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A Synthetic Single-Site Fe Nitrogenase: High Turnover, Freeze-Quench ^(57)Fe Mössbauer Data, and a Hydride Resting State

Del Castillo, Trevor J. and Thompson, Niklas B. and Peters, Jonas C. (2016) A Synthetic Single-Site Fe Nitrogenase: High Turnover, Freeze-Quench ^(57)Fe Mössbauer Data, and a Hydride Resting State. Journal of the American Chemical Society, 138 (16). pp. 5341-5350. ISSN 0002-7863. PMCID PMC5079282. http://resolver.caltech.edu/CaltechAUTHORS:20160420-105550849

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Abstract

The mechanisms of the few known molecular nitrogen-fixing systems, including nitrogenase enzymes, are of much interest but are not fully understood. We recently reported that Fe–N_2 complexes of tetradentate P_3^E ligands (E = B, C) generate catalytic yields of NH_3 under an atmosphere of N_2 with acid and reductant at low temperatures. Here we show that these Fe catalysts are unexpectedly robust and retain activity after multiple reloadings. Nearly an order of magnitude improvement in yield of NH_3 for each Fe catalyst has been realized (up to 64 equiv of NH_3 produced per Fe for P_3^B and up to 47 equiv for P_3^C) by increasing acid/reductant loading with highly purified acid. Cyclic voltammetry shows the apparent onset of catalysis at the P_3^BFe–N_2/P_3^BFe–N_2– couple and controlled-potential electrolysis of P_3^BFe^+ at −45 °C demonstrates that electrolytic N_2 reduction to NH_3 is feasible. Kinetic studies reveal first-order rate dependence on Fe catalyst concentration (P_3^B), consistent with a single-site catalyst model. An isostructural system (P_3^(Si)) is shown to be appreciably more selective for hydrogen evolution. In situ freeze-quench Mössbauer spectroscopy during turnover reveals an iron–borohydrido–hydride complex as a likely resting state of the P_3^BFe catalyst system. We postulate that hydrogen-evolving reaction activity may prevent iron hydride formation from poisoning the P_3^BFe system. This idea may be important to consider in the design of synthetic nitrogenases and may also have broader significance given that intermediate metal hydrides and hydrogen evolution may play a key role in biological nitrogen fixation.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/jacs.6b01706DOIArticle
http://pubs.acs.org/doi/abs/10.1021/jacs.6b01706PublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/jacs.6b01706PublisherSupporting Information
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5079282PubMed CentralArticle
ORCID:
AuthorORCID
Thompson, Niklas B.0000-0003-2745-4945
Peters, Jonas C.0000-0002-6610-4414
Alternate Title:A Synthetic Single-Site Fe Nitrogenase: High Turnover, Freeze-Quench 57Fe Mössbauer Data, and a Hydride Resting State
Additional Information:© 2016 American Chemical Society. Received: February 16, 2016; Publication Date (Web): March 29, 2016. This work was supported by the NIH (GM 070757) and the Gordon and Betty Moore Foundation. T.J.D.C. acknowledges the support of the NSF for a Graduate Fellowship (GRFP), and N.B.T. acknowledges the support of the Resnick Sustainability Institute at Caltech for a Graduate Fellowship. T.J.D.C. and N.B.T. contributed equally to this work. The authors declare no competing financial interest.
Group:Resnick Sustainability Institute
Funders:
Funding AgencyGrant Number
NIHGM 070757
Gordon and Betty Moore FoundationUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Resnick Sustainability InstituteUNSPECIFIED
PubMed Central ID:PMC5079282
Record Number:CaltechAUTHORS:20160420-105550849
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160420-105550849
Official Citation:A Synthetic Single-Site Fe Nitrogenase: High Turnover, Freeze-Quench 57Fe Mössbauer Data, and a Hydride Resting State Trevor J. Del Castillo, Niklas B. Thompson, and Jonas C. Peters Journal of the American Chemical Society 2016 138 (16), 5341-5350 DOI: 10.1021/jacs.6b01706
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66312
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:20 Apr 2016 18:31
Last Modified:27 Nov 2017 21:35

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