Synthesis of the First Persilylated Ammonium Ion, [(Me₃Si)₃NSi(H)Me₂]⁺, by Silylium-Catalyzed Methyl/Hydrogen Exchange Reactions

Abstract

This work describes the unexpected synthesis and characterization of the first persilylated ammonium ion, [(Me3Si)3NSi(H)Me2]+, in the reaction of (Me3Si)3N with [Me3Si–H–SiMe3][B(C6F5)4]. NMR and Raman studies revealed a transition-metal-free silylium ion catalyzed substituent redistribution process when [Me3Si–H–SiMe3]+ was used as the silylating reagent. These observations were affirmed in the reaction with [Et3Si–H–SiEt3][B(C6F5)4]. A Lewis acid catalyzed scrambling process always occurs if an excess of silanes is present in the formation of silylium cations while employing the standard Bartlett–Schneider–Condon type reaction. Additionally, the thermodynamics of this process was accessed by DFT computations at the pbe1pbe/aug-cc-pVDZ level, indicating alkyl substituent exchange equilibria at the silane and preference of the formation of [(Me3Si)3NSi(H)Me2]+ over [(Me3Si)4N]+.