Homoleptic Acetylacetonate (acac) and ?-Ketoiminate (acnac) Complexes of Uranium

Waldschmidt P, Riedhammer J, Hartline D, Heinemann FW, Meyer K (2023)

Publication Type: Journal article

Publication year: 2023


DOI: 10.1021/acs.inorgchem.2c03520


Transmetalation of potassium salts of differently substituted acetylacetonate (acac) and beta-ketoiminate (acnac) with [U(I)3(dioxane)1.5] and [U(I)4(dioxane)2] resulted in the formation of homoleptic, octahedral complexes [U(tBuacnacPh)3] (with tBuacnacPh = 2,2,6,6-tetramethyl-5-(phenylimino)heptan-3-onate) in the oxidation states +III and +IV and the homoleptic, square prismatic complexes [UIV(MeacnacPh)4] (with MeacnacPh = 4(phenylimino)pentan-2-onate) and the homoleptic, square anti prismatic complexes [U(tBuacac)4] [with acac = 2,2,6,6-tetramethyl3,5-heptanedionate (tBuacac), 2,2,6,6-tetramethyl,4-methyl-3,5-heptanedionate (tBuacMeac), and 2,2,6,6-tetramethyl-4-phenyl-3,5-heptanedionate (tBuacPhac)] in oxidation states +III, +IV, and +V. Oxidation of [UIII(tBuacnacPh)3] (1) with AgOTf yielded [UIV(tBuacnacPh)3][OTf] (2), which was fully characterized by single-crystal X-ray diffraction analysis, a combination of ultraviolet/visible/near-infrared, nuclear magnetic resonance, and infrared spectroscopies, and solid-state superconducting quantum interference device magnetization studies. Complexation of the sterically less encumbering ligand derivative MeacnacPh provided access to the tetravalent, square antiprismatic complex [UIV(MeacnacPh)4] (3). Cyclovoltammetric analysis of the square antiprismatic [UIV(tBuacac)4] (4), [UIV(tBuacMeac)4] (5), and [UIV(tBuacPhac)4] (6) revealed reversible anodic and cathodic waves, attributable to the U(III/IV) and U(IV/V) redox couples, both being chemically accessible, as tested in the case of 5. The corresponding U(III) and U(V) compounds, [K(2.2.2-cryptand)][UIII(tBuacMeac)4] (7) and [UV(tBuacMeac)4][SbF6] (8), were synthesized accordingly. Unfortunately, reduced 7 proved to be too reactive for isolation and could only be detected by electron paramagnetic resonance spectroscopy. Notably, electrochemical studies on homoleptic uranium(IV) complexes with differently derivatized (R) acRac ligands (R = H, Me, or Ph) feature large electrochemical windows of up to 2.91 V, measured between the uranium(III) and the uranium(V) species, in addition to high stability toward repeated potential scans.

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Waldschmidt, P., Riedhammer, J., Hartline, D., Heinemann, F.W., & Meyer, K. (2023). Homoleptic Acetylacetonate (acac) and ?-Ketoiminate (acnac) Complexes of Uranium. Inorganic Chemistry. https://doi.org/10.1021/acs.inorgchem.2c03520


Waldschmidt, Pablo, et al. "Homoleptic Acetylacetonate (acac) and ?-Ketoiminate (acnac) Complexes of Uranium." Inorganic Chemistry (2023).

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