Tuning double metal cyanide catalysts with complexing agents for the selective production of cyclic carbonates over polycarbonates

A double metal cyanide (DMC) complex based on (Zn3[Co(CN)6]2), an effective catalyst for the ring opening polymerization of epoxides and the copolymerization of carbon dioxide with epoxides, was successfully utilized for the solvent-free cycloaddition of CO2 to styrene oxide (SO) by the introduction of cetyltrimethylammonium bromide (CTAB) as a complexing agent (CA). Several DMC catalysts were prepared by introducing co-complexing agents (co-CAs) along with the CA. From the XRD data, it was clear that all the catalysts were amorphous with no peak corresponding to the precursor ZnCl2. XPS analysis was performed to explain the successful introduction of the CA to the DMC catalyst, in which the binding energy of the zinc atom shifted from precursor ZnCl2 to DMC. Elemental analysis and FT-IR also confirmed the incorporation of the CA with Zn3[Co(CN)6]2. The DMC complex was proven to be an effective catalyst for the solvent-free synthesis of styrene carbonate by the cycloaddition of styrene oxide and CO2. This paper reports the tunability of the metal cyanide catalysts with CA for the selective preparation of cyclic carbonates over polycarbonates. 1H NMR and FT-IR confirmed product formation. The effects of reaction parameters like catalyst amount, temperature, CO2 pressure, and reaction time were also investigated.

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► Double metal cyanide (DMC) complexes based on (Zn3[Co(CN)6]2) were successfully synthesized.
► Cetyltrimethylammonium bromide (CTAB), tert-butanol and/or PEG–PPG–PEG were used as complexing agents.
► The DMC catalysts were very efficient for the selective production of styrene carbonate over polycarbonate.
► No additional solvent was used for the cycloaddition of carbon dioxide and styrene oxide.