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

Reactions of Os-3(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 Os-3(CO)(10)(mu-eta(1))(mu-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 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 a-bonding between the ipso-carbon atom and the two proximate metal atoms and pi-donation from the pi-orbitals of the ring to those same metal atoms. There is no significant metal to ring pi-back-bonding. Compound 3 exists as two isomers, 3a and 3h. Compound 3a contains a mu-eta(1)-2-Np ligand. Compound 3h contains a mu-eta(2)-2-Np ligand. The pyryl complexes 4 and 5 also exist as two isomers. These differ by the point of attachment of the eta(1)-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 Os-3(CO)9(mu(3)-Ar)(mu-AuPPh3)(mu-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.