"Homobimetallic Ruthenium-N-Heterocyclic Carbene Complexes for Olefin Metathesis"

Xavier Sauvage, Albert Demonceau, and Lionel Delaude

book cover 
           title: Metathesis Chemistry: From Nanostructure Design
                  to Synthesis of Advanced Materials
          series: NATO Science Series II. Mathematics, Physics and Chemistry
         editors: Yavuz Imamoglu and Valerian Dragutan
       publisher: Springer
            city: Dordrecht
            year: 2007
          volume: 243
      first page: 91
       last page: 109
            isbn: 978-1-4020-6090-8 (Print) 978-1-4020-6091-5 (Online)
             doi: 10.1007/978-1-4020-6091-5_5

Abstract: In this chapter, the synthesis and catalytic activity towards olefin metathesis of homobimetallic ruthenium (Ru)-alkylidene, -cyclodiene or -arene complexes bearing phosphine or N-heterocyclic carbene (NHC) ligands are reviewed. Emphasis is placed on the last category of bimetallic compounds. Three representatives of this new type of molecular scaffold were investigated. Thus, [(p-cymene)Ru(μ-Cl)3RuCl(η2-C2H4)(L)] complexes with L = PCy3 (15a), IMes (16a), or IMesCl2 (16b) were prepared. They served as catalyst precursors for cross-metathesis (CM) of various styrene derivatives. These experiments revealed the outstanding aptitude of complex 16a (and to a lesser extent of 16b) to catalyze olefin metathesis reactions. Contrary to monometallic Ru-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound nor visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were exposed to 16a,b, a mixture of cycloisomerization and ring-closing metathesis (RCM) products was obtained in a non-selective way. Addition of phenylacetylene enhanced the metathetical activity while completely repressing the cycloisomerization process.

Keywords: Alkylidene Ligands, Arene Ligands, Cycloisomerization, Homogeneous Catalysis, Stilbene Formation

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