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 R3 PC(R1 )E(Cl)R2 2 (R=Ph; R1 =Me, Et, Ph; R2 =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 Ph3 PC(Me)Si(Cl)Me2 (1) with Na[B(C6 F5 )4 ] furnished the dimeric phosphonium-like dication [Ph3 PC(Me)SiMe2 ]2 [B(C6 F5 )4 ]2 (8). The highly reactive, mesityl- or iPr-substituted cationic species [Ph3 PC(Me)SiMes2 ][B(C6 F5 )4 ] (9) and [Ph3 PC(Et)SiiPr2 ][B(C6 F5 )4 ] (10) could be characterized by NMR spectroscopy. Carrying out the halide abstraction reaction in the sterically demanding ether iPr2 O afforded the protonated α-SiCP [Ph3 PCH(Et)Si(Cl)iPr2 ][B(C6 F5 )4 ] (6 dec) by sodium-mediated basic ether decomposition, whereas successfully synthesized [Ph3 PC(Et)SiiPr2 ][B(C6 F5 )4 ] (10) readily cleaves the F-C bond in fluorobenzene. Thus, the ambiphilic character of α-SiCPs is clearly demonstrated. The less reactive germanium analogue [Ph3 PC(Me)GeMes2 ][B{3,5-(CF3 )2 C6 H3 }4 ] (14) was obtained by treating 11 with Na[B{3,5-(CF3 )2 C6 H3 }4 ] and fully characterized including by X-ray diffraction analysis. Structural parameters indicate a strong CYlide -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.
Keywords: ambiphilic molecules; electronic frustration; germylium cations; silylium cations; ylides.
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