Inverse Trans Influence and Uranium-Arene σ-Bonding Drive Molecular Geometry: Ligand Modification from Hard to Soft Flips the Oxide from Axial to Equatorial

Kestel B, Pividori DM, Chowdhury SR, Heinemann FW, Vlaisavljevich B, Meyer K (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Book Volume: 147

Pages Range: 27515-27524

Journal Issue: 31

DOI: 10.1021/jacs.5c05029

Abstract

A rare example of an equatorially bound terminal uranium(V) oxo complex in a chelating sulfur-based ligand environment, namely [(mes(^Me,AdArS)3)U^V(Oeq)(THF)] (2), is presented. Octahedrally coordinated 2 is obtained by reaction of the mesitylene-anchored tris-thiophenolate-coordinated uranium(III) complex [U^III((SAr^Ad,Me)3mes)] (1) with the oxygen-atom transfer reagent N2O. The observed, equatorially bound oxo ligand in 2 is in stark contrast to its known tris-aryloxide analog, [(mes(^Me,AdArO)3)U^V(Oax)(THF)] (A), where the oxo ligand occupies the typically observed axial coordination site. Complexes 1 and 2 are characterized by single-crystal X-ray diffraction analyses and spectroscopic and magnetochemical methods, including¹H NMR, UV/vis/NIR electronic absorption, as well as EPR spectroscopy and SQUID magnetometry, thus confirming the CS symmetry and the pentavalent oxidation state of 2. Encompassing quantum chemical calculations (DFT and CASPT2) on 2 and its tris-phenolate analog A, support and rationalize the structural and electronic differences. The molecular orbital pictures show that a stabilizing σ-bonding interaction arising from the U–Oeq inverse trans influence (ITI) is present in 2 but missing in A. In 2, the sulfur 3p orbitals are closer in energy to the uranium 5f manifold than the arene π-system, leading to an ITI, while U–arene σ- or δ-bonding is not observed. Although the arene orbitals remain separated from the uranium 5f orbitals in A, the absence of an ITI allows the arene a2u orbital to engage in a σ-type interaction with the metal. Thus, incorporating a tris-thiophenolate to an arene anchor introduces a new design concept in molecular f-element chemistry. This approach stabilizes an equatorially bound U(V) oxo center, contrasting with its tris-phenolate counterpart, where oxo coordination is axial. The observed geometric divergence, driven by competing ITI and U–arene interactions, not only tunes electronic structure but also leads to differentiated reactivity: only the phenolate analogs activate H2O, while the thiolates do not.

Authors with CRIS profile

Involved external institutions

University of South Dakota United States (USA) (US)

How to cite

APA:

Kestel, B., Pividori, D.M., Chowdhury, S.R., Heinemann, F.W., Vlaisavljevich, B., & Meyer, K. (2025). Inverse Trans Influence and Uranium-Arene σ-Bonding Drive Molecular Geometry: Ligand Modification from Hard to Soft Flips the Oxide from Axial to Equatorial. Journal of the American Chemical Society, 147(31), 27515-27524. https://doi.org/10.1021/jacs.5c05029

MLA:

Kestel, Benedikt, et al. "Inverse Trans Influence and Uranium-Arene σ-Bonding Drive Molecular Geometry: Ligand Modification from Hard to Soft Flips the Oxide from Axial to Equatorial." Journal of the American Chemical Society 147.31 (2025): 27515-27524.

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