EPR and 31P ENDOR Characterization of Pseudo-Jahn–Teller Dynamics and N2 Activation in Functional Nitrogenase Models, P3EM(N2) (M = Fe, Co; E = Si, B, C)
Year: 2025
Type: article
Abstract: The nominally trigonal, pseudo-Jahn–Teller (PJT)-active, S = 1/2 N 2 -bound complexes, P 3 E M(N 2 ), 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 2 to NH 3 . We applied EPR, 31 P ENDOR spectroscopy, and DFT computations to characterize the PJT-induced distortions of four selected P 3 E M(N 2 ), revealing how the metal ion and axial ligand E together tune both PJT dynamics, as revealed by 31 P ENDOR and N 2 activation, as indicated by a decrease in N≡N stretching frequency, ν(N≡N). P 3 Si Fe(N 2 ), P 3 B Fe(N 2 ) –, and P 3 B Co(N 2 ) each exhibit a single 31 P isotropic hyperfine coupling, revealing dynamic pseudorotation of the PJT distortion, producing averaged C 3 symmetry with equivalent phosphine ligands. Conversely, P 3 C Co(N 2 ) + exhibits a static PJT distortion directed toward a phosphine bonded to a d x2-y2 SOMO lobe, leading to the exceptional isotropic 31 P coupling a iso ( 31 P) = +250 MHz, leaving two phosphines, a iso ( 31 P) ≈ −20 MHz. Importantly, minimization of metal ‘doming’ out of the P 3 C Co(N 2 ) + phosphine plane toward N 2 imposed by C–Co bond ‘inelasticity’ yields the longest M–N 2 bond and the least-activated N 2, as measured by ν(N≡N). Comparisons reveal an unrecognized correlation among PJT distortion, M-E bond elasticity, and N 2 activation, providing guidelines for designing bioinspired N 2 -reduction catalysts.
Source: Inorganic Chemistry
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4414023698