Multiphase Homogeneous Catalysis: Common Procedures and Recent Applications

A top priority in the development of new catalytic processes is the challenging full separation of the catalyst components from the products. Only extremely small residues of metals or ligands are often tolerated in the final product, particularly in the case of active pharmaceutical ingredients; additionally, environmental and cost considerations urge the development of processes that enable the separation and reuse of the catalyst. Multiphase homogeneous catalysis provides technical solutions to these needs, as witnessed by the rapidly accelerating development of this field. Through the analysis of recent examples, the creativity in devising technical solutions for multiphase homogeneous reactions is outlined and the potential rewards are illustrated. 1 Introduction 2 Catalyst Design 3 Classic Multiphase Homogeneous Procedures 3.1 Thermoregulated Solvent Pairs 3.2 Temperature-Induced Catalyst Phase Transfer in a Liquid Liquid Biphasic System 3.3 Quaternary Ammonium Salts in Phase Transfer Catalytic Applications 3.4 Quaternary Ammonium Salts as Metal Nanoparticle Stabilizers 4 Liquid-Liquid Biphasic Catalysis with Ion-Tagged Catalysts 4.1 Ionic Tags and the 'Electrosteric' Activation of a Catalytic Cycle 4.2 Water-Organic Phase Interface Catalysis, Micelles and Emulsions 5 Switchable Catalysts in Liquid-Liquid Biphasic Systems 6 Homogeneous Catalysis Followed by Post-Reaction Heterogenization 6.1 One-Phase Homogeneous Reaction Followed by Catalyst Precipitation with the Aid of an Antisolvent 6.2 Solventless Reactions and Highly Concentrated Organic Phases 7 Multiphase Homogeneous Catalysis and Flow Chemistry 8 Conclusion