Synthesis of Heterometallic Rare Earth(III)–Cobalt(II) Complexes and Their Application in Alternating Copolymerization of Cyclohexene Oxide and Carbon Dioxide

Abstract

Four heterometallic rare earth(III)-cobalt(II) complexes (rare earth = Y (1), Sm (2), Nd (3), La (4)) stabilized by an o-phenylenediamine-bridged tris(phenolato) ligand (L) have been synthesized and characterized. In these tetranuclear complexes, one polydentate L coordinates to one rare earth(III) ion, and one cobalt(II) ion, respectively, while two rare earth ions are bridged by four acetate groups. These complexes were applied in the copolymerization of cyclohexene oxide and CO2, which showed good activity (TON up to 440) and high poly(cyclohexene carbonate) selectivity (>99%). Kinetic studies determined the equation as rate = k[CHO]1[CO2]0[initiator]1, which proves a first-order dependence on initiator concentrations and implies a synergistic mechanism with rare earth and cobalt ions cooperating in epoxide ring-opening and chain propagation.