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

Abstract

A procedure was developed for the synthesis of trinuclear cyclic (ZrIII)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.