Synthesis, Structural Characterization and Complexation Properties of the First "Crowned" Dipyrrolylquinoxalines

• Published in: European journal of organic chemistry Vol. 2002; no. 22; pp. 3768 - 3778
• Main Authors: Kirkovits, Gregory J., Zimmerman, Rebecca S., Huggins, Michael T., Lynch, Vincent M., Sessler, Jonathan L.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.11.2002; WILEY‐VCH Verlag; Wiley
• Subjects: Chemistry; Chemistry, Organic; Crown compounds; Host-guest chemistry; Hydrogen bonds; Physical Sciences; Science & Technology; Supramolecular chemistry; ION-PAIR; FLUORIDE ANION; FACILITATED TRANSPORT; RHENIUM(I) BIPYRIDYL; SELECTIVE RECOGNITION; NEUTRAL ANION RECEPTORS; host-guest chemistry; DITOPIC CARRIERS; hydrogen bonds; SOLVENT-EXTRACTION; crown compounds; supramolecular chemistry; BINDING
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/1099-0690(200211)2002:22<3768::AID-EJOC3768>3.0.CO;2-R

The synthesis of four crown‐substituted dipyrrolylquinoxalines 1−4 is reported. The key step in the synthesis is reaction of a 1,2‐diaminobenzocrown with 1,2‐bis(1H‐pyrrol‐2‐yl)ethanedione (20). A single crystal X‐ray diffraction analysis of the 18‐crown‐6‐dipyrrolylquinoxaline 1 revealed that this molecule forms a tetramer centered around a single molecule of water, with no fewer than 10 hydrogen bonds holding the supramolecular structure together. In the case of the 15‐crown‐5‐dipyrrolylquinoxaline 2, however, X‐ray diffraction analysis revealed that this species exists as a dimeric pair in the solid state, with the NH protons of one pyrrole lying within hydrogen‐bonding distance of two oxygen atoms on an adjacent crown ether. A second single crystal structure of 2 was solved; it demonstrated that this system is able to coordinate a potassium cation, thereby forming an intermolecular sandwich complex, at least in the solid state. In [D6]acetone solution receptor 2 and congeners 1, 3 and 4 were also found to complex sodium and potassium cations within the crown diethyl ether binding sites, in a 1:1 manner as judged by 1H NMR spectroscopic analyses. Although systems 1−4 appear to bind fluoride anion as well as cations, the inability to obtain quantitative binding affinities of 1−4 with fluoride anion rendered the evaluation of the systems for cooperative binding impossible. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)