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

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

“…It can be seen that the parameters of these structures depend only slightly on the nature of the X atom in the Zr-X-Zr bridge. This fact is in con tradiction with the assumption that the X atom serves as a mediator for d 1 -d 1 interactions between the zirconium centers (model A) 3 and is most likely indicative of the …”

“…Although the for mation of compounds 1 is a rather complicated process, 1, 3 it can be formally represented as cobalt bromide cata lyzed decomposition of intermediate 2 generated in the first step of the reaction (Scheme 1). 3 complexes 1a and 1b. The mechanism of this effect re mains largely unclear.…”

“…In all spectra, these signals are partially or completely broadened due to dynamic processes in the [H 2 Al(Hal) 2 ] fragment and the influence of the 27 Al nucleus, as have been demonstrated using complex 1a as an example. 3 A comparison of the spectra of complex 1a in various solvents shows that the signals of all groups of protons are gradually shifted downfield but remain to be of the same type in going from toluene d 8 to THF d 8 and then to pyridine d 5 , which indicates that the structure of com plex 1a remains virtually unchanged. This is consistent with the fact that the 27 Al NMR spectrum of 1a has peaks at δ 199.08 (in THF d 8 ) 3 and 192.44 (in pyridine d 5 ) corresponding to the four coordinate aluminum atom.…”

“…3 A comparison of the spectra of complex 1a in various solvents shows that the signals of all groups of protons are gradually shifted downfield but remain to be of the same type in going from toluene d 8 to THF d 8 and then to pyridine d 5 , which indicates that the structure of com plex 1a remains virtually unchanged. This is consistent with the fact that the 27 Al NMR spectrum of 1a has peaks at δ 199.08 (in THF d 8 ) 3 and 192.44 (in pyridine d 5 ) corresponding to the four coordinate aluminum atom. 11 Therefore, complex 1a remains unsolvated not only in THF but also in pyridine.…”

“…1-3 However, known methods produce complexes 1 in low yields (∼25%), which seriously complicates studies of their prop erties. [1][2][3] In the present study, we developed a more efficient procedure for the synthesis of complexes 1a,b, which al lowed us to prepare these compounds in 60-65% yields. In addition, we examined the reactivity of complexes 1 toward basic and acidic reagents.…”