Lewis acid immobilization onto polymer-supported ionic liquid phases: a x-ray photoelectron spectroscopy study

Abstract

X-Ray Photoelectron Spectroscopy is a well-established technique to study physical and chemical properties of ionic liquids as well as quantitative elemental composition (purity) of a sample. In addition, XPS can be used as a probe of the interaction between metal catalysts dissolved in ionic liquid samples, in order to understand the impact of the ionic liquid on the chemical and electronic environment of the metal center and/or ligands, tuning the catalytic activity of these systems. The use of ionic liquids to immobilize catalysts, either organometallic or organocatalyst, is relatively well explored and this heterogenization approach usually offers many advantages in a great number of organic reactions, one of these being easy separation of the products from the reaction media. This research proposal aims to develop new strategies to overcome challenging chemical transformations in a more sustainable way. More specifically, we propose the preparation and XPS characterization of different polymer-supported ionic liquid phases containing rare earth triflates - i.e. PS-ImC8X/RE(OTf)3 where X = Cl, NTF2 and SbF6; RE = Sc and Y - to be used as recyclable Lewis acid catalytic systems in Diels-Alder cycloadditions and Friedel-Crafts alkylation, among others. We expect that the catalytic materials thus obtained will be able to be recycled and reused in successive runs, improving the green metrics of such reactions. XPS will be used to analyze the incorporation of the metal catalyst onto the polymeric matrix as well as to determine whether or not the polymeric and ionic liquid structures may have impact on the electronic environment of the metallic center. Also, fitting models for main photoemission lines for all elements present within the samples will be developed. The X-Ray Photoelectron Spectroscopy analysis will be carried out using a Kratos Axis Ultra Spectrometer, located at the Nanoscale and Microscale Research Centre (NMRC) of the School of Chemistry/The University of Nottingham. Calculation of TON and TOF metrics, as well as evaluation of the recyclability, will provide us with comparative data to select the best catalyst systems. After each run, the polymeric material incorporating the RE(OTF)3 salt will be re-analyzed by XPS and related techniques to identify possible leaching or poisoning effects, which may contribute for catalyst deactivation. Our approach will be based on informed experimentation where fundamental spectroscopy will lead as criteria in experimental design. By understanding the fundamental principles and processes that underpin this chemistry, we will capitalize on its utility in downstream chemistries and the development of new and sustainable strategies to reach complex organic structures in a more sustainable way. (AU)