The thermal reaction of [Mo 2 (O)(μ-O)(μ-C 4 Ph 4 )(η-C 5 H 5 ) 2 ] with [Ru 3 (CO) 1 2 ] gives the pentanuclear cluster [Mo 2 Ru 3 (μ 3 -O) 2 (μ 3 CPh)(μ-C 3 Ph 3 )(CO) 8 (η-C 5 H 5 ) 2 ], which has been crystallographically characterised. The compound displays several unusual features: (i) a highly distorted bow-tie structure in which the two metal triangles are virtually perpendicular; (ii) the cleavage of the initial four carbon chain into a dimetalla-allyl fragment and an alkylidyne group; (iii) the presence of two triply-bridging oxo ligands; and (iv) the coordination of one of the phenyl groups of the C 3 Ph 3 ligand to ruthenium.