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