Reactions of alkynes with [RuCl(cyclopentadienyl)] complexes: The important first steps

Barnali Dutta, Basile F E Curchod, Pablo Campomanes, Euro Solari, Rosario Scopelliti, Ursula Rothlisberger, Kay Severin*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

39 Citations (Scopus)

Abstract

Cyclopentadienyl-ruthenium half-sandwich complexes with η2-bound alkyne ligands have been suggested as catalytic intermediates in the early stages of Ru-catalyzed reactions with alkynes. We show that electronically unsaturated complexes of the formula [RuCl(Cp̂)(η2-RC=CR')] can be stabilized and crystallized by using the sterically demanding cyclopentadienyl ligand Cp̂ (Cp̂ = η5-l-methoxy-2,4tert-butyl-3-neopentyl-cyclopentadienyl). Furthermore we demonstrate that [RuCl2(Cp̂)]2 is an active and regioselective catalyst for the [2+2+2] cyclotrimerization of alkynes. The first elementary steps of the reaction of mono(η2- alkyne) complexes containing {RuCl(Cp*)} (Cp* = η5- C5Me5) and (RuCl(Cp̂)} fragments with alkynes were investigated by DFT calculations at the M06/6-31G* level in combination with a continuum solvent model. Theoretical results are able to rationalize and complement the experimental findings. The presence of the sterically demanding Cp̂ ligand increases the activation energy required for the formation of the corresponding di(η2alkyne) complexes, enhancing the initial regioselectivity, but avoiding the evolution of the system towards the expected cyclotrimerization product when bulky substituents are present. Theoretical results also show that the electronic structure and stability of a metallacyclic intermediate is strongly dependent on the nature of the substituents present in the alkyne.

Original languageEnglish
Pages (from-to)8400-8409
Number of pages10
JournalChemistry - A European Journal
Volume16
Issue number28
DOIs
Publication statusPublished - 26 Jul 2010

Keywords

  • Alkynes
  • Cyclotrimerization
  • Density functional calculations
  • Organometallic chemistry
  • Ruthenium

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