Homogeneous and Semi-Heterogeneous Magnetically Retrievable Bis-N-Heterocyclic Carbene Rhodium(I) Based Catalysts for Selective Hydroaminomethylation Reactions

The preparation of various bis-N-heterocyclic carbene (bis-NHC) complexes of rhodium and their application in the hydroaminomethylation of vinyl arenes was investigated. Various reaction parameters such as solvent, temperature, and pressure were tested, and the optimized protocol was applied to a wide variety of vinyl arenes and amines to afford the corresponding amines in good yields with high selectivity towards the branched product. The bis-NHC-based catalyst demonstrated superior reactivity and selectivity compared to catalysts containing bidentate phosphine or monodentate NHC ligands. A triethoxysilyl-functionalized bis-NHC ligand was immobilized on magnetic nanoparticles and then utilized to bind a rhodium catalyst. The resulting catalytic system was successfully employed in hydroaminomethylation reactions. The catalyst exhibited excellent reactivity, high selectivity, and was simply recovered from the reaction medium by applying an external magnetic field.