Amine-bis(phenolato)cobalt(II) Catalysts for the Formation of Organic Carbonates from Carbon Dioxide and Epoxides

New monometallic amine-bis(phenolato)cobalt(II) [(ONNO)^RCo^II] (R = CMe₂Ph; Cl; Br) complexes have been synthesized and fully characterized including X-ray crystallographic analysis. These Co^II complexes show good activity for the formation of cyclic propylene carbonate in combination with tetrabutylammonium bromide (TBAB) as a co-catalyst. The reaction parameters such as carbon dioxide pressure, co-catalyst loadings and temperature were varied to determine the ideal reaction conditions. These catalysts were also employed in copolymerization reactions of cyclohexene oxide/CO₂ and propylene oxide/CO₂. [(ONNO)^ClCo^II]∗(MeOH) was found to effectively copolymerize cyclohexene oxide (CHO) and CO₂. This is the first reported amine-bis(phenolato) cobalt(II) complex to be active in the copolymerization of CO₂ and CHO. In-depth stability studies were conducted (Evan's method) to validate Co^II as the active species required for copolymerization. End-group analysis via NMR, ESI-MS and MALDI-TOF revealed the presence of 4-(dimethylamino)pyridine (DMAP) and methoxy terminated chains. New amine-bis(phenolato)cobalt(II) complexes were synthesized and employed in the coupling and copolymerization of carbon dioxide and epoxides. In combination with DMAP, complex 3 enabled poly(cyclohexene) carbonate generation. End-group analysis found DMAP and methoxy terminated polymer chains due to chain-transfer and the active species for CHO/CO₂copolymerization was found to be Co^II.