Photocatalytic Giese‐Type Reaction with Alkylsilicates Bearing C,O‐Bidentate Ligands

Abstract

Herein, a photocatalytic Giese‐type reaction with alkylsilicates bearing C,O‐bidentate ligands as stable alkyl radical precursors has been reported. The alkylsilicates were prepared in one step from organometallic reagents. Not only primary, secondary, and tertiary alkyl radicals, but also elusive methyl radicals, could be generated by using the present reaction system. The generated radicals were trapped by electron‐deficient olefins bearing various functional groups to give the desired alkyl adducts. The silicon byproduct can be recovered after the photoreaction. The radical generation process was investigated by theoretical calculations, which provided an insight into the facile generation of methyl radicals from methylsilicate bearing C,O‐bidentate ligands.

Phenyl Silicates with Substituted Catecholate Ligands: Synthesis, Structural Studies and Reactivity

“…The presence of two isomers was also confirmed by 13 C NMR. All resonances of the non-symmetrical catechol moieties in 13 C NMR were doubled with identical integration for both species in the case of 1 d, but also for the other nonsymmetrical phenylsilicates 1 b, 1 c, 1 h. It has to be mentioned that this type of 1 : 1 mixture of two isomers was also observed in the cyclohexyl series (silicates 6 b-d).…”

“…Intrigued by this finding, we wondered if an equilibrium exists between both cis and trans isomers in solution. To answer this question, 13 C NMR of 1 h at various temperatures was conducted (in [D 6 ]acetone at low temperature (below 273 K) and [D 6 ]DMSO at higher temperature (from 303 K), Figure 3). [19] A coalescence of the peaks was observed above 333 K probably due to Berry pseudo-rotation [20] suggesting that an equilibrium exists between the two isomers.…”

“…[12] Up to 150 mol % of biphenyl (BP)/1,4-dicyanonaphthalene (DCN) as photocatalytic mixture had to be used under UV irradiation to provide moderate yields (~50 %) of aryl radical adducts. Of note also, at the occasion of a very recent study by Morofuji and Kano [13] dedicated to the photo-oxidation of alkylsilicates bearing the hexafluorocumyl alcohol dianion ligand (Martin's ligand), a single example of oxidation of the corresponding phenylsilicate gave 10 % of Giese-type adduct from the phenyl radical. This underlines that the generation of aryl radicals under photo-oxidative conditions is highly challenging.…”

Photocatalytic C(sp3) radical generationviaC–H, C–C, and C–X bond cleavage

“…220 Interestingly, with the [Mes-Acr + -Ph]BF 4 − photocatalyst ( = +2.08 V vs. SCE in MeCN), radical addition to electron-deficient alkenes was also achieved by the same group, including methylation. 221…”

Boron, silicon, nitrogen and sulfur-based contemporary precursors for the generation of alkyl radicals by single electron transfer and their synthetic utilization

“…In 2021, the same authors applied the use of silicates 111 in Giese-type additions with several activated olefins 114 in the presence of a catalytic amount of di- t Bu-Mes-acridinium photocatalyst ([di- t Bu-Mes-AcrBF 4 ], = +2.08 V vs. SCE) under blue light irradiation (Scheme 37). 79 The reaction proceeds smoothly through reductive quenching between the photocatalyst and the silicates. A wide range of primary, secondary and tertiary alkyl radicals could be generated and efficiently coupled with olefins affording the Giese adduct 115 in good to excellent yields.…”