Recognition of Achiral and Chiral Ammonium Salts by Neutral Ditopic Receptors Based on Chiral Salen-UO(2) Macrocycles

Amononuclear (M20) and a dinuclear (M40) uranyl chiral macrocyclic complex, incorporating both a salen unit containing two phenyl rings linked to a chiral diimine bridge and the (R)-BINOL unit,behaves as an efficient ditopic receptor for achiral and chiral quaternary ammonium salts. Binding affinities in chloroform solution have been measured for 1:1 complexes of many quaternary saltsencompassing tetramethylammonium (TMA), tetraethylammonium (TEA), tetrabutylammonium(TBA), and acetylcholine (ACh), as well as trimethylanilinium (TriMAn), benzyltrimethylammonium(BnTriMA), (R-methylbenzyl)trimethylammonium and pyrrolidinium cations. The anion ofthe salt is bound by the hard Lewis acidic uranyl site, with an increasing binding efficiency onincreasing the anion hardness (I-