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Development and Characterization of Photoactive Copper(I) Complexes and their Applications in Photoredox Catalysis of Organic Reactions

par Beaudelot, Jérôme
Président du jury Doneux, Thomas
Promoteur Evano, Gwilherm
Co-Promoteur Moucheron, Cécile
Publication Non publié, 2023-02-24

Thèse de doctorat

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Résumé :

Photoredox catalysis combines the energy of light with a photocatalyst able to absorb it and promote electron transfers toward a substrate. In the last two decades, it has been increasingly used in the field of synthetic chemistry, where it allows the generation of highly reactive radical species under mild reaction conditions but has found limited industrial applications due to the needs for expensive noble metal photocatalysts to conduct these reactions.Photoactive copper(I) complexes have been increasingly studied since the discovery of their photochemical properties in 1977, not only because of the attractive availability of copper but also thanks to their innate properties, which upon careful ligand design allow them to compete with photoactive noble metal complexes, notably in the development of OLEDs and for molecular sensing.Therefore, it was not long before scientists started exploiting the interesting photophysical properties and the availability of copper(I) complexes in photoredox catalysis of organic transformations, and in the last ten years, an exponentially-growing number of reports have been published in this regard. These reports demonstrated that copper complexes were efficient to induce a broad range of transformations, but mostly relied on state-of-the-art copper complexes developed for their use in other applications.In this framework, this thesis intends to explore the structure-properties and structure-activity relationships in a class of copper complexes that has been particularly fruitful in photoredox catalysis of organic transformations, and to use the information gathered to design new complexes optimized for their use as photoredox catalysts.To this end, a family of these complexes, designed to exhibit an increased absorption of visible light compared to state-of-the-art complexes of this class, has been developed and their properties have been extensively studied. Their activity on a prototypical photoredox-catalyzed process was also investigated, which allowed to correlate the structure of the complexes to their properties and the influence of these properties on their photocatalytic activity. The information gathered across this study allowed us to develop a second generation of complexes based on a similar ligand scaffold, but with other ligand variations. In this second-generation, the combination of our successful strategy with a previously reported one further increased the absorption of visible light by the complexes, making them ideal candidates for sunlight energy conversion. Together with the study of another family of copper complexes, these investigations expand the existing knowledge on the structure-properties relationships of photoactive copper complexes and should help to design new efficient photocatalysts.In the meantime, a state-of-the-art copper photocatalyst was exploited in three distinctive photoinduced transformations, in which its activity often outcompetes the evaluated noble metal photocatalysts. It notably allowed the perfluoroalkylation of heteroarenes in milder reaction conditions than those previously reported, with a similar but also complementary reaction scope. In a second transformation, its ability to reduce unactivated organic halides was used to access highly-functionalized azetidines, small heterocycles that can be found in several natural products and bioactive compounds. For this transformation, an extensive mechanistic study was conducted and lifted the veil on the catalytic cycle involved in the transformation. This second transformation relied on the activation of organic halides that are difficult to access, which led us to target the proof-of-concept deoxygenation of activated esters, which can be readily obtained from widely available alcohols, as an alternative to the activation of halides. Following an optimization of the reaction conditions, a preliminary scope demonstrated the potential of this method, which was further emphasized by developing one-pot conditions for the deoxygenative activation of alcohols by photoredox catalysis.In the course of this study, a comprehensive investigation on copper-based photocatalysts and on their use in photoredox catalysis of organic transformations has been conducted and gives valuable insights that should participate in the development of copper photoredox catalysis.