Copper and Copper Oxide Nanoparticles in the Synthesis of N-Arylamines of the Adamantane Series

N-Arylation of a number of adamantane-containing amines with iodobenzene and its derivatives bearing electron-donating and electron-withdrawing substituents at the para or meta position was studied using unsupported copper and copper oxide nanoparticles as catalysts. The best yields of the target N-aryl derivatives were achieved in DMSO at 110°C in the presence of the catalytic system CuNPs 10/80 nm/rac-BINOL. In some cases, the use of 2-acetylcyclohexanone or 2-isobutyrylcyclohexanone as a ligand and DMF as a solvent at 140°C was possible. The maximum yields of N-arylamines exceeded 90%. The efficiency of the arylation reaction was found to depend on the substrate structure, whereas the effect of substituents in the aromatic ring was not so significant. Study of the copper leaching to solution in the course of the model reaction showed that the degree of leaching depends on the ligand nature. For comparison, N-heteroarylation of adamantane-containing amines with trifluoromethyl-substituted 2-bromopyridines was found to be accompanied by more significant leaching of copper. According to the transmission electron microscopy, electron diffraction, and energy-dispersive X-ray spectroscopy data, copper nanoparticles with an average particle size of 25 nm are converted during the reaction mainly to copper(I) oxide, the average particle size remaining almost unchanged.