Syntheses of Heterometallic Neodymium-Zinc Complexes and Their Performance in the Copolymerization of CO 2 and Cyclohexene Oxide.

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 ( Cl LNdZnOBn CF 3 ) was found to be highly active for the copolymerization of CO 2 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 CO 2 pressure. The kinetics study showed that CO 2 /CHO copolymerization catalyzed by 12 was the first order dependence of 12 and CHO concentration and the zero-order dependence of CO 2 pressure. The reaction of 12 with CO 2 generated a carbonate-coordinated [NdZnNd] trinuclear complex 13 , which was believed to be the key intermediate to initiate CO 2 /CHO copolymerization. On the basis of some experiments, a plausible synergistic polymerization mechanism was proposed.