Phosphazene-Phosphazane Transitions

Examples of phosphazene-phosphazane transitions already given are the hydrolysis of cyclic chlo-rophosphazenes to give cyclic metaphosphimates (7.263) and (7.264) and the isomerisation of certain esters simply by heating (7.327). 

Imide-amide isomerisations, first established by Kabachnik, also represent phosphazene-phosphazane transitions. Some of these involve simple hydrolysis as in Equation 7.506, or thermally induced rearrangements as in Equation 7.507. 

Triethyl phenylimidophosphate rearranges according to Equation 7.508 on heating with ethyl iodide, and with trimethylchlorosilane the reaction is (7.509). Other examples of imide-amide isomerisations are indicated in Equations 7.510 and 7.511. 

In Equation 7.511 the rate of isomerisation is very dependent upon the nature of R and R. Phosphazene-phosphazane isomerisations essentially involve the replacement of P=N by P-N and the establishment of a P=0 linkage. 

Some isomerisations (imide-imide transitions) involve merely a shift in the position of the P=N linkage, but a phosphoryl linkage is established on the P atom which has become singly linked to nitrogen. 

---

Movement of alkyl can occur between 0 and N atoms as in Equations 13.266 and 7.327. In addition to these phosphazene-phosphazane rearrangements, there are also other transitions (7.507) and (7.511). 

M. Witt and H. W. Roesky. Transition and main group metals in cyclic phosphazanes and phosphazenes. Chem. Rev. 94, 1163 (1994). 

---