Abstract
Herein, we present the synthesis and anion binding studies of a family of homologous molecular receptors 4–7 based on a DITIPIRAM (8-propyldithieno-[3,2-b:2′,3′-e]-pyridine-3,5-di-amine) platform decorated with various urea para-phenyl substituents (NO2, F, CF3, and Me). Solution, X-ray, and DFT studies reveal that the presented host–guest system offers a convergent array of four urea NH hydrogen bond donors to anions allowing the formation of remarkably stable complexes with carboxylates (acetate, benzoate) and chloride anions in solution, even in competitive solvent mixtures such as DMSO-d6/H2O 99.5/0.5 (v/v) and DMSO-d3/MeOH-d3 9:1 (v/v). The most effective derivatives among the series turned out to be receptors 5 and 6 containing electron-withdrawing F- and -CF3 para-substituents, respectively.
Highlights
IntroductionNeutral anion receptors have generally an advantage over the positively charged systems due to their much higher selectivity, despite the lower stabilities of receptor–anion complexes
Cholewiak-Janusz, A.; Jurczak, J.For over twenty years, many groups working in the field of supramolecular chemistry have made substantial efforts to restore the parity between the molecular chemistry of anions and cations
Our results proved DITIPIRAM to be an excellent choice as a platform for putative anion receptors
Summary
Neutral anion receptors have generally an advantage over the positively charged systems due to their much higher selectivity, despite the lower stabilities of receptor–anion complexes These result from the presence of binding groups such as hydrogen bond donors, which allow for the establishment of highly directional interactions with the anion [30–36]. The structure of acyclic receptors is generally tunable, allowing facile post-functionalization (to increase the binding affinity or to modify selectivity) compared to macrocyclic architectures Among other factors, this turned researchers’ attention to the acyclic systems in the molecular recognition of anions [37–40]. Considering the above-mentioned conditions, 8-propyldithieno [3,2-b:20 ,30 -e]pyridine3,5-diamine (DITIPIRAM) (1) fits perfectly to the role of the platform for designing potent acyclic receptors for anions (Figure 1) This unique building block was recently introduced by us into supramolecular chemistry [41]. Our results proved DITIPIRAM to be an excellent choice as a platform for putative anion receptors
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