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1.
J Org Chem ; 83(16): 9381-9390, 2018 Aug 17.
Artículo en Inglés | MEDLINE | ID: mdl-30005575

RESUMEN

Carbon radicals are reactive species useful in various organic transformations. The C-X bond cleavage of organohalides by photoirradiation is a common method to generate carbon radicals in a controlled fashion. The use of organochloride substrates is still a formidable challenge due to the low reduction potential and the high dissociation energy of the C-Cl bond. In this report, we address these issues by using a nonmetal organic molecule with a relatively simple structure as a photocatalyst. In this catalyst (bis(dimethylamino)carbazole), the amino groups increase both the HOMO and LUMO energy levels, especially in the former. As a result, compared to the parent molecule, the new catalyst shows experimentally red-shifted absorption in the visible region and forms an excited state with better reducing capability. This photocatalyst was used in the reduction of unactivated aryl chlorides and alkyl chlorides in the presence of hydrogen atom donor at room temperature. The catalytic system can also be applied to the coupling of aryl chlorides with electron-rich arene and heteroarenes to affect the C-C bond-forming reactions. Our mechanistic study results support the assumption that carbon radicals are formed from the organochlorides via a single-electron-transfer step.

2.
Nat Chem ; 15(6): 794-802, 2023 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-36959509

RESUMEN

Increasing levels of CO2 in the atmosphere is a problem that must be urgently resolved if the rise in current global temperatures is to be slowed. Chemically reducing CO2 into compounds that are useful as energy sources and carbon-based materials could be helpful in this regard. However, for the CO2 reduction reaction (CO2RR) to be operational on a global scale, the catalyst system must: use only renewable energy, be built from abundantly available elements and not require high-energy reactants. Although light is an attractive renewable energy source, most existing CO2RR methods use electricity and many of the catalysts used are based on rare heavy metals. Here we present a transition-metal-free catalyst system that uses an organohydride catalyst based on benzimidazoline for the CO2RR that can be regenerated using a carbazole photosensitizer and visible light. The system is capable of producing formate with a turnover number exceeding 8,000 and generates no other reduced products (such as H2 and CO).

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