Scheme 6. Chlorine radial and benzoate radical competition for hydrogen atom abstraction. The experimental findings indicate that benzoic acid can act as HAT catalyst for the reaction to progress, with higher yields of product 4 observed in the presence of a base (Table , entry b and d). In entries a-d, both benzoic acid radicals and chlorine radicals, which are generated during a LMCT reaction with cerium, may act as HAT reagents, but the overall product formation is less efficient given their competitive coordination to cerium. While the reaction gave decent yields in the presence of benzoic acid as a hydrogen atom transfer reagent (entries ad), utilising exclusively cerium-ate-complexes was most efficient in the presence of an additional base (entry h). Activation of the Ce-Cl bond through LMCT leads to the generation of chlorine radicals. Product 4 was formed in good yields using the reactive CeCl6 2-species (entries g and h). and only in traces with CeCl3 as the metal salt (entries e and f). The performance of CeCl3 can be improved by introducing additional halide or alcoholate ligands, whereas CeCl6 2-exhibits fast photo-degradation once exposed to irradiation in polar aprotic solvents. These experimental findings resonate with the outcomes obtained from mechanistic investigations on the CeCl6 2-and CeCl3 photoactivation by the Schelter and Zuo group (Scheme 7). Scheme 7. C-H activation of cyclohexane by CeCl6 2-ligand-tometal charge transfer. Herein, di-tert-butyl-(azodicarboxylate) (DBAD) was employed as a trapping reagent for the nucleophilic carbon-centred radical generated through chlorine-radical induced C-H abstraction on cyclohexane in slight excess. The research group indicated that the reagent served the dual function of a radical trapping agent and an effective photocatalyst. It was anticipated to facilitate the closure of the photocatalytic cycle of Ce 3+ to Ce 4+ through a suitable redox potential for single electron transfer. . In the benchmark reaction outlined in Scheme 4.6, phthalimide 2 was utilised instead of DBAD as a single electron transfer reagent in 1.5 equivalents. Unlike DBAD, the phthalimide reagent could not be excited directly upon irradiation. Hence, no product formation was observed when irradiating the phthalimide species with the starting material 1 in the absence of either the cerium salt or the benzoic acid catalyst, indicating that phthalimide 2 did not function as a photocatalyst (Table entries b and e). The reaction from Table worked upon Ce-Cl LMCT of CeCl6 2-yielding compound 4 in good yields in the presence of an additional base (entry h).