The synthesis of well-defined heterometallic complexes remains a frontier challenge in inorganic chemistry. We report an approach that relies on the sequential insertion of electrophilic metal fragments into electron-rich Ru-B bonds of the η2-BB-carboryne complex (POBBOP)Ru(CO)2 [POBBOP = 1,7-OP(iPr)2-m-2,6-dehydrocarborane]. Utilizing this synthetic strategy, bimetallic (POBBOP)(Ru)(CO)2[Pd(PtBu3)] and trimetallic (POBBOP)(Ru)(CO)2[Pd(PtBu3)](CuBr) complexes were selectively prepared. Structural and theoretical analysis of the features of chemical bonding within Ru-B-B-Cu and Ru-B-B-Pd fragments is presented.