Tetravalent Uranium and Thorium Complexes: Elucidating Disparate Reactivities of An^IVCl₂ (An = U, Th) Supported by a Pyridine-Decorated Dianionic Ligand

Abstract

Although synthesis, reactivity, and bonding of U­(IV) and Th­(IV) complexes have been extensively studied, direct comparison of fully analogous compounds is rare. Herein, we report corresponding complexes 1-U and 1-Th, in which U­(IV) and Th­(IV) are supported by the tetradentate pyridine-decorated dianionic ligand N2NN′ (1,1,1-trimethyl-N-(2-(((pyridin-2-ylmethyl)­(2-((trimethylsilyl)­amino)­benzyl)­amino)­methyl)­phenyl)­silanamine). Although 1-U and 1-Th are structurally very similar, they display disparate reactivities with TMS3SiK (tris­(trimethylsilyl)­silylpotassium). The reaction of (N2NN′)­UCl2 (1-U) and 1 equiv of TMS3SiK in THF unexpectedly formed [Cl­(N2NN′)­U]2O (2-U) featuring an unusual bent U–O–U moiety. In contrast, a salt elimination reaction between (N2NN′)­ThCl2 (1-Th) and 1 equiv of TMS3SiK led to thorium complex 2-Th, in which the pyridyl group has undergone a 1,4-addition nucleophilic attack. Complex 2-Th serves as a synthon for preparing dimetallic bis-azide complex 3-Th by reaction with NaN3. The complexes were characterized by X-ray crystal diffraction, solution NMR, FT-IR, and elemental analysis. Computations of the formation mechanism of 2-U from 1-U suggest reduced U­(III) as a key intermediate for promoting the cleavage of the C–O bonds of THF. The inaccessible nature of Th­(III) as an intermediate oxidation state explains the very different reactivity of 1-Th versus 1-U. Given that reactants 1-U and 1-Th and products 2-U and 2-Th all comprise tetravalent actinides, this is an unusual case of very disparate reactivity despite no net change in the oxidation state. Complexes 2-U and 3-Th provide a basis for the synthesis of other dinuclear actinide complexes with novel reactivity and properties.

Mining for Metal–Organic Systems: Chemistry Frontiers of Th-, U-, and Zr-Materials

“…Despite structural similarities, these two complexes exhibit notably different reactivities when interacting with tris(trimethylsilyl)silylpotassium (TMS 3 SiK) . In the case of the U-based complex, the reaction with one equivalent of TMS 3 SiK in tetrahydrofuran (THF) leads to the formation of a dimer as shown in Figure . In contrast, the Th-based complex undergoes a salt elimination reaction with one equivalent of (TMS) 3 SiK, resulting in a thorium-containing molecular complex where the pyridyl group is subjected to a 1,4-addition nucleophilic attack (Figure ).…”

“…At the same time, while zirconium compounds can certainly serve as a useful surrogate for thorium-based ones in many cases, it is also valuable to view many aspects of thorium chemistry in light of other actinides like uranium, especially considering the distinct properties of actinides influenced by the presence of f -electrons. For example, careful analysis of the literature concerning zirconium- and actinide-based structures sheds light on how even subtle differences in the mentioned aspects (i.e., charge density, Lewis acidity, or oxophilicity) can result in drastically different properties for organometallic complexes, POMs, or MOFs. ,,,,,,,− For instance, combining either Zr, U, or Th with identical organic ligands often leads to different metal coordination environments, structural topologies, and chemical stability and reactivity. ,,,,,,,− Such differences in the structure and reactivity of Th-, U-, and Zr-based compounds often become even more pronounced upon transitioning from discrete molecular systems (i.e., metal–organic complexes and cages) to extended structures, like MOFs. As a result, the choice of MOF metal nodes based on either Zr, U, or Th can be used as a variable to tailor the material performance toward a desired application by altering properties like gas sorption, density of states near the Fermi edge, stability, and reactivity. ,,,,, Therefore, the common assumption that metal oxidation state and Lewis acidity alone are sufficient to select zirconium as a reliable nonradioactive surrogate for Th-based materials development needs to be considered as a first approximation.…”

Study on the affinity sites of cadmium's binding to ligands by thermodynamics and nuclear magnetic resonance spectroscopy

“…Currently, there are several screening methods for ion-imprinted polymer functional monomers: 29–31 (1) ultraviolet spectroscopy, which is the most commonly used method for screening ion-imprinted functional monomers; (2) ion simulation technology, where computer simulation software is used to simulate the interaction forces between template ions and some functional monomers and to calculate the magnitude of these forces, enabling the best functional monomers to be selected; (3) nuclear magnetic resonance spectroscopy (NMR), which can also be used to screen functional monomers. 32–36 However, these methods have some limitations. For example, ultraviolet spectroscopy is mainly suitable for the screening of functional monomers containing special functional groups; some substances without absorption peaks in the ultraviolet range cannot be screened by this method.…”

Modulating the Magnetic Dynamics of Five‐Coordinate DyIII Single‐Molecule Magnets by the Substitution Effect on the Axial Ligand

“…Moreover, some related studies have shown that tripod ligands have advantages in the construction of fivecoordinate triangular bipyramidal complexes. [27][28][29][30][31][32] Inspired by previous work, we were interested in preparing a new class of five-coordinate triangular bipyramid mononuclear Dy III -based SIMs with local D 3h symmetry. For deeper understanding of magneto-structural correlation and detailed theoretical elucidations of the dynamic magnetic behaviors in five-coordinate Dy III SIMs.…”