Synthesis and reactivity of 1-phosphadienes and their precursors

Abstract

The sequential reaction of PCl$\sb3$ with lithium bis(trimethylsilyl)amide and 1,3-bis(trimethylsilyl)propenyllithium gives the chlorophosphine, (Me$\sb3$Si)$\sb2$NP(Cl)C(H)(SiMe$\sb3$)CH=C(H)(SiMe$\sb3$) (1). (Disilylpropenyl)phosphines, similar to 1, have been prepared with varying substituents (e.g., H, Me, t-Bu, Ph, Cl, NMe$\sb2$, N(SiMe$\sb3)\sb2$) on phosphorus by starting from either PCl$\sb3$, PhPCl$\sb2$, or Ph$\sb2$PCl. Dehydrohalogenation of several substituted allyl(chloro)phosphines, RP(Cl)C(H)(SiMe$\sb3$)CH=C(H)(SiMe$\sb3$) (R = Cl, t-Bu, (Me$\sb3$Si)$\sb2$N), was attempted with decomposition occurring for R = Cl, cyclization (DBU) or (2+2) cycloaddition (DBN) occurring for R = t-Bu, and formation of the 1-phosphadiene (Me$\sb3$Si)$\sb2$NP=C(SiMe$\sb3$)CH=C(H)(SiMe$\sb3$) (21) occurring for R = (Me$\sb3$Si)$\sb2$N. Reaction of 21 with sulfur or trimethylsilylazide gives the cyclic phosphetenes (Me$\sb3$Si)$\sb2$N(E=)P-C(SiMe$\sb3$)=CH-C(H)(SiMe$\sb3$) (27: E = S; 29: E = N(SiMe$\sb3)\sb2$). A structural isomer of 29, ((Me$\sb3$Si)$\sb2$N) (SiMe$\sb3$N=)P-C(H)=C(SiMe$\sb3$)-C(H)(SiMe$\sb3$), was prepared by treating an animo(imino)phosphorane with trimethylsilylacetylene. Reaction of the 1-phosphadiene 21 with alkyllithium reagents affords the nucleophilic/1,4-addition products R$\sb2$PC(SiMe$\sb3$)=CHC(H)(SiMe$\sb3)\sb2$ (32a,b) (R = Me, t-Bu) and their condensation analogues 33a,b which contains a linear P$\sb2$C$\sb6$ backbone. The structure of 33b was determined by X-ray spectroscopic analysis. Oxidation of the vinyl phosphines 32 by sulfur or trimethylsilylazide gave the corresponding vinyl phosphoranes. Coordination of the 1-phosphadiene was achieved by treating 21 with Mo(CO)$\sb6$. The complex was studied by X-ray spectroscopic analysis and the coordination to the metal was found to be through the phosphorus lone pair.