The readily available mixed-valent iron trifluoroacetate complex [Fe2IIIFeII(mu 3-O)(O2CCF3)6(H2O)3] is an effective catalyst for the polymerization of epoxides. A very small amount of the catalyst (1.00.01 mol%) could initiate the polymerization of cyclohexene oxide, cyclopentene oxide and epichlorohydrin. Based on quantitative end-group analysis by 19F NMR spectroscopy, a Lewis acid (LA?) catalyzed anionic reaction mechanism is proposed. Copyright (c) 2012 Society of Chemical Industry