CATION COMPLEXATION BY CHEMICALLY-MODIFIED CALIXARENES - 11 - COMPLEXATION AND EXTRACTION OF ALKALI CATIONS BY CALIX[5]-ARENE AND CALIX-[6]ARENE KETONES - CRYSTAL AND MOLECULAR-STRUCTURES OF CALIX[5]ARENE KETONES AND NA+ AND RB+ COMPLEXES

A series of four calix[5]arenes and three calix[6]arenes (R-calixarene -OCH2COR1) (R = H or Bu-t) with alkyl ketone residues (R-1 = Me or Bu- t) on the lower rim have been synthesized, and their affinity for comp lexation of alkali cations has been assessed through phase-transfer ex periments and stability constant measurements. The conformations of th ese ketones have been probed by H-1 NMR and X-ray diffraction analysis , and by molecular mechanics calculations. Pentamer 3 (R R-1 = Bu-t) p ossesses a symmetrical cone conformation in solution and a very distor ted cone conformation in the solid state. Pentamer 5 (R = H, R-1 = Bu- t) exists in a distorted 1,2-alternate conformation in the solid state , but in solution two slowly interconverting conformations, one a cone and the other presumed to be 1,2-alternate, can be detected. X-ray st ructure analysis of the sodium and rubidium perchlorate complexes of 3 reveal the cations deeply encapsulated by the ethereal and carbonyl o xygen atoms in distorted cone conformations which can be accurately re produced by molecular mechanics calculations. The phase-transfer and s tability constant data reveal that the extent of complexation depends on calixarene size and the nature of the alkyl residues adjacent to th e ketonic carbonyls with tert-butyl much more efficacious than methyl.