Some reactions of [Os₃(CO)₁₀(NCMe)₂] with arenes; the molecular structure of [Os₃H₂(CO)₉(C₆H₄)]

The cluster [Os₃H₂(CO)₉(C₆H₄)] was obtained in good yield by the reaction of [Os₃(CO)₁₀(NCMe)₂] with benzene under reflux. This benzyne cluster crystallises in space group P2₁/c with a = 17.391(5), b = 13.190(2), c = 16.512(3) Å, β = 92.39(2)°, and Z = 8. The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by blocked-cascade least squares to R = 0.079 for 3 438 observed diffractometer data. In each of the two independent molecules the three Os atoms define an irregular triangle the longest edge [mean 3.034(4) Å] of which is bridged by the benzyne ligand which is co-ordinated to the third Os atom via a π bond. This long edge is also bridged by a hydride and the other hydride bridges one of the other Os-Os edges [mean 2.858(3) Å]. The third Os-Os edge [mean 2.751(2) Å] is unbridged. When the reaction is carried out in toluene or chlorobenzene rather than benzene the complexes [Os₃H₂(CO)₉(C₆H₃Me)] and [Os₃H₂(CO)₉(C₆H₃Cl)] are obtained. In each case two isomers have been identified by ¹H n.m.r. spectroscopy. With trans-stilbene the only complex characterised has been formulated as [Os₃H₂(CO)₉(C₆H ₃CHCHC₆H₅)] in which one ring is co-ordinated to the cluster in a similar manner to that in [Os₃H₂(CO)₉(C₆H₄)].