Synergistic effects of macrocyclic polyethers and converging anionic binding sites : Synthesis of biphenyl crown ethers and lipophilization of divalent cations

The synthesis of nine novel macrocyclic polyethers with a 1,1'-biphenyl subunit is described. Crown ethers 2,4,5 and 7 have substituents with terminal acid groups at the 4- and 4'- positions of the 1,1'-biphenyl subunit and crown ethers 9, 11, 12 and 14 have similar substituents at the 3- and 3'-positions. In the ionic form these crown ethers extract divalent cations (Ca²⁺, Sr²⁺ and Ba²⁺) from basic aqueous solutions into chloroform. The degree of lipophilization varies with the size of the cation and of the crown ether cavity, with the position and the length of the substituents and with the nature of the terminal acid groups. ¹H NMR spectroscopic data of the complexes in chloroform are in agreement with a structure of the complexes in which the cation is encapsulated by oxygen atoms and anionic groups.