Cross-coupling reactions catalyzed by transition metal complexes have an enormous synthetic utility in the preparation of complex biologically active organic molecules. Their potential relies on the construction of a wide range of C-C bonds under mild reaction conditions and with excellent functional group tolerance. In the quest of more sustainable methodologies, the synergistic merger of photoredox and metal catalysis has appeared as a promising strategy for practical C-C bond forming reactions using the energy of light. In contrast to classical cross-coupling reactions, which rely on two-electron elementary steps, photoredox and metal dual catalysis takes advantage of the ability of first-row transition metals (TMs) to participate in single-electron transfer reactions. In this regard, nickel is at the forefront of photoredox metal dual catalysis, while the rest of the first row TMs pass unnoticed in this field. Thus, since ligand design is a key factor in coordination complexes for modulating their reactivity, exploration of other metal complexes in combination with photoredox catalysts will open a venue for C-C bond forming transformations showing a new variety of reactivity patterns.<br/>Indeed, the high nucleophilicity of low valent cobalt(I) complexes can be exploited for the cleavage of strong carbon-halogen. Thus, we disclose here a family of photogenerated cobalt(I) complexes based on tetra- and pentacoordinated polyaminopyridyl ligands that enable radical cyclizations as well as intermolecular C-C bond forming reactions. The use of copper photoredox catalyst, instead of typical Ru and Ir polypyridyl complexes, makes the developed process appealing for green radical cyclizations. The discovery of highly robust and selective catalytic systems is speeded up by using a parallel photoredox screening platform for high-throughput experimentation.

Visible-light radical cyclizations by photoredox/cobalt dual catalysis

253rd National Meeting (2017)

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