Synthesis of Heavy Fluorous Ruthenium Metathesis Catalysts Using the Stereoselective Addition of Polyfluoroalkyllithium to Sterically Hindered Diimines

Abstract

The stereoselective addition of 2-(perfluorohexyl)ethyllithium to moderately hindered diimines led to racemic diamines, which were further transformed to light or heavy fluorous analogues of Hoveyda–Grubbs second-generation precatalysts. The complex bearing the NHC ligand modified with four polyfluoroalkyl ponytails represents the first known example of an alkene metathesis precatalyst retaining its heavy fluorous properties in the active catalytic form. The synthesized complexes match the activity and stability of a commercial Hoveyda–Grubbs second-generation precatalyst in model RCM reactions forming tri- and tetrasubstituted double bonds. The fluorophilic catalyst was successfully recycled using heavy fluorous separation techniques.