Dibutylphosphinoylmethyloxythiacalix[4]arenes. Synthesis, structure, americium, europium and technetium extraction

Abstract

<div><p>A series of thiacalix[4]arenes bearing one, two or four chelating dibutylphopshinoylmethoxy groups have been synthesised and studied in the context of this paper. The synthesis consisted of precise Williamson alkylation of thiacalixarene tetrols with tosylate of dibutylhydroxymethyl phosphine oxide in the presence of alkali metal carbonates or sodium hydride. Stereochemical yield of the reaction (<i>cone</i> or 1,3-<i>alternate</i> conformer) depends on the nature of alkali metal. Small-sized ‘hard’ sodium cation organises the macrocyclic platform in the <i>cone</i> conformation, but larger and ‘soft’ potassium and cesium cations stabilise the macrocycle in the <i>1,3</i>-<i>alternate</i> conformation. All synthesised compounds (except monophosphine monoxide) possess either moderate or high extraction ability towards pertechnetate ion. The <i>cone</i>-shaped thiacalix[4]arene tetraphosphine tetraoxide due to cooperative (macrocyclic) effect of eight oxygen atoms of the phosphinoylmetoxy-binding groups effectively extract spherical americium, europium cations due to cooperative (macrocyclic) effect of eight oxygen atoms of the phosphinoylmetoxy-binding groups. The extraction ability is very similar to that of calix[5]arene pentaphosphine pentaoxide existing in the <i>cone</i> conformation.</p></div