Fe-mediated HER vs N_2RR: Exploring Factors that Contribute to Selectivity in P_3^EFe(N_2) (E = B, Si, C) Catalyst Model Systems
- Creators
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Matson, Benjamin D.
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Peters, Jonas C.
Abstract
Mitigation of the hydrogen evolution reaction (HER) is a key challenge in selective small molecule reduction catalysis. This is especially true of catalytic nitrogen (N_2) and carbon dioxide (CO_2) reduction reactions (N_2RR and CO_2RR, respectively) using H^+/e• currency. Here we explore, via DFT calculations, three iron model systems, P_3^EFe (E = B, Si, C), known to mediate both N_2RR and HER, but with different selectivity depending on the identity of the auxiliary ligand. It is suggested that the respective efficiencies of these systems for N_2RR trend with the predicted N–H bonds strengths of two putative hydrazido intermediates of the proposed catalytic cycle, P_3^EFe(NNH_2)^+ and P_3^EFe(NNH_2). Further, a mechanism is presented for undesired HER consistent with DFT studies, and previously reported experimental data, for these systems; bimolecular proton-coupled-electron-transfer (PCET) from intermediates with weak N–H bonds is posited as an important source of H_2, instead of more traditional scenarios that proceed via metal hydride intermediates and proton transfer/electron transfer (PT/ET) pathways. Wiberg bond indices provide additional insight into key factors related to the degree of stabilization of P_3^EFe(NNH_2) species, factors that trend with overall product selectivity.
Additional Information
© 2018 American Chemical Society. Received: September 7, 2017; Revised: January 3, 2018; Published: January 3, 2018. This work was supported by the NIH (GM 070757) and the Gordon and Betty Moore Foundation, and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. B.D.M. acknowledges the support of the NSF for a Graduate Fellowship (GRFP). We thank Matthew Chalkley for insightful input. No competing financial interests have been declared.Attached Files
Accepted Version - nihms-975016.pdf
Supplemental Material - cs7b03068_si_001.pdf
Supplemental Material - cs7b03068_si_002.mol
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Additional details
- Alternative title
- Fe-mediated HER vs N2RR: Exploring Factors that Contribute to Selectivity in P3EFe(N2) (E = B, Si, C) Catalyst Model Systems
- PMCID
- PMC6289286
- Eprint ID
- 84084
- DOI
- 10.1021/acscatal.7b03068
- Resolver ID
- CaltechAUTHORS:20180104-140230786
- NIH
- GM-070757
- Gordon and Betty Moore Foundation
- NSF
- ACI-1053575
- NSF Graduate Research Fellowship
- Created
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2018-01-04Created from EPrint's datestamp field
- Updated
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2022-03-18Created from EPrint's last_modified field