The synthesis and characterization of the roomtemperature and solution-stable silylpalladium cations (PCy 3 ) 2 Pd−SiR 3 + (C 6 F 5 ) 4 B − (SiR 3 = SiMe 2 Et, SiHEt 2 ) and (Xantphos)Pd−SiR 3 + (BAr f 4 ) (SiR 3 = SiMe 2 Et, SiHEt 2 ; Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; BAr f 4 = (3,5-(CF 3 ) 2 C 6 H 3 ) 4 B − ) are reported. Spectroscopic and ligand addition experiments suggest that silylpalladium complexes of the type (PCy 3 ) 2 Pd−SiR 3 + are three-coordinate and T-shaped. Addition of dialkyl ethers to both the PCy 3 and Xantphos-based silylpalladium cations resulted in the cleavage of C(sp 3 )−O bonds and the generation of cationic Pd−alkyl complexes. Mechanistically enabling is the ability of silylpalladium cations to behave as sources of both electrophilic silylium ions and nucleophilic L n Pd(0).

The stoichiometric addition of aryl and alkyl nitriles to the silylpalladium cation [(PCy 3 ) 2 Pd−SiMe 2 Et + ][(C 6 F 5 ) 4 B − ] (1) resulted in the cleavage of the nitrile C−CN bond and the formation of palladium−aryl and palladium−alkyl cations. Low-temperature experiments support a mechanism where silylpalladium cation 1 transfers silylium to nitrile, generating a silylnitrilium cation and the reduced, zerovalent complex Pd(PCy 3 ) 2 . These two intermediates readily recombine at low temperatures to generate palladium−(N-silyl)iminoacyl complexes, which upon warming can undergo aryl/alkyl group migration from the iminoacyl ligand to the metal. Additional experiments show that palladium−(N-silyl)iminoacyl cations are potent sources of silylium, capable of cleaving the methyl C−O bond of an ether, while DFT calculations confirm the electrophilicity of the silyl moiety.

An experimental method of determining the electrophilicity of silicon in phosphinosilylium cations is reported and compared to Djukic's DFT method of computing relative intrinsic silylicity, Π. We also establish linear correlations between silicon electrophilicity and 29 Si NMR chemical shifts, DFT-computed silylicities, and the Tolman electronic parameter of the phosphine. These correlations were not universal, as deviations were observed for the most sterically hindered phosphines. Intermolecular silylium transfer experiments between phosphinosilyliums and added phosphines provided a thermodynamic assessment of the electrophilic character at silicon. This confirmed that relative intrinsic silylicity (Π) and 29 Si NMR chemical shifts are useful parameters for semiquantitatively determining the electrophilicity of the silyl group in a Lewis pair.