Re(V)-mediated living radical polymerization of styrene:: ReO2I(PPh3)2/R-I initiating systems

Rhenium(V) iododioxobis(triphenyl phosphine) [Re O2I(PPh3)(2)] proved an effective metal catalyst for living radical polymerization of styrene in conjunction with alkyl iodide as an initiator [R-I: CH3CH(Ph)I, (CH3)(2)C(CO2Et)I, and CH3CH(CO2Et)I] in the presence of Al(Oi-Pr)(3). Compared to RuCl2-(PPh3)(3), the group 7 complex was highly effective for styrene, so as to induce the living polymerization even at 30 degrees C to yield well-controlled polystyrene, with (M) over bar(n), up to similar to 4 x 10(4) and very narrow molecular weight distributions (MWDs) ((M) over bar(w)/(M) over bar(n) = 1.19). The polystyrene thus obtained possessed one initiator moiety (R) at the alpha-end and one iodine atom at the omega-end, both from the initiator R-I, which indicates that the polymerization proceeds via activation of the C-I terminal, derived from R-I, by the Re(V) complex. Addition of methanol or water did not inhibit these polymerizations, while a stable nitroxide radical (TEMPO) immediately and completely quenched them. The quenching experiments thereby supported intervention of radical species in the Re(V)-mediated living polymerization.