Accessing Cationic α-Silylated and α-Germylated Phosphorus Ylides.

The synthesis and full characterization of α-silylated (α-SiCPs; 1-7) and α-germylated (α-GeCPs; 11-13) phosphorus ylides bearing one chloride substituent R PC(R )E(Cl)R (R=Ph; R =Me, Et, Ph; R =Me, Et, iPr, Mes; E=Si, Ge) is presented. The molecular structures were determined by X-ray diffraction studies. The title compounds were applied in halide abstraction studies in order to access cationic species. The reaction of Ph PC(Me)Si(Cl)Me (1) with Na[B(C F ) ] furnished the dimeric phosphonium-like dication [Ph PC(Me)SiMe ] [B(C F ) ] (8). The highly reactive, mesityl- or iPr-substituted cationic species [Ph PC(Me)SiMes ][B(C F ) ] (9) and [Ph PC(Et)SiiPr ][B(C F ) ] (10) could be characterized by NMR spectroscopy. Carrying out the halide abstraction reaction in the sterically demanding ether iPr O afforded the protonated α-SiCP [Ph PCH(Et)Si(Cl)iPr ][B(C F ) ] (6 dec) by sodium-mediated basic ether decomposition, whereas successfully synthesized [Ph PC(Et)SiiPr ][B(C F ) ] (10) readily cleaves the F-C bond in fluorobenzene. Thus, the ambiphilic character of α-SiCPs is clearly demonstrated. The less reactive germanium analogue [Ph PC(Me)GeMes ][B{3,5-(CF ) C H } ] (14) was obtained by treating 11 with Na[B{3,5-(CF ) C H } ] and fully characterized including by X-ray diffraction analysis. Structural parameters indicate a strong C -Ge interaction with high double bond character, and consequently the C-E (E=Si, Ge) bonds in 9, 10 and 14 were analyzed with NBO and AIM methods.