Synthesis and Isolation of a Silylsilicate Containing Two Pentacoordinated Silicon Atoms by Monoprotonation of a Disilicate and Monodeprotonation of a Disilane

Abstract

A silylsilicate, which is an intermediate in double protonation of a disilicate bearing two sets of a C,O-bidentate ligand at two pentacoordinated silicon atoms to give a disilane, was synthesized and isolated. The X-ray crystallographic analysis of both the silylsilicate and the disilane revealed intramolecular O···Si coordination, giving the silicon atoms pentacoordinated states. In the silylsilicate, the Si1–O2 and Si2–O3 bonds are almost in parallel. Deprotonation of the silylsilicate, which was also prepared by monodeprotonation of the disilane, gave the disilicate. The oxidation potential and UV/vis absorption maximum are both intermediate between those of the disilicate and the disilane, reflecting the changes in the charges.

Oxidative Bond Cleavage of the Silicon-Silicon Bond of a Pentacoordinated Disilicate

“…Monitoring of the reaction solution in THF by 19 F NMR spectroscopy before the quenching revealed complete disappearance of the peaks (δ F -76.9 and -75.7 ppm) from disilicate 1-Li and appearance of the peaks (δ F -77.7 and -77.2 ppm) from hydroxysilicate 5-Li [16] within 10 min. The 19 F NMR chemical shifts of the latter minor product 2-Li were different from those of the reported data in the previous paper [15], and it was caused by strong dependence of the NMR spectra of 2-Li on the solvent and the concentration of water in the solution. Monitoring of the reaction in the absence of the base revealed formation of hydroxysilicate 5-Li (89%) together with a minor product, silylsilicate 2-Li [15] (11%), which showed peaks at δ F -76.5, -76.2, -75.6, and -74.3 ppm in THF.…”

“…As we previously reported, the electron-releasing ability of the Si Si bond compounds should decrease in the order of disilicates 1, silylsilicates 2, and disilane 3 considering the oxidation potentials (1-TBA: -0.22 and 0.83 V, 2-TBA: E pa = 0.76 V vs. Fc/Fc + , and no peak was observed for 3) [14,15]. The key should be formation of 2-Li as a coproduct in the absence of a base.…”

“…The countercation of the intermediary silicate could not be determined because more than one cation exist in the solution. Monitoring of the reaction in the absence of the base revealed formation of hydroxysilicate 5-Li (89%) together with a minor product, silylsilicate 2-Li [15] (11%), which showed peaks at δ F -76.5, -76.2, -75.6, and -74.3 ppm in THF. The 19 F NMR chemical shifts of the latter minor product 2-Li were different from those of the reported data in the previous paper [15], and it was caused by strong dependence of the NMR spectra of 2-Li on the solvent and the concentration of water in the solution.…”

“…However, cleavage of a pentacoordinated silicon-pentacoordinated silicon bond is quite rare [12], despite the fact that there are several known neutral silicon species bearing such a Si Si bond [13]. In reactions of disilicates 1 with an acid, monoanionic silylsilicates 2 and neutral disilane 3 formed by protonation at one and two oxygen atoms, respectively (Scheme 1) [15]. In reactions of disilicates 1 with an acid, monoanionic silylsilicates 2 and neutral disilane 3 formed by protonation at one and two oxygen atoms, respectively (Scheme 1) [15].…”

“…We previously reported the synthesis of disilicates 1, dianionic Si Si σ -bond compounds consisting of two pentacoordinated silicon atoms [14]. In reactions of disilicates 1 with an acid, monoanionic silylsilicates 2 and neutral disilane 3 formed by protonation at one and two oxygen atoms, respectively (Scheme 1) [15]. In the protonation reactions as well as their reverse deprotonation reactions with bases, the Si Si bond did not cleave SCHEME 1…”