Highly Active Di- and Trimetallic Cobalt Catalysts for the Copolymerization of CHO and CO₂ at Atmospheric Pressure

The synthesis and characterization of three new cobalt catalysts for the copolymerization of carbon dioxide and cyclohexene oxide are reported. All the complexes are extremely active at just 1 atm pressure of carbon dioxide, with very high selectivity for copolymerization and carbonate formation. The catalysts are dicobalt(II/II and II/III) and tricobalt(II/II/II) complexes coordinated by a macrocyclic, reduced “Robson” type ancillary ligand and by acetate groups. The complexes are significantly more active than their direct zinc analogues, which we attribute to the increased nucleophilicity of the cobalt−oxygen bond in the cobalt−carbonate propagating species. All three complexes are characterized using mass spectrometry, infrared and ultraviolet−visible spectroscopies, elemental analysis, and, for the tricobalt complex and mixed valence dicobalt species, single-crystal X-ray crystallography.