Reactions between alkyl grignard reagents and aminophosphazenes: Synthesis of alkylchlorocyclotriphosphazenes

The reactions between alkyl Grignard reagents and aminophosphazenes have been investigated. The products formed when l, 3, 5-tris(dimethylamino)-l, 3, 5-trichlorocyclotriphosphazene (4) reacts with alkyl Grignard reagents depend on the concentrations of the reagents in solution, on the solvent employed, and on the method of product isolation. Reaction between 4 and CH₃MgBr in diethyl ether, followed by treatment with triethylamine, results in chlorine replacement to yield the trialkylphosphazene, 5, and an ethoxy-substituted product, 6. Formation of 5 is favored by increases in the concentration of 4 and use of a larger excess of Grignard reagent. Similar results were obtained when C₂H₅MgBr was used. The proposed mechanism for the replacement of chlorine by ethoxy involves an interaction between the phosphazene substrate, magnesium species in solution, and diethyl ether solvent. Chlorine replacement by 4-chlorobutoxy side groups predominates when 4 reacts with CH₃MgCl in tetrahydrofuran. Compounds of formula N₃P₃C1₃R₃(2) were prepared by the reaction of 5 with hydrogen chloride in refluxing toluene. Species N₃P₃C1₄R2 were synthesized by allowing l, 3, 5, 5-tetrakis(dimethylamino)-l, 3-dichlorocyclotriphosphazene (14) to react with excess Grignard reagent in diethyl ether to yield the dialkyl species 15 (R = CH₃, C₂H₅). The reaction between 15 and hydrogen chloride in refluxing toluene yields l, 3-dialkyl-l, 3, 5-trichloro-5-(dimethylamino)cyclotriphosphazene (16). Removal of the last dimethylamino residue was accomplished by treatment of 16 with hydrogen chloride in a sealed tube at 100 °C. Structural characterization was obtained for all the new cyclophosphazenes by elemental analysis, mass spectrometry, infrared spectroscopy, and NMR (³¹P, ¹³C, ¹H) spectroscopy. NMR evidence is presented for the presence of geometrical isomers.