A pair of homologous and soluble reversible polymers display nearly identical solution structures but dramatically different dissociation dynamics (1.0 vs ca. 100 s-1) along their main chains. The polymers are formed by organopalladium-pyridine coordination, and steric effects at the metal center control the dynamics. Importantly, the association constant is not significantly affected by the sterics. The resulting orthogonal control over dissociation kinetics provides a general tool for studying the effects of dynamics independent of thermodynamics in supramolecular systems, particularly main-chain reversible polymers.

Manipulation of weak intermolecular interactions guides the rational design [1] of sensors, drugs, and foldamers-synthetic, [2] nonnatural backbones that fold into an ordered, biomimetic array. 1,4-Substituted 1,2,3-triazoles, which are readily accessible through the Cu I -catalyzed Huisgen 1,3-dipolar cycloaddition of azides and alkynes, [3] are seemingly universal ligation tools [4] whose capacity for independent function has received far less attention. Recent reports, however, indicate that the size and dipole moment ( % 5 D) of triazoles make them interesting candidates for amide bond surrogates, [5] and Arora and co-workers have reported the contributions of triazoles to the conformational preferences of peptidotriazole oligomers. [6] We hypothesized that oligomer 1 would fold in a manner similar to other linear, flexible oligomers [7] to provide a model cavity by which to explore the intermolecular interactions between the electropositive CH side of 1,4-triazoles and electron-rich guests such as anions ( Figure 1). Our expectations were buoyed by previous reports of anion-induced folding, [8,9] in particular by a recent demonstration by Jeong and co-workers [8] that the folding of oligoindoles can be directed through a helical arrangement of NH···anion hydrogen bonds. Herein, we report 1) that 1:1 interactions between diaryl triazoles and chloride ions in acetone are directional and sufficiently strong as to be observable by 1 H NMR spectroscopy, 2) that the strength of the interaction increases with the generation of triazole-containing oligomer, and 3) that CH···anion contacts guide the folding of aryl triazole oligomers in solution and in the solid state.While the "click" coupling of alkyl azides with alkynes is highly efficient, [10] the formation of diaryl triazoles has, until recently, been relatively more difficult and less efficient. [11] Nonetheless, under modified conditions, the Cu I -catalyzed cycloaddition produces acceptable yields of the desired 1,4-diaryl-1,2,3-triazole-containing compounds 1-3. A tetraethylene glycol unit was introduced outside of the cavity for solubility.Oligomer 1 has appreciable conformational freedom only around the arene-triazole single bonds. Molecular modeling [12] suggested no significant preference for a particular rotamer, a prediction that is supported by NOESY spectra of 1 in [D 6 ]acetone (Figure 2 a). Modeling studies also show that complexation of 1 with Cl À aligns the electropositive triazole CH units toward the interior of a helix, within which the Cl À is bound.The computer modeling holds true in solution, where the chloride-induced folding of 1 is revealed by 1 H NMR spectroscopy. The 1 H NMR spectrum of 1 changes considerably upon the addition of tetrabutylammonium chloride

This tutorial review provides a summary of anion-mediated folding of linear and cyclic oligomers as well as anion-responsive behaviours of related polymeric architectures. Anions have emerged as a significant focus of the supramolecular community and here we review their impact on directing the secondary structures of synthetic oligomers and polymers while modulating physical properties e.g. molecular recognition. Oligomers and polymers responsive to anionic guests are typically constructed with hydrogen bond donors complementary to the target anions. Anion binding within the cavities leads to folding and helical wrapping of linear and cyclic oligomers as well as control over macromolecular properties of polymers. This review covers the impact of anion binding on guiding the secondary structures of single-stranded folded oligomers (foldamers) and cyclic oligomers (macrocycles), and on modulating the physical properties of select polymer architectures.

The flexible, electropositive cavity of linear 1,4-diaryl-1,2,3-triazole oligomers provides a suitable host for complexation of various anions. The binding affinities for various combinations of oligomer and anion were determined by (1)H NMR titrations. Effective ionic radius is found to be a primary determinant of the relative binding interactions of various guests, with small but measurable deviations in the case of nonspherical anions. Solvent effects are significant, and the strength of the binding interaction is found to depend directly on the donor ability of the solvent. A picture emerges in which anion binding can be effectively interpreted in terms of a competition between two solvation spheres: one provided by the solvent and a second dominated by a folded cavity lined with electropositive 1,2,3-triazole CH protons. Implications for rigid macrocycles and other multivalent hosts are discussed.