Tetrakis(methylimidazole) and tetrakis(methylimidazolium) calix[4]arenes: competitive anion binding and deprotonation

Abstract

Neutral tetrakis(methylimidazole) (1) and the novel cationic tetrakis(methylimidazolium) (2) calixarenes have been prepared and their solid-state and solution behaviour examined. The neutral imidazole forms a mono-zwitterion at elevated temperature, a feature that has been observed both in solution and in the solid-state. The cationic imidazolium exhibits a range of hydrogen bond interactions with anions, with the titration curves upon binding to basic anions suggesting sequential binding to both the upper and lower rims.

Electrochemical Synthesis of a Tetradentate Copper N-Heterocyclic Carbene Calix[4]arene and Its Transmetalation to Palladium: Activity of the Palladium Complex in Suzuki–Miyaura Cross-Coupling

“…Imidazolium units are effective anion receptors, due to their strongly ionic hydrogen bonding [(C–H) + ····X – ] interactions . Bis-, tris-, and tetrakis(imidazolium) receptors built around calix[4]arene anchors have been prepared and their anion binding properties reported. − Preorganized cavities such as calixarenes can lead to selectivity, and a conformational change upon binding may bring about a photophysical, colorimetric, or electrochemical response . Imidazolium units also serve as precursors to N-heterocyclic carbenes (NHCs).…”

Structural Diversity of Copper(I)–N‐Heterocyclic Carbene Complexes; Ligand Tuning Facilitates Isolation of the First Structurally Characterised Copper(I)–NHC Containing a Copper(I)–Alkene Interaction

“…The presence of anion-interactions in these structures may facilitate the use of imidazolium salts as anion-binders. [36,37] Reaction should be taken when interpreting the ESI+ mass spectra of copper(I)-NHC complexes, since their labile nature can lead to ligand scrambling resulting in the appearance of bis-NHC species in samples of pure mono-NHC compounds. This ligand scrambling behaviour is well documented for silver(I)-NHC complexes.…”

Colorimetric and Luminescent Sensors for Chloride: Hydrogen Bonding vs Deprotonation

“…a color change, are modulated by addition of the external analyte has become a popular method of sensing chemical species . Anion recognition has been successfully achieved through the use of numerous neutral receptors including imidazoles, , pyrroles, calixarenes, amides, ureas, − thioureas, − amidothioureas, and recently thiosemicarbazides leading to a large body of research in the area. More recently, a characteristically different class of compounds, the squaramides, have been explored for their molecular recognition properties .…”