Oxygen and nitrogen Lewis base adducts of [UO2(OTf)2]. Crystal structures of polypyridine complexes with out-of-plane uranyl equatorial coordination.

Dissolution of [UO2(OTf)2](1) in anhydrous thf, dme or py led to the formation of the complexes [UO2(OTf)2(thf)3](2), [UO2(OTf)2(dme)](3) and [UO2(OTf)2(py)3](4), respectively. Compounds 2 and 4 are neutral monomers in the solid state as well as the chloride [UO2Cl2(py)3](5) which was prepared in a similar way as for from the dimer [[UO2Cl2(thf)2]2]. Addition of 4 equivalents of triphenylphosphine oxide (tppo) to 1 afforded, in pyridine, the dicationic species [UO2(tppo)4][OTf]2 (6). The bi- or terdentate nitrogen molecules 2,2'-bipy, phen or terpy reacted with 1 in acetonitrile or pyridine to give [UO2(OTf)2(bipy)2](7), [UO2(phen)3][OTf]2(8), [UO2(OTf)2(terpy)](9) and [UO2(terpy)2][OTf]2(10), respectively. The hydroxide compound [[UO2(OH)(terpy)]2][OTf]2(11) was obtained by hydrolysis in air of 1 in a mixture of acetonitrile and ethanol in the presence of terpyridine. The X-ray crystal structures of , and reveal a novel coordination geometry for the uranyl ion, the uranium atom being in a rhombohedral environment; the six coordinating ligands atoms of the [UO2]2+ ion are separated into two parallel and staggered equilateral triangles and the UO2 axis is perpendicular to these triangles, passing through their centre. The structures of the mono(terpy) complexes 9 and 11 show the uranium atoms in a distorted pentagonal bipyramidal configuration with the nitrogen atom of the central pyridine ring of the terpy ligand significantly displaced from the equatorial plane.

Reactions of aliphatic ketones R2CO (R=Me, Et, iPr and tBu) with the MCI4/Li(Hg) system (M=U or Ti): mechanistic analogies between the McMurry, Wittig, and Clemmensen reactions.

Analysis of the products of the reactions of ketones R2CO (R = Me, Et, iPr, tBu) with the MCl4/Li(Hg) system (M = U, Ti) at 20 degrees C revealed significant differences. For R = Me, the reaction proceeded exclusively (M = U) or preferentially (M = Ti) via a metallopinacol intermediate resulting from dimerization of ketyl radicals. Pinacol was liberated by hydrolysis, and tetramethylethylene was obtained after further reduction at 65 degrees C. For R=iPr, formation of iPr2C=CiPr2 as the only coupling product, the nonproduction of this alkene by reduction of the uranium pinacolate [U]-OCR2CR2O-[U] (R= iPr) at 20 degrees C, and the instability of the corresponding titanium pinacolate towards rupture of the pinacolic C-C bond indicated that reductive coupling of iPr2CO did not proceed by dimerization of ketyl radicals. Formation of 2,4-dimethyl-2-pentene was in favor of a carbenoid intermediate resulting from deoxygenative reduction of the ketyl. These results revealed that for sterically hindered ketones, McMurry reactions can be viewed as Wittig-like olefination reactions. For R=tBu, no coupling product was obtained and the alkane tBu2CH2 was the major product. The involvement of the carbenoid species [M]=CtBu2 was confirmed by its trapping with H2O, leading to tBu2CH2, and with the aldehydes RCHO, giving the cross-coupling products tBu2C=C(R)H (R = Me, tBu). Therefore, in the case of severely congested ketones, McMurry reactions present strong similarities to the Clemmensen reduction of ketones, owing to the involvement in both reactions of carbenoid species which exhibit similar reactivity.

Complexation studies of iodides of trivalent uranium and lanthanides (Ce and Nd) with 2,2'-bipyridine in anhydrous pyridine solutions.

In anhydrous pyridine solution at 294 K, U(III) and Ce(III) triiodides were found to form both 1:1 (ML) and 1:2 (ML(2)) complexes with bipyridine (bipy = L) while Nd(III) triodide formed only a 1:2 complex. The 1:3 (ML(3)) complexes were identified at low temperature with a large excess of L. Conductometry measurements showed for U(III) a large increase in the conductivity when increasing the molar ratio L:U. The complex UL(2) was found to be a 1:1 electrolyte and the species UI(2)(+) was more reactive toward L in comparison with UI(3). For Ce(III) and Nd(III), MI(2)(+) and MI(3) present about the same affinity for L. The stability of the complexes is limited, and U(III) possesses a slightly higher affinity for bipy than the trivalent lanthanides. Interestingly, a preference for the formation of ML(2) complex was shown for all the studied M(III) ions. The driving force for complex formation was always the enthalpy, and, surprisingly for a bidendate ligand (bipy), no favorable entropy contribution to complex formation was observed. The X-ray crystal structures of [CeI(3)(bipy)(2)(py)](4).5py.bipy and UI(3)(bipy)(2)(py).2py were determined. The structures of the molecules MI(3)(bipy)(2)(py) are almost identical for U and Ce. The mean M(III)-N(bipy) bond distances are equal to 2.67(3) A for Ce(III) and 2.65(4) A for U(III). The slightly smaller M(III)-N(bipy) distances observed for U(III) would reflect a slightly more important covalent character of the U(III)-N(bipy) bonds, in agreement with the slightly better affinity of U(III) than Ce(III) or Nd(III) toward bipy observed in solution and with the fact that the enthalpy is the driving force for complex formation.

An ion pair uniting a gadolinium(III)-Schiff base complex and uranyl tetrachloride.

The Schiff base N-(tert-butyl)-3-methoxysalicylaldimine (LH) forms a complex with gadolinium(III) chloride, [GdCl(2)(LH)(2)(C(5)H(5)N)(2)](+), in which the two O atoms of each ligand are coordinated (the phenolic O atom being deprotonated) and the imine N atom is protonated and involved in a hydrogen bond with the phenoxide group. This complex crystallizes as an ion pair with uranyl tetrachloride, i.e. bis(bis[2-(tert-butyliminiomethyl)-6-methoxyphenolato-O,O']dichlorobis(pyridine-N)gadolinium(III)) tetrachlorodioxouranium(VI) tetrapyridine solvate [GdCl(2)(C(12)H(17)NO(2))(2)(C(5)H(5)N)(2)](2)[UCl(4)O(2)].4C(5)H(5)N. The U atom of the UCl(4)O(2) anion lies on an inversion centre.