Cyclic Carbonate Synthesis from Epoxides and CO2 Catalyzed by Aluminum-Salen Complexes Bearing a nido-C2B9 Carborane Ligand

The active and well-designed Schiff base ligands are considered privileged ligands. The so-called salen ligands, i.e., the tetradentate [O, N, N, O] bis-Schiff base ligands, have also found broad applications in many homogeneous catalytic reactions. Modification of the salen ligands has concentrated on altering the substituents in the phenolate rings and variations in the diamine backbones. Herein, o-carborane-supported salen ligands (2) were designed and prepared. A series of aluminum-salen complexes (3 center dot(sol)(2)), which were supported by the nido-C2B9 carborane anions, were synthesized. These Al(III) complexes showed high activities (TOF up to 1500 h(-1)) in catalyzing the cycloaddition of epoxides and CO2 at atmospheric pressure and near room temperature. Complexes 3 center dot(sol)(2) are one of the rare examples of Al-based catalysts capable of promoting cycloaddition at 1 bar pressure of CO2. Density functional theory (DFT) studies combined with the catalytic results reveal that the catalytic cycles occur on two axial sites of the Al(III) center.

Automated summary

The active and well-designed Schiff base ligands are considered privileged ligands and have found broad applications in many homogeneous catalytic reactions. In this study, o-carborane-supported Salen ligands were designed and prepared, and a series of aluminum-Salen complexes supported by nido-C2B9 carborane anions were synthesized. These complexes showed high activities in catalyzing the cycloaddition of epoxides and CO2 at atmospheric pressure and near room temperature, making them rare examples of Al-based catalysts capable of promoting cycloaddition at 1 bar pressure of CO2.