Group IIIA Halometallate Ionic Liquids: Speciation and Applications in Catalysis

Abstract

Group IIIA halometallate ionic liquids (ILs) present fascinating properties for the field of catalysis, particularly through the ability to tune their Lewis acidity solely by changing the metal complex speciation. In this Review, we present a critical perspective on the use of Group IIIA halide-derived ILs in catalysis, focusing on the effect of speciation of the metal-containing ions on various acid-catalyzed reactions, some of which are applied industrially. We summarize all applications of Group IIIA halometallates in catalysis (where they are notably well-represented in reactions of importance in petroleum refining and processing), compare the authors' investigations or assumptions with regard to chemical speciation, and present examples of how the tunability of these materials is used to overcome their initially perceived drawbacks. Further, advances in the field of halometallate ILs such as the role of the cations in the IL, IL analogues, and heterogenization strategies are discussed. High selectivity, reactivity, and stability are the cornerstones of the ideal catalyst, and the journey of catalysis research toward the ideal catalyst will be possible only with rational catalyst design and innovative thinking.

An Oxalate‐Bridged Binuclear Iron(III) Ionic Liquid for the Highly Efficient Glycolysis of Polyethylene Terephthalate under Microwave Irradiation

“…The iron complex 3 was investigated in detail by Raman and IR spectroscopies, since these techniques are extremely useful for studying the bonding and type of imidazolium compounds and the metal coordination environments of halometallate species . Figure displays the non‐polarized Raman and FT‐IR spectra of 3 in the range of 150–3900 cm −1 at K. The vibrational assignments proposed herein are based on the comparison of spectroscopic behavior of the “free” oxalate anion with the data described in the literature for iron oxalate complexes and those published in our previous study of (dimim)[FeCl 4 ] complex (Table S1, Supporting Information) .…”

Post-Synthetic Modification of Ionic Liquids Using Ligand-Exchange and Redox Coordination Chemistry

“…A promising platform for such structure-property investigations is the perhalometallate anions because they can be prepared with alkaline earth and transition metals, and main group and f-block elements through single-step halide abstraction reactions (Scheme 1B). 10,[37][38][39][40][41][42][43] To-date, most perhalometallate anion examples include only chloride ligands, however, and little is known about how the composition of these anions dictate supramolecular ordering, which, in turn, controls functional behavior such as viscosity, conductivity, and electrical double layer capacitance. Additionally, certain perhalometallate anions, including SnCl3 -, ZnCl4 2-, and 10,37,38 exist in dynamic equilibrium with species of varying nuclearities and coordination numbers.…”

Mixed Chlorometallate Ionic Liquids as C4 Alkylation Catalysts: A Quantitative Study of Acceptor Properties

“…They proposed that Cu(I) could substitute the proton in the [(C 2 H 5 ) 3 NH] + cation and generate [(C 2 H 5 ) 3 N•Cu] + and HCl [19]. Generally, the speciation of chlorometallate ionic liquids are closely related to their Lewis acidity [1,5,32]. Thus, a quantitative study of the Lewis acidity may be helpful to clarify the speciation of the ionic liquids.…”

“…With the mole ratio of CuCl to AlCl 3 increasing, the 31 P shifts shows a monotonic decreasing trend (Figure 3b). When CuCl continues to be added to [Bmim]Cl−AlCl 3 , CuCl would react with chloroaluminate anions according to the reaction (1) (Figure 4). Therefore, the interaction model between AlCl 3 and the original cations/anions may be deduced through these phenomena.…”

“…In the last decade, the use of chloroaluminate ionic liquids (ILs) to replace conventional acid catalysts has received much attention [1,2]. Due to their versatile properties, ionic liquids have been used in many fields [3].…”