The reactivity and catalytic activities of the tert-butoxy aluminium hydride reagents [(^tBuO)_xAlH_3−x] [x = 1 (1), 2 (2)] and (L)Li[(^tBuO)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.