Chemistry of poly(phosphazene) precursors

Abstract

Certain types of N-silylphosphoranimines are starting materials for the synthesis of P-C bonded poly(phosphazenes). The physical properties of poly(phosphazenes) as well as their chemical versatility depend on the identity of the side groups, especially on the presence of various functional groups. The chemistry of N-trimethylsilyl-P,P-dimethyl-P-trifluoroethoxy- phosphoranimine (1) was studied. The deprotonation of Me(,3)SiN= PMe(,2)OCH(,2)CF(,3) (1) generates a reactive anion, stable at low temper- ature. The anion reacted with several organic and silyl halides to yield phosphoranimines bearing benzyl, allyl, or functionalized silyl groups. When two equivalents of n-BuLi were used in the deprotona- tion reaction in the presence of Me(,3)SiCl, two protons on the same methyl group were substituted. (UNFORMATTED TABLE FOLLOWS) Me Me (VBAR) n-BuLi (VBAR) Me(,3)SiN=P-OCH(,2)CF(,3) (--->) Me(,3)SiN=P-OCH(,2)CF(,3) (VBAR) Et(,2)O, -78(DEGREES)C (VBAR) Me ('-)CH(,2) Li('+) 1 (TABLE ENDS) The new derivatized phosphoranimines were used in the thermolysis reaction to make polymers and copolymers with 1. The reactivity of the Si-N bond in phosphoranimine 1 was also studied. Compound 1 undergoes easy transilylation reactions with various chlorosilanes, dichlorosilanes, and dichlorosiloxanes to yield new N-silylphosphoranimines containing functional groups on silicon. Compound 1 also reacted with equimolar amounts of dichloro- silanes and siloxanes to give unstable chlorosilyl compounds that served as intermediates in various derivatization reactions. Ther- molysis of phosphoranimine-siloxane compounds alone and in mixtures with 1 gave poly(dimethylphosphazene) and trifluoro- ethoxysiloxanes. Phosphoranimine 1 reacted with Ph(,2)POCH(,2)CF(,3) to give a p('III)N-P('V) compound. With Ph(,2)PCl, the formation of a P-P bonded phosphor- animino-phosphonium salt, Ph(,2)P-PPh(,2)-N=P(OCH(,2)CF(,3))Me(,2) ('+)Cl('-) was obtained. Surprisingly, phosphoranimine 1 reacts with Me(,2)HSiCl to give an analogous P-P bonded phosphoranimino-phosphonium salt. It is believed that the silane acts as a reducing agent to form Me(,2)PCl which spontaneously adds to 1 to form the P-P salt.