Unsaturated Triosmium Carbonyl Cluster Complexes with Bridging Aryl Ligands: Structures, Bonding, and Transformations

Reactions of Os3(CO)10(NCMe)2, 1, with the series of aryl-gold complexes ArylAu­(PPh3) [Aryl = phenyl = Ph, 2-naphthyl = 2-Np (2-C10H7) and 1-pyryl (1-C16H10)] have provided the series of electronically unsaturated triosmium complexes Os3(CO)10(μ-η1-Ar)­(μ-AuPPh3) [2, Ar = phenyl = Ph; 3, Ar = 2-naphthyl = 2-Np (2-C10H7); and Ar = 4 and 5, 2-pyryl and 4-pyryl], containing bridging η1-Ar ligands and a bridging Au­(PPh3) group that bridges the same unsaturated Os–Os bond in the 46-electron cluster complex. All new compounds were characterized by single-crystal X-ray diffraction analyses. A DFT computational analysis of 2 has revealed that bonding of the bridging phenyl ligand to the metal atoms consists of a combination of delocalized σ-bonding between the ipso-carbon atom and the two proximate metal atoms and π-donation from the π-orbitals of the ring to those same metal atoms. There is no significant metal to ring π-back-bonding. Compound 3 exists as two isomers, 3a and 3b. Compound 3a contains a μ-η1-2-Np ligand. Compound 3b contains a μ-η2-2-Np ligand. The pyryl complexes 4 and 5 also exist as two isomers. These differ by the point of attachment of the η1-Ar ligand to the metal atoms. When heated to reflux in an octane solution (125 °C), compounds 2, 3, 4, and 5 were decarbonylated and converted to the corresponding aryne complexes Os3(CO)9(μ3-Ar)­(μ-AuPPh3)­(μ-H), 6–9, which contain a triply bridging aryne ligand formed by the loss of one CO ligand from the complex and by a CH cleavage on the bridging Ar ligand. A mechanism for the transformation of 3b into the naphthyne complex 7 was established by DFT computational analyses.