Synthesis, characterization, and reactivity of (N-Silyl)diphosphazenes

Abstract

N-Silylphosphoranimines of the type Me$\sb3$SiN=PR$\sb2$X (X = Br, Cl, OPh, and OCH$\sb2$CF$\sb3$) undergo condensation polymerization to cyclic and polymeric phosphazenes. In addition to this polymerization process, they also exhibit three other modes of reactivity: (1) nucleophilic substitution at the P-X site, (2) deprotonation-substitution reaction at the P-methyl group, and (3) silicon-nitrogen bond cleavage reaction. In order to further expand the scope of the derivative chemistry of N-silylphosphoranimines, especially the silicon-nitrogen bond cleavage reaction, a methodology has been developed to convert the N-silylphosphoranimines (I) to the corresponding anions (II). From these anions a series of novel acyclic (N-silyl)diphosphazenes (III) have been prepared. Preliminary studies of the reactivity of these (N-silyl)diphosphazenes indicated that thermolysis of these diphosphazenes affords new polymeric (IV) and/or cyclic (V) phosphazenes with very well-defined substituent pattems. These diphosphazenes also readily undergo hydrolysis to yield new types of N-phosphorylphosphoranimines (VI) which retain the intact -N-P=N-P= skeleton. Initial studies of reactions of CH$\sb3$CH$\sb2$OH with N-silylphosphoranimines led to a new route to (alkyl/aryl)cyclophosphazene trimers such as compound (VII). The molecular structures of several of these new cyclic phosphazenes (V and VII) and N-phosphorylphosphoranimines (VI) have been determined by single-crystal X-ray diffraction studies.