Phosphorus-containing podands. 9. Synthesis of oligoethylene glycol bis(diphenylphosphinylethyl) esters and their complexing properties with respect to alkali metal cations in a low-polarity solvent

The complexing ability of phosphoryl-containing monopodands with the general formula Ph2P(O)CH2CH2O(CH2CH2O)nCH2CH2P(O)Ph2 (n=0–5, 6.4, 8.7, 13.2) with respect to alkali metal cations was investigated conductometrically in tetrahydrofuran:chloroform mixed solvent (4:1, vol.) at 25°C. It was found that ligands of this type are efficient complexing agents relative to all alkali metal cations, and the monopodand with n=0 also exhibits elevated Li/Na and Li/K selectivity. The effect of the structure, particularly the "rigidity" of the terminal fragments of the monopodands, on their complexing capacity was discussed. The method of synthesis of this type of ligand was described.