Syntheses of Heterometallic Neodymium–Zinc Complexes and Their Performance in the Copolymerization of CO<sub>2</sub> and Cyclohexene Oxide
Quanyou Yao, Yaorong Wang, Bei Zhao, Xuehua Zhu, Yunjie Luo, Dan Yuan, Yingming Yao
Abstract
A series of Nd–Zn heterometallic complexes bearing o-phenylenediamine-bridged tris(phenolato) ligands (L) were synthesized and characterized. By tuning the backbones of ancillary tris(phenolato) ligands and initiating benzyloxy groups, a Nd–Zn heterometallic complex 12 (ClLNdZnOBnCF3) was found to be highly active for the copolymerization of CO2 and cyclohexene oxide (CHO) to produce perfect alternating poly(cyclohexene carbonate) with a high turnover frequency up to 5640 h–1 under the polymerization of 90 °C and 20 bar CO2 pressure. The kinetics study showed that CO2/CHO copolymerization catalyzed by 12 was the first order dependence of 12 and CHO concentration and the zero-order dependence of CO2 pressure. The reaction of 12 with CO2 generated a carbonate-coordinated [NdZnNd] trinuclear complex 13, which was believed to be the key intermediate to initiate CO2/CHO copolymerization. On the basis of some experiments, a plausible synergistic polymerization mechanism was proposed.