Construction of a Bifunctional Redox-Site Conjugated Covalent-Organic Framework for Photoinduced Precision Trapping of Uranyl Ions

The performance of covalent-organic frameworks (COFs) for the photocatalytic extraction of uranium is greatly limited by the number of adsorption sites. Herein, inspired by electronegative redox reactions, we designed a nitrogen-oxygen rich pyrazine connected COF (TQY-COF) with multiple redox sites as a platform for extracting uranium via combining superaffinity and enhanced photoinduction. The preorganized bisnitrogen-bisoxygen donor configuration on TQY-COF is entirely matched with the typical geometric coordination of hexavalent uranyl ions, which demonstrates high affinity (tetra-coordination). In addition, the presence of the carbonyl group and pyrazine ring effectively stores and controls electron flow, which efficaciously facilitates the separation of e-/h+ and enhances photocatalytic performance. The experimental results show that TQY-COF removes up to 99.8% of uranyl ions from actual uranium mine wastewater under the light conditions without a sacrificial agent, and the separation coefficient reaches 1.73 × 106 mL g-1 in the presence of multiple metal ions, which realizes the precise separation in the complex environment. Importantly, DFT calculations further elucidate the coordination mechanism of uranium and demonstrate the necessity of the presence of N/O atoms in the photocatalytic adsorption of uranium.

Uranyl-catalyzed hydrosilylation of para-quinone methides: access to diarylmethane derivatives

An efficient and convenient uranyl-catalyzed reductive hydrosilylation reaction of para-quinone methides (p-QMs) was developed by employing silane as the reductant. The hydrosilylation procedure using the UO2(NO3)2·6H2O/Et3SiH catalytic system proceeded smoothly and provided an expedient method for the construction of various diarylmethane derivatives in one step with good to excellent yields.

Pyrrophens: Pyrrole-Based Hexadentate Ligands Tailor-Made for Uranyl (UO22+) Coordination and Molecular Recognition

Derivatives of a novel pyrrole-containing Schiff base ligand system (called "pyrrophen") are presented which feature substituted phenylene linkers (R¹ = R² = H (H₂L¹); R¹ = R² = CH₃ (H₂L²)) and a binding pocket modeled after macrocyclic species. These ligands bind neutral CH₃OH in the solid state through pyrrolic hydrogen-bonding. The interaction of the uranyl cation (UO₂²⁺) and H₂L^1-2 yields planar hexagonal bipyramdial uranyl complexes, while the Cu²⁺ and Zn²⁺ complexes were found to self-assemble as dinuclear helicate complexes (M₂L₂) with H₂L¹ under identical conditions. The favorable binding of UO₂²⁺ over Zn²⁺ provides insight into the molecular recognition of uranyl over other metal species. Structural features of these complexes are examined with special attention to features of the UO₂²⁺ coordination environment which distinguish them from other related salophen and porphyrinoid complexes.

Complex formation between UO22+ and α-isosaccharinic acid: insights on a molecular level

This study elucidates the mutual influence of the interaction of ISA with UO₂²⁺ on their speciation, based on spectroscopic techniques.

Controlling the lability of uranyl(vi) through intramolecular π-π stacking

A reaction of UO₂²⁺ with cyclohexyldiphenylphosphine oxide (OPCyPh₂) in ethanol resulted in a perchlorate salt of the 4-fold homoleptic complex, [UO₂(OPCyPh₂)₄](ClO₄)₂·EtOH. X-ray structure determination revealed that [UO₂(OPCyPh₂)₄]²⁺ shows a highly symmetric molecular structure supported by the intramolecular π-π stacking interactions between the phenyl groups of the neighbouring OPCyPh₂ in the equatorial plane of UO₂²⁺. To clarify whether the reactivity of UO₂²⁺ is affected by such a unique coordination structure, the ligand exchange kinetics of [UO₂(OPCyPh₂)₄]²⁺ in non-coordinating solvents has been studied using an NMR line-broadening method. In CD₂Cl₂ and CD₃NO₂ solutions, both signals of coordinated and free OPCyPh₂ appeared distinctively even at 298 K, while 2D EXSY experiment provided evidence that a chemical exchange between [UO₂(OPCyPh₂)₄]²⁺ and free OPCyPh₂ occurs in these systems. Thus, this ligand exchange reaction is quite slow on the NMR time-scale. The dependency of the apparent first-order rate constant (k_obs) on temperature and the free OPCyPh₂ concentration suggested that this ligand exchange reaction involves associative and dissociative mechanisms both governed by large negative ΔS^‡ terms predominantly. Compared with the kinetic data of ligand exchange reactions of other UO₂²⁺ complexes reported so far, the lability of UO₂²⁺ in [UO₂(OPCyPh₂)₄]²⁺ is found to be significantly suppressed due to the intramolecular π-π stacking interactions as observed in the crystal structure. The DFT calculations successfully reproduced the intramolecular π-π stacking in [UO₂(OPCyPh₂)₄]²⁺ by considering the empirical dispersion corrections, and provided theoretical rationales to the A and D mechanisms of the ligand exchange reaction of [UO₂(OPCyPh₂)₄]²⁺.

Organoactinides in catalytic transformations: scope, mechanisms and Quo Vadis

The last decade has witnessed brilliant and remarkable advances in the chemistry of the early actinides in stoichiometric and in challenging catalytic processes. This canvas of knowledge allows the design of chemical reactivities reaching a high level of sophistication. This review highlights the latest results obtained since 2008 on those catalytic processes.