Ionic Liquids—New “Solutions” for Transition Metal Catalysis

TLDR

Ionic liquids, low‑temperature salts with nonmolecular ionic character, have emerged as a novel class of solvents for transition‑metal catalysis, forming biphasic systems with many organic product mixtures. The authors propose to investigate ionic liquids as solvents for transition‑metal catalysis, opening a wide field for future studies. Ionic liquids enable multiphase reactions that allow easy isolation and recovery of homogeneous catalysts, and their negligible vapor pressure facilitates product separation by distillation. Replacing organic solvents with ionic liquids has led to remarkable improvements in known processes and indications of novel, unusual reactivity.

Abstract

Ionic liquids are salts that are liquid at low temperature (<100 degrees C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.