BF2 Complexes of β-Tetraethyl-Substituted Dipyrrolyldiketones as Anion Receptors:  Potential Building Subunits for Oligomeric Systems

Synthesis and anion binding properties of BF2 complexes of β-tetraethyl-substituted dipyrrolyldiketones, with and without electron-withdrawing ethoxycarbonyl moieties at pyrrole α-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.