Synthesis, Structure, and Reactivity of a Novel Hafnium Carboranyl Hydride Complex

The reaction of Cp*2(C2B9H11)2Hf2Me2 (1b; Cp* = C5Me5) with H2 yields the novel hafnium carboranyl hydride complex (Cp*)(η5-C2B9H11)Hf(μ-η5:η1-C2B9H10)Hf(Cp*)(H) (4), in which the two metal centers are linked by a C-metalated μ-η5:η1-C2B9H10 ligand and Hf−H−Hf and B−H−Hf bridges. Complex 4 catalyzes the hydrogenation of internal alkynes to cis-alkenes. It is proposed that the active species in this reaction is the mononuclear hydride Cp*(C2B9H11)Hf(H) (5), which is formed by hydrogenolysis of 4 and undergoes rapid alkyne or alkene insertion and Hf-C hydrogenolysis steps.