Bis(difluoromethyl)trimethylsilicate Anion: A Key Intermediate in Nucleophilic Difluoromethylation of Enolizable Ketones with Me3SiCF2H

n A pentacoordinate bis(difluoromethyl)silicate anion, [Me3Si(CF2H)(2)](-), is observed for the first time by the activation of Me3SiCF2H with a nucleophilic alkali-metal salt and 18-crown-6. Further study on its reactivity by tuning the countercation effect led to the discovery and development of an efficient, catalytic nucleophilic difluoromethylation of enolizable ketones with Me3SiCF2H by using a combination of CsF ad 18-crown-6 as the initiation system. Mechanistic investigations demonstrate that [(18-crown-6)Cs](+)[Me3Si(CF2H)(2)](-) is a key intermediate in this catalytic reaction.