Functionalization of organophosphazene trimers: synthesis and characterization of hexakis(dicarboxylic amino acid ester)cyclotriphosphazenes and their salt derivatives

Abstract

New cyclotriphosphazenes fully substituted with dicarboxylic amino acid esters (aminomalonate, aspartate and glutamate) were synthesized and characterized by means of elemental analysis, IR and multinuclear ( 1H, 13C and 31P) NMR spectroscopies, and X-ray crystallography. The rate of full substitution of hexachlorocyclotriphosphazene with the amino acid esters has been found to be largely dependent on the steric hindrance of the corresponding amino acid esters. The full substitution of the chlorotrimer with aminomalonate was completed in 6 h when the reactants were refluxed in tetrahydrofuran (THF), but the full substitution with aspartate or glutamate required more severe conditions: The substitution with aspartate was completed in 12 h by refluxing the reactants in the presence of n-Bu 4NBr as the catalyst in toluene, but the substitution with glutamate could not be completed even after refluxing for more than two days in the presence of the same catalyst in toluene. To endow the above compounds with the functionality for incorporation of metal moiety, they have been hydrolyzed in aqueous solutions of alkali metal hydroxides to yield the corresponding metal salts, which can afford twelve active sites.