New cyclic and polymeric phosphazenes derived from N-silylphosphoranimines

Silicon-nitrogen-phosphorus compounds of the type Me3SiN=PR(R')X (X = Cl, Br, OCH2CF3, OPh), known as N-silylphosphoranimines, are useful precursors to both cyclic and polymeric phosphazenes. Depending on the leaving group (X), thermolysis reactions afford either cyclic trimers, [N=PR(R')](3) (when X = Cl, Br), or linear polymers, [N=PR(R')](n) (when X = OCH2CF3 or OPh). Treatment of the P-trifluoroethoxy and P-phenoxy derivatives, Me3SiN=PR(R')X (X = OCH2CF3, OPh), with alcohols at lower temperature usually results in the formation of cyclic phosphazene trimers via silyl ether elimination. Recently, we have applied these synthetic methods to the preparation of some new phosphazene systems including a series of 4-aryl-functionalized trimers and polymers and a variety of non-geminal, mixed-substituent cyclic trimers. Representative examples of the synthesis, structural characterization, and reactivity of these new phosphazenes and their Si-N-P precursors are reported here.