Selective hydrogenation of 1,10-phenanthrolines by silica-supported palladium nanoparticles

The catalytic hydrogenation of 1,10-phenanthroline (Phen) or 2,9-dimethyl-1,10- phenanthroline (DMPhen) has been achieved using silica-supported palladium nanoparticles (Pd/SiO2) with metal contents of 1.98 or 9.95 wt%. With either catalyst, the hydrogenation regiochemistry has been effectively controlled by the reaction temperature. The catalyst with the higher metal content was selective for the hydrogenation of one heterocyclic ring of either substrate at 80 degrees C and for both external rings at 130 degrees C for Phen and at 160 degrees C for DMPhen. The catalyst with the lower metal content was more active and exhibited comparable selectivity.