Actinides: Pentavalent Organometallics

Abstract

In this article, we describe the recent developments in the chemistry and understanding of the organometallic compounds of pentavalent uranium.

Structural, Electrochemical, and Magnetic Studies of Bulky Uranium(III) and Uranium(IV) Metallocenes

“…The organometallic chemistry of uranium prominently features complexes containing substituted or unsubstituted cyclopentadienyl ligands, Cp R . − In particular, uranium metallocenes featuring the (Cp R ) 2 U moiety have supported a large variety of intriguingand often quite reactivestructural motifs, such as uranium–ligand multiple bonds, − a uranium–aluminum interaction, uranium­(V) complexes, − cationic uranium­(III) species, , and uranium hydrides. − In the past few years, bulky [Cp R ] − ligands have also enabled the synthesis of base-free dysprosium­(III) metallocenium cation salts [(Cp R ) 2 Dy]­[B­(C 6 F 5 ) 4 ], which, incredibly, function as single-molecule magnets with magnetic blocking temperatures near and exceeding 77 K, higher than any previously reported systems. − This synthetic strategy was also very recently extended to the preparation of the uranium­(III) metallocenium complex [(Cp iPr5 ) 2 U]­[B­(C 6 F 5 ) 4 ] (Cp iPr5 = penta­(isopropyl)­cyclopentadienyl), which was also found to exhibit slow magnetic relaxation in the presence of an applied magnetic field …”

Actinide arene-metalates: ion pairing effects on the electronic structure of unsupported uranium–arenide sandwich complexes

“…34 These complexes have provided valuable electronic insight into actinide bonding, particularly with respect to d-interactions, while enabling rich redox chemistry and other novel reactivity patterns such as the C-H borylation of arenes. [34][35][36][37][38][39][40][41][42][43][44][45][46] For example, U(O-2,6-t Bu 2 C 6 H 3 ) 3 reacts with benzene in the presence of HBBN (HBBN ¼ 9-bora- 9-bicylononane) 47 and U(k 1 :h 6 48 where the uranium-arene bonds are enforced through intramolecular ligand tethering. Interestingly, it has been predicted by means of density functional theory (DFT) that uranium-arene complexes may also provide access to the unknown U(I) oxidation state.…”

Unusual redox stability of pentavalent uranium with hetero-bifunctional phosphonocarboxylate: insight into aqueous speciation

“…U is a redox-sensitive element and exists in various oxidation states such as III, IV, V and VI 7,8 out of which the pentavalent uranium (i.e., U V O 2 + or U(V)) has historically been reported as an unusual (rare) oxidation state of uranium in aqueous solution. [9][10][11] In linear actinyl(VI/V) cations, the pentavalent uranium species is particularly intriguing because of its high instability due to its propensity for instantaneous disproportionation (eqn (S1) †) to thermodynamically favoured U(IV) and U(VI) products in aqueous solutions. [9][10][11] In addition, it exhibits high susceptibility to air and water, as well as ease of conversion and oxidation to hexavalent U in the presence of trace amounts of oxygen or water.…”