Dibenzylamine substituted cyclotetraphosphazenes: Synthesis, characterization and their stereogenic properties

Abstract

In this study, octachlorocyclotetraphosphazene, (1) and mono-spiro-1,3-propanedioxycyclotetraphosphazene, (2) were reacted with dibenzylamine to obtain cyclotetraphosphazenes having one and two stereogenic centres and to investigate the stereogenic properties of them. The reactions of compound 1 with bulky reagent, dibenzylamine might progress to until the tetrakis stage of chlorine replacement occurs and further substitutions by dibenzyamine do not occur. The structures of the products (3, 4, 5a, 5b, 6a, 6b, 7a and 7b) were determined by elemental and mass analyses, H-1 and P-31 NMR spectroscopies and for compounds 3, 4 and 5a where suitable single crystals were obtained, the structures were characterised by X-ray crystallography. The stereogenic properties of compound 3 which has one stereogenic centre and compound 5b which has two stereogenic centres were investigated by P-31 NMR spectroscopy on the addition of a chiral solvating agent. It was found that P-31 NMR/CSA method did not lead to the expected separation of the signals of enantiomers (3, 5b), even molar ratio of CSA:compound is up to 100:1 for dibenzylamine derivatives of cyclotetraphosphazene. Hence X-ray crystallography (for 3) and chiral HPLC method (for 5b) were used in order to determine their stereogenic properties.