Tetrameric cubane Al₉Ln₇ (Ln = Ce, Pr, Nd) clusters as aldol addition catalysts

Studies on the preparation, structures, and properties of heterometallic complexes are currently of great interest because of their emergent synergistic properties. Although both rare earth and aluminum oxo clusters have been developed, only a few heterometallic compounds combine the two clusters. In this study, using “ligand-controlled partial hydrolysis”, we synthesize three hat-shaped cationic Al₉Ln₇ (Ln = Ce, Pr, Nd) clusters comprising tetrameric cubane units. Their unique vertex-to-edge-sharing arrangements have not been reported in either rare earth or aluminum oxo clusters. Apart from single-crystal X-ray diffraction, these compounds were characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, thermogravimetric analysis, and energy dispersive spectroscopy. Al₉Ln₇ clusters could serve as efficient catalysts for aldol condensation reactions between acetone and p-nitrobenzaldehyde under mild conditions, with an excellent yield of 86% by AlOC-129Ce.