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An Fe-N_2 Complex That Generates Hydrazine and Ammonia via Fe═NNH_2: Demonstrating a Hybrid Distal-to-Alternating Pathway for N_2 Reduction

Rittle, Jonathan and Peters, Jonas C. (2016) An Fe-N_2 Complex That Generates Hydrazine and Ammonia via Fe═NNH_2: Demonstrating a Hybrid Distal-to-Alternating Pathway for N_2 Reduction. Journal of the American Chemical Society, 138 (12). pp. 4243-4248. ISSN 0002-7863. PMCID PMC5065353. http://resolver.caltech.edu/CaltechAUTHORS:20160328-143527690

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Abstract

Biological N_2 fixation to NH_3 may proceed at one or more Fe sites in the active-site cofactors of nitrogenases. Modeling individual e–/H+ transfer steps of iron-ligated N_2 in well-defined synthetic systems is hence of much interest but remains a significant challenge. While iron complexes have been recently discovered that catalyze the formation of NH_3 from N_2, mechanistic details remain uncertain. Herein, we report the synthesis and isolation of a diamagnetic, 5-coordinate Fe═NNH_2+ species supported by a tris(phosphino)silyl ligand via the direct protonation of a terminally bound Fe-N_2– complex. The Fe═NNH_2+ complex is redox-active, and low-temperature spectroscopic data and DFT calculations evidence an accumulation of significant radical character on the hydrazido ligand upon one-electron reduction to S = 1/2 Fe═NNH_2. At warmer temperatures, Fe═NNH_2 rapidly converts to an iron hydrazine complex, Fe-NH_2NH_2+, via the additional transfer of proton and electron equivalents in solution. Fe-NH_2NH_2+ can liberate NH_3, and the sequence of reactions described here hence demonstrates that an iron site can shuttle from a distal intermediate (Fe═NNH_2+) to an alternating intermediate (Fe-NH_2NH_2+) en route to NH_3 liberation from N_2. It is interesting to consider the possibility that similar hybrid distal/alternating crossover mechanisms for N_2 reduction may be operative in biological N_2 fixation.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/jacs.6b01230DOIArticle
http://pubs.acs.org/doi/abs/10.1021/jacs.6b01230PublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/jacs.6b01230PublisherSupporting Information
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5065353PubMed CentralArticle
ORCID:
AuthorORCID
Peters, Jonas C.0000-0002-6610-4414
Alternate Title:An Fe-N2 Complex That Generates Hydrazine and Ammonia via Fe═NNH2: Demonstrating a Hybrid Distal-to-Alternating Pathway for N2 Reduction
Additional Information:© 2016 American Chemical Society. Received: February 2, 2016; Publication Date (Web): March 03, 2016. This work was supported by the NIH (GM 070757) and the Gordon and Betty Moore Foundation. J.R. was additionally supported by a fellowship from the Caltech Center for Environmental Microbial Interactions (CEMI). The authors declare no competing financial interest.
Group:Caltech Center for Environmental Microbial Interactions (CEMI)
Funders:
Funding AgencyGrant Number
NIHGM 070757
Gordon and Betty Moore FoundationUNSPECIFIED
Caltech Center for Environmental Microbial Interactions (CEMI)UNSPECIFIED
PubMed Central ID:PMC5065353
Record Number:CaltechAUTHORS:20160328-143527690
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160328-143527690
Official Citation:An Fe-N2 Complex That Generates Hydrazine and Ammonia via Fe═NNH2: Demonstrating a Hybrid Distal-to-Alternating Pathway for N2 Reduction Jonathan Rittle and Jonas C. Peters Journal of the American Chemical Society 2016 138 (12), 4243-4248 DOI: 10.1021/jacs.6b01230
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65712
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:28 Mar 2016 23:35
Last Modified:20 Oct 2017 22:17

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