Synthesis and reactivity of 1-phosphadienes and P-acetylenic silicon-nitrogen-phosphorus compounds

Abstract

Low coordinate phosphorus compounds have received a great deal of attention over the last twenty years. Furthermore, the reactivity of phosphorus-carbon $\pi$ bonds has provided new perspectives on bonding in two-coordinate systems. In particular, 1-phosphadienes (I) and their precursors exhibit different modes of reactivity. This contrast in reactivity can in some cases be attributed to the nature of the substituent (R) bound to the phosphorus.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)These compounds are frequently synthesized via base induced 1,2-elimination reactions. However, exclusive formation of the desired 1-phosphadiene does not occur in some cases. In a similar manner, the derivative chemistry of these systems also depends on the nature of the R group bound to the phosphorus. For example, alkyllithium reagents undergo 1,4-addition across the conjugated framework. However, stoichiometric additions are not observed in all cases. Furthermore, the oxidation chemistry of these systems demonstate differing reactivity. For example, oxidation of 1-phosphadienes with $\rm Me\sb3SiN\sb3$ has produced both three-coordinate P(V) compounds (II, R = (Me$\sb3$Si)$\sb2$CH; R$\sp\prime$ = CH=C(H)SiMe$\sb3$) as well as some interesting cyclic derivatives (III, R = (Me$\sb3$Si)$\sb2$CH & (Me$\sb3$Si)$\sb2$N).(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) Further studies of one particular three coordinate P(V) system (II,R = (Me$\sb3$Si)$\sb2$N; R$\sp\prime$ = H) led to a more general method for attaching acetylenic linkages to phosphorus. Initially, this was attempted by addition of acetylenic reagants across the phosphorus-carbon $\pi$-bond. However, the constraints of this method resulted in the development of a more versatile synthetic strategy. In essence, by utilizing the Wilburn method in tandem with lithium acetylides or acetylenic Grignard reagants, a variety of (silylamino)phosphines have been prepared (IV).(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) In addition, oxidative halogenation and substitution with lithium trifluoroethoxide provides functionalized P-acetylenic N-silylphosphoranimines (V). In both cases (IV and V), phosphorus compounds containing two acetylenic substituents have also been prepared.