Synthesis and complexing ability of a C-pivot type of double-armed 15-crown-5 ethers toward alkali metal cations

Three kinds of positional isomers of the C-pivot type of double-armed 15-crown-5 ethers (cis and trans isomers for each positional isomer) bearing two 8-quinolyloxy moieties as part of the electron-donating sidearms were prepared, and their complexation properties were evaluated by measuring the stability constant in THF, the extractability, and passive transport velocity. Cis isomers were found to be much better host compounds toward alkali metal cations than trans isomers possibly because of the potential cooperative coordination of two electron-donating sidearms. All trans isomers showed almost the same stability constants toward Na+ and K+. On the other hand, in the case of cis isomers, the difference in the position of the two sidearms on the crown ring was found to remarkably affect the complexation properties toward alkali metal cations.