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Catalytic conversion of nitrogen to ammonia by an iron model complex

Anderson, John S. and Rittle, Jonathan and Peters, Jonas C. (2013) Catalytic conversion of nitrogen to ammonia by an iron model complex. Nature, 501 (7465). pp. 84-87. ISSN 0028-0836. http://resolver.caltech.edu/CaltechAUTHORS:20131002-154839797

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Abstract

The reduction of nitrogen (N_2) to ammonia (NH_3) is a requisite transformation for life. Although it is widely appreciated that the iron-rich cofactors of nitrogenase enzymes facilitate this transformation, how they do so remains poorly understood. A central element of debate has been the exact site or sites of N_2 coordination and reduction. In synthetic inorganic chemistry, an early emphasis was placed on molybdenum because it was thought to be an essential element of nitrogenases and because it had been established that well-defined molybdenum model complexes could mediate the stoichiometric conversion of N_2 to NH_3 (ref. 9). This chemical transformation can be performed in a catalytic fashion by two well-defined molecular systems that feature molybdenum centres. However, it is now thought that iron is the only transition metal essential to all nitrogenases, and recent biochemical and spectroscopic data have implicated iron instead of molybdenum as the site of N_2 binding in the FeMo-cofactor. Here we describe a tris(phosphine)borane-supported iron complex that catalyses the reduction of N_2 to NH_3 under mild conditions, and in which more than 40 per cent of the proton and reducing equivalents are delivered to N_2. Our results indicate that a single iron site may be capable of stabilizing the various N_xH_y intermediates generated during catalytic NH_3 formation. Geometric tunability at iron imparted by a flexible iron–boron interaction in our model system seems to be important for efficient catalysis. We propose that the interstitial carbon atom recently assigned in the nitrogenase cofactor may have a similar role, perhaps by enabling a single iron site to mediate the enzymatic catalysis through a flexible iron–carbon interaction.


Item Type:Article
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http://dx.doi.org/10.1038/nature12435 DOIArticle
http://www.nature.com/nature/journal/v501/n7465/full/nature12435.htmlPublisherArticle
Additional Information:© 2013 Macmillan Publishers Limited. Received 08 February 2013; Accepted 04 July 2013; Published online 04 September 2013. This work was supported by the NIH (GM 070757) and the Gordon and Betty Moore Foundation. A. Takaoka is thanked for developing the calibration curves used for ammonia and hydrazine quantification. D. Rees and D. Newman are acknowledged for many discussions. Author Contributions: J.S.A., J.R. and J.C.P. designed the study. J.S.A. and J.R. conducted the experiments. J.S.A., J.R. and J.C.P. interpreted the data. J.S.A., J.R. and J.C.P. wrote the manuscript.
Funders:
Funding AgencyGrant Number
NIHGM 070757
Gordon and Betty Moore FoundationUNSPECIFIED
Subject Keywords:Catalysis; Inorganic chemistry
Record Number:CaltechAUTHORS:20131002-154839797
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20131002-154839797
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41645
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:03 Oct 2013 04:30
Last Modified:03 Oct 2013 04:30

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