Infrared Spectroscopy of a Wilkinson Catalyst in a Room-Temperature Ionic Liquid

Johannes Kiefer, Katharina Obert, Simone Himmler, Peter S. Schulz, Peter Wasserscheid, Alfred Leipertz

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Abstract

Homogeneous catalysis in room-temperature ionic liquids (ILs) constitutes a most interesting field of research with high potential in technical applications. As concerns the hydrogenation of unsaturated hydrocarbons, Wilkinson's compound RhCl(PPh3)(3) represents a catalyst that provides high selectivity and activity. Herein, we demonstrate the application of infrared spectroscopy to the quantitative analysis of the Wilkinson catalyst in the IL 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]). Our study demonstrates for the first time the quantitative, accurate and reproducible determination of the concentration of a rhodium catalyst by means of IR spectroscopy and, moreover, allows the investigation of intermolecular interactions. Spectral features, located mainly in the fingerprint region of the IR spectrum, are identified revealing the influence of the dissolved catalyst on the IL's vibrational structure. In particular, the ring-bending mode of the imidazolium ring shows a frequency shift as a function of catalyst concentration, probably due to hydrogen-bond formation between the IL cation and the Rh complex. The results show the potential of IR spectroscopy both for application as a quick process control technology in catalytic processes and as a toot for better understanding of IL-catalyst interactions.
Original languageEnglish
Pages (from-to)2207-2213
Number of pages7
JournalChemPhysChem
Volume9
Issue number15
Early online date12 Sep 2008
DOIs
Publication statusPublished - 24 Oct 2008

Keywords

  • homogeneous catalysis
  • ionic liquids
  • IR spectroscopy
  • quantitative spectroscopy
  • rhodium
  • midinfrared polarization spectroscopy
  • initio calculations
  • AB-INITIO
  • raman
  • mixtures
  • phase
  • water
  • hexafluorophosphate

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    Kiefer, J., Obert, K., Himmler, S., Schulz, P. S., Wasserscheid, P., & Leipertz, A. (2008). Infrared Spectroscopy of a Wilkinson Catalyst in a Room-Temperature Ionic Liquid. ChemPhysChem, 9(15), 2207-2213. https://doi.org/10.1002/cphc.200800450