Multiple Modes for Coordination of Phenazine to Molybdenum: Ring Fusion Promotes Access to η4-Coordination, Oxidative Addition of Dihydrogen and Hydrogenation of Aromatic Nitrogen Compounds

Mo(PMe3)6 reacts with phenazine (PhzH) to give (η6-C6-PhzH)Mo(PMe3)3, (μ-η6,η6-PhzH)[Mo(PMe3)3]2 and (η4-C4-PhzH)2Mo(PMe3)2, each of which displays previously unknown coordination modes for phenazine. Both mononuclear (η6-C6-PhzH)Mo(PMe3)3 and dinuclear (μ-η6,η6-PhzH)[Mo(PMe3)3]2 react with H2 at room temperature to give the respective dihydride complexes, (η4-C4-PhzH)Mo(PMe3)3H2 and (μ-η6,η4-PhzH)[Mo(PMe3)3][Mo(PMe3)3H2]. A comparison of (η6-C6-PhzH)Mo(PMe3)3 with the anthracene (AnH) and acridine (AcrH) counterparts, (η6-AnH)Mo(PMe3)3 and (η6-C6-AcrH)Mo(PMe3)3, indicates that oxidative addition of H2 is promoted by incorporation of nitrogen substituents into the central ring. Furthermore, comparison of (η6-C6-PhzH)Mo(PMe3)3 with the quinoxaline (QoxH) analogue, (η6-C6-QoxH)Mo(PMe3)3, indicates that ring fusion also promotes oxidative addition of H2. The mononitrogen quinoline (QH) and acridine compounds, (η6-C6-QH)Mo(PMe3)3 and (η6-C6-AcrH)Mo(PMe3)3, which respectively possess two and three fused six-membered rings, exhibit a similar trend, with the former being inert towards H2, while the latter reacts rapidly to yield (η4-C4-AcrH)Mo(PMe3)3H2. Ring fusion also promotes hydrogenation of the heterocyclic ligand, with (η6-C6-AcrH)Mo(PMe3)3 releasing 9,10-dihydroacridine upon treatment with H2 in benzene at 95 °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 (η6-C6-AcrH)Mo(PMe3)3 with acridine and H2 at 95 °C.

Mo(PMe3)6与苯并芴(PhzH)反应，生成(η6-C6-PhzH)Mo(PMe3)3、(μ-η6,η6-PhzH)[Mo(PMe3)3]2以及(η4-C4-PhzH)2Mo(PMe3)2，这些化合物均展现出苯并芴前所未有的配位模式。单核(η6-C6-PhzH)Mo(PMe3)3和双核(μ-η6,η6-PhzH)[Mo(PMe3)3]2在室温下与氢气反应，分别生成相应的二氢化物络合物，即(η4-C4-PhzH)Mo(PMe3)3H2和(μ-η6,η4-PhzH)[Mo(PMe3)3][Mo(PMe3)3H2]。将(η6-C6-PhzH)Mo(PMe3)3与蒽(AnH)及吖啶(AcrH)的对应物(η6-AnH)Mo(PMe3)3和(η6-C6-AcrH)Mo(PMe3)3进行比较，发现将氮取代基引入中心环中可促进氢气的氧化加成反应。此外，与喹唑啉(QoxH)类似物(η6-C6-QoxH)Mo(PMe3)3的比较表明，环的融合也能促进氢气的氧化加成。含有两个和三个融合六元环的单氮喹啉(QH)和吖啶化合物，即(η6-C6-QH)Mo(PMe3)3和(η6-C6-AcrH)Mo(PMe3)3，也显示出类似趋势，前者对氢气惰性，而后者则迅速反应生成(η4-C4-AcrH)Mo(PMe3)3H2。环的融合同样促进杂环配体的氢化，(η6-C6-AcrH)Mo(PMe3)3在苯中95°C处理下释放9,10-二氢吖啶。此外，通过在95°C下将(η6-C6-AcrH)Mo(PMe3)3与吖啶和氢气混合处理，可以实现将吖啶催化加氢为9,10-二氢吖啶和1,2,3,4-四氢吖啶的混合物。