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$_{3}$PC(R$^{1}$)E(Cl)R$^{2}$$_{2}$ (R=Ph; R$^{1}$=Me, Et, Ph; R$^{2}$=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$^{3}$PC(Me)Si(Cl)Me$^{2}$ (1) with Na[B(C$^{6}$F$^{5}$)$^{4}$] furnished the dimeric phosphonium-like dication [Ph$^{3}$PC(Me)SiMe$^{2}$]$^{2}$[B(C$^{6}$F$^{5}$)$^{4}$]$^{2}$ (8). The highly reactive, mesityl- or iPr-substituted cationic species [Ph$^{3}$PC(Me)SiMes$^{2}$][B(C$^{6}$F$^{5}$)$^{4}$] (9) and [Ph$^{3}$PC(Et)SiiPr$^{2}$][B(C$^{6}$F$^{5}$)$^{4}$] (10) could be characterized by NMR spectroscopy. Carrying out the halide abstraction reaction in the sterically demanding ether iPr$^{2}$O afforded the protonated α-SiCP [Ph$^{3}$PCH(Et)Si(Cl)iPr$^{2}$][B(C$^{6}$F$^{5}$)$^{4}$] (6 dec) by sodium-mediated basic ether decomposition, whereas successfully synthesized [Ph$^{3}$PC(Et)SiiPr$^{2}$][B(C$^{6}$F$^{5}$)$^{4}$] (10) readily cleaves the F−C bond in fluorobenzene. ... mehrThus, the ambiphilic character of α-SiCPs is clearly demonstrated. The less reactive germanium analogue [Ph$^{3}$PC(Me)GeMes$^{2}$][B{3,5-(CF$^{3}$)$^{2}$C$^{6}$H$^{3}$}$^{4}$] (14) was obtained by treating 11 with Na[B{3,5-(CF$^{3}$)$^{2}$C$^{6}$H$^{3}$}$^{4}$] and fully characterized including by X-ray diffraction analysis. Structural parameters indicate a strong C$^{Ylide}$−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.