Development of Visible-Light Photoredox Methodologies towards the Activation of Carbon-Halogen Bonds

Visible light photoredox Catalysis have been accomplished with several readily available bench-stable chemicals such as carboxylic acids, potassium alkyltrifluoroborates, ammonium alkyl silicates or redox-active esters among others. Under light irradiation, these precursors get activated by single-electron transfer processes with photoexcitable catalysts (PCs). Among them, organic halides are convenient coupling partners in photocatalysis since they undergo reductive C-halogen bond cleavage catalysed by several PCs in the presence of a sacrificial electron-donor. Non-activated alkyl chlorides, which are readily available and bench-stable feedstocks, exhibit an inherent chemical inertness, in part, due to their large negative reduction potentials. This precluded their widespread use as radical precursors in visible-light photocatalysis. In this doctoral dissertation we explored the use of a dual catalyst system based on first-row transition metals (Cu, Co, Ni) for the activation of these inert Carbon-Halogen bonds. Catalyst design has been key for developing a mild and general photoredox methodology for the dehydrodehalogenation reaction and the intramolecular reductive cyclization of non-activated alkyl halides with tethered alkenes or alkynes. The cleavage of strong Csp3-X bonds is mediated by a highly nucleophilic low-valent cobalt or nickel intermediate generated by visible-light photoredox reduction employing a copper photosensitizer.

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