Synthesis And Application Of Zwitterionic Chiral Phosphine Ligands Based PPM

Homogeneous asymmetric hydrogenation is now a well-used methodology in organic synthesis due to the high activities and stereoselectivities. However, only a few examples have been developed into industrial processes due to the problems of separation and recycling of the expensive chiral catalysts.In this study,the zwitterionic water-soluble chiral diphosphines ligands with amino acid moieties were designed and synthesized for catalytic asymmetric hydrogenation. A novel catalytic system denoted homogeneous catalysis-immobilization separation was developed based on zwitterionic diphosphines ligands. Under this catalytic system, catalytic reaction takes place in polar solvent such as methanol and the catalysts can be recovered by ion exchange resin. The relationship between structure and catalytic activities, stereoselectivities of different phosphine-rhodium complex was studied by model reaction of hydrogenation of prochiral amino acids derivatives. Influences of reaction conditions such as solvent, additives,reaction temperature and pressure on the catalytic activities and stereoselectivities were examined. The activities and stereoselectivities of recovered phosphine-rhodium complex by immobilization separation were tested. The results show that the obtained zwitterionic phosphine-rhodium catalysts are highly effective, and that reduction of prochiral amino acids derivatives gave the corresponding amino acids derivatives with conversion of up to 100% and enantioselectivity of up to 95% ee. However, significant decrease in the activity and selectivity was observed after three catalytic runs. This work enriches the variety of chiral phosphines ligands and provides a new methodology for separation and recycling of the expensive chiral catalysts.