Temperature-controlled catalyst recycling: New protocols based upon temperature-dependent solubilities of fluorous compounds and solid/ liquid phase separations

Abstract

The absolute solubilities of fluorous compounds can be tailored by varying the lengths of the (CF2)n-1 CF3 (Rfn) segments. Many such compounds exhibit immense solubility increases in organic solvents or neat liquid reactants upon heating. Suitably designed fluorous catalysts can therefore be employed under homogeneous conditions at elevated temperatures, and recovered by solid/liquid phase separation at lower temperatures. Expensive fluorous solvents are avoided. Fluorous supports can be used to aid the recovery of small catalyst quantities, and render phase separation more efficient. Other design considerations, such as the nature of the catalyst rest state, are analyzed. Examples from the authors' laboratory arising from a multi-investigator project on multiphase catalysis are emphasized. These include phosphine-catalyzed additions, metallacycle syntheses and reactions, and rhodium-catalyzed hydrosilylations. Results from other laboratories are briefly described. © 2006 Springer-Verlag Berlin Heidelberg.