Reactivity and catalytic activity of tert-butoxy-aluminium hydride reagents.

The reactivity and catalytic activities of the tert-butoxy aluminium hydride reagents [((t)BuO)xAlH3-x] [x = 1 (1), 2 (2)] and (L)Li[((t)BuO)2AlH2] [L = THF (3), 1,4-dioxane (4)] are investigated. The structural characterisation of the novel compounds 3 and 4 shows that the nature of the hydridic species present is affected dramatically by the donor ligand coordinating the Li(+) cation. Stoichiometric reaction of 1 with pyridine gives [(1,4-H-pyrid-1-yl)4Al](-)[(pyridine)4AlH2](+) (5) while reaction with the amine-borane Me2NHBH3 in the presence of PMDETA [(Me2NCH2CH2)2NMe] affords [(PMDETA)AlH2](+)[(BH3)2NMe2](-) (6). The reagents 1-4 catalyse the dehydrocoupling reaction of the amine-borane Me2NHBH3 into the ring compound [Me2NBH2]2, with the activity decreasing in the order 1≫2∼3 > 4. The greater reactivity of the neutral dihydride 1 provides the potential basis for future catalytic optimisation.