REACTION OF AMINES WITH [((T)BU)AL(MU(3)-O)](6) - DETERMINATION OF THE STERIC LIMITATION OF A LATENT LEWIS-ACID

The reaction of primary and secondary amines with the hexameric tert-b utylalumoxane, [((t)Bu)Al(mu(3)-O)](6), has been investigated. Reactio n of [((t)Bu)Al(mu(3)-O)](6) with 2 equiv of RNH(2) (R=Et, Pr-n, Pr-i, (n)Bu, (t)Bu) results in the formation of [((t)Bu)(6)Al-6(mu(3)-O)(4) (mu-O)(2)(NH(2)R)(2)], R=Et (1), Pr-n (2), Pr-i (3), (n)Bu (4) and (t) Bu (5). The molecular structure of compound 4 has been determined by X -ray crystallography, the Al6O6 core structure of which consists of tw o fused boat-conformation Al3O3 rings, derived from the opening of two opposing edges of the Al6O6 cage of [((t)Bu)Al(mu(3)-O)](6). The (n)B uNH(2) groups are bound to the aluminum atoms of the open cage. Compou nds 1-3 and 5 are isostructural to compound 4 on the basis of H-1 and C-13 NMR spectroscopy. No reaction is observed for R(2)NH (R=Et, Pr-i, (n)Bu, Ph). On the basis of the cone angle (theta) of the amine, we s uggest that steric hindrance is the reason for the lack of reactivity of the secondary amines R(2)NH. A discussion of the steric constraints imposed on a latent Lewis acid is presented.