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

Thermolysis of [Ru3RhH2(CO)(10)(eta(5)-C5Me5)], 1, in hydrocarbon solvents affords the new pentanuclear cluster [Ru3Rh2(mu(3)-H)(mu(2)-CO)(mu(3)-CO)(6)(CO)(6)(mu:eta(1):eta(5)-CH2C5Me4)(eta(5)-C5Me5)], 2, together with the known complex [Ru2Rh2(CO)(8)(eta(5)-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(mu-H)(2)(mu(4)-eta(2)-CO)(mu(2)-CO)(2)(CO)(6)(PPh3)(eta(5)-C5Me5)], 4, and [Ru3Rh(mu-H)(2)(mu(4)-eta(2)-CO)(mu(2)-CO)(2)(CO)(5)(PPh3)(2)(eta(5)-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 eta(5)-bonding mode, the second cyclopentadienyl ligand has lost a methyl proton and the resultant -CH2 group is sigma-bonded to one Ru atom while the C5Me4 ring is eta(5)-bound to the adjacent Rh atom. The metal framework in 5 has opened out to give a butterfly arrangement with the Rh(eta(5)-C5Me5) unit in one of the wing-tip positions. The butterfly is spanned by a novel mu(4)-eta(2)-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.