Merging Heterogeneous Graphitic Carbon Nitride Photocatalysis with Cobaloxime Catalysis in Uphill Dehydrogenative Synthesis of Anilines

Abstract

Synthesis of substituted anilines upon nucleophilic addition of secondary amines to cyclohexanone derivatives followed by aromatization of the enamine by employing a combination of Ir-polypyridine complex as a photoredox catalyst and cobaloxime as H₂-evolution catalyst is developed recently by Leonori et al. In this work, the homogeneous photoredox catalyst is replaced by a heterogeneous and metal-free mesoporous graphitic carbon nitride (mpg-CN). Substituted aromatic amine and H₂ are formed simultaneously. Combination of X-ray spectroscopies reveals charge transfer from cobaloxime to mpg-CN in the dark. Illumination of the catalytic system with visible light induces electron transfer from mpg-CN to cobaloxime and formation of persistent Co(II) species. The results of density functional theory modeling suggest that the studied reaction is strongly endothermic and endergonic. Thus, energy of photons is stored in the reaction products—H₂ and the aromatic amine.