Transition metal-catalyzed reduction of ZrIV in Cp2ZrX2LiAlH4 and Cp2ZrX2AlH3 (X=Cl, Br, I) systems: structural study of resulting zirconocene(III) aluminum hydride complexes

The reactions of Cp2ZrX2 (X=Cl, Br, or I) with LiAlH4 or AlH3 in the presence of catalytic amounts of transition metal compounds afford the ZrIIIAl hydride complexes [(Cp2Zr)2(μ-H)](μ-H)2AlX2 (1). Complexes 1 were isolated as crystal solvates with either benzene or benzene and 1,4-dioxane of compositions [(Cp2Zr)2H](H)2AlCl2·C6H6 (2), [(Cp2Zr)2H](H)2AlBr2·C6H6 (3), [(Cp2Zr)2H](H)2AlBr2·C4H8O2·C6H6 (4), and [(Cp2Zr)2H](H)2AlI2·2C6H6 (5) and their structures were studied by X-ray diffraction analysis. Molecules 1 contain the six-membered Zr2AlH3 ring as the central fragment, in which the metal atoms are linked by hydride bridges. The bonding models for 1 are considered and the reasons for stability of 1 are discussed.