Transforming Non-innocent Phenalenyl to a Potent Photoreductant: Captivating Reductive Functionalization of Aryl...

Herein, we have established a phenalenyl-based molecular scaffold which serves as a potent photoreductant utilizing the empty NBMO in the presence of a base to form a radical anion which, upon photoexcitation, behaves as a stronger reductant and accomplishes the cleavage of strong C-X (X = Cl, Br, I) bonds under milder reaction conditions. The base was found to be involved in a dual role of electron and hydrogen atom donor. Further, the aryl radical formed by the homolysis of C-X bonds in this technique was captured for the C_sp2-C_sp2 coupling with unactivated arenes. The photoreductant potency of the phenalenyl-based catalytic system was further extended to C-P as well as C-B bond formation reactions. EPR and lifetime studies reveal the formation of a persistent radical having a sufficient lifetime to take part in the reaction by the PET mechanism. Different spectroscopic techniques combined with DFT calculations were utilized for the characterization of active catalytic species and for the elucidation of plausible mechanistic pathways. This not only is the initial report of the application of phenalenyl as a photoreductant but also provides a completely metal-free (alkali and transition metal) approach for the challenging reductive functionalization of aryl halides at room temperature.