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

Reactions of Os₃(CO)₁₀(NCMe)₂, <b>1</b>, 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) [<b>2</b>, Ar = phenyl = Ph; <b>3</b>, Ar = 2-naphthyl = 2-Np (2-C₁₀H₇); and Ar = <b>4</b> and <b>5</b>, 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 <b>2</b> 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 <b>3</b> exists as two isomers, <b>3a</b> and <b>3b</b>. Compound <b>3a</b> contains a μ-η¹-2-Np ligand. Compound <b>3b</b> contains a μ-η²-2-Np ligand. The pyryl complexes <b>4</b> and <b>5</b> 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 <b>2</b>, <b>3</b>, <b>4</b>, and <b>5</b> were decarbonylated and converted to the corresponding aryne complexes Os₃(CO)₉(μ₃-Ar)­(μ-AuPPh₃)­(μ-H), <b>6</b>–<b>9</b>, 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 <b>3b</b> into the naphthyne complex <b>7</b> was established by DFT computational analyses