston, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Inst. of Health (NIH) (United States); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1347701