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 and medicine, etc., and these properties are closely related to the bonded metal ions. Although the metal clusters constructed by calixarene and its derivatives have achieved great progress, the Al clusters based on this macrocyclic ligand 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 the formulas as 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 three AlOCs with different coordinated solvents display different catalytic activities and Al4-DMF shows highest catalytic yield up to 99%. This work not only reveals three interesting calixarene-based Al cluster structures, but realize 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 catalyst.