Synthesis of cesium selective pyridyl azocalix[n]arenes

Abstract A series of pyridylazo calix[ n ]arenes ( n =4, 6, 8) including the first examples of mixed hetroaryl azocalix( n )arenes have been synthesized by coupling calix[ n ]arenes with diazonium salts derived from amino pyridines. It has been observed that the coupling reaction of diazonium salt obtained from 3-aminopyridine with calix[ n ]arene gives tetrakis-, hexakis- and octakis (pyridylazo)calix[ n ]arenes ( n =4,6,8) while those derived from 4-aminopyridine give partially substituted (4-pyridylazo)calix[ n ]arene analogs. There is no reaction of calix( n )arenes with diazonium salts derived from 2-aminopyridine under identical conditions of experiments. The conformational analysis of synthesized compounds have been ascertained by detailed spectral measurements and single crystal X-ray analysis of 5-(3′-pyridylazo)-25,26,27,28-tetrahydroxycalix[4]arene. A rational explanation for the observed partial and exhaustive coupling reaction in the synthesis of heteroaryl azocalix( n )arenes has been suggested. Preliminary evaluation of synthesized derivatives as molecular receptors for metal ions indicates that they have good potential to function as selective ionic filters for cesium ions.