Homogeneous perdehydrogenation of saturated bicyclic 2,6-dimethyldecahydro-1,5-naphthyridine and perhydrogenation of aromatic 2,6-dimethyl-1,5-naphthyridine with release and uptake of five molecules of H-2 are efficiently achieved by iridium complexes bearing a functional bipyridonate ligand. Successive perhydrogenation and perdehydrogenation of 2,6-dimethyl-1,5-naphthryridine using a single iridium complex also proceed with the reversible inter-conversion of the catalytic species, depending on the presence or absence of H-2.