Reactivity of Dimetallapentaboranes—nido-[Cp$\rm{^{{\ast}}_{2}}$M2B3H7]—with Alkynes: Insertion to Form a Ruthenacarborane (M=RuH) versus Catalytic Cyclotrimerization to Form Arenes (M=Rh) This work was supported by the National Science Foundation. Cp*=η-C5Me5.