Exploring the first steps of an electrochemically-triggered controlled polymerization sequence: Activation of alkyl- and benzyl halide initiators by an electrogenerated FeIISalen complex

This works investigates the mechanistic features related to the reactions between FeIISalen and several organic halides used as initiators in Atom Transfer Radical Polymerization. Within the time scale of cyclic voltammetry, a fast reaction is observed between electrogenerated FeIISalen and either ethyl 2-bromoisobutyrate, carbon tetrachloride or 1-chloro-1-phenylethane. Since no catalytic current is observed in cyclic voltammetry in the presence of RX, no fast mediated reductive cleavage of RX into R + X− occured. An intermediate [R··X··FeSalen] complex was formed which was either relatively stable (ethyl 2-bromoisobutyrate and 1-chloro-1-phenylethane) or underwent further reduction (CCl4). In the presence of styrene and at 110 °C, polymerization is observed and the polydispersity of the resulting polystyrene appears to depend on the FeIIISalen/FeIISalen initial ratio. The role of both FeIIISalen and FeIISalen in the regulation of radical concentration provided a controlled character to the polymerization.