Visible‐Light‐Mediated Metal‐Free Hydrosilylation of Alkenes through Selective Hydrogen Atom Transfer for Si−H Activation

Abstract

Although there has been significant progress in the development of transition-metal-catalyzed hydrosilylations of alkenes over the past several decades, metal-free hydrosilylation is still rare and highly desirable. Herein, we report a convenient visible-light-driven metal-free hydrosilylation of both electron-deficient and electron-rich alkenes that proceeds through selective hydrogen atom transfer for Si-H activation. The synergistic combination of the organophotoredox catalyst 4CzIPN with quinuclidin-3-yl acetate enabled the hydrosilylation of electron-deficient alkenes by selective Si-H activation while the hydrosilylation of electron-rich alkenes was achieved by merging photoredox and polarity-reversal catalysis.

Recent Developments in the Photo‐Mediated Generation of Silyl Radicals and Their Application in Organic Synthesis

“… Representative scope of metal‐free hydrosilylation of electron‐deficient alkenes. [a] Reactions carried out in stop‐flow microtubing (SFMT) reactors …”

“…In 2017, Wu group demonstrated the visible-light mediated metal free hydrosilylation of both electron-deficient and electron-rich alkenes. [19] The hydrosilylation of electron-deficient alkenes was accomplished through SiÀH activation by merging organophotocatalyst 1,2,3,5-tetrakis (carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) and quinuclidinium HAT catalyst (Scheme 6). Hydrosilylation product was obtained using trialkyl silanes without any CÀH activation by-products, highlighting the effectiveness of this electron-deficient HAT catalyst for the selective SiÀH activation.…”

“…[a] Reactions carried out in stop-flow microtubing (SFMT) reactors. [19] Scheme 7. Plausible mechanism for the hydrosilylation of electron-poor alkenes.…”

“…[18] To the best of our knowledge, there is no recent review on photo generation of silyl radicals with or without the aid of catalysts. In line with our recent work on visible-light mediated metalfree hydrosilylation, [19] this mini review seeks to showcase the recent development on photo-mediated generation of silyl radicals and their application in organic synthesis.…”

Activation and Deactivation Strategies Promoted by Medium Effects for Selective Aliphatic C−H Bond Functionalization

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ther eagents that are typically involved in these processes include heteroatomcentered radicals and radical ions,p hotoexcited species and photocatalysts (carbonyl compounds,polyoxometalates), biocatalysts (cytochrome P450 and oxygenases) and bioinspired catalysts,a swell as closed-shell species such as dioxiranes. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ther eagents that are typically involved in these processes include heteroatomcentered radicals and radical ions,p hotoexcited species and photocatalysts (carbonyl compounds,polyoxometalates), biocatalysts (cytochrome P450 and oxygenases) and bioinspired catalysts,a swell as closed-shell species such as dioxiranes.…”