Visible-light metallaphotoredox strategies for organic transformations through the cleavage of Csp3−Cl bonds

Recent photocatalytic methods based on the visible-light-induced generation of reactive radicals have allowed the construction of a large variety of C−C bonds. The inertness of chloroalkanes has precluded them as prevailing coupling partners in both conventional and photocatalytic cross-coupling reactions. In fact, few examples of using unactivated alkyl chlorides as building blocks have been developed, presenting limitations in their applicability for a general methodology. In the last years, our research group has been focused on the understanding of visible light photo-induced generation of radicals, using a dual bimetallic system based on earth-abundant metals.

In this line, this thesis describes the development of a new familiy of tetradentate aminopyridine Co and Ni complexes able to activate different chloroalkanes. The ligand availability, modularity and versatility let us the tune of the metal first coordination sphere by changing the electronic and structural features of the ligand. A collection of eighteen new Co and Ni complexes have been studied presenting a playground for synthetic methodology development.

As a main project, we disclosed a novel photoredox-catalyzed reductive cross-coupling reaction using inert chloroalkanes and alkenes as coupling partners. The general applicability of this methodology displays inert alkyl chlorides as interesting electrophiles for C−C bond formation in organic synthesis.

Finally, we went one step further, reporting the photoredox-catalyzed activation of inert and common chlorinated solvents (CH₂Cl₂ and CHCl₃) for the tuneable functionalization of aromatic olefins, affording a straightforward cyclopropanation method and/or a chloroalkanes synthesis.

The combination of spectroscopical (fluorescence quenching, UV-Vis, EPR, NMR) and electrochemical techniques (CV, SEC) with DFT studies and reactivity allowed us to shine light into the reaction mechanism, wherein a photogenerated low-valent metal species reacts with the chloride substrate forming a carbon-centered radical. We also discussed the nucleophilic capacity of the low oxidation state metal center in relation with the Csp³−Cl activation mechanism.

This thesis paves the way for a widespread extension of earth-abundant metallaphotoredox protocols for the implementing common and inert alkyl chlorides as feasible coupling partners.

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