251. Mechanism of BPh 3 -Catalyzed N-Methylation of Amines with CO 2 and Phenylsilane: Cooperative Activation of Hydrosilane.
- Author
-
Ratanasak M, Murata T, Adachi T, Hasegawa JY, and Ema T
- Subjects
- Methylation, Catalysis, Lewis Acids, Acetals, Water, Carbamates, Formates, Amines chemistry, Carbon Dioxide chemistry
- Abstract
BPh
3 catalyzes the N-methylation of secondary amines and the C-methylenation (methylene-bridge formation between aromatic rings) of N,N-dimethylanilines or 1-methylindoles in the presence of CO2 and PhSiH3 ; these reactions proceed at 30-40 °C under solvent-free conditions. In contrast, B(C6 F5 )3 shows little or no activity.11 B NMR spectra suggested the generation of [HBPh3 ]- . The detailed mechanism of the BPh3 -catalyzed N-methylation of N-methylaniline (1) with CO2 and PhSiH3 was studied by using DFT calculations. BPh3 promotes the conversion of two substrates (N-methylaniline and CO2 ) into a zwitterionic carbamate to give three-component species [Ph(Me)(H)N+ CO2 - ⋅⋅⋅BPh3 ]. The carbamate and BPh3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH3 to generate [HBPh3 ]- , which is used to produce key CO2 -derived species, such as silyl formate and bis(silyl)acetal, essential for the N-methylation of 1. DFT calculations also suggested other mechanisms involving water for the generation of [HBPh3 ]- species., (© 2022 Wiley-VCH GmbH.)- Published
- 2022
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