Dehalogenation and Hydrogenation of Aromatic Compounds Catalyzed by Nanoparticles Generated from Rhodium Bis(imino)pyridine Complexes

Abstract

Chloro[2,6-bis{1-(phenyl)iminoethyl}pyridine]rhodium(I) complexes (RhCl(N,N,N); 1−11) have been prepared by reaction of the dimer [Rh(μ-Cl)(η2-C2H4)2]2 with the corresponding nitrogen donor ligand. These complexes afford nanoparticles with a mean diameter of 1.5 ± 0.2 nm stabilized by the partially hydrogenated ligand, under 1 atm of hydrogen, in 2-propanol as solvent, at 60 °C, and in the presence of KtBuO. Under a constant atmospheric pressure of hydrogen, the nanoparticles catalyze the dehalogenation of the chlorobenzene 1,2-, 1,3-, and 1,4-dichlorobenzene, 1,2,4-trichlorobenzene, fluorobenzene, 2-, 3-, and 4-chlorobiphenyl, and 4,4′- and 3,5-dichlorobiphenyl and the hydrogenation of benzene, toluene, p-xylene, styrene, α-methylstyrene, biphenyl, aniline, phenol, and pyridine. A Hg(0) poisoning test reveals that homogeneous and heterogeneous catalysis coexist during the dehalogenation reactions, whereas the hydrogenation processes are heterogeneous. The nanoparticles can be also generated in the presence of basic aluminum oxide of 150 mesh, which at the same time acts as a support. When they are deposited on the alumina, the nanoparticles do not significantly modify their catalytic activity.