The preparation and study of alkylated phosphazenes

The reaction of the model compound hexachlorocyclotriphosphazene (N₃P₃Cl₆) with various organometallic reagents have been studied in some detail. These reactions are quite complex yielding substitution products as well as degradation products. The reaction of alkyl Grignard reagents, in the presence of a copper complex ((n-Bu₃PCuI)₄), have been studied and produce good yields of mono- and di-alkylated chlorocyclotriphosphazenes. This method is limited in that higher substitution products can not be obtained.

The reaction of trimethylaluminum (TMA) with (N₃P₃Cl₆) was examined and found to yield the fully substituted hexamethylcyclotriphosphazene (N₃P₃(CH₃)₆) in modest yield (40 %). The study of this reaction, with respect to time allowed for the determination of the substitution pathway and the preparation of two new methylated chlorocyclotriphosphazenes. It was then possible to prepare a nearly complete set of methylated chlorocyclotriphosphazenes (N₃P₃(CH₃)_nCl_6-n) using this method and the Grignard route. The reactions of other alkylaluminum reagents were also examined and are discussed. The effects of the complexation of TMA with the homologous series was next examined using ¹H, and ³¹P NMR. The results for these investigations indicate that the overall electron donating ablity of the phosphazene ring increased with increasing methyl substitution. Variable temperature NMR studies allowed for the determination of the sites of complexation and their relative strengths with respect to the number of methyl groups on the phosphazene ring.