EPR and <sup>31</sup>P ENDOR Characterization of Pseudo-Jahn–Teller Dynamics and N<sub>2</sub> Activation in Functional Nitrogenase Models, P<sub>3</sub><sup>E</sup>M(N<sub>2</sub>) (M = Fe, Co; E = Si, B, C)
The nominally trigonal, pseudo-Jahn-Teller (PJT)-active, <i>S</i> = 1/2 N<sub>2</sub>-bound complexes, <b>P</b><sub><b>3</b></sub><sup><b>E</b></sup><b>M(N</b><sub><b>2</b></sub><b>)</b>, M = Fe, Co, with three in-plane phosphine ligands and axial donors, E = Si, B, C, include functional nitrogenase models that catalyze the reduction of N<sub>2</sub> to NH<sub>3</sub>. We applied EPR, <sup>31</sup>P ENDOR spectroscopy, and DFT computations to characterize the PJT-induced distortions of four selected <b>P</b><sub><b>3</b></sub><sup><b>E</b></sup><b>M(N</b><sub><b>2</b></sub><b>)</b>, revealing how the metal ion and axial ligand E together tune both PJT dynamics, as revealed by <sup>31</sup>P ENDOR and N<sub>2</sub> activation, as indicated by a decrease in N≡N stretching frequency, ν(N≡N). <b>P</b><sub><b>3</b></sub><sup><b>Si</b></sup><b>Fe(N</b><sub><b>2</b></sub><b>), P</b><sub><b>3</b></sub><sup><b>B</b></sup><b>Fe(N</b><sub><b>2</b></sub><b>)</b><sup><b>-</b></sup>, and <b>P</b><sub><b>3</b></sub><sup><b>B</b></sup><b>Co(N</b><sub><b>2</b></sub><b>)</b> each exhibit a single <sup>31</sup>P isotropic hyperfine coupling, revealing dynamic pseudorotation of the PJT distortion, producing averaged <i>C</i><sub><i>3</i></sub> symmetry with equivalent phosphine ligands. Conversely, <b>P</b><sub><b>3</b></sub><sup><b>C</b></sup><b>Co(N</b><sub><b>2</b></sub><b>)</b><sup><b>+</b></sup> exhibits a static PJT distortion directed toward a phosphine bonded to a d<sub>x2-y2</sub> SOMO lobe, leading to the exceptional isotropic <sup>31</sup>P coupling <i>a</i><sub>iso</sub>(<sup>31</sup>P) = +250 MHz, leaving two phosphines, <i>a</i><sub>iso</sub>(<sup>31</sup>P) ≈ -20 MHz. Importantly, minimization of metal 'doming' out of the <b>P</b><sub><b>3</b></sub><sup><b>C</b></sup><b>Co(N</b><sub><b>2</b></sub><b>)</b><sup><b>+</b></sup> phosphine plane toward N<sub>2</sub> imposed by C-Co bond 'inelasticity' yields the longest M-N<sub>2</sub> bond and the least-activated N<sub>2</sub>, as measured by ν(N≡N). Comparisons reveal an unrecognized correlation among PJT distortion, M-E bond elasticity, and N<sub>2</sub> activation, providing guidelines for designing bioinspired N<sub>2</sub>-reduction catalysts.
Authors
- George E. Cutsail (ORCID: https://orcid.org/0000-0002-7378-9474)
- Hao Yang (ORCID: https://orcid.org/0000-0001-7229-0957)
- Jonas C. Peters (ORCID: https://orcid.org/0000-0002-6610-4414)
- Brian M. Hoffman (ORCID: https://orcid.org/0000-0002-3100-0746)
- Alex Drena (ORCID: https://orcid.org/0000-0002-8864-6740)
Institutions
- Northwestern University (US)
- California Institute of Technology (US)
- Division of Chemistry (US)
- Ludwig-Maximilians-Universität München (DE)
Publication Details
- Journal
- Inorganic Chemistry
- Published
- 2025-09-04
- DOI
- https://doi.org/10.1021/acs.inorgchem.5c02760
- Citations
- 1
- Primary Topic
- Metalloenzymes and iron-sulfur proteins
- Type
- article
- Field-Weighted Citation Impact
- 0.36
Funders
- Office of Science
- National Institute of General Medical Sciences
- Division of Chemistry
- Basic Energy Sciences