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Tripodal P₃^XFe–N₂ Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N₂-to-NH₃ Conversion

Fajardo, Javier, Jr. and Peters, Jonas C. (2021) Tripodal P₃^XFe–N₂ Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N₂-to-NH₃ Conversion. Inorganic Chemistry, 60 (2). pp. 1220-1227. ISSN 0020-1669. https://resolver.caltech.edu/CaltechAUTHORS:20210112-091401610

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Abstract

Terminal dinitrogen complexes of iron ligated by tripodal, tetradentate P₃^X ligands (X = B, C, Si) have previously been shown to mediate catalytic N₂-to-NH₃ conversion (N₂RR) with external proton and electron sources. From this set of compounds, the tris(phosphino)borane (P₃^B) system is most active under all conditions canvassed thus far. To further probe the effects of the apical Lewis acidic atom on structure, bonding, and N₂RR activity, Fe–N₂ complexes supported by analogous group 13 tris(phosphino)alane (P₃^(Al)) and tris(phosphino)gallane (P₃^(Ga)) ligands are synthesized. The series of P₃^XFe–N₂^([0/1−]) compounds (X = B, Al, Ga) possess similar electronic structures, degrees of N₂ activation, and geometric flexibility as determined from spectroscopic, structural, electrochemical, and computational (DFT) studies. However, treatment of [Na(12-crown-4)₂][P₃^XFe–N₂] (X = Al, Ga) with excess acid/reductant in the form of HBAr^F₄/KC₈ generates only 2.5 ± 0.1 and 2.7 ± 0.2 equiv of NH₃ per Fe, respectively. Similarly, the use of [H₂NPh₂][OTf]/Cp^*₂Co leads to the production of 4.1 ± 0.9 (X = Al) and 3.6 ± 0.3 (X = Ga) equiv of NH₃. Preliminary reactivity studies confirming P₃^XFe framework stability under pseudocatalytic conditions suggest that a greater selectivity for hydrogen evolution versus N₂RR may be responsible for the attenuated yields of NH₃ observed for P₃^(Al)Fe and P₃^(Ga)Fe relative to P₃^BFe.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/acs.inorgchem.0c03354DOIArticle
ORCID:
AuthorORCID
Fajardo, Javier, Jr.0000-0003-0612-7953
Peters, Jonas C.0000-0002-6610-4414
Alternate Title:Tripodal P3XFe–N2 Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N2-to-NH3 Conversion
Additional Information:© 2021 American Chemical Society. Received 12 November 2020. Published online 7 January 2021. This work was supported by the NIH (GM070757). We thank Dr. Michael K. Takase, Lawrence M. Henling, Prof. Gaël Ung, and Prof. Jonathan Rittle for crystallographic assistance. We also thank Dr. Matthew J. Chalkley and Dr. Nina X. Gu for feedback in the preparation of this manuscript. J.F.J. acknowledges the support of the NSF for a Graduate Fellowship (GRFP). The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
NIHGM070757
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:Redox reactions, Electronic structure, Catalysts, Nitrogen, Evolution reactions
Issue or Number:2
Record Number:CaltechAUTHORS:20210112-091401610
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210112-091401610
Official Citation:Tripodal P3XFe–N2 Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N2-to-NH3 Conversion. Javier Fajardo and Jonas C. Peters. Inorganic Chemistry 2021 60 (2), 1220-1227; DOI: 10.1021/acs.inorgchem.0c03354
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107418
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:12 Jan 2021 17:42
Last Modified:22 Jan 2021 21:25

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