Silylpalladium Cations Enable the Cleavage of Nitrile C–CN Bonds

Abstract

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.

Spectroscopic and Computational Assessment of Silicon’s Electrophilicity in Phosphinosilylium Cations

“…As discussed herein, significant charge localizes on both Si and P, but since we probe their use as silylium sources, we refer to them as phosphinosilylium ions. This study reports strong correlations between the 29 27 which completely transfers the silylium to added phosphine (Scheme 1). No interaction between the released Ph 2 O and the resulting phosphinosilylium cation is detectable by 13 C{ 1 H} NMR spectroscopy.…”

“…A family of phosphinosilylium cations were synthesized by treating HSiMe 2 Et with a combination of [Ph 3 C]­[B­(C 6 F 5 ) 4 ] and Ph 2 O to afford a weakly stabilized source of silylium (Ph 2 O–SiMe 2 Et + ), which completely transfers the silylium to added phosphine (Scheme ). No interaction between the released Ph 2 O and the resulting phosphinosilylium cation is detectable by 13 C­{ 1 H} NMR spectroscopy.…”

Metal-mediated C–CN Bond Activation in Organic Synthesis

“…A cationic silylpalladium complex shows a similar reactivity through an Nsilyl η 1 -iminoacylpalladium complex identified by stoichiometric experiments. 46 It is experimentally 47,48 and theoretically 49 proved that borylrhodium complexes also activate C−CN bonds through N-boryl η 1 -iminoacylrhodium complexes. Silylene complexes of Fe 50 and Ru 51…”

“…A similar mechanism has been proposed for the activation of C–CN bonds by a silylnickel complex as a possible elemental step in the Ni-catalyzed cyanation of aryl halides with acetonitrile (vide infra), albeit with poor experimental evidence. A cationic silylpalladium complex shows a similar reactivity through an N -silyl η 1 -iminoacylpalladium complex identified by stoichiometric experiments . It is experimentally , and theoretically proved that borylrhodium complexes also activate C–CN bonds through N -boryl η 1 -iminoacylrhodium complexes.…”

Swift C–C bond insertion by a 12-electron palladium(0) surrogate

“…11,18 Thus, it requires in the case of palladium the addition of Lewis-acids such as BEt 3 19 or silylium cations as studied by Gagné and coworkers (Scheme 1b). 20,21…”