Tripodal P₃^XFe–N₂ Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N₂-to-NH₃ Conversion
- Creators
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Fajardo, Javier, Jr.
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Peters, Jonas C.
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.
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.Attached Files
Accepted Version - nihms-1714068.pdf
Supplemental Material - ic0c03354_si_001.pdf
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Additional details
- Alternative title
- Tripodal P3XFe–N2 Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N2-to-NH3 Conversion
- PMCID
- PMC8279418
- Eprint ID
- 107418
- Resolver ID
- CaltechAUTHORS:20210112-091401610
- NIH
- GM070757
- NSF Graduate Research Fellowship
- Created
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2021-01-12Created from EPrint's datestamp field
- Updated
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2022-02-08Created from EPrint's last_modified field