Iron–Aryloxide Complex Bearing Bis(dipyrromethene) Ligands for the Ring-Opening Polymerization of Ε-Caprolactone

We report a high-spin iron system supported by two dipyrromethene ligands for ring-opening polymerization of epsilon-caprolactone. The four-coordination iron(II) complex, (dipyrrin)2Fe, features an S = 2 electronic configuration. It readily reacts with 2,4,6-tri-tert-butylphenoxyl radical (tBu3ArO center dot) by one-electron oxidation to afford (dipyrrin)2Fe-OArtBu3, a high-spin S = 5/2 iron(III) aryloxide complex. At 0.1 mol % loading, this ferric aryloxide efficiently performs CL polymerization, producing PCLs with a high molecular weight (Mn = 84,871) and narrow polydispersity (PDI = 1.23-1.26).