The polyhydride [Cp*HfHzC1]42 waa prepared by high-pressure hydrogenation of Cp*Hf(C6Hlo)C1 (C6H10 = 2,3-dimethyl-l,3-butadiene) or Cp*Hf(COT)Cl (COT = cyclooctatetraene). The structure of [Cp*HfH2C1], was determined by X-ray diffraction. The compound crystallizes in the tetragonal space group P42'm with a = 21.454 (3) A, c = 10.525 (3) A, and Z = 4. The structure was refined to R = 0.030 and R, = 0.039 for 303 parameters and 2839 reflections with I > 2.5a(T). The molecule has four Hf atoms in a butterfly arrangement with alternating Cp* and C1 ligands (Hf-Ct = 2.15,2.23, and 2.27 A; Hf-Cl = 2.397 (3), 2.438 (3), and 2.432 (3) A). Hydride positions could not be found due to disorder in one of the Cp* ligands probably caused by the presence of a benzene solvate molecule. IR and NMR studies indicate the presence of two sets of four equivalent hydrides bridging the edges of a Hf4 butterfly arrangement. Bridging hydride ligands account for the low reactivity of the complex.

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