Highly efficient and quantitative synthesis of a cyclic carbonate by iron complex catalysts

The novel iron complexes [N,N′-bis-2-pyridinylmethylene-cyclohexane-1,2- diamine]iron(II) chloride (1) and [N,N′-bis-2-pyridinylmethyl-cyclohexane-1,2-diamine]iron(II) chloride (2) were designed, and they showed excellent activity for the coupling reaction epoxides and CO2 to generate the corresponding cyclic carbonates. When complex 2 was used alone as a catalyst for the cycloaddition of propylene oxide (PO) and CO2, the PO conversion was 95% at 130 °C and 4 MPa CO2 pressure in 4 h. Once a co-catalyst like tetrabutylammonium bromide (TBAB) was added, the conversion could reach 100% with nearly 100% selectivity for propylene carbonate (PC), with a turnover number (TON) of 1000 at 100 °C and 4 MPa CO2 pressure in 6 h, i.e. the quantitative synthesis of propylene carbonate can be realized. Moreover, in combination with TBAB, the iron complex can also catalyze the cycloaddition of cyclohexene oxide (CHO) and epichlorohydrin (ECH) with CO2 to produce the corresponding cyclic carbonates, and the cyclohexene carbonate obtained was mainly the cis-isomer.

Novel iron complexes in combination with TBAB showed excellent activity for the coupling reaction of epoxides and CO2 to generate the corresponding cyclic carbonates.Figure optionsDownload as PowerPoint slide