BF₂Complexes of β-Tetraethyl-Substituted Dipyrrolyldiketones as Anion Receptors:  Potential Building Subunits for Oligomeric Systems

Abstract

Synthesis and anion binding properties of BF2 complexes of beta-tetraethyl-substituted dipyrrolyldiketones, with and without electron-withdrawing ethoxycarbonyl moieties at pyrrole alpha-positions, are reported. The substituents at pyrrole rings of these acyclic anion receptors are found to play a key role to control not only the polarization of binding sites (NH and CH) but also the relative stabilities of the preorganized conformations and the degrees of sterical repulsion, both of which notably affect the affinities for anions.

Artificial Receptors for the Recognition of Phosphorylated Molecules

“…Further studies involving the β-tetraethyl substituted dipyrrolylketones 408c and 408d were also conducted. 485 It was found that receptor 408c displayed higher anion affinities (e.g., K (H 2 PO 4 - ) = 9.1 × 10 4 M -1 ) than receptor 408a , with the exception of fluoride. These results were attributed to the presence of a relatively stable inverted conformation in the case of 408c .…”

Supramolecular Chemistry of Acyclic Oligopyrroles

“…[35][36][37][38] Ester-appended 8e was obtained by a similar procedure with the use of ethoxycarbonyl-substituted β-diethylpyrrole as the starting material. "Blocked" derivatives 9a-c were also synthesized from 4d, 4c, and 4a, respectively.…”

Acyclic Oligopyrrolic Anion Receptors

“…35). Maeda building blocks for covalently linked oligomers due to their free a-positions [120,122,126]. In addition, receptor molecules 150-152, whose binding sites are (partially) protected, were also synthesized [121].…”

“…À , and HSO 4 À were determined from UV/vis absorption spectral changes upon the addition of anions [119,120,122,124,126]. Enhanced values were obtained for unsubstituted 144 because of the less steric hindrance at the pyrrole a-positions and for b-fluorinated derivative 149 because of the polarized NH and CH binding sites.…”

“…Maeda et al synthesized catechol-substituted receptors 153-156 (Fig. 36a) from the corresponding dipyrrolyldiketones [119,122] by treatment with BCl 3 and then with excess catechol (147). The K a values of 156 for anions are higher than those of 154, because of the electron-withdrawing effect of the nitro groups [132].…”