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Catalytic N_2-to-NH_3 Conversion by Fe at Lower Driving Force: A Proposed Role for Metallocene-Mediated PCET

Chalkley, Matthew J. and Del Castillo, Trevor J. and Matson, Benjamin D. and Roddy, Joseph P. and Peters, Jonas C. (2017) Catalytic N_2-to-NH_3 Conversion by Fe at Lower Driving Force: A Proposed Role for Metallocene-Mediated PCET. ACS Central Science, 3 (3). pp. 217-223. ISSN 2374-7943. PMCID PMC5364448. http://resolver.caltech.edu/CaltechAUTHORS:20170221-122959469

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Abstract

We have recently reported on several Fe catalysts for N_2-to-NH_3 conversion that operate at low temperature (−78 °C) and atmospheric pressure while relying on a very strong reductant (KC_8) and acid ([H(OEt_2)_2][BArF_4]). Here we show that our original catalyst system, P_3^BFe, achieves both significantly improved efficiency for NH_3 formation (up to 72% for e^– delivery) and a comparatively high turnover number for a synthetic molecular Fe catalyst (84 equiv of NH_3 per Fe site), when employing a significantly weaker combination of reductant (Cp*_2Co) and acid ([Ph_2NH_2][OTf] or [PhNH_3][OTf]). Relative to the previously reported catalysis, freeze-quench Mössbauer spectroscopy under turnover conditions suggests a change in the rate of key elementary steps; formation of a previously characterized off-path borohydrido–hydrido resting state is also suppressed. Theoretical and experimental studies are presented that highlight the possibility of protonated metallocenes as discrete PCET reagents under the present (and related) catalytic conditions, offering a plausible rationale for the increased efficiency at reduced driving force of this Fe catalyst system.


Item Type:Article
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URLURL TypeDescription
http://dx.doi.org/10.1021/acscentsci.7b00014DOIArticle
http://pubs.acs.org/doi/abs/10.1021/acscentsci.7b00014PublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/acscentsci.7b00014PublisherSupporting Information
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5364448/PubMed CentralArticle
ORCID:
AuthorORCID
Peters, Jonas C.0000-0002-6610-4414
Additional Information:© 2017 American Chemical Society. ACS AuthorChoice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: January 9, 2017. Publication Date (Web): February 14, 2017. This work was supported by the NIH (GM 070757) and the Gordon and Betty Moore Foundation. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant No. ACI-1053575. M.J.C., T.J.D.C., and B.D.M. acknowledge the support of the NSF for Graduate Fellowships (GRFP). Author Contributions: M.J.C., T.J.D.C., and B.D.M. contributed equally to this work. The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
NIHGM070757
Gordon and Betty Moore FoundationUNSPECIFIED
NSFACI-1053575
NSF Graduate Research FellowshipUNSPECIFIED
PubMed Central ID:PMC5364448
Record Number:CaltechAUTHORS:20170221-122959469
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170221-122959469
Official Citation:Catalytic N2-to-NH3 Conversion by Fe at Lower Driving Force: A Proposed Role for Metallocene-Mediated PCET Matthew J. Chalkley, Trevor J. Del Castillo, Benjamin D. Matson, Joseph P. Roddy, and Jonas C. Peters ACS Central Science 2017 3 (3), 217-223 DOI: 10.1021/acscentsci.7b00014
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74426
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:21 Feb 2017 21:05
Last Modified:18 Jul 2017 19:32

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