Direct observation of reaction intermediates for a well defined heterogeneous alkene metathesis catalyst

Frédéric Blanc; Romain Berthoud; Christophe Copéret; Anne Lesage; Lyndon Emsley; Rojendra Singh; Thorsten Kreickmann; Richard R Schrock

doi:10.1073/pnas.0802147105

Direct observation of reaction intermediates for a well defined heterogeneous alkene metathesis catalyst

Proc Natl Acad Sci U S A. 2008 Aug 26;105(34):12123-7. doi: 10.1073/pnas.0802147105. Epub 2008 Aug 22.

Authors

Frédéric Blanc¹, Romain Berthoud, Christophe Copéret, Anne Lesage, Lyndon Emsley, Rojendra Singh, Thorsten Kreickmann, Richard R Schrock

Affiliation

¹ Institut de Chimie de Lyon, Ecole Supérieure Chimie Physique Electronique de Lyon/Centre National de la Recherche Scientifique/Université Lyon 1, Villeurbanne, France.

Abstract

Grafting of [W([triple bond]NAr)(=CHtBu)(2,5-Me(2)NC(4)H(2))(2)] on a silica partially dehydroxylated at 700 degrees C (SiO(2- (700))) generates the corresponding monosiloxy complex [([triple bond]SiO)W([triple bond]NAr)(=CHtBu)(2,5-Me(2)NC(4)H(2))] as the major species (approximately 90%) along with [([triple bond]SiO)W([triple bond]NAr)(CH(2)tBu)(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 [([triple bond]SiO)W([triple bond]NAr)(=CHtBu)(2,5-Me(2)NC(4)H(2))], which shows that they are the key intermediates of alkene metathesis.