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Iron(II) Bis-CNN Pincer Complex-Catalyzed Cyclic Carbonate Synthesis at Room Temperature

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journal contribution
posted on 07.09.2017, 00:00 by Fei Chen, Ning Liu, Bin Dai
A series of unsymmetrical pyridine-bridged bis-pincer-type iron­(II) complexes were synthesized, and the complexes were used as catalysts for the cycloaddition of CO2 and epoxides. At ambient temperature, the combined use of iron complexes and tetrabutyl ammonium bromide (TBAB) resulted in an efficient catalytic system for the synthesis of cyclic carbonates under low CO2 pressure (0.5 MPa) and solvent-free conditions. More importantly, in the absence of TBAB, propylene oxide was also easily converted to the target products when the temperature was increased to 100 °C, and a turnover frequency (TOF) value of 7900 h–1 was achieved at 120 °C. An elevated reaction temperature (80 °C) was required to achieve high conversion of challenging internal epoxides and oxetanes to their respective carbonates with good yields. Moreover, the iron catalyst can be easily recycled six times via simple filtration without any significant loss of activity.