Completing the Heterocubane Family [Cp*AlE]₄ (E = O, S, Se, and Te) by Selective Oxygenation and Sulfuration of [Cp*Al]₄: Density Functional Theory Calculations of [Cp*AlE]₄ and Reactivity of [Cp*AlO]₄ toward Hydrolysis

The subvalent aluminum compound [Cp*Al]₄ (1) reacts with dioxygen, N₂O, or sulfur to yield the heterocubane complexes [Cp*AlX]₄ [X = O (2) and S (3)]. Treatment of [Cp*AlO]₄ (2) with (tBuO)₃SiOH gave [(tBuO)₃SiOAlO]₄ (6) and Cp*H. The structures and spectroscopic data of the Al clusters are supported by density functional theory (DFT) calculations, which also demonstrate the importance of noncovalent interactions (NCI) in oligomeric Al­(I) complexes as well as in [Cp*AlS]₄ and the heavier homologues of Se and Te. The computed ²⁷Al NMR shifts indicate a deshielding at the Al centers with increasing electronegativity of the chalcogen atom as well as significant spin–orbit shielding effects within the heavier heterocubane [Al₄E₄] cores. Further hydrolysis of 6 with an additional amount of silanol in the presence of water resulted in the formation of [Al₄(OH)₆(OH₂)₂(OSiOtBu₃)₆] (7), which shows a structural motif found in boehmite and diaspore.