Phenazine-substituted polynuclear osmium clusters: Synthesis and DFT evaluation of the C-metalated derivatives Os3(CO)9(μ3,η2-C12H7N2)(μ-H) and Os3(CO)9(μ3,η2-C12H6N2)(μ-H)2

• New triosmium clusters that contain a metalated phenazine ligand.
• DFT evaluation of the reaction surface in phenazine activation by Os3(CO)12.
• Phenazine coordination chemistry.

Os3(CO)12 reacts with phenazine in refluxing xylene to yield the monohydride cluster Os3(CO)9(μ3,η2-C12H7N2)(μ-H) (1) in 18% yield and the dihydride cluster Os3(CO)9(μ3,η2-C12H6N2)(μ-H)2 (2) in 21% yield. Compound 1 reacts reversibly with CO to give the decacarbonyl compound Os3(CO)10(μ,η2-C12H7N2)(μ-H) (3) and with PPh3 to afford the addition product Os3(CO)9(μ,η2-C12H7N2)(PPh3)(μ-H) (4). Compounds 1, 2, and 4 have been structurally characterized. 1 contains a C-metalated phenazine ligand that is coordinated to the cluster by a dative nitrogen bond and a benzylidene-type bond, the latter which bridges the same cluster edge as the bridging hydride. The activated phenazine ligand in 2 derives from a double C–H bond metalation sequence, affording a face-capping heterocyclic ligand that binds adjacent osmium centers through two σ–Os–C bonds and the third osmium atom via an aryl π bond in an η2 fashion. Compound 4 exhibits a closed trimetallic Os3(CO)9 core that contains edge-bridging phenazine (C,N coordination) and hydride moieties, and a triphenylphosphine ligand that is coordinated at the non-phenazine-ligated osmium center. These compounds represent rare examples of polynuclear osmium clusters containing C-metalated phenazine ligands. The potential energy surfaces that afford clusters 1 and 2 from Os3(CO)12 and phenazine have been modeled by DFT calculations, and these data indicate that both product clusters originate from the unsaturated cluster Os3(CO)11.

The reaction between Os3(CO)12 and phenazine has been examined and found to give the isomeric C-metalated clusters Os3(CO)9(μ3,η2-C12H7N2)(μ-H) (1) and Os3(CO)9(μ3,η2-C12H6N2)(μ-H)2 (2) as the principal products. The coordination mode adopted by the activated heterocyclic ligand in each cluster has been established by X-ray crystallography.Figure optionsDownload as PowerPoint slide