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1. Ab Initio Calculations on the Ground and Excited Electronic States of Thorium–Ammonia, Thorium–Aza-Crown, and Thorium–Crown Ether Complexes

   https://doi.org/10.3390/molecules28124712  

   Lu, Zhongyuan; Jackson, Benjamin A; Miliordos, Evangelos (June 2023, Molecules)

   Positively charged metal–ammonia complexes are known to host peripheral, diffuse electrons around their molecular skeleton. The resulting neutral species form materials known as expanded or liquid metals. Alkali, alkaline earth, and transition metals have been investigated previously in experimental and theoretical studies of both the gas and condensed phase. This work is the first ab initio exploration of an f-block metal–ammonia complex. The ground and excited states are calculated for Th0–3+ complexes with ammonia, crown ethers, and aza-crown ethers. For Th3+ complexes, the one valence electron Th populates the metal’s 6d or 7f orbitals. For Th0–2+, the additional electrons prefer occupation of the outer s- and p-type orbitals of the complex, except Th(NH3)10, which uniquely places all four electrons in outer orbitals of the complex. Although thorium coordinates up to ten ammonia ligands, octa-coordinated complexes are more stable. Crown ether complexes have a similar electronic spectrum to ammonia complexes, but excitations of electrons in the outer orbitals of the complex are higher in energy. Aza-crown ethers disfavor the orbitals perpendicular to the crowns, attributed to the N-H bonds pointing along the plane of the crowns. 

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2. A Theoretical Investigation of the Selectivity of Aza-Crown Ether Structures Chelating Alkali Metal Cations for Potential Biosensing Applications

   https://doi.org/10.3390/molecules30122571  

   Elayyan, Mouhmad; Hoffmann, Mark R; Sui, Binglin (June 2025, Molecules)

   Aza-crown ether structures have been proven to be effective in constructing fluorescent biosensors for selectively detecting and imaging alkali metal ions in biological environments. However, choosing the right aza-crown ether for a specific alkali metal ion remains challenging for synthetic chemists because theoretical guidance on the chelating activities between aza-crown ethers and alkali metal ions has not been available up to now. Predicting the physical properties of the chelator–metal complexations poses a greater challenge due to the numerous quantum mechanical functionals and basis sets to be used in any theoretical investigation. In this study, we report a theoretical investigation of different aza-crown ether structures and their selectivities to alkali metal ions via a novel relationship between the binding energy and charge transfer calculated using twelve different quantum mechanical methods, using a myriad of bases, within the Jacob’s Ladder of Chemical Accuracies. Furthermore, this report represents a guide for the synthetic chemist in the selection of aza-crown ethers in the capturing of specific alkali metal ions, primary objectives, while benchmarking different quantum mechanical calculations, as a secondary objective. 

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3. Selective demethylation of O -aryl glycosides by iridium-catalyzed hydrosilylation

   https://doi.org/10.1039/D1CC00496D  

   Jones, Caleb A.; Schley, Nathan D. (June 2021, Chemical Communications)

   null (Ed.)

   The cleavage of alkyl ethers by hydrosilylation is a powerful synthetic tool for the generation of silyl ethers. Previous attempts to apply this transformation to carbohydrate derivatives have been constrained by poor selectivity and preferential reduction of the anomeric position. O -Aryl glycosides are found to be stable under iridium- and borane-catalyzed hydrosilylation conditions, allowing for alkyl ether cleavage without loss of anomeric functionality. A cationic bis(phosphine)iridium complex catalyzes the selective 3-demethylation of a variety of 2,3,4-tri- O -methyl pyranoses, offering a unique approach to 3-hydroxy or 3-acetyl 2,4-di- O -methylpyranoses. 

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4. Synthesis and Electrochemical Studies of Nickel Complexes with a Flexidentate Bipyridine-aza-crown Ether Ligand

   https://doi.org/10.26434/chemrxiv-2024-l9608  

   Acosta-Calle, Sebastian; Huebsch, Elsa; Halenda, Jenna; Stuart, Zoe; Chen, Chun-Hsing; Miller, Alexander (September 2024, American Chemical Society)

   Bipyridine ligands have been extensively employed in nickel catalysis, with ligand modifications focused on steric or electronic tuning. In this work, we explore modifications designed to modulate the coordination mode using a 2,2'-bipyridine derivative with an appended aza-crown ether macrocycle capable of flexidentate binding to nickel. A series of complexes varying in charge from neutral to dicationic demonstrates the flexibility of the macrocycle, with bipyridine-aza-crown ether denticity changing from к4 to к6 upon sequential abstraction of chloride ligands. The changes in binding mode can be reversed by addition of chloride ion. Comparisons between the macrocycle-containing ligand and an analogous ligand with a non-macrocyclic diethylamine donor provide insight into the role of the crown ether, including in electrochemical reductions probed via cyclic voltammetry. 

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5. Conversion of esters to thioesters under mild conditions

   https://doi.org/10.1039/D1OB00187F  

   Shi, Yijun; Liu, Xuejing; Cao, Han; Bie, Fusheng; Han, Ying; Yan, Peng; Szostak, Roman; Szostak, Michal; Liu, Chengwei (April 2021, Organic & Biomolecular Chemistry)

   null (Ed.)

   We report conversion of esters to thioesters via selective C–O bond cleavage/weak C–S bond formation under transition-metal-free conditions. The method is notable for a general and practical transition-metal-free system, broad substrate scope and excellent functional group tolerance. The strategy was successfully deployed in late-stage thioesterification, site-selective cross-coupling/thioesterification/decarbonylation and easy-to-handle gram scale thioesterification. Selectivity and computational studies were performed to gain insight into the formation of weak C–S bonds by C–O bond cleavage, which contrasts with the traditional trend of nucleophilic additions to carboxylic acid derivatives. 

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