Group IIIA Halometallate Ionic Liquids: Speciation and Applications in Catalysis

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.