Alkali Metal Complexation. Binding Properties of cone and partial-cone Calix[4]arenes Bearing a Mixed (O 2 , O 2 ') Donor Set (O = Phosphine Oxide; O ' = Amide or Ester)

The stability constants of alkali metal complexes obtained from the followingO-substituted calix4]arenes were determined by UV/Vis spectroscopy inmethanol at 20°C: 5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-bis(diphenylphosphinoylmethoxy)calix4]arene(cone-1), 25,27-syn-26,28-anti-5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-bis(diphenylphosphinoylmethoxy)calix4]arene (paco-1),5,11,17,23-tetra-tert-butyl-25,27-diethoxycarbonylmethoxy-26,28-bis(diphenylphosphinoylmethoxy)calix4]arene(cone-2) and25,27-syn-26,28-anti-5,11,17,23-tetra-tert-butyl-25,27-diethoxycarbonylmethoxy-26,28-bis(diphenylphosphinoylmethoxy)calix4]arene(paco-2). All ligands form 1:1 complexes with alkali metal cations. The amide-containing calixarenes were found to be more efficient for alkali metalcomplexation than those bearing ester substituents. While sodium ions are selectivelycomplexed by the two mixed amide-(phosphine oxide) calixarenes, the twoester-containing isomers cone-2 and paco-2 turned out to be selective towards potassium and rubidium ions, respectively. With allfour ligands the lowest stability constants were found for the lithium andcesium ions.