Bowl vs Saddle Conformations in Cyclononatriene-Based Anion Binding Hosts

Tracking the absence of anion–π interactions in modified [23](1,3,5)cyclophanes: insights from computation

[2₃](1,3,5)Cyclophanes containing 1,3,5-triazine and 1,3,5-triphosphinine planar rings present different degrees of aromaticity as well as σ-donor and π-acceptor abilities.

Towards design strategies for anion–π interactions in crystal engineering

This highlight article summarizes some of the fundamental aspects of the anion–π interaction leading to several design strategies for generating it in solids. In the main body we highlight some relevant examples that illustrate the viability of these strategies and the importance of anion–π interactions in crystal engineering.

Pd-catalyzed benzylic C–H oxidation of cyclotriveratrylene – product diversity

The inner-rim oxidation of CTV has been explored with palladium and an interesting array of CTV derivatives has been obtained by simple changes in the solvent/conditions employed.

Putting anion-π interactions into perspective

Supramolecular chemistry is a field of scientific exploration that probes the relationship between molecular structure and function. It is the chemistry of the noncovalent bond, which forms the basis of highly specific recognition, transport, and regulation events that actuate biological processes. The classic design principles of supramolecular chemistry include strong, directional interactions like hydrogen bonding, halogen bonding, and cation-π complexation, as well as less directional forces like ion pairing, π-π, solvophobic, and van der Waals potentials. In recent years, the anion-π interaction (an attractive force between an electron-deficient aromatic π system and an anion) has been recognized as a hitherto unexplored noncovalent bond, the nature of which has been interpreted through both experimental and theoretical investigations. The design of selective anion receptors and channels based on this interaction represent important advances in the field of supramolecular chemistry. The objectives of this Review are 1) to discuss current thinking on the nature of this interaction, 2) to survey key experimental work in which anion-π bonding is demonstrated, and 3) to provide insights into the directional nature of anion-π contact in X-ray crystal structures.

Pyridinium CH...anion and pi-stacking interactions in modular tripodal anion binding hosts: ATP binding and solid-state chiral induction

The preparation of two new tripodal "pinwheel" type anion hosts based on a triethylbenzene core and bipyridinium or ethylnicotinium arms is reported. The new materials bind anions via CH...anion interactions. Complexes with Br(-) and PF(6)(-) have been characterised by X-ray crystallography as both solvates in a pure form. In the bipyridinium host CH...F interactions to PF(6)(-) induce a chiral C(3) symmetric conformation that is disrupted in the hydrate. The compound is also selective for ATP(2-) in aqueous acetonitrile.

Modular assembly of a preorganised, ditopic receptor for dicarboxylates

Two types of calix[4]arene derived hosts for anions with, respectively, 1,3-alternate and cone conformations have been prepared; the 1,3-alternate system binds dicarboxylate anions in a ditopic manner while the cone compounds are deprotonated by carboxylates.

Sensing and fixation of NO2/N2O4 by calix[4]arenes

An approach toward visual detection and chemical utilization of NO(2)/N(2)O(4) is proposed, which employs simple calix[4]arenes. Exposure of tetra-O-alkylated calix[4]arenes 1 and 2, possessing either a cone or a 1,3-alternate conformation, to NO(2)/N(2)O(4), both in chloroform solution and in the solid state, results in deeply colored calixarene-nitrosonium (NO(+)) complexes. In the presence of a Lewis acid, such as SnCl(4), stable calixarene-NO(+) complexes 7 and 8 were isolated in a quantitative yield and characterized by UV-vis, FTIR, high-resolution (1)H NMR spectroscopy and elemental analysis. NO(+) is found encapsulated within the calixarene cavity, and stable charge-transfer complexes result with K(ass) > 10(6) M(-1) (CDCl(3)). The NO(+) encapsulation was also demonstrated in titration experiments with calixarenes 1, 2, and 5 and commercially available NO(+)SbF(6)(-) salt in chloroform. The complexation process is reversible, and the complexes dissociate upon addition of water and alcohol, recovering the parent calixarenes. Attachment of functionalized calix[4]arenes to silica gel was demonstrated, which afforded a solid material 15 capable of visual detection and entrapment of NO(2)/N(2)O(4). Calixarene-NO(+) complexes can be utilized for the NO(+) transfer processes and nitrosation reactions. The NO(+) guest transfer between two calixarene containers 2 and 5 was achieved and studied by UV-vis and (1)H NMR spectroscopy. Chemical fixation of NO(2)/N(2)O(4) was demonstrated through their quantitative transformation into the calixarene-NO(+) complex and its use as a nitrosonium transfer agent in the synthesis of N-nitrosoamides. These results may lead toward novel nitrogen oxides storing materials.