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

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.