Alkoxy(tetraaryl)silicates bearing 9,10-disilatriptycene skeleton

Abstract

As anionic five-coordinate silicon species (five-coordinate silicates) exhibit high reactivity and unique fluxional behavior, their structure and property have received substantial attention. We report herein synthesis, structure, and fluxional behavior of alkoxy(tetraaryl)silicates having the 9,10-disilatriptycene skeleton (6⁻ and 7⁻). The molecular structure of the cryptate salt [Li(crypt-222)]⁺7⁻ shows that the five-coordinate silicon adopts a distorted trigonal bipyramidal structure with oxygen atom occupying an equatorial position. In the ¹H and ¹³C{¹H} NMR spectra of [Li(crypt-222)]⁺7⁻, a set of signals due to o-phenylene blades in 7⁻ was observed at room temperature, which indicates fluxional behavior of 7⁻ on the NMR timescale. Computational study suggests that the observed process proceeds via a 120° rotation of bidentate ligand around the Si-Si axis that consists of two sequential Berry pseudorotations.