The ionic coupling reaction of the dianion [Os-3(CO)(9)(R2C2)](2-) (R = Me, Ph) with two equivalents of the monocation [Ru-(eta(5)-C5H5)(CH3CN)(3)](+) affords the neutral clusters [Os3Ru2(CO)(9)(R2C2)(eta(5) - C5H5)(2)] [R = Me, 1 and R = Ph, 2] in ca. 80% yield. An X-ray crystallographic study of 1 confirms that these clusters exhibit a capped pseudo-octahedral Os3Ru2C2 core, with the alkyne bonded parallel to the hinge bond of the capped butterfly metal geometry in a mu(4)-eta(2) manner, the Ru atoms adopting the wing-tip and capping positions. Reaction of the activated cluster [Os3RuH(eta(5)-C5H5)(CO)(10)(MeCN)] (3) with RCCR (R = Me, Ph) affords the related clusters [Os3RuH(CO)(9)(eta(5)-C5H5)(R2C2)] (R = Me, 4 and R = Ph, 5) in ca. 35% yield. The reaction with PhCCPh also produces [Os3Ru(CO)(8)(eta(5)-C5H5)(PhCCPh)(PhCC(H)Ph)] (6) in ca. 15% yield. An X-ray crystallographic study shows that this cluster has a pseudo-octahedral Os3RuC2 core, with the Ru(eta(5)-C5H5) unit adopting the wing-tip position, the alkyne bonded in a mu(4)-eta(2) arrangement and the ethenyl ligand bridging an Os-Os edge in a mu(2)-eta(1):eta(2) configuration. (c) 2005 Elsevier Ltd. All rights reserved.