Catalysis of Cycloaddition of Carbon Dioxide and Epoxides Using a Bifunctional Schiff Base Iron(III) Catalyst

Cyclic carbonates are solvents with high boiling points and low toxicity. For synthesis of cyclic carbonates we report on bifunctional Schiff base iron(III) complex for catalytic coupling reaction of propylene oxide and CO2. Due to the presence of two imidazole groups in the ligand framework it facilitates the coupling reaction in the absence of co-catalyst with good activity reaching TON value 225 within 4 h. Among various solvents used, the catalyst gives the highest activity in dichloromethane. Moreover, the complex catalyses also the cycloaddition reactions of CO2 and epichlorohydrin, styrene, 1-hexene and cyclohexene oxides. The iron catalysed coupling reaction was followed with in situ infrared spectroscopy giving an apparent first order reaction (n ≈ 1) towards catalyst concentration. Accordingly, a monomolecular mechanism involving imidazole carbamate is proposed.