On activation with Me₃NO the tetrahydrido-tetranuclear cluster [Os₄(µ-H)₄(CO)₁₂]1 underwent reaction with cyclohexa-1,3-diene in CH₂Cl₂ under ambient conditions to give, as the major products, the four organometallic clusters [Os₄(µ-H)₃(CO)₁₁(η³-C₆H₉)]2, [Os₄(µ-H)₂(CO)₁₂(η²-C₆H₈)]3, [Os₄(µ-H)₂(CO)₁₁(η⁴-C₆H₈)]4 and [Os₄(µ-H)₂(CO)₁₀(η⁶-C₆C₆)]5. On heating in hexane, 3 is converted into 4 and subsequently 4 into 5. Compound 5 underwent further reaction with Me₃NO in CH₂Cl₂ in the presence of cyclohexa-1,3-diene to produce [Os₄(CO)₉(η⁶-C₆H₆)(η⁴-C₆H₈)]6 and [Os₄(µ-H)₂(CO)₈(η⁶-C₆H₆)(η⁴-C₆H₈)]7. Structural analyses of 4 and 7 by single-crystal X-ray diffraction have shown that the C₆H₈ ligand is bonded through two alkene bonds and that the benzene ligand in 7 is co-ordinated in an η⁶ fashion. In each case the ligands are bonded to single osmium atoms only. Compound 5 was also found to react with Me₃NO in CH₂Cl₂ in the presence of benzene yielding [Os₄(CO)₈(η⁶-C₆H₆)₂]8, whilst with either toluene or mesitylene it undergoes arene displacement to produce [OS₄(µ-H)₂(CO)₁₀(η⁶-C₆H₅Me)]9 or [Os⁴(µ-H)₂(CO)₁₀(η⁶-C₆H₄Me₂-1,3)]10 respectively.