Phenazine-Based Donor Acceptor Systems as Organic Photocatalysts for “Metal-free” C–N/C–C Cross-Coupling
Harnimarta Deol, Gurpreet Singh, M. Kumar, Vandana Bhalla
Abstract
With an aim to achieve a balance between ground-state and excited-state reduction potential of donor acceptor systems for efficient C–N/C–C cross-coupling, a series of donor acceptor systems DA1–DA4 have been synthesized by varying the donor strength and connecting positions. With an increase in donor strength, systematic elevation in the ground-state reduction potential and decrease in the HOMO–LUMO gap was observed. Interestingly, all the derivatives DA1–DA4 could catalyze the C–N bond formation reaction between activated aryl halides and amines at low catalytic loading under metal-free conditions without the need of any external base upon irradiation with white LED. A balance was realized in the case of derivative DA2, which exhibits high efficiency in C–N couplings. Different control experiments support the validity of the energy as well as electron transfer pathways in the visible light-mediated C–N bond formation. This study further reveals the potential of derivative DA1 in “metal-free” Sonogashira coupling involving activated aryl halides which is attributed to its high excited-state reduction potential.