β-H transfer from the metallacyclobutane: A key step in the deactivation and byproduct formation for the well-defined silica-supported rhenium alkylidene alkene metathesis catalyst

Anne Marie Leduc, Alain Salameh, Daravong Soulivong, Mathieu Chabanas, Jean Marie Basset, Christophe Copéret, Xavier Solans-Monfort, Eric Clot, Odile Eisenstein, Volker P.W. Böhm, Michael Röper

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67 Citations (Scopus)

Abstract

The surface complex [(=SiO)Re(=CtBu)(=CHtBu)(CH2tBu)] (1) is a highly efficient propene metathesis catalyst with high initial activities and a good productivity. However, it undergoes a fast deactivation process with time on stream, which is first order in active sites and ethene. Noteworthy, 1-butene and pentenes, unexpected products in the metathesis of propene, are formed as primary products, in large amount relative to Re (> > 1 equiv/Re), showing that their formation is not associated with the formation of inactive species. DFT calculations on molecular model systems show that byproduct formation and deactivation start by a β-H transfer trans to the weak σ-donor ligand (siloxy) at the metallacyclobutane intermediate having a square-based pyramid geometry. This key step has an energy barrier slightly higher than that calculated for olefin metathesis. After β-H transfer, the most accessible pathway is the insertion of ethene in the Re-H bond. The resulting pentacoordinated trisperhydrocarbyl complex rearranges via either (1) α-H abstraction yielding the unexpected 1-butene byproduct and the regeneration of the catalyst or (2) β-H abstraction leading to degrafting. These deactivation and byproduct formation pathways are in full agreement with the experimental data. © 2008 American Chemical Society.
Original languageEnglish
Pages (from-to)6288-6297
JournalJournal of the American Chemical Society
Volume130
Issue number19
DOIs
Publication statusPublished - 14 May 2008

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