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

The reactivity and catalytic activities of the tert-butoxy aluminium hydride reagents [((BuO)-Bu-t)(x)AlH3-x] [x = 1 (1), 2 (2)] and (L) Li[((BuO)-Bu-t)(2)AlH2] [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)(4)Al](-)[(pyridine)(4)AlH2](+) (5) while reaction with the amine-borane Me2NHBH3 in the presence of PMDETA [(Me2NCH2CH2)(2)NMe] affords [(PMDETA)AlH2](+)[(BH3)(2)NMe2](-) (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 similar to 3 > 4. The greater reactivity of the neutral dihydride 1 provides the potential basis for future catalytic optimisation.