Treatment of a dirhodium analogue of pentaborane(9), [(Cp*Rh)2B3H7] (nido-1; Cp* = η5-C5Me5), with [Fe2(CO)9] at room temperature led to the formation of [(Cp*Rh)2Fe(CO)3(µ-CO)B3H2Cl] (2) and the metal-rich metallaborane [(Cp*Rh)2Fe(CO)3Fe(CO)2(µ-CO)2B2H2] (3). When the same reaction was carried out at moderate temperature, two metal-rich metallaboranes, [(Cp*Rh)3Fe(CO)2(µ3-CO)2B2HX] 4 (X = H) and 5 (X = Cl) and a heterometallic µ9-boride cluster, [(Cp*Rh)3(RhCO)3Fe(CO)3(µ-CO)3B3H2] (6), were obtained. Compounds 4 and 5 can be viewed as cubane clusters with 62 cluster valence electrons (cves) and five metal–metal bonds. In another reaction, the treatment of nido-1 with [Mn2(CO)10] yielded the heterometallic µ9-boride cluster [(Cp*Rh)3Rh(CO)2{Mn(CO)3}2B4H3] (7). The cluster cores of both 6 and 7 are comprised of tricapped trigonal prisms containing a µ9-B atom bonded to seven/six metals and two/three boron atoms, respectively. All the new compounds have been characterized by mass spectrometry, IR, 1H, 11B{1H} and 13C{1H} NMR spectroscopy and X-ray crystallographic analysis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim