751. Direct observation of reaction intermediates for a well defined heterogeneous alkene metathesis catalyst
- Author
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Anne Lesage, Frédéric Blanc, Rojendra Singh, Thorsten Kreickmann, Richard R. Schrock, Lyndon Emsley, Christophe Copéret, and Romain Berthoud
- Subjects
chemistry.chemical_classification ,solid state NMR ,Multidisciplinary ,Chemistry ,Alkene ,Reaction intermediate ,Metathesis ,Heterogeneous catalysis ,Catalysis ,Propene ,chemistry.chemical_compound ,heterogeneous catalysis ,Solid-state nuclear magnetic resonance ,metallacyclobutanes ,Physical Sciences ,Polymer chemistry ,alkylidene ,Organic chemistry ,Reactivity (chemistry) - Abstract
Grafting of [W(≡NAr)(=CH t Bu)(2,5-Me 2 NC 4 H 2 ) 2 ] on a silica partially dehydroxylated at 700°C (SiO 2- (700) ) generates the corresponding monosiloxy complex [(≡SiO)W(≡NAr)(=CH t Bu)(2,5-Me 2 NC 4 H 2 )] as the major species (≈90%) along with [(≡SiO)W(≡NAr)(CH 2 t Bu)(2,5-Me 2 NC 4 H 2 ) 2 ], according to mass balance analysis, IR, and NMR studies. This heterogeneous catalyst displays good activity and stability in the metathesis of propene. Very importantly, solid state NMR spectroscopy allows observation of the propagating alkylidene as well as stable metallacyclobutane intermediates. These species have the same reactivity as the initial surface complex [(≡SiO)W(≡NAr)(=CH t Bu)(2,5-Me 2 NC 4 H 2 )], which shows that they are the key intermediates of alkene metathesis.