Mo(PMe3)(6) reacts with phenazine (PhzH) to give (eta(6)-C-6-PhzH)Mo(PMe3)(3), (mu-eta(6), eta(6)-PhzH)[Mo(PMe3)(3)](2) and (eta(4)-C-4-PhzH)(2)Mo(PMe3)(2), each of which displays previously unknown coordination modes for phenazine. Both mononuclear (eta(6)-C-6-PhzH)Mo(PMe3)(3) and dinuclear (mu-eta(6), eta(6)-PhzH)[Mo(PMe3)(3)](2) react with H-2 at room temperature to give the respective dihydride complexes, (eta(4)-C-4-PhzH)Mo(PMe3)(3)H-2 and (mu-eta(6), eta(4)-PhzH)[Mo(PMe3)(3)][Mo(PMe3)(3)H-2]. A comparison of (eta(6)-C-6-PhzH)Mo(PMe3)(3) with the anthracene (AnH) and acridine (AcrH) counterparts, (eta(6)-AnH)Mo(PMe3)(3) and (eta(6)-C-6-AcrH)Mo(PMe3)(3), indicates that oxidative addition of H-2 is promoted by incorporation of nitrogen substituents into the central ring. Furthermore, comparison of (eta(6)-C-6-PhzH)Mo(PMe3)(3) with the quinoxaline (QoxH) analogue, (eta(6)-C-6-QoxH)Mo(PMe3)(3), indicates that ring fusion also promotes oxidative addition of H-2. The mononitrogen quinoline (QH) and acridine compounds, (eta(6)-C-6-QH)Mo(PMe3)(3) and (eta(6)-C-6-AcrH)Mo(PMe3)(3), which respectively possess two and three fused six-membered rings, exhibit a similar trend, with the former being inert towards H-2, while the latter reacts rapidly to yield (eta(4)-C-4-AcrH)Mo(PMe3)(3)H-2. Ring fusion also promotes hydrogenation of the heterocyclic ligand, with (eta(6)-C-6-AcrH)Mo(PMe3)(3) releasing 9,10-dihydroacridine upon treatment with H-2 in benzene at 95 degrees C. Furthermore, catalytic hydrogenation of acridine to a mixture of 9,10-dihydroacridine and 1,2,3,4-tetrahydroacridine may be achieved by treatment of (eta(6)-C-6-AcrH)Mo(PMe3)(3) with acridine and H-2 at 95 degrees C.