Sulfonylcalix[4]arene-based Al4 clusters: three aluminum oxo clusters with different coordinated solvents for the CO2 cycloaddition reaction†

Calixarene compounds are widely used in molecular recognition, complexation, extraction, catalysis, medicine, etc., and these properties are closely related to the bonded metal ions. Although the metal clusters constructed using calixarene and its derivatives have achieved great progress, Al clusters based on these macrocyclic ligands are still in the preliminary research stage due to the obvious hydrolysis of Al³⁺ ions in solution. It is a great challenge to obtain high-quality measurable single crystals of aluminum oxo clusters (AlOCs). Herein, we used an oxygen-rich organic macrocyclic ligand of p-tertbutylsulfonylcalix[4]arene (H₄BTC4A-SO₂) to synthesize three Al₄ clusters with formulas Al₄(OH)₂(BTC4A-SO₂)₂(MeO)₂(DMA)₂(MeOH)₂ (Al₄-DMA·MeOH), Al₄(OH)₄(BTC₄A-SO₂)₂(DMA)₄ (Al₄-DMA), and Al₄(OH)₄(BTC4A-SO₂)₂(DMF)₄ (Al₄-DMF) which are combined by different solvents. Interestingly, the cycloaddition of carbon dioxide proves that the three AlOCs with different coordinated solvents exhibit different catalytic activities and Al₄-DMF shows the highest catalytic yield up to 99%. This work not only reveals three interesting calixarene-based Al cluster structures, but also realizes the regulation of catalytic activities for the reaction of the cycloaddition of carbon dioxide. This provides insights into the assembly of AlOCs and their study as catalysts.