Phosphorus–fluorine chemistry. Part XXV. Synthesis and properties of fluoro-1,2,4-phosphadiazetidin-3-ones

The preparation of a series of heterocyclic fluorophosphoranes, the 1-fluoro-NN′-dimethyl-(or N-methyl-N′-phenyl)-1,2,4-phosphadiazetidin-3-ones, is described. These compounds have been prepared by the cleavage of the silicon–nitrogen bonds in the appropriate NN′-dimethyl-(or N-methyl-N′-phenyl)-NN′-bis(trimethylsilyl)-urea with fluorophosphoranes. 1,1,1-Trifluoro-NN′-dimethyl-1,2,4-phosphadiazetidin-3-one has only been prepared by chlorine/fluorine exchange, using antimony trifluoride, in the known trichloro-compound. The reaction of NN′-dimethyl-NN′-bis(trimethylsilyl)urea with phosphorus pentafluoride and the fluorination of 1,1,1-trichloro-NN′-dimethyl-1,2,4-phosphadiazetidin-3-one with sodium fluoride dispersed in acetonitrile and with antimony trifluoride above 60° give rise to the formation of a spiro-phosphonium hexafluorophosphate. The structure of all products has been investigated using 1H, 19F and 31P n.m.r. spectroscopy.