Yannick Borguet - Homobimetallic Ruthenium−Arene Complexes Bearing Vinylidene Ligands: Synthesis, Characterization, and Catalytic Application in Olefin Metathesis

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  Yannick Borguet, Xavier Sauvage, Guillermo Zaragoza, Albert   Demonceau, and Lionel Delaude*,   Organometallics, 2010, 29 (24), pp   6675–6686


  Five new arylvinylidene complexes with substituents ranging from   electron-donating to strongly withdrawing (p-OMe,   p-Me, p-Cl, p-CF3, and   m-(CF3)2) were isolated in high   yields by reacting   [(p-cymene)Ru(μ-Cl)3RuCl(η2-C2H4)(PCy3)]   (3) with the corresponding phenylacetylene   derivatives. The known phenylvinylidene complex   [(p-cymene)Ru(μ-Cl)3RuCl(═C═CHPh)(PCy3)]   (5) was also obtained from   [RuCl2(p-cymene)]2,   tricyclohexylphosphine, and phenylacetylene under microwave   irradiation. The influence of the remote aryl substituents on   structural features was investigated by IR, NMR, and XRD   spectroscopies. A very good linear relationship was observed   between the chemical shift of the vinylidene α-carbon atom and   the Hammett σ-constants of the aryl group substituents. The   catalytic activity of the six homobimetallic complexes was probed   in various types of olefin metathesis reactions. Unsubstituted   phenylvinylidene compound 5 served as a lead   structure for these experiments. Its reaction with norbornene   afforded high molecular weight polymers with a broad   polydispersity index and mostly trans double bonds.   Aluminum chloride was a suitable cocatalyst for the ring-opening   metathesis polymerization of cyclooctene and led to the formation   of high molecular weight polyoctenamer with a rather narrow   polydispersity index   (Mw/Mn = 1.25) and an   almost equimolar proportion of cis and trans  double bonds. No major changes were observed in the polymer   yields and microstructures when complexes bearing donor groups on   their aryl rings were employed as catalyst precursors. On the   other hand, compounds bearing strongly electron-withdrawing   substituents were significantly less active. Model vinylidene   compound 5 and its ruthenium−ethylene parent   (3) both required the addition of   phenylacetylene to achieve the ring-closing metathesis of diethyl   2,2-diallylmalonate. Thus, the role of this terminal alkyne   cocatalyst goes beyond the facile replacement of the   η2-alkene ligand with a vinylidene fragment.

  Address (URL): http://pubs.acs.org/doi/abs/10.1021/om1006177?prevSearch=%2528borguet%2529%2BNOT %2B%255Batype%253A%2Bad%255D%2BNOT%2B%255Batype%253A%2Bacs-toc%255D&searchHisto r yKey=