Living radical polymerization of styrene by half-metallocene iron carbonyl complexes

A series of half-metallocene Fe(II) complexes [FeLX(CO)(2); X = I, Br; L = eta(5)-C5H5 (CP), eta(5-)C(5)Me(5) (Cp*)] were employed for living radical polymerization of styrene in conjunction with halide initiators [(CH3)(2)C(CO2Et)X; X = I and Br] in the presence or absence of Ti(Oi-Pr)(4). The iron-based systems induced living radical polymerization of styrene to give polymers of narrow molecular weight distributions (MWDs) in the presence of Ti(Oi-Pr)(4). The Cp*-iodide complex [FeCp*I(CO)(2)] gave the narrowest MWDs (M-w/M-n = 1.05-1.09) when coupled with the iodoester initiator. The polymerization with FeCpI(CO)(2) was examined in several ether solvents, where dioxane proved most effective. Dinuclear iron(I) complexes [Fe2Cp2(CO)(4)] were also employed for living radical polymerization of styrene coupled with the iodoester initiator. Dinuclear half-metallocenes induced faster living polymerization even without Ti(Oi-Pr)(4). Cyclic voltammetric analysis showed that the redox potential of the dinuclear complex is lower than that of the mononuclear one. Some interactions of Ti(Oi-Pr)(4) with the iron complexes were observed by cyclic voltammetric and NMR analysis of the mixtures.