Preparation Of Salen ALX Catalysts And Their Catalytic Properties In The Coupling Reaction Of Carbon Dioxide With Epoxides

Chemical fixation of CO₂ is of great interest in connection with the development of a truly environmentally benign process. An alternative solution to the problem would be to convert the carbon dioxide at source into a chemical for which there is a significant commercial demand. One of the most promising methodologies in this area is the synthesis of five-membered cyclic carbonates via the coupling of CO₂ and epoxides. In this paper, a series of aluminum salen complexes (SalenAlX) were synthesized. The SalenAlX were probed their catalytic behaviors in the process of coupling reaction CO₂ with epoxides. The influences of substituent groups on the phenoic ring of ligand, diamine skeletons of complexes, anions of substituent groups of ligand, and the coupling reaction conditions on the coupling reaction were systemally investigated. The stability of the supported SalenAlX systems had been studied by carrying out reused tests. We also studied catalytic performance of the supported SalenAlX on the coupling reaction. Some conclusions were made as follows:1. Ten kinds of SalenAlX were succesfully synthesized and characterized by NMR, FT-IR, and UV-Vis.2. The SalenAlX showed good activity in coupling of CO₂ and propylene oxide, and the SalenAlX (2m) whose substituent group was PPh3 and diamine skeleton was phenylethylenediamine had the best catalytic efficiency. Under the suited conditions, the TOF could reach 1121h-1, while the total conversion of propylene oxide was up to 84.1%.3. The SalenAlX (2e) which contained DMAP group could be reused at least four times with only a slight loss of catalytic activity, and the catalyst was found to be applicable to propylene oxide, ethylene oxide, and epichlorohydrin.4. The catalytic activity of the supported SalenAlX (2p) which contained PPh3 group showed a sharp decrease when the catalyst was reused for the first time. The supported SalenAlX (2n) which contained DMAP group had a better stability. After the catalyst (2n) was reused for three times, the catalytic activity reduced to the half of the first used.