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

Jingzhen Du,Stephen T Liddle,Floriana Tuna,Erli Lu,Ashley J Wooles,Laurent Maron,John A Seed,Iskander Douair

doi:10.1038/s41467-021-25151-z

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.

Highlights

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 disproportionation reaction reported here suggests an unusual level of external control over the thermodynamic properties of uranium, further diminishing the general imperviousness of uranium (IV) with respect to (III) and (V)[15], and our results provide insight into the factors that are dictating the reactivity
We reported previously[17] that the uranium(IV)-amide complex [UIV(TrenTIPS)(NH2)] (1, TrenTIPS = {N(CH2CH2NSiPri3)3}3−) can be deprotonated by alkali metal alkyl reagents to produce the pink uranium(IV)-imido dimers [{UIV(TrenTIPS)(μ-NH)(μ-M)}2] (2M, M = Li, Na, K, Rb, Cs), Fig. 1, which are insoluble in benzene or toluene at ambient conditions

Summary

Introduction

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. 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 byproducts. Deprotonation of a uranium (IV)-amide to give -imido derivatives promotes, with mild heating, disproportionation to the corresponding uranium(III)-amide and uranium(V)-nitride complexes for three alkali metal salts in benzene, but not toluene, solvent This reaction is conceptually the reverse reaction to the above example, namely imido to nitride/amide as opposed to nitride to imido/triflate. The reactivity outlined here has parallels to that of uranyl(V)[10,11], possibly suggesting a potentially wider prevalence in highly radiolytic and environmental scenarios[16]

Methods

Results

Conclusion