Synthesis and Characterization of Cobalt(II/II) and Cobalt(II/III) Macrocyclic Complexes and Their Application in the Copolymerization of Epoxides and CO2

Abstract

The synthesis and characterization of six dinuclear cobalt complexes bearing a conjugated macrocyclic ligand are reported. The condensation of 2,6-diformylphenol and o-phenylenediamine led to semi-hydrogenated macrocycles A–C. The ligand precursor A reacted with Co(OAc)2·4H2O and generated the Co(II/II) complex 1, and a conjugated macrocyclic ligand was formed during the complexation. The partial oxidation of 1 with air resulted in mixed-valence Co(II/III) complexes 2 and 3 bearing different anionic ligands. Analogous Co(II/III) complexes 4–6 of Cl- and F-substituted ligand backbones were also synthesized. Structural characterization and charge determination of all complexes were achieved through X-ray diffraction analysis and X-ray photoelectron spectroscopy. These complexes were applied in the copolymerization of CO2 and cyclohexene oxide (CHO), and the mixed valence Co(II/III) complex 2 showed good reactivity and selectivity (>99% polycarbonate).