Structure and fluxional behaviour of µ-diphenylacetylene-closo-tetrakis(tricarbonylruthenium)(4 Ru–Ru)

The X-ray structure determination of [Ru4(CO)12(C2Ph2)] confirms the previously proposed closo-Ru4C2 unit with the alkyne capping a butterfly arrangement of the four ruthenium atoms. Crystals are monoclinic, space group P21/c, Z= 4, a= 9.69(1), b= 16.88(2), c= 17.13(2)Å, β= 90.67(5)°; R 0.056 for 2 929 independent reflections. Variable-temperature 13C n.m.r. spectroscopy has enabled the activation energy and entropy to be measured for the mutual exchange of three carbonyl groups attached to one ruthenium, and also indicates that no exchange of carbonyls between different rutheniums occurs at <373 K.