Selective oxygen capture by lithium aluminates: a solid state and theoretical structural study

Reaction of PhC(O)N(Me)H with AlMe3 in toluene results in facile CH4 evolut ion and formation of the amidoalane PhC(O)N(Me)AlMe2, 6. The addition of 1 eq. (BuLi)-Li-t affords the lithium aluminate [PhC(O)N(Me)Al(Me)(2)Bu-t]Li, 7, which on treatment with oxygen yields the mixed-anion species [PhC(O)N( Me)Al(Me)(Bu-t)OMe]Li . [PhC(O)N(Me)Al(Me)(OBut)OMe]Li, 8. In the solid sta te 8 forms a dimer based on a tetranuclear (LiO)(4) ladder structure in whi ch terminal mono-oxygenated aluminate ligands and tripodal bis-oxygenated a luminate ligands span end and central Li+ cations. Replacement of PhC(O)N(M e)H in the above reaction sequence with the more sterically congested amide PhC(O)N(Ph)H results in the formation of the amidoalane PhC(O)N(Ph)AlMe2, 9, which in turn affords the lithium aluminate [PhC(O)N(Ph)Al(Me)(2)Bu-t]Li , 10, and upon treatment of this with oxygen, the 70:30 11a:11b mixture [Ph C(O)N(Ph)Al(Me)(OR)R']Li, 11 (R=Bu-t, R'=Me, 11a; R'=Bu-t, R=Me, 11b). Both 10 and 11 are dimeric in the solid state, suggesting that the selective ox ygenation process, and therefore the character of the oxygenated product, i s templated by the structure of the precursor aluminate complex. Calculatio ns are presented which corroborate the competitive nature of the inclusion of oxygen atoms into Al-Me and Al-Bu-t groups in species of the type report ed here.