CHAPTER 3: Homogeneous Catalysis in Ionic Liquids

The past decade has witnessed an explosive growth in the applications of ionic liquids in homogeneous catalysis and the emphasis is no longer solely based on their use as green alternatives to volatile organic solvents but on understanding their physiochemical properties and their effect on reactivity such as enhancements in activity, selectivity, catalyst stability/longevity, improving catalyst separation/recovery protocols as well as recycling and engineering new processes. Other recent developments include the introduction of task specific functionality such as Brønsted acidic groups and heteroatom donors to target specific properties which will undoubtedly present opportunities to engineer new and/or improved processes and strategies. This chapter attempts to provide a practical and working overview that will enable a researcher inexperienced in the use of ionic liquids to make an informed decision about the possible benefits of applying ionic liquids to their research. An overview covers up-to-date synthesis, details about the non-innocent character of ionic liquids, ionic liquid effects on selectivity and activity, strategies in ionic liquid-based catalysis such as homogeneous and liquid–liquid biphasic catalysis and catalyst immobilisation, thermoregulated reversible ionic liquid biphasic systems, ionic liquid–scCO₂ biphasic catalysis and supported ionic liquid phase catalysis, as well as a discussion of the use of polymer immobilised ionic liquids in catalysis. The survey is not exhaustive and has been limited to selected key and evolving areas including carbonylation-based transformations and cross-couplings, oxidations and hydrogenations, Lewis and Brønsted acid catalysis, organocatalysis, metathesis, ring opening polymerisation and dimerisation/oligomerisation, biomass transformations and concluding with catalysis by transition metal nanoparticles; a number of these overviews complement coverage provided by other chapters. For ease of navigation the chapter has been divided into five main sections “Carbonylation, Hydroformylation and Cross-Coupling”, “Oxidation and Hydrogenation”, “Lewis and Brønsted Acid Catalysis”, “Organocatalysis, Metathesis, Ring Opening Polymerisation and Dimerisation/Oligomerisation”, “Biomass Transformations and Catalysis with Transition Metal Nanoparticles”.