Blue‐LED oxidative coupling of amines to N‐alkyl imines by metal‐free meso‐tetraphenyl porphyrin/lignin‐nanoparticles

Photocatalysts based on the immobilization of meso-TPP on lignin-nanoparticles were prepared and applied in the one-pot oxidative coupling of aromatic amines to N-alkyl imines. Heterogeneous catalysts were effective in both homocoupling and cross-coupling conditions, affording desired products in high yield. Among the immobilization procedures tested, the dialysis method afforded the most effective photocatalyst, which was characterized by the lower energy gap between the HOMO and LUMO of lignin. Lignin-nanoparticles alone showed the capacity to catalyze the oxidative coupling, suggesting the possibility of a synergy effect with immobilized meso-TPP. The sustainability of the procedure was confirmed by the use of the photocatalyst for more runs.