Synthesis and silicon-nitrogen bond cleavage reactions of n-silylphosphoranimines

Abstract

N-Silylphosphoranimines have been shown to exhibit multiple modes of reactivity such as: (1) substitution at phosphorus, (2) polymerization by loss of a silyl moiety (Me$\sb3$SiX), (3) alkyl group modification by deprotonation-substitution reactions, and (4) silicon-nitrogen bond cleavage reactions. By exploiting this wide range of reactivity many derivatives can and have(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)been prepared which have the potential to undergo interesting thermolysis reactions. It is well known that suitably constructed phosphoranimines are used as phosphazene, (N=PR$\sb2$) $\sb{\rm n}$, precursors. Three classes of new compounds were synthesized via Si-N bond cleavage reactions. Diene-like compounds A, contain two types of phosphorus centers, a two-coordinate P(III) center and a four-coordinate P(V) center. These products are synthesized by reacting a P-chloro(methylene)phosphine, Cl-P=C(SiMe$\sb3)\sb2$, with N-silylphosphoranimines in the presence of n-Bu$\sb4$NF catalyst. This reaction is interesting since it proceeds with the preservation of the double bond in the chlorophosphaalkene moiety, thus yielding a mixed coordinate phosphorus system.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) Compounds of type B are synthesized from phosphoryl chlorides RP(O)Cl$\sb2$ and N-silylphosphoranimines by the intermolecular elimination of chlorosilane. These reactions proceed at room temperature to give B in very high yield. These products are of particular interest because they are the substituted analogs of pentachlorophosphorylphos- phoranimine, Cl$\sb2$P(O)N=P(Cl)$\sb3$, a known precursor to poly (dichlorophosphazene), (N=P(Cl)$\sb2$) $\sb{\rm n}$.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) Transsilylation reactions of N-trimethylsilylphosphoranimines were also carried out to afford new Si-N-P compounds C. In this investigation, the presence of methoxy on the silicon was studied to determine what effect, if any, the group may have on the synthesis and the thermolysis of C.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) In addition, N-silyl-P-siloxyphosphoranimines D were synthesized as part of an ongoing search for new phosphazene precursors. Alkylation of dichlorosiloxyphosphoranimine, Me$\sb3$Si-N=P(Cl)$\sb2$OSiMe$\sb3$, with standard organolithium or Grignard reagents was not straightforward. However, this dichlorophosphoranimine reacted with Me$\sb3$SiNMe$\sb2$ to give the readily isolable diaminosiloxyphosphoranimine Me$\sb3$Si-N=P(NMe$\sb2)\sb2$OSiMe$\sb3 $.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) Thermolysis experiments were carried out on each of these products, but none of them formed characterizable cyclic, oligomeric, or polymeric materials. The volatile by-products of the thermolysis of B and D were identified, giving some insight to their mode of decomposition.