Cyclometalated 2‐phenylpyridine complex [Ru^II(o‐C₆H₄‐py)(MeCN)₄]PF₆ as a tunable catalyst for living radical polymerization

Abstract

The cyclometalated complex [RuII(o‐C6H4‐py)(MeCN)4]PF6 (1) with a σ‐RuC bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n‐butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2‐bromoisobutyrate, methyl 2‐bromopropionate, and 1‐phenylethyl bromide. The polymerization requires the presence of Al(OiPr)3 and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)3 and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl2 as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion‐dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst (1), when the added amount of (1) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the (1)‐catalyzed polymerization are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193–4204, 2008

Light-Driven Living/Controlled Radical Polymerization of Hydrophobic Monomers Catalyzed by Ruthenium(II) Metalacycles

“…38 The interval of 110−80 °C is a commonly employed temperature range for the saturated ruthenium complexes with relatively strongly bound ligands in ATRP of hydrophobic monomers. 27,28,36,37,40,45,46,48 The polymerizations catalyzed by coordinatively unsaturated complexes or complexes with extremely labile ligands occur at lower temperatures. 26,41,42 Resistant to thermo-substitution, compounds I and II undergo readily photo-substitution under mild irradiation by visible light.…”

Homogeneous radical polymerization of 2‐hydroxyethyl methacrylate mediated by cyclometalated cationic Ruthenium(II) complexes with PF6− and Cl− in protic media

“…During the past 10 years, easy and efficient synthesis of cyclometalated ruthenium(II) complexes has been developed by our group 32, 33. Some of the complexes have been successfully applied to controlled/living radical polymerizations of traditional hydrophobic monomers, such as styrene and acrylates 34, 35. The complexes are cationic and do not contain chloride or phosphine ligands as the grand majority of the ruthenium catalysts so far used in ATRP.…”

Di-μ2-bromido-bis[bromido(η6-1,2,4,5-tetramethylbenzene)ruthenium(II)]

“…For our work on the synthesis and catalytic applications of ruthenium-arene complexes, see: Ceró n- Camacho et al (2006); Díaz Camacho et al (2008). For related structures, see: Gonzá lez-Torres et al (2009) and references therein.…”