Consecutive Photocatalysis vs Electro-Photocatalysis. Excitation of Radical Anions of Naphthalene Diimides.
Photo- and electrochemical transformations represent excellent opportunities for the development of methodologies environmentally friendly and combination of both techniques would result in improved methodologies. Recently, photochemical transformations involving the excitation of open-shell species has become a reality. Photostimulated electron transfer (PET) from radical anions of organic dyes have been used in consecutive photoredox catalysis and electro-photocatalysis transformation, allowing the transformation of aryl halides in valuable compounds under mild conditions. The similarities of both techniques raises the question of the convenience of using one or other related and a close evaluation is necessary to drive further development and have been shyly done in previous works. However, an objective comparison of both approaches will require using the same chemical system. We present here a direct comparison of a “pure” photochemical and an electrophotochemical transformartion studying a model transformation, namely, a C-H substitution in (hetero)aromatic systems with a C-C bond formation through reaction of halogenated substrates. Through a detailed investigation of both mechanisms, we identify a system that could be applied in both approaches with minor (necessaries) changes in the reaction conditions and clearly identify the excitation of radical anion of naphthalene diimides as the key intermediates. Both approaches are comparable in yields and kinetics with slightly better yields for the consecutive PET reaction and better selectivity for the electro-PET process. Our work offers a system that could be used for a more profound comparison of the experimental setups which could include, for instance, the important factor of energy consumption.