Study On Synthesis And Catalytic Performance Of New Cobalt Complexes

For the asymmetric altemating copolymerization of CO₂ and propylene oxide(PO) to produce poly(propylene carbonate)(PPC),the binary catalyst system composed of the chiral tetradentate Schiff base cobalt complex(SalenCo(â…¢)â…©) as the electrophlie and ionic ammonium salt or organic sterically hindered strong base as the nucleophile can exhibit excellent activity and＞99%carbonate linkages.But there still remain some problems to be further solved,such as the poor activity at a low catalyst concentration,the low polymer regioselectivity(head-to-tail linkage) and enantioselectivity(ee value).In this dissertation,according to the "intramolecular cooperative catalysis" mechanism,a series of new bifunctional cobalt complexes were first synthesized,which bear both the electrophlie and the nucleophile in a molecule by introducing a quaternary ammonium salt. The complex with an anchored small quaternary ammonium cation on its ligand framework by three methylene units exhibited high activity at a low catalyst concentration and high polymer selectivity even at a high temperature for the copolymerization of CO₂ and propylene oxide.An activity of 5863 h^-1 and up to 95%polymer selectivity were achieved at 90℃and the [PO]/[catalyst]ratio of 25000.It is one of the catalyst systems that can combine high activity and high selectivity under such high temperature.On the basis of "double chiral induction",the cobalt complex containing a chiral quatemary ammonium salt was synthesized and applied in the asymmetric copolymerization of CO2 and propylene oxide to control the stereo-chemistry selectivity.The polymer obtained only had an ee of 52%.To control the regioselectivity,the ligand was modified by using non-chiral diamine backbones and sterically hindered quaternary ammonium cation.The produced polymer had a head-to-tail linkage of 95%.