Use of the monocationic fragment [Ru(η5-C5H5)(MeCN)3]+ as a capping reagent in the synthesis of mixed-metal clusters:: synthesis and structural characterisation of [Os3RuH(CO)11(η5-C5H5)] and [Os3Ru2(CO)9(η3-CO)2(η5-C5H5)2]

The reaction of the monoanion [Os3H(CO)(11)](-) 1 with 1 equivalent of the cation [Ru(C5H5)(MeCN)(3)](+) 2, in CH2Cl2, formed the mixed-metal, tetranuclear cluster [Os3RuH(CO)11(eta(5)-C5H5)] 3 in high yield. Subsequent deprotonation of 3 with 1,8-diazabicyclo[5.4.0]undec-7-ene, in CH2Cl2, afforded the anion [Os3Ru(CO)(11)-(eta(5)-C5H5)](-) 4, and reaction of 4 with a second equivalent of [Ru(C5H5)(MeCN)(3)](+) provided the new bis-(cyclopentadienyl) cluster [Os3Ru2(CO)(9)(mu(3)-CO)(2)(eta(5)-C5H5)(2)] 5 in ca. 80% yield. Alternatively, reduction of [Os-3(CO)(12)] with K/Ph2CO afforded the known cluster dianion [Os-3(CO)(11)](2-) 6 which can be treated with 2 equivalents of [Ru(C5H5)(MeCN)(3)](+) to produce 5 in 75% yield. The clusters 3 and 5 have been fully characterised by both spectroscopic and crystallographic methods. The structure of 3 contains an Os3Ru tetrahedron in which the cyclopentadienyl ligand is co-ordinated to the Ru atom in an eta(5) terminal mode. The metal framework in 5 is a trigonal bipyramid, but may be viewed as an Os3Ru tetrahedral unit, as in 3, to which a second Ru atom capping an Os2Ru triangular face has been added. Both the cyclopentadienyl ligands remain in eta(5) terminal bonding sites co-ordinated to the two Ru atoms.