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Enhanced Ammonia Oxidation Catalysis by a Low-Spin Iron Complex Featuring Cis Coordination Sites

Zott, Michael D. and Peters, Jonas C. (2021) Enhanced Ammonia Oxidation Catalysis by a Low-Spin Iron Complex Featuring Cis Coordination Sites. Journal of the American Chemical Society, 143 (20). pp. 7612-7616. ISSN 0002-7863. PMCID PMC8238494. doi:10.1021/jacs.1c02232.

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The goal of using ammonia as a solar fuel motivates the development of selective ammonia oxidation (AO) catalysts for fuel cell applications. Herein, we describe Fe-mediated AO electrocatalysis with [(bpyPy₂Me)Fe(MeCN)₂]²⁺, exhibiting the highest turnover number (TON) reported to date for a molecular system. To improve on our recent report of a related iron AO electrocatalyst, [(TPA)Fe(MeCN)₂]²⁺ (TON of 16), the present [(bpyPy₂Me)Fe(MeCN)₂]²⁺ system (TON of 149) features a stronger-field, more rigid auxiliary ligand that maintains cis-labile sites and a dominant low-spin population at the Fe(II) state. The latter is posited to mitigate demetalation and hence catalyst degradation by the presence of a large excess of ammonia under the catalytic conditions. Additionally, the [(bpyPy₂Me)Fe(MeCN)₂]²⁺ system exhibits a substantially faster AO rate (ca. 50×) at significantly lower (∼250 mV) applied bias compared to [(TPA)Fe(MeCN)₂]²⁺. Electrochemical data are consistent with an initial E₁ net H-atom abstraction step that furnishes the cis amide/ammine complex [(bpyPy₂Me)Fe(NH₂)(NH₃)]²⁺, followed by the onset of catalysis at E₂. Theoretical calculations suggest the possibility of N–N bond formation via multiple thermodynamically plausible pathways, including both reductive elimination and ammonia nucleophilic attack. In sum, this study underscores that Fe, an earth-abundant metal, is a promising metal for further development in metal-mediated AO catalysis by molecular systems.

Item Type:Article
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URLURL TypeDescription ItemAccession Codes CentralArticle
Zott, Michael D.0000-0003-0535-0512
Peters, Jonas C.0000-0002-6610-4414
Additional Information:© 2021 American Chemical Society. Received: February 28, 2021; Published: May 17, 2021. Accession Codes: CCDC 2065372−2065373 contain the supplementary crystallographic data for this paper. The authors thank the National Institutes of Health (NIH GM070757). M.D.Z. acknowledges the Resnick Sustainability Institute at Caltech and NSF for support via Graduate Fellowships. The Beckman Institute at Caltech supports the X-ray crystallography facility. We also acknowledge Dr. Matthew J. Chalkley and Dr. Pablo Garrido-Barros for insightful discussions. The authors declare no competing financial interest.
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
Resnick Sustainability InstituteUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:Iron, Ligands, Ammonia, Catalysts, Oxidation
Issue or Number:20
PubMed Central ID:PMC8238494
Record Number:CaltechAUTHORS:20210518-100146952
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Official Citation:Enhanced Ammonia Oxidation Catalysis by a Low-Spin Iron Complex Featuring Cis Coordination Sites. Michael D. Zott and Jonas C. Peters. Journal of the American Chemical Society 2021 143 (20), 7612-7616; DOI: 10.1021/jacs.1c02232
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109173
Deposited By: Tony Diaz
Deposited On:19 May 2021 18:31
Last Modified:01 Jun 2022 18:05

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