The Role of Alkoxide Initiator, Spin State, and Oxidation State in Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Iron Bis(imino)pyridine Complexes

Density functional theory (DFT) is employed to characterize in detail the mechanism for the ring-opening polymerization (ROP) of epsilon-caprolactone catalyzed by iron alkoxide complexes bearing redox-active bis(imino)pyridine ligands. The combination of iron with the non-innocent bis(imino)pyridine ligand permits comparison of catalytic activity as a function of oxidation state (and overall spin state). The reactivities of aryl oxide versus alkoxide initiators for the ROP of E-caprolactone are also examined. An experimental test of a computational prediction reveals an Fe(III) bis(imino)pyridine bis-neopentoxide complex to be competent for ROP of epsilon-caprolactone.