Synthesis and computational studies for halide-free, neutral, and bifunctional one-component ferrocene-based catalysts for the coupling of carbon dioxide and epoxides

We used stable and nontoxic [(dimethylamino)methyl]ferrocene (Fc-N), (hydroxymethyl)ferrocene (Fc-O), 1,2-bis[(dimethylamino)methyl]ferrocene (Fc-N2), and 1-[(dimethylamino)methyl]-2-(hydroxymethyl)ferrocene (Fc-NO) as halide-free, neutral, and bifunctional one-component catalysts for the synthesis of cyclic carbonates. They do not need halide-based additives or tethered salts attached to ligands when used for this coupling reaction. Among them, Fc-N2 exhibited the best catalytic activity under the same reaction conditions. Catalytic activity decreased rapidly in the order Fc-N2 > Fc-NO > Fc-N > Fc-O, and interestingly, the more amino groups introduced into the Cp groups, the higher the activity. Various terminal and internal epoxides were easily converted into the corresponding cyclic carbonates. Calculations based on the density functional theory were also carried out to elucidate the mechanism of the coupling reaction.