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(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 tool for better understanding of IL–catalyst interactions.

Influence of water on phase transition and rheological behavior of cellulose/ionic liquid/water ternary systems

“…MCC/EmimAc/water systems with high concentration, ranging from 6 to 16 wt %, were prepared by adding different amount of MCC (by drying weight) to the mixed solvents, and dissolving them by stirring vigorously at 80 °C for 5 h in closed containers to avoid any change in water content. These concentrations were chosen because it has been reported that cellulose/IL solutions become optically anisotropic at high concentrations (near 10 wt %), which can greatly influence spinning process, structure, and mechanical properties of the cellulose fiber . In addition, a sample without water was prepared under the same conditions.…”

Activation of Small Molecules by P-Ligand—Platinum Metal Complexes in Ionic Liquids

“…The detailed analysis of the fingerprint region revealed that the ring bending mode of the imidazolium moiety shows a frequency shift as a function of the catalyst concentration. Thus, a hydrogen-bond between the imidazolium cation and the rhodium complex was supposed [43].…”

Vibrational Spectroscopy for Studying Hydrogen Bonding in Imidazolium Ionic Liquids and their Mixtures with Cosolvents

“…However, there are efforts going on to make vibrational spectroscopy a tool for more complex systems. For instance, IR spectroscopy has been employed for quantitative measurements of carbohydrates or a Wilkinson catalyst dissolved in ionic liquids [41,42]. In the case of the catalyst experiments, the spectra revealed a red-shift of imidazolium ring bending mode with increasing catalyst concentration.…”