Search

A series of dimeric aluminum compounds [Al(OCMe2CH2N(R)CH2X)]2 [X=pyridin‐2‐yl, R=H (PyrH); X= pyridin‐2‐yl, R=Me (PyrMe); X=furan‐2‐yl, R=H (FurH); X= furan‐2‐yl, R=Me (FurMe); X=thiophen‐2‐yl, R=H (ThioH); X= thiophen‐2‐yl, R=Me (ThioMe)] containing heterocyclic pendant group attached to the nitrogen catalyze the coupling of CO2 with epoxides under ambient conditions. In a comparison of their catalytic activities with those of aluminum complexes without pendant groups at N [X=H, R=H (HH); X=H, R=Me (HMe)] or with non‐heterocyclic pendant groups [X=CH2CH2OMe, R=H (OMeH); X=CH2CH2NMe2, R=H (NMe2H); X=CH2CH2NMe2, R=Me (NMe2Me)], complexes containing heterocycles, in conjunction with (nBu)4NBr as a cocatalyst, show higher catalytic activities for the synthesis of cyclic carbonates under the same ambient conditions. The best catalyst system for this reaction is PyrH/(nBu)4NBr system, which gives a turnover number of 99 and a turnover frequency of 4.1 h−1, making it 14‐ and 20‐times more effective than HH/(nBu)4NBr and HMe/(nBu)4NBr, respectively. Although there are no direct interactions between the aluminum and the heteroatoms in the heterocyclic pendants, electronic effects combined with the increased local concentration of CO2 around the active centers influences the catalytic activity in the coupling of CO2 with epoxides. In addition, PyrH/(nBu)4NBr shows broad epoxide substrate scope and seven terminal epoxides and two internal epoxides undergo the designed reaction. [ABSTRACT FROM AUTHOR]

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]