Mechanistic Study of the Fluoride-Induced Activation of a Kobayashi Precursor: Pseudo-SN2 Pathway via a Pentacoordinated Silicon Ate Complex.

Density functional theory calculations were used to reveal the mechanistic pathway of benzyne formation from a Kobayashi precursor, for which two methods were employed: (1) direct geometry optimization in solvent; (2) single-point energy calculations in solvent on the basis of the gas-phase-optimized geometries. The first method suggested that the overall process involved fluoride ion attack to afford a pentacoordinate silicon ate complex, aryl-Si bond cleavage, and consequent irreversible triflate dissociation to produce the benzyne intermediate. The rate-determining step was found to be the addition of the fluoride ion to the trimethylsilyl group. However, this step was missing in the second method. Moreover, the mechanism and reactivity of this transformation were also studied by natural population charge analysis and the Hammett model. [ABSTRACT FROM AUTHOR]