Synthesis and crystal structure of pentavalent uranyl complexes. The remarkable stability of UO2X (X = I, SO3CF3) in non-aqueous solutions

Abstract

The reaction of [UO(2)I(2)(THF)3] with KC(5)R(5) (R = H, Me) or K(2)C(8)H(8) in pyridine gave crystals of [{UO(2)(py)(5)}{KI2(py)2}]. (1), which were desolvated under vacuum into pulverulent [UO(2)(py)2.2KI2] (2).Similar reactions with [UO2(OTf)2] afforded [UO2(py)2.3K(OTf)2] (3) as a powder and crystals of [{UO(2)(py)(5)}2{K(3)(OTf)(5)}. py]. (4.py), which were also obtained together with crystals of [{UO2(py)5}2{K(OTf)2(py)2}][OTf] py (5. py) by treating [UO2(OTf)2] with KC(4)Me(4)P. Crystals of 6. py, the thallium analogue of 5. py, were isolated from the reaction of [UO2(OTf)2] and TlC5H5. Treatment of[UO2I2(THF)3] with LiCH2SiMe3 in pyridine afforded crystals of [{UO(2)(py)5}{LiI(py)2}][I] (7) while[UO(2)(OTf)2] reacted with the alkyllithium reagent in acetonitrile to give crystals of [{UO2(py)5}{Li2(OTf)3}]. (8) in pyridine. The crystal structures of 1, 4. py, 5. py, 6. py, 7 and 8 revealed the presence of U=O-->M interactions (M = Li, K, Tl), and the rich diversity of these structures, from dinuclear (7) to 3D polymeric (4), is related to the distinct coordination numbers of the M+ ion and ligation modes of the bridging iodide and triflate ligands as well as the presence of U=O-->M interactions. The mononuclear complexes [UO2(OTf)(THF)n] (9) and [UO2(OTf)(Et2O)0.5] (10) were respectively obtained by reaction of [UO2(OTf)2] with KC5R5 in THF or LiCH2SiMe3 in Et2O, and were transformed into [UO(2)(OTf)(py)2] (11) in pyridine. Treatment of [UO(2)I(2)(THF)3] with TlC5H5 inpyridine afforded crystals of [UO2(py)5][I]. py (12. py) which were desolvated under vacuum into the powder of [UO(2)I(py)2.5] (14). The same reaction in THF gave [UO2I(THF)2.7] (13) in powder form.Crystals of [UO(2)(CyMe4BTBP)(py)][OTf]. 1.5py (15. 1.5py) and the powder of [UO2I(CyMe4BTBP)](16) were obtained by treating [UO(2)(CyMeBTBP)X2] (X= OTf, I) with KC5Me5 or TlC5H5,respectively. The uranyl(V) chloride and nitrate compounds [UO(2)Cl(py)3] (17) and [UO2(NO3)(py)3] (18)were prepared by reaction of the uranyl(VI) precursors with TlC5H5 in pyridine; complex 18 was also obtained by treating 13 with TlNO3. Crystals of the neutral mononuclear complex [UO(2)(OTf)(py)4] (19)were isolated from reaction of [UO(2)(OTf)2] with Me3SiC5H5 in acetonitrile. Similar reaction with [UO(2)Cl(2)(THF)2]2 in pyridine gave crystals of [UO(2)Cl(2)(py)3]. The crystal structures of 12 py, 15. 1.5py and 19 were determined; the structure of 15 was compared with that of the uranyl(VI) counterpart. All the uranyl(V) compounds are remarkably stable in pyridine solution; the IR absorption at 816 cm-1 is attributed to the v (asym)(U=O) of the ubiquitous [UO(2)(py)(5)]+ species.

Oxo-Functionalization and Reduction of the Uranyl Ion through Lanthanide-Element Bond Homolysis: Synthetic, Structural, and Bonding Analysis of a Series of Singly Reduced Uranyl–Rare Earth 5f1-4fn Complexes

“…Crystals of all complexes apart from 2-Gd were grown from pyridine solutions at either room temperature or −30°C and were found to be suitable for single crystal X-ray diffraction studies; selected bond lengths and angles for 2-Ln are detailed in Table 1. (11) 172.73 (16) The general synthetic procedure was also successful in THF solvent to afford the analogous THF adducts [{UO 2 Ln-(THF) 2 (L)} 2 ] 2THF-Ln (Ln = Ce, Sm, Dy, Yb). These complexes were prepared on a small scale in NMR tubes, although 2THF-Sm and 2THF-Dy were also prepared and isolated from bulk-scale reactions as pink-red (28% yield) or pale brown (16%) powders, respectively; the THF adducts are as poorly soluble in common organic solvents as the pyridine adducts.…”

A Rare Uranyl(VI)–Alkyl Ate Complex [Li(DME)1.5]2[UO2(CH2SiMe3)4] and Its Comparison with a Homoleptic Uranium(VI)–Hexaalkyl

“…[9] It is now clear that many initial synthetic attempts resulted only in uranyl reduction, and not in alkylation. [10] For example, Ephritikhine and co-workers demonstrated that reaction of one equivalent of Li(CH 2 SiMe 3 ) with [UO 2 I 2 (THF) 3 ] or [UO 2 (OTf) 2 ] in pyridine resulted in the formation of a uranyl(V) complex, [11] while Seyam observed formation of UO 2 and biphenyl upon reaction of UO 2 Cl 2 with two equivalents of phenyllithium. [12] Only recently have chemists developed strategies for inhibiting the reduction of uranyl.…”

Oxo Group Protonation and Silylation of Pentavalent Uranyl Pacman Complexes

“…[1,2] For example, new routes to the singly reduced, pentavalent uranyl have been developed and have facilitated fascinating new Lewis acidbase interactions between the oxo groups and alkali metals, [3,4] boranes, [5][6][7] transition metals, [8] rare earth metals, [9] and other uranyl cations. [10] In some cases it is evident that oxo group functionalization can modify the U VI / U V reduction potential such that reduction is facilitated.…”