Nucleophilic substitution pathways in the reactions of 3-amino-1-propanol with mono substituted cyclotriphosphazene derivatives

Abstract

This study was planned to determine the reaction pathway and mechanism in the nucleophilic substitution reactions of cyclotriphosphazene derivatives with amino alcohol and to put an end to the spiro versus ansa dilemma. Three different monosubstituted cyclotriphosphazene compounds N3P3Cl5R [R = -NHPri (1a), -NMe2 (1b) and R = -OMe (1c)] were reacted with 3-amino-1-propanol. These reactions led to new cyclotriphosphazenes bearing aminoalkoxy: single-bridged (2a), mono-ansa (3a, 3c) and mono-spiro (4b-I, 4b-II and 4c-I). The structures of isolated products (2a, 3a, 4b-I, 4c-I and 4c-II) were characterized by elemental analysis, mass spectrometry and (1H, 13C and 31P) NMR spectroscopies. The structures of 3a, 4b-I and 4c-I were further determined by single crystal X-Ray crystallography. The functional groups on cyclotriphosphazenes provide an opportunity to generate both ansa and spiro isomers which can be formed by intramolecular pathway. Additionally, the formation of bridged products can also be explained by intermolecular route, depending on the orientation effect of the substituted groups on incoming amino alcohols.