Isolation of a Star‐Shaped Uranium(V/VI) Cluster from the Anaerobic Photochemical Reduction of Uranyl(VI)

Abstract

Actinide oxo clusters are an important class of compounds due to their impact on actinide migration in the environment. The photolytic reduction of uranyl(VI) has potential application in catalysis and spent nuclear fuel reprocessing, but the intermediate species involved in this reduction have not yet been elucidated. Here we show that the photolysis of partially hydrated uranyl(VI) in anaerobic conditions leads to the reduction of uranyl(VI), and to the incorporation of the resulting U species into the stable mixed-valent star-shaped U /U oxo cluster [U(UO ) (μ -O) (PhCOO) (Py) ] (1). This cluster is only the second example of a U /U cluster and the first one associating uranyl groups to a non-uranyl(V) center. The U center in 1 is stable, while the reaction of uranyl(V) iodide with potassium benzoate leads to immediate disproportionation and formation of the U U O cluster {[K(Py) ] [K(Py)] [U O (PhCOO) (Py) ]} (5).

Homoleptic U(iii) and U(iv) amidate complexes

“…[13][14][15][16] Uranium coordination complexes are of interest to chemists due to their wide array of accessible geometries and unusual reactivity. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Due to the electropositive nature and large atomic size of uranium, coordination chemists frequently employ sterically-encumbered ligands to stabilize uranium complexes in non-aqueous systems. Cyclopentadienyl (Cp) derivatives are often used to provide steric support around the uranium center, but a large amount of research has been directed towards developing actinide complexes using alternative ligand systems, 18,26,32 including carbenes, 33,34 carboxylates, 28,29,35 and amidinates.…”

Facile Reductive Silylation of UO22+ to Uranium(IV) Chloride

“…[2] The persistence of these uranium(VI) species in nature is problematic due to their high water solubility and subsequent mobility;h owever, reduction to tetravalent species through pentavalent [UO 2 ] + intermediates in anaerobic conditions can mitigate this on account of the poor solubility of lower valent forms. [1] Though studied using avariety of methods, [2] including electrochemically [3] and photochemically, [4] af ruitful strategy for U = Or eduction is reductive silylation, where the driving force is formation of O À Si bonds.P revious reductive silylation systems are limited by the need for large excesses of silyl halides, [5][6][7] side reactivity of coordinated ligands [5,6] or their use as sacrificial reductants, [8] the need for pre-activation, [9][10][11] or the requirement of complex macrocyclic ligands. [12] Our progress in reductive silylation has suffered from similar flaws.W er ecently reported an ovel uranyl species,[ Cp*UO 2 ( Mes PDI Me )] (Cp* = 1,2,3,4,5-pentamethylcyclopentadienide, Mes PDI Me = 2,6-((Mes)N = CMe) 2 -C 5 H 3 N, Mes = 2,4,6-trimethylphenyl), bound by ar edox active pyridine(diimine) ligand.…”

“…[14] While the organometallic uranyls eluded isolation, the organic byproducts formed upon warming were derived through:1 )H-atom abstraction, 2) b-hydride elimination, and 3) reductive elimination (R = Ph only). Subsequently,t he first uranyl alkyl complex, [Li(DME) 1.5 ] 2 [UO 2 -(CH 2 SiMe 3 ) 4 ], has been isolated and characterized by Hayton et al [15] To test this theory,athawing THF slurry of [UO 2 Cl 2 -(OPPh 3 ) 2 ](1)was treated with 2equiv NaCH 2 SiMe 3 ,causing an immediate color change from yellow to light brown. After ca.…”

Controlling Cation‐Cation Interactions in Uranyl Coordination Dimers by Varying the Length of the Dicarboxylate Linker

“…Although it does not possess a dioxo uranyl(V) center, a stunning mixedvalence complex is a star-shaped U V/VI oxo-cluster supported by benzoate ligands. [52] A more directly pertinent case, also from Mazzanti, is a uranyl(V/VI) complex that exhibits a so-called "cation-cation" interaction (CCI). [53] In such a CCI a Lewis base O yl , typically from a uranyl(V), datively binds to an acidic U V center, a situation denoted as U [54] The two essential types of CCIs exhibited by actinyls, end-on and side-on, are shown for uranyl in Scheme 1.…”