Alternating copolymerization of CO2 and cyclohexene oxide initiated by rare-earth metal complexes stabilized by o-phenylenediamine-bridged tris(phenolate) ligand

A series of o -phenylenediamine bridged tris(phenolate) ligand-stabilized rare-earth metal complexes were synthesized and characterized. Lanthanum (complex 1) , neodymium (complex 2 t Bu ), and yttrium (complex 3 ) complexes stabilized by ligand of bulky tert -butyl substituents are mononuclear, whereas neodymium complexes 2 Me and 2 Cl bearing smaller methyl and chloro substituents are dinuclear, respectively. They were applied in the alternating copolymerization of CO 2 and cyclohexene oxide. The addition of benzyl alcohol is beneficial to improving yields (up to 86%) and selectivity of poly(carbonate) (up to 99%). Stoichiometric reaction of benzyl alcohol with rare-earth metal complexes 1 and 2 t Bu results in formation of complexes 4 and 5 as dinuclear complexes with benzyl alcohol coordination, which was confirmed via single crystal X-ray diffraction analysis, and nuclear magnetic resonance (NMR) spectroscopy (for 4 ). Complex 5 shows equally good activity and selectivity of that of complex 2 t Bu and benzyl alcohol, consolidating that complex 5 is indeed generated during polymerization. The neodymium tris(phenolate) 5 is one of the few examples of rare-earth metal complex as a single-component initiator for copolymerization of epoxide and CO 2 . Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry analysis proves benzyloxy group as the chain end. 1 H NMR monitoring suggests that the insertion of CO 2 may be the first step in the growth of the polymer chain. Benzyl alcohol-coordinating rare earth metal complexes as single-component initiators for copolymerization of CO 2 and cyclohexane oxide, without halide co-catalyst. >99 % polycarbonate selectivity, while no polyether or cyclic carbonate formation. • Benzyl alcohol-coordinating rare earth metal complexes as initiators for copolymerization of CO 2 and CHO. • 70 °C and 2.0 MPa CO 2 . • >99% polycarbonate, up to 86% yield. • No co-catalyst required.