Selective photocatalytic reactions with organic photocatalysts

Abstract

Selective photocatalytic oxygenation of various substrates has been achieved using organic photocatalysts via photoinduced electron-transfer reactions of photocatalysts with substrates and dioxygen under visible light irradiation. Photoinduced electron transfer from benzene to the singlet-excited state of the 3-cyano-1-methylquinolinium ion has enabled the oxidation of benzene by dioxygen with water to yield phenol selectively. Alkoxybenzenes were obtained when water was replaced by alcohols under otherwise the same experimental conditions. Photocatalytic selective oxygenation reactions of aromatic compounds have also been achieved using an electron donor-acceptor linked dyad, 9-mesityl-10-methylacridinium ion (Acr + -Mes) acting as a photocatalyst and dioxygen as an oxidant under visible light irradiation. The oxygenation reaction is initiated by intramolecular photoinduced electron transfer from the mesitylene moiety to the singlet-excited state of the acridinium moiety of Acr + -Mes to afford an extremely longlived electron-transfer state. The electron-transfer state can oxidize and reduce substrates and dioxygen, respectively, leading to selective oxygenation and halogenation of substrates. C-C bond formation of substrates has also been made possible by using Acr + -Mes as a photocatalyst.

Detection of Fleeting Amine Radical Cations and Elucidation of Chain Processes in Visible-Light-Mediated [3 + 2] Annulation by Online Mass Spectrometric Techniques

“…The protonated CPA-d 5 reaction product [ 3 -d 5 +H] + at m/z 243 was not observed (Figure S6, Supporting information). Presumably, because the lifetime of the photo-excited 4 is much shorter than the transportation time for the reaction mixture to flow from the irradiation window to the Tee mixer (0.74 μs 1a vs. about 472 ms), the photochemically pre-excited Ru catalyst 4 could be deactivated before reaching CPA-d 5. …”

“…1 The heightened interest in this topic is likely attributed to photoredox catalysis’ versatility in generating radicals using light under mild conditions, a specific mode of activation, which is different from how radicals are produced under non-photo conditions. 2 As such, it provides means to explore radical chemistry that is complementary to those under non-photo conditions.…”

Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis

“…These catalysts have been employed to achieve a vast range of bond-forming reactions of broad utility in organic synthesis. 16 Visible light photocatalysis has also been carried out with heterogeneous semiconductors such as mesoporous carbon nitride 17 and various metal oxides and sulfides. 18 These approaches are often complementary to photoredox catalysis with transition metal-polypyridyl complexes, and we have referred to work in these areas when it is similar to the chemistry under discussion.…”

“…However, an in-depth discussion of the extensive literature in these fields is outside the scope of this Review, and readers are directed to existing reviews on these topics. 16–18 …”

Light on Unsaturated Hydrocarbons – “Gotta Heterofunctionalize Them All”

“…This strategy has been developed mainly by Nicewicz and coworkers. For this purpose, the previous research into moreoxidative photocatalysts of Fukuzumi and coworkers [27] led to the development of acridinium photocatalysts with high oxidation potentials (i.e., +2.0 V vs. SCE). This kind of catalyst is able to oxidize alkenes to the corresponding radical cation alkenes, which may then be engaged in radical reactions, especially hydroamination reactions.…”