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

Abstract

Silicon radicals play important roles in diverse areas of organic synthesis and material science. With the rapid development of photocatalysis over the past decades, photochemistry may potentially serve as an appealing approach for the generation of silyl radicals. This Minireview will focus on recent photo‐mediated generation of silyl radicals in the area of organic synthesis.

Neutral‐Eosin‐Y‐Photocatalyzed Silane Chlorination Using Dichloromethane

“…Photo‐induced direct HAT catalysis has endowed with a wide range of reaction patterns to allow C−H functionalization . However, Si−H activation has rarely been investigated as a means of synthesizing value‐added silicon compounds through the use of modern photocatalysis strategy . As silicon is more electropositive than carbon (electronegativity of 1.90 vs. 2.55 on the Pauling scale), Si−H bonds are generally more hydridic than C−H bonds.…”

“…[2] However,S i À H activation has rarely been investigated as am eans of synthesizing value-added silicon compounds through the use of modern photocatalysis strategy. [3] As silicon is more electropositive than carbon (electronegativity of 1.90 vs. 2.55 on the Pauling scale), SiÀHb onds are generally more hydridic than C À Hb onds.I nt his context, we have recently achieved av isible-light mediated hydrosilylation of both electron-deficient and electron-rich alkenes through the synergistic merger of ap hotoredox catalysts and aH AT mediator. [4] Additionally,w er ecently disclosed the unique property of neutral eosin Y, which can function as an ideal direct HATp hotocatalyst owing to its visible-light-absorption, metal-free,r eadily available,a nd low-cost nature.…”

“…[16] They provide an excellent platform for photochemical reactions owing to the enhanced and uniform light irradiation and ease of scaling up. [17] As demonstrated in Scheme 4, the silane chlorination assisted by an operationally simple continuous-flow microtubing reactor was amenable to gram-scale production (2,3,11). More intriguingly,s tepwise chlorination of di-and trihydrosilanes (R 1 R 2 SiH 2 and RSiH 3 )w as successfully achieved in ahighly selective manner (23 vs. 17; 24 vs. 25 vs. 22).…”

Sila‐ and Germacarboxylic Acids: Precursors for the Corresponding Silyl and Germyl Radicals

“…[4] In this context, photoinduced protocols incorporating aH AT process have also been established for the generation of R 3 SiC from R 3 SiH (Scheme 1B). [5][6][7][8][9] In 2015, the group of Fagnoni and Ravelli demonstrated aH AT-photocatalysis pathway for the preparation of silyl radicals,i nw hich the photocatalyst (PC) also acts as an HC acceptor. [6] Meanwhile,t he MacMillan group developed ap rotocol that involves dual catalytic cycles (transition-metal or HATc atalysis combined with photocatalysis).…”

“…[6] Meanwhile,t he MacMillan group developed ap rotocol that involves dual catalytic cycles (transition-metal or HATc atalysis combined with photocatalysis). [7] More recently,Wuand co-workers established an elegant catalytic protocol for the generation of various types of R 3 SiC, [8] in which the combination of HATand photoredox reactions enabled the catalytic use of the HATr eagent, resulting in high atom efficiency.Although these reactions are synthetically useful, few alternatives are available, [5] and R 3 SiH remains the most widely used precursor of R 3 SiC, despite the fact that it is readily oxidized in air (or even combustible). Herein, we describe anew method to generate silyl or germyl radicals through the visible-light-induced decarboxylation reaction of silacarboxylic or germacarboxylic acids,r espectively [10] (Scheme 1C).…”