Synthetic and mechanistic studies of ruthenium catalyzed carbon-hydrogen and nitrogen-hydrogen bond activation of amines

The ruthenium-hydride complex (PCy3)2(CO)RuHCl was found to be an effective catalyst for the dehydrogenative coupling reaction of cyclic amines and alkenes. The reaction of secondary cyclic amines with unactivated alkenes preferentially gave the C--H bond insertion products in which both C--H and N--H bonds of amines have been selectively activated. The preliminary mechanistic studies suggested that both C--H and N--H bond activation steps are mediated by a highly unsaturated ruthenium species. An efficient catalytic C--H bond activation/hydroamination protocol has been developed for the synthesis for quinoline derivatives. A catalytically active cationic ruthenium-acetylide complex has been isolated and characterized. The normal isotope effect (kCH/ kCD = 2.5) and a highly negative Hammett rho value are consistent with a mechanism involving ortho-C--H bond activation rate-determining step. Efforts to establish a detailed mechanism as well as the role of ruthenium-acetylide species in amination reactions are currently underway.