Dual Photosensitizer Cycles Working Synergistically in a C(sp)-C(sp3) Cross-Coupling Reaction

To assess the value and reactivity of new photocatalysts (PCs), their performance should be evaluated in one or more established reactions and benchmarked against the performance using known PCs. Here, we evaluated our recently developed PC, pDTCz-DPmS, in a C(sp)-C(sp3) cross-coupling reaction that had been documented in the literature. Previous findings indicated this reaction could not proceed in the absence of PC; however, under our conditions this was not the case. Without PC, a moderate product yield was obtained, while this yield increased significantly upon addition of pDTCz-DPmS. UV-Vis absorption studies indicated that the Hantzsch ester (HE) additive was acting as a competitive absorber of the light from the excitation source, and quenching studies confirmed that the HE was quenched by the radical precursor, N-(acyloxy)phthalimide. Mechanistic investigations established that two parallel photosensitization pathways were in operation; a reductive quenching photocatalytic pathway (using pDTCz-DPmS) and a sacrificial photoreductant pathway (employing HE). These pathways work synergistically to enhance the yield of target product.