The Development and Investigation of Catalytic Photochemical Radical Reactions Mediated by Visible Light.

[摘要] Metal-based polypyridyl photocatalysts such as [Ru(bpy)3]Cl2, [Ir(ppy)2(dtbbpy)]PF6, [Ir{dF(CF3)ppy}2(dtbbpy)]PF6, and fac-Ir(ppy)3have been shown to be effective for the cleavage of C–Y bonds (Y = Cl, Br, I, O, N, P, H, and B) mediated by single electron transfers. All of the photocatalysts mentioned above share similar modes of action and are all excited by visible light via absorption of a photon by the ground state photocatalyst to generate a spin-allowed high energy singlet excited state. In terms of electron transfer processes, the excited state species is ;;bipolar” in nature and can either undergo a single electron oxidation (oxidative quenching) or a single electron reduction (reductive quenching). The oxidative quenching pathway involves a direct single electron transfer (SET) from the excited state of the catalyst (*PCn to PC(n+1)) to the substrate to reduce the C–Y bond, while the reductive quenching pathway involves two SET processes whereby the excited state is reduced by an electron donor to generate a strong reductant (PC(n-1)) which can then transfer an electron to the substrate to effect reduction of the C–Y bond. I have successfully utilized these photocatalysts to reduce C–Cl, C–Br, C–I, and C–O bonds to generate carbon-centered radicals capable of undergoing H-atom abstraction (Chapter 2), intramolecular cyclization (Chapter 2) and intermolecular coupling (Chapter 3). In addition, these methods have been applied to biomass conversion (Chapter 4).

[发布机构] University of Michigan

[效力级别] photoredox catalysis

[关键词] visible light;photoredox catalysis;reductive radical dehalogenation;atom transfer radical addition;lignin degradation;Chemistry;Science;Chemistry