Multiple modes for coordination of phenazine to molybdenum: ring fusion promotes access to eta4-coordination, oxidative addition of dihydrogen and hydrogenation of aromatic nitrogen compounds.

Mo(PMe(3))(6) reacts with phenazine (PhzH) to give (eta(6)-C(6)-PhzH)Mo(PMe(3))(3), (mu-eta(6),eta(6)-PhzH)Mo(PMe(3))(3) and (eta(4)-C(4)-PhzH)(2)Mo(PMe(3))(2), each of which displays previously unknown coordination modes for phenazine. Both mononuclear (eta(6)-C(6)-PhzH)Mo(PMe(3))(3) and dinuclear (mu-eta(6),eta(6)-PhzH)Mo(PMe(3))(3) react with H(2) at room temperature to give the respective dihydride complexes, (eta(4)-C(4)-PhzH)Mo(PMe(3))(3)H(2) and (mu-eta(6),eta(4)-PhzH)[Mo(PMe(3))(3)][Mo(PMe(3))(3)H(2)]. A comparison of (eta(6)-C(6)-PhzH)Mo(PMe(3))(3) with the anthracene (AnH) and acridine (AcrH) counterparts, (eta(6)-AnH)Mo(PMe(3))(3) and (eta(6)-C(6)-AcrH)Mo(PMe(3))(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(PMe(3))(3) with the quinoxaline (QoxH) analogue, (eta(6)-C(6)-QoxH)Mo(PMe(3))(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(PMe(3))(3) and (eta(6)-C(6)-AcrH)Mo(PMe(3))(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(PMe(3))(3)H(2). Ring fusion also promotes hydrogenation of the heterocyclic ligand, with (eta(6)-C(6)-AcrH)Mo(PMe(3))(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(PMe(3))(3) with acridine and H(2) at 95 degrees C.