Evidence for ligand- and solvent-induced disproportionation of uranium(IV)

Abstract

Disproportionation, where a chemical element converts its oxidation state to two different ones, one higher and one lower, underpins the fundamental chemistry of metal ions. The overwhelming majority of uranium disproportionations involve uranium(III) and (V), with a singular example of uranium(IV) to uranium(V/III) disproportionation known, involving a nitride to imido/triflate transformation. Here, we report a conceptually opposite disproportionation of uranium(IV)-imido complexes to uranium(V)-nitride/uranium(III)-amide mixtures. This is facilitated by benzene, but not toluene, since benzene engages in a redox reaction with the uranium(III)-amide product to give uranium(IV)-amide and reduced arene. These disproportionations occur with potassium, rubidium, and cesium counter cations, but not lithium or sodium, reflecting the stability of the corresponding alkali metal-arene by-products. This reveals an exceptional level of ligand- and solvent-control over a key thermodynamic property of uranium, and is complementary to isolobal uranium(V)-oxo disproportionations, suggesting a potentially wider prevalence possibly with broad implications for the chemistry of uranium.

Heterometallic uranium/molybdenum nitride synthesis via partial N-atom transfer

“…This polarized triple bond is in line with the obtained Wiberg Bond Index (WBI) found for the UN (2.26), indicative of some degree of covalency in the bond and it compares well with the UN WBI of 2.58 found in the Na-capped terminal uranium( v ) nitride reported by Liddle. 4 a ,20 This bonding is in accordance with the experimental analysis where the N–Mo interaction was expected to occur from a partial delocalization of the U–N interaction, in line with the presence of three (UN)–Mo 3c–2e bonds and N–Mo WBI of 0.73.…”

“…16,17 The uranium species formed in the reaction could not be identified, but the formation of NaN 13 CO was unambiguously demonstrated by 13 C NMR spectroscopy of the reaction mixture in D 2 O. Reports of nitride/CO coupling are scarce 3 b ,3 e ,3 f ,20,21 but include examples of terminal and bridging U( v ) nitrides. 3 b ,3 h The Mo binding to the U( v ) nitride does not result in a reduced reactivity of the bridging nitride and reductive carbonylation of the U( v ) nitride likely proceeds with release of the Mo(0) fragment, though direct reaction with 1 cannot be ruled out.…”

Insights into the Electronic Structure of a U(IV) Amido and U(V) Imido Complex

“…However, the Mazzanti group could identify a water stable U(V) complex [11] and Liddle et al. were able to find U(V) also as a disproportionation product recently [12] . The main factors influencing the stability of a certain oxidation state and thus reactivity arise from differences of the actinides’ electronic structure, which is strongly affected by for example organic ligands as complexation partners but also by the reaction conditions.…”

“…However, the Mazzanti group could identify a water stable U(V) complex [11] and Liddle et al were able to find U(V) also as a disproportionation product recently. [12] The main factors influencing the stability of a certain oxidation state and thus reactivity arise from differences of the actinides' electronic structure, which is strongly affected by for example organic ligands as complexation partners but also by the reaction conditions. In recent years, N donor ligands gained centre stage for stabilizing uranium over a wide range of oxidation states due to the quite flexible number of bonds they can form: They can thus be utilized as amide [12][13][14][15] or imine [16][17][18][19] functionalities, and even triple bonds as nitrides [12,[20][21][22][23] are possible.…”

“…[12] The main factors influencing the stability of a certain oxidation state and thus reactivity arise from differences of the actinides' electronic structure, which is strongly affected by for example organic ligands as complexation partners but also by the reaction conditions. In recent years, N donor ligands gained centre stage for stabilizing uranium over a wide range of oxidation states due to the quite flexible number of bonds they can form: They can thus be utilized as amide [12][13][14][15] or imine [16][17][18][19] functionalities, and even triple bonds as nitrides [12,[20][21][22][23] are possible. Interestingly, bonds from imino ligands to U(VI) are more covalent compared to their dioxo analogues and capable of inducing further electronic effects like the inverse trans influence (ITI), opening an opportunity to shed light on 5forbital involvement.…”