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, i Pr, 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 i Pr‐substituted cationic species [Ph 3 PC(Me)SiMes 2 ][B(C 6 F 5 ) 4 ] ( 9 ) and [Ph 3 PC(Et)Si i Pr 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 i Pr 2 O afforded the protonated α‐SiCP [Ph 3 PCH(Et)Si(Cl) i Pr 2 ][B(C 6 F 5 ) 4 ] ( 6 dec ) by sodium‐mediated basic ether decomposition, whereas successfully synthesized [Ph 3 PC(Et)Si i Pr 2 ][B(C 6 F 5 ) 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 [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.