Sigma-Hole Interactions in Anion Recognition

Abstract

Sigma (s)-holes are electron-deficient regions that arise from the anisotropic distribution of electron density on the atom of group 14 (tetrels), 15 (pnictogens), 16 (chalcogens), and 17 (halogens) elements when covalently bonded to electron-withdrawing groups. Named after the donor atom's group, the s-hole interactions, halogen bonding, and chalcogen bonding with anionic species have found ground-breaking applications in anion supramolecular chemistry within the last decade. In this review, we feature key recent discoveries and advances across the whole range of s-hole interactions for anion recognition, from the familiar halogen bonding to the almost unknown pnictogen and tetrel bonding. In particular, the novel anion recognition properties and applications that result from the unique aspects of each s-hole interaction, together with detailed design considerations of anion-binding receptor motifs, are highlighted.

Chalcogen‐Bonding Catalysis: From Neutral to Cationic Benzodiselenazole Scaffolds

“…The large, polarizable, almost directionless π surface offered by anion‐ π interactions appears ideal to stabilize anionic transition states that involve charge displacements over longer distances, e.g ., cascade cyclizations . The advantages of σ ‐hole interactions, the unorthodox counterpart of hydrogen bonds, appear almost complementary: More hydrophobic and directional than hydrogen bonds, they should be ideal for high‐precision catalysis in apolar media.…”

“…Originating from anti‐bonding σ * orbitals, chalcogen bonds extend linearly from the covalent bonds (bond angle Φ 1 ~ 180°) and thus appear on the side of the chalcogen atom (bond angle Φ 2 ~ 70°, Figure ,a ) . They have been studied extensively in crystal engineering and for intramolecular conformational control in solution, including prominent use in medicinal chemistry and pioneering applications in covalent catalysis . The use of intermolecular chalcogen bonds in functional systems in solution is rare and recent, non‐covalent chalcogen‐bonding catalysis has been introduced only last year.…”

“…They have been studied extensively in crystal engineering and for intramolecular conformational control in solution, including prominent use in medicinal chemistry and pioneering applications in covalent catalysis . The use of intermolecular chalcogen bonds in functional systems in solution is rare and recent, non‐covalent chalcogen‐bonding catalysis has been introduced only last year. [ ][ ][ ] The key to success was the idea that the somewhat awkwardly ‘hidden’ position of the σ holes on the side of chalcogen‐bond donors turns into an advantage as soon as transition‐state recognition in the focal point of two adjacent donors is considered .…”

Anion Recognition by Neutral Chalcogen Bonding Receptors: Experimental and Theoretical Investigations

“…Chalcogen bonding (ChB) is a subgroup of the σ‐hole family that originates from the interaction between an electron‐rich atom or group of atoms and the σ‐hole of an element belonging to group 16 . In fact, chalcogen bonding has been recently defined by a IUPAC commission as “net attractive interaction between an electrophilic region associated with a chalcogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity” .…”

“…In fact, these distinctive characteristics of ChBs have been used in crystal engineering, pharmaceutics, catalysis, anion transport, self‐assembly processes, and materials design . However, studies of ChB interactions in solution remain scarce . For instance, Zibarev et al .…”