Carbon-coated Cu nanoparticles as heterogeneous catalysts for cycloaddition of propargylamine to cyclic ketones

A set of 22 composites was prepared by pyrolysis of Cu2+ complexes with phenanthroline and 1,2-diaminobenzene, deposited on SiO2 (Aerosil). All composites contained Cu and carboneous components, while some of them additionally contained Cu2O or CuCl. According to the data of powder X-ray diffraction, the size of Cu nanoparticles was 20-37 nm. The presence of Cu nanoparticles was confirmed by TEM, while some aggregates were found by SEM. The composites were tested as the heterogeneous catalysts in the process of cycloaddition of propargylamine with 4-oxocyclohexanecarboxylate leading to ethyl 5,6,7,8-tetrahydroquinoline-6-carboxylate. It was found that the product yield did not correlate with Cu content in the reaction mixture or other single parameters, but reached maximal values at certain values of parameters, proportional to the surface of Cu and surface of C, exposed to the reagents. It was found that the leaching of Cu takes place upon repeated use of the composites.