Mechanistic investigations of Co(II)-Catalyzed C-N coupling reactions

The density functional theory (DFT) method was used to investigate the mechanism of N-arylation of nitrogen heterocycles with aryl halides catalyzed by CoCl₂·6H₂O in the presence of different chelating ligands. Cobalt complexes of N, Nˊ-dimethylethenediamine ligand were selected as model catalytic system. Calculations were carried out for single electron transfer, oxidative addition/reductive elimination, iodine atom transfer and σ-bond metathesis mechanism for different possible intermediate cobalt complexes in the reaction solution. According to calculation results, the single electron transfer mechanism has the lowest activation energy (23.3 kcal/mol) for the C-N coupling reaction. Iodine atom transfer mechanism shows 25.6 kcal/mol activation energy for the reaction. Activation energy for oxidative addition/reductive elimination (49.2 kcal/mol) and σ-bond metathesis mechanism (45.5 kcal/mol) is very high under the given experimental conditions.