CeCl3-N-Hydroxyphthalimide Complex as Semi-Heterogeneous Photocatalyst for Selective Oxidation of Toluene to Benzaldehyde.
Abstract
The activation of inert C(sp3)-H bonds is the rate-determining step in photocatalytic selective oxidation of toluene, and the easy over-oxidation of target products makes it a great challenge in green organic synthesis. Herein, we report a semi-heterogeneous CeClx-NHPI complex, which is constructed via the coordination of CeCl3 and N-Hydroxyphthalimide (NHPI) for the efficient visible-light-driven selective oxidation of toluene to benzaldehyde under ambient conditions. Impressively, the catalyst achieved a maximum benzaldehyde formation rate of up to 2 mmol·g-1·h-1 in 5 h, with a benzaldehyde selectivity of 80.6%. Mechanistic studies show that the chlorine radicals (Cl·) generated from the coordinated Ce─Cl bond via the ligand-to-metal charge transfer (LMCT) process, and the phthalimide-N-oxyl (PINO) radicals formed from NHPI via single-electron transfer jointly promote the efficient activation of the inert C(sp3)-H bond in toluene. In addition, the CeClx-NHPI complex exhibits good recyclability and broad substrate tolerance for the selective oxidation of various toluene derivatives. This work provides a novel strategy for the design of efficient rare earth-based semi-heterogeneous photocatalysts for the activation of C(sp3)-H bonds.