CeCl₃-Mediated Photocatalytic Selective N-Alkylation of Aniline with Benzyl Alcohol over CdS

As the rate-determining step, the activation of alcohol significantly influences the product yield in photocatalytic C-N coupling reactions. Generally, the bare semiconductor-based photocatalysts exhibit poor selectivity of secondary amine during photocatalytic N-alkylation of amine with alcohol due to the excessive oxidation of alcohol to the corresponding aldehyde by photogenerated holes and subsequent easier imine formation without noble metal cocatalysts as hydrogen transfer centers. Herein, we reported a simple and efficient strategy via in situ coordination of an alcohol substrate with the inexpensive and readily available cerium(III) trichloride (CeCl₃) to form Ce(OR)_<i>n</i>Cl_<i>m</i> complexes for photocatalytic selective N-alkylation of aniline with benzyl alcohol over the CdS photocatalyst. Remarkably, 100% aniline conversion and 88.5% selectivity with a formation yield of 9.56 mmol·g^-1·h^-1 toward the secondary amine <i>N</i>-benzylaniline were achieved in 5 h. The mechanistic studies reveal that the generated cerium complexes (Ce(OR)_<i>n</i>Cl_<i>m</i>) act as donors of transient benzaldehyde radicals (RCHO^•) via a Ce^IV/Ce^III redox cycle and a ligand-to-metal charge transfer (LMCT) process for subsequent radicals' addition to <i>N</i>-benzylaniline. In addition, the designed catalytic system demonstrates superior stability and substrate tolerance in the photocatalytic N-alkylation of diverse alcohols and amines.