Halogenation Reactions of Phosphiniminocyclotrithiazenes: Search for New Inorganic Heterocycles

Though the chemistry of tetrasulfur tetranitride is very well developed and studied, that of phosphiniminocyclotrithiazenes is not. Reactions of symmetrically substituted R3PN-S3N3 [R = Ph, OC4H8N, MeNC4H8N, and C5H10N] with halogens and halogen sources (SO2Cl2, PhICl2, Br2, and I2) gave rise to various products. In case of R = Ph, the ring-retained product, while for others, ring-degraded products were obtained. A novel cyclotrithiazene heterocycle, [Ph3PN]2S3N3+I3− containing a tetracoordinated sulfur atom with two phosphinimino substituents was obtained, which was further established by IR, NMR (1H-, 13C-, and 31P-) and elemental analysis. Cyclic voltammetric studies indicated the redox behavior as well as the presence of triiodide. Theoretical calculations clearly indicate the residence of maximum positive charge (close to unity) on the tetracoordinated sulfur atom.