Tetrathiafulvalene-Calix[4]pyrroles:  Synthesis, Anion Binding, and Electrochemical Properties

Abstract

The syntheses of monotetrathiafulvalene-calix[4]pyrrole 5 and bistetrathiafulvalene-calix[4]pyrrole 6, prepared from the acid-catalyzed condensation of monopyrrolo[3,4-d]tetrathiafulvalene (MPTTF, 7) with acetone in the presence of tripyrrane 8 and dipyrromethane 9, respectively, are described. Compound 5 and the previously reported tetrathiafulvalene-calix[4]pyrrole 4 both adopt a 1,3-alternative conformation in the solid state, as determined from X-ray crystallographic analysis. The anion binding properties of the tetrathiafulvalene-calix[4]pyrroles 5 and 6, as well as those of the parent meso-octamethylcalix[4]pyrrole (1), were investigated in acetone using (1)H NMR spectroscopic and isothermal titration calorimetry (ITC) techniques and, within the error limits of the methods, were generally found to give concordant results. On the basis of the results of the ITC studies carried out in 1,2-dichloroethane, increasing the number of tetrathiafulvalene units annulated to the calix[4]pyrrole system serves to enhance the anion binding affinities substantially but at the price of lowered selectivity. Cyclic voltammetry (CV) studies, carried out in 1,2-dichloroethane, provided evidence of an anion-dependent electrochemical response with Cl(-) and Br(-) ions. This response was particularly dramatic in the case of the monotetrathiafulvalene-calix[4]pyrrole 5, with a DeltaE(max) of -145 mV being seen after the addition of approximately 1 equiv of Cl(-) ion.

Supramolecular Receptor Design: Anion‐Triggered Binding of C60

“…[39,40] As is true for most other calix [4]pyrroles, 1 exists (Figure 1 B) predominantly in the 1,3-alternate conformation in the absence of anions. However, in halogenated solvents 1 binds chloride anions very tightlya binding constant (K a ) of 2.5 10 6 m À1 has been reported [39,40] for the complexation of 1 with chloride ions in 1,2-dichloroethane (DCE) at 298 K, thus leading it to adopt (Figure 1 C) a bowl-like conformation. In the case of 1, the resulting bowlshaped receptor system possesses TTF-derived electron-rich "walls" and was thus expected to act as a receptor for electron-deficient spherical guests such as fullerene, for example.…”

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

“…Analysis of the UV-Vis spectroscopic data [68] provided a binding constant of 11,000,000 M À1 (CH 2 Cl 2 , 298 K), which rivaled [69] and, in some cases, exceeded [70] receptors utilizing traditional hydrogen bond donors under the same conditions. The inherent size selectivity built into the macrocyclic receptor through its preorganized structure was mapped through titrations of various halides (F À , Br À and I À ).…”

Detection of Nitroaromatic Explosives Using Tetrathiafulvalene‐Calix[4]pyrroles

“…These N-H•••X -interactions switch the receptor from the 1,3-alternate conformation, which favors TNB binding, to the corresponding cone conformation, which lack binding sites toward TNB [25,27].…”