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 t 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 nBu₄NI 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. [ABSTRACT FROM AUTHOR]