Dirhenium complexes containing two, three, and four linked acetylene molecules derived from the reaction of [Re₂(CO)₁₀] with RC₂R (R = Ph or Me); the X-ray crystal structure of [Re₂(CO)₄{(PhCCPh)₃}(CNCH₂SO ₂C₆H₄Me-p)₂] · CH₂Cl₂

The reaction of [Re₂(CO)₁₀] with PhCCPh at 190 °C gives [Re₂(CO)₇(PhCCPh)₂] (1), [Re₂(CO)₆(PhCCPh)₃] (2), and [Re₂(CO)₄(PhCCPh)₄] (3). Complex (3) reacts instantaneously at room-temperature with excess of RNC (R = Bu^t, Buⁿ, p-MeOC₆H₄, or p-MeC₆H₄SO₂CH₂) to give [Re₂(CO)₄(PhCCPh)₃(CNR)₂] (4). A single-crystal X-ray analysis of (4d) (R = CH₂SO₂C₆H₄Me-p) reveals that the acetylene molecules are linked in a chain. The end carbon atoms of the chain are each bonded to one metal atom and, with the two neighbouring carbon atoms, form an η³-allyl linkage to the other metal atom. The two RNC ligands are terminally bonded to only one rhenium atom. The complex crystallises with a molecule of CH₂Cl₂ solvent in the triclinic space group P1 with a = 13.190(3), b = 14.066(3), c = 17.554(5) Å, α = 83.06(2), β = 75.75(2), γ = 70.40(2)°, and Z = 2. The structure was solved by a combination of Patterson and Fourier-difference techniques, and refined by blocked-cascade least squares to R = 0.032 for 6 315 unique observed intensities [F > 3σ(F)]. The reaction of [Re₂(CO)₁₀] with MeCCMe at 190 °C leads to extensive decomposition, but a yellow product, isolated in low yield, was identified spectroscopically as [Re₂(CO)₅(MeCCMe)₄] (5). On the basis of the known structure of (4d) and on chemical and spectroscopic evidence, structures are proposed for all the complexes which have been isolated. Complex (3) probably contains a Re-Re multiple bond.