title: Infrared spectroscopy of a Wilkinson catalyst in a room-temperature ionic liquid.
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(PPh(3))(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 tool for better understanding of IL-catalyst interactions.
authors.affiliation: Lehrstuhl für Technische Thermodynamik (LTT), Universität Erlangen-Nürnberg, Erlangen, Germany. jk@ltt.uni-erlangen.de
authors.forename: Johannes
authors.initials: J
authors.lastname: Kiefer
authors.forename: Katharina
authors.initials: K
authors.lastname: Obert
authors.forename: Simone
authors.initials: S
authors.lastname: Himmler
authors.forename: Peter S
authors.initials: PS
authors.lastname: Schulz
authors.forename: Peter
authors.initials: P
authors.lastname: Wasserscheid
authors.forename: Alfred
authors.initials: A
authors.lastname: Leipertz
mesh_terms: D002384:Catalysis; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods; D013696:Temperature
chemical_list: D007093:Imidazoles; D052578:Ionic Liquids; D009942:Organometallic Compounds; D009943:Organophosphorus Compounds; C016305:chlorotris(triphenylphosphine)rhodium; C518739:1-ethyl-3-methylimidazolium