Facile cleavage of phenyl groups from BiPh3 in its reactions with Os3(CO)10(NCMe)2 and evidence for localization of π-bonding in a bridging benzyne ligand

Three new compounds were obtained from the reaction of Os3(CO)10(NCMe)2, 1 with BiPh3 in a methylene chloride solution at reflux. These have been identified as Os3(CO)10(μ3-C6H4), 3, Os3(CO)10Ph(μ-η2- Odouble bond; length as m-dashCPh), 4, and HOs6(CO)20(μ-η2-C6H4)(μ4-Bi), 6. Two other products Os2(CO)8(μ-BiPh), 2, and HOs5(CO)18(μ-η2-C6H4)(μ4-Bi), 5 were obtained previously from the reaction of Os3(CO)11(NCMe) with BiPh3. Cleavage of the phenyl groups from the BiPh3 was the dominant reaction pathway and two of the products 3 and 4 contain rings but no bismuth. Each of the new compounds was characterized structurally by single-crystal X-ray diffraction methods. Compound 3 contains a triply-bridging benzyne (C6H4) ligand that exhibits a pattern of alternating long and short C–C bonds that can be attributed to partial localization of the π-bonding in the C6 ring. The localization in the π-bonding in the ring is supported by DFT calculations. Compound 4 contains a triangular cluster of three osmium atoms with a bridging benzoyl ligand and a terminally coordinated phenyl ligand. Compound 6 contains six osmium atoms divided into two groups of four and two and the two groups are linked by a spiro-bridging bismuth atom. The group of two osmium atoms contains a bridging C6H4 ligand. When heated, compound 4 was converted into 3 and the compound Os3(CO)10(μ-η2-Odouble bond; length as m-dashCPh)2, 7. Compound 7 contains two bridging benzoyl ligands.