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 SN1-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.