5 research outputs found
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 AnāC 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(Ī¼-Ī·1:Ī·1-O2CCH2SiMe3)2(Ī¼-Ī·1:Ī·2-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 AnO<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub><sup>ā</sup> are actinylĀ(V) cores, An<sup>V</sup>O<sub>2</sub><sup>+</sup> (An = U, Np, Pu), coordinated by two acetate
anion ligands. Whereas the addition of O<sub>2</sub> to U<sup>V</sup>O<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub><sup>ā</sup> exothermically produces the superoxide complex U<sup>VI</sup>O<sub>2</sub>(O<sub>2</sub>)Ā(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub><sup>ā</sup>, this oxidation does not occur for Np<sup>V</sup>O<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub><sup>ā</sup> or Pu<sup>V</sup>O<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub><sup>ā</sup> because of the higher reduction potentials
for Np<sup>V</sup> and Pu<sup>V</sup>. It is demonstrated that NO<sub>2</sub> is a more effective electron-withdrawing oxidant than O<sub>2</sub>, with the result that all three An<sup>V</sup>O<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub><sup>ā</sup> exothermically
react with NO<sub>2</sub> to form nitrite complexes, An<sup>VI</sup>O<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub>(NO<sub>2</sub>)<sup>ā</sup>. The assignment of the NO<sub>2</sub><sup>ā</sup> anion ligand in these complexes, resulting in oxidation from An<sup>V</sup> to An<sup>VI</sup>, is substantiated by the replacement of
the acetate ligands in AnO<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub>(NO<sub>2</sub>)<sup>ā</sup> and AnO<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>3</sub><sup>ā</sup> by
nitrites, to produce the trisĀ(nitrite) complexes AnO<sub>2</sub>(NO<sub>2</sub>)<sub>3</sub><sup>ā</sup>. The key chemistry of oxidation
of An<sup>V</sup> to An<sup>VI</sup> by the addition of neutral NO<sub>2</sub> is established by the substitution of acetate by nitrite.
The replacement of acetate ligands by NO<sub>2</sub><sup>ā</sup> 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 ComplexesīøSynthesis and Characterization of New Superoxides of Uranyl(VI)
Gas-phase
complexes of uranylĀ(V) ligated to anions X<sup>ā</sup> (X =
F, Cl, Br, I, OH, NO<sub>3</sub>, ClO<sub>4</sub>, HCO<sub>2</sub>, CH<sub>3</sub>CO<sub>2</sub>, CF<sub>3</sub>CO<sub>2</sub>, CH<sub>3</sub>COS, NCS, N<sub>3</sub>), [UO<sub>2</sub>X<sub>2</sub>]<sup>ā</sup>, were produced by electrospray ionization and
reacted with O<sub>2</sub> in a quadrupole ion trap mass spectrometer
to form uranylĀ(VI) anionic complexes, [UO<sub>2</sub>X<sub>2</sub>(O<sub>2</sub>)]<sup>ā</sup>, comprising a superoxo ligand.
The comparative rates for the oxidation reactions were measured, ranging
from relatively fast [UO<sub>2</sub>(OH)<sub>2</sub>]<sup>ā</sup> to slow [UO<sub>2</sub>I<sub>2</sub>]<sup>ā</sup>. The reaction
rates of [UO<sub>2</sub>X<sub>2</sub>]<sup>ā</sup> 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 O<sub>2</sub>-association complexes. The
effect of the basicity of the X<sup>ā</sup> ligands was also
apparent in the relative rates for O<sub>2</sub> addition, with a
general correlation between increasing ligand basicity and O<sub>2</sub>-addition efficiency for polyatomic ligands. Collision-induced dissociation
of the superoxo complexes showed in all cases loss of O<sub>2</sub> to form the [UO<sub>2</sub>X<sub>2</sub>]<sup>ā</sup> anions,
indicating weaker binding of the O<sub>2</sub><sup>ā</sup> ligand
compared to the X<sup>ā</sup> 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
MMā²A<sub>(<i>m+n+</i>1)</sub><sup>ā</sup>,
where the two metal ions have formal charge states M<sup><i>m+</i></sup> and Mā²<sup><i>n+</i></sup> and A is an anion,
NO<sub>3</sub><sup>ā</sup>, Cl<sup>ā</sup>, or F<sup>ā</sup> in this work. Results for alkaline earth and lanthanide
metal ions reveal that cluster CID generally preferentially produces
MA<sub>(<i>m+</i>1)</sub><sup>ā</sup> and neutral
Mā²A<sub><i>n</i></sub> if the surface charge density
of M is greater than that of Mā²: 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, UO<sub>2</sub><sup>2+</sup>, 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 [UĀ(salan-R<sub>2</sub>)<sub>2</sub>] (R = Me (<b>1</b>), <sup>t</sup>Bu (<b>2</b>)) were prepared in high yield by salt-metathesis reactions between
UI<sub>4</sub>(L)<sub>2</sub> (L = Et<sub>2</sub>O, PhCN) and 2 equiv
of [K<sub>2</sub>(salan-R<sub>2</sub>)] in THF. In contrast, the reaction
of the tetradentate ligands salan-R<sub>2</sub> with UI<sub>3</sub>(THF)<sub>4</sub> leads to disproportionation of the metal and to
mixtures of UĀ(IV) [UĀ(salan-R<sub>2</sub>)<sub>2</sub>] and [UĀ(salan-R<sub>2</sub>)ĀI<sub>2</sub>] complexes, depending on the ligand to M ratio.
The reaction of K<sub>2</sub>salan-Me<sub>2</sub> ligand with UĀ(IV)
iodide and chloride salts always leads to mixtures of the homoleptic
bis-ligand complex [UĀ(salan-Me<sub>2</sub>)<sub>2</sub>] and heteroleptic
complexes [UĀ(salan-Me<sub>2</sub>)ĀX<sub>2</sub>] in different organic
solvents. The structure of the heteroleptic complex [UĀ(salan-Me<sub>2</sub>)ĀI<sub>2</sub>(CH<sub>3</sub>CN)] (<b>4</b>) was determined
by X-ray studies. Heteroleptic UĀ(IV) and ThĀ(IV) chloride complexes
were obtained in good yield using the bulky salan-<sup>t</sup>Bu<sub>2</sub> ligand. The new complexes [UĀ(salan-<sup>t</sup>Bu<sub>2</sub>)ĀCl<sub>2</sub>(bipy)] (<b>5</b>) and [ThĀ(salan-<sup>t</sup>Bu<sub>2</sub>)ĀCl<sub>2</sub>(bipy)] (<b>8</b>) were crystallographically
characterized. The salan-<sup>t</sup>Bu<sub>2</sub> halide complexes
of UĀ(IV) and ThĀ(IV) revealed good precursors for the synthesis of
stable dialkyl complexes. The six-coordinated alkyl complexes [ThĀ(salan-<sup>t</sup>Bu<sub>2</sub>)Ā(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>] (<b>9</b>) and [UĀ(salan-<sup>t</sup>Bu<sub>2</sub>)Ā(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>] (<b>10</b>) were prepared
by addition of LiCH<sub>2</sub>SiMe<sub>3</sub> 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 CO<sub>2</sub> inserts into the AnāC bond to afford
a mixture of carboxylate products. In the presence of traces of LiCl,
crystals of the dimeric insertion product [Th<sub>2</sub>ClĀ(salan-<sup>t</sup>Bu<sub>2</sub>)<sub>2</sub>(Ī¼-Ī·<sup>1</sup>:Ī·<sup>1</sup>-O<sub>2</sub>CCH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(Ī¼-Ī·<sup>1</sup>:Ī·<sup>2</sup>-O<sub>2</sub>CCH<sub>2</sub>SiMe<sub>3</sub>)] (<b>11</b>) were isolated. The structure
shows that CO<sub>2</sub> insertion occurs in both alkyl groups and
that the resulting carboxylate is easily displaced by a chloride anion