Triorganylphosphoranides: Realization of an Unusual Structural Motif Utilizing Electron Withdrawing Pentafluoroethyl Groups.

Phosphoranides comprising three phosphorus carbon bonds are scarcely represented in the literature. We now utilized tris(pentafluoroethyl)phosphane, P(C ₂ F ₅ ) ₃ , and cyanobis(pentafluoroethyl)phosphane, P(C ₂ F ₅ ) ₂ (CN), featuring electron withdrawing pentafluoroethyl groups, to synthesize such compounds. Metal fluorides MF (M=Ag, Cs) add to P(C ₂ F ₅ ) ₃ yielding respective M[P(C ₂ F ₅ ) ₃ F] salts. Those M[P(C ₂ F ₅ ) ₃ F] subsequently suffer a loss of C ₂ F ₄ , furnishing M[P(C ₂ F ₅ ) ₂ F ₂ ]. The cesium salt decomposes instantaneously when warmed to rt, whereas the silver salt decomposes slowly over several days at rt. Treatment of Ag[P(C ₂ F ₅ ) ₃ F] with 2,2'-bipyridine facilitated the isolation and structural characterization of [Ag(bipy){P(C ₂ F ₅ ) ₃ F}]. With P(C ₂ F ₅ ) ₂ (CN), AgF reacts under substitution of the cyano group yielding P(C ₂ F ₅ ) ₂ F, rather than phosphoranide formation. However, [K(18-crown-6)]F adds to P(C ₂ F ₅ ) ₂ (CN) furnishing [K(18-crown-6)][P(C ₂ F ₅ ) ₂ (CN)F]. Its structural characterization was successful, despite its tendency to undergo an exchange of substituents, yielding [K(18-crown-6)][P(C ₂ F ₅ ) ₂ F ₂ ] and presumably [K(18-crown-6)][P(C ₂ F ₅ ) ₂ (CN) ₂ ]. The latter forms an equilibrium with [K(18-crown-6)]CN and P(C ₂ F ₅ ) ₂ (CN) which lies well on side of the phosphane and cyanide salt.
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