The hexanuclear cluster [Ru₆C(CO)₁₄(η⁶-arene)]1(arene = C₆H₆, C₆H₅Me, C₆H₄Me₂-1,3 or C₆H₃Me₃-1,3,5) reacts with Me₃NO–CH₂Cl₂ in the presence of cyclohexa-1,3-diene or cyclohexa-1,4-diene to yield compound [Ru₆C(CO)₁₂(η⁶-arene)(µ-η²:η²-C₆H₈)]2 in which the diene spans one metal edge of the octahedral cluster unit. Further treatment of 2 with Me₃NO–CH₂Cl₂ affords the bis(arene) derivative [Ru₆C(CO)₁₁(η⁶-arene)(C₆H₆)]. On the basis of spectroscopic data and single-crystal X-ray data it appears that these bis(arene) derivatives exist in two isomeric forms, viz. [Ru₆C(CO)₁₁(η⁶-arene)(µ₃-η²:η²:η²-C₆H₆)]3 and [Ru₆C(CO)₁₁(η⁶-arene)(η⁶-C₆H₆)]4. Evidence that compound 3 is formed initially, followed by isomerisation to 4 is presented. The structures of [Ru₆C(CO)₁₁(η⁶-C₆H₅Me)(µ₃-η²:η²:η²-C₆H₆)]3b and [Ru₆C(CO)₁₁(η⁶-C₆H₄Me₂-1,3)(µ₃-η²:η²:η²-C₆H₆)]3c have been determined by single-crystal X-ray diffraction. Compound 3b is orthorhombic, space group Pnma, a= 9.035(5), b= 14.796(2), c= 20.534(4)Å, Z= 4, 1770 unique observed reflections [I > 2σ(I)], R= 0.020; 3c is monoclinic, space group P2₁/n, a= 18.27(2), b= 9.729(2), c= 34.39(3), Å, β= 94.94(6)°, Z= 8, 7833 unique observed reflections [I > 2.0σ(I)], R= 0.058, R′= 0.062.