Synthesis and Characterization of Dinuclear Allenediide Bridged Hafnocene(IV) Complexes

We describe reactions of the dilithioallene precursor Li2(Me3SiC3SiMe3) (1) with Cp2HfCl2, which depending on the stoichiometric ratio furnishes either a highly sensitive dinuclear allenediide bridged hafnocene dichloride complex (2-Hf) or a chemically robust dihafnacyclooctatetraene (3-Hf). Both complexes were fully characterized, and their formation was analyzed by in situ NMR spectroscopy. Other than that described before for the Zr analogues, the generation of both isolated complexes occurs via a Li containing, yet structurally elusive, metallocene intermediate.