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

The reaction of Cp* 2 (C 2 B 9 H 11 ) 2 Hf 2 Me 2 ( 1b; Cp* = C 5 Me 5 ) with H 2 yields the novel hafnium carboranyl hydride complex (Cp*)(η 5 -C 2 B 9 H 11 )Hf(μ-η 5:η 1 -C 2 B 9 H 10 )Hf(Cp*)(H) ( 4 ), in which the two metal centers are linked by a C-metalated μ-η 5:η 1 -C 2 B 9 H 10 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*(C 2 B 9 H 11 )Hf(H) ( 5 ), which is formed by hydrogenolysis of 4 and undergoes rapid alkyne or alkene insertion and Hf-C hydrogenolysis steps.