Structure-alkali metal cation complexation relationships for macrocyclic PNP-lariat ether ligands

Water-insoluble, mono- and diarmed PNP-lariat ethers containing various aryloxy and regioisomerically-positioned binaphthylylenedioxy substituents linked to the phosphorus atoms of the cyclophosphazene ring via oxygen atoms are synthesized by regioselective, sodium ion-assisted arylolysis of tetrachloro-16-PNP-6 crown ether 1. Heterogeneously-substituted, mixed aryloxy-amino PNP-lariat ethers and bis-lariat ethers with two different substituents linked to the PNP-macrocycle via an oxygen and a nitrogen atom are prepared by stepwise arylolysis and aminolysis reactions of 1. The alkali-metal cation complexation behavior of the PNP-lariat ethers is evaluated in solvent polymeric membrane electrodes. The PNP-lariat and bis-lariat ethers exhibit pronounced selectivity for large alkali metal cations (Rb+ and Cs+) over small ones (Li+ and Na+). The selectivity is influenced by the configuration of the crown ether ring and the number of oxygen donor atoms in the ligand. For some PNP-lariat ethers, evidence for formation of 2 : 1 (ligand-metal ion) complexes with Rb+ and Cs+ is provided by ESI-MS.