Carbon‐Coated Copper Nanoparticles for Heterogeneous Catalytic Synthesis of Fused Pyridines: The Role of Cu and C Components

ABSTRACT A set of 17 composites was prepared by pyrolysis of Cu 2+ complexes with phenanthroline and 1,2‐diaminobenzene (DAB), deposited on SiO 2 (Aerosil). All composites contained Cu and N‐doped carbonaceous component, while some of them additionally contained Cu 2 O or CuCl. According to the data of powder x‐ray diffraction (PXRD), the size of Cu nanoparticles was 20–37 nm. The size of Cu nanoparticles found by transmission electron microscopy (TEM) was consistent with that one determined by PXRD. Surface area of the catalysts was determined from low‐temperature nitrogen adsorption. In addition, one Cu‐free composite was prepared from MgCl 2 and DAB. The composites were tested as the heterogeneous catalysts in the process of cycloaddition of propargylamine to ethyl 4‐oxocyclohexanecarboxylate, leading to ethyl 5,6,7,8‐tetrahydroquinoline‐6‐carboxylate. It was found that the reaction could be catalyzed by the carbonaceous materials without Cu. An increase of the carbon content in the reaction mixture led to a decrease in the product yield, while the product yield did not correlate with the content of Cu. It was shown that Cu partially dissolved in the course of the catalytic reaction. The obtained catalysts were used for the synthesis of a series of substituted fused pyridines.