Isomerism in Cyclophosphazenes

In the previous section it was mentioned that the reactions of chlorocyclo-phosphazenes with amines proceed to afford persubstituted (completely substituted) products. However, sequential replacement of chlorine atoms is also possible with many nucleophilic reagents by a simple control of stoichiometry. Various stages of chlorine replacement reactions lead to products ranging from monosubstituted derivatives to persubstituted ones. 

Similar isomer formation is potentially present at the tris and tetrakis stages of substitution as well. However, at the pentakis and hexakis stages only one isomer can be realized. These possibilities are summarized in Fig. 3.16. 

Obviously the number of products that are possible in the replacement reactions of the higher-membered cyclophosphazenes such as N4P4CI8 are even larger. Although studies on chiral cyclophosphazenes are very limited it can be shown that nonsuperimposable mirror images are possible for raAW-N3P3X2R4 [12]. 

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