摘要
The selective synthesis of polypropylene carbonate （PPC） and cyclic propylene carbonate （CPC） from coupling reaction of CO_2 and propylene oxide （PO） is a long term pursuing target. Here we report that a temperature controllable porphyrin aluminum catalyst using 5,10,15,20-tetra（1,2,3,4,5,6, 7,8-octahydro-1,4：5,8-dimethanoanthracen-g-yl）porphyrin as ligand, once in conjunction with suitable onium salt, achieved single cycloaddition or co- polymerization reaction. Only cydoaddition reaction happened at temperature above 75 ℃ to produce 100% CPC, whereas copolymerization became dominant to afford PPC with selectivity over 99% at 25℃, and the obtained PPC showed over 99% carbonate linkage and 92% head-to-tail structure. Based on systematic analysis of the electronic and steric feature in the porphyrin ligand, it was found that the electronic feature of the substituent in porphyrin ligand was decisive for PPC selectivity, porphyrin ligand bearing strong electron-donating substituents displayed a significantly reduced toler- ance towards increased temperature with respect to PPC formation. Therefore, temperature-responsive catalyst could be designed by suitable modifica- tion in porphyrin ligand, and such accurate synthesis of target product by one catalyst may create a useful and facile platform for selective PPC or CPC production.
The selective synthesis of polypropylene carbonate （PPC） and cyclic propylene carbonate （CPC） from coupling reaction of CO_2 and propylene oxide （PO） is a long term pursuing target. Here we report that a temperature controllable porphyrin aluminum catalyst using 5,10,15,20-tetra（1,2,3,4,5,6, 7,8-octahydro-1,4：5,8-dimethanoanthracen-g-yl）porphyrin as ligand, once in conjunction with suitable onium salt, achieved single cycloaddition or co- polymerization reaction. Only cydoaddition reaction happened at temperature above 75 ℃ to produce 100% CPC, whereas copolymerization became dominant to afford PPC with selectivity over 99% at 25℃, and the obtained PPC showed over 99% carbonate linkage and 92% head-to-tail structure. Based on systematic analysis of the electronic and steric feature in the porphyrin ligand, it was found that the electronic feature of the substituent in porphyrin ligand was decisive for PPC selectivity, porphyrin ligand bearing strong electron-donating substituents displayed a significantly reduced toler- ance towards increased temperature with respect to PPC formation. Therefore, temperature-responsive catalyst could be designed by suitable modifica- tion in porphyrin ligand, and such accurate synthesis of target product by one catalyst may create a useful and facile platform for selective PPC or CPC production.
