Diamine bis (phenolate) as supporting ligands in organoactinide (iv) chemistry. Synthesis, structural characterization, and reactivity of stable dialkyl derivatives

International audienceThe homoleptic compounds [U(salan-R2)2] (R = Me (1), tBu (2)) were prepared in high yield by salt-metathesis reactions between UI4(L)2 (L = Et2O, PhCN) and 2 equiv of [K2(salan-R2)] in THF. In contrast, the reaction of the tetradentate ligands salan-R2 with UI3(THF)4 leads to disproportionation of the metal and to mixtures of U(IV) [U(salan-R2)2] and [U(salan-R2)I2] complexes, depending on the ligand to M ratio. The reaction of K2salan-Me2 ligand with U(IV) iodide and chloride salts always leads to mixtures of the homoleptic bis-ligand complex [U(salan-Me2)2] and heteroleptic complexes [U(salan-Me2)X2] in different organic solvents. The structure of the heteroleptic complex [U(salan-Me2)I2(CH3CN)] (4) was determined by X-ray studies. Heteroleptic U(IV) and Th(IV) chloride complexes were obtained in good yield using the bulky salan-tBu2 ligand. The new complexes [U(salan-tBu2)Cl2(bipy)] (5) and [Th(salan-tBu2)Cl2(bipy)] (8) were crystallographically characterized. The salan-tBu2 halide complexes of U(IV) and Th(IV) revealed good precursors for the synthesis of stable dialkyl complexes. The six-coordinated alkyl complexes [Th(salan-tBu2)(CH2SiMe3)2] (9) and [U(salan-tBu2)(CH2SiMe3)2] (10) were prepared by addition of LiCH2SiMe3 to the chloride precursor in toluene, and their solution and solid-state structures (for 9) were determined by NMR and X-ray studies. These complexes are stable for days at room temperature. Preliminary reactivity studies show that CO2 inserts into the An–C bond to afford a mixture of carboxylate products. In the presence of traces of LiCl, crystals of the dimeric insertion product [Th2Cl(salan-tBu2)2(μ-η1:η1-O2CCH2SiMe3)2(μ-η1:η2-O2CCH2SiMe3)] (11) were isolated. The structure shows that CO2 insertion occurs in both alkyl groups and that the resulting carboxylate is easily displaced by a chloride anion

Oxidation of Actinyl(V) Complexes by the Addition of Nitrogen Dioxide Is Revealed via the Replacement of Acetate by Nitrite

The gas-phase complexes AnO₂(CH₃CO₂)₂^– are actinyl­(V) cores, An^VO₂⁺ (An = U, Np, Pu), coordinated by two acetate anion ligands. Whereas the addition of O₂ to U^VO₂(CH₃CO₂)₂^– exothermically produces the superoxide complex U^VIO₂(O₂)­(CH₃CO₂)₂^–, this oxidation does not occur for Np^VO₂(CH₃CO₂)₂^– or Pu^VO₂(CH₃CO₂)₂^– because of the higher reduction potentials for Np^V and Pu^V. It is demonstrated that NO₂ is a more effective electron-withdrawing oxidant than O₂, with the result that all three An^VO₂(CH₃CO₂)₂^– exothermically react with NO₂ to form nitrite complexes, An^VIO₂(CH₃CO₂)₂(NO₂)⁻. The assignment of the NO₂^– anion ligand in these complexes, resulting in oxidation from An^V to An^VI, is substantiated by the replacement of the acetate ligands in AnO₂(CH₃CO₂)₂(NO₂)⁻ and AnO₂(CH₃CO₂)₃^– by nitrites, to produce the tris­(nitrite) complexes AnO₂(NO₂)₃^–. The key chemistry of oxidation of An^V to An^VI by the addition of neutral NO₂ is established by the substitution of acetate by nitrite. The replacement of acetate ligands by NO₂^– is attributed to a metathesis reaction with nitrous acid to produce acetic acid and nitrite

Gas-Phase Reactions of Molecular Oxygen with Uranyl(V) Anionic ComplexesSynthesis and Characterization of New Superoxides of Uranyl(VI)

Gas-phase complexes of uranyl­(V) ligated to anions X^– (X = F, Cl, Br, I, OH, NO₃, ClO₄, HCO₂, CH₃CO₂, CF₃CO₂, CH₃COS, NCS, N₃), [UO₂X₂]⁻, were produced by electrospray ionization and reacted with O₂ in a quadrupole ion trap mass spectrometer to form uranyl­(VI) anionic complexes, [UO₂X₂(O₂)]⁻, comprising a superoxo ligand. The comparative rates for the oxidation reactions were measured, ranging from relatively fast [UO₂(OH)₂]⁻ to slow [UO₂I₂]⁻. The reaction rates of [UO₂X₂]⁻ ions containing polyatomic ligands were significantly faster than those containing the monatomic halogens, which can be attributed to the greater number of vibrational degrees of freedom in the polyatomic ligands to dissipate the energy of the initial O₂-association complexes. The effect of the basicity of the X^– ligands was also apparent in the relative rates for O₂ addition, with a general correlation between increasing ligand basicity and O₂-addition efficiency for polyatomic ligands. Collision-induced dissociation of the superoxo complexes showed in all cases loss of O₂ to form the [UO₂X₂]⁻ anions, indicating weaker binding of the O₂^– ligand compared to the X^– ligands. Density functional theory computations of the structures and energetics of selected species are in accord with the experimental observations

Dissociation of Gas-Phase Bimetallic Clusters as a Probe of Charge Densities: The Effective Charge of Uranyl

Complementary experimental and computational methods for evaluating relative charge densities of metal cations in gas-phase clusters are presented. Collision-induced dissociation (CID) and/or density functional theory computations were performed on anion clusters of composition MM′A_{(<i>m+n+</i>1)}^–, where the two metal ions have formal charge states M^<i>m+</i> and M′^<i>n+</i> and A is an anion, NO₃^–, Cl^–, or F^– in this work. Results for alkaline earth and lanthanide metal ions reveal that cluster CID generally preferentially produces MA_(<i>m+</i>1)^– and neutral M′A_<i>n</i> if the surface charge density of M is greater than that of M′: the metal ion with the higher charge density takes the extra anion. Computed dissociation energies corroborate that dissociation occurs via the lowest energy process. CID of clusters in which one of the two metal ions is uranyl, UO₂²⁺, shows that the effective charge density of U in uranyl is greater than that of alkaline earths and comparable to that of the late trivalent lanthanides; this is in accord with previous solution results for uranyl, from which an effective charge of 3.2+ was derived

Diamine Bis(phenolate) as Supporting Ligands in Organoactinide(IV) Chemistry. Synthesis, Structural Characterization, and Reactivity of Stable Dialkyl Derivatives

The homoleptic compounds [U­(salan-R₂)₂] (R = Me (<b>1</b>), ^tBu (<b>2</b>)) were prepared in high yield by salt-metathesis reactions between UI₄(L)₂ (L = Et₂O, PhCN) and 2 equiv of [K₂(salan-R₂)] in THF. In contrast, the reaction of the tetradentate ligands salan-R₂ with UI₃(THF)₄ leads to disproportionation of the metal and to mixtures of U­(IV) [U­(salan-R₂)₂] and [U­(salan-R₂)­I₂] complexes, depending on the ligand to M ratio. The reaction of K₂salan-Me₂ ligand with U­(IV) iodide and chloride salts always leads to mixtures of the homoleptic bis-ligand complex [U­(salan-Me₂)₂] and heteroleptic complexes [U­(salan-Me₂)­X₂] in different organic solvents. The structure of the heteroleptic complex [U­(salan-Me₂)­I₂(CH₃CN)] (<b>4</b>) was determined by X-ray studies. Heteroleptic U­(IV) and Th­(IV) chloride complexes were obtained in good yield using the bulky salan-^tBu₂ ligand. The new complexes [U­(salan-^tBu₂)­Cl₂(bipy)] (<b>5</b>) and [Th­(salan-^tBu₂)­Cl₂(bipy)] (<b>8</b>) were crystallographically characterized. The salan-^tBu₂ halide complexes of U­(IV) and Th­(IV) revealed good precursors for the synthesis of stable dialkyl complexes. The six-coordinated alkyl complexes [Th­(salan-^tBu₂)­(CH₂SiMe₃)₂] (<b>9</b>) and [U­(salan-^tBu₂)­(CH₂SiMe₃)₂] (<b>10</b>) were prepared by addition of LiCH₂SiMe₃ to the chloride precursor in toluene, and their solution and solid-state structures (for <b>9</b>) were determined by NMR and X-ray studies. These complexes are stable for days at room temperature. Preliminary reactivity studies show that CO₂ inserts into the An–C bond to afford a mixture of carboxylate products. In the presence of traces of LiCl, crystals of the dimeric insertion product [Th₂Cl­(salan-^tBu₂)₂(μ-η¹:η¹-O₂CCH₂SiMe₃)₂(μ-η¹:η²-O₂CCH₂SiMe₃)] (<b>11</b>) were isolated. The structure shows that CO₂ insertion occurs in both alkyl groups and that the resulting carboxylate is easily displaced by a chloride anion