Unusual carbonyl and pentamethylcyclopentadienyl bonding modes in mixed rhodium–ruthenium clusters

Abstract

Thermolysis of [Ru₃RhH₂(CO)₁₀(η⁵-C₅Me₅)], 1, in hydrocarbon solvents affords the new pentanuclear cluster [Ru₃Rh₂(µ₃-H)(µ₂-CO)(µ₃-CO)₂(CO)₆(µ-η¹:η⁵-CH₂C₅Me₄)(η⁵-C₅Me₅)], 2, together with the known complex [Ru₂Rh₂(CO)₈(η⁵-C₅Me₅)₂], 3. The reaction of 1 with Me₃NO, in MeCN solution, followed by the immediate addition of one or two equivalents of PPh₃ lead to the isolation of the mono– and di-phosphine substituted complexes [Ru₃Rh(µ-H)₂(µ₄-η²-CO)(µ₂-CO)₂(CO)₆(PPh₃)(η⁵-C₅Me₅)], 4, and [Ru₃Rh(µ-H)₂(µ₄-η²-CO)(µ₂-CO)₂(CO)₅(PPh₃)₂(η⁵-C₅Me₅)], 5, respectively. The new clusters have been characterised spectroscopically, and the structures of 2 and 5 established by single-crystal X-ray analyses. The metal framework in 2 is trigonal bipyramidal, with one C₅Me₅ ligand co-ordinated to a Rh atom in a terminal η⁵-bonding mode, the second cyclopentadienyl ligand has lost a methyl proton and the resultant –CH₂ group is σ-bonded to one Ru atom while the C₅Me₄ ring is η⁵-bound to the adjacent Rh atom. The metal framework in 5 has opened out to give a butterfly arrangement with the Rh(η⁵-C₅Me₅) unit in one of the wing-tip positions. The butterfly is spanned by a novel µ₄-η²-bonded carbonyl ligand, and the two phosphines are terminally bound to two Ru atoms, one in a wing-tip site and the other in a hinge site.