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

Abstract

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 R3PC(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 Ph3PC(Me)Si(Cl)Me2 (1) with Na[B(C6F5)4] furnished the dimeric phosphonium‐like dication [Ph3PC(Me)SiMe2]2[B(C6F5)4]2 (8). The highly reactive, mesityl‐ or iPr‐substituted cationic species [Ph3PC(Me)SiMes2][B(C6F5)4] (9) and [Ph3PC(Et)SiiPr2][B(C6F5)4] (10) could be characterized by NMR spectroscopy. Carrying out the halide abstraction reaction in the sterically demanding ether iPr2O afforded the protonated α‐SiCP [Ph3PCH(Et)Si(Cl)iPr2][B(C6F5)4] (6 dec) by sodium‐mediated basic ether decomposition, whereas successfully synthesized [Ph3PC(Et)SiiPr2][B(C6F5)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 [Ph3PC(Me)GeMes2][B{3,5‐(CF3)2C6H3}4] (14) was obtained by treating 11 with Na[B{3,5‐(CF3)2C6H3}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.