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Ruthenium Alkylidenes: Modulation of a New Class of Catalysts for Controlled Radical Polymerization of Vinyl Monomers
Author(s) -
Simal François,
Delfosse Sébastien,
Demonceau Albert,
Noels Alfred F.,
Denk Karin,
Kohl Florian J.,
Weskamp Thomas,
Herrmann Wolfgang A.
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020703)8:13<3047::aid-chem3047>3.0.co;2-v
Subject(s) - carbene , ruthenium , chemistry , moiety , polymer chemistry , styrene , polymerization , methyl methacrylate , radical polymerization , cobalt mediated radical polymerization , atom transfer radical polymerization , monomer , catalysis , photochemistry , nitroxide mediated radical polymerization , organic chemistry , copolymer , polymer
Air‐stable and readily available ruthenium benzylidene complexes of the general type [RuCl 2 (CHPh)(L)(L′)] (L, L′=PCy 3 and/or N ‐heterocyclic carbene) constitute a new class of catalyst precursors for atom‐transfer radical polymerization (ATRP) of methyl methacrylate and styrene, and provide an unprecedented example for the involvement of ruthenium alkylidenes in radical reactions. They promote the polymerization of various monomers with good to excellent yields, and in a controlled way with methyl methacrylate and styrene. Variations of their basic structural motif provide insights into the essential parameters responsible for catalytic activity. The ligands L (PCy 3 and/or N ‐heterocyclic carbene) turned out to play a particularly important role in determining the rate of the polymerizations. A similarly pronounced influence is exerted by the substituents on the N ‐heterocyclic carbene. Our results indicate that the catalysts decompose quickly under ATRP conditions, and polymerizations are mediated by both [RuCl 2 (CHPh)(L)(L′)] complexes and ruthenium species bereft of the benzylidene moiety, through a pathway in which both tricyclohexylphosphane and/or N ‐heterocyclic carbene ligands remain bound to the metal center. Polymerization of n ‐butyl acrylate and vinyl acetate is not controlled and most probably takes place through a redox‐initiated free‐radical process.