1,2,3-Triazoles and the Expanding Utility of Charge Neutral CH···Anion Interactions

Abstract

As the field of anion supramolecular chemistry continues to grow in its sophistication and understanding of the noncovalent interactions used to effectively bind anions, there exists new theoretical and experimental evidence for a necessary reexamination of the way in which the field views hydrogen bond donors. The heteroatom based hydrogen-bond donors (e.g., NH and OH) are well-known to provide strong stabilization to negatively charged species. However, new findings point to the untapped stabilization energy that lay dormant in extrinsically-activated CH hydrogen bonds. Computational studies showed that an activated aliphatic or aromatic CH can provide an amount of anion stabilization in the gas phase approaching that of conventional NH based donors. Discovery of the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition to provide 1,2,3-triazoles and the ability to readily "click" this functionality into anion receptors has allowed extensive experimental investigation of the ideas posed by these calculations. This chapter will focus on the evolution of the CH hydrogen bond from being viewed as a weak, secondary interaction to now being utilized as a powerful source of anion stabilization in macrocyclic and oligomeric receptors. In addition, the application of the anion binding power of the 1,2,3-triazole towards the preparation of mechanically interlocked structures will also be discussed.

Substituent Effects in CH Hydrogen Bond Interactions: Linear Free Energy Relationships and Influence of Anions

“…1,2 CH donors play important and previously unrecognized roles in the multidisciplinary fields of molecular biology, supramolecular chemistry, 3–5 and catalysis. 1,6 CH⋯O HBs are common in protein folding and are found in the minor groove of DNA.…”

Anion Receptors Based on Organic Frameworks: Recent Advances

“…In 2008, Li and Flood reported the synthesis of macrocycles containing 1,2,3-triazole heterocycles as C-H hydrogen bond donors for the complexation of anions [3][4][5]. The initial report of the synthesis of compound 1 (Scheme 1) [4] included an UV/vis titration study of this compound with tetrabutylammonium chloride in dichloromethane which demonstrated that the macrocycle binds chloride with a stability constant of 130,000 AE 30,000 M À1 .…”

Pyrrole N–H anion complexes

“…The use of CH-derived hydrogen bonding as a motif for anion recognition was first demonstrated experimentally using other classes of receptors [61]. …”