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 (<b>1</b>) reacts with dioxygen, N₂O, or sulfur to yield the heterocubane complexes [Cp*AlX]₄ [X = O (<b>2</b>) and S (<b>3</b>)]. Treatment of [Cp*AlO]₄ (<b>2</b>) with (<i>t</i>BuO)₃SiOH gave [(<i>t</i>BuO)₃SiOAlO]₄ (<b>6</b>) 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 <b>6</b> with an additional amount of silanol in the presence of water resulted in the formation of [Al₄(OH)₆(OH₂)₂(OSiO<i>t</i>Bu₃)₆] (<b>7</b>), which shows a structural motif found in boehmite and diaspore.