Abstract
Alkylation of HfCl4 with 6 equiv of ethyllithium followed by the addition of N,N,N′,N′-tetramethylethylenediamine gives the d2 hafnium(II) alkyl/alkene complex [Li(tmed)]2[HfEt4(C2H4)]. The X-ray crystal structure of this complex shows that the ethylene ligand has considerable metallacyclopropane character. The C−C distance of 1.49(6) A and the 1JCH coupling constant of 119 Hz both support this formulation. A labeling study showed that the ethylene ligand is formed by means of a β-hydrogen abstraction process. Similar treatment of TaCl2(OMe)3 and WCl3(OMe)3 with ethyllithium affords the d6 tantalum(−I) and d8 tungsten(−II) complexes [Li(tmed)]3[TaHEt(C2H4)3]·1/2tmed and [Li(tmed)]3[WH(C2H4)4]. Both trianionic complexes, in which the metal centers have negative oxidation states, adopt distorted-square-pyramidal geometries with the hydride group in the axial position. The C−C bond lengths of 1.484(8), 1.502(8), and 1.515(8) A for the ethylene groups in the tantalum complex are somewhat longer than those of ...
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