Kiefer Johannes, Obert Katharina, Himmler Simone, Schulz Peter S, Wasserscheid Peter, Leipertz Alfred
Lehrstuhl für Technische Thermodynamik (LTT), Universität Erlangen-Nürnberg, Erlangen, Germany.
Chemphyschem. 2008 Oct 24;9(15):2207-13. doi: 10.1002/cphc.200800450.
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.
室温离子液体（ILs）中的均相催化是一个极具研究价值且在技术应用方面具有巨大潜力的领域。关于不饱和烃的氢化反应，威尔金森化合物RhCl(PPh(3))(3)是一种具有高选择性和活性的催化剂。在此，我们展示了红外光谱在定量分析离子液体1-乙基-3-甲基咪唑醋酸盐（[EMIM][OAc]）中威尔金森催化剂的应用。我们的研究首次证明了通过红外光谱能够对铑催化剂浓度进行定量、准确且可重复的测定，此外，还能对分子间相互作用进行研究。主要位于红外光谱指纹区的光谱特征被识别出来，揭示了溶解的催化剂对离子液体振动结构的影响。特别是，咪唑环的环弯曲模式显示出频率随催化剂浓度的变化而发生偏移，这可能是由于离子液体阳离子与铑配合物之间形成了氢键。结果表明，红外光谱既具有作为催化过程中快速过程控制技术的应用潜力，又可作为更好地理解离子液体与催化剂相互作用的工具。
