Are Anion/π Interactions Actually a Case of Simple Charge−Dipole Interactions?^†

Abstract

Substituent effects in Cl − ••• C 6 H 6−n X n complexes, models for anion/π interactions, have been examined using density functional theory and robust ab initio methods paired with large basis sets. Predicted interaction energies for 83 model Cl − ••• C 6 H 6−n X n complexes span almost 40 kcal mol −1 and show an excellent correlation (r = 0.99) with computed electrostatic potentials. In contrast to prevailing models of anion/π interactions, which rely on substituent-induced changes in the aryl π-system, it is shown that substituent effects in these systems are due mostly to direct interactions between the anion and the substituents. Specifically, interaction energies for Cl − ••• C 6 H 6−n X n complexes are recovered using a model system in which the substituents are isolated from the aromatic ring and π-resonance effects are impossible. Additionally, accurate potential energy curves for Cl − interacting with prototypical anion-binding arenes can be qualitatively reproduced by adding a classical charge-dipole interaction to the Cl − ••• C 6 H 6 interaction potential. In substituted benzenes, binding of anions arises primarily from interactions of the anion with the local dipoles induced by the substituents, not changes in the interaction with the aromatic ring itself. When designing anion-binding motifs, phenyl rings should be viewed as a scaffold upon which appropriate substituents can be placed, because there are no attractive interactions between anions and the aryl π-system of substituted benzenes.

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

“…[65] However, Wheeler and Houk presented that the interactions between arene and anion could not be described by quadrupole moment as quantitative predictor. [67] It is because attractive interaction between anion and the local dipole associated with the substituent in arene makes anion-p complexes energetically favorable. It is worth mentioning that the electrostatic term of anion-p interaction can also be described in terms of ESP as the quantitative predictor of anion-binding energies which are widely used to characterize p-acidity of aromatics and heterocycles.…”

“…[90] Sensors based on noncovalent p-interactions recognize anions via three modes of interactions: (1) r-interaction with partially positively-charged CH or NH of arenes (C-H 1 ÁÁÁX 2 and (2) anion-p interaction between anion and arenes with large, positive quadrupole moment (Q zz ), [21] and (3) C-H hydrogen bond with carbon atom of electron-deficient arene (Lewis acidic aromatic rings). [67,91] The r/p-anion interactions can be significantly enhanced by increasing the magnitude of electron deficiency in arene. …”

Anion-π Interactions in Supramolecular Chemistry and Catalysis

“…Therefore, a polarization contribution to the total interaction energy is derived from the interaction of the anion with the induced dipole [73][74][75][76]. An alternative explanation on the nature of anion-π interactions involving benzene rings has been proposed by Wheeler and Houk [78], who examined substituent effects in Cl − · · · · C 6 H 6 − n X n complexes. In contrast to the intuitive view where the substituent induces changes in the aryl π system, Wheeler and Houk propose a model where substituent effects in these systems can be attributed mainly to direct interactions between the anion and local C-X dipoles.…”

Anion‐π‐Wechselwirkungen ins rechte Licht gerückt

“…[88] Der direkte Vergleich analoger Kation-p-und Anion-pKomplexe zeigt allgemein, dass der Anion-p-Abstand grçßer und die entsprechende Wechselwirkung energetisch schwä-cher ist. [84] Wheeler und Houk warfen kürzlich einen anderen Blick auf die Natur der Anion-p-Wechselwirkungen mit Benzolringen, [95] indem sie Substitutionseffekte in Cl À ···C 6 H 6Àn X nKomplexen mit der DFT-Methode in Verbindung mit robus-…”