Transition-metal-catalyzed decaborane alkyne hydroboration reactions have been developed that provide high-yield routes to the previously unknown di- and monoalkenyldecaboranes. These alkenyl derivatives should be easily modified starting materials for many biomedical and/or materials applications. Unusual catalyst product selectivity was observed that suggests quite different mechanistic steps, with the reactions catalyzed by the [RuCl2(p-cymene)](2) and [Cp*IrCl2](2) complexes giving the beta-E alkenylde-caboranes and the corresponding reactions with the [Rul(2)(p-cymene)](2) complex giving the a-alkenyldecaborane isomers.