We report the synthesis, isolation and structural characterization of several moderately air stable nido-metallaboranes that represent boron rich open cage systems. The reaction of [Cp∗CoCl]2, (Cp∗ = η5-C5Me5), with [BH3·thf] in toluene at ice cold temperature, followed by thermolysis in boiling toluene produced [(Cp∗Co)B9H13], 1 [(Cp∗Co)2B8H12], 2 and [(Cp∗Co)2B6H10] 3. Building upon our earlier reactivity studies on rhodaboranes, we continue to explore the reactivity of dicobalt analogues of octaborane(12) cluster 3 with [Fe2(CO)9] and [Ru3(CO)12] at ambient conditions that yielded novel fused clusters [Fe2(CO)6(Cp∗Co)2B6H10], 4 and [Ru4(CO)11(Cp∗Co)2B3H3], 5 respectively. In an attempt to synthesize a heterometallic metallaborane compound we performed the reaction of [(Cp∗Rh)2B6H10], 6 with [Cp∗IrH4] that yielded a Ir-Ir double bonded compound [(Cp∗Ir)2H3][B(OH)4], 7. All the new compounds have been characterized by IR, 1H, 11B, 13C NMR spectroscopy, and the molecular structures were unambiguously established by X-ray diffraction analysis. This journal is © The Royal Society of Chemistry.