Jean-Claude Berthet

Exploring the uranyl organometallic chemistry: from single to double uranium-carbon bonds.

Uranyl organometallic complexes featuring uranium(VI)-carbon single and double bonds have been obtained from uranyl UO(2)X(2) precursors by avoiding reduction of the metal center. X-ray diffraction and density functional theory analyses of these complexes showed that the U-C and U=C bonds are polarized toward the nucleophilic carbon.

The affinity and selectivity of terdentate nitrogen ligands towards trivalent lanthanide and uranium ions viewed from the crystal structures of the 1 ∶ 3 complexes

Treatment of LnI3 (Ln = La, Ce) or [UI3(py)4] with 3 equivalents of terpy in acetonitrile gave the tris(terpy) complexes [M(terpy)3]I3. Addition of 3 equivalents of Rbtp (2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine) to MX3 (X = I or OSO2CF3) in pyridine or acetonitrile afforded the tris(Rbtp) compounds [M(Rbtp)3]X3. By comparison with terpy, the Rbtp ligand has a better affinity for the 4f and 5f ions and is more selective for U(III) than for Ce(III) or La(III). This trend has been revealed by 1H NMR competition experiments and X-ray crystallographic studies which show that in the [M(terpy)3]3+ and [M(Rbtp)3]3+ cations, the M–N(Rbtp) bond lengths are shorter than the M–N(terpy) bond lengths, and the U–N bond lengths are shorter than the corresponding Ce–N or La–N bond distances.

NEW ADVANCES IN THE CHEMISTRY OF URANIUM AMIDE COMPOUNDS

Abstract The chloroamide complexes U(NEt 2 ) 4− x Cl x ( x =1, 2) were obtained by comproportionation of UCl 4 and U(NEt 2 ) 4 . The novel protonolysis reaction of a metal–amide bond with an acidic ammonium salt proved to be an efficient and convenient synthesis of cationic compounds. Thus were synthesized a series of metallo-organic and organometallic uranium cations in the oxidation states +3, +4, +5. The cationic amide compounds were valuable precursors of new derivatives, as they reacted with anionic reagents, acidic substrates and unsaturated molecules to give the addition, substitution and insertion products; in particular, such reactions were useful for the synthesis of monocyclooctatetraene uranium compounds. The dialkyl amide ligand was found able to stabilize the +5 oxidation state of uranium; neutral and cationic uranium(V) complexes were obtained by oxidation of their corresponding anionic and neutral U(IV) precursors.

Easy access to stable pentavalent uranyl complexes

Reaction of UO2I2(THF)3 with 1 molar equivalent of KC5R5 (R = H, Me) in pyridine led to the uranyl(V) compound {[UO2(Py)5][KI2(Py)2]}(infinity), which is an infinite 1D polymer in its crystalline form; the UO2X(THF)n (X = I, OSO2CF3) complexes were obtained by reduction of their U(VI) parents with TlC5H5 or KC5R5 in THF.

Synthesis and crystal structure of the oxo-bridged bimetallic organouranium complex [(Me3SiC5H4)3U]2[μ-O]

Abstract The compound (Me 3 SiC 5 H 4 ) 3 U (I) reacts with CO 2 or N 2 O to give [(Me 3 SiC 5 H 4 ) 3 U] 2 [μ-O] (II), the crystal structure of which reveals presence of a linear U-O-U bridge with U-O distances of 2.1053 (2) A.

Dehydrocoupling reactions of amines with silanes catalyzed by [(Et2N)3U][BPh4]

Abstract Dehydrocoupling reactions of primary amines RNH2 with PhSiH3 were catalyzed by [(Et2N)3U][BPh4] to give the corresponding aminosilanes PhSiH3−n(NHR)n (n=1–3), the relative yields of the products were found to be dependent on the experimental conditions and on the nature of R. For a primary silane (PhSiH3), the reactivity of RNH2 follows the order primary>secondary>tertiary. Similar dehydrocoupling reactions using secondary amines with secondary silanes were found to be less reactive. Homodehydrocoupling of the silane was found not to be a competing reaction at room temperature. The hydride [(RNH)2UH][BPh4], which is plausibly formed in the reaction of [(RNH)3U][BPh4] with PhSiH3 is a likely intermediate in the catalytic cycle.

Efficient Disproportionation of Formic Acid to Methanol Using Molecular Ruthenium Catalysts

The disproportionation of formic acid to methanol was unveiled in 2013 using iridium catalysts. Although attractive, this transformation suffers from very low yields; methanol was produced in less than 2% yield, because the competitive dehydrogenation of formic acid (to CO2 and H2) is favored. We report herein the efficient and selective conversion of HCOOH to methanol in 50% yield, utilizing ruthenium(II) phosphine complexes under mild conditions. Experimental and theoretical (DFT) results show that different convergent pathways are involved in the production of methanol, depending on the nature of the catalyst. Reaction intermediates have been isolated and fully characterized and the reaction chemistry of the resulting ruthenium complexes has been studied.

Lanthanide(III)/actinide(III) differentiation in coordination of azine molecules to tris(cyclopentadienyl) complexes of cerium and uranium

Reaction of azine molecules L with the trivalent metallocenes [M(C5H4R)3](M = Ce, U; R = But, SiMe3) in toluene gave the Lewis base adducts [M(C5H4R)3(L)](L = pyridine, 3-picoline, 3,5-lutidine, 3-chloropyridine, pyridazine, pyrimidine, pyrazine, 3,5-dimethylpyrazine and s-triazine), except in the cases of M = U and L = 3-chloropyridine, pyridazine, pyrazine and s-triazine where oxidation of U(III) was found to occur. In the pairs of analogous compounds of Ce(III) and U(III), i.e.[M(C5H4But)3(L)](L = pyridine, picoline) and [M(C5H4SiMe3)3(L)](L = pyridine, lutidine, pyrimidine and dimethylpyrazine), the M-N and average M-C distances are longer for M = Ce than for M = U; however, within a series of azine adducts of the same metallocene, no significant variation is noted in the M-N and average M-C distances. The equilibria between [M(C5H4R)3], L and [M(C5H4R)3(L)] were studied by 1H NMR spectroscopy. The stability constants of the uranium complexes, KUL, are greater than those of the cerium counterparts, KCeL. The values of KML are much greater for R = SiMe3 than for R = But and a linear correlation is found between the logarithms of KML and the hydrogen-bond basicity pKHB scale of the azines. Thermodynamic parameters indicate that the enthalpy-entropy compensation effect holds for these complexation reactions. Competition reactions of [Ce(C5H4R)3] and [U(C5H4R)3] with L show that the selectivity of L in favour of U(III) increases with the [small pi] donor character of the metallocene and is proportional to the pi accepting ability of the azine molecule, measured by its reduction potential.

Simple Preparations of the Anhydrous and Solvent‐Free Uranyl and Cerium(IV) Triflates UO2(OTf)2 and Ce(OTf)4 − Crystal Structures of UO2(OTf)2(py)3 and [{UO2(py)4}2(μ‐O)][OTf]2

Treatment of UO3 with pure triflic acid TfOH at 110 °C or with boiling triflic anhydride TfOTf afforded [UO2(OTf)2] (1) in high yields. The latter was also prepared by the reaction of UO3 with TfOH in water, or by dehydration of [UO2(OTf)2(H2O)n] in boiling TfOTf. Anhydrous [Ce(OTf)4] (2) was similarly obtained from the commercially hydrated compound. X-ray analysis revealed that in [UO2(OTf)2(py)3] (3), the triflate ligands are monodentate whereas they are dissociated in [{UO2(py)4}2(μ-O)][OTf]2 (4).

The first cyclopentadienyl complex of uranyl

The U(IV) linear pentacyano metallocene [U(C(5)Me(5))(2)(CN)(5)][NEt(4)](3) reacted with 2 molar equivalents of pyridine N-oxide in THF or acetonitrile to give the U(VI) complex [UO(2)(C(5)Me(5))(CN)(3)][NEt(4)](2), the first uranyl species containing the cyclopentadienyl ligand; the crystal structure revealed that the steric effects of the (C(5)Me(5)) ligand force the {UO(2)}2+ ion to deviate from linearity.