Geminal bis[(triphenylphosphoranylidene)amino]cyclotriphosphazenes synthesis: substitution reactions, and nuclear magnetic resonance spectra

Abstract

Cyclotriphosphazenes bearing an amino ligand are readily converted into the corresponding (triphenylphosphoranylidene)amino (–NPPh₃) derivatives by means of an excess of triphenylphosphine–tetrachloromethane in an acetonitrile–triethylamine medium (Appel reaction). Thus prepared, N₃P₃Cl₄(NPPh₃)₂ reacts with dimethylamine in various solvents according to a geminal substitution pattern; this is an indication of S_N1-type reactions, as a result of the strong electron-donating character of the ligands. The ultimate substitution product N₃P₃(NMe₂)₄(NPPh₃)₂, also prepared from N₃P₃(NMe₂)₄(NH₂)₂, is isolated as its HCl or 2HCl adduct, depending on the method of preparation. In both adducts the protons are attached to ring nitrogen atoms, and variable-temperature ¹H and ³¹P n.m.r. measurements show prototropic behaviour at elevated temperatures. Trends within the ³¹P n.m.r. parameters of the derivatives are discussed in terms of the electron-donating ability of the ligands.