Iron Complexes of Bis(oxazoline) Ligand as Novel Catalysts for Efficient Atom Transfer Radical Polymerization of Styrene

The polymerization of styrene mediated by the bis(oxazoline) iron complexes Fe(box)Cl2 and Fe(box)Cl3 proceeds throughout a classical ATRP (Atom transfer radical polymerisation) mechanism. Complex Fe(box)Cl3 is the firstexample of iron(III)-based catalytic systems showing an effectivecontrol in reverse ATRP styrene polymerization. The iron-(II) species Fe(box)Cl2 corresponding to the reduced form ofthe iron(II)/iron(III) redox couple has been fully characterized by X-ray diffraction; this supports the stability of the coordinative unsaturated iron complex in pseudo-tetrahedral coordination environment under monomeric form. The reverse approach used with the title catalysts exhibitstwo main advantages: the radical initiator is generally less toxic and less expensive than alkyl halides used in the ATRP protocol, and the iron(III) catalyst precursor is more soluble, more stable thermally, and in air. In the light of these results the scarce control operated by Fe(box)Cl2 in the ATRP of styrene could be ascribed to the slow reaction between the initiator 1-PEBr and the iron complex.