Synthetic and Structural Chemistry of Ligand-substituted Triosmium Clusters and a Rhenium(i) Complex

The reaction of 2-[(diphenylphosphino)methyl]-6-methylpyridine (PN) with Os3(CO)12-n(MeCN)n [where n = 0 (1), 1 (2), 2 (3)] has been investigated. Os3(CO)12 reacts with PN in the presence of Me3NO to afford the clusters Os3(CO)11(1-PN) (4) and 1,2-Os3(CO)10(1-PN)2 (5). X-ray diffraction analyses confirm the equatorial coordination of the phosphine(s) in 4 and 5, with the two phosphines in the latter cluster exhibiting a 1,2-trans orientation about the Os-Os vector that contains the two ligands. Treatment of the MeCN-substituted cluster Os3(CO)11(MeCN) and PN (1:1 ratio) in CH2Cl2 gives clusters 4 and 5, in addition to HOs3(η1-Cl)(CO)10(1-PN) (6) as a result of competitive activation of the reaction solvent. Cluster 6 contains 48e- and the diffraction structure reveals the presence of axial chloride and equatorial phosphine ligands which are located on adjacent osmium atoms. The bridging hydride ligand in 6 spans the Cl,P-substituted Os-Os vector. The reaction of Os3(CO)10(MeCN)2 with PN furnishes 5, 6, and 1,1-Os3(CO)10(2-PN) (7) in yields that are dependent on the reagent stoichiometry and reaction solvent. The solid-state structure of 7 confirms the chelation of the PN ligand to a single osmium atom via the pyridine and phosphine moieties at axial and equatorial sites, respectively. The bonding in 7 relative to other possible stereoisomers has been explored by DFT calculations, and the diffraction structure is computed as the thermodynamically most stable form of this cluster. Cluster 4 is photosensitive and CO loss gives 7, in addition to the formation of the dihydride H2Os3(CO)8[µ-CH(NC5H3)CH2PPh2] (8), whose origin derives from the double metalation of the C-6 methyl group of the PN ligand in 7. Photolysis of 7 yields 8 without detectable observation of the expected intermediate hydride HOs3(CO)9[µ-CH2(NC5H3)CH2PPh2]. The PN ligand in 7 undergoes P-C bond activation in toluene at 110 °C to afford the 50e cluster Os3(CO)9(µ-C6H4)(µ-PPh), which contains face-capping benzyne and phosphinidene moieties. The bonding between the benzyne moiety and the opened Os3 frame in 9 has been examined computationally, and these data are discussed relative to and π bonding contributions from the metalated aryl ring to the cluster polyhedron. Thermolysis of BrRe(CO)5 with 4-(2,2-dimethylhydrazino)dimethylhydrazone-3(Z)-penten-2-one in toluene at 70 °C furnishes the new β-diketimine-substituted complex fac-BrRe(CO)3[(Me2NNCMe)2CH2] (1) in 50-70 isolated yield. Product 1 is also obtained in comparable yield when the same reactants are irradiated at 366 nm at room temperature in fluid solution. Treatment of the parent ligand with the "lightly stabilized" rhenium compound fac-BrRe(CO)3(THF)2 affords 1 as the sole observable rhenium product. Complex 1 has been characterized in solution by IR and 1H NMR spectroscopy, and the molecular structure has been determined by single-crystal X-ray diffraction analysis