Evolution of iron catalysts for effective living radical polymerization: P–N chelate ligand for enhancement of catalytic performances

Iron catalysts were evolved for more active transition metal‐catalyzed living radical polymerization through design of the ligands. In situ introduction of P–N chelate‐ligands, consisting of hetero‐coordinating atoms [phosphine (P) and nitrogene (N)], onto FeBr₂ effectively catalyzed living radical polymerization of methyl methacrylate (MMA) in conjunction with a bromide initiator, where the monomer‐conversion reached over 90% without dropping the rates and the molecular weights of obtained PMMAs were well controlled. The benign effects of the “hetero‐chelation” were demonstrated by comparative experiments with homo‐chelate ligands (P–P, N–N), model compounds of the composed coordination site, and the combinations. We successfully achieved an isolation of iron complex with a P–N ligand [FeBr₂(DMDPE); DMDPE: (R)‐N,N‐dimethyl‐1‐(2‐(diphenylphosphino)phenyl)‐ethanamine], which was superior to the conventional catalyst [FeBr₂(Pn‐Bu)₂] with respect to controllability and activity, especially at the latter stage. The catalyst was almost quantitatively removed by water washing after polymerization. It was also effective for living polymerization of styrene. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6819–6827, 2008