Building upon our earlier work on low-boron containing molybdaborane arachno-[Cp∗Mo(CO)2B3H8], 1 we continue to investigate the reactivity of the same system with group 8 metal carbonyl compounds. As a result, thermolysis of arachno-1 in presence of [Ru3(CO)12] led to the formation of neutral heterometallic ketenylidene cluster [Cp∗Mo(CO)2(μ-H)Ru2(CO)6(μ3-É1-CCO)], 2, in which the triply bridged ketenylidene fragment (CCO) is lying perpendicular to the plane of the metal triangle (Ru-Mo-Ru). In addition to the formation of cluster 2, the reaction also yielded a semi-interstitial boride cluster [Cp∗Mo(CO)2{Ru(CO)3}4B], 3 and a known bimetallic cluster [Cp∗Mo(CO)3]2, 4 in moderate yields. The geometry of 3 can be described as a square pyramidal, in which the boron atom caps the square face formed by three Ru and one Mo atoms respectively. All the new compounds have been characterized by multinuclear NMR spectroscopy, IR spectroscopy and mass spectrometry. In addition to these, the solid state structure of 2 and 3 were unequivocally established by single crystal X-ray diffraction analysis. © 2015 Elsevier B.V.