Putting Anion–π Interactions Into Perspective

Abstract

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.

Functional molecules and materials by π‐Interaction based quantum theoretical design

“…[2][3][4] p-Systems can noncovalently bind to diverse molecular systems. Various types of p-interactions include Hp, [5,6] p-p, [7][8][9] p 1 -p, [10] p 1 -p 1 , [11] cation-p, [7,[12][13][14] p --p, p --p -, [15] and anion-p [16][17][18][19][20][21] interactions (Fig. 1).…”

Pre-organisation or a hydrogen bonding mismatch: silver(I) diamide ligand coordination polymers versus discrete metallo-macrocyclic assemblies

“…[7][8][9][10][11][12] This birth of anion coordination chemistry 13 stems from the significant impact anions have in environmental, biological and medicinal settings. Strategies to selectively complex anions require the synthesis of hosts utilising one or more of a toolbox of interactions, 11 including hydrogen bonding donor groups, 10,12 π-acidic heteroarene scaffolds, [14][15][16][17] cationic groups for electrostatic interactions 11,18 and Lewis acidic moieties. 11 The investigation of metallo-supramolecular assemblies 5,[19][20][21][22] and coordination polymers [23][24][25] as anion receptors and for anion separation or sequestration has also received attention.…”

Enolate chemistry with anion–π interactions

“…Pertinent anion transport experiments have identified anion-p interactions 1,4 and halogen bonds 5,6 as promising candidates to contribute to the acceleration of transformations with anionic transition states. Anion-p interactions [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] are particularly intriguing because the complementary cation-p interactions are essential in biocatalysis 25,26 and are increasingly used in organocatalysis 25,27,28 . In sharp contrast, anion-p interactions are essentially unexplored in catalysis 23,24 .…”

“…To attract anions, the negative quadrupole moment of p-basic aromatics has to be inverted. This is possible with the introduction of strongly electron-withdrawing substituents 1,4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] . Popular examples are hexafluorobenzene or 2,4,6-trinitrotoluene.…”

“…However, it was not easy to confirm their functional relevance in solution 4,10,14,16 . It has been particularly demanding to differentiate anion-p interactions, that is the interaction of anions with the electron-deficient p-orbitals on p-acidic aromatic planes with positive quadrupole moment [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] , from other phenomena. Examples include lateral contacts with p-basic aromatics by C-H y anion or dipolar interactions 29 , or even charge-transfer type interactions, which relate to anion-p interactions as conjugate acid-base pairings do to hydrogen bonds 30 .…”