Copper Nanoparticles and Copper-Containing Metal-Organic Coordination Polymers in the Catalytic Amination of 2-Halopyridines

The efficiencies of copper-containing metal-organic coordination polymers (Cu-MOFs) and commercially available unsupported copper nanoparticles (CuNPs) in the amination of 2-iodopyridine, 2-bromopyridine, 2-bromo-5-(trifluoromethyl)pyridine, and 2-bromo-6-(trifluoromethyl)pyridine with n-octylamine and adamantane-containing amines with different steric environments of the amino group have been compared. Under the optimized conditions, the yields of the amination products in the presence of both catalytic systems were generally similar. In the reactions with 2-bromopyridine, increased reactant concentration and the use of 2 equiv of the substrate were necessary to achieve good yields. The presence of a trifluoromethyl group at the 6-position of the pyridine ring improved the yield of the amination products. An increase in steric hindrances at the amino group resulted in an appreciable decrease in the yield under catalysis by Cu-MOFs; however, reactions with such amines were successfully performed in the presence of CuNPs, and CuNPs of the average size 25 nm proved to be superior to bifractional nanoparticles with average sizes of 10 and 80 nm. On the other hand, increased concentration of the reactants in the Cu-MOF-catalyzed amination provided good yields of the target compounds in the absence of a ligand.