Direct Observation of a 14-Electron Ruthenacyclobutane Relevant to Olefin Metathesis

Abstract

The 14-electron ruthenium phosphonium alkylidene complex [(IH2Mes)Cl2Ru=CH(PCy3)][B(C6F5)4], 1b, a highly active olefin metathesis catalyst, reacts with stoichiometric quantities of ethylene at -50 degrees C in CD2Cl2 to generate the ruthenacyclobutane complex [(IH2Mes)Cl2RuCH2CH2CH2], 2, and [CH2=CH(PCy3)][B(C6F5)4] in quantitative yield by NMR spectroscopy. 1H and 13C NMR spectroscopies on 2 and 2-13C3 are consistent with a symmetrical C2v structure, providing the first experimental information concerning this crucial intermediate in ruthenium-mediated olefin metathesis. At -50 degrees C, exchange with free ethylene takes place on the chemical time scale. Complex 2 decomposes in solution upon warming to room temperature, generating propene and unknown ruthenium product(s).

Assignment of pre-edge features in the Ru K-edge X-ray absorption spectra of organometallic ruthenium complexes

“…Given the nature of the Ru K-edge preedge transitions as described herein, it should be possible to evaluate the coordination number and geometry of key intermediates in the organometallic chemistry of Ru species relevant to catalysis. We are currently exploring the electronic and geometric structure of olefin metathesis intermediates -including the putative four-coordinate active catalyst as well as the recently isolated ruthenacyclobutane intermediate [24], for which little geometric or electronic information is available. The addition of Ru K-edge XAS pre-edge analysis as a tool in this effort should yield significant results.…”

Ligand Influence on Metathesis Activity of Ruthenium Carbene Catalysts: A DFT Study

“…[12] Second-generation ruthenacycle 11 is predicted to be more stable than the isomeric alkene carbene conformers -and indeed, it has been detected in solution by Piers group. [13] Chloride ligands are the standard anionic ligands in ruthenium carbene catalysts. Anionic ligands superior to chloride have not yet been found.…”

Ring closing metathesis employing organometallic substrates and the templated synthesis of macrocycles

“…1 for a small selection of metathesis catalysts with some selected properties. Recent results with Ru-based systems have also probed the nature of the elusive "active catalytic species" [17] and detailed kinetic studies have helped to unravel the intimate mechanistic details of this important reaction [18,19]. While lagging somewhat behind the advances in the metathesis chemistry of alkenes, recent developments in alkyne metathesis show this area to also be of great potential benefit to the above mentioned areas [20,21].…”