Manifestation of the β-Silicon Effect in the Reactions of Unsaturated Systems Involving a 1,2-Silyl Shift

Abstract

Many chemical transformations of organosilicon compounds proceed due to the capability of silyl substituents to stabilize a positive charge in its β-position. This short review provides an overview of the present understanding of the β-silicon effect and focusses on the synthetic applications of 1,2-silyl shifts resulting from non-vertical stabilization of alkylcarbenium ions and vinyl cations. The reactions of silicon containing unsaturated starting materials, alkenes, allenes, and alkynes, involving β-silyl group stabilized cationic intermediates, transition metal carbenes, or vinylidene complexes will be discussed.1 Introduction2 Origins of the β-Silicon Effect3 Reactions of Allenylsilanes4 Reactions of Alkynes4.1 Propargylsilanes4.2 Alkynylsilanes5 Reactions of Alkenes5.1 Allylsilanes5.2 Vinylsilanes6 Conclusions

Hydrosilylation of BB triple bonds: catalyst- and reductant-free construction of B–Si bonds and B2Si heterocycles

“…Indeed, carbon centers contribute to these orbitals in the range of 10–16%. This donation from the B–Si σ bonds to the vacant p orbitals at the NHC carbon atoms is likely an example of a form of hyperconjugation known as the β-silicon effect, 22 similar to that observed by Siehl et al in a β-silyl-substituted vinyl cation. 23 Similar to the diborene, these donations exhibit uneven distribution, stemming from distinct tilting angles arising from unequal steric effects.…”

Skeletal Rearrangements Involving Cyclopropyl- and Alkene-Stabilized Silylium Ions

“…Based on this effect, commonly referred to as the -silicon effect (Scheme 1b), [3][4][5][6] various synthetically useful transformations with vinyl, allyl, propargyl, allenyl and other silanes have been established in both Lewis acid and transitionmetal catalysis. 3,4 Of note, there is another, far less exploited role of C(sp 3 )-Si bonds that helps stabilizing carbenium ions, the socalled -silicon effect. 7,8 More precisely, the back lobe of a C(sp 3 )-Si bond can interact with the empty p-orbital by percaudal homohyperconjugation (Scheme 1c).…”

Ligand-controlled regiodivergence in cobalt-catalyzed hydrosilylation of isoprene

“…Owing to the abundance of silicon in the Earth's crust and the unique stability of C–Si bonds, organosilicon compounds have been extensively applied in materials science, 1 medicinal chemistry, 2 and organic synthesis. 3 During the past decades, catalytic hydrosilylation of unsaturated C–C bonds has been established as one of the most straightforward methods and atom-economical approaches for the preparation of value-added organosilanes. 4 In this context, tremendous efforts have been made toward the Markovnikov or anti-Markovnikov hydrosilylation reactions of alkenes 5 and alkynes.…”