Anionic tert-butyl-calix[4]arenes substituted at the narrow and wide rim by cobalt bis(dicarbollide)(1−) ions and CMPO-groups. Effect of stereochemistry and ratios of the functional groups on the platform on the extraction efficiency for Ln(III)/An(III)

Abstract

Two ionic calix[4]arenes substituted at the narrow rim with an unpaired number (n) of cobalt bis(dicarbollide)(1−) anions (1−) (n = 1 and 3) and (4 − n) CMPO groups (3c, 4c) have been synthesized via a three-step procedure based on nitrile substituted calix[4]arene precursors. Conjointly with them, the compound with a paired ratio of the groups, where n = 2 and the same substituents are located in mutually adjacent 1,2-positions, is reported (5c). Another compound with the paired ratio, but from a wide rim series (6c) (n = 2) was successfully prepared starting from calix[4]arenes substituted with two nitro functions and two –OH sites available for further modifications. The reaction steps included, a) O-alkylation of the hydroxy functions present on the same rim by the 1-dioxane derivative [8-O(CH2CH2)2O(+)-1,2-C2B9H10)-(1′,2′-C2B9H11)-3,3′-Co] (2) used as the reactive building block resulting in the respective ionic nitriles (3a–5a) or nitro compound (6a); b) Reduction of the nitrile or nitro function(s) to the respective amino/ammonio derivatives (3b–6b) using either a BH3SMe2 or Pd catalyzed reaction with hydrazine hydrate (for 6b); c) the ammonio functions in these derivatives were subsequently converted to CMPO group(s) by the reaction with nitrophenyl ester of diphenylphosphoric acid. Pure cone conformers were isolated in moderate to good yields. The extraction properties for the An(III)/Ln(III) group of elements have been studied. The new ionic calixarenes still proved highly efficient extraction properties for M3+, but lower than the previously reported lower rim calixarene with n = 2, used here as the reference compounds R-7 and R-8 for comparison. This observation further confirms that the preorganization of the two functions (ion 1− and CMPO) in the paired ratios and in alternating fashion at calixarene low rim has the unique character for attaining the highest extraction efficiency.