Diaza-18-crown-6 Ethers Containing Partially-fluorinated Benzyl Sidearms:Effects of Covalently Bonded Fluorine on the Alkali Metal Complexation

摘要

The stability constants for the diaza-18-crown-6 ethers 2-6 and alkali metal cations(Na~+,K~+,Rb~+ and Cs~+)were determined using potentiometry in 95% methanol.For each metal ion the stability constants of the partially-fluorinated ligands 3-6 were larger than that of the non-fluorinated ligand 2,which might reflect an interaction between fluorine atoms and alkali metal cations.The stability constant of the ligand 4 was larger than that of the ligand 5 for each metal cation tested.This finding was also supported by the results of cation-induced chemical shifts in~1H-,~(19)F-NMR and extraction experiment.The potentiometry and NMR results as well as the X-ray crystal structures revealed that the position and number of fluorine atoms in the benzyl side arms was crucial for the enhanced interaction between a ligand and an alkali metal.