Single-component systems of iron(II) half-sandwich complexes catalyze epichlorohydrin/CO2 condensation

Abstract

Half-sandwich Fe(II) complexes bearing 2-(diphenylphosphino)ethylamine chelating ligand [(η5-C5H5)Fe(CO)(NH2(CH2)2PPh2)]X, where X = I (1), Br (2), Cl (3), OTf (4) were successfully prepared under mild reaction conditions. Their catalytic activity was evaluated systematically on the (chloromethyl)ethylene carbonate synthesis starting from CO2 and epichlorohydrin. The influence of the counterion has been established, where the single-component catalyst 1 showed low catalytic activity under mild conditions for CO2 and epoxide condensation. The exchange of iodide by bromide showed a higher catalytic activity and a higher conversion with compound 2 as a catalyst, while a decrease and no conversion were observed for 3 (X = Cl) and 4 (X = OTf), respectively. Optimization of the catalytic conditions was carried out using epichlorohydrin in dry chloroform, along with modification of the reaction conditions. Of the synthesized compounds (1–4), only 2 showed conversions to (chloromethyl)ethylene carbonate >99 % at 100 °C, 0.34 MPa of CO2, 14 h and 2 % mol of catalyst, or by modifying the temperature to 80 °C and the pressure to 0.69 MPa of CO2. Catalyst 2 proved to be very selective, although it has modest activity, reaching low values of TON (124) and TOF (8.17 h−1).