The Non-Ancillary Nature of Trimethylsilylamide Substituents in Boranes and Borinium Cations
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Updated: Oct 1, 2025

Synthesis of a Borylated Ibuprofen Derivative Through Suzuki Cross-Coupling and Alkene Boracarboxylation Reactions
Published on: November 30, 2022
Christopher J Major1, Zheng-Wang Qu2, Stefan Grimme2
1Department of Chemistry, University of Toronto, 80 St. George St, Toronto, ON, M5S3H6, Canada.
Abstract:
The known boranes (R(Me3 Si)N)2 BF (R=Me3 Si 1, tBu 2, C6 F5 3, o-tol 4, Mes 5, Dipp 6) and borinium salts (R(Me3 Si)N)2 B][B(C6 F5 )4 ] (R=Me3 Si 7, tBu 8) are prepared and fully characterized. Compound 7 is shown to react with phosphines to generate [R3 PSiMe3 ]+ and [R3 PH]+ (R=Me, tBu). Efforts to generate related borinium cations via fluoride abstraction from (R(Me3 Si)N)2 BF (R=C6 F5 3, o-tol 4, Mes 5) gave complex mixtures suggesting multiple reaction pathways. However for R=Dipp 6, the species [(μ-F)(SiMe2 N(Dipp))2 BMe][B(C6 F5 )4 ] was isolated as the major product, indicating methyl abstraction from silicon and F/Me exchange on boron. These observations together with state-of-the-art DFT mechanistic studies reveal that the trimethylsilyl-substituents do not behave as ancillary subsitutents but rather act as sources of proton, SiMe3 and methyl groups.
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