Tetraruthenium cluster isomers containing both C6H8 and [2.2]paracyclophane ligands: a new face-bridging co-ordination mode for a C6 aromatic ring

Abstract

The reaction of [Ru₃(CO)₉(µ₃-η² : η² : η²-C₁₆H₁₆)]1 with 2.2 molar equivalents of Me₃NO in dichloromethane containing cyclohexa-1,3-diene afforded the new tetrahedral complex [Ru₄(CO)₉(η⁴-C₆H₈)(µ₃-C₁₆H₁₆)]2 in modest yield. The thermolysis of [Ru₄(CO)₁₂(µ₄-C₆H₈)]3 in octane containing an excess of [2,2]paracyclophane (C₁₆H₁₆) and Me₃NO afforded the two new butterfly isomers [Ru₄(CO)₉(µ₄-C₆H₈)(η⁶-C₁₆H₁₆)]4 and [Ru₄(CO)₉(µ₄-C₆H₈)(µ₃-η² : η² : η²-C₁₆H₁₆)]5. Heating compound 4 results in its irreversible conversion to 5. Compounds 2 and 4 have been characterised in the solid state by single-crystal X-ray diffraction and in 2 the [2,2]paracyclophane ring bonds to the cluster via an unusual µ₃-η¹ : η² : η² bonding mode unseen before for an arene ring.