Ternary rare earth metal coordination catalysts prepared from Y(CCl3COO)3

glycerin

and ZnEt2 were confirmed to be effective for the copolymerization of carbon dioxide and various epoxides.Whereas their precise modification was hampered by the lack of insight into active centers.Here an X-ray photoelectron spectroscopy (XPS) technique was employed to study the interaction of various components

especially the central metal atoms in these catalysts.Copolymerization experiments with typical conditions were also carried out to investigate the correlation between the binding energy (BE) of central metals and the catalytic activity.The BE of Zn2p3/2 in Y(CCl3COO)3-glycerin-ZnEt2 ternary catalyst was tested to be 0.3 eV higher than that in glycerin-ZnEt2 binary catalyst

while the BE of O1s increased by 0.4 eV; On the contrary

the BE of Y3d5/2 in the ternary catalyst system decreased by 1.4 eV than that in Y(CCl3COO)3

while Cl2p decreased by 1.6 eV.The BE shifts showed that the rare-earth-metal compound has assuredly coordinated with zincoxygen bond in the ternary catalyst.Active center for the copolymerization is the coordinating activated zinc-oxygen bond

and rareearthmetal compounds shift the electron distribution of active center by a conjectured “double metal bridged coordinating" mode.Electrons around Zn partially flow to Y via coordinating

resulting in decrease of electron cloud density and increase of the Lewis acidity around catalytic centre.That makes the activated zinc-oxygen bond more liable to be attacked by carbon dioxide and epoxide monomer

thereby it enhances the catalytic activity.As a result

the activity of Y(CCl3COO)3 based ternary catalyst reached 563.0 g polymer/(mol Zn h) in the copolymerization

which is 23.6% higher than the activity of the binary catalyst system without rare-earth-metal compounds.Yttrium compounds with various anionic groups were also investigated to study the influences of Lewis acidity on central site.A consistent relationship was found among the pKa of ligands in yttrium compounds

BE of the coordinated catalysts and catalytic activities.