Highly Active Salen-Based Aluminum Catalyst for the Coupling of Carbon Dioxide with Epoxides at Ambient Temperature

Aluminum complex [(naph)salen]AlMe [(naph)salen = N,N-(2,3-naphthalene)bis(3,5-dimethylsalicylideneiminato)] was synthesized and fully characterized by NMR spectroscopy, high-resolution mass spectrometry, elemental analysis, and single-crystal XRD. The complex exhibits square-pyramidal geometry around the aluminum center in the solid-state structure, and it has a trigonality parameter of 0.13. Comparison of the catalytic activity of [(naph)salen]AlMe with that of four related aluminum complexes containing tetradentate salen ligands with different bridging groups revealed that the naphthyl-bridged salen-based aluminum complex, in conjunction with nBu(4)NI as cocatalyst, showed higher catalytic activity than the other complexes for the coupling of CO2 with epoxides under the mild conditions of room temperature and 5 bar of CO2 in 12 h. In addition, [(naph)salen]AlMe showed favorable features, such as requiring low catalyst loading (0.5 mol-%) and broad epoxide substrate scope, including six terminal epoxides and three internal epoxides.