Capture and displacement-based release of the bicarbonate anion by calix[4]pyrroles with small rigid straps

Abstract

Two-phenoxy walled calix[4]pyrroles1and2strapped with small rigid linkers containing pyridine and benzene, respectively, have been synthesized.H-1 NMR spectroscopic analyses carried out in CDCl(3)revealed that both of receptors1and2recognize only F(-)and HCO(3)(-)among various test anions with high preference for HCO3-(as the tetraethylammonium, TEA(+)salt) relative to F-(as the TBA(+)salt). The bound HCO(3)(-)anion was completely released out of the receptors upon the addition of F-(as the tetrabutylammonium, TBA(+)salt) as a result of significantly enhanced affinities and selectivities of the receptors for F(-)once converted to the TEAHCO(3)complexes. Consequently, relatively stable TEAF complexes of receptors1and2were formedviaanion metathesis occurring within the receptor cavities. By contrast, the direct addition of TEAF to receptors1and2produces different complexation products initially, although eventually the same TEAF complexes are produced asviasequential TEAHCO(3)and TBAF addition. These findings are rationalized in terms of the formation of different ion pair complexes involving interactions both inside and outside of the core receptor framework.