We report the first use of solution-phase halogen bonding to control and facilitate the assembly of an interlocked structure through the bromide anion-templated formation of a rotaxane based upon an iodotriazolium axle. The incorporation of a halogen atom into the rotaxane host cavity dramatically improves the anion-recognition capabilities of the interlocked receptor, giving unusual iodide selectivity in a competitive aqueous medium.

Cyclo[18]carbon (C 18 , a molecular carbon allotrope) can be synthesized by dehalogenation of a bromocyclocarbon precursor, C 18 Br 6 , in 64% yield, by atomic manipulation on a sodium chloride bilayer on Cu(111) at 5 K, and imaged by high-resolution atomic force microscopy. This method of generating C 18 gives a higher yield than that reported previously from the cyclocarbon oxide C 24 O 6 . The experimental images of C 18 were compared with simulated images for four theoretical model geometries, including possible bond-angle alternation: D 18 h cumulene, D 9 h polyyne, D 9 h cumulene, and C 9 h polyyne. Cumulenic structures, with ( D 9 h ) and without ( D 18 h ) bond-angle alternation, can be excluded. Polyynic structures, with ( C 9 h ) and without ( D 9 h ) bond-angle alternation, both show a good agreement with the experiment and are challenging to differentiate.

Electron-deficient heavy chalcogen atoms contain Lewis acidic σ-holes which are able to form attractive supramolecular interactions, known as chalcogen bonding (ChB), with Lewis bases. However, their potential in solution-phase anion binding applications is only just beginning to be realized in simple acyclic systems. Herein, we explore the 5-(methylchalcogeno)-1,2,3-triazole (chalcogen = Se, Te) motif as a novel ChB donor for anion binding. Other than being chemically robust enough to be incorporated into macrocyclic structures, thereby significantly expanding the scope and complexity of ChB host systems, we also demonstrate, by H NMR and DFT calculations, that the chalcogen atoms oriented within the macrocycle cavity are able to chelate copper(I) endotopically. Exploiting this property, the first examples of mechanically interlocked [2]rotaxanes containing ChB-donor groups are prepared via an active metal template strategy. Solution-phaseH NMR and molecular modeling studies provide compelling evidence for the dominant influence of ChB in anion binding by these interlocked host systems. In addition, unprecedented charge-assisted ChB-mediated anion binding was also studied in aqueous solvent mixtures, which revealed considerable differences in anion recognition behavior in comparison with chalcogen-free host analogues. Moreover, DFT calculations and molecular dynamics simulations in aqueous solvent mixtures indicate that the selectivity is determined by the different hydrophilic characters of the anions allied to the hydration of the binding units in the presence of the anions. Exploiting the NMR-active nuclei of the ChB-donor chalcogen atoms, heteronuclear Se andTe NMR were used to directly study how anion recognition influences the local electronic environment of the chalcogen atoms in the mechanically bonded rotaxane binding sites in organic and aqueous solvent mixtures.

Common anionic nucleophiles such as those derived from inorganic salts have not been used for enantioselective catalysis because of their insolubility. Here, we report that merging hydrogen bonding and phase-transfer catalysis provides an effective mode of activation for nucleophiles that are insoluble in organic solvents. This catalytic manifold relies on hydrogen bonding complexation to render nucleophiles soluble and reactive, while simultaneously inducing asymmetry in the ensuing transformation. We demonstrate the concept using a chiral bis-urea catalyst to form a tridentate hydrogen bonding complex with fluoride from its cesium salt, thereby enabling highly efficient enantioselective ring opening of episulfonium ion. This fluorination method is synthetically valuable considering the scarcity of alternative protocols and points the way to wider application of the catalytic approach with diverse anionic nucleophiles.