Heterometallic (ZrIII)2—Al hydrides [(Cp2Zr)2(μ-H)](μ-H)2AlX2 (X = Cl or Br): preparative synthesis and reactivity. Molecular structure of [(Cp2Zr)2(μ-Cl)](μ-H)2AlCl2

A procedure was developed for the synthesis of trinuclear cyclic (Zr^III)₂—Al hydrides (Cp₂Zr)₂(μ-H)](μ-H)₂AlX₂ (X = Cl (1a) or Br (1b)). These complexes were prepared in 60–65% yields by the reaction of Cp₂ZrX₂ with LiAlH₄ in the presence of CoBr₂ and tolane. The structures of complexes 1a and 1b and iodide 1c (X = I) were studied by NMR spectroscopy in solvents of different basicities (toluene, THF, and pyridine). Complex 1a is unsolvated and monomeric in all solvents; complex 1b, in toluene and THF; complex 1c, in toluene only. At room temperature, complex 1a does not catalyze hydrogenation of hex-1-ene and does not react with tolane, but reacts with the latter at high temperature to give bis(η⁵-cyclopentadienyl)-2,3,4,5-tetraphenylzirconacyclopentadiene. The reaction of equivalent amounts of complex 1a and HCl produces the (Cp₂Zr)₂(μ-Cl)](μ-H)₂AlCl₂ complex. The structure of the latter was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2418–2423, November, 2005.