Some reactions of dodecacarbonyltetrahydridotetraosmium with olefins; The molecular structure of 1,1,1,2,2,3,3,3,4,4,4-undecacarbonyl-1,2-μ-(1′-σ,1′- 2′-η-cyclohexenyl)-tri-μ-hydrido-tetrahedro-tetraosmium

The complexes [Os₄(CO)₁₁(cyclo-olefin - H)H₃] (cyclo-olefin = cyclo-octatetraene, cyclo-octa-1,5-diene, cyclo-hexene, or norbornene) have been identified as the products of reaction of [Os₄(CO)₁₂H₄] with the appropriate cyclic olefin. The structures of these complexes are discussed in terms of available spectroscopic data and in the case of the title complex [Os₄(CO)₁₁(C₆H₉)H₃] on the basis of a single-crystal X-ray analysis. This molecule crystallises in space group P2₁/n with a = 9.266(4), b = 14.850(8), c = 16.847(9) Å, β = 93.39(3)°, and Z = 4. The osmium atoms define a tetrahedron, with the cyclohexene ring σ-bonded to one metal and π-bonded to another. The complex [Os₄(CO)₁₂H₄] also reacts with the acyclic olefins CH₂=CH₂, CH₂=CHPh, CH₂=CHCMe₃, CH₂=CMeCMe₃, and cis-CHPh=CHPh to give the related complexes [Os₄(CO)₁₁(olefin - H)H₃]. On heating, apart from the complex where the olefin is CH₂=CMeCMe₃, dehydrogenation occurs to produce the dihydrido-complexes [Os₄(CO)₁₁(R¹C=CR²)H₂] (R¹ = H, R² = H, Ph, or CMe₃; R¹ = R² = Ph). These complexes have been shown to contain a R¹C=CR² fragment bound via two σ and one π bond to one tetrahedral face of the Os₄ cluster unit.