PENTAMACROCYCLIC TRIS-CROWN HOSTS - SELECTIVE BINDING OF CATIONIC, ANIONIC, AND NEUTRAL GUEST COMPOUNDS

Pentamacrocyclic Tris‐Crown Hosts. – Selective Binding of Cationic, Anionic, and Neutral Guest Compounds The tris‐crown host compounds 1–4 were synthesized for the first time. The X‐ray crystal structures of 2 and of the 1:3 complex of 1 and KSCN were determined. Whereas in the free crown 2 a less well preorganized molecular cavity is encountered, in the complex of 1 with KSCN one potassium ion is bound to each crown ether unit. One of the three SCN− anions is situated in the interior of the cavity and in addition is disordered in such a way as to be bound to the K+ using partially the S atom of the SCN− ion. Organic guest molecules like 1,2‐, 1,3‐, 1,5‐, 2,6‐, and 2,7‐naphthalenediol as well as β‐naphthol in acidic water solution are bound selectively in the interior of the cavities of the host molecules 2 and 3, but not by 1 and 4, the cavities of which seem to be too small and too large, respectively. In contrast, the binding of α‐naphthol and of smaller phenolic guest molecules like phenol, resorcinol, pyrocatechol, phloroglucinol, pyrogallol, and 1,2,4‐trihydroxy‐benzene with the host 1–4 is much less pronounced (1H‐ NMR highfield shifts). Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim