The reaction of [Ru₅C(CO)₁₅]1 with cyclohexa-1,3-diene and three equivalents of Me₃NO yielded the new compound [Ru₅C(CO)₁₁(η⁴-C₆H₈)₂]2 and also [Ru₅C(CO)₁₂(µ₃-η²:η²:η²-C₆H₆)]3 and [Ru₅C(CO)₁₂(η⁶-C₆H₆)]4 in approximately equal yields. The molecular structure of 2 has been established by single-crystal X-ray diffraction. The two cyclohexadiene ligands are terminally bound on opposite basal ruthenium atoms of the square-pyramidal metal framework. Compound 2 may be converted to 3 by reaction with carbon monoxide. The isomeric pair [Ru₅C(CO)₁₀(µ₃-η²:η²:η²-C₆H₆)(µ-η²:η²-C₆H₈)]5 and [Ru₅C(CO)₁₀(η⁶-C₆H₆)(µ-η²:η²-C₆H₈)]6 may be prepared from 3 and 4, respectively, upon reaction with cyclohexa-1,3-diene and two equivalents of Me₃NO. Clusters 5 and 6 have also been studied by single-crystal X-ray diffraction. In both molecules the cyclohexadiene ligand bridges a basal edge of the square pyramid, while the benzene fragment is in face-capping and terminal bonding mode, respectively.