A versatile photoactivated catalytic system based on a cyclometalated ruthenium(II) complex, composed of strongly coordinating bidentate and relatively labile ligands, in conjunction with a traditional alkyl bromide initiator, has been developed for living/controlled radical polymerization. Polymerizations of three typical hydrophobic monomersmethyl methacrylate (MMA), styrene (St), and n-butyl acrylate (BA)proceeded to high conversions under visible light irradiation. The polymerization process was photoresponsive, i.e., took place only under irradiation and immediately stopped when the light was turned off. Block copolymers of MMA with St and BA with St, as well as statistical copolymer of BA and St, could also be conveniently prepared. 1 H NMR and electrochemical studies suggest a mechanism of the catalytic activation, which involves a photoinduced formation of the solvento 18-electron species cis-[Ru(o-C 6 H 4 -2-py)(phen)(MeCN)(acetone)] + through the intermediacy of the 16-electron five-coordinated complex cis-[Ru(o-C 6 H 4 -2-py)(phen)(MeCN)] + which is believed to be a crucial intermediate of the overall ATRP process.

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Summary: Cyclometalated complex, cis-[Ru(phpy)(phen)(MeCN) 2 ]PF 6 , bearing strongly bound ligands (phpy ¼ 2-phenylpyridine, phen ¼ 1, 10-phenantroline) and relatively labile (MeCN) ligands, in conjunction with ethyl 2-bromoisobutyrate (EBiB), was used for radical polymerization of three hydrophobic, styrene (St), methyl methacrylate (MMA), n-butyl acrylate (BA), and one hydrophilic, 2-hydroxyethyl methacrylate (HEMA), monomers. The polymerizations were fast and reasonably controlled; the molecular weights increased with conversion and were close to the calculated values. The best control was achieved in polymerization of St. The complex was able to mediate this polymerization with acceptable rate and level of control even at a monomer/catalyst ratio of 2000. The living character of the polymerizations was confirmed by chain extension experiments; the degree of polymer ''livingness'' was less for PMMA than for PSt. Because of ionic nature, the complex was well soluble in MeOH and thus catalyzed polymerization of HEMA under homogeneous conditions at 50 8C.