Syntheses and structural characterizations of 2-pyridyl(N/O)spirocyclotriphosphazene derivatives

The Cl exchange reaction of hexachlorocyclotriphosphazene, N3P3Cl6 (1), with one equimolar amount of sodium salt of N/O donor type bidentate ligand containing a 2-pyridyl pendant arm (2) afforded, regioselectively, the partly substituted 2-pyridyl(N/O)spirocyclotriphosphazene (3; with a yield of 65%) in THF. The reactions of 3 with excess pyrrolidine, morpholine and 1,4-dioxa-8-azaspiro[4,5]decane (DASD) led to the formation of the tetraamino-2-pyridyl(N/O)spirocyclotriphosphazenes (3a-3c) in high yields. Compound 3 also gave both tetrapiperidino (3d) and gem-bispiperidino (3e) products with excess piperidine. The structures of all the compounds were determined by elemental analyses, ESI-MS, FTIR, HSQC, HMBC and H-1, C-13, and P-31 NMR techniques. The crystal structure of 3c was identified by single crystal X-ray crystallography. Besides, the compound 3e had one stereogenic P atom, and its chirality was verified by P-31 NMR spectroscopy in the presence of (S)-(+)-2,2,2-trifluoro-1-(9'-anthryl)-ethanol (CSA).